Role of Metal Contacts in High-Performance Phototransistors Based on WSe 2 Monolayers

KAUST Repository

Zhang, Wenjing; Chiu, Ming-Hui; Chen, Chang-Hsiao; Chen, Wei; Li, Lain-Jong; Wee, Andrew Thye Shen

2014-01-01

Phototransistors based on monolayer transition metal dichalcogenides (TMD) have high photosensitivity due to their direct band gap transition. However, there is a lack of understanding of the effect of metal contacts on the performance of atomically thin TMD phototransistors. Here, we fabricate phototransistors based on large-area chemical vapor deposition (CVD) tungsten diselenide (WSe2) monolayers contacted with the metals of different work function values. We found that the low Schottky-contact WSe2 phototransistors exhibit a very high photo gain (105) and specific detectivity (1014Jones), values higher than commercial Si- and InGaAs-based photodetectors; however, the response speed is longer than 5 s in ambient air. In contrast, the high Schottky-contact phototransistors display a fast response time shorter than 23 ms, but the photo gain and specific detectivity decrease by several orders of magnitude. Moreover, the fast response speed of the high Schottky-contact devices is maintained for a few months in ambient air. This study demonstrates that the contact plays an important role in TMD phototransistors, and barrier height tuning is critical for optimizing the photoresponse and photoresponsivity. © 2014 American Chemical Society.

Role of Metal Contacts in High-Performance Phototransistors Based on WSe 2 Monolayers

KAUST Repository

Zhang, Wenjing

2014-08-26

Phototransistors based on monolayer transition metal dichalcogenides (TMD) have high photosensitivity due to their direct band gap transition. However, there is a lack of understanding of the effect of metal contacts on the performance of atomically thin TMD phototransistors. Here, we fabricate phototransistors based on large-area chemical vapor deposition (CVD) tungsten diselenide (WSe2) monolayers contacted with the metals of different work function values. We found that the low Schottky-contact WSe2 phototransistors exhibit a very high photo gain (105) and specific detectivity (1014Jones), values higher than commercial Si- and InGaAs-based photodetectors; however, the response speed is longer than 5 s in ambient air. In contrast, the high Schottky-contact phototransistors display a fast response time shorter than 23 ms, but the photo gain and specific detectivity decrease by several orders of magnitude. Moreover, the fast response speed of the high Schottky-contact devices is maintained for a few months in ambient air. This study demonstrates that the contact plays an important role in TMD phototransistors, and barrier height tuning is critical for optimizing the photoresponse and photoresponsivity. © 2014 American Chemical Society.

Diamondoid monolayers as electron emitters

Science.gov (United States)

Yang, Wanli [El Cerrito, CA; Fabbri, Jason D [San Francisco, CA; Melosh, Nicholas A [Menlo Park, CA; Hussain, Zahid [Orinda, CA; Shen, Zhi-Xun [Stanford, CA

2012-04-10

Provided are electron emitters based upon diamondoid monolayers, preferably self-assembled higher diamondoid monolayers. High intensity electron emission has been demonstrated employing such diamondoid monolayers, particularly when the monolayers are comprised of higher diamondoids. The application of such diamondoid monolayers can alter the band structure of substrates, as well as emit monochromatic electrons, and the high intensity electron emissions can also greatly improve the efficiency of field-effect electron emitters as applied to industrial and commercial applications.

Suppressing segregation in highly phosphorus doped silicon monolayers

NARCIS (Netherlands)

Keizer, Joris; Kölling, Sebastian; Koenraad, Paul; Simmons, Michelle Y.

2015-01-01

Sharply defined dopant profiles and low resistivity are highly desired qualities in the microelectronic industry, and more recently, in the development of an all epitaxial Si:P based quantum computer. In this work, we use thin (monolayers thick) room temperature grown silicon layers, so-called

Epitaxially Grown Ultra-Flat Self-Assembling Monolayers with Dendrimers

Directory of Open Access Journals (Sweden)

Takane Imaoka

2018-02-01

Full Text Available Mono-molecular films formed by physical adsorption and dendrimer self-assembly were prepared on various substrate surfaces. It was demonstrated that a uniform dendrimer-based monolayer on the subnanometer scale can be easily constructed via simple dip coating. Furthermore, it was shown that an epitaxially grown monolayer film reflecting the crystal structure of the substrate (highly ordered pyrolytic graphite (HOPG can also be formed by aligning specific conditions.

Vapor-transport growth of high optical quality WSe2 monolayers

Directory of Open Access Journals (Sweden)

Genevieve Clark

2014-10-01

Full Text Available Monolayer transition metal dichalcogenides are atomically thin direct-gap semiconductors that show a variety of novel electronic and optical properties with an optically accessible valley degree of freedom. While they are ideal materials for developing optical-driven valleytronics, the restrictions of exfoliated samples have limited exploration of their potential. Here, we present a physical vapor transport growth method for triangular WSe2 sheets of up to 30 μm in edge length on insulating SiO2 substrates. Characterization using atomic force microscopy and optical microscopy reveals that they are uniform, monolayer crystals. Low temperature photoluminescence shows well resolved and electrically tunable excitonic features similar to those in exfoliated samples, with substantial valley polarization and valley coherence. The monolayers grown using this method are therefore of high enough optical quality for routine use in the investigation of optoelectronics and valleytronics.

Nanoparticle layer deposition for highly controlled multilayer formation based on high-coverage monolayers of nanoparticles

International Nuclear Information System (INIS)

Liu, Yue; Williams, Mackenzie G.; Miller, Timothy J.; Teplyakov, Andrew V.

2016-01-01

This paper establishes a strategy for chemical deposition of functionalized nanoparticles onto solid substrates in a layer-by-layer process based on self-limiting surface chemical reactions leading to complete monolayer formation within the multilayer system without any additional intermediate layers — nanoparticle layer deposition (NPLD). This approach is fundamentally different from previously established traditional layer-by-layer deposition techniques and is conceptually more similar to well-known atomic and molecular layer deposition processes. The NPLD approach uses efficient chemical functionalization of the solid substrate material and complementary functionalization of nanoparticles to produce a nearly 100% coverage of these nanoparticles with the use of “click chemistry”. Following this initial deposition, a second complete monolayer of nanoparticles is deposited using a copper-catalyzed “click reaction” with the azide-terminated silica nanoparticles of a different size. This layer-by-layer growth is demonstrated to produce stable covalently-bound multilayers of nearly perfect structure over macroscopic solid substrates. The formation of stable covalent bonds is confirmed spectroscopically and the stability of the multilayers produced is tested by sonication in a variety of common solvents. The 1-, 2- and 3-layer structures are interrogated by electron microscopy and atomic force microscopy and the thickness of the multilayers formed is fully consistent with that expected for highly efficient monolayer formation with each cycle of growth. This approach can be extended to include a variety of materials deposited in a predesigned sequence on different substrates with a highly conformal filling. - Highlights: • We investigate the formation of high-coverage monolayers of nanoparticles. • We use “click chemistry” to form these monolayers. • We form multiple layers based on the same strategy. • We confirm the formation of covalent bonds

Nonlinear optical characteristics of monolayer MoSe{sub 2}

Energy Technology Data Exchange (ETDEWEB)

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)

2016-08-15

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)

MgO monolayer epitaxy on Ni (100)

Science.gov (United States)

Sarpi, B.; Putero, M.; Hemeryck, A.; Vizzini, S.

2017-11-01

The growth of two-dimensional oxide films with accurate control of their structural and electronic properties is considered challenging for engineering nanotechnological applications. We address here the particular case of MgO ultrathin films grown on Ni (100), a system for which neither crystallization nor extended surface ordering has been established previously in the monolayer range. Using Scanning Tunneling Microscopy and Auger Electron Spectroscopy, we report on experiments showing MgO monolayer (ML) epitaxy on a ferromagnetic nickel surface, down to the limit of atomic thickness. Alternate steps of Mg ML deposition, O2 gas exposure, and ultrahigh vacuum thermal treatment enable the production of a textured film of ordered MgO nano-domains. This study could open interesting prospects for controlled epitaxy of ultrathin oxide films with a high magneto-resistance ratio on ferromagnetic substrates, enabling improvement in high-efficiency spintronics and magnetic tunnel junction devices.

Conformal and highly luminescent monolayers of Alq3 prepared by gas-phase molecular layer deposition.

Science.gov (United States)

Räupke, André; Albrecht, Fabian; Maibach, Julia; Behrendt, Andreas; Polywka, Andreas; Heiderhoff, Ralf; Helzel, Jonatan; Rabe, Torsten; Johannes, Hans-Hermann; Kowalsky, Wolfgang; Mankel, Eric; Mayer, Thomas; Görrn, Patrick; Riedl, Thomas

2014-01-22

The gas-phase molecular layer deposition (MLD) of conformal and highly luminescent monolayers of tris(8-hydroxyquinolinato)aluminum (Alq3) is reported. The controlled formation of Alq3 monolayers is achieved for the first time by functionalization of the substrate with amino groups, which serve as initial docking sites for trimethyl aluminum (TMA) molecules binding datively to the amine. Thereby, upon exposure to 8-hydroxyquinoline (8-HQ), the self-limiting formation of highly luminescent Alq3 monolayers is afforded. The growth process and monolayer formation were studied and verified by in situ quartz crystal monitoring, optical emission and absorption spectroscopy, and X-ray photoelectron spectroscopy. The nature of the MLD process provides an avenue to coat arbitrarily shaped 3D surfaces and porous structures with high surface areas, as demonstrated in this work for silica aerogels. The concept presented here paves the way to highly sensitive luminescent sensors and dye-sensitized metal oxides for future applications (e.g., in photocatalysis and solar cells).

Fabrication of SnO2-Reduced Graphite Oxide Monolayer-Ordered Porous Film Gas Sensor with Tunable Sensitivity through Ultra-Violet Light Irradiation

Science.gov (United States)

Xu, Shipu; Sun, Fengqiang; Yang, Shumin; Pan, Zizhao; Long, Jinfeng; Gu, Fenglong

2015-01-01

A new graphene-based composite structure, monolayer-ordered macroporous film composed of a layer of orderly arranged macropores, was reported. As an example, SnO2-reduced graphite oxide monolayer-ordered macroporous film was fabricated on a ceramic tube substrate under the irradiation of ultra-violet light (UV), by taking the latex microsphere two-dimensional colloid crystal as a template. Graphite oxide sheets dispersed in SnSO4 aqueous solution exhibited excellent affinity with template microspheres and were in situ incorporated into the pore walls during UV-induced growth of SnO2. The growing and the as-formed SnO2, just like other photocatalytic semiconductor, could be excited to produce electrons and holes under UV irradiation. Electrons reduced GO and holes adsorbed corresponding negative ions, which changed the properties of the composite film. This film was directly used as gas-sensor and was able to display high sensitivity in detecting ethanol gas. More interestingly, on the basis of SnO2-induced photochemical behaviours, this sensor demonstrated tunable sensitivity when UV irradiation time was controlled during the fabrication process and post in water, respectively. This study provides efficient ways of conducting the in situ fabrication of a semiconductor-reduced graphite oxide film device with uniform surface structure and controllable properties. PMID:25758292

Monolayer atomic crystal molecular superlattices

Science.gov (United States)

Wang, Chen; He, Qiyuan; Halim, Udayabagya; Liu, Yuanyue; Zhu, Enbo; Lin, Zhaoyang; Xiao, Hai; Duan, Xidong; Feng, Ziying; Cheng, Rui; Weiss, Nathan O.; Ye, Guojun; Huang, Yun-Chiao; Wu, Hao; Cheng, Hung-Chieh; Shakir, Imran; Liao, Lei; Chen, Xianhui; Goddard, William A., III; Huang, Yu; Duan, Xiangfeng

2018-03-01

Artificial superlattices, based on van der Waals heterostructures of two-dimensional atomic crystals such as graphene or molybdenum disulfide, offer technological opportunities beyond the reach of existing materials. Typical strategies for creating such artificial superlattices rely on arduous layer-by-layer exfoliation and restacking, with limited yield and reproducibility. The bottom-up approach of using chemical-vapour deposition produces high-quality heterostructures but becomes increasingly difficult for high-order superlattices. The intercalation of selected two-dimensional atomic crystals with alkali metal ions offers an alternative way to superlattice structures, but these usually have poor stability and seriously altered electronic properties. Here we report an electrochemical molecular intercalation approach to a new class of stable superlattices in which monolayer atomic crystals alternate with molecular layers. Using black phosphorus as a model system, we show that intercalation with cetyl-trimethylammonium bromide produces monolayer phosphorene molecular superlattices in which the interlayer distance is more than double that in black phosphorus, effectively isolating the phosphorene monolayers. Electrical transport studies of transistors fabricated from the monolayer phosphorene molecular superlattice show an on/off current ratio exceeding 107, along with excellent mobility and superior stability. We further show that several different two-dimensional atomic crystals, such as molybdenum disulfide and tungsten diselenide, can be intercalated with quaternary ammonium molecules of varying sizes and symmetries to produce a broad class of superlattices with tailored molecular structures, interlayer distances, phase compositions, electronic and optical properties. These studies define a versatile material platform for fundamental studies and potential technological applications.

Unveiling the Structural Origin of the High Carrier Mobility of a Molecular Monolayer on Boron Nitride

OpenAIRE

Xu, Rui; He, Daowei; Zhang, Yuhan; Wu, Bing; Liu, Fengyuan; Meng, Lan; Liu, Jun-Fang; Wu, Qisheng; Shi, Yi; Wang, Jinlan; Nie, Jia-Cai; Wang, Xinran; He, Lin

2014-01-01

Very recently, it was demonstrated that the carrier mobility of a molecular monolayer dioctylbenzothienobenzothiophene (C8-BTBT) on boron nitride can reach 10 cm2/Vs, the highest among the previously reported monolayer molecular field-effect transistors. Here we show that the high-quality single crystal of the C8-BTBT monolayer may be the key origin of the record-high carrier mobility. We discover that the C8-BTBT molecules prefer layer-by-layer growth on both hexagonal boron nitride and grap...

On the influence of the aliphatic linker on fabrication of highly ordered and orientated self-assembled monolayers of aromatic selenols on AU(111)

KAUST Repository

Azzam, Waleed

2014-03-06

Self-assembled monolayers (SAMs) formed by adsorption of 1,2-dibenzyldiselenide (DPMSe) and 1,2-diphenyldiselenide (DBSe) on Au(111) substrates at room temperature have been characterized using scanning tunnelling microscopy, X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and low-energy electron diffraction. Upon adsorption, the Se-Se bonds in DPMSe and DBSe were cleaved on the gold surface to form phenylmethaneselenolate (PMSe) and benzeneselenolate (BSe) species, respectively. Although both PMSe and BSe molecular entities only differ in their structure (an additional methyl group in PMSe), the resulting monolayer films revealed noteworthy dissimilarities regarding their adlayer SAM structure and surface morphology. The molecular adlayer structure and orientation of PMSe and BSe species were found to vary significantly with the immersion time (IT). The resulting PMSe films were poorly organized, and the structure was described by a (4√3 × 2) rectangular unit cell for the SAMs prepared with 24 h of IT. Moreover, the PMSe-SAMs were found to be unstable upon exposure to air for a long time. Our results showed that exposure to air for 48 h results in the formation of small bright ad-islands, which have a height corresponding to that of a single atomic step on the Au(111). Contrary, BSe-SAMs exhibited densely packed and well-ordered monolayers, and two different structural phases were resolved at short and long ITs. The most densely packed structure was obtained for SAMs prepared with very short ITs (10 min). Upon increasing the IT, the SAMs exhibited structural changes to a lower density of molecular packing structure. The spectroscopic data also confirmed this structural transformation by suggesting an upright orientation for BSe-SAMs prepared after short ITs and strongly inclined adsorption geometry for SAMs prepared after long ITs. © 2014 American Chemical Society.

Highly Flexible and High-Performance Complementary Inverters of Large-Area Transition Metal Dichalcogenide Monolayers

KAUST Repository

Pu, Jiang; Funahashi, Kazuma; Chen, Chang-Hsiao; Li, Ming-yang; Li, Lain-Jong; Takenobu, Taishi

2016-01-01

Complementary inverters constructed from large-area monolayers of WSe2 and MoS2 achieve excellent logic swings and yield an extremely high gain, large total noise margin, low power consumption, and good switching speed. Moreover, the WSe2

Broadband and high absorption in Fibonacci photonic crystal including MoS2 monolayer in the visible range

Science.gov (United States)

Ansari, Narges; Mohebbi, Ensiyeh

2018-03-01

2D molybdenum disulfide MoS2, has represented potential applications in optoelectronic devices based on their promising optical absorption responses. However, for practical applications, absorption should increase furthermore in a wide wavelength window. In this paper, we design Fibonacci photonic crystals (PCs) based on Si, SiO2 and MoS2 monolayer and we calculate their absorption responses based on the transfer matrix method. The optical refractive index of the MoS2 monolayer was determined based on the Lorentz-Drude-Gauss model. Effects of Fibonacci order, periodicity, incident light angle and polarization are included in our calculations. Finally, an absorption as large as 90% in a wide optical wavelength range is achieved for both polarizations and incident angle down to 60°. Our results are useful for designing photonic devices with high absorption efficiency.

11-Hydroxyundecyl octadecyl disulfide self-assembled monolayers on Au(1 1 1)

Energy Technology Data Exchange (ETDEWEB)

Albayrak, Erol [Department of Materials and Metallurgical Engineering, Ahi Evran University, Kırşehir 40000 (Turkey); Karabuga, Semistan [Department of Chemistry, Kahramanmaraş Sütçü İmam University, Kahramanmaraş 46030 (Turkey); Bracco, Gianangelo [CNR-IMEM and Department of Physics, University of Genoa, via Dodecaneso 33, Genoa 16146 (Italy); Danışman, M. Fatih, E-mail: danisman@metu.edu.tr [Department of Chemistry, Middle East Technical University, Ankara 06800 (Turkey)

2014-08-30

Highlights: • 11-Hydroxyundecyl octadecyl disulfide self-assembled monolayers on Au(1 1 1) surface were grown by supersonic molecular beam deposition. • Two different lying down monolayer phases were observed depending on the substrate temperature. • High temperature monolayer phase has a diffraction pattern similar to that of mercaptoundecanol SAMs. • Desorption from several different chemisorbed and physisorbed states were observed. - Abstract: Here, we report a helium atom diffraction study of 11-hydroxyundecyl octadecyl disulfide (CH{sub 3}-(CH{sub 2}){sub 17}-S-S-(CH{sub 2}){sub 11}-OH, HOD) self-assembled monolayers (SAMs) produced by supersonic molecular beam deposition (SMBD). Two different lying down monolayer phases were observed depending on the substrate temperature. At low temperatures a poorly ordered phase was observed, while the diffraction patterns of the film grown at high temperatures were similar to that of mercaptoundecanol (MUD) SAMs reported previously in the literature. The transition from the low temperature phase to the high temperature phase is due to S-S bond cleavage at the surface. Desorption from several different chemisorbed and physisorbed states were observed with energies in the same range as observed for MUD and octadecanelthiol (ODT) SAMs.

A trough for improved SFG spectroscopy of lipid monolayers

Science.gov (United States)

Franz, Johannes; van Zadel, Marc-Jan; Weidner, Tobias

2017-05-01

Lipid monolayers are indispensable model systems for biological membranes. The main advantage over bilayer model systems is that the surface pressure within the layer can be directly and reliably controlled. The sensitive interplay between surface pressure and temperature determines the molecular order within a model membrane and consequently determines the membrane phase behavior. The lipid phase is of crucial importance for a range of membrane functions such as protein interactions and membrane permeability. A very reliable method to probe the structure of lipid monolayers is sum frequency generation (SFG) vibrational spectroscopy. Not only is SFG extremely surface sensitive but it can also directly access critical parameters such as lipid order and orientation, and it can provide valuable information about protein interactions along with interfacial hydration. However, recent studies have shown that temperature gradients caused by high power laser beams perturb the lipid layers and potentially obscure the spectroscopic results. Here we demonstrate how the local heating problem can be effectively reduced by spatially distributing the laser pulses on the sample surface using a translating Langmuir trough for SFG experiments at lipid monolayers. The efficiency of the trough is illustrated by the detection of enhanced molecular order due to reduced heat load.

High-efficiency omnidirectional photoresponses based on monolayer lateral p–n heterojunctions

KAUST Repository

Tsai, Meng-Lin; Li, Ming-yang; Shi, Yumeng; Chen, Lih-Juann; Li, Lain-Jong; He, Jr-Hau

2016-01-01

Electrical and optical properties of lateral monolayer WSe2–MoS2 p–n heterojunctions were characterized to demonstrate a high responsivity of 0.26 A W−1 with an excellent omnidirectional photodetection capability. The heterojunction functioning as a

Conformational order of n-dodecanethiol and n-dodecaneselenol monolayers on polycrystalline copper investigated by PM-IRRAS and SFG spectroscopy

Science.gov (United States)

Fonder, G.; Cecchet, F.; Peremans, A.; Thiry, P. A.; Delhalle, J.; Mekhalif, Z.

2009-08-01

Self-assembled monolayers (SAMs) of n-dodecanethiol (C 12H 25SH) and n-dodecaneselenol (C 12H 25SeH) on polycrystalline copper have been elaborated with the purpose of achieving densely packed and crystalline-like assemblies. By combining the surface sensitivity of polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) and sum-frequency generation spectroscopy (SFG), the effect of the self-assembly time (15 min, 30 min, 1 h, 2 h and 24 h) on the formation of n-dodecanethiol and n-dodecaneselenol monolayers on untreated and electrochemically reduced polycrystalline copper has been investigated. On electrochemically reduced copper, PM-IRRAS spectroscopy shows that both molecules are able to form well organized layers. SFG spectroscopy indicates that the C 12H 25SeH SAMs are slightly better ordered than those achieved with C 12H 25SH. On untreated copper, the two molecules lead to different film organizations. Both PM-IRRAS and SFG indicate that C 12H 25SH SAMs are of the same film quality as those obtained on electrochemically reduced copper. On the contrary, C 12H 25SeH monolayers are invariably poorly organized at the molecular level.

High-Efficiency Colloidal Quantum Dot Photovoltaics via Robust Self-Assembled Monolayers

KAUST Repository

Kim, Gi-Hwan; Garcí a de Arquer, F. Pelayo; Yoon, Yung Jin; Lan, Xinzheng; Liu, Mengxia; Voznyy, Oleksandr; Yang, Zhenyu; Fan, Fengjia; Ip, Alexander H.; Kanjanaboos, Pongsakorn; Hoogland, Sjoerd; Kim, Jin Young; Sargent, Edward H.

2015-01-01

to voltage. With this goal in mind, self-assembled monolayers (SAMs) can be used to modify interface energy levels locally. However, to be effective SAMs must be made robust to treatment using the various solvents and ligands required for to fabricate high

Highly Flexible and High-Performance Complementary Inverters of Large-Area Transition Metal Dichalcogenide Monolayers

KAUST Repository

Pu, Jiang

2016-03-23

Complementary inverters constructed from large-area monolayers of WSe2 and MoS2 achieve excellent logic swings and yield an extremely high gain, large total noise margin, low power consumption, and good switching speed. Moreover, the WSe2 complementary-like inverters built on plastic substrates exhibit high mechanical stability. The results provide a path toward large-area flexible electronics. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-temperature electron-hole superfluidity with strong anisotropic gaps in double phosphorene monolayers

Science.gov (United States)

Saberi-Pouya, S.; Zarenia, M.; Perali, A.; Vazifehshenas, T.; Peeters, F. M.

2018-05-01

Excitonic superfluidity in double phosphorene monolayers is investigated using the BCS mean-field equations. Highly anisotropic superfluidity is predicted where we found that the maximum superfluid gap is in the Bose-Einstein condensate (BEC) regime along the armchair direction and in the BCS-BEC crossover regime along the zigzag direction. We estimate the highest Kosterlitz-Thouless transition temperature with maximum value up to ˜90 K with onset carrier densities as high as 4 ×1012cm-2 . This transition temperature is significantly larger than what is found in double electron-hole few-layers graphene. Our results can guide experimental research toward the realization of anisotropic condensate states in electron-hole phosphorene monolayers.

Conformation, orientation and interaction in molecular monolayers

International Nuclear Information System (INIS)

Superfine, R.; Huang, J.Y.; Shen, Y.R.

1989-01-01

Knowledge of the conformation and ordering of molecular monolayers is essential for a detailed understanding of a wide variety of surface and interfacial phenomena. Over the past several years, surface second harmonic generation (SHG) has proven to be a valuable and versatile probe of monolayer systems. Our group has recently extended the technique to infrared-visible sum frequency generation (SFG) which has unique capabilities for surface vibrational spectroscopy. Like second harmonic generation, SFG is highly surface specific with submonolayer sensitivity at all interfaces accessible by light. The orientation of individual groups within an adsorbate molecule can be deduced by a polarization analysis of the SFG signal from the vibrational modes of the groups. The authors have used SHG and SFG to study orientations and conformations of surfactant and liquid crystal (LC) monolayers and their interaction on a substrate. The interfacial properties of LC are of great interest to many researchers for both basic science understanding and practical application to LC devices. It is well known that the bulk alignment of a liquid crystal in a cell is strongly affected by the surface treatment of the cell walls. The reason behind it is not yet clear. The theoretical background and experimental arrangement of SHG and SFG have been described elsewhere. In the setup, a 30 psec. Nd:YAG mode-locked laser system together with nonlinear accessories generates a visible beam at .532μm and an infrared beam tunable about 3.4μm. Both beams are focused to a common spot of 300μm dia. The typical signal off the surface from a compact ordered alkyl chain monolayer is ∼500 photons per pulse, easily detected with a photomultiplier tube

1-Dodecanethiol based highly stable self-assembled monolayers for germanium passivation

International Nuclear Information System (INIS)

Cai, Qi; Xu, Baojian; Ye, Lin; Di, Zengfeng; Huang, Shanluo; Du, Xiaowei; Zhang, Jishen; Jin, Qinghui; Zhao, Jianlong

2015-01-01

Highlights: • A simple and effective approach for higly stable germanium passivation. • 1-Dodecanethiol self-assembled monolayers for germanium oxidation resistance. • The influence factors of germanium passivation were systematically studied. • The stability of the passivated Ge was more than 10 days even in water conditions. - Abstract: As a typical semiconductor material, germanium has the potential to replace silicon for future-generation microelectronics, due to its better electrical properties. However, the lack of stable surface state has limited its extensive use for several decades. In this work, we demonstrated highly stable self-assembled monolayers (SAMs) on Ge surface to prevent oxidization for further applications. After the pretreatment in hydrochloric acid, the oxide-free and Cl-terminated Ge could be further coated with 1-dodecanethiol (NDM) SAMs. The influence factors including reaction time, solvent component and reaction temperature were optimized to obtain stable passivated monolayer for oxidation resistance. Contact angle analysis, atomic force microscopy, ellipsometer and X-ray photoelectron spectroscopy were performed to characterize the functionalized Ge surface respectively. Meanwhile, the reaction mechanism and stability of thiols SAMs on Ge (1 1 1) surface were investigated. Finally, highly stable passivated NDM SAMs on Ge surface could be formed through immersing oxide-free Ge in mixture solvent (water/ethanol, v/v = 1:1) at appropriately elevated temperature (∼80 °C) for 24 h. And the corresponding optimized passivated Ge surface was stable for more than 10 days even in water condition, which was much longer than the data reported and paved the way for the future practical applications of Ge.

1-Dodecanethiol based highly stable self-assembled monolayers for germanium passivation

Energy Technology Data Exchange (ETDEWEB)

Cai, Qi [State Key Laboratory of Transducer Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, No. 865, Changning Road, Shanghai 200050 (China); University of Chinese Academy of Sciences, No. 19A, Yuquan Road, Beijing 100049 (China); Xu, Baojian, E-mail: xbj@mail.sim.ac.cn [State Key Laboratory of Transducer Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, No. 865, Changning Road, Shanghai 200050 (China); Shanghai Internet of Things Co., LTD, No. 1455, Pingcheng Road, Shanghai 201899 (China); Ye, Lin [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, No. 865, Changning Road, Shanghai 200050 (China); University of Chinese Academy of Sciences, No. 19A, Yuquan Road, Beijing 100049 (China); Di, Zengfeng [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, No. 865, Changning Road, Shanghai 200050 (China); Huang, Shanluo; Du, Xiaowei [State Key Laboratory of Transducer Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, No. 865, Changning Road, Shanghai 200050 (China); University of Chinese Academy of Sciences, No. 19A, Yuquan Road, Beijing 100049 (China); Zhang, Jishen; Jin, Qinghui [State Key Laboratory of Transducer Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, No. 865, Changning Road, Shanghai 200050 (China); Zhao, Jianlong, E-mail: jlzhao@mail.sim.ac.cn [State Key Laboratory of Transducer Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, No. 865, Changning Road, Shanghai 200050 (China)

2015-10-30

Highlights: • A simple and effective approach for higly stable germanium passivation. • 1-Dodecanethiol self-assembled monolayers for germanium oxidation resistance. • The influence factors of germanium passivation were systematically studied. • The stability of the passivated Ge was more than 10 days even in water conditions. - Abstract: As a typical semiconductor material, germanium has the potential to replace silicon for future-generation microelectronics, due to its better electrical properties. However, the lack of stable surface state has limited its extensive use for several decades. In this work, we demonstrated highly stable self-assembled monolayers (SAMs) on Ge surface to prevent oxidization for further applications. After the pretreatment in hydrochloric acid, the oxide-free and Cl-terminated Ge could be further coated with 1-dodecanethiol (NDM) SAMs. The influence factors including reaction time, solvent component and reaction temperature were optimized to obtain stable passivated monolayer for oxidation resistance. Contact angle analysis, atomic force microscopy, ellipsometer and X-ray photoelectron spectroscopy were performed to characterize the functionalized Ge surface respectively. Meanwhile, the reaction mechanism and stability of thiols SAMs on Ge (1 1 1) surface were investigated. Finally, highly stable passivated NDM SAMs on Ge surface could be formed through immersing oxide-free Ge in mixture solvent (water/ethanol, v/v = 1:1) at appropriately elevated temperature (∼80 °C) for 24 h. And the corresponding optimized passivated Ge surface was stable for more than 10 days even in water condition, which was much longer than the data reported and paved the way for the future practical applications of Ge.

Surface chemistry of lipid raft and amyloid Aβ (1-40) Langmuir monolayer.

Science.gov (United States)

Thakur, Garima; Pao, Christine; Micic, Miodrag; Johnson, Sheba; Leblanc, Roger M

2011-10-15

Lipid rafts being rich in cholesterol and sphingolipids are considered to provide ordered lipid environment in the neuronal membranes, where it is hypothesized that the cleavage of amyloid precursor protein (APP) to Aβ (1-40) and Aβ (1-42) takes place. It is highly likely that the interaction of lipid raft components like cholesterol, sphingomylein or GM1 leads to nucleation of Aβ and results in aggregation or accumulation of amyloid plaques. One has investigated surface pressure-area isotherms of the lipid raft and Aβ (1-40) Langmuir monolayer. The compression-decompression cycles and the stability of the lipid raft Langmuir monolayer are crucial parameters for the investigation of interaction of Aβ (1-40) with the lipid raft Langmuir monolayer. It was revealed that GM1 provides instability to the lipid raft Langmuir monolayer. Adsorption of Aβ (1-40) onto the lipid raft Langmuir monolayer containing neutral (POPC) or negatively charged phospholipid (DPPG) was examined. The adsorption isotherms revealed that the concentration of cholesterol was important for adsorption of Aβ (1-40) onto the lipid raft Langmuir monolayer containing POPC whereas for the lipid raft Langmuir monolayer containing DPPG:cholesterol or GM1 did not play any role. In situ UV-vis absorption spectroscopy supported the interpretation of results for the adsorption isotherms. Copyright © 2011 Elsevier B.V. All rights reserved.

Surface-directed molecular assembly of pentacene on monolayer graphene for high-performance organic transistors.

Science.gov (United States)

Lee, Wi Hyoung; Park, Jaesung; Sim, Sung Hyun; Lim, Soojin; Kim, Kwang S; Hong, Byung Hee; Cho, Kilwon

2011-03-30

Organic electronic devices that use graphene electrodes have received considerable attention because graphene is regarded as an ideal candidate electrode material. Transfer and lithographic processes during fabrication of patterned graphene electrodes typically leave polymer residues on the graphene surfaces. However, the impact of these residues on the organic semiconductor growth mechanism on graphene surface has not been reported yet. Here, we demonstrate that polymer residues remaining on graphene surfaces induce a stand-up orientation of pentacene, thereby controlling pentacene growth such that the molecular assembly is optimal for charge transport. Thus, pentacene field-effect transistors (FETs) using source/drain monolayer graphene electrodes with polymer residues show a high field-effect mobility of 1.2 cm(2)/V s. In contrast, epitaxial growth of pentacene having molecular assembly of lying-down structure is facilitated by π-π interaction between pentacene and the clean graphene electrode without polymer residues, which adversely affects lateral charge transport at the interface between electrode and channel. Our studies provide that the obtained high field-effect mobility in pentacene FETs using monolayer graphene electrodes arises from the extrinsic effects of polymer residues as well as the intrinsic characteristics of the highly conductive, ultrathin two-dimensional monolayer graphene electrodes.

Building high-coverage monolayers of covalently bound magnetic nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Williams, Mackenzie G.; Teplyakov, Andrew V., E-mail: andrewt@udel.edu

2016-12-01

Graphical abstract: - Highlights: • A method for forming a layer of covalently bound nanoparticles is offered. • A nearly perfect monolayer of covalently bound magnetic nanoparticles was formed on gold. • Spectroscopic techniques confirmed covalent binding by the “click” reaction. • The influence of the functionalization scheme on surface coverage was investigated. - Abstract: This work presents an approach for producing a high-coverage single monolayer of magnetic nanoparticles using “click chemistry” between complementarily functionalized nanoparticles and a flat substrate. This method highlights essential aspects of the functionalization scheme for substrate surface and nanoparticles to produce exceptionally high surface coverage without sacrificing selectivity or control over the layer produced. The deposition of one single layer of magnetic particles without agglomeration, over a large area, with a nearly 100% coverage is confirmed by electron microscopy. Spectroscopic techniques, supplemented by computational predictions, are used to interrogate the chemistry of the attachment and to confirm covalent binding, rather than attachment through self-assembly or weak van der Waals bonding. Density functional theory calculations for the surface intermediate of this copper-catalyzed process provide mechanistic insight into the effects of the functionalization scheme on surface coverage. Based on this analysis, it appears that steric limitations of the intermediate structure affect nanoparticle coverage on a flat solid substrate; however, this can be overcome by designing a functionalization scheme in such a way that the copper-based intermediate is formed on the spherical nanoparticles instead. This observation can be carried over to other approaches for creating highly controlled single- or multilayered nanostructures of a wide range of materials to result in high coverage and possibly, conformal filling.

Formation of high-quality self-assembled monolayers of conjugated dithiols on gold: base matters.

Science.gov (United States)

Valkenier, Hennie; Huisman, Everardus H; van Hal, Paul A; de Leeuw, Dago M; Chiechi, Ryan C; Hummelen, Jan C

2011-04-06

This Article reports a systematic study on the formation of self-assembled monolayers (SAMs) of conjugated molecules for molecular electronic (ME) devices. We monitored the deprotection reaction of acetyl protected dithiols of oligophenylene ethynylenes (OPEs) in solution using two different bases and studied the quality of the resulting SAMs on gold. We found that the optimal conditions to reproducibly form dense, high-quality monolayers are 9-15% triethylamine (Et(3)N) in THF. The deprotection base tetrabutylammonium hydroxide (Bu(4)NOH) leads to less dense SAMs and the incorporation of Bu(4)N into the monolayer. Furthermore, our results show the importance of the equilibrium concentrations of (di)thiolate in solution on the quality of the SAM. To demonstrate the relevance of these results for molecular electronics applications, large-area molecular junctions were fabricated using no base, Et(3)N, and Bu(4)NOH. The magnitude of the current-densities in these devices is highly dependent on the base. A value of β=0.15 Å(-1) for the exponential decay of the current-density of OPEs of varying length formed using Et(3)N was obtained. © 2011 American Chemical Society

Highly active engineered-enzyme oriented monolayers: formation, characterization and sensing applications

Directory of Open Access Journals (Sweden)

Patolsky Fernando

2011-06-01

Full Text Available Abstract Background The interest in introducing ecologically-clean, and efficient enzymes into modern industry has been growing steadily. However, difficulties associated with controlling their orientation, and maintaining their selectivity and reactivity is still a significant obstacle. We have developed precise immobilization of biomolecules, while retaining their native functionality, and report a new, fast, easy, and reliable procedure of protein immobilization, with the use of Adenylate kinase as a model system. Methods Self-assembled monolayers of hexane-1,6-dithiol were formed on gold surfaces. The monolayers were characterized by contact-angle measurements, Elman-reagent reaction, QCM, and XPS. A specifically designed, mutated Adenylate kinase, where cysteine was inserted at the 75 residue, and the cysteine at residue 77 was replaced by serine, was used for attachment to the SAM surface via spontaneously formed disulfide (S-S bonds. QCM, and XPS were used for characterization of the immobilized protein layer. Curve fitting in XPS measurements used a Gaussian-Lorentzian function. Results and Discussion Water contact angle (65-70°, as well as all characterization techniques used, confirmed the formation of self-assembled monolayer with surface SH groups. X-ray photoelectron spectroscopy showed clearly the two types of sulfur atom, one attached to the gold (triolate and the other (SH/S-S at the ω-position for the hexane-1,6-dithiol SAMs. The formation of a protein monolayer was confirmed using XPS, and QCM, where the QCM-determined amount of protein on the surface was in agreement with a model that considered the surface area of a single protein molecule. Enzymatic activity tests of the immobilized protein confirmed that there is no change in enzymatic functionality, and reveal activity ~100 times that expected for the same amount of protein in solution. Conclusions To the best of our knowledge, immobilization of a protein by the method

Nonlinear optical studies of organic monolayers

International Nuclear Information System (INIS)

Shen, Y.R.

1988-02-01

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

Toward tunable doping in graphene FETs by molecular self-assembled monolayers

Science.gov (United States)

Li, Bing; Klekachev, Alexander V.; Cantoro, Mirco; Huyghebaert, Cedric; Stesmans, André; Asselberghs, Inge; de Gendt, Stefan; de Feyter, Steven

2013-09-01

In this paper, we report the formation of self-assembled monolayers (SAMs) of oleylamine (OA) on highly oriented pyrolytic graphite (HOPG) and graphene surfaces and demonstrate the potential of using such organic SAMs to tailor the electronic properties of graphene. Molecular resolution Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) images reveal the detailed molecular ordering. The electrical measurements show that OA strongly interacts with graphene leading to n-doping effects in graphene devices. The doping levels are tunable by varying the OA deposition conditions. Importantly, neither hole nor electron mobilities are decreased by the OA modification. As a benefit from this noncovalent modification strategy, the pristine characteristics of the device are recoverable upon OA removal. From this study, one can envision the possibility to correlate the graphene-based device performance with the molecular structure and supramolecular ordering of the organic dopant.In this paper, we report the formation of self-assembled monolayers (SAMs) of oleylamine (OA) on highly oriented pyrolytic graphite (HOPG) and graphene surfaces and demonstrate the potential of using such organic SAMs to tailor the electronic properties of graphene. Molecular resolution Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) images reveal the detailed molecular ordering. The electrical measurements show that OA strongly interacts with graphene leading to n-doping effects in graphene devices. The doping levels are tunable by varying the OA deposition conditions. Importantly, neither hole nor electron mobilities are decreased by the OA modification. As a benefit from this noncovalent modification strategy, the pristine characteristics of the device are recoverable upon OA removal. From this study, one can envision the possibility to correlate the graphene-based device performance with the molecular structure and supramolecular ordering of the organic

Molecular printboards: monolayers of beta-cyclodextrins on silicon oxide surfaces

NARCIS (Netherlands)

Onclin, S.; Mulder, A.; Huskens, Jurriaan; Ravoo, B.J.; Reinhoudt, David

2004-01-01

Monolayers of β-cyclodextrin host molecules have been prepared on SiO2 surfaces. An ordered and stable cyano-terminated monolayer was modified in three consecutive surface reactions. First, the cyanide groups were reduced to their corresponding free amines using Red Al as a reducing agent. Second,

Phosphatidylcholine-fatty Alcohols Equilibria in Monolayers at the Air/Water Interface.

