Sample records for h2o-oh monolayer films

  1. The structure of mixed H2O-OH monolayer films on Ru(0001)

    Tatarkhanov, M.; Fomin, E.; Salmeron, M.


    Scanning tunneling microscopy (STM) and x-ray absorption spectroscopy (XAS) have been used to study the structures produced by water on Ru(0001) at temperatures above 140 K. It was found that while undissociated water layers are metastable below 140 K, heating above this temperature produces dras...

  2. The structure of mixed H2O-OH monolayer films on Ru(0001)

    Tatarkhanov, M.; Fomin, E.; Salmeron, M.; Andersson, K.; Ogasawara, H.; Pettersson, L.G.M.; Nilsson, A.; Cerda, J.I.


    Scanning tunneling microscopy (STM) and x-ray absorption spectroscopy (XAS) have been used to study the structures produced by water on Ru(0001) at temperatures above 140 K. It was found that while undissociated water layers are metastable below 140 K, heating above this temperature produces drastic transformations whereby a fraction of the water molecules partially dissociate and form mixed H{sub 2}O-OH structures. XPS and XAS revealed the presence of hydroxyl groups with their O-H bond essentially parallel to the surface. STM images show that the mixed H{sub 2}O-OH structures consist of long narrow stripes aligned with the three crystallographic directions perpendicular to the close-packed atomic rows of the Ru(0001) substrate. The internal structure of the stripes is a honeycomb network of H-bonded water and hydroxyl species. We found that the metastable low temperature molecular phase can also be converted to a mixed H{sub 2}O-OH phase through excitation by the tunneling electrons when their energy is 0.5 eV or higher above the Fermi level. Structural models based on the STM images were used for Density Functional Theory optimizations of the stripe geometry. The optimized geometry was then utilized to calculate STM images for comparison with the experiment.

  3. Theoretical study of the rovibrational spectrum of H2O-H2

    Wang, Xiao-Gang; Carrington, Tucker


    In this paper we report transition frequencies and line strengths computed for H_2O-H_2 and compare with the experimental observations of [M. J. Weida and D. J. Nesbitt, J. Chem. Phys. 110, 156 (1999)]. To compute the spectra we use a symmetry adapted Lanczos algorithm and an uncoupled product basis set. Our results corroborate the assignments of Weida and Nesbitt and there is good agreement between calculated and observed transitions. Possible candidates for lines that Weida and Nesbitt were not able to assign are presented. Several other bands that may be observable are also discovered. Although all the observed bands are associated with states localized near the global potential minimum, at which H_2O acts as proton acceptor, a state with significant amplitude near the T-shape secondary potential minimum at which H_2O acts as proton donor is identified by examining many different probability density plots.

  4. Rovibrational states of the H2O-H2 complex: An ab initio calculation

    van der Avoird, Ad; Nesbitt, David J.


    All bound rovibrational levels of the H2O-H2 dimer are calculated for total angular momentum J = 0-5 on two recent intermolecular potential surfaces reported by Valiron et al. [J. Chem. Phys. 129, 134306 (2008)] and Hodges et al. [J. Chem. Phys. 120, 710 (2004)] obtained through ab initio calculations. The method used handles correctly the large amplitude internal motions in this complex; it involves a discrete variable representation of the intermolecular distance coordinate R and a basis of coupled free rotor wave functions for the hindered internal rotations and the overall rotation of the dimer. The basis is adapted to the permutation symmetry associated with the para/ortho (p/o) nature of both H2O and H2 as well as to inversion symmetry. Dimers containing oH2 are more strongly bound than dimers with pH2, as expected, with dissociation energies D_0 of 33.57, 36.63, 53.60, and 59.04 cm^{-1}for pH2O-pH2, oH2O-pH2, pH2O-oH2, and oH2O-oH2, respectively, on the potential of Valiron et al. that corresponds to a binding energy D_e of 235.14 cm^{-1}. Rovibrational wave functions are computed as well and the nature of the bound states in the four different dimer species is discussed. Converged rovibrational levels on both potentials agree well with the high-resolution spectrum reported by Weida and Nesbitt [J. Chem. Phys. 110, 156 (1999)]; the hindered internal rotor model that was used to interpret this spectrum is qualitatively correct.

  5. Variations in H2O+/H2O ratios toward massive star-forming regions

    Wyrowski, F; Herpin, F; Baudry, A; Bontemps, S; Chavarria, L; Frieswijk, W; Jacq, T; Marseille, M; Shipman, R; van Dishoeck, E F; Benz, A O; Caselli, P; Hogerheijde, M R; Johnstone, D; Liseau, R; Bachiller, R; Benedettini, M; Bergin, E; Bjerkeli, P; Blake, G; Braine, J; Bruderer, S; Cernicharo, J; Codella, C; Daniel, F; di Giorgio, A M; Dominik, C; Doty, S D; Encrenaz, P; Fich, M; Fuente, A; Giannini, T; Goicoechea, J R; de Graauw, Th; Helmich, F; Herczeg, G J; Jørgensen, J K; Kristensen, L E; Larsson, B; Lis, D; McCoey, C; Melnick, G; Nisini, B; Olberg, M; Parise, B; Pearson, J C; Plume, R; Risacher, C; Santiago, J; Saraceno, P; Tafalla, M; van Kempen, T A; Visser, R; Wampfler, S; Yıldız, U A; Black, J H; Falgarone, E; Gerin, M; Roelfsema, P; Dieleman, P; Beintema, D; De Jonge, A; Whyborn, N; Stutzki, J; Ossenkopf, V


    Early results from the Herschel Space Observatory revealed the water cation H2O+ to be an abundant ingredient of the interstellar medium. Here we present new observations of the H2O and H2O+ lines at 1113.3 and 1115.2 GHz using the Herschel Space Observatory toward a sample of high-mass star-forming regions to observationally study the relation between H2O and H2O+ . Nine out of ten sources show absorption from H2O+ in a range of environments: the molecular clumps surrounding the forming and newly formed massive stars, bright high-velocity outflows associated with the massive protostars, and unrelated low-density clouds along the line of sight. Column densities per velocity component of H2 O+ are found in the range of 10^12 to a few 10^13 cm-2 . The highest N(H2O+) column densities are found in the outflows of the sources. The ratios of H2O+/H2O are determined in a range from 0.01 to a few and are found to differ strongly between the observed environments with much lower ratios in the massive (proto)cluster e...

  6. I + (H2O)2 → HI + (H2O)OH Forward and Reverse Reactions. CCSD(T) Studies Including Spin-Orbit Coupling.

    Wang, Hui; Li, Guoliang; Li, Qian-Shu; Xie, Yaoming; Schaefer, Henry F


    The potential energy profile for the atomic iodine plus water dimer reaction I + (H2O)2 → HI + (H2O)OH has been explored using the "Gold Standard" CCSD(T) method with quadruple-ζ correlation-consistent basis sets. The corresponding information for the reverse reaction HI + (H2O)OH → I + (H2O)2 is also derived. Both zero-point vibrational energies (ZPVEs) and spin-orbit (SO) coupling are considered, and these notably alter the classical energetics. On the basis of the CCSD(T)/cc-pVQZ-PP results, including ZPVE and SO coupling, the forward reaction is found to be endothermic by 47.4 kcal/mol, implying a significant exothermicity for the reverse reaction. The entrance complex I···(H2O)2 is bound by 1.8 kcal/mol, and this dissociation energy is significantly affected by SO coupling. The reaction barrier lies 45.1 kcal/mol higher than the reactants. The exit complex HI···(H2O)OH is bound by 3.0 kcal/mol relative to the asymptotic limit. At every level of theory, the reverse reaction HI + (H2O)OH → I + (H2O)2 proceeds without a barrier. Compared with the analogous water monomer reaction I + H2O → HI + OH, the additional water molecule reduces the relative energies of the entrance stationary point, transition state, and exit complex by 3-5 kcal/mol. The I + (H2O)2 reaction is related to the valence isoelectronic bromine and chlorine reactions but is distinctly different from the F + (H2O)2 system.

  7. Quantum tunneling during interstellar surface-catalyzed formation of water: the reaction H + H$_2$O$_2$ $\\rightarrow$ H$_2$O + OH

    Lamberts, Thanja; Köhn, Andreas; Kästner, Johannes


    The final step of the water formation network on interstellar grain surfaces starting from the H + O$_2$ route is the reaction between H and H$_2$O$_2$. This reaction is known to have a high activation energy and therefore at low temperatures it can only proceed via tunneling. To date, however, no rate constants are available at temperatures below 200 K. In this work, we use instanton theory to compute rate constants for the title reaction with and without isotopic substitutions down to temperatures of 50 K. The calculations are based on density functional theory, with additional benchmarks for the activation energy using unrestricted single-reference and multireference coupled-cluster single-point energies. Gas-phase bimolecular rate constants are calculated and compared with available experimental data not only for H + H$_2$O$_2$ $\\rightarrow$ H$_2$O + OH, but also for H + H$_2$O$_2$ $\\rightarrow$ H$_2$ + HO$_2$. We find a branching ratio where the title reaction is favored by at least two orders of magnitu...

  8. Herschel Far-Infrared Spectral-mapping of Orion BN/KL Outflows: Spatial distribution of excited CO, H2O, OH, O and C+ in shocked gas

    Goicoechea, Javier R; Cernicharo, Jose; Neufeld, David A; Vavrek, Roland; Bergin, Edwin A; Cuadrado, Sara; Encrenaz, Pierre; Etxaluze, Mireya; Melnick, Gary J; Polehampton, Edward


    We present ~2'x2' spectral-maps of Orion BN/KL outflows taken with Herschel at ~12'' resolution. For the first time in the far-IR domain, we spatially resolve the emission associated with the bright H2 shocked regions "Peak 1" and "Peak 2" from that of the Hot Core and ambient cloud. We analyze the ~54-310um spectra taken with the PACS and SPIRE spectrometers. More than 100 lines are detected, most of them rotationally excited lines of 12CO (up to J=48-47), H2O, OH, 13CO, and HCN. Peaks 1/2 are characterized by a very high L(CO)/L(FIR)~5x10^{-3} ratio and a plethora of far-IR H2O emission lines. The high-J CO and OH lines are a factor ~2 brighter toward Peak 1 whereas several excited H2O lines are ~50% brighter toward Peak 2. A simplified non-LTE model allowed us to constrain the dominant gas temperature components. Most of the CO column density arises from Tk~200-500 K gas that we associate with low-velocity shocks that fail to sputter grain ice mantles and show a maximum gas-phase H2O/CO~10^{-2} abundance r...

  9. Corrosion of 310 stainless steel in H2-H2O-H2S gas mixtures: Studies at constant temperature and fixed oxygen potential

    Rao, D. B.; Jacob, K. T.; Nelson, H. G.


    Corrosion of SAE 310 stainless steel in H2-H2O-H2S gas mixtures was studied at a constant temperature of 1150 K. Reactive gas mixtures were chosen to yield a constant oxygen potential of approximately 6 x 10 to the minus 13th power/cu Nm and sulfur potentials ranging from 0.19 x 10 to the minus 2nd power/cu Nm to 33 x 10 to the minus 2nd power/cu Nm. The kinetics of corrosion were determined using a thermobalance, and the scales were analyzed using metallography, scanning electron microscopy, and energy dispersive X-ray analysis. Two corrosion regimes, which were dependent on sulfur potential, were identified. At high sulfur potentials (p sub S sub 2 less than or equal to 2.7 x 10 to the minus 2nd power/cu Nm) the corrosion rates were high, the kinetics obeyed a linear rate equation, and the scales consisted mainly of sulfide phases similar to those observed from pure sulfication. At low sulfur potentials (P sub S sub 2 less than or equal to 0.19 x 10 to the minus 2nd power/cu Nm) the corrosion rates were low, the kinetics obeyed a parabolic rate equation, and scales consisted mainly of oxide phases.

  10. [Sr(CHZ)(TNR)(H2O)(OH)]2·2H2O的晶体结构和热分解机理%Crystal Structure and Thermal Decomposition Mechanism of [Sr(CHZ)(TNR)(H2O)(OH)]2· 2H2O

    郑红; 张同来; 张建国; 乔小晶; 杨利; 孙远华


    The coordination compound of [Sr(CHZ) (TNR)(H2O) (OH)]2· 2H2O (TNR: 2,4,6-trinitroesorcinol, CHZ:carbohydrazide) was prepared by reacting CHZ solution and strontium styphnate solution (obtained through the reaction of strontium carbonate and styphnic acid). The molecular structure was characterized by using X-ray diffraction analysis, element analysis and FTIR analysis. The crystal belongs to triclinic with space group P(-1). The unit cell parameters were as follows: a=0.725 2(2) nm, b=1.021 2(2) nm, c=1.144 0(2) nm, α=69.50(3)°, β=78.82(3)°, γ=84.64(3)° and Z=2. The thermal decomposition of the compound is studied using differential scanning calorimetry (DSC) and thermogravimetry thermogravimetry-derivative (TG-DTG) techniques. CCDC: 269310.

  11. ZStudies on the Phase Equilibrium of BaCl2-C6H12O6-H2O/(H2O and CH3CH2OH) at 30 ℃%BaCl2-C6H12O6-H2O/(H2O+CH3CH2OH)体系在30 ℃时的相平衡研究

    王飞利; 胡道道; 李淑妮; 朱西燕; 李君; 唐宗薰


    用等温溶解度法研究了BaCl2-C6H12O6-H2O/(H2O+CH3CH2OH)体系在30 ℃时的相平衡, 发现在体系中有一未见文献报道的不一致溶解的化合物BaCl2*2C6H12O6*2H2O生成. 研究结果为肌醇生产除杂质工艺提供了理论依据.

  12. β,β-Isomer of Open-Wells–Dawson Polyoxometalate Containing a Tetra-Iron(III Hydroxide Cluster: [{Fe4(H2O(OH5}(β,β-Si2W18O66]9−

    Satoshi Matsunaga


    Full Text Available The β,β-isomer of open-Wells–Dawson polyoxometalate (POM containing a tetra-iron(III cluster, K9[{Fe4(H2O(OH5}(β,β-Si2W18O66]·17H2O (potassium salt of β,β-Fe4-open, was synthesized by reacting Na9H[A-β-SiW9O34]·23H2O with FeCl3·6H2O at pH 3, and characterized by X-ray crystallography, FTIR, elemental analysis, TG/DTA, UV–Vis, and cyclic voltammetry. X-ray crystallography revealed that the {Fe3+4(H2O(OH5}7+ cluster was included in the open pocket of the β,β-type open-Wells–Dawson polyanion [β,β-Si2W18O66]16− formed by the fusion of two trilacunary β-Keggin POMs, [A-β-SiW9O34]10−, via two W–O–W bonds. The β,β-open-Wells–Dawson polyanion corresponds to an open structure of the standard γ-Wells–Dawson POM. β,β-Fe4-open is the first example of the compound containing a geometrical isomer of α,α-open-Wells–Dawson structural POM.

  13. Iron uptake in ferritin is blocked by binding of [Cr(TREN)(H(2)O)(OH)](2+), a slow dissociating model for [Fe(H(2)O)(6)](2+).

    Barnés, Carmen M; Theil, Elizabeth C; Raymond, Kenneth N


    Ferritin concentrates iron as a hydrous ferric oxide in a protein cavity (8 nm in diameter) by using eight pores along the threefold symmetry axes of the octahedral supramolecular structure. The role of ligand exchange in the entry of Fe(II) hexahydrate into ferritin protein has been studied with [Cr(TREN)(H(2)O)(OH)](2+) [TREN = N(CH(2)CH(2)NH(2))(3)], a model for Fe(H(2)O)(6)2+ with only two exchangeable ligands. The results show that five different ferritin proteins, varying in pore structure, oxidation sites, and nucleation sites, bind Cr(TREN) at functional protein sites, based on inhibition of iron mineralization and oxidation. Properties of Cr(TREN)-ferritin adducts include an increased isoelectric point, a shift in the Cr(TREN) UV/vis spectrum consistent with exchange of water for protein carboxylate or thiolate ligands, binding affinities of 50-250 microM, and a slow rate of dissociation (k = 4 x 10(-6) sec(-1)). The relationship of Cr(TREN) inhibition of iron oxidation and mineralization by Cr(TREN) to the known structures of the various ferritins tested suggests that Cr(TREN) plugs the ferritin pores, obstructing Fe(II) entry in folded and unfolded pores. Because only two exchangeable waters are sufficient for pore binding of Cr(TREN), the physiological Fe(II) donor must bind to the pore with few exchangeable ligands. These results show the advantage of using stable model complexes to explore properties of transient Fe-protein complexes during Fe mineralization in ferritin.

  14. Selective photocatalytic reduction of CO2 by H2O/H2 to CH4 and CH3OH over Cu-promoted In2O3/TiO2 nanocatalyst

    Tahir, Muhammad; Tahir, Beenish; Saidina Amin, Nor Aishah; Alias, Hajar


    Photocatalytic CO2 reduction by H2O and/or H2 reductant to selective fuels over Cu-promoted In2O3/TiO2 photocatalyst has been investigated. The samples, prepared via a simple and direct sol-gel method, were characterized by XRD, SEM, TEM, XPS, N2 adsorption-desorption, UV-vis diffuse reflectance, Raman and PL spectroscopy. Cu and In loaded into TiO2, oxidized as Cu2+ and In3+, promoted efficient separation of photo-generated electron/hole pairs (e-/h+). The results indicate that the reduction rate of CO2 by H2O to CH4 approached to 181 μmol g-1 h-1 using 0.5% Cu-3% In2O3/TiO2 catalyst, a 1.53 fold higher than the production rate over the 3% In2O3/TiO2 and 5 times the amount produced over the pure TiO2. In addition, Cu was found to promote efficient production of CH3OH and yield rate reached to 68 μmol g-1 h-1 over 1% Cu-3% In2O3/TiO2 catalyst. This improvement was attributed to charge transfer property and suppressed recombination rate by Cu-metal. More importantly, H2 reductant was less favorable for CH4 production, yet a significant amount of CH4 and CH3OH were obtained using a mixture of H2O/H2 reductant. Therefore, Cu-loaded In2O3/TiO2 catalyst has shown to be capable for methanol production, whereas product selectivity was greatly depending on the amount of Cu-loading and the type of reductant. A photocatalytic reaction mechanism was proposed to understand the experimental results over the Cu-loaded In2O3/TiO2 catalyst.

  15. Competition studies in horse spleen ferritin probed by a kinetically inert inhibitor, [Cr(TREN)(H(2)O)(OH)](2+), and a highly luminescent Tb(III) reagent.

    Barnés, Carmen M; Petoud, Stéphane; Cohen, Seth M; Raymond, Kenneth N


    The ability of ferritin as an Fe(II) detoxifier and Fe(III) storage protein is limited by its ability to recognize and incorporate Fe(II), which is then oxidized and mineralized at internal protein sites. The Cr(III) amine complex [Cr(N(CH(2)CH(2)NH(2))(3)(H(2)O)(OH)](2+) [abbreviated as Cr(TREN)] is a kinetically inert inhibitor of iron incorporation and mineralization in ferritin. Unlike other inhibitors, Cr(TREN) can only exchange its two aqua/hydroxy ligands. Competition studies between Cr(TREN) and Tb(III) binding have been performed in horse spleen ferritin (HoSF) to probe uptake of Fe(II). From these studies, we propose that Cr(TREN) inhibits Fe(II) uptake by obstructing the routes of metal uptake and by disrupting the early recognition events at the protein surface that precede metal ion uptake. Using an improved luminescence approach to quantify Tb(III) binding to the protein, we demonstrate that Tb(III) cannot interfere with Cr(TREN) binding to ferritin, but that Cr(TREN) dramatically inhibits Tb(III) binding. We show that bound Tb(III) serves as a reliable reporter for Cr(TREN) binding, as the latter efficiently quenches the Tb(III) luminescence via inter-ion energy transfer. Two types of Cr(TREN) binding sites were successfully distinguished from these competition experiments. A common Tb(III)/Cr(TREN) site was identified with stoichiometry of approximately 0.6 equivalents of metal cation per ferritin subunit. We propose that the sites along the three-fold channels and the ferroxidase sites are common binding sites for Tb(III) and Cr(TREN). The remaining Cr(TREN) (2.4 equivalents of metal ions/subunit) does not compete with Tb(III) but rather blocks Tb(III) access into the cavity and decreases the protein's affinity for Tb(III).

  16. Ellipsometry of clean surfaces, submonolayer and monolayer films

    Habraken, F.H.P.M.; Gijzeman, O.L.J.; Bootsma, G.A.


    The geometric and electronic structure of the surface region of a crystal is often different from the bulk structure and therefore the optical properties differ in principle also. Theories for the optical properties of (sub)monolayer films are compared, with special attention to anisotropic layers.

  17. Controlled electrodeposition of Au monolayer film on ionic liquid

    Ma, Qiang; Pang, Liuqing; Li, Man; Zhang, Yunxia; Ren, Xianpei; Liu, Shengzhong Frank


    Gold (Au) nanoparticles have been attractive for centuries for their vibrant appearance enhanced by their interaction with sunlight. Nowadays, there have been tremendous research efforts to develop them for high-tech applications including therapeutic agents, sensors, organic photovoltaics, medical applications, electronics and catalysis. However, there remains to be a challenge to fabricate a monolayer Au coating with complete coverage in controlled fashion. Here we present a facile method to deposit a uniform Au monolayer (ML) film on the [BMIM][PF6] ionic liquid substrate using an electrochemical deposition process. It demonstrates that it is feasible to prepare a solid phase coating on the liquid-based substrate. Moreover, the thickness of the monolayer coating can be controlled to a layer-by-layer accuracy.

  18. Photoresponsive Wettability in Monolayer Films from Sinapinic Acid

    Cleverson A. S. Moura


    Full Text Available Sinapinic acid is an interesting material because it is both antioxidant and antibacterial agent. In addition, when illuminated with ultraviolet light, it can exhibit the so-called photodimerization process. In this paper, we report on the investigation of monolayer films from 3,5-dimethoxy-4-hydroxycinnamic acid (sinapinic acid, SinA deposited onto poly(allylamine hydrochloride, PAH, films. SinA monolayers were prepared by using the layer-by-layer (LbL self-assembly technique. Adsorption kinetics curves were well fitted by a biexponential function suggesting that the adsorption process is determined by two mechanisms: nucleation and growth of aggregates. By using wetting contact angle analysis, we have found that SinA monolayers exhibit photoresponsive wettability under UV irradiation (365 nm; that is, wettability decreases with increasing UV irradiation time. The photoresponse of wettability was attributed to photodimerization process. This hypothesis was supported by the dependence of surface morphological structure and absorption on UV irradiation time. The mechanism found in the well-known transcinnamic acid crystals is used to explain the photodimerization process in SinA monolayers.

  19. Graphene-like monolayer low-buckled honeycomb germanium film

    He, Yezeng; Luo, Haibo; Li, Hui; Sui, Yanwei; Wei, Fuxiang; Meng, Qingkun; Yang, Weiming; Qi, Jiqiu


    Molecular dynamics simulations have been performed to study the cooling process of two-dimensional liquid germanium under nanoslit confinement. The results clearly indicates that the liquid germanium undergoes an obvious liquid-solid phase transition to a monolayer honeycomb film with the decrease of temperature, accompanying the rapid change in potential energy, atomic volume, coordination number and lateral radial distribution function. During the solidification process, some hexagonal atomic islands first randomly emerge in the disordered liquid film and then grow up to stable crystal grains which keep growing and finally connect together to form a honeycomb polycrystalline film. It is worth noting that the honeycomb germanium film is low-buckled, quite different from the planar graphene.

  20. Ubiquitous pentacene monolayer on metals deposited onto pentacene films.

    Jaeckel, B; Sambur, J B; Parkinson, B A


    Photoelectron spectroscopy (XPS and UPS) was used to study the deposition of metal layers (Ag, Cu, and Au) onto pentacene films. Very low work functions were measured (PhiAg = 3.91 eV, PhiCu = 3.93 eV, and PhiAu = 4.3 eV) for all of the metals, in agreement with results from the literature. The intensities of the C 1s core-level signals from pentacene that were monitored during stepwise metal deposition leveled off at a value of about 30% of a thick pentacene film. This C 1s intensity is comparable to that of one monolayer of pentacene deposited onto the respective metal. The valence band spectra of metals deposited onto pentacene and spectra collected for pentacene deposited onto bare metal surfaces are very similar. These findings lead to the conclusion that approximately one monolayer of pentacene is always present on top of the freshly deposited metal film, which explains the very low work function of the metals when they are deposited onto organic films. We expect similar behavior with other nonreactive metals deposited onto stable organic layers.

  1. Mixed DPPC/DPPG monolayers at very high film compression.

    Saad, Sameh M I; Policova, Zdenka; Acosta, Edgar J; Hair, Michael L; Neumann, A Wilhelm


    A drop shape technique using a constrained sessile drop constellation (ADSA-CSD) has been introduced as a superior technique for studying spread films specially at high collapse pressures [Saad et al. Langmuir 2008, 24, 10843-10850]. It has been shown that ADSA-CSD has certain advantages including the need only for small quantities of liquid and insoluble surfactants, the ability to measure very low surface tension values, easier deposition procedure, and leak-proof design. Here, this technique was applied to investigate mixed DPPC/DPPG monolayers to characterize the role of such molecules in maintaining stable film properties and surface activity of lung surfactant preparations. Results of compression isotherms were obtained for different DPPC/DPPG mixture ratios: 90/10, 80/20, 70/30, 60/40, and 50/50 in addition to pure DPPC and pure DPPG at room temperature of 24 degrees C. The ultimate collapse pressure of DPPC/DPPG mixtures was found to be 70.5 mJ/m2 (similar to pure DPPC) for the cases of low DPPG content (up to 20%). Increasing the DPPG content in the mixture (up to 40%) caused a slight decrease in the ultimate collapse pressure. However, further increase of DPPG in the mixture (50% or more) caused a sharp decrease in the ultimate collapse pressure to a value of 59.9 mJ/m2 (similar to pure DPPG). The change in film elasticity was also tracked for the range of mixture ratios studied. The physical reasons for such changes and the interaction between DPPC and DPPG molecules are discussed. The results also show a change in the film hysteresis upon successive compression and expansion cycles for different mixture ratios.

  2. Electrodeposition of a Pt monolayer film: using kinetic limitations for atomic layer epitaxy.

    Brimaud, Sylvain; Behm, R Jürgen


    A new and facile one-step method to prepare a smooth Pt monolayer film on a metallic substrate in the absence of underpotential deposition-type stabilizations is presented as a general approach and applied to the growth of Pt monolayer films on Au. The strongly modified electronic properties of these films were demonstrated by in situ IR spectroscopy at the electrified solid-liquid interface with adsorbed carbon monoxide serving as a probe molecule. The Pt monolayer on Au is kinetically stabilized by adsorbed CO, inhibiting further Pt deposition in higher layers.

  3. Effect of Impurity Concentration on the Depth Profile of the Electric Field within Monolayer Thin Film

    N.F. Habubi


    Full Text Available The effect of impurity concentration ratios on the depth profile of electric field within monolayer film is presented. SnO2 monolayer thin film material was prepared and doped with Co using spray chemical pyrolysis. The concentration ratios of impurity were 1 %, 3 %, 5 % and 7 %. The analysis utilizes matrix formulas based on Abele's formulas from the calculation of reflectance and transmittance. Present study gives an information to contamination sensitivity in optical coating issue.

  4. Stiffness of polyelectrolyte multilayer film influences endothelial function of endothelial cell monolayer.

    Chang, Hao; Zhang, He; Hu, Mi; Chen, Jia-Yan; Li, Bo-Chao; Ren, Ke-Feng; Martins, M Cristina L; Barbosa, Mário A; Ji, Jian


    Endothelialization has proved to be critical for maintaining long-term success of implantable vascular devices. The formation of monolayer of endothelial cells (ECs) on the implant surfaces is one of the most important factors for the endothelialization. However, endothelial function of regenerated EC monolayer, which plays a much more important role in preventing the complications of post-implantation, has not received enough attention. Here, a vascular endothelial growth factor (VEGF)-incorporated poly(l-lysine)/hyaluronan (PLL/HA) polyelectrolyte multilayer film was fabricated. Through varying the crosslinking degree, stiffness of the film was manipulated, offering either soft or stiff film. We demonstrated that ECs were able to adhere and proliferate on both soft and stiff films, subsequently forming an integrated EC monolayer. Furthermore, endothelial functions were evaluated by characterizing EC monolayer integrity, expression of genes correlated with the endothelial functions, and nitric oxide production. It demonstrated that EC monolayer on the soft film displayed higher endothelial function compared to that on the stiff film. Our study highlights the influence of substrate stiffness on endothelial function, which offers a new criterion for surface design of vascular implants. Copyright © 2016 Elsevier B.V. All rights reserved.

  5. Growing extremely thin bulklike metal film on a semiconductor surface: Monolayer Al(111) on Si(111)

    Jiang, Ying; Kim, Yong-Hyun; Zhang, S. B.; Ebert, Philipp; Yang, Shenyuan; Tang, Zhe; Wu, Kehui; Wang, E. G.


    We report combined scanning tunneling microscopy, x-ray photoelectron emission spectroscopy, electron energy loss spectroscopy, and theoretical study of the growth of ultrathin Al film on the Si(111) substrate. We show that by (i) a modification of the substrate reconstruction with a √3×√3 surface and (ii) a choice of materials with commensurate lattices, atomically flat film can be obtained even at the ultimate one monolayer limit, while maintaining a bulklike atomic structure. Detailed analysis shows that this monolayer Al(111)-1×1Al(111)-1×1 film is electronically decoupled from the Si substrate, and it shows metallic characteristics.

  6. A Solid Ag Film Deposited from Solution on Self-assembled Mercaptopropyltrimethoxysilane (MPTS) Monolayer


    Mercaptopropyltrimethoxysilane (MPTS) bearing mercapto groups was used to form self-assembly monolayers (SAMs) on glass substrates by solution extraction. SEM, XRD and rubbing test analysis illustrated that the Ag film on the SAMs-modified glass was more durable than that on the commonly-modified glass and that the crystallinity of Ag film on the SAMs-modified glass was identical with those of the Ag film on the commonly-modified glass and pure Ag.

  7. Controlled Synthesis of Monolayer Graphene Toward Transparent Flexible Conductive Film Application

    Yu Han-Young


    Full Text Available Abstract We demonstrate the synthesis of monolayer graphene using thermal chemical vapor deposition and successive transfer onto arbitrary substrates toward transparent flexible conductive film application. We used electron-beam-deposited Ni thin film as a synthetic catalyst and introduced a gas mixture consisting of methane and hydrogen. To optimize the synthesis condition, we investigated the effects of synthetic temperature and cooling rate in the ranges of 850–1,000°C and 2–8°C/min, respectively. It was found that a cooling rate of 4°C/min after 1,000°C synthesis is the most effective condition for monolayer graphene production. We also successfully transferred as-synthesized graphene films to arbitrary substrates such as silicon-dioxide-coated wafers, glass, and polyethylene terephthalate sheets to develop transparent, flexible, and conductive film application.

  8. Comparative study of normal and branched alkane monolayer films adsorbed on a solid surface. I. Structure

    Enevoldsen, A. D.; Hansen, F. Y.; Diama, A.; Criswell, L.; Taub, H.


    The structure of a monolayer film of the branched alkane squalane (C30H62) adsorbed on graphite has been studied by neutron diffraction and molecular dynamics (MD) simulations and compared with a similar study of the n-alkane tetracosane (n-C24H52). Both molecules have 24 carbon atoms along their backbone and squalane has, in addition, six methyl side groups. Upon adsorption, there are significant differences as well as similarities in the behavior of these molecular films. Both molecules form ordered structures at low temperatures; however, while the melting point of the two-dimensional (2D) tetracosane film is roughly the same as the bulk melting point, the surface strongly stabilizes the 2D squalane film such that its melting point is 91K above its value in bulk. Therefore, squalane, like tetracosane, will be a poor lubricant in those nanoscale devices that require a fluid lubricant at room temperature. The neutron diffraction data show that the translational order in the squalane monolayer is significantly less than in the tetracosane monolayer. The authors' MD simulations suggest that this is caused by a distortion of the squalane molecules upon adsorption on the graphite surface. When the molecules are allowed to relax on the surface, they distort such that all six methyl groups point away from the surface. This results in a reduction in the monolayer's translational order characterized by a decrease in its coherence length and hence a broadening of the diffraction peaks. The MD simulations also show that the melting mechanism in the squalane monolayer is the same footprint reduction mechanism found in the tetracosane monolayer, where a chain melting drives the lattice melting.

  9. Comparative study of normal and branched alkane monolayer films adsorbed on a solid surface. I. Structure

    Enevoldsen, Ann Dorrit; Hansen, Flemming Yssing; Diama, A.


    The structure of a monolayer film of the branched alkane squalane (C30H62) adsorbed on graphite has been studied by neutron diffraction and molecular dynamics (MD) simulations and compared with a similar study of the n-alkane tetracosane (n-C24H52). Both molecules have 24 carbon atoms along their...

  10. Comparative study of normal and branched alkane monolayer films adsorbed on a solid surface. II. Dynamics

    Enevoldsen, Ann Dorrit; Hansen, Flemming Yssing; Diama, A.;


    The dynamics of monolayer films of the n-alkane tetracosane (n-C24H52) and the branched alkane squalane (C30H62) adsorbed on graphite have been studied by quasielastic and inelastic neutron scattering and molecular dynamics (MD) simulations. Both molecules have 24 carbon atoms along their carbon...

  11. Ultrafast electron diffraction optimized for studying structural dynamics in thin films and monolayers

    Badali, D. S.; Gengler, R. Y. N.; Miller, R. J. D.


    A compact electron source specifically designed for time-resolved diffraction studies of free-standing thin films and monolayers is presented here. The sensitivity to thin samples is achieved by extending the established technique of ultrafast electron diffraction to the "medium" energy regime (1-10

  12. The lipase monolayer film self-assembly on the negatively charged poly(ethylene terephthalate) substrate


    The PET-CO2- film was prepared and the lipase was assembled on the surface of the PET-CO2- substrate. The structure at the surface and activity of lipase/PET monolayer were studied by ATR-FTIR and AFM, and other methods.

  13. Rapid permeation measurement system for the production control of monolayer and multilayer films

    Botos, J.; Müller, K.; Heidemeyer, P.; Kretschmer, K.; Bastian, M.; Hochrein, T.


    Plastics have been used for packaging films for a long time. Until now the development of new formulations for film applications, including process optimization, has been a time-consuming and cost-intensive process for gases like oxygen (O2) or carbon dioxide (CO2). By using helium (He) the permeation measurement can be accelerated from hours or days to a few minutes. Therefore a manometric measuring system for tests according to ISO 15105-1 is coupled with a mass spectrometer to determine the helium flow rate and to calculate the helium permeation rate. Due to the accelerated determination the permeation quality of monolayer and multilayer films can be measured atline. Such a system can be used to predict for example the helium permeation rate of filled polymer films. Defined quality limits for the permeation rate can be specified as well as the prompt correction of process parameters if the results do not meet the specification. This method for process control was tested on a pilot line with a corotating twin-screw extruder for monolayer films. Selected process parameters were varied iteratively without changing the material formulation to obtain the best process parameter set and thus the lowest permeation rate. Beyond that the influence of different parameters on the helium permeation rate was examined on monolayer films. The results were evaluated conventional as well as with artificial neuronal networks in order to determine the non-linear correlation between all process parameters.

  14. Electric filed induced self-assembly of monolayers of sub-micron sized particles on flexible thin films

    Shah, K.; Hossain, M.; Janjua, M.; Aubry, N.; Fischer, I. S.; Singh, P.


    We present a technique that uses an electric field in the direction normal to the interface for self-assembling particle monolayers of sub-micron sized particles on fluid-liquid interfaces and freezing these monolayers onto the surface of a flexible thin film. The electric field gives rise to dipole-dipole and capillary forces which cause the particles to arrange in a triangular pattern. The technique involves assembling the monolayer on the interface between a UV-curable resin and another fluid by applying an electric field, and then curing the resin by applying UV light. The monolayer becomes embedded on the surface of the solidified resin film.

  15. Monolayer film behavior of lipopolysaccharide from Pseudomonas aeruginosa at the air-water interface.

    Abraham, Thomas; Schooling, Sarah R; Beveridge, Terry J; Katsaras, John


    Lipopolysaccharide (LPS) is an essential biomacromolecule making up approximately 50% of the outer membrane of gram-negative bacteria. LPS chemistry facilitates cellular barrier and permeability functions and mediates interactions between the cell and its environment. To better understand the local interactions within LPS membranes, the monolayer film behavior of LPS extracted from Pseudomonas aeruginosa, an opportunistic pathogen of medical importance, was investigated by Langmuir film balance. LPS formed stable monolayers at the air-water interface and the measured lateral stresses and modulus (rigidity) of the LPS film in the compressed monolayer region were found to be appreciable. Scaling theories for two-dimensional (2D) polymer chain conformations were used to describe the pi-A profile, in particular, the high lateral stress region suggested that the polysaccharide segments reside at the 2D air-water interface. Although the addition of monovalent and divalent salts caused LPS molecules to adopt a compact conformation at the air-water interface, they did not appear to have any influence on the modulus (rigidity) of the LPS monolayer film under biologically relevant stressed conditions. With increasing divalent salt (CaCl2) content in the subphase, however, there is a progressive reduction of the LPS monolayer's collapse pressure, signifying that, at high concentrations, divalent salts weaken the ability of the membrane to withstand elevated stress. Finally, based on the measured viscoelastic response of the LPS films, we hypothesize that this property of LPS-rich outer membranes of bacteria permits the deformation of the membrane and may consequently protect bacteria from catastrophic structural failure when under mechanical-stress.

  16. Underpotential deposition of a copper monolayer on a gold film sensed by integrated optical surface plasmon resonance

    Abanulo, J.C.; Harris, R.D.; Bartlett, P.N.; Wilkinson, J.S.


    An integrated optical surface plasmon resonance sensor combined with electrochemical control is used to monitor the underpotential deposition of a copper monolayer onto a gold film from 1 mM Cu2+ in 0.1 M perchloric acid.

  17. Epitaxial growth and structure of monolayer cerium oxide films on Rh(111)

    Chan, Lap Hong; Yuhara, Junji


    We prepared monolayer cerium (Ce) oxide films on Rh(111) to investigate their growth and structure using scanning tunneling microscopy (STM), low-energy electron diffraction, X-ray photoemission spectroscopy (XPS), and density functional theory (DFT) calculations. For quantitative analysis of Ce-oxide films, we used the combined techniques of XPS and Rutherford backscattering spectrometry to determine the concentration of Ce and O atoms. We prepared a monolayer (ML) Ce-oxide film by annealing a metallic Ce film at 0.3 ML coverage in an oxygen atmosphere. A well-ordered Ce-oxide phase with a (4×4) unit cell was obtained. The epitaxially grown Ce-oxide film aligned along the azimuthal direction of Rh(111). The number of Ce and O atoms in the (4×4) unit cell was estimated. The STM images indicated that the two-dimensional island growth of the p(4×4) phase with p3m1 symmetry can be explained using the missing Ce atoms model. A simulated STM image of the p(4×4) structural model was in good agreement with the experimental STM image. The formation of Ce-oxide films on Rh(111) at submonolayer coverage was discussed on the basis of the results of DFT+U calculations.

  18. Quantitative determination of melamine in milk using Ag nanoparticle monolayer film as SERS substrate

    Li, Ruoping; Yang, Jingliang; Han, Junhe; Liu, Junhui; Huang, Mingju


    A Raman method employing silver nanoparticle (Ag NP) monolayer film as Surface-enhanced Raman Scattering (SERS) substrate was presented to rapidly detect melamine in milk. The Ag NPs with 80 nm diameter were modified by polyvinylpyrrolidone to improve their uniformity and chemical stability. The treatment procedure of liquid milk required only addition of acetic acid and centrifugation, and required time is less than 15 min. The Ag NP monolayer film significantly enhanced Raman signal from melamine and allowed experimentally reproducible determination of the melamine concentration. A good linear relationship (R2=0.994) between the concentration and Raman peak intensity of melamine at 681 cm-1 was obtained for melamine concentrations between 0.10 mg L-1 and 5.00 mg L-1. This implies that this method can detect melamine concentrations below 1.0 mg L-1, the concentration currently considered unsafe.

  19. Growth of polypyrrole ultrathin films on MoS₂ monolayers as high-performance supercapacitor electrodes.

    Tang, Hongjie; Wang, Jiangyan; Yin, Huajie; Zhao, Huijun; Wang, Dan; Tang, Zhiyong


    A scalable solution-based approach is developed to controllably grow PPy ultrathin films on 2D MoS2 monolayers. When these sandwiched nanocomposites are utilized as supercapacitor electrodes, a record high specific capacitance, remarkable rate capability, and improved cycling stability are achieved, offering a feasible solution to create the next generation of energy-storage device with superior power density and energy density.

  20. Catalystlike behavior of Si adatoms in the growth of monolayer Al film on Si(111).

    Teng, Jing; Zhang, Lixin; Jiang, Ying; Guo, Jiandong; Guo, Qinlin; Wang, Enge; Ebert, Philipp; Sakurai, T; Wu, Kehui


    The formation mechanism of monolayer Al(111)1x1 film on the Si(111) radical3x radical3-Al substrate was studied by scanning tunneling microscopy and first-principles calculations. We found that the Si adatoms on the radical3x radical3-Al substrate play important roles in the growth process. The growth of Al-1x1 islands is mediated by the formation and decomposition of SiAl(2) clusters. Based on experiments and theoretical simulations we propose a model where free Si atoms exhibit a catalystlike behavior by capturing and releasing Al atoms during the Al film growth.

  1. Self-assembly of monolayer-thick alumina particle-epoxy composite films.

    Jackson, Bryan R; Liu, Xiangyuan; McCandlish, Elizabeth F; Riman, Richard E


    Monolayer-thick composite films composed of alpha-alumina and Spurr's epoxy were prepared via a self-assembly process known as fluid forming. The process makes use of a high-spreading-tension fluid composed of volatile and nonvolatile components to propel particles across the air-water interface within a water bath. Continuous addition of the particle suspension builds a 2D particle film at the air-water interface. The spreading fluid compresses the film into a densely packed array against a submerged substrate. The assembled monolayer is deposited onto the substrate by removing the substrate from the bath. A dispersion containing a narrow size distribution, 10 microm alpha-alumina particles, light mineral oil, and 2-propanol was spread at the air-water interface and the alumina particles were assembled into densely packed arrays with an aerial packing fraction (APF) of 0.88. However, when mineral oil was replaced by Spurr's epoxy nonuniform films with low packing density resulted. It was found that replacing 2-propanol with a mixture of 2-propanol and 1-butanol with a volume ratio of 4:1 produced uniform, densely packed alumina/epoxy composite films. The role of the solvent mixture will be discussed.

  2. Comparative study of normal and branched alkane monolayer films adsorbed on a solid surface. II. Dynamics

    Enevoldsen, A. D.; Hansen, F. Y.; Diama, A.; Taub, H.; Dimeo, R. M.; Neumann, D. A.; Copley, J. R. D.


    The dynamics of monolayer films of the n-alkane tetracosane (n-C24H52) and the branched alkane squalane (C30H62) adsorbed on graphite have been studied by quasielastic and inelastic neutron scattering and molecular dynamics (MD) simulations. Both molecules have 24 carbon atoms along their carbon backbone, and squalane has an additional six methyl side groups symmetrically placed along its length. The authors' principal objective has been to determine the influence of the side groups on the dynamics of the squalane monolayer and thereby assess its potential as a nanoscale lubricant. To investigate the dynamics of these monolayers they used both the disk chopper spectrometer (DCS) and the high flux backscattering spectrometer (HFBS) at the National Institute of Standards and Technology. These instruments made it possible to study dynamical processes such as molecular diffusive motions and vibrations on very different time scales: 1-40ps (DCS) and 0.1-4ns (HFBS). The MD simulations were done on corresponding time scales and were used to interpret the neutron spectra. The authors found that the dynamics of the two monolayers are qualitatively similar on the respective time scales and that there are only small quantitative differences that can be understood in terms of the different masses and moments of inertia of the two molecules. In the course of this study, the authors developed a procedure to separate out the low-frequency vibrational modes in the spectra, thereby facilitating an analysis of the quasielastic scattering. They conclude that there are no major differences in the monolayer dynamics caused by intramolecular branching. It remains to be seen whether this similarity in monolayer dynamics also holds for the lubricating properties of these molecules in confined geometries.

  3. Achieving Uniform Monolayer Transition Metal Dichalcogenides Film on Silicon Wafer via Silanization Treatment: A Typical Study on WS2.

    Chen, Ying; Gan, Lin; Li, Huiqiao; Ma, Ying; Zhai, Tianyou


    A silanization reaction is employed to improve the dispersion of precursors on a silicon wafer for a large-size uniform transition metal dichalcogenide (TMD) film synthesis and to achieve a highly crystalline monolayer WS2 film up to 1 cm(2) . The novel strategy is also verified for the synthesis of WSe2 and MoS2 uniform films, suggesting universality for TMD film fabrication.

  4. Physical and monolayer film properties of potential fatty ester biolubricants

    Yao, Linxing [Iowa State University; Hammond, Earl G [Iowa State University; Wang, Tong [Iowa State University; Bu, Wei [Ames Laboratory; Vaknin, David [Ames Laboratory


    The desire to replace petroleum-based lubricants with alternatives that are environmentally friendly and made from sustainable sources has encouraged the development of biolubricants based on vegetable oils. To be good lubricants, the materials should have low melting points, appropriate viscosity and oxidative stability. In this paper, we report the melting point and viscosity of oleate esters of ethylene glycol, 1,2-propanediol, 2,3-butanediol, and pentaerythritol as well as the decanoate esters of 2,3-butanediol and the 12-methyltetradecanoate esters of 1,2-propanediol. Polyol esters that have a free hydroxy group had lower melting points than the completely esterified polyols, but the completely esterified polyol esters exhibited less change in viscosity with temperature than those having a free hydroxy group. 2, 3-Butanediol monooleate, which melted at -48.6°C shows promise as a biolubricant, but its viscosity index was estimated to be 100. Pentaerythritol oleate esters, with melting points below -10°C and viscosity indices in the range of 170–197, may be suitable candidates as biolubricants. The behavior of esters spread as a monomolecular film at air/water interface may provide insight into the way they behave when spread on metal or polar surfaces, so the pressure-area isotherms of 2,3-butanediol monoleate and selected esters are also reported.

  5. Characterization of monolayer formation on aluminum-doped zinc oxide thin films.

    Rhodes, Crissy L; Lappi, Simon; Fischer, Daniel; Sambasivan, Sharadha; Genzer, Jan; Franzen, Stefan


    The optical and electronic properties of aluminum-doped zinc oxide (AZO) thin films on a glass substrate are investigated experimentally and theoretically. Optical studies with coupling in the Kretschmann configuration reveal an angle-dependent plasma frequency in the mid-IR for p-polarized radiation, suggestive of the detection of a Drude plasma frequency. These studies are complemented by oxygen depletion density functional theory studies for the calculation of the charge carrier concentration and plasma frequency for bulk AZO. In addition, we report on the optical and physical properties of thin film adlayers of n-hexadecanethiol (HDT) and n-octadecanethiol (ODT) self-assembled monolayers (SAMs) on AZO surfaces using reflectance FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Our characterization of the SAM deposition onto the AZO thin film reveals a range of possible applications for this conducting metal oxide.

  6. The influence of the surface composition of mixed monolayer films on the evaporation coefficient of water.

    Miles, Rachael E H; Davies, James F; Reid, Jonathan P


    We explore the dependence of the evaporation coefficient of water from aqueous droplets on the composition of a surface film, considering in particular the influence of monolayer mixed component films on the evaporative mass flux. Measurements with binary component films formed from long chain alcohols, specifically tridecanol (C13H27OH) and pentadecanol (C15H31OH), and tetradecanol (C14H29OH) and hexadecanol (C16H33OH), show that the evaporation coefficient is dependent on the mole fractions of the two components forming the monolayer film. Immediately at the point of film formation and commensurate reduction in droplet evaporation rate, the evaporation coefficient is equal to a mole fraction weighted average of the evaporation coefficients through the equivalent single component films. As a droplet continues to diminish in surface area with continued loss of water, the more-soluble, shorter alkyl chain component preferentially partitions into the droplet bulk with the evaporation coefficient tending towards that through a single component film formed simply from the less-soluble, longer chain alcohol. We also show that the addition of a long chain alcohol to an aqueous-sucrose droplet can facilitate control over the degree of dehydration achieved during evaporation. After undergoing rapid gas-phase diffusion limited water evaporation, binary aqueous-sucrose droplets show a continued slow evaporative flux that is limited by slow diffusional mass transport within the particle bulk due to the rapidly increasing particle viscosity and strong concentration gradients that are established. The addition of a long chain alcohol to the droplet is shown to slow the initial rate of water loss, leading to a droplet composition that remains more homogeneous for a longer period of time. When the sucrose concentration has achieved a sufficiently high value, and the diffusion constant of water has decreased accordingly so that bulk phase diffusion arrest occurs in the monolayer

  7. Comparative study of electroless copper film on different self-assembled monolayers modified ABS substrate.

    Xu, Jiushuai; Fan, Ruibin; Wang, Jiaolong; Jia, Mengke; Xiong, Xuanrui; Wang, Fang


    Copper films were grown on (3-Mercaptopropyl)trimethoxysilane (MPTMS), (3-Aminopropyl)triethoxysilane (APTES) and 6-(3-(triethoxysilyl)propylamino)-1,3,5- triazine-2,4-dithiol monosodium (TES) self-assembled monolayers (SAMs) modified acrylonitrile-butadiene-styrene (ABS) substrate via electroless copper plating. The copper films were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Their individual deposition rate and contact angle were also investigated to compare the properties of SAMs and electroless copper films. The results indicated that the formation of copper nuclei on the TES-SAMs modified ABS substrate was faster than those on the MPTMS-SAMs and APTES-SAMs modified ABS substrate. SEM images revealed that the copper film on TES-SAM modified ABS substrate was smooth and uniform, and the density of copper nuclei was much higher. Compared with that of TES-SAMs modified resin, the coverage of copper nuclei on MPTMS and APTES modified ABS substrate was very limited and the copper particle size was too big. The adhesion property test demonstrated that all the SAMs enhanced the interfacial interaction between copper plating and ABS substrate. XRD analysis showed that the copper film deposited on SAM-modified ABS substrate had a structure with Cu(111) preferred orientation, and the copper film deposited on TES-SAMs modified ABS substrate is better than that deposited on MPTMS-SAMs or APTES-SAMs modified ABS resins in electromigrtion resistance.

  8. Comparative Study of Electroless Copper Film on Different Self-Assembled Monolayers Modified ABS Substrate

    Jiushuai Xu


    Full Text Available Copper films were grown on (3-Mercaptopropyltrimethoxysilane (MPTMS, (3-Aminopropyltriethoxysilane (APTES and 6-(3-(triethoxysilylpropylamino-1,3,5- triazine-2,4-dithiol monosodium (TES self-assembled monolayers (SAMs modified acrylonitrile-butadiene-styrene (ABS substrate via electroless copper plating. The copper films were examined using scanning electron microscopy (SEM and X-ray diffraction (XRD. Their individual deposition rate and contact angle were also investigated to compare the properties of SAMs and electroless copper films. The results indicated that the formation of copper nuclei on the TES-SAMs modified ABS substrate was faster than those on the MPTMS-SAMs and APTES-SAMs modified ABS substrate. SEM images revealed that the copper film on TES-SAM modified ABS substrate was smooth and uniform, and the density of copper nuclei was much higher. Compared with that of TES-SAMs modified resin, the coverage of copper nuclei on MPTMS and APTES modified ABS substrate was very limited and the copper particle size was too big. The adhesion property test demonstrated that all the SAMs enhanced the interfacial interaction between copper plating and ABS substrate. XRD analysis showed that the copper film deposited on SAM-modified ABS substrate had a structure with Cu(111 preferred orientation, and the copper film deposited on TES-SAMs modified ABS substrate is better than that deposited on MPTMS-SAMs or APTES-SAMs modified ABS resins in electromigrtion resistance.

  9. Ultrafast electron diffraction optimized for studying structural dynamics in thin films and monolayers.

    Badali, D S; Gengler, R Y N; Miller, R J D


    A compact electron source specifically designed for time-resolved diffraction studies of free-standing thin films and monolayers is presented here. The sensitivity to thin samples is achieved by extending the established technique of ultrafast electron diffraction to the "medium" energy regime (1-10 kV). An extremely compact design, in combination with low bunch charges, allows for high quality diffraction in a lensless geometry. The measured and simulated characteristics of the experimental system reveal sub-picosecond temporal resolution, while demonstrating the ability to produce high quality diffraction patterns from atomically thin samples.

  10. Ultrafast electron diffraction optimized for studying structural dynamics in thin films and monolayers

    D. S. Badali


    Full Text Available A compact electron source specifically designed for time-resolved diffraction studies of free-standing thin films and monolayers is presented here. The sensitivity to thin samples is achieved by extending the established technique of ultrafast electron diffraction to the “medium” energy regime (1–10 kV. An extremely compact design, in combination with low bunch charges, allows for high quality diffraction in a lensless geometry. The measured and simulated characteristics of the experimental system reveal sub-picosecond temporal resolution, while demonstrating the ability to produce high quality diffraction patterns from atomically thin samples.

  11. Antibacterial activity of large-area monolayer graphene film manipulated by charge transfer.

    Li, Jinhua; Wang, Gang; Zhu, Hongqin; Zhang, Miao; Zheng, Xiaohu; Di, Zengfeng; Liu, Xuanyong; Wang, Xi


    Graphene has attracted increasing attention for potential applications in biotechnology due to its excellent electronic property and biocompatibility. Here we use both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) to investigate the antibacterial actions of large-area monolayer graphene film on conductor Cu, semiconductor Ge and insulator SiO2. The results show that the graphene films on Cu and Ge can surprisingly inhibit the growth of both bacteria, especially the former. However, the proliferation of both bacteria cannot be significantly restricted by the graphene film on SiO2. The morphology of S. aureus and E. coli on graphene films further confirms that the direct contact of both bacteria with graphene on Cu and Ge can cause membrane damage and destroy membrane integrity, while no evident membrane destruction is induced by graphene on SiO2. From the viewpoint of charge transfer, a plausible mechanism is proposed here to explain this phenomenon. This study may provide new insights for the better understanding of antibacterial actions of graphene film and for the better designing of graphene-based antibiotics or other biomedical applications.

  12. Chemically sensitive surface plasmon devices employing a self-assembled monolayer composite film

    DePriest, J. C.; Meriaudeau, Fabrice; Oden, Patrick I.; Downey, Todd R.; Passian, A.; Wig, A. G.; Ferrell, Trinidad L.


    In this paper the results of detecting volatile organic compounds (VOC) employing surface plasmon-based sensors are presented. The initial step in preparing the sensing elements herein requires depositing Au degree(s) on a quartz slide. The sensing elements are based on either (1) freshly deposited Au degree(s) or (2) growth of a self assembled monolayer composite film (SAM) on to a freshly deposited Au degree(s) surface. The desired SAM is either (1) acid terminated using (omega) -mercaptoundecanoic acid (MUA-COOH) or (2) Cu2+ metal ion terminated yielding (omega) - mercaptoundecanoic acid-Cu2+ (MUA-Cu2+). The experimental apparatus shown here measures the reflectivity of the Au degree(s) surface as a function of time at a given angle. The response of this surface plasmon device to various VOC's is correlated to the composition of the SAM film.

  13. Sub-monolayer film growth of a volatile lanthanide complex on metallic surfaces

    Chen, Jinjie; Edelmann, Kevin; Wulfhekel, Wulf


    Summary We deposited a volatile lanthanide complex, tris(2,2,6,6-tetramethyl-3,5-heptanedionato)terbium(III), onto metal surfaces of Cu(111), Ag(111) and Au(111) in vacuum and observed well-ordered sub-monolayer films with low temperature (5 K) scanning tunneling microscopy. The films show a distorted three-fold symmetry with a commensurate structure. Scanning tunneling spectroscopy reveals molecular orbitals delocalized on the ligands of the molecule. Our results imply that this complex can be transferred onto the metal substrates without molecular decomposition or contamination of the surface. This new rare-earth-based class of molecules broadens the choice of molecular magnets to study with scanning tunneling microscopy. PMID:26733215

  14. Sub-monolayer film growth of a volatile lanthanide complex on metallic surfaces

    Hironari Isshiki


    Full Text Available We deposited a volatile lanthanide complex, tris(2,2,6,6-tetramethyl-3,5-heptanedionatoterbium(III, onto metal surfaces of Cu(111, Ag(111 and Au(111 in vacuum and observed well-ordered sub-monolayer films with low temperature (5 K scanning tunneling microscopy. The films show a distorted three-fold symmetry with a commensurate structure. Scanning tunneling spectroscopy reveals molecular orbitals delocalized on the ligands of the molecule. Our results imply that this complex can be transferred onto the metal substrates without molecular decomposition or contamination of the surface. This new rare-earth-based class of molecules broadens the choice of molecular magnets to study with scanning tunneling microscopy.

  15. Angle-resolved XPS analysis and characterization of monolayer and multilayer silane films for DNA coupling to silica.

    Shircliff, Rebecca A; Stradins, Paul; Moutinho, Helio; Fennell, John; Ghirardi, Maria L; Cowley, Scott W; Branz, Howard M; Martin, Ina T


    We measure silane density and Sulfo-EMCS cross-linker coupling efficiency on aminosilane films by high-resolution X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements. We then characterize DNA immobilization and hybridization on these films by (32)P-radiometry. We find that the silane film structure controls the efficiency of the subsequent steps toward DNA hybridization. A self-limited silane monolayer produced from 3-aminopropyldimethylethoxysilane (APDMES) provides a silane surface density of ~3 nm(-2). Thin (1 h deposition) and thick (19 h deposition) multilayer films are generated from 3-aminopropyltriethoxysilane (APTES), resulting in surfaces with increased roughness compared to the APDMES monolayer. Increased silane surface density is estimated for the 19 h APTES film, due to a ∼32% increase in surface area compared to the APDMES monolayer. High cross-linker coupling efficiencies are measured for all three silane films. DNA immobilization densities are similar for the APDMES monolayer and 1 h APTES. However, the DNA immobilization density is double for the 19 h APTES, suggesting that increased surface area allows for a higher probe attachment. The APDMES monolayer has the lowest DNA target density and hybridization efficiency. This is attributed to the steric hindrance as the random packing limit is approached for DNA double helices (dsDNA, diameter ≥ 2 nm) on a plane. The heterogeneity and roughness of the APTES films reduce this steric hindrance and allow for tighter packing of DNA double helices, resulting in higher hybridization densities and efficiencies. The low steric hindrance of the thin, one to two layer APTES film provides the highest hybridization efficiency of nearly 88%, with 0.21 dsDNA/nm(2). The XPS data also reveal water on the cross-linker-treated surface that is implicated in device aging.

  16. Monolayer and bilayer structures in ionic liquids and their mixtures confined to nano-films.

    Smith, Alexander M; Lovelock, Kevin R J; Perkin, Susan


    The confinement of liquids to thin films can lead to dramatic changes in their structural arrangement and dynamic properties. Ionic liquids display nano-structures in the bulk of the liquid, consisting of polar and non-polar domains, whereas a solid surface can induce layered structures in the near-surface liquid. Here we compare and contrast the layer structures in a series of imidazolium and pyrrolidinium-based ionic liquids upon confinement of the liquids to films of approximately 0-20 nm between two negatively charged mica surfaces. Using a surface force balance (SFB) we measured the force between the two atomically smooth mica surfaces with ionic liquid between, directly revealing the ion packing and dimensions of layered structures for each liquid. The ionic liquids with shorter alkyl chain substituents form alternating cation-anion monolayer structures on confinement, whilst a longer alkyl chain leads to alignment of the cations in bilayer formation. The crossover from monolayers to bilayers, however, occurs at different alkyl chain lengths for imidazolium- and pyrrolidinium-based ionic liquids with a common anion. In addition, we find that imidazolium cation bilayers are arranged in toe-to-toe orientation, whereas pyrrolidinium cations form bilayers consisting of fully interdigitated alkyl chains. Results for a mixture of monolayer-preferring (i.e. short alkyl chain) and bilayer-preferring (i.e. long alkyl chain) liquids indicate alkyl chain segregation and bilayer-like structures. We discuss the driving forces for these self-assembly effects, and the contrasting behaviour of the imidazolium and pyrrolidinium-type ionic liquids.

  17. Evanescent wave absorption sensor based on tapered multimode fiber coated with monolayer graphene film

    Qiu, Hengwei; Gao, Saisai; Chen, Peixi; Li, Zhen; Liu, Xiaoyun; Zhang, Chao; Xu, Yuanyuan; Jiang, Shouzhen; Yang, Cheng; Huo, Yanyan; Yue, Weiwei


    An evanescent wave absorption (EWA) sensor based on tapered multimode fiber (TMMF) coated with monolayer graphene film for the detection of double-stranded DNA (DS-DNA) is investigated in this work. The TMMF is a silica multimode fiber (nominally at 62.5 μm), which was tapered to symmetric taper with waist diameters of ~30 μm and total length of ~3 mm. Monolayer graphene film was grown on a copper foil via chemical vapor deposition (CVD) technology and transferred onto skinless tapered fiber core via dry transfer technology. All the components of the sensor are coupled together by fusion splicer in order to eliminate the external disturbance. DS-DNA is created by the assembly of two relatively complemented oligonucleotides. The measurements are obtained by using a spectrometer in the optical wavelength range of 400-900 nm. With the increase of DS-DNA concentration, the output light intensity (OPLI) arisen an obvious attenuation. Importantly, the absorbance (A) and the DS-DNA concentrations shown a reasonable linear variation in a wide range of 5-400 μM. Through a series of comparison, the accuracy of TMMF sensor with graphene (G-TMMF) is much better than that without graphene (TMMF), which can be attributed to the molecular enrichment of graphene by π-π stacking.

  18. Tribology of monolayer films: comparison between n-alkanethiols on gold and n-alkyl trichlorosilanes on silicon.

    Booth, Brandon D; Vilt, Steven G; McCabe, Clare; Jennings, G Kane


    This Article presents a quantitative comparison of the frictional performance for monolayers derived from n-alkanethiolates on gold and n-alkyl trichlorosilanes on silicon. Monolayers were characterized by pin-on-disk tribometry, contact angle analysis, ellipsometry, and electrochemical impedance spectroscopy (EIS). Pin-on-disk microtribometry provided frictional analysis at applied normal loads from 10 to 1000 mN at a speed of 0.1 mm/s. At low loads (10 mN), methyl-terminated n-alkanethiolate self-assembled monolayers (SAMs) exhibited a 3-fold improvement in coefficient of friction over SAMs with hydroxyl- or carboxylic-acid-terminated surfaces. For monolayers prepared from both n-alkanethiols on gold and n-alkyl trichlorosilanes on silicon, a critical chain length of at least eight carbons is required for beneficial tribological performance at an applied load of 9.8 mN. Evidence for disruption of chemisorbed alkanethiolate SAMs with chain lengths n tribology wear tracks. The direct comparison between the tribological stability of alkanethiolate and silane monolayers shows that monolayers prepared from n-octadecyl dimethylchlorosilane and n-octadecyl trichlorosilane withstood normal loads at least 30 times larger than those that damaged octadecanethiolate SAMs. Collectively, our results show that the tribological properties of monolayer films are dependent on their internal stabilities, which are influenced by cohesive chain interactions (van der Waals) and the adsorbate-substrate bond.

  19. Active Antifogging Property of Monolayer SiO2 Film with Bioinspired Multiscale Hierarchical Pagoda Structures.

    Han, Zhiwu; Mu, Zhengzhi; Li, Bo; Wang, Ze; Zhang, Junqiu; Niu, Shichao; Ren, Luquan


    Antifogging surfaces with hydrophilic or even superhydrophilic wetting behavior have received significant attention due to their ability to reduce light scattering by film-like condensation. However, a major challenge remains in achieving high-speed antifogging performance and revealing the hydrophilic-based antifogging mechanism of glass or other transparent materials under aggressive fogging conditions. Herein, with inspiration from the fog-free property of the typical Morpho menelaus terrestris butterfly (Butler, 1866) wing scales, a monolayer SiO2 film with multiscale hierarchical pagoda structures (MHPSs) based on glass substrate was designed and fabricated using an optimized biotemplate-assisted wet chemical method without any post-treatments. The biomimetic monolayer film (BMF) composed of nanoscale SiO2 3D networks displayed excellent antifogging properties, which is superior to that of the glass substrate itself. The MHPS-based BMF even kept high transmittance (∼95%) under aggressive fog conditions, and it almost instantaneously recovered to a fog-free state (properties mainly benefit from the synergistic effect of both hydrophilic chemical compositions (nanoscale SiO2) and physical structures (biomimetic MHPSs) of the BMF. High-speed active antifogging performance of the glass materials enabled the retention of a high transmittance property even in humid conditions, heralding reliable optical performance in outdoor practical applications, especially in aggressive foggy environments. More importantly, the investigations in this work offer a promising way to handily design and fabricate quasi-textured surfaces with multiscale hierarchical structures that possess high-performance physicochemical properties.

  20. Interfacial Reactions in Confinement: Kinetics and Temperature Dependence of Reactions in Self-Assembled Monolayers Compared to Ultrathin Polymer Films

    Schönherr, Holger; Feng, C.L.; Shovsky, A.


    We report on a comparative study of the temperature dependence of the alkaline hydrolysis of N-hydroxy-succinimide (NHS) ester groups confined in self-assembled monolayers (SAMs) of 11,11'-dithiobis(N-hydroxysuccinimidylundecanoate) (NHS-C10) on gold and ultrathin films of poly(N-hydroxysuccinimidyl

  1. Easily processable highly ordered Langmuir-Blodgett films of quaterthiophene disiloxane dimer for monolayer organic field-effect transistors.

    Sizov, Alexey S; Anisimov, Daniil S; Agina, Elena V; Borshchev, Oleg V; Bakirov, Artem V; Shcherbina, Maxim A; Grigorian, Souren; Bruevich, Vladimir V; Chvalun, Sergei N; Paraschuk, Dmitry Yu; Ponomarenko, Sergei A


    Self-assembly of highly soluble water-stable tetramethyldisiloxane-based dimer of α,α'-dialkylquaterthiophene on the water-air interface was investigated by Langmuir, grazing incidence X-ray diffraction, and X-ray reflectivity techniques. The conditions for formation of very homogeneous crystalline monolayer Langmuir-Blodgett (LB) films of the oligomer were found. Monolayer organic field-effect transistors (OFETs) based on these LB films as a semiconducting layer showed hole mobilities up to 3 × 10(-3) cm(2)/(V s), on-off ratio of 10(5), small hysteresis, and high long-term stability. The electrical performance of the LB films studied is close to that for the same material in the bulk or in the monolayer OFETs prepared from water vapor sensitive chlorosilyl derivatives of quaterthiophene by self-assembling from solution. These findings show high potential of disiloxane-based LB films in monolayer OFETs for large-area organic electronics.

  2. Paths to collapse for isolated skyrmions in few-monolayer ferromagnetic films

    Stosic, Dusan; Mulkers, Jeroen; Van Waeyenberge, Bartel; Ludermir, Teresa B.; Milošević, Milorad V.


    Magnetic skyrmions are topological spin configurations in materials with chiral Dzyaloshinskii-Moriya interaction (DMI), that are potentially useful for storing or processing information. To date, DMI has been found in few bulk materials, but can also be induced in atomically thin magnetic films in contact with surfaces with large spin-orbit interactions. Recent experiments have reported that isolated magnetic skyrmions can be stabilized even near room temperature in few-atom-thick magnetic layers sandwiched between materials that provide asymmetric spin-orbit coupling. Here we present the minimum-energy path analysis of three distinct mechanisms for the skyrmion collapse, based on ab initio input and the performed atomic-spin simulations. We focus on the stability of a skyrmion in three atomic layers of Co, either epitaxial on the Pt(111) surface or within a hybrid multilayer where DMI nontrivially varies per monolayer due to competition between different symmetry breaking from two sides of the Co film. In laterally finite systems, their constrained geometry causes poor thermal stability of the skyrmion toward collapse at the boundary, which we show to be resolved by designing the high-DMI structure within an extended film with lower or no DMI.

  3. Assembly of gold composite thin films by spontaneous reduction of subphase chloroaurate anions beneath vitamin E Langmuir monolayers

    Zhang, L. [School of Chemistry and Chemical Engineering, Anhui University, Hefei 230039 (China); Department of Chemistry-Biology, Suzhou College, Suzhou 234000 (China); Shen, Y.H. [School of Chemistry and Chemical Engineering, Anhui University, Hefei 230039 (China)], E-mail:; Xie, A.J.; Li, S.K.; Qiu, L.G.; Li, Y.M. [School of Chemistry and Chemical Engineering, Anhui University, Hefei 230039 (China)


    Gold composite thin films were generated by the spontaneous reduction of chloroaurate (AuCl{sub 4}{sup -}) ions beneath vitamin E (VE) Langmuir monolayer. The monolayer and gold nanocomposite LB films were then characterized by surface pressure-area ({pi}-A) isotherms, ultraviolet-visible spectroscopy (UV-vis), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction analysis (XRD), respectively. The results showed that the limiting area/VE molecule on the HAuCl{sub 4} solution subphase was larger than that on the pure water subphase, and it increased with reaction time. The morphologies of Au particles such as spherical-like, triangular and multiply-twinned particles (MTPs) could be observed. The XRD pattern indicated that the gold particles in LB films were face-centered cubic (fcc) polycrystalline. The plasmon absorption intensities of gold composite LB films increased with the film thickness, which suggested that the monolayer containing gold particles could be transferred successfully onto the substrates.