Science.gov (United States)

Serafin, Agnieszka; Figaszewski, Zbigniew Artur; Petelska, Aneta Dorota

2015-08-01

Monolayers of phosphatidylcholine (PC), tetradecanol (TD), hexadecanol (HD), octadecanol (OD) and eicosanol (E) and their binary mixtures were investigated at the air/water interface. The surface tension values of pure and mixed monolayers were used to calculate π-A isotherms. The surface tension measurements were carried out at 22 °C using a Teflon trough and a Nima 9000 tensiometer. The interactions between phosphatidylcholine and fatty alcohols (tetradecanol, hexadecanol, octadecanol, eicosanol) result in significant deviations from the additivity rule. An equilibrium theory to describe the behavior of monolayer components at the air/water interface was developed in order to obtain the stability constants, Gibbs free energy values and areas occupied by one molecules of PC-TD, PC-HD, PC-OD and PC-E complexes. We considered the equilibrium between the individual components and the complex and established that phosphatidylcholine and fatty alcohols formed highly stable 1:1 complexes.

High-efficiency omnidirectional photoresponses based on monolayer lateral p–n heterojunctions

KAUST Repository

Tsai, Meng-Lin

2016-10-28

Electrical and optical properties of lateral monolayer WSe2–MoS2 p–n heterojunctions were characterized to demonstrate a high responsivity of 0.26 A W−1 with an excellent omnidirectional photodetection capability. The heterojunction functioning as a diode exhibits a prominent gate-tuning behavior with an ideality factor of 1.25. In addition, ultrafast photoresponse, low-light detectability, and high-temperature operation have been achieved. These unique characteristics pave a way for the future development of sub-nano semiconductor devices.

Integrated circuits based on conjugated polymer monolayer.

Science.gov (United States)

Li, Mengmeng; Mangalore, Deepthi Kamath; Zhao, Jingbo; Carpenter, Joshua H; Yan, Hongping; Ade, Harald; Yan, He; Müllen, Klaus; Blom, Paul W M; Pisula, Wojciech; de Leeuw, Dago M; Asadi, Kamal

2018-01-31

It is still a great challenge to fabricate conjugated polymer monolayer field-effect transistors (PoM-FETs) due to intricate crystallization and film formation of conjugated polymers. Here we demonstrate PoM-FETs based on a single monolayer of a conjugated polymer. The resulting PoM-FETs are highly reproducible and exhibit charge carrier mobilities reaching 3 cm 2  V -1  s -1 . The high performance is attributed to the strong interactions of the polymer chains present already in solution leading to pronounced edge-on packing and well-defined microstructure in the monolayer. The high reproducibility enables the integration of discrete unipolar PoM-FETs into inverters and ring oscillators. Real logic functionality has been demonstrated by constructing a 15-bit code generator in which hundreds of self-assembled PoM-FETs are addressed simultaneously. Our results provide the state-of-the-art example of integrated circuits based on a conjugated polymer monolayer, opening prospective pathways for bottom-up organic electronics.

Janus Monolayer Transition-Metal Dichalcogenides.

Science.gov (United States)

Zhang, Jing; Jia, Shuai; Kholmanov, Iskandar; Dong, Liang; Er, Dequan; Chen, Weibing; Guo, Hua; Jin, Zehua; Shenoy, Vivek B; Shi, Li; Lou, Jun

2017-08-22

The crystal configuration of sandwiched S-Mo-Se structure (Janus SMoSe) at the monolayer limit has been synthesized and carefully characterized in this work. By controlled sulfurization of monolayer MoSe 2 , the top layer of selenium atoms is substituted by sulfur atoms, while the bottom selenium layer remains intact. The structure of this material is systematically investigated by Raman, photoluminescence, transmission electron microscopy, and X-ray photoelectron spectroscopy and confirmed by time-of-flight secondary ion mass spectrometry. Density functional theory (DFT) calculations are performed to better understand the Raman vibration modes and electronic structures of the Janus SMoSe monolayer, which are found to correlate well with corresponding experimental results. Finally, high basal plane hydrogen evolution reaction activity is discovered for the Janus monolayer, and DFT calculation implies that the activity originates from the synergistic effect of the intrinsic defects and structural strain inherent in the Janus structure.

Fabrication and surface transformation of FePt nanoparticle monolayer

International Nuclear Information System (INIS)

Wang Ying; Ding Baojun; Li Hua; Zhang Xiaoyan; Cai Bingchu; Zhang Yafei

2007-01-01

The monolayer of FePt nanoparticles with the mean size of ∼4 nm was fabricated on a glass substrate by the Langmuir--Blodgett (LB) technology. The monolayer of FePt nanoparticles has a smooth surface and a high density structure as shown by the AFM image. The array structure of FePt nanoparticles on the surface of the film is clearly with a cubic symmetry in appropriate condition. Small-angle X-ray diffraction (SXRD) measurement of multilayer structure for the FePt nanoparticles has indicated that the superlattices consist of well-defined smooth layers. The transfer of nanoparticle layers onto a solid substrate surface was quite efficient for the first few layers, exhibiting a proportional increase of optical absorption in the UV-vis range. This results potentially opens up a new approach to the long-range ordered array of FePt nanoparticles capped by organic molecules on substrate and provide a promising thin film, which may exhibit the excellent ultra-high density magnetic recording properties

Monolayer MoS2 heterojunction solar cells

KAUST Repository

Tsai, Menglin

2014-08-26

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.

Chemically Transformable Configurations of Mercaptohexadecanoic Acid Self-Assembled Monolayers Adsorbed on Au(111)

International Nuclear Information System (INIS)

van Buuren, T; Bostedt, C; Nelson, A J; Terminello, L J; Vance, A L; Fadley, C S; Willey, T M

2003-01-01

Carboxyl terminated Self-Assembled Monolayers (SAMs) are commonly used in a variety of applications, with the assumption that the molecules form well ordered monolayers. In this work, NEXAFS verifies well ordered monolayers can be formed using acetic acid in the solvent. Disordered monolayers with unbound molecules present in the result using only ethanol. A stark reorientation occurs upon deprotonation of the endgroup by rinsing in a KOH solution. This reorientation of the endgroup is reversible with tilted over, hydrogen bound carboxyl groups while carboxylate-ion endgroups are upright. C1s photoemission shows that SAMs formed and rinsed with acetic acid in ethanol, the endgroups are protonated, while without, a large fraction of the molecules on the surface are carboxylate terminated

Simulation studies of pore and domain formation in a phospholipid monolayer

NARCIS (Netherlands)

Knecht, Volker; Muller, M; Bonn, M; Marrink, SJ; Mark, AE

2005-01-01

Despite extensive study the phase behavior of phospholipid monolayers at an air-water interface is still not fully understood. In particular recent vibrational sum-frequency generation (VSFG) spectra of DPPC monolayers as a function of area density show a sharp transition in the order of the lipid

Unanticipated C=C bonds in covalent monolayers on silicon revealed by NEXAFS.

Science.gov (United States)

Lee, Michael V; Lee, Jonathan R I; Brehmer, Daniel E; Linford, Matthew R; Willey, Trevor M

2010-02-02

Interfaces are crucial to material properties. In the case of covalent organic monolayers on silicon, molecular structure at the interface controls the self-assembly of the monolayers, which in turn influences the optical properties and electrical transport. These properties intrinsically affect their application in biology, tribology, optics, and electronics. We use near-edge X-ray absorption fine structure spectroscopy to show that the most basic covalent monolayers formed from 1-alkenes on silicon retain a double bond in one-fifth to two-fifths of the resultant molecules. Unsaturation in the predominantly saturated monolayers will perturb the regular order and affect the dependent properties. The presence of unsaturation in monolayers produced by two different methods also prompts the re-evaluation of other radical-based mechanisms for forming covalent monolayers on silicon.

A new Dirac cone material: a graphene-like Be3C2 monolayer.

Science.gov (United States)

Wang, Bing; Yuan, Shijun; Li, Yunhai; Shi, Li; Wang, Jinlan

2017-05-04

Two-dimensional (2D) materials with Dirac cones exhibit rich physics and many intriguing properties, but the search for new 2D Dirac materials is still a current hotspot. Using the global particle-swarm optimization method and density functional theory, we predict a new stable graphene-like 2D Dirac material: a Be 3 C 2 monolayer with a hexagonal honeycomb structure. The Dirac point occurs exactly at the Fermi level and arises from the merging of the hybridized p z bands of Be and C atoms. Most interestingly, this monolayer exhibits a high Fermi velocity in the same order of graphene. Moreover, the Dirac cone is very robust and retains even included spin-orbit coupling or external strain. These outstanding properties render the Be 3 C 2 monolayer a promising 2D material for special electronics applications.

Testing the effectiveness of monolayers under wind and wave conditions.

Science.gov (United States)

Palada, C; Schouten, P; Lemckert, C

2012-01-01

Monolayers are highly desirable for their evaporation reducing capabilities due to their relatively minimal cost and ease of application. Despite these positive attributes, monolayers have consistently failed to perform effectively due to the harsh wind and wave conditions prevalent across real-world water reserves. An exhaustive and consistent study testing the influence of wind and wave combinations on monolayer performance has yet to be presented in the literature. To remedy this, the effect of simultaneous wind and wave conditions on a benchmark high-performance monolayer (octadecanol suspension, CH(3)(CH(2))(16)CH(2)OH) has been analysed. Subjected only to waves, the monolayer remained intact due to its innate ability to compress and expand. However, the constant simultaneous application of wind and waves caused the monolayer to break up and gather down-wind where it volatilised over time. At wind speeds above 1.3 m s(-1) the monolayer was completely ineffective. For wind speeds below this threshold, the monolayer had an influence on the evaporation rate dependent on wind speed. From these results a series of application protocols can now be developed for the optimised deployment of monolayers in real-world water reserves. This will be of interest to private, commercial and government organisations involved in the storage and management of water resources.

Monolayer collapse regulating process of adsorption-desorption of palladium nanoparticles at fatty acid monolayers at the air-water interface.

Science.gov (United States)

Goto, Thiago E; Lopez, Ricardo F; Iost, Rodrigo M; Crespilho, Frank N; Caseli, Luciano

2011-03-15

In this paper, we investigate the affinity of palladium nanoparticles, stabilized with glucose oxidase, for fatty acid monolayers at the air-water interface, exploiting the interaction between a planar system and spheroids coming from the aqueous subphase. A decrease of the monolayer collapse pressure in the second cycle of interface compression proved that the presence of the nanoparticles causes destabilization of the monolayer in a mechanism driven by the interpenetration of the enzyme into the bilayer/multilayer structure formed during collapse, which is not immediately reversible after monolayer expansion. Surface pressure and surface potential-area isotherms, as well as infrared spectroscopy [polarization modulation infrared reflection adsorption spectroscopy (PM-IRRAS)] and deposition onto solid plates as Langmuir-Blodgett (LB) films, were employed to construct a model in which the nanoparticle has a high affinity for the hydrophobic core of the structure formed after collapse, which provides a slow desorption rate from the interface after monolayer decompression. This may have important consequences on the interaction between the metallic particles and fatty acid monolayers, which implies the regulation of the multifunctional properties of the hybrid material.

Monolayer CS as a metal-free photocatalyst with high carrier mobility and tunable band structure: a first-principles study

Science.gov (United States)

Yang, Xiao-Le; Ye, Xiao-Juan; Liu, Chun-Sheng; Yan, Xiao-Hong

2018-02-01

Producing hydrogen fuel using suitable photocatalysts from water splitting is a feasible method to harvest solar energy. A desired photocatalyst is expected to have suitable band gap, moderate band edge position, and high carrier mobility. By employing first-principles calculations, we explore a α-CS monolayer as a metal-free efficient photocatalyst. The α-CS monolayer shows good energetic, dynamic, and thermal stabilities and is insoluble in water, suggesting its experimental practicability. Monolayer and bilayer α-CS present not only appropriate band gaps for visible and ultraviolet light absorption but also moderate band alignments with water redox potentials in pH neutral water. Remarkably, the α-CS monolayer exhibits high (up to 8453.19 cm2 V-1s-1 for hole) and anisotropic carrier mobility, which is favorable to the migration and separation of photogenerated carriers. In addition, monolayer α-CS experiences an interesting semiconductor-metal transition by applying uniaxial strain and external electric field. Moreover, α-CS under certain strain and electric field is still dynamically stable with the absence of imaginary frequencies. Furthermore, we demonstrate that the graphite (0 0 1) surface is a potential substrate for the α-CS growth with the intrinsic properties of α-CS maintaining. Therefore, our results could pave the way for the application of α-CS as a promising photocatalyst.

Influence of indium-tin oxide surface structure on the ordering and coverage of carboxylic acid and thiol monolayers

International Nuclear Information System (INIS)

Cerruti, Marta; Rhodes, Crissy; Losego, Mark; Efremenko, Alina; Maria, Jon-Paul; Fischer, Daniel; Franzen, Stefan; Genzer, Jan

2007-01-01

This paper analyses the variability of self-assembled monolayers (SAMs) formation on ITO depending on the substrate surface features. In particular, we report on the formation of carboxylic acid- and thiol-based SAMs on two lots of commercially prepared indium-tin oxide (ITO) thin films. Contact angle measurements, electrochemical experiments, and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy showed that the quality of monolayers formed differed substantially between the two ITO batches. Only one of the two ITO substrates was capable of forming well-organized thiol- and carboxylic acid-based SAMs. In order to rationalize these observations, atomic force microscopy and x-ray diffraction analyses were carried out, and SAMs were prepared on ITO substrates fabricated by sputtering in our laboratories. An attempt was made to influence the film microstructure and surface morphology by varying substrate temperatures during ITO deposition. Good-quality thiol and carboxylic acid SAMs were obtained on one of the ITO substrates prepared in-house. While our characterization could not single out conclusively one specific parameter in ITO surface structure that could be responsible for good SAMs formation, we could point out homogeneous surface morphology as a relevant factor for the quality of the SAMs. Evidence was also found for ITO crystallographic orientation to be a parameter influencing SAMs organization

The Interface between Gd and Monolayer MoS2: A First-Principles Study

KAUST Repository

Zhang, Xuejing

2014-12-08

We analyze the electronic structure of interfaces between two-, four- and six-layer Gd(0001) and monolayer MoS2 by first-principles calculations. Strong chemical bonds shift the Fermi energy of MoS2 upwards into the conduction band. At the surface and interface the Gd f states shift to lower energy and new surface/interface Gd d states appear at the Fermi energy, which are strongly hybridized with the Mo 4d states and thus lead to a high spin-polarization (ferromagnetically ordered Mo magnetic moments of 0.15 μB). Gd therefore is an interesting candidate for spin injection into monolayer MoS2.

Stress relaxation in quasi-two-dimensional self-assembled nanoparticle monolayers

Science.gov (United States)

Boucheron, Leandra S.; Stanley, Jacob T.; Dai, Yeling; You, Siheng Sean; Parzyck, Christopher T.; Narayanan, Suresh; Sandy, Alec R.; Jiang, Zhang; Meron, Mati; Lin, Binhua; Shpyrko, Oleg G.

2018-05-01

We experimentally probed the stress relaxation of a monolayer of iron oxide nanoparticles at the water-air interface. Upon drop-casting onto a water surface, the nanoparticles self-assembled into islands of two-dimensional hexagonally close packed crystalline domains surrounded by large voids. When compressed laterally, the voids gradually disappeared as the surface pressure increased. After the compression was stopped, the surface pressure (as measured by a Wilhelmy plate) evolved as a function of the film aging time with three distinct timescales. These aging dynamics were intrinsic to the stressed state built up during the non-equilibrium compression of the film. Utilizing x-ray photon correlation spectroscopy, we measured the characteristic relaxation time (τ ) of in-plane nanoparticle motion as a function of the aging time through both second-order and two-time autocorrelation analysis. Compressed and stretched exponential fitting of the intermediate scattering function yielded exponents (β ) indicating different relaxation mechanisms of the films under different compression stresses. For a monolayer compressed to a lower surface pressure (between 20 mN/m and 30 mN/m), the relaxation time (τ ) decreased continuously as a function of the aging time, as did the fitted exponent, which transitioned from being compressed (>1 ) to stretched (stress release through crystalline domain reorganization. However, for a monolayer compressed to a higher surface pressure (around 40 mN/m), the relaxation time increased continuously and the compressed exponent varied very little from a value of 1.6, suggesting that the system may have been highly stressed and jammed. Despite the interesting stress relaxation signatures seen in these samples, the structural ordering of the monolayer remained the same over the sample lifetime, as revealed by grazing incidence x-ray diffraction.

Effects of self-assembled monolayer structural order, surface homogeneity and surface energy on pentacene morphology and thin film transistor device performance.

Science.gov (United States)

Hutchins, Daniel Orrin; Weidner, Tobias; Baio, Joe; Polishak, Brent; Acton, Orb; Cernetic, Nathan; Ma, Hong; Jen, Alex K-Y

2013-01-04

A systematic study of six phosphonic acid (PA) self-assembled monolayers (SAMs) with tailored molecular structures is performed to evaluate their effectiveness as dielectric modifying layers in organic field-effect transistors (OFETs) and determine the relationship between SAM structural order, surface homogeneity, and surface energy in dictating device performance. SAM structures and surface properties are examined by near edge X-ray absorption fine structure (NEXAFS) spectroscopy, contact angle goniometry, and atomic force microscopy (AFM). Top-contact pentacene OFET devices are fabricated on SAM modified Si with a thermally grown oxide layer as a dielectric. For less ordered methyl- and phenyl-terminated alkyl ~(CH 2 ) 12 PA SAMs of varying surface energies, pentacene OFETs show high charge carrier mobilities up to 4.1 cm 2 V -1 s -1 . It is hypothesized that for these SAMs, mitigation of molecular scale roughness and subsequent control of surface homogeneity allow for large pentacene grain growth leading to high performance pentacene OFET devices. PA SAMs that contain bulky terminal groups or are highly crystalline in nature do not allow for a homogenous surface at a molecular level and result in charge carrier mobilities of 1.3 cm 2 V -1 s -1 or less. For all molecules used in this study, no causal relationship between SAM surface energy and charge carrier mobility in pentacene FET devices is observed.

Intramolecular diffusive motion in alkane monolayers studied by high-resolution quasielastic neutron scattering and molecular dynamics simulations

DEFF Research Database (Denmark)

Hansen, Flemming Yssing; Criswell, L.; Fuhrmann, D

2004-01-01

Molecular dynamics simulations of a tetracosane (n-C24H50) monolayer adsorbed on a graphite basal-plane surface show that there are diffusive motions associated with the creation and annihilation of gauche defects occurring on a time scale of similar to0.1-4 ns. We present evidence...... that these relatively slow motions are observable by high-energy-resolution quasielastic neutron scattering (QNS) thus demonstrating QNS as a technique, complementary to nuclear magnetic resonance, for studying conformational dynamics on a nanosecond time scale in molecular monolayers....

Molecular printboards: monolayers of beta-cyclodextrins on silicon oxide surfaces.

Science.gov (United States)

Onclin, Steffen; Mulder, Alart; Huskens, Jurriaan; Ravoo, Bart Jan; Reinhoudt, David N

2004-06-22

Monolayers of beta-cyclodextrin host molecules have been prepared on SiO2 surfaces. An ordered and stable cyano-terminated monolayer was modified in three consecutive surface reactions. First, the cyanide groups were reduced to their corresponding free amines using Red Al as a reducing agent. Second, 1,4-phenylene diisothiocyanate was used to react with the amine monolayer where it acts as a linking molecule, exposing isothiocyanates that can be derivatized further. Finally, per-6-amino beta-cyclodextrin was reacted with these isothiocyanate functions to yield a monolayer exposing beta-cyclodextrin. All monolayers were characterized by contact angle measurements, ellipsometric thickness measurements, Brewster angle Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry, which indicate the formation of a densely packed cyclodextrin surface. It was demonstrated that the beta-cyclodextrin monolayer could bind suitable guest molecules in a reversible manner. A fluorescent molecule (1), equipped with two adamantyl groups for complexation, was adsorbed onto the host monolayer from solution to form a monolayer of guest molecules. Subsequently, the guest molecules were desorbed from the surface by competition with increasing beta-cyclodextrin concentration in solution. The data were fitted using a model. An intrinsic binding constant of 3.3 +/- 1 x 10(5) M(-1) was obtained, which corresponds well to previously obtained results with a divalent guest molecule on beta-cyclodextrin monolayers on gold. In addition, the number of guest molecules bound to the host surface was determined, and a surface coverage of ca. 30% was found.

Transport properties in monolayer-bilayer-monolayer graphene planar junctions

Institute of Scientific and Technical Information of China (English)

Kai-Long Chu; Zi-Bo Wang; Jiao-Jiao Zhou; Hua Jiang

2017-01-01

The transport study of graphene based junctions has become one of the focuses in graphene research.There are two stacking configurations for monolayer-bilayer-monolayer graphene planar junctions.One is the two monolayer graphene contacting the same side of the bilayer graphene,and the other is the two-monolayer graphene contacting the different layers of the bilayer graphene.In this paper,according to the Landauer-Büttiker formula,we study the transport properties of these two configurations.The influences of the local gate potential in each part,the bias potential in bilayer graphene,the disorder and external magnetic field on conductance are obtained.We find the conductances of the two configurations can be manipulated by all of these effects.Especially,one can distinguish the two stacking configurations by introducing the bias potential into the bilayer graphene.The strong disorder and the external magnetic field will make the two stacking configurations indistinguishable in the transport experiment.

High-Efficiency Colloidal Quantum Dot Photovoltaics via Robust Self-Assembled Monolayers

KAUST Repository

Kim, Gi-Hwan

2015-11-11

© 2015 American Chemical Society. The optoelectronic tunability offered by colloidal quantum dots (CQDs) is attractive for photovoltaic applications but demands proper band alignment at electrodes for efficient charge extraction at minimal cost to voltage. With this goal in mind, self-assembled monolayers (SAMs) can be used to modify interface energy levels locally. However, to be effective SAMs must be made robust to treatment using the various solvents and ligands required for to fabricate high quality CQD solids. We report robust self-assembled monolayers (R-SAMs) that enable us to increase the efficiency of CQD photovoltaics. Only by developing a process for secure anchoring of aromatic SAMs, aided by deposition of the SAMs in a water-free deposition environment, were we able to provide an interface modification that was robust against the ensuing chemical treatments needed in the fabrication of CQD solids. The energy alignment at the rectifying interface was tailored by tuning the R-SAM for optimal alignment relative to the CQD quantum-confined electron energy levels. This resulted in a CQD PV record power conversion efficiency (PCE) of 10.7% with enhanced reproducibility relative to controls.

Vacancy-Rich Monolayer BiO2-x as a Highly Efficient UV, Visible, and Near-Infrared Responsive Photocatalyst.

Science.gov (United States)

Li, Jun; Wu, Xiaoyong; Pan, Wenfeng; Zhang, Gaoke; Chen, Hong

2018-01-08

Vacancy-rich layered materials with good electron-transfer property are of great interest. Herein, a full-spectrum responsive vacancy-rich monolayer BiO 2-x has been synthesized. The increased density of states at the conduction band (CB) minimum in the monolayer BiO 2-x is responsible for the enhanced photon response and photo-absorption, which were confirmed by UV/Vis-NIR diffuse reflectance spectra (DRS) and photocurrent measurements. Compared to bulk BiO 2-x , monolayer BiO 2-x has exhibited enhanced photocatalytic performance for rhodamine B and phenol removal under UV, visible, and near-infrared light (NIR) irradiation, which can be attributed to the vacancy V Bi-O ''' as confirmed by the positron annihilation spectra. The presence of V Bi-O ''' defects in monolayer BiO 2-x promoted the separation of electrons and holes. This finding provides an atomic level understanding for developing highly efficient UV, visible, and NIR light responsive photocatalysts. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Infrared spectroscopy of self-assembled monolayer films on silicon

Science.gov (United States)

Rowell, N. L.; Tay, Lilin; Boukherroub, R.; Lockwood, D. J.

2007-07-01

Infrared vibrational spectroscopy in an attenuated total reflection (ATR) geometry has been employed to investigate the presence of organic thin layers on Si-wafer surfaces. The phenomena have been simulated to show there can be a field enhancement with the presented single-reflection ATR (SR-ATR) approach which is substantially larger than for conventional ATR or specular reflection. In SR-ATR, a discontinuity of the field normal to the film contributes a field enhancement in the lower index thin film causing a two order of magnitude increase in sensitivity. SR-ATR was employed to characterize a single monolayer of undecylenic acid self-assembled on Si(1 1 1) and to investigate a two monolayer system obtained by adding a monolayer of bovine serum albumin protein.

Strong room-temperature ferromagnetism in VSe2 monolayers on van der Waals substrates

Science.gov (United States)

Bonilla, Manuel; Kolekar, Sadhu; Ma, Yujing; Diaz, Horacio Coy; Kalappattil, Vijaysankar; Das, Raja; Eggers, Tatiana; Gutierrez, Humberto R.; Phan, Manh-Huong; Batzill, Matthias

2018-04-01

Reduced dimensionality and interlayer coupling in van der Waals materials gives rise to fundamentally different electronic1, optical2 and many-body quantum3-5 properties in monolayers compared with the bulk. This layer-dependence permits the discovery of novel material properties in the monolayer regime. Ferromagnetic order in two-dimensional materials is a coveted property that would allow fundamental studies of spin behaviour in low dimensions and enable new spintronics applications6-8. Recent studies have shown that for the bulk-ferromagnetic layered materials CrI3 (ref. 9) and Cr2Ge2Te6 (ref. 10), ferromagnetic order is maintained down to the ultrathin limit at low temperatures. Contrary to these observations, we report the emergence of strong ferromagnetic ordering for monolayer VSe2, a material that is paramagnetic in the bulk11,12. Importantly, the ferromagnetic ordering with a large magnetic moment persists to above room temperature, making VSe2 an attractive material for van der Waals spintronics applications.

Electrochemical behavior of monolayer and bilayer graphene.

Science.gov (United States)

Valota, Anna T; Kinloch, Ian A; Novoselov, Kostya S; Casiraghi, Cinzia; Eckmann, Axel; Hill, Ernie W; Dryfe, Robert A W

2011-11-22

Results of a study on the electrochemical properties of exfoliated single and multilayer graphene flakes are presented. Graphene flakes were deposited on silicon/silicon oxide wafers to enable fast and accurate characterization by optical microscopy and Raman spectroscopy. Conductive silver paint and silver wires were used to fabricate contacts; epoxy resin was employed as a masking coating in order to expose a stable, well-defined area of graphene. Both multilayer and monolayer graphene microelectrodes showed quasi-reversible behavior during voltammetric measurements in potassium ferricyanide. However, the standard heterogeneous charge transfer rate constant, k°, was estimated to be higher for monolayer graphene flakes. © 2011 American Chemical Society

Multispectral selective near-perfect light absorption by graphene monolayer using aperiodic multilayer microstructures

Science.gov (United States)

Zand, Iman; Dalir, Hamed; Chen, Ray T.; Dowling, Jonathan P.

2018-03-01

We investigate one-dimensional aperiodic multilayer microstructures in order to achieve near-total absorptions at preselected wavelengths in a graphene monolayer. The proposed structures are designed using a genetic optimization algorithm coupled to a transfer matrix code. Coupled-mode-theory analysis, consistent with transfer matrix method results, indicates the existence of a critical coupling in the graphene monolayer for perfect absorptions. Our findings show that the near-total-absorption peaks are highly tunable and can be controlled simultaneously or independently in a wide range of wavelengths in the near-infrared and visible ranges. The proposed approach is metal-free, does not require surface texturing or patterning, and can be also applied for other two-dimensional materials.

Cation effects on phosphatidic acid monolayers at various pH conditions.

Science.gov (United States)

Zhang, Ting; Cathcart, Matthew G; Vidalis, Andrew S; Allen, Heather C

2016-10-01

The impact of pH and cations on phase behavior, stability, and surface morphology for dipalmitoylphosphatidic acid (DPPA) monolayers was investigated. At pHCations are found to expand and stabilize the monolayer in the following order of increasing magnitude at pH 5.6: Na + >K + ∼Mg 2+ >Ca 2+ . Additionally, cation complexation is tied to the pH and protonation state of DPPA, which are the primary factors controlling the monolayer surface behavior. The binding affinity of cations to the headgroup and thus deprotonation capability of the cation, ranked in the order of Ca 2+ >Mg 2+ >Na + >K + , is found to be well explained by the law of matching water affinities. Nucleation of surface 3D lipid structures is observed from Ca 2+ , Mg 2+ , and Na + , but not from K + , consistent with the lowest binding affinity of K + . Unraveling cation and pH effects on DPPA monolayers is useful in further understanding the surface properties of complex systems such as organic-coated marine aerosols where organic films are directly influenced by the pH and ionic composition of the underlying aqueous phase. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Controlled electrodeposition of Au monolayer film on ionic liquid

Energy Technology Data Exchange (ETDEWEB)

Ma, Qiang; Pang, Liuqing; Li, Man; Zhang, Yunxia; Ren, Xianpei [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710062 (China); Liu, Shengzhong Frank, E-mail: szliu@dicp.ac.cn [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710062 (China); Dalian Institute of Chemical Physics, Dalian National Laboratory for Clean Energy, Chinese Academy of Sciences, Dalian 116023 (China)

2016-05-15

Highlights: • We fabricate Au monolayer film on Ionic liquid substrate using an electrochemical deposition technique. • Au monolayer film was deposited on a “soft substrate” for the first time. • Au monolayer film can contribute extra Raman enhancement. - Abstract: 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][PF{sub 6}] 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.

Optical diffraction by ordered 2D arrays of silica microspheres

International Nuclear Information System (INIS)

Shcherbakov, A.A.; Shavdina, O.; Tishchenko, A.V.; Veillas, C.; Verrier, I.; Dellea, O.; Jourlin, Y.

2017-01-01

The article presents experimental and theoretical studies of angular dependent diffraction properties of 2D monolayer arrays of silica microspheres. High-quality large area defect-free monolayers of 1 μm diameter silica microspheres were deposited by the Langmuir-Blodgett technique under an accurate optical control. Measured angular dependencies of zeroth and one of the first order diffraction efficiencies produced by deposited samples were simulated by the rigorous Generalized Source Method taking into account particle size dispersion and lattice nonideality. - Highlights: • High quality silica microsphere monolayer was fabricated. • Accurate measurements of diffraction efficiency angular dependencies. • Rigorous diffraction simulation of both ideal hexagonal and realistic microsphere arrangements. • Qualitative rationalization of the obtained results and the observed differences between the experiment and the theory.

High-efficient light absorption of monolayer graphene via cylindrical dielectric arrays and the sensing application

Science.gov (United States)

Zhou, Peng; Zheng, Gaige

2018-04-01

The efficiency of graphene-based optoelectronic devices is typically limited by the poor absolute absorption of light. A hybrid structure of monolayer graphene with cylindrical titanium dioxide (TiO2) array and aluminum oxide (Al2O3) spacer layer on aluminum (Al) substrate has been proposed to enhance the absorption for two-dimensional (2D) materials. By combining dielectric array with metal substrate, the structure achieves multiple absorption peaks with near unity absorbance at near-infrared wavelengths due to the resonant effect of dielectric array. Completed monolayer graphene is utilized in the design without any demand of manufacture process to form the periodic patterns. Further analysis indicates that the near-field enhancement induced by surface modes gives rise to the high absorption. This favorable field enhancement and tunability of absorption not only open up new approaches to accelerate the light-graphene interaction, but also show great potential for practical applications in high-performance optoelectronic devices, such as modulators and sensors.

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

DEFF Research Database (Denmark)

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 the alveolae monolayer and at the same time allows reduction of the interfacial tension to ~0mN/m....

ATR-IR spectroscopy for the detection of induced-phase transition in Langmuir-Blodgett monolayer film

International Nuclear Information System (INIS)

Widayati, Suci

1996-01-01

The rate at which a solid substrate is transferred through the Air/Water interface in the Langmuir-Blodgett process of preparing monomolecular films influences the final structure of the transferred film. This phenomenon has been observed from the attenuated total reflectance infra-red (ATR-IR) spectra of fatty acid monolayer transferred onto germanium substrate. This transfer-induced effect is most evidence when the monolayer is transferred from an expanded region of the surface-pressure-molecular area isotherm, but has limited influence on the hydrocarbon chain conformation of film molecules transferred in the condensed phases at high surface pressure. Such a conformational ordering may due to a kinetically limited phase transition taking place in the meniscus formed between the solid substrate and aqueous sub phase. In addition, these results suggest that the structure of the amphiphilic molecules may modulate the extent and nature of the dipping-speed-induced structural changes taking place in the monomolecular L-B film. In order to use monomolecular L-B films to accurately characterize the structure, orientation and phase properties of monolayers at the Air/Water interface, the L-B transfer must be performed at transfer speeds that minimize this structural phase transition

Monolayer-by-monolayer growth of platinum films on complex carbon fiber paper structure

Energy Technology Data Exchange (ETDEWEB)

Pang, Liuqing; Zhang, Yunxia [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Key Laboratory for Advanced Energy Devices, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119 (China); Liu, Shengzhong, E-mail: szliu@dicp.ac.cn [Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Key Laboratory for Advanced Energy Devices, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an 710119 (China); Dalian National Laboratory for Clean Energy, iChEM, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023 (China)

2017-06-15

Graphical abstract: A controlled monolayer-by-monolayer deposition process has been developed to fabricate Pt coating on carbon fiber paper with complex network structures using a dual buffer strategy. This development may pave a way to fabricate superior Pt catalysts with the minimal Pt usage. In fact, the present Pt group metal loading is 25 times lower than the U.S. DOE 2017 target value. - Highlights: • Developed a controlled monolayer-by-monolayer Pt deposition using a dual buffer strategy. • The present Pt group metal loading is 25 times lower than the U.S. DOE 2017 target value. • This development may pave a way to fabricate superior Pt catalysts with the minimal Pt usage. - Abstract: A controlled monolayer-by-monolayer deposition process has been developed to fabricate Pt coating on carbon fiber paper with complex network structures using a dual buffer (Au/Ni) strategy. The X-ray diffraction, electrochemical quartz crystal microbalance, current density analyses, and X-ray photoelectron spectroscopy results conclude that the monolayer deposition process accomplishes full coverage on the substrate and that the thickness of the deposition layer can be controlled on a single atom scale. This development may pave a way to fabricate superior Pt catalysts with the minimal Pt usage. In fact, the present Pt group metal loading is 25 times lower than the U.S. DOE 2017 target value.

X-Ray Reflectometry of DMPS Monolayers on a Water Substrate

Science.gov (United States)

Tikhonov, A. M.; Asadchikov, V. E.; Volkov, Yu. O.; Roshchin, B. S.; Ermakov, Yu. A.

2017-12-01

The molecular structure of dimyristoyl phosphatidylserine (DMPS) monolayers on a water substrate in different phase states has been investigated by X-ray reflectometry with a photon energy of 8 keV. According to the experimental data, the transition from a two-dimensional expanded liquid state to a solid gel state (liquid crystal) accompanied by the ordering of the hydrocarbon tails C14H27 of the DMPS molecule occurs in the monolayer as the surface pressure rises. The monolayer thickness is 20 ± 3 and 28 ± 2 Å in the liquid and solid phases, respectively, with the deflection angle of the molecular tail axis from the normal to the surface in the gel phase being 26° ± 8°. At least a twofold decrease in the degree of hydration of the polar lipid groups also occurs under two-dimensional monolayer compression. The reflectometry data have been analyzed using two approaches: under the assumption about the presence of two layers with different electron densities in the monolayer and without any assumptions about the transverse surface structure. Both approaches demonstrate satisfactory agreement between themselves in describing the experimental results.

Gas sensing with self-assembled monolayer field-effect transistors

NARCIS (Netherlands)

Andringa, Anne-Marije; Spijkman, Mark-Jan; Smits, Edsger C. P.; Mathijssen, Simon G. J.; van Hal, Paul A.; Setayesh, Sepas; Willard, Nico P.; Borshchev, Oleg V.; Ponomarenko, Sergei A.; Blom, Paul W. M.; de Leeuw, Dago M.

A new sensitive gas sensor based on a self-assembled monolayer field-effect transistor (SAMFET) was used to detect the biomarker nitric oxide. A SAMFET based sensor is highly sensitive because the analyte and the active channel are separated by only one monolayer. SAMFETs were functionalised for

Characterisation of phase transition in adsorbed monolayers at the air/water interface.

Science.gov (United States)

Vollhardt, D; Fainerman, V B

2010-02-26

Recent work has provided experimental and theoretical evidence that a first order fluid/condensed (LE/LC) phase transition can occur in adsorbed monolayers of amphiphiles and surfactants which are dissolved in aqueous solution. Similar to Langmuir monolayers, also in the case of adsorbed monolayers, the existence of a G/LE phase transition, as assumed by several authors, is a matter of question. Representative studies, at first performed with a tailored amphiphile and later with numerous other amphiphiles, also with n-dodecanol, provide insight into the main characteristics of the adsorbed monolayer during the adsorption kinetics. The general conditions necessary for the formation of a two-phase coexistence in adsorbed monolayers can be optimally studied using dynamic surface pressure measurements, Brewster angle microscopy (BAM) and synchrotron X-ray diffraction at grazing incidence (GIXD). A characteristic break point in the time dependence of the adsorption kinetics curves indicates the phase transition which is largely affected by the concentration of the amphiphile in the aqueous solution and on the temperature. Formation and growth of condensed phase domains after the phase transition point are visualised by BAM. As demonstrated by a tailored amphiphile, various types of morphological textures of the condensed phase can occur in different temperature regions. Lattice structure and tilt angle of the alkyl chains in the condensed phase of the adsorbed monolayer are determined using GIXD. The main growth directions of the condensed phase textures are correlated with the two-dimensional lattice structure. The results, obtained for the characteristics of the condensed phase after a first order main transition, are supported by experimental bridging to the Langmuir monolayers. Phase transition of adsorbing trace impurities in model surfactants can strongly affect the characteristics of the main component. Dodecanol present as minor component in aqueous sodium

Defects and oxidation of group-III monochalcogenide monolayers

Science.gov (United States)

Guo, Yu; Zhou, Si; Bai, Yizhen; Zhao, Jijun

2017-09-01

Among various two-dimensional (2D) materials, monolayer group-III monochalcogenides (GaS, GaSe, InS, and InSe) stand out owing to their potential applications in microelectronics and optoelectronics. Devices made of these novel 2D materials are sensitive to environmental gases, especially O2 molecules. To address this critical issue, here we systematically investigate the oxidization behaviors of perfect and defective group-III monochalcogenide monolayers by first-principles calculations. The perfect monolayers show superior oxidation resistance with large barriers of 3.02-3.20 eV for the dissociation and chemisorption of O2 molecules. In contrast, the defective monolayers with single chalcogen vacancy are vulnerable to O2, showing small barriers of only 0.26-0.36 eV for the chemisorption of an O2 molecule. Interestingly, filling an O2 molecule to the chalcogen vacancy of group-III monochalcogenide monolayers could preserve the electronic band structure of the perfect system—the bandgaps are almost intact and the carrier effective masses are only moderately disturbed. On the other hand, the defective monolayers with single vacancies of group-III atoms carry local magnetic moments of 1-2 μB. These results help experimental design and synthesis of group-III monochalcogenides based 2D devices with high performance and stability.

Exploring atomic defects in molybdenum disulphide monolayers

KAUST Repository

Hong, Jinhua; Hu, Zhixin; Probert, Matt; Li, Kun; Lv, Danhui; Yang, Xinan; Gu, Lin; Mao, Nannan; Feng, Qingliang; Xie, Liming; Zhang, Jin; Wu, Dianzhong; Zhang, Zhiyong; Jin, Chuanhong; Ji, Wei; Zhang, Xixiang; Yuan, Jun; Zhang, Ze

2015-01-01

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.

Exploring atomic defects in molybdenum disulphide monolayers

KAUST Repository

Hong, Jinhua

2015-02-19

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.

Packing of ganglioside-phospholipid monolayers

DEFF Research Database (Denmark)

Majewski, J.; Kuhl, T.L.; Kjær, K.

2001-01-01

Using synchrotron grazing-incidence x-ray diffraction (GIXD) and reflectivity, the in-plane and out-of-plane structure of mixed ganglioside-phospholipid monolayers was investigated at the air-water interface. Mixed monolayers of 0, 5, 10, 20, and 100 mol% ganglioside GM, and the phospholipid...... 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...

Fabrication of Silicon nanostructures by UHV-STM lithography in Self-Assembled Monolayers

International Nuclear Information System (INIS)

Sundermann, M.; Brechling, A.; Rott, K.; Meyners, D.; Kleineberg, U.; Heinzmann, U.; Knueller, A.; Eck, W.; Goelzhueuser, A.; Grunze, M.

2002-01-01

Our approach utilizes UHV-STM writing in Self-Assembled Monolayers (SAM). SAMs form highly-ordered ultrathin (∼2-3 nm) monomolecular layers on top of pre-activated Si(100) or Si(111) surfaces. After patterning by UHV-STM writing in constant-current mode at different write parameters (gap voltage, electron dose) the modified Self-Assembled Monolayer serves as an etch mask for an anisotropic wet etch transfer (two-step etch process in aqueous solutions of 5 % HF and 1 M KOH), of the write structure into the silicon substrate. The corresponding silicon nano-structures have been analyzed afterwards by AFM or SEM to characterize the pattern accuracy. We have studied the suitability of three different types of SAMs on silicon single-crystals. Alkyl-chain-type SAMs like Octadecylsilane (ODS) monolayer have been formed by immersion of hydroxylated Si(100) in Octadecyltrichlorosilane (CH 3 (CH 27 SiCl 3 ) while SAMs with aromatic spacer groups such as Hydroxybiphenyl (HBP, (C 6 H 6 ) 2 OH) and Ethoxybiphenyl silane (EBP, (C 6 H 6 ) 2 O(CH 2 ) 3 Si(OCH 3 ) 3 ) are formed on Si(111). (Authors)

He/Ar-atom scattering from molecular monolayers: C{sub 60}/Pt(111) and graphene/Pt(111)

Energy Technology Data Exchange (ETDEWEB)

Yamada, Y; Sugawara, C; Satake, Y; Yokoyama, Y; Okada, R; Nakayama, T; Sasaki, M [Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki (Japan); Kondo, T; Oh, J; Nakamura, J [Institute of Material Science, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki (Japan); Hayes, W W [Department of Physics and Astronomy, Clemson University, Clemson, SC 29634 (United States)

2010-08-04

Supersonic He and Ar atomic beam scattering from C{sub 60} and graphene monolayers adsorbed on a Pt(111) surface are demonstrated in order to obtain detailed insight into a gas-molecule collision that has not been studied in detail so far. The effective masses and phonon spectral densities of the monolayers seen by different projectiles are discussed based on classical models such as the hard cube model and the recently developed smooth surface model. Large effective masses are deduced for both the monolayers, suggesting collective effects of surface atoms in the single collision event. The effective Debye temperature of graphene was found to be similar to that reported in highly oriented pyrolytic graphite (HOPG), indicating that the graphene is decoupled well from the Pt substrate. A much smaller Debye-Waller factor was found for the C{sub 60} layer, probably reflecting the strong C{sub 60}-Pt(111) interaction.

Triptycene-terminated thiolate and selenolate monolayers on Au(111

Directory of Open Access Journals (Sweden)

Jinxuan Liu

2017-04-01

Full Text Available To study the implications of highly space-demanding organic moieties on the properties of self-assembled monolayers (SAMs, triptycyl thiolates and selenolates with and without methylene spacers on Au(111 surfaces were comprehensively studied using ultra-high vacuum infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy and thermal desorption spectroscopy. Due to packing effects, the molecules in all monolayers are substantially tilted. In the presence of a methylene spacer the tilt is slightly less pronounced. The selenolate monolayers exhibit smaller defect densities and therefore are more densely packed than their thiolate analogues. The Se–Au binding energy in the investigated SAMs was found to be higher than the S–Au binding energy.

Monolayer MoSe 2 Grown by Chemical Vapor Deposition for Fast Photodetection

KAUST Repository

Chang, Yung-Huang

2014-08-26

Monolayer molybdenum disulfide (MoS2) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the electrical and optoelectronic properties of monolayer MoS2 devices. Here, highly crystalline molybdenum diselenide (MoSe2) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS2 and MoSe 2 monolayers reveals that the MoSe2 monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe2 presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS2 monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS2. This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe2 and MoS2 and is useful for guiding future designs in 2D material-based optoelectronic devices. © 2014 American Chemical Society.

Defect-Mediated Lithium Adsorption and Diffusion on Monolayer Molybdenum Disulfide

OpenAIRE

Sun, Xiaoli; Wang, Zhiguo; Fu, Yong Qing

2015-01-01

Monolayer Molybdenum Disulfide (MoS2) is a promising anode material for lithium ion batteries because of its high capacities. In this work, first principle calculations based on spin density functional theory were performed to investigate adsorption and diffusion of lithium on monolayer MoS2 with defects, such as single- and few-atom vacancies, antisite, and grain boundary. The values of adsorption energies on the monolayer MoS2 with the defects were increased compared to those on the pristin...

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

Energy Technology Data Exchange (ETDEWEB)

Das, Kaushik, E-mail: kaushikdas2089@gmail.com; Kundu, Sarathi [Physical Sciences Division, Institute of Advanced Study in Science and Technology, Vigyan Path, Paschim Boragaon, Garchuk, Guwahati, Assam 781035 (India)

2016-05-23

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.

Optical diffraction by ordered 2D arrays of silica microspheres

Science.gov (United States)

Shcherbakov, A. A.; Shavdina, O.; Tishchenko, A. V.; Veillas, C.; Verrier, I.; Dellea, O.; Jourlin, Y.

2017-03-01

The article presents experimental and theoretical studies of angular dependent diffraction properties of 2D monolayer arrays of silica microspheres. High-quality large area defect-free monolayers of 1 μm diameter silica microspheres were deposited by the Langmuir-Blodgett technique under an accurate optical control. Measured angular dependencies of zeroth and one of the first order diffraction efficiencies produced by deposited samples were simulated by the rigorous Generalized Source Method taking into account particle size dispersion and lattice nonideality.

Specific ion effects on the properties of cationic Gemini surfactant monolayers

International Nuclear Information System (INIS)

Alejo, T.; Merchan, M.D.; Velazquez, M.M.

2011-01-01

The effects of some anions of the Hofmeister series and different divalent cations of alkaline earth metals on the properties of Langmuir monolayers of the cationic Gemini surfactant ethyl-bis (dimethyl octadecylammonium bromide) have been investigated. Surface pressure and potential isotherms at the air-water interface were obtained on aqueous subphases containing sodium salts with several anions of the Hofmeister series (Cl - , NO 3 - , Br - , I - , ClO 4 - , and SCN - ). The influence of the investigated anions on the monolayer properties can be ordered according to the Hofmeister series with a change in the order between bromide and nitrate anions. On the other hand, for a given anion, the cation of the salt also influences the surface properties of the Langmuir films. The monolayers can be transferred onto mica by the Langmuir-Blodgett technique and then the Langmuir-Blodgett films were characterized by atomic force microscopy (AFM). The AFM images show that the molecules become more closely packed and nearly vertical to the surface when anions screen the electric charge of the surfactant molecules.

Specific ion effects on the properties of cationic Gemini surfactant monolayers

Energy Technology Data Exchange (ETDEWEB)

Alejo, T.; Merchan, M.D.; Velazquez, M.M., E-mail: mvsal@usal.es

2011-06-01

The effects of some anions of the Hofmeister series and different divalent cations of alkaline earth metals on the properties of Langmuir monolayers of the cationic Gemini surfactant ethyl-bis (dimethyl octadecylammonium bromide) have been investigated. Surface pressure and potential isotherms at the air-water interface were obtained on aqueous subphases containing sodium salts with several anions of the Hofmeister series (Cl{sup -}, NO{sub 3}{sup -}, Br{sup -}, I{sup -}, ClO{sub 4}{sup -}, and SCN{sup -}). The influence of the investigated anions on the monolayer properties can be ordered according to the Hofmeister series with a change in the order between bromide and nitrate anions. On the other hand, for a given anion, the cation of the salt also influences the surface properties of the Langmuir films. The monolayers can be transferred onto mica by the Langmuir-Blodgett technique and then the Langmuir-Blodgett films were characterized by atomic force microscopy (AFM). The AFM images show that the molecules become more closely packed and nearly vertical to the surface when anions screen the electric charge of the surfactant molecules.

Metal ion interaction with phosphorylated tyrosine analogue monolayers on gold.

Science.gov (United States)

Petoral, Rodrigo M; Björefors, Fredrik; Uvdal, Kajsa

2006-11-23

Phosphorylated tyrosine analogue molecules (pTyr-PT) were assembled onto gold substrates, and the resulting monolayers were used for metal ion interaction studies. The monolayers were characterized by X-ray photoelectron spectroscopy (XPS), infrared reflection-absorption spectroscopy (IRAS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), both prior to and after exposure to metal ions. XPS verified the elemental composition of the molecular adsorbate and the presence of metal ions coordinated to the phosphate groups. Both the angle-dependent XPS and IRAS results were consistent with the change in the structural orientation of the pTyr-PT monolayer upon exposure to metal ions. The differential capacitance of the monolayers upon coordination of the metal ions was evaluated using EIS. These metal ions were found to significantly change the capacitance of the pTyr-PT monolayers in contrast to the nonphosphorylated tyrosine analogue (TPT). CV results showed reduced electrochemical blocking capabilities of the phosphorylated analogue monolayer when exposed to metal ions, supporting the change in the structure of the monolayer observed by XPS and IRAS. The largest change in the structure and interfacial capacitance was observed for aluminum ions, compared to calcium, magnesium, and chromium ions. This type of monolayer shows an excellent capability to coordinate metal ions and has a high potential for use as sensing layers in biochip applications to monitor the presence of metal ions.

Surface Charge Transfer Doping of Monolayer Phosphorene via Molecular Adsorption.

Science.gov (United States)

He, Yuanyuan; Xia, Feifei; Shao, Zhibin; Zhao, Jianwei; Jie, Jiansheng

2015-12-03

Monolayer phosphorene has attracted much attention owing to its extraordinary electronic, optical, and structural properties. Rationally tuning the electrical transport characteristics of monolayer phosphorene is essential to its applications in electronic and optoelectronic devices. Herein, we study the electronic transport behaviors of monolayer phosphorene with surface charge transfer doping of electrophilic molecules, including 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), NO2, and MoO3, using density functional theory combined with the nonequilibrium Green's function formalism. F4TCNQ shows optimal performance in enhancing the p-type conductance of monolayer phosphorene. Static electronic properties indicate that the enhancement is originated from the charge transfer between adsorbed molecule and phosphorene layer. Dynamic transport behaviors demonstrate that additional channels for hole transport in host monolayer phosphorene were generated upon the adsorption of molecule. Our work unveils the great potential of surface charge transfer doping in tuning the electronic properties of monolayer phosphorene and is of significance to its application in high-performance devices.

Producing air-stable monolayers of phosphorene and their defect engineering.

Science.gov (United States)

Pei, Jiajie; Gai, Xin; Yang, Jiong; Wang, Xibin; Yu, Zongfu; Choi, Duk-Yong; Luther-Davies, Barry; Lu, Yuerui

2016-01-22

It has been a long-standing challenge to produce air-stable few- or monolayer samples of phosphorene because thin phosphorene films degrade rapidly in ambient conditions. Here we demonstrate a new highly controllable method for fabricating high quality, air-stable phosphorene films with a designated number of layers ranging from a few down to monolayer. Our approach involves the use of oxygen plasma dry etching to thin down thick-exfoliated phosphorene flakes, layer by layer with atomic precision. Moreover, in a stabilized phosphorene monolayer, we were able to precisely engineer defects for the first time, which led to efficient emission of photons at new frequencies in the near infrared at room temperature. In addition, we demonstrate the use of an electrostatic gate to tune the photon emission from the defects in a monolayer phosphorene. This could lead to new electronic and optoelectronic devices, such as electrically tunable, broadband near infrared lighting devices operating at room temperature.

Anisotropic charged impurity-limited carrier mobility in monolayer phosphorene

International Nuclear Information System (INIS)

Ong, Zhun-Yong; Zhang, Gang; Zhang, Yong Wei

2014-01-01

The room temperature carrier mobility in atomically thin 2D materials is usually far below the intrinsic limit imposed by phonon scattering as a result of scattering by remote charged impurities in its environment. We simulate the charged impurity-limited carrier mobility μ in bare and encapsulated monolayer phosphorene. We find a significant temperature dependence in the carrier mobilities (μ ∝ T −γ ) that results from the temperature variability of the charge screening and varies with the crystal orientation. The anisotropy in the effective mass leads to an anisotropic carrier mobility, with the mobility in the armchair direction about one order of magnitude larger than in the zigzag direction. In particular, this mobility anisotropy is enhanced at low temperatures and high carrier densities. Under encapsulation with a high-κ overlayer, the mobility increases by up to an order of magnitude although its temperature dependence and its anisotropy are reduced

Anisotropic charged impurity-limited carrier mobility in monolayer phosphorene

Energy Technology Data Exchange (ETDEWEB)

Ong, Zhun-Yong; Zhang, Gang; Zhang, Yong Wei [Institute of High Performance Computing, A*STAR, Singapore 138632 (Singapore)

2014-12-07

The room temperature carrier mobility in atomically thin 2D materials is usually far below the intrinsic limit imposed by phonon scattering as a result of scattering by remote charged impurities in its environment. We simulate the charged impurity-limited carrier mobility μ in bare and encapsulated monolayer phosphorene. We find a significant temperature dependence in the carrier mobilities (μ ∝ T{sup −γ}) that results from the temperature variability of the charge screening and varies with the crystal orientation. The anisotropy in the effective mass leads to an anisotropic carrier mobility, with the mobility in the armchair direction about one order of magnitude larger than in the zigzag direction. In particular, this mobility anisotropy is enhanced at low temperatures and high carrier densities. Under encapsulation with a high-κ overlayer, the mobility increases by up to an order of magnitude although its temperature dependence and its anisotropy are reduced.

Temperature-dependent surface density of alkylthiol monolayers on gold nanocrystals

Science.gov (United States)

Liu, Xuepeng; Lu, Pin; Zhai, Hua; Wu, Yucheng

2018-03-01

Atomistic molecular dynamics (MD) simulations are performed to study the surface density of passivating monolayers of alkylthiol chains on gold nanocrystals at temperatures ranging from 1 to 800 K. The results show that the surface density of alkylthiol monolayer reaches a maximum value at near room temperature (200-300 K), while significantly decreases with increasing temperature in the higher temperature region (> 300 {{K}}), and slightly decreases with decreasing temperature at low temperature (< 200 {{K}}). We find that the temperature dependence of surface ligand density in the higher temperature region is attributed to the substantial ligand desorption induced by the thermal fluctuation, while that at low temperature results from the reduction in entropy caused by the change in the ordering of passivating monolayer. These results are expected helpful to understand the temperature-dependent surface coverage of gold nanocrystals.

Self-assembly Ag nanoparticle monolayer film as SERS Substrate for pesticide detection

Energy Technology Data Exchange (ETDEWEB)

Zhang, Li, E-mail: zhlisuzh@163.com [School of Chemistry and Life Science, Anhui Key Laboratory of Spin Electron and Nanomaterials (Cultivating Base), Suzhou University, SuZhou 234000 (China)

2013-04-01

A self-assembled protocol is introduced to provide effective platforms for the fabrication of ordered Ag nanosized monolayer film. The assembled Ag nanosized monolayer film was characterized using scanning electronic microscopy and surface-enhanced Raman scattering (SERS). The results show that the assembled SERS substrate own excellent Raman enhancement and reproducibility. The synthesized SERS-active substrate was further used to detect methyl-parathion, and the limitation of detection can reach 10{sup −7} M.

Molecular dynamics and energy landscape of decanethiolates in self-assembled monolayers on Au(111) by STM

NARCIS (Netherlands)

Sotthewes, Kai; Wu, Hairong; Kumar, Avijit; Vancso, Gyula J.; Schön, Peter Manfred; Zandvliet, Henricus J.W.

2013-01-01

The energetics and dynamics of the various phases of decanethiolate self-assembled monolayers on Au(111) surfaces were studied with scanning tunneling microscopy. We have observed five different phases of the decanethiolate monolayer on Au(111): four ordered phases (β, δ, χ*, and ) and one

Monolayer Nickel Cobalt Hydroxyl Carbonate for High Performance All-Solid-State Asymmetric Supercapacitors.

Science.gov (United States)

Zhao, Yufeng; Ma, Hongnan; Huang, Shifei; Zhang, Xuejiao; Xia, Meirong; Tang, Yongfu; Ma, Zi-Feng

2016-09-07

The emergence of atomically thick nanolayer materials, which feature a short ion diffusion channel and provide more exposed atoms in the electrochemical reactions, offers a promising occasion to optimize the performance of supercapacitors on the atomic level. In this work, a novel monolayer Ni-Co hydroxyl carbonate with an average thickness of 1.07 nm is synthesized via an ordinary one-pot hydrothermal route for the first time. This unique monolayer structure can efficiently rise up the exposed electroactive sites and facilitate the surface dependent electrochemical reaction processes, and thus results in outstanding specific capacitance of 2266 F g(-1). Based on this material, an all-solid-state asymmetric supercapacitor is developed adopting alkaline PVA (poly(vinyl alcohol)) gel (PVA/KOH) as electrolyte, which performs remarkable cycling stability (no capacitance fade after 19 000 cycles) together with promising energy density of 50 Wh kg(-1) (202 μWh cm(-2)) and high power density of 8.69 kW kg(-1) (35.1 mW cm(-2)). This as-assembled all-solid-state asymmetric supercapacitor (AASC) holds great potential in the field of portable energy storage devices.

Synthesis of high quality single-walled carbon nanotubes via a catalytic layer reinforced by self-assembled monolayers

International Nuclear Information System (INIS)

Adhikari, Prashanta Dhoj; Song, Wooseok; Cha, Myoung-Jun; Park, Chong-Yun

2013-01-01

This work reports the synthesis of high quality single-walled carbon nanotubes (SWCNT) using a catalytic layer reinforced by self-assembled monolayers (SAM). Amine-SAM was introduced on a SiO 2 /Si substrate and then an iron nanoparticles solution was dropped on the substrate by spin-coating. This catalytic template was used to grow carbon nanotubes by chemical vapor deposition and the synthesized SWCNT were observed to be prominent, based on the size distribution. Highly dense SWCNT with a diameter of about 1.1-1.2 nm were produced at 800-850 °C. Moreover, the diameter distribution of the SWCNT was more selective at a growth temperature of 900 °C. These findings provide important insights for a SAM support layer that can play the role as a restriction for the agglomeration of iron catalyst and is promising for the synthesis of high quality SWCNT. - Highlights: • Fe nanoparticles on self-assembled monolayers (SAM) containing template is underlined. • Its catalytic behavior to synthesis single-walled carbon nanotubes is studied. • The role of SAM on catalytic template is explored

Highly ordered self-assembly of one-dimensional nanoparticles in amphiphilic molecular systems

International Nuclear Information System (INIS)

Kim, Tae Hwan

2009-02-01

cationic surfactant, CTVB which has polymerizable counterions, and 2) permanently fixing the surfactant monolayer on the SWNTs by in situ free radical polymerization of the counterions, followed by freeze drying. UV-vis-NIR spectra of p-SWNT in water and alcohol showed very sharp van Hove transition which is typical for isolated SWNT, and were essentially identical after redispersion, indicating the excellent redispersibility. The in-situ microstructures of the p-SWNTs dispersed in water and alcohols were measured with SANS, which showed the encapsulation of SWNT by the surfactant monolayer cylindrically and by a swollen polymerized surfactant layer, respectively. It should be noted that the p-SWNTs are readily redispersible in water or alcohol by only 10 minutes of mild vortex mixing after harsh processing such as freeze-drying. Two kinds of cationic liposomes (CLs) consisting of univalent cationic and zwitterionic lipids were used as the amphiphilic molecular template for the interaction with 1D nanoparticles. For highly ordered superstructure of the cROD n (n is the number of carbon in the alkyl chain) in amphiphilic molecular systems, the CLs composed of DOTAP (catioinc) and DOPC (zwitterionic) lipids with various ratios (5:5 and 3:7) were prepared. The small angle x-ray scattering (SAXS) intensities of cROD n -DOTAP/DOPC complexes showed three different highly ordered phases, intercalated lamellar, doubly intercalated lamellar and centered rectangular phases, depending on particle diameter and charge interactions between cROD n and CLs. The phase behavior of cROD n -CL complexes was explained by the d spacing /d rod ratio and a new phase diagram of the complexes was established. It should be noted that the centered rectangular columnar phase of 1D nanoparticle-CL complexes has not been previously reported while the intercalated lamellar and the doubly intercalated lamellar structures were observed in rod-like biomolecule-CL complexes. For highly ordered superstructure

One-pot synthesis of powder-form β-Ni(OH)2 monolayer nanosheets with high electrochemical performance

International Nuclear Information System (INIS)

Wang, Minmin; Ren, Wanzhong; Zhao, Yunan; Liu, Yan; Cui, Hongtao

2013-01-01

In this work, β-Ni(OH) 2 monolayer nanosheets, which had been thought to be unachievable, were successfully prepared for the first time by a one-pot strategy using epoxide as precipitation agent and sodium dodecyl sulfate (SDS) as surfactant. The characterization results indicate that the formation of monolayer morphology depends on the mediation of SDS molecules. The XRD patterns demonstrate the loose and defective packing of Ni(OH) 2 layers in the SDS intercalated samples. The disappearing of vibration band of free hydroxyl groups in the FTIR spectra suggests the interlayer separation resulted by SDS. The TEM and AFM images further confirm the formation of monolayer nanosheets. It is proposed that the in situ modification of the secondary growth unit of β-Ni(OH) 2 by SDS allows its two-dimensional anisotropic growth through steric hindrance of SDS molecules. In addition, this effect allows isolation of β-Ni(OH) 2 from solvent with keeping of monolayer nanosheet state in dry powder. The electrochemical measurement results indicate that β-Ni(OH) 2 monolayer nanosheets own much higher urea electrolysis performance than their corresponding multilayer structure

Defect-Mediated Lithium Adsorption and Diffusion on Monolayer Molybdenum Disulfide.

Science.gov (United States)

Sun, Xiaoli; Wang, Zhiguo; Fu, Y Q

2015-12-22

Monolayer Molybdenum Disulfide (MoS2) is a promising anode material for lithium ion batteries because of its high capacities. In this work, first principle calculations based on spin density functional theory were performed to investigate adsorption and diffusion of lithium on monolayer MoS2 with defects, such as single- and few-atom vacancies, antisite, and grain boundary. The values of adsorption energies on the monolayer MoS2 with the defects were increased compared to those on the pristine MoS2. The presence of defects causes that the Li is strongly bound to the monolayer MoS2 with adsorption energies in the range between 2.81 and 3.80 eV. The donation of Li 2s electron to the defects causes an enhancement of adsorption of Li on the monolayer MoS2. At the same time, the presence of defects does not apparently affect the diffusion of Li, and the energy barriers are in the range of 0.25-0.42 eV. The presence of the defects can enhance the energy storage capacity, suggesting that the monolayer MoS2 with defects is a suitable anode material for the Li-ion batteries.

Liquid-Phase Exfoliation into Monolayered BiOBr Nanosheets for Photocatalytic Oxidation and Reduction

Energy Technology Data Exchange (ETDEWEB)

Yu, Hongjian [Beijing; Huang, Hongwei [Beijing; Xu, Kang [Center; Hao, Weichang [Center; Guo, Yuxi [Beijing; Wang, Shuobo [Beijing; Shen, Xiulin [Beijing; Pan, Shaofeng [Beijing; Zhang, Yihe [Beijing

2017-09-26

Monolayered photocatalytic materials have attracted huge research interests in terms of their large specific surface area and ample active sites. Sillén-structured layered BiOX (X = Cl, Br, I) casts great prospects owing to their strong photo-oxidation ability and high stability. Fabrication of monolayered BiOX by a facile, low-cost, and scalable approach is highly challenging and anticipated. Herein, we describe the large-scale preparation of monolayered BiOBr nanosheets with a thickness of ~0.85 nm via a readily achievable liquid-phase exfoliation strategy with assistance of formamide at ambient conditions. The as-obtained monolayered BiOBr nanosheets are allowed diverse superiorities, such as enhanced specific surface area, promoted band structure, and strengthened charge separation. Profiting from these benefits, the advanced BiOBr monolayers not only show excellent adsorption and photodegradation performance for treating contaminants, but also demonstrate a greatly promoted photocatalytic activity for CO2 reduction into CO and CH4. Additionally, monolayered BiOI nanosheets have also been obtained by the same synthetic approach. Our work offers a mild and general approach for preparation of monolayered BiOX, and may have huge potential to be extended to the synthesis of other single-layer two-dimensional materials.

Spontaneous phase separation during self-assembly in bi-dispersed spherical iron oxide nanoparticle monolayers

International Nuclear Information System (INIS)

Stanley, Jacob; Boucheron, Leandra; Shpyrko, Oleg; Lin, Binhua; Meron, Mati

2015-01-01

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

Spontaneous phase separation during self-assembly in bi-dispersed spherical iron oxide nanoparticle monolayers

Energy Technology Data Exchange (ETDEWEB)

Stanley, Jacob; Boucheron, Leandra; Shpyrko, Oleg, E-mail: lin@cars.uchicago.edu, E-mail: oshpyrko@physics.ucsd.edu [Department of Physics, University of California, San Diego, La Jolla, California 92093 (United States); Lin, Binhua, E-mail: lin@cars.uchicago.edu, E-mail: oshpyrko@physics.ucsd.edu; Meron, Mati [Center for Advanced Radiation Sources (CARS), University of Chicago, Chicago, Illinois 60637 (United States)

2015-04-20

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.

Novel top-contact monolayer pentacene-based thin-film transistor for ammonia gas detection.

Science.gov (United States)

Mirza, Misbah; Wang, Jiawei; Li, Dexing; Arabi, S Atika; Jiang, Chao

2014-04-23

We report on the fabrication of an organic field-effect transistor (OFET) of a monolayer pentacene thin film with top-contact electrodes for the aim of ammonia (NH3) gas detection by monitoring changes in its drain current. A top-contact configuration, in which source and drain electrodes on a flexible stamp [poly(dimethylsiloxane)] were directly contacted with the monolayer pentacene film, was applied to maintain pentacene arrangement ordering and enhance the monolayer OFET detection performance. After exposure to NH3 gas, the carrier mobility at the monolayer OFET channel decreased down to one-third of its original value, leading to a several orders of magnitude decrease in the drain current, which tremendously enhanced the gas detection sensitivity. This sensitivity enhancement to a limit of the 10 ppm level was attributed to an increase of charge trapping in the carrier channel, and the amount of trapped states was experimentally evaluated by the threshold voltage shift induced by the absorbed NH3 molecular analyte. In contrast, a conventional device with a 50-nm-thick pentacene layer displayed much higher mobility but lower response to NH3 gas, arising from the impediment of analyte penetrating into the conductive channel, owing to the thick pentacene film.

High-Yield Excited Triplet States in Pentacene Self-Assembled Monolayers on Gold Nanoparticles through Singlet Exciton Fission.

Science.gov (United States)

Kato, Daiki; Sakai, Hayato; Tkachenko, Nikolai V; Hasobe, Taku

2016-04-18

One of the major drawbacks of organic-dye-modified self-assembled monolayers on metal nanoparticles when employed for efficient use of light energy is the fact that singlet excited states on dye molecules can be easily deactivated by means of energy transfer to the metal surface. In this study, a series of 6,13-bis(triisopropylsilylethynyl)pentacene-alkanethiolate monolayer protected gold nanoparticles with different particle sizes and alkane chain lengths were successfully synthesized and were employed for the efficient generation of excited triplet states of the pentacene derivatives by singlet fission. Time-resolved transient absorption measurements revealed the formation of excited triplet states in high yield (172±26 %) by suppressing energy transfer to the gold surface. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Evaluation of monolayers and mixed monolayers formed from mercaptobenzothiazole and decanethiol as sensing platforms

International Nuclear Information System (INIS)

Mary Vergheese, T.; Berchmans, Sheela

2004-01-01

In this investigation, the characterisation of monolayer and mixed monolayers formed from mercaptobenzothiazole (MBT) and decanethiol (DT) has been carried out with cyclic voltammetry. The SAMs have been tested for their stability and electron transfer blocking properties. The redox probes used in the present study are [Fe(China) 6 ] 4- , [Ru(NH 3 ) 6 ] 2+ and Cu underpotential deposition (upd). The electron transfer kinetics is investigated in acid and neutral pH range. Electron transfer kinetics is altered by the nature of charge on the redox probe and the charge on the monolayer. Electron transfer kinetics of negatively charged redox probes like ferrocyanide ions is blocked when the surface pK a medium and at pK a >pH medium reversible features is observed for negatively charged probes. An exactly reverse effect is observed in the case of positively charged redox species like [Ru(NH 3 ) 6 ] 2+/3+ . Cu under potential deposition studies reflects the structural integrity and compactness of the SAM layer. The utility of these monolayers and mixed monolayer for selective sensing of dopamine is discussed based on their ability to discriminate between positively and negatively charged redox species at different pH

Microchannel-flowed-plasma modification of octadecyltrichlorosilane self-assembled-monolayers for liquid crystal alignment

International Nuclear Information System (INIS)

Zheng, W.; Chiang, C.-Y.; Underwood, I.

2013-01-01

We report that a chemical patterning technique based on local plasma modification of self-assembled monolayers has been utilized to fabricate surfaces for domain liquid crystal alignment. Highly hydrophobic octadecyltrichlorosilane monolayers deposited on glass substrates coated with Indium-Tin-Oxide were brought into contact with elastomeric stamps comprising trenches on a micro scale, and then exposed to an oxygen plasma. In the regions exposed to the plasma the monolayer was etched away leaving a patterned surface that exhibited surface energy differences between surface domains. The surfaces that bear the micropatterns have been shown to be capable of producing patterned alignment of nematic liquid crystal. - Highlights: • Chemical surface-patterning is used to fabricate liquid crystal alignment surface. • Highly hydrophobic octadecyltrichlorosilane monolayer is deposited on substrate. • O 2 plasma flow is used to etch the monolayer to form patterned surface. • The patterned surface exhibits surface energy differences between surface domains. • The surface borne the micropatterns is capable of domain liquid crystal alignment

Chiral and herringbone symmetry breaking in water-surface monolayers

DEFF Research Database (Denmark)

Peterson, I.R.; Kenn, R.M.; Goudot, A.

1996-01-01

We report the observation from monolayers of eicosanoic acid in the L(2)' phase of three distinct out-of-plane first-order diffraction peaks, indicating molecular tilt in a nonsymmetry direction and hence the absence of mirror symmetry. At lower pressures the molecules tilt in the direction of th...

Structures and shear response of lipid monolayers

International Nuclear Information System (INIS)

Dutta, P.; Ketterson, J.B.

1993-02-01

This report discusses our work during the last 3 years using x-ray diffraction and shear measurements to study lipid monolayers (membranes). The report is divided into: (1) structure: phase diagram of saturated fatty acid Langmuir monolayers, effect of head group interactions, studies of transferred monolayers (LB films); (2) mechanical properties: fiber=optic capillary wave probe and centrosymmetric trough, mechanical behavior of heneicosanoic acid monolayer phases

Overcrowding drives the unjamming transition of gap-free monolayers

Science.gov (United States)

Lan, Ganhui; Su, Tao

Collective cell motility plays central roles in various biological phenomena such as wound healing, cancer metastasis and embryogenesis. These are demonstrations of the unjamming transition in biology. However, contradictory to the typical density-driven jamming in particulate assemblies, cellular systems often get unjammed in highly packed, sometimes overcrowding environments. Here, we investigate monolayers' collective behaviors when cell number changes under the gap-free constraint. We report that overcrowding can unjam gap-free monolayers through increasing isotropic compression. We show that the transition boundary is determined by the isotropic compression and the cell-cell adhesion. Furthermore, we construct the free energy landscape for the T1 topological transition during monolayer rearrangement, and discover that the landscape evolves from single-barrier W shape to double-barrier M shape during the unjamming process. We also discover a distributed-to-disordered morphological transition of cells' geometry, coinciding with the unjamming transition. Our analyses reveal that the overcrowding and adhesion induced unjamming reflects the mechanical yielding of the highly deformable monolayer, suggesting an alternative mechanism that cells may robustly gain collective mobility through proliferation in confined environments, which differs from those caused by loosing up a packed particulate assembly. This work is supported by the GWU College Facilitating Funds.

Intact penetratin metabolite permeates across Caco-2 monolayers

DEFF Research Database (Denmark)

Birch, Ditlev; Christensen, Malene Vinther; Stærk, Dan

. Previous studies have demonstrated that cell-penetrating peptides (CPPs) may be used as carriers in order to improve the bioavailability of a therapeutic cargo like insulin after oral administration. Penetratin, a commonly used CPP, has been shown to increase the uptake of insulin across Caco-2 cell......-2 cells cultured on permeable filter inserts and in cell lysates, respectively. The epithelial permeation of penetratin and the formed metabolites was assessed by using Caco-2 monolayers cultured on permeable filter inserts. Results Preliminary data revealed that at least one specific metabolite...... is formed upon both intracellular and extracellular degradation of penetratin (figure 1A). Following incubation with epithelium for 4 hours, the metabolite permeated the Caco-2 monolayer and the concentration increased approximately 10-fold when compared to a sample collected following 15 minutes...

Enhancement of hole mobility in InSe monolayer via an InSe and black phosphorus heterostructure.

Science.gov (United States)

Ding, Yi-Min; Shi, Jun-Jie; Xia, Congxin; Zhang, Min; Du, Juan; Huang, Pu; Wu, Meng; Wang, Hui; Cen, Yu-Lang; Pan, Shu-Hang

2017-10-05

To enhance the low hole mobility (∼40 cm 2 V -1 s -1 ) of InSe monolayer, a novel two-dimensional (2D) van der Waals heterostructure made of InSe and black phosphorus (BP) monolayers with high hole mobility (∼10 3 cm 2 V -1 s -1 ) has been constructed and its structural and electronic properties are investigated using first-principles calculations. We find that the InSe/BP heterostructure exhibits a direct band gap of 1.39 eV and type-II band alignment with electrons (holes) located in the InSe (BP) layer. The band offsets of InSe and BP are 0.78 eV for the conduction band minimum and 0.86 eV for the valence band maximum, respectively. Surprisingly, the hole mobility in the InSe/BP heterostructure exceeds 10 4 cm 2 V -1 s -1 , which is one order of magnitude larger than the hole mobility of BP and three orders larger than that of the InSe monolayer. The electron mobility is also increased to 3 × 10 3 cm 2 V -1 s -1 . The physical reason has been analyzed deeply, and a universal method is proposed to improve the carrier mobility of 2D materials by forming heterostructures with them and other 2D materials with complementary properties. The InSe/BP heterostructure can thus be widely used in nanoscale InSe-based field-effect transistors, photodetectors and photovoltaic devices due to its type-II band alignment and high carrier mobility.

Enhanced thermoelectric power in two-dimensional transition metal dichalcogenide monolayers

KAUST Repository

Pu, Jiang

2016-07-27

The carrier-density-dependent conductance and thermoelectric properties of large-area MoS2 and WSe2 monolayers are simultaneously investigated using the electrolyte gating method. The sign of the thermoelectric power changes across the transistor off-state in the ambipolar WSe2 transistor as the majority carrier density switches from electron to hole. The thermopower and thermoelectric power factor of monolayer samples are one order of magnitude larger than that of bulk materials, and their carrier-density dependences exhibit a quantitative agreement with the semiclassical Mott relation based on the two-dimensional energy band structure, concluding the thermoelectric properties are enhanced by the low-dimensional effect.

Swift heavy ions induced irradiation effects in monolayer graphene and highly oriented pyrolytic graphite

International Nuclear Information System (INIS)

Zeng, J.; Yao, H.J.; Zhang, S.X.; Zhai, P.F.; Duan, J.L.; Sun, Y.M.; Li, G.P.; Liu, J.

2014-01-01

Monolayer graphene and highly oriented pyrolytic graphite (HOPG) were irradiated by swift heavy ions ( 209 Bi and 112 Sn) with the fluence between 10 11 and 10 14 ions/cm 2 . Both pristine and irradiated samples were investigated by Raman spectroscopy. It was found that D and D′ peaks appear after irradiation, which indicated the ion irradiation introduced damage both in the graphene and graphite lattice. Due to the special single atomic layer structure of graphene, the irradiation fluence threshold Φ th of the D band of graphene is significantly lower ( 11 ions/cm 2 ) than that (2.5 × 10 12 ions/cm 2 ) of HOPG. The larger defect density in graphene than in HOPG indicates that the monolayer graphene is much easier to be damaged than bulk graphite by swift heavy ions. Moreover, different defect types in graphene and HOPG were detected by the different values of I D /I D′ . For the irradiation with the same electronic energy loss, the velocity effect was found in HOPG. However, in this experiment, the velocity effect was not observed in graphene samples irradiated by swift heavy ions

Molecular Monolayers for Electrical Passivation and Functionalization of Silicon-Based Solar Energy Devices.

Science.gov (United States)

Veerbeek, Janneke; Firet, Nienke J; Vijselaar, Wouter; Elbersen, Rick; Gardeniers, Han; Huskens, Jurriaan

2017-01-11

Silicon-based solar fuel devices require passivation for optimal performance yet at the same time need functionalization with (photo)catalysts for efficient solar fuel production. Here, we use molecular monolayers to enable electrical passivation and simultaneous functionalization of silicon-based solar cells. Organic monolayers were coupled to silicon surfaces by hydrosilylation in order to avoid an insulating silicon oxide layer at the surface. Monolayers of 1-tetradecyne were shown to passivate silicon micropillar-based solar cells with radial junctions, by which the efficiency increased from 8.7% to 9.9% for n + /p junctions and from 7.8% to 8.8% for p + /n junctions. This electrical passivation of the surface, most likely by removal of dangling bonds, is reflected in a higher shunt resistance in the J-V measurements. Monolayers of 1,8-nonadiyne were still reactive for click chemistry with a model catalyst, thus enabling simultaneous passivation and future catalyst coupling.