  4. Wetting transitions of simple liquid films adsorbed on selfassembled monolayer substrates: an ellipsometric study

    Batchelder, D. N.; Cheng, Y. L.; Evans, S. D.; Henderson, J. R.

    We report on an ellipsometric experimental study designed to explore the relevance of the wetting phase diagram predicted by liquid state physics of basic models, to the wide class of simple organic liquid films that adsorb from saturated vapour onto planar substrates at room temperature. The wetting properties are explored by measuring adsorption isotherms in the approach to saturation, in particular, for adsorption of n -hexane on a variety of specially constructed substrates (self-assembled monolayers) spanning a wide range of surface energy, and by carrying out the microscopic equivalent of contact angle experiments at saturation. We locate a wetting transition, which in our case is continuous, and then study its properties in detail. The general prediction of the wetting phase diagram, that wetting transitions should be ubiquitous in nature and readily located via control over the substrate field, is supported by our data, but the quantitative nature of the thick film adsorption regime is not in agreement with Lifshitz theory. This conclusion supports the work of a variety of earlier related studies, but contrasts with recent results for adsorption onto the surface of water. In addition, the correlation length determined from our complete wetting adsorption isotherms is mesoscopic, suggesting that equilibrium statistical mechanics of simple models of inhomogeneous fluids cannot explain the data.

  5. Investigation of Tribological Behavior of Lanthanum-Based Thin Films Deposited on Sulfonated Self-Assembled Monolayer


    3-mercaptopropyl trimethoxysilane (MPTS) was prepared on glass substrate so as to form a two-dimensional self-assembled monolayer (SAM), and the terminal -SH group in the film was in situ oxidized to -SO3H group to confer good chemisorption ability to the film. Thus, lanthanum-based thin films were deposited on oxidized MPTS-SAM, making use of the chemisorption ability of -SO3H group. Atomic force microscopy (AFM) and X-ray photoelectron spectrometry (XPS) and contact angle measurements were used to characterize the thin films. The tribological properties of the as-prepared thin films sliding against a steel ball were evaluated on a friction and wear tester. Tribological experiment shows that the friction coefficient of glass substrate decreases from 0.8 to 0.08 after the rare earth (RE) self-assembled films (SAMs) are formed on its surface. And the RE self-assembled films have longer wear life (500 sliding passes). It is demonstrated that RE self-assembled film exhibits good wear-resistant property. The marked decrease in friction and the longer wear life of RE films are attributed to the excellent adhesion of the film to the substrate and to the special characteristics of the RE elements. The frictional behaviors of RE thin-films-coated silicon surface were sensitive to the applied load and the sliding velocity of the steel ball.

  6. Fabrication of P3HT/gold nanoparticle LB films by P3HT templating Langmuir monolayer

    Chen, Liang-Huei [Department of Medicinal Chemistry, Chia-Nan University of Pharmacy and Science, Tainan, Taiwan (China); Hsu, Wen-Ping, E-mail: [Department of Chemical Engineering, National United University, Miao-Li, Taiwan 36063 (China); Chan, Han-Wen [Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan 70101 (China); Lee, Yuh-Lang, E-mail: [Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan 70101 (China)


    Highlights: • Addition of ODA into the P3HT monolayer can significantly improve the dispersion ability of P3HT molecules. • The adsorption ability of the P3HT monolayer to the dispersed AuNPs can also be enhanced by the presence of ODA. - Abstract: Regioregular poly(3-hexyl thiophene) (rr-P3HT) and mixed P3HT/octadecyl amine (ODA) were used as template monolayers to adsorb the gold nanoparticles (AuNPs) dispersed in subphase. The behaviors of P3HT and P3HT/ODA monolayers were investigated by surface pressure area per molecule (π–A) isotherms, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The experimental results show that P3HT does not form a homogeneous film and tends to aggregate at the air/water interface. Meanwhile, the amount of AuNPs adsorbed by the P3HT monolayers is low, attributable to the weak interaction between AuNPs and P3HT. By introduction of ODA molecules into the P3HT monolayer, the spreading of P3HT molecules at the air/water interface is improved and the aggregation of P3HT is significantly inhibited. A nearly uniform and homogeneously mixed P3HT/ODA monolayer can be obtained when 50% of ODA is introduced. It is also found that the introduction of ODA can significantly increase the adsorption of AuNPs. For the mixed monolayer with low ratio of ODA (P3HT/ODA = 1/0.2), a higher concentration of adsorbed AuNPs was observed on the corresponding monolayer. However, when the ODA/P3HT ratio increases to 1/1, the AuNPs tend to form three-dimensional (3D) aggregates and the AuNPs cannot distribute well as a homogeneous monolayer. This result is ascribed to the increasing hydrophobicity of the adsorbed AuNPs because of capping of more ODA molecules.

  7. Two-component Langmuir monolayers and LB films of DPPC with partially fluorinated alcohol (F8H9OH).

    Nakahara, Hiromichi; Hirano, Chikayo; Shibata, Osamu


    The interaction of (perfluorooctyl)nonanol (F8H9OH) with dipalmitoylphosphatidylcholine (DPPC) was systematically studied in two-component monolayers at air-water interface. The thermodynamic property and phase morphology of the monolayers were investigated by isotherm measurements and several microscopic methods such as Brewster angle microscopy, fluorescence microscopy, and atomic force microscopy (AFM). The AFM topographies for Langmuir-Blodgett films of F8H9OH exhibit the formation of monodispersed surface micelles. In the two-component system, the incorporation of F8H9OH induces condensation (or solidification) of DPPC monolayers. The excess Gibbs free energy and interaction parameter (or energy) of the two components were calculated from the isotherm data. Both the phase transition pressure for the coexistence of ordered and disordered phases and collapse pressure of monolayers vary with the mole fraction of F8H9OH, indicating binary miscibility between F8H9OH and DPPC within a monolayer state. The miscibility is also confirmed visually by in situ and ex situ microscopy at micro- and nanometer scales.

  8. Interfacial properties in Langmuir monolayers and LB films of DPPC with partially fluorinated alcohol (F8H7OH).

    Nakahara, Hiromichi; Hirano, Chikayo; Fujita, Ichiro; Shibata, Osamu


    Two-component interactions between (perfluorooctyl) heptanol (F8H7OH) and dipalmitoylphosphatidylcholine (DPPC), which is a major component of pulmonary surfactants in mammals, were systematically elucidated using Langmuir monolayers and Langmuir-Blodgett (LB) films of the compounds. The interactions such as the miscibility of the compounds and their phase behavior were examined from thermodynamic and morphological perspectives. The surface pressure (π)-molecular area (A) and surface potential (ΔV)-A isotherms of the binary monolayers containing F8H7OH in different mole fractions (XF8H7OH) were measured simultaneously. The excess Gibbs free energy of mixing of the two components was calculated from the π-A isotherms. The resulting isotherm data were employed to construct a two-dimensional (2D) phase diagram of the system. The phase diagram revealed that the transition pressure as well as the monolayer collapse pressure change with changes in XF8H7OH. These thermodynamic analyses suggested that the miscibility of the two components and the solidification of DPPC monolayers can be induced by the addition of F8H7OH. The phase behavior upon monolayer compression was observed morphologically in situ using Brewster angle microscopy (BAM) and fluorescence microscopy (FM), as well as ex situ using atomic force microscopy (AFM). Interestingly, the AFM-based analysis revealed the formation of monodispersed 2D micelles consisting of F8H7OH at low surface pressures.

  9. Tracing the 4000 year history of organic thin films: From monolayers on liquids to multilayers on solids

    Greene, J. E. [University of Illinois, Urbana, Illinois 61801 (United States); Linköping University, 581 83 Linköping (Sweden); National Taiwan University of Science and Technology, Taipei 10607, Taiwan (China)


    The recorded history of organic monolayer and multilayer thin films spans approximately 4000 years. Fatty-acid-based monolayers were deposited on water by the ancients for applications ranging from fortune telling in King Hammurabi's time (∼1800 BC, Mesopotamia) to stilling choppy waters for sailors and divers as reported by the Roman philosopher Pliny the Elder in ∼78 AD, and then much later (1774) by the peripatetic American statesman and natural philosopher Benjamin Franklin, to Japanese “floating-ink” art (suminagashi) developed ∼1000 years ago. The modern science of organic monolayers began in the late-1800s/early-1900s with experiments by Lord Rayleigh and the important development by Agnes Pockels, followed two decades later by Irving Langmuir, of the tools and technology to measure the surface tension of liquids, the surface pressure of organic monolayers deposited on water, interfacial properties, molecular conformation of the organic layers, and phase transitions which occur upon compressing the monolayers. In 1935, Katherine Blodgett published a landmark paper showing that multilayers can be synthesized on solid substrates, with controlled thickness and composition, using an apparatus now known as the Langmuir-Blodgett (L-B) trough. A disadvantage of LB films for some applications is that they form weak physisorbed bonds to the substrate. In 1946, Bigelow, Pickett, and Zisman demonstrated, in another seminal paper, the growth of organic self-assembled monolayers (SAMs) via spontaneous adsorption from solution, rather than from the water/air interface, onto SiO{sub 2} and metal substrates. SAMs are close-packed two-dimensional organic crystals which exhibit strong covalent bonding to the substrate. The first multicomponent adsorbed monolayers and multilayer SAMs were produced in the early 1980s. Langmuir monolayers, L-B multilayers, and self-assembled mono- and multilayers have found an extraordinarily broad range of applications including

  10. Tracing the 4000 year history of organic thin films: From monolayers on liquids to multilayers on solidsa)

    Greene, J. E.


    The recorded history of organic monolayer and multilayer thin films spans approximately 4000 years. Fatty-acid-based monolayers were deposited on water by the ancients for applications ranging from fortune telling in King Hammurabi's time (˜1800 BC, Mesopotamia) to stilling choppy waters for sailors and divers as reported by the Roman philosopher Pliny the Elder in ˜78 AD, and then much later (1774) by the peripatetic American statesman and natural philosopher Benjamin Franklin, to Japanese "floating-ink" art (suminagashi) developed ˜1000 years ago. The modern science of organic monolayers began in the late-1800s/early-1900s with experiments by Lord Rayleigh and the important development by Agnes Pockels, followed two decades later by Irving Langmuir, of the tools and technology to measure the surface tension of liquids, the surface pressure of organic monolayers deposited on water, interfacial properties, molecular conformation of the organic layers, and phase transitions which occur upon compressing the monolayers. In 1935, Katherine Blodgett published a landmark paper showing that multilayers can be synthesized on solid substrates, with controlled thickness and composition, using an apparatus now known as the Langmuir-Blodgett (L-B) trough. A disadvantage of LB films for some applications is that they form weak physisorbed bonds to the substrate. In 1946, Bigelow, Pickett, and Zisman demonstrated, in another seminal paper, the growth of organic self-assembled monolayers (SAMs) via spontaneous adsorption from solution, rather than from the water/air interface, onto SiO2 and metal substrates. SAMs are close-packed two-dimensional organic crystals which exhibit strong covalent bonding to the substrate. The first multicomponent adsorbed monolayers and multilayer SAMs were produced in the early 1980s. Langmuir monolayers, L-B multilayers, and self-assembled mono- and multilayers have found an extraordinarily broad range of applications including controlled wetting

  11. Inorganic-organic composite nanoengineered films using self-assembled monolayers for directed zeolite film growth

    Dye, R.C.; Hermes, R.E.; Martinez, M.G.; Peachey, N.M.


    This is the final report of a one-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Zeolites, or molecular sieves, are aluminosilicate cage structures that are typically grown from a heterogeneous mixture of organic template molecules, inorganic salts of alumina and silica, and water. These zeolites are used in industry for catalytic cracking of hydrocarbons (gasoline manufacture from oil), and contaminant removal from chemical production processes. Within one year, we developed a viable method for the deposition of a quaternary ammonium salt amphiphile onto silicon wafer substrates. Using a biomimetic growth process, we were also able to demonstrate the first thin-film formation of a zeolite structure from such an organic template. Additionally, we synthesized the precursor to another amphiphile which was to be for further studies.

  12. Resist Pattern Inspection Using Fluorescent Dye-Doped Polystyrene Thin Films in Reactive-Monolayer-Assisted Thermal Nanoimprint Lithography

    Kubo, Shoichi; Sato, Yuko; Hirai, Yoshihiko; Nakagawa, Masaru


    Fluorescent dye-doped polystyrene (PS) thin films were studied for defect inspection of PS resist patterns by fluorescence microscopy in reactive-monolayer-assisted thermal nanoimprint lithography using a photoreactive monolayer. A fluorescent dye of N,N '-bis(2,6-dimethylphenyl-perylene-3,4,9,10-tetracarboxylic diimide doped in a PS resist thin film maintained an almost identical fluorescence intensity after annealing at a temperature necessary for thermal nanoimprinting. To avoid degradation of a dye doped in a resist film owing to exposure to ultraviolet light for preparing a PS graft layer on the photoreactive monolayer, a double coating method for preparing a dye-doped PS resist layer on the PS graft layer was adopted. It was demonstrated by the fluorescent microscopic defect inspection that resist pattern defects due to unleveled residual layers after thermal nanoimprinting were significantly decreased by adding low-molecular-weight PS (5,100 g mol-1) to high-molecular-weight PS (360,000 g mol-1). The rheological study revealed that the low-molecular-weight PS obviously functioned as a plasticizer, which flattened residual layers and decreased their thickness.

  13. Support-Free Transfer of Ultrasmooth Graphene Films Facilitated by Self-Assembled Monolayers for Electronic Devices and Patterns.

    Wang, Bin; Huang, Ming; Tao, Li; Lee, Sun Hwa; Jang, A-Rang; Li, Bao-Wen; Shin, Hyeon Suk; Akinwande, Deji; Ruoff, Rodney S


    We explored a support-free method for transferring large area graphene films grown by chemical vapor deposition to various fluoric self-assembled monolayer (F-SAM) modified substrates including SiO2/Si wafers, polyethylene terephthalate films, and glass. This method yields clean, ultrasmooth, and high-quality graphene films for promising applications such as transparent, conductive, and flexible films due to the absence of residues and limited structural defects such as cracks. The F-SAM introduced in the transfer process can also lead to graphene transistors with enhanced field-effect mobility (up to 10,663 cm(2)/Vs) and resistance modulation (up to 12×) on a standard silicon dioxide dielectric. Clean graphene patterns can be realized by transfer of graphene onto only the F-SAM modified surfaces.

  14. Nano-tribological characteristics of lanthanum-based thin films on sulfonated self-assembled monolayer of 3-mercaptopropyl trimethoxysilane

    BAI Tao; CHENG Xianhua


    Silane coupling reagent (3-mercaptopropyl trimethoxysilane (MPTS)) was prepared on silicon substrate to form two-dimensional Self-Assembled Monolayer (SAM) and the terminal -SH group in the film was in situ oxidized to -SO3H group to endow the film with good chemisorption ability. Thus, lanthanum-based thin films were deposited on oxidized MPTS-SAM to form rare earth composite thin films (RE thin films), making use of the chemisorption ability of the --SO3H group. Atomic Force Microscope (AFM), X-ray Photoelectron Spectrometry (XPS), and contact angle measurements were used to characterize the RE thin films. Adhesive force and friction force of the RE thin films and silicon substrate were measured under various applied normal loads and scanning speed of AFM tip. The results showed that the friction force increased with applied normal loads and scanning speed of AFM tip. To study the effect of capillary force, tests were performed in various relative humidities. The results showed that the adhesive force of silicon substrate increased with relative humidity and the adhesive force of RE thin films only increased slightly with relative humidity. Research showed that surfaces with higher hydrophobic property reveal lowered adhesive and friction forces.

  15. Surface properties of self-assembled monolayer films of tetra-substituted cobalt, iron and manganese alkylthio phthalocyanine complexes

    Akinbulu, Isaac Adebayo; Khene, Samson [Department of Chemistry, Rhodes University, Grahamstown 6140 (South Africa); Nyokong, Tebello, E-mail: [Department of Chemistry, Rhodes University, Grahamstown 6140 (South Africa)


    Self-assembled monolayer (SAM) films of iron (SAM-1), cobalt (SAM-2) and manganese (SAM-3) phthalocyanine complexes, tetra-substituted with diethylaminoethanethio at the non-peripheral positions, were formed on gold electrode in dimethylformamide (DMF). Electrochemical, impedimentary and surface properties of the SAM films were investigated. Cyclic voltammetry was used to investigate the electrochemical properties of the films. Ability of the films to inhibit common faradaic processes on bare gold surface (gold oxidation, solution redox chemistry of [Fe(H{sub 2}O){sub 6}]{sup 3+}/[Fe(H{sub 2}O){sub 6}]{sup 2+} and underpotential deposition (UDP) of copper) was investigated. Electrochemical impedance spectroscopy (EIS), using [Fe(CN){sub 6}]{sup 3-/4-} redox process as a probe, offered insights into the electrical properties of the films/electrode interfaces. Surface properties of the films were probed using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The films were employed for the electrocatalytic oxidation of the pesticide, carbofuran. Electrocatalysis was evidenced from enhanced current signal and less positive oxidation potential of the pesticide on each film, relative to that observed on the bare gold electrode. Mechanism of electrocatalytic oxidation of the pesticide was studied using rotating disc electrode voltammetry.

  16. Magnetic measurements of monolayer-thickness films of Cr sandwiched by Au

    Brodsky, M.B.; Sill, L.R.; Sowers, C.H.


    Calculations show ferromagnetic moments ( B/) in Au-Cr-Au sandwiches, for monolayers of Cr. The measured moment ( B/ at 2/sup 0/K) is larger in Cr monolayers than for thicker Cr samples. Results are discussed in terms of other studies of this system including those which showed superconductivity.

  17. A comparative analysis of graphene oxide films as proton conductors

    Smirnov, V. A.; Denisov, N. N.; Dremova, N. N.; Vol'fkovich, Y. M.; Rychagov, A. Y.; Sosenkin, V. E.; Belay, K. G.; Gutsev, G. L.; Shulga, N. Yu.; Shulga, Y. M.


    The electrical conductivity of graphene oxide (GO) films in vapors of water and acid solutions is found to be close to the conductivity of a film formed after drying the solution of phenol-2,4-disulfonic acid in polyvinyl alcohol, which is known to be a proton conductor. We found that the conductivity of a GO film in vapors of the H2O-H2SO4 electrolyte possesses a sharp maximum at ~1 % by weight of sulfuric acid. The highest conductivity of GO films can be expected when placing the films over acid vapors where the acid concentration is essentially lower than in the acid solutions at their maximum conductivity. Since the conductivity of the H2O-H2SO4 electrolyte itself has a maximum at ~30 % by weight of sulfuric acid, the use of intermediate concentrations of H2SO4 is recommended in practical applications. The GO films permeated with water or acid solution in water are expected to possess the proton-exchange properties similar to those of other proton-exchanging membranes.

  18. Low adhesion, non-wetting phosphonate self-assembled monolayer films formed on copper oxide surfaces.

    Hoque, E; DeRose, J A; Bhushan, B; Hipps, K W


    Self-assembled monolayer (SAM) films have been formed on oxidized copper (Cu) substrates by reaction with 1H,1H,2H,2H-perfluorodecylphosphonic acid (PFDP), octadecylphosphonic acid (ODP), decylphosphonic acid (DP), and octylphosphonic acid (OP) and then investigated by X-ray photoelectron spectroscopy (XPS), contact angle measurement (CAM), and atomic force microscopy (AFM). The presence of alkyl phosphonate molecules, PFDP, ODP, DP, and OP, on Cu were confirmed by CAM and XPS analysis. No alkyl phosphonate molecules were seen by XPS on unmodified Cu as a control. The PFDP/Cu and ODP/Cu SAMs were found to be very hydrophobic having water sessile drop static contact angles of more than 140 degrees , while DP/Cu and OP/Cu have contact angles of 119 degrees and 76 degrees , respectively. PFDP/Cu, ODP/Cu, DP/Cu, and OP/Cu SAMs were studied by friction force microscopy, a derivative of AFM, to better understand their micro/nanotribological properties. PFDP/Cu, ODP/Cu, and DP/Cu had comparable adhesive force, which is much lower than that for unmodified Cu. ODP/Cu had the lowest friction coefficient followed by PFDP/Cu, DP/Cu, and OP/Cu while unmodified Cu had the highest. XPS data gives some indication that a bidentate bond forms between the alkyl phosphonate molecules and the oxidized Cu surface. Hydrophobic phosphonate SAMs could be useful as corrosion inhibitors in micro/nanoelectronic devices and/or as promoters for anti-wetting, low adhesion surfaces.

  19. The role of surface Pt on the coadsorption of hydrogen and CO on Pt monolayer film modified Ru(0001) surfaces

    Diemant, T.; Hartmann, H.; Bansmann, J.; Behm, R. J.


    We have investigated the impact and role of the Pt surface modification on the coadsorption of hydrogen and CO on structurally well defined bimetallic Pt monolayer island/film modified Ru(0001) surfaces with Pt contents up to a complete Pt layer, employing temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRRAS). Kinetic limitations in the surface diffusion are shown to play an important role for adsorption at 90 K, and lead to profound effects of the dosing sequence on the adsorption and desorption characteristics. Furthermore, they are responsible for spill-over effects during the TPD measurements, where COad becomes mobile and can spill-over from weakly bonding Pt monolayer areas to strongly bonding Pt-free Ru(0001) areas, which displaces Dad from these surface areas. The present findings are discussed in comparison with previous results on related metallic and bimetallic adsorption and coadsorption systems.

  20. Phase transitions in polymer monolayers: Application of the Clapeyron equation to PEO in PPO-PEO Langmuir films.

    Deschênes, Louise; Lyklema, Johannes; Danis, Claude; Saint-Germain, François


    In this paper we investigate the application of the two-dimensional Clapeyron law to polymer monolayers. This is a largely unexplored area of research. The main problems are (1) establishing if equilibrium is reached and (2) if so, identifying and defining phases as functions of the temperature. Once this is validated, the Clapeyron law allows us to obtain the entropy and enthalpy differences between two coexisting phases. In turn, this information can be used to obtain insight into the conformational properties of the films and changes therein. This approach has a wide potential for obtaining additional information on polymer adsorption at interfaces and the structure of their monolayer films. The 2D Clapeyron law was applied emphasizing polyethylene oxide (PEO) in polypropylene oxide (PPO)-PEO block copolymers, based on new well-defined data for their Langmuir films. Values for enthalpy per monomer of 0.12 and 0.23 kT were obtained for the phase transition of two different PEO chains (Neo of 2295 and 409, respectively). This enthalpy was estimated to correspond to 1.2±0.4 kT per EO monomer present in train conformation at the air/water interface.

  1. Effects of Odd–Even Side Chain Length of Alkyl-Substituted Diphenylbithiophenes on First Monolayer Thin Film Packing Structure

    Akkerman, Hylke B.


    Because of their preferential two-dimensional layer-by-layer growth in thin films, 5,5′bis(4-alkylphenyl)-2,2′-bithiophenes (P2TPs) are model compounds for studying the effects of systematic chemical structure variations on thin-film structure and morphology, which in turn, impact the charge transport in organic field-effect transistors. For the first time, we observed, by grazing incidence X-ray diffraction (GIXD), a strong change in molecular tilt angle in a monolayer of P2TP, depending on whether the alkyl chain on the P2TP molecules was of odd or even length. The monolayers were deposited on densely packed ultrasmooth self-assembled alkane silane modified SiO2 surfaces. Our work shows that a subtle change in molecular structure can have a significant impact on the molecular packing structure in thin film, which in turn, will have a strong impact on charge transport of organic semiconductors. This was verified by quantum-chemical calculations that predict a corresponding odd-even effect in the strength of the intermolecular electronic coupling. © 2013 American Chemical Society.

  2. Effects of poly (ethylene glycol) chains conformational transition on the properties of mixed DMPC/DMPE-PEG thin liquid films and monolayers.

    Georgiev, Georgi As; Sarker, Dipak K; Al-Hanbali, Othman; Georgiev, Georgi D; Lalchev, Zdravko


    Foam thin liquid films (TLF) and monolayers at the air-water interface formed by DMPC mixed with DMPE-bonded poly (ethylene glycol)s (DMPE-PEG(550), DMPE-PEG(2000) and DMPE-PEG(5000)) were obtained. The influence of both (i) PEG chain size (evaluated in terms of Mw) and mushroom-to-brush conformational transition and (ii) of the liposome/micelle ratio in the film-forming dispersions, on the interfacial properties of mixed DMPC/DMPE-PEG films was compared. Foam film studies demonstrated that DMPE-PEG addition to foam TLFs caused (i) delayed kinetics of film thinning and black spot expansion and (ii) film stabilization. At the mushroom-to-brush transition, due to steric repulsion increased DMPE-PEG films thickness reached 25 nm while pure DMPC films were only 8 nm thick Newton black films. It was possible to differentiate DMPE-PEG(2000/5000) from DMPE-PEG(550) by the ability to change foam TLF formation mechanism, which could be of great importance for "stealth" liposome design. Monolayer studies showed improved formation kinetics and equilibrium surface tension decrease for DMPE-PEG monolayers compared with DMPC pure films. SEM observations revealed "smoothing" and "sealing" of the defects in the solid-supported layer surface by DMPE-PEGs adsorption, which could explain DMPE-PEGs ability to stabilize TLFs and to decrease monolayer surface tension. All effects in monolayers, foam TLFs and solid-supported layers increased with the increase of PEG Mw and DMPE-PEG concentration. However, at the critical DMPE-PEG concentration (where mushroom-to-brush conformational transition occurred) maximal magnitude of the effects was reached, which only slightly changed at further DMPE-PEG content and micelle/liposome ratio increase.

  3. Structure and dynamics of monolayer films of squalane molecules adsorbed on a solid surface

    D. T Enevoldsen, A.; Hansen, F. Y.; Diama, A.; Taub, H.


    Squalane is a branched alkane (C_30H_62). It consists of a straight chain with 24 carbon atoms, as in tetracosane (C_24H_50), and has six methyl side groups. Branched polymers such as squalane are thought to be better lubricants than n-alkanes. At low temperature, our molecular dynamics (MD) simulations show that the molecules form an ordered monolayer which melts at approximately 325 K compared to the tetracosane monolayer melting point of ˜ 340 K. Our MD simulations indicate the same melting mechanism in the squalane monolayer that was found previously for tetracosane (F. Y. Hansen and H. Taub, Phys. Rev. Lett. 69, 652 (1992).) They also show that the adsorbed molecules are distorted from an all-trans carbon backbone in contrast to what was found for tetracosane. This may explain why the Bragg diffraction peaks were observed to be broader for the squalane monolayer than for tetracosane (D. Fuhrmann, A. P. Graham, L. Criswell, H. Mo, B. Matthies, K. W. Herwig, and H. Taub, Surf. Sci. 482-485, 77 (2001).). The diffusive motion in a squalane monolayer has been investigated by both quasielastic neutron scattering and MD simulations and compared to the dynamics in tetracosane monolayers. Focus will be on differences in the dynamics.

  4. Preparation of TiO2 thin film by the LPD method on functionalized organic self-assembled monolayers


    In this paper, uniform titania (TiO2) films have been formed at 50℃ on silanol SAMs by the liquid-phase deposition (LPD) method at a temperature below 100℃. OTS (Octadecyltrichloro-Silane) selfassembled monolayers (SAMs) on glass wafers were used as substrates for the deposition of titanium dioxide thin films. This functionalized organic surface has shown to be effective for promoting the growth of films from titanic aqueous solutions by the LPD method at a low temperature below 100℃. The crystal phase composition, microstructure and topography of the as-prepared films were characterized by various techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The results indicate that the as-prepared thin films are purely crystallized anatase TiO2 constituted by nanorods after being annealed at 500℃. The pH values, concentration of reactants, and deposition temperatures play important roles in the growth of TiO2 thin films.

  5. Nano-tribological characteristics of TiO2 films on 3-mercaptopropyl trimethoxysilane sulfonated self-assembled monolayer

    J Li; X H Sheng


    Silane coupling reagent (3-mercaptopropyl trimethoxysilane (MPTS)) was used to prepare twodimensional self-assembled monolayer (SAM) on silicon substrate. The terminal –SH group was in situ oxidized to –SO3H group to endow the film with good chemisorption ability. Then TiO2 thin films were deposited on the oxidized MPTS–SAM to form composite thin films, making use of the chemisorption ability of the –SO3H group. Atomic force microscope (AFM) and contact angle measurements were used to characterize TiO2 films. Adhesive force and friction force of TiO2 thin films and silicon substrate were measured under various applied normal loads and scanning speed of AFM tip. Results showed that the friction force increased with applied normal loads and scanning speed of AFM tip. In order to study the effect of capillary force, tests were performed in various relative humidities. Results showed that the adhesive force of silicon substrate increases with relative humidities and the adhesive force of TiO2 thin films only increases slightly with relative humidity. Research showed that surfaces with more hydrophobic property revealed the lower adhesive and friction forces.

  6. Continuous ultrathin silver films deposited on SiO2 and SiNx using a self-assembled monolayer

    Hafezian, Soroush; Maloney, Kate; Lefebvre, Josianne; Martinu, Ludvik; Kéna-Cohen, Stéphane


    In this letter, we study the deposition of ultrathin silver films on silicon oxide and nitride surfaces functionalized with self-assembled monolayers of (3-mercaptopropyl)-trimethoxysilane. First, we compare both solution and vapour-phase functionalization techniques and find the greatest improvement in electrical and optical properties using deposition from solution. Using X-ray photoelectron spectroscopy, we demonstrate that the formation of silver-sulfur covalent bonds is at the root of the improved wetting confirmed by ellipsometry, sheet resistance measurement, and atomic force microscopy. Second, we show that this technique can be extended to functionalize silicon nitride. Finally, we demonstrate a simple, but efficient, low-emissivity optical filter.

  7. Self-assembled monolayer initiated electropolymerization: a route to thin-film materials with enhanced photovoltaic performance.

    Hwang, Euiyong; de Silva, K M Nalin; Seevers, Chad B; Li, Jie-Ren; Garno, Jayne C; Nesterov, Evgueni E


    Continuing progress in the field of organic polymer photovoltaic (PV) devices requires the development of new materials with better charge-transport efficiency. To improve this parameter, we have investigated surface-attached bilayer polymer PV thin films prepared starting from a covalently attached monolayer of an electroactive initiator using sequential electropolymerization of dithiophene and its derivatives. These systems were found to show significantly increased photocurrent generation quantum yields as compared to systems made through conventional approaches. In addition, the described PV thin films possess remarkable mechanical, air, and photostability. These properties likely arise from the more uniform and better ordered bulk layer morphologies as well as tighter covalently bonded contacts at the interfacial junctions, contributing to improved charge transport. While more studies on the fundamental reasons behind the discovered phenomenon are currently underway, this information can be readily applied to build more efficient organic polymer photovoltaics.

  8. Two photon absorption and its saturation of WS2 and MoS2 monolayer and few-layer films

    Zhang, Saifeng; McEvoy, Niall; O'Brien, Maria; Winters, Sinéad; Berner, Nina C; Yim, Chanyoung; Zhang, Xiaoyan; Chen, Zhanghai; Zhang, Long; Duesberg, Georg S; Wang, Jun


    The optical nonlinearity of WS2, MoS2 monolayer and few-layer films was investigated using the Z-scan technique with femtosecond pulses from the visible to the near infrared. The dependence of nonlinear absorption of the WS2 and MoS2 films on layer number and excitation wavelength was studied systematically. WS2 with 1~3 layers exhibits a giant two-photon absorption (TPA) coefficient. Saturation of TPA for WS2 with 1~3 layers and MoS2 with 25~27 layers was observed. The giant nonlinearity of WS2 and MoS2 is attributed to two dimensional confinement, a giant exciton effect and the band edge resonance of TPA.

  9. Growth of monolayer MoS2 films in a quasi-closed crucible encapsulated substrates by chemical vapor deposition

    Yang, Yong; Pu, Hongbin; Lin, Tao; Li, Lianbi; Zhang, Shan; Sun, Gaopeng


    Monolayer molybdenum disulfide (m-MoS2) has attracted significant interest due to its unique electronic and optical properties. Herein, we report the successful fabrication of high quality and continuous m-MoS2 films in a quasi-closed crucible encapsulated substrates via a three-zone chemical vapor deposition (CVD) system. Quasi-closed crucible lowers the concentration of precursors around substrates and makes the sulfurization rate gentle, which is beneficial for invariable m-MoS2 growth. Characterization results indicate that as-grown m-MoS2 films are of high crystallinity and high quality comparable to the exfoliated MoS2. This approach is also adapted to the growth of other transition metal dichalcogenides.

  10. Site-selective electroless metallization on porous organosilica films by multisurface modification of alkyl monolayer and vacuum plasma.

    Chen, Giin-Shan; Chen, Sung-Te; Chen, Yenying W; Hsu, Yen-Che


    Taking plasma-enhanced chemical vapor deposited porous SiOCH (p-SiOCH) and octadecyltrichlorosilane (OTS) as model cases, this study elucidates the chemical reaction pathways for alkyl-based self-assembled monolayers (SAMs) on porous carbon-doped organosilica films under N(2)-H(2) vacuum plasma illumination. In contrast to previous findings that carboxylic groups are found in alkyl-based SAMs only by exposure to oxygen-based plasma, this study discovers that, upon exposure to reductive nitrogen-based vacuum plasma, surface carboxylic functional groups can be instantly formed on OTS-coated p-SiOCH films. Particular attention is given to developing a multisurface modification process, starting with the modification of p-SiOCH films by N(2)-H(2) plasma and continuing with SAM deposition and plasma patterning; this ultimately leads to site-selective seeding for the spatially controlled fabrication of Cu-wire metallization by electroless deposition. Plasma diagnosis and X-ray near-edge absorption and Fourier transform infrared spectroscopies show that, by adequately controlling the plasma parameters, the bulk of the p-SiOCH films are free from plasma damage (in terms of degradation in bonding structures and electrical properties); the formation of the seed-trapping carboxylic functional groups on the surface, the key factor for the validity of this new seeding process, is due to a water-mediated chemical oxygenation route.

  11. Electrical property and water repellency of a networked monolayer film prepared from Au nanoparticles.

    Shiigi, Hiroshi; Yamamoto, Yojiro; Yakabe, Hidetaka; Tokonami, Shiho; Nagaoka, Tsutomu


    Gold nanoparticles, modified with alkyl thiol, formed a film on polystyrene substrate, and it was found that the deposited film drastically changes its conductivity and hydrophobicity, depending on the alkyl chain length of the thiol used.

  12. Ionic Self-Assembled Monolayer (ISAM) Nonlinear Optical Thin Films and Devices


    elevated temperatures that is accompanied by a decreased film thickness. As the temperature is decreased water is reabsorbed , and the film swells to its...Vogtle, Supramolecular Chemistry; Wiley, New York, 1993. ISAM NLO Thin Films and Devices Final Report 28 [6] J. H. Fuhrhop and J. Koning, Membrane and

  13. Large-roll growth of 25-inch hexagonal BN monolayer film for self-release buffer layer of free-standing GaN wafer

    Wu, Chenping; Soomro, Abdul Majid; Sun, Feipeng; Wang, Huachun; Huang, Youyang; Wu, Jiejun; Liu, Chuan; Yang, Xiaodong; Gao, Na; Chen, Xiaohong; Kang, Junyong; Cai, Duanjun


    Hexagonal boron nitride (h-BN) is known as promising 2D material with a wide band-gap (~6 eV). However, the growth size of h-BN film is strongly limited by the size of reaction chamber. Here, we demonstrate the large-roll synthesis of monolayer and controllable sub-monolayer h-BN film on wound Cu foil by low pressure chemical vapor deposition (LPCVD) method. By winding the Cu foil substrate into mainspring shape supported by a multi-prong quartz fork, the reactor size limit could be overcome by extending the substrate area to a continuous 2D curl of plane inward. An extremely large-size monolayer h-BN film has been achieved over 25 inches in a 1.2” tube. The optical band gap of h-BN monolayer was determined to be 6.0 eV. The h-BN film was uniformly transferred onto 2” GaN or 4” Si wafer surfaces as a release buffer layer. By HVPE method, overgrowth of thick GaN wafer over 200 μm has been achieved free of residual strain, which could provide high quality homo-epitaxial substrate. PMID:27756906

  14. Neutron scattering study of 36 Ar monolayer films adsorbed on graphite

    Taub, H.; da Costa Carneiro, Kim; Kjems, Jørgen;


    surfaces at low temperatures) are observed to decrease smoothly above 40 K, falling from 100 to 15 Å at 80 K. Little if any positional order remains at temperatures where the nearest-neighbor distance in the monolayer matches that of a registered √3×√3 phase. The spectrum of neutrons inelastically......Diffraction of neutrons from 36 Ar monolayers adsorbed on graphite basal planes indicates that an ordered, two-dimensional (2D) triangular lattice is formed at low temperature. The lattice constant is found to be slightly larger than that of the bulk 3D solid but significantly smaller than...... that of a registered √3×√3 overlayer. Thermal expansion of the monolayer is anomalously large; up to 60 K the linear expansion is 4.5 times greater than in the 3D solid. There is no evidence of a sharp melting transition. Instead, the positional correlations (which extend to the full dimensions of the crystallite...

  15. Monolayer graphene film on ZnO nanorod array for high-performance Schottky junction ultraviolet photodetectors.

    Nie, Biao; Hu, Ji-Gang; Luo, Lin-Bao; Xie, Chao; Zeng, Long-Hui; Lv, Peng; Li, Fang-Ze; Jie, Jian-Sheng; Feng, Mei; Wu, Chun-Yan; Yu, Yong-Qiang; Yu, Shu-Hong


    A new Schottky junction ultraviolet photodetector (UVPD) is fabricated by coating a free-standing ZnO nanorod (ZnONR) array with a layer of transparent monolayer graphene (MLG) film. The single-crystalline [0001]-oriented ZnONR array has a length of about 8-11 μm, and a diameter of 100∼600 nm. Finite element method (FEM) simulation results show that this novel nanostructure array/MLG heterojunction can trap UV photons effectively within the ZnONRs. By studying the I-V characteristics in the temperature range of 80-300 K, the barrier heights of the MLG film/ZnONR array Schottky barrier are estimated at different temperatures. Interestingly, the heterojunction diode with typical rectifying characteristics exhibits a high sensitivity to UV light illumination and a quick response of millisecond rise time/fall times with excellent reproducibility, whereas it is weakly sensitive to visible light irradiation. It is also observed that this UV photodetector (PD) is capable of monitoring a fast switching light with a frequency as high as 2250 Hz. The generality of the above results suggest that this MLG film/ZnONR array Schottky junction UVPD will have potential application in future optoelectronic devices.

  16. Change of the surface electronic structure of Au(111) by a monolayer MgO(001) film

    Pan, Yi; Nilius, Niklas; Freund, Hans-Joachim [Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin (Germany); Benedetti, Stefania [CNR, Istituto Nanoscienze, Centro S3, Via G. Campi 213/a, 41100 Modena (Italy)


    Monolayer films of MgO(001) have been prepared on an Au(111) surface and explored with scanning tunneling microscopy and spectroscopy. The symmetry mismatch between the hexagonal substrate and the squared over-layer results in the formation of a (6 x 1) super-lattice, as revealed from the distinct stripe pattern observed in the STM. The presence of the oxide film modifies the potential situation at the interface, which induces a substantial up-shift of the Shockley-type surface band on Au(111). The resulting MgO/Au interface band is also characterized by a pseudo-gap at around 0.5 eV that opens at the position of the new Brillouin zone of the enlarged (6 x 1) cell. In addition, the oxide layer gives rise to a drastic decrease of the Au(111) work function, as deduced from the energy position of field-emission resonance on the bare and MgO-covered surface. The work function drop is explained by an interfacial charge transfer from the oxide film into the electro-negative gold surface.

  17. Efficient Confinement of Ultraviolet Light into the Self-Assembled, Dielectric Colloidal Monolayer on a Flat Aluminum Film

    Lee, Seungwoo


    Here we propose the efficient confinement of ultraviolet (UV) light into the plasmonic-photonic crystal hybrid, which can be practically developed by the self-assembly of dielectric colloidal nanosphere monolayer onto a flat aluminum (Al) film. Using a numerical approach, we analyzed modal characteristics of each different resonant mode at the UV wavelengths including surface plasmon polariton (SPP) mode and waveguided (WG) mode and tuned these resonant modes from deep to far UV simply by adjusting the size of dielectric colloidal nanosphere. The calculated quality-factor (Q-factor) of such plasmonic-photonic crystal hybrid is at least one order of magnitude higher than that of the existing Al nanostructures (Al nanoparticles, nanodisks, nanovoids, or nanogratings) standing on the dielectric substrate. Also, we systematically studied how the amount of native oxide, which can be generated during the general process for the deposition of Al, can influence on both the SPP and WG modes of such plasmonic-photonic ...

  18. Langmuir monolayers and thin films of amphifilic thiacalix[4]arenes. Properties and matrix for the immobilization of cytochrome c.

    Solovieva, Svetlana E; Safiullin, Roman A; Kochetkov, Evgeni N; Melnikova, Nina B; Kadirov, Marsil K; Popova, Elena V; Antipin, Igor S; Konovalov, Alexander I


    Formation and properties of Langmuir films of thiacalix[4]arene (TCA) derivatives containing N-donor groups on the lower rim (Y═O(CH2)3CN; OCH2CN; NH2; OCH2ArCN-p) in 1,3-alternate conformation on aqueous subphase and solid substrates have been studied. Only tetra-cyanopropoxy-p-tert-butylthiacalix[4]arene 1 forms a typical monomolecular layer with perpendicular orientation of the macrocycle relative to the water-air interface that is able to immobilize cytochrome c in the entire range of the surface pressure. Obtained monolayers were transferred by Langmuir-Schaefer technique onto quartz, indium-tin oxide (ITO), and silicon. It was demonstrated that protein activity is retained after immobilization on the substrate.

  19. Direct observation of spin-layer locking by local Rashba effect in monolayer semiconducting PtSe2 film

    Yao, Wei; Wang, Eryin; Huang, Huaqing; Deng, Ke; Yan, Mingzhe; Zhang, Kenan; Miyamoto, Koji; Okuda, Taichi; Li, Linfei; Wang, Yeliang; Gao, Hongjun; Liu, Chaoxing; Duan, Wenhui; Zhou, Shuyun


    The generally accepted view that spin polarization in non-magnetic solids is induced by the asymmetry of the global crystal space group has limited the search for spintronics materials mainly to non-centrosymmetric materials. In recent times it has been suggested that spin polarization originates fundamentally from local atomic site asymmetries and therefore centrosymmetric materials may exhibit previously overlooked spin polarizations. Here, by using spin- and angle-resolved photoemission spectroscopy, we report the observation of helical spin texture in monolayer, centrosymmetric and semiconducting PtSe2 film without the characteristic spin splitting in conventional Rashba effect (R-1). First-principles calculations and effective analytical model analysis suggest local dipole induced Rashba effect (R-2) with spin-layer locking: opposite spins are degenerate in energy, while spatially separated in the top and bottom Se layers. These results not only enrich our understanding of the spin polarization physics but also may find applications in electrically tunable spintronics.

  20. On the determination of Poisson's ratio of stressed monolayer and bilayer submicron thick films

    Martins, P; Brida, S; Barbier, D


    In this paper, the bulge test is used to determine the mechanical properties of very thin dielectric membranes. Commonly, this experimental method permits to determine the residual stress (s0) and biaxial Young's modulus (E/(1-u)). Associating square and rectangular membranes with different length to width ratios, the Poisson's ratio (u) can also be determined. LPCVD Si3N4 monolayer and Si3N4/SiO2 bilayer membranes, with thicknesses down to 100 nm, have been characterized giving results in agreement with literature for Si3N4, E = 212 $\\pm$ 14 GPa, s0 = 420 $\\pm$ 8 and u = 0.29.

  1. Effects of electrolyte gating on photoluminescence spectra of large-area WSe2monolayer films

    Matsuki, Keiichiro


    We fabricated electric double-layer transistors comprising large-area WSe2 monolayers and investigated the effects of electrolyte gating on their photoluminescence (PL) spectra. Using the efficient gating effects of electric double layers, we succeeded in the application of a large electric field (>107Vcm%1) and the accumulation of high carrier density (>1013cm%2). As a result, we observed PL spectra based on both positively and negatively charged excitons and their gate-voltage-dependent redshifts, suggesting the effects of both an electric field and charge accumulation. © 2016 The Japan Society of Applied Physics.

  2. Size-dependent filtration of nanoparticles on porous films composed by polystyrene microsphere monolayers and applications in site-selective deposition of nanoparticles

    Ruan, Weidong [Jilin University, State Key Laboratory of Supramolecular Structure and Materials (China); Zhou, Tieli [Changchun University, College of Food Engineering and Landscape Architecture (China); Sun, Chengbin; Tao, Yanchun; Lu, Fei; Wang, Xu; Zhao, Bing, E-mail: [Jilin University, State Key Laboratory of Supramolecular Structure and Materials (China); Cui, Yinqiu, E-mail: [Jilin University, School of Life Sciences (China)


    Composite films composed of polystyrene (PS) microsphere monolayers and gold (Au) and/or silver (Ag) nanoparticles (NPs) decorations were prepared by a novel size-dependent filtration effect on close-packed PS microsphere arrays. The uniform pores inlaid in the PS monolayer films acted as the transport tunnels for NPs. The steric restriction induced by the size of the pores was used as a main strategy to fabricate hybrid micro/nano films, which were composed of PS microspheres with inhomogeneous anisotropic decorations. The Au and Ag NPs were used as the building blocks to decorate the PS microspheres through a layer-by-layer self-assembly technique with the aid of polyelectrolyte coupling agents. Only the small particles which could pass through the micropores could reach to and deposit on the inner surfaces of the PS microsphere monolayer films. Large particles remained on the outside and could only deposit on the outer surfaces. Thus, the inhomogeneous anisotropic decoration was obtained. This study provides a novel strategy for fabricating anisotropic micro/nanostructures by the size-dependent filtration effect of NPs on porous films and has the potential in applications of anisotropic self-assembly, sensor, and surface modifications at nanoscale.

  3. Phase behavior of mixed Ar-Kr, Ar-Xe and Kr-Xe monolayer films on graphite: a Monte Carlo study.

    Patrykiejew, A


    Using Monte Carlo simulation methods in the grand canonical ensemble we have studied the behavior of mixed Ar-Kr, Ar-Xe and Kr-Xe monolayer films on the graphite basal plane. We have considered the adsorption of the lighter component, either argon or krypton, under the condition of a fixed chemical potential of the heavier component (krypton or xenon), as well as on the graphite surface with preadsorbed small amounts of a heavier noble gas. In both types of simulation the composition of the adsorbed layer is not conserved. We discuss the phase behavior of mixed films emerging from both types of 'computer experiment'. We also demonstrate that Monte Carlo simulation allows us to estimate the effects of preadsorbed xenon on the commensurate-incommensurate transition in the krypton monolayer film and gives the results that are in good quantitative agreement with experimental data.

  4. Improved microstructure and performance of PbS thin films via in-situ thermal decomposition of lead xanthate precursors using self-assembling monolayer

    Wang, Jingni; Yao, Kai; Jia, Zhenrong; Wang, Xiaofeng; Li, Fan


    Microstructure control is critical to achieve thin film-based devices with high performance. The surface properties of the substrates on which thin films grow are expected to greatly influence the morphology and the resulting performance. Generally, homogeneous, dense and highly crystalline films are required. However, "island" like structures are usually obtained mainly due to the non-uniform nucleation. In this article, the self-assembling monolayer (SAM) strategy was applied to efficiently realize the uniform nucleation and modulate the microstructure of lead sulfide (PbS) thin films, which were fabricated on the modified ZnO-coated substrates with 3-mercaptopropionic acid (MPA) SAM via in-situ thermal decomposition of lead xanthate precursors. The results showed that PbS thin films with reduced pin-holes and uniform crystalline grains were fabricated with the incorporation of MPA SAM. More importantly, PbS thin films modulated by MPA showed better photoelectric response.

  5. Effects on the structure of monolayer and submonolayer fluid nitrogen films by the corrugation in the holding potential of nitrogen molecules

    Hansen, Flemming Yssing


    of interactions were indicated by the comparison of the calculated and measured isosteric heats of adsorption in fluid films of nitrogen molecules on graphite. The melting temperatures were lowered by 7K and a region of liquid-gas coexistence was observed for films on the smooth graphite surface indicating......The effects of corrugation in the holding potential of nitrogen molecules on the structure of fluid monolayer and submonolayer films of the molecules on a solid substrate was studied using molecular dynamics simulation. Including McLachlan mediation of the intermolecular potential in a model...

  6. Studies on Mixed Monolayers and Langmuir-Blodgett Films of Schiff-Base Complex Cu(SBC(18))(2) and Calix

    Pang, Shufeng; Ye, Zhifeng; Li, Chun; Liang, Yingqiu


    Mixed monolayers of Schiff-base complex Cu(SBC(18))(2) with an octadecyl hydrocarbon chain and Calix[4]arene without a long alkyl chain at an air/water interface were studied in ultrapure water at different temperatures. Interface behavior and thermodynamic estimation of the mixed monolayer indicate that a strong intermolecular interaction exists between the mixed components (Cu(SBC(18))(2) and calix[4]arene) and the two-dimensional miscibility decreases with the molar fraction of Cu(SBC(18))(2). It is noticeable that the calix[4]arene monolayer can be transferred successfully onto solid substrates due to the introduction of Cu(SBC(18))(2). FTIR transmission and UV-Vis absorption spectra of mixed LB films provide further evidence of molecular interaction between the headgroups. Copyright 2001 Academic Press.

  7. Two-dimensional Pb–Sn alloy monolayer films on Ag(1 1 1)

    Yuhara, J., E-mail:; Ako, T.


    Highlights: • Both Pb and Sn films form a hexagonal close-packed structure on Ag(1 1 1). • The 2D binary films of Pb and Sn exhibit an incommensurate structure close to (√13 × √13). • The binary 2D film is considered to follow the Hume-Rothery rule. - Abstract: Single and binary two-dimensional (2D) films of Pb and Sn on Ag(1 1 1) prepared at room temperature have been investigated using low-energy electron diffraction (LEED) and scanning tunneling microscopy. (√28 × √28)-Pb is observed in addition to (√3 × √3)-Pb at coverages higher than 0.35 ML. The nominal coverages for the (√28 × √28)-Pb and (√3 × √3)-Pb structures are determined to be 0.68 and 1/3 ML, respectively. The (1 × 1)-Sn structure is formed at coverages less than 1 ML. Both Pb and Sn films form a hexagonal close-packed structure on Ag(1 1 1). When the Sn coverage increases to more than 1 ML, excess Sn atoms form a (√3 × √3) structure on the (1 × 1)-Sn surface. The 2D binary films exhibit an incommensurate structure close to (√13 × √13) at Pb and Sn coverages of 0.5 and 0.25 ML, respectively. Atomic-resolution STM images exhibit a hexagonal close-packed structure. From the DFT total energy calculations, it is concluded that the Pb and Sn atoms of the (“√13 × √13″) structure do not form an ordered alloy but, rather, form a solid solution alloy. From these results, it is concluded that the binary 2D films also follow the Hume-Rothery rule.

  8. Coexistence of Replica Bands and Superconductivity in FeSe Monolayer Films

    Rebec, S. N.; Jia, T.; Zhang, C.; Hashimoto, M.; Lu, D.-H.; Moore, R. G.; Shen, Z.-X.


    To elucidate the mechanisms behind the enhanced Tc in monolayer (1 ML) FeSe on SrTiO3 (STO), we grew highly strained 1 ML FeSe on the rectangular (100) face of rutile TiO2 , and observed the coexistence of replica bands and superconductivity with a Tc of 63 K. From the similar Tc between this system and 1ML FeSe on STO (001), we conclude that strain and dielectric constant are likely unimportant to the enhanced Tc in these systems. A systematic comparison of 1 ML FeSe on TiO2 with other systems in the FeSe family shows that while charge transfer alone can enhance Tc, it is only with the addition of interfacial electron-phonon coupling that Tc can be increased to the level seen in 1 ML FeSe on STO.

  9. Structure and spectroscopic analysis of the graphene monolayer film directly grown on the quartz substrate via the HF-CVD technique

    Mahmoud, Waleed E.; Al-Hazmi, Farag S.; Al-Ghamdi, A. A.; Shokr, F. S.; Beall, Gary W.; Bronstein, Lyudmila M.


    Direct growth of a monolayer graphene film on a quartz substrate by a hot filament chemical vapor deposition technique is reported. The monolayer graphene film prepared was characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), selected area electron diffraction (SAED), and atomic force microscopy (AFM). The optical properties were studied by spectroscopic elliposmetry. The experimental data were fitted by the Forouhi-Bloomer model to estimate the extinction coefficient and the refractive index of the monolayer graphene film. The refractive index spectrum in the visible region was studied based on the harmonic oscillator model. The lattice dielectric constant, real and imaginary dielectric constants and the ratio of the charge carrier number to the effective mass were determined. The surface and volume energy loss parameters were also found and showed that the value of the surface energy loss is greater than the volume energy loss. The determination of these optical constants will open new avenue for novel applications of graphene films in the field of wave plates, light modulators, ultrahigh-frequency signal processing and LCDs.

  10. Adsorption of H2O,OH,and O on CuCl(111) Surface: A Density Functional Theory Study

    Xia Wang; Wen-kai Chen; Bao-zhen Sun; Chun-hai Lu


    The adsorption of H2O molecule and its dissociation products,O and OH,on CuCl(111) surface was studied with periodic slab model by PW91 approach of GGA within the framework of density functional theory.The results of geometry optimization indicate that the top site is stable energetically for H2O adsorbed over the CuCl(111) surface.The threefold hollow site is found to be the most stable adsorption site for OH and O,and the calculated adsorption energies are 309.5 and 416.5 k J/mol,respectively.Adsorption of H2O on oxygen-precovered CuCl(111) surface to form surface hydroxyl groups is predicted to be exothermic by 180.1 kJ/mol.The stretching vibrational frequencies,MuUiken population analysis and density of states analysis are employed to interpret the possible mechanism for the computed results.

  11. Photolysis of H2O-H2O2 Mixtures: The Destruction of H2O2

    Loeffler, M. J.; Fama, M.; Baragiola, R. A.; Carlson, R. W.


    We present laboratory results on the loss of H2O2 in solid H2O + H2O2 mixtures at temperatures between 21 and 145 K initiated by UV photolysis (193 nm). Using infrared spectroscopy and microbalance gravimetry, we measured the decrease of the 3.5 micrometer infrared absorption band during UV irradiation and obtained a photodestruction cross section that varies with temperature, being lowest at 70 K. We use our results, along with our previously measured H2O2 production rates via ionizing radiation and ion energy fluxes from the spacecraft to compare H2O2 creation and destruction at icy satellites by ions from their planetary magnetosphere and from solar UV photons. We conclude that, in many cases, H2O2 is not observed on icy satellite surfaces because the H2O2 photodestruction rate is much higher than the production rate via energetic particles, effectively keeping the H2O2 infrared signature at or below the noise level.

  12. Solubility of ammonium paratungstate in the system NH3·H2O-H2O


    The equilibrium solubilities of 5(NH4)O@ 12WO3 @ 5H2O (APT@ 5H2O) were determined at the terminal ammoniaconcentration of 2 mol/L at 87-95℃. Experimental data were regressed. The linear functional relation between the solubilityof APT@ 5H2O and the temperature (t / ℃) is given as y = - 588.08 + 7.28t. The solubility of the species as a function of theterminal ammonia concentration (x / mol@ L-1) is also achieved: y = 36.76 + 18.86x. The solubility of APT@ 5H2O producedby ion-exchange method in China is much lower, which is due to much lower silica, much higher NH4C1, and a smallamount of APT@ 7H2O with low solubility in the APT crystals. APT@ 7H2O forms because of a large amount of NH4Cl andthe low activity of water in the crystallization.

  13. Preparation and electrochemical and photoelectrochemical properties of a covalently self-assembled monolayer film based on a bis-terpyridyl ruthenium(II) complex

    Lin, Hao; Dai, Yong-Cheng; Chen, Xi; Huang, Qiu-Ying; Wang, Ke-Zhi, E-mail:


    A bis-terpyridyl Ru(II) complex of Ru{sup II}(IPTP){sub 2}(ClO{sub 4}){sub 2} (in which IPTP = 4′-(4-(imidazol-1-yl)phenyl)-2,2′:6′,2″-terpyridine) has been synthesized using a microwave irradiation method, and characterized by elementary analysis, and proton nuclear magnetic resonance, and mass spectroscopy. A Ru{sup II}(IPTP){sub 2}(ClO{sub 4}){sub 2} based covalently self-assembled monolayer film was prepared and characterized by UV–Vis spectroscopy and cyclic voltammetry. The cyclic voltammograms demonstrated that Ru{sup II}(IPTP){sub 2}(ClO{sub 4}){sub 2} assembled in the film was redox active with surface-confined characteristics. The photoelectrochemical properties and electron-transfer mechanism of the film were studied. It was found that the Ru{sup II}(IPTP){sub 2}(ClO{sub 4}){sub 2}/ITO electrode film exhibited a large cathodic photocurrent density of 2.72 μA/cm{sup 2} while irradiated with polychromatic light (325 nm < λ < 730 nm) at an applied potential of − 0.4 V versus saturated calomel electrode. The photocurrent action spectrum was in agreement with the metal-to-ligand charge-transfer (MLCT) absorption band of Ru{sup II}(IPTP){sub 2}(ClO{sub 4}){sub 2}, indicating that the photocurrent was generated based on MLCT excitation of the Ru{sup II}(IPTP){sub 2}(ClO{sub 4}){sub 2} in the film. An incident monochromatic photon-to-current conversion efficiency of this monolayer film was calculated to be 1.8% at 500 nm. - Highlights: • Ru complex covalently self-assembled monolayer film. • Reversible electrochemical activity. • Large cathodic photocurrent density of 2.72 μA/cm{sup 2}. • Photoelectric conversion efficiency of 1.8%.

  14. Monolayer Iron Carbide Films on Au(111) as a Fischer–Tropsch Model Catalyst

    Mannie, Gilbère; Lammich, Lutz; Li, Yong-Wang;


    Using scanning tunneling microscopy (STM), we characterize the atomic-scale details of ultrathin films of iron carbide (FexCy) on Au(111) synthesized as a potential model system for the active iron carbide phase in iron Fischer–Tropsch synthesis (FTS) catalysts. The experiments show that room...

  15. Chemical stability of nonwetting, low adhesion self-assembled monolayer films formed by perfluoroalkylsilanization of copper

    Hoque, E.; DeRose, J. A.; Hoffmann, P.; Bhushan, B.; Mathieu, H. J.


    A self-assembled monolayer (SAM) has been produced by reaction of 1H,1H,2H,2H-perfluorodecyldimethylchlorosilane (PFMS) with an oxidized copper (Cu) substrate and investigated by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), friction force microscopy (FFM), a derivative of AFM, and contact angle measurement. FFM showed a significant reduction in the adhesive force and friction coefficient of PFMS modified Cu (PFMS/Cu) compared to unmodified Cu. The perfluoroalkyl SAM on Cu is found to be extremely hydrophobic, yielding sessile drop static contact angles of more than 130° for pure water and a "surface energy" (which is proportional to the Zisman critical surface tension for a Cu surface with 0rms roughness) of 14.5mJ/m2(nM/m). Treatment by exposure to harsh conditions showed that PFMS/Cu SAM can withstand boiling nitric acid (pH=1.8), boiling water, and warm sodium hydroxide (pH =12, 60°C) solutions for at least 30min. Furthermore, no SAM degradation was observed when PFMS/Cu was exposed to warm nitric acid solution for up to 70min at 60°C or 50min at 80°C. Extremely hydrophobic (low surface energy) and stable PFMS/Cu SAMs could be useful as corrosion inhibitors in micro/nanoelectronic devices and/or as promoters for antiwetting, low adhesion surfaces or dropwise condensation on heat exchange surfaces.

  16. Surface-enhanced Raman scattering-active gold nanoparticles modified with a monolayer of silver film.

    Chang, Chun-Chao; Yang, Kuang-Hsuan; Liu, Yu-Chuan; Yu, Chung-Chin; Wu, Yi-Hao


    As shown in the literature, electrochemical underpotential deposition (UPD) offers the ability to deposit up to a monolayer of one metal onto a more noble metal with a flat surface. In this work, we develop an electrochemical pathway to prepare more surface-enhanced Raman scattering (SERS)-active substrates with Ag UPD-modified Au nanoparticles (NPs) by using sonoelectrochemical deposition-dissolution cycles (SEDDCs). Encouragingly, the SERS of Rhodamine 6G (R6G) adsorbed on these Ag UPD-modified Au NPs exhibits a higher intensity by ca. 12-fold magnitude, as compared with that of R6G adsorbed on unmodified Au NPs. The prepared SERS-active substrate demonstrates a large Raman scattering enhancement for R6G with a detection limit of 2 × 10(-14) M and an enhancement factor of 5.0 × 10(8). Also, the strategy proposed in this work to improve the SERS effects by using UPD Ag based on SEDDCs has an effect on the smaller probe molecules of 2,2'-bipyridine (BPy).

  17. Enhanced vertical carrier mobility in poly(3-alkylthiophene) thin films sandwiched between self-assembled monolayers and surface-segregated layers.

    Ma, Jusha; Hashimoto, Kazuhito; Koganezawa, Tomoyuki; Tajima, Keisuke


    End-functionalized poly(3-butylthiophene) with a thiol group (P3BT-S) was synthesized and used to form a self-assembled monolayer (SAM). It can induce the end-on orientation in the thin film which has the potential to further enhance hole mobility up to 1.1 × 10(-2) cm(2) V(-1) s(-1) in the vertical direction.

  18. Large area growth of monolayer MoS2 film on quartz and its use as a saturable absorber in laser mode-locking

    Zhao, Wei-fang; Yu, Hua; Liao, Meng-zhou; Zhang, Ling; Zou, Shu-zhen; Yu, Hai-juan; He, Chao-jian; Zhang, Jing-yuan; Zhang, Guang-yu; Lin, Xue-chun


    Monolayer MoS2 film on quartz was fabricated by a home-made three-temperature zone chemical vapor deposition method. The photo, AFM image, Raman spectroscopy and HRTEM image showed that high quality as-grown MoS2 film completely covered the whole quartz substrate of a few cm2. A Nd:YVO4 laser with mode-locking operation was obtained by using the monolayer MoS2 on quartz as the saturable absorber (SA). To the best of our knowledge, this is the first report on large-area growth of high quality monolayer MoS2 film on transparent quartz substrate, and the first time that the CVD MoS2 SA was used in mode-locked solid state lasers. Because of the large area, high transmission, low non-saturable loss and high optical damage threshold of this material, it is very suitable for application in mode-locked solid state lasers.

  19. Langmuir monolayer and Langmuir-Blodgett films formed by a melamine-headed azobenzene-derived amphiphile: interfacial assembly affected by host-guest interaction.

    Xu, Weihong; Wang, Yanhua; Xiao, Yunxia; Liu, Fang; Lu, Guo-Yuan


    A novel azobenzene-derived amphiphile with a melamine head, 2Azo-2C12H2-melamine, has been synthesized. pi-A isotherm measurements displayed that this amphiphile is able to form a stable Langmuir monolayer on both pure water and barbituric acid (BA)- or thymine (T)-containing subphases. The collapse surface pressure and limiting molecular area of its Langmuir monolayer on pure water are 40 mN/m and 0.56 nm2, respectively. However, when barbituric acid or thymine was introduced into the subphase, the corresponding pi-A isotherms of the monolayers exhibited a lower collapse surface pressure (22 mN/m for BA, 21 mN/m for T) and smaller limiting molecular area (0.54 nm2 for BA and 0.52 nm2 for T). UV-vis and FT-IR studies of the LB films formed by 2Azo-2C12H25-melamine have also been carried out. The results indicated that the LB films of 2Azo-2C12H25-melamine deposited from pure water undergo distinct collapse of the H-aggregate upon UV irradiation, while the LB films deposited from a BA- or T-containing subphase retain the H-aggregate. The host-guest-interaction-induced blockage of azobenzene photoisomerization should be responsible for the stabilized H-aggregate. A 1:1 host/guest binding mode to form a linear supramolecular polymeric chain has been proposed in the Langmuir monolayers formed on a BA- or T-containing subphase. The current results suggest that the host-guest interaction should be an effective means to manipulate the interfacial assembly of azobenzene-derived amphiphiles.

  20. Equilibrium and Kinetic Aspects in the Sensitization of Monolayer Transparent TiO2 Thin Films with Porphyrin Dyes for DSSC Applications

    Rita Giovannetti


    Full Text Available Free base, Cu(II and Zn(II complexes of the 2,7,12,17-tetrapropionic acid of 3,8,13,18-tetramethyl-21H,23H porphyrin (CPI in solution and bounded to transparent monolayer TiO2 nanoparticle films were studied to determine their adsorption on TiO2 surface, to measure the adsorption kinetics and isotherms, and to use the results obtained to optimize the preparation of DSSC photovoltaic cells. Adsorption studies were carried out on monolayer transparent TiO2 films of a known thickness. Langmuir and Frendlich adsorption constants of CPI-dyes on TiO2 monolayer surface have been calculated as a function of the equilibrium concentrations in the solutions. The amount of these adsorbed dyes showed the accordance with Langmuir isotherm. Kinetic data on the adsorption of dyes showed significantly better fits to pseudo-first-order model and the evaluated rate constants linearly increased with the grow of initial dye concentrations. The stoichiometry of the adsorption of CPI-dyes into TiO2 and the influence of presence of coadsorbent (chenodeoxycholic acid have been established. The DSSC obtained in the similar conditions showed that the best efficiency can be obtained in the absence of coadsorbent with short and established immersion times.

  1. Observation of dopant-profile independent electron transport in sub-monolayer TiO{sub x} stacked ZnO thin films grown by atomic layer deposition

    Saha, D., E-mail:, E-mail:; Misra, P., E-mail:, E-mail:; Joshi, M. P.; Kukreja, L. M. [Laser Materials Processing Division, Raja Ramanna Centre for Advanced Technology, Indore 452 013 (India); Das, Gangadhar [Indus Synchrotrons Utilisation Division, Raja Ramanna Centre for Advanced Technology, Indore 452 013 (India)


    Dopant-profile independent electron transport has been observed through a combined study of temperature dependent electrical resistivity and magnetoresistance measurements on a series of Ti incorporated ZnO thin films with varying degree of static-disorder. These films were grown by atomic layer deposition through in-situ vertical stacking of multiple sub-monolayers of TiO{sub x} in ZnO. Upon decreasing ZnO spacer layer thickness, electron transport smoothly evolved from a good metallic to an incipient non-metallic regime due to the intricate interplay of screening of spatial potential fluctuations and strength of static-disorder in the films. Temperature dependent phase-coherence length as extracted from the magnetotransport measurement revealed insignificant role of inter sub-monolayer scattering as an additional channel for electron dephasing, indicating that films were homogeneously disordered three-dimensional electronic systems irrespective of their dopant-profiles. Results of this study are worthy enough for both fundamental physics perspective and efficient applications of multi-stacked ZnO/TiO{sub x} structures in the emerging field of transparent oxide electronics.

  2. Iso-oriented monolayer α-MoO 3 (010) films epitaxially grown on SrTiO 3 (001)

    Du, Yingge; Li, Guoqiang; Peterson, Erik W.; Zhou, Jing; Zhang, Xin; Mu, Rentao; Dohnálek, Zdenek; Bowden, Mark; Lyubinetsky, Igor; Chambers, Scott A.


    The ability to synthesis well-ordered two-dimensional materials under ultra-high vacuum and directly characterize them by other techniques in-situ can greatly advance our current understanding on their physical and chemical properties. In this paper, we demonstrate that iso-oriented α-MoO3 films with as low as single monolayer thickness can be reproducibly grown on SrTiO3(001) substrates by molecular beam epitaxy ( (010)MoO3 || (001)STO, [100]MoO3 || [100]STO or [010]STO) through a self-limiting process. While one in-plane lattice parameter of the MoO3 is very close to that of the SrTiO3 (aMoO3 = 3.96 Å, aSTO = 3.905 Å), the lattice mismatch along other direction is large (~5%, cMoO3 = 3.70 Å), which leads to relaxation as clearly observed from the splitting of streaks in reflection high-energy electron diffraction (RHEED) patterns. A narrow range in the growth temperature is found to be optimal for the growth of monolayer α-MoO3 films. Increasing deposition time will not lead to further increase in thickness, which is explained by a balance between deposition and thermal desorption due to the weak van der Waals force between α-MoO3 layers. Lowering growth temperature after the initial iso-oriented α-MoO3 monolayer leads to thicker α-MoO3(010) films with excellent crystallinity.

  3. Preparation of Carbazole Polymer Thin Films Chemically Bound to Substrate Surface by Physical Vapor Deposition Combined with Self-Assembled Monolayer

    Katsuki, Kiyoi; Bekku, Hiroshi; Kawakami, Akira; Locklin, Jason; Patton, Derek; Tanaka, Kuniaki; Advincula, Rigoberto; Usui, Hiroaki


    Vinyl polymer thin films having carbazole units were prepared by a new method combining physical vapor deposition and self-assembled monolayer (SAM) techniques. 3-(N-carbazolyl)propyl acrylate monomer was evaporated onto a gold substrate that had a VAZO 56 (DuPont) initiator attached as a SAM. The VAZO initiator was activated by irradiating ultraviolet light after depositing the monomer. Although the polymerization reaction can proceed even without the surface initiator, the SAM was effective in improving the surface smoothness, thermal stability, and film-substrate adhesion as a consequence of the formation of covalent chemical bonds between the film and the substrate. Thermal activation of the initiator was examined for the deposition polymerization of 9-H-carbazole-9-ethylmethacryrate. Substrate heating during the evaporation was not effective for accumulating thin films. On the other hand, performing postdeposition annealing on the film after deposition at room temperature resulted in the formation of a polymer thin film chemically bound to the substrate.

  4. Self-assembled monolayers of cyclohexyl-terminated phosphonic acids as a general dielectric surface for high-performance organic thin-film transistors.

    Liu, Danqing; He, Zikai; Su, Yaorong; Diao, Ying; Mannsfeld, Stefan C B; Bao, Zhenan; Xu, Jianbin; Miao, Qian


    A novel self-assembled monolayer (SAM) on AlOy /TiOx is terminated with cyclohexyl groups, an unprecedented terminal group for all kinds of SAMs. The SAM-modified AlOy /TiOx functions as a general dielectric, enabling organic thin-film transistors with a field-effect mobility higher than 5 cm(2) V(-1) s(-1) for both holes and electrons, good air stability with low operating voltage, and general applicability to solution-processed and vacuum-deposited n-type and p-type organic semiconductors.

  5. Highly ordered monolayer/bilayer TiO2 hollow sphere films with widely tunable visible-light reflection and absorption bands

    Li, Jie; Qin, Yao; Jin, Chao; Li, Ying; Shi, Donglu; Schmidt-Mende, Lukas; Gan, Lihua; Yang, Jinhu


    Monolayer and bilayer TiO2 hollow hemisphere/sphere (THH/THS) films consisting of highly ordered hexagonal-patterned THHs/THSs with thin shells of ~10 nm and different diameters of ~170 and ~470 nm have been prepared by templating of two-dimensional polystyrene sphere (PS) assembly films coupled with TiO2 sputtering/wet coating approaches. Owing to their precisely adjustable structural parameters, such as THH/THS shape and diameter as well as film layer thickness, the prepared THH/THS films exhibit widely tunable visible-light reflection and absorption bands, i.e. from 380 to 850 nm for reflection and 390 to 520 nm for absorption, respectively. The mechanism of the novel optical behaviors of the THH/THS films has been discussed in depth, combined with some calculations according to Bragg's law. In addition, photocatalytic experiments of RhB degradation employing the THH/THS films as recyclable catalysts have been conducted. The THH/THS films with controlled structures and precisely tunable optical properties are attractive for a wide range of applications, such as recyclable catalysts for photocatalysis, efficient oxide electrodes or scattering layers for solar cells, gas-permeable electrode materials for high-performance sensors and so on.Monolayer and bilayer TiO2 hollow hemisphere/sphere (THH/THS) films consisting of highly ordered hexagonal-patterned THHs/THSs with thin shells of ~10 nm and different diameters of ~170 and ~470 nm have been prepared by templating of two-dimensional polystyrene sphere (PS) assembly films coupled with TiO2 sputtering/wet coating approaches. Owing to their precisely adjustable structural parameters, such as THH/THS shape and diameter as well as film layer thickness, the prepared THH/THS films exhibit widely tunable visible-light reflection and absorption bands, i.e. from 380 to 850 nm for reflection and 390 to 520 nm for absorption, respectively. The mechanism of the novel optical behaviors of the THH/THS films has been discussed

  6. Emergence of Dirac-like bands in the monolayer limit of epitaxial Ge films on Au(1 1 1)

    Schröter, Niels B. M.; Watson, Matthew D.; Duffy, Liam B.; Hoesch, Moritz; Chen, Yulin; Hesjedal, Thorsten; Kim, Timur K.


    After the discovery of Dirac fermions in graphene, it has become a natural question to ask whether it is possible to realize Dirac fermions in other two-dimensional (2D) materials as well. In this work, we report the discovery of multiple Dirac-like electronic bands in ultrathin Ge films grown on Au(1 1 1) by angle-resolved photoelectron spectroscopy. By tuning the thickness of the films, we are able to observe the evolution of their electronic structure when passing through the monolayer limit. Our discovery may signify the synthesis of germanene, a 2D honeycomb structure made of Ge, which is a promising platform for exploring exotic topological phenomena and enabling potential applications.

  7. Study of Fused Thiophene Based Organic Semiconductors and Interfacial Self-Assembled Monolayer (SAM) for Thin-Film Transistor (TFT) Application

    Youn, Jangdae

    In this thesis, the molecular packing motifs of our newly designed fused thiophenes, benzo[d,d]thieno[3,2-b;4,5-b]dithiophene (BTDT) derivatives, were studied by utilizing grazing incidence wide angle X-ray scattering (GIWAXS). Considering the potential of fused thiophene molecules as an environmentally stable, high performance semiconductor building block, it must be an important groundwork to investigate their thin film structures in relation to molecular structures, single crystal structures, and organic thin-film transistors (OTFT) performances. OTFT device performance is not only determined by semiconductor materials, but also influenced by the interfacial properties. Since there are three major components in TFT structures---electrodes, semiconductors, and dielectrics, two types of major interfaces exist. One is the semiconductor-electrode interface, and the other is the semiconductor-dielectric interface. Both of these interfaces have critical roles for TFT operation. For example, the semiconductor-electrode interface determines the charge injection barrier. Before charge carriers go through the electrode (source)-semiconductor-electrode (drain) pathways, the energy gaps between the work function of the electrodes and the HOMO energy of the semiconductor materials must be overcome for hole injection, or the energy gap between the metal work function of the electrodes and the LUMO energy of the semiconductor materials must be overcome for electron injection. These charge injection barriers are largely determined by the energetic structure of the semiconductor material and work function of the electrode. However, the size of energy gap can be modified by introducing an organic self-assembled monolayer (SAM) on the surface of metal electrode. In addition, the structure of semiconductor films, especially within several monolayers right above the electrode, is greatly influenced by the SAM, and it changes charge injection property of OTFT devices. In this thesis

  8. Order of magnitude enhancement of monolayer MoS2 photoluminescence due to near-field energy influx from nanocrystal films

    Guo, Tianle; Sampat, Siddharth; Zhang, Kehao; Robinson, Joshua A.; Rupich, Sara M.; Chabal, Yves J.; Gartstein, Yuri N.; Malko, Anton V.


    Two-dimensional transition metal dichalcogenides (TMDCs) like MoS2 are promising candidates for various optoelectronic applications. The typical photoluminescence (PL) of monolayer MoS2 is however known to suffer very low quantum yields. We demonstrate a 10-fold increase of MoS2 excitonic PL enabled by nonradiative energy transfer (NRET) from adjacent nanocrystal quantum dot (NQD) films. The understanding of this effect is facilitated by our application of transient absorption (TA) spectroscopy to monitor the energy influx into the monolayer MoS2 in the process of ET from photoexcited CdSe/ZnS nanocrystals. In contrast to PL spectroscopy, TA can detect even non-emissive excitons, and we register an order of magnitude enhancement of the MoS2 excitonic TA signatures in hybrids with NQDs. The appearance of ET-induced nanosecond-scale kinetics in TA features is consistent with PL dynamics of energy-accepting MoS2 and PL quenching data of the energy-donating NQDs. The observed enhancement is attributed to the reduction of recombination losses for excitons gradually transferred into MoS2 under quasi-resonant conditions as compared with their direct photoproduction. The TA and PL data clearly illustrate the efficacy of MoS2 and likely other TMDC materials as energy acceptors and the possibility of their practical utilization in NRET-coupled hybrid nanostructures.

  9. Transparent conductive oxide layer with monolayer closed-pack Al-doped ZnO spheres and their application to a-Si thin-film solar cells.

    Lo, Shih-Shou; Lin, Chen-Yu; Jan, Der-Jun


    We report a new (to the best of our knowledge) transparent conductive oxide (TCO) layer with a monolayer of closed-pack Al-doped ZnO (AZO) spheres partly embedded in an AZO thin film. The average transmittance and haze ratio in the wavelength range of 380-800 nm achieves 65% and 55%, respectively, when AZO spheres with a diameter of 500 nm are embedded in a thickness of 240 nm AZO thin films. The a-Si thin-film solar cell with a regular p-i-n TCO structure is demonstrated. Under air mass 1.5 global illumination, conversion efficiencies of 5.6%, a fill factor of 0.55, V(oc) of 0.81 V, and a J(sc) of 2.44 mA/cm² are obtained. The Letter helps us to open up potential applications of a new TCO in advanced solar cells and light-emitting diodes.

  10. Enhanced bias stability of solution-processed zinc-tin-oxide thin film transistors using self-assembled monolayer as a selective channel passivation.

    Heo, Jae-Sang; Park, Sung-Kyu


    The enhanced positive bias stability of amorphous zinc-tin-oxide thin-film transistors (a-ZTO TFTs) were obtained by applying self-assembled monolayer (SAM) as a selective passivation layer on the metal-oxide back channel area. The a-ZTO TFTs with passivation layers such as poly(methyl methacylate) (PMMA), SAM, and SAM/PMMA were fabricated by simple solution methods. After deposition of the passivation layers, the electrical characteristics of a-ZTO TFTs have not been changed and the threshold voltage shift (deltaV(th)) under gate-bias stress for around 10(4) seconds was improved. The deltaV(th) of the devices with PMMA, SAM, and SAM/PMMA dual layer were 3.79 V, 3.2 V, and 2.17 V, respectively.

  11. XPS and electrochemical evaluation of two-dimensional organic films obtained by chemical modification of self-assembled monolayers of (3-mercaptopropyl)trimethoxysilane on copper surfaces

    Sinapi, Fabrice; Delhalle, Joseph; Mekhalif, Zineb


    In this study, a protective film consisting of an ultrathin two-dimensional polymer was prepared by hydrolysis of a (3-mercaptopropyl)trimethoxysilane (ethanol, 10{sup -3} M) self-assembled monolayer grafted onto copper and a subsequent modification with 3(heptofluoroisopropoxy)propyltrichlorosilane (toluene, 10{sup -3} M). Each stage of the preparation was characterized by X-ray photoelectron spectroscopy (XPS) while copper's corrosion-inhibitive properties were assessed by cyclic voltammetry measurements carried on in a 0.1 M NaOH medium. A remarkable enhancement of the copper's corrosion protection was obtained by the formation of lateral siloxane linkages between MPTS molecules absorbed followed by the grafting of the second molecular layer.

  12. Role of Self-Assembled Monolayers on Improved Electrical Stability of Amorphous In-Ga-Zn-O Thin-Film Transistors

    Du, Xiaosong; Motley, Joshua R; Stickle, William F; Bluhm, Hendrik; Herman, Gregory S


    Self-assembled monolayers (SAMs) have been used to improve both the positive and negative bias-stress stability of amorphous indium gallium zinc oxide (IGZO) bottom gate thin film transistors (TFTs). N-hexylphosphonic acid (HPA) and fluorinated hexylphosphonic acid (FPA) SAMs adsorbed on IGZO back channel surfaces were shown to significantly reduce bias stress turn-on voltage shifts compared to IGZO back channel surfaces with no SAMs. FPA was found to have a lower surface energy and lower packing density than HPA, as well as lower bias stress turn-on voltage shifts. The improved stability of IGZO TFTs with SAMs can be primarily attributed to a reduction in molecular adsorption of contaminants on the IGZO back channel surface and minimal trapping states present with phosphonic acid binding to the IGZO surface.

  13. In vitro comparative evaluation of monolayered multipolymeric films embedded with didanosine-loaded solid lipid nanoparticles: a potential buccal drug delivery system for ARV therapy.

    Jones, Elsabé; Ojewole, Elizabeth; Kalhapure, Rahul; Govender, Thirumala


    Drug delivery via the buccal route has emerged as a promising alternative to oral drug delivery. Didanosine (DDI) undergoes rapid degradation in the gastrointestinal tract, has a short half-life and low oral bioavailability, making DDI a suitable candidate for buccal delivery. Recent developments in buccal drug delivery show an increased interest toward nano-enabled delivery systems. The advantages of buccal drug delivery can be combined with that of nanoparticulate delivery systems to provide a superior delivery system. The aim of this study was to design and evaluate the preparation of novel nano-enabled films for buccal delivery of DDI. Solid lipid nanoparticles (SLNs) were prepared via hot homogenization followed by ultrasonication and were characterized before being incorporated into nano-enabled monolayered multipolymeric films (MMFs). Glyceryl tripalmitate with Poloxamer 188 was identified as most suitable for the preparation of DDI-loaded SLNs. SLNs with desired particle size (PS) (201 nm), polydispersity index (PDI) (0.168) and zeta potential (-18.8 mV) were incorporated into MMFs and characterized. Conventional and nano-enabled MMFs were prepared via solvent casting/evaporation using Eudragit RS100 and hydroxypropyl methylcellulose. Drug release from the nano-enabled films was found to be faster (56% versus 20% in first hour). Conventional MMFs exhibited higher mucoadhesion and mechanical strength than nano-enabled MMFs. SLNs did not adversely affect the steady state flux (71.63 ± 13.54 µg/cm(2) h versus 74.39 ± 15.95 µg/cm(2) h) thereby confirming the potential transbuccal delivery of DDI using nano-enabled MMFs. Nano-enabled buccal films for delivery of DDI can be successfully prepared, and these physico-mechanical studies serve as a platform for future formulation optimization work in this emerging field.

  14. Assembly of CdSe onto mesoporous TiO{sub 2} films induced by a self-assembled monolayer for quantum dot-sensitized solar cell applications

    Chong, Lai-Wan; Chien, Huei-Ting; Lee, Yuh-Lang [Department of Chemical Engineering, National Cheng Kung University, No. 1 University Road, Tainan 70101 (China)


    A self-assembled monolayer (SAM) of 3-mercaptopropyl-trimethyoxysilane (MPTMS) is pre-assembled onto a mesoporous TiO{sub 2} film and is used as a surface-modified layer to induce the growth of CdSe QDs in the successive ionic layer adsorption and reaction (SILAR) process. Due to the specific interaction of the terminal thiol groups to CdSe, the MPTMS SAM is found to increase the nucleation and growth rates of CdSe in the SILAR process, leading to a well covering and higher uniform CdSe layer which has a superior ability, compared with the electrode without MPTMS, in inhibiting the charge recombination at the electrode/electrolyte interface. Furthermore, the performance of the CdSe-sensitized TiO{sub 2} electrode can further be improved by an additional heat annealing after film deposition, attributable to a better interfacial connection between CdSe and TiO{sub 2}, as well as a better connection among CdSe QDs. The CdSe-sensitized solar cell prepared by the present strategy can achieve an energy conversion efficiency of 2.65% under the illumination of one sun (AM 1.5, 100 mW cm{sup -2}). (author)

  15. Synchrotron radiation stimulated etching of SiO sub 2 thin films with a Co contact mask for the area-selective deposition of self-assembled monolayer

    Wang, C


    The area-selective deposition of a self-assembled monolayer (SAM) was demonstrated on a pattern structure fabricated by synchrotron radiation (SR) stimulated etching of a SiO sub 2 thin film on the Si substrate. The etching was conducted by irradiating the SiO sub 2 thin film with SR through a Co contact mask and using a mixture of SF sub 6 + O sub 2 as the reaction gas. The SR etching stopped completely at the SiO sub 2 /Si interface. After the SR etching, the Si surface and the SiO sub 2 surface beneath the Co mask were evaluated by an atomic force microscope (AFM). A dodecene SAM was deposited on the Si surface, and trichlorosilane-derived SAMs (octadecyltrichlorosilane, and octenyltrichlorosilane) were deposited on the SiO sub 2 surface beneath the Co mask. The structure of the deposited SAMs showed a densely packed and well-ordered molecular architecture, which was characterized by infrared spectroscopy, ellipsometry, and water contact angle (WCA) measurements. (author)

  16. Structural Order in Ultrathin Films of the Monolayer Protected Clusters Based Upon 4-nm Gold Nanocrystals: An Experimental and Theoretical Study

    Bhattarai, Nabraj; Khanal, Subarna; Bahena, Daniel; Olmos-Asar, Jimena A.; Ponce, Arturo; Whetten, Robert L.; Mariscal, Marcelo M.; Jose-Yacaman, Miguel


    The structural order in ultrathin films of monolayer protected clusters (MPCs) is important in a number of application areas but can be difficult to demonstrate by conventional methods, particularly when the metallic core dimension, d, is in the intermediate size-range, 1.5 < d < 5.0 nm. Here, improved techniques for the synthesis of monodisperse thiolate-protected gold nanoparticles have made possible the production of dodecane-thiolate saturated ~ 4 ± 0.5 nm Au clusters with single-crystal core structure and morphology. An ultrathin ordered film or superlattice of these nanocrystal-core MPCs is prepared and investigated using aberration corrected scanning/transmission electron microscopy (STEM) which allowed imaging of long-range hexagonally ordered superlattices of the nanocrystals, separated by the thiolate groups. The lattice constants determined by direct imaging are in good agreement with those determined by small-angle electron diffraction. The STEM image revealed the characteristic grain boundary (GB) with sigma (Σ) 13 in the interface between two crystals. The formation and structures found are interpreted on the basis of theoretical calculations employing molecular dynamics (MD) simulations and coarse-grained (CG) approach. PMID:24875295

  17. Positional order in Langmuir monolayers

    Kaganer, V.M.; Brezesinski, G.; Möhwald, H.;


    We find that a structural solid-solid phase transition in a two-dimensional Langmuir film is accompanied by strong positional disorder. Specifically, we find by a grazing-incidence x-ray diffraction experiment that in monolayers of octadecanol both the hexagonal phase LS and the centered rectangu......We find that a structural solid-solid phase transition in a two-dimensional Langmuir film is accompanied by strong positional disorder. Specifically, we find by a grazing-incidence x-ray diffraction experiment that in monolayers of octadecanol both the hexagonal phase LS and the centered...

  18. Van der Waals materials for the passivation of monolayer closed-packed films of CdSe quantum dots

    Wang, Dennis Zi-Ren; Zhang, Datong; Creswell, Richard; Lu, Chenguang; Hu, Jiayang; Herman, Irving P.


    Van der Waals (vdW) materials are shown to protect CdSe quantum dots (QDs) from oxidization. Few-layer vdW materials, e.g. graphene and MoS2, were transferred onto a monolayer closed-packed CdSe quantum dots and were examined by photoluminescence (PL) after different time periods. By comparing the PL of CdSe QDs in uncovered areas and those covered by different numbers of layers of graphene and MoS2, we saw that vdW encapsulation slows down the aging of CdSe QDs dramatically. PL mapping results clearly showed better protection of the CdSe QDs under the central part of the vdW material compared to that at the edge; this can be explained by the diffusion of oxygen and water vapor from the edge of the vdW materials.

  19. Photoelectron spectroscopic study on monolayer pentacene thin-film/polar ZnO single-crystal hybrid interface

    Nagata, Takahiro; Nakamura, Tatsuru; Hayakawa, Ryoma; Yoshimura, Takeshi; Oh, Seungjun; Hiroshiba, Nobuya; Chikyow, Toyohiro; Fujimura, Norifumi; Wakayama, Yutaka


    The polarity effects of ZnO on the electronic state of a monolayer pentacene/ZnO interface were investigated by X-ray photoelectron spectroscopy (XPS). XPS revealed that the Zn-polar ZnO (Zn-ZnO) strongly depleted electrons in pentacene at the interface. The O-polar ZnO showed greater electron transfer from ZnO to pentacene than Zn-ZnO. The surface potential of pentacene on ZnO was larger than that of bulk pentacene regardless of the ZnO polarity. These findings indicate that the polarity of ZnO has the potential to control the electronic state of the organic/inorganic semiconductor interface.

  20. Ferroelectric Switching of Vinylidene and Trifluoroethylene Copolymer Thin Films on Au Electrodes Modified with Self-Assembled Monolayers

    Naoto Tsutsumi


    Full Text Available The ferroelectric switching characteristics of a vinylidene fluoride and trifluoroethylene copolymer were significantly changed via the chemical modification of a gold electrode with an alkanethiol self-assembled monolayer (SAM. The alkanethiol SAM-Au electrode successfully suppressed the leakage current (dark current from the electrode to the bulk ferroelectric. Smaller leakage currents led to the formation of an effective electric field in the bulk ferroelectric. At switching cycles ranging from 10 to 100 kHz, significant changes in the ferroelectric properties were observed. At 100 kHz, a remanent polarization (Pr of 68 mC·m−2 was measured, whereas a very small Pr value of 2.4 mC·m−2 was measured for the sample without a SAM. The switching speed of the SAM-Au electrode is as twice as fast as that of the unmodified electrode. A large potential barrier was formed via the insertion of a SAM between the Au electrode and the ferroelectric, effectively changing the ferroelectric switching characteristics.

  1. Prediction of large-gap quantum spin hall insulator and Rashba-Dresselhaus effect in two-dimensional g-TIA (A = N, P, As, and Sb) monolayer films

    Xinru Li[1; Ying Dai[1; Yandong Ma[1; Wei Wei[1; Lin Yu[1; Baibiao Huang[2


    A new family of two-dimensional (2D) topological insulators (TIs) comprising g-TIA (A = N, P, As, and Sb) monolayers constructed by T1 and group-V elements is predicted by first-principles calculations and molecular-dynamics (MD) simulations. The geometric stability, band inversion, nontrivial edge states, and electric polarity are investigated to predict the large-gap quantum spin Hall insulator and Rashba-Dresselhaus effects. The MD results reveal that the g-T1A monolayers remain stable even at room temperature. The g-T1A (A = As, Sb) monolayers become TIs under the influence of strong spin-orbit couplings with large bulk bandgaps of 131 and 268 meV, respectively. A single band inversion is observed in each g-T1A (A = As, Sb) monolayer, indicating a nontrivial topological nature. Furthermore, the topological edge states are described by introducing a sufficiently wide zigzag-nanoribbon. A Dirac point in the middle of the bulk gap connects the valence- and conduction-band edges. The Fermi velocity near the Dirac point with a linear band dispersion is -0.51 × 106 m/s, which is comparable to that of many other 2D nanomaterials. More importantly, owing to the broken inversion symmetry normal to the plane of the g-T1A films, a promising Rashba-Dresselhaus effect with the parameter up to 0.85 eV-A is observed in the g-T1A (A = As, Sb) monolayers. Our findings regarding 2D topological g-T1A monolayers with room-temperature bandgaps, intriguing topological edge states, and a promising Rashba-Dresselhaus effect are of fundamental value and suggest potential applications in nanoelectronic devices.

  2. (H2O)-H-2 turnover method as a means to detect bias in estimations of intake of nonbreast milk liquids in breast-fed infants

    Haisma, H; Coward, WA; Albernaz, E; Barros, A; Victora, CG; Wright, A; Visser, GH


    Objective: Firstly, to compare food, and macronutrient intake as obtained from a single 24-h recall and a frequency questionnaire (FQ) covering a 14-day period in breast-fed infants aged 4 months of age. Secondly, nonbreast milk water intake (NB-WI, ml/day) was used as an estimation of energy and ma

  3. Study of the transient "free" OH radical generated in H2O-H2O2 mixtures by stimulated Raman scattering

    Li, Fangfang; Ma, Zhiwei; Wang, Shenghan; Li, Tianyu; Sun, Chenglin; Li, Zhanlong; Men, Zhiwei


    Forward and backward stimulated Raman scattering (SRS) were studied in the H2O2-H2O mixtures by a strong excitation laser with 532 nm. Only the backward SRS (BSRS) of the H2O2-H2O system shows an unexpected SRS shoulder peak at around 3600 cm- 1, which is similar to the characteristic peak of "free" OH radical. The generation of the "free" OH radical is mainly attributed to the dissociation of hydrogen peroxide (HP) molecules. Simultaneously, the ionization of HP-water clusters generates a part of "free" OH radical under the Laser-induced breakdown (LIB). The interaction of water and HP is also discussed.

  4. Penetration of lipid monolayers by psychoactive drugs

    Demel, R.A.; Deenen, L.L.M. van


    The ability of a number of psychoactive drugs to penetrate lipid monolayers of varying composition was examined, and the following observation were made: (1) The increase in surface pressure of a monomolecular film appeared to depend on the chemical nature of the lipid as well as on the initial film

  5. Fullerene monolayer formation by spray coating.

    Cervenka, J; Flipse, C F J


    Many large molecular complexes are limited in thin film applications by their insufficient thermal stability, which excludes deposition via commonly used vapour phase deposition methods. Here we demonstrate an alternative way of monolayer formation of large molecules by a simple spray coating method under ambient conditions. This technique has been successfully applied on C(60) dissolved in toluene and carbon disulfide. Monolayer thick C(60) films have been formed on graphite and gold surfaces at particular deposition parameters, as confirmed by atomic force and scanning tunnelling microscopies. Structural and electronic properties of spray coated C(60) films on Au(111) have been found comparable to thermally evaporated C(60). We attribute the monolayer formation in spray coating to a crystallization process mediated by an ultrathin solution film on a sample surface.

  6. Electrochemical Deposition Of Thiolate Monolayers On Metals

    Porter, Marc D.; Weissharr, Duane E.


    Electrochemical method devised for coating metal (usually, gold) surfaces with adherent thiolate monolayers. Affords greater control over location and amount of material deposited and makes it easier to control chemical composition of deposits. One important potential use for this method lies in fabrication of chemically selective thin-film resonators for microwave oscillators used to detect pollutants: monolayer formulated to bind selectively pollutant chemical species of interest, causing increase in mass of monolayer and corresponding decrease in frequency of resonance. Another important potential use lies in selective chemical derivatization for purposes of improving adhesion, lubrication, protection against corrosion, electrocatalysis, and electroanalysis.

  7. Molecular orientation of copper phthalocyanine thin films on different monolayers of fullerene on SiO{sub 2} or highly oriented pyrolytic graphite

    Wang, Chenggong; Wang, Congcong [Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627 (United States); Liu, Xiaoliang [Institute for Super-microstructure and Ultrafast Process in Advanced Materials (ISUPAM), Central South University, Changsha, Hunan 410083 (China); Xu, Xumei; Li, Youzhen [School of Physics and Electronics, Central South University, Changsha, Hunan 410083 (China); Xie, Fangyan [Instrumental Analysis Center, Sun Yat-Sen University, Guangzhou 510275 (China); Gao, Yongli [Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627 (United States); Institute for Super-microstructure and Ultrafast Process in Advanced Materials (ISUPAM), Central South University, Changsha, Hunan 410083 (China)


    The interface electronic structures of copper phthalocyanine (CuPc) have been studied using ultraviolet photoemission spectroscopy as different monolayers of C{sub 60} were inserted between CuPc and a SiO{sub 2} or highly ordered pyrolytic graphite (HOPG) substrate. The results show that CuPc has standing up configuration with one monolayer of C{sub 60} insertion on SiO{sub 2} while lying down on HOPG, indicating that the insertion layer propagates the CuPc-substrate interaction. Meanwhile, CuPc on more than one monolayers of C{sub 60} on different substrates show that the substrate orientation effect quickly vanished. Our study elucidates intriguing molecular interactions that manipulate molecular orientation and donor-acceptor energy level alignment.

  8. Application of disorganized monolayer films on gold electrodes to the prevention of surfactant inhibition of the voltammetric detection of trace metals via anodic stripping of underpotential deposits: detection of copper.

    Herzog, Grégoire; Arrigan, Damien W M


    Development of an approach to prevention of electrode surface fouling by surfactants in samples is demonstrated. Spontaneously adsorbed monolayer systems employing short alkyl chains and bulky end groups are used to form porous disorganized monolayers on gold electrodes. Detection of copper by stripping of underpotential deposits formed at electrodes modified with disorganized films of mercaptoethanesulfonate (MES), mercaptopropanesulfonate, mercaptoacetic acid, and mercaptopropanoic acid was possible, and to a much lesser extent at aminoethanethiol and L-cysteine films. Use of short deposition times in conjunction with linear sweep anodic stripping voltammetry allowed detection of Cu2+ ions down to 1 x 10(-6) M in sulfuric acid solution, using underpotential deposition as the deposition step of the procedure. Calibration graphs were linear in the concentration range (1-80) x 10(-6) M Cu2+ using 15-s deposition at 0.00 V versus Ag/AgCl. The surfactants Tween 20, Tween 80, and Triton X-100 were found to have no affect on detection of Cu2+ ions in the calibration curve concentration range using MES-modified gold electrodes, whereas at unmodified gold electrodes very severe attenuation of the detection capability was manifested. The average slope for all calibration curves at the MES-modified electrode in the absence and presence of the surfactants at two different concentration levels was 0.0710 +/- 0.0024 microA microM(-1); in contrast, the slope of the calibration line at uncoated gold electrodes in the presence of surfactant was 0.0268 microA microM(-1). These results indicate the excellent ability of a disorganized, porous monolayer for prevention of fouling of the electrode surface by the surfactants.

  9. Molecular-dynamics study of the dynamical excitations in commensurate monolayer films of nitrogen molecules on graphite: A test of the corrugation in the nitrogen-graphite potential

    Hansen, Flemming Yssing; Bruch, Ludwig Walter


    The dynamical excitations in a commensurate monolayer solid of N2 molecules adsorbed on graphite have been studied using molecular-dynamics simulations. Velocity and rotational correlation functions as well as coherent intermediate scattering functions and dynamical structure factors have been ca...... demonstrated from the time dependence of the mean-square displacement of the molecules and the two-dimensional diffusion coefficient is estimated to be 2–3×10-5 cm2/s at 75–80 K.......The dynamical excitations in a commensurate monolayer solid of N2 molecules adsorbed on graphite have been studied using molecular-dynamics simulations. Velocity and rotational correlation functions as well as coherent intermediate scattering functions and dynamical structure factors have been...

  10. Enhanced absorption of monolayer MoS2 with resonant back reflector

    Liu, Jiang-Tao; Li, Xiao-Jing; Liu, Nian-Hua


    By extracting the permittivity of monolayer MoS2 from experiments, the optical absorption of monolayer MoS2 prepared on top of one-dimensional photonic crystal (1DPC) or metal films is investigated theoretically. The 1DPC and metal films act as resonant back reflectors that can enhance absorption of monolayer MoS2 substantially over a broad spectral range due to the Fabry-Perot cavity effect. The absorption of monolayer MoS2 can also be tuned by varying either the distance between the monolayer MoS2 and the back reflector or the thickness of the cover layers.

  11. Preparation, characterization and mechanical properties of Y 2O 3 thin film deposited on sulfonated self-assembled monolayer of 3-mercaptopropyl trimethoxysilane

    Wang, Jinqing; Liu, Xiaohong; Guan, Fei; Wang, Bo; Yang, Shengrong


    Silane coupling reagent (3-mercaptopropyl)trimethoxysilane was self-assembled on a single-crystal Si substrate to form a two-dimensional organic monoalyer (MPTS-SAM) and the terminal -SH group in the film was in-situ oxidized to -SO 3H group to endow the film with good chemisorption ability. Thus Y 2O 3 thin film were deposited on the oxidized MPTS-SAM, by enhanced hydrolysis of yttrium nitrate (Y(NO 3) 3 · 6H 2O) solution in the presence of urea (CO(NH 2) 2) at 80 °C, making use of the chemisorption ability of the -SO 3H group. The thickness and refractive index of the films were determined with an ellipsometer. The morphologies of the films were observed on an atomic force microscope. The adhesion strength and friction behavior of the films on the silicon substrate sliding against a steel ball was examined on a UMT-2MT friction and wear test system. It was found that the Y 2O 3-600 thin film was well adhered to the substrate with a critical load ( Lc) of 2.8 N and had excellent antiwear and friction-reduction performance under a low load of 0.2 N. Thus the Y 2O 3 film might find promising application in the surface-protection of single crystal Si and SiC in microelectromechanical systems (MEMS).

  12. Formation, surface characterization, and electrocatalytic application of self-assembled monolayer films of tetra-substituted manganese, iron, and cobalt benzylthio phthalocyanine complexes

    Akinbulu, IA


    Full Text Available property of the films was evidenced from better voltammetry responses (less positive oxidation potential and better current signal) of the insecticide, carbofuran, on these films, relative to that on bare gold electrode. In terms of less positive oxidation...

  13. Light-Modulation of the Charge Injection in a Polymer Thin-Film Transistor by Functionalizing the Electrodes with Bistable Photochromic Self-Assembled Monolayers.

    Mosciatti, Thomas; Del Rosso, Maria G; Herder, Martin; Frisch, Johannes; Koch, Norbert; Hecht, Stefan; Orgiu, Emanuele; Samorì, Paolo


    High fatigue resistance, bistability, and drastic property changes among isomers allow efficient modulation of the current output of organic thin-film transistors (OTFTs) to be obtained by a photogating of the charge-injection mechanism.

  14. Dynamic in-plane potential gradients for actively controlling electrochemical reactions: Part I. Characterization of 1- and 2-component alkanethiol monolayer gradients on thin gold films. Part II. Applications of in-plane potential gradients

    Balss, Karin Maria

    The research contained in this thesis is focused on the formation and characterization of surface composition gradients on thin gold films that are formed by applications of in-plane potential gradients. Injecting milliamp currents into thin Au films yields significant in-plane voltage drops so that, rather than assuming a single value of potential, an in-plane potential gradient is imposed on the film which depends on the resistivity of the film, the cross sectional area and the magnitude of the potential drop. Furthermore, the in-plane electric potential gradient means that, relative to a solution reference couple, electrochemical reactions occurs at defined spatial positions corresponding to the local potential, V(x) ˜ E0. The spatial gradient in electrochemical potential can then produce spatially dependent electrochemistry. Surface-chemical potential gradients can be prepared by arranging the spread of potentials to span an electrochemical wave mediating redox-associated adsorption or desorption. Examples of reactions that can be spatially patterned include the electrosorption of alkanethiols and over-potential metal deposition. The unique advantage of this method for patterning spatial compositions is the control of surface coverage in both space and time. The thesis is organized into two parts. In Part I, formation and characterization of 1- and 2-component alkanethiol monolayer gradients is investigated. Numerous surface science tools are employed to examine the distribution in coverage obtained by application of in-plane potential gradients. Macroscopic characterization was obtained by sessile water drop contact angle measurements and surface plasmon resonance imaging. Gradients were also imaged on micron length scales with pulsed-force mode atomic force microscopy. Direct chemical evidence of surface compositions in aromatic thiol surface coverage was obtained by surface-enhanced Raman spectroscopy. In Part II, the applications of in-plane potential

  15. Fullerene films and fullerene-dodecylamine adduct monolayers at air-water interfaces studied by neutron and x-ray reflection

    Wang, J.Y.; Vaknin, D.; Uphaus, R.A.;


    Neutron and X-ray reflection measurements and surface pressure isotherms of spread films of the fullerene-dodecylamine adduct C60-[NH2(CH2)11CH3]x all indicate that this material may form monomolecular layers on water surfaces. The reflection data sets (neutron on both H2O and D2O) can be accounted...

  16. Persistent monolayer-scale chemical ordering in Si{sub 1−x}Ge{sub x} heteroepitaxial films during surface roughening and strain relaxation

    Amatya, J. M.; Floro, J. A. [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States)


    Chemical ordering in semiconductor alloys could modify thermal and electronic transport, with potential benefits to thermoelectric properties. Here, metastable ordering that occurs during heteroepitaxial growth of Si{sub 1−x}Ge{sub x} thin film alloys on Si(001) and Ge(001) substrates is investigated. A parametric study was performed to study how strain, surface roughness, and growth parameters affect the order parameter during the alloy growth. The order parameter for the alloy films was carefully quantified using x-ray diffraction, taking into account an often-overlooked issue associated with the presence of multiple spatial variants associated with ordering along equivalent <111> directions. Optimal ordering was observed in the films having the smoothest surfaces. Extended strain relaxation is suggested to reduce the apparent order through creation of anti-phase boundaries. Ordering surprisingly persists even when the film surface extensively roughens to form (105) facets. Growth on deliberately miscut Si(001) surfaces does not affect the volume-averaged order parameter but does impact the relative volume fractions of the equivalent ordered variants in a manner consistent with geometrically necessary changes in step populations. These results provide somewhat self-contradictory implications for the role of step edges in controlling the ordering process, indicating that our understanding is still incomplete.

  17. Ionization of covalent immobilized poly(4-vinylphenol) monolayers measured by ellipsometry, QCM and SPR

    Uppalapati, Suji [Department of Chemistry, University of Massachusetts Lowell, 1 University Ave., Lowell, MA 01854 (United States); Kong, Na; Norberg, Oscar [KTH-Royal Institute of Technology, Department of Chemistry, Teknikringen 30, S-10044 Stockholm (Sweden); Ramström, Olof, E-mail: [KTH-Royal Institute of Technology, Department of Chemistry, Teknikringen 30, S-10044 Stockholm (Sweden); Yan, Mingdi, E-mail: [Department of Chemistry, University of Massachusetts Lowell, 1 University Ave., Lowell, MA 01854 (United States); KTH-Royal Institute of Technology, Department of Chemistry, Teknikringen 30, S-10044 Stockholm (Sweden)


    Covalently immobilized poly(4-vinylphenol) (PVP) monolayer films were fabricated by spin coating PVP on perfluorophenyl azide (PFPA)-functionalized surfaces followed by UV irradiation. The pH-responsive behavior of these PVP ultrathin films was evaluated by ellipsometry, quartz crystal microbalance (QCM) and surface plasmon resonance (SPR). By monitoring the responses of these films to pH in situ, the ionization constant of the monolayer thin films was obtained. The apparent pK{sub a} value of these covalently immobilized PVP monolayers, 13.4 by SPR, was 3 units higher than that of the free polymer in aqueous solution.

  18. Study of the improvements in the electrical performance of solution-processed metal oxide thin-film transistors using self-assembled monolayers

    Park, Jin-Woo; Kim, Hyungjoong; Kim, Dae Hwan; Lee, Mijung


    Thin-film transistors (TFTs) of a metal oxide semiconductor typically are transparent and have high mobility to be paid attention for back plane of displays. One of the most actively studied fabrication methods of metal oxide semiconductors is the solution processing (sol-gel) method, owing to its low-cost, simple and fast steps that ensure good product uniformity, and applicability to roll-to-roll processing. Our study focused on probing the electronic properties of solution-processed metal oxide TFTs. We have calculated the density of state (DOS) with monochromatic photonic capacitance-voltage (MPCV) measurements. Improvements in device are proved by electronic and photo-electronic methods.

  19. Adsorption of Ions at Uncharged Insoluble Monolayers

    Peshkova, T. V.; Minkov, I. L.; Tsekov, R.; Slavchov, R. I.


    A method is proposed for the experimental determination of the adsorption of inorganic electrolytes at a surface covered with insoluble surfactant monolayer. This task is complicated by the fact that the change of the salt concentration alters both chemical potentials of the electrolyte and the surfactant. Our method resolves the question by combining data for the surface pressure versus area of the monolayer at several salt concentrations with data for the equilibrium spreading pressure of crystals of the surfactant (used to fix a standard state). We applied the method to alcohols spread at the surface of concentrated halide solutions. The measured salt adsorption is positive and has nonmonotonic dependence on the area per surfactant molecule. For the liquid expanded film, depending on the concentration, there is one couple of ions adsorbed per each 3–30 surfactant molecules. We analyzed which ion, the positive or the negative, stands closer to the surface, by measuring the effect of NaCl on the Volta potential of the monolayer. The potentiometric data suggest that Na+ is specifically adsorbed, while Cl– remains in the diffuse layer, i.e., the surface is positively charged. The observed reverse Hofmeister series of the adsorptions of NaF, NaCl, and NaBr suggests the same conclusion holds for all these salts. The force that causes the adsorption of Na+ seems to be the interaction of the ion with the dipole moment of the monolayer.

  20. Magnetic and Structural Phases of Monolayer 02 on Graphite

    McTague, J. P.; Nielsen, Mourits


    Neutron diffraction studies of O2 thin films physisorbed on the basal plane of graphite show three distinct two-dimensional crystalline phases, all incommensurate with the substrate lattice. The low-temperature monolayer phase has a distorted triangular structure analogous to the closest-packed p......Neutron diffraction studies of O2 thin films physisorbed on the basal plane of graphite show three distinct two-dimensional crystalline phases, all incommensurate with the substrate lattice. The low-temperature monolayer phase has a distorted triangular structure analogous to the closest...

  1. Nonlinear optical characteristics of monolayer MoSe{sub 2}

    Le, Chinh Tam; Ullah, Farman; Senthilkumar, Velusamy; Kim, Yong Soo [Department of Physics and Energy Harvest Storage Research Center, University of Ulsan (Korea, Republic of); Clark, Daniel J.; Jang, Joon I. [Department of Physics, Applied Physics and Astronomy, Binghamton University, Binghamton, NY (United States); Sim, Yumin; Seong, Maeng-Je [Department of Physics, Chung-Ang University, Seoul (Korea, Republic of); Chung, Koo-Hyun [School of Mechanical Engineering, University of Ulsan (Korea, Republic of); Park, Hyoyeol [Electronics, Communication and Semiconductor Applications Department, Ulsan College (Korea, Republic of)


    In this study, we utilized picosecond pulses from an Nd:YAG laser to investigate the nonlinear optical characteristics of monolayer MoSe{sub 2}. Two-step growth involving the selenization of pulsed-laser-deposited MoO{sub 3} film was employed to yield the MoSe{sub 2} monolayer on a SiO{sub 2}/Si substrate. Raman scattering, photoluminescence (PL) spectroscopy, and atomic force microscopy verified the high optical quality of the monolayer. The second-order susceptibility χ{sup (2)} was calculated to be ∝50 pm V{sup -1} at the second harmonic wavelength λ{sub SHG} ∝810 nm, which is near the optical gap of the monolayer. Interestingly, our wavelength-dependent second harmonic scan can identify the bound excitonic states including negatively charged excitons much more efficiently, compared with the PL method at room temperature. Additionally, the MoSe{sub 2} monolayer exhibits a strong laser-induced damage threshold ∝16 GW cm{sup -2} under picosecond-pulse excitation{sub .} Our findings suggest that monolayer MoSe{sub 2} can be considered as a promising candidate for high-power, thin-film-based nonlinear optical devices and applications. (copyright 2016 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. A self-assembled monolayer-assisted surface microfabrication and release technique

    Kim, B.J.; Liebau, M.; Huskens, J.; Reinhoudt, D.N.; Brugger, J.P.


    This paper describes a method of thin film and MEMS processing which uses self-assembled monolayers as ultra-thin organic surface coating to enable a simple removal of microfabricated devices off the surface without wet chemical etching. A 1.5-nm thick self-assembled monolayer of dodecyltrichlorosil

  3. Experimental study of thermal rectification in suspended monolayer graphene

    Wang, Haidong; Hu, Shiqian; Takahashi, Koji; Zhang, Xing; Takamatsu, Hiroshi; Chen, Jie


    Thermal rectification is a fundamental phenomenon for active heat flow control. Significant thermal rectification is expected to exist in the asymmetric nanostructures, such as nanowires and thin films. As a one-atom-thick membrane, graphene has attracted much attention for realizing thermal rectification as shown by many molecular dynamics simulations. Here, we experimentally demonstrate thermal rectification in various asymmetric monolayer graphene nanostructures. A large thermal rectification factor of 26% is achieved in a defect-engineered monolayer graphene with nanopores on one side. A thermal rectification factor of 10% is achieved in a pristine monolayer graphene with nanoparticles deposited on one side or with a tapered width. The results indicate that the monolayer graphene has great potential to be used for designing high-performance thermal rectifiers for heat flow control and energy harvesting.

  4. Patterning Self-Assembled Monolayers on Gold: Green Materials Chemistry in the Teaching Laboratory

    McFarland, Adam D.; Huffman, Lauren M.; Parent, Kathryn, E.; Hutchison, James E.; Thompson, John E.


    An experiment demonstrating self-assembled monolayer (SAM) chemistry, organic thin-film patterning and the use of molecular functionality to control macroscopic properties is described. Several important green chemistry principles are introduced.

  5. Studies of Self-assembled Monolayers Formed by Imidazoline on Iron Surface by SEM and SECM

    Xiu Yu LIU; Shen Hao CHEN; Shuai MIAO; Su Xiang WU; Li Xia SHEN; Yuan Xing CAI; Hong Yan ZHAI


    The self-assembled monolayers (SAMs) of imidazoline (IM) on the iron surface were characterized by scanning electron microscope (SEM) and scanning electrochemical microscopy(SECM). The results showed that SAMs were an effective inhibition film for iron.

  6. Neutron Reflectivity Measurement for Polymer Dynamics near Graphene Oxide Monolayers

    Koo, Jaseung

    We investigated the diffusion dynamics of polymer chains confined between graphene oxide layers using neutron reflectivity (NR). The bilayers of polymethylmetacrylate (PMMA)/ deuterated PMMA (d-PMMA) films and polystyrene (PS)/d-PS films with various film thickness sandwiched between Langmuir-Blodgett (LB) monolayers of graphene oxide (GO) were prepared. From the NR results, we found that PMMA diffusion dynamics was reduced near the GO surface while the PS diffusion was not significantly changed. This is due to the different strength of GO-polymer interaction. In this talk, these diffusion results will be compared with dewetting dynamics of polymer thin films on the GO monolayers. This has given us the basis for development of graphene-based nanoelectronics with high efficiency, such as heterojunction devices for polymer photovoltaic (OPV) applications.

  7. Total cross sections for scattering of electrons from O2,H2O,H2,O3, CO and CO2 at 100-2000eV

    Shi De-Heng; Sun Jin-Feng; Yang Xiang-Dong; Zhu Zun-Lue; Liu Yu-Fang


    A complex optical model potential rewritten by the concept of bonded atom, which considers the overlap of electron clouds, is employed to calculate the total cross sections for electron scattering from several simple molecules (O2, H2O, H2, O3, CO and CO2) consisting of C, H and O atoms in an incident energy range of 100-2000eV by the use of the additivity rule at Hartree-Fock level. In the study, the complex optical potential composed of static, exchange,correlation polarization plus absorption contributions firstly uses the bonded-atom concept. The quantitative molecular total cross section results are compared with experimental data and with the other calculations wherever available and good agreement is obtained. It is shown that the additivity rule along with the complex optical model potential rewritten by the concept of bonded atom can be used successfully to calculate the total cross section of electron-molecule scattering above 100eV, whereas the rule together with the complex optical model potential not rewritten by the concept of bonded atom is only successfully used above 300-500eV. So, the introduction of the bonded-atom concept in the complex optical potential can improve the accuracy of the total cross section calculations.

  8. Kinetic double-layer model of aerosol surface chemistry and gas-particle interactions (K2-SURF): Degradation of polycyclic aromatic hydrocarbons exposed to O3, NO2, H2O, OH and NO3

    Shiraiwa, Manabu; Garland, Rebecca M.; Pöschl, Ulrich


    We present a kinetic double-layer surface model (K2-SURF) that describes the degradation of polycyclic aromatic hydrocarbons (PAHs) on aerosol particles exposed to ozone, nitrogen dioxide, water vapor, hydroxyl and nitrate radicals [1]. The model is based on multiple experimental studies of PAH degradation and on the Pöschl-Rudich-Ammann (PRA) framework [2] for aerosol and cloud surface chemistry and gas-particle interactions. For a wide range of substrates, including solid and liquid organic and inorganic substances (soot, silica, sodium chloride, octanol/decanol, organic acids, etc.), the concentration- and time-dependence of the heterogeneous reaction between PAHs and O3 can be efficiently described with a Langmuir-Hinshelwood-type mechanism. Depending on the substrate material, the Langmuir adsorption constants for O3 vary over three orders of magnitude, and the second-order rate coefficients for the surface layer reaction of O3 with different PAH vary over two orders of magnitude. The available data indicate that the Langmuir adsorption constants for NO2 are similar to those of O3, while those of H2O are several orders of magnitude smaller. The desorption lifetimes and adsorption enthalpies suggest chemisorption of NO2 and O3 and physisorption of H2O. Note, however, that the exact reaction mechanisms, rate limiting steps and possible intermediates still remain to be resolved (e.g., surface diffusion and formation of O atoms or O3- ions at the surface). The K2-SURF model enables the calculation of ozone uptake coefficients, γO3, and of PAH concentrations in the quasi-static particle surface layer. Competitive adsorption and chemical transformation of the surface (aging) lead to a strong non-linear dependence of γO3 on time and gas phase composition, with different characteristics under dilute atmospheric and concentrated laboratory conditions. Under typical ambient conditions, γO3 of PAH-coated aerosol particles are expected to be in the range of 10-6 - 10-5. At ambient temperatures, NO2 alone does not efficiently degrade PAHs, but it was found to accelerate the degradation of PAHs exposed to O3. The accelerating effect can be attributed to highly reactive NO3 radicals formed in the gas phase or on the surface. Estimated second-order rate coefficients for O3-NO2 and PAH-NO3 surface layer reactions are in the range of 10-17 - 10-16 cm2 s-1 and 10-15 - 10-12 cm2 s-1, respectively. The chemical half-life of PAHs is expected to range from a few minutes on the surface of soot to multiple hours on organic and inorganic solid particles and days on liquid particles. On soot, the degradation of particle-bound PAHs in the atmosphere appears to be dominated by a surface layer reaction with adsorbed ozone. On other substrates, it is likely dominated by gas-surface reactions with OH or NO3 radicals (Eley-Rideal-type mechanism). To our knowledge, K2-SURF is the first atmospheric process model describing multiple types of parallel and sequential surface reactions between multiple gaseous and particle-bound chemical species. It illustrates how the general equations of the PRA framework can be simplified and adapted for specific reaction systems. References: [1] Shiraiwa et al., Atmos. Chem. and Phys., 9, 9571-9586 (2009). [2] Pöschl et al., Atmos. Chem. and Phys., 7, 5989-6023 (2007).

  9. Synthesis and characterization of a chiral dimeric copper(II) complex: Crystal structure of [Cu2(-Cl)2(HL)2].H2O(H2L = -(-)-2-[(2-hydroxy-1-phenyl-ethylimino)-methyl]-phenol)

    Chullikkattil P Pradeep; Panthapally S Zacharias; Samar K Das


    Synthesis and characterization of an optically active binuclear dichloro-bridged copper(II) complex [Cu2(-Cl)2(HL)2]$\\cdot$H2O 1 (H2L = -(-)-2-[(2-hydroxy-1-phenyl-ethylimino)-methyl]-phenol) of a Schiff-base derived from salicylaldehyde and ()-(+)-2-phenylglycinol are described. Compound 1 crystallizes in the orthorhombic chiral P212121 space group with = 4, = 10.21(2), = 11.574(3), = 25.364(9). Each copper shows square pyramidal geometry with O2NCl2 coordination and the Cu2Cl2 core geometry adopts a butterfly shape. Crystals of 1 were further characterized by elemental analysis, IR, UV-visible and EPR spectroscopy and circular dichroism (CD) studies.

  10. Chemistry, Raman and infrared spectroscopic characterization of the phosphate mineral reddingite: (MnFe)3(PO4)2(H2O,OH)3, a mineral found in lithium-bearing pegmatite

    Frost, Ray L.; Xi, Yunfei; Scholz, Ricardo; Belotti, Fernanda M.; Lagoeiro, Leonardo E.


    Detailed investigation of an intermediate member of the reddingite-phosphoferrite series, using infrared and Raman spectroscopy, scanning electron microcopy and electron microprobe analysis, has been carried out on a homogeneous sample from a lithium-bearing pegmatite named Cigana mine, near Conselheiro Pena, Minas Gerais, Brazil. The determined formula is ({{Mn}}_{1.60} {{Fe}}_{1.21} {{Ca}}_{0.01} {{Mg}}_{0.01} )_{sum 2.83} ({{PO}}4 )_{2.12} \\cdot ({{H}}2 {{O}}_{2.85} {{F}}_{0.01} )_{sum 2.86} , indicating predominance in the reddingite member. Raman spectroscopy coupled with infrared spectroscopy supports the concept of phosphate, hydrogen phosphate and dihydrogen phosphate units in the structure of reddingite-phosphoferrite. Infrared and Raman bands attributed to water and hydroxyl stretching modes are identified. Vibrational spectroscopy adds useful information to the molecular structure of reddingite-phosphoferrite.

  11. Collapse of Langmuir monolayer at lower surface pressure: Effect of hydrophobic chain length

    Das, Kaushik, E-mail:; Kundu, Sarathi [Physical Sciences Division, Institute of Advanced Study in Science and Technology, Vigyan Path, Paschim Boragaon, Garchuk, Guwahati, Assam 781035 (India)


    Long chain fatty acid molecules (e.g., stearic and behenic acids) form a monolayer on water surface in the presence of Ba{sup 2+} ions at low subphase pH (≈ 5.5) and remain as a monolayer before collapse generally occurs at higher surface pressure (π{sub c} > 50 mN/m). Monolayer formation is verified from the surface pressure vs. area per molecule (π-A) isotherms and also from the atomic force microscopy (AFM) analysis of the films deposited by single upstroke of hydrophilic Si (001) substrate through the monolayer covered water surface. At high subphase pH (≈ 9.5), barium stearate molecules form multilayer structure at lower surface pressure which is verified from the π-A isotherms and AFM analysis of the film deposited at 25 mN/m. Such monolayer to multilayer structure formation or monolayer collapse at lower surface pressure is unusual as at this surface pressure generally fatty acid salt molecules form a monolayer on the water surface. Formation of bidentate chelate coordination in the metal containing headgroups is the reason for such monolayer to multilayer transition. However, for longer chain barium behenate molecules only monolayer structure is maintained at that high subphase pH (≈ 9.5) due to the presence of relatively more tail-tail hydrophobic interaction.

  12. Preparation and Characterization of Covalently Binding of Rat Anti-human IgG Monolayer on Thiol-Modified Gold Surface

    Lv Zhengjian


    Full Text Available Abstract The 16-mercaptohexadecanoic acid (MHA film and rat anti-human IgG protein monolayer were fabricated on gold substrates using self-assembled monolayer (SAM method. The surface properties of the bare gold substrate, the MHA film and the protein monolayer were characterized by contact angle measurements, atomic force microscopy (AFM, grazing incidence X-ray diffraction (GIXRD method and X-ray photoelectron spectroscopy, respectively. The contact angles of the MHA film and the protein monolayer were 18° and 12°, respectively, all being hydrophilic. AFM images show dissimilar topographic nanostructures between different surfaces, and the thickness of the MHA film and the protein monolayer was estimated to be 1.51 and 5.53 nm, respectively. The GIXRD 2θ degrees of the MHA film and the protein monolayer ranged from 0° to 15°, significantly smaller than that of the bare gold surface, but the MHA film and the protein monolayer displayed very different profiles and distributions of their diffraction peaks. Moreover, the spectra of binding energy measured from these different surfaces could be well fitted with either Au4f, S2p or N1s, respectively. Taken together, these results indicate that MHA film and protein monolayer were successfully formed with homogeneous surfaces, and thus demonstrate that the SAM method is a reliable technique for fabricating protein monolayer.

  13. Graphene-like Boron-Carbon-Nitrogen Monolayers.

    Beniwal, Sumit; Hooper, James; Miller, Daniel P; Costa, Paulo S; Chen, Gang; Liu, Shih-Yuan; Dowben, Peter A; Sykes, E Charles H; Zurek, Eva; Enders, Axel


    A strategy to synthesize a 2D graphenic but ternary monolayer containing atoms of carbon, nitrogen, and boron, h-BCN, is presented. The synthesis utilizes bis-BN cyclohexane, B2N2C2H12, as a precursor molecule and relies on thermally induced dehydrogenation of the precursor molecules and the formation of an epitaxial monolayer on Ir(111) through covalent bond formation. The lattice mismatch between the film and substrate causes a strain-driven periodic buckling of the film. The structure of the film and its corrugated morphology is discussed based on comprehensive data from molecular-resolved scanning tunneling microscopy imaging, X-ray photoelectron spectroscopy, low-energy electron diffraction, and density functional theory. First-principles calculations further predict a direct electronic band gap that is intermediate between gapless graphene and insulating h-BN.

  14. Monolayers and mixed-layers on copper towards corrosion protection

    Sinapi, F. [Fonds pour la Formation a la Recherche dans l' Industrie et dans l' Agriculture, Rue d' Egmont 5, B-1000 Brussels (Belgium); Julien, S.; Auguste, D.; Hevesi, L.; Delhalle, J. [Laboratory of Chemistry and Electrochemistry of Surfaces, University of Namur, FUNDP, Rue de Bruxelles, 61, B-5000 Namur (Belgium); Mekhalif, Z. [Laboratory of Chemistry and Electrochemistry of Surfaces, University of Namur, FUNDP, Rue de Bruxelles, 61, B-5000 Namur (Belgium)], E-mail:


    In order to improve the protection abilities of (3-mercaptopropy)trimethoxysilane (MPTS) self-assembled monolayers on copper surfaces, mixed monolayers have been formed successfully by successive immersions in MPTS and in n-dodecanethiol (DT). A newly synthesised molecule, (11-mercaptoundecyl)trimethoxysilane (MUTS), has also been employed to form a thicker organic film on copper surfaces and, thereby, enhance the inhibitory action of the coating. The grafting has been confirmed by X-ray photoelectron spectroscopy (XPS), polarization modulation infrared reflection adsorption spectroscopy (PM-IRRAS) and water contact angle. The protective efficiency of each protective organic film has been evidenced by cyclic voltammetry (CV) and polarization curve measurements (CP). It was shown that the MUTS and unhydrolyzed MPTS/DT films exhibited significant corrosion protection properties.

  15. Free exciton emission and vibrations in pentacene monolayers

    He, Rui


    Pentacene is a benchmark organic semiconductor material because of its potential applications in electronic and optoelectronic devices. Recently we demonstrated that optical and vibrational characterizations of pentacene films can be carried out down to the sub-monolayer limit. These milestones were achieved in highly uniform pentacene films that were grown on a compliant polymeric substrate. Films with thickness ranging from sub- monolayer to tens of monolayers were studied at low temperatures. The intensity of the free exciton (FE) luminescence band increases quadratically with the number of layers N when N is small. This quadratic dependence is explained as arising from the linear dependence of the intensity of absorption and the probability of emission on the number of layers N. Large enhancements of Raman scattering intensities at the FE resonance enable the first observations of low-lying lattice modes in the monolayers. The measured low- lying modes (in the 20 to 100 cm-1 range) display characteristic changes when going from a single monolayer to two layers. The Raman intensities by high frequency intra-molecular vibrations display resonance enhancement double-peaks when incident or scattered photon energies overlap the FE optical emission. The double resonances are about the same strength which suggests that Franck-Condon overlap integrals for the respective vibronic transitions have the same magnitude. The interference between scattering amplitudes in the Raman resonance reveals quantum coherence of the symmetry-split states (Davydov doublet) of the lowest intrinsic singlet exciton. These results demonstrate novel venues for ultra-thin film characterization and studies of fundamental physics in organic semiconductor structures. In collaboration with Nancy G. Tassi (Dupont), Graciela B. Blanchet (Nanoterra, Cambridge, MA), and Aron Pinczuk (Columbia University).

  16. Phospholipidic Monolayers on Formamide

    Graner, François; Perez-Oyarzun, Santiago; Saint-Jalmes, Arnaud; Flament, Cyrille; Gallet, François


    We report the first phase diagram of a Langmuir film at the air-formamide interface. Stable films of phospholipids such as DPPC or DSPC undergo phase transitions observed on isotherms or by fluorescence microscopy. They display bidimensional gas, liquid and solid phases, as well as two mesophases; the latter coexist with liquid on a sharp first-order transition plateau. We compare these observations with known results on films on water. Nous présentons le premier diagramme de phase d'un film de Langmuir à l'interface air-formamide. On observe, sur des isothermes et par microscopie de fluorescence, des transitions de phase dans des films stables de phospholipides comme le DPPC ou le DSPC. Cinq phases bidimensionnelles sont mises en évidence : gaz, liquide, solide, ainsi que deux mésophases ; ces deux dernières coexistent avec le liquide sur un plateau très marqué de transition du premier ordre. Nous comparons ces observations avec les résultats connus pour les films sur l'eau.

  17. Self assembled monolayers of octadecyltrichlorosilane for dielectric materials

    Kumar, Vijay, E-mail: [Centre for Nanoscience and Engineering, Indian Institute of Science-Bangalore (India); Mechanical Engineering Department, Birla Institute of Technology and Science-Pilani (India); Puri, Paridhi; Nain, Shivani [Mechanical Engineering Department, Birla Institute of Technology and Science-Pilani (India); Bhat, K. N. [Centre for Nanoscience and Engineering, Indian Institute of Science-Bangalore (India); Sharma, N. N. [Mechanical Engineering Department, Birla Institute of Technology and Science-Pilani (India); School of Automobile, Mechanical & Mechatronics, Manipal University-Jaipur (India)


    Treatment of surfaces to change the interaction of fluids with them is a critical step in constructing useful microfluidics devices, especially those used in biological applications. Selective modification of inorganic materials such as Si, SiO{sub 2} and Si{sub 3}N{sub 4} is of great interest in research and technology. We evaluated the chemical formation of OTS self-assembled monolayers on silicon substrates with different dielectric materials. Our investigations were focused on surface modification of formerly used common dielectric materials SiO{sub 2}, Si{sub 3}N{sub 4} and a-poly. The improvement of wetting behaviour and quality of monolayer films were characterized using Atomic force microscope, Scanning electron microscope, Contact angle goniometer, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) monolayer deposited oxide surface.

  18. A New Strategy for Architecture of Robust Monolayer Based on Binuclear Palladium (II) Complex of Calix[4]arene Derivative


    A monolayer which is formed by a binuclear palladium complex of low rim methionine-disubstituted calix[4]arene exhibits extraordinary cohesiveness. Cohesiveness measurement and Brewster Angle Microscopy observation show that the monolayer is uniform and robust. This film is probably formed by self-assembly of precursor complex through strong chloride ion bridge between palladium centers.

  19. Self-assembly of Carboxyl Functionalized Polystyrene Nanospheres into Close-packed Monolayers via Chemical Adsorption

    LI,Zhi-Wei(李志伟); ZHOU,Jing-Fang(周静芳); ZHANG,Zhi-Jun(张治军); DANG,Hong-Xin(党鸿辛)


    The polyacrylic acid functionalized polystyrene nanospheres were synthesized and self-assembled into irregular,densely packed monolayers in non-aqueous media. The polymer nanoparticles were chemically adhered to substrates. The morphologies of the resulting films were investigated. The impact of the volume fraction of alcohol in the mixed solvents on the particle adsorption and fabrication of nanosphere assembled films was examined.

  20. Monolayer patterning using ketone dipoles.

    Kim, Min Kyoung; Xue, Yi; Pašková, Tereza; Zimmt, Matthew B


    The self-assembly of multi-component monolayers with designed patterns requires molecular recognition among components. Dipolar interactions have been found to influence morphologies of self-assembled monolayers and can affect molecular recognition functions. Ketone groups have large dipole moments (2.6 D) and are easily incorporated into molecules. The potential of ketone groups for dipolar patterning has been evaluated through synthesis of two 1,5-disubstituted anthracenes bearing mono-ketone side chains, STM characterization of monolayers self-assembled from their single and two component solutions and molecular mechanics simulations to determine their self-assembly energetics. The results reveal that (i) anthracenes bearing self-repulsive mono-ketone side chains assemble in an atypical monolayer morphology that establishes dipolar attraction, instead of repulsion, between ketones in adjacent side chains; (ii) pairs of anthracene molecules whose self-repulsive ketone side chains are dipolar complementary spontaneously assemble compositionally patterned monolayers, in which the two components segregate into neighboring, single component columns, driven by side chain dipolar interactions; (iii) compositionally patterned monolayers also assemble from dipolar complementary anthracene pairs that employ different dipolar groups (ketones or CF2 groups) in their side chains; (iv) the ketone group, with its larger dipole moment and size, provides comparable driving force for patterned monolayer formation to that of the smaller dipole, and smaller size, CF2 group.

  1. Structure and Function Evolution of Thiolate Monolayers on Gold

    Edwards, Grant Alvin [Iowa State Univ., Ames, IA (United States)


    The use of n-alkanethiolate self-assembled monolayers on gold has blossomed in the past few years. These systems have functioned as models for common interfaces. Thiolate monolayers are ideal because they are easily modified before or after deposition. The works contained within this dissertation include interfacial characterization (inbred reflection absorption spectroscopy, ellipsometry, contact angle, scanning probe microscopy, and heterogeneous electron-transfer kinetics) and various modeling scenarios. The results of these characterizations present ground-breaking insights into the structure, function, and reproducible preparation of these monolayers. Surprisingly, three interfacial properties (electron-transfer, contact angle, and ellipsometry) were discovered to depend directly on the odd-even character of the monolayer components. Molecular modeling was utilized to investigate adlayer orientation, and suggests that these effects are adlayer structure specific. Finally, the electric force microscopy and theoretical modeling investigations of monolayer samples are presented, which show that the film dielectric constant, thickness, and dipole moment directly affect image contrast. In addition, the prospects for utilization of this emerging technique are outlined.

  2. Structure and function evolution of thiolate monolayers on gold

    Edwards, Grant Alvin [Iowa State Univ., Ames, IA (United States)


    The use of n-alkanethiolate self-assembled monolayers on gold has blossomed in the past few years. These systems have functioned as models for common interfaces. Thiolate monolayers are ideal because they are easily modified before or after deposition. The works contained within this dissertation include interfacial characterization (infrared reflection absorption spectroscopy, ellipsometry, contact angle, scanning probe microscopy, and heterogeneous electron-transfer kinetics) and various modeling scenarios. The results of these characterizations present ground-breaking insights into the structure, function, and reproducible preparation of these monolayers. Surprisingly, three interfacial properties (electron-transfer, contact angle, and ellipsometry) were discovered to depend directly on the odd-even character of the monolayer components. Molecular modeling was utilized to investigate adlayer orientation, and suggests that these effects are adlayer structure specific. Finally, the electric force microscopy and theoretical modeling investigations of monolayer samples are presented, which show that the film dielectric constant, thickness, and dipole moment directly affect image contrast. In addition, the prospects for utilization of this emerging technique are outlined.

  3. Penetration of surfactin into phospholipid monolayers: nanoscale interfacial organization.

    Eeman, M; Berquand, A; Dufrêne, Y F; Paquot, M; Dufour, S; Deleu, M


    Atomic force microscopy (AFM) combined with surface pressure-area isotherms were used to probe the interfacial behavior of phospholipid monolayers following penetration of surfactin, a cyclic lipopeptide produced by Bacillus subtilis strains. Prior to penetration experiments, interfacial behavior of different surfactin molecules (cyclic surfactins with three different aliphatic chain lengths--S13, S14, and S15--and a linear surfactin obtained by chemical cleavage of the cycle of the surfactin S15) has been investigated. A more hydrophobic aliphatic chain induces greater surface-active properties of the lipopeptide. The opening of the peptide ring reduces the surface activity. The effect of phospholipid acyl chain length (dimyristoylphosphatidylcholine, dipalmitoylphosphatidylcholine- (DPPC), and distearoylphosphatidylcholine) and phospholipid polar head (DPPC, dipalmitoylphosphatidylethanolamine and dipalmitoylphosphatidylserine) on monolayer penetration properties of the surfactin S15 has been explored. Results showed that while the lipid monolayer thickness and the presence of electrostatic repulsions from the interfacial film do not significantly influence surfactin insertion, these parameters strongly modulate the ability of the surfactin to alter the nanoscale organization of the lipid films. We also probed the effect of surfactin structure (influence of the aliphatic chain length and of the cyclic structure of the peptide ring) on the behavior of DPPC monolayers. AFM images and isotherms showed that surfactin penetration is promoted by longer lipopeptide chain length and a cyclic polar head. This indicates that hydrophobic interactions are of main importance for the penetration power of surfactin molecules.

  4. Ambient STM study of sequentially adsorbed octanethiol and biphenylthiol monolayers on Au(111)

    Fitzgerald, Danielle M.; Krisanda, Emily K.; Szypko, Colleen G.; Gaby Avila-Bront, L.


    The mixed monolayers of biphenyl-4-thiol (BPT) and octanethiol (OT) are studied at the molecular level using scanning tunneling microscopy (STM) in ambient conditions and X-ray photoelectron spectroscopy (XPS) on Au(111). The effect of both the sequence of deposition, and the concentration of the BPT solution used is investigated. We observe signs of coexisting domains in the form of disordered patches surrounding flat patches when a 100 μM solution of BPT is used. This observation holds for both OT being deposited first, and BPT being deposited first. The most clear formation of coexisting domains occurs when an OT monolayer is immersed in a 100 μM solution of BPT. The XP spectra reveal a shift in the C 1s signal of the monolayers that is unique to what films are deposited on the surface. These data demonstrate the importance characterizing mixed self-assembled monolayers that form final monolayer structures unique to each mixture.

  5. A simple method to tune graphene growth between monolayer and bilayer

    Xiaozhi Xu


    Full Text Available Selective growth of either monolayer or bilayer graphene is of great importance. We developed a method to readily tune large area graphene growth from complete monolayer to complete bilayer. In an ambient pressure chemical vapor deposition process, we used the sample temperature at which to start the H2 flow as the control parameter and realized the change from monolayer to bilayer growth of graphene on Cu foil. When the H2 starting temperature was above 700°C, continuous monolayer graphene films were obtained. When the H2 starting temperature was below 350°C, continuous bilayer films were obtained. Detailed characterization of the samples treated under various conditions revealed that heating without the H2 flow caused Cu oxidation. The more the Cu substrate oxidized, the less graphene bilayer could form.