Solution-processable septithiophene monolayer transistor

NARCIS (Netherlands)

Defaux, M.; Gholamrezaie, F.; Wang, J.; Kreyes, A.; Ziener, U.; Anokhin, D.V.; Ivanov, D.A.; Moser, A.; Neuhold, A.; Salzmann, I.; Resel, R.; Leeuw, de D.M.; Meskers, S.C.J.; Moeller, M.; Mourran, A.

2012-01-01

Septithiophene with endgroups designed to form liquid crystalline phases and allows controlled deposition of an electrically connected monolayer. Field effect mobilies mobilities of charge carriers and spectroscopic properties of the monolayer provide evidence of sustainable transport and

Solution-Processable Septithiophene Monolayer Transistor

NARCIS (Netherlands)

Defaux, Matthieu; Gholamrezaie, Fatemeh; Wang, Jingbo; Kreyes, Andreas; Ziener, Ulrich; Anokhin, Denis V.; Ivanov, Dimitri A.; Moser, Armin; Neuhold, Alfred; Salzmann, Ingo; Resel, Roland; de Leeuw, Dago M.; Meskers, Stefan C. J.; Moeller, Martin; Mourran, Ahmed

2012-01-01

Septithiophene with endgroups designed to form liquid crystalline phases and allows controlled deposition of an electrically connected monolayer. Field effect mobilies mobilities of charge carriers and spectroscopic properties of the monolayer provide evidence of sustainable transport and

One-pot synthesis of powder-form {beta}-Ni(OH){sub 2} monolayer nanosheets with high electrochemical performance

Energy Technology Data Exchange (ETDEWEB)

Wang, Minmin; Ren, Wanzhong; Zhao, Yunan; Liu, Yan; Cui, Hongtao, E-mail: htcui@ytu.edu.cn [Yantai University, Shandong Provincial Engineering Research Center for Light Hydrocarbon Comprehensive Utilization, College of Chemistry and Chemical Engineering (China)

2013-08-15

In this work, {beta}-Ni(OH){sub 2} monolayer nanosheets, which had been thought to be unachievable, were successfully prepared for the first time by a one-pot strategy using epoxide as precipitation agent and sodium dodecyl sulfate (SDS) as surfactant. The characterization results indicate that the formation of monolayer morphology depends on the mediation of SDS molecules. The XRD patterns demonstrate the loose and defective packing of Ni(OH){sub 2} layers in the SDS intercalated samples. The disappearing of vibration band of free hydroxyl groups in the FTIR spectra suggests the interlayer separation resulted by SDS. The TEM and AFM images further confirm the formation of monolayer nanosheets. It is proposed that the in situ modification of the secondary growth unit of {beta}-Ni(OH){sub 2} by SDS allows its two-dimensional anisotropic growth through steric hindrance of SDS molecules. In addition, this effect allows isolation of {beta}-Ni(OH){sub 2} from solvent with keeping of monolayer nanosheet state in dry powder. The electrochemical measurement results indicate that {beta}-Ni(OH){sub 2} monolayer nanosheets own much higher urea electrolysis performance than their corresponding multilayer structure.

Evaluation of monolayers and mixed monolayers formed from mercaptobenzothiazole and decanethiol as sensing platforms

Energy Technology Data Exchange (ETDEWEB)

Mary Vergheese, T.; Berchmans, Sheela

2004-02-15

In this investigation, the characterisation of monolayer and mixed monolayers formed from mercaptobenzothiazole (MBT) and decanethiol (DT) has been carried out with cyclic voltammetry. The SAMs have been tested for their stability and electron transfer blocking properties. The redox probes used in the present study are [Fe(China){sub 6}]{sup 4-}, [Ru(NH{sub 3}){sub 6}]{sup 2+} and Cu underpotential deposition (upd). The electron transfer kinetics is investigated in acid and neutral pH range. Electron transfer kinetics is altered by the nature of charge on the redox probe and the charge on the monolayer. Electron transfer kinetics of negatively charged redox probes like ferrocyanide ions is blocked when the surface pK{sub a}pH{sub medium} reversible features is observed for negatively charged probes. An exactly reverse effect is observed in the case of positively charged redox species like [Ru(NH{sub 3}){sub 6}]{sup 2+/3+}. Cu under potential deposition studies reflects the structural integrity and compactness of the SAM layer. The utility of these monolayers and mixed monolayer for selective sensing of dopamine is discussed based on their ability to discriminate between positively and negatively charged redox species at different pH.

Current Transport Properties of Monolayer Graphene/n-Si Schottky Diodes

Science.gov (United States)

Pathak, C. S.; Garg, Manjari; Singh, J. P.; Singh, R.

2018-05-01

The present work reports on the fabrication and the detailed macroscopic and nanoscale electrical characteristics of monolayer graphene/n-Si Schottky diodes. The temperature dependent electrical transport properties of monolayer graphene/n-Si Schottky diodes were investigated. Nanoscale electrical characterizations were carried out using Kelvin probe force microscopy and conducting atomic force microscopy. Most the values of ideality factor and barrier height are found to be in the range of 2.0–4.4 and 0.50–0.70 eV for monolayer graphene/n-Si nanoscale Schottky contacts. The tunneling of electrons is found to be responsible for the high value of ideality factor for nanoscale Schottky contacts.

Controlled electrodeposition of Au monolayer film on ionic liquid

Science.gov (United States)

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

2016-05-01

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.

Single Atomically Sharp Lateral Monolayer p-n Heterojunction Solar Cells with Extraordinarily High Power Conversion Efficiency

KAUST Repository

Tsai, Meng-Lin

2017-06-26

The recent development of 2D monolayer lateral semiconductor has created new paradigm to develop p-n heterojunctions. Albeit, the growth methods of these heterostructures typically result in alloy structures at the interface, limiting the development for high-efficiency photovoltaic (PV) devices. Here, the PV properties of sequentially grown alloy-free 2D monolayer WSe-MoS lateral p-n heterojunction are explores. The PV devices show an extraordinary power conversion efficiency of 2.56% under AM 1.5G illumination. The large surface active area enables the full exposure of the depletion region, leading to excellent omnidirectional light harvesting characteristic with only 5% reduction of efficiency at incident angles up to 75°. Modeling studies demonstrate the PV devices comply with typical principles, increasing the feasibility for further development. Furthermore, the appropriate electrode-spacing design can lead to environment-independent PV properties. These robust PV properties deriving from the atomically sharp lateral p-n interface can help develop the next-generation photovoltaics.

Surface structures of normal paraffins and cyclohexane monolayers and thin crystals grown on the (111) crystal face of platinum. A low-energy electron diffraction study

International Nuclear Information System (INIS)

Firment, L.E.; Somorjai, G.A.

1977-01-01

The surfaces of the normal paraffins (C 3 --C 8 ) and cyclohexane have been studied using low-energy electron diffraction (LEED). The samples were prepared by vapor deposition on the (111) face of a platinum single crystal in ultrahigh vacuum, and were studied both as thick films and as adsorbed monolayers. These molecules form ordered monolayers on the clean metal surface in the temperature range 100--220 K and at a vapor flux corresponding to 10 -7 Torr. In the adsorbed monolayers of the normal paraffins (C 4 --C 8 ), the molecules lie with their chain axes parallel to the Pt surface and Pt[110]. The paraffin monolayer structures undergo order--disorder transitions as a function of temperature. Multilayers condensed upon the ordered monolayers maintained the same orientation and packing as found in the monolayers. The surface structures of the growing organic crystals do not corresond to planes in their reported bulk crystal structures and are evidence for epitaxial growth of pseudomorphic crystal forms. Multilayers of n-octane and n-heptane condensed upon disordered monolayers have also grown with the (001) plane of the triclinic bulk crystal structures parallel to the surface. n-Butane has three monolayer structures on Pt(111) and one of the three is maintained during growth of the crystal. Cyclohexane forms an ordered monolayer, upon which a multilayer of cyclohexane grows exhibiting the (001) surface orientation of the monoclinic bulk crystal structure. Surface structures of saturated hydrocarbons are found to be very susceptible to electron beam induced damage. Surface charging interferes with LEED only at sample thicknesses greater than 200 A

The langmuir monolayer: an efficient model for studying interfacial properties of biomembranes

International Nuclear Information System (INIS)

Cirak, J.; Sokolsky, M.; Dobrocka, E.; Weis, M.

2012-01-01

In this communication, we describe aspects of monolayer technology by focusing on effects of calcium ions on physical properties of phospholipid monolayers using results of measurements of surface pressure, x-ray reflectivity and AFM. These experiments are motivated by the search for lipid-DNA complexes with high transfection efficiency but without toxicity which might be a promising tool in gene therapy. In each part methodological importance is stressed and its specificity for studying molecular interactions at a lipid monolayer. (authors)

Examination of fluorination effect on physical properties of saturated long-chain alcohols by DSC and Langmuir monolayer.

Science.gov (United States)

Nakahara, Hiromichi; Nakamura, Shohei; Okahashi, Yoshinori; Kitaguchi, Daisuke; Kawabata, Noritake; Sakamoto, Seiichi; Shibata, Osamu

2013-02-01

Partially fluorinated long-chain alcohols have been newly synthesized from a radical reaction, which is followed by a reductive reaction. The fluorinated alcohols have been investigated by differential scanning calorimetry (DSC) and compression isotherms in a Langmuir monolayer state. Their melting points increase with an increase in chain length due to elongation of methylene groups. However, the melting points for the alcohols containing shorter fluorinated moieties are lower than those for the typical hydrogenated fatty alcohols. Using the Langmuir monolayer technique, surface pressure (π)-molecular area (A) and surface potential (ΔV)-A isotherms of monolayers of the fluorinated alcohols have been measured in the temperature range from 281.2 to 303.2K. In addition, a compressibility modulus (Cs(-1)) is calculated from the π-A isotherms. Four kinds of the alcohol monolayers show a phase transition (π(eq)) from a disordered to an ordered state upon lateral compression. The π(eq) values increase linearly with increasing temperatures. A slope of π(eq) against temperature for the alcohols with shorter fluorocarbons is unexpectedly larger than that for the corresponding fatty alcohols. Generally, fluorinated amphiphiles have a greater thermal stability (or resistance), which is a characteristic of highly fluorinated or perfluorinated compounds. Herein, however, the alcohols containing perfluorobutylated and perfluorohexylated chains show the irregular thermal behavior in both the solid and monolayer states. Copyright © 2012 Elsevier B.V. All rights reserved.

Tuning of metal work functions with self-assembled monolayers

NARCIS (Netherlands)

de Boer, B; Hadipour, A; Mandoc, MM; van Woudenbergh, T; Blom, PWM

2005-01-01

Work functions of gold and silver are varied by over 1.4 and 1.7 eV, respectively, by using self-assembled monolayers. Using these modified electrodes, the hole current in a poly(2-methoxy-5-(2'-ethylhexyloxy)- 1,4-phenylene vinylene) light-emitting diode is tuned by more than six orders of

Strain-mediated electronic properties of pristine and Mn-doped GaN monolayers

Science.gov (United States)

Sharma, Venus; Srivastava, Sunita

2018-04-01

Graphene-like two-dimensional (2D) monolayer structures GaN has gained enormous amount of interest due to high thermal stability and inherent energy band gap for practical applications. First principles calculations are performed to investigate the electronic structure and strain-mediated electronic properties of pristine and Mn-doped GaN monolayer. Binding energy of Mn dopant at various adsorption site is found to be nearly same indicating these sites to be equally favorable for adsorption of foreign atom. Depending on the adsorption site, GaN monolayer can act as p-type or n-type magnetic semiconductor. The tensile strength of both pristine and doped GaN monolayer (∼24 GPa) at ultimate tensile strain of 34% is comparable with the tensile strength of graphene. The in-plane biaxial strain modulate the energy band gap of both pristine and doped-monolayer from direct to indirect gap semiconductor and finally retendered theme into metal at critical value of applied strain. These characteristics make GaN monolayer to be potential candidate for the future applications in tunable optoelectronics.

Polycyclic aromatic hydrocarbons in model bacterial membranes - Langmuir monolayer studies.

Science.gov (United States)

Broniatowski, Marcin; Binczycka, Martyna; Wójcik, Aneta; Flasiński, Michał; Wydro, Paweł

2017-12-01

High molecular weight polycyclic aromatic hydrocarbons (HMW-PAHs) are persistent organic pollutants which due to their limited biodegradability accumulate in soils where their increased presence can lead to the impoverishment of the decomposer organisms. As very hydrophobic PAHs easily penetrate cellular membranes of soil bacteria and can be incorporated therein, changing the membrane fluidity and other functions which in consequence can lead to the death of the organism. The structure and size of PAH molecule can be crucial for its membrane activity; however the correlation between PAH structure and its interaction with phospholipids have not been investigated so far. In our studies we applied phospholipid Langmuir monolayers as model bacterial membranes and investigated how the incorporation of six structurally different PAH molecules change the membrane texture and physical properties. In our studies we registered surface pressure and surface potential isotherms upon the monolayer compression, visualized the monolayer texture with the application of Brewster angle microscopy and searched the ordering of the film-forming molecules with molecular resolution with the application of grazing incidence X-ray diffraction (GIXD) method. It turned out that the phospholipid-PAH interactions are strictly structure dependent. Four and five-ring PAHs of the angular or cluster geometry can be incorporated into the model membranes changing profoundly their textures and fluidity; whereas linear or large cluster PAHs cannot be incorporated and separate from the lipid matrix. The observed phenomena were explained based on structural similarities of the applied PAHs with membrane steroids and hopanoids. Copyright © 2017. Published by Elsevier B.V.

Selectively Plasmon-Enhanced Second-Harmonic Generation from Monolayer Tungsten Diselenide on Flexible Substrates

KAUST Repository

Wang, Zhuo

2018-01-04

Monolayer two-dimensional transition metal dichalcogenides (2D TMDCs) exhibit promising characteristics in miniaturized nonlinear optical frequency converters, due to their inversion asymmetry and large second-order nonlinear susceptibility. However, these materials usually have a very short light interaction lengths with the pump laser because they are atomically thin, such that second-harmonic generation (SHG) is generally inefficient. In this paper, we fabricate a judiciously structured 150-nm-thick planar surface consisting of monolayer tungsten diselenide and sub-20-nm-wide gold trenches on flexible substrates, reporting ~7000-fold SHG enhancement without peak broadening or background in the spectra as compared to WSe2 on as-grown sapphire substrates. Our proof-of-concept experiment yields effective second-order nonlinear susceptibility of 2.1 × 104 pm/V. Three orders of magnitude enhancement is maintained with pump wavelength ranging from 800 nm to 900 nm, breaking the limitation of narrow pump wavelength range for cavity-enhanced SHG. In addition, SHG amplitude can be dynamically controlled via selective excitation of the lateral gap plasmon by rotating the laser polarization. Such fully open, flat and ultrathin profile enables a great variety of functional samples with high SHG from one patterned silicon substrate, favoring scalable production of nonlinear converters. The surface accessibility also enables integration with other optical components for information processing in an ultrathin and flexible form.

Selectively Plasmon-Enhanced Second-Harmonic Generation from Monolayer Tungsten Diselenide on Flexible Substrates

KAUST Repository

Wang, Zhuo; Dong, Zhaogang; Zhu, Hai; Jin, Lei; Chiu, Ming-Hui; Li, Lain-Jong; Xu, Qing-Hua; Eda, Goki; Maier, Stefan A.; Wee, Andrew T. S.; Qiu, Cheng-Wei; Yang, Joel K.W.

2018-01-01

Monolayer two-dimensional transition metal dichalcogenides (2D TMDCs) exhibit promising characteristics in miniaturized nonlinear optical frequency converters, due to their inversion asymmetry and large second-order nonlinear susceptibility. However, these materials usually have a very short light interaction lengths with the pump laser because they are atomically thin, such that second-harmonic generation (SHG) is generally inefficient. In this paper, we fabricate a judiciously structured 150-nm-thick planar surface consisting of monolayer tungsten diselenide and sub-20-nm-wide gold trenches on flexible substrates, reporting ~7000-fold SHG enhancement without peak broadening or background in the spectra as compared to WSe2 on as-grown sapphire substrates. Our proof-of-concept experiment yields effective second-order nonlinear susceptibility of 2.1 × 104 pm/V. Three orders of magnitude enhancement is maintained with pump wavelength ranging from 800 nm to 900 nm, breaking the limitation of narrow pump wavelength range for cavity-enhanced SHG. In addition, SHG amplitude can be dynamically controlled via selective excitation of the lateral gap plasmon by rotating the laser polarization. Such fully open, flat and ultrathin profile enables a great variety of functional samples with high SHG from one patterned silicon substrate, favoring scalable production of nonlinear converters. The surface accessibility also enables integration with other optical components for information processing in an ultrathin and flexible form.

Low temperature photoresponse of monolayer tungsten disulphide

Directory of Open Access Journals (Sweden)

Bingchen Cao

2014-11-01

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.

Potential-induced structural transitions of DL-homocysteine monolayers on Au(111) electrode surfaces

DEFF Research Database (Denmark)

Zhang, Jingdong; Demetriou, Anna; Welinder, Anne Christina

2005-01-01

Monolayers of homocysteine on Au(111)-surfaces have been investigated by voltammetry, in situ scanning tunnelling microscopy (STM) and subtractively normalised interfacial Fourier transform spectroscopy (SNIFTIRS). A pair of sharp voltammetric peaks build up in the potential range 0 to -0.1 V (vs...... potentials at pH 7.7. The molecules pack into highly ordered domains around the peak potential. High-resolution in situ STM reveals a (root 3 x 5) R30 degrees lattice with three homocysteine molecules in each unit cell. The adlayer changes into disordered structures on either side of the peak potential...

High-Order Hamilton's Principle and the Hamilton's Principle of High-Order Lagrangian Function

International Nuclear Information System (INIS)

Zhao Hongxia; Ma Shanjun

2008-01-01

In this paper, based on the theorem of the high-order velocity energy, integration and variation principle, the high-order Hamilton's principle of general holonomic systems is given. Then, three-order Lagrangian equations and four-order Lagrangian equations are obtained from the high-order Hamilton's principle. Finally, the Hamilton's principle of high-order Lagrangian function is given.

Substrate effect on the growth of monolayer dendritic MoS2 on LaAlO3 (100) and its electrocatalytic applications

Science.gov (United States)

Li, Cong; Zhang, Yu; Ji, Qingqing; Shi, Jianping; Chen, Zhaolong; Zhou, Xiebo; Fang, Qiyi; Zhang, Yanfeng

2016-09-01

In accommodating the rapid development of two-dimensional (2D) nanomaterials, chemical vapor deposition (CVD) has become a powerful tool for their batch production with desirable characteristics, such as high crystal quality, large domain size, and tunable domain shape. The crystallinity and morphology of the growth substrates usually play a crucial role in the CVD synthesis of high-quality monolayer MoS2, a kind of 2D layered material which has ignited huge interest in nanoelectronics, optoelectronics and energy harvesting, etc. Herein, by utilizing a low-pressure chemical vapor deposition (LPCVD) system, we demonstrate a regioselective synthesis of monolayer MoS2 on the corrugated single-crystal LaAlO3 (100) with twin crystal domains induced by the second-order phase transition. Unique dendritic morphologies with tunable nucleation densities were obtained in different regions of the undulated substrate, presenting a strong substrate modulation effect. Interestingly, the exposure of abundant active edge sites along with the rather high nucleation density makes the monolayer dendritic MoS2 a good electrocatalyst for hydrogen evolution reaction (HER), particularly featured by a rather high exchange current density (70.4 μA cm-2). Furthermore, uniform monolayer MoS2 films can also be obtained and transferred to arbitrary substrates. We believe that this work provides a new growth system for the controllable synthesis of 2D layered materials with unique dendritic morphologies, as well as its great application potential in energy conversion and harvesting.

Organosilicon derivatives of BTBT for monolayer organic field effect transistors

Science.gov (United States)

Agina, Elena V.; Polinskaya, Marina S.; Trul, Askold A.; Chekusova, Viktoria P.; Sizov, Alexey S.; Borshchev, Oleg V.; Ponomarenko, Sergey A.

2017-08-01

Synthesis of novel organosilicon derivatives of [1]benzothieno[3,2-b][1]-benzothiophene (BTBT) linked though flexible aliphatic spacers to a disiloxane anchor group is reported. They were successfully used in monolayer OFETs with the charge carrier mobilities up to 0.02 cm2 /Vs, threshold voltage close to 0 V and On/Off ratio up to 10,000. Influence of the chemical structure of the molecules synthesized on the morphology, molecular 2D ordering in the monolayers and their semiconducting properties is considered. The effect of different methods of the ultrathin semiconducting layer preparation, such as Langmuir-Blodgett, Langmuir-Schaefer, spin coating or doctor blade, on the OFET performance is discussed.

Electrochemical behaviour of monolayer and bilayer graphene

OpenAIRE

Valota, Anna T.; Kinloch, Ian A.; Novoselov, Kostya S.; Casiraghi, Cinzia; Eckmann, Axel; Hill, Ernie W.; Dryfe, Robert A. W.

2011-01-01

Results of a study on the electrochemical properties of exfoliated single and multilayer graphene flakes are presented. Graphene flakes were deposited on silicon/silicon oxide wafers to enable fast and accurate characterization by optical microscopy and Raman spectroscopy. Conductive silver paint and silver wires were used to fabricate contacts; epoxy resin was employed as masking coating in order to expose a stable, well defined area of graphene. Both multilayer and monolayer graphene microe...

Changes in work function due to NO2 adsorption on monolayer and bilayer epitaxial graphene on SiC(0001)

Science.gov (United States)

Caffrey, Nuala M.; Armiento, Rickard; Yakimova, Rositsa; Abrikosov, Igor A.

2016-11-01

The electronic properties of monolayer graphene grown epitaxially on SiC(0001) are known to be highly sensitive to the presence of NO2 molecules. The presence of small areas of bilayer graphene, on the other hand, considerably reduces the overall sensitivity of the surface. We investigate how NO2 molecules interact with monolayer and bilayer graphene, both free-standing and on a SiC(0001) substrate. We show that it is necessary to explicitly include the effect of the substrate in order to reproduce the experimental results. When monolayer graphene is present on SiC, there is a large charge transfer from the interface between the buffer layer and the SiC substrate to the molecule. As a result, the surface work function increases by 0.9 eV after molecular adsorption. A graphene bilayer is more effective at screening this interfacial charge, and so the charge transfer and change in work function after NO2 adsorption is much smaller.

Formation of intra-island grain boundaries in pentacene monolayers.

Science.gov (United States)

Zhang, Jian; Wu, Yu; Duhm, Steffen; Rabe, Jürgen P; Rudolf, Petra; Koch, Norbert

2011-12-21

To assess the formation of intra-island grain boundaries during the early stages of pentacene film growth, we studied sub-monolayers of pentacene on pristine silicon oxide and silicon oxide with high pinning centre density (induced by UV/O(3) treatment). We investigated the influence of the kinetic energy of the impinging molecules on the sub-monolayer growth by comparing organic molecular beam deposition (OMBD) and supersonic molecular beam deposition (SuMBD). For pentacene films fabricated by OMBD, higher pentacene island-density and higher polycrystalline island density were observed on UV/O(3)-treated silicon oxide as compared to pristine silicon oxide. Pentacene films deposited by SuMBD exhibited about one order of magnitude lower island- and polycrystalline island densities compared to OMBD, on both types of substrates. Our results suggest that polycrystalline growth of single islands on amorphous silicon oxide is facilitated by structural/chemical surface pinning centres, which act as nucleation centres for multiple grain formation in a single island. Furthermore, the overall lower intra-island grain boundary density in pentacene films fabricated by SuMBD reduces the number of charge carrier trapping sites specific to grain boundaries and should thus help achieving higher charge carrier mobilities, which are advantageous for their use in organic thin-film transistors.

Preparation and Photoluminescence of Tungsten Disulfide Monolayer

Directory of Open Access Journals (Sweden)

Yanfei Lv

2018-05-01

Full Text Available Tungsten disulfide (WS2 monolayer is a direct band gap semiconductor. The growth of WS2 monolayer hinders the progress of its investigation. In this paper, we prepared the WS2 monolayer through chemical vapor transport deposition. This method makes it easier for the growth of WS2 monolayer through the heterogeneous nucleation-and-growth process. The crystal defects introduced by the heterogeneous nucleation could promote the photoluminescence (PL emission. We observed the strong photoluminescence emission in the WS2 monolayer, as well as thermal quenching, and the PL energy redshift as the temperature increases. We attribute the thermal quenching to the energy or charge transfer of the excitons. The redshift is related to the dipole moment of WS2.

Lanthanide Selective Sorbents: Self-Assembled Monolayers on Mesoporous Supports (SAMMS)

Energy Technology Data Exchange (ETDEWEB)

Fryxell, Glen E.; Wu, Hong; Lin, Yuehe; Shaw, Wendy J.; Birnbaum, Jerome C.; Linehan, John C.; Nie, Zimin; Kemner, K. M.; Kelly, Shelley

2004-11-01

Through the marriage of mesoporous ceramics with self-assembled monolayer chemistry, the genesis of a powerful new class of environmental sorbent materials has been realized. By coating the mesoporous ceramic backbone with a monolayer terminated with a lanthanide-specific ligand, it is possible to couple high lanthanide binding affinity with the high loading capacity (resulting from the extremely high surface area of the support). This lanthanide-specific ligand field is created by pairing a ''hard'' anionic Lewis base with a suitable synergistic ligand, in a favorable chelating geometry. Details of the synthesis, characterization, lanthanide binding studies, binding kinetics, competition experiments and sorbent regeneration studies are summarized

Lanthanide Selective Sorbents: Self-Assembled Monolayers on Mesoporous Supports (SAMMS)

Energy Technology Data Exchange (ETDEWEB)

Fryxell, Glen E.; Wu, Hong; Lin, Yuehe; Shaw, Wendy J.; Birnbaum, Jerome C.; Linehan, John C.; Nie, Zimin; Kemner, Kenneth M.; Kelly, Shelley

2004-11-01

Through the marriage of mesoporous ceramics with self-assembled monolayer chemistry, the genesis of a powerful new class of environmental sorbent materials has been realized. By coating the mesoporous ceramic backbone with a monolayer terminated with a lanthanide-specific ligand, it is possible to couple high lanthanide binding affinity with the high loading capacity (resulting from the extremely high surface area of the support). This lanthanide-specific ligand field is created by pairing a “hard” anionic Lewis base with a suitable synergistic ligand, in a favorable chelating geometry. Details of the synthesis, characterization, lanthanide binding studies, binding kinetics, competition experiments and sorbent regeneration studies are summarized.

Nanoscale Trapping and Squeeze-Out of Confined Alkane Monolayers.

Science.gov (United States)

Gosvami, N N; O'Shea, S J

2015-12-01

We present combined force curve and conduction atomic force microscopy (AFM) data for the linear alkanes CnH2n+2 (n = 10, 12, 14, 16) confined between a gold-coated AFM tip and a graphite surface. Solvation layering is observed in the force curves for all liquids, and conduction AFM is used to study in detail the removal of the confined (mono)layer closest to the graphite surface. The squeeze-out behavior of the monolayer can be very different depending upon the temperature. Below the monolayer melting transition temperatures the molecules are in an ordered state on the graphite surface, and fast and complete removal of the confined molecules is observed. However, above the melting transition temperature the molecules are in a disordered state, and even at large applied pressure a few liquid molecules are trapped within the tip-sample contact zone. These findings are similar to a previous study for branched alkanes [ Gosvami Phys. Rev. Lett. 2008, 100, 076101 ], but the observation for the linear alkane homologue series demonstrates clearly the dependence of the squeeze-out and trapping on the state of the confined material.

Structure and shear response of lipid monolayers

International Nuclear Information System (INIS)

Dutta, P.; Ketterson, J.B.

1990-02-01

Organic monolayers and multilayers are both scientifically fascinating and technologically promising; they are, however, both complex systems and relatively inaccessible to experimental probes. In this Progress Report, we describe our X-ray diffraction studies, which have given us substantial new information about the structures and phase transitions in monolayers on the surface of water; our use of these monolayers as a unique probe of the dynamics of wetting and spreading; and our studies of monolayer mechanical properties using a simple but effective technique available to anyone using the Wilhelmy method to measure surface tension

Monolayer Superconductivity in WS2

NARCIS (Netherlands)

Zheliuk, Oleksandr; Lu, Jianming; Yang, Jie; Ye, Jianting

Superconductivity in monolayer tungsten disulfide (2H-WS2) is achieved by strong electrostatic electron doping of an electric double-layer transistor (EDLT). Single crystals of WS2 are grown by a scalable method - chemical vapor deposition (CVD) on standard Si/SiO2 substrate. The monolayers are

Near-Edge X-ray Absorption Fine Structure Spectroscopy of Diamondoid Thiol Monolayers on Gold

Energy Technology Data Exchange (ETDEWEB)

Willey, T M; Fabbri, J; Lee, J I; Schreiner, P; Fokin, A A; Tkachenko, B A; Fokina, N A; Dahl, J; Carlson, B; Vance, A L; Yang, W; Terminello, L J; van Buuren, T; Melosh, N

2007-11-27

Diamondoids, hydrocarbon molecules with cubic-diamond-cage structures, have unique properties with potential value for nanotechnology. The availability and ability to selectively functionalize this special class of nanodiamond materials opens new possibilities for surface-modification, for high-efficiency field emitters in molecular electronics, as seed crystals for diamond growth, or as robust mechanical coatings. The properties of self-assembled monolayers (SAMs) of diamondoids are thus of fundamental interest for a variety of emerging applications. This paper presents the effects of thiol substitution position and polymantane order on diamondoid SAMs on gold using near-edge X-ray absorption fine structure spectroscopy (NEXAFS) and X-ray photoelectron spectroscopy (XPS). A framework to determine both molecular tilt and twist through NEXAFS is presented and reveals highly ordered diamondoid SAMs, with the molecular orientation controlled by the thiol location. C 1s and S 2p binding energies are lower in adamantane thiol than alkane thiols on gold by 0.67 {+-} 0.05 eV and 0.16 {+-} 0.04 eV respectively. These binding energies vary with diamondoid monolayer structure and thiol substitution position, consistent with different amounts of steric strain and electronic interaction with the substrate. This work demonstrates control over the assembly, in particular the orientational and electronic structure, providing a flexible design of surface properties with this exciting new class of diamond clusters.

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

DEFF Research Database (Denmark)

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

2007-01-01

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......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...... 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...

Platinum Monolayer Electrocatalysts for Anodic Oxidation of Alcohols.

Science.gov (United States)

Li, Meng; Liu, Ping; Adzic, Radoslav R

2012-12-06

The slow, incomplete oxidation of methanol and ethanol on platinum-based anodes as well as the high price and limited reserves of Pt has hampered the practical application of direct alcohol fuel cells. We describe the electrocatalysts consisting of one Pt monolayer (one atom thick layer) placed on extended or nanoparticle surfaces having the activity and selectivity for the oxidation of alcohol molecules that can be controlled with platinum-support interaction. The suitably expanded Pt monolayer (i.e., Pt/Au(111)) exhibits a factor of 7 activity increase in catalyzing methanol electrooxidation relative to Pt(111). Sizable enhancement is also observed for ethanol electrooxidation. Furthermore, a correlation between substrate-induced lateral strain in a Pt monolayer and its activity/selectivity is established and rationalized by experimental and theoretical studies. The knowledge we gained with single-crystal model catalysts was successfully applied in designing real nanocatalysts. These findings for alcohols are likely to be applicable for the oxidation of other classes of organic molecules.

Measuring the Edge Recombination Velocity of Monolayer Semiconductors.

Science.gov (United States)

Zhao, Peida; Amani, Matin; Lien, Der-Hsien; Ahn, Geun Ho; Kiriya, Daisuke; Mastandrea, James P; Ager, Joel W; Yablonovitch, Eli; Chrzan, Daryl C; Javey, Ali

2017-09-13

Understanding edge effects and quantifying their impact on the carrier properties of two-dimensional (2D) semiconductors is an essential step toward utilizing this material for high performance electronic and optoelectronic devices. WS 2 monolayers patterned into disks of varying diameters are used to experimentally explore the influence of edges on the material's optical properties. Carrier lifetime measurements show a decrease in the effective lifetime, τ effective , as a function of decreasing diameter, suggesting that the edges are active sites for carrier recombination. Accordingly, we introduce a metric called edge recombination velocity (ERV) to characterize the impact of 2D material edges on nonradiative carrier recombination. The unpassivated WS 2 monolayer disks yield an ERV ∼ 4 × 10 4 cm/s. This work quantifies the nonradiative recombination edge effects in monolayer semiconductors, while simultaneously establishing a practical characterization approach that can be used to experimentally explore edge passivation methods for 2D materials.

Giant photoresponse in quantized SrRuO3 monolayer at oxide interfaces

KAUST Repository

Liu, Heng-Jui

2018-02-01

The photoelectric effect in semiconductors is the main mechanism for most modern optoelectronic devices, in which the adequate bandgap plays the key role for acquiring high photoresponse. Among numerous material categories applied in this field, the complex oxides exhibit great possibilities because they present a wide distribution of band gaps for absorbing light with any wavelength. Their physical properties and lattice structures are always strongly coupled and sensitive to light illumination. Moreover, the confinement of dimensionality of the complex oxides in the heterostructures can provide more diversities in designing and modulating the band structures. On the basis of this perspective, we have chosen itinerary ferromagnetic SrRuO3 as the model material, and fabricated it in one-unit-cell thickness in order to open a small band gap for effective utilization of visible light. By inserting this SrRuO3 monolayer at the interface of the well-developed two-dimensional electron gas system (LaAlO3/SrTiO3), the resistance of the monolayer can be further revealed. In addition, a giant enhancement (>300%) of photoresponse under illumination of visible light with power density of 500 mW/cm2 is also observed. Such can be ascribed to the further modulation of band structure of the SrRuO3 monolayer under the illumination, confirmed by cross-section scanning tunneling microscopy (XSTM). Therefore, this study demonstrates a simple route to design and explore the potential low dimensional oxide materials for future optoelectronic devices.

Giant photoresponse in quantized SrRuO3 monolayer at oxide interfaces

KAUST Repository

Liu, Heng-Jui; Wang, Jing-Ching; Cho, Deok-Yong; Ho, Kang-Ting; Lin, Jheng-Cyuan; Huang, Bo-Chao; Fang, Yue-Wen; Zhu, Yuan-Min; Zhan, Qian; Xie, Lin; Pan, Xiao-Qing; Chiu, Ya-Ping; Duan, Chun-Gang; He, Jr-Hau; Chu, Ying-Hao

2018-01-01

The photoelectric effect in semiconductors is the main mechanism for most modern optoelectronic devices, in which the adequate bandgap plays the key role for acquiring high photoresponse. Among numerous material categories applied in this field, the complex oxides exhibit great possibilities because they present a wide distribution of band gaps for absorbing light with any wavelength. Their physical properties and lattice structures are always strongly coupled and sensitive to light illumination. Moreover, the confinement of dimensionality of the complex oxides in the heterostructures can provide more diversities in designing and modulating the band structures. On the basis of this perspective, we have chosen itinerary ferromagnetic SrRuO3 as the model material, and fabricated it in one-unit-cell thickness in order to open a small band gap for effective utilization of visible light. By inserting this SrRuO3 monolayer at the interface of the well-developed two-dimensional electron gas system (LaAlO3/SrTiO3), the resistance of the monolayer can be further revealed. In addition, a giant enhancement (>300%) of photoresponse under illumination of visible light with power density of 500 mW/cm2 is also observed. Such can be ascribed to the further modulation of band structure of the SrRuO3 monolayer under the illumination, confirmed by cross-section scanning tunneling microscopy (XSTM). Therefore, this study demonstrates a simple route to design and explore the potential low dimensional oxide materials for future optoelectronic devices.

Effect of Time and Deposition Method on Quality of Phosphonic Acid Modifier Self-Assembled Monolayers on Indium Zinc Oxide

Energy Technology Data Exchange (ETDEWEB)

Sang, Lingzi; Knesting, Kristina M.; Bulusu, Anuradha; Sigdel, Ajaya K.; Giordano, Anthony J.; Marder, Seth R.; Berry, Joseph J.; Graham, Samuel; Ginger, David S.; Pemberton, Jeanne E.

2016-12-15

Phosphonic acid (PA) self-assembled monolayers (SAMs) are utilized at critical interfaces between transparent conductive oxides (TCO) and organic active layers in organic photovoltaic devices (OPVs). The effects of PA deposition method and time on the formation of close-packed, high-quality monolayers is investigated here for SAMs fabricated by solution deposition, micro-contact printing, and spray coating. The solution deposition isotherm for pentafluorinated benzylphosphonic acid (F5BnPA) on indium-doped zinc oxide (IZO) is studied using polarization modulation-infrared reflection-absorption spectroscopy (PM-IRRAS) at room temperature as a model PA/IZO system. Fast surface adsorption occurs within the first min; however, well-oriented high-quality SAMs are reached only after -48 h, presumably through a continual process of molecular adsorption/desorption and monolayer filling accompanied by molecular reorientation. Two other rapid, soak-free deposition techniques, micro-contact printing and spray coating, are also explored. SAM quality is compared for deposition of phenyl phosphonic acid (PPA), F13-octylphosphonic acid (F13OPA), and pentafluorinated benzyl phosphonic acid (F5BnPA) by solution deposition, micro-contact printing and spray coating using PM-IRRAS. In contrast to micro-contact printing and spray coating techniques, 48-168 h solution deposition at both room temperature and 70 degrees C result in contamination- and surface etch-free close-packed monolayers with good reproducibility. SAMs fabricated by micro-contact printing and spray coating are much less well ordered.

Lateral electron transport in monolayers of short chains at interfaces: A Monte Carlo study

International Nuclear Information System (INIS)

George, Christopher B.; Szleifer, Igal; Ratner, Mark A.

2010-01-01

Graphical abstract: Electron hopping between electroactive sites in a monolayer composed of redox-active and redox-passive molecules. - Abstract: Using Monte Carlo simulations, we study lateral electronic diffusion in dense monolayers composed of a mixture of redox-active and redox-passive chains tethered to a surface. Two charge transport mechanisms are considered: the physical diffusion of electroactive chains and electron hopping between redox-active sites. Results indicate that by varying the monolayer density, the mole fraction of electroactive chains, and the electron hopping range, the dominant charge transport mechanism can be changed. For high density monolayers in a semi-crystalline phase, electron diffusion proceeds via electron hopping almost exclusively, leading to static percolation behavior. In fluid monolayers, the diffusion of chains may contribute more to the overall electronic diffusion, reducing the observed static percolation effects.