  6. Pulsed laser deposition for the synthesis of monolayer WSe2

    Mohammed, A.; Nakamura, H.; Wochner, P.; Ibrahimkutty, S.; Schulz, A.; Müller, K.; Starke, U.; Stuhlhofer, B.; Cristiani, G.; Logvenov, G.; Takagi, H.


    Atomically thin films of WSe2 from one monolayer up to 8 layers were deposited on an Al2O3 r-cut ( 1 1 ¯ 02 ) substrate using a hybrid-Pulsed Laser Deposition (PLD) system where a laser ablation of pure W is combined with a flux of Se. Specular X-ray reflectivities of films were analysed and were consistent with the expected thickness. Raman measurement and atomic force microscopy confirmed the formation of a WSe2 monolayer and its spatial homogeneity over the substrate. Grazing-incidence X-ray diffraction uncovered an in-plane texture in which WSe2 [ 10 1 ¯ 0 ] preferentially aligned with Al2O3 [ 11 2 ¯ 0 ]. These results present a potential to create 2D transition metal dichalcogenides by PLD, where the growth kinetics can be steered in contrast to common growth techniques like chemical vapor deposition and molecular beam epitaxy.

  7. Phenomenological Modeling for Langmuir Monolayers

    Baptiste, Dimitri; Kelly, David; Safford, Twymun; Prayaga, Chandra; Varney, Christopher N.; Wade, Aaron

    Experimentally, Langmuir monolayers have applications in molecular optical, electronic, and sensor devices. Traditionally, Langmuir monolayers are described by a rigid rod model where the rods interact via a Leonard-Jones potential. Here, we propose effective phenomenological models and utilize Monte Carlo simulations to analyze the phase behavior and compare with experimental isotherms. Research reported in this abstract was supported by UWF NIH MARC U-STAR 1T34GM110517-01.

  8. A new ethylene glycol-silane monolayer for highly-specific DNA detection on Silicon Chips


    Monolayer thin films with ethylene-glycol function onto gold surfaces by using thiols have been extensively investigated. They have been proposed as precursors for applications to bio-detection, where their hydrophilic character improves both specificity and sensitivity. The aim of this letter is to characterize ethylene-glycol monolayer precursors formed onto silicon chips by using silanes. The importance of the ethylene-glycol function is demonstrated by comparing with the well known 3-Amin...

  9. Langmuir-Blodgett monolayers of InP quantum dots with short chain ligands.

    Lambert, K; Wittebrood, L; Moreels, I; Deresmes, D; Grandidier, B; Hens, Z


    We demonstrate the organization of nearly monodisperse colloidal InP quantum dots at the air/water interface in Langmuir monolayers. The organization of the particles is monitored in situ by surface pressure-surface area measurements and ex situ by AFM measurements on films transferred to mica by Langmuir-Blodgett deposition. The influence of different ligands on the quality of the monolayer formed has been studied. We show that densely packed monolayers with little holes can be formed using short chain ligands like pyridine and pentamethylene sulfide. The advantage of using short chain ligands for electron tunneling to or from the quantum dots is demonstrated using scanning tunneling spectroscopy.

  10. Electron microscopic observation of LE/LC phase transition in dipalmitoyl phosphatidylcholine monolayers

    Neuman, R.D.; Fereshtehkhou, S.; Ovalle, R.


    The monolayer structure of L-..cap alpha..-dipalmitoyl phosphatidylcholine (DPPC) at the air/water interface was examined using improved electron microscopic techniques. The DPPC monolayer is homogeneous in both the liquid-expanded (LE) and liquid-condensed (LC) states. In the intermediate LE/LC region, however, the monolayer is nonhomogeneous and biphasic. The results of two coexisting phases are consistent with the interpretation of a first-order phase transition occurring between the LE and LC states in monomolecular films. 20 references, 2 figures.

  11. Buckling in polymer monolayers: Molecular-weight dependence

    Srivastava, S.; Basu, J.K.; (IIS)


    We present systematic investigations of buckling in Langmuir monolayers of polyvinyl acetate formed at the air-water interface. On compression the polymer monolayers are converted to a continuous membrane with a thickness of {approx}2-3 nm of well-defined periodicity, {lambda}{sub b}. Above a certain surface concentration the membrane undergoes a morphological transition buckling, leading to the formation of striped patterns. The periodicity seems to depend on molecular weight as per the predictions of the gravity-bending buckling formalism of Milner et al. for fluidlike films on water. However anomalously low values of bending rigidity and Young's modulus are obtained using this formalism. Hence we have considered an alternative model of buckling-based solidlike films on viscoelastic substrates. The values of bending rigidity and Young's modulus obtained by this method, although lower than expected, are closer to the bulk values. Remarkably, no buckling is found to occur above a certain molecular weight. We have tried to explain the observed molecular-weight dependence in terms of the variation in isothermal compressive modulus of the monolayers with surface concentration as well as provided possible explanations for the obtained low values of mechanical properties similar to that observed for ultrathin polymer films.

  12. Photopatterning of self-assembled alkanethiolate monolayers on gold. A simple monolayer photoresist utilizing aqueous chemistry

    Huang, J.; Hemminger, J.C. (Univ. of California, Irvine, CA (United States)); Dahlgren, D.A. (Photometrics, Huntington Beach, CA (United States))


    In this paper we demonstrate that self-assembled monolayers (SAMs) of alkanethiols on gold can be used as effective photoresists. UV photolysis of an alkanethiol SAM generates the corresponding sulfonate in the monolayer film. The sulfonate is easily rinsed off of the surface with water, exposing a clean gold substrate, which can then be modified with subsequent chemistry. We describe here experiments in which an alkanethiol SAM on a gold film on silicon is irradiated through a mask, followed by immersion of the sample in an aqueous acid etching solution (HCI:HNO[sub 3]:H[sub 2]O = 3:1:4). The gold is etched away from the areas which have been exposed to UV radiation leaving a pattern which reproduces the original mask. The spatial resolution in the present experiments is limited by the mask which is a 6-[mu]m wire grid. Scanning electron microscopy images of patterned samples show sharp edges to the features suggesting that spatial patterning on the 1-[mu]m scale should be attainable with this simple chemistry. 11 refs., 4 figs.

  13. Formation of thin luminescent Eu{sup 3+}-LB films by in situ coordination with 2,3,5,6-tetra(2 Prime -pyridyl)pyrazine and 1-octadecanol in pure and mixed Langmuir monolayers

    Fugisawa, Fernanda P. [Departamento de Quimica, Faculdade de Filosofia, Ciencias e Letras de Ribeirao Preto, Universidade de Sao Paulo, 14040-901 Ribeirao Preto, SP (Brazil); Ramos, Ana P., E-mail: [Departamento de Quimica, Faculdade de Filosofia, Ciencias e Letras de Ribeirao Preto, Universidade de Sao Paulo, 14040-901 Ribeirao Preto, SP (Brazil); Sousa Filho, Paulo C. de; Serra, Osvaldo A.; Zaniquelli, Maria E.D. [Departamento de Quimica, Faculdade de Filosofia, Ciencias e Letras de Ribeirao Preto, Universidade de Sao Paulo, 14040-901 Ribeirao Preto, SP (Brazil)


    The in situ complexation between 2,3,5,6-tetra(2-pyridyl)pyrazine (tppz) molecules and europium ions at the air-liquid interface by means of mixed 1-octadecanol Langmuir films is reported. These films were transferred to solid supports by means of the Langmuir-Blodgett (LB) technique. The EDS maps attested the homogeneity of the LB films as well as the presence of the europium ions. The mixed alcohol/tppz LB film contained a larger amount of europium ions as compared to the pure octadecanol LB film. This work reports the production of a thin luminescent Eu{sup 3+} film containing europium ions using only alcohol molecules as ligands-an unexpected result, since it is well known that there is an occurrence of non-radiative deactivation of excited europium by hydroxyl groups. Europium ion multiple binding sites were detected from lifetime decay measurements of these films in the presence of tppz molecules. - Highlights: Black-Right-Pointing-Pointer In situ complexation of Eu (III) ions with 1-octadecanol and tppz. Black-Right-Pointing-Pointer Formation of thin luminescent Eu(III)-LB films. Black-Right-Pointing-Pointer EDS and luminescence studies attest to the presence of Eu(III) in the films. Black-Right-Pointing-Pointer Eu(III) coordinates with both tppz and alcohol molecules at air/liquid interface. Black-Right-Pointing-Pointer Relatively strong luminescence is observed in LB-films containing only Eu(III) and O-H oscillators.

  14. Water-binding phospholipid nanodomains and phase-separated diacylglycerol nanodomains regulate enzyme reactions in lipid monolayers.

    Nagashima, Teruyoshi; Uematsu, Shogo


    Phospholipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) nanodomains covered with bound water as well as diacylglycerol 1-palmitoyl-2-oleoyl-sn-glycerol (POG) nanodomains separated from a lipid membrane were studied, using monolayer surfaces of POPC hydrolyzed by phospholipase C (PLC). The investigation was based on the analysis of compression isotherms and on atomic force microscope (AFM) observations of Langmuir-Blodgett (LB) films and Langmuir-Schaefer (LS) films. The results included reaction rate constants obtained by kinetic analysis of phosphocholine at surface pressures from 0.1 to 31 mN/m and determined by a luminol-enhanced chemiluminescence method. Monolayer elastic modulus values and fluorescence microscopic images confirmed that hydrolysis by PLC progressed in the intermediate monolayer between a liquid-expanded (L1) film and a liquid-condensed (L2) film at 2-17 mN/m. Furthermore, the intermediate film was confirmed to consist of L1 film and the POPC nanodomains in the L2 state are covered with bound water, conclusions based on the following AFM results: (1) nanodomains in POPC LS films were catalyzed by PLC, (2) POG nanodomains extended out from LB films of mixed POPC/POG 9/1 (mol/mol) monolayers, and (3) POPC LS films were covered with bound water, as indicated by cross-sectional analysis. At the optimal surface pressure of 10 mN/m, when POPC nanodomains (L2), with internal diameters of ∼75 nm, were hydrolyzed by PLC, they shrank down into pockets of the same size as those that appeared with POG. The resulting pocket sizes on LS films were in agreement with POG nanodomain sizes on LB films. This study demonstrated that PLC reacted with POPC nanodomains (L2) dispersed in L1/L2 mixed phase monolayers selectively and that POG nanodomains were phase-separated from the monolayer as hydrolysis proceeded.

  15. Nanopatterning of mobile lipid monolayers on electron-beam-sculpted Teflon AF surfaces.

    Shaali, Mehrnaz; Lara-Avila, Samuel; Dommersnes, Paul; Ainla, Alar; Kubatkin, Sergey; Jesorka, Aldo


    Direct electron-beam lithography is used to fabricate nanostructured Teflon AF surfaces, which are utilized to pattern surface-supported monolayer phospholipid films with 50 nm lateral feature size. In comparison with unexposed Teflon AF coatings, e-beam-irradiated areas show reduced surface tension and surface potential. For phospholipid monolayer spreading experiments, these areas can be designed to function as barriers that enclose unexposed areas of nanometer dimensions and confine the lipid film within. We show that the effectiveness of the barrier is defined by pattern geometry and radiation dose. This surface preparation technique represents an efficient, yet simple, nanopatterning strategy supporting studies of lipid monolayer behavior in ultraconfined spaces. The generated structures are useful for imaging studies of biomimetic membranes and other specialized surface applications requiring spatially controlled formation of self-assembled, molecularly thin films on optically transparent patterned polymer surfaces with very low autofluorescence.

  16. Platinum monolayer electrocatalyst on gold nanostructures on silicon for photoelectrochemical hydrogen evolution.

    Kye, Joohong; Shin, Muncheol; Lim, Bora; Jang, Jae-Won; Oh, Ilwhan; Hwang, Seongpil


    Pt monolayer decorated gold nanostructured film on planar p-type silicon is utilized for photoelectrochemical H2 generation in this work. First, gold nanostructured film on silicon was spontaneously produced by galvanic displacement of the reduction of gold ion and the oxidation of silicon in the presence of fluoride anion. Second, underpotential deposition (UPD) of copper under illumination produced Cu monolayer on gold nanostructured film followed by galvanic exchange of less-noble Cu monolayer with more-noble PtCl6(2-). Pt(shell)/Au(core) on p-type silicon showed the similar activity with platinum nanoparticle on silicon for photoelectrochemical hydrogen evolution reaction in spite of low platinum loading. From Tafel analysis, Pt(shell)/Au(core) electrocatalyst shows the higher area-specific activity than platinum nanoparticle on silicon demonstrating the significant role of underlying gold for charge transfer reaction from silicon to H(+) through platinum catalyst.

  17. Large-area, high-quality monolayer graphene from polystyrene at atmospheric pressure

    Xu, Junqi; Fu, Can; Sun, Haibin; Meng, Lanxiang; Xia, Yanjie; Zhang, Chongwu; Yi, Xiaolei; Yang, Wenchao; Guo, Pengfei; Wang, Chunlei; Liu, Jiangfeng


    Graphene films have been attracting great interest owing to their unique physical properties. In this paper, we develop an efficient method to prepare large-area monolayer graphene (97.5% coverage) by atmospheric pressure chemical vapor deposition on Cu foils using polystyrene in a short time (3 min). Raman spectroscopy, transmission electron microscopy and scanning electron microscopy are employed to confirm the thickness and uniformity of the graphene films. Graphene films on glass substrates show high optical transmittance and electrical conductivity. Magnetic transport studies demonstrate that the as-grown monolayer graphene exhibits a high carrier mobility of 3395 cm2 V‑1 s‑1 at 25 K. On the basis of the analysis, it is concluded that our method is a simple, safe and versatile approach for the synthesis of monolayer graphene.

  18. Thin Film Assembly of Spider Silk-like Block Copolymers


    Film Assembly of Spider Silk -like Block Copolymers Sreevidhya T. Krishnaji,†,‡ Wenwen Huang,§ Olena Rabotyagova,†,‡ Eugenia Kharlampieva, ) Ikjun Choi...Received November 26, 2010 We report the self-assembly of monolayers of spider silk -like block copolymers. Langmuir isotherms were obtained for a series of...bioengineered variants of the spider silks , and stable monolayers were generated. Langmuir-Blodgett films were prepared by transferring the monolayers

  19. Mechanical Properties of Water-Assembled Graphene Oxide Langmuir Monolayers: Guiding Controlled Transfer.

    Harrison, Katharine L; Biedermann, Laura B; Zavadil, Kevin R


    Liquid-phase transfer of graphene oxide (GO) and reduced graphene oxide (RGO) monolayers is investigated from the perspective of the mechanical properties of these films. Monolayers are assembled in a Langmuir-Blodgett trough, and oscillatory barrier measurements are used to characterize the resulting compressive and shear moduli as a function of surface pressure. GO monolayers are shown to develop a significant shear modulus (10-25 mN/m) at relevant surface pressures while RGO monolayers do not. The existence of a shear modulus indicates that GO is acting as a two-dimensional solid driven by strong interaction between the individual GO sheets. The absence of such behavior in RGO is attributed to the decrease in oxygen moieties on the sheet basal plane, permitting RGO sheets to slide across one another with minimum energy dissipation. Knowledge of this two-dimensional solid behavior is exploited to successfully transfer large-area, continuous GO films to hydrophobic Au substrates. The key to successful transfer is the use of shallow-angle dipping designed to minimize tensile stress present during the insertion or extraction of the substrate. A shallow dip angle on hydrophobic Au does not impart a beneficial effect for RGO monolayers, as these monolayers do not behave as two-dimensional solids and do not remain coherent during the transfer process. We hypothesize that this observed correlation between monolayer mechanical properties and continuous film transfer success is more universally applicable across substrate hydrophobicities and could be exploited to control the transfer of films composed of two-dimensional materials.

  20. Electromelting of Confined Monolayer Ice

    Qiu, Hu


    In sharp contrast to the prevailing view that electric fields promote water freezing, here we show by molecular dynamics simulations that monolayer ice confined between two parallel plates can melt into liquid water under perpendicularly applied electric field. The melting temperature of the monolayer ice decreases with the increasing strength of the external field due to field-induced disruption of the water-wall interaction induced well-ordered network of hydrogen bond. This electromelting process should add an important new ingredient to the physics of water.

  1. Oleic acid disorders stratum corneum lipids in Langmuir monolayers.

    Mao, Guangru; VanWyck, Dina; Xiao, Xin; Mack Correa, M Catherine; Gunn, Euen; Flach, Carol R; Mendelsohn, Richard; Walters, Russel M


    Oleic acid (OA) is well-known to affect the function of the skin barrier. In this study, the molecular interactions between OA and model stratum corneum (SC) lipids consisting of ceramide, cholesterol, and palmitic acid (PA) were investigated with Langmuir monolayer and associated techniques. Mixtures with different OA/SC lipid compositions were spread at the air/water interface, and the phase behavior was tracked with surface pressure-molecular area (π-A) isotherms. With increasing OA levels in the monolayer, the films became more fluid and more compressible. The thermodynamic parameters derived from π-A isotherms indicated that there are preferential interactions between OA and SC lipids and that films of their mixtures were thermodynamically stable. The domain structure and lipid conformational order of the monolayers were studied through Brewster angle microscopy (BAM) and infrared reflection absorption spectroscopy (IRRAS), respectively. Results indicate that lower concentrations of OA preferentially mix with and disorder the ceramide-enriched domains, followed by perturbation of the PA-enriched domains and disruption of SC lipid domain separation at higher OA levels.

  2. Palmitic Acid on Salt Subphases and in Mixed Monolayers of Cerebrosides: Application to Atmospheric Aerosol Chemistry

    Ellen M. Adams


    Full Text Available Palmitic acid (PA has been found to be a major constituent in marine aerosols, and is commonly used to investigate organic containing atmospheric aerosols, and is therefore used here as a proxy system. Surface pressure-area isotherms (π-A, Brewster angle microscopy (BAM, and vibrational sum frequency generation (VSFG were used to observe a PA monolayer during film compression on subphases of ultrapure water, CaCl2 and MgCl2 aqueous solutions, and artificial seawater (ASW. π-A isotherms indicate that salt subphases alter the phase behavior of PA, and BAM further reveals that a condensation of the monolayer occurs when compared to pure water. VSFG spectra and BAM images show that Mg2+ and Ca2+ induce ordering of the PA acyl chains, and it was determined that the interaction of Mg2+ with the monolayer is weaker than Ca2+. π-A isotherms and BAM were also used to monitor mixed monolayers of PA and cerebroside, a simple glycolipid. Results reveal that PA also has a condensing effect on the cerebroside monolayer. Thermodynamic analysis indicates that attractive interactions between the two components exist; this may be due to hydrogen bonding of the galactose and carbonyl headgroups. BAM images of the collapse structures show that mixed monolayers of PA and cerebroside are miscible at all surface pressures. These results suggest that the surface morphology of organic-coated aerosols is influenced by the chemical composition of the aqueous core and the organic film itself.

  3. Fruit and vegetable films and uses thereof

    The present invention is directed to monolayer, bilayer, and multilayer films made from fruit, vegetable or a combination thereof, which films have the thinness, strength, flexibility and crispness to serve as alternates or substitutes for seaweed-based films such as nori, while providing nutrition ...

  4. Photoluminescence of monolayer MoS2 on LaAlO3 and SrTiO3 substrates.

    Li, Yuanyuan; Qi, Zeming; Liu, Miao; Wang, Yuyin; Cheng, Xuerui; Zhang, Guobin; Sheng, Liusi


    In an atomically thin-film/dielectric-substrate heterostructure, the elemental physical properties of the atomically thin-film are influenced by the interaction between the thin-film and the substrate. In this article, utilizing monolayer MoS(2) on LaAlO(3) and SrTiO(3) substrates, as well as SiO2 and Gel-film as reference substrates similar to previously reported work [Nano Res, 2014, 7, 561], we systematically investigate the substrate effect on the photoluminescence of monolayer MoS(2). We observed significantly substrate-dependant photoluminescence of monolayer MoS(2), originating from substrate-to-film charge transfer. We found that SiO2 substrate introduces the most charge doping while SrTiO(3) introduces less charge transfer. Through the selection of desired substrate, we are able to induce different amounts of charge into the monolayer MoS(2), which consequently modifies the neutral exciton and charged exciton (trion) emissions. Finally, we proposed a band-diagram model to elucidate the relation between charge transfer and the substrate Fermi level and work function. Our work demonstrates that the substrate charge transfer exerts a strong influence on the monolayer MoS(2) photoluminescence property, which should be considered during device design and application. The work also provides a possible route to modify the thin-film photoluminescence property via substrate engineering for future device design.

  5. Oxygen adsorption on palladium monolayer as a surface catalyst

    Shah, Janki; Kansara, Shivam; Gupta, Sanjeev K.; Sonvane, Yogesh


    In the recent work, we study on the structural and electronic properties of the graphene like Pd monolayer with the adsorption of oxygen adatoms by using first-principles calculations. The electronic band structure and projected density of states investigate that Pd-surface with oxygen molecule adsorption gives metallic behaviour. We found that the behaviour changed at M-point in the electronic band structure as adding oxygen atoms. The oxygen adsorption was dissociative until the Pd surface immersed with oxygen atoms. The electron charge density increases as the number of oxygen atoms on Pd-surface increases. The noticeable observation is that by adding 7th oxygen atom, they started to ripple from fixed Pd-surface without making a bond due to oxygen coverage increases. The results show that Pd monolayer has different applications as a oxygen catalyst and it can be utilized as the pellet, surface, and film materials to safeguard sustenance from oxidation.

  6. The Electrochemical Characteristics of Multilayer Assembly of Hemoglobin and Polystyrene Sulfonate at Self-assembled Monolayer Surface


    A multilayer film of hemoglobin (Hb) molecules and polyelectrolyte sulfonate were fabricated on a thiol self-assembled monolayers (SAMs) by electrostatic force.The Hb maintains electroactive property in the multilayer film, methylene blue (MB) incorporated into the multilayer can enhance the electron transfer rate between the Hb and the electrode surface.

  7. Organized organic ultrathin films fundamentals and applications

    Ariga, Katsuhiko


    This handy reference is the first comprehensive book covering both fundamentals and recent developments in the field with an emphasis on nanotechnology. Written by a highly regarded author in the field, the book details state-of-the-art preparation, characterization and applications of thin films of organic molecules and biomaterials fabricated by wet processes and also highlights applications in nanotechnology The categories of films covered include monomolecular films (monolayers) both on a water surface and on a solid plate, Langmuir-Blodgett films (transferred multilayer films on a solid plate from a water surface), layer-by-layer films (adsorbed multilayer films on a solid support), and spontaneously assembled films in solution.

  8. Single-monolayer in situ modulus measurements using a SAW device: Photocrosslinking of a diacetylenic thiol-based monolayer

    Ricco, A.J.; Staton, A.W. [Sandia National Labs., Albuquerque, NM (United States); Crooks, R.M. [Texas A& M Univ., College Station, TX (United States). Dept. of Chemistry; Kim, Taisun [Hallym Univ., Kang-Won Do (Korea, Republic of). Dept. of Chemistry


    We report direct measurement of the modulus change that accompanies the crosslinking of a single molecular monolayer. We measured a change in elastic modulus of 5 x 10{sup 10} dyn/cm{sup 2} as a result of ultraviolet-induced photocrosslinking of a single surface-confined monolayer of the conjugated diacetylenic thiol HS(CH{sub 2}){sub 10}C{triple_bond}CC{triple_bond}C(CH{sub 2}){sub 10}COOH, designated {open_quotes}DAT{close_quotes} hereafter. The modulus measurement was made on a monolayer of DAT chemisorbed upon a gold film on the surface of a 97-MHz ST-quartz surface acoustic wave delay line. The ratio of the changes recorded in SAW velocity and attenuation, approximately 4:1, suggests that the measured effect is mainly a change in the elastic (real) component of the complex shear modulus, viscous changes playing a lesser role. In relation to typical polymer modulus values, the change of 5 x 10{sup 10} dyn/cm{sup 2} is consistent with a change from a rubbery material (G{prime} {approximately} 10{sup 7} - 10{sup 8} dyn/cm{sup 2}) to a fairly rigid, glassy material (G{prime} {approximately} 10{sup 10} dyn/cm{sup 2}), reasonable for comparison of the monolayer in its as-adsorbed and crosslinked forms. This report of the direct SAW-based measurement of the modulus change associated with the crosslinking of a single molecular monolayer is complementary to and consistent with previous in-situ measurements of this process using thickness-shear mode resonators.

  9. Structure and dynamics of lipid monolayers: Implications for enzyme catalysed lipolysis

    Peters, Günther H.J.; Toxværd, S.; Larsen, N.B.;


    We have investigated the role of the substrate on the interfacial activation of Upases by an interdisciplinary study of the structure and dynamics of 1,2-sn dipalmitoylglycerol monolayers at distinct surface pressures. The diglyceride Langmuir film undergoes two phase transitions occurring at 38....

  10. Electron transport nonlocality in monolayer graphene modified with hydrogen silsesquioxane polymerization

    Kaverzin, A. A.; van Wees, B. J.


    A number of practical and fundamental applications of graphene requires modification of some of its properties. In this paper we study the effect of polymerization of a hydrogen silsesquioxane film on top of monolayer graphene with the intent to increase the strength of the spin-orbit interaction. T

  11. Synthesis of Novel Amphiphilic Azobenzenes and X-ray Scattering Studies of Their Langmuir Monolayers

    Sørensen, Thomas Just; Kjær, Kristian; Breiby, Dag Werner;


    . At the air-water interface, the amphiphilic azobenzenes form noncrystalline but stable Langmuir films that display an unusual reversible monolayer collapse close to 35 mN/m. The structures and phase transitions were studied by X-ray reflectivity (XR) and grazing-incidence X-ray diffraction, both utilizing...

  12. A note on the use of ellipsometry for studying the kinetics of formation of self-assembled monolayers

    Murali Sastry


    Ellipsometry is currently one of the most important techniques for characterization of the deposition and growth mode of ultra thin organic films. However, it is well known that for thicknesses normally encountered in organic monolayer films, as would occur for example in self-assembled monolayers, ellipsometry cannot be used to simultaneously determine the thickness and refractive index of the monolayer film. Current practice is to assume a reasonable value for the film refractive index and calculate an effective ‘ellipsometric thickness’. This communication seeks to show that the alternative approach of assuming a thickness for the monolayer (determined by the length of the molecule) and calculating the effective film refractive index lends itself to easier and more meaningful physical interpretation. The Lorentz–Lorenz formula is then used to transform the effective refractive index into a surface coverage and hence to an effective mass coverage. The methodology advanced is applied to the kinetics of formation of a self-assembled monolayer of a well-studied molecule, octadecanethiol on Au.

  13. Mixed carboranethiol self-assembled monolayers on gold surfaces

    Yavuz, Adem; Sohrabnia, Nima; Yilmaz, Ayşen; Danışman, M. Fatih


    Carboranethiol self-assembled monolayers on metal surfaces have been shown to be very convenient systems for surface engineering. Here we have studied pure and mixed self-assembled monolayers (SAMs) of three different carboranethiol (CT) isomers on gold surfaces. The isomers were chosen with dipole moments pointing parallel to (m-1-carboranethiol, M1), out of (m-9-carboranethiol, M9) and into (o-1-carboranethiol, O1) the surface plane, in order to investigate the effect of dipole moment orientation on the film properties. In addition, influence of the substrate surface morphology on the film properties was also studied by using flame annealed (FA) and template stripped (TS) gold surfaces. Contact angle measurements indicate that in M1/M9 and M1/O1 mixed SAMs, M1 is the dominant species on the surface even for low M1 ratio in the growth solution. Whereas for O1/M9 mixed SAMs no clear evidence could be observed indicating dominance of one of the species over the other one. Though contact angle values were lower and hysteresis values were higher for SAMs grown on TS gold surfaces, the trends in the behavior of the contact angles with changing mixing ratio were identical for SAMs grown on both substrates. Atomic force microscopy images of the SAMs on TS gold surfaces indicate that the films have similar morphological properties regardless of mixing ratio.

  14. Morphology in electrochemically grown conducting polymer films

    Rubinstein, Israel; Gottesfeld, Shimshon; Sabatani, Eyal


    A conducting polymer film with an improved space filling is formed on a metal electrode surface. A self-assembling monolayer is formed directly on the metal surface where the monolayer has a first functional group that binds to the metal surface and a second chemical group that forms a chemical bonding site for molecules forming the conducting polymer. The conducting polymer is then conventioonally deposited by electrochemical deposition. In one example, a conducting film of polyaniline is formed on a gold electrode surface with an intermediate monolayer of p-aminothiophenol.

  15. Assembly of citrate gold nanoparticles on hydrophilic monolayers

    Vikholm-Lundin, Inger; Rosqvist, Emil; Ihalainen, Petri; Munter, Tony; Honkimaa, Anni; Marjomäki, Varpu; Albers, Willem M.; Peltonen, Jouko


    Self-assembled monolayers (SAMs) as model surfaces were linked onto planar gold films thorough lipoic acid or disulfide groups. The molecules used were polyethylene glycol (EG-S-S), N-[tris-(hydroxymethyl)methyl]acrylamide polymers with and without lipoic acid (Lipa-pTHMMAA and pTHMMAA) and a lipoic acid triazine derivative (Lipa-MF). All the layers, but Lipa-MF with a primary amino group were hydroxyl terminated. The layers were characterized by contact angle measurements and atomic force mi...

  16. Immobilization of Colloidal Monolayers at Fluid–Fluid Interfaces

    Peter T. Bähler


    Full Text Available Monolayers of colloidal particles trapped at an interface between two immiscible fluids play a pivotal role in many applications and act as essential models in fundamental studies. One of the main advantages of these systems is that non-close packed monolayers with tunable inter-particle spacing can be formed, as required, for instance, in surface patterning and sensing applications. At the same time, the immobilization of particles locked into desired structures to be transferred to solid substrates remains challenging. Here, we describe three different strategies to immobilize monolayers of polystyrene microparticles at water–decane interfaces. The first route is based on the leaking of polystyrene oligomers from the particles themselves, which leads to the formation of a rigid interfacial film. The other two rely on in situ interfacial polymerization routes that embed the particles into a polymer membrane. By tracking the motion of the colloids at the interface, we can follow in real-time the formation of the polymer membranes and we interestingly find that the onset of the polymerization reaction is accompanied by an increase in particle mobility determined by Marangoni flows at the interface. These results pave the way for future developments in the realization of thin tailored composite polymer-particle membranes.

  17. Self-assembled biomimetic monolayers using phospholipid-containing disulfides.

    Chung, Yi Chang; Chiu, Yi Hong; Wu, Yin Wei; Tao, Yu Tai


    Several phospholipid-based disulfide molecules were synthesized and attached onto the gold-coated silicon wafer using the self-assembling method. The syntheses of these surface-modifying agents were conducted by introducing bromoethylphosphorate (PBr), phosphorylcholine (PC) or phosphorylethanolamine (PE) groups on the terminals of a dialkyl disulfide. After disulfides adsorption onto gold substrate surfaces, the composition, the film thickness, and the conformational order of self-assembled monolayer surfaces were explored and discussed in detail based on reflection-absorption infrared spectroscopy, contact angle measurement, Auger electron spectroscopy, X-ray photoelectron spectroscopy, and so on. The monolayer having the PBr end group could also be converted to a PC surface by treating with trimethylamine. The model functional surfaces of Au-SC11-PC, -PE, -PBr, -OH or corresponding mixed layers were used to mimic biomembrane surfaces. The monolayer having PC groups was found to reduce fibrinogen adsorption as evaluated from protein adsorption experiments using quartz crystal microbalance. It also showed relatively low platelet adherence compare to the glass, PBr and PE surfaces. The cell viability test also revealed that the PC surface displayed lower cytotoxicity than other surfaces.

  18. Assembly of citrate gold nanoparticles on hydrophilic monolayers

    Vikholm-Lundin, Inger; Rosqvist, Emil; Ihalainen, Petri; Munter, Tony; Honkimaa, Anni; Marjomäki, Varpu; Albers, Willem M.; Peltonen, Jouko


    Self-assembled monolayers (SAMs) as model surfaces were linked onto planar gold films thorough lipoic acid or disulfide groups. The molecules used were polyethylene glycol (EG-S-S), N-[tris-(hydroxymethyl)methyl]acrylamide polymers with and without lipoic acid (Lipa-pTHMMAA and pTHMMAA) and a lipoic acid triazine derivative (Lipa-MF). All the layers, but Lipa-MF with a primary amino group were hydroxyl terminated. The layers were characterized by contact angle measurements and atomic force microscopy, AFM. Citrate stabilized nanoparticles, AuNPs in water and phosphate buffer were allowed to assemble on the layers for 10 min and the binding was followed in real-time with surface plasmon resonance, SPR. The SPR resonance curves were observed to shift to higher angles and become increasingly damped, while also the peaks strongly broaden when large nanoparticles assembled on the surface. Both the angular shift and the damping of the curve was largest for nanoparticles assembling on the EG-S-S monolayer. High amounts of particles were also assembled on the pTHMMAA layer without the lipoic acid group, but the damping of the curve was considerably lower with a more even distribution of the particles. Topographical images confirmed that the highest number of particles were assembled on the polyethylene glycol monolayer. By increasing the interaction time more particles could be assembled on the surface.

  19. Thermal stability and molecular ordering of organic semiconductor monolayers: effect of an anchor group.

    Jones, Andrew O F; Knauer, Philipp; Resel, Roland; Ringk, Andreas; Strohriegl, Peter; Werzer, Oliver; Sferrazza, Michele


    The thermal stability and molecular order in monolayers of two organic semiconductors, PBI-PA and PBI-alkyl, based on perylene derivatives with an identical molecular structure except for an anchor group for attachment to the substrate in PBI-PA, are reported. In situ X-ray reflectivity measurements are used to follow the stability of these monolayers in terms of order and thickness as temperature is increased. Films have thicknesses corresponding approximately to the length of one molecule; molecules stand upright on the substrate with a defined structure. PBI-PA monolayers have a high degree of order at room temperature and a stable film exists up to 250 °C, but decomposes rapidly above 300 °C. In contrast, stable physisorbed PBI-alkyl monolayers only exist up to 100 °C. Above the bulk melting point at 200 °C no more order exists. The results encourage using anchor groups in monolayers for various applications as it allows enhanced stability at the interface with the substrate.

  20. Electrochemical and scanning probe microscopic characterization of spontaneously adsorbed organothiolate monolayers at gold

    Wong, Sze-Shun Season [Iowa State Univ., Ames, IA (United States)


    This dissertation presented several results which add to the general knowledge base regarding organothiolates monolayer spontaneously adsorbed at gold films. Common to the body of this work is the use of voltammetric reductive resorption and variants of scanning probe microscopy to gain insight into the nature of the monolayer formation process as well as the resulting interface. The most significant result from this work is the success of using friction force microscopy to discriminate the end group orientation of monolayer chemisorbed at smooth gold surfaces with micrometer resolution (Chapter 4). The ability to detect the differences in the orientational disposition is demonstrated by the use PDMS polymer stamp to microcontact print an adlayer of n-alkanethiolate of length n in a predefine pattern onto a gold surface, followed by the solution deposition of a n-alkanethiol of n ± 1 to fill in the areas on the gold surface intentionally not coated by the stamping process. These two-component monolayers can be discriminated by using friction force microscopy which detects differences in friction contributed by the differences in the orientation of the terminal groups at surfaces. This success has recently led to the detection of the orientation differences at nanometer scale. Although the substrates examined in this work consisted entirely of smooth gold films, the same test can be performed on other smooth substrates and monolayer materials.

  1. Characterization and reactivity of organic monolayers on gold and platinum surfaces

    Wu, Chien-Ching [Iowa State Univ., Ames, IA (United States)


    Purpose is to understand how the mobilization, dielectric, orientation, composition, coverage, and structure of self-assembled organic monolayers on metal surfaces affects the surface reactivities and properties of these films in order to facilitate the construction of desired films. Two model systems were used: tiols at Au and aromatic acids at Pt. Surface analysis methods, including contact angle, electrochemistry, ellipsometry, infrared reflection absorption spectroscopy (IRRAS), and x-ray photospectroscopy, were used to study the self-assembled organic monolayers on Au and Pt. IRRAS, contact angle, and electrochemistry were used to determine the surface pKa of phenylcarboxylic acids and pyridylcarboxylic acids monolayers on Pt. These techniques were also used to determine the orientation of polymethylene chain axis and the carboxylic follow the structural evolution of the chains and end group of the thiolate monolayers during formation. IRRAS was also used to assess the carboxylic acid group in terms of its possible existence as the non-hydrogen-bonded species, the hydrogen-bonded dimeric group, and the hydrogen-bonded polymeric group. These different forms of the end group were also followed vs coverage, as well as the reactivity vs solution pH. IRRAS and contact angle were used to calculate the rate constant of the esterification of carboxylic acid-terminated monolayers on Au.

  2. Specific Ion Effects in Cholesterol Monolayers

    Teresa Del Castillo-Santaella


    Full Text Available The interaction of ions with interfaces and, in particular, the high specificity of these interactions to the particular ions considered, are central questions in the field of surface forces. Here we study the effect of different salts (NaI, NaCl, CaCl2 and MgCl2 on monolayers made of cholesterol molecules, both experimentally (surface area vs. lateral pressure isotherms measured by a Langmuir Film Balance and theoretically (molecular dynamics (MD all-atomic simulations. We found that surface isotherms depend, both quantitatively and qualitatively, on the nature of the ions by altering the shape and features of the isotherm. In line with the experiments, MD simulations show clear evidences of specific ionic effects and also provide molecular level details on ion specific interactions with cholesterol. More importantly, MD simulations show that the interaction of a particular ion with the surface depends strongly on its counterion, a feature ignored so far in most theories of specific ionic effects in surface forces.

  3. Anti-fouling chemistry of chiral monolayers: enhancing biofilm resistance on racemic surface.

    Bandyopadhyay, Debjyoti; Prashar, Deepali; Luk, Yan-Yeung


    This work reports the resistance to protein adsorption and bacterial biofilm formation by chiral monolayers of polyol-terminated alkanethiols surrounding micrometer-sized patterns of methyl-terminated alkanethiols on gold films. We discover that patterned surfaces surrounded by chiral polyol monolayers can distinguish different stages of biofilm formation. After inoculation on the surfaces, bacteria first reversibly attached on the chiral polyol monolayers. Over time, the bacteria detached from the polyol surfaces, and attached on the hydrophobic micropatterns to form biofilms. Interestingly, while both enantiomers of gulitol- and mannonamide-terminated monolayer resisted adsorption of proteins (bovine serum albumin, lysozyme, and fibrinogen) and confined biofilms formed on the micropatterns, the monolayers formed by the racemic mixture of either pair of enantiomers exhibited stronger antifouling chemistry against both protein adsorption and biofilm formation than monolayers formed by one enantiomer alone. These results reveal the different chemistries that separate the different stages of biofilm formation, and the stereochemical influence on resisting biofoulings at a molecular-level.

  4. Packing of ganglioside-phospholipid monolayers

    Majewski, J.; Kuhl, T.L.; Kjær, K.


    DPPE monolayer and does not distort the hexagonal in-plane unit cell or out-of-plane two-dimensional (2-D) packing compared with a pure DPPE monolayer. The oligosaccharide headgroups were found to extend normally from the monolayer surface, and the incorporation of these glycolipids into DPPE...... monolayers did not affect hydrocarbon tail packing (fluidization or condensation of the hydrocarbon region). This is in contrast to previous investigations of lipopolymer-lipid mixtures, where the packing structure of phospholipid monolayers was greatly altered by the inclusion of lipids bearing hydrophilic...... polymer groups. Indeed, the lack of packing disruptions by the oligosaccharide groups indicates that protein-GM, interactions, including binding, insertion, chain fluidization, and domain formation (lipid rafts), can be studied in 2-D monolayers using scattering techniques....

  5. Modeling Stimuli-Responsive Nanoparticle Monolayer

    Yong, Xin


    Using dissipative particle dynamics (DPD), we model a monolayer formed at the water-oil interface, which comprises stimuli-responsive nanoparticles. The solid core of the nanoparticle encompasses beads arranged in an fcc lattice structure and its surface is uniformly grafted with stimuli-responsive polymer chains. The surface-active nanoparticles adsorb to the interface from the suspension to minimize total energy of the system and create a monolayer covering the interface. We investigate the monolayer formation by characterizing the detailed adsorption kinetics. We explore the microstructure of the monolayer at different surface coverage, including the particle crowding and ordering, and elucidate the response of monolayer to external stimuli. The collective behavior of the particles within the monolayer is demonstrated quantitatively by vector-vector autocorrelation functions. This study provides a fundamental understanding of the interfacial behavior of stimuli-responsive nanoparticles.

  6. Syntheses, spectral, electrochemical and thermal studies of mononuclear manganese(III) complexes with ligands derived from 1,2-propanediamine and 2-hydroxy-3 or 5-methoxybenzaldehyde: Self-assembled monolayer formation on nanostructure zinc oxide thin film

    Habibi, Mohammad Hossein; Askari, Elham; Amirnasr, Mehdi; Amiri, Ahmad; Yamane, Yuki; Suzuki, Takayoshi


    Mononuclear Mn(III) complexes have been prepared via the Mn(II) reaction of an equimolar of Schiff-bases derived from reaction of 2-hydroxy-3-methoxybenzaldehyde or 2-hydroxy-5-methoxybenzaldehyde with 1,2-diaminopropane. Axial ligands L include: pyridine (py) and H 2O. The resulting complexes have been characterized by FT-IR and UV-vis spectroscopy. The crystal structures of the complexes were determined and indicate that in the solid state the complex adopts a slightly distorted octahedral environment of the imine N and hydroxo O with the two axial ligands. The electrochemical reduction of these complexes at a glassy carbon electrode in acetonitrile solution indicates that the first reduction process corresponding to Mn III-Mn II is electrochemically quasi-reversible. Thermal stability of these complexes was determined by TG and DTG. Layers of these complexes were formed on nanostructure zinc oxide thin film and a red shift was observed when zinc oxide thin film is modified by complex.

  7. Improved aging performance of vapor phase deposited hydrophobic self-assembled monolayers

    Gnanappa, Arun Kumar, E-mail: [Tyndall National Institute, Lee Maltings, Prospect Row, Cork (Ireland); Institute of Microelectronics, NCSR Demokritos, Athens (Greece); O' Murchu, Cian; Slattery, Orla; Peters, Frank [Tyndall National Institute, Lee Maltings, Prospect Row, Cork (Ireland); O' Hara, Tony [Memsstar Technology (registered) , Starlaw Park, Starlaw Road, Livingston (United Kingdom); Aszalos-Kiss, Balazs; Tofail, Syed A.M. [Materials and Surface Science Institute, University of Limerick, Limerick (Ireland)


    A hydrophobic self-assembled monolayer (SAM) of fluoro-octyl-trichloro-silane (FOTS) was deposited on silicon using a vapor phase technique. The aging of the hydrophobic layer was examined using water contact angle measurements. It has been found that while such monolayer films suffer from a loss of hydrophobicity with time, pre-immersion nitrogen annealing can significantly improve the aging characteristics of these monolayers. The effect of nitrogen annealing on the improved aging properties of SAM coatings has been investigated by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The hydrolytic stability and the effect of nitrogen annealing were studied by morphological evolution during immersion. A spontaneous formation of silane mounds on the surface of the monolayers was found by AFM. These mounds have been irreversibly transformed from initially uniform hydrophobic surface layers. It is highly probable that the compliance of these mounds can reasonably allow hydrophilic sites to be located around the mounds. Interestingly, the density of these mounds formation is very less on the annealed samples. XPS reveals a higher level of coverage by the N{sub 2}-annealed film due to agglomeration. A relative abundance of CF{sub 3} and CF{sub 2} moieties in the annealed film may explain the enhancement of the hydrophobicity as revealed by higher level of water contact angle. This hydrophobicity was found to be significantly stable in water. This novel finding explains the improved hydrophobic stability of FOTS monolayers as primarily a morpho-chemical effect that originates from the densification of the monolayers upon annealing.

  8. Influence of calcium on ceramide-1-phosphate monolayers

    Joana S. L. Oliveira


    Full Text Available Ceramide-1-phosphate (C1P plays an important role in several biological processes, being identified as a key regulator of many protein functions. For instance, it acts as a mediator of inflammatory responses. The mediation of the inflammation process happens due to the interaction of C1P with the C2 domain of cPLA2α, an effector protein that needs the presence of submicromolar concentrations of calcium ions. The aim of this study was to determine the phase behaviour and structural properties of C1P in the presence and absence of millimolar quantities of calcium in a well-defined pH environment. For that purpose, we used monomolecular films of C1P at the soft air/liquid interface with calcium ions in the subphase. The pH was varied to change the protonation degree of the C1P head group. We used surface pressure versus molecular area isotherms coupled with other monolayer techniques as Brewster angle microscopy (BAM, infrared reflection–absorption spectroscopy (IRRAS and grazing incidence X-ray diffraction (GIXD. The isotherms indicate that C1P monolayers are in a condensed state in the presence of calcium ions, regardless of the pH. At higher pH without calcium ions, the monolayer is in a liquid-expanded state due to repulsion between the negatively charged phosphate groups of the C1P molecules. When divalent calcium ions are added, they are able to bridge the highly charged phosphate groups, enhancing the regular arrangement of the head groups. Similar solidification of the monolayer structure can be seen in the presence of a 150 times larger concentration of monovalent sodium ions. Therefore, calcium ions have clearly a strong affinity for the phosphomonoester of C1P.

  9. Assembly of citrate gold nanoparticles on hydrophilic monolayers

    Vikholm-Lundin, Inger, E-mail: [University of Tampere, BioMediTech, Tampere (Finland); Fimlab Laboratories Ltd., Tampere (Finland); Rosqvist, Emil; Ihalainen, Petri [Abo Akademi University, Center for Functional Materials, Laboratory of Physical Chemistry (Finland); Munter, Tony [VTT Technical Research Centre of Finland, Process Chemistry end Environmental Engineering, Tampere (Finland); Honkimaa, Anni [University of Tampere, Department of Virology, School of Medicine, Tampere (Finland); Marjomäki, Varpu [University of Jyväskylä, Department of Biological and Environmental Science, Nanoscience Center, Jyväskylä (Finland); Albers, Willem M. [BioNavis Oy Ltd., Ylöjärvi, Tampere (Finland); Peltonen, Jouko [Abo Akademi University, Center for Functional Materials, Laboratory of Physical Chemistry (Finland)


    Highlights: • The self-assembled layers were all hydrophilic with Lipa-pTHMMAA exhibiting close to full wetting. • The polyacrylamide layers smoothen the gold surface to a higher extent than the polyethylene glycol and lipoic acid terminated with an amino group. • SPR resonance curves shift to higher angles and become increasingly damped when large nanoparticles assembled on the surface. • Topographical images confirmed that the highest number of particles were assembled on the polyethylene glycol monolayer. • By increasing the interaction time more particles could be assembled on the surface. - Abstract: Self-assembled monolayers (SAMs) as model surfaces were linked onto planar gold films thorough lipoic acid or disulfide groups. The molecules used were polyethylene glycol (EG-S-S), N-[tris-(hydroxymethyl)methyl]acrylamide polymers with and without lipoic acid (Lipa-pTHMMAA and pTHMMAA) and a lipoic acid triazine derivative (Lipa-MF). All the layers, but Lipa-MF with a primary amino group were hydroxyl terminated. The layers were characterized by contact angle measurements and atomic force microscopy, AFM. Citrate stabilized nanoparticles, AuNPs in water and phosphate buffer were allowed to assemble on the layers for 10 min and the binding was followed in real-time with surface plasmon resonance, SPR. The SPR resonance curves were observed to shift to higher angles and become increasingly damped, while also the peaks strongly broaden when large nanoparticles assembled on the surface. Both the angular shift and the damping of the curve was largest for nanoparticles assembling on the EG-S-S monolayer. High amounts of particles were also assembled on the pTHMMAA layer without the lipoic acid group, but the damping of the curve was considerably lower with a more even distribution of the particles. Topographical images confirmed that the highest number of particles were assembled on the polyethylene glycol monolayer. By increasing the interaction time more

  10. Preparation, characterization, and photoelectric properties of a covalently self-assembled monolayer of ferrocenyl hemicyanine.

    Li, Lin-Ying; Chen, Xi; Xu, Meng-Yun; Zhang, Qian-Jin; Wang, Ke-Zhi


    A monolayer of a ferrocenyl hemicyanine was covalently self-assembled on an indium tin oxide (ITO)-coated glass substrate, and was characterized by UV/Vis absorption and X-ray photoelectron spectroscopy, and cyclic voltammetry. The photoelectrochemical properties and mechanism of photocurrent generation have also been studied. This monolayer film was found to exhibit a large anodic photocurrent density of 0.13 microA/cm2 with the highest photoelectric yield of 3.32% under irradiation of white light (730 nm > lambda > 325 nm) at a bias potential of +0.4 V versus saturated calomel electrode.

  11. Binary functionalization of H:Si(111) surfaces by alkyl monolayers with different linker atoms enhances monolayer stability and packing.

    Arefi, Hadi H; Nolan, Michael; Fagas, Giorgos


    Alkyl monolayer modified Si forms a class of inorganic-organic hybrid materials with applications across many technologies such as thin-films, fuel/solar-cells and biosensors. Previous studies have shown that the linker atom, through which the monolayer binds to the Si substrate, and any tail group in the alkyl chain, can tune the monolayer stability and electronic properties. In this paper we study the H:Si(111) surface functionalized with binary SAMs: these are composed of alkyl chains that are linked to the surface by two different linker groups. Aiming to enhance SAM stability and increase coverage over singly functionalized Si, we examine with density functional theory simulations that incorporate vdW interactions, a range of linker groups which we denote as -X-(alkyl) with X = CH2, O(H), S(H) or NH(2) (alkyl = C6 and C12 chains). We show how the stability of the SAM can be enhanced by adsorbing alkyl chains with two different linkers, e.g. Si-[C, NH]-alkyl, through which the adsorption energy is increased compared to functionalization with the individual -X-alkyl chains. Our results show that it is possible to improve stability and optimum coverage of alkyl functionalized SAMs linked through a direct Si-C bond by incorporating alkyl chains linked to Si through a different linker group, while preserving the interface electronic structure that determines key electronic properties. This is important since any enhancement in stability and coverage to give more densely packed monolayers will result in fewer defects. We also show that the work function can be tuned within the interval of 3.65-4.94 eV (4.55 eV for bare H:Si(111)).

  12. Force modulated conductance of artificial coiled-coil protein monolayers.

    Atanassov, Alexander; Hendler, Ziv; Berkovich, Inbal; Ashkenasy, Gonen; Ashkenasy, Nurit


    Studies of charge transport through proteins bridged between two electrodes have been the subject of intense research in recent years. However, the complex structure of proteins makes it difficult to elucidate transport mechanisms, and the use of simple peptide oligomers may be an over simplified model of the proteins. To bridge this structural gap, we present here studies of charge transport through artificial parallel coiled-coil proteins conducted in dry environment. Protein monolayers uniaxially oriented at an angle of ∼ 30° with respect to the surface normal were prepared. Current voltage measurements, obtained using conductive-probe atomic force microscopy, revealed the mechano-electronic behavior of the protein films. It was found that the low voltage conductance of the protein monolayer increases linearly with applied force, mainly due to increase in the tip contact area. Negligible compression of the films for loads below 26 nN allowed estimating a tunneling attenuation factor, β(0) , of 0.5-0.6 Å(-1) , which is akin to charge transfer by tunneling mechanism, despite the comparably large charge transport distance. These studies show that mechano-electronic behavior of proteins can shed light on their complex charge transport mechanisms, and on how these mechanisms depend on the detailed structure of the proteins. Such studies may provide insightful information on charge transfer in biological systems.

  13. Lateral pressure profiles in lipid monolayers

    Baoukina, Svetlana; Marrink, Siewert J.; Tieleman, D. Peter


    We have used molecular dynamics simulations with coarse-grained and atomistic models to study the lateral pressure profiles in lipid monolayers. We first consider simple oil/air and oil/water interfaces, and then proceed to lipid monolayers at air/water and oil/water interfaces. The results are qual

  14. A new ethylene glycol-silane monolayer for highly-specific DNA detection on Silicon Chips

    Carrara, Sandro; Cavallini, Andrea; Maruyama, Yuki; Charbon, Edoardo; De Micheli, Giovanni


    Monolayer thin films with ethylene-glycol function onto gold surfaces by using thiols have been extensively investigated. They have been proposed as precursors for applications to bio-detection, where their hydrophilic character improves both specificity and sensitivity. The aim of this letter is to characterize ethylene-glycol monolayer precursors formed onto silicon chips by using silanes. The importance of the ethylene-glycol function is demonstrated by comparing with the well known 3-Aminopropyltriethoxysilane. The different nano-scale structures of the two precursor monolayers are investigated by using atomic force microscopy (AFM). Longer, wider, and deeper grooves were measured in the images acquired on 3-Aminopropyltriethoxysilane. Fluorescence investigation demonstrates that the presence of ethylene-glycol function improves target hybridization onto silicon chips, assuring highly-specific detection of DNA.

  15. Thin-Film Behavior of Poly(methyl methacrylates). 3. Epitaxial Crystallization in Thin Films of Isotactic Poly(methyl methacrylate) Using Crystalline Langmuir-Blodgett Layers

    Brinkhuis, R.H.G.; Schouten, A.J.


    A procedure is introduced using monolayer crystallized films of isotactic poly(methyl methacrylate) (i-PMMA) to induce crystallization in amorphous films of i-PMMA. Use of the Langmuir-Blodgett films as surface crystallization nuclei permits the preparation of highly crystalline films with thickness

  16. Coulomb excitations of monolayer germanene

    Shih, Po-Hsin; Chiu, Yu-Huang; Wu, Jhao-Ying; Shyu, Feng-Lin; Lin, Ming-Fa


    The feature-rich electronic excitations of monolayer germanene lie in the significant spin-orbit coupling and the buckled structure. The collective and single-particle excitations are diversified by the magnitude and direction of transferred momentum, the Fermi energy and the gate voltage. There are four kinds of plasmon modes, according to the unique frequency- and momentum-dependent phase diagrams. They behave as two-dimensional acoustic modes at long wavelength. However, for the larger momenta, they might change into another kind of undamped plasmons, become the seriously suppressed modes in the heavy intraband e–h excitations, keep the same undamped plasmons, or decline and then vanish in the strong interband e–h excitations. Germanene, silicene and graphene are quite different from one another in the main features of the diverse plasmon modes. PMID:28091555

  17. Large-area synthesis of high-quality and uniform monolayer WS2 on reusable Au foils

    Gao, Yang; Liu, Zhibo; Sun, Dong-Ming; Huang, Le; Ma, Lai-Peng; Yin, Li-Chang; Ma, Teng; Zhang, Zhiyong; Ma, Xiu-Liang; Peng, Lian-Mao; Cheng, Hui-Ming; Ren, Wencai


    Large-area monolayer WS2 is a desirable material for applications in next-generation electronics and optoelectronics. However, the chemical vapour deposition (CVD) with rigid and inert substrates for large-area sample growth suffers from a non-uniform number of layers, small domain size and many defects, and is not compatible with the fabrication process of flexible devices. Here we report the self-limited catalytic surface growth of uniform monolayer WS2 single crystals of millimetre size and large-area films by ambient-pressure CVD on Au. The weak interaction between the WS2 and Au enables the intact transfer of the monolayers to arbitrary substrates using the electrochemical bubbling method without sacrificing Au. The WS2 shows high crystal quality and optical and electrical properties comparable or superior to mechanically exfoliated samples. We also demonstrate the roll-to-roll/bubbling production of large-area flexible films of uniform monolayer, double-layer WS2 and WS2/graphene heterostructures, and batch fabrication of large-area flexible monolayer WS2 film transistor arrays.

  18. Miscibility of dl-α-tocopherol β-glucoside in DPPC monolayer at air/water and air/solid interfaces

    Neunert, G. [Department of Physics and Biophysics, Poznan University of Life Sciences, 60-637 Poznan (Poland); Makowiecki, J.; Piosik, E.; Hertmanowski, R. [Faculty of Technical Physics, Poznan University of Technology, 60-965 Poznan (Poland); Polewski, K. [Department of Physics and Biophysics, Poznan University of Life Sciences, 60-637 Poznan (Poland); Martynski, T., E-mail: [Faculty of Technical Physics, Poznan University of Technology, 60-965 Poznan (Poland)


    The role of newly synthesized tocopherol glycosidic derivative in modifying molecular organization and phase transitions of phospholipid monolayer at the air/water interface has been investigated. Two-component Langmuir films of dl-α-tocopheryl β-D-glucopyranoside (BG) mixed with dipalmitoyl phosphatidylcholine (DPPC) in the whole range of mole fractions were formed at the water surface. An analysis of surface pressure versus mean molecular area (π-A) isotherms and Brewster angle microscope images showed that the presence of BG molecules changes the structure and packing of the DPPC monolayer in a BG concentration dependent manner. BG molecules incorporated into DPPC monolayer inhibit its liquid expanded to liquid condensed phase transition proportionally to the BG concentration. The monolayers were also transferred onto solid substrates and visualized using an atomic force microscope. The results obtained indicate almost complete miscibility of BG and DPPC in the monolayers at surface pressures present in the biological cell membrane (30-35·10{sup -3} N·m{sup -1}) for a BG mole fraction as high as 0.3. This makes the monolayer less packed and more disordered, leading to an increased permeability. The results support our previous molecular dynamics simulation data. - Highlights: • Langmuir films of α-tocopherol derivative with DPPC was studied thermodynamically. • Mixed DPPC/BG films were transferred onto mica substrates for topography imaging by using AFM. • Miscibility of BG/DPPC films at surface pressures present in membranes was observed up to MF = 0.3.

  19. Langmuir-Blodgett film of phycobilisomes from blue-green alga Spirulina platensis.

    Chen, Chao; Zhang, Yu-Zhong; Chen, Xiu-Lan; Zhou, Bai-Cheng; Gao, Hong-Jun


    The phycobilisomes were isolated from blue-green alga Spirulina platensis, and could form monolayer film at air/water interface. The monolayer film of phycobilisomes was transferred to newly cleaved mica, and coated with gold. Scanning tunneling microscope was used to investigate the structure of the Langmuir-Blodgett film of phycobilisomes. It was shown that phycobilisomes in the monolayer arrayed in rows with core attaching on the substrate surface and rods radiating towards the air phase, this phenomenon was similar to the arrangement of phycobilisomes on cytoplasmic surface of thylakoid membrane in vivo. The possible applications of the Langmuir-Blodgett film of phycobilisomes were also discussed.

  20. Magnetism of coherent Co and Ni thin films on Cu(111) and Au(111) substrates: An ab initio study

    Zelený, Martin; Dlouhý, Ivo


    We present an ab initio study of structural and magnetic properties of coherent Co and Ni thin films on Cu(111) and Au(111) substrates with thicknesses of up to 6 monolayers. All studied films on Cu(111) substrates prefer structures close their ground state (hcp for Co and fcc for Ni), whereas only the hcp stacking sequence has been found for both films on Au(111) substrates. All studied films exhibit instability of the first monolayer with respect to decomposition into 2-monolayer- or 3-monolayer-high islands, which is in agreement with experimental findings. All studied films are also ferromagnetic, nevertheless the Ni/Cu(111) films reduce their magnetic moments in the layer adjacent to the substrate due to a stronger Cu-Ni interaction at the interface. The magnetic anisotropy of a Co film does not depend on the film thickness: all the studied Co/Au(111) films exhibit a perpendicular magnetic anisotropy, whereas all the Co/Cu(111) films prefer in-plane magnetization. On the other hand, both Ni films change their preference for in-plane orientation of their easy axis to out-of-plane orientation at a critical thickness of 2 monolayers, however, the magnetic anisotropy energies for films thicker than 1 monolayer are smaller than 1 meV/Ni atom. These behaviors of magnetic anisotropy do not depend on the structure of the studied films.

  1. Overpotential deposition of Ag monolayer and bilayer on Au(1 1 1) mediated by Pb adlayer underpotential deposition/stripping cycles

    Wang, J. X.; Ocko, B. M.; Adzic, R. R.


    Ultra-thin Ag films on the Au(1 1 1) surface were prepared via overpotential deposition (OPD) in the presence of Pb 2+ ions. By carrying out repetitive Pb adlayer underpotential deposition (UPD) and stripping cycles during Ag bulk deposition, the two-dimensional growth of Ag films was significantly enhanced in high OPD. The Ag monolayer sample was made by comparing the voltammetry curves, in which the signatures for Pb adlayer UPD on Au(1 1 1) changed to that on Ag(1 1 1). As demonstrated by the X-ray specular reflectivity measurements, nearly complete monolayer and bilayer films can be made with optimized deposition procedures. On subatomic scale, however, we found that these films have significant higher root-mean-square displacement amplitudes than those underpotentially deposited Ag monolayer and bilayer on either Au(1 1 1) or Pt(1 1 1).

  2. The Effects of Contact Interface on the Friction Characteristics of Self-assembly Monolayers

    ZHANGHui-chen; GAOYu-zhou; YANLi


    The effects of different contact interfaces on the friction characteristics of OTS self-assembled monolayers were investigated by a universal micro-tribometer in different sliding velocities. The results indicate that there exist lower friction coefficients between OTS SAMs and Ti, Ni and Cu films deposited on GCrl5 steel balls than those between OTS SAMs and GCr15 steel ball. The friction coefftcient between OTS SAMs and Ti film is the largest, and the friction coefficient between OTS SAMs and Cu film is the least in these three films, which depends the iatrinsic characteristics of the materials. The friction coefficients between OTS SAMs and GCrI5 steel balland three nanometer films increase with the sliding velachy increasing, which can be explained by the relaxationcharacteristics of OTS molecules.

  3. Drug induced `softening' in phospholipid monolayers

    Basak, Uttam Kumar; Datta, Alokmay; Bhattacharya, Dhananjay


    Compressibility measurements on Langmuir monolayers of the phospholipid Dimystoryl Phospatidylcholine (DMPC) in pristine form and in the presence of the Non-steroidal Anti-inflammatory Drug (NSAID) Piroxicam at 0.025 drug/lipid (D/L) molecular ratio at different temperatures, show that the monolayer exhibits large increase (and subsequent decrease) in compressibility due to the drug in the vicinity of the Liquid Expanded - Liquid Condensed (LE-LC) phase transition. Molecular dynamics simulations of the lipid monolayer in presence of drug molecules show a disordering of the tail tilt, which is consistent with the above result.

  4. Nanoscale observation of delayering in alkane films

    Bai, M.; Knorr, K.; Simpson, M.J.


    Tapping-mode Atomic Force Microscopy and synchrotron X-ray scattering measurements on dotriacontane ( n-C32H66 or C-32) films adsorbed on SiO2- coated Si( 100) wafers reveal a narrow temperature range near the bulk C32 melting point T-b in which a monolayer phase of C32 molecules oriented perpend...... and receding of the monolayer observed in transitions to and from the respective 3D phases....

  5. Corrosion protection ability of self-assembled monolayer of 3-amino-5-mercapto-1,2,4-triazole on copper electrode

    Rajkumar, Ganesan; Sethuraman, Mathur Gopalakrishnan, E-mail:


    The self-assembled monolayer (SAM) of 3-amino-5-mercapto-1,2,4-triazole (AMTa) was formed on a copper surface and characterized using cyclic voltammetry, Fourier Transform Infra-red spectroscopy and scanning electron microscopy. Quantum chemical calculations suggested the stronger interaction between AMTa and copper. The protection ability of SAM has been evaluated using electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The formed monolayer showed significant protection ability in 1% NaCl medium. The enhanced corrosion protection ability could be due to the compact film structure which blocks the electron transfer from the solution to AMTa monolayer modified copper substrate. - Highlights: • Self-assembled monolayer (SAM) of AMTa has been achieved on copper surface. • Monolayer formed has been duly characterized. • SAM of AMTa has been shown to offer significant protection to copper in NaCl medium.

  6. Factors Influencing the 2D Elastic Moduli of Self-Assembled Nanoparticle Monolayers

    You, Sihen; Rashkov, Rossen; Kanjanaboos, Pongsakorn; Calderon, Ignavio; Meron, Mati; Jaeger, Heinrich; Lin, Binhua


    Nanoparticles with hydrophobic capping ligands are found to self-assemble into monolayer films when deposited on the air/water interface. Different nanoparticle monolayers exhibit a rich morphology of wrinkling, folding and buckling behavior that indicates interesting elastic properties. We obtain the 2D bulk and shear moduli of several different nanoparticle films by measuring the anisotropic stress response of the film under uniaxial compression using a Langmuir trough, a method previously applied to lipid and protein membranes. We find that the elastic properties of the nanoparticle film are affected by size distribution of the nanoparticles and the properties of their capping ligands. Higher polydispersity results in a greater number of packing defects that weaken the assembled film. The ligands mediate the particle-particle interaction, acting like elastic springs that join together hard spheres. The strength of such ``springs'' is determined by the degree of interdigitation of ligands between neighboring nanoparticles as well as the shapes of the capping ligands. These results suggest that the elastic moduli of nanoparticle films can be tuned through careful alteration of size distribution and capping ligand's shape and density. This work is supported by the University of Chicago MRSEC of the NSF (DMR-0820054) and ChemMatCARS (NSF/DOE, Grant No. CHE-0822838).

  7. Understanding the collapse mechanism in Langmuir monolayers through polarization modulation-infrared reflection absorption spectroscopy.

    Goto, Thiago Eichi; Caseli, Luciano


    The collapse of films at the air-water interface is related to a type of 2D-to-3D transition that occurs when a Langmuir monolayer is compressed beyond its stability limit. Studies on this issue are extremely important because defects in ultrathin solid films can be better understood if the molecular mechanisms related to collapse processes are elucidated. This paper explores how the changes of vibration of specific groups of lipid molecules, as revealed by polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS), are affected by the monolayer collapse. Different mechanisms of collapse were studied, for those lipids that undergo constant-area collapse (such as stearic acid) and for those that undergo constant-pressure collapse (such as DPPC, DPPG, and DODAB). Lipid charges also affect the mechanism of collapse, as demonstrated for two oppositely charged lipids.

  8. Self-Assembled Monolayers Generated from Unsymmetrical Partially Fluorinated Spiroalkanedithiols.

    Chinwangso, Pawilai; Lee, Han Ju; Lee, T Randall


    Self-assembled monolayers (SAMs) were prepared on gold substrates from an unsymmetrical partially fluorinated spiroalkanedithiol adsorbate with the specific structure of [CH3(CH2)7][CF3(CF2)7(CH2)8]C[CH2SH]2 (SADT) and compared to SAMs formed from the semifluorinated monothiol F8H10SH [CF3(CF2)7(CH2)10SH] of analogous chain length and n-octadecanethiol. The adsorbate with two alkyl chains, one terminally fluorinated and the other nonfluorinated, was designed to form monolayers in which the bulky helical fluorocarbon segments assemble on top of an underlying layer of well-packed trans-extended alkyl chains. Different combinations of deposition solvents and temperatures were used to produce the bidentate SAMs. Characterization of the resulting monolayers revealed that SAMs formed in DMF at room temperature allow complete binding of the sulfur headgroups to the surface and exhibit higher conformational order than those produced using alternative solvent/temperature combinations. The reduced film thicknesses and enhanced wettability of the SADT SAMs, as compared to the SAMs generated from F8H10SH, suggest loose packing and an increase in the tilt of the terminal fluorocarbon chain segments. Nevertheless, the density of the underlying hydrocarbon chains of the SADT SAMs was higher than that of the F8H10SH SAMs, owing to the double-chained structure of the new adsorbate. The conformational orders of the SAM systems were observed to decrease as follows: C18SH > F8H10SH > SADT. However, the SAMs formed from this new double-chained bidentate adsorbate in DMF expose a fluorinated interface with a relatively low surface roughness, as determined by contact-angle hysteresis.

  9. Phase transitions in diglyceride monolayers studied by computer simulations, pressure-area isotherms and x-ray diffraction

    Peters, Günther H.J.; Toxværd, S.; Larsen, N.B.


    1,2-sn-diglyceride monolayers exhibit unique and complex phase transitions as a function of surface pressure. The dynamical response of the layer on expanding the film has been investigated by computer simulations, (π-A) isotherms and grazing-incidence X-ray diffraction. Good agreement is found b...

  10. Dip-Pen Nanolithography on (Bio)Reactive Monolayer and Block-Copolymer Platforms: Deposition of Lines of Single Macromolecules

    Salazar, Ramon B.; Shovsky, A.; Schönherr, Holger; Vancso, Gyula J.


    The application of atomic force microscopy (AFM) tip-mediated molecular transfer (dip-pen nanolithography or DPN) to fabricate nanopatterned (bio)reactive platforms based on dendrimers on reactive self-assembled monolayer (SAM) and polymer thin films is discussed. The transfer of high-molar-mass

  11. Method to synthesize metal chalcogenide monolayer nanomaterials

    Hernandez-Sanchez, Bernadette A.; Boyle, Timothy J.


    Metal chalcogenide monolayer nanomaterials can be synthesized from metal alkoxide precursors by solution precipitation or solvothermal processing. The synthesis routes are more scalable, less complex and easier to implement than other synthesis routes.