Controllable Growth of Monolayer MoS2 and MoSe2 Crystals Using Three-temperature-zone Furnace

Science.gov (United States)

Zheng, Binjie; Chen, Yuanfu

2017-12-01

Monolayer molybdenum disulfide (MoS2) and molybdenum diselenide (MoSe2) have attracted a great attention for their exceptional electronic and optoelectronic properties among the two dimensional family. However, controllable synthesis of monolayer crystals with high quality needs to be improved urgently. Here we demonstrate a chemical vapor deposition (CVD) growth of monolayer MoS2 and MoSe2 crystals using three-temperature-zone furnace. Systematical study of the effects of growth pressure, temperature and time on the thickness, morphology and grain size of crystals shows the good controllability. The photoluminescence (PL) characterizations indicate that the as-grown monolayer MoS2 and MoSe2 crystals possess excellent optical qualities with very small full-width-half-maximum (FWHM) of 96 me V and 57 me V, respectively. It is comparable to that of exfoliated monolayers and reveals their high crystal quality. It is promising that our strategy should be applicable for the growth of other transition metal dichalcogenides (TMDs) monolayer crystals.

Disorder-derived, strong tunneling attenuation in bis-phosphonate monolayers

Science.gov (United States)

Pathak, Anshuma; Bora, Achyut; Liao, Kung-Ching; Schmolke, Hannah; Jung, Antje; Klages, Claus-Peter; Schwartz, Jeffrey; Tornow, Marc

2016-03-01

Monolayers of alkyl bisphosphonic acids (bisPAs) of various carbon chain lengths (C4, C8, C10, C12) were grown on aluminum oxide (AlO x ) surfaces from solution. The structural and electrical properties of these self-assembled monolayers (SAMs) were compared with those of alkyl monophosphonic acids (monoPAs). Through contact angle (CA) and Kelvin-probe (KP) measurements, ellipsometry, and infrared (IR) and x-ray photoelectron (XPS) spectroscopies, it was found that bisPAs form monolayers that are relatively disordered compared to their monoPA analogs. Current-voltage (J-V) measurements made with a hanging Hg drop top contact show tunneling to be the prevailing transport mechanism. However, while the monoPAs have an observed decay constant within the typical range for dense monolayers, β mono  =  0.85  ±  0.03 per carbon atom, a surprisingly high value, β bis  =  1.40  ±  0.05 per carbon atom, was measured for the bisPAs. We attribute this to a strong contribution of ‘through-space’ tunneling, which derives from conformational disorder in the monolayer due to strong interactions of the distal phosphonic acid groups; they likely form a hydrogen-bonding network that largely determines the molecular layer structure. Since bisPA SAMs attenuate tunnel currents more effectively than do the corresponding monoPA SAMs, they may find future application as gate dielectric modification in organic thin film devices.

Monolayer graphene dispersion and radiative cooling for high power LED

Science.gov (United States)

Hsiao, Tun-Jen; Eyassu, Tsehaye; Henderson, Kimberly; Kim, Taesam; Lin, Chhiu-Tsu

2013-10-01

Molecular fan, a radiative cooling by thin film, has been developed and its application for compact electronic devices has been evaluated. The enhanced surface emissivity and heat dissipation efficiency of the molecular fan coating are shown to correlate with the quantization of lattice modes in active nanomaterials. The highly quantized G and 2D bands in graphene are achieved by our dispersion technique, and then incorporated in an organic-inorganic acrylate emulsion to form a coating assembly on heat sinks (for LED and CPU). This water-based dielectric layer coating has been formulated and applied on metal core printed circuit boards. The heat dissipation efficiency and breakdown voltage are evaluated by a temperature-monitoring system and a high-voltage breakdown tester. The molecular fan coating on heat dissipation units is able to decrease the equilibrium junction temperature by 29.1 ° C, while functioning as a dielectric layer with a high breakdown voltage (>5 kV). The heat dissipation performance of the molecular fan coating applied on LED devices shows that the coated 50 W LED gives an enhanced cooling of 20% at constant light brightness. The schematics of monolayer graphene dispersion, undispersed graphene platelet, and continuous graphene sheet are illustrated and discussed to explain the mechanisms of radiative cooling, radiative/non-radiative, and non-radiative heat re-accumulation.

Monolayer graphene dispersion and radiative cooling for high power LED

International Nuclear Information System (INIS)

Hsiao, Tun-Jen; Eyassu, Tsehaye; Henderson, Kimberly; Kim, Taesam; Lin, Chhiu-Tsu

2013-01-01

Molecular fan, a radiative cooling by thin film, has been developed and its application for compact electronic devices has been evaluated. The enhanced surface emissivity and heat dissipation efficiency of the molecular fan coating are shown to correlate with the quantization of lattice modes in active nanomaterials. The highly quantized G and 2D bands in graphene are achieved by our dispersion technique, and then incorporated in an organic-inorganic acrylate emulsion to form a coating assembly on heat sinks (for LED and CPU). This water-based dielectric layer coating has been formulated and applied on metal core printed circuit boards. The heat dissipation efficiency and breakdown voltage are evaluated by a temperature-monitoring system and a high-voltage breakdown tester. The molecular fan coating on heat dissipation units is able to decrease the equilibrium junction temperature by 29.1 ° C, while functioning as a dielectric layer with a high breakdown voltage (>5 kV). The heat dissipation performance of the molecular fan coating applied on LED devices shows that the coated 50 W LED gives an enhanced cooling of 20% at constant light brightness. The schematics of monolayer graphene dispersion, undispersed graphene platelet, and continuous graphene sheet are illustrated and discussed to explain the mechanisms of radiative cooling, radiative/non-radiative, and non-radiative heat re-accumulation. (paper)

Proton and hydrogen transport through two-dimensional monolayers

International Nuclear Information System (INIS)

Seel, Max; Pandey, Ravindra

2016-01-01

Diffusion of protons and hydrogen atoms in representative two-dimensional materials is investigated. Specifically, density functional calculations were performed on graphene, hexagonal boron nitride (h-BN), phosphorene, silicene, and molybdenum disulfide (MoS 2 ) monolayers to study the surface interaction and penetration barriers for protons and hydrogen atoms employing finite cluster models. The calculated barrier heights correlate approximately with the size of the opening formed by the three-fold open sites in the monolayers considered. They range from 1.56 eV (proton) and 4.61 eV (H) for graphene to 0.12 eV (proton) and 0.20 eV (H) for silicene. The results indicate that only graphene and h-BN monolayers have the potential for membranes with high selective permeability. The MoS 2 monolayer behaves differently: protons and H atoms become trapped between the outer S layers in the Mo plane in a well with a depth of 1.56 eV (proton) and 1.5 eV (H atom), possibly explaining why no proton transport was detected, suggesting MoS 2 as a hydrogen storage material instead. For graphene and h-BN, off-center proton penetration reduces the barrier to 1.38 eV for graphene and 0.11 eV for h-BN. Furthermore, Pt acting as a substrate was found to have a negligible effect on the barrier height. In defective graphene, the smallest barrier for proton diffusion (1.05 eV) is found for an oxygen-terminated defect. Therefore, it seems more likely that thermal protons can penetrate a monolayer of h-BN but not graphene and defects are necessary to facilitate the proton transport in graphene. (paper)

Proton and hydrogen transport through two-dimensional monolayers

Science.gov (United States)

Seel, Max; Pandey, Ravindra

2016-06-01

Diffusion of protons and hydrogen atoms in representative two-dimensional materials is investigated. Specifically, density functional calculations were performed on graphene, hexagonal boron nitride (h-BN), phosphorene, silicene, and molybdenum disulfide (MoS2) monolayers to study the surface interaction and penetration barriers for protons and hydrogen atoms employing finite cluster models. The calculated barrier heights correlate approximately with the size of the opening formed by the three-fold open sites in the monolayers considered. They range from 1.56 eV (proton) and 4.61 eV (H) for graphene to 0.12 eV (proton) and 0.20 eV (H) for silicene. The results indicate that only graphene and h-BN monolayers have the potential for membranes with high selective permeability. The MoS2 monolayer behaves differently: protons and H atoms become trapped between the outer S layers in the Mo plane in a well with a depth of 1.56 eV (proton) and 1.5 eV (H atom), possibly explaining why no proton transport was detected, suggesting MoS2 as a hydrogen storage material instead. For graphene and h-BN, off-center proton penetration reduces the barrier to 1.38 eV for graphene and 0.11 eV for h-BN. Furthermore, Pt acting as a substrate was found to have a negligible effect on the barrier height. In defective graphene, the smallest barrier for proton diffusion (1.05 eV) is found for an oxygen-terminated defect. Therefore, it seems more likely that thermal protons can penetrate a monolayer of h-BN but not graphene and defects are necessary to facilitate the proton transport in graphene.

Functionalizable self-assembled trichlorosilyl-based monolayer for application in biosensor technology

Energy Technology Data Exchange (ETDEWEB)

De La Franier, Brian; Jankowski, Alexander; Thompson, Michael, E-mail: mikethom@chem.utoronto.ca

2017-08-31

This paper describes the design and synthesis of 3-(3-(trichlorosilyl)propoxy)propanoyl chloride (MEG-Cl), a compound capable of forming functionalizable monolayers on hydroxylated surfaces. The compound was synthesized in high purity, as suggested by nuclear magnetic resonance analysis, and in moderate overall yield. Contact angle measurement and X-ray photoelectron spectroscopy confirm the binding of MEG-Cl to an amorphous glass substrate and the further modification of the monolayer with a nickel (II)-binding ligand for the purpose of binding polyhistidine-tagged proteins. The compound will be useful in biosensing applications due to its ability to be easily modified with any number of nucleophilic functional groups subsequent to substrate monolayer formation.

Effect of time and deposition method on quality of phosphonic acid modifier self-assembled monolayers on indium zinc oxide

Energy Technology Data Exchange (ETDEWEB)

Sang, Lingzi [Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721 (United States); Knesting, Kristina M. [Department of Chemistry, University of Washington, Seattle, WA 98195-1700 (United States); Bulusu, Anuradha [School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332 (United States); Sigdel, Ajaya K. [National Renewable Energy Laboratory, Golden, CO 80401 (United States); Giordano, Anthony J.; Marder, Seth R. [School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA 30332-0400 (United States); Berry, Joseph J. [National Renewable Energy Laboratory, Golden, CO 80401 (United States); Graham, Samuel [School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332 (United States); Ginger, David S. [Department of Chemistry, University of Washington, Seattle, WA 98195-1700 (United States); Pemberton, Jeanne E., E-mail: pembertn@email.arizona.edu [Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721 (United States)

2016-12-15

Highlights: • Deposition of phosphonic acid monolayers on oxides from ethanol solutions occurs by rapid adsorption within 10 s with slower equilibration complete in 48 h. • The slower equilibration step involves molecular reorientation and vacancy filling on the oxide surface. • Soak-free deposition by spray coating and microcontact printing do not provide reproducible, fully-covered, uniform monolayers without substrate etching. • Adjustments to exposure time, substrate temperature, and solution/substrate contact efficiency are necessary to optimize soak-free methods. - Abstract: Phosphonic acid (PA) self-assembled monolayers (SAMs) are utilized at critical interfaces between transparent conductive oxides (TCO) and organic active layers in organic photovoltaic devices (OPVs). The effects of PA deposition method and time on the formation of close-packed, high-quality monolayers is investigated here for SAMs fabricated by solution deposition, micro-contact printing, and spray coating. The solution deposition isotherm for pentafluorinated benzylphosphonic acid (F{sub 5}BnPA) on indium-doped zinc oxide (IZO) is studied using polarization modulation-infrared reflection-absorption spectroscopy (PM-IRRAS) at room temperature as a model PA/IZO system. Fast surface adsorption occurs within the first min; however, well-oriented high-quality SAMs are reached only after ∼48 h, presumably through a continual process of molecular adsorption/desorption and monolayer filling accompanied by molecular reorientation. Two other rapid, soak-free deposition techniques, micro-contact printing and spray coating, are also explored. SAM quality is compared for deposition of phenyl phosphonic acid (PPA), F{sub 13}-octylphosphonic acid (F{sub 13}OPA), and pentafluorinated benzyl phosphonic acid (F{sub 5}BnPA) by solution deposition, micro-contact printing and spray coating using PM-IRRAS. In contrast to micro-contact printing and spray coating techniques, 48–168 h solution

A model for the direct-to-indirect band-gap transition in monolayer ...

Indian Academy of Sciences (India)

Abstract. A monolayer of MoSe2 is found to be a direct band-gap semiconductor. We show, ... In order to determine appropriate basis for the tight-binding model, the Mo and Se ..... RD thanks the Council of Scientific and Industrial Research.

Pressure-dependent optical and vibrational properties of monolayer molybdenum disulfide

KAUST Repository

Nayak, Avinash P.

2015-01-14

Controlling the band gap by tuning the lattice structure through pressure engineering is a relatively new route for tailoring the optoelectronic properties of two-dimensional (2D) materials. Here, we investigate the electronic structure and lattice vibrational dynamics of the distorted monolayer 1T-MoS2 (1T′) and the monolayer 2H-MoS2 via a diamond anvil cell (DAC) and density functional theory (DFT) calculations. The direct optical band gap of the monolayer 2H-MoS2 increases by 11.7% from 1.85 to 2.08 eV, which is the highest reported for a 2D transition metal dichalcogenide (TMD) material. DFT calculations reveal a subsequent decrease in the band gap with eventual metallization of the monolayer 2H-MoS2, an overall complex structure-property relation due to the rich band structure of MoS2. Remarkably, the metastable 1T′-MoS2 metallic state remains invariant with pressure, with the J2, A1g, and E2g modes becoming dominant at high pressures. This substantial reversible tunability of the electronic and vibrational properties of the MoS2 family can be extended to other 2D TMDs. These results present an important advance toward controlling the band structure and optoelectronic properties of monolayer MoS2 via pressure, which has vital implications for enhanced device applications.

Conformations and orientations of a signal peptide interacting with phospholipid monolayers

International Nuclear Information System (INIS)

Cornell, D.G.; Dluhy, R.A.; Briggs, M.S.; McKnight, C.J.; Gierasch, L.M.

1989-01-01

The interaction of a chemically synthesized 25-residue signal peptide of LamB protein from Escherichia coli with phospholipids has been studied with a film balance technique. The conformation, orientation, and concentration of the peptides in lipid monolayers have been determined from polarized infrared spectroscopy, ultraviolet spectroscopy, and assay of 14 C-labeled peptide in transferred films. When the LamB signal peptide in injected into the subphase under a phosphatidylethanolamine-phosphatidylglycerol monolayer at low initial pressure, insertion of a portion of the peptide into the lipid film is evidenced by a rapid rise in film pressure. Spectroscopic results obtained on films transferred to quartz plates and Ge crystals show that the peptide is a mixture of α-helix and β-conformation where the long axis of the α-helix penetrates the monolayer plane and the β-structure which is coplanar with the film. By contrast, when peptide is injected under lipid at high initial pressure, no pressure rise is observed, and the spectroscopic results show the presence of only β-structure which is coplanar with the monolayer. The spectroscopic and radioassay results are all consistent with the picture of a peptide anchored to the monolayer through electrostatic binding with a helical portion inserted into the lipid region of the monolayer and a β-structure portion resident in the aqueous phase. The negative charges on the lipid molecules are roughly neutralized by the positive charges of the peptide

Substrate induced ordering of molecular adsorbates on Au(111)

International Nuclear Information System (INIS)

Schott, J.H.; White, H.S.; Arana, C.R.

1992-01-01

Using scanning tunneling microscopy in dimethylformate, [Ru(bpy) 2 (bpy-(CH 2 ) x -bpy) 2+ ] (x = 4 and 5) monolayers adsorbed on the unreconstructed and √3 x 22 reconstructed surfaces of Au(111) were imaged in this paper. The substrate had a highly ordered pattern on the reconstructed surface, but random spatial distribution on the unreconstructed surface. 17 refs., 3 figs

Disorder-derived, strong tunneling attenuation in bis-phosphonate monolayers

International Nuclear Information System (INIS)

Pathak, Anshuma; Bora, Achyut; Tornow, Marc; Liao, Kung-Ching; Schwartz, Jeffrey; Schmolke, Hannah; Jung, Antje; Klages, Claus-Peter

2016-01-01

Monolayers of alkyl bisphosphonic acids (bisPAs) of various carbon chain lengths (C4, C8, C10, C12) were grown on aluminum oxide (AlO x ) surfaces from solution. The structural and electrical properties of these self-assembled monolayers (SAMs) were compared with those of alkyl monophosphonic acids (monoPAs). Through contact angle (CA) and Kelvin-probe (KP) measurements, ellipsometry, and infrared (IR) and x-ray photoelectron (XPS) spectroscopies, it was found that bisPAs form monolayers that are relatively disordered compared to their monoPA analogs. Current–voltage (J–V) measurements made with a hanging Hg drop top contact show tunneling to be the prevailing transport mechanism. However, while the monoPAs have an observed decay constant within the typical range for dense monolayers, β mono   =  0.85  ±  0.03 per carbon atom, a surprisingly high value, β bis   =  1.40  ±  0.05 per carbon atom, was measured for the bisPAs. We attribute this to a strong contribution of ‘through-space’ tunneling, which derives from conformational disorder in the monolayer due to strong interactions of the distal phosphonic acid groups; they likely form a hydrogen-bonding network that largely determines the molecular layer structure. Since bisPA SAMs attenuate tunnel currents more effectively than do the corresponding monoPA SAMs, they may find future application as gate dielectric modification in organic thin film devices. (paper)

Piezoelectric effect in chemical vapour deposition-grown atomic-monolayer triangular molybdenum disulfide piezotronics

Science.gov (United States)

Qi, Junjie; Lan, Yann-Wen; Stieg, Adam Z.; Chen, Jyun-Hong; Zhong, Yuan-Liang; Li, Lain-Jong; Chen, Chii-Dong; Zhang, Yue; Wang, Kang L.

2015-01-01

High-performance piezoelectricity in monolayer semiconducting transition metal dichalcogenides is highly desirable for the development of nanosensors, piezotronics and photo-piezotransistors. Here we report the experimental study of the theoretically predicted piezoelectric effect in triangle monolayer MoS2 devices under isotropic mechanical deformation. The experimental observation indicates that the conductivity of MoS2 devices can be actively modulated by the piezoelectric charge polarization-induced built-in electric field under strain variation. These polarization charges alter the Schottky barrier height on both contacts, resulting in a barrier height increase with increasing compressive strain and decrease with increasing tensile strain. The underlying mechanism of strain-induced in-plane charge polarization is proposed and discussed using energy band diagrams. In addition, a new type of MoS2 strain/force sensor built using a monolayer MoS2 triangle is also demonstrated. Our results provide evidence for strain-gating monolayer MoS2 piezotronics, a promising avenue for achieving augmented functionalities in next-generation electronic and mechanical–electronic nanodevices. PMID:26109177

Piezoelectric effect in chemical vapour deposition-grown atomic-monolayer triangular molybdenum disulfide piezotronics

KAUST Repository

Qi, Junjie

2015-06-25

High-performance piezoelectricity in monolayer semiconducting transition metal dichalcogenides is highly desirable for the development of nanosensors, piezotronics and photo-piezotransistors. Here we report the experimental study of the theoretically predicted piezoelectric effect in triangle monolayer MoS2 devices under isotropic mechanical deformation. The experimental observation indicates that the conductivity of MoS2 devices can be actively modulated by the piezoelectric charge polarization-induced built-in electric field under strain variation. These polarization charges alter the Schottky barrier height on both contacts, resulting in a barrier height increase with increasing compressive strain and decrease with increasing tensile strain. The underlying mechanism of strain-induced in-plane charge polarization is proposed and discussed using energy band diagrams. In addition, a new type of MoS2 strain/force sensor built using a monolayer MoS2 triangle is also demonstrated. Our results provide evidence for strain-gating monolayer MoS2 piezotronics, a promising avenue for achieving augmented functionalities in next-generation electronic and mechanical–electronic nanodevices.

Lateral pressure profiles in lipid monolayers

NARCIS (Netherlands)

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

2010-01-01

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

Conductance fluctuations in high mobility monolayer graphene: Nonergodicity, lack of determinism and chaotic behavior.

Science.gov (United States)

da Cunha, C R; Mineharu, M; Matsunaga, M; Matsumoto, N; Chuang, C; Ochiai, Y; Kim, G-H; Watanabe, K; Taniguchi, T; Ferry, D K; Aoki, N

2016-09-09

We have fabricated a high mobility device, composed of a monolayer graphene flake sandwiched between two sheets of hexagonal boron nitride. Conductance fluctuations as functions of a back gate voltage and magnetic field were obtained to check for ergodicity. Non-linear dynamics concepts were used to study the nature of these fluctuations. The distribution of eigenvalues was estimated from the conductance fluctuations with Gaussian kernels and it indicates that the carrier motion is chaotic at low temperatures. We argue that a two-phase dynamical fluid model best describes the transport in this system and can be used to explain the violation of the so-called ergodic hypothesis found in graphene.

Large Friction Anisotropy of a Polydiacetylene Monolayer

International Nuclear Information System (INIS)

Burns, A.R.; Carpick, R.W.; Sasaki, D.Y.

1999-01-01

Friction force microscopy measurements of a polydiacetylene monolayer film reveal a 300% friction anisotropy that is correlated with the film structure. The film consists of a monolayer of the red form of N-(2-ethanol)- 10,12 pentacosadiynamide, prepared on a Langmuir trough and deposited on a mica substrate. As confirmed by atomic force microscopy and fluorescence microscopy, the monolayer consists of domains of linearly oriented conjugated backbones with pendant hydrocarbon side chains above and below the backbones. Maximum friction occurs when the sliding direction is perpendicular to the backbone. We propose that the backbones impose anisotropic packing of the hydrocarbon side chains which leads to the observed friction anisotropy. Friction anisotropy is therefore a sensitive, optically-independent indicator of polymer backbone direction and monolayer structural properties

Thermal conductivity of a h-BCN monolayer.

Science.gov (United States)

Zhang, Ying-Yan; Pei, Qing-Xiang; Liu, Hong-Yuan; Wei, Ning

2017-10-18

A hexagonal graphene-like boron-carbon-nitrogen (h-BCN) monolayer, a new two-dimensional (2D) material, has been synthesized recently. Herein we investigate for the first time the thermal conductivity of this novel 2D material. Using molecular dynamics simulations based on the optimized Tersoff potential, we found that the h-BCN monolayers are isotropic in the basal plane with close thermal conductivity magnitudes. Though h-BCN has the same hexagonal lattice as graphene and hexagonal boron nitride (h-BN), it exhibits a much lower thermal conductivity than the latter two materials. In addition, the thermal conductivity of h-BCN monolayers is found to be size-dependent but less temperature-dependent. Modulation of the thermal conductivity of h-BCN monolayers can also be realized by strain engineering. Compressive strain leads to a monotonic decrease in the thermal conductivity while the tensile strain induces an up-then-down trend in the thermal conductivity. Surprisingly, the small tensile strain can facilitate the heat transport of the h-BCN monolayers.

Monolayer MoS{sub 2} self-switching diodes

Energy Technology Data Exchange (ETDEWEB)

Al-Dirini, Feras, E-mail: alf@unimelb.edu.au; Hossain, Md Sharafat [Department of Electrical and Electronic Engineering, University of Melbourne, Victoria (Australia); Centre for Neural Engineering, University of Melbourne, Victoria (Australia); Victorian Research Laboratory, National ICT Australia, West Melbourne, Victoria (Australia); Hossain, Faruque M.; Skafidas, Efstratios [Department of Electrical and Electronic Engineering, University of Melbourne, Victoria (Australia); Centre for Neural Engineering, University of Melbourne, Victoria (Australia); Mohammed, Mahmood A. [Princess Sumaya University for Technology, Amman (Jordan); Nirmalathas, Ampalavanapillai [Department of Electrical and Electronic Engineering, University of Melbourne, Victoria (Australia); Melbourne Networked Society Institute (MNSI), University of Melbourne, Victoria (Australia)

2016-01-28

This paper presents a new molybdenum disulphide (MoS{sub 2}) nanodevice that acts as a two-terminal field-effect rectifier. The device is an atomically-thin two-dimensional self-switching diode (SSD) that can be realized within a single MoS{sub 2} monolayer with very minimal process steps. Quantum simulation results are presented confirming the device's operation as a diode and showing strong non-linear I-V characteristics. Interestingly, the device shows p-type behavior, in which conduction is dominated by holes as majority charge carriers and the flow of reverse current is enhanced, while the flow of forward current is suppressed, in contrast to monolayer graphene SSDs, which behave as n-type devices. The presence of a large bandgap in monolayer MoS{sub 2} results in strong control over the channel, showing complete channel pinch-off in forward conduction, which was confirmed with transmission pathways plots. The device exhibited large leakage tunnelling current through the insulating trenches, which may have been due to the lack of passivation; nevertheless, reverse current remained to be 6 times higher than forward current, showing strong rectification. The effect of p-type substitutional channel doping of sulphur with phosphorus was investigated and showed that it greatly enhances the performance of the device, increasing the reverse-to-forward current rectification ratio more than an order of magnitude, up to a value of 70.

Out-of-Plane Electromechanical Response of Monolayer Molybdenum Disulfide Measured by Piezoresponse Force Microscopy.

Science.gov (United States)

Brennan, Christopher J; Ghosh, Rudresh; Koul, Kalhan; Banerjee, Sanjay K; Lu, Nanshu; Yu, Edward T

2017-09-13

Two-dimensional (2D) materials have recently been theoretically predicted and experimentally confirmed to exhibit electromechanical coupling. Specifically, monolayer and few-layer molybdenum disulfide (MoS 2 ) have been measured to be piezoelectric within the plane of their atoms. This work demonstrates and quantifies a nonzero out-of-plane electromechanical response of monolayer MoS 2 and discusses its possible origins. A piezoresponse force microscope was used to measure the out-of-plane deformation of monolayer MoS 2 on Au/Si and Al 2 O 3 /Si substrates. Using a vectorial background subtraction technique, we estimate the effective out-of-plane piezoelectric coefficient, d 33 eff , for monolayer MoS 2 to be 1.03 ± 0.22 pm/V when measured on the Au/Si substrate and 1.35 ± 0.24 pm/V when measured on Al 2 O 3 /Si. This is on the same order as the in-plane coefficient d 11 reported for monolayer MoS 2 . Interpreting the out-of-plane response as a flexoelectric response, the effective flexoelectric coefficient, μ eff * , is estimated to be 0.10 nC/m. Analysis has ruled out the possibility of elastic and electrostatic forces contributing to the measured electromechanical response. X-ray photoelectron spectroscopy detected some contaminants on both MoS 2 and its substrate, but the background subtraction technique is expected to remove major contributions from the unwanted contaminants. These measurements provide evidence that monolayer MoS 2 exhibits an out-of-plane electromechanical response and our analysis offers estimates of the effective piezoelectric and flexoelectric coefficients.

Conformation, orientation and interaction in molecular monolayers: A surface second harmonic and sum frequency generation study

International Nuclear Information System (INIS)

Superfine, R.; Huang, J.Y.; Shen, Y.R.

1988-12-01

We have used sum frequency generation (SFG) to study the order in a silane monolayer before and after the deposition of a coadsorbed liquid crystal monolayer. We observe an increase in the order of the chain of the silane molecule induced by the interpenetration of the liquid crystal molecules. By using second harmonic generation (SHG) and SFG, we have studied the orientation and conformation of the liquid crystal molecule on clean and silane coated glass surfaces. On both surfaces, the biphenyl group is tilted by 70 degree with the alkyl chain end pointing away from the surface. The shift in the C-H stretch frequencies in the coadsorbed system indicates a significant interaction between molecules. 9 refs., 3 figs

Vanadium impurity effects on optical properties of Ti3N2 mono-layer: An ab-initio study

Directory of Open Access Journals (Sweden)

Manuchehr Babaeipour

2018-06-01

Full Text Available The present work is investigated the effect of vanadium impurity on electronic and optical properties of Ti3N2 monolayer by using density function theory (DFT implemented in Wien2k code. In order to study optical properties in two polarization directions of photons, namely E||x and E||z, dielectric function, absorption coefficient, optical conductivity, refraction index, extinction index, reflectivity, and energy loss function of Ti3N2 and Ti3N2-V monolayer have been evaluated within GGA (PBE approximation. Although, Ti3N2 monolayer is a good infrared reflector and can be used as an infrared mirror, introducing V atom in the infrared area will decrease optical conductivity because optical conductivity of a pure form of a material is higher than its doped form. Keywords: Dielectric function, Optical conductivity, DFT, Ti3N2: V mono-layer

Strain engineering on electronic structure and carrier mobility in monolayer GeP3

Science.gov (United States)

Zeng, Bowen; Long, Mengqiu; Zhang, Xiaojiao; Dong, Yulan; Li, Mingjun; Yi, Yougen; Duan, Haiming

2018-06-01

Using density functional theory coupled with the Boltzmann transport equation with relaxation time approximation, we have studied the strain effect on the electronic structure and carrier mobility of two-dimensional monolayer GeP3. We find that the energies of valence band maximum and conduction band minimum are nearly linearly shifted with a biaxial strain in the range of  ‑4% to 6%, and the band structure experiences a remarkable transition from semiconductor to metal with the appropriate compression (‑5% strain). Under biaxial strain, the mobility of the electron and hole in monolayer GeP3 reduces and increases by more than one order of magnitude, respectively. It is suggested that it is possible to perform successive transitions from an n-type semiconductor (‑4% strain) to a good performance p-semiconductor (+6% strain) by applying strain in monolayer GeP3, which is potentially useful for flexible electronics and nanosized mechanical sensors.

Wafer-scale synthesis of monolayer and few-layer MoS2 via thermal vapor sulfurization

Science.gov (United States)

Robertson, John; Liu, Xue; Yue, Chunlei; Escarra, Matthew; Wei, Jiang

2017-12-01

Monolayer molybdenum disulfide (MoS2) is an atomically thin, direct bandgap semiconductor crystal potentially capable of miniaturizing optoelectronic devices to an atomic scale. However, the development of 2D MoS2-based optoelectronic devices depends upon the existence of a high optical quality and large-area monolayer MoS2 synthesis technique. To address this need, we present a thermal vapor sulfurization (TVS) technique that uses powder MoS2 as a sulfur vapor source. The technique reduces and stabilizes the flow of sulfur vapor, enabling monolayer wafer-scale MoS2 growth. MoS2 thickness is also controlled with great precision; we demonstrate the ability to synthesize MoS2 sheets between 1 and 4 layers thick, while also showing the ability to create films with average thickness intermediate between integer layer numbers. The films exhibit wafer-scale coverage and uniformity, with electrical quality varying depending on the final thickness of the grown MoS2. The direct bandgap of grown monolayer MoS2 is analyzed using internal and external photoluminescence quantum efficiency. The photoluminescence quantum efficiency is shown to be competitive with untreated exfoliated MoS2 monolayer crystals. The ability to consistently grow wafer-scale monolayer MoS2 with high optical quality makes this technique a valuable tool for the development of 2D optoelectronic devices such as photovoltaics, detectors, and light emitters.

Cavity plasmon polaritons in monolayer graphene

International Nuclear Information System (INIS)

Kotov, O.V.; Lozovik, Yu.E.

2011-01-01

Plasmon polaritons in a new system, a monolayer doped graphene embedded in optical microcavity, are studied here. The dispersion law for lower and upper cavity plasmon polaritons is obtained. Peculiarities of Rabi splitting for the system are analyzed; particularly, role of Dirac-like spinor (envelope) wave functions in graphene and corresponding angle factors are considered. Typical Rabi frequencies for maximal (acceptable for Dirac-like electron spectra) Fermi energy and frequencies of polaritons near polariton gap are estimated. The plasmon polaritons in considered system can be used for high-speed information transfer in the THz region. -- Highlights: → Plasmon polaritons in a monolayer doped graphene embedded in optical microcavity, are studied here. → The dispersion law for lower and upper cavity plasmon polaritons is obtained. → Peculiarities of Rabi splitting for the system are analyzed. → Role of Dirac-like wave functions in graphene and corresponding angle factors are considered. → Typical Rabi frequencies and frequencies of polaritons near polariton gap are estimated.

Nonequilibrium 2-hydroxyoctadecanoic acid monolayers: effect of electrolytes.

Science.gov (United States)

Lendrum, Conrad D; Ingham, Bridget; Lin, Binhua; Meron, Mati; Toney, Michael F; McGrath, Kathryn M

2011-04-19

2-Hydroxyacids display complex monolayer phase behavior due to the additional hydrogen bonding afforded by the presence of the second hydroxy group. The placement of this group at the position α to the carboxylic acid functionality also introduces the possibility of chelation, a utility important in crystallization including biomineralization. Biomineralization, like many biological processes, is inherently a nonequilibrium process. The nonequilibrium monolayer phase behavior of 2-hydroxyoctadecanoic acid was investigated on each of pure water, calcium chloride, sodium bicarbonate and calcium carbonate crystallizing subphases as a precursor study to a model calcium carbonate biomineralizing system, each at a pH of ∼6. The role of the bicarbonate co-ion in manipulating the monolayer structure was determined by comparison with monolayer phase behavior on a sodium chloride subphase. Monolayer phase behavior was probed using surface pressure/area isotherms, surface potential, Brewster angle microscopy, and synchrotron-based grazing incidence X-ray diffraction and X-ray reflectivity. Complex phase behavior was observed for all but the sodium chloride subphase with hydrogen bonding, electrostatic and steric effects defining the symmetry of the monolayer. On a pure water subphase hydrogen bonding dominates with three phases coexisting at low pressures. Introduction of calcium ions into the aqueous subphase ensures strong cation binding to the surfactant head groups through chelation. The monolayer becomes very unstable in the presence of bicarbonate ions within the subphase due to short-range hydrogen bonding interactions between the monolayer and bicarbonate ions facilitated by the sodium cation enhancing surfactant solubility. The combined effects of electrostatics and hydrogen bonding are observed on the calcium carbonate crystallizing subphase. © 2011 American Chemical Society

Zitterbewegung in monolayer silicene in a magnetic field

International Nuclear Information System (INIS)

Romera, E.; Roldán, J.B.; Santos, F. de los

2014-01-01

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 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 2 )

Zitterbewegung in monolayer silicene in a magnetic field

Energy Technology Data Exchange (ETDEWEB)

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)

2014-07-04

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})

First-principles study on the electronic, optical, and transport properties of monolayer α - and β -GeSe

Science.gov (United States)

Xu, Yuanfeng; Zhang, Hao; Shao, Hezhu; Ni, Gang; Li, Jing; Lu, Hongliang; Zhang, Rongjun; Peng, Bo; Zhu, Yongyuan; Zhu, Heyuan; Soukoulis, Costas M.

2017-12-01

The extraordinary properties and the novel applications of black phosphorene induce the research interest in the monolayer group-IV monochalcogenides. Here using first-principles calculations, we systematically investigate the electronic, transport, and optical properties of monolayer α - and β -GeSe, revealing a direct band gap of 1.61 eV for monolayer α -GeSe and an indirect band gap of 2.47 eV for monolayer β -GeSe. For monolayer β -GeSe, the electronic/hole transport is anisotropic, with an extremely high electron mobility of 2.93 ×104cm2/Vs along the armchair direction, comparable to that of black phosphorene. Furthermore, for β -GeSe, robust band gaps nearly independent of the applied tensile strain along the armchair direction are observed. Both monolayer α - and β -GeSe exhibit anisotropic optical absorption in the visible spectrum.

Evidence of indirect gap in monolayer WSe2

KAUST Repository

Hsu, Wei-Ting

2017-10-09

Monolayer transition metal dichalcogenides, such as MoS2 and WSe2, have been known as direct gap semiconductors and emerged as new optically active materials for novel device applications. Here we reexamine their direct gap properties by investigating the strain effects on the photoluminescence of monolayer MoS2 and WSe2. Instead of applying stress, we investigate the strain effects by imaging the direct exciton populations in monolayer WSe2–MoS2 and MoSe2–WSe2 lateral heterojunctions with inherent strain inhomogeneity. We find that unstrained monolayer WSe2 is actually an indirect gap material, as manifested in the observed photoluminescence intensity–energy correlation, from which the difference between the direct and indirect optical gaps can be extracted by analyzing the exciton thermal populations. Our findings combined with the estimated exciton binding energy further indicate that monolayer WSe2 exhibits an indirect quasiparticle gap, which has to be reconsidered in further studies for its fundamental properties and device applications.

Large-area and bright pulsed electroluminescence in monolayer semiconductors

KAUST Repository

Lien, Der-Hsien; Amani, Matin; Desai, Sujay B.; Ahn, Geun Ho; Han, Kevin; He, Jr-Hau; Ager, Joel W.; Wu, Ming C.; Javey, Ali

2018-01-01

Transition-metal dichalcogenide monolayers have naturally terminated surfaces and can exhibit a near-unity photoluminescence quantum yield in the presence of suitable defect passivation. To date, steady-state monolayer light-emitting devices suffer from Schottky contacts or require complex heterostructures. We demonstrate a transient-mode electroluminescent device based on transition-metal dichalcogenide monolayers (MoS, WS, MoSe, and WSe) to overcome these problems. Electroluminescence from this dopant-free two-terminal device is obtained by applying an AC voltage between the gate and the semiconductor. Notably, the electroluminescence intensity is weakly dependent on the Schottky barrier height or polarity of the contact. We fabricate a monolayer seven-segment display and achieve the first transparent and bright millimeter-scale light-emitting monolayer semiconductor device.

Large-area and bright pulsed electroluminescence in monolayer semiconductors

KAUST Repository

Lien, Der-Hsien

2018-04-04

Transition-metal dichalcogenide monolayers have naturally terminated surfaces and can exhibit a near-unity photoluminescence quantum yield in the presence of suitable defect passivation. To date, steady-state monolayer light-emitting devices suffer from Schottky contacts or require complex heterostructures. We demonstrate a transient-mode electroluminescent device based on transition-metal dichalcogenide monolayers (MoS, WS, MoSe, and WSe) to overcome these problems. Electroluminescence from this dopant-free two-terminal device is obtained by applying an AC voltage between the gate and the semiconductor. Notably, the electroluminescence intensity is weakly dependent on the Schottky barrier height or polarity of the contact. We fabricate a monolayer seven-segment display and achieve the first transparent and bright millimeter-scale light-emitting monolayer semiconductor device.

Channel formation in single-monolayer pentacene thin film transistors

International Nuclear Information System (INIS)

Park, B-N; Seo, Soonjoo; Evans, Paul G

2007-01-01

The geometrical arrangement of single-molecule-high islands and the contact between them have large roles in determining the electrical properties of field effect transistors (FETs) based on monolayer-scale pentacene thin films. As the pentacene coverage increases through the submonolayer regime there is a percolation transition where islands come into contact and a simultaneous rapid onset of current. At coverages just above the percolation threshold, the electrical properties vary with geometrical changes in the contacts between the pentacene islands. At higher coverages, the FET mobility is much lower than the mobility measured by the van der Pauw method because of high contact resistances in monolayer-scale pentacene film devices. An increase in the van der Pauw mobility of holes as a function of pentacene coverage shows that second layer islands take part in charge transport

Protonation of octadecylamine Langmuir monolayer by adsorption of halide counterions

Science.gov (United States)

Sung, Woongmo; Avazbaeva, Zaure; Lee, Jonggwan; Kim, Doseok

Langmuir monolayer consisting of octadecylamine (C18H37NH2, ODA) was investigated by heterodyne vibrational sum-frequency generation (HD-VSFG) spectroscopy in conjunction with surface pressure-area (π- A) isotherm, and the result was compared with that from cationic-lipid (DPTAP) Langmuir monolayer. In case of ODA monolayer on pure water, both SF intensity of water OH band and the surface pressure were significantly smaller than those of the DPTAP monolayer implying that only small portion of the amine groups (-NH3+ is protonated in the monolayer. In the presence of sodium halides (NaCl and NaI) in the subphase water, it was found that the sign of Imχ (2) of water OH band remained the same as that of the ODA monolayer on pure water, but there was a substantial increase in the SF amplitude. From this, we propose that surface excess of the halide counterions (Cl- and I-) makes the solution condition near the ODA monolayer/water interface more acidic so that ODA molecules in the monolayer are more positively charged, which works to align the water dipoles at the interface.

Density functional study on the mechanism for the highly active palladium monolayer supported on titanium carbide for the oxygen reduction reaction

International Nuclear Information System (INIS)

Mao, Jianjun; Zhang, Yanxing; Chu, Xingli; Li, Shasha; Yang, Zongxian

2016-01-01

The adsorption, diffusion, and dissociation of O 2 on the palladium monolayer supported on TiC(001) surface, MLPd/TiC(001), are investigated using ab initio density functional theory calculations. Strong adhesion of palladium monolayer to the TiC(001) support, accompanied by a modification of electronic structure of the supported palladium, is evidenced. Compared with Pt(111) surface, the MLPd/TiC(001) can enhance the adsorption of O 2 , leading to comparable dissociation barrier and a smaller diffusion barrier of O 2 . Whilst the adsorption strength of atomic O (the dissociation product of O 2 ) on MLPd/TiC(001) is similar to that on the Pt(111) surface, possessing high mobility, our theoretical results indicate that MLPd/TiC(001) may serve as a good catalyst for the oxygen reduction reaction.

Highly n -doped graphene generated through intercalated terbium atoms

Science.gov (United States)

Daukiya, L.; Nair, M. N.; Hajjar-Garreau, S.; Vonau, F.; Aubel, D.; Bubendorff, J. L.; Cranney, M.; Denys, E.; Florentin, A.; Reiter, G.; Simon, L.

2018-01-01

We obtained highly n -type doped graphene by intercalating terbium atoms between graphene and SiC(0001) through appropriate annealing in ultrahigh vacuum. After terbium intercalation angle-resolved-photoelectron spectroscopy (ARPES) showed a drastic change in the band structure around the K points of the Brillouin zone: the well-known conical dispersion band of a graphene monolayer was superposed by a second conical dispersion band of a graphene monolayer with an electron density reaching 1015cm-2 . In addition, we demonstrate that atom intercalation proceeds either below the buffer layer or between the buffer layer and the monolayer graphene. The intercalation of terbium below a pure buffer layer led to the formation of a highly n -doped graphene monolayer decoupled from the SiC substrate, as evidenced by ARPES and x-ray photoelectron spectroscopy measurements. The band structure of this highly n -doped monolayer graphene showed a kink (a deviation from the linear dispersion of the Dirac cone), which has been associated with an electron-phonon coupling constant one order of magnitude larger than those usually obtained for graphene with intercalated alkali metals.

Effects of interface roughness on cohesive strength of self-assembled monolayers

Energy Technology Data Exchange (ETDEWEB)

Zhang, Chen [Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, IL 61801 (United States); Awasthi, Amnaya P. [Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, 32611 (United States); Geubelle, Philippe H., E-mail: geubelle@illinois.edu [Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, IL 61801 (United States); Grady, Martha E.; Sottos, Nancy R. [Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, IL 61801 (United States)

2017-03-01

Highlights: • Self-assembled monolayer/transfer-printed gold interface modeled using continuum-level simulation. • Initial deformed film profile analyzed and instability assessed. • Effective cohesive response of SAM-enhanced interface extracted from spallation model. • Reduction of up to 70% cohesive strength of the interface from incorporation of roughness demonstrated. - Abstract: 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

The Thioacetate-Functionalized Self-Assembled Monolayers on Au: Toward High-Performance Ion-Selective Electrode for Ag{sup +}

Energy Technology Data Exchange (ETDEWEB)

Jin, Jian; Zhou, Weijie; Chen, Ying; Liu, Yilong; Sun, Xiaoqiang; Xi Haitao [Changzhou Univ., Changzhou (China)

2014-02-15

Two classes of morpholino-substituted thioacetate have been successfully synthesized and their electrochemical properties of self-assembled monolayers (SAMs) on Au electrode are measured by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The barrier property of the SAMs-modified surfaces is evaluated by using potassium ferro/ferri cyanide. The results suggest that the arenethioacetate forms higher-quality close-packed blocking monolayers in comparison with alkanethioacetate. Furthermore, it has shown that the barrier properties of these monolayers can be significantly improved by mixed SAMs formation with decanethiol. From our experimental results we find that the electron transfer reaction of [Fe(CN){sub 6}]{sup 3-/4-} redox couple occurs predominantly through the pinholes and defects present in the SAM and both SAMs show a good and fast capacity in recognition for Ag{sup +}. The morphological and elementary composition have also been examined by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS)

Hole mobility enhancement and p-doping in monolayer WSe2 by gold decoration

KAUST Repository

Chen, Chang-Hsiao

2014-10-28

Tungsten diselenide (WSe2) is an attractive transition metal dichalcogenide material, since its Fermi energy close to the mid gap makes it an excellent candidate for realizing p-n junction devices and complementary digital logic applications. Doping is one of the most important technologies for controlling the Fermi energy in semiconductors, including 2D materials. Here we present a simple, stable and controllable p-doping technique on a WSe2 monolayer, where a more p-typed WSe2 field effect transistor is realized by electron transfer from the WSe2 to the gold (Au) decorated on the WSe2 surfaces. Related changes in Raman spectroscopy are also reported. The p-doping caused by Au on WSe2 monolayers lowers the channel resistance by orders of magnitude. The effective hole mobility is ~100 (cm2/Vs) and the near ideal subthreshold swing of ~60 mV/decade and high on/off current ratio of >106 are observed. The Au deposited on the WSe2 also serves as a protection layer to prevent a reaction between the WSe2 and the environment, making the doping stable and promising for future scalable fabrication.

Imaginary geometric phases of quantum trajectories in high-order terahertz sideband generation

Science.gov (United States)

Yang, Fan; Liu, Ren-Bao

2014-03-01

Quantum evolution of particles under strong fields can be described by a small number of quantum trajectories that satisfy the stationary phase condition in the Dirac-Feynmann path integral. The quantum trajectories are the key concept to understand the high-order terahertz siedeband generation (HSG) in semiconductors. Due to the nontrivial ``vacuum'' states of band materials, the quantum trajectories of optically excited electron-hole pairs in semiconductors can accumulate geometric phases under the driving of an elliptically polarized THz field. We find that the geometric phase of the stationary trajectory is generally complex with both real and imaginary parts. In monolayer MoS2, the imaginary parts of the geometric phase leads to a changing of the polarization ellipticity of the sideband. We further show that the imaginary part originates from the quantum interference of many trajectories with different phases. Thus the observation of the polarization ellipticity of the sideband shall be a good indication of the quantum nature of the stationary trajectory. This work is supported by Hong Kong RGC/GRF 401512 and the CUHK Focused Investments Scheme.

Antibiotic interaction with phospholipid monolayers

International Nuclear Information System (INIS)

Gambinossi, F.; Mecheri, B.; Caminati, G.; Nocentini, M.; Puggelli, M.; Gabrielli, G.

2002-01-01

We studied the interactions of tetracycline (TC) antibiotic molecules with phospholipid monolayers with the two-fold aim of elucidating the mechanism of action and providing a first step for the realization of bio-mimetic sensors for such drugs by means of the Langmuir-Blodgett technique. We examined spreading monolayers of three phospholipids in the presence of tetracycline in the subphase by means of surface pressure-area and surface potential-area isotherms as a function of bulk pH. We selected phospholipids with hydrophobic chains of the same length but polar head groups differing either in dimensions and protonation equilibria, i.e. dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE) and dipalmitoylphosphatidic acid (DPPA). The interaction of tetracycline with the three phospholipids was found to be highly dependent on the electric charge of the antibiotic and on the ionization state of the lipid. Significant interactions are established between the negatively charged form of dipalmitoylphosphatidic acid and the zwitterionic form of tetracycline. The drug was found to migrate at the interface where it is adsorbed underneath or/and among the head groups, depending on the surface pressure of the film, whereas penetration through the hydrophobic layer was excluded for all the three phospholipids

Antibiotic interaction with phospholipid monolayers

Energy Technology Data Exchange (ETDEWEB)

Gambinossi, F.; Mecheri, B.; Caminati, G.; Nocentini, M.; Puggelli, M.; Gabrielli, G

2002-12-01

We studied the interactions of tetracycline (TC) antibiotic molecules with phospholipid monolayers with the two-fold aim of elucidating the mechanism of action and providing a first step for the realization of bio-mimetic sensors for such drugs by means of the Langmuir-Blodgett technique. We examined spreading monolayers of three phospholipids in the presence of tetracycline in the subphase by means of surface pressure-area and surface potential-area isotherms as a function of bulk pH. We selected phospholipids with hydrophobic chains of the same length but polar head groups differing either in dimensions and protonation equilibria, i.e. dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE) and dipalmitoylphosphatidic acid (DPPA). The interaction of tetracycline with the three phospholipids was found to be highly dependent on the electric charge of the antibiotic and on the ionization state of the lipid. Significant interactions are established between the negatively charged form of dipalmitoylphosphatidic acid and the zwitterionic form of tetracycline. The drug was found to migrate at the interface where it is adsorbed underneath or/and among the head groups, depending on the surface pressure of the film, whereas penetration through the hydrophobic layer was excluded for all the three phospholipids.

Doping effect on monolayer MoS2 for visible light dye degradation - A DFT study

Science.gov (United States)

Cheriyan, Silpa; Balamurgan, D.; Sriram, S.

2018-04-01

The electronic and optical properties of, Nitrogen (N), Cobalt (Co), and Co-N co-doped monolayers of MoS2 has been studied by using density functional theory (DFT) for visible light photocatalytic activity. From the calculations, it has been observed that the band gap of monolayer MoS2 has been reduced while doping. However, the band gaps of pristine and N doped MoS2 monolayers only falls in the visible region while for Co and Co-N co-doped systems, the band gap shifted to IR region. The optical calculation also confirms the results. The formation energy values of the doped system reaveal that MoS2 monolayer drops its stability while doping. To evaluate the photocatalytic response, band edge potentials of pristine and N-MoS2 are calculated, and the observed results show that compared to N-doped MoS2 monolayer, pure MoS2 is highly suitable for visible light photocatalytic dye degradation.

Interfacial and thermal energy driven growth and evolution of Langmuir-Schaefer monolayers of Au-nanoparticles.

Science.gov (United States)

Mukhopadhyay, Mala; Hazra, S

2018-01-03

Structures of Langmuir-Schaefer (LS) monolayers of thiol-coated Au-nanoparticles (DT-AuNPs) deposited on H-terminated and OTS self-assembled Si substrates (of different hydrophobic strength and stability) and their evolution with time under ambient conditions, which plays an important role for their practical use as 2D-nanostructures over large areas, were investigated using the X-ray reflectivity technique. The strong effect of substrate surface energy (γ) on the initial structures and the competitive role of room temperature thermal energy (kT) and the change in interfacial energy (Δγ) at ambient conditions on the evolution and final structures of the DT-AuNP LS monolayers are evident. The strong-hydrophobic OTS-Si substrate, during transfer, seems to induce strong attraction towards hydrophobic DT-AuNPs on hydrophilic (repulsive) water to form vertically compact partially covered (with voids) monolayer structures (of perfect monolayer thickness) at low pressure and nearly covered buckled monolayer structures (of enhanced monolayer thickness) at high pressure. After transfer, the small kT-energy (in absence of repulsive water) probably fluctuates the DT-AuNPs to form vertically expanded monolayer structures, through systematic exponential growth with time. The effect is prominent for the film deposited at low pressure, where the initial film-coverage and film-thickness are low. On the other hand, the weak-hydrophobic H-Si substrate, during transfer, appears to induce optimum attraction towards DT-AuNPs to better mimic the Langmuir monolayer structures on it. After transfer, the change in the substrate surface nature, from weak-hydrophobic to weak-hydrophilic with time (i.e. Δγ-energy, apart from the kT-energy), enhances the size of the voids and weakens the monolayer/bilayer structure to form a similar expanded monolayer structure, the thickness of which is probably optimized by the available thermal energy.

Formation of high-quality self-assembled monolayers of conjugated dithiols on gold : Base matters

NARCIS (Netherlands)

Valkenier, Hennie; Huisman, Everardus H.; Hal, Paul A. van; de Leeuw, Dagobert; Chiechi, Ryan C.; Hummelen, Jan C.

2011-01-01

This Article reports a systematic study on the formation of self-assembled monolayers (SAMs) of conjugated molecules for molecular electronic (ME) devices. We monitored the deprotection reaction of acetyl protected dithiols of oligophenylene ethynylenes (OPEs) in solution using two different bases

Large-area snow-like MoSe2 monolayers: synthesis, growth mechanism, and efficient electrocatalyst application.

Science.gov (United States)

Huang, Jingwen; Liu, Huiqiang; Jin, Bo; Liu, Min; Zhang, Qingchun; Luo, Liqiong; Chu, Shijin; Chu, Sheng; Peng, Rufang

2017-07-07

This study explores the large-area synthesis of controllable morphology, uniform, and high-quality monolayer. MoSe 2 is essential for its potential application in optoelectronics, photocatalysis, and renewable energy sources. In this study, we successfully synthesized snow-like MoSe 2 monolayers using a simple chemical vapor deposition method. Results reveal that snow-like MoSe 2 is a single crystal with a hexagonal structure, a thickness of ∼0.9 nm, and a lateral dimension of up to 20 μm. The peak position of the photoluminescence spectra is ∼1.52 eV corresponding to MoSe 2 monolayer. The growth mechanism of the snow-like MoSe 2 monolayer was investigated and comprised a four-step process during growth. Finally, we demonstrate that the snow-like MoSe 2 monolayers are ideal electrocatalysts for hydrogen evolution reactions (HERs), reflected by a low Tafel slope of ∼68 mV/decade. Compared with the triangular-shaped MoSe 2 monolayer, the hexangular snow-like shape with plentiful edges is superior for perfect electrocatalysts for HERs or transmission devices of optoelectronic signals.

Prediction of Intrinsic Ferromagnetic Ferroelectricity in a Transition-Metal Halide Monolayer

Science.gov (United States)

Huang, Chengxi; Du, Yongping; Wu, Haiping; Xiang, Hongjun; Deng, Kaiming; Kan, Erjun

2018-04-01

The realization of multiferroics in nanostructures, combined with a large electric dipole and ferromagnetic ordering, could lead to new applications, such as high-density multistate data storage. Although multiferroics have been broadly studied for decades, ferromagnetic ferroelectricity is rarely explored, especially in two-dimensional (2D) systems. Here we report the discovery of 2D ferromagnetic ferroelectricity in layered transition-metal halide systems. On the basis of first-principles calculations, we reveal that a charged CrBr3 monolayer exhibits in-plane multiferroicity, which is ensured by the combination of orbital and charge ordering as realized by the asymmetric Jahn-Teller distortions of octahedral Cr - Br6 units. As an example, we further show that (CrBr3)2Li is a ferromagnetic ferroelectric multiferroic. The explored phenomena and mechanism of multiferroics in this 2D system not only are useful for fundamental research in multiferroics but also enable a wide range of applications in nanodevices.

A MOLECULAR-DYNAMICS STUDY OF LECITHIN MONOLAYERS

NARCIS (Netherlands)

AHLSTROM, P; BERENDSEN, HJC

1993-01-01

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)

WSe2 Monolayer

KAUST Repository

Zhang, Shuai; Wang, Chen-Guang; Li, Ming-yang; Huang, Di; Li, Lain-Jong; Ji, Wei; Wu, Shiwei

2017-01-01

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

Actinide Sequestration Using Self-Assembled Monolayers on Mesoporous Supports

International Nuclear Information System (INIS)

Fryxell, Glen E.; Lin, Yuehe; Fiskum, Sandra K.; Birnbaum, Jerome C.; Wu, Hong; Kemner, K. M.; Kelly, Shelley

2005-01-01

Surfactant templated synthesis of mesoporous ceramics provides a versatile foundation upon which to create high efficiency environmental sorbents. These nanoporous ceramic oxides condense a huge amount of surface area into a very small volume. The ceramic oxide interface is receptive to surface functionalization through molecular self-assembly. The marriage of mesoporous ceramics with self-assembled monolayer chemistry creates a powerful new class of environmental sorbent materials called self-assembled monolayers on mesoporous supports (SAMMS). These SAMMS materials are highly efficient sorbents, whose interfacial chemistry can be fine-tuned to selectively sequester a specific target species, such as heavy metals, tetrahedral oxometallate anions and radionuclides. Details addressing the design, synthesis and characterization of SAMMS materials specifically designed to sequester actinides, of central importance to the environmental clean-up necessary after 40 years of weapons grade plutonium production, as well as evaluation of their binding affinities and kinetics are presented

Piezoelectric effect in chemical vapour deposition-grown atomic-monolayer triangular molybdenum disulfide piezotronics

KAUST Repository

Qi, Junjie; Lan, Yann-Wen; Stieg, Adam Z.; Chen, Jyun-Hong; Zhong, Yuan-Liang; Li, Lain-Jong; Chen, Chii-Dong; Zhang, Yue; Wang, Kang L.

2015-01-01

High-performance piezoelectricity in monolayer semiconducting transition metal dichalcogenides is highly desirable for the development of nanosensors, piezotronics and photo-piezotransistors. Here we report the experimental study

High-order finite volume advection

OpenAIRE

Shaw, James

2018-01-01

The cubicFit advection scheme is limited to second-order convergence because it uses a polynomial reconstruction fitted to point values at cell centres. The highOrderFit advection scheme achieves higher than second order by calculating high-order moments over the mesh geometry.

Orientational epitaxy in adsorbed monolayers

International Nuclear Information System (INIS)

Novaco, A.D.; McTague, J.P.

1977-01-01

The ground state for adsorbed monolayers on crystalline substrates is shown to involve a definite relative orientation of the substrate and adsorbate crystal axes, even when the relative lattice parameters are incommensurate. The rotation angle which defines the structure of the monolayer-substrate system is determined by the competition between adsorbate-substrate and adsorbate-adsorbate energy terms, and is generally not a symmetry angle. Numerical predictions are presented for the rare gas-graphite systems, whose interaction potentials are rather well known. Recent LEED data for some of these systems appear to corroborate these predictions

Subcellular topological effect of particle monolayers on cell shapes and functions.

Science.gov (United States)

Miura, Manabu; Fujimoto, Keiji

2006-12-01

We studied topological effects of subcellular roughness displayed by a closely packed particle monolayer on adhesion and growth of endothelial cells. Poly(styrene-co-acrylamide) (SA) particles were prepared by soap-free emulsion copolymerization. Particle monolayers were prepared by Langmuir-Blodgett deposition using particles, which were 527 (SA053) and 1270 nm (SA127) in diameter. After 24-h incubation, cells tightly adhered on a tissue culture polystyrene dish and randomly spread. On the other hand, cells attached on particle monolayers were stretched into a narrow stalk-like shape. Lamellipodia spread from the leading edge of cells attached on SA053 monolayer to the top of the particles and gradually gathered to form clusters. This shows that cell-cell adhesion became stronger than cell-substrate interaction. Cells attached to SA127 monolayer extended to the reverse side of a particle monolayer and engulfed particles. They remained immobile without migration 24h after incubation. This shows that the inhibition of extensions on SA127 monolayer could inhibit cell migration and cell proliferation. Cell growth on the particle monolayers was suppressed compared with a flat TCPS dish. The number of cells on SA053 gradually increased, whereas that on SA127 decreased with time. When the cell seeding density was increased to 200,000 cells cm(-2), some adherent cells gradually became into contact with adjacent cells. F-actin condensations were formed at the frame of adherent cells and the thin filaments grew from the edges to connect each other with time. For the cell culture on SA053 monolayer, elongated cells showed a little alignment. Cells showed not arrangement of actin stress fibers but F-actin condensation at the contact regions with neighboring cells. Interestingly, the formed cell monolayer could be readily peeled from the particle monolayer. These results indicate that endothelial cells could recognize the surface roughness displayed by particle monolayers and

Mechanical and electronic properties of Janus monolayer transition metal dichalcogenides

Science.gov (United States)

Shi, Wenwu; Wang, Zhiguo

2018-05-01

The mechanical and electronic properties of Janus monolayer transition metal dichalcogenides MXY (M  =  Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W; X/Y  =  S, Se, Te) were investigated using density functional theory. Results show that breaking the out-of-plane structural symmetry can be used to tune the electronic and mechanical behavior of monolayer transition metal dichalcogenides. The band gaps of monolayer WXY and MoXY are in the ranges of 0.16–1.91 and 0.94–1.69 eV, respectively. A semiconductor to metallic phase transition occurred in Janus monolayer MXY (M  =  Ti, Zr and Hf). The monolayers MXY (M  =  V, Nb, Ta and Cr) show metallic characteristics, which show no dependence on the structural symmetry breaking. The mechanical properties of MXY depended on the composition. Monolayer MXY (M  =  Mo, Ti, Zr, Hf and W) showed brittle characteristic, whereas monolayer CrXY and VXY are with ductile characteristic. The in-plane stiffness of pristine and Janus monolayer MXY are in the range between 22 and 158 N m‑1. The tunable electronic and mechanical properties of these 2D materials would advance the development of ultra-sensitive detectors, nanogenerators, low-power electronics, and energy harvesting and electromechanical systems.

Dynamics of decanethiol self-assembled monolayers on Au(111) studied by Scanning tunnelling microscopy

NARCIS (Netherlands)

Wu, Hairong; Sotthewes, Kai; Kumar, Avijit; Vancso, Gyula J.; Schön, Peter Manfred; Zandvliet, Henricus J.W.

2013-01-01

We investigated the dynamics of decanethiol self-assembled monolayers on Au(111) surfaces using time-resolved scanning tunneling microscopy at room temperature. The expected ordered phases (β, δ, χ*, and ) and a disordered phase (ε) were observed. Current–time traces with the feedback loop disabled

High-Order Frequency-Locked Loops

DEFF Research Database (Denmark)

Golestan, Saeed; Guerrero, Josep M.; Quintero, Juan Carlos Vasquez

2017-01-01

In very recent years, some attempts for designing high-order frequency-locked loops (FLLs) have been made. Nevertheless, the advantages and disadvantages of these structures, particularly in comparison with a standard FLL and high-order phase-locked loops (PLLs), are rather unclear. This lack...... study, and its small-signal modeling, stability analysis, and parameter tuning are presented. Finally, to gain insight about advantages and disadvantages of high-order FLLs, a theoretical and experimental performance comparison between the designed second-order FLL and a standard FLL (first-order FLL...

Ultrafast Transient Terahertz Conductivity of Monolayer MoS 2 and WSe 2 Grown by Chemical Vapor Deposition

KAUST Repository

Docherty, Callum J.

2014-11-25

We have measured ultrafast charge carrier dynamics in monolayers and trilayers of the transition metal dichalcogenides MoS2 and WSe2 using a combination of time-resolved photoluminescence and terahertz spectroscopy. We recorded a photoconductivity and photoluminescence response time of just 350 fs from CVD-grown monolayer MoS2, and 1 ps from trilayer MoS2 and monolayer WSe2. Our results indicate the potential of these materials as high-speed optoelectronic materials.

Ultrafast Transient Terahertz Conductivity of Monolayer MoS 2 and WSe 2 Grown by Chemical Vapor Deposition

KAUST Repository

Docherty, Callum J.; Parkinson, Patrick; Joyce, Hannah J.; Chiu, Ming-Hui; Chen, Chang-Hsiao; Lee, Ming-Yang; Li, Lain-Jong; Herz, Laura M.; Johnston, Michael B.

2014-01-01

We have measured ultrafast charge carrier dynamics in monolayers and trilayers of the transition metal dichalcogenides MoS2 and WSe2 using a combination of time-resolved photoluminescence and terahertz spectroscopy. We recorded a photoconductivity and photoluminescence response time of just 350 fs from CVD-grown monolayer MoS2, and 1 ps from trilayer MoS2 and monolayer WSe2. Our results indicate the potential of these materials as high-speed optoelectronic materials.

Vanadium impurity effects on optical properties of Ti3N2 mono-layer: An ab-initio study

Science.gov (United States)

Babaeipour, Manuchehr; Eslam, Farzaneh Ghafari; Boochani, Arash; Nezafat, Negin Beryani

2018-06-01

The present work is investigated the effect of vanadium impurity on electronic and optical properties of Ti3N2 monolayer by using density function theory (DFT) implemented in Wien2k code. In order to study optical properties in two polarization directions of photons, namely E||x and E||z, dielectric function, absorption coefficient, optical conductivity, refraction index, extinction index, reflectivity, and energy loss function of Ti3N2 and Ti3N2-V monolayer have been evaluated within GGA (PBE) approximation. Although, Ti3N2 monolayer is a good infrared reflector and can be used as an infrared mirror, introducing V atom in the infrared area will decrease optical conductivity because optical conductivity of a pure form of a material is higher than its doped form.

Neutron scattering study of ³⁶ Ar monolayer films adsorbed on graphite

DEFF Research Database (Denmark)

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

1977-01-01

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 o...

Approaching total absorption at near infrared in a large area monolayer graphene by critical coupling

Energy Technology Data Exchange (ETDEWEB)

Liu, Yonghao; Chadha, Arvinder; Zhao, Deyin; Shuai, Yichen; Menon, Laxmy; Yang, Hongjun; Zhou, Weidong, E-mail: wzhou@uta.edu [Nanophotonics Lab, Department of Electrical Engineering, University of Texas at Arlington, Arlington, Texas 76019 (United States); Piper, Jessica R.; Fan, Shanhui [Ginzton Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States); Jia, Yichen; Xia, Fengnian [Department of Electrical Engineering, Yale University, New Haven, Connecticut 06520 (United States); Ma, Zhenqiang [Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

2014-11-03

We demonstrate experimentally close to total absorption in monolayer graphene based on critical coupling with guided resonances in transfer printed photonic crystal Fano resonance filters at near infrared. Measured peak absorptions of 35% and 85% were obtained from cavity coupled monolayer graphene for the structures without and with back reflectors, respectively. These measured values agree very well with the theoretical values predicted with the coupled mode theory based critical coupling design. Such strong light-matter interactions can lead to extremely compact and high performance photonic devices based on large area monolayer graphene and other two–dimensional materials.

Superior Valley Polarization and Coherence of 2s Excitons in Monolayer WSe_{2}.

Science.gov (United States)

Chen, Shao-Yu; Goldstein, Thomas; Tong, Jiayue; Taniguchi, Takashi; Watanabe, Kenji; Yan, Jun

2018-01-26

We report the experimental observation of 2s exciton radiative emission from monolayer tungsten diselenide, enabled by hexagonal boron nitride protected high-quality samples. The 2s luminescence is highly robust and persists up to 150 K, offering a new quantum entity for manipulating the valley degree of freedom. Remarkably, the 2s exciton displays superior valley polarization and coherence than 1s under similar experimental conditions. This observation provides evidence that the Coulomb-exchange-interaction-driven valley-depolarization process, the Maialle-Silva-Sham mechanism, plays an important role in valley excitons of monolayer transition metal dichalcogenides.

Superior Valley Polarization and Coherence of 2 s Excitons in Monolayer WSe2

Science.gov (United States)

Chen, Shao-Yu; Goldstein, Thomas; Tong, Jiayue; Taniguchi, Takashi; Watanabe, Kenji; Yan, Jun

2018-01-01

We report the experimental observation of 2 s exciton radiative emission from monolayer tungsten diselenide, enabled by hexagonal boron nitride protected high-quality samples. The 2 s luminescence is highly robust and persists up to 150 K, offering a new quantum entity for manipulating the valley degree of freedom. Remarkably, the 2 s exciton displays superior valley polarization and coherence than 1 s under similar experimental conditions. This observation provides evidence that the Coulomb-exchange-interaction-driven valley-depolarization process, the Maialle-Silva-Sham mechanism, plays an important role in valley excitons of monolayer transition metal dichalcogenides.

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

Directory of Open Access Journals (Sweden)

Ellen M. Adams

2013-10-01

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.

Synchrotron X-ray diffraction studies of phase transitions in physisorbed monolayers of rare gases on graphite

International Nuclear Information System (INIS)

Bohr, J.

1984-01-01

This study is an investigation of phase transition in monoatomic layers adsorbed on graphite. Such effects can be considered physical realizations of two-dimensional systems. The experimental technique used is synchrotron X-ray diffraction. Systems which have been investigated include the commensurate-incommensurate phase transition in krypton monolayer. By adjusting the spreading pressure in the krypton layer by means of a coadsorbent deuterium gas it has been unambiguously demonstrated that at low temperatures the phase transition is of first order. A melting study of incommensurate argon monolayers demonstrates an experimental verification of the possibility for having a continuous melting transition in two-dimensions. Mixtures of two-components have been investigated for their phases. No (chemical) order-disorder transition is seen. A discussion is given on this lack of a chemical order. This lack is utilized to study the commensurate-incommensurate phase transition driven by average particle size. Finally, a special low-temperature phase is identified in a xenon monlayer which is diluted with freon. (Auth.)

Hole mobility enhancement and p -doping in monolayer WSe2 by gold decoration

International Nuclear Information System (INIS)

Chen, Chang-Hsiao; Wu, Chun-Lan; Kumar, Pushpendra; Pu, Jiang; Takenobu, Taishi; Chiu, Ming-Hui; Li, Lain-Jong

2014-01-01

Tungsten diselenide (WSe 2 ) is an attractive transition metal dichalcogenide material, since its Fermi energy close to the mid gap makes it an excellent candidate for realizing p–n junction devices and complementary digital logic applications. Doping is one of the most important technologies for controlling the Fermi energy in semiconductors, including 2D materials. Here we present a simple, stable and controllable p-doping technique on a WSe 2 monolayer, where a more p-typed WSe 2 field effect transistor is realized by electron transfer from the WSe 2 to the gold (Au) decorated on the WSe 2 surfaces. Related changes in Raman spectroscopy are also reported. The p-doping caused by Au on WSe 2 monolayers lowers the channel resistance by orders of magnitude. The effective hole mobility is ∼100 (cm 2 /Vs) and the near ideal subthreshold swing of ∼60 mV/decade and high on/off current ratio of >10 6 are observed. The Au deposited on the WSe 2 also serves as a protection layer to prevent a reaction between the WSe 2 and the environment, making the doping stable and promising for future scalable fabrication. (paper)

A pentacene monolayer trapped between graphene and a substrate.

Science.gov (United States)

Zhang, Qicheng; Peng, Boyu; Chan, Paddy Kwok Leung; Luo, Zhengtang

2015-09-21

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.

Anomalous lattice vibrations of monolayer MoS 2 probed by ultraviolet Raman scattering

KAUST Repository

Liu, Hsiang Lin; Guo, Huaihong; Yang, Teng; Zhang, Zhidong; Kumamoto, Yasuaki; Shen, Chih Chiang; Hsu, Yu Te; Li, Lain-Jong; Saito, Riichiro; Kawata, Satoshi

2015-01-01

We present a comprehensive Raman scattering study of monolayer MoS2 with increasing laser excitation energies ranging from the near-infrared to the deep-ultraviolet. The Raman scattering intensities from the second-order phonon modes are revealed to be enhanced anomalously by only the ultraviolet excitation wavelength 354 nm. We demonstrate theoretically that such resonant behavior arises from a strong optical absorption that forms near the Γ point and of the band structure and an inter-valley resonant electronic scattering by the M-point phonons. These results advance our understanding of the double resonance Raman scattering process in low-dimensional semiconducting nanomaterials and provide a foundation for the technological development of monolayer MoS2 in the ultraviolet frequency range. © the Owner Societies 2015.

Self-assembled monolayers of perfluoroalkylsilane on plasma-hydroxylated silicon substrates

Energy Technology Data Exchange (ETDEWEB)

Wu, Lin; Cai, Lu; Liu, Anqi; Wang, Wei; Yuan, Yanhua [College of Textile, Clothing Engineering, Soochow University, Suzhou 215021 (China); National Engineering Laboratory for Modern Silk, Suzhou 215123 (China); Li, Zhanxiong, E-mail: lizhanxiong@suda.edu.cn [College of Textile, Clothing Engineering, Soochow University, Suzhou 215021 (China); State Key Laboratory of Disaster Prevention & Mitigation of Explosion & Impact, Nanjing 210007 (China)

2015-09-15

Highlights: • A novel kind of fluoroalkylsilane monomers with different fluoroalkyl chain length was synthesized. • The fluoroalkyl-terminated self-assembled monolayers (SAMs) on silanol-terminated silicon substrates were chemically fabricated using the liquid phase deposition method. • Fluoroalkylsilanes were used for the self-assembly rather than the silane coupling agents and fluorochemicals to fabricate controllable, ordered SAMs. • The angle-dependent XPS study was conducted to investigate the changes of surface structures as well as elemental compositions of the SAMs. • The results indicated that fluoroalkyl groups would migrate from the inner part of the monolayers to the outermost interface after heat treatment, resulting into the microphase separation of the SAMs surface. - Abstract: In this study, a novel kind of fluoroalkylsilane monomers with different fluoroalkyl chain lengths was synthesized via three steps method and characterized by Fourier transform infrared (FT-IR) spectroscopy, {sup 1}H and {sup 19}F nuclear magnetic resonance ({sup 1}H NMR and {sup 19}F NMR), and mass spectra (MS). Fluoroalkyl-terminated self-assembled monolayers (SAMs) on silanol-terminated silicon substrates (O{sub 2} plasma treatment) were chemically fabricated via –Si–O– covalent bonds using the liquid phase deposition method (LPD). The wetabilities of the SAMs were characterized by water contact angles (CA), surface free energies and adhesive force (AF) measurements. 3-(1H,1H,2H,2H-perfluorooctyloxycarbonyl) -propionamidepropyl-triethoxysilane (PFOPT) assembled monolayer was chosen for in-depth investigation as its CA was higher than the others. Attenuated total reflection infrared spectroscopy (ATR-IR) and X-ray photoelectron spectroscopy (XPS) were used to validate the attachment of PFOPT on the silicon substrate, together with the chemical composition and structure of the SAMs. The surface morphologies and roughness of the monolayers were obtained and

Challenges in analysing and visualizing large-scale molecular dynamics simulations: domain and defect formation in lung surfactant monolayers

International Nuclear Information System (INIS)

Mendez-Villuendas, E; Baoukina, S; Tieleman, D P

2012-01-01

Molecular dynamics simulations have rapidly grown in size and complexity, as computers have become more powerful and molecular dynamics software more efficient. Using coarse-grained models like MARTINI system sizes of the order of 50 nm × 50 nm × 50 nm can be simulated on commodity clusters on microsecond time scales. For simulations of biological membranes and monolayers mimicking lung surfactant this enables large-scale transformation and complex mixtures of lipids and proteins. Here we use a simulation of a monolayer with three phospholipid components, cholesterol, lung surfactant proteins, water, and ions on a ten microsecond time scale to illustrate some current challenges in analysis. In the simulation, phase separation occurs followed by formation of a bilayer fold in which lipids and lung surfactant protein form a highly curved structure in the aqueous phase. We use Voronoi analysis to obtain detailed physical properties of the different components and phases, and calculate local mean and Gaussian curvatures of the bilayer fold.

Density determination of langmuir-blodgett monolayer films using x-ray reflectivity technique

International Nuclear Information System (INIS)

Damar Yoga Kusuma

2015-01-01

Monolayer deposition by Langmuir-Blodgett technique produces monolayer films that are uniform with controllable thickness down to nanometer scale. To evaluate the quality of the monolayer deposition, X-ray reflectivity technique are employed to monitor the monolayers density. Langmuir-Blodgett monolayer with good coverage and uniformity results in film density close to its macroscopic film counterpart whereas films with presence of air gaps shows lower density compared to its macroscopic film counterpart. (author)

Facile fabrication of highly ordered poly(vinylidene fluoride-trifluoroethylene) nanodot arrays for organic ferroelectric memory

International Nuclear Information System (INIS)

Fang, Huajing; Yan, Qingfeng; Geng, Chong; Li, Qiang; Chan, Ngai Yui; Au, Kit; Ng, Sheung Mei; Leung, Chi Wah; Wa Chan, Helen Lai; Dai, Jiyan; Yao, Jianjun; Guo, Dong

2016-01-01

Nano-patterned ferroelectric materials have attracted significant attention as the presence of two or more thermodynamically equivalent switchable polarization states can be employed in many applications such as non-volatile memory. In this work, a simple and effective approach for fabrication of highly ordered poly(vinylidene fluoride–trifluoroethylene) P(VDF-TrFE) nanodot arrays is demonstrated. By using a soft polydimethylsiloxane mold, we successfully transferred the 2D array pattern from the initial monolayer of colloidal polystyrene nanospheres to the imprinted P(VDF-TrFE) films via nanoimprinting. The existence of a preferred orientation of the copolymer chain after nanoimprinting was confirmed by Fourier transform infrared spectra. Local polarization switching behavior was measured by piezoresponse force microscopy, and each nanodot showed well-formed hysteresis curve and butterfly loop with a coercive field of ∼62.5 MV/m. To illustrate the potential application of these ordered P(VDF-TrFE) nanodot arrays, the writing and reading process as non-volatile memory was demonstrated at a relatively low voltage. As such, our results offer a facile and promising route to produce arrays of ferroelectric polymer nanodots with improved piezoelectric functionality

Facile fabrication of highly ordered poly(vinylidene fluoride-trifluoroethylene) nanodot arrays for organic ferroelectric memory

Energy Technology Data Exchange (ETDEWEB)

Fang, Huajing [Department of Applied Physics, The Hong Kong Polytechnic University (PolyU) Hunghom, Kowloon (Hong Kong); Department of Chemistry, Tsinghua University, Beijing 100084 (China); Yan, Qingfeng, E-mail: yanqf@mail.tsinghua.edu.cn, E-mail: jiyan.dai@polyu.edu.hk; Geng, Chong; Li, Qiang [Department of Chemistry, Tsinghua University, Beijing 100084 (China); Chan, Ngai Yui; Au, Kit; Ng, Sheung Mei; Leung, Chi Wah; Wa Chan, Helen Lai; Dai, Jiyan, E-mail: yanqf@mail.tsinghua.edu.cn, E-mail: jiyan.dai@polyu.edu.hk [Department of Applied Physics, The Hong Kong Polytechnic University (PolyU) Hunghom, Kowloon (Hong Kong); Yao, Jianjun [Asylum Research, Oxford Instruments, Shanghai 200233 (China); Guo, Dong [Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190 (China)

2016-01-07

Nano-patterned ferroelectric materials have attracted significant attention as the presence of two or more thermodynamically equivalent switchable polarization states can be employed in many applications such as non-volatile memory. In this work, a simple and effective approach for fabrication of highly ordered poly(vinylidene fluoride–trifluoroethylene) P(VDF-TrFE) nanodot arrays is demonstrated. By using a soft polydimethylsiloxane mold, we successfully transferred the 2D array pattern from the initial monolayer of colloidal polystyrene nanospheres to the imprinted P(VDF-TrFE) films via nanoimprinting. The existence of a preferred orientation of the copolymer chain after nanoimprinting was confirmed by Fourier transform infrared spectra. Local polarization switching behavior was measured by piezoresponse force microscopy, and each nanodot showed well-formed hysteresis curve and butterfly loop with a coercive field of ∼62.5 MV/m. To illustrate the potential application of these ordered P(VDF-TrFE) nanodot arrays, the writing and reading process as non-volatile memory was demonstrated at a relatively low voltage. As such, our results offer a facile and promising route to produce arrays of ferroelectric polymer nanodots with improved piezoelectric functionality.