  12. 热处理对LiFe1-0.01xY0.005xAg0.005xPO4薄膜光波导传感元件气敏性的影响%Effect of Heat Treatment on LiFe1-0.01xY0.005xAg0.005xPO4 Thin Film Optical Waveguide's Gas Sensing Properties

    帕提曼·尼扎木丁; 阿布力孜·伊米提; 米日古丽·依明; 帕提曼·亚森; 艾拜都拉·热合曼; 司马义·努尔拉


    以FeSO4·7H2O,H3PO4,LiOH·H2O,AgNO3及Y(NO3)3·6H2O为原料,利用水热法一步合成出了LiFe1 -0.01xY0.005xAg0.005PO4粉体(x=0.5,1.0),并将该材料作为敏感试剂,用旋转-甩涂法做成纳米薄膜固定在锡掺杂玻璃光波导表面,在不同温度下进行热处理.采用紫外-可见分光光度计、测厚仪以及自组装的玻璃光波导气敏测试仪研究了热处理对LiFe1-0.01xY0.005xAg0.005xPO4薄膜光学及气敏特性的影响.研究结果表明:在450℃下进行热处理的薄膜元件具有良好的光学透明及较好的气敏特性.相同浓度的不同挥发性有机气体中,该传感元件对二甲苯气体有很好的选择性响应,其检测响应范围为1×10-7~1×10-3(V/V),响应-恢复时间分别小于5和100s.%LiFe1 -0.01xY0.005xAg0.005PO4 ( x =0.5,1.0) was synthesized via hydrothermal method by one step using FeSO4·7H2O,H3PO4,LiOH·H2O,AgNO3 and Y(NO3)3·6H2O as precursors. LiFe1-0.01xY0.005xAg0.005xPO4 was selected as sensing materials and was subsequently utilized in a spin-coating procedure for the fabrication of LiFe1-0.01x Y0.005x Ag0.005xPO4 thin Elms,and then the coated film was dried at different temperatures. The effect of heat treatment on LiFe1-0.01xY0.005xAg0.005xPO4 thin film optical waveguide's gas sensing properties were studiedusing ultraviolet spectrophotometer,ellipsometer and self assembled optical waveguide gases testing apparatus. The experimental results indicated that the thin film sensing element,which was dried at 450℃,was exhibited good sensing capabilities and optical transparent. The sensor had higher response to the xylene gas than the other various volatile organic compounds at same concentration. These sensors exhibited good response to xylene gas in the range of 1×l0-7 to 1× 10-3 with response and recovery times less than 5 and 100 s.

  13. “Lotus” Domain Formation by the Hydrolysis Reaction of Phospholipase D to Phospholipid Monolayer

    Qiang HE; Jun Bai LI


    Hydrolysis reaction of L-α-dipalmitoylphosphatidylcholine (L-DPPC) monolayer with phospholipase D (PLD) has been investigated by Brewster angle microscopy (BAM) combined with the film balance. It has been found that the L-DPPC domains were changed into the "lotus" structure by PLD. It suggests that the hydrolysis reaction is incomplete and the products together with the nonreacted materials undergo a molecular rearrangement at the interface.

  14. Fracture Characteristics of Monolayer CVD-Graphene

    Hwangbo, Yun; Lee, Choong-Kwang; Kim, Sang-Min; Kim, Jae-Hyun; Kim, Kwang-Seop; Jang, Bongkyun; Lee, Hak-Joo; Lee, Seoung-Ki; Kim, Seong-Su; Ahn, Jong-Hyun; Lee, Seung-Mo


    We have observed and analyzed the fracture characteristics of the monolayer CVD-graphene using pressure bulge testing setup. The monolayer CVD-graphene has appeared to undergo environmentally assisted subcritical crack growth in room condition, i.e. stress corrosion cracking arising from the adsorption of water vapor on the graphene and the subsequent chemical reactions. The crack propagation in graphene has appeared to be able to be reasonably tamed by adjusting applied humidity and stress. ...

  15. Protein-induced surface structuring in myelin membrane monolayers.

    Rosetti, Carla M; Maggio, Bruno


    Monolayers prepared from myelin conserve all the compositional complexity of the natural membrane when spread at the air-water interface. They show a complex pressure-dependent surface pattern that, on compression, changes from the coexistence of two liquid phases to a viscous fractal phase embedded in a liquid phase. We dissected the role of major myelin protein components, myelin basic protein (MBP), and Folch-Lees proteolipid protein (PLP) as crucial factors determining the structural dynamics of the interface. By analyzing mixtures of a single protein with the myelin lipids we found that MBP and PLP have different surface pressure-dependent behaviors. MBP stabilizes the segregation of two liquid phases at low pressures and becomes excluded from the film under compression, remaining adjacent to the interface. PLP, on the contrary, organizes a fractal-like pattern at all surface pressures when included in a monolayer of the protein-free myelin lipids but it remains mixed in the MBP-induced liquid phase. The resultant surface topography and dynamics is regulated by combined near to equilibrium and out-of-equilibrium effects. PLP appears to act as a surface skeleton for the whole components whereas MBP couples the structuring to surface pressure-dependent extrusion and adsorption processes.

  16. Mass spectrometric analysis of monolayer protected nanoparticles

    Zhu, Zhengjiang

    Monolayer protected nanoparticles (NPs) include an inorganic core and a monolayer of organic ligands. The wide variety of core materials and the tunable surface monolayers make NPs promising materials for numerous applications. Concerns related to unforeseen human health and environmental impacts of NPs have also been raised. In this thesis, new analytical methods based on mass spectrometry are developed to understand the fate, transport, and biodistributions of NPs in the complex biological systems. A laser desorption/ionization mass spectrometry (LDI-MS) method has been developed to characterize the monolayers on NP surface. LDI-MS allows multiple NPs taken up by cells to be measured and quantified in a multiplexed fashion. The correlations between surface properties of NPs and cellular uptake have also been explored. LDI-MS is further coupled with inductively coupled plasma mass spectrometry (ICP-MS) to quantitatively measure monolayer stability of gold NPs (AuNPs) and quantum dots (QDs), respectively, in live cells. This label-free approach allows correlating monolayer structure and particle size with NP stability in various cellular environments. Finally, uptake, distribution, accumulation, and excretion of NPs in higher order organisms, such as fish and plants, have been investigated to understand the environmental impact of nanomaterials. The results indicate that surface chemistry is a primary determinant. NPs with hydrophilic surfaces are substantially less toxic and present a lower degree of bioaccumulation, making these nanomaterials attractive for sustainable nanotechnology.

  17. The effect of β-sitosterol on the properties of cholesterol/phosphatidylcholine/ganglioside monolayers--the impact of monolayer fluidity.

    Hąc-Wydro, Katarzyna


    In this paper the influence of one of phytosterols, namely β-sitosterol on cholesterol (Chol)/phosphatidylcholine (PC)/ganglioside (GM3) monolayers was examined to find the correlation between the properties of model system and the effect of phytocompound. The studied monolayers differed in condensation and fluidity, which were modified by the structure of phosphatidylcholine. It was found that the incorporation of β-sitosterol into cholesterol/phosphatidylcholine/ganglioside films changes their morphology, condensation and interactions between the lipids. The substitution of cholesterol more strongly decreased the condensation and stability of the film containing PC molecules having monounsaturated chains than more densely packed monolayer composed of saturated phosphatidylcholine. However, thorough analysis of data obtained so far suggests that the magnitude of β-sitosterol effect is determined by the composition of the system rather than its fluidity itself. Moreover, the results collected herein correlate well with the findings that phytosterol more strongly inhibits the growth of cancer cells, which at a given proportion of cholesterol to phospholipids in membranes, have more unsaturated fatty acids within phospholipids molecules.

  18. First-principles study on magnetism of Ru monolayer under an external electric field

    Kitaoka, Yukie; Imamura, Hiroshi

    Electric field control of magnetic properties such as magnetic moment and magnetic anisotropy has been attracted. For the 4 d TM films, on the other hand, it was recently reported that the ferromagnetism Pd thin-film is induced by application of an external electric field otherwise Pd thin-film shows paramagnetic. However, little attention has been paid to the magnetism of other 4 d TMs. Here, we investigate the magnetism of the free-standing Ru monolayer and that on MgO(001) substrate under an external electric field by using first-principles FLAPW method. We found that the free-standing Ru monolayer is ferromagnet with magnetic moment of 1.50 ¥muB /atom. The MA energy is 3.45 meV/atom, indicating perpendicular MA, at zero electric field (E=0) and increases up to 3.84 meV/atom by application of E=1 (V/¥AA). The Ru monolayer on MgO(001) substrate is also ferromagnet with magnetic moment of 0.89 ¥muB /atom. The MA energy is 1.49 meV/atom, indicating perpendicular MA, at E=0 and decreases to 1.33 meV/atom by application of E=1 (V/¥AA).

  19. Enhanced superconductivity accompanying a Lifshitz transition in electron-doped FeSe monolayer

    Shi, X.; Han, Z.-Q.; Peng, X.-L.; Richard, P.; Qian, T.; Wu, X.-X.; Qiu, M.-W.; Wang, S. C.; Hu, J. P.; Sun, Y.-J.; Ding, H.


    The origin of enhanced superconductivity over 50 K in the recently discovered FeSe monolayer films grown on SrTiO3 (STO), as compared to 8 K in bulk FeSe, is intensely debated. As with the ferrochalcogenides AxFe2-ySe2 and potassium-doped FeSe, which also have a relatively high-superconducting critical temperature (Tc), the Fermi surface (FS) of the FeSe/STO monolayer films is free of hole-like FS, suggesting that a Lifshitz transition by which these hole FSs vanish may help increasing Tc. However, the fundamental reasons explaining this increase of Tc remain unclear. Here we report a 15 K jump of Tc accompanying a second Lifshitz transition characterized by the emergence of an electron pocket at the Brillouin zone centre, which is triggered by high-electron doping following in situ deposition of potassium on FeSe/STO monolayer films. Our results suggest that the pairing interactions are orbital dependent in generating enhanced superconductivity in FeSe.

  20. Effects of irradiated biodegradable polymer in endothelial cell monolayer formation

    Arbeitman, Claudia R.; Grosso, Mariela F. del [CONICET – Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina); Gerencia de Investigación y Aplicaciones, TANDAR-CNEA (Argentina); Behar, Moni [Instituto de Física, UFRGS, Porto Alegre, RS (Brazil); García Bermúdez, Gerardo, E-mail: [CONICET – Consejo Nacional de Investigaciones Científicas y Técnicas (Argentina); Gerencia de Investigación y Aplicaciones, TANDAR-CNEA (Argentina); Escuela de Ciencia y Tecnología, UNSAM (Argentina)


    In this work we study cell adhesion, proliferation and cell morphology of endothelial cell cultured on poly-L-lactide acid (PLLA) modified by heavy ion irradiation. Thin films of PLLA samples were irradiated with sulfur (S) at energies of 75 MeV and gold (Au) at 18 MeV ion-beams. Ion beams were provided by the Tandar (Buenos Aires, Argentina) and Tandetron (Porto Alegre, Brazil) accelerators, respectively. The growth of a monolayer of bovine aortic endothelial cells (BAEC) onto unirradiated and irradiated surfaces has been studied by in vitro techniques in static culture. Cell viability and proliferation increased on modified substrates. But the results on unirradiated samples, indicate cell death (necrosis/apoptosis) with the consequent decrease in proliferation. We analyzed the correlation between irradiation parameters and cell metabolism and morphology.

  1. Determination of three characteristic regimes of weakly charged polyelectrolytes monolayers

    Ahmad, Farhan [Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju 500-712 (Korea, Republic of); Shin, Kwanwoo [Department of Chemistry and Interdisciplinary Program of Integrated Biotechnology, Sogang University, Seoul 121-742 (Korea, Republic of)], E-mail:; Choi, Jae-Hak [Advanced Radiation Technology Institute, KAERI, Jeongeup 580-185 (Korea, Republic of); Satija, Sushil K. [National Institute of Standards and Technology, Gaithersburg, MD 20899 (United States); Kim, Joon-Seop [Department of Polymer Science and Engineering, Chosun University (Korea, Republic of); Rafailovich, Miriam H.; Sokolov, Jon [Department of Materials Science and Engineering, Stony Brook University, Stony Brook, NY 11794 (United States)


    We have demonstrated that monolayer films of randomly charged polystyrene sulfonated acid (PSSA) can be produced by the Langmuir technique, and observed the micro-domain structures, produced by the phase separation of electrostatically charged moieties and the hydrophobic moieties. Using atomic force microscopy and Langmuir isotherm, we found three specific regimes for the polyelectrolytes with various degrees of sulfonation (4-35%); very low charged PSSA (4-5%) in the hydrophobic regime, moderately charged PSSA (6-16%) which possessed a well-balanced nature between electrostatic and the hydrophobic interactions, and strongly amphiphilic nature of PSSA (6-16%) in the ionomer regime. Finally, we could categorize PSSA 35% in the polyelectrolyte regime, due to the dominance of the electrostatic interactions over the hydrophobic interactions.

  2. Enhanced near-field heat flow of a monolayer dielectric island.

    Worbes, Ludwig; Hellmann, David; Kittel, Achim


    We have investigated the influence of thin films of a dielectric material on the near-field mediated heat transfer at the fundamental limit of single monolayer islands on a metallic substrate. We present spatially resolved measurements by near-field scanning thermal microscopy showing a distinct enhancement in heat transfer above NaCl islands compared to the bare Au(111) film. Experiments at this subnanometer scale call for a microscopic theory beyond the macroscopic fluctuational electrodynamics used to describe near-field heat transfer today. The method facilitates the possibility of developing designs of nanostructured surfaces with respect to specific requirements in heat transfer down to a single atomic layer.

  3. Enhanced Near-Field Heat Flow of a Monolayer Dielectric Island

    Worbes, Ludwig; Hellmann, David; Kittel, Achim


    We have investigated the influence of thin films of a dielectric material on the near-field mediated heat transfer at the fundamental limit of single monolayer islands on a metallic substrate. We present spatially resolved measurements by near-field scanning thermal microscopy showing a distinct enhancement in heat transfer above NaCl islands compared to the bare Au(111) film. Experiments at this subnanometer scale call for a microscopic theory beyond the macroscopic fluctuational electrodynamics used to describe near-field heat transfer today. The method facilitates the possibility of developing designs of nanostructured surfaces with respect to specific requirements in heat transfer down to a single atomic layer.

  4. Measurements of monolayer hydrodynamics at an air/water interface

    Vogel, Michael James


    Growing interest in monomolecular films is driven in part by their numerous applications, which include coating technologies, chemical and bio-sensors, and optoelectronic devices. In the present research, a study involving several different experiments has focused on an improved understanding and quantification of the physics of monolayer-influenced flows. Measurements were made with laser-based nonintrusive techniques, including boundary-fitted digital particle image velocimetry (BFDPIV) to obtain interfacial velocity and shear data, and reflected second-harmonic generation (SHG) to directly measure surfactant concentration at the interface. A simple geometry consisting of uniform bulk flow and a planar surface-piercing barrier which resulted in the phenomenon commonly referred to as a Reynolds ridge was used to study the elasticity of a monolayer. A novel technique was developed in which velocity and surfactant concentration measurements are made simultaneously with a single laser beam which is scanned along the interface. Additionally, a theoretical model balancing surface elasticity and bulk shear at the interface was developed to predict the concentration profile for any insoluble monolayer. The predicted concentration profiles were found to be in agreement with experimental results. Additionally, global predictions from the model for four different insoluble surfactant systems also showed agreement with experimental measurements. In order to study the interfacial dilatational viscosity (kappa s) of a monolayer, for which there are no consistently measured values in the literature, a cavity flow was utilized in which the floor oscillates in the direction parallel to itself. Initially, a baseline study was performed to establish the range of parameters for which the flow is essentially two-dimensional (2D). Three flow regimes were found in the parameter space considered: an essentially 2D time-periodic flow, a time-periodic three-dimensional (3D) flow with a

  5. Conformational morphology of polyaniline grown on self-assembled monolayer modified silicon

    Sutar, D.S., E-mail: [Central Surface Analytical Facility, Indian Institute of Technology Bombay, Mumbai 400076 (India); Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Major, S.S. [Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076 (India); Srinivasa, R.S. [Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Mumbai 400076 (India); Yakhmi, J.V. [Technical Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India)


    Polyaniline (PANI) films with pyramidal shaped crystallites were prepared by self-organization on self-assembled monolayer (SAM) modified Si substrates. High-resolution atomic force microscopy (HR-AFM) shows that SAM has tridymite structural order and the PANI film has biphasic conformational morphology corresponding to face-on orientation and edge-on orientation. Order parameters obtained from power spectral density analysis of HR-AFM images of SAM and PANI films show that the pyramidal crystallites are in emeraldine salt (ES-I) form and the region between the crystallites is in emeraldine base (EB-II) form. The ordered lattice of PANI crystallites as observed by cross-sectional HR-TEM confirms its single crystalline nature as well as epitaxial growth. The heteroepitaxial growth of PANI is attributed to the structural order of interfacial SAM on Si. - Highlights: > The structural order of self-assembled monolayer (SAM) on Si assists in hetero-epitaxial growth of polyaniline (PANI) films. > The power spectral density (PSD) analysis of the high-resolution AFM images provides the order parameters, which help to elucidate the ordering in SAM and PANI films. > PSD function could be used to analyze the high-resolution AFM images, which hitherto has been used mainly for low-resolution image analysis. > The ordered lattice image and SAED pattern obtained by HR-TEM confirms the single crystalline nature of pyramidal crystallites and their epitaxial growth at the interface.

  6. Capping-ligand effect on the stability of CdSe quantum dot Langmuir monolayers.

    Radhakrishnan, Chander; Lo, Michael K F; Knobler, Charles M; Garcia-Garibay, Miguel A; Monbouquette, Harold G


    The stability of Langmuir monolayers of CdSe Qdots capped with dodecan-ethiol (DDT), with dithiocarbamates having one, two, or three long alkyl chains (DTC-1, DTC-2 and DTC-3) or with tri-n-octylphosphine oxide (TOPO), was investigated and linked to the transport of Qdots into the subphase via a dissolution and diffusion mechanism. Langmuir films of Qdots were created by depositing droplets of purified Qdots in chloroform at the air-water interface. While holding the Qdot films at 13 mN/m for 1 h in a Langmuir trough, the average monolayer areas decreased by roughly 9% for TOPO-capped Qdots, ∼15-18% for the three DTC-capped Qdot preparations, and ∼21% for DDT-capped Qdots. Using the model of Ter Minassian-Saraga, the relative stabilities of the Qdot films studied were related to differences in equilibrium partitioning into the subphase and to apparent Qdot diffusivities within the subphase. An analysis of the Qdot preparations by Fourier-transform infrared spectroscopy (FTIR) revealed that the aliphatic tails of capping ligands were assembled on Qdot surfaces with similar packing densities for all ligand chemistries. A combined analysis of the film-area contraction and FTIR data suggested that, for the chemistries examined in this study, both the capping-ligand headgroup and the aliphatic tail groups impact Qdot Langmuir film stability through their joint influence on nanoparticle wettability and the tendency to aggregate upon partitioning into the subphase.

  7. Interaction of methionine-enkephalins with raft-forming lipids: monolayers and BAM experiments.

    Tsanova, A; Jordanova, A; Dzimbova, T; Pajpanova, T; Golovinsky, E; Lalchev, Z


    Enkephalins (Tyr-Gly-Gly-Phe-Met/Leu) are opioid peptides with proven antinociceptive action in organism. They interact with opioid receptors belonging to G-protein coupled receptor superfamily. It is known that these receptors are located preferably in membrane rafts composed mainly of sphingomyelin (Sm), cholesterol (Cho), and phosphatidylcholine. In the present work, using Langmuir's monolayer technique in combination with Wilhelmy's method for measuring the surface pressure, the interaction of synthetic methionine-enkephalin and its amidated derivative with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), Sm, and Cho, as well as with their double and triple mixtures, was studied. From the pressure/area isotherms measured, the compressional moduli of the lipids and lipid-peptide monolayers were determined. Our results showed that the addition of the synthetic enkephalins to the monolayers studied led to change in the lipid monolayers characteristics, which was more evident in enkephalinamide case. In addition, using Brewster angle microscopy (BAM), the surface morphology of the lipid monolayers, before and after the injection of both enkephalins, was determined. The BAM images showed an increase in surface density of the mixed surface lipids/enkephalins films, especially with double and triple component lipid mixtures. This effect was more pronounced for the enkephalinamide as well. These observations showed that there was an interaction between the peptides and the raft-forming lipids, which was stronger for the amidated peptide, suggesting a difference in folding of both enkephalins. Our research demonstrates the potential of lipid monolayers for elegant and simple membrane models to study lipid-peptide interactions at the plane of biomembranes.

  8. Lupane-type pentacyclic triterpenes in Langmuir monolayers: a synchrotron radiation scattering study.

    Broniatowski, Marcin; Flasiński, Michał; Wydro, Paweł


    Lupane-type pentacyclic triterpenes (lupeol, betulin, and betulinic acid) are natural products isolated from various plant sources. The terpenes exhibit a vast spectrum of biological activity and are applied in therapies for different diseases, among which the anticancer, anti-HIV, antihypercholesteremic, and antiinflammatory are the most promising. These chemicals possess amphiphilic structure and were proved to interact strongly with biomembranes, which can be the key stage in their mechanism of action. In our studies, we applied Langmuir monolayers as versatile models of biomembranes. It turned out that the three investigated terpenes are capable of stable monolayer formation; however, these monolayers differ profoundly regarding their physicochemical characteristics. In our research, we applied the Langmuir technique (surface pressure-mean molecular area (π-A) isotherm registration) coupled with Brewster angle microscopy (BAM), but the main focus was on the synchrotron radiation scattering method, grazing incidence X-ray diffraction (GIXD), which provides information on the amphiphilic molecule ordering in the angström scale. It was proved that all the investigated terpenes form crystalline phases in their monolayers. In the case of lupeol, only the closely packed upright phase was observed, whereas for betulin and betulinic acid, the phase situation was more complex. Betulinic acid molecules can be organized in an upright phase, which is crystalline, and in a tilted phase, which is amorphous. The betulin film is a conglomerate of an upright crystalline monolayer phase, tilted amorphous monolayer phase, and a crystalline tilted bilayer. In our paper, we discuss the factors leading to the formation of the observed phases and the implications of our results to the therapeutic applications of the native lupane-type triterpenes.

  9. Assembly of organic monolayers on polydicyclopentadiene.

    Perring, Mathew; Bowden, Ned B


    The first well-defined organic monolayers assembled on polydicyclopentadiene is reported. Commercial grade dicyclopentadiene was polymerized with the Grubbs' second-generation catalyst in a fume hood under ambient conditions at very low monomer to catalyst loadings of 20 000 to 1. This simple method resulted in a polymer that was a hard solid and appeared slightly yellow. Brief exposures of a few seconds of this polymer to Br 2 lead to a surface with approximately half of the olefins brominated as shown by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection-infrared (ATR-IR) spectroscopy. The ATR-IR spectroscopy was carried out with the polymer in contact with a Ge hemisphere housed in a GATR accessory from Harrick. This brominated polydicyclopentadiene was immersed in DMF with 4-(trifluoromethyl)benzylamine to assemble a monolayer. The amines displaced Br on the surface to form a monolayer that exposed a CF 3 group on the surface. The surface was extensively studied by XPS using the method described by Tougaard to find the distribution of F within the surface layer. The ratio for the peak area, Ap, to the background height, B, measured 30 eV below the peak maximum was 109.8 eV. This value clearly indicated that F was found only at the surface and was not found within the polymer. A surface coverage of 1.37 amines per nm (2) was estimated and indicated that the monolayer was 28% as dense as a similar monolayer assembled from thiols on gold. Finally, a simple method to pattern these monolayers using soft lithography is described. This work is critically important because it reports the first monolayers on a relatively new and emerging polymer that has many desirable physical characteristics such as high hardness, chemical stability, and ease of forming different shapes.

  10. Nanofriction properties of molecular deposition films

    王强斌; 高芒来; 张嗣伟


    The nanofriction properties of Au substrate and monolayer molecular deposition film and multilayer molecular deposition films on Au substrate and the molecular deposition films modified with alkyl-terminal molecule have been investigated by using an atomic force microscope. It is concluded that ( i ) the deposition of molecular deposition films on Au substrate and the modification of alkyl-terminal molecule to the molecular deposition films can reduce the frictional force; (ii) the molecular deposition films with the same terminal exhibit similar nanofriction properties, which has nothing to do with the molecular chain-length and the layer number; (iii) the unstable nanofriction properties of molecular deposition films are contributed to the active terminal of the molecular deposition film, which can be eliminated by decorating the active molecular deposition film with alkyl-terminal molecule, moreover, the decoration of alkyl-terminal molecule can lower the frictional force conspicuously; (iv) the relat

  11. Anodic passivation of tin by alkanethiol self-assembled monolayers examined by cyclic voltammetry and coulometry.

    Worley, Barrett C; Ricks, William A; Prendergast, Michael P; Gregory, Brian W; Collins, Ross; Cassimus, John J; Thompson, Raymond G


    The self-assembly of medium chain length alkanethiol monolayers on polycrystalline Sn electrodes has been investigated by cyclic voltammetry and coulometry. These studies have been performed in order to ascertain the conditions under which their oxidative deposition can be achieved directly on the oxide-free Sn surface, and the extent to which these electrochemically prepared self-assembled monolayers (SAMs) act as barriers to surface oxide growth. This work has shown that the potentials for their oxidative deposition are more cathodic (by 100-200 mV) than those for Sn surface oxidation and that the passivating abilities of these SAMs improve with increasing film thickness (or chain length). Oxidative desorption potentials for these films have been observed to shift more positively, and in a highly linear fashion, with increasing film thickness (~75 mV/CH2). Although reductive desorption potentials for the SAMs are in close proximity to those for reduction of the surface oxide (SnOx), little or no SnOx formation occurs unless the potential is made sufficiently anodic that the monolayers start to be removed oxidatively. Our coulometric data indicate that the charge involved with alkanethiol reductive desorption or oxidative deposition is consistent with the formation of a close-packed monolayer, given uncertainties attributable to surface roughness and heterogeneity phenomena. These experiments also reveal that the quantity of charge passed during oxidative desorption is significantly larger than what would be predicted for simple alkylsulfinate or alkylsulfonate formation, suggesting that oxidative removal involves a more complex oxidation mechanism. Analogous chronocoulometric experiments for short-chain alkanethiols on polycrystalline Au electrodes have evidenced similar oxidative charge densities. This implies that the mechanism for oxidative desorption on both surfaces may be very similar, despite the significant differences in the inherent dissolution

  12. Thermal ripples in model molybdenum disulfide monolayers

    Remsing, Richard C.; Klein, Michael L. [Institute for Computational Molecular Science, Center for the Computational, Design of Functional Layered Materials, and Department of Chemistry, Temple University, 1925 N. 12th St., 19122, Philadelphia, PA (United States); Waghmare, Umesh V. [Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, 560 064, Jakkur, Bangalore (India)


    Molybdenum disulfide (MoS{sub 2}) monolayers have the potential to revolutionize nanotechnology. To reach this potential, it will be necessary to understand the behavior of this two-dimensional (2D) material on large length scales and under thermal conditions. Herein, we use molecular dynamics (MD) simulations to investigate the nature of the rippling induced by thermal fluctuations in monolayers of the 2H and 1T phases of MoS{sub 2}. The 1T phase is found to be more rigid than the 2H phase. Both monolayer phases are predicted to follow long wavelength scaling behavior typical of systems with anharmonic coupling between vibrational modes as predicted by classic theories of membrane-like systems. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  13. Thermal transport in monolayer InSe

    Nissimagoudar, Arun S.; Ma, Jinlong; Chen, Yani; Li, Wu


    Two-dimensional InSe, a recently synthesized semiconductor having a moderate band gap, has gained attention due to its ultra high mobility and high photo-responsivity. In this work, we calculate the lattice thermal conductivity (κ) of monolayer InSe by solving the phonon Boltzmann transport equation (BTE) with first-principles calculated inter atomic force constants. κ of monolayer InSe is isotropic and found to be around 27.6 W m K-1 at room temperature along the in-plane direction. The size dependence of κ shows the size effect can persist up to 20 μm. Further, κ can be reduced to half by tuning the sample size to 300 nm. This low value suggests that κ might be a limiting factor for emerging nanoelectronic applications of monolayer InSe.

  14. Elastic bending modulus of monolayer graphene

    Lu Qiang; Huang Rui [Department of Aerospace Engineering and Engineering Mechanics, University of Texas, Austin, TX 78712 (United States); Arroyo, Marino [Department of Applied Mathematics 3, LaCaN, Universitat Politecnica de Catalunya (UPC), Barcelona 08034 (Spain)


    An analytic formula is derived for the elastic bending modulus of monolayer graphene based on an empirical potential for solid-state carbon atoms. Two physical origins are identified for the non-vanishing bending stiffness of the atomically thin graphene sheet, one due to the bond-angle effect and the other resulting from the bond-order term associated with the dihedral angles. The analytical prediction compares closely with ab initio energy calculations. Pure bending of graphene monolayers into cylindrical tubes is simulated by a molecular mechanics approach, showing slight nonlinearity and anisotropy in the tangent bending modulus as the bending curvature increases. An intrinsic coupling between bending and in-plane strain is noted for graphene monolayers rolled into carbon nanotubes. (fast track communication)

  15. Magneto photoluminescence measurements of tungsten disulphide monolayers

    Kuhnert, Jan; Rahimi-Iman, Arash; Heimbrodt, Wolfram


    Layered transition-metal dichalcogenides have attracted great interest in the last few years. Thinned down to the monolayer limit they change from an indirect band structure to a direct band gap in the visible region. Due to the monolayer thickness the inversion symmetry of the crystal is broken and spin and valley are coupled to each other. The degeneracy between the two equivalent valleys, K and K‧, respectively, can be lifted by applying an external magnetic field. Here, we present photoluminescence measurements of CVD-grown tungsten disulphide (WS2) monolayers at temperatures of 2 K. By applying magnetic fields up to 7 T in Faraday geometry, a splitting of the photoluminescence peaks can be observed. The magnetic field dependence of the A-exciton, the trion and three bound exciton states is discussed and the corresponding g-factors are determined.

  16. Synthesis of Vertically Aligned Carbon Nanotubes on Silicalite-1 Monolayer-Supported Substrate

    Wei Zhao


    Full Text Available Monodisperse magnetic Fe3O4 nanoparticles (NPs with the size of ca. 3.5 nm were prepared and used as the catalysts for the synthesis of vertically aligned carbon nanotube (VACNT arrays. A silicalite-1 microcrystal monolayer was used as the support layer between catalyst NPs and the silicon substrate. Compared to our previous report which used radio-frequency- (rf- sputtered Fe2O3 film as the catalyst, Fe3O4 NPs that were synthesized by wet chemical method showed an improved catalytic ability with less agglomeration. The silicalite-1 crystal monolayer acted as an effective “buffer” layer to prevent the catalyst NPs from agglomerating during the reaction process. It is believed that this is the first report that realizes the vertical alignment of CNTs over the zeolite monolayer, namely, silicalite-1 microcrystal monolayer, instead of using the intermediate anodic aluminum oxide (AAO scaffold to regulate the growth direction of CNT products.

  17. High quality and large-scale manually operated monolayer graphene pasters

    Wei, Yuke; Zhang, Yan; Liu, Zhenghao; Wang, Yue; Ke, Fen; Meng, Jie; Guo, Yanjun; Ma, Ping; Feng, Qingrong; Gan, Zizhao


    Graphene is a well-known material with various potential applications. Here we report the manufacture of high-quality and large-scale monolayer graphene pasters via polyvinyl butyral (PVB). These pasters have good self-supporting properties and overcome the drawback of weak mechanical strength of PMMA. Manual manipulations to monolayer graphene become realizable via graphene pasters. Graphene pasters can be quickly diverted onto any substrate with sufficient contact and greatly minimize the challenges in graphene transfer, measurements, and other applications. The improved transfer process via graphene pasters protects the integrity of monolayer graphene and introduces few cracks or tears into graphene. Large-scale monolayer graphene films diverted onto SiO2/Si by using graphene pasters maintain low resistivity and low Dirac point, while also exhibiting a higher magnetoresistance than traditional results. High magnetoresistance up to 600% and signs of saturation at high magnetic fields can be seen. Obvious negative magnetoresistance at low magnetic fields due to weak localization also can be observed. Graphene pasters can be used in many different domains and will promote future studies and applications of graphene.

  18. The additional phase transition of DPPC monolayers at high surface pressure confirmed by GIXD study

    Shen, Chen; Serna, Jorge B. de la; Struth, Bernd

    Pulmonary surfactant forms the alveolar monolayer at the air/aqueous interface within the lung. During the breathing process, the surface pressure periodically varies from ~40mN/m up to ~70mN/m. The film is mechanically stable during this rapid and reversible expansion. The monolayer consists...... of ~90% of lipid with 10% integrated proteins. Among its lipid compounds, di- palmitoyl-phosphatidylcholine (DPPC) dominates (~45wt%). No other lipid but DPPC was so far reported to be compressible to very high surface pressure (~70mN/m) before its monolayer collapsed. Its liquid......-expanded/liquid-condensed (LE/LC) phase transition at ~10mN/m is well known. Here we present results from Langmuir isotherm measurements that evidence a so far not documented second phase transition at elevated surface pressure Π (~50mN/m). The varying lateral structures of the monolayer at 8mN/m, 20mN/m, 30mN/m, 40mN/m, 50m...

  19. Static and dynamic electronic characterization of organic monolayers grafted on a silicon surface.

    Pluchery, O; Zhang, Y; Benbalagh, R; Caillard, L; Gallet, J J; Bournel, F; Lamic-Humblot, A-F; Salmeron, M; Chabal, Y J; Rochet, F


    Organic layers chemically grafted on silicon offer excellent interfaces that may open up the way for new organic-inorganic hybrid nanoelectronic devices. However, technological achievements rely on the precise electronic characterization of such organic layers. We have prepared ordered grafted organic monolayers (GOMs) on Si(111), sometimes termed self-assembled monolayers (SAMs), by a hydrosilylation reaction with either a 7-carbon or an 11-carbon alkyl chain, with further modification to obtain amine-terminated surfaces. X-ray photoelectron spectroscopy (XPS) is used to determine the band bending (∼ 0.3 eV), and ultraviolet photoelectron spectroscopy (UPS) to measure the work function (∼ 3.4 eV) and the HOMO edge. Scanning tunneling microscopy (STM) confirms that the GOM surface is clean and smooth. Finally, conductive AFM is used to measure electron transport through the monolayer and to identify transition between the tunneling and the field emission regimes. These organic monolayers offer a promising alternative to silicon dioxide thin films for fabricating metal-insulator-semiconductor (MIS) junctions. We show that gold nanoparticles can be covalently attached to mimic metallic nano-electrodes and that the electrical quality of the GOMs is completely preserved in the process.

  20. Interfacial Interactions and Nanostructure Changes in DPPG/HD Monolayer at the Air/Water Interface

    Huaze Zhu


    Full Text Available Lung surfactant (LS plays a crucial role in regulating surface tension during normal respiration cycles by decreasing the work associated with lung expansion and therefore decreases the metabolic energy consumed. Monolayer surfactant films composed of a mixture of phospholipids and spreading additives are of optional utility for applications in lung surfactant-based therapies. A simple, minimal model of such a lung surfactant system, composed of 1,2-dipalmitoyl-sn-glycero-3-[phosphor-rac-(1-gylcerol] (DPPG and hexadecanol (HD, was prepared, and the surface pressure-area (π-A isotherms and nanostructure characteristics of the binary mixture were investigated at the air/water interface using a combination of Langmuir-Blodgett (LB and atomic force microscopy (AFM techniques. Based on the regular solution theory, the miscibility and stability of the two components in the monolayer were analyzed in terms of compression modulus (Cs-1 , excess Gibbs free energy (ΔGexcπ , activity coefficients (γ, and interaction parameter (ξ. The results of this paper provide valuable insight into basic thermodynamics and nanostructure of mixed DPPG/HD monolayers; it is helpful to understand the thermodynamic behavior of HD as spreading additive in LS monolayer with a view toward characterizing potential improvements to LS performance brought about by addition of HD to lung phospholipids.

  1. Stiffness of lipid monolayers with phase coexistence.

    Caruso, Benjamín; Mangiarotti, Agustín; Wilke, Natalia


    The surface dilational modulus--or compressibility modulus--has been previously studied for monolayers composed of pure materials, where a jump in this modulus was related with the onset of percolation as a result of the establishment of a connected structure at the molecular level. In this work, we focused on monolayers composed of two components of low lateral miscibility. Our aim was to investigate the compressibility of mixed monolayers at pressures and compositions in the two-phase region of the phase diagram, in order to analyze the effect of the mechanical properties of each phase on the stiffness of the composite. In nine different systems with distinct molecular dipoles and charges, the stiffness of each phase and the texture at the plane of the monolayer were studied. In this way, we were able to analyze the general compressibility of two-phase lipid monolayers, regardless of the properties of their constituent parts. The results are discussed in the light of the following two hypotheses: first, the stiffness of the composite could be dominated by the stiffness of each phase as a weighted sum according to the percentage of each phase area, regardless of the distribution of the phases in the plane of the monolayer. Alternatively, the stiffness of the composite could be dominated by the mechanical properties of the continuous phase. Our results were better explained by this latter proposal, as in all the analyzed mixtures it was found that the mechanical properties of the percolating phase were the determining factors. The value of the compression modulus was closer to the value of the connected phase than to that of the dispersed phase, indicating that the bidimensional composites displayed mechanical properties that were related to the properties of each phases in a rather complex manner.

  2. Pattern formation in fatty acid-nanoparticle and lipid-nanoparticle mixed monolayers at water surface

    Choudhuri, M.; Datta, A.; Iyengar, A. N. Sekar; Janaki, M. S.


    Dodecanethiol-capped gold nanoparticles (AuNPs) are self-organized in two different amphiphilic monolayers one of which is a single-tailed fatty acid Stearic acid (StA) and the other a double-tailed lipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). In the StA-AuNP film the AuNPs self-organize to form an interconnected network of nanoclusters on compression while in the DMPC-AuNP film the AuNPs aggregate to form random, isolated clusters in the film. The long time evolution of the films at constant surface pressure reveals ring structures in the former and diffusion limited aggregates in the latter that with time evolve into an irregular porous maze of AuNPs in the DMPC film. The difference in structure of the AuNP patterns in the two films can be attributed to a difference in the lipophilic interactions between the NPs and the amphiphilic molecules. The mean square intensity fluctuations f(ln) calculated along a typical line for the 2D structures in both the films at initial and final stages of long time evolution reflect the structural changes in the films over time.

  3. Low temperature photoresponse of monolayer tungsten disulphide

    Bingchen Cao


    Full Text Available High photoresponse can be achieved in monolayers of transition metal dichalcogenides. However, the response times are inconveniently limited by defects. Here, we report low temperature photoresponse of monolayer tungsten disulphide prepared by exfoliation and chemical vapour deposition (CVD method. The exfoliated device exhibits n-type behaviour; while the CVD device exhibits intrinsic behaviour. In off state, the CVD device has four times larger ratio of photoresponse for laser on/off and photoresponse decay–rise times are 0.1 s (limited by our setup, while the exfoliated device has few seconds. These findings are discussed in terms of charge trapping and localization.

  4. Sub-THz Characterisation of Monolayer Graphene

    Ehsan Dadrasnia


    Full Text Available We explore the optical and electrical characteristics of monolayer graphene by using pulsed optoelectronic terahertz time-domain spectroscopy in the frequency range of 325–500 GHz based on fast direct measurements of phase and amplitude. We also show that these parameters can, however, be measured with higher resolution using a free space continuous wave measurement technique associated with a vector network analyzer that offers a good dynamic range. All the scattering parameters (both magnitude and phase are measured simultaneously. The Nicholson-Ross-Weir method is implemented to extract the monolayer graphene parameters at the aforementioned frequency range.

  5. Nonlinear optical studies of organic monolayers

    Shen, Y.R.


    Second-order nonlinear optical effects are forbidden in a medium with inversion symmetry, but are necessarily allowed at a surface where the inversion summary is broken. They are often sufficiently strong so that a submonolayer perturbation of the surface can be readily detected. They can therefore be used as effective tools to study monolayers adsorbed at various interfaces. We discuss here a number of recent experiments in which optical second harmonic generation (SHG) and sum-frequency generation (SFG) are employed to probe and characterize organic monolayers. 15 refs., 5 figs.

  6. High-Quality Alkyl Monolayers on Silicon Surfaces

    Sieval, A.B.; Linke, R.; Zuilhof, H.; Sudh"lter, E.J.R.


    Covalent attachment of functionalized monolayers onto silicon surfaces (see Figure for examples) is presented here as a strategy for surface modification. The preparation and structure of both unfunctionalized and functionalized alkyl-based monolayers are described, as are potential applications,

  7. Gold Nanoparticle Monolayers from Sequential Interfacial Ligand Exchange and Migration in a Three-Phase System

    Yang, Guang; Hallinan, Daniel T.


    Using a three-phase system, centimeter-scale monolayer gold nanoparticle (Au NP) films have been prepared that have long-range order and hydrophobic ligands. The system contains an interface between an aqueous phase containing Au NPs and an oil phase containing one of various types of amine ligands, and a water/air interface. As the Au NPs diffuse to the water/oil interface, ligand exchange takes place which temporarily traps them at the water/oil interface. The ligand-exchanged particles then spontaneously migrate to the air/water interface, where they self-assemble, forming a monolayer under certain conditions. The spontaneous formation of the NP film at the air/water interface was due to the minimization of the system Helmholtz free energy. However, the extent of surface functionalization was dictated by kinetics. This decouples interfacial ligand exchange from interfacial self-assembly, while maintaining the simplicity of a single system. The interparticle center-to-center distance was dictated by the amine ligand length. The Au NP monolayers exhibit tunable surface plasma resonance and excellent spatial homogeneity, which is useful for surface-enhanced Raman scattering. The “air/water/oil” self-assembly method developed here not only benefits the fundamental understanding of NP ligand conformations, but is also applicable to the manufacture of plasmonic nanoparticle devices with precisely designed optical properties.

  8. Gold Nanoparticle Monolayers from Sequential Interfacial Ligand Exchange and Migration in a Three-Phase System

    Yang, Guang; Hallinan, Daniel T.


    Using a three-phase system, centimeter-scale monolayer gold nanoparticle (Au NP) films have been prepared that have long-range order and hydrophobic ligands. The system contains an interface between an aqueous phase containing Au NPs and an oil phase containing one of various types of amine ligands, and a water/air interface. As the Au NPs diffuse to the water/oil interface, ligand exchange takes place which temporarily traps them at the water/oil interface. The ligand-exchanged particles then spontaneously migrate to the air/water interface, where they self-assemble, forming a monolayer under certain conditions. The spontaneous formation of the NP film at the air/water interface was due to the minimization of the system Helmholtz free energy. However, the extent of surface functionalization was dictated by kinetics. This decouples interfacial ligand exchange from interfacial self-assembly, while maintaining the simplicity of a single system. The interparticle center-to-center distance was dictated by the amine ligand length. The Au NP monolayers exhibit tunable surface plasma resonance and excellent spatial homogeneity, which is useful for surface-enhanced Raman scattering. The “air/water/oil” self-assembly method developed here not only benefits the fundamental understanding of NP ligand conformations, but is also applicable to the manufacture of plasmonic nanoparticle devices with precisely designed optical properties. PMID:27762394

  9. Bovine and human insulin adsorption at lipid monolayers: a comparison

    Sergio eMauri


    Full Text Available Insulin is a widely used peptide in protein research and it is utilised as a model peptide to understand the mechanics of fibril formation, which is believed to be the cause of diseases such as Alzheimer and Creutzfeld-Jakob syndrome. Insulin has been used as a model system due to its biomedical relevance, small size and relatively simple tertiary structure. The adsorption of insu lin on a variety of surfaces has become the focus of numerous studies lately. These works have helped in elucidating the consequence of surface/protein hydrophilic/hydrophobic interaction in terms of protein refolding and aggregation. Unfortunately, such model surfaces differ significantly from physiological surfaces. Here we spectroscopically investigate the adsorption of insulin at lipid monolayers, to further our understanding of the interaction of insulin with biological surfaces.In particular we study the effect of minor mutations of insulin’s primary amino acid sequence on its interaction with 1,2-Dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG model lipid layers. We probe the structure of bovine and human insulin at the lipid/water interface using sum frequency generation spectroscopy (SFG. The SFG experiments are complemented with XPS analysis of Langmuir-Schaefer deposited lipid/insulin films. We find that bovine and human insulin, even though very similar in sequence, show a substantially different behavior when interacting with lipid films.

  10. Glitter in a 2D monolayer.

    Yang, Li-Ming; Dornfeld, Matthew; Frauenheim, Thomas; Ganz, Eric


    We predict a highly stable and robust atomically thin gold monolayer with a hexagonal close packed lattice stabilized by metallic bonding with contributions from strong relativistic effects and aurophilic interactions. We have shown that the framework of the Au monolayer can survive 10 ps MD annealing simulations up to 1400 K. The framework is also able to survive large motions out of the plane. Due to the smaller number of bonds per atom in the 2D layer compared to the 3D bulk we observe significantly enhanced energy per bond (0.94 vs. 0.52 eV per bond). This is similar to the increase in bond strength going from 3D diamond to 2D graphene. It is a non-magnetic metal, and was found to be the global minima in the 2D space. Phonon dispersion calculations demonstrate high kinetic stability with no negative modes. This 2D gold monolayer corresponds to the top monolayer of the bulk Au(111) face-centered cubic lattice. The close-packed lattice maximizes the aurophilic interactions. We find that the electrons are completely delocalized in the plane and behave as 2D nearly free electron gas. We hope that the present work can inspire the experimental fabrication of novel free standing 2D metal systems.

  11. Nanotubes based on monolayer blue phosphorus

    Montes Muñoz, Enrique


    We demonstrate structural stability of monolayer zigzag and armchair blue phosphorus nanotubes by means of molecular dynamics simulations. The vibrational spectrum and electronic band structure are determined and analyzed as functions of the tube diameter and axial strain. The nanotubes are found to be semiconductors with a sensitive indirect band gap that allows flexible tuning.

  12. Non-rotator phases in phospholipid monolayers?

    Kenn, R.M.; Kjær, K.; Möhwald, H.


    Monolayers of diacylphosphatidylethanolamines at the air/water interface are studied by grazing incidence X-ray diffraction. The results prove the existence of phases which show analogies with the rotator phases of single-chain surfactants: hexagonal tail lattice with no tilt; rectangular lattice...

  13. Statistical mechanics of a lipid monolayer

    Kox, A.J.; Wiegel, F.W.


    We calculate from first principles the equation of state of a simple type of membrane: a monolayer consisting of lipid chain molecules with short-range repulsive and long-range attractive forces. An approximate solution to the packing problem of the hydrocarbon chains is obtained by using a mathemat

  14. Semiconductor monolayer assemblies with oriented crystal faces

    Ma, Guijun


    Fabrication of two-dimensional monolayers of crystalline oxide and oxynitride particles was attempted on glass plate substrates. X-Ray diffraction patterns of the assemblies show only specific crystal facets, indicative of the uniform orientation of the particles on the substrate. The selectivity afforded by this immobilization technique enables the organization of randomly distributed polycrystalline powders in a controlled manner.

  15. Structure of cholesterol/ceramide monolayer mixtures

    Scheffer, L.; Solomonov, I.; Weygand, M.J.


    The structure of monolayers of cholesterol/ ceramide mixtures was investigated using grazing incidence x-ray diffraction, immunofluorescence, and atomic force microscopy techniques. Grazing incidence x-ray diffraction measurements showed the existence of a crystalline mixed phase of the two...

  16. Edge conduction in monolayer WTe2

    Fei, Zaiyao; Palomaki, Tauno; Wu, Sanfeng; Zhao, Wenjin; Cai, Xinghan; Sun, Bosong; Nguyen, Paul; Finney, Joseph; Xu, Xiaodong; Cobden, David H.


    A two-dimensional topological insulator (2DTI) is guaranteed to have a helical one-dimensional edge mode in which spin is locked to momentum, producing the quantum spin Hall effect and prohibiting elastic backscattering at zero magnetic field. No monolayer material has yet been shown to be a 2DTI, but recently the Weyl semimetal WTe2 was predicted to become a 2DTI in monolayer form if a bulk gap opens. Here, we report that, at temperatures below about 100 K, monolayer WTe2 does become insulating in its interior, while the edges still conduct. The edge conduction is strongly suppressed by an in-plane magnetic field and is independent of gate voltage, save for mesoscopic fluctuations that grow on cooling due to a zero-bias anomaly, which reduces the linear-response conductance. Bilayer WTe2 also becomes insulating at low temperatures but does not show edge conduction. Many of these observations are consistent with monolayer WTe2 being a 2DTI. However, the low-temperature edge conductance, for contacts spacings down to 150 nm, never reaches values higher than ~20 μS, about half the predicted value of e2/h, suggesting significant elastic scattering in the edge.

  17. Molecular diffusion in monolayer and submonolayer nitrogen

    Hansen, Flemming Yssing; Bruch, Ludwig Walter


    The orientational and translational motions in a monolayer fluid of physisorbed molecular nitrogen are treated using molecular dynamics simulations. Dynamical response functions and several approximations to the coefficient of translational diffusion are determined for adsorption on the basal pla...... where the ballistic approximation to the translational molecular self-correlation function is accurate....

  18. A dielectric model of self-assembled monolayer interfaces by capacitive spectroscopy.

    Góes, Márcio S; Rahman, Habibur; Ryall, Joshua; Davis, Jason J; Bueno, Paulo R


    The presence of self-assembled monolayers at an electrode introduces capacitance and resistance contributions that can profoundly affect subsequently observed electronic characteristics. Despite the impact of this on any voltammetry, these contributions are not directly resolvable with any clarity by standard electrochemical means. A capacitive analysis of such interfaces (by capacitance spectroscopy), introduced here, enables a clean mapping of these features and additionally presents a means of studying layer polarizability and Cole-Cole relaxation effects. The resolved resistive term contributes directly to an intrinsic monolayer uncompensated resistance that has a linear dependence on the layer thickness. The dielectric model proposed is fully aligned with the classic Helmholtz plate capacitor model and additionally explains the inherently associated resistive features of molecular films.

  19. Strain-relief by single dislocation loops in calcite crystals grown on self-assembled monolayers

    Ihli, Johannes; Clark, Jesse N.; Côté, Alexander S.; Kim, Yi-Yeoun; Schenk, Anna S.; Kulak, Alexander N.; Comyn, Timothy P.; Chammas, Oliver; Harder, Ross J.; Duffy, Dorothy M.; Robinson, Ian K.; Meldrum, Fiona C.


    Most of our knowledge of dislocation-mediated stress relaxation during epitaxial crystal growth comes from the study of inorganic heterostructures. Here we use Bragg coherent diffraction imaging to investigate a contrasting system, the epitaxial growth of calcite (CaCO3) crystals on organic self-assembled monolayers, where these are widely used as a model for biomineralization processes. The calcite crystals are imaged to simultaneously visualize the crystal morphology and internal strain fields. Our data reveal that each crystal possesses a single dislocation loop that occupies a common position in every crystal. The loops exhibit entirely different geometries to misfit dislocations generated in conventional epitaxial thin films and are suggested to form in response to the stress field, arising from interfacial defects and the nanoscale roughness of the substrate. This work provides unique insight into how self-assembled monolayers control the growth of inorganic crystals and demonstrates important differences as compared with inorganic substrates.

  20. Preparation of organothiol self-assembled monolayers for use in templated crystallization.

    Nielsen, Michael H; Lee, Jonathan R I


    Organothiol self-assembled monolayers (SAMs) have garnered much interest as templates for oriented crystallization of biominerals. While, on the surface, SAM preparation appears to be straightforward, there are many subtleties that may yield films that lack the desired effect on the mineral component in subsequent use for templated mineralization. Herein, we discuss literature that uses organothiol SAMs to understand various principles in biomineralization, to motivate the following discussion of preparation procedures and pitfalls that may arise while working with SAMs. We provide a range of parameters for each element of a SAM-forming process, which have been shown in the literature to produce monolayers suitable for mineralization experiments, and close with a step-by-step procedure, based on findings in the cited literature, that yields functional SAMs with very high fidelity.

  1. Self-assembling monolayers of helical oligopeptides with applications in molecular electronics

    Strong, A E


    prepared. Transformation of the two (Trt)Cys residues of the resin-bound peptide to the intramolecular disulphide by iodine was achieved in acetonitrile but not in DMF. CD suggested that the conformation of this peptide was a mixture of helix and random coil. Films of the peptide-disulphide and the peptide-dithiol adsorbed from protic solvents were characterised as multilayers by ellipsometry. However CV and ellipsometry showed that a monolayer was successfully prepared from acetonitrile. Future targets for improving and extending this method to form monolayers of linked disulphides are presented. The aim of this project was to develop a generic method of preparing a 'molecular architecture' containing functional groups on a surface at predetermined relative positions several nm apart. This would be of great utility in molecular electronics, chemical sensors and other fields. It was proposed that such an architecture could be prepared on gold using linked, helical oligopeptides that contained the components o...

  2. Monolayer to Bilayer Structural Transition in Confined Pyrrolidinium-Based Ionic Liquids.

    Smith, Alexander M; Lovelock, Kevin R J; Gosvami, Nitya Nand; Licence, Peter; Dolan, Andrew; Welton, Tom; Perkin, Susan


    Ionic liquids can be intricately nanostructured in the bulk and at interfaces resulting from a delicate interplay between interionic and surface forces. Here we report the structuring of a series of dialkylpyrrolidinium-based ionic liquids induced by confinement. The ionic liquids containing cations with shorter alkyl chain substituents form alternating cation-anion monolayer structures on confinement to a thin film, whereas a cation with a longer alkyl chain substituent leads to bilayer formation. The crossover from monolayer to bilayer structure occurs between chain lengths of n = 8 and 10 for these pyrrolidinium-based ionic liquids. The bilayer structure for n = 10 involves full interdigitation of the alkyl chains; this is in contrast with previous observations for imidazolium-based ionic liquids. The results are pertinent to these liquids' application as electrolytes, where the electrolyte is confined inside the pores of a nanoporous electrode, for example, in devices such as supercapacitors or batteries.

  3. Pit Formation during the Self-Assembly of Dithiol Monolayers on Au(111)

    Macdairmid, A. R.; Cappello, M. L.; Keeler, W. J.; Banks, J. T.; Gallagher, M. C.


    The formation of pits one gold atom deep during the growth of alkanethiol monolayers on Au(111), has been observed previously by others. Explanations for pit formation include etching of the substrate, or mass transport of gold atom + thiol molecule on the surface, due to changes in surface energy^1. We have investigated the structure of dithiothreitol (DTT) SAMs on Au(111). Ex situ STM measurements indicate similar pitting occurs during formation of the dithiol monolayer. The degree of pitting depends on exposure time, sample temperature during formation, and subsequent annealing of the sample. Pitting is enhanced considerasbly when DTT is coordinated with Ti, in fact DTT/Ti films exhibit considerable pit motion during STM imaging. ^1 F. Teran et al. Electrochimica Acta 44, 1053 (1998).

  4. X-ray diffraction studies of organic monolayers on the surface of water

    Dutta, P.; Peng, J.B.; Lin, B.; Ketterson, J.B.; Prakash, M.; Georgopoulos, P.; Ehrlich, S.


    We have used synchrotron radiation to study organic monolayers on water (''Langmuir films''). At high monolayer pressures, lead stearate (Pb(C/sub 17/H/sub 35/COO)/sub 2/) shows a powder peak at 1.60 A/sup -1/, implying an area per unit cell of 17.8 A/sup 2/ if the lattice is triangular. The correlation length is about 250 A. Lignoceric acid (C/sub 23/H/sub 47/COOH) shows a similar peak even though no heavy ions are attached. When the pressure is reduced, the peak in lead stearate does not observably move or broaden; below the ''knee'' in the isotherm, however, the peak height decreases slowly with increasing area, implying a first-order melting transition.

  5. Nanoparticle monolayer-based flexible strain gauge with ultrafast dynamic response for acoustic vibration detection

    Lizhi Yi[1; Weihong Jiao[1; Ke Wu[1; Lihua Qian[1; Xunxing Yu[2; Qi Xia[2; Kuanmin Mao[2; Songliu Yuan[1; Shuai Wang[3; Yingtao Jiang[4


    The relatively poor dynamic response of current flexible strain gauges has prevented their wide adoption in portable electronics. In this work, we present a greatly improved flexible strain gauge, where one strip of Au nanoparticle (NP) monolayer assembled on a polyethylene terephthalate film is utilized as the active unit. The proposed flexible gauge is capable of responding to applied stimuli without detectable hysteresis via electron tunneling between adjacent nanoparticles within the Au NP monolayer. Based on experimental quantification of the time and frequency domain dependence of the electrical resistance of the proposed strain gauge, acoustic vibrations in the frequency range of 1 to 20,000 Hz could be reliably detected. In addition to being used to measure musical tone, audible speech, and creature vocalization, as demonstrated in this study, the ultrafast dynamic response of this flexible strain gauge can be used in a wide range of applications, including miniaturized vibratory sensors, safe entrance guard management systems, and ultrasensitive pressure sensors.

  6. Q-factors of CVD monolayer graphene and graphite inductors

    Wang, Zidong; Zhang, Qingping; Peng, Pei; Tian, Zhongzheng; Ren, Liming; Zhang, Xing; Huang, Ru; Wen, Jincai; Fu, Yunyi


    A carbon-based inductor may serve as an important passive component in a carbon-based radio-frequency (RF) integrated circuit (IC). In this work, chemical vapor deposition (CVD) synthesized monolayer graphene and graphite inductors are fabricated and their Q-factors are investigated. We find that the large series resistance of signal path (including coil resistance and contact resistance) in monolayer graphene inductors causes negative Q-factors at the whole frequency range in measurement. Comparatively, some of the graphite inductors have all of their Q-factors above zero, due to their small signal path resistance. We also note that some other graphite inductors have negative Q-factor values at low frequency regions, but positive Q-factor values at high frequency regions. With an equivalent circuit model, we confirm that the negative Q-factors of some graphite inductors at low frequency regions are related to their relatively large contact resistances, and we are able to eliminate these negative Q-factors by improving the graphite-metal contact. Furthermore, the peak Q-factor (Q p) can be enhanced by lowering down the resistance of graphite coil. For an optimized 3/4-turn graphite inductor, the measured maximum Q-factor (Q m) can reach 2.36 and the peak Q-factor is theoretically predicted by the equivalent circuit to be as high as 6.46 at a high resonant frequency, which is beyond the testing frequency range. This research indicates that CVD synthesized graphite thin film is more suitable than graphene for fabricating inductors in carbon-based RF IC in the future.

  7. Study of the aggregation of human insulin Langmuir monolayer.

    Liu, Wei; Johnson, Sheba; Micic, Miodrag; Orbulescu, Jhony; Whyte, Jeffrey; Garcia, Andrew R; Leblanc, Roger M


    The human insulin (HI) Langmuir monolayer at the air-water interface was systematically investigated in the presence and absence of Zn(II) ions in the subphase. HI samples were dissolved in acidic (pH 2) and basic (pH 9) aqueous solutions and then spread at the air-water interface. Spectroscopic data of aqueous solutions of HI show a difference in HI conformation at different pH values. Moreover, the dynamics of the insulin protein showed a dependence on the concentration of Zn(II) ions. In the absence of Zn(II) ions in the subphase, the acidic and basic solutions showed similar behavior at the air-water interface. In the presence of Zn(II) ions in the subphase, the surface pressure-area and surface potential-area isotherms suggest that HI may aggregate at the air-water interface. It was observed that increasing the concentration of Zn(II) ions in the acidic (pH 2) aqueous solution of HI led to an increase of the area at a specific surface pressure. It was also seen that the conformation of HI in the basic (pH 9) medium had a reverse effect (decrease in the surface area) with the increase of the concentration of Zn(II) ions in solution. From the compression-decompression cycles we can conclude that the aggregated HI film at air-water interface is not stable and tends to restore a monolayer of monomers. These results were confirmed from UV-vis and fluorescence spectroscopy analysis. Infrared reflection-absorption and circular dichroism spectroscopy techniques were used to determine the secondary structure and orientation changes of HI by zinc ions. Generally, the aggregation process leads to a conformation change from α-helix to β-strand and β-turn, and at the air-water interface, the aggregation process was likewise seen to induce specific orientations for HI in the acidic and basic media. A proposed surface orientation model is presented here as an explanation to the experimental data, shedding light for further research on the behavior of insulin as a Langmuir

  8. Surface enhanced second harmonic generation from macrocycle, catenane, and rotaxane thin films : Experiments and theory

    Arfaoui, [No Value; Bermudez, [No Value; Bottari, G; De Nadai, C; Jalkanen, JP; Kajzar, F; Leigh, DA; Lubomska, M; Mendoza, SM; Niziol, J; Rudolf, P; Zerbetto, F; Arfaoui, Imad; Bermúdez, Verónica; Jalkanen, Jukka-Pekka


    Surface enhanced second harmonic generation (SE SHG) experiments on molecular structures, macrocycles, catenanes, and rotaxanes, deposited as monolayers and multilayers by vacuum sublimation on silver, are reported. The measurements show that the molecules form ordered thin films, where the highest

  9. Improvements in the characterization of the crystalline structure of acid-terminated alkanethiol self-assembled monolayers on Au(111).

    Mendoza, Sandra M; Arfaoui, Imad; Zanarini, Simone; Paolucci, Francesco; Rudolf, Petra


    We report a study of acid-terminated self-assembled monolayers of alkanethiols of different length, 11-mercaptoundecanoic acid (11-MUA) and 16-mercaptohexadecanoic acid (16-MHDA), on Au(111). Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and contact angle techniques were used for characterization, and the results were compared with those obtained from n-alkanethiols of similar chain length, providing a detailed description of the two-dimensional crystalline structure. Molecular resolution STM images show that 11-MUA forms a dense-packed monolayer arranged in a (square root 3 x square root 3)R30 degrees structure with a c(2 x 4) superlattice, where the simple hexagonal phase, the c(2 x 4) superlattice, and nonordered areas coexist. 16-MHDA assembles in a uniform monolayer with similar morphology to that of 11-MUA, but molecular resolution could not be reached in STM due to both the hydrophilicity of the acid groups and the poor conductivity of the thick monolayer. Nevertheless, the monolayer thicknesses estimated by XPS and electrochemistry and the highly blocking character of the film observed by electrochemistry as well as the low water contact angle are consistent with 16-MHDA molecules forming a compact monolayer on the Au(111) substrate with fully extended alkyl chains and acid groups pointing away from the surface. The results obtained for 16-MHDA were reproducible under different preparation conditions such as the addition or omission of acetic acid to the ethanolic solution. Contrary to other reports, we demonstrate that ordered acid-terminated self-assembled monolayers are obtained with the same preparation conditions as those of the methyl-terminated ones, without any additional treatment.

  10. Interaction of L-Phenylalanine with a Phospholipid Monolayer at the Water-Air Interface.

    Griffith, Elizabeth C; Perkins, Russell J; Telesford, Dana-Marie; Adams, Ellen M; Cwiklik, Lukasz; Allen, Heather C; Roeselová, Martina; Vaida, Veronica


    The interaction of L-phenylalanine with a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayer at the air-water interface was explored using a combination of experimental techniques and molecular dynamics (MD) simulations. By means of Langmuir trough methods and Brewster angle microscopy, L-phenylalanine was shown to significantly alter the interfacial tension and the surface domain morphology of the DPPC film. In addition, confocal microscopy was used to explore the aggregation state of L-phenylalanine in the bulk aqueous phase. Finally, MD simulations were performed to gain molecular-level information on the interactions of L-phenylalanine and DPPC at the interface. Taken together, these results show that L-phenylalanine intercalates into a DPPC film at the air-water interface, thereby affecting the surface tension, phase morphology, and ordering of the DPPC film. The results are discussed in the context of biological systems and the mechanism of diseases such as phenylketonuria.

  11. Molecular phospholipid films on solid supports

    Czolkos, Ilja; Jesorka, Aldo; Orwar, Owe


    Phospholipid membranes are versatile structures for mimicking biological surfaces. Bilayer and monolayer membranes can be formed on solid supports, leading to enhanced stability and accessibility of the biomimetic molecular film. This has facilitated functional studies of membrane proteins...... stable lipid membranes. In this review, the current state of the art of molecularly thin lipid layer fabrication is presented with an emphasis on support materials, film formation mechanisms, characterisation methods, and applications....

  12. Ligand Replacement Approach to Raman-Responded Molecularly Imprinted Monolayer for Rapid Determination of Penicilloic Acid in Penicillin.

    Zhang, Liying; Jin, Yang; Huang, Xiaoyan; Zhou, Yujie; Du, Shuhu; Zhang, Zhongping


    Penicilloic acid (PA) is a degraded byproduct of penicillin and often causes fatal allergies to humans, but its rapid detection in penicillin drugs remains a challenge due to its similarity to the mother structure of penicillin. Here, we reported a ligand-replaced molecularly imprinted monolayer strategy on a surface-enhanced Raman scattering (SERS) substrate for the specific recognition and rapid detection of Raman-inactive PA in penicillin. The bis(phenylenediamine)-Cu(2+)-PA complex was first synthesized and stabilized onto the surface of silver nanoparticle film that was fabricated by a bromide ion-added silver mirror reaction. A molecularly imprinted monolayer was formed by the further modification of alkanethiol around the stabilized complex on the Ag film substrate, and the imprinted recognition site was then created by the replacement of the complex template with Raman-active probe molecule p-aminothiophenol. When PA rebound into the imprinted site in the alkanethiol monolayer, the SERS signal of p-aminothiophenol exhibited remarkable enhancement with a detection limit of 0.10 nM. The imprinted monolayer can efficiently exclude the interference of penicillin and thus provides a selective determination of 0.10‰ (w/w) PA in penicillin, which is about 1 order of magnitude lower than the prescribed residual amount of 1.0‰. The strategy reported here is simple, rapid and inexpensive compared to the traditional chromatography-based methods.

  13. A Novel Synthesis of Two-dimensional Nanopatterned TiO2 Thin Film

    Ming Xian LIU; Li Hua GAN; Gen CHEN; Zi Jie XU; Zhi Xian HAO; Long Wu CHEN


    A novel two-dimensional nanopatterned TiO2 thin film has been synthesized through the interaction between cationic Gemini surfactant molecules and the prepared TiO2 colloid nanoparticles with average diameters of 8 nm by controlling the surface pressure of the monolayer. TEM photographs from the formed Gemini-TiO2 composite monolayer confirm that the prepared TiO2 film is of a branch nanopattem.

  14. Effect of 3-Aminopropyltriethoxysilane Monolayer Self-Assembled Quartz Substrate on the Quality of Vapor Phase-Polymerized Poly(3,4-ethylenedioxythiophene) Nanofilm.

    Choi, Byoungbok; Choi, Sangil; Sohn, Honglae; Kim, Sungsoo


    Polymer thin film coated on the delay line section of a surface acoustic wave (SAW) sensor has been a main focus in sensor industry to improve its sensitivity. In this study, for an effort to build a highly sensitive SAW sensor, a versatile conducting polymer, Poly(3,4-ethylenedioxythiophene) (PEDOT), has been vapor phase polymerized on 3-aminopropyltriethoxysilane (APS) monolayer self-assembled quartz substrate, which is a representative piezoelectric materials for SAW sensor. And then, the quality and electrical properties of the thin film were evaluated by several thin film analyzing tools such as contact angle analyzer, FE-SEM, optical microscope, adhesion test and 4 point probe. From the evaluation, it was discovered that PEDOT nanofilm is highly smooth and dense, and it is strongly adhered to the substrate particularly when the quartz surface was coated with APS monolayer. Such good quality PEDOT thin film could be a potential candidate for a base platform of highly sensitive SAW sensor devices.

  15. Mechanical Properties and Thermal Stability of TiN/Ta Multilayer Film Deposited by Ion Beam Assisted Deposition

    Hongfei Shang


    Full Text Available TiN/Ta multilayer film with a modulation period of 5.6 nm and modulation ratio of 1 : 1 was produced by ion beam assisted deposition. Microstructure of the as-deposited TiN/Ta multilayer film was observed by transmission electron microscopy and mechanical properties were investigated. Residual stress in the TiN/Ta multilayer film was about 72% of that of a TiN monolayer film with equivalent thickness deposited under the same conditions. Partial residual stress was released in the Ta sublayers during deposition, which led to the decrease of the residual stress of the TiN/Ta multilayer film. Nanohardness (H of the TiN/Ta multilayer film was 24 GPa, 14% higher than that of the TiN monolayer film. It is suggested that the increase of the nanohardness is due to the introduction of the Ta layers which restrained the growth of TiN crystal and led to the decrease of the grain size. A significant increase (3.5 times of the H3/E2 (E elastic modulus value indicated that the TiN/Ta multilayer film has higher elasticity than the TiN monolayer film. The Lc (critical load in nano-scratch test value of the TiN monolayer film was 45 mN, which was far lower than that of the TiN/Ta multilayer film (around 75 mN. Results of the indentation test showed a higher fracture toughness of the TiN/Ta multilayer film than that of the TiN monolayer film. Results of differential scanning calorimetric (DSC and thermo gravimetric analysis (TGA indicate that the TiN/Ta multilayer film has better thermal stability than the TiN monolayer film.

  16. Self-assembly of large-scale crack-free gold nanoparticle films using a ‘drain-to-deposit’ strategy

    Yang, Guang; Hallinan, Daniel T.


    Gold nanoparticles are widely studied due to the ease of controlled synthesis, facile surface modification, and interesting physical properties. However, a technique for depositing large-area, crack-free monolayers on solid substrates is lacking. Herein is presented a method for accomplishing this. Spherical gold nanoparticles were synthesized as an aqueous dispersion. Assembly into monolayers and ligand exchange occurred simultaneously at an organic/aqueous interface. Then the monolayer film was deposited onto arbitrary solid substrates by slowly pumping out the lower, aqueous phase. This allowed the monolayer film (and liquid–liquid interface) to descend without significant disturbance, eventually reaching substrates contained in the aqueous phase. The resulting macroscopic quality of the films was found to be superior to films transferred by Langmuir techniques. The surface plasmon resonance and Raman enhancement of the films were evaluated and found to be uniform across the surface of each film.