Facile fabrication of highly ordered poly(vinylidene fluoride-trifluoroethylene) nanodot arrays for organic ferroelectric memory

Science.gov (United States)

Fang, Huajing; Yan, Qingfeng; Geng, Chong; Chan, Ngai Yui; Au, Kit; Yao, Jianjun; Ng, Sheung Mei; Leung, Chi Wah; Li, Qiang; Guo, Dong; Wa Chan, Helen Lai; Dai, Jiyan

2016-01-01

Nano-patterned ferroelectric materials have attracted significant attention as the presence of two or more thermodynamically equivalent switchable polarization states can be employed in many applications such as non-volatile memory. In this work, a simple and effective approach for fabrication of highly ordered poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) nanodot arrays is demonstrated. By using a soft polydimethylsiloxane mold, we successfully transferred the 2D array pattern from the initial monolayer of colloidal polystyrene nanospheres to the imprinted P(VDF-TrFE) films via nanoimprinting. The existence of a preferred orientation of the copolymer chain after nanoimprinting was confirmed by Fourier transform infrared spectra. Local polarization switching behavior was measured by piezoresponse force microscopy, and each nanodot showed well-formed hysteresis curve and butterfly loop with a coercive field of ˜62.5 MV/m. To illustrate the potential application of these ordered P(VDF-TrFE) nanodot arrays, the writing and reading process as non-volatile memory was demonstrated at a relatively low voltage. As such, our results offer a facile and promising route to produce arrays of ferroelectric polymer nanodots with improved piezoelectric functionality.

Deep level transient spectroscopic investigation of phosphorus-doped silicon by self-assembled molecular monolayers.

Science.gov (United States)

Gao, Xuejiao; Guan, Bin; Mesli, Abdelmadjid; Chen, Kaixiang; Dan, Yaping

2018-01-09

It is known that self-assembled molecular monolayer doping technique has the advantages of forming ultra-shallow junctions and introducing minimal defects in semiconductors. In this paper, we report however the formation of carbon-related defects in the molecular monolayer-doped silicon as detected by deep-level transient spectroscopy and low-temperature Hall measurements. The molecular monolayer doping process is performed by modifying silicon substrate with phosphorus-containing molecules and annealing at high temperature. The subsequent rapid thermal annealing drives phosphorus dopants along with carbon contaminants into the silicon substrate, resulting in a dramatic decrease of sheet resistance for the intrinsic silicon substrate. Low-temperature Hall measurements and secondary ion mass spectrometry indicate that phosphorus is the only electrically active dopant after the molecular monolayer doping. However, during this process, at least 20% of the phosphorus dopants are electrically deactivated. The deep-level transient spectroscopy shows that carbon-related defects are responsible for such deactivation.

Influence of calcium on ceramide-1-phosphate monolayers

Directory of Open Access Journals (Sweden)

Joana S. L. Oliveira

2016-02-01

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.

Phases and phase transition in insoluble and adsorbed monolayers of amide amphiphiles: Specific characteristics of the condensed phases.

Science.gov (United States)

Vollhardt, D

2015-08-01

For understanding the role of amide containing amphiphiles in inherently complex biological processes, monolayers at the air-water interface are used as simple biomimetic model systems. The specific characteristics of the condensed phases and phase transition in insoluble and adsorbed monolayers of amide amphiphiles are surveyed to highlight the effect of the chemical structure of the amide amphiphiles on the interfacial interactions in model monolayers. The mesoscopic topography and/or two-dimensional lattice structures of selected amino acid amphiphiles, amphiphilic N-alkylaldonamide, amide amphiphiles with specific tailored headgroups, such as amide amphiphiles based on derivatized ethanolamine, e.g. acylethanolamines (NAEs) and N-,O-diacylethanolamines (DAEs) are presented. Special attention is devoted the dominance of N,O-diacylated ethanolamine in mixed amphiphilic acid amide monolayers. The evidence that a first order phase transition can occur in adsorption layers and that condensed phase domains of mesoscopic scale can be formed in adsorption layers was first obtained on the basis of the experimental characteristics of a tailored amide amphiphile. New thermodynamic and kinetic concepts for the theoretical description of the characteristics of amide amphiphile's monolayers were developed. In particular, the equation of state for Langmuir monolayers generalized for the case that one, two or more phase transitions occur, and the new theory for phase transition in adsorbed monolayers are experimentally confirmed at first by amide amphiphile monolayers. Despite the significant progress made towards the understanding the model systems, these model studies are still limited to transfer the gained knowledge to biological systems where the fundamental physical principles are operative in the same way. The study of biomimetic systems, as described in this review, is only a first step in this direction. Copyright © 2014 Elsevier B.V. All rights reserved.

Electrical resistivity of monolayers and bilayers of alkanethiols in tunnel junction with gate electrode

International Nuclear Information System (INIS)

York, Roger L.; Nacionales, David; Slowinski, Krzysztof

2005-01-01

The tunneling resistances of monolayers and bilayers of n-alkanethiols in macroscopic Hg-Hg junctions with an electrochemical gate are reported. The resistances near zero bias calculated per 1 hydrocarbon chain vary from (5 ± 4) x 10 12 Ω for n-nonanethiol to (4 ± 2) x 10 16 Ω for n-octadecanethiol. These values indicate that monolayers of hydrocarbons in Hg-Hg junctions are substantially more resistive as compared to measurements employing microscopic tunnel junctions. The tunneling resistances of monolayer junctions are approximately 1 order of magnitude larger than those of bilayer junctions containing the same number of atoms indicating inefficient electronic coupling across the non-bonded -CH 3 |Hg interface. The symmetric current-voltage curves observed for the asymmetric junctions of Hg-S-(CH 2 ) n -CH 3 |Hg type suggest that these junctions do not behave as molecular diodes. Additional experimental evidence for the nature of the -CH 3 |Hg interface in the Hg-S-(CH 2 ) n -CH 3 |Hg junction is also presented

Advanced chemistry of monolayers at interfaces trends in methodology and technology

CERN Document Server

Imae, Toyoko

2007-01-01

Advanced Chemistry of Monolayers at Interfaces describes the advanced chemistry of monolayers at interfaces. Focusing on the recent trends of methodology and technology, which are indispensable in monolayer science. They are applied to monolayers of surfactants, amphiphiles, polymers, dendrimers, enzymes, and proteins, which serve many uses.Introduces the methodologies of scanning probe microscopy, surface force instrumentation, surface spectroscopy, surface plasmon optics, reflectometry, and near-field scanning optical microscopy. Modern interface reaction method, lithographic tech

Pressure-dependent optical and vibrational properties of monolayer molybdenum disulfide

KAUST Repository

Nayak, Avinash P.; Pandey, Tribhuwan; Voiry, Damien; Liu, Jin; Moran, Samuel T.; Sharma, Ankit; Tan, Cheng; Chen, Changhsiao; Li, Lain-Jong; Chhowalla, Manish U.; Lin, Jungfu; Singh, Abhishek Kumar; Akinwande, Deji

2015-01-01

vibrational dynamics of the distorted monolayer 1T-MoS2 (1T′) and the monolayer 2H-MoS2 via a diamond anvil cell (DAC) and density functional theory (DFT) calculations. The direct optical band gap of the monolayer 2H-MoS2 increases by 11.7% from 1.85 to 2.08 e

Highly anisotropic electronic transport properties of monolayer and bilayer phosphorene from first principles

Energy Technology Data Exchange (ETDEWEB)

Jin, Zhenghe; Mullen, Jeffrey T. [Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Kim, Ki Wook, E-mail: kwk@ncsu.edu [Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Department of Physics, North Carolina State University, Raleigh, North Carolina 27695 (United States)

2016-08-01

The intrinsic carrier transport dynamics in phosphorene is theoretically examined. Utilizing a density functional theory treatment, the low-field mobility and the saturation velocity are characterized for both electrons and holes in the monolayer and bilayer structures. The analysis clearly elucidates the crystal orientation dependence manifested through the anisotropic band structure and the carrier-phonon scattering rates. In the monolayer, the hole mobility in the armchair direction is estimated to be approximately five times larger than in the zigzag direction at room temperature (460 cm{sup 2}/V s vs. 90 cm{sup 2}/V s). The bilayer transport, on the other hand, exhibits a more modest anisotropy with substantially higher mobilities (1610 cm{sup 2}/V s and 760 cm{sup 2}/V s, respectively). The calculations on the conduction-band electrons indicate a comparable dependence while the characteristic values are generally smaller by about a factor of two. The variation in the saturation velocity is found to be less pronounced. With the anticipated superior performance and the diminished anisotropy, few-layer phosphorene offers a promising opportunity particularly in p-type applications.

Electrochemical characterization of a 1,8-octanedithiol self-assembled monolayer (ODT-SAM) on a Au(111) single crystal electrode

Energy Technology Data Exchange (ETDEWEB)

Garcia-Raya, Daniel; Madueno, Rafael; Sevilla, Jose Manuel; Blazquez, Manuel; Pineda, Teresa [Departamento de Quimica Fisica y Termodinamica Aplicada, Universidad de Cordoba, Campus de Rabanales, Cordoba (Spain)

2008-11-15

Recently, it has becoming increasingly important to control the organization of self-assembled monolayers (SAMs) of {omega}-functionalized thiols for its potential applications in the construction of more complex molecular architectures. In this paper, we report on the spontaneous formation of a SAM of octanedithiol (ODT) as a function of the modification time. Electrochemical techniques such as cyclic voltammetry, double layer capacitance and electrochemical impedance spectroscopy are used for the characterization of this monolayer. The increase in modification time brings about changes in the octanedithiol self-assembled monolayer (ODT-SAM) reductive desorption voltammograms that indicate an evolution toward a more ordered and compact monolayer. This trend has also been found by following the changes in the electron transfer processes of the redox probe K{sub 3}Fe(CN){sub 6}. In fact, the ODT-SAM formed at low-modification time does not significantly perturb the electrochemical response as it is typical of either a low coverage or of the presence of large defects in the layer. Upon increasing the modification time, the voltammograms of the redox probe adopt a sigmoidal shape indicating the existence of pinholes in the monolayer distributed as an array of microelectrodes. The surface coverage as well as the size and distribution of these pinholes have been determined by the impedance technique that gives a more reliable evaluation of these monolayer structural parameters. (author)

Penta-P2X (X=C, Si) monolayers as wide-bandgap semiconductors: A first principles prediction

Science.gov (United States)

Naseri, Mosayeb; Lin, Shiru; Jalilian, Jaafar; Gu, Jinxing; Chen, Zhongfang

2018-06-01

By means of density functional theory computations, we predicted two novel two-dimensional (2D) nanomaterials, namely P2X (X=C, Si) monolayers with pentagonal configurations. Their structures, stabilities, intrinsic electronic, and optical properties as well as the effect of external strain to the electronic properties have been systematically examined. Our computations showed that these P2C and P2Si monolayers have rather high thermodynamic, kinetic, and thermal stabilities, and are indirect semiconductors with wide bandgaps (2.76 eV and 2.69 eV, respectively) which can be tuned by an external strain. These monolayers exhibit high absorptions in the UV region, but behave as almost transparent layers for visible light in the electromagnetic spectrum. Their high stabilities and exceptional electronic and optical properties suggest them as promising candidates for future applications in UV-light shielding and antireflection layers in solar cells.

Enhanced piezoelectricity of monolayer phosphorene oxides: a theoretical study.

Science.gov (United States)

Yin, Huabing; Zheng, Guang-Ping; Gao, Jingwei; Wang, Yuanxu; Ma, Yuchen

2017-10-18

Two-dimensional (2D) piezoelectric materials have potential applications in miniaturized sensors and energy conversion devices. In this work, using first-principles simulations at different scales, we systematically study the electronic structures and piezoelectricity of a series of 2D monolayer phosphorene oxides (POs). Our calculations show that the monolayer POs have tunable band gaps along with remarkable piezoelectric properties. The calculated piezoelectric coefficient d 11 of 54 pm V -1 in POs is much larger than those of 2D transition metal dichalcogenide monolayers and the widely used bulk α-quartz and AlN, and almost reaches the level of the piezoelectric effect in recently discovered 2D GeS. Furthermore, two other considerable piezoelectric coefficients, i.e., d 31 and d 26 with values of -10 pm V -1 and 21 pm V -1 , respectively, are predicted in some monolayer POs. We also examine the correlation between the piezoelectric coefficients and energy stability. The enhancement of piezoelectricity for monolayer phosphorene by oxidation will broaden the applications of phosphorene and phosphorene derivatives in nano-sized electronic and piezotronic devices.

Monolayer arrangement of fatty hydroxystearic acids on graphite: Influence of hydroxyl groups

Energy Technology Data Exchange (ETDEWEB)

Medina, S. [Laboratorio de Rayos-X, Centro de Investigación Tecnología e Innovación, de la Universidad de Sevilla (CITIUS), Universidad de Sevilla, Avenida Reina Mercedes, 4B. 41012, Sevilla (Spain); Benítez, J.J.; Castro, M.A. [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain); Cerrillos, C. [Servicio de Microscopía, Centro de Investigación Tecnología e Innovación, de la Universidad de Sevilla (CITIUS), Universidad de Sevilla, Avenida Reina Mercedes, 4B. 41012, Sevilla (Spain); Millán, C. [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain); Alba, M.D., E-mail: alba@icmse.csic.es [Instituto de Ciencia de Materiales de Sevilla, Consejo Superior de Investigaciones Científicas-Universidad de Sevilla, Avenida Américo Vespucio, 49. 41092, Sevilla (Spain)

2013-07-31

Previous studies have indicated that long-chain linear carboxylic acids form commensurate packed crystalline monolayers on graphite even at temperatures above their melting point. This study examines the effect on the monolayer formation and structure of adding one or more secondary hydroxyl, functional groups to the stearic acid skeleton (namely, 12-hydroxystearic and 9,10-dihydroxystearic acid). Moreover, a comparative study of the monolayer formation on recompressed and monocrystalline graphite has been performed through X-ray diffraction (XRD) and Scanning Tunneling Microscopy (STM), respectively. The Differential Scanning Calorimetry (DSC) and XRD data were used to confirm the formation of solid monolayers and XRD data have provided a detailed structural analysis of the monolayers in good correspondence with obtained STM images. DSC and XRD have demonstrated that, in stearic acid and 12-hydroxystearic acid adsorbed onto graphite, the monolayer melted at a higher temperature than the bulk form of the carboxylic acid. However, no difference was observed between the melting point of the monolayer and the bulk form for 9,10-dihydroxystearic acid adsorbed onto graphite. STM results indicated that all acids on the surface have a rectangular p2 monolayer structure, whose lattice parameters were uniaxially commensurate on the a-axis. This structure does not correlate with the initial structure of the pure compounds after dissolving, but it is conditioned to favor a) hydrogen bond formation between the carboxylic groups and b) formation of hydrogen bonds between secondary hydroxyl groups, if spatially permissible. Therefore, the presence of hydroxyl functional groups affects the secondary structure and behavior of stearic acid in the monolayer. - Highlights: • Hydroxyl functional groups affect structure and behavior of acids in the monolayer. • Acids on the surface have a rectangular p2 monolayer structure. • Lattice parameters of acids are uniaxially

Highly Surface-Active Ca(OH)2 Monolayer as a CO2 Capture Material.

Science.gov (United States)

Özçelik, V Ongun; Gong, Kai; White, Claire E

2018-03-14

Greenhouse gas emissions originating from fossil fuel combustion contribute significantly to global warming, and therefore the design of novel materials that efficiently capture CO 2 can play a crucial role in solving this challenge. Here, we show that reducing the dimensionality of bulk crystalline portlandite results in a stable monolayer material, named portlandene, that is highly effective at capturing CO 2 . On the basis of theoretical analysis comprised of ab initio quantum mechanical calculations and force-field molecular dynamics simulations, we show that this single-layer phase is robust and maintains its stability even at high temperatures. The chemical activity of portlandene is seen to further increase upon defect engineering of its surface using vacancy sites. Defect-containing portlandene is capable of separating CO and CO 2 from a syngas (CO/CO 2 /H 2 ) stream, yet is inert to water vapor. This selective behavior and the associated mechanisms have been elucidated by examining the electronic structure, local charge distribution, and bonding orbitals of portlandene. Additionally, unlike conventional CO 2 capturing technologies, the regeneration process of portlandene does not require high temperature heat treatment because it can release the captured CO 2 by application of a mild external electric field, making portlandene an ideal CO 2 capturing material for both pre- and postcombustion processes.

Kohn-Luttinger superconductivity in monolayer and bilayer semimetals with the Dirac spectrum

International Nuclear Information System (INIS)

Kagan, M. Yu.; Mitskan, V. A.; Korovushkin, M. M.

2014-01-01

The effect of Coulomb interaction in an ensemble of Dirac fermions on the formation of superconducting pairing in monolayer and bilayer doped graphene is studied using the Kohn-Luttinger mechanism disregarding the Van der Waals potential of the substrate and impurities. The electronic structure of graphene is described using the Shubin-Vonsovsky model taking into account the intratomic, interatomic, and interlayer (in the case of bilayer graphene) Coulomb interactions between electrons. The Cooper instability is determined by solving the Bethe-Saltpeter integral equation. The renormalized scattering amplitude is obtained with allowance for the Kohn-Luttinger polarization contributions up to the second order of perturbation theory in the Coulomb interaction. It plays the role of effective interaction in the Bethe-Salpeter integral equation. It is shown that the allowance for the Kohn-Luttinger renormalizations as well as intersite Coulomb interaction noticeably affects the competition between the superconducting phases with the f-wave and d + id-wave symmetries of the order parameter. It is demonstrated that the superconducting transition temperature for an idealized graphene bilayer with significant interlayer Coulomb interaction between electrons is noticeably higher than in the monolayer case

Exciton Binding Energy of Monolayer WS2

Science.gov (United States)

Zhu, Bairen; Chen, Xi; Cui, Xiaodong

2015-03-01

The optical properties of monolayer transition metal dichalcogenides (TMDC) feature prominent excitonic natures. Here we report an experimental approach to measuring the exciton binding energy of monolayer WS2 with linear differential transmission spectroscopy and two-photon photoluminescence excitation spectroscopy (TP-PLE). TP-PLE measurements show the exciton binding energy of 0.71 +/- 0.01 eV around K valley in the Brillouin zone.

GeAs and SiAs monolayers: Novel 2D semiconductors with suitable band structures

Science.gov (United States)

Zhou, Liqin; Guo, Yu; Zhao, Jijun

2018-01-01

Two dimensional (2D) materials provide a versatile platform for nanoelectronics, optoelectronics and clean energy conversion. Based on first-principles calculations, we propose a novel kind of 2D materials - GeAs and SiAs monolayers and investigate their atomic structure, thermodynamic stability, and electronic properties. The calculations show that monolayer GeAs and SiAs sheets are energetically and dynamically stable. Their small interlayer cohesion energies (0.191 eV/atom for GeAs and 0.178 eV/atom for SiAs) suggest easy exfoliation from the bulk solids that exist in nature. As 2D semiconductors, GeAs and SiAs monolayers possess band gap of 2.06 eV and 2.50 eV from HSE06 calculations, respectively, while their band gap can be further engineered by the number of layers. The relatively small and anisotropic carrier effective masses imply fast electric transport in these 2D semiconductors. In particular, monolayer SiAs is a direct gap semiconductor and a potential photocatalyst for water splitting. These theoretical results shine light on utilization of monolayer or few-layer GeAs and SiAs materials for the next-generation 2D electronics and optoelectronics with high performance and satisfactory stability.

Highly Sensitive Aluminium(III) Ion Sensor Based on a Self-assembled Monolayer on a Gold Nanoparticles Modified Screen-printed Carbon Electrode.

Science.gov (United States)

See, Wong Pooi; Heng, Lee Yook; Nathan, Sheila

2015-01-01

A new approach for the development of a highly sensitive aluminium(III) ion sensor via the preconcentration of aluminium(III) ion with a self-assembled monolayer on a gold nanoparticles modified screen-printed carbon electrode and current mediation by potassium ferricyanide redox behavior during aluminium(III) ion binding has been attempted. A monolayer of mercaptosuccinic acid served as an effective complexation ligand for the preconcentration of trace aluminium; this led to an enhancement of aluminium(III) ion capture and thus improved the sensitivity of the sensor with a detection limit of down to the ppb level. Under the optimum experimental conditions, the sensor exhibited a wide linear dynamic range from 0.041 to 12.4 μM. The lower detection limit of the developed sensor was 0.037 μM (8.90 ppb) using a 10 min preconcentration time. The sensor showed excellent selectivity towards aluminium(III) ion over other interference ions.

Monolayer assembly and striped architecture of Co nanoparticles on organic functionalized Si surfaces

Energy Technology Data Exchange (ETDEWEB)

Bae, S.-S.; Lim, D.K.; Park, J.-I.; Kim, S. [Korea Advanced Institute of Science and Technology, Department of Chemistry and School of Molecular Science (BK 21), Daejeon (Korea); Cheon, J. [Yonsei University, Department of Chemistry, College of Sciences, Seoul (Korea); Jeon, I.C. [Chonbuk National University, Department of Chemistry, College of Natural Sciences, Chonbuk (Korea)

2005-03-01

We present a new strategy to fabricate a monolayer assembly of Br-terminated Co nanoparticles on functionalized Si surfaces by using chemical covalent bonding and microcontact printing method. Self-assembled monolayers (SAMs) of the Co nanoparticles formed on the hydroxyl-terminated Si surface exhibit two-dimensional island networks with locally ordered arrays via covalent linkage between nanoparticles and surface. On the other hand, SAMs of the nanoparticles on the aminopropyl-terminated Si surface show an individual and random distribution over an entire surface. Furthermore, we have fabricated striped architectures of Co nanoparticles using a combination of microcontact printing and covalent linkage. Microcontact printing of octadecyltrichlorosilane and selective covalent linkage between nanoparticles and functionalized Si surfaces lead to a hybrid nanostructure with selectively assembled nanoparticles stripes on the patterned functionalized Si surfaces. (orig.)

Thermal ripples in model molybdenum disulfide monolayers

Energy Technology Data Exchange (ETDEWEB)

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)

2017-01-15

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)

Direct imaging by atomic force microscopy of surface-localized self-assembled monolayers on a cuprate superconductor and surface X-ray scattering analysis of analogous monolayers on the surface of water

DEFF Research Database (Denmark)

Schougaard, Steen B.; Reitzel, Niels; Bjørnholm, Thomas

2007-01-01

A self-assembled monolayer of CF3(CF2)(3)(CH2)(11)NH2 atop the (001) surface of the high-temperature superconductor YBa2Cu3O7-x was imaged by atomic force microscopy (AFM). The AFM images provide direct 2D-structural evidence for the epitaxial 5.5 angstrom square root 2 x root 2R45 degrees unit...... was studied by grazing-incidence X-ray diffraction and specular X-ray reflectivity. Structural differences and similarities between the water-supported and superconductor-localized monolayers are discussed....

Cooperative light-induced molecular movements of highly ordered azobenzene self-assembled monolayers.

Science.gov (United States)

Pace, Giuseppina; Ferri, Violetta; Grave, Christian; Elbing, Mark; von Hänisch, Carsten; Zharnikov, Michael; Mayor, Marcel; Rampi, Maria Anita; Samorì, Paolo

2007-06-12

Photochromic systems can convert light energy into mechanical energy, thus they can be used as building blocks for the fabrication of prototypes of molecular devices that are based on the photomechanical effect. Hitherto a controlled photochromic switch on surfaces has been achieved either on isolated chromophores or within assemblies of randomly arranged molecules. Here we show by scanning tunneling microscopy imaging the photochemical switching of a new terminally thiolated azobiphenyl rigid rod molecule. Interestingly, the switching of entire molecular 2D crystalline domains is observed, which is ruled by the interactions between nearest neighbors. This observation of azobenzene-based systems displaying collective switching might be of interest for applications in high-density data storage.

Single Atomically Sharp Lateral Monolayer p-n Heterojunction Solar Cells with Extraordinarily High Power Conversion Efficiency

KAUST Repository

Tsai, Meng-Lin; Li, Ming-yang; Duran Retamal, Jose Ramon; Lam, Kai-Tak; Lin, Yung-Chang; Suenaga, Kazu; Chen, Lih-Juann; Liang, Gengchiau; Li, Lain-Jong; He, Jr-Hau

2017-01-01

The recent development of 2D monolayer lateral semiconductor has created new paradigm to develop p-n heterojunctions. Albeit, the growth methods of these heterostructures typically result in alloy structures at the interface, limiting

The interaction of insulin, glucose, and insulin-glucose mixtures with a phospholipid monolayer.

Science.gov (United States)

Shigenobu, Hayato; McNamee, Cathy E

2012-12-15

We determined how glucose or insulin interacts with a phospholipid monolayer at the air/water interface and explained these mechanisms from a physico-chemical point of view. The 1,2-dipalmitoyl-2-sn-glycero-3-phosphatidylcholine (DPPC) monolayer at an air/water interface acted as a model membrane, which allowed the effect of the molecular packing density in the monolayer on the interactions to be determined. The interaction of glucose, insulin, and a mixture of glucose and insulin to the DPPC monolayer were investigated via surface pressure-area per molecule Langmuir isotherms and fluorescence microscopy. Glucose adsorbed to the underside of the DPPC monolayer, while insulin was able to penetrate through the monolayer when the phospholipid molecules were not densely packed. The presence of a mixture of insulin and glucose affected the molecular packing in the DPPC monolayer differently than the pure insulin or glucose solutions, and the glucose-insulin mixture was seen to be able to penetrate through the monolayer. These results indicated that glucose and insulin interact with one another, giving a material that may then transported through a pore in the monolayer or through the spaces between the molecules of the monolayer. Copyright © 2012 Elsevier Inc. All rights reserved.

Studying the influence of substrate conductivity on the optoelectronic properties of quantum dots langmuir monolayer

Science.gov (United States)

Al-Alwani, Ammar J.; Chumakov, A. S.; Begletsova, N. N.; Shinkarenko, O. A.; Markin, A. V.; Gorbachev, I. A.; Bratashov, D. N.; Gavrikov, M. V.; Venig, S. B.; Glukhovskoy, E. G.

2018-04-01

The formation of CdSe quantum dots (QDs) monolayers was studied by Langmuir Blodgett method. The fluorescence (PL) spectra of QD monolayers were investigated at different substrate type (glass, silicon and ITO glass) and the influence of graphene sheets layer (as a conductive surface) on the QDs properties has also been studied. The optoelectronic properties of QDs can be tuned by deposition of insulating nano-size layers of the liquid crystal between QDs and conductive substrate. The monolayer of QDs transferred on conductive surface (glass with ITO) has lowest intensity of PL spectra due to quenching effect. The PL intensity of QDs could be tuned by using various type of substrates or/and by transformed high conductive layer. Also the photooxidation processes of CdSe QDs monolayer on the solid surface can be controlled by selection of suitable substrate. The current-voltage (I–V) characteristics of QDs thin film on ITO surface was studied using scanning tunneling microscope (STM).

High-T{sub c} superconductivity in monolayer FeSe on SrTiO{sub 3} via interface-induced small-q electron-phonon coupling

Energy Technology Data Exchange (ETDEWEB)

Aperis, Alexandros; Oppeneer, Peter M. [Uppsala University (Sweden)

2016-07-01

A monolayer of FeSe deposited on SrTiO{sub 3} becomes superconducting at temperatures that exceed T{sub c}=100 K, as compared to a bulk T{sub c} of 8 K. Recent ARPES measurements have provided strong evidence that an interfaced-induced electron-phonon interaction between FeSe electrons and SrTiO{sub 3} phonons plays a decisive role in this phenomenon. However, the mechanism that drives this tantalizing high-T{sub c} boost is still unclear. Here, we examine the recent experimental findings using fully anisotropic, full bandwidth multiband Eliashberg calculations focusing on the superconducting state of FeSe/STO. We use a realistic ten band tight-binding band structure for the electrons of monolayer FeSe and study how the suggested interface-induced small-q electron-phonon interaction mediates superconductivity. Our calculations produce a high-T{sub c} s-wave superconducting state with the experimentally resolved momentum dependence. Further, we calculate the normal metal/insulator/superconductor tunneling spectrum and identify fingerprints of the interface-induced phonon mechanism.

Mechanical characterization of disordered and anisotropic cellular monolayers

Science.gov (United States)

Nestor-Bergmann, Alexander; Johns, Emma; Woolner, Sarah; Jensen, Oliver E.

2018-05-01

We consider a cellular monolayer, described using a vertex-based model, for which cells form a spatially disordered array of convex polygons that tile the plane. Equilibrium cell configurations are assumed to minimize a global energy defined in terms of cell areas and perimeters; energy is dissipated via dynamic area and length changes, as well as cell neighbor exchanges. The model captures our observations of an epithelium from a Xenopus embryo showing that uniaxial stretching induces spatial ordering, with cells under net tension (compression) tending to align with (against) the direction of stretch, but with the stress remaining heterogeneous at the single-cell level. We use the vertex model to derive the linearized relation between tissue-level stress, strain, and strain rate about a deformed base state, which can be used to characterize the tissue's anisotropic mechanical properties; expressions for viscoelastic tissue moduli are given as direct sums over cells. When the base state is isotropic, the model predicts that tissue properties can be tuned to a regime with high elastic shear resistance but low resistance to area changes, or vice versa.

The interaction of trace heavy metal with lipid monolayer in the sea surface microlayer.

Science.gov (United States)

Li, Siyang; Du, Lin; Tsona, Narcisse T; Wang, Wenxing

2018-04-01

Lipid molecules and trace heavy metals are enriched in sea surface microlayer and can be transferred into the sea spray aerosol. To better understand their impact on marine aerosol generation and evolution, we investigated the interaction of trace heavy metals including Fe 3+ , Pb 2+ , Zn 2+ , Cu 2+ , Ni 2+ , Cr 3+ , Cd 2+ , and Co 2+ , with dipalmitoylphosphatidylcholine (DPPC) monolayers at the air-water interface. Phase behavior of the DPPC monolayer on heavy metal solutions was probed with surface pressure-area (π-A) isotherms. The conformation order and orientation of DPPC alkyl chains were characterized by infrared reflection-absorption spectroscopy (IRRAS). The π-A isotherms show that Zn 2+ and Fe 3+ strongly interact with DPPC molecules, and induce condensation of the monolayers in a concentration-dependent manner. IRRAS spectra show that the formation of cation-DPPC complex gives rise to conformational changes and immobilization of the headgroups. The current results suggest that the enrichment of Zn 2+ in sea spray aerosols is due to strong binding to the DPPC film. The interaction of Fe 3+ with DPPC monolayers can significantly influence their surface organizations through the formation of lipid-coated particles. These results suggest that the sea surface microlayer is capable of accumulating much higher amounts of these metals than the subsurface water. The organic and metal pollutants may transfer into the atmosphere by this interaction. Copyright © 2017 Elsevier Ltd. All rights reserved.

Interactions between an anticancer drug - edelfosine - and cholesterol in Langmuir monolayers

International Nuclear Information System (INIS)

Wiecek, Agata; Dynarowicz-Latka, Patrycja; Minones, J.; Conde, Olga; Casas, Matilde

2008-01-01

Edelfosine (1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine, abbr. Et-18-OCH 3 ) is a new generation anticancer drug based on a phospholipids-like structure. Since its mechanism of action is believed to be related to the lipids of cellular membrane, we have investigated the interactions between edelfosine and main mammalian sterol: cholesterol, using the Langmuir monolayer technique. The interactions have been analyzed by comparing the experimental curves with theoretical ones, obtained basing on the additivity rule. The observed contraction together with negative deviations from ideality observed on the mean molecular area (A 12 ) vs film composition plots proves the existence of strong attractive forces between edelfosine and cholesterol, which have been quantified with the excess free energy of mixing (ΔG exc ) values, calculated from the surface pressure-area isotherms datapoints. The most negative values of ΔG exc have been found for the mixture of equimolar composition, proving its highest thermodynamic stability and the existence of the strongest interactions between film components. Thus, it has been postulated that at the surface edelfosine and cholesterol form stable complexes of 1:1 stoichiometry. The analysis of the collapse pressure values for the investigated mixed monolayers proves that films of edelfosine mole fraction ≤ 0.5 are miscible within the whole range of surface pressures, while monolayers richer in edelfosine mix in the pressure region below ca. 37.6 mN/m, which corresponds to the collapse of pure edelfosine monolayer. At this very surface pressure, edelfosine is expelled from the mixed monolayer and the remaining film is composed by surface complexes of high stability. The hypothesis of complex formation explains the results performed in vitro on cell cultures, indicating that the increase of cholesterol content significantly reduces the uptake of edelfosine

Characterization of self-assembled monolayers on a ruthenium surface

NARCIS (Netherlands)

Shaheen, Amrozia; Sturm, Jacobus Marinus; Ricciardi, R.; Huskens, Jurriaan; Lee, Christopher James; Bijkerk, Frederik

2017-01-01

We have modified and stabilized the ruthenium surface by depositing a self-assembled monolayer (SAM) of 1-hexadecanethiol on a polycrystalline ruthenium thin film. The growth mechanism, dynamics, and stability of these monolayers were studied. SAMs, deposited under ambient conditions, on

Heterointerface Screening Effects between Organic Monolayers and Monolayer Transition Metal Dichalcogenides

KAUST Repository

Zheng, Yu Jie; Huang, Yu Li; Chen, Yifeng; Zhao, Weijie; Eda, Goki; Spataru, Catalin D.; Zhang, Wenjing; Chang, Yung-Huang; Li, Lain-Jong; Chi, Dongzhi; Quek, Su Ying; Wee, Andrew Thye Shen

2016-01-01

© 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.

Heterointerface Screening Effects between Organic Monolayers and Monolayer Transition Metal Dichalcogenides

KAUST Repository

Zheng, Yu Jie

2016-01-21

© 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.

Ordered array of CoPc-vacancies filled with single-molecule rotors

Science.gov (United States)

Xie, Zheng-Bo; Wang, Ya-Li; Tao, Min-Long; Sun, Kai; Tu, Yu-Bing; Yuan, Hong-Kuan; Wang, Jun-Zhong

2018-05-01

We report the highly ordered array of CoPc-vacancies and the single-molecule rotors inside the vacancies. When CoPc molecules are deposited on Cd(0001) at low-temperature, three types of molecular vacancies appeared randomly in the CoPc monolayer. Annealing the sample to higher temperature leads to the spontaneous phase separation and self-organized arrangement of the vacancies. Highly ordered arrays of two-molecule vacancies and single-molecule vacancies have been obtained. In particular, there is a rotating CoPc molecule inside each single-molecule vacancy, which constitutes the array of single-molecule rotors. These results provide a new routine to fabricate the nano-machines on a large scale.

Suitability of using monolayered and multilayered emulsions for microencapsulation of ω-3 fatty acids by spray drying

DEFF Research Database (Denmark)

Jiménez-Martín, Estefanía; Gharsallaoui, Adem; Pérez-Palacios, Trinidad

2015-01-01

Microencapsulation of ω-3 fatty acids by spray drying was studied using both monolayered (lecithin) and multilayered (lecithin-chitosan) fish oil emulsions with maltodextrin as wall material. Stability of the multilayered emulsions was higher than the monolayered ones, and increased...... with the highest concentration of chitosan (1 % w/w), being related with lower detection of TBARS at high storage temperatures. Overall, this study shows the suitability of microencapsulating ω-3 fatty acids by spray drying using both monolayered and multilayered fish oil emulsions with maltodextrin as wall...... material. Multilayered microcapsules prepared with lecithin-chitosan emulsions provide a great protective effect against lipid oxidation of fish oil during storage at moderate to high temperatures (30 °C and 60 °C). These multilayered microcapsules could be therefore successfully used as a fish oil...

Diverse carrier mobility of monolayer BNCx: A combined density functional theory and Boltzmann transport theory study.

Science.gov (United States)

Wu, Tao; Deng, Kaiming; Deng, Wei-Qiao; Lu, Ruifeng

2017-09-19

BNCX monolayer as a kind of two-dimensional material has numerous chemical atomic ratios and arrangements with different electronic structures. Via calculations on the basis of density functional theory and Boltzmann transport theory under deformation potential approximation, the band structures and carrier mobilities of BNCX (x=1,2,3,4) nanosheets are systematically investigated. The calculated results show that BNC2-1 is a material with very small band gap (0.02 eV) among all the structures while other BNCX monolayers are semiconductors with band gap ranging from 0.51 to 1.32 eV. The carrier mobility of BNCX varies considerably from tens to millions of cm2 V-1 s-1. For BNC2-1, the hole mobility and electron mobility along both x and y directions can reach 105 orders of magnitude, which is similar to the carrier mobility of graphene. Besides, all studied BNCX monolayers obviously have anisotropic hole mobility and electron mobility. In particular, for semiconductor BNC4, its hole mobility along y direction and electron mobility along x direction unexpectedly reach 106 orders of magnitude, even higher than that of graphene. Our findings suggest that BNCX layered materials with proper ratio and arrangement of carbon atoms will possess desirable charge transport properties, exhibiting potential applications in nanoelectronic devices. © 2017 IOP Publishing Ltd.

Pt Monolayer Shell on Nitrided Alloy Core—A Path to Highly Stable Oxygen Reduction Catalyst

Directory of Open Access Journals (Sweden)

Jue Hu

2015-07-01

Full Text Available The inadequate activity and stability of Pt as a cathode catalyst under the severe operation conditions are the critical problems facing the application of the proton exchange membrane fuel cell (PEMFC. Here we report on a novel route to synthesize highly active and stable oxygen reduction catalysts by depositing Pt monolayer on a nitrided alloy core. The prepared PtMLPdNiN/C catalyst retains 89% of the initial electrochemical surface area after 50,000 cycles between potentials 0.6 and 1.0 V. By correlating electron energy-loss spectroscopy and X-ray absorption spectroscopy analyses with electrochemical measurements, we found that the significant improvement of stability of the PtMLPdNiN/C catalyst is caused by nitrogen doping while reducing the total precious metal loading.

Low-cost fabrication and polar-dependent switching uniformity of memory devices using alumina interfacial layer and Ag nanoparticle monolayer

Directory of Open Access Journals (Sweden)

Peng Xia

2017-11-01

Full Text Available A facile and low-cost process was developed for fabricating write-once-read-many-times (WORM Cu/Ag NPs/Alumina/Al memory devices, where the alumina passivation layer formed naturally in air at room temperature, whereas the Ag nanoparticle monolayer was in situ prepared through thermal annealing of a 4.5 nm Ag film in air at 150°C. The devices exhibit irreversible transition from initial high resistance (OFF state to low resistance (ON state, with ON/OFF ratio of 107, indicating the introduction of Ag nanoparticle monolayer greatly improves ON/OFF ratio by four orders of magnitude. The uniformity of threshold voltages exhibits a polar-dependent behavior, and a narrow range of threshold voltages of 0.40 V among individual devices was achieved upon the forward voltage. The memory device can be regarded as two switching units connected in series. The uniform alumina interfacial layer and the non-uniform distribution of local electric fields originated from Ag nanoparticles might be responsible for excellent switching uniformity. Since silver ions in active layer can act as fast ion conductor, a plausible mechanism relating to the formation of filaments sequentially among the two switching units connected in series is suggested for the polar-dependent switching behavior. Furthermore, we demonstrate both alumina layer and Ag NPs monolayer play essential roles in improving switching parameters based on comparative experiments.

Low-cost fabrication and polar-dependent switching uniformity of memory devices using alumina interfacial layer and Ag nanoparticle monolayer

Science.gov (United States)

Xia, Peng; Li, Luman; Wang, Pengfei; Gan, Ying; Xu, Wei

2017-11-01

A facile and low-cost process was developed for fabricating write-once-read-many-times (WORM) Cu/Ag NPs/Alumina/Al memory devices, where the alumina passivation layer formed naturally in air at room temperature, whereas the Ag nanoparticle monolayer was in situ prepared through thermal annealing of a 4.5 nm Ag film in air at 150°C. The devices exhibit irreversible transition from initial high resistance (OFF) state to low resistance (ON) state, with ON/OFF ratio of 107, indicating the introduction of Ag nanoparticle monolayer greatly improves ON/OFF ratio by four orders of magnitude. The uniformity of threshold voltages exhibits a polar-dependent behavior, and a narrow range of threshold voltages of 0.40 V among individual devices was achieved upon the forward voltage. The memory device can be regarded as two switching units connected in series. The uniform alumina interfacial layer and the non-uniform distribution of local electric fields originated from Ag nanoparticles might be responsible for excellent switching uniformity. Since silver ions in active layer can act as fast ion conductor, a plausible mechanism relating to the formation of filaments sequentially among the two switching units connected in series is suggested for the polar-dependent switching behavior. Furthermore, we demonstrate both alumina layer and Ag NPs monolayer play essential roles in improving switching parameters based on comparative experiments.

Template-Directed Self-Assembly of Alkanethiol Monolayers: Selective Growth on Preexisting Monolayer Edges

NARCIS (Netherlands)

Sharpe, R.B.A.; Burdinski, Dirk; Huskens, Jurriaan; Zandvliet, Henricus J.W.; Reinhoudt, David; Poelsema, Bene

2007-01-01

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.

Adsorption of gas molecules on Cu impurities embedded monolayer MoS{sub 2}: A first- principles study

Energy Technology Data Exchange (ETDEWEB)

Zhao, B.; Li, C.Y. [Hubei Nuclear Solid Physics Key Laboratory, Department of Physics, Wuhan University, Wuhan 430072 (China); Liu, L.L. [Key Lab for Special Functional Materials of Ministry of Eduaction, Henan Province, Henan University, Kaifeng 475004 (China); Zhou, B.; Zhang, Q.K. [Hubei Nuclear Solid Physics Key Laboratory, Department of Physics, Wuhan University, Wuhan 430072 (China); Chen, Z.Q., E-mail: chenzq@whu.edu.cn [Hubei Nuclear Solid Physics Key Laboratory, Department of Physics, Wuhan University, Wuhan 430072 (China); Tang, Z., E-mail: ztang@ee.ecnu.edu.cn [Key Laboratory of Polar Materials and Devices, Ministry of Education of China, East China Normal University, Shanghai 200241 (China)

2016-09-30

Highlights: • Embedded Cu atom is strongly constrained on the sulfur vacancy of monolayer MoS{sub 2}. • Transition-metal Cu atom can break the chemical inactivation of MoS{sub 2} surface. • MoS{sub 2}-Cu system is a promising for future application in gas molecules sensing. - Abstract: Adsorption of small gas molecules (O{sub 2}, NO, NO{sub 2} and NH{sub 3}) on transition-metal Cu atom embedded monolayer MoS{sub 2} was investigated by first-principles calculations based on the density-functional theory (DFT). The embedded Cu atom is strongly constrained on the sulfur vacancy of monolayer MoS{sub 2} with a high diffusion barrier. The stable adsorption geometry, charge transfer and electronic structures of these gas molecules on monolayer MoS{sub 2} embedded with transition-metal Cu atom are discussed in detail. It is found that the monolayer MoS{sub 2} with embedded Cu atom can effectively capture these gas molecules with high adsorption energy. The NH{sub 3} molecule acts as electron donor after adsorption, which is different from the other gas molecules (O{sub 2}, NO, and NO{sub 2}). The results suggest that MoS{sub 2}-Cu system may be promising for future applications in gas molecules sensing and catalysis, which is similar to those of the transition-metal embedded graphene.

Covalently Attached Organic Monolayers onto Silicon Carbide from 1-Alkynes: Molecular Structure and Tribological Properties

NARCIS (Netherlands)

Pujari, S.P.; Scheres, L.M.W.; Weidner, T.; Baio, J.E.; Cohen Stuart, M.A.; Rijn, van C.J.M.; Zuilhof, H.

2013-01-01

In order to achieve improved tribological and wear properties at semiconductor interfaces, we have investigated the thermal grafting of both alkylated and fluorine-containing ((CxF2x+1)–(CH2)n-) 1-alkynes and 1-alkenes onto silicon carbide (SiC). The resulting monolayers display static water contact

A kinetic model of the formation of organic monolayers on hydrogen-terminated silicon by hydrosilation of alkenes.

Science.gov (United States)

Woods, M; Carlsson, S; Hong, Q; Patole, S N; Lie, L H; Houlton, A; Horrocks, B R

2005-12-22

We have analyzed a kinetic model for the formation of organic monolayers based on a previously suggested free radical chain mechanism for the reaction of unsaturated molecules with hydrogen-terminated silicon surfaces (Linford, M. R.; Fenter, P. M.; Chidsey, C. E. D. J. Am. Chem. Soc 1995, 117, 3145). A direct consequence of this mechanism is the nonexponential growth of the monolayer, and this has been observed spectroscopically. In the model, the initiation of silyl radicals on the surface is pseudo first order with rate constant, ki, and the rate of propagation is determined by the concentration of radicals and unreacted Si-H nearest neighbor sites with a rate constant, kp. This propagation step determines the rate at which the monolayer forms by addition of alkene molecules to form a track of molecules that constitute a self-avoiding random walk on the surface. The initiation step describes how frequently new random walks commence. A termination step by which the radicals are destroyed is also included. The solution of the kinetic equations yields the fraction of alkylated surface sites and the mean length of the random walks as a function of time. In mean-field approximation we show that (1) the average length of the random walk is proportional to (kp/ki)1/2, (2) the monolayer surface coverage grows exponentially only after an induction period, (3) the effective first-order rate constant describing the growth of the monolayer and the induction period (kt) is k = (2ki kp)1/2, (4) at long times the effective first-order rate constant drops to ki, and (5) the overall activation energy for the growth kinetics is the mean of the activation energies for the initiation and propagation steps. Monte Carlo simulations of the mechanism produce qualitatively similar kinetic plots, but the mean random walk length (and effective rate constant) is overestimated by the mean field approximation and when kp > ki, we find k approximately ki0.7kp0.3 and Ea = (0.7Ei+ 0.3Ep

Highly Ordered Periodic Au/TiO₂ Hetero-Nanostructures for Plasmon-Induced Enhancement of the Activity and Stability for Ethanol Electro-oxidation.

Science.gov (United States)

Jin, Zhao; Wang, Qiyu; Zheng, Weitao; Cui, Xiaoqiang

2016-03-02

The catalytic electro-oxidation of ethanol is the essential technique for direct alcohol fuel cells (DAFCs) in the area of alternative energy for the ability of converting the chemical energy of alcohol into the electric energy directly. Developing highly efficient and stable electrode materials with antipoisoning ability for ethanol electro-oxidation remains a challenge. A highly ordered periodic Au-nanoparticle (NP)-decorated bilayer TiO2 nanotube (BTNT) heteronanostructure was fabricated by a two-step anodic oxidation of Ti foil and the subsequent photoreduction of HAuCl4. The plasmon-induced charge separation on the heterointerface of Au/TiO2 electrode enhances the electrocatalytic activity and stability for the ethanol oxidation under visible light irradiation. The highly ordered periodic heterostructure on the electrode surface enhanced the light harvesting and led to the greater performance of ethanol electro-oxidation under irradiation compared with the ordinary Au NPs-decorated monolayer TiO2 nanotube (MTNT). This novel Au/TiO2 electrode also performed a self-cleaning property under visible light attributed to the enhanced electro-oxidation of the adsorbed intermediates. This light-driven enhancement of the electrochemical performances provides a development strategy for the design and construction of DAFCs.

A physically based compact I-V model for monolayer TMDC channel MOSFET and DMFET biosensor.

Science.gov (United States)

Rahman, Ehsanur; Shadman, Abir; Ahmed, Imtiaz; Khan, Saeed Uz Zaman; Khosru, Quazi D M

2018-06-08

In this work, a compact transport model has been developed for monolayer transition metal dichalcogenide (TMDC) channel MOSFET. The analytical model solves the Poisson's equation for the inversion charge density to get the electrostatic potential in the channel. Current is then calculated by solving the drift-diffusion equation. The model makes gradual channel approximation to simplify the solution procedure. The appropriate density of states obtained from the first principle density functional theory simulation has been considered to keep the model physically accurate for monolayer TMDC channel FET. The outcome of the model has been benchmarked against both experimental and numerical quantum simulation results with the help of a few fitting parameters. Using the compact model, detailed output and transfer characteristics of monolayer WSe 2 FET have been studied, and various performance parameters have been determined. The study confirms excellent ON and OFF state performances of monolayer WSe 2 FET which could be viable for the next generation high-speed, low power applications. Also, the proposed model has been extended to study the operation of a biosensor. A monolayer MoS 2 channel based dielectric modulated FET is investigated using the compact model for detection of a biomolecule in a dry environment.

A physically based compact I–V model for monolayer TMDC channel MOSFET and DMFET biosensor

Science.gov (United States)

Rahman, Ehsanur; Shadman, Abir; Ahmed, Imtiaz; Zaman Khan, Saeed Uz; Khosru, Quazi D. M.

2018-06-01

In this work, a compact transport model has been developed for monolayer transition metal dichalcogenide (TMDC) channel MOSFET. The analytical model solves the Poisson’s equation for the inversion charge density to get the electrostatic potential in the channel. Current is then calculated by solving the drift–diffusion equation. The model makes gradual channel approximation to simplify the solution procedure. The appropriate density of states obtained from the first principle density functional theory simulation has been considered to keep the model physically accurate for monolayer TMDC channel FET. The outcome of the model has been benchmarked against both experimental and numerical quantum simulation results with the help of a few fitting parameters. Using the compact model, detailed output and transfer characteristics of monolayer WSe2 FET have been studied, and various performance parameters have been determined. The study confirms excellent ON and OFF state performances of monolayer WSe2 FET which could be viable for the next generation high-speed, low power applications. Also, the proposed model has been extended to study the operation of a biosensor. A monolayer MoS2 channel based dielectric modulated FET is investigated using the compact model for detection of a biomolecule in a dry environment.

Structural, electronic, and magnetic properties of 3D metal trioxide and tetraoxide superhalogen cluster-doped monolayer BN

International Nuclear Information System (INIS)

Meng, Jingjing; Li, Dan; Niu, Yuan; Zhao, Hongmin; Liang, Chunjun; He, Zhiqun

2016-01-01

The structural, electronic, and magnetic properties of monolayer BN doped with 3D metal trioxide and tetraoxide superhalogen clusters are investigated using first-principle calculations. TMO_3_(_4_)-doped monolayer BN exhibits a low negative formation energy, whereas TM atoms embedded in monolayer BN show a high positive formation energy. TMO_3_(_4_) clusters are embedded more easily in monolayer BN than TM atoms. Compared with TMO_3-doped structures, TMO_4-doped structures have a higher structural stability because of their higher binding energies. Given their low negative formation energies, TMO_4-doped structures are more favored for specific applications than TMO_3-doped structures and TM atom-doped structures. Large magnetic moments per supercell and significant ferromagnetic couplings between a TM atom and neighboring B and N atoms on the BN layer were observed in all TMO_4-doped structures, except for TiO_4-doped structures. - Highlights: • TMO_3_(_4_) superhalogen clusters incorporated into monolayer BN were investigated. • TMO_3_(_4_) clusters are embedded more easily in monolayer BN than TM atoms. • TMO_4-doped structures are more favored for specific applications. • Large magnetic moments were observed in TMO_4-doped structures. • The band gap was sensitively dependent on the doped clusters.

Structural, electronic and magnetic properties of Au-based monolayer derivatives in honeycomb structure

Energy Technology Data Exchange (ETDEWEB)

Kapoor, Pooja, E-mail: pupooja16@gmail.com; Sharma, Munish; Ahluwalia, P. K. [Physics Department, Himachal Pradesh University, Shimla, Himachal Pradesh, India 171005 (India); Kumar, Ashok [Centre for Physical Sciences, School of Basic and Applied Sciences, Central University of Punjab, Bathinda, India, 151001 (India)

2016-05-23

We present electronic properties of atomic layer of Au, Au{sub 2}-N, Au{sub 2}-O and Au{sub 2}-F in graphene-like structure within the framework of density functional theory (DFT). The lattice constant of derived monolayers are found to be higher than the pristine Au monolayer. Au monolayer is metallic in nature with quantum ballistic conductance calculated as 4G{sub 0}. Similarly, Au{sub 2}-N and Au{sub 2}-F monolayers show 4G{sub 0} and 2G{sub 0} quantum conductance respectively while semiconducting nature with calculated band gap of 0.28 eV has been observed for Au{sub 2}-O monolayer. Most interestingly, half metalicity has been predicted for Au{sub 2}-N and Au{sub 2}-F monolayers. Our findings may have importance for the application of these monolayers in nanoelectronic and spintronics.

Sub-THz Characterisation of Monolayer Graphene

Directory of Open Access Journals (Sweden)

Ehsan Dadrasnia

2014-01-01

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.

Study of the interaction of lactoferricin B with phospholipid monolayers and bilayers.

Science.gov (United States)

Arseneault, Marjolaine; Bédard, Sarah; Boulet-Audet, Maxime; Pézolet, Michel

2010-03-02

Bovine lactoferricin (LfcinB) is an antimicrobial peptide obtained from the pepsin cleavage of lactoferrin. The activity of LfcinB has been extensively studied on diverse pathogens, but its mechanism of action still has to be elucidated. Because of its nonspecificity, its mode of action is assumed to be related to interactions with membranes. In this study, the interaction of LfcinB with a negatively charged monolayer of dipalmitoylphosphatidylglycerol has been investigated as a function of the surface pressure of the lipid film using in situ Brewster angle and polarization modulation infrared reflection absorption spectroscopy and on transferred monolayers by atomic force microscopy and polarized attenuated total reflection infrared spectroscopy. The data show clearly that LfcinB forms stable films at the air-water interface. They also reveal that the interaction of LfcinB with the lipid monolayer is modulated by the surface pressure. At low surface pressure, LfcinB inserts within the lipid film with its long molecular axis oriented mainly parallel to the acyl chains, while at high surface pressure, LfcinB is adsorbed under the lipid film, the hairpin being preferentially aligned parallel to the plane of the interface. The threshold for which the behavior changes is 20 mN/m. At this critical surface pressure, LfcinB interacts with the monolayer to form discoidal lipid-peptide assemblies. This structure may actually represent the mechanism of action of this peptide. The results obtained on monolayers are correlated by fluorescent probe release measurements of dye-containing vesicles made of lipids in different phases and support the important role of the lipid fluidity and packing on the activity of LfcinB.

Neutron Reflectivity Measurement for Polymer Dynamics near Graphene Oxide Monolayers

Science.gov (United States)

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.

Strain-induced band engineering in monolayer stanene on Sb(111)

Science.gov (United States)

Gou, Jian; Kong, Longjuan; Li, Hui; Zhong, Qing; Li, Wenbin; Cheng, Peng; Chen, Lan; Wu, Kehui

2017-10-01

The two-dimensional (2D) allotrope of tin with low buckled honeycomb structure named stanene is proposed to be an ideal 2D topological insulator with a nontrivial gap larger than 0.1 eV. Theoretical works also pointed out the topological property of stanene amenability to strain tuning. In this paper we report the successful realization of high quality, monolayer stanene film as well as monolayer stanene nanoribbons on Sb(111) surface by molecular-beam epitaxy, providing an ideal platform to the study of stanene. More importantly, we observed a continuous evolution of the electronic bands of stanene across the nanoribbon, related to the strain field gradient in stanene. Our work experimentally confirmed that strain is an effective method for band engineering in stanene, which is important for fundamental research and application of stanene.

Electrochemical characterization of a 1,8-octanedithiol self-assembled monolayer (ODT-SAM) on a Au(1 1 1) single crystal electrode

Energy Technology Data Exchange (ETDEWEB)

Garcia-Raya, Daniel; Madueno, Rafael; Sevilla, Jose Manuel; Blazquez, Manuel [Departamento de Quimica Fisica y Termodinamica Aplicada, Universidad de Cordoba, Campus de Rabanales, Ed. Marie Curie, E-14071 Cordoba (Spain); Pineda, Teresa [Departamento de Quimica Fisica y Termodinamica Aplicada, Universidad de Cordoba, Campus de Rabanales, Ed. Marie Curie, E-14071 Cordoba (Spain)], E-mail: tpineda@uco.es

2008-11-15

Recently, it has becoming increasingly important to control the organization of self-assembled monolayers (SAMs) of {omega}-functionalized thiols for its potential applications in the construction of more complex molecular architectures. In this paper, we report on the spontaneous formation of a SAM of octanedithiol (ODT) as a function of the modification time. Electrochemical techniques such as cyclic voltammetry, double layer capacitance and electrochemical impedance spectroscopy are used for the characterization of this monolayer. The increase in modification time brings about changes in the octanedithiol self-assembled monolayer (ODT-SAM) reductive desorption voltammograms that indicate an evolution toward a more ordered and compact monolayer. This trend has also been found by following the changes in the electron transfer processes of the redox probe K{sub 3}Fe(CN){sub 6}. In fact, the ODT-SAM formed at low-modification time does not significantly perturb the electrochemical response as it is typical of either a low coverage or of the presence of large defects in the layer. Upon increasing the modification time, the voltammograms of the redox probe adopt a sigmoidal shape indicating the existence of pinholes in the monolayer distributed as an array of microelectrodes. The surface coverage as well as the size and distribution of these pinholes have been determined by the impedance technique that gives a more reliable evaluation of these monolayer structural parameters.

Piezoelectric effect on the thermal conductivity of monolayer gallium nitride

Science.gov (United States)

Zhang, Jin

2018-01-01

Using molecular dynamics and density functional theory simulations, in this work, we find that the heat transport property of the monolayer gallium nitride (GaN) can be efficiently tailored by external electric field due to its unique piezoelectric characteristic. As the monolayer GaN possesses different piezoelectric properties in armchair and zigzag directions, different effects of the external electric field on thermal conductivity are observed when it is applied in the armchair and zigzag directions. Our further study reveals that due to the elastoelectric effect in the monolayer GaN, the external electric field changes the Young's modulus and therefore changes the phonon group velocity. Also, due to the inverse piezoelectric effect, the applied electric field induces in-plane stress in the monolayer GaN subject to a length constraint, which results in the change in the lattice anharmonicity and therefore affects the phonon mean free path. Furthermore, for relatively long GaN monolayers, the in-plane stress may trigger the buckling instability, which can significantly reduce the phonon mean free path.

Multiscale high-order/low-order (HOLO) algorithms and applications

International Nuclear Information System (INIS)

Chacón, L.; Chen, G.; Knoll, D.A.; Newman, C.; Park, H.; Taitano, W.; Willert, J.A.; Womeldorff, G.

2017-01-01

We review the state of the art in the formulation, implementation, and performance of so-called high-order/low-order (HOLO) algorithms for challenging multiscale problems. HOLO algorithms attempt to couple one or several high-complexity physical models (the high-order model, HO) with low-complexity ones (the low-order model, LO). The primary goal of HOLO algorithms is to achieve nonlinear convergence between HO and LO components while minimizing memory footprint and managing the computational complexity in a practical manner. Key to the HOLO approach is the use of the LO representations to address temporal stiffness, effectively accelerating the convergence of the HO/LO coupled system. The HOLO approach is broadly underpinned by the concept of nonlinear elimination, which enables segregation of the HO and LO components in ways that can effectively use heterogeneous architectures. The accuracy and efficiency benefits of HOLO algorithms are demonstrated with specific applications to radiation transport, gas dynamics, plasmas (both Eulerian and Lagrangian formulations), and ocean modeling. Across this broad application spectrum, HOLO algorithms achieve significant accuracy improvements at a fraction of the cost compared to conventional approaches. It follows that HOLO algorithms hold significant potential for high-fidelity system scale multiscale simulations leveraging exascale computing.

Multiscale high-order/low-order (HOLO) algorithms and applications

Energy Technology Data Exchange (ETDEWEB)

Chacón, L., E-mail: chacon@lanl.gov [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Chen, G.; Knoll, D.A.; Newman, C.; Park, H.; Taitano, W. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Willert, J.A. [Institute for Defense Analyses, Alexandria, VA 22311 (United States); Womeldorff, G. [Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2017-02-01

We review the state of the art in the formulation, implementation, and performance of so-called high-order/low-order (HOLO) algorithms for challenging multiscale problems. HOLO algorithms attempt to couple one or several high-complexity physical models (the high-order model, HO) with low-complexity ones (the low-order model, LO). The primary goal of HOLO algorithms is to achieve nonlinear convergence between HO and LO components while minimizing memory footprint and managing the computational complexity in a practical manner. Key to the HOLO approach is the use of the LO representations to address temporal stiffness, effectively accelerating the convergence of the HO/LO coupled system. The HOLO approach is broadly underpinned by the concept of nonlinear elimination, which enables segregation of the HO and LO components in ways that can effectively use heterogeneous architectures. The accuracy and efficiency benefits of HOLO algorithms are demonstrated with specific applications to radiation transport, gas dynamics, plasmas (both Eulerian and Lagrangian formulations), and ocean modeling. Across this broad application spectrum, HOLO algorithms achieve significant accuracy improvements at a fraction of the cost compared to conventional approaches. It follows that HOLO algorithms hold significant potential for high-fidelity system scale multiscale simulations leveraging exascale computing.

Total internal reflection sum-frequency generation spectroscopy and dense gold nanoparticles monolayer: a route for probing adsorbed molecules

International Nuclear Information System (INIS)

Tourillon, Gerard; Dreesen, Laurent; Volcke, Cedric; Sartenaer, Yannick; Thiry, Paul A; Peremans, Andre

2007-01-01

We show that sum-frequency generation spectroscopy performed in the total internal reflection configuration (TIR-SFG) combined with a dense gold nanoparticles monolayer allows us to study, with an excellent signal to noise ratio and high signal to background ratio, the conformation of adsorbed molecules. Dodecanethiol (DDT) was used as probe molecules in order to assess the potentialities of the approach. An enhancement of more than one order of magnitude of the SFG signals arising from the adsorbed species is observed with the TIR geometry compared to the external reflection one while the SFG non-resonant contribution remains the same for both configurations. Although further work is required to fully understand the origin of the SFG process on nanoparticles, our work opens new possibilities for studying nanostructures

Fluorinated alkyne-derived monolayers on oxide-free silicon nanowires via one-step hydrosilylation

International Nuclear Information System (INIS)

Nguyen Minh, Quyen; Pujari, Sidharam P.; Wang, Bin; Wang, Zhanhua; Haick, Hossam; Zuilhof, Han; Rijn, Cees J.M. van

2016-01-01

Highlights: • Oxide-free H-terminated silicon nanowires undergo efficient surface modification by reaction with fluorinated 1-alkynes (HC≡C−(CH 2 ) 6 C 8 H 17−x F x ; x = 0–17). • These surface-modified Si NWs are chemically stable under range of conditions (including acid, base). • The surface coating yields efficient electrical passivation as demonstrated by a near-zero electrochemical activity of the surface. - Abstract: Passivation of oxide-free silicon nanowires (Si NWs) by the formation of high-quality fluorinated 1-hexadecyne-derived monolayers with varying fluorine content has been investigated. Alkyl chain monolayers (C 16 H 30−x F x ) with a varying number of fluorine substituents (x = 0, 1, 3, 9, 17) were attached onto hydrogen-terminated silicon (Si−H) surfaces with an effective one-step hydrosilylation. This surface chemistry gives well-defined monolayers on nanowires that have a cylindrical core–shell structure, as characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and static contact angle (SCA) analysis. The monolayers were stable under acidic and basic conditions, as well as under extreme conditions (such as UV exposure), and provide excellent surface passivation, which opens up applications in the fields of field effect transistors, optoelectronics and especially for disease diagnosis.

Topography and instability of monolayers near domain boundaries

International Nuclear Information System (INIS)

Diamant, H.; Witten, T. A.; Ege, C.; Gopal, A.; Lee, K. Y. C.

2001-01-01

We theoretically study the topography of a biphasic surfactant monolayer in the vicinity of domain boundaries. The differing elastic properties of the two phases generally lead to a nonflat topography of 'mesas,' where domains of one phase are elevated with respect to the other phase. The mesas are steep but low, having heights of up to 10 nm. As the monolayer is laterally compressed, the mesas develop overhangs and eventually become unstable at a surface tension of about K(δc 0 ) 2 (δc 0 being the difference in spontaneous curvature and K a bending modulus). In addition, the boundary is found to undergo a topography-induced rippling instability upon compression, if its line tension is smaller than about Kδc 0 . The effect of diffuse boundaries on these features and the topographic behavior near a critical point are also examined. We discuss the relevance of our findings to several experimental observations related to surfactant monolayers: (i) small topographic features recently found near domain boundaries; (ii) folding behavior observed in mixed phospholipid monolayers and model lung surfactants; (iii) roughening of domain boundaries seen under lateral compression; (iv) the absence of biphasic structures in tensionless surfactant films

Investigating Alkylsilane Monolayer Tribology at a Single-Asperity Contact with Molecular Dynamics Simulation.

Science.gov (United States)

Summers, Andrew Z; Iacovella, Christopher R; Cummings, Peter T; McCabe, Clare

2017-10-24

Chemisorbed monolayer films are known to possess favorable characteristics for nanoscale lubrication of micro- and nanoelectromechanical systems (MEMS/NEMS). Prior studies have shown that the friction observed for monolayer-coated surfaces features a strong dependence on the geometry of contact. Specifically, tip-like geometries have been shown to penetrate into monolayer films, inducing defects in the monolayer chains and leading to plowing mechanisms during shear, which result in higher coefficients of friction (COF) than those observed for planar geometries. In this work, we use molecular dynamics simulations to examine the tribology of model silica single-asperity contacts under shear with monolayer-coated substrates featuring various film densities. It is observed that lower monolayer densities lead to reduced COFs, in contrast to results for planar systems where COF is found to be nearly independent of monolayer density. This is attributed to a liquid-like response to shear, whereby fewer defects are imparted in monolayer chains from the asperity, and chains are easily displaced by the tip as a result of the higher free volume. This transition in the mechanism of molecular plowing suggests that liquid-like films should provide favorable lubrication at single-asperity contacts.

Monolayer group-III monochalcogenides by oxygen functionalization: a promising class of two-dimensional topological insulators

Science.gov (United States)

Zhou, Si; Liu, Cheng-Cheng; Zhao, Jijun; Yao, Yugui

2018-03-01

Monolayer group-III monochalcogenides (MX, M = Ga, In; X = S, Se, Te), an emerging category of two-dimensional (2D) semiconductors, hold great promise for electronics, optoelectronics and catalysts. By first-principles calculations, we show that the phonon dispersion and Raman spectra, as well as the electronic and topological properties of monolayer MX can be tuned by oxygen functionalization. Chemisorption of oxygen atoms on one side or both sides of the MX sheet narrows or even closes the band gap, enlarges work function, and significantly reduces the carrier effective mass. More excitingly, InS, InSe, and InTe monolayers with double-side oxygen functionalization are 2D topological insulators with sizeable bulk gap up to 0.21 eV. Their low-energy bands near the Fermi level are dominated by the px and py orbitals of atoms, allowing band engineering via in-plane strains. Our studies provide viable strategy for realizing quantum spin Hall effect in monolayer group-III monochalcogenides at room temperature, and utilizing these novel 2D materials for high-speed and dissipationless transport devices.

Transfer matrix theory of monolayer graphene/bilayer graphene heterostructure superlattice

International Nuclear Information System (INIS)

Wang, Yu

2014-01-01

We have formulated a transfer matrix method to investigate electronic properties of graphene heterostructure consisting of monolayer graphene and bilayer counterpart. By evaluating transmission, conductance, and band dispersion, we show that, irrespective of the different carrier chiralities in monolayer graphene and bilayer graphene, superlattice consisting of biased bilayer graphene barrier and monolayer graphene well can mimic the electronic properties of conventional semiconductor superlattice, displaying the extended subbands in the quantum tunneling regime and producing anisotropic minigaps for the classically allowed transport. Due to the lateral confinement, the lowest mode has shifted away from the charge neutral point of monolayer graphene component, opening a sizeable gap in concerned structure. Following the gate-field and geometry modulation, all electronic states and gaps between them can be externally engineered in an electric-controllable strategy.

Affinity of serum apolipoproteins for lipid monolayers

International Nuclear Information System (INIS)

Ibdah, J.A.

1987-01-01

The effects of lipid composition and packing as well as the structure of the protein on the affinities of apolipoproteins for lipid monolayers have been investigated. The adsorption of 14 C-reductively methylated human apolipoproteins A-I and A-II at saturating subphase concentrations to monolayers prepared with synthetic lipids or lipoprotein surface lipids spread at various initial surface pressures has been studied. The adsorption of apolipoproteins is monitored by following the surface radioactivity using a gas flow counter and Wilhelmy plate, respectively. The physical states of the lipid monolayers are evaluated by measurement of the surface pressure-molecular area isotherms using a Langmuir-Adam surface balance. The probable helical regions in various apolipoproteins have been predicted using a secondary structure analysis computer program. The mean residue hydrophobicity and mean residue hydrophobic moment for the predicted helical segments have been calculated. The surface properties of synthetic peptides which are amphipathic helix analogs have been investigated at the air-water and lipid-water interfaces

Repair during multifraction exposures: spheroids versus monolayers

International Nuclear Information System (INIS)

Durand, R.E.

1984-01-01

Many type of mammalian cells, when grown in culture as multicell spheroids, display an increased ability to accumulate and repair sublethal radiation damage which has been called the ''contact effect''. Since this effect has the potential to markedly modify the multifraction radiation response of cells in V79 spheroids relative to cells in monolayer cultures, an investigation was made of regimens ranging from 1 to 100 fractions. Effective dose rates were chosen near 1 Gy h -1 to inhibit cell progression and thus simplify analysis of the results. As expected, larger doses per fraction produced more net cell killing in both systems than lower doses per fraction. Additionally, less killing of spheroid cells was observed in all regimens, in accord with their greater potential for repair. However, when the data were expressed as isoeffect curves, the spheroid and monolayer curves converged as the number of fractions increased. Thus, quite similar inherent sensitivity and repair capabilities would be predicted for ultra-low doses per fraction. High precision techniques for defining survival after doses of radiation from 0.2 to 1 Gy were, however, still able to demonstrate a survival advantage for cells grown as spheroids. (author)

Impact of Anchoring Groups on Ballistic Transport: Single Molecule vs Monolayer Junctions

Science.gov (United States)

2015-01-01

Tuning the transport properties of molecular junctions by chemically modifying the molecular structure is one of the key challenges for advancing the field of molecular electronics. In the present contribution, we investigate current–voltage characteristics of differently linked metal–molecule–metal systems that comprise either a single molecule or a molecular assembly. This is achieved by employing density functional theory in conjunction with a Green’s function approach. We show that the conductance of a molecular system with a specific anchoring group is fundamentally different depending on whether a single molecule or a continuous monolayer forms the junction. This is a consequence of collective electrostatic effects that arise from dipolar elements contained in the monolayer and from interfacial charge rearrangements. As a consequence of these collective effects, the “ideal” choice for an anchoring group is clearly different for monolayer and single molecule devices. A particularly striking effect is observed for pyridine-docked systems. These are subject to Fermi-level pinning at high molecular packing densities, causing an abrupt increase of the junction current already at small voltages. PMID:26401191

Photovoltaic heterojunctions of fullerenes with MoS2 and WS2 monolayers

KAUST Repository

Gan, Liyong

2014-04-17

First-principles calculations are performed to explore the geometry, bonding, and electronic structures of six ultrathin photovoltaic heterostructures consisting of pristine and B- or N-doped fullerenes and MoS2 or WS2 monolayers. The fullerenes prefer to be attached with a hexagon parallel to the monolayer, where B and N favor proximity to the monolayer. The main electronic properties of the subsystems stay intact, suggesting weak interfacial interaction. Both the C60/MoS 2 and C60/WS2 systems show type-II band alignments. However, the built-in potential in the former case is too small to effectively drive electron-hole separation across the interface, whereas the latter system is predicted to show good photovoltaic performance. Unfortunately, B and N doping destroys the type-II band alignment on MoS2 and preserves it only in one spin channel on WS2, which is unsuitable for excitonic solar cells. Our results suggest that the C60/WS 2 system is highly promising for excitonic solar cells. © 2014 American Chemical Society.

Multifunctional Binary Monolayers Ge xP y: Tunable Band Gap, Ferromagnetism, and Photocatalyst for Water Splitting.

Science.gov (United States)

Li, Pengfei; Zhang, Wei; Li, Dongdong; Liang, Changhao; Zeng, Xiao Cheng

2018-06-04

The most stable structures of two-dimensional Ge x P y and Ge x As y monolayers with different stoichiometries (e.g., GeP, GeP 2 , and GeP 3 ) are explored systematically through the combination of the particle-swarm optimization technique and density functional theory optimization. For GeP 3 , we show that the newly predicted most stable C2/ m structure is 0.16 eV/atom lower in energy than the state-of-the-art P3̅m1 structure reported previously ( Nano Lett. 2017, 17, 1833). The computed electronic band structures suggest that all the stable and metastable monolayers of Ge x P y are semiconductors with highly tunable band gaps under the biaxial strain, allowing strain engineering of their band gaps within nearly the whole visible-light range. More interestingly, the hole doping can convert the C2/ m GeP 3 monolayer from nonmagnetic to ferromagnetic because of its unique valence band structure. For the GeP 2 monolayer, the predicted most stable Pmc2 1 structure is a (quasi) direct-gap semiconductor that possesses a high electron mobility of ∼800 cm 2 V -1 s -1 along the k a direction, which is much higher than that of MoS 2 (∼200 cm 2 V -1 s -1 ). More importantly, the Pmc2 1 GeP 2 monolayer not only can serve as an n-type channel material in field-effect transistors but also can be an effective catalyst for splitting water.

Janus monolayers of transition metal dichalcogenides

KAUST Repository

Lu, Ang-Yu

2017-05-15

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.

Dirac State in the FeB2 Monolayer with Graphene-Like Boron Sheet.

Science.gov (United States)

Zhang, Haijun; Li, Yafei; Hou, Jianhou; Du, Aijun; Chen, Zhongfang

2016-10-12

By introducing the commonly utilized Fe atoms into a two-dimensional (2D) honeycomb boron network, we theoretically designed a new Dirac material of FeB 2 monolayer with a Fermi velocity in the same order of graphene. The electron transfer from Fe atoms to B networks not only effectively stabilizes the FeB 2 networks but also leads to the strong interaction between the Fe and B atoms. The Dirac state in FeB 2 system primarily arises from the Fe d orbitals and hybridized orbital from Fe-d and B-p states. The newly predicted FeB 2 monolayer has excellent dynamic and thermal stabilities and is also the global minimum of 2D FeB 2 system, implying its experimental feasibility. Our results are beneficial to further uncovering the mechanism of the Dirac cones and providing a feasible strategy for Dirac materials design.

Mixed DPPC/POPC Monolayers: All-atom Molecular Dynamics Simulations and Langmuir Monolayer Experiments

Czech Academy of Sciences Publication Activity Database

Olžyńska, Agnieszka; Zubek, M.; Roeselová, Martina; Korchowiec, J.; Cwiklik, Lukasz

2016-01-01

Roč. 1858, č. 12 (2016), s. 3120-3130 ISSN 0005-2736 R&D Projects: GA ČR GA15-14292S Institutional support: RVO:61388955 ; RVO:61388963 Keywords : phospholipid monolayers * Lung surfactant * molecular dynamics Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.498, year: 2016

Surface chemistry and electrocatalytic behaviour of tetra-carboxy substituted iron, cobalt and manganese phthalocyanine monolayers on gold electrode

International Nuclear Information System (INIS)

Mashazi, Philani N.; Westbroek, Philippe; Ozoemena, Kenneth I.; Nyokong, Tebello

2007-01-01

Surface chemistry and electrocatalytic properties of self-assembled monolayers of metal tetra-carboxylic acid phthalocyanine complexes with cobalt (Co), iron (Fe) and manganese (Mn) as central metal ions have been studied. These phthalocyanine molecules are immobilized on gold electrode via the coupling reaction between the ring substituents and pre-formed mercaptoethanol self-assembled monolayer (Au-ME SAM). X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy confirmed chemisorption of mercaptoethanol via sulfur group on gold electrode and also coupling reaction between phthalocyanines and Au-ME SAM. Electrochemical parameters of the immobilized molecules show that these molecules are densely packed with a perpendicular orientation. The potential applications of the gold modified electrodes were investigated towards L-cysteine detection and the analysis at phthalocyanine SAMs. Cobalt and iron tetra-carboxylic acid phthalocyanine monolayers showed good oxidation peak for L-cysteine at potentials where metal oxidation (M III /M II ) takes place and this metal oxidation mediates the catalytic oxidation of L-cysteine. Manganese tetra-carboxylic acid phthalocyanine monolayer also exhibited a good catalytic oxidation peak towards L-cysteine at potentials where Mn IV /Mn III redox peak occurs and this redox peak mediates L-cysteine oxidation. The analysis of cysteine at phthalocyanine monolayers displayed good analytical parameters with good detection limits of the orders of 10 -7 mol L -1 and good linearity for a studied concentration range up to 60 μmol L -1

Self assembled monolayers of octadecyltrichlorosilane for dielectric materials

Energy Technology Data Exchange (ETDEWEB)

Kumar, Vijay, E-mail: cirivijaypilani@gmail.com [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)

2016-04-13

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.

On the utility of vacancies and tensile strain-induced quality factor enhancement for mass sensing using graphene monolayers

International Nuclear Information System (INIS)

Kim, Sung Youb; Park, Harold S

2010-01-01

We have utilized classical molecular dynamics to investigate the mass sensing potential of graphene monolayers, using gold as the model adsorbed atom. In doing so, we report two key findings. First, we find that while perfect graphene monolayers are effective mass sensors at very low (T < 10 K) temperatures, their mass sensing capability is lost at higher temperatures due to diffusion of the adsorbed atom at elevated temperatures. We demonstrate that even if the quality (Q) factors are significantly elevated through the application of tensile mechanical strain, the mass sensing resolution is still lost at elevated temperatures, which demonstrates that high Q-factors alone are insufficient to ensure the mass sensing capability of graphene. Second, we find that while the introduction of single vacancies into the graphene monolayer prevents the diffusion of the adsorbed atom, the mass sensing resolution is still lost at higher temperatures, again due to Q-factor degradation. We finally demonstrate that if the Q-factors of the graphene monolayers with single vacancies are kept acceptably high through the application of tensile strain, then the high Q-factors, in conjunction with the single atom vacancies to stop the diffusion of the adsorbed atom, enable graphene to maintain its mass sensing capability across a range of technologically relevant operating temperatures.

High-Order Curvilinear Finite Element Methods for Lagrangian Hydrodynamics [High Order Curvilinear Finite Elements for Lagrangian Hydrodynamics

Energy Technology Data Exchange (ETDEWEB)

Dobrev, Veselin A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Kolev, Tzanio V. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Rieben, Robert N. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

2012-09-20

The numerical approximation of the Euler equations of gas dynamics in a movingLagrangian frame is at the heart of many multiphysics simulation algorithms