  17. Self-assembly of large-scale crack-free gold nanoparticle films using a ‘drain-to-deposit’ strategy

    Yang, Guang; Hallinan, Daniel T., Jr.


    Gold nanoparticles are widely studied due to the ease of controlled synthesis, facile surface modification, and interesting physical properties. However, a technique for depositing large-area, crack-free monolayers on solid substrates is lacking. Herein is presented a method for accomplishing this. Spherical gold nanoparticles were synthesized as an aqueous dispersion. Assembly into monolayers and ligand exchange occurred simultaneously at an organic/aqueous interface. Then the monolayer film was deposited onto arbitrary solid substrates by slowly pumping out the lower, aqueous phase. This allowed the monolayer film (and liquid-liquid interface) to descend without significant disturbance, eventually reaching substrates contained in the aqueous phase. The resulting macroscopic quality of the films was found to be superior to films transferred by Langmuir techniques. The surface plasmon resonance and Raman enhancement of the films were evaluated and found to be uniform across the surface of each film.

  18. Effect of the conditions of transfer on the structure and optical properties of Langmuir graphene oxide films during deposition on a substrate

    Seliverstova, E. V.; Ibrayev, N. Kh.; Dzhanabekova, R. Kh.


    The effect the solvent and transfer pressure of graphene oxide (SLGO) Langmuir-Blodgett films on the physicochemical properties of monolayers, and on their structural and optical properties, is studied. Examination of the physicochemical properties of SLGO monolayers on subphase surfaces that are formed from SLGO dispersions in different organic solvents reveals that monolayer behavior is virtually independent of the solvent. Electron microscope and optical studies show that the monolayers formed from SLGO dispersions in DMF and acetone have the highest transfer coefficients. It is concluded that the structural heterogeneity of the surfaces of graphene oxide films results from simultaneous effect of electrostatic interactions between graphene oxide particles and Van der Waals interactions with the solvation shell of the particles. Studies focusing on the effect the pressure of transferring a graphene oxide monolayer onto the surface of a solid substrate has on structural features of LB films show that films produced at low surface pressures have more homogeneous structures.

  19. Towards the hybrid organic semiconductor fet (hosfet) : electrical and electrochemical characterization of functionalized and unfunctionalized, covalently bound organic monolayers on silicon surfaces

    Faber, Erik Jouwert


    Since their introduction in 1993 the class of covalently bound organic monolayers on oxide free silicon surfaces have found their way to multiple application fields such as passivation layers in solar cells, masking layers in lithographic processing, insulating films in hybrid moleculesilicon electr

  20. Thermodynamic behavior of D-sphingosine/cholesterol monolayers and the topography observed by AFM

    HAO ChangChun; SUN RunGuang; ZHANG Jing; CHANG YiGuang; NIU ChunLing


    Lipid rafts are of a dynamic microdomain structure found in recent years, enriched in sphingolipids, cholesterol and particular proteins. The change of structure and function of lipid rafts could result in many diseases. In this work, the monolayer behavior of mixed systems of D-sphingosine with choles-terol was investigated in terms of the mean surface area per molecule (Am), excess molecular area (△Aex), surface excess Gibbs energy (△Gex), interaction parameter (ω) activity coefficients (f1 and f2) as well as elasticity (Cs-1) of formed films. The deposited Langmuir-Blodgett (LB) monolayers were inves-tigated with atomic force microscopy (AFM). Thermodynamic analysis indicates △Aex and △Gex in the binary systems with negative deviations from the ideal behavior, suggesting attractive interaction be-tween molecules. The stability, elasticity and activity coefficients show a marked dependence on the mole faction of D-sphingosine. The results of observation by AFM show that the single D-sphingosine molecular film took on small granule structure. When mixing the D-sphingosine and cholesterol at dif-ferent ratios, the mixed films transform from the chains structure to larger slice and net coexisting structure with the increasing of the cholesterol content. In the end, pure cholesterol forms more ag-gregated structure. AFM experiments effectively support the above findings and interpretation.

  1. Growth and spectroscopic characterization of monolayer and few-layer hexagonal boron nitride on metal substrates

    Feigelson, Boris N.; Bermudez, Victor M.; Hite, Jennifer K.; Robinson, Zachary R.; Wheeler, Virginia D.; Sridhara, Karthik; Hernández, Sandra C.


    Atomically thin two dimensional hexagonal boron nitride (2D h-BN) is one of the key materials in the development of new van der Waals heterostructures due to its outstanding properties including an atomically smooth surface, high thermal conductivity, high mechanical strength, chemical inertness and high electrical resistance. The development of 2D h-BN growth is still in the early stages and largely depends on rapid and accurate characterization of the grown monolayer or few layers h-BN films. This paper demonstrates a new approach to characterizing monolayer h-BN films directly on metal substrates by grazing-incidence infrared reflection absorption spectroscopy (IRRAS). Using h-BN films grown by atmospheric-pressure chemical vapor deposition on Cu and Ni substrates, two new sub-bands are found for the A2u out-of-plane stretching mode. It is shown, using both experimental and computational methods, that the lower-energy sub-band is related to 2D h-BN coupled with substrate, while the higher energy sub-band is related to decoupled (or free-standing) 2D h-BN. It is further shown that this newly-observed fine structure in the A2u mode can be used to assess, quickly and easily, the homogeneity of the h-BN-metal interface and the effects of metal surface contamination on adhesion of the layer.

  2. Spontaneous phase separation during self-assembly in bi-dispersed spherical iron oxide nanoparticle monolayers

    Stanley, Jacob; Boucheron, Leandra; Shpyrko, Oleg, E-mail:, E-mail: [Department of Physics, University of California, San Diego, La Jolla, California 92093 (United States); Lin, Binhua, E-mail:, E-mail:; Meron, Mati [Center for Advanced Radiation Sources (CARS), University of Chicago, Chicago, Illinois 60637 (United States)


    Recent developments in the synthesis of iron oxide nanoparticles have resulted in the ability to fabricate roughly spherical particles with extremely high size uniformity (low polydispersity). These particles can form self-assembled monolayer films at an air-water interface. When the polydispersity of the particles is low, these monolayers can be well-ordered over a length scale dozens of times the particle size. The van der Waals force between the particles is what drives this self-assembly. Through the use of Grazing Incidence X-Ray Diffraction we demonstrate that, when these films are formed at the liquid surface from bi-dispersed solutions containing 10 and 20 nm spherical particles suspended in chloroform, the particles phase separate into well-ordered patches during the self-assembly process. Furthermore, the domain sizes of these phase separated regions are at most 2–3 times smaller than that of a film comprising only mono-dispersed particles and their degree of disorder is comparable. This is shown for multiple solutions with differing ratios of 10 and 20 nm particles.

  3. Thermodynamic behavior of D-sphingosine/cholesterol monolayers and the topography observed by AFM


    Lipid rafts are of a dynamic microdomain structure found in recent years,enriched in sphingolipids,cholesterol and particular proteins.The change of structure and function of lipid rafts could result in many diseases.In this work,the monolayer behavior of mixed systems of D-sphingosine with choles-terol was investigated in terms of the mean surface area per molecule(Am),excess molecular area(Aex),surface excess Gibbs energy(Gex),interaction parameter(ω),activity coefficients(1 and 2) as well as elasticity(Cs1) of formed films.The deposited Langmuir-Blodgett(LB) monolayers were inves-tigated with atomic force microscopy(AFM).Thermodynamic analysis indicates Aex and Gex in the binary systems with negative deviations from the ideal behavior,suggesting attractive interaction be-tween molecules.The stability,elasticity and activity coefficients show a marked dependence on the mole faction of D-sphingosine.The results of observation by AFM show that the single D-sphingosine molecular film took on small granule structure.When mixing the D-sphingosine and cholesterol at dif-ferent ratios,the mixed films transform from the chains structure to larger slice and net coexisting structure with the increasing of the cholesterol content.In the end,pure cholesterol forms more ag-gregated structure.AFM experiments effectively support the above findings and interpretation.

  4. Epitaxial growth by monolayer restricted galvanic displacement

    Vasilić Rastko


    Full Text Available The development of a new method for epitaxial growth of metals in solution by galvanic displacement of layers pre-deposited by underpotential deposition (UPD was discussed and experimentally illustrated throughout the lecture. Cyclic voltammetry (CV and scanning tunneling microscopy (STM are employed to carry out and monitor a “quasi-perfect”, two-dimensional growth of Ag on Au(111, Cu on Ag(111, and Cu on Au(111 by repetitive galvanic displacement of underpotentially deposited monolayers. A comparative study emphasizes the displacement stoichiometry as an efficient tool for thickness control during the deposition process and as a key parameter that affects the deposit morphology. The excellent quality of layers deposited by monolayer-restricted galvanic displacement is manifested by a steady UPD voltammetry and ascertained by a flat and uniform surface morphology maintained during the entire growth process.

  5. Transport measurement of Li doped monolayer graphene

    Khademi, Ali; Sajadi, Ebrahim; Dosanjh, Pinder; Folk, Joshua; Stöhr, Alexander; Forti, Stiven; Starke, Ulrich

    Lithium adatoms on monolayer graphene have been predicted to induce superconductivity with a critical temperature near 8 K, and recent experimental evidence by ARPES indicates a critical temperature nearly that high. Encouraged by these results, we investigated the effects of lithium deposited at cryogenic temperatures on the electronic transport properties of epitaxial and CVD monolayer graphene down to 3 K. The change of charge carrier density due to Li deposition was monitored both by the gate voltage shift of the Dirac point and by Hall measurements, in low and high doping regimes. In the high doping regime, a saturation density of 2×1013 cm-2 was observed independent of sample type, initial carrier density and deposition conditions. No signatures of superconductivity were observed down to 3 K.

  6. Fracture Characteristics of Monolayer CVD-Graphene

    Hwangbo, Yun; Lee, Choong-Kwang; Kim, Sang-Min; Kim, Jae-Hyun; Kim, Kwang-Seop; Jang, Bongkyun; Lee, Hak-Joo; Lee, Seoung-Ki; Kim, Seong-Su; Ahn, Jong-Hyun; Lee, Seung-Mo


    We have observed and analyzed the fracture characteristics of the monolayer CVD-graphene using pressure bulge testing setup. The monolayer CVD-graphene has appeared to undergo environmentally assisted subcritical crack growth in room condition, i.e. stress corrosion cracking arising from the adsorption of water vapor on the graphene and the subsequent chemical reactions. The crack propagation in graphene has appeared to be able to be reasonably tamed by adjusting applied humidity and stress. The fracture toughness, describing the ability of a material containing inherent flaws to resist catastrophic failure, of the CVD-graphene has turned out to be exceptionally high, as compared to other carbon based 3D materials. These results imply that the CVD-graphene could be an ideal candidate as a structural material notwithstanding environmental susceptibility. In addition, the measurements reported here suggest that specific non-continuum fracture behaviors occurring in 2D monoatomic structures can be macroscopically well visualized and characterized.

  7. Molecular tilt on monolayer-protected nanoparticles

    Giomi, L.


    The structure of the tilted phase of monolayer-protected nanoparticles is investigated by means of a simple Ginzburg-Landau model. The theory contains two dimensionless parameters representing the preferential tilt angle and the ratio ε between the energy cost due to spatial variations in the tilt of the coating molecules and that of the van der Waals interactions which favors the preferential tilt. We analyze the model for both spherical and octahedral particles. On spherical particles, we find a transition from a tilted phase, at small ε, to a phase where the molecules spontaneously align along the surface normal and tilt disappears. Octahedral particles have an additional phase at small ε characterized by the presence of six topological defects. These defective configurations provide preferred sites for the chemical functionalization of monolayer-protected nanoparticles via place-exchange reactions and their consequent linking to form molecules and bulk materials. Copyright © EPLA, 2012.

  8. Monolayer solid of N-2/Ag(111)

    Bruch, L.W.; Hansen, Flemming Yssing


    An incommensurate monolayer solid of N-2/Ag(111) is modeled using extensive molecular-dynamics simulations. The conditions treated range from the low-temperature orientationally ordered solid to the melting of the solid. The properties are evaluated as a function of spreading pressure. Comparison...... is made to recent experimental data for N-2/Ag(111) and to results for N-2 adsorbed on graphite. Cu(110), and MgO(001). [S0163-1829(98)02715-5]....

  9. Physiological hydrostatic pressure protects endothelial monolayer integrity.

    Müller-Marschhausen, K; Waschke, J; Drenckhahn, D


    Endothelial monolayer integrity is required to maintain endothelial barrier functions and has found to be impaired in several disorders like inflammatory edema, allergic shock, or artherosclerosis. Under physiologic conditions in vivo, endothelial cells are exposed to mechanical forces such as hydrostatic pressure, shear stress, and cyclic stretch. However, insight into the effects of hydrostatic pressure on endothelial cell biology is very limited at present. Therefore, in this study, we tested the hypothesis that physiological hydrostatic pressure protects endothelial monolayer integrity in vitro. We investigated the protective efficacy of hydrostatic pressure in microvascular myocardial endothelial (MyEnd) cells and macrovascular pulmonary artery endothelial cells (PAECs) by the application of selected pharmacological agents known to alter monolayer integrity in the absence or presence of hydrostatic pressure. In both endothelial cell lines, extracellular Ca(2+) depletion by EGTA was followed by a loss of vascular-endothelial cadherin (VE-caherin) immunostaining at cell junctions. However, hydrostatic pressure (15 cmH(2)O) blocked this effect of EGTA. Similarly, cytochalasin D-induced actin depolymerization and intercellular gap formation and cell detachment in response to the Ca(2+)/calmodulin antagonist trifluperazine (TFP) as well as thrombin-induced cell dissociation were also reduced by hydrostatic pressure. Moreover, hydrostatic pressure significantly reduced the loss of VE-cadherin-mediated adhesion in response to EGTA, cytochalasin D, and TFP in MyEnd cells as determined by laser tweezer trapping using VE-cadherin-coated microbeads. In caveolin-1-deficient MyEnd cells, which lack caveolae, hydrostatic pressure did not protect monolayer integrity compromised by EGTA, indicating that caveolae-dependent mechanisms are involved in hydrostatic pressure sensing and signaling.

  10. Elasticity of a quantum monolayer solid

    Bruch, Ludwig Walter


    A perturbation-theory formulation of the zero-temperature elastic constants is used to verify symmetry relations for a (monolayer) triangluar lattice. A generalization of the Cauchy relation between the two elastic constants of the triangular lattice with central-pair-potential interactions is gi...... is given for the quantum solid. The first-order quantum corrections are rederived in this formalism, and previous calculations are reanalyzed....

  11. Characterization of 10,12-pentacosadiynoic acid Langmuir–Blodgett monolayers and their use in metal–insulator–metal tunnel devices

    Saumya Sharma


    Full Text Available The characterization of Langmuir–Blodgett thin films of 10,12-pentacosadiynoic acid (PDA and their use in metal–insulator–metal (MIM devices were studied. The Langmuir monolayer behavior of the PDA film was studied at the air/water interface using surface tension–area isotherms of polymeric and monomeric PDA. Langmuir–Blodgett (LB, vertical deposition and Langmuir–Schaefer (LS, horizontal deposition techniques were used to deposit the PDA film on various substrates (glass, quartz, silicon, and nickel-coated film on glass. The electrochemical, electrical and optical properties of the LB and LS PDA films were studied using cyclic voltammetry, current–voltage characteristics (I–V, and UV–vis and FTIR spectroscopies. Atomic force microscopy measurements were performed in order to analyze the surface morphology and roughness of the films. A MIM tunnel diode was fabricated using a PDA monolayer assembly as the insulating barrier, which was sandwiched between two nickel layers. The precise control of the thickness of the insulating monolayers proved critical for electron tunneling to take place in the MIM structure. The current–voltage characteristics of the MIM diode revealed tunneling behavior in the fabricated Ni–PDA LB film–Ni structures.

  12. Strain mapping in a graphene monolayer nanocomposite.

    Young, Robert J; Gong, Lei; Kinloch, Ian A; Riaz, Ibtsam; Jalil, Rashed; Novoselov, Kostya S


    Model composite specimens have been prepared consisting of a graphene monolayer sandwiched between two thin layers of polymer on the surface of a poly(methyl methacrylate) beam. It has been found that well-defined Raman spectra can be obtained from the single graphene atomic layer and that stress-induced Raman band shifts enable the strain distribution in the monolayer to be mapped with a high degree of precision. It has been demonstrated that the distribution of strain across the graphene monolayer is relatively uniform at levels of applied strain up to 0.6% but that it becomes highly nonuniform above this strain. The change in the strain distributions has been shown to be due to a fragmentation process due to the development of cracks, most likely in the polymer coating layers, with the graphene remaining intact. The strain distributions in the graphene between the cracks are approximately triangular in shape, and the interfacial shear stress in the fragments is only about 0.25 MPa, which is an order of magnitude lower than the interfacial shear stress before fragmentation. This relatively poor level of adhesion between the graphene and polymer layers has important implications for the use of graphene in nanocomposites, and methods of strengthening the graphene-polymer interface are discussed.

  13. Grafted silane monolayers: reconsideration of growth mechanisms

    Ivanov, D. A.; Nysten, B.; Jonas, A. M.; Legras, R.


    Chemical force microscopy is a new technique devised to image chemical heterogeneities on surfaces. It requires the chemical modification of Atomic Force Microscopy (AFM) tips in order to create chemical probes. In this respect, self-assembled monolayers (SAM) of alkylchlorosilanes are particularly interesting as modifying agents for AFM tips. We report here our results on the kinetics of silanization and on the structure of such SAM's grafted on model surfaces (hydroxylated Si(100) wafers). AFM, contact angle measurements, X-ray reflectivity and X-ray photoelectron spectroscopy were used to characterize SAM's of octadecyltrichlorosilane (OTS) and octadecyldimethylchlorosilane (ODMS) grown from hexadecane and toluene solutions. The mechanism of grafting of OTS follows two stages. The first rapid stage corresponds to the nucleation and growth of island-like monolayer domains. The second slower stage is related to the densification of the monolayer. SAM's of ODMS were found to form thinner layers as compared to OTS, due to their lower grafting density probably resulting in a more disordered state of grafted alkyl chains. We also address the problems concerning the relationships between the quality of final SAM structures and the water content as well as the nature of the solvent used for silanization.

  14. Janus monolayers of transition metal dichalcogenides

    Lu, Ang-Yu


    Structural symmetry-breaking plays a crucial role in determining the electronic band structures of two-dimensional materials. Tremendous efforts have been devoted to breaking the in-plane symmetry of graphene with electric fields on AB-stacked bilayers or stacked van der Waals heterostructures. In contrast, transition metal dichalcogenide monolayers are semiconductors with intrinsic in-plane asymmetry, leading to direct electronic bandgaps, distinctive optical properties and great potential in optoelectronics. Apart from their in-plane inversion asymmetry, an additional degree of freedom allowing spin manipulation can be induced by breaking the out-of-plane mirror symmetry with external electric fields or, as theoretically proposed, with an asymmetric out-of-plane structural configuration. Here, we report a synthetic strategy to grow Janus monolayers of transition metal dichalcogenides breaking the out-of-plane structural symmetry. In particular, based on a MoS2 monolayer, we fully replace the top-layer S with Se atoms. We confirm the Janus structure of MoSSe directly by means of scanning transmission electron microscopy and energy-dependent X-ray photoelectron spectroscopy, and prove the existence of vertical dipoles by second harmonic generation and piezoresponse force microscopy measurements.

  15. Investigation on gallium ions impacting monolayer graphene

    Xin Wu


    Full Text Available In this paper, the physical phenomena of gallium (Ga+ ion impacting monolayer graphene in the nanosculpting process are investigated experimentally, and the mechanisms are explained by using Monte Carlo (MC and molecular dynamics (MD simulations. Firstly, the MC method is employed to clarify the phenomena happened to the monolayer graphene target under Ga+ ion irradiation. It is found that substrate has strong influence on the damage mode of graphene. The mean sputtering yield of graphene under 30 keV Ga+ ion irradiation is 1.77 and the least ion dose to completely remove carbon atoms in graphene is 21.6 ion/nm2. Afterwards, the focused ion beam over 21.6 ion/nm2 is used for the irradiation on a monolayer graphene supported by SiO2 experimentally, resulting in the nanostructures, i.e., nanodot and nanowire array on the graphene. The performances of the nanostructures are characterized by atomic force microscopy and Raman spectrum. A plasma plume shielding model is put forward to explain the nanosculpting results of graphene under different irradiation parameters. In addition, two damage mechanisms are found existing in the fabrication process of the nanostructures by using empirical MD simulations. The results can help us open the possibilities for better control of nanocarbon devices.

  16. Investigation on gallium ions impacting monolayer graphene

    Wu, Xin; Zhao, Haiyan, E-mail:; Yan, Dong; Pei, Jiayun [State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, P. R. Chinaand Department of Mechanical Engineering, Tsinghua University, Beijing 100084 (China)


    In this paper, the physical phenomena of gallium (Ga{sup +}) ion impacting monolayer graphene in the nanosculpting process are investigated experimentally, and the mechanisms are explained by using Monte Carlo (MC) and molecular dynamics (MD) simulations. Firstly, the MC method is employed to clarify the phenomena happened to the monolayer graphene target under Ga{sup +} ion irradiation. It is found that substrate has strong influence on the damage mode of graphene. The mean sputtering yield of graphene under 30 keV Ga{sup +} ion irradiation is 1.77 and the least ion dose to completely remove carbon atoms in graphene is 21.6 ion/nm{sup 2}. Afterwards, the focused ion beam over 21.6 ion/nm{sup 2} is used for the irradiation on a monolayer graphene supported by SiO2 experimentally, resulting in the nanostructures, i.e., nanodot and nanowire array on the graphene. The performances of the nanostructures are characterized by atomic force microscopy and Raman spectrum. A plasma plume shielding model is put forward to explain the nanosculpting results of graphene under different irradiation parameters. In addition, two damage mechanisms are found existing in the fabrication process of the nanostructures by using empirical MD simulations. The results can help us open the possibilities for better control of nanocarbon devices.

  17. Exploring atomic defects in molybdenum disulphide monolayers

    Hong, Jinhua


    Defects usually play an important role in tailoring various properties of two-dimensional materials. Defects in two-dimensional monolayer molybdenum disulphide may be responsible for large variation of electric and optical properties. Here we present a comprehensive joint experiment-theory investigation of point defects in monolayer molybdenum disulphide prepared by mechanical exfoliation, physical and chemical vapour deposition. Defect species are systematically identified and their concentrations determined by aberration-corrected scanning transmission electron microscopy, and also studied by ab-initio calculation. Defect density up to 3.5 × 10 13 cm \\'2 is found and the dominant category of defects changes from sulphur vacancy in mechanical exfoliation and chemical vapour deposition samples to molybdenum antisite in physical vapour deposition samples. Influence of defects on electronic structure and charge-carrier mobility are predicted by calculation and observed by electric transport measurement. In light of these results, the growth of ultra-high-quality monolayer molybdenum disulphide appears a primary task for the community pursuing high-performance electronic devices.

  18. Monolayers and multilayers of conjugated polymers as nanosized electronic components.

    Zotti, Gianni; Vercelli, Barbara; Berlin, Anna


    Conjugated polymers (CPs) are interesting materials for preparing devices based on nanoscopic molecular architectures because they exhibit electrical, electronic, magnetic, and optical properties similar to those of metals or semiconductors while maintaining the flexibility and ease of processing of polymers. The production of well-defined mono- and multilayers of CPs on electrodes with nanometer-scale, one-dimensional resolution remains, however, an important challenge. In this Account, we describe the preparation and conductive properties of nanometer-sized CP molecular structures formed on electrode surfaces--namely, self-assembled monolayer (SAM), brush-type, and self-assembled multilayer CPs--and in combination with gold nanoparticles (AuNPs). We have electrochemically polymerized SAMs of carboxyalkyl-functionalized terthiophenes aligned either perpendicular or parallel to the electrode surface. Anodic coupling of various pyrrole- and thiophene-based monomers in solution with the oligothiophene-based SAMs produced brush-like films. Microcontact printing of these SAMs produced patterns that, after heterocoupling, exhibited large height enhancements, as measured using atomic force microscopy (AFM). We have employed layer-by-layer self-assembly of water-soluble polythiophene-based polyelectrolytes to form self-assembled multilayers. The combination of isostructural polycationic and polyanionic polythiophenes produced layers of chains aligned parallel to the substrate plane. These stable, robust, and dense layers formed with high regularity on the preformed monolayers, with minimal interchain penetration. Infrared reflection/adsorption spectroscopy and X-ray diffraction analyses revealed unprecedented degrees of order. Deposition of soluble polypyrroles produced molecular layers that, when analyzed using a gold-coated AFM tip, formed gold-polymer-gold junctions that were either ohmic or rectifying, depending of the layer sequence. We also describe the electronic

  19. Preparation and gaseous photocatalytic activity of smooth potassium dititanate film

    Qinghua QIAN; Yuyan HU; Gaofei WEN; Xin FENG; Xiaohua LU


    A new smooth potassium dititanate film was prepared by sol-gel method and characterized by thermo-gravimetry (TG) and differential scanning calorimetry (DSC),X-ray diffraction (XRD),atomic force microscopy (AFM),UV-Visible diffuse reflectance and Raman spectro-scopy.The gaseous photocatalytic activity of smooth K2Ti2O5 films was studied using contact angle analysis from the photocatalytic decomposition of octadecyltri-chlo-rosilane (OTS) based self-assembled monolayers (SAMs) formed on K2Ti2O5 films.The photocurrent res-ponse of the film was determined by an electrochemical method.It was shown that the films were smooth,compact,and transparent when formed on glass.Compared with TiO2 film,the K2Ti2O5 film showed wide absorption in the ultraviolet and visible region.It was found that the monolayers on K2Ti2O5 decomposed much faster than those on TiO2 under UV irradiation of 254 nm in air.The film also exhibited a stronger photoresponse and a more stable anodic photocurrent.The K2Ti2O5 film effi-ciently decomposes the alkylsiloxane monolayers under UV irradiation in air and it was found to be a good photo-catalyst for gaseous organic pollutant treatment.

  20. Functional monolayers for direct electrical biosensing

    Clare, Tami Lasseter

    Frequency-dependent electrochemical impedance spectroscopy has been used to characterize changes in electrical response that accompany specific binding of a protein to its substrate, using the biotin-avidin system as a model. This thesis work shows that avidin, at concentrations in the nanomolar range, can be detected electrically in a completely label-free manner under conditions of zero average current flow and without the use of any auxiliary redox agents. Electrical circuit modeling of the interface was used to relate the frequency-dependent electrical response to the physical picture of the interface before and after avidin binding. The interaction of proteins with semiconductors such as silicon and diamond is of great interest for applications such as electronic biosensing. Investigations into the use of covalently bound oligo(ethylene glycol), EG, monolayers on diamond and silicon to minimize nonspecific protein adsorption were conducted. Protein adsorption was monitored by fluorescence scanning as a function the length of the ethylene glycol chain (EG3 through EG6) and the terminal functional group (methyl- versus hydroxyl-terminated EG3 monolayer). More quantitative measurements were made by eluting adsorbed avidin from the surface and measuring the intensity of fluorescence in the solution. This thesis work shows that high quality EG monolayers are formed on silicon and diamond and that these EG3 monolayers are as effective as EG3 self-assembled monolayers on gold at resisting nonspecific avidin adsorption. These results show promise for use of silicon and diamond materials in many potential applications such as biosensing and medical implants. Substrate roughness is shown to play a role in nonspecific protein adsorption, where carbon-based surfaces having features less than approximately 5 nm, are highly resistant to protein adsorption. Functionalization of the surfaces with hexaethylene glycol confers additional resistance to protein adsorption. These

  1. Direct transfer of graphene films for polyurethane substrate

    Vilani, C.; Romani, E.C.; Larrudé, D.G. [Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, 22451-900 Rio de Janeiro, RJ (Brazil); Barbosa, Gelza M. [Diretoria de Sistemas de Armas da Marinha, Marinha do Brasil, 20010-00 Rio de Janeiro, RJ (Brazil); Freire, F.L., E-mail: [Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, 22451-900 Rio de Janeiro, RJ (Brazil); Centro Brasileiro de Pesquisas Físicas, 22290-180 Rio de Janeiro, RJ (Brazil)


    Highlights: • Graphene was prepared by CVD using copper foils as substrates. • Monolayer, bilayer and multilayer graphene were transferred to PU. • Samples were characterized by Raman and optical spectroscopies. • PU/monolayer graphene has transmittance around 80% in visible range. - Abstract: We have proposed the direct transfer of large-area graphene films grown by chemical vapor deposition to polymeric substrate by evaporating of solvents of polyurethane/tetrahydrofurane solution. The graphene films on polyurethane substrates were characterized by Raman spectroscopy, optical and atomic force microscopies and UV–vis spectroscopy measurements. The Raman spectra revealed that it is possible to transfer in a controlled manner monolayer, bilayer and multilayer graphene films over polyurethane substrate.

  2. Facile Fabrication of Large Area Polystyrene Colloidal Crystal Monolayer via Surfactant-free Langmuir-Blodgett Technique

    RUAN Wei-dong; L(U) Zhi-cheng; JI Nan; WANG Chun-xu; ZHAO Bing; ZHANG Jun-hu


    A facile and novel method for the production of a large area of well-ordered polystyrene(PS) colloidal crystal monolayer was established using the surfactant-free Langmuir-Blodgett (LB) technique. The hydrophobic property(film-forming ability) of PS spheres was improved by a thermo-rheology treatment before LB assembly, and a large film was obtained. In contrast to the traditional LB technique, no surfactant was needed in this method, which could eliminate the additional contamination of surfactants in the preparation process and provided the products with versatile applications in nanosphere lithography(NSL) for biosensor, surface plasmon resonance, and surface enhanced Raman spectroscopy.

  3. Fabrication of grating-like polystyrene latex monolayer structure as three-dimensional calibration standards for scanning probe microscope

    Zhu Guo-Dong; Zeng Zhi-Gang; Guo Zhang; Du Qiang-Guo; Yan Xue-Jian


    This paper illuminates the preparation of grating-like polystyrene latex monolayer structure, which can minimize the effects of the size deviation of spheres and the defect transfer on the accuracy as calibration samples for micro-scopes. The latex films are grown on freshly cleaved mica substrates by vertical deposition method. The concentration dependence of the structure and the topography of latex films is characterized by optical microscope, ultraviolet-visible transmission spectrum and scanning probe microscope. The origination of such a grating-like structure is also discussed.

  4. MoS2 monolayers on nanocavities: enhancement in light-matter interaction

    Janisch, Corey; Song, Haomin; Zhou, Chanjing; Lin, Zhong; Elías, Ana Laura; Ji, Dengxin; Terrones, Mauricio; Gan, Qiaoqiang; Liu, Zhiwen


    Two-dimensional (2D) atomic crystals and van der Waals heterostructures constitute an emerging platform for developing new functional ultra-thin electronic and optoelectronic materials for novel energy-efficient devices. However, in most thin-film optical applications, there is a long-existing trade-off between the effectiveness of light-matter interactions and the thickness of semiconductor materials, especially when the materials are scaled down to atom thick dimensions. Consequently, enhancement strategies can introduce significant advances to these atomically thick materials and devices. Here we demonstrate enhanced absorption and photoluminescence generation from MoS2 monolayers coupled with a planar nanocavity. This nanocavity consists of an alumina nanolayer spacer sandwiched between monolayer MoS2 and an aluminum reflector, and can strongly enhance the light-matter interaction within the MoS2, increasing the exclusive absorption of monolayer MoS2 to nearly 70% at a wavelength of 450 nm. The nanocavity also modifies the spontaneous emission rate, providing an additional design freedom to control the interaction between light and 2D materials.

  5. Sub-micron scale patterning using femtosecond laser and self-assembled monolayers interaction

    Chang, Wonseok [Nanoprocess Group, Korea Institute of Machinery and Materials, 171 Jang-dong, Yusong-gu, Daejeon 305-343 (Korea, Republic of)]. E-mail:; Choi, Moojin [Nanoprocess Group, Korea Institute of Machinery and Materials, 171 Jang-dong, Yusong-gu, Daejeon 305-343 (Korea, Republic of); Kim, Jaegu [Nanoprocess Group, Korea Institute of Machinery and Materials, 171 Jang-dong, Yusong-gu, Daejeon 305-343 (Korea, Republic of); Cho, Sunghak [Nanoprocess Group, Korea Institute of Machinery and Materials, 171 Jang-dong, Yusong-gu, Daejeon 305-343 (Korea, Republic of); Whang, Kyunghyun [Nanoprocess Group, Korea Institute of Machinery and Materials, 171 Jang-dong, Yusong-gu, Daejeon 305-343 (Korea, Republic of)


    Standard positive photoresist techniques were adapted to generate sub-micron scale patterns of gold substrate using self-assembled monolayers (SAMs) and femtosecond laser. Self-assembled monolayers formed by the adsorption of alkanethiols onto gold substrate are employed as very thin photoresists. The process underlying photopatterning of SAMs on gold is well-known at the phenomenological level. Alkanethiolates formed by the adsorption of alkanethiols are oxidized on exposure to UV light in the presence of air to alkylsulfonates. Specifically, it is known that deep UV light of wavelength less than 200 nm is necessary for oxidation to occur. In this study, solid state femtosecond laser of wavelength 800 nm is applied for photolithography. The results show that ultrafast laser of near infrared (NIR) range wavelength can replace deep UV laser source for photopatterning using thin organic films. The essential basis of our approach is the photochemical excitation of specific reactions in a particular functional group (in this case a thiolate sulfur atom) distributed with monolayer coverage on a solid surface. Femtosecond laser photolithography could be applied to fabricate the patterning of surface chemical structure and the creation of three-dimensional nanostructures by combination with suitable etching methods.

  6. Effect of colloidal particle size on adsorbed monodisperse and bidisperse monolayers.

    Rosenberg, Rachel T; Dan, Nily


    Coating hydrogel films or microspheres by an adsorbed colloidal shell is one synthesis method for forming colloidosomes. The colloidal shell allows control of the release rate of encapsulated materials, as well as selective transport. Previous studies found that the packing density of self-assembled, adsorbed colloidal monolayers is independent of the colloidal particle size. In this paper we develop an equilibrium model that correlates the packing density of charged colloidal particles in an adsorbed shell to the particle dimensions in monodisperse and bidisperse systems. In systems where the molar concentration in solution is fixed, the increase in adsorption energy with increasing particle size leads to a monotonic increase in the monolayer packing density with particle radius. However, in systems where the mass fraction of the particles in the adsorbing solutions is fixed, increasing particle size also reduces the molar concentration of particles in solution, thereby reducing the probability of adsorption. The result is a nonmonotonic dependence of the packing density in the adsorbed layer on the particle radius. In bidisperse monolayers composed of two particle sizes, the packing density in the layer increases significantly with size asymmetry. These results may be utilized to design the properties of colloidal shells and coatings to achieve specific properties such as transport rate and selectivity.

  7. Cholesterol-Induced Buckling in Physisorbed Polymer-Tethered Lipid Monolayers

    Christoph A. Naumann


    Full Text Available The influence of cholesterol concentration on the formation of buckling structures is studied in a physisorbed polymer-tethered lipid monolayer system using epifluorescence microscopy (EPI and atomic force microscopy (AFM. The monolayer system, built using the Langmuir-Blodgett (LB technique, consists of 3 mol % poly(ethylene glycol (PEG lipopolymers and various concentrations of the phospholipid, 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC, and cholesterol (CHOL. In the absence of CHOL, AFM micrographs show only occasional buckling structures, which is caused by the presence of the lipopolymers in the monolayer. In contrast, a gradual increase of CHOL concentration in the range of 0–40 mol % leads to fascinating film stress relaxation phenomena in the form of enhanced membrane buckling. Buckling structures are moderately deficient in CHOL, but do not cause any notable phospholipid-lipopolymer phase separation. Our experiments demonstrate that membrane buckling in physisorbed polymer-tethered membranes can be controlled through CHOL-mediated adjustment of membrane elastic properties. They further show that CHOL may have a notable impact on molecular confinement in the presence of crowding agents, such as lipopolymers. Our results are significant, because they offer an intriguing prospective on the role of CHOL on the material properties in complex membrane architecture.

  8. Embedding Ba Monolayers and Bilayers in Boron Carbide Nanowires

    Yu, Zhiyang; Luo, Jian; Shi, Baiou; Zhao, Jiong; Harmer, Martin P.; Zhu, Jing


    Aberration corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) was employed to study the distribution of barium atoms on the surfaces and in the interiors of boron carbide based nanowires. Barium based dopants, which were used to control the crystal growth, adsorbed to the surfaces of the boron-rich crystals in the form of nanometer-thick surficial films (a type of surface complexion). During the crystal growth, these dopant-based surface complexions became embedded inside the single crystalline segments of fivefold boron-rich nanowires collectively, where they were converted to more ordered monolayer and bilayer modified complexions. Another form of bilayer complexion stabilized at stacking faults has also been identified. Numerous previous works suggested that dopants/impurities tended to segregate at the stacking faults or twinned boundaries. In contrast, our study revealed the previously-unrecognized possibility of incorporating dopants and impurities inside an otherwise perfect crystal without the association to any twin boundary or stacking fault. Moreover, we revealed the amount of barium dopants incorporated was non-equilibrium and far beyond the bulk solubility, which might lead to unique properties.

  9. Surface Modification through Chemically Adsorbed Monolayer of Thiophene Molecules

    Yamamoto, Shin-ichi; Ogawa, Kazufumi


    Using a time-averaged dielectrophoretic force from an applied electric field, we have observed the assembly of a chemically adsorbed monomolecular layer (CAM) on microwires and connections and the formation of an electric path between a lithographically patterned array of two platinum (Pt) electrodes. A Pt electrode/monolayer/Pt electrode junction was fabricated by the self-assembly of a rigid monomolecular layer, namely 3-{6-[11-(trichlorosilyl)undecanoyl]hexyl} thiophene (TEN) with thiophene groups in the lateral direction between the Pt electrodes. Conductive probe AFM (CP-AFM) was used to investigate the forward bias conduction properties of a TEN film grown by a wet deposition process on a glass substrate. The self-assembly depends on the ideal rigidity of the CAM and the strong affinity of the thiophene end groups of the CAM for the Pt electrode. The current-voltage (I-V) characteristics of the conjugated thiophene junction exhibited stepwise features at room temperature. The I-V characteristics can be explained by electron transport through the junction. From the results of experiments carried out under ambient conditions, the conductivity of the laterally conjugated polythiophene groups was calculated to be 5.0 ×104 S/cm. Understanding and using these effects will allow the controlled fabrication and positioning of microwires or connections at densities much greater than those now achievable.

  10. Manganese Atom Ordered Monolayer on Wurtzite Gallium Nitride

    Chinchore, Abhijit; Wang, Kangkang; Lin, Wenzhi; Pak, Jeongihm; Liu, Yinghao; Smith, Arthur


    While transition-metal-doped gallium nitride (GaN) thin films have been explored as potential dilute magnetic semiconductor bulk layers, the structural and magnetic effects of various transition metal adatoms on GaN surfaces are not even well understood. In this work, we investigate the sub-monolayer deposition of manganese (Mn) onto the N-polar wurtzite GaN (000-1) 1x1 surface. The growth is monitored in-situ using reflection high energy electron diffraction (RHEED). A fresh GaN(000-1) 1x1 surface is prepared by rf nitrogen plasma-assisted MBE followed by annealing to remove excess gallium adatoms. The atomically flat GaN surface, held at 200^o C, is then exposed to submonolayer doses of Mn. The deposition rate is maintained at 0.007 ML per second, and a 3x pattern develops along [10-10]; whereas, only 1x is seen along [11-20]. Analysis of the RHEED pattern and subsequent modeling indicates a 3 x3 R 30^o structure consisting of 2/3 ML Mn atoms in a row-like arrangement having spacing 3a/2 along rows and 3a/2 between rows. Scanning tunneling microscopy/spectroscopy studies are currently underway to explore this surface further. This work is supported by DOE (Grant No.DE-FG02-06ER46317) and NSF (Grant No. 0730257).

  11. Embedding Ba Monolayers and Bilayers in Boron Carbide Nanowires.

    Yu, Zhiyang; Luo, Jian; Shi, Baiou; Zhao, Jiong; Harmer, Martin P; Zhu, Jing


    Aberration corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) was employed to study the distribution of barium atoms on the surfaces and in the interiors of boron carbide based nanowires. Barium based dopants, which were used to control the crystal growth, adsorbed to the surfaces of the boron-rich crystals in the form of nanometer-thick surficial films (a type of surface complexion). During the crystal growth, these dopant-based surface complexions became embedded inside the single crystalline segments of fivefold boron-rich nanowires collectively, where they were converted to more ordered monolayer and bilayer modified complexions. Another form of bilayer complexion stabilized at stacking faults has also been identified. Numerous previous works suggested that dopants/impurities tended to segregate at the stacking faults or twinned boundaries. In contrast, our study revealed the previously-unrecognized possibility of incorporating dopants and impurities inside an otherwise perfect crystal without the association to any twin boundary or stacking fault. Moreover, we revealed the amount of barium dopants incorporated was non-equilibrium and far beyond the bulk solubility, which might lead to unique properties.

  12. Corrosion resistance of sintered NdFeB coated with SiC/Al bilayer thin films by magnetron sputtering

    Huang, Yiqin; Li, Heqin; Zuo, Min; Tao, Lei; Wang, Wei; Zhang, Jing; Tang, Qiong; Bai, Peiwen


    The poor corrosion resistance of sintered NdFeB imposes a great challenge in industrial applications. In this work, the SiC/Al bilayer thin films with the thickness of 510 nm were deposited on sintered NdFeB by magnetron sputtering to improve the corrosion resistance. A 100 nm Al buffer film was used to reduce the internal stress between SiC and NdFeB and improve the surface roughness of the SiC thin film. The morphologies and structures of SiC/Al bilayer thin films and SiC monolayer film were investigated with FESEM, AFM and X-ray diffraction. The corrosion behaviors of sintered NdFeB coated with SiC monolayer film and SiC/Al bilayer thin films were analyzed by polarization curves. The magnetic properties were measured with an ultra-high coercivity permanent magnet pulse tester. The results show that the surface of SiC/Al bilayer thin films is more compact and uniform than that of SiC monolayer film. The corrosion current densities of SiC/Al bilayer films coated on NdFeB in acid, alkali and salt solutions are much lower than that of SiC monolayer film. The SiC/Al bilayer thin films have little influence to the magnetic properties of NdFeB.

  13. Electrochemical metallization of self-assembled porphyrin monolayers.

    Nann, Thomas; Kielmann, Udo; Dietrich, Christoph


    Multifunctional sensor systems are becoming increasingly important in electroanalytical chemistry. Together with ongoing miniaturization there is a need for micro- and nanopatterning tools for thin electroactive layers (e.g. self-assembling monolayers). This paper documents a method for production of a micro-array of different metal-porphyrin monolayers with different sensor properties. A new method has been developed for the selective and local metallization of bare porphyrin monolayers by cathodic pulsing and sweeping. The metal-porphyrin monolayers obtained were characterized by cyclic voltammetry. It was shown that porphyrin monolayers can be metallized with manganese, iron, cobalt, and nickel by use of the new method. It is expected that all types of metal-porphyrin monolayers can be produced in the same manner.

  14. Controlled crystallization of hydroxyapatite under hexadecylamine self-assembled monolayer

    黄苏萍; 周科朝; 刘咏; 黄伯云


    The role of self-assembled monolayer in inducing the crystal growth was investigated by X-ray diffractions (XRD), and scanning electron microscopy (SEM). Results show that crystallization in the absence of monolayer results in a mixture of poorly crystallized calcium phosphates, including hydroxyapatite (HAP) and octacalcium phosphate (OCP), while the presence of self-assembled monolayer gives rise to oriented and well crystallized HAP crystals. Moreover, the HAP crystal grows very quickly under the self-assembled monolayer, whereas very little calcium phosphate crystals grow without the monolayer. It is rationalized that the hexadecylamine monolayer with high polarity and charged density leads to increase supersaturation and lower the interfacial energy, which attributes to the HAP crystals nucleation. On the other hand, the positive headgroups construct the ordered "recognized site" with distinct size and topology, which results in the oriented HAP crystals deposit.



    The dynamic elasticity of linoleic acid monolayer on a subphase of 10-4mol/L TbCla at various surface pressure has been measured by means of dynamic oscillation method in measuring the change of surface pressure caused by periodic compressionexpansion cycles of the barrier. The elasticity of monolayer increases with increasing of surface pressure linegrly. The linoleic acid polymer monolayer has been obtained under UV-irradiation in situ when keeping a constant surface pressure. But the elasticity of the resulting polymerized monolayer is even smaller than that of its corresponding monomer monolayer. The elasticity of the polymerized linoleic acid monolayer decreases with increasing polymerization time. The explanation based on entropy has been presented.

  16. In Situ Monitoring of the Thermal-Annealing Effect in a Monolayer of MoS2

    Su, Liqin; Yu, Yifei; Cao, Linyou; Zhang, Yong


    We perform in situ two-cycle thermal-annealing studies for a transferred CVD-grown monolayer MoS2 on a SiO2/Si substrate, using spatially resolved micro-Raman and photoluminescence spectroscopy. The evolution in film morphology and film-substrate bonding is continuously monitored by Raman spectroscopy. After the thermal cycling and being annealed at 305 °C twice, the film morphology and film-substrate bonding are significantly modified, which together with the removal of polymer residues causes major changes in the strain and doping distribution over the film, and thus the optical properties. Before annealing, the strain associated with ripples in the transferred film dominates the spatial distributions of the photoluminescence peak position and intensity over the film; after annealing, the variation in film-substrate bonding, affecting both strain and doping, becomes the leading factor. This work reveals that the film-substrate bonding, and thus the strain and doping, is nonstationary under thermal stress, which is important for understanding the substrate effects on the optical and transport properties of the 2D material and their impact on device applications.

  17. Water clustering on nanostructured iron oxide films

    Merte, Lindsay Richard; Bechstein, Ralf; Peng, G.;


    , but it is not well-understood how these hydroxyl groups and their distribution on a surface affect the molecular-scale structure at the interface. Here we report a study of water clustering on a moire-structured iron oxide thin film with a controlled density of hydroxyl groups. While large amorphous monolayer...... islands form on the bare film, the hydroxylated iron oxide film acts as a hydrophilic nanotemplate, causing the formation of a regular array of ice-like hexameric nanoclusters. The formation of this ordered phase is localized at the nanometre scale; with increasing water coverage, ordered and amorphous...

  18. On the inclusion of alkanes into the monolayer of aliphatic alcohols at the water/alkane vapor interface: a quantum chemical approach.

    Vysotsky, Yuri B; Fomina, Elena S; Belyaeva, Elena A; Fainerman, Valentin B; Vollhardt, Dieter


    In the framework of the quantum chemical semiempirical PM3 method thermodynamic and structural parameters of the formation and clusterization of aliphatic alcohols C(n)H(2n+1)OH (n(OH) = 8-16) at 298 K at the water/alkane vapor C(n)H(2n+2), (n(CH(3)) = 6-16) interface were calculated. The dependencies of enthalpy, entropy and Gibbs' energy of clusterization per one monomer molecule of 2D films on the alkyl chain length of corresponding alcohols and alkanes, the molar fraction of alkanes in the monolayers and the immersion degree of alcohol molecules into the water phase were shown to be linear or stepwise. The threshold of spontaneous clusterization of aliphatic alcohols at the water/alkane vapor interface was 10-11 carbon atoms at 298 K which is in line with experimental data at the air/water interface. It is shown that the presence of alkane vapor does not influence the process of alcohol monolayer formation. The structure of these monolayers is analogous to those obtained at the air/water interface in agreement with experimental data. The inclusion of alkane molecules into the amphiphilic monolayer at the water/alkane vapor interface is possible for amphiphiles with the spontaneous clusterization threshold at the air/water interface (n(s)(0)) of at least 16 methylene units in the alkyl chain, and it does not depend on the molar fraction of alkanes in the corresponding monolayer. The inclusion of alkanes from the vapor phase into the amphiphilic monolayer also requires that the difference between the alkyl chain lengths of alcohols and alkanes is not larger than n(s)(0) - 15 and n(s)(0) - 14 for the 2D film 1 and 2D film 2, respectively.

  19. Zitterbewegung in monolayer silicene in a magnetic field

    Romera, E. [Departamento de Física Atómica, Molecular y Nuclear and Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain); Roldán, J.B. [Departamento de Electrónica y Tecnología de Computadores and CITIC, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain); Santos, F. de los [Departamento de Electromagnetismo y Física de la Materia, and Instituto Carlos I de Física Teórica y Computacional, Universidad de Granada, Fuentenueva s/n, 18071 Granada (Spain)


    We study the Zitterbewegung in monolayer silicene under a perpendicular magnetic field. Using an effective Hamiltonian, we have investigated the autocorrelation function and the density currents in this material. Moreover, we have analyzed other types of periodicities of the system (classical and revival times). Finally, the above results are compared with their counterparts in two other monolayer materials subject to a magnetic field: graphene and MoS{sub 2}. - Highlights: • We study Zitterbewegung in monolayer silicene in a magnetic field. • We have analyzed other types of periodicities in silicene. • The above results are compared with other monolayer materials (graphene and MoS{sub 2})

  20. Carbon phosphide monolayers with superior carrier mobility

    Wang, Gaoxue; Pandey, Ravindra; Karna, Shashi P.


    Two dimensional (2D) materials with a finite band gap and high carrier mobility are sought after materials from both fundamental and technological perspectives. In this paper, we present the results based on the particle swarm optimization method and density functional theory which predict three geometrically different phases of the carbon phosphide (CP) monolayer consisting of sp2 hybridized C atoms and sp3 hybridized P atoms in hexagonal networks. Two of the phases, referred to as α-CP and β-CP with puckered or buckled surfaces are semiconducting with highly anisotropic electronic and mechanical properties. More remarkably, they have the lightest electrons and holes among the known 2D semiconductors, yielding superior carrier mobility. The γ-CP has a distorted hexagonal network and exhibits a semi-metallic behavior with Dirac cones. These theoretical findings suggest that the binary CP monolayer is a yet unexplored 2D material holding great promise for applications in high-performance electronics and optoelectronics.Two dimensional (2D) materials with a finite band gap and high carrier mobility are sought after materials from both fundamental and technological perspectives. In this paper, we present the results based on the particle swarm optimization method and density functional theory which predict three geometrically different phases of the carbon phosphide (CP) monolayer consisting of sp2 hybridized C atoms and sp3 hybridized P atoms in hexagonal networks. Two of the phases, referred to as α-CP and β-CP with puckered or buckled surfaces are semiconducting with highly anisotropic electronic and mechanical properties. More remarkably, they have the lightest electrons and holes among the known 2D semiconductors, yielding superior carrier mobility. The γ-CP has a distorted hexagonal network and exhibits a semi-metallic behavior with Dirac cones. These theoretical findings suggest that the binary CP monolayer is a yet unexplored 2D material holding great

  1. Critical Point of Ising Films with Different Growth Directions

    WANG Huai-yu; ZHOU Yun-song; D.L.Lin


    The critical temperature Tc of a spin-l/2 Ising film of cubic structures is calculated by the variational cumulant expansion method for three directions of growth. The results from different growth directions are analysed and compared with each other. In the present model, the Tc values depend largely on the number of nearest neighbors in a monolayer for films with the same number of monolayers but grown in different directions. For sc, bcc and fcc structures, the highest Tc is found along the (100), (110), and (111) direction, respectively.

  2. Low-Pressure No-Flow Cvd Synthesis of Graphene Films

    Kononenko, O. V.; Matveev, V. N.; Vdovin, E. E.; Shestakov, M. V.; Baranov, A. N.


    Graphene films were synthesized by the single injection and fast evacuation of acetylene on polycrystalline nickel catalyst films. They were transferred to a SiO2/Si substrate using PMMA. Raman spectra and mapping images were used for characterization of the films. It was found that nearly 95% of the Raman spectra show a hallmark of monolayer/bilayer graphene. The transport properties of the films were investigated with Hall measurements.

  3. Diacetylene mixed Langmuir monolayers for interfacial polymerization.

    Ariza-Carmona, Luisa; Rubia-Payá, Carlos; García-Espejo, G; Martín-Romero, María T; Giner-Casares, Juan J; Camacho, Luis


    Polydiacetylene (PDA) and its derivatives are promising materials for applications in a vast number of fields, from organic electronics to biosensing. PDA is obtained through polymerization of diacetylene (DA) monomers, typically using UV irradiation. DA polymerization is a 1-4 addition reaction with both initiation and growth steps with topochemical control, leading to the "blue" polymer form as primary reaction product in bulk and at interfaces. Herein, the diacetylene monomer 10,12-pentacosadiynoic acid (DA) and the amphiphilic cationic N,N'-dioctadecylthiapentacarbocyanine (OTCC) have been used to build a mixed Langmuir monolayer. The presence of OTCC imposes a monolayer supramolecular structure instead of the typical trilayer of pure DA. Surface pressure, Brewster angle microscopy, and UV-vis reflection spectroscopy measurements, as well as computer simulations, have been used to assess in detail the supramolecular structure of the DA:OTCC Langmuir monolayer. Our experimental results indicate that the DA and OTCC molecules are sequentially arranged, with the two OTCC alkyl chains acting as spacing diacetylene units. Despite this configuration is expected to prevent photopolymerization of DA, the polymerization takes place without phase segregation, thus exclusively leading to the red polydiacetylene form. We propose a simple model for the initial formation of the "blue" or "red" PDA forms as a function of the relative orientation of the DA units. The structural insights and the proposed model concerning the supramolecular structure of the "blue" and "red" forms of the PDA are aimed at the understanding of the relation between the molecular and macroscopical features of PDAs.

  4. Surface interactions, thermodynamics and topography of binary monolayers of Insulin with dipalmitoylphosphatidylcholine and 1-palmitoyl-2-oleoylphosphatidylcholine at the air/water interface.

    Grasso, E J; Oliveira, R G; Maggio, B


    The molecular packing, thermodynamics and surface topography of binary Langmuir monolayers of Insulin and DPPC (dipalmitoylphosphatidylcholine) or POCP (1-palmitoyl-2-oleoylphosphatidylcholine) at the air/water interface on Zn(2+) containing solutions were studied. Miscibility and interactions were ascertained by the variation of surface pressure-mean molecular area isotherms, surface compressional modulus and surface (dipole) potential with the film composition. Brewster Angle Microscopy was used to visualize the surface topography of the monolayers. Below 20mN/m Insulin forms stable homogenous films with DPPC and POPC at all mole fractions studied (except for films with XINS=0.05 at 10mN/m where domain coexistence was observed). Above 20mN/m, a segregation process between mixed phases occurred in all monolayers without squeezing out of individual components. Under compression the films exhibit formation of a viscoelastic or kinetically trapped organization leading to considerable composition-dependent hysteresis under expansion that occurs with entropic-enthalpic compensation. The spontaneously unfavorable interactions of Insulin with DPPC are driven by favorable enthalpy that is overcome by unfavorable entropic ordering; in films with POPC both the enthalpic and entropic effects are unfavorable. The surface topography reveals domain coexistence at relatively high pressure showing a striped appearance. The interactions of Insulin with two major membrane phospholipids induces composition-dependent and long-range changes of the surface organization that ought to be considered in the context of the information-transducing capabilities of the hormone for cell functioning.

  5. Fluidization of a horizontally driven granular monolayer.

    Heckel, Michael; Sack, Achim; Kollmer, Jonathan E; Pöschel, Thorsten


    We consider the transition of a horizontally vibrated monodisperse granular monolayer between its condensed state and its three-dimensional gaseous state as a function of the vibration parameters, amplitude, and frequency as well as particle number density. The transition is characterized by an abrupt change of the dynamical state which leaves its fingerprints in several measurable quantities including dissipation rate, sound emission, and a gap size which characterizes the sloshing motion of the material. The transition and its pronounced hysteresis is explained through the energy due to the collective motion of the particles relative to the container.

  6. Processing of monolayer materials via interfacial reactions

    Sutter, Peter Werner; Sutter, Eli Anguelova


    A method of forming and processing of graphene is disclosed based on exposure and selective intercalation of the partially graphene-covered metal substrate with atomic or molecular intercalation species such as oxygen (O.sub.2) and nitrogen oxide (NO.sub.2). The process of intercalation lifts the strong metal-carbon coupling and restores the characteristic Dirac behavior of isolated monolayer graphene. The interface of graphene with metals or metal-decorated substrates also provides for controlled chemical reactions based on novel functionality of the confined space between a metal surface and a graphene sheet.

  7. Template-Directed Self-Assembly of Alkanethiol Monolayers: Selective Growth on Preexisting Monolayer Edges

    Sharpe, Ruben B.A.; Burdinski, Dirk; Huskens, Jurriaan; Zandvliet, Harold J.W.; Reinhoudt, David N.; Poelsema, Bene


    Self-assembled monolayers were investigated for their suitability as two-dimensional scaffolds for the selective growth of alkanethiol edge structures. Heterostructures with chemical contrast could be grown, whose dimensions were governed by both the initial pattern sizes and the process time. n-Oct

  8. Filled and empty states of Zn-TPP films deposited on Fe(001-p(1×1O

    Gianlorenzo Bussetti


    Full Text Available Zn-tetraphenylporphyrin (Zn-TPP was deposited on a single layer of metal oxide, namely an Fe(001-p(1×1O surface. The filled and empty electronic states were measured by means of UV photoemission and inverse photoemission spectroscopy on a single monolayer and a 20 monolayer thick film. The ionization energy and the electron affinity of the organic film were deduced and the interface dipole was determined and compared with data available in the literature.

  9. Atomic stick-slip friction between commensurate self-assembled monolayers


    The classical molecular dynamics simulations have been used to examine the compression and friction between commensurate self-assembled monolayers (SAMs) on Au (111). The friction force changes in a period corresponding to the geometric structure of sliding surfaces. The simulations reveal an ordered atomic stick-slip motion and discontinuous movements of diverse monomers, mainly head and tail groups. All of the head groups of the static film have 2~3 metastable positions (MPs). They oscillate around one of the MPs in stick phases and jump simultaneously to a new MP in slip phases. The tail groups of the sliding film are pulled forward together with opposite ones while sticking and jump forward half of the lattice constant relative to opposite ones while slipping. A complete vision of the motion of SAM chains is thereby built up and compared with the molecule behavior predicted by the Tomlinson model.

  10. Imaging lipid distributions in model monolayers by ToF-SIMS with selectively deuterated components and principal components analysis

    Biesinger, Mark C. [Surface Science Western, University of Western Ontario, London, Ont., N6A 5B7 (Canada)]. E-mail:; Miller, David J. [Surface Science Western, University of Western Ontario, London, Ont., N6A 5B7 (Canada); Department of Chemistry, University of Western Ontario, London, Ont., N6A 5B7 (Canada); Harbottle, Robert R. [Department of Chemistry, University of Western Ontario, London, Ont., N6A 5B7 (Canada); Possmayer, Fred [Department of Obstetrics and Gynecology, University of Western Ontario, London, Ont., N6A 5B7 (Canada); McIntyre, N. Stewart [Surface Science Western, University of Western Ontario, London, Ont., N6A 5B7 (Canada); Department of Chemistry, University of Western Ontario, London, Ont., N6A 5B7 (Canada); Petersen, Nils O. [National Institute for Nanotechnology and Department of Chemistry, University of Alberta W6-017 ECERF Bldg, 9107-116th Street, Edmonton, Alta., T6G 2V4 (Canada)


    Time of flight secondary ion mass spectrometry (ToF-SIMS) provides the capability to image the distribution of molecular ions and their associated fragments that are emitted from monolayer films. ToF-SIMS can be applied to the analysis of monolayers of complex lipid mixtures that act as a model to understand the organization of cell membranes into solid-like domains called lipid rafts. The ability to determine the molecular distribution of lipids using ToF-SIMS in monolayer films is also important in studies of the function of pulmonary surfactant. One of the limitations of the use of ToF-SIMS to studies of complex lipid mixtures found in biological systems, arises from the similarity of the mass fragments that are emitted from the components of the lipid mixture. The use of selectively deuterated components in a mixture overcomes this limitation and results in an unambiguous assignment of specific lipids to particular surface domains. The use of deuterium labeling to identify specific lipids in a multi-component mixture can be done by the deuteration of a single lipid or by the addition of more than one lipid with selectively deuterated components. The incorporation of deuterium into the lipid chains does not alter the miscibility or phase behavior of these systems. The use of deuterium labeling to identify lipids and determine their distribution in monolayer films will be demonstrated using two biological systems. Principal components analysis (PCA) is used to further analyze these deuterated systems checking for the origin of the various mass fragments present.

  11. Surface-enhanced infrared absorption spectroscopy (SEIRAS) to probe monolayers of membrane proteins.

    Ataka, Kenichi; Stripp, Sven Timo; Heberle, Joachim


    Surface-enhanced infrared absorption spectroscopy (SEIRAS) represents a variation of conventional infrared spectroscopy and exploits the signal enhancement exerted by the plasmon resonance of nano-structured metal thin films. The surface enhancement decays in about 10nm with the distance from the surface and is, thus, perfectly suited to selectively probe monolayers of biomembranes. Peculiar to membrane proteins is their vectorial functionality, the probing of which requires proper orientation within the membrane. To this end, the metal surface used in SEIRAS is chemically modified to generate an oriented membrane protein film. Monolayers of uniformly oriented membrane proteins are formed by tethering His-tagged proteins to a nickel nitrilo-triacetic acid (Ni-NTA) modified gold surface and SEIRAS commands molecular sensitivity to probe each step of surface modification. The solid surface used as plasmonic substrate for SEIRAS, can also be employed as an electrode to investigate systems where electron transfer reactions are relevant, like e.g. cytochrome c oxidase or plant-type photosystems. Furthermore, the interaction of these membrane proteins with water-soluble proteins, like cytochrome c or hydrogenase, is studied on the molecular level by SEIRAS. The impact of the membrane potential on protein functionality is verified by monitoring light-dark difference spectra of a monolayer of sensory rhodopsin (SRII) at different applied potentials. It is demonstrated that the interpretations of all of these experiments critically depend on the orientation of the solid-supported membrane protein. Finally, future directions of SEIRAS including cellular systems are discussed. This article is part of a Special Issue entitled: FTIR in membrane proteins and peptide studies.

  12. Film Reviews.

    Lance, Larry M.; Atwater, Lynn


    Reviews four Human Sexuality films and videos. These are: "Personal Decisions" (Planned Parenthood Federation of America, 1985); "The Touch Film" (Sterling Production, 1986); "Rethinking Rape" (Film Distribution Center, 1985); "Not A Love Story" (National Film Board of Canada, 1981). (AEM)

  13. Effect of Subphase $Ca^{++}$ Ions on the Viscoelastic Properties of Langmuir Monolayers

    Ghaskadvi, R S; Dennin, M; Carr, Sharon; Dennin, Michael


    It is known that the presence of cations like Ca++ or Pb++ in the water subphase alters the pressure-area isotherms for fatty acid monolayers. The corresponding lattice constant changes have been studied using x-ray diffraction. Reflection-absorption spectroscopy has been used to probe the chemical composition of the film. We report on the first measurements of the time evolution of the shear viscosity of arachidic acid monolayers in the presence of Ca++ ions in the subphase. We find that the introduction of Ca++ ions to the water subphase results in an increase of the film's viscosity by at least three orders of magnitude. This increase occurs in three distinct stages. First, there is a rapid change in the viscosity of up to one order of magnitude. This is followed by two periods, with very different time constants, of a relatively slow increase in the viscosity over the next 10 or more hours. The corresponding time constants for this rise decrease as either the subphase pH or Ca++ concentration is increased...

  14. Preparation of surface-tethered polymer layer on inorganic substrates by photoreactive self-assembled monolayer

    Kim, Seong-Ho; Ohtsuka, Hanae [Tokyo University of Agriculture and Technology, Department of Organic and Polymer Materials Chemistry, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588 (Japan); Tria, Maria Celeste R. [University of Houston, Department of Chemistry, 136 Fleming Building, Houston, TX 77204-5008 (United States); Tanaka, Kuniaki [Tokyo University of Agriculture and Technology, Department of Organic and Polymer Materials Chemistry, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588 (Japan); Advincula, Rigoberto C. [Case Western Reserve University, Department of Macromolecular Science and Engineering, 2100 Adelbert Road, Cleveland, OH 44106 (United States); Usui, Hiroaki, E-mail: [Tokyo University of Agriculture and Technology, Department of Organic and Polymer Materials Chemistry, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588 (Japan)


    A self-assembled monolayer (SAM) that has benzophenone (BP) terminal group was prepared on Si and indium–tin oxide (ITO) substrates, on which poly(9-vinyl carbazol) (PVK) was spin-coated and then irradiated with ultraviolet (UV) light. Upon UV irradiation, the BP unit reacted with the PVK backbone, yielding a crosslinked PVK layer that was covalently tethered to the substrate surface. Using this procedure, a patterned thin film of PVK was obtained by irradiating UV light through a photomask and then rinsing in chloroform. When polystylene (PSt) was spin-coated on the BP-SAM, only a thin interfacial layer was tethered by UV irradiation because PSt does not crosslink upon UV irradiation. The BP-SAM improved the adhesion strength between the PVK layer and ITO substrate without reducing the carrier injection from ITO to PVK. The photoreactive BP-SAM appeared to be an effective method to improve the interface between an inorganic electrode and a polymer layer deposited on its surface. - Highlights: • Polyvinylcarbazole (PVK) was tethered to substrate by self-assembled monolayer (SAM). • The photoreactive SAM was effective in improving adhesion strength of the films. • This process was applied for photopatterning of PVK layer. • The photoreactive SAM did not impede carrier injection from electrode to PVK.

  15. Fabrication of protein chips based on 3-aminopropyltriethoxysilane as a monolayer.

    Jang, Ling-Sheng; Liu, Hao-Juin


    Although 3-aminopropyltriethoxysilane (APTES) is widely adopted as a monolayer in biosensors, experimental silanization takes at least 1 h at high temperature. Therefore, the feasibility of the silanization with APTES in a short reaction time and at room temperature was investigated. The surface modification of glass slides using a self-assembled monolayer of APTES with a concentration of 10% was studied by immobilizing FITC. APTES was successfully immobilized on the glass slide. The effect of reaction temperature and time of silanization were investigated. Various silanization conditions of APTES were examined by contact angle measurement and fluorescence microscopy. The surface of glass patterns with a gold thin film as background was characterized by determining the fluorescent intensities following the immobilization of fluorescein isothiocyanate (FITC), protein A-FITC, antimouse IgG-FITC and sheep anti-bovine albumin-FITC. The normalized fluorescent intensity indicated that a short period (4 min) of silanization at 25 degrees C suffices to form an APTES thin film by the immobilization of protein A on a glass surface. Such a condition does not require microheaters and temperature sensors in a microfluidic system, which will significantly reduce the manufacturing process, cost, and reaction time in the future.

  16. Polymerization of a diacetylenic phospholipid monolayer at the air-water interface

    Bourdieu, L.; Chatenay, D.; Daillant, J.; Luzet, D.


    Monolayers of a polymerizable phospholipid on water have been studied both before and after polymerization. Before polymerization, the phase diagram is established by isotherm measurements and optical microscopy (epifluorescence and direct observation between crossed polarizer and analyzer). This allows us to bring into evidence a coexistence region between a condensed and an expanded phase, above a triple point temperature T_t = 20 ^{circ}C. The dramatic influence of impurities on the size of coexistence domains between the condensed phase and the expanded one is clearly demonstrated, even at a very low concentration of impurities. Structural and morphological modifications during the polymerization where investigated using X-ray surface scattering together with atomic force microscopy. Whatever the polymerization conditions (constant area or constant pressure), X-ray reflectivity clearly shows the reorientation of the diacetylenic links. Only constant area polymerization leads to a viscoelastic behavior of the film, as shown by talcum decoration. The topochemical nature of the polymerization of diacetylenic groups induces strong constraints on the monolayers and, when the polymerization is achieved at constant area, leads to the collapse of the films evidenced by both techniques.

  17. Effect of precursor on growth and morphology of MoS2 monolayer and multilayer

    Ganorkar, Shraddha; Kim, Jungyoon; Kim, Young-Hwan; Kim, Seong-II


    The rise of two-dimensional (2D) material is one of the results of successful efforts of researchers which laid the path to the new era of electronics. One of the most exciting materials is MoS2. Synthesis has been always a major issue as electronic devices need reproducibility along with similar properties for mass productions. Chemical vapor deposition (CVD) is one of the successful methods for 2D materials including graphene. Furthermore, the choice of starting materials for Mo and S source is crucial. The different source has different effects on the layers and morphology of MoS2 films. In this work, we have extensively studied the CVD technique to grow few layers of MoS2 with two precursors MoO3 and MoCl5, show remarkable changes. The MoO3 source gives a triangular shaped MoS2 monolayer while that of MoCl5 can achieve uniform MoS2 without triangle. The absence of geometric shapes with MoCl5 is poorly understood. We tried to explain with MoCl5 precursor, the formation of continuous monolayer of MoS2 without any triangle on the basis of chemical reaction formalism mostly due to one step reaction process and formation of MoS2 from gas phase to the solid phase. The film synthesized by MoCl5 is more continuous and it would be a good choice for device applications.

  18. The Shell Structure Effect on the Vapor Selectivity of Monolayer-Protected Gold Nanoparticle Sensors

    Rui-Xuan Huang


    Full Text Available Four types of monolayer-protected gold nanoclusters (MPCs were synthesized and characterized as active layers of vapor sensors. An interdigitated microelectrode (IDE and quartz crystal microbalance (QCM were used to measure the electrical resistance and mass loading changes of MPC films during vapor sorption. The vapor sensing selectivity was influenced by the ligand structure of the monolayer on the surface of gold nanoparticles. The responses of MPC-coated QCM were mainly determined according to the affinity between the vapors and surface ligands of MPCs. The responses to the resistance changes of the MPC films were due to the effectiveness of the swelling when vapor was absorbed. It was observed that resistive sensitivity to polar organics could be greatly enhanced when the MPC contained ligands that contain interior polar functional groups with exterior nonpolar groups. This finding reveals that reducing interparticle attraction by using non-polar exterior groups could increase effective swelling and therefore enhance the sensitivity of MPC-coated chemiresistors.

  19. Atomic force microscopy reveals two phases in single stranded DNA self-assembled monolayers

    Kosaka, Priscila M.; González, Sheila; Domínguez, Carmen M.; Cebollada, Alfonso; San Paulo, Alvaro; Calleja, Montserrat; Tamayo, Javier


    We have investigated the structure of single-stranded (ss) DNA self-assembled monolayers (SAMs) on gold by combining peak force tapping, Kelvin probe and phase contrast atomic force microscopy (AFM) techniques. The adhesion, surface potential and phase shift signals show heterogeneities in the DNA film structure at two levels: microscale and nanoscale; which cannot be clearly discerned in the topography. Firstly, there is multilayer aggregation covering less than 5% of the surface. The DNA multilayers seem to be ordered phases and their existence suggests that DNA end-to-end interaction can play a role in the self-assembly process. Secondly, we find the formation of two phases in the DNA monolayer, which differ both in surface energy and surface potential. We relate the two domains to differences in the packing density and in the ssDNA conformation. The discovered heterogeneities in ssDNA SAMs provide a new scenario in our vision of these relevant films that have direct consequences on their biological, chemical and physical properties.

  20. Tuning the molecular order of C60-based self-assembled monolayers in field-effect transistors.

    Schmaltz, Thomas; Khassanov, Artoem; Steinrück, Hans-Georg; Magerl, Andreas; Hirsch, Andreas; Halik, Marcus


    The control of order in organic semiconductor systems is crucial to achieve desired properties in electronic devices. We have studied the order in fullerene functionalized self-assembled monolayers by mixing the active molecules with supporting alkyl phosphonic acids of different chain length. By adjusting the length of the molecules, structural modifications of the alignment of the C60 head groups within the SAM can be tuned in a controlled way. These changes on the sub-nanometre scale were analysed by grazing incidence X-ray diffraction and X-ray reflectivity. To study the electron transport properties across these layers, self-assembled monolayer field-effect transistors (SAMFETs) were fabricated containing only the single fullerene monolayer as semiconductor. Electrical measurements revealed that a high 2D crystalline order is not the only important aspect. If the fullerene head groups are too confined by the supporting alkyl phosphonic acid molecules, defects in the crystalline C60 film, such as grain boundaries, start to strongly limit the charge transport properties. By close interpretation of the results of structural investigations and correlating them to the results of electrical characterization, an optimum chain length of the supporting alkyl phosphonic acids in the range of C10 was determined. With this study we show that minor changes in the order on the sub-nanometre scale, can strongly influence electronic properties of functional self-assembled monolayers.

  1. Trion valley coherence in monolayer semiconductors

    Hao, Kai; Xu, Lixiang; Wu, Fengcheng; Nagler, Philipp; Tran, Kha; Ma, Xin; Schüller, Christian; Korn, Tobias; MacDonald, Allan H.; Moody, Galan; Li, Xiaoqin


    The emerging field of valleytronics aims to exploit the valley pseudospin of electrons residing near Bloch band extrema as an information carrier. Recent experiments demonstrating optical generation and manipulation of exciton valley coherence (the superposition of electron-hole pairs at opposite valleys) in monolayer transition metal dichalcogenides (TMDs) provide a critical step towards control of this quantum degree of freedom. The charged exciton (trion) in TMDs is an intriguing alternative to the neutral exciton for control of valley pseudospin because of its long spontaneous recombination lifetime, its robust valley polarization, and its coupling to residual electronic spin. Trion valley coherence has however been unexplored due to experimental challenges in accessing it spectroscopically. In this work, we employ ultrafast 2D coherent spectroscopy to resonantly generate and detect trion valley coherence in monolayer MoSe2 demonstrating that it persists for a few-hundred femtoseconds. We conclude that the underlying mechanisms limiting trion valley coherence are fundamentally different from those applicable to exciton valley coherence.

  2. Mediated Electron Transfer at Redox Active Monolayers

    Michael E.G. Lyons


    Full Text Available A theoretical model describing the transport and kinetic processes involved in heterogeneous redox catalysis of solution phase reactants at electrode surfaces coated with redox active monolayers is presented. Although the analysis presented has quite general applicability, a specific focus of the paper is concerned with the idea that redox active monolayers can be used to model an ensemble of individual molecular nanoelectrodes. Three possible rate determining steps are considered: heterogeneous electron transfer between immobilized mediator and support electrode ; bimolecular chemical reaction between redox mediator and reactant species in the solution phase, and diffusional mass transport of reactant in solution. A general expression for the steady state reaction flux is derived which is valid for any degree of reversibility of both the heterogeneous electron transfer reaction involving immobilized mediator species and of the bimolecular cross exchange reaction between immobilized mediator and solution phase reactant. The influence of reactant transport in solution is also specifically considered. Simplified analytical expressions for the net reaction flux are derived for experimentally reasonable situations and a kinetic case diagram is constructed outlining the relationships between the various approximate solutions. The theory enables simple diagnostic plots to be constructed which can be used to analyse experimental data.

  3. Predicting Two-Dimensional Silicon Carbide Monolayers.

    Shi, Zhiming; Zhang, Zhuhua; Kutana, Alex; Yakobson, Boris I


    Intrinsic semimetallicity of graphene and silicene largely limits their applications in functional devices. Mixing carbon and silicon atoms to form two-dimensional (2D) silicon carbide (SixC1-x) sheets is promising to overcome this issue. Using first-principles calculations combined with the cluster expansion method, we perform a comprehensive study on the thermodynamic stability and electronic properties of 2D SixC1-x monolayers with 0 ≤ x ≤ 1. Upon varying the silicon concentration, the 2D SixC1-x presents two distinct structural phases, a homogeneous phase with well dispersed Si (or C) atoms and an in-plane hybrid phase rich in SiC domains. While the in-plane hybrid structure shows uniform semiconducting properties with widely tunable band gap from 0 to 2.87 eV due to quantum confinement effect imposed by the SiC domains, the homogeneous structures can be semiconducting or remain semimetallic depending on a superlattice vector which dictates whether the sublattice symmetry is topologically broken. Moreover, we reveal a universal rule for describing the electronic properties of the homogeneous SixC1-x structures. These findings suggest that the 2D SixC1-x monolayers may present a new "family" of 2D materials, with a rich variety of properties for applications in electronics and optoelectronics.

  4. Melting mechanism in monolayers of flexible rod-shaped molecules

    Hansen, Flemming Yssing; Taub, H.


    mechanism for melting in monolayers of flexible rod-shaped molecules. Melting requires the formation of vacancies in the monolayer by molecular motion perpendicular to the surface. This ‘‘footprint reduction’’ mechanism implies that strictly two-dimensional theories of melting are inapplicable...

  5. Modelling Organic Surfaces with Self-Assembled Monolayers


    reactive organic liquids. Fluorinated thiols form monolayers that are more water and oil-repellent than Teflon. The hydrophobicity and oleophobicity of...and are both hydrophobic and oleophobic . The surface of a monolayer containing an approximately equal mixture of the two components 13 resembles a




    Two monolayers of didecanoyllecithin at the air-water interface have been studied using molecular dynamics simulations. The model system consisted of two monolayers of 42 lecithin molecules each separated by a roughly 4 nm thick slab of SPC water. The area per lecithin molecule was 0.78 nm(2)

  7. Temperature programmed desorption and infrared spectroscopic studies of thin water films on MgO(1 0 0)

    Hawkins, S.; Kumi, G.; Malyk, S.; Reisler, H.; Wittig, C.


    Thin water (D 2O) films on MgO(1 0 0) surfaces have been studied. Water was deposited at 115 K and monolayer and multilayer films were prepared by annealing above 150 K, where the transition from amorphous solid to cubic ice is known to take place, and then re-cooling. Temperature programmed desorption traces and transmission Fourier transform infrared spectra were recorded. For the monolayer, results are consistent with an essentially flat, hydrogen-bonded water network without a significant amount of dangling OD. Ice growing on the monolayer appears to be a blend of amorphous and crystalline solid at 115 K, becoming more crystalline when annealed.

  8. Improved mechanical stability of acetoxypropyl cellulose upon blending with ultranarrow PbS nanowires in Langmuir monolayer matrix.

    Maji, Subrata; Kundu, Sudarshan; Pinto, L F V; Godinho, M H; Khan, Ali Hossain; Acharya, Somobrata


    Cellulose and cellulose derivatives have long been used as membrane fabrication. Langmuir monolayer behavior, which naturally mimics membranes, of acetoxypropyl cellulose (APC) and lead sulfide (PbS) nanowire mixtures at different volume ratios is reported. Surface pressure (π)-area (A) isotherms of APC and PbS nanowires mixtures at different volume ratios show a gradual decrease in the monolayer area with increasing volume fraction of PbS nanowires. Change of surface potential with monolayer area at different volume ratios also reveals a gradual increase in the surface potential indicating incorporation of PbS nanowires within APC matrix. The compressibility and elastic constants measurements reveal an enhancement of the elasticity upon incorporation of PbS nanowires up to certain volume fractions. An enhancement in stability of the blend is observed upon PbS nanowire incorporation to the APC matrix. Rheological measurements also support the robustness of the mixture of APC and PbS nanowires in 3D bulk phase. Such robust ultrathin films of cellulose based-nanowire blend obtained by means of the Langmuir technique may lead to novel routes for designing cellulosic-based thin films and membranes.

  9. Characteristics of localized surface plasmons excited on mixed monolayers composed of self-assembled Ag and Au nanoparticles.

    Tanaka, Daisuke; Imazu, Keisuke; Sung, Jinwoo; Park, Cheolmin; Okamoto, Koichi; Tamada, Kaoru


    The fundamental characteristics of localized surface plasmon resonance (LSPR) excited on mixed monolayers composed of self-assembled Ag and Au nanoparticles (AgNPs and AuNPs, respectively) were investigated. Mixed monolayered films were fabricated at the air-water interface at different mixing ratios. The films retained their phase-segregated morphologies in which AuNPs formed several 10 to 100 nm island domains in a homogeneous AgNP matrix phase. The LSPR bands originating from the self-assembled domains shifted to longer wavelengths as the domain size increased, as predicted by a finite-difference time-domain (FDTD) simulation. The FDTD simulation also revealed that even an alternating-lattice-structured two-dimensional (2D) AgNP/AuNP film retained two isolated LSPR bands, revealing that the plasmon resonances excited on each particle did not couple even in a continuous 2D sheet, unlike in the homologous NP system. The fluorescence quenching test of Cy3 and Cy5 dyes confirmed that the independent functions of AuNPs and AgNPs remained in the mixed films, whereas the AuNPs exhibited significantly higher quenching efficiency for the Cy3 dye compared with AgNPs due to the overlap of the excitation/emission bands of the dyes with the AuNP LSPR band. Various applications can be considered using this nanoheterostructured plasmonic assembly to excite spatially designed, high-density LSPR on macroscopic surfaces.

  10. Monolayer-by-monolayer stacked pyramid-like MoS2 nanodots on monolayered MoS2 flakes with enhanced photoluminescence.

    Yuan, Cailei; Cao, Yingjie; Luo, Xingfang; Yu, Ting; Huang, Zhenping; Xu, Bo; Yang, Yong; Li, Qinliang; Gu, Gang; Lei, Wen


    The precise control of the morphology and crystal shape of MoS2 nanostructures is of particular importance for their application in nanoelectronic and optoelectronic devices. Here, we describe a single step route for the synthesis of monolayer-by-monolayer stacked pyramid-like MoS2 nanodots on monolayered MoS2 flakes using a chemical vapor deposition method. First-principles calculations demonstrated that the bandgap of the pyramid-like MoS2 nanodot is a direct bandgap. Enhanced local photoluminescence emission was observed in the pyramid-like MoS2 nanodot, in comparison with monolayered MoS2 flakes. The findings presented here provide new opportunities to tailor the physical properties of MoS2via morphology-controlled synthesis.

  11. Controllable fabrication of 2D colloidal-crystal films with polystyrene nanospheres of various diameters by spin-coating

    Chen, Jian; Dong, Peitao [College of Mechatronics Engineering and Automation, National University of Defense Technology, Changsha, Hunan, 410073 (China); State Key Laboratory of Transducer Technology, Chinese Academy of Science (China); Di, Di; Wang, Chaoguang; Wang, Haoxu; Wang, Junfeng [College of Mechatronics Engineering and Automation, National University of Defense Technology, Changsha, Hunan, 410073 (China); Wu, Xuezhong, E-mail: [College of Mechatronics Engineering and Automation, National University of Defense Technology, Changsha, Hunan, 410073 (China)


    Monolayer and bilayer colloidal-crystal films are used as physical mask in nanosphere lithography (NSL). So far, spin-coating experiments have mainly been designed to form nanosphere monolayer with one given size or obtain small areas of polystyrene (PS) nanosphere monolayer which limited the application of these films used as physical masks. The development of NSL required more study focused on the preparation of colloidal-crystal films with large-scale, high ordering degree and nanospheres of different diameters. In this study, PS nanospheres were self-assembled to form monolayer and bilayer colloidal-crystal films by employing spin-coating technology. Based on our experiments, we have built an experiment system of PS nanospheres of certain size ranging from 200 nm to 1300 nm. To give an instance, we have chosen PS nanospheres of four diameters (223 nm, 347 nm, 509 nm, 1300 nm) to fabricate colloidal-crystal films by adjusting the spin speed and acceleration, and we have investigated the relationship between the monolayer coverage areas and spin parameters by designing different spin speed and acceleration for 509 nm nanosphere. Results revealed that monolayer and bilayer films of PS nanospheres with four different diameters were prepared successfully and the single structure where PS nanospheres were in hexagonal close-packed (HCP) order dominated the surface morphologies of both monolayer and bilayer colloidal-crystal films. For 509 nm PS nanosphere, as the spin speed and acceleration increasing, the monolayer coverage areas increase firstly then decrease and at spin speed 1750 rpm and acceleration 600 rpm/s, the areas reaches the biggest.

  12. A pentacene monolayer trapped between graphene and a substrate

    Zhang, Qicheng; Peng, Boyu; Chan, Paddy Kwok Leung; Luo, Zhengtang


    A self-assembled pentacene monolayer can be fabricated between the solid-solid interface of few-layered graphene (FLG) and the mica substrate, through a diffusion-spreading method. By utilizing a transfer method that allows us to sandwich pentacene between graphene and mica, followed by controlled annealing, we enabled the diffused pentacene to be trapped in the interfaces and led to the formation of a stable monolayer. We found that the formation of a monolayer is kinetically favored by using a 2D Ising lattice gas model for pentacene trapped between the graphene-substrate interfaces. This kinetic Monte Carlo simulation results indicate that, due to the graphene substrate enclosure, the spreading of the first layer proceeds faster than the second layer, as the kinetics favors the filling of voids by molecules from the second layer. This graphene assisted monolayer assembly method provides a new avenue for the fabrication of two-dimensional monolayer structures.A self-assembled pentacene monolayer can be fabricated between the solid-solid interface of few-layered graphene (FLG) and the mica substrate, through a diffusion-spreading method. By utilizing a transfer method that allows us to sandwich pentacene between graphene and mica, followed by controlled annealing, we enabled the diffused pentacene to be trapped in the interfaces and led to the formation of a stable monolayer. We found that the formation of a monolayer is kinetically favored by using a 2D Ising lattice gas model for pentacene trapped between the graphene-substrate interfaces. This kinetic Monte Carlo simulation results indicate that, due to the graphene substrate enclosure, the spreading of the first layer proceeds faster than the second layer, as the kinetics favors the filling of voids by molecules from the second layer. This graphene assisted monolayer assembly method provides a new avenue for the fabrication of two-dimensional monolayer structures. Electronic supplementary information (ESI

  13. Highly-charged-ion-induced electron emission from C-60 thin films

    Bodewits, E.; Hoekstra, R.; Kowarik, G.; Dobes, K.; Aumayr, F.


    The secondary electron yields as a result of highly charged ions impinging on clean Au(111) and thin films of C-60 on Au have been measured. This has been done for film thicknesses of one to five monolayers and several charge states of Ar and Xe ions. For all ions an increase of 35% in the secondary

  14. Multilayer Film Fabrication and Photoelectric Conversion Property of Two Pyrrolidinofullerene Carboxylic Acid Derivatives


    Two multilayer films of pyrrolidinofullerene carboxylic acid derivatives, which exhibit photoelectric conversion property, are reported here. The first monolayers were fabricated on hydrophilic indium-tin-oxide (ITO), quartz, and mica by esterification reaction. The multilayers were characterized by contact angle and UV spectrum. The photoelectric conversion properties of both multilayer films were studied.

  15. Langmuir and Langmuir-Blodgett films of a maleic anhydride derivative: effect of subphase divalent cations.

    Martín-García, B; Velázquez, M Mercedes; Pérez-Hernández, J A; Hernández-Toro, J


    We report the study of the equilibrium and dynamic properties of Langmuir monolayers of poly(styrene-co-maleic anhydride) partial 2-buthoxyethyl ester cumene terminated polymer and the effect of the Mg(NO(3))(2) addition in the water subphase on the film properties. Results show that the polymer monolayer becomes more expanded when the electrolyte concentration in the subphase increases. Dense polymer films aggregate at the interface. The aggregates are transferred onto silicon wafers using the Langmuir-Blodgett methodology and the morphology is observed by AFM. The structure of aggregates depends on the subphase composition of the Langmuir film transferred onto the silicon wafer.

  16. Hexadecadienyl Monolayers on Hydrogen-Terminated Si(III): Faster Monolayer Formation and Improved Surface Coverage Using the Enyne Moiety

    Rijksen, B.M.G.; Pujari, S.P.; Scheres, L.M.W.; Rijn, van C.J.M.; Baio, J.E.; Weidner, T.; Zuilhof, H.


    To further improve the coverage of organic monolayers on hydrogen-terminated silicon (H–Si) surfaces with respect to the hitherto best agents (1-alkynes), it was hypothesized that enynes (H–C=C–HC-CH–R) would be even better reagents for dense monolayer formation. To investigate whether the increased

  17. Physisorbed Films on Planar and Nonplanar Surfaces.

    Cheng, E.


    In the case of multilayer liquid films on planar surfaces, we found that the widely used Frenkel-Halsey -Hill theory is the leading term of a many-body expansion of the more general Dzyaloshinskii-Lifshitz-Pitaevskii theory in the nonretardation limit. While the FHH theory is a good approximation in the thin film region, retardation has been shown to be important at thickness d >=q 100 A. A universal behavior of the retardation has also been found. Submonolayer He film on weak-binding substrate surfaces have been found to have unexpected and exciting new features. The weak binding of the substrate potential supports only low density monolayer He films so that the monolayer He solid can be eliminated. Meanwhile, the z -wise delocalization of He atoms reduces the He-He interaction and the lateral binding. It is possible that the 2D liquid film will be eliminated as well and a quasi-2D bose gas is expected. A further possibility is that no He monolayer film at all will be present on a weak-binding substrate. The possibility of using the fractal geometry to describe (global) surface roughness has been investigated. A power-law relation between the coverage and thickness is found on a fractally rough surface, with its exponent determined by the surface fractal dimension. A new and interesting phenomenon has been found: the adsorbed film "defractalizes" the substrate surface; this is observable by small angle x-ray and neutron scattering measurements. Adsorption inside a cylindrical pore and near an oblique corner have also been discussed.

  18. Defect-Tolerant Monolayer Transition Metal Dichalcogenides

    Pandey, Mohnish; Rasmussen, Filip Anselm; Kuhar, Korina;


    -principles investigation of defect tolerance in 29 monolayer transition metal dichalcogenides (TMDs) of interest for nanoscale optoelectronics. We find that the TMDs based on group VI and X metals form deep gap states upon creation of a chalcogen (S, Se, Te) vacancy, while the TMDs based on group IV metals form only...... shallow defect levels and are thus predicted to be defect-tolerant. Interestingly, all the defect sensitive TMDs have valence and conduction bands with a very similar orbital composition. This indicates a bonding/antibonding nature of the gap, which in turn suggests that dangling bonds will fall inside...... the gap. These ideas are made quantitative by introducing a descriptor that measures the degree of similarity of the conduction and valence band manifolds. Finally, the study is generalized to nonpolar nanoribbons of the TMDs where we find that only the defect sensitive materials form edge states within...

  19. Vector assembly of colloids on monolayer substrates

    Jiang, Lingxiang; Yang, Shenyu; Tsang, Boyce; Tu, Mei; Granick, Steve


    The key to spontaneous and directed assembly is to encode the desired assembly information to building blocks in a programmable and efficient way. In computer graphics, raster graphics encodes images on a single-pixel level, conferring fine details at the expense of large file sizes, whereas vector graphics encrypts shape information into vectors that allow small file sizes and operational transformations. Here, we adapt this raster/vector concept to a 2D colloidal system and realize `vector assembly' by manipulating particles on a colloidal monolayer substrate with optical tweezers. In contrast to raster assembly that assigns optical tweezers to each particle, vector assembly requires a minimal number of optical tweezers that allow operations like chain elongation and shortening. This vector approach enables simple uniform particles to form a vast collection of colloidal arenes and colloidenes, the spontaneous dissociation of which is achieved with precision and stage-by-stage complexity by simply removing the optical tweezers.

  20. Why fluorination of the polar heads reverses the positive sign of the dipole potential of Langmuir monolayers: a vibrational sum frequency spectroscopic study.

    Karageorgiev, Peter; Petrov, Jordan G; Motschmann, Hubert; Moehwald, Helmuth


    Natural nonionic amphiphiles forming monolayers, bilayers, micelles, or biomembranes create a positive dipole potential at the boundary with water. In a series of papers we have reported on Langmuir monolayers with CF3 terminals of the polar heads, which show a negative surface dipole potential ΔV (Petrov , J. G.; Andreeva, T. D.; Kurt, D. K.; Möhwald, H. J. Phys. Chem. B 2005, 109, 14102). Here we use vibrational sum frequency spectroscopy (SF) to study the origin of the opposite ΔV signs of Langmuir films of CH3(CH2)20COCH2CH3 (ethyl ether, EE) and CH3(CH2)20COCH2CF3 (fluorinated ethyl ether, FEE). The vibrational sum frequency spectra are recorded at the same film density of the S-phase of the EE and FEE monolayers and analyzed in the spectral regions of OH, COC, CH3, and CF3 stretching vibrations because these functional groups could be responsible for the different dipole potentials. We compare the rearrangement of the pure water surface by EE and FEE monolayers and the conformations of EE and FEE polar heads. The analysis is performed according to the three-capacitor model of the dipole potential of Langmuir monolayers (Demchak, R. T.; Fort, T., Jr. J. Colloid Interface Sci. 1974, 46, 191). The results show that reversal of the ΔV sign caused by fluorination of the polar heads originates from the upward-oriented CF3 terminals of the FEE heads, whose negative normal dipole moment component determines the negative dipole potential of the FEE monolayer.

  1. Giant perpendicular magnetic anisotropy of an Ir monolayer on a NiAl(001) surface

    Kim, Dongyoo; Yang, Jeonghwa; Hong, Jisang


    Using the state-of-the-art full potential linearized augmented plane-wave method, we have investigated the magnetic properties of Os and Ir monolayer (ML) film on NiAl(001) surface. It has been found that the one ML of Os and Ir film can have ferromagnetic ground state with magnetic moment of 0.35 and 0.64μB on Ni terminated surface, whereas both films display no sign of magnetic state on Al terminated surface. In addition, the surface Ni atom has an induced magnetic moment of 0.26μB in Ir/NiAl(001), while only 0.09μB is observed in Os/NiAl(001). We attribute the existence of magnetism to the interaction between 5d of adlayer and 3d of surface Ni. Moreover, we have obtained that the Os/NiAl(001) and Ir/NiAl(001) films show a perpendicular magnetic anisotropy (PMA). Surprisingly, it appears that the Ir/NiAl(001) has a giant PMA energy of 7.18 meV.

  2. Molecular beam epitaxy of large-area SnSe2 with monolayer thickness fluctuation

    Park, Young Woon; Jerng, Sahng-Kyoon; Jeon, Jae Ho; Roy, Sanjib Baran; Akbar, Kamran; Kim, Jeong; Sim, Yumin; Seong, Maeng-Je; Kim, Jung Hwa; Lee, Zonghoon; Kim, Minju; Yi, Yeonjin; Kim, Jinwoo; Noh, Do Young; Chun, Seung-Hyun


    The interest in layered materials is largely based on the expectation that they will be beneficial for a variety of applications, from low-power-consuming, wearable electronics to energy harvesting. However, the properties of layered materials are highly dependent on thickness, and the difficulty of controlling thickness over a large area has been a bottleneck for commercial applications. Here, we report layer-by-layer growth of SnSe2, a layered semiconducting material, via van der Waals epitaxy. The films were fabricated on insulating mica substrates with substrate temperatures in the range of 210 °C-370 °C. The surface consists of a mixture of N and (N ± 1) layers, showing that the thickness of the film can be defined with monolayer accuracy (±0.6 nm). High-resolution transmission electron microscopy reveals a polycrystalline film with a grain size of ˜100 nm and clear Moiré patterns from overlapped grains with similar thickness. We also report field effect mobility values of 3.7 cm2 V-1 s-1 and 6.7 cm2 V-1 s-1 for 11 and 22 nm thick SnSe2, respectively. SnSe2 films with customizable thickness can provide valuable platforms for industry and academic researchers to fully exploit the potential of layered materials.

  3. Formation of a Pt-Decorated Au Nanoparticle Monolayer Floating on an Ionic Liquid by the Ionic Liquid/Metal Sputtering Method and Tunable Electrocatalytic Activities of the Resulting Monolayer.

    Sugioka, Daisuke; Kameyama, Tatsuya; Kuwabata, Susumu; Yamamoto, Takahisa; Torimoto, Tsukasa


    A novel strategy to prepare a bimetallic Au-Pt particle film was developed through sequential sputter deposition of Au and Pt on a room temperature ionic liquid (RTIL). Au sputter deposition onto an RTIL containing hydroxyl-functionalized cations produced a monolayer of Au particles 4.2 nm in size on the liquid surface. Subsequent Pt sputtering onto the original Au particle monolayer floating on the RTIL enabled decoration of individual Au particles with Pt metals, resulting in the formation of a bimetallic Au-Pt particle monolayer with a Pt-enriched particle surface. The particle size slightly increased to 4.8 nm with Pt deposition for 120 min. The shell layer of a bimetallic particle was composed of Au-Pt alloy, the composition of which was tunable by controlling the Pt sputter deposition time. The electrochemical surface area (ECSA) was determined by cyclic voltammetry of bimetallic Au-Pt particle monolayers transferred onto HOPG electrodes by a horizontal liftoff method. The Pt surface coverage, determined by ECSAs of Au and Pt, increased from 0 to 56 mol % with elapse of the Pt sputter deposition time up to 120 min. Thus-obtained Au-Pt particle films exhibited electrocatalytic activity for methanol oxidation reaction (MOR) superior to the activities of pure Au or Pt particles. Volcano-type dependence was observed between the MOR activity and Pt surface coverage on the particles. Maximum activity was obtained for Au-Pt particles with a Pt coverage of 49 mol %, being ca. 120 times higher than that of pure Pt particles. This method enables direct decoration of metal particles with different noble metal atoms, providing a novel strategy to develop highly efficient multinary particle catalysts.

  4. Study of the ability of self-assembled N-vinylcarbazole monolayers to protect copper against corrosion



    Full Text Available N-Vinylcarbazole (NVC monolayers were self-assembled on copper surfaces. The electrochemical properties of the copper surfaces modified by NVC self-assembled monolayers (SAMs were investigated using polarization and electrochemical impedance spectroscopic (EIS methods. The polarization measurements indicated that the NVC SAMs could reduce the rates of the anodic and cathodic reaction on the surface of copper electrodes in 0.5 mol dm-3 NaCl solution. The EIS results showed the NVC formed a closely packed film that was able to inhibit copper corrosion. X-Ray photoelectron spectroscopy (XPS analysis of the copper samples and atomic adsorption analysis of the solution showed that the copper surfaces were covered by NVC SAMs, and the adsorption of NVC on the copper surfaces was accompanied with dissolution of Cu into the solution.

  5. Detection of Volatile Organic Compounds by Self-assembled Monolayer Coated Sensor Array with Concentration-independent Fingerprints

    Chang, Ye; Tang, Ning; Qu, Hemi; Liu, Jing; Zhang, Daihua; Zhang, Hao; Pang, Wei; Duan, Xuexin


    In this paper, we have modeled and analyzed affinities and kinetics of volatile organic compounds (VOCs) adsorption (and desorption) on various surface chemical groups using multiple self-assembled monolayers (SAMs) functionalized film bulk acoustic resonator (FBAR) array. The high-frequency and micro-scale resonator provides improved sensitivity in the detections of VOCs at trace levels. With the study of affinities and kinetics, three concentration-independent intrinsic parameters (monolayer adsorption capacity, adsorption energy constant and desorption rate) of gas-surface interactions are obtained to contribute to a multi-parameter fingerprint library of VOC analytes. Effects of functional group’s properties on gas-surface interactions are also discussed. The proposed sensor array with concentration-independent fingerprint library shows potential as a portable electronic nose (e-nose) system for VOCs discrimination and gas-sensitive materials selections.

  6. Lubrication of polysilicon micromechanisms with self-assembled monolayers

    Srinivasan, U.; Foster, J.D.; Habib, U.; Howe, R.T.; Maboudian, R. [Berkeley Sensor and Actuator Center, CA (United States); Senft, D.C.; Dugger, M.T. [Sandia National Labs., Albuquerque, NM (United States)


    Here, the authors report on the lubricating effects of self-assembled monolayers (SAMs) on MEMS by measuring static and dynamic friction with two polysilicon surface- micromachined devices. The first test structure is used to study friction between laterally sliding surfaces and with the second, friction between vertical sidewalls can be investigated. Both devices are SAM-coated following the sacrificial oxide etch and the microstructures emerge released and dry from the final water rinse. The coefficient of static friction, {mu}{sub s} was found to decrease from 2.1 {+-} 0.8 for the SiO{sub 2} coating to 0.11 {+-} 0.01 and 0.10 {+-} 0.01 for films derived from octadecyltrichloro-silane (OTS) and 1H,1H,2H,2H-perfluorodecyl-trichlorosilane (FDTS). Both OTS and FDTS SAM-coated structures exhibit dynamic coefficients of friction, {mu}{sub d} of 0.08 {+-} 0.01. These values were found to be independent of the apparent contact area, and remain unchanged after 1 million impacts at 5.6 {micro}N (17 kPa), indicating that these SAMs continue to act as boundary lubricants despite repeated impacts. Measurements during sliding friction from the sidewall friction testing structure give comparable initial {mu}{sub d} values of 0.02 at a contact pressure of 84 MPa. After 15 million wear cycles, {mu}{sub d} was found to rise to 0.27. Wear of the contacting surfaces was examined by SEM. Standard deviations in the {mu} data for SAM treatments indicate uniform coating coverage.

  7. Theory of spin excitations in Fe(110) monolayers

    Muniz, R. B.; Mills, D. L.


    We present theoretical studies of short-wavelength spin excitations in ferromagnetic Fe(110) monolayers either adsorbed on a W(110) substrate or free standing. We use an itinerant model of electrons as the basis for our analysis, with nine bands (the five 3d bands and the 4sp complex) included. The bands are described within an empirical tight-binding scheme, and the ferromagnetic ground state is generated from on-site intraatomic Coulomb interactions, described in mean-field theory. The random phase approximation (RPA) is employed to describe the spin excitations through analysis of the wave vector and frequency dependence of the dynamic transverse susceptibility. Several issues are explored. We compare the spin-wave stiffness and other features of the spin-wave spectrum for the free standing film and that adsorbed on the substrate to find substantial quantitative differences with origin in spin-spin interactions mediated by the substrate. We also compare the spin-wave spectrum calculated through use of the RPA, an approximate theory, but a scheme that does not invoke the adiabatic approximation, with results generated within the framework of the adiabatic approach. While the spin-wave exchange stiffnesses produced by the two methods are in agreement, there are substantial differences between excitation spectra at short wavelengths. We argue that effective interspin exchange couplings generated within the framework of the adiabatic approximation fail to provide a description of the spin-wave spectrum in the itinerant ferromagnets, beyond the low-frequency, long-wavelength regime where the spin-wave exchange stiffness suffices to describe the spectrum. We also discuss apparent hybridization gaps in the spin-wave spectrum. We show that in some cases they can be artifact of a poorly converged numerical analysis and, in one instance, on use of an inappropriate form for the intra-atomic Coulomb interaction.

  8. Monolayer semiconductor nanocavity lasers with ultralow thresholds

    Wu, Sanfeng; Buckley, Sonia; Schaibley, John R.; Feng, Liefeng; Yan, Jiaqiang; Mandrus, David G.; Hatami, Fariba; Yao, Wang; Vučković, Jelena; Majumdar, Arka; Xu, Xiaodong


    Engineering the electromagnetic environment of a nanometre-scale light emitter by use of a photonic cavity can significantly enhance its spontaneous emission rate, through cavity quantum electrodynamics in the Purcell regime. This effect can greatly reduce the lasing threshold of the emitter, providing a low-threshold laser system with small footprint, low power consumption and ultrafast modulation. An ultralow-threshold nanoscale laser has been successfully developed by embedding quantum dots into a photonic crystal cavity (PCC). However, several challenges impede the practical application of this architecture, including the random positions and compositional fluctuations of the dots, extreme difficulty in current injection, and lack of compatibility with electronic circuits. Here we report a new lasing strategy: an atomically thin crystalline semiconductor--that is, a tungsten diselenide monolayer--is non-destructively and deterministically introduced as a gain medium at the surface of a pre-fabricated PCC. A continuous-wave nanolaser operating in the visible regime is thereby achieved with an optical pumping threshold as low as 27 nanowatts at 130 kelvin, similar to the value achieved in quantum-dot PCC lasers. The key to the lasing action lies in the monolayer nature of the gain medium, which confines direct-gap excitons to within one nanometre of the PCC surface. The surface-gain geometry gives unprecedented accessibility and hence the ability to tailor gain properties via external controls such as electrostatic gating and current injection, enabling electrically pumped operation. Our scheme is scalable and compatible with integrated photonics for on-chip optical communication technologies.

  9. Acid monolayer functionalized iron oxide nanoparticle catalysts

    Ikenberry, Myles

    Superparamagnetic iron oxide nanoparticle functionalization is an area of intensely active research, with applications across disciplines such as biomedical science and heterogeneous catalysis. This work demonstrates the functionalization of iron oxide nanoparticles with a quasi-monolayer of 11-sulfoundecanoic acid, 10-phosphono-1-decanesulfonic acid, and 11-aminoundecanoic acid. The carboxylic and phosphonic moieties form bonds to the iron oxide particle core, while the sulfonic acid groups face outward where they are available for catalysis. The particles were characterized by thermogravimetric analysis (TGA), transmission electron microscopy (TEM), potentiometric titration, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray photoelectron spectrometry (XPS), and dynamic light scattering (DLS). The sulfonic acid functionalized particles were used to catalyze the hydrolysis of sucrose at 80° and starch at 130°, showing a higher activity per acid site than the traditional solid acid catalyst Amberlyst-15, and comparing well against results reported in the literature for sulfonic acid functionalized mesoporous silicas. In sucrose catalysis reactions, the phosphonic-sulfonic nanoparticles (PSNPs) were seen to be incompletely recovered by an external magnetic field, while the carboxylic-sulfonic nanoparticles (CSNPs) showed a trend of increasing activity over the first four recycle runs. Between the two sulfonic ligands, the phosphonates produced a more tightly packed monolayer, which corresponded to a higher sulfonic acid loading, lower agglomeration, lower recoverability through application of an external magnetic field, and higher activity per acid site for the hydrolysis of starch. Functionalizations with 11-aminoundecanoic acid resulted in some amine groups binding to the surfaces of iron oxide nanoparticles. This amine binding is commonly ignored in iron oxide

  10. Foam film permeability: theory and experiment.

    Farajzadeh, R; Krastev, R; Zitha, Pacelli L J


    The mass transfer of gas through foam films is a prototype of various industrial and biological processes. The aim of this paper is to give a perspective and critical overview of studies carried out to date on the mass transfer of gas through foam films. Contemporary experimental data are summarized, and a comprehensive overview of the theoretical models used to explain the observed effects is given. A detailed description of the processes that occur when a gas molecule passes through each layer that forms a foam film is shown. The permeability of the film-building surfactant monolayers plays an important role for the whole permeability process. It can be successfully described by the models used to explain the permeability of surfactant monolayers on aqueous sub-phase. For this reason, the present paper briefly discusses the surfactant-induced resistance to mass transfer of gases through gas-liquid interface. One part of the paper discusses the experimental and theoretical aspects of the foam film permeability in a train of foam films in a matrix or a cylinder. This special case is important to explain the gas transfer in porous media or in foams. Finally, this paper will highlight the gaps and challenges and sketch possible directions for future research.

  11. Opening and retraction of particulate soap films

    Timounay, Yousra; Lorenceau, Elise; Rouyer, Florence


    We study for the first time the bursting dynamics of thin liquid films laden with hydrophobic micronic particles either with free or constrained edges. We highlight that the particles can arrange in bilayer or monolayer configurations and explore a range of particles coverage from zero to random close packing. When the particles bridge the two interfaces (monolayer configuration) of free-edge films, the hole opens intermittently. For the other cases, we observe constant retraction velocities, modeled by balancing liquid and particles inertia against surface tension as in Taylor-Culick theory. But, this approach is only valid up to a critical value of particles coverage due to the interplay between the interfaces and the friction between particles.

  12. Adhesive and conformational behaviour of mycolic acid monolayers.

    Zhang, Zhenyu; Pen, Yu; Edyvean, Robert G; Banwart, Steven A; Dalgliesh, Robert M; Geoghegan, Mark


    We have studied the pH-dependent interaction between mycolic acid (MA) monolayers and hydrophobic and hydrophilic surfaces using molecular (colloidal probe) force spectroscopy. In both cases, hydrophobic and hydrophilic monolayers (prepared by Langmuir-Blodgett and Langmuir-Schaefer deposition on silicon or hydrophobized silicon substrates, respectively) were studied. The force spectroscopy data, fitted with classical DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory to examine the contribution of electrostatic and van der Waals forces, revealed that electrostatic forces are the dominant contribution to the repulsive force between the approaching colloidal probe and MA monolayers. The good agreement between data and the DLVO model suggest that beyond a few nm away from the surface, hydrophobic, hydration, and specific chemical bonding are unlikely to contribute to any significant extent to the interaction energy between the probe and the surface. The pH-dependent conformation of MA molecules in the monolayer at the solid-liquid interface was studied by ellipsometry, neutron reflectometry, and with a quartz crystal microbalance. Monolayers prepared by the Langmuir-Blodgett method demonstrated a distinct pH-responsive behaviour, while monolayers prepared by the Langmuir-Schaefer method were less sensitive to pH variation. It was found that the attachment of water molecules plays a vital role in determining the conformation of the MA monolayers.

  13. The Modeling of Pulmonary Particulate Matter Transport Using Langmuir Monolayers

    Eaton, Jeremy M.

    The effects of a barrier in proximity to the air-water interface on the dynamics of a Langmuir monolayer system are observed. A monolayer of Survanta, bovine lung surfactant, is deposited onto the interface of an aqueous buffer solution. Polystyrene particles one micron in diameter and tagged with fluorescent carboxylate groups are distributed evenly throughout the monolayer surface. The bead-monolayer system is compressed and expanded to induce folding. A polydimethylsiloxane (PDMS) substrate is placed below the monolayer in the buffer solution to study interactions between the folding monolayer and a barrier. The presence of the substrate is shown to shift surface pressure-area isotherms toward regions of lower area by an average of 8.9 mN/m. The surface of the PDMS substrate can be imaged using fluorescence microscopy to detect the presence of particles or surfactant that may have been transported there from the air-water interface during folding. Images show the transferral of particles and monolayer together suggesting the pinch-off of a fold or the direct interaction of a fold with the barrier.

  14. Monolayer MoS2 Nanoribbons as a Promising Material for Both n-type and p-type Legs in Thermoelectric Generators

    Arab, A.; Davydov, A. V.; Papaconstantopoulos, D. A.; Li, Q.


    First-principles calculations have been performed to study the thermoelectric properties of monolayer MoS2 armchair nanoribbons (ACNRs). The electronic behavior of nanoribbons is dominated by the presence of edge states that are dependent on the number of zigzag chains across the nanoribbon. In addition, it is found that the phonon thermal conductance of monolayer MoS2 ACNRs is smaller than monolayer films due to phonon edge scattering. This effect is more pronounced in narrower nanoribbons, which leads to a higher ZT value compared to a monolayer MoS2 sheet. The effects of sulfur vacancy and edge roughness on the thermoelectric properties of MoS2 ACNRs have also been studied. We found that edge roughness decreased ZT values compared to those of perfect nanoribbons, as its impact on electrical conductance is more severe than on phonon thermal conductance. Sulfur vacancy, however, improved ZT in some subbands. It is shown that ZT values as high as 4 for electron-doped and 3 for hole-doped nanoribbons can be achieved at T = 500 K. The ability to achieve high ZT values for both p-type and n-type nanoribbons makes monolayer MoS2 ACNR a promising candidate for future solid-state thermoelectric generators.

  15. Review of 2D superconductivity: the ultimate case of epitaxial monolayers

    Brun, Christophe; Cren, Tristan; Roditchev, Dimitri


    The purpose of this review is to focus from an experimental point-of-view on the new physical properties of some of the thinnest superconducting films that can be fabricated and studied in situ nowadays with state-of-the-art methods. An important characteristic of the films we address is that the underlying electronic system forms a two-dimensional electron gas (2DEG). Up to now there are only few of these systems. Such true 2D superconductors can be divided into two classes: surface-confined or interface-confined films. Because the second types of films are burried below the surface, they are not accessible to purely surface-sensitive techniques like angular-resolved photoemission spectroscopy (ARPES) or scanning tunneling spectroscopy (STS). As a consequence the bandstructure characteristics of the 2DEG cannot be probed nor the local superconducting properties. On the other hand, in situ prepared surface-confined films are nowadays accessible not only to ARPES and STS but also to electrical transport measurements. As a consequence surface-confined systems represent at present the best archetypes on which can be summarized the new properties emerging in ultimately thin superconducting films hosting a 2DEG, probed by both macroscopic and microscopic measurement techniques. The model system we will widely refer to consists of a single atomic plane of a conventional superconductor, like for example lead (Pb), grown on top of a semiconducting substrate, like Si(111). In the introductory part 1 we first introduce the topic and give historical insights into this field. Then in the section 2, we introduce useful concepts worked out in studies of so-called ‘granular’ and ‘homogeneous’ superconducting thin films that will be necessary to understand the role of non-magnetic disorder on 2DEG superconductors. In this section, we also briefly review the superconducting properties of crystalline Pb/Si(111) ultrathin films grown under ultrahigh vacuum (UHV) conditions in

  16. Ultra Thin Film Characterization of the Organic Rectifier Project


    coating by the oleophobic method 𔃼 ito a monofunctionalized TCNQ acceptor. prepared in high y ield. hsdrox\\sl-coated electrode ". As discussed above...Bigelow oleophobic (BO) film-casting technique [29-321. The forces binding an LB or BO monolayer to the substrate are usually weak physisorptive or

  17. SQUID-magnetometry on Fe monolayers on GaAs(001) in UHV

    Kebe, T.


    This thesis deals with the characterization of the growth and of the magnetic properties of ultrathin Fe films on GaAs(001). In particular, a scanning SQUID (superconducting quantum interference device) magnetometer was used in ultrahigh vacuum (UHV), whose performance has been improved within the scope of this thesis. By probing the magnetic stray field of a magnetized film, the absolute remanent magnetization can be determined with submonolayer sensitivity. In the context of this thesis the magnetic stray field has been calculated analytically. The combined use of SQUID and ferromagnetic resonance (FMR) on the same film in UHV allows for the independent determination of the magnetization and the magnetic anisotropy constants as a function of temperature, film thickness, topography of the substrate and oxygen exposure. The results of this thesis are: 1. The thickness dependent remanent magnetization from 2 to 20 monolayer (ML) Fe on GaAs(001) without cap layer was measured as a function of temperature. 2. The continuous in-plane reorientation of the magnetization (from [1 1 0] to [1 0 0]) of Fe films with increasing film thickness was observed using the scanning SQUID technique and showed good agreement with FMR measurements. 3. The influence of controlled oxygen exposure on the remanent magnetization and the magnetic anisotropy constants of 5 to 16 ML Fe was investigated. A faster reduction of the magnetization is found for the thinner Fe films when the volume of the Fe oxide is taken into consideration. At low oxygen exposure (<10 Langmuir), the perpendicular uniaxial anisotropy constant K{sub 2} {sub perpendicular} {sub to} is reduced by about 40% whereas other anisotropy contributions remain virtually unchanged. In addition, structural investigations using IV-LEED during the oxygen exposure were carried out. 4. An 8.6 ML Fe/GaAs(001) film which was exposed to 25000 L O{sub 2} exhibits a spontaneous magnetization perpendicular to the film plane at low

  18. Conditioning of self-assembled monolayers at two static immersion test sites along the east coast of Florida and its effect on early fouling development.

    Thome, I; Bauer, S; Vater, S; Zargiel, K; Finlay, J A; Arpa-Sancet, M P; Alles, M; Callow, J A; Callow, M E; Swain, G W; Grunze, M; Rosenhahn, A


    Among the first events after immersion of surfaces in the ocean is surface 'conditioning'. Here, the accumulation and composition of the conditioning films formed after immersion in the ocean are analyzed. In order to account for different surface chemistries, five self-assembled monolayers that differ in resistance to microfouling and wettability were used. Water samples from two static immersion test sites along the east coast of Florida were collected at two different times of the year and used for experiments. Spectral ellipsometry revealed that conditioning films were formed within the first 24 h and contact angle goniometry showed that these films changed the wettability and rendered hydrophobic surfaces more hydrophilic and vice versa. Infrared reflection adsorption spectroscopy showed that the composition of the conditioning film depended on both the wettability and immersion site. Laboratory and field assays showed that the presence of a conditioning film did not markedly influence settlement of microorganisms.

  19. A New Method For The Simulation Of Lipid Monolayer Dynamics

    Griesbauer, J; Seeger, H M; Schneider, M F


    In this paper we present a predictive numerical model to describe dynamic properties of lipid monolayers. Its thermodynamic basis simply assumes a hexagonal lattice which can be occupied by lipids which may be ordered or disordered. Since the lattice sites are translational lose and interconnected by Newtonian springs, dynamic movements of the lipids are included. All necessary parameters directly follow from experiments. This approach allows the calculation of isotherms of lipid monolayers, which can be directly compared to experimentally determined ones, both quantitatively and qualitatively. Apart from that the monolayers heat capacity profile can be calculated, which otherwise cannot be easily extracted.

  20. Defect Structure of Localized Excitons in a WSe2 Monolayer

    Zhang, Shuai


    The atomic and electronic structure of intrinsic defects in a WSe2 monolayer grown on graphite was revealed by low temperature scanning tunneling microscopy and spectroscopy. Instead of chalcogen vacancies that prevail in other transition metal dichalcogenide materials, intrinsic defects in WSe2 arise surprisingly from single tungsten vacancies, leading to the hole (p-type) doping. Furthermore, we found these defects to dominate the excitonic emission of the WSe2 monolayer at low temperature. Our work provided the first atomic-scale understanding of defect excitons and paved the way toward deciphering the defect structure of single quantum emitters previously discovered in the WSe2 monolayer.

  1. Ordered Porous Pd Octahedra Covered with Monolayer Ru Atoms.

    Ge, Jingjie; He, Dongsheng; Bai, Lei; You, Rui; Lu, Haiyuan; Lin, Yue; Tan, Chaoliang; Kang, Yan-Biao; Xiao, Bin; Wu, Yuen; Deng, Zhaoxiang; Huang, Weixin; Zhang, Hua; Hong, Xun; Li, Yadong


    Monolayer Ru atoms covered highly ordered porous Pd octahedra have been synthesized via the underpotential deposition and thermodynamic control. Shape evolution from concave nanocube to octahedron with six hollow cavities was observed. Using aberration-corrected high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy, we provide quantitative evidence to prove that only a monolayer of Ru atoms was deposited on the surface of porous Pd octahedra. The as-prepared monolayer Ru atoms covered Pd nanostructures exhibited excellent catalytic property in terms of semihydrogenation of alkynes.

  2. Film/NotFilm

    Willems, Gertjan


    Although Samuel Beckett (1906-1989) showed a genuine interest in audio-visual media in his fascinating and innovative radio plays and television works, and in 1936 even wrote a letter to Sergei Eisenstein to be accepted to the famous Soviet film school VGIK, the 22-minute Film (1965) was his only venture into cinema. Beckett conceived the film, wrote the screenplay, supervised the production and, as one of the film’s crew members recalled and as the director Alan Schneider himself acknowledge...

  3. A quantum size effect in infrared optical response of aliminum thin films

    Xiao, Mufei; Villagómez, Ricardo


    We present a quantum mechanical calculation for diamagnetic optical response of metallic thin films. The study shows that in the optical response of the thin films, such as the reflectance, there exists an oscillatory dependence on the film thickness when the film contents less than about 100 monolayers, and the period of the oscillation corresponds to one or few monolayers. We show that the oscillation can be attributed to the intraband fluctuations of the valence electrons at discrete energy states as well as at continuum energy states. For comparison, we present some experimental results for Aluminum thin films of thickness 5 ~112ÅInfrared (λ=9.2μ m) optical reflectance of the films was measured, which demonstrates experimentally the predicted oscillating fine structures.


    Tokuji Miyashita; Tatsuo Taniguchi; Yoshihito Fukasawa


    Polymer LB films containing photofuntional groups were prepared by the copolymerization of N-dodecylacrylamide (DDA), which has an excellent property to form a stable monolayer and LB multilayers with photofunctional monomers. Tris(2, 2'-bipyridine) ruthenium complex, Ru(bpy)32+, one of the most wellknown redox-active sensitizer, was incorporated into the DDA copolymer. The photogalvanic effect based on the photoinduced electron transfer using the ruthenium complex in the polymer LB monolayer was discussed.

  5. Photopatterning of stable, low-density, self-assembled monolayers on gold.

    Safazadeh, Leila; Berron, Brad J


    Photoinitiated thiol-yne chemistry is utilized as a click reaction for grafting of acid-terminated alkynes to thiol-terminated monolayers on a gold substrate to create stable, low-density monolayers. The resulting monolayers are compared with a well-packed 11-mercaptoundecanoic acid monolayer and the analogous low-density monolayers prepared through a solution phase synthetic approach. The overall structuring of the monolayer prepared by solid-phase grafting is characterized by contact angle goniometry and Fourier transform infrared spectroscopy. The results show that the product monolayer has an intermediate surface energy and a more disordered chemical structuring compared to a traditional well-packed self-assembled monolayer, showing a low-packing density of the chains at the monolayer surface. The monolayer's structure and electrochemical stability were studied by reductive desorption of the thiolates. The prepared low-density monolayers have a higher electrochemical stability than traditional well-packed monolayers, which results from the crystalline structure at the gold interface. This technique allows for simple, fast preparation of low-density monolayers of higher stability than well-packed monolayers. The use of a photomask to restrict light access to the substrate yielded these low-density monolayers in patterned regions defined by light exposure. This general thiol-yne approach is adaptable to a variety of analogous low-density monolayers with diverse chemical functionalities.

  6. Thin Films

    M. Benmouss


    the optical absorption are consistent with the film color changes. Finally, the optical and electrochromic properties of the films prepared by this method are compared with those of our sputtered films already studied and with other works.

  7. Small-scale field evaluation of the monomolecular surface film 'Arosurf MSF' against Anopheles arabiensis Patton.

    Karanja, D M; Githeko, A K; Vulule, J M


    A field trial was conducted to test the insecticidal action of the monolayer surface film 'Arosurf MSF' applied by knapsack sprayers, against larvae and pupae of Anopheles arabiensis Patton in a rice irrigation scheme in Western Kenya. Larval and pupal densities and the number of emerging adults were determined by dipping and emergence cages respectively. Application of the monolayer by knapsack sprayers provided good coverage. There were high daily mortalities of the fourth instar larvae, with no adult emergence from 'Arosurf MSF' treated plots compared to lower fourth instar mortalities and continuous adult emergence from untreated control plots, indicating the potential of the monolayer for control of An. arabiensis mosquitoes in rice fields.

  8. Structure of solid monolayers and multilayers of -hexane on graphite

    M Krishnan; S Balasubramanian; S Clarke


    We present all-atom molecular dynamics simulations of -hexane on the basal plane of graphite at monolayer and multilayer coverages. In keeping with experimental data, we find the presence of ordered adsorbed layers both at single monolayer coverage and when the adsorbed layer coexists with excess liquid adsorbate. Using a simulation method that does not impose any particular periodicity on the adsorbed layer, we quantitatively compare our results to the results of neutron diffraction experiments and find a structural transition from a uniaxially incommensurate lattice to a fully commensurate structure on increasing the coverage from a monolayer to a multilayer. The zig-zag backbone planes of all the alkane molecules lie parallel to the graphite surface at the multilayer coverage, while a few molecules are observed to attain the perpendicular orientation at monolayer coverage.

  9. Monolayer MoS2 heterojunction solar cells

    Tsai, Menglin


    We realized photovoltaic operation in large-scale MoS2 monolayers by the formation of a type-II heterojunction with p-Si. The MoS 2 monolayer introduces a built-in electric field near the interface between MoS2 and p-Si to help photogenerated carrier separation. Such a heterojunction photovoltaic device achieves a power conversion efficiency of 5.23%, which is the highest efficiency among all monolayer transition-metal dichalcogenide-based solar cells. The demonstrated results of monolayer MoS 2/Si-based solar cells hold the promise for integration of 2D materials with commercially available Si-based electronics in highly efficient devices. © 2014 American Chemical Society.

  10. Unsupported single-atom-thick copper oxide monolayers

    Yin, Kuibo; Zhang, Yu-Yang; Zhou, Yilong; Sun, Litao; Chisholm, Matthew F.; Pantelides, Sokrates T.; Zhou, Wu


    Oxide monolayers may present unique opportunities because of the great diversity of properties of these materials in bulk form. However, reports on oxide monolayers are still limited. Here we report the formation of single-atom-thick copper oxide layers with a square lattice both in graphene pores and on graphene substrates using aberration-corrected scanning transmission electron microscopy. First-principles calculations find that CuO is energetically stable and its calculated lattice spacing matches well with the measured value. Furthermore, free-standing copper oxide monolayers are predicted to be semiconductors with band gaps ∼3 eV. The new wide-bandgap single-atom-thick copper oxide monolayers usher a new frontier to study the highly diverse family of two-dimensional oxides and explore their properties and their potential for new applications.

  11. Membrane Insertion by Trichosanthin Using the Monolayer Method

    薛毅; 夏晓峰; 隋森芳


    A monolayer technique was used to investigate the interaction between the ribosome inactivating protein trichosanthin (TCS) and phospholipid membrane.The adsorption experiments show that the negatively charged 1,2-dipalmitoyl-sn-glycerol-3-phosphoglycerol (DPPG) causes obvious enrichment of TCS beneath the monolayer, indicating electrostatic attraction between TCS and the negatively charged phospholipid.When TCS was incorporated into the DPPG monolayer at low pH, it could not be completely squeezed out until the monolayer collapsed.The results suggest that the electrostatic attraction and the hydrophobic force are involved in the interaction between TCS and phospholipids at different stages.These findings may be correlated with the membrane translocation mechanism of TCS.

  12. Tribological properties of OTS self-assembled monolayers


    Octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs)were prepared on the substrates of silicon and glass. The tribological properties were tested with a self-made point-contact pure sliding micro tribometer. The effect of humidity on the tribological properties of both OTS SAMs and the naked substrates were studied. When the substrate is covered by OTS monolayer, the friction coefficient is reduced from 0.5 to 0.1 and the stick-slip phenomenon is weakened. OTS monolayer can keep its friction coefficient steady in a wide range of humidity, because it is highly hydrophobic and thus not sensitive to humidity. In addition, the OTS monolayer has a considerable anti-wear ability.

  13. Coexistence of multiple conformations in cysteamine monolayers on Au(111)

    Zhang, Jingdong; Bilic, A; Reimers, JR


    The structural organization, catalytic function, and electronic properties of cysteamine monolayers on Au(111) have been addressed comprehensively by voltammetry, in situ scanning tunneling microscopy (STM) in anaerobic environment, and a priori molecular dynamics (MD) simulation and STM image si...

  14. Intrinsic instability of thin liquid films on nanostructured surfaces

    Rokoni, Arif; Hu, Han; Sun, Liyong; Sun, Ying


    The instability of a thin liquid film on nanostructures is not well understood but is important in liquid-vapor two-phase heat transfer (e.g., thin film evaporation and boiling), lubrication, and nanomanufacturing. In thin film evaporation, the comparison between the non-evaporating film thickness and the critical film breakup thickness determines the stability of the film: the film becomes unstable when the critical film breakup thickness is larger than the non-evaporating film thickness. In this study, a closed-form model is developed to predict the critical breakup thickness of a thin liquid film on 2D periodic nanostructures based on minimization of system free energy in the limit of a liquid monolayer. Molecular dynamics simulations are performed for water thin films on square nanostructures of varying depth and wettability and the simulations agree with the model predictions. The results show that the critical film breakup thickness increases with the nanostructure depth and the surface wettability. The model developed here enables the prediction of the minimum film thickness for stable thin film evaporation on a given nanostructure.

  15. Electrochemical Properties of Organosilane Self Assembled Monolayers on Aluminum 2024

    Hintze, Paul E.; Calle, Luz Marina


    Self assembled monolayers are commonly used to modify surfaces. Within the last 15 years, self assembled monolayers have been investigated as a way to protect from corrosion[1,2] or biofouling.[3] In this study, self assembled monolayers of decitriethoxysilane (C10H21Si(OC2H5)3) and octadecyltriethoxysilane (C18H37Si(OC2H5)3) were formed on aluminum 2024-T3. The modified surfaces and bare Al 2024 were characterized by dynamic water contact angle measurements, x-ray photoelectron spectroscopy (XIPS) and infrared spectroscopy. Electrochemical impedance spectroscopy (EIS) in 0.5 M NaCl was used to characterize the monolayers and evaluate their corrosion protection properties. The advancing water contact angle and infrared measurements show that the mono layers form a surface where the hydrocarbon chains are packed and oriented away from the surface, consistent with what is found in similar systems. The contact angle hysteresis measured in these systems is relatively large, perhaps indicating that the hydrocarbon chains are not as well packed as monolayers formed on other substrates. The results of the EIS measurements were modeled using a Randle's circuit modified by changing the capacitor to a constant phase element. The constant phase element values were found to characterize the monolayer. The capacitance of the monolayer modified surface starts lower than the bare Al 2024, but approaches values similar to the bare Al 2024 within 24 hours as the monolayer is degraded. The n values found for bare Al 2024 quickly approach the value of a true capacitor and are greater than 0.9 within hours after the start of exposure. For the monolayer modified structure, n can stay lower than 0.9 for a longer period of time. In fact, n for the monolayer modified surfaces is different from the bare surface even after the capacitance values have converged. This indicates that the deviation from ideal capacitance is the most sensitive indicator of the presence of the monolayer.

  16. Magnetic monolayers on semiconducting substrates. An in situ FMR study of Fe-based heterostructures

    Zakeri Lori, K.


    The growth, magnetic anisotropy, g-factor, and magnetization of Fe monolayers grown on GaAs(001), InAs(001), and InP(001) are investigated by a combination of in situ ferromagnetic resonance and SQUID magnetometry as a function of temperature and film thickness. The effect of stress caused by the lattice mismatch and the surface reconstruction on the magnetic anisotropy is quantified. An in-plane spin reorientation transition as a function of film thickness is observed at room temperature for all systems. A magneto-elastic model is used to explain the direction of the easy axis, the spin reorientation transition, and the contributions to the magnetic anisotropy terms using the stress components measured directly by in situ IV-low-energy electron diffraction. While the model gives a quantitative explanation of the out-of-plane magnetic anisotropy, changes of the electronic interface structure have to be taken into account for the in-plane magnetic anisotropy. The influence of Ag and Au buffer and cap layers on the magnetic anisotropy terms are determined. The temperature dependence of the total magnetic anisotropy, as well as the surface-interface and volume contribution to the magnetic anisotropy are determined for Fe monolayers on GaAs(001). It is demonstrated that the temperature dependence of the magnetic anisotropy is correlated with the temperature dependence of the magnetization according to the Callen-Callen model. The temperature dependence of the volume contribution to the perpendicular magnetic anisotropy is fully explained by the temperature dependence of the magneto-elastic anisotropy. A temperature-driven morphological transformation occurring at a temperature higher than 550 K depending on the film thickness is observed. The thin Fe3Si binary Heusler structure epitaxially grown on MgO(001) is investigated. In addition to the structural properties, magnetic anisotropy, magnetization, g-factor, spin, and orbital magnetism, the magnetic relaxation

  17. Adhesive and conformational behaviour of mycolic acid monolayers


    We have studied the pH-dependent interaction between mycolic acid (MA) monolayers and hydrophobic and hydrophilic surfaces using molecular (colloidal probe) force spectroscopy. In both cases, hydrophobic and hydrophilic monolayers (prepared by Langmuir-Blodgett and Langmuir-Schaefer deposition on silicon or hydrophobized silicon substrates, respectively) were studied. The force spectroscopy data, fitted with classical DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory to examine the contri...

  18. Surface dilatational viscosity of Langmuir monolayers

    Lopez, Juan; Vogel, Michael; Hirsa, Amir


    With increased interest in microfluidic systems, interfacial phenomena is receiving more attention. As the length scales of fluid problems decrease, the surface to volume ratio increases and the coupling between interfacial flow and bulk flow becomes increasingly dominated by effects due to intrinsic surface viscosities (shear and dilatational), in comparison to elastic effects (due to surface tension gradients). The surface shear viscosity is well-characterized, as cm-scale laboratory experiments are able to isolate its effects from other interfacial processes (e.g., in the deep-channel viscometer). The same is not true for the dilatational viscosity, because it acts in the direction of surface tension gradients. Their relative strength scale with the capillary number, and for cm-scale laboratory flows, surface tension effects tend to dominate. In microfluidic scale flows, the scaling favors viscosity. We have devised an experimental apparatus which is capable of isolating and enhancing the effects of dilatational viscosity at the cm scales by driving the interface harmonically in time, while keeping the interface flat. In this talk, we shall present both the theory for how this works as well as experimental measurements of surface velocity from which we deduce the dilatational viscosity of several monolayers on the air-water interface over a substantial range of surface concentrations. Anomalous behavior over some range of concentration, which superficially indicates negative viscosity, maybe explained in terms of compositional effects due to large spatial and temporal variations in concentration and corresponding viscosity.

  19. Induction of homochirality in achiral enantiomorphous monolayers.

    Parschau, Manfred; Romer, Sara; Ernst, Karl-Heinz


    We report the induction of homochirality in enantiomorphous layers of achiral succinic acid on a Cu(110) surface after doping with tartaric acid (TA) enantiomers. Succinic acid becomes chiral upon adsorption due to symmetry-breaking interactions with the Cu(110) surface. The doubly deprotonated bisuccinate forms mirror domains on the surface, which leads to a superposition of (11,-90) and (90,-11) patterns observed by low-energy electron diffraction (LEED). On average, however, the surface layer is racemic. An amount of 2 mol % of (R,R)- or (S,S)-tartaric acid in the monolayer, corresponding to an absolute coverage of 0.001 tartaric acid molecule per surface copper atom, is sufficient to make the LEED spots of one enantiomorphous lattice disappear. After thermally induced desorption of TA, the succinic acid lattice turns racemic again. In analogy to the "sergeants-and-soldiers" principle described for helical polymers, this effect is explained by a lateral cooperative interaction within the two-dimensional lattice.

  20. Structural phase transitions in monolayer molybdenum dichalcogenides

    Choe, Duk-Hyun; Sung, Ha June; Chang, Kee Joo


    The recent discovery of two-dimensional materials such as graphene and transition metal dichalcogenides (TMDs) has provided opportunities to develop ultimate thin channel devices. In contrast to graphene, the existence of moderate band gap and strong spin-orbit coupling gives rise to exotic electronic properties which vary with layer thickness, lattice structure, and symmetry. TMDs commonly appear in two structures with distinct symmetries, trigonal prismatic 2H and octahedral 1T phases which are semiconducting and metallic, respectively. In this work, we investigate the structural and electronic properties of monolayer molybdenum dichalcogenides (MoX2, where X = S, Se, Te) through first-principles density functional calculations. We find a tendency that the semiconducting 2H phase is more stable than the metallic 1T phase. We show that a spontaneous symmetry breaking of 1T phase leads to various distorted octahedral (1T') phases, thus inducing a metal-to-semiconductor transition. We discuss the effects of carrier doping on the structural stability and the modification of the electronic structure. This work was supported by the National Research Foundation of Korea (NRF) under Grant No. NRF-2005-0093845 and Samsung Science and Technology Foundation under Grant No. SSTFBA1401-08.

  1. Atomic-Scale Spectroscopy of Gated Monolayer MoS2.

    Zhou, Xiaodong; Kang, Kibum; Xie, Saien; Dadgar, Ali; Monahan, Nicholas R; Zhu, X-Y; Park, Jiwoong; Pasupathy, Abhay N


    The electronic properties of semiconducting monolayer transition-metal dichalcogenides can be tuned by electrostatic gate potentials. Here we report gate-tunable imaging and spectroscopy of monolayer MoS2 by atomic-resolution scanning tunneling microscopy/spectroscopy (STM/STS). Our measurements are performed on large-area samples grown by metal-organic chemical vapor deposition (MOCVD) techniques on a silicon oxide substrate. Topographic measurements of defect density indicate a sample quality comparable to single-crystal MoS2. From gate voltage dependent spectroscopic measurements, we determine that in-gap states exist in or near the MoS2 film at a density of 1.3 × 10(12) eV(-1) cm(-2). By combining the single-particle band gap measured by STS with optical measurements, we estimate an exciton binding energy of 230 meV on this substrate, in qualitative agreement with numerical simulation. Grain boundaries are observed in these polycrystalline samples, which are seen to not have strong electronic signatures in STM imaging.

  2. Micro-patterning of self-assembled organic monolayers by using tunable ultrafast laser pulses

    Maragkaki, Stella; Aumann, Andreas; Schulz, Florian; Schröter, Anja; Schöps, Benjamin; Franzka, Steffen; Hartmann, Nils; Ostendorf, Andreas


    We study the application of tunable ultrafast laser pulses in micropatterning self- assembled organic monolayer (SAMs) employing non collinear optical parametric amplification (NOPA). SAMs are ultrathin organic monolayers, which can be used in a variety of ways to assemble functionalized surface structures. In our study, we investigate the characteristics of SAMs as monomolecular resists during etching of gold. NOPA is a versatile method which provides the generation of ultrafast laser pulses, with a tunable wavelength in the visible and near infrared range. Due to the noncollinear geometry, a broadened spectral range can be amplified. The NOPA delivers wavelengths in the range of 480 nm to 950 nm at laser pulse lengths in the sub- 30 femtosecond range using a prism compressor after the nonlinear conversion. The ultrashort laser technology together with the advantages of the NOPA system guarantee high precision and allows us to determine the optimum conditions of sub-wavelength patterning by studying the effects of the fluence and the wavelength. At the same time, single-pulse processing allows us to selectively remove the ultrathin organic coating, while it ensures short processing time. In our study we used thiol-based SAMs as ultrathin layers on gold-coated glass substrates with a film thickness of 1-2 nm and 40 nm respectively.

  3. Localized dealloying corrosion mediated by self-assembled monolayers used as an inhibitor system.

    Shrestha, B R; Bashir, A; Ankah, G N; Valtiner, M; Renner, F U


    The structure and chemistry of thiol or selenol self-assembled organic monolayers have been frequently addressed due to the unique opportunities in functionalization of materials. Such organic films can also act as effective inhibition layers to mitigate oxidation or corrosion. Cu-Au alloy substrates covered by self-assembled monolayers show a different dealloying mechanism compared to bare surfaces. The organic surface layer inhibits dealloying of noble metal alloys by a suppression of surface diffusion at lower potentials but at higher applied potentials dealloying proceeds in localized regions due to passivity breakdown. We present an in situ atomic force microscopy study of a patterned thiol layer applied on Cu-Au alloy surfaces and further explore approaches to change the local composition of the surface layers by exchange of molecules. The pattern for the in situ experiment has been applied by micro-contact printing. This allows the study of corrosion protection with its dependence on different molecule densities at different sites. Low-density thiol areas surrounding the high-density patterns are completely protected and initiation of dealloying proceeds only along the areas with the lowest inhibitor concentration. Dealloying patterns are highly influenced and controlled by molecular thiol to selenol exchange and are also affected by introducing structural defects such as scratches or polishing defects.

  4. Visualizing band offsets and edge states in bilayer–monolayer transition metal dichalcogenides lateral heterojunction

    Zhang, Chendong; Chen, Yuxuan; Huang, Jing-Kai; Wu, Xianxin; Li, Lain-Jong; Yao, Wang; Tersoff, Jerry; Shih, Chih-Kang


    Semiconductor heterostructures are fundamental building blocks for many important device applications. The emergence of two-dimensional semiconductors opens up a new realm for creating heterostructures. As the bandgaps of transition metal dichalcogenides thin films have sensitive layer dependence, it is natural to create lateral heterojunctions (HJs) using the same materials with different thicknesses. Here we show the real space image of electronic structures across the bilayer–monolayer interface in MoSe2 and WSe2, using scanning tunnelling microscopy and spectroscopy. Most bilayer–monolayer HJs are found to have a zig-zag-orientated interface, and the band alignment of such atomically sharp HJs is of type-I with a well-defined interface mode that acts as a narrower-gap quantum wire. The ability to utilize such commonly existing thickness terraces as lateral HJs is a crucial addition to the tool set for device applications based on atomically thin transition metal dichalcogenides, with the advantage of easy and flexible implementation. PMID:26778119

  5. Visualizing band offsets and edge states in bilayer-monolayer transition metal dichalcogenides lateral heterojunction

    Zhang, Chendong; Chen, Yuxuan; Huang, Jing-Kai; Wu, Xianxin; Li, Lain-Jong; Yao, Wang; Tersoff, Jerry; Shih, Chih-Kang


    Semiconductor heterostructures are fundamental building blocks for many important device applications. The emergence of two-dimensional semiconductors opens up a new realm for creating heterostructures. As the bandgaps of transition metal dichalcogenides thin films have sensitive layer dependence, it is natural to create lateral heterojunctions (HJs) using the same materials with different thicknesses. Here we show the real space image of electronic structures across the bilayer-monolayer interface in MoSe2 and WSe2, using scanning tunnelling microscopy and spectroscopy. Most bilayer-monolayer HJs are found to have a zig-zag-orientated interface, and the band alignment of such atomically sharp HJs is of type-I with a well-defined interface mode that acts as a narrower-gap quantum wire. The ability to utilize such commonly existing thickness terraces as lateral HJs is a crucial addition to the tool set for device applications based on atomically thin transition metal dichalcogenides, with the advantage of easy and flexible implementation.

  6. Quantum Mechanical Rippling of a MoS2 Monolayer Controlled by Interlayer Bilayer Coupling

    Zheng, Yi; Chen, Jianyi; Ng, M.-F.; Xu, Hai; Liu, Yan Peng; Li, Ang; O'Shea, Sean J.; Dumitricǎ, T.; Loh, Kian Ping


    Nanoscale corrugations are of great importance in determining the physical properties of two-dimensional crystals. However, the mechanical behavior of atomically thin films under strain is not fully understood. In this Letter, we show a layer-dependent mechanical response of molybdenum disulfide (MoS2 ) subject to atomistic-precision strain induced by 2 H -bilayer island epitaxy. Dimensional crossover in the mechanical properties is evidenced by the formation of star-shaped nanoripple arrays in the first monolayer, while rippling instability is completely suppressed in the bilayer. Microscopic-level quantum mechanical simulations reveal that the nanoscale rippling is realized by the twisting of neighboring Mo—S bonds without modifying the chemical bond length, and thus invalidates the classical continuum mechanics. The formation of nanoripple arrays significantly changes the electronic and nanotribological properties of monolayer MoS2 . Our results suggest that quantum mechanical behavior is not unique for s p2 bonding but general for atomic membranes under strain.

  7. Synthesis of nanoparticle-cored dendrimers by convergent dendritic functionalization of monolayer-protected nanoparticles.

    Shon, Young-Seok; Choi, Daeock; Dare, Jonathan; Dinh, Tuong


    This article presents a synthesis method for nanoparticle-cored dendrimers (NCDs), which have dendritic architectures around a monolayer-protected gold nanoparticle. The synthesis method is based on a strategy in which the synthesis of monolayer-protected nanoparticles is followed by adding dendrons on functionalized nanoparticles by a single coupling reaction. NMR spectroscopy, IR spectroscopy, and thermogravimetric analysis (TGA) characterizations confirmed the successful coupling reaction between dendrons with different generations ([G1], [G2], and [G3]) and COOH-functionalized nanoparticles ( approximately Au201L71). The dendrimer wedge density also could be controlled by reacting nanoparticles having different loading of COOH groups ( approximately 60 and approximately 10% COOH of the 71 ligands per gold nanoparticle) with functionalized dendrons. Transmission electron microscope results showed that this synthesis strategy maintains the average size of the nanoparticle core during dendron coupling reactions. This control over the composition and core size makes the systematic study of NCDs with different generations possible. The chemical stability of NCDs was found to be affected by dendron generation around the nanoparticle core. The current-potential response of NCD films on microelectrode arrays exhibited better electrical conductivity for NCDs with lower dendron generation.

  8. Self-assembled monolayer-functionalized half-metallic manganite for molecular spintronics.

    Tatay, Sergio; Barraud, Clément; Galbiati, Marta; Seneor, Pierre; Mattana, Richard; Bouzehouane, Karim; Deranlot, Cyrile; Jacquet, Eric; Forment-Aliaga, Alicia; Jegou, Pascale; Fert, Albert; Petroff, Frédéric


    (La,Sr)MnO(3) manganite (LSMO) has emerged as the standard ferromagnetic electrode in organic spintronic devices due to its highly spin-polarized character and air stability. Whereas organic semiconductors and polymers have been mainly envisaged to propagate spin information, self-assembled monolayers (SAMs) have been overlooked and should be considered as promising materials for molecular engineering of spintronic devices. Surprisingly, up to now the first key step of SAM grafting protocols over LSMO surface thin films is still missing. We report the grafting of dodecyl (C12P) and octadecyl (C18P) phosphonic acids over the LSMO half-metallic oxide. Alkylphosphonic acids form ordered self-assembled monolayers, with the phosphonic group coordinated to the surface and alkyl chains tilted from the surface vertical by 43° (C12P) and 27° (C18P). We have electrically characterized these SAMs in nanodevices and found that they act as tunnel barriers, opening the door toward the integration of alkylphosphonic acid//LSMO SAMs into future molecular/organic spintronic devices such as spin OLEDs.

  9. Fabrication of Calix[4]arene Derivative Monolayers to Control Orientation of Antibody Immobilization

    Hongxia Chen


    Full Text Available Three calix[4]arene (Cal-4 derivatives which separately contain ethylester (1, carboxylic acid (2, and crownether (3 at the lower rim with a common reactive thiol at the upper rim were synthesized and constructed to self-assembled monolayers (SAMs on Au films. After spectroscopic characterization of the monolayers, surface coverage and orientation of antibody immobilized on the Cal-4 derivative SAMs were studied by surface plasmon resonance (SPR technique. Experimental results revealed that the antibody could be immobilized on the Cal-4 derivatives spontaneously. The orientation of absorbed antibody on the Cal-4 derivative SAMs is related to the SAM’s dipole moment. The possible orientations of the antibody immobilized on the Cal-4 derivative 1 SAM are lying-on or side-on, while on the Cal-4 derivative 2 and Cal-4 derivative 3 head-on and end-on respectively. These experimental results demonstrate the surface dipole moment of Cal-4 derivative appears to be an important factor to antibody orientation. Cal-4 derivatives are useful in developing site direct protein chips.

  10. Heterogeneous nanotribological response of polymorphic self-assembled monolayers arising from domain and phase dependent friction.

    Paradinas, Markos; Munuera, Carmen; Silien, Christophe; Buck, Manfred; Ocal, Carmen


    Micro-/nanoelectromechanical systems demand robust ultrathin films for lubrication. As they can drastically modify the frictional properties of surfaces, few nanometers thick self-assembled monolayers (SAMs) constitute accepted candidates as boundary lubricants. Their high stability and easy preparation make them attractive also for low cost applications. Given their high order, organosulfur SAMs have been archetypal systems for structural investigations, but few efforts have been devoted to analyze the influence of lateral inhomogeneities on their surface properties. The impact on the frictional response of the surface due to the existence of crystalline domains with lateral dimension in the sub-micrometer range is considered here. To this end, two polymorphic structures of self-assembled monolayers of ω-(4'-methylbiphenyl-4-yl) butane-1-thiol coexisting on Au(111) are investigated by scanning tunneling and force microscopy. Described by rectangular 5√5 × 3 (α-phase) and oblique 6√3 × 2√3 (β-phase) unit cells, they exhibit pronouncedly different frictional responses. The lateral nano-tribological heterogeneity of the surface is further influenced by the azimuthal orientation dependence of friction for each phase. In particular, this phenomenon is exploited in the less densely packed β-phase for which the separate analysis of forward and backward lateral force scans is used to differentiate domains rotated 180°. The results demonstrate the level of structural control required in the design of SAMs for nano-tribology applications.

  11. Fabrication of a Polyaniline Ultramicroelectrode via a Self Assembled Monolayer Modified Gold Electrode

    Bolat, Gulcin; Kuralay, Filiz; Eroglu, Gunes; Abaci, Serdar


    Herein, we report a simple and inexpensive way for the fabrication of an ultramicroelectrode and present its characterization by electrochemical techniques. The fabrication of polyaniline UME involves only two steps: modification of a gold (Au) electrode by self assembled monolayers (SAM) and then electrodeposition of polyaniline film on this thiol-coated Au electrode by using cyclic voltammetry and constant potential electrolysis methods. Two types of self-assembled monolayers (4-mercapto-1-butanol, MB, and 11-mercaptoundecanoic acid, MUA) were used, respectively, to see the effect of chain length on microelectrode formation. Microelectrode fabrication and utility of the surface was investigated by cyclic voltammetric measurements in a redox probe. The thus prepared polyaniline microelectrode was then used for DNA immobilization. Discrimination between double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA) was obtained with enhanced electrochemical signals compared to a polyaniline-coated Au electrode. Different modifications on the electrode surfaces were examined using scanning electron microscopy (SEM). PMID:23797740

  12. Visualizing band offsets and edge states in bilayer–monolayer transition metal dichalcogenides lateral heterojunction

    Zhang, Chendong


    Semiconductor heterostructures are fundamental building blocks for many important device applications. The emergence of two-dimensional semiconductors opens up a new realm for creating heterostructures. As the bandgaps of transition metal dichalcogenides thin films have sensitive layer dependence, it is natural to create lateral heterojunctions (HJs) using the same materials with different thicknesses. Here we show the real space image of electronic structures across the bilayer–monolayer interface in MoSe2 and WSe2, using scanning tunnelling microscopy and spectroscopy. Most bilayer–monolayer HJs are found to have a zig-zag-orientated interface, and the band alignment of such atomically sharp HJs is of type-I with a well-defined interface mode that acts as a narrower-gap quantum wire. The ability to utilize such commonly existing thickness terraces as lateral HJs is a crucial addition to the tool set for device applications based on atomically thin transition metal dichalcogenides, with the advantage of easy and flexible implementation.

  13. Gold electrode modified by self-assembled monolayers of thiols to determine DNA sequences hybridization

    Mízia M S Silva; Igor T Cavalcanti; M Fátima Barroso; M Goreti F Sales; Rosa Fireman Dutra


    The process of immobilization of biological molecules is one of the most important steps in the construction of a biosensor. In the case of DNA, the way it exposes its bases can result in electrochemical signals to acceptable levels. The use of self-assembled monolayer that allows a connection to the gold thiol group and DNA binding to an aldehydic ligand resulted in the possibility of determining DNA hybridization. Immobilized single strand of DNA (ssDNA) from calf thymus pre-formed from alkanethiol film was formed by incubating a solution of 2-aminoethanothiol (Cys) followed by glutaraldehyde (Glu). Cyclic voltammetry (CV) was used to characterize the self-assembled monolayer on the gold electrode and, also, to study the immobilization of ssDNA probe and hybridization with the complementary sequence (target ssDNA). The ssDNA probe presents a well-defined oxidation peak at +0.158 V. When the hybridization occurs, this peak disappears which confirms the efficacy of the annealing and the DNA double helix performing without the presence of electroactive indicators. The use of SAM resulted in a stable immobilization of the ssDNA probe, enabling the hybridization detection without labels. This study represents a promising approach for molecular biosensor with sensible and reproducible results.

  14. Thermoelectric properties of SnSe2 monolayer

    Li, Guanpeng; Ding, Guangqian; Gao, Guoying


    The 2H (MoS2-type) phase of 2D transition metal dichalcogenides (TMDCs) has been extensively studied and exhibits excellent electronic and optoelectronic properties, but the high phonon thermal conductivity is detrimental to the thermoelectric performances. Here, we use first-principles methods combined with Boltzmann transport theory to calculate the electronic and phononic transport properties of 1T (CdI2-type) SnSe2 monolayer, a recently realized 2D metal dichalcogenide semiconductor. The calculated band gap is 0.85 eV, which is a little larger than the bulk value. Lower phonon thermal conductivity and higher power factor are obtained in 1T-SnSe2 monolayer compared to 2H-TMDCs monolayers. The low phonon thermal conductivity (3.27 W mK-1 at room temperature) is mainly due to the low phonon frequency of acoustic modes and the coupling of acoustic modes with optical modes. We also find that the p-type has better thermoelectric performance than the n-type, and the figure of merit within p-type can reach 0.94 at 600 K for 1T-SnSe2 monolayer, which is higher than those of most 2H-TMDCs monolayers, making 1T-SnSe2 monolayer a promising candidate for thermoelectric applications.

  15. Treponema pallidum Invades Intercellular Junctions of Endothelial Cell Monolayers

    Thomas, D. Denee; Navab, Mahamad; Haake, David A.; Fogelman, Alan M.; Miller, James N.; Lovett, Michael A.


    The pathogenesis of syphilis reflects invasive properties of Treponema pallidum, but the actual mode of tissue invasion is unknown. We have found two in vitro parallels of treponemal invasiveness. We tested whether motile T. pallidum could invade host cells by determining the fate of radiolabeled motile organisms added to a HeLa cell monolayer; 26% of treponemes associated with the monolayer in a trypsin-resistant niche, presumably between the monolayer and the surface to which it adhered, but did not attain intracellularity. Attachment of T. pallidum to cultured human and rabbit aortic and human umbilical vein endothelial cells was 2-fold greater than to HeLa cells. We added T. pallidum to aortic endothelial cells grown on membrane filters under conditions in which tight intercellular junctions had formed. T. pallidum was able to pass through the endothelial cell monolayers without altering tight junctions, as measured by electrical resistance. In contrast, heat-killed T. pallidum and the nonpathogen Treponema phagedenis biotype Reiter failed to penetrate the monolayer. Transmission electron micrographs of sections of the monolayer showed T. pallidum in intercellular junctions. Our in vitro observations suggest that these highly motile spirochetes may leave the circulation by invading the junctions between endothelial cells.

  16. Optoelectronics of Transition Metal Dichalcogenide Monolayers and Heterostructures

    Schaibley, John


    Monolayer transition metal dichalcogenides (TMDs) contain 2D valley excitons which reside in two degenerate momentum space valleys at the edges of the Brillouin zone. It is crucially important to understand fundamental 2D exciton properties in TMD monolayers and van der Waals heterostructures. By performing coherent nonlinear optical spectroscopy with high spectral resolution, we observe nanosecond decay dynamics in single monolayers of MoSe2, implying the presence of a previously unreported long-lived state that appears to trap the exciton population. In MoSe2-WSe2 vertical heterostructures, we observe intralayer excitons, where the electron and hole are confined to different monolayers, and show evidence of strong exciton-exciton interaction effects and long lifetimes. Based on TMD monolayer excitons, we have also investigated a variety of fundamental quantum devices, including a nano-cavity laser and a second-harmonic generation transistor. Finally, we report a new type of single quantum emitter, based on single localized excitons spatially confined to defects in monolayers of WSe2. The photoluminescence from these localized excitons is spectrally narrow and shows strong anti-bunching, demonstrating the single photon nature of the emission.

  17. Manipulation of electronic structure in WSe2 monolayer by strain

    Yang, Cong-xia; Zhao, Xu; Wei, Shu-yi


    In this paper, we study the electronic properties of WSe2 monolayer with biaxial tensile strain and compressive strain by using first principles based on the density function theory. Under the biaxial tensile strain, WSe2 monolayer retains direct band gap with increasing strain and the band gap of WSe2 continuously decreases with increasing strain, eventually turn to metal when strain is equal to or more than 13%. Under the biaxial compressive strain, WSe2 monolayer turns to indirect gap and the band gap continuously decreases with increasing strain, finally turn to metal when strain is up to -7%. The strain can reduce the band gap of the WSe2 monolayer regardless of the strain direction. By comparison, we can see that the tensile strain appears to be more effective in reducing the band gap of pristine WSe2 monolayer than the compressive strain from -5% to 5%. But the band gap turns to zero quickly from -6% to -7% under compressive strain, however for tensile strain from 5% to 13%, the band gap decreases slowly. Based on the further analysis of the projected charge density for WSe2 monolayer, the fundamental reason of the change of band structure under biaxial tensile strain is revealed.

  18. Structural and electronic properties of arsenic nitrogen monolayer

    Liu, Pei; Nie, Yao-zhuang, E-mail:; Xia, Qing-lin; Guo, Guang-hua, E-mail:


    We present our first-principles calculations of a new two-dimensional material, arsenic nitrogen monolayer. The structural, electronic, and mechanical properties are investigated in detail by means of density functional theory computations. The calculated binding energy and the phonon spectra demonstrate that the AsN can form stable monolayer in puckered honeycomb structure. It is a semiconductor with indirect band gap of 0.73 eV, and displays highly anisotropic mechanical properties. Strain has obvious influence on the electronic properties of AsN monolayer. It is found that in the armchair direction, a moderate compression strain (−12%) can trigger an indirect to direct band gap transition and a tensile strain of 18% can make the AsN becoming a stable metal. In the zigzag direction, a rather smaller strain than armchair direction (12% for compression and 8% for stretch) can induce the indirect band gap to metal transition. - Highlights: • A new two-dimensional material, arsenic nitrogen monolayer is predicated by first-principles calculations. • Arsenic nitrogen monolayer displays highly anisotropic mechanical properties. • Electronic structures of arsenic nitrogen monolayer can be effectively manipulated by applied strains.

  19. Controlling the molecular architecture of lactase immobilized in Langmuir-Blodgett films of phospholipids to modulate the enzyme activity.

    Ayoub, Fábio de Paula; Caseli, Luciano


    In this present work, the adsorption of the enzyme lactase onto Langmuir monolayers of the phospholipid dimyristoylphosphatidic acid (DMPA) was investigated and characterized with surface pressure-area isotherms, surface potential-area isotherms and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). The adsorption of the enzyme at the air-water interface expanded the lipid monolayer and increased the film compressibility at high surface pressures. Amide bands in the PM-IRRAS spectra were identified, with the CN and CO dipole moments lying parallel to the monolayer plane, revealing that the structuring of the enzyme into β-sheets was kept in the mixed monolayer. The enzyme-lipid films were transferred from the floating monolayer to solid supports as Langmuir-Blodgett (LB) films and characterized with fluorescence spectroscopy and atomic force microscopy. The catalytic activity of the films was measured and compared to the homogenous medium. The enzyme accommodated in the LB films preserved more than 80% of the enzyme activity after 20days, in contrast for the homogeneous medium, which preserved less than 60% of the enzyme activity. The method presented in this present work not only allows for an enhanced catalytic activity toward lactose, but also can help explain why certain film architectures exhibit better performance.

  20. An NMR study of adsorbed helium films

    Kent, Anthony Joseph

    The properties of sub-monolayer Helium-3 films adsorbed on two totally different but planar substrates, Mylar† film and exfoliated graphite have been studied using NMR. The nuclear magnetic relaxation times T1 and T 2 have been measured as functions of fractional monolayer completion, temperature, substrate plane orientation and Larmor frequency using a specially designed and constructed NMR spectrometer system. The results obtained with a Mylar film substrate are consistent3with the formation of patches of solid 3He at regions of preferential adsorption on the substrate. Measurements of T2 m very low coverage 3He films on exfoliated graphite also indicate that the adsorbate forms areas of relatively high density solid, in agreement with the thermodynamic analysis of Elgin and Goodstein. Finally, detailed measurements of T2 as a function of all of the above parameters at low areal densities will help us to characterise the relaxation processes for the fluid phase of 33He on exfoliated graphite. †Mylar is the tradename of poly(ethelene-terephthalate) film, marketed by Du Pont.

  1. Microstructure evolution and device performance in solution-processed polymeric field-effect transistors: the key role of the first monolayer.

    Wang, Suhao; Kiersnowski, Adam; Pisula, Wojciech; Müllen, Klaus


    Probing the role of the first monolayer in the evolution of the film polymer microstructure is essential for the fundamental understanding of the charge carrier transport in polymeric field-effect transistors (FETs). The monolayer and its subsequent microstructure of a conjugated polymer [poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene), PBTTT] film were fabricated via solution deposition by tuning the dip-coating speed and were then studied as accumulation and transporting layers in FETs. Investigation of the microstructure of the layers prepared at different coating velocities revealed that the monolayer serves as an important base for further development of the film. Significant improvement of the charge carrier transport occurs only at a critical multilayer network density that establishes the required percolation pathways for the charge carriers. Finally, at a low dip-coating speed, the polymer chains are uniaxially oriented, yielding pronounced structural anisotropy and high charge carrier mobilities of 1.3 cm(2) V(-1) s(-1) in the alignment direction. © 2012 American Chemical Society

  2. Properties of mixed monolayers of clinical lung surfactant, serum albumin and hydrophilic polymers.

    Minkov, I; Mircheva, K; Grozev, N; Tz, Ivanova; Panaiotov, I


    It is now established that the surface activity of the clinically used lung surfactant is reduced by serum proteins and can be restored by adding the hydrophilic polymers. The mechanisms of lung surfactant inactivation by serum proteins and restoring effect by the hydrophilic polymers remain not completely understood. In this paper the state and rheological dilatational properties of surface films formed from clinical lung surfactant Exosurf, Survanta, Curosurf and Alveofact in the presence of serum albumin (BSA) and hydrophilic polymers polyvinylpyrrolidone (PVP), polyethylene glycol (PEG) and Dextran were studied. The obtained results suggest that the lung surfactant and BSA mixtures spread at air-water interface form a DPPC/BSA mixed monolayers with lower content of DPPC. The presence of hydrophilic polymers PVP, PEG and Dextran restore the DPPC content in the surface film. The effectiveness of the DPPC spreading and formation of better compacted film increases in order Exosurf, Survanta, Curosurf, Alveofact. The obtained results are in accordance with the generally admitted ideas about the mechanisms of serum protein inactivation and restoring effect of hydrophilic polymers based on the previously studies of the lung surfactant adsorption rate.

  3. Structure and dynamics of pentacene on SiO2: From monolayer to bulk structure

    Brillante, Aldo; Bilotti, Ivano; Della Valle, Raffaele Guido; Venuti, Elisabetta; Girlando, Alberto; Masino, Matteo; Liscio, Fabiola; Milita, Silvia; Albonetti, Cristiano; D'angelo, Pasquale; Shehu, Arian; Biscarini, Fabio


    We have used confocal micro Raman spectroscopy, atomic force microscopy (AFM), and x-ray diffraction (XRD) to investigate pentacene films obtained by vacuum deposition on SiO2 substrates. These methods allow us to follow the evolution of lattice structure, vibrational dynamics, and crystal morphology during the growth from monolayer, to TF, and, finally, to bulk crystal. The Raman measurements, supported by the AFM and XRD data, indicate that the film morphology depends on the deposition rate. High deposition rates yield two-dimensional nucleation and quasi-layer-by-layer growth of the T-F form only. Low rates yield three-dimensional nucleation and growth, with phase mixing occurring in sufficiently thick films, where the T-F form is accompanied by the “high-temperature” bulk phase. Our general findings are consistent with those of previous work. However, the Raman measurements, supported by lattice dynamics calculations, provide additional insight into the nature of the TFs, showing that their characteristic spectra originate from a loss of dynamical correlation between adjacent layers.

  4. Photoactive hybrid material based on pyrene functionalized PbS nanocrystals decorating CVD monolayer graphene.

    Ingrosso, Chiara; Bianco, Giuseppe V; Corricelli, Michela; Comparelli, Roberto; Altamura, Davide; Agostiano, Angela; Striccoli, Marinella; Losurdo, Maria; Curri, M Lucia; Bruno, Giovanni


    A simple and facile solution-based procedure is implemented for decorating a large area, monolayer graphene film, grown by chemical vapor deposition, with size-tunable light absorbing colloidal PbS nanocrystals (NCs). The hybrid is obtained by exposing a large area graphene film to a solution of 1-pyrene butyric acid surface coated PbS NCs, obtained by a capping exchange procedure onto presynthesized organic-capped NCs. The results demonstrate that at the interface, multiple and cooperative π-π stacking interactions promoted by the pyrene ligand coordinating the NC surface lead to a successful anchoring of the nano-objects on the graphene platform which concomitantly preserves its aromatic structure. Interligand interactions provide organization of the nano-objects in highly interconnected nanostructured multilayer coatings, where the NCs retain geometry and composition. The resulting hybrid exhibits a sheet resistance lower than that of bare graphene, which is explained in terms of electronic communication in the hybrid, due to the interconnection of the NC film and to a hole transfer from photoexcited PbS NCs to graphene, channelled at the interface by pyrene. Such a direct electron coupling makes the manufactured hybrid material an interesting component for optoelectronics, sensors and for optical communication and information technology.

  5. Effects of interface roughness on cohesive strength of self-assembled monolayers

    Zhang, Chen; Awasthi, Amnaya P.; Geubelle, Philippe H.; Grady, Martha E.; Sottos, Nancy R.


    Self-assembled monolayers (SAMs) are aggregates of small molecular chains that have the property to form highly ordered assemblies. The choice of terminal groups on the chains makes them excellent contenders of molecular-level tailoring. Molecular dynamics (MD) simulations and experimental observations of spallation of two SAM-enhanced gold-film/silicon-substrate interfaces have shown that the cohesive strength of SAM-enriched transfer-printed interfaces is strongly dependent on the choice of terminal groups. Though the MD results of perfectly ordered atomistic surfaces show the same qualitative trend as the experiments, they over-predict the interfacial cohesive strengths by a factor of about 50. Results from AFM studies have revealed that the roughness of these interfaces is of the same order (∼1 nm) as the range of atomistic interactions. Hence, surface roughness is a key contributor in significantly reducing interfacial cohesive strength in these systems. In this manuscript, a continuum-level study is performed to investigate the influence of surface roughness on the cohesive strength of the interface between a Si/SAM substrate and a transfer-printed gold film. We approximate the film as a deformable continuum interacting with a rough substrate of SAMs represented by a harmonic function. Using a cohesive law derived from MD, spallation is simulated to evaluate the effective traction-separation characteristics for the rough SAM-gold interface. Our analysis shows that incorporating roughness may reduce the interfacial cohesive strength by an order of magnitude depending on the film properties and the surface roughness. Additionally, we observe that the gold film adopts unique separation attributes based on roughness parameters and material properties.

  6. Photochemical CVD of Ru on functionalized self-assembled monolayers from organometallic precursors

    Johnson, Kelsea R.; Arevalo Rodriguez, Paul; Brewer, Christopher R.; Brannaka, Joseph A.; Shi, Zhiwei; Yang, Jing; Salazar, Bryan; McElwee-White, Lisa; Walker, Amy V.


    Chemical vapor deposition (CVD) is an attractive technique for the metallization of organic thin films because it is selective and the thickness of the deposited film can easily be controlled. However, thermal CVD processes often require high temperatures which are generally incompatible with organic films. In this paper, we perform proof-of-concept studies of photochemical CVD to metallize organic thin films. In this method, a precursor undergoes photolytic decomposition to generate thermally labile intermediates prior to adsorption on the sample. Three readily available Ru precursors, CpRu(CO)2Me, (η3-allyl)Ru(CO)3Br, and (COT)Ru(CO)3, were employed to investigate the role of precursor quantum yield, ligand chemistry, and the Ru oxidation state on the deposition. To investigate the role of the substrate chemistry on deposition, carboxylic acid-, hydroxyl-, and methyl-terminated self-assembled monolayers were used. The data indicate that moderate quantum yields for ligand loss (φ ≥ 0.4) are required for ruthenium deposition, and the deposition is wavelength dependent. Second, anionic polyhapto ligands such as cyclopentadienyl and allyl are more difficult to remove than carbonyls, halides, and alkyls. Third, in contrast to the atomic layer deposition, acid-base reactions between the precursor and the substrate are more effective for deposition than nucleophilic reactions. Finally, the data suggest that selective deposition can be achieved on organic thin films by judicious choice of precursor and functional groups present on the substrate. These studies thus provide guidelines for the rational design of new precursors specifically for selective photochemical CVD on organic substrates.

  7. Raman Identification of Polymorphs in Pentacene Films

    Alberto Girlando


    Full Text Available We use Raman spectroscopy to characterize thin films of pentacene grown on Si/SiO x by Supersonic Molecular Beam Deposition (SuMBD. We find that films up to a thickness of about 781 Å (∼ 52 monolayers all belong to the so-called thin-film (TF phase. The appearance with strong intensity of some lattice phonons suggests that the films are characterized by good intra-layer order. A comparison of the Raman spectra in the lattice and CH bending spectral regions of the TF polymorph with the corresponding ones of the high-temperature (HT and low-temperature (LT bulk pentacene polymorphs provides a quick and nondestructive method to identify the different phases.

  8. Growth and characterization of oriented cadmium sulphide nanocrystals under Langmuir-Blodgett monolayer of arachidic acid

    Roy, U. N.; Ingale, A.; Kukreja, L. M.; Mishra, S.; Ganesan, V.; Rustagi, K. C.

    Cadmium sulphide nanocrystals were grown at room temperature (20 °C) under arachidic acid monolayers floating over an aqueous solution of CdCl2 inside an enclosed Langmuir-Blodgett set-up, through slow infusion of H2S gas. X-ray diffraction spectra suggest an oriented growth of the crystallites. The particle sizes were found to increase with duration of exposure to the H2S gas. Atomic force microscopy indicated that the particles were nearly circular pellets with uniform morphology throughout. In Raman spectra, the FWHM of the LO phonon was found to be large ( 20 cm-1) for all the films grown with different exposure times in H2S gas, and was found to reduce to 8 cm-1 after annealing a typical sample at 500 °C for 45 min.

  9. Optical constants and self-assembly of phenylene ethynylene oligomer monolayers

    Marx, E.; Walzer, Karsten; Less, R.J.;


    This paper studies the self-assembly on gold surfaces of 1,4-ethynylphenyl-4'-ethynylphenyl-2'-nitro-1-benzenedithiolate (EP2NO(2)), a substituted phenylene ethynylene trimer with applications in molecular electronics. We develop an ellipsometric technique to measure the optical constants of thes...... of these self-assembled monolayers, and we also use attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and scanning tunneling microscopy (STM) to confirm the structure of the films.......This paper studies the self-assembly on gold surfaces of 1,4-ethynylphenyl-4'-ethynylphenyl-2'-nitro-1-benzenedithiolate (EP2NO(2)), a substituted phenylene ethynylene trimer with applications in molecular electronics. We develop an ellipsometric technique to measure the optical constants...

  10. Preparation and characterization of 3-(triethoxysilyl) propyl isocyanate self-assembled monolayer on surface of chip

    XIE Yao; GENG LiNa; QU Feng; LUO AiQin; QU Feng; DENG YuLin


    Monolayer of 3-(triethoxysilyl) propyl isocyanate was prepared on the slide by self-assembled tech-nique. X-ray photoelectron spectroscopy (XPS) was employed to analyze the elementary composition of the film. Contact angle of distilled water was measured to characterize the surface state. It was shown that 3-(triethoxysilyl) propyl isocyanate had been successfully assembled on the slide. The in-crease of contact angle to 80 demonstrated that the hydrophobicity of the surface of chip was in-creased significantly. Moreover, further self-assembly of bovine serum albumin (BSA) on 3-(trietho-xysilyl) propyl isocyanate was also carried out with the advantages such as simple and convenient preparation. Therefore, the potential of broader applications in the modification of micro-channel in the μ-TAS system, the immobilization of protein or peptide and the surface modification of materials are all expectative.

  11. Characterization of self-assembled monolayers of thiols on Au(111)

    邓文礼; 杨大本; 方晔; 白春礼


    Self-assembled monolayers (SAMs) of n-butanethiol, n-dodecanethiol and their equimolar mixture on Au(111) were prepared and characterized by ellipsometry, contact angle measurement, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Results revealed that these SAMs are oriented ultrathin films with the thickness of nanometer scale, and the SAMs were influenced by the molecular chain length, the lattice orientation and cleanliness of the substrates. The surface of the longer chain SAM is hydrophobic. The thicknesses of three SAMs of n-butanethiol, n-dodecanethiol and their mixture revealed by ellipsometry and XPS are about 0.59 - 0.67nm, 1.60- 1.69 nm and 1.23 - 1.32nm, respectively. AFM images further demonstrated that the SAM formed by the mixture has some microdomains with two different thicknesses.

  12. Influence of surface properties of mix-monolayers on lipolytic hydrolysis

    Peters, Günther H. J.; Dahmen, U.; Brezesinski, G.


    Fluorescence microscopy, surface potential, and activity measurements were used to investigate the influence of fatty acids and fatty alcohols on the lipolytic activity of several lipases. We have determined the lateral lipid distribution and interfacial properties of Langmuir mixed monolayers...... correlates with the isoelectric point (pI) of the enzymes. A simpler mechanism is observed by the addition of fatty alcohol. Within the concentration range studied, 1-octadecanol is immiscible in the diacylglyceride matrix, forming liquid-condensed domains. The inhibitory effect is related to the reduction...... composed of 1,2-didecanoylglycerol/eicosanoic acid or 1,2-didecanoylglycerol/1-octadecanol molecules and have measured lipase activities toward these films. Enzymatic activities are remarkably influenced by the addition of fatty acid. Activity decreases continuously up to a mole fraction of ≈ 0.1 fatty...

  13. Electric properties and fabrication of IMI-O LB films containing the imidazole group

    Yoo, S Y; Kwon, Y S; Park, J C


    We fabricated an IMI-O polymer containing an imidazole group that could form a complex structure between the monolayer and the metal ions at the air-water interface. Also, the monolayer behavior at the air-water interface and the electrical properties of metal-complexed Langmuir-Blodgett (LB) films were investigated by using Brewster angle microscopy (BAM) and current-voltage(I-V) measurements. The difference in the BAM images between the pure water and the aqueous metal ions is attributed to the interactions of the copolymers with the metal ions at the interface and the consequent change of the monolayer organization. In the I-V characteristics, the current for LB films with different metal ion depended on the quantity of the metal-ion complexed with the LB film due to the interaction between the metal ion and the IMI-O polymer.

  14. Heterointerface Screening Effects between Organic Monolayers and Monolayer Transition Metal Dichalcogenides

    Zheng, Yu Jie


    © 2016 American Chemical Society. The nature and extent of electronic screening at heterointerfaces and their consequences on energy level alignment are of profound importance in numerous applications, such as solar cells, electronics etc. The increasing availability of two-dimensional (2D) transition metal dichalcogenides (TMDs) brings additional opportunities for them to be used as interlayers in "van der Waals (vdW) heterostructures" and organic/inorganic flexible devices. These innovations raise the question of the extent to which the 2D TMDs participate actively in dielectric screening at the interface. Here we study perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) monolayers adsorbed on single-layer tungsten diselenide (WSe2), bare graphite, and Au(111) surfaces, revealing a strong dependence of the PTCDA HOMO-LUMO gap on the electronic screening effects from the substrate. The monolayer WSe2 interlayer provides substantial, but not complete, screening at the organic/inorganic interface. Our results lay a foundation for the exploitation of the complex interfacial properties of hybrid systems based on TMD materials.

  15. Electrocatalytic oxidation of GMP on an ITO electrode modified by the photoposition of Pd nanoparticles onto a monolayer TiO2-Ru(Ⅱ)complex hybrid film%Pd纳米粒子敏化的纳米单层TiO2-Ru(Ⅱ)螯合物修饰电极对单磷酸鸟苷的电催化氧化行为

    陈锡安; 王舜; 林娟娟; 刘爱丽; 黄少铭


    利用LB膜技术可控制备了纳米单层的二氧化钛-有机钌螯合物杂化膜,并研究了上述无机-有机杂化膜修饰电极在Pd纳米粒子敏化后对单磷酸鸟苷(GMP)的电催化氧化行为.实验结果表明:(1)纳米单层TiO2/[Ru(phen)2(dC18bpy)]2+(简称为TiO2-Ru)杂化膜的平均厚度为(3.2±0.5)nm;(2)在光照条件下TiO2-Ru杂化膜能有效催化还原[Pd(NH3)4]2+形成粒径位于20~200 nm之间的Pd纳米粒子;(3)纳米单层TiO2-Ru/Pd杂化膜能高效催化氧化具有供电子能力的单磷酸鸟苷(GMP),与纳米单层TiO2-Ru杂化膜修饰的ITO电极(ITO/TiO2-Ru)相比,当工作电压为1200mV时,ITO/TiO2-Ru/Pd电极在含有1×10-3 mol L-1 GMP的磷酸盐缓冲液中,单位面积的催化氧化电流提高了约36倍;(4)Pd纳米粒子的引入消除了金属钌螯合物中配体对电子传递的阻碍作用,改变了电子传递途径,从而有效减少了电子空穴对的复合,提高了杂化膜修饰电极(ITO/TiO2-Ru/Pd)的电子传递效率.%An indium tin oxide (ITO) electrode coated with monolayer TiO2/[Ru(phen)2(dC18bpy)]2+ (phen =1,10-phenanthroline, dC18bpy = 4,4'-dioctadecyl-2,2'-bipyridyl) hybrid film (denoted as ITO/TiO2-Ru) has been prepared by the modified Langmuir-Blodgctt (LB) method, and the electrocatalytic oxidation of mononuclcotide of guanosine 5'-monophosphate (GMP) on an ITO/TiO2-Ru electrode after Pd-photodeposition (denoted as ITO/TiO2-Ru/Pd) has been studied.Atomic force microscopy reveals that the single-layered hybrid film of TiO2 nanosheets/[Ru(phen)2(dCl 8bpy)]2+ is closely packed at a surface pressure of 25 mN m-1 and has a thickness of (3.20 ± 0.5) nm.X-ray photoelectron spectra shows the formation of Pd nanoparticlcs on the surface of hybrid film with radii of 20~200 nm by the reduction of [Pd(NH3)4]2+ under light irradiation.When being applied to oxidize GMP, a larger catalytic oxidative current is achieved on thc ITO/TiO2-Ru/Pd electrode at the external potential above 700 m

  16. Structural studies of ultrathin organic films

    Yim, Hyun


    Ultrathin organic films have been a focus of research due to the growing interest in optoelectronics and molecular electronics. In both areas, it is believed that self-assembled (SA) films and Langmuir-Blodgett (LB) films may provide the desired control of order at the molecular level. The tethering of polyglutamate molecules to surfaces is of special interest due to nonlinear optical properties which can be achieved when the molecules are oriented. The tethering of poly(benzyl-L-glutamate) to silicon has been done by polymerization of benzyl-L-glutamate-N-carboxyanhydride using self-assembled monolayers with various concentrations of amino end groups as initiating layers. X-ray reflectivity results show that a minimum concentration of initiator sites on the surface is required. The second tethering system is a polystyrene brush. The polystyrene brush is expected to give strong sensitivity to solvent swelling. The structure of the polystyrene brush, which was chemically grafted to a substrate, in poor solvent and its change at different temperatures were investigated by neutron reflectometry. When temperature increases up to 30sp°C, both the thickness and roughness increase greatly, which indicates that the polystyrene brush changes from a collapsed state to a theta state. Hairy-rod polyimide molecules are of interest due to their interesting physical properties. Multilayer films of preformed polyimide molecules (6FDA-C18) have been obtained for the first time by the LB technique. The multilayer films do not display a distinctively periodic structure. Upon annealing for a few hours at 180sp°C, the structure relaxes slightly. The alkyl side chain substituted polyimides (BACBF/BPDA) can form metastable monolayers for which the pressure-area isotherms vary markedly with side chain length. For the polyimide with octadecyl side chains, a sharp reduction in zero pressure area occurs between 20 and 24sp°C, suggesting an important change in side chain mobility

  17. Coherent thermal radiation in thin films and its application in the emissivity design of multilayer films

    LIANG XinGang; HAN MaoHua


    The Infrared transmission spectra of a 0.54-μm-thick Ge film and a 20-μm-thick Si film were experimentally measured.As the incident radiation was in the wavelength range from 1.5 μm to 10 μm,the Ge film demonstrated a strongly spectral coherence.However,thermal radiation of the Ge film was found to be spatially incoherent due to its extreme thinness.The Si film exhibited significantly spectral and spatial coherence.The results confirmed that thermal radiation of a monolayer film could be coherent spectrally and spatially if the film thickness was comparable with the wavelength.The optical characteristic matrix method was applied to calculate the transmission spectra of the Si and Ge film,and the results agreed well with the measurements.This method was further used to analyze two multilayer films composed of five low emissive layers.Their emissivities were found to be highly emissive at a certain zenith angle,and the emissive peak could be controlled by careful selection of film thickness.

  18. Observation of monolayer valence band spin-orbit effect and induced quantum well states in MoX2

    Alidoust, Nasser; Bian, Guang; Xu, Su-Yang; Sankar, Raman; Neupane, Madhab; Liu, Chang; Belopolski, Ilya; Qu, Dong-Xia; Denlinger, Jonathan D.; Chou, Fang-Cheng; Hasan, M. Zahid


    Transition metal dichalcogenides transition metal dichalcogenides have attracted much attention recently due to their potential applications in spintronics and photonics because of the indirect to direct band gap transition and the emergence of the spin-valley coupling phenomenon upon moving from the bulk to monolayer limit. Here, we report high-resolution angle-resolved photoemission spectroscopy on MoSe2 single crystals and monolayer films of MoS2 grown on highly ordered pyrolytic graphite substrate. Our experimental results resolve the Fermi surface trigonal warping of bulk MoSe2, and provide evidence for the critically important spin-orbit split valence bands of monolayer MoS2. Moreover, we systematically image the formation of quantum well states on the surfaces of these materials, and present a theoretical model to account for these experimental observations. Our findings provide important insights into future applications of transition metal dichalcogenides in nanoelectronics, spintronics and photonics devices as they critically depend on the spin-orbit physics of these materials.

  19. Fabrication of molecular nanopatterns at aluminium oxide surfaces by nanoshaving of self-assembled monolayers of alkylphosphonates.

    El Zubir, Osama; Barlow, Iain; Leggett, Graham J; Williams, Nicholas H


    Nanoshaving, by tracing an atomic force microscope probe across a surface at elevated load, has been used to fabricate nanostructures in self-assembled monolayers of alkylphosphonates adsorbed at aluminium oxide surfaces. The simple process is implemented under ambient conditions. Because of the strong bond between the alkylphosphonates and the oxide surface, loads in excess of 400 nN are required to pattern the monolayer. Following patterning of octadecylphosphonate SAMs, adsorption of aminobutyl phosphonate yielded features as small as 39 nm. Shaving of monolayers of aryl azide-terminated alkylphosphonates, followed by attachment of polyethylene glycol to unmodified regions in a photochemical coupling reaction, yielded 102 nm trenches into which NeutrAvidin coated, dye-labelled, polymer nanospheres could be deposited, yielding bright fluorescence with little evidence of non-specific adsorption to other regions of the surface. Structures formed in alkylphosphonate films by nanoshaving were used to etch structures into the underlying metal. Because of the isotropic nature of the etch process, and the large grain size, some broadening was observed, but features 25-35 nm deep and 180 nm wide were fabricated.

  20. Taking another look with fluorescence microscopy: image processing techniques in Langmuir monolayers for the twenty-first century.

    Stottrup, Benjamin L; Nguyen, Andrew H; Tüzel, Erkan


    Fluorescence microscopy has become a powerful and standard complementary technique in the study of amphiphilic films at the air-water interface. For nearly three decades the coupling of traditional thermodynamic measurements with direct visualization has provided a better understanding of self-assembled Langmuir monolayers and their application in the study of the physical properties of membranes and interfaces. As an introduction we provide a brief overview of this established technique and demonstrate its continued utility in the recent observation of novel phase behavior in monolayers of 25-hydroxycholesterol (25-OH) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). We then focus our review on new analysis techniques which take advantage of the ability to store, process, and analyze large sets of images. We pay particular attention to efforts measuring the line tension between coexisting two dimensional fluid phases in the Langmuir monolayer. Using non-perturbative methods, we can measure fundamental mechanical properties of these two dimensional systems. Finally, we highlight the use of Model Convolution Microscopy as a new tool to provide insight on the experimental limits in these studies. Copyright 2009 Elsevier B.V. All rights reserved.

  1. Langmuir monolayers of cerebroside originated from Linckia laevigata: binary systems of cerebrosides and phospholipid.

    Maruta, Tomoki; Hoda, Kazuki; Inagaki, Masanori; Higuchi, Ryuichi; Shibata, Osamu


    The surface pressure (pi)-area (A), the surface potential (DeltaV)-A and the dipole moment (mu( perpendicular))-A isotherms were obtained for six cerebrosides of LLC-2, LLC-2-1, LLC-2-8, LLC-2-10, LLC-2-12, and LLC-2-15, which were isolated from Linckia laevigata, and two-component monolayers of two different cerebrosides (LLC-2 and LLC-2-8) with phospholipid of dipalmitoylphosphatidylcholine (DPPC) on a subphase of 0.15 M sodium chloride solution as a function of cerebroside compositions in the two-component systems by employing the Wilhelmy method, the ionizing electrode method, and the fluorescence microscopy. The new finding was that LLC-2 showed a stable and liquid expanded type film. Four of them (LLC-2-8, -10, -12, and -15) had the phase transition from the liquid-expanded (LE) to the liquid-condensed (LC) states at 298.2 K. The apparent molar quantity changes (Deltas(gamma), Deltah(gamma), and Deltau(gamma)) on their phase transition on 0.15M at 298.2 K were calculated. The miscibility of cerebroside and phospholipid in the two-component monolayers was examined by plotting the variation of the molecular area and the surface potential as a function of the cerebroside molar fraction (X(cerebroside)), using the additivity rule. From the A-X(cerebroside) and DeltaV(m)-X(phospholipid) plots, a partial molecular surface area (PMA) and an apparent partial molecular surface potential (APSP) were determined at the discrete surface pressure. The PMA and APSP with the mole fraction were extensively discussed for the miscible systems. Judging from the two-dimensional phase diagrams, these were found to be one type, a positive azeotropic type; all the cerebrosides were miscible with DPPC. Furthermore, assuming a regular surface mixture, the Joos equation for the analysis of the collapse pressure of two-component monolayers allowed calculation of the interaction parameter (xi) and the interaction energy (-Deltavarepsilon) between the cerebrosides and DPPC. The

  2. Monte Carlo studies of model Langmuir monolayers.

    Opps, S B; Yang, B; Gray, C G; Sullivan, D E


    This paper examines some of the basic properties of a model Langmuir monolayer, consisting of surfactant molecules deposited onto a water subphase. The surfactants are modeled as rigid rods composed of a head and tail segment of diameters sigma(hh) and sigma(tt), respectively. The tails consist of n(t) approximately 4-7 effective monomers representing methylene groups. These rigid rods interact via site-site Lennard-Jones potentials with different interaction parameters for the tail-tail, head-tail, and head-head interactions. In a previous paper, we studied the ground-state properties of this system using a Landau approach. In the present paper, Monte Carlo simulations were performed in the canonical ensemble to elucidate the finite-temperature behavior of this system. Simulation techniques, incorporating a system of dynamic filters, allow us to decrease CPU time with negligible statistical error. This paper focuses on several of the key parameters, such as density, head-tail diameter mismatch, and chain length, responsible for driving transitions from uniformly tilted to untilted phases and between different tilt-ordered phases. Upon varying the density of the system, with sigma(hh)=sigma(tt), we observe a transition from a tilted (NNN)-condensed phase to an untilted-liquid phase and, upon comparison with recent experiments with fatty acid-alcohol and fatty acid-ester mixtures [M. C. Shih, M. K. Durbin, A. Malik, P. Zschack, and P. Dutta, J. Chem. Phys. 101, 9132 (1994); E. Teer, C. M. Knobler, C. Lautz, S. Wurlitzer, J. Kildae, and T. M. Fischer, J. Chem. Phys. 106, 1913 (1997)], we identify this as the L'(2)/Ov-L1 phase boundary. By varying the head-tail diameter ratio, we observe a decrease in T(c) with increasing mismatch. However, as the chain length was increased we observed that the transition temperatures increased and differences in T(c) due to head-tail diameter mismatch were diminished. In most of the present research, the water was treated as a hard

  3. First-principles study of thermodynamical and mechanical stabilities of thin copper film on tantalum

    Hashibon, Adham; Elsässer, Christian; Mishin, Yuri; Gumbsch, Peter


    The adhesion, stability, and wetting behavior at interfaces between thin Cu films and clean Ta (110) substrates are investigated by first-principles calculations using density functional theory (DFT) in the local-density approximation. Interfaces between pseudomorphic body-centered-tetragonal thin films of Cu, strained face-centered-cubic thin films of Cu, and a single pseudomorphic monolayer of Cu on body-centered-cubic Ta (110) surfaces are studied. Various high-symmetry interface configurations are considered for each case. The mechanical stability of the interfaces is studied by the ideal work of separation, while the thermodynamic stability is investigated by Gibbs’ excess interface energy. All three interfaces are found to be thermodynamically unstable. An energy-weighting scheme extends the use of the DFT calculations to the case of an incoherent misfitting interface. The incoherent monolayer of Cu on Ta is thereby found to be thermodynamically stable. For coverages by more than a monolayer, the Cu atoms are expected to form three-dimensional islands on top of the Cu monolayer. With respect to interface separation, the monolayer is found to be bound more strongly to the Ta substrate than the thin film. Hence, failure is expected to occur not at the Cu/Ta interface but inside the Cu.

  4. The Spectrum of Quantum Dots Film for UV CCD

    Lin Jiang


    Full Text Available A new kind of UV-responsive film with quantum dots (QDs fabricated by a spin-coating method is proposed in this paper. In a previous study, the monolayer QDs film is deposited onto fused silica slides by the spin-coating way, which has some luminous problem. The introduction of composite QDs coating which adds PEDOT:PSS and poly-TPD films to the monolayer QDs film is found to have excellent performance. The reason can be that PEDOT:PSS and poly-TPD weaken the scattering and enhance the emitting of quantum dot fluorescence. The intensity of photoluminescence (PL for composite QDs coating is dozens of times stronger than that for monolayer QDs film. Experiment results show that this composite coating has excellent fluorescent properties and emits a blue purple glow together a wide excitation spectrum field from 190 nm to 300 nm. The spectrum of the composite coating matches accurately with the detected zone of CCD, which achieves an outstanding UV-responsive coating for conventional silicon-based image sensors.

  5. Self-assembly of organic films on a liquid metal

    Magnussen, Olaf M.; Ocko, Benjamin M.; Deutsch, Moshe; Regan, Michael J.; Pershan, Peter S.; Abernathy, Douglas; Grübel, Gerhard; Legrand, Jean-François


    THE structure and phase behaviour of organic thin films result from the subtle interplay of intermolecular Van der Waals interactions, which promote self-assembly and long-ranged order, and the more complex interactions between the end groups of the organic chains and the substrate. The structure of molecular films of amphiphiles has been extensively studied on subphases of dielectric liquids, notably water (Langmuir mono-layers) and on solid surfaces (self-assembled monolayers, SAMs)1-4. Here we report structural studies, by synchrotron X-ray scattering, of an intermediate case: densely packed alka-nethiol films on the surface of liquid mercury. While, like SAMs, these films form strong chemical bonds to the subphase, this subphase is smooth and unstructured, as in the case of Langmuir monolayers. But unlike either of these1,2,5-7, our films have no in-plane long-range order. We suggest that the strong interaction of the thiol group with the underlying disordered liquid dominates here over the order-promoting interactions of the alkyl chains.

  6. Materials science in microelectronics I the relationships between thin film processing and structure

    Machlin, Eugene


    Thin films play a key role in the material science of microelectronics, and the subject matter of thin-films divides naturally into two headings: processing / structure relationship, and structure / properties relationship.The first volume of Materials Science in Microelectronics focuses on the first relationship - that between processing and the structure of the thin-film. The state of the thin film's surface during the period that one monolayer exists - before being buried in the next layer - determines the ultimate structure of the thin film, and thus its properties. This

  7. Mode of interaction of ganglioside Langmuir monolayer originated from echinoderms: three binary systems of ganglioside/DPPC, ganglioside/DMPE, and ganglioside/cholesterol.

    Hoda, Kazuki; Ikeda, Yuriko; Kawasaki, Hideya; Yamada, Koji; Higuchi, Ryuichi; Shibata, Osamu


    The surface pressure (pi)-area (A), the surface potential (DeltaV)-A, and the dipole moment (mu( perpendicular))-A isotherms were obtained for monolayers made from a ganglioside originated from echinoderms [Diadema setosum ganglioside (DSG-1)], dipalmitoylphosphatidylcholine (DPPC), dimyristoylphosphatidylethanolamine (DMPE), cholesterol (Ch), and their combinations. Monolayers spread on several different substrates were investigated at the air/water interface by the Wilhelmy method, ionizing electrode method, fluorescence microscopy (FM) and atomic force microscopy (AFM). Surface potentials (DeltaV) of pure components were analyzed using the three-layer model proposed by Demchak and Fort [R.J. Demchak, T. Fort, J. Colloid Interface Sci. 46 (1974) 191-202]. The new finding was that DSG-1 was stable and showed a liquid-expanded film and that its monolayer behavior of DeltaV was sensitive for the change of the NaCl concentration in the subphase. Moreover, the miscibility of DSG-1 and three major lipids in the two-component monolayers was examined by plotting the variation of the molecular area and the surface potential as a function of the DSG-1 molar fraction (X(DSG-1)), using the additivity rule. From the A-X(DSG-1) and DeltaV(m)-X(DSG-1) plots, partial molecular surface area (PMA) and apparent partial molecular surface potential (APSP) were determined at the discrete surface pressure. The PMA and APSP with the mole fraction were extensively discussed for the miscible system. The miscibility was also investigated from the two-dimensional phase diagrams. Furthermore, a regular surface mixture, for which the Joos equation was used for the analysis of the collapse pressure of two-component monolayers, allowed calculation of the interaction parameter (xi) and the interaction energy (-Deltavarepsilon) between them. The observations using fluorescence microscopy and AFM image also provide us the miscibility in the monolayer state.

  8. Monolayer and Brewster angle microscopy study of human serum albumin-dipalmitoyl phosphatidyl choline mixtures at the air-water interface.

    Toimil, Paula; Prieto, Gerardo; Miñones, José; Trillo, José M; Sarmiento, Félix


    The aim of this study is to deepen the understanding of the behavior of human serum albumin (HSA) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) mixed monolayers. For this purpose, different amounts of DPPC were spread at 25°C on the water surface containing a monolayer of HSA. Surface film balance and Brewster angle microscopy techniques have been used to analyze the structural and energetic characteristics (structure, topography, thickness, miscibility and interactions) of these mixtures. HSA/DPPC mixed monolayers exhibit two phase transitions evidenced by two discontinuities in the corresponding π-A isotherms and by two minimum values in the compressional modulus (C(s)(-1))-surface pressure (π) curves. The plot of the molecular areas occupied by the mixed monolayers as function of the mass fraction of DPPC shows the absence of deviations from linearity, a typical behavior for ideal or inmiscible system. This result was confirmed from the values calculated for the free energy of excess (ΔG(exc)), which are practically zero whatever the composition of the mixtures and the surface pressures at which ΔG(exc) values were calculated. In addition, relative thickness values of HSA/DPPC mixed monolayers showed the existence of an exclusion surface pressure (π(exc)), below which the monolayer is composed of a mixture of both components, while above π(exc) the HSA molecules are squeezed out the interface, but not totally. In fact, although in this region DPPC domains predominate at the interface, the existence of protein molecules in a packing "loops" configuration can be observed in BAM images. Moreover, relative thickness measurements confirm this hypothesis.

  9. Platinum monolayer electrocatalysts for oxygen reduction in fuel cells

    Zhang, Junliang

    Fuel cells are expected to be one of the major clean energy sources in the near future. However, the slow kinetics of electrocatalytic oxygen reduction reaction (ORR) and the high loading of Pt for the cathode material are the urgent issues to be addressed since they determine the efficiency and the cost of this energy source. In this study, a new approach was developed for designing electrocatalysts for the ORR in fuel cells. These electrocatalysts consist of only one Pt monolayer, or mixed transition metal-Pt monolayer, on suitable carbon-supported metal, or alloy nanoparticles. The synthesis involved depositing a monolayer of Cu on a suitable transition metal or metal alloy surface at underpotentials, followed by galvanic displacement of the Cu monolayer with Pt or mixed metal-Pt. It was found that the electronic properties of Pt monolayer could be fine-tuned by the electronic and geometric effects introduced by the substrate metal (or alloy) and the lateral effects of the neighboring metal atoms. The role of substrates was found reflected in a "volcano" plot of the monolayer activity for the ORR as a function of their calculated d-band centers. The Pt mass-specific activity of the new Pt monolayer electrocatalysts was up to twenty times higher than the state-of-the-art commercial Pt/C catalysts. The enhancement of the activity is caused mainly by decreased formation of PtOH (the blocking species for ORR), and to a lesser degree by the electronic effects. Fuel cell tests showed a very good long term stability of the new electrocatalysts. Our results demonstrated a viable way to designing the electrocatalysts which could successfully alleviate two issues facing the commercialization of fuel cells---the costs of electrocatalysts and their efficiency.

  10. Biophysical characterization of monofilm model systems composed of selected tear film phospholipids.

    Patterson, Matthew; Vogel, Hans J; Prenner, Elmar J


    The tear film protects the eye from foreign particles and pathogens, prevents excess evaporation, provides lubrication, and maintains a high quality optical surface necessary for vision. The anterior layer of tear film consists of polar and non-polar lipid layers. The polar lipids form a monolayer on the aqueous subphase, acting as surfactants for the non-polar lipid multilayer. A tear film polar lipid biomimetic consisting of dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylethanolamine (DPPE), palmitoyl glucosylceramide (PGC), and palmitoyl sphingomyelin (PSM) was characterized using Langmuir monolayers and Brewster angle microscopy (BAM). Lipid combinations formed very stable monolayers, especially those containing DPPC or PSM. Surface experiments and elasticity analyses revealed that PGC resulted in more condensed and rigid mixed monolayers. DPPE provided resistance to large changes in lipid ordering over a wide surface pressure range. Ternary mixtures containing DPPE and PGC with either DPPC or PSM experienced the greatest lipid ordering within the natural tear film surface pressure range suggesting that these lipids are important to maintain tear film integrity during the inter-blink period. Finally, BAM images revealed unique structures within monolayers of DPPC, DPPE, and PGC at the natural tear film surface pressure. 3D analysis of these domains suggested either the formation of multilayers or outward protrusions at surface pressures far below the point of irreversible collapse as seen on the isotherm. This entails that the polar lipids of tear film may be capable of multilayer formation or outward folding as a mechanism to prevent rupture of the tear film during a blink.

  11. Secondary structure and lipid interactions of the N-terminal segment of pulmonary surfactant SP-C in Langmuir films: IR reflection-absorption spectroscopy and surface pressure studies

    Bi, Xiaohong; Flach, Carol R; Pérez-Gil, Jesus


    syndrome, a pathological condition resulting from deficiency in surfactant. To facilitate rational design of therapeutic agents, a molecular level understanding of lipid interaction with surfactant proteins or their analogues in aqueous monolayer films is necessary. The current work uses infrared...

  12. Dimensionality crossover in critical behaviour of ultrathin ferromagnetic films

    Prudnikov, Pavel V., E-mail:; Prudnikov, Vladimir V.; Menshikova, Maria A.; Piskunova, Natalia I.


    We propose the model which takes account of magnetocrystalline anisotropy effects in thin magnetic films. The dimensionality crossover from two-dimensional monolayer to three-dimensional system in multilayer magnetic films is studied using a Monte Carlo technique. Finite-size scaling is applied for the determination of the critical characteristics as a function of film thickness. The transition to intermediate planar phase is discussed. - Highlights: • We make Monte Carlo simulations in a anisotropy Heisenberg films. • Anisotropy effects lead to dimensionality crossover in Heisenberg films. • The transition to intermediate XY-like phase for 14–19 ML was discovered. • The critical exponents agree with experiments for Ni and Co films.

  13. Multilayers Polyethylene Film for Crop Protection in Harsh Climatic Conditions

    A. Dehbi


    Full Text Available In this work the performance and durability of a new generation of greenhouse covers, in which the cover is composed of five layers, are investigated. A sand wind ageing was performed under different exposure conditions. Surface morphology and chemical, physical, and thermal characteristics were investigated by using optical microscopy, FTIR, and tensile test techniques. In addition, the mechanical integrity of the five-layer film was assessed. The analysis indicated that the sand wind treatments have a significant influence only on the performance of the film. An attempt has been done to compare the properties of the five-layer film with the monolayer and trilayer films with or without air bubble under similar conditions. The results revealed that the five-layer film proved to be a promising greenhouse covering film.


    Ding Jianning; Yang Jichang; Wen Shizhu


    In order to accomplish reliable mechanical design of MEMS, the influences of surface roughness and octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) on the mechanical properties of micromachined polysilicon films for MEMS are investigated. Surface effect on the fracture properties of micromachined polysilicon films is evaluated with a new microtensile testing method using a magnet-coil force actuator. Statistical analysis of the surface roughness effects on the tensile strength predicated the surface roughness characterization of polysilicon films being tested and the direct relation of the mechanical properties with the surface roughness features. The fracture strength decreases with the increase of the surface roughness. The octadecyltrichlorosilane self-assembled monolayers coating leads to an increase of the average fracture strength up to 32.46%. Surface roughness and the hydrophobic properties of specimen when coated with OTS films are the two main factors influencing the tensile strength of micromachined polysilicon films for MEMS.

  15. Structural studies of Langmuir-Blodgett films containing rare-earth metal cations

    Khomutov, G.B.; Antipina, M.N.; Bykov, I.V.


    Comparative structural study of gadolinium stearate Langmuir-Blodgett (LB) films formed by monolayer deposition from either aqueous gadolinium acetate or gadolinium chloride solutions have been carried out. Structure of the films was characterized by X-ray diffraction, Fourier transform infrared...... spectroscopy, high-energy electron diffraction, atomic force microscopy and scanning electron microscopy. It was found that when subphase pH had a value at which all monolayer stearic acid molecules were ionized and bound with Gd3+ cations (pH > 5), the LB films deposited from gadolinium acetate and gadolinium...... chloride subphases had substantially different structure. The gadolinium stearate LB films formed with gadolinium acetate subphase were highly ordered and consisted of hexagonal layers with unit cell parameter a approximate to 4.8 Angstrom and interlayer spacing d approximate to 49 Angstrom. LB films...

  16. Proliferation of pulmonary endothelial cells: time-lapse cinematography of growth to confluence and restitution of monolayer after wounding.

    Ryan, U S; Absher, M; Olazabal, B M; Brown, L M; Ryan, J W


    A fundamental characteristic of vascular endothelium is that it exists as a monolayer, a condition that must be met in both vascular growth and repair. Maintenance of the monolayer is important both for the exchange of nutrients and for interactions between blood solutes and endothelial enzymes and transport systems. We have used time-lapse cinematography to compare proliferative behavior of bovine pulmonary endothelial cells in (1) establishment of a monolayer from a low-density seed (7.5 X 10(4) cells in a 60 mm dish) and (2) restitution of a confluent monolayer (approx. 2.9 x 10(6) cells in a 60 mm dish) following a mechanical wound (removal of cells from an area 5 x 15 mm by scraping). Culture 2 was not refed after wounding. In culture 2, approx. 30% of the cells accounted for repopulation (confluence in 40 hr). In culture 1, all cells entered into division. Participating cells of culture 2 began division immediately (69 divisions/filmed area in 10 hr, vs. four divisions in culture 1). Interdivision times (IDT) were longer and relatively constant in culture 1 until near confluence; none were less than 10 h, whereas in 2, 24% of the IDT's were less than or equal to 10 hr. Remarkably, IDTs of culture 2 decreased steadily until confluence was re-established. Cell migration in culture 1 was multidirectional while direction of migration in culture 2 was always into the wound area. Mean migration rate (MIG) in culture 2 was related to the site of origin of the cells, those dividing farthest from the unwounded area had fastest MIGs. Neither culture formed more than a single layer of cells. Although the cell kinetics of cultures 1 and 2 differed, the same goal, confluence, was achieved in either case.

  17. The crystalline structures of carboxylic acid monolayers adsorbed on graphite.

    Bickerstaffe, A K; Cheah, N P; Clarke, S M; Parker, J E; Perdigon, A; Messe, L; Inaba, A


    X-ray and neutron diffraction have been used to investigate the formation of solid crystalline monolayers of all of the linear carboxylic acids from C(6) to C(14) at submonolayer coverage and from C(8) to C(14) at multilayer coverages, and to characterize their structures. X-rays and neutrons highlight different aspects of the monolayer structures, and their combination is therefore important in structural determination. For all of the acids with an odd number of carbon atoms, the unit cell is rectangular of plane group pgg containing four molecules. The members of the homologous series with an even number of carbon atoms have an oblique unit cell with two molecules per unit cell and plane group p2. This odd-even variation in crystal structure provides an explanation for the odd-even variation observed in monolayer melting points and mixing behavior. In all cases, the molecules are arranged in strongly hydrogen-bonded dimers with their extended axes parallel to the surface and the plane of the carbon skeleton essentially parallel to the graphite surface. The monolayer crystal structures have unit cell dimensions similar to certain close-packed planes of the bulk crystals, but the molecular arrangements are different. There is a 1-3% compression on increasing the coverage over a monolayer.

  18. Molecular Dynamic Studies on Langmuir Monolayers of Stearic Acid

    KONG Chui-peng; ZHANG Hong-xing; ZHAO Zeng-xia; ZHENG Qing-chuan


    Compression isotherm for stearic acid was obtained by means of molecular dynamic simulation and compared to experimentally measured values for the Langmuir monolayers.Compared to the previous simulation,the present simulation has provided a method to reproduce the compression of the monolayer.The result is consistent with other experimental results.By analyzing the alkyl tails,the configuration of stearic acid molecules during the compression process was studied and a uniform monolayer was obtained after compression.Stearic acid molecules were observed to form fine organized monolayer from completely random structure.Hexatic order of the arrangement has been identified for the distribution of stearic acid molecules in the monolayer.At the end of the compression,the stearic acid molecules were tightly packed in the gap of two other molecules.At last,the hydrogen bonds in the system were analyzed.The main hydrogen bonds were from stearic acid-water interaction and their intensities constantly decreased with the decreased of surface area per molecule.The weak hydrogen bond interaction between stearic acid molecules may be the reason of easy collapse.

  19. Novel self-assembled phosphonic acids monolayers applied in N-channel perylene diimide (PDI) organic field effect transistors

    Cheng, Heng; Huai, Jinyue; Cao, Li; Li, Zhefeng


    Phosphoric acid (PA) self-assembled monolayers (SAMs) have been developed for applications in organic field-effect transistors (OFETs). This efficient interface modification is helpful for semiconductor layer to form crystal thin film during vapor deposition. Results show that the PDI-i8C based OFETs with PA SAMs exhibit field-effect mobilities up to 0.014 cm2 V-1 s-1 (with ODPA as SAMs), which is over 500 times higher than the device without SAMs. Also, transistors with Naph6PA as SAMs show up to 1.5 × 10-3 cm2 V-1 s-1. By studying the morphology of semiconductor layer and SAMs surface, it is found that ODPA bilayer structure plays a key role in inducing PDI-i8C to form orderly crystal thin film.

  20. A study on oxygen reduction inhibition at pyridine-terminated self assembled monolayer modified Au(111) electrodes

    Muglali, Mutlu Iskender; Bashir, Asif; Rohwerder, Michael [Max-Planck-Institut fuer Eisenforschung GmbH, Duesseldorf (Germany)


    The electroreduction of oxygen on self-assembled monolayers (SAMs) of various pyridinedisulfides and pyridinethiols on Au(111) surfaces has been investigated in alkaline solutions. Electrochemical experiments that were carried out in three-electrode cell reveal a good correlation between the chain-length of thiol molecules and the oxygen reduction inhibition of the resulting adlayer films. The effect of retarded diffusion of oxygen through the protective film has been investigated by forming additional layer of immobilized cytochrome c (cyt.c) metalloprotein on pyridine moiety during linear sweep voltammetry (LSV) scans. At sufficiently negative cathodic potentials the electrochemical reaction rate has been observed to increase together with the density of defects. Morphological changes at different levels of cathodic polarization were investigated by ex situ scanning tunneling microscopy (STM), indicating oxygen reduction reaction (ORR) induced structural defects at the metallorganic interface. (Abstract Copyright [2010], Wiley Periodicals, Inc.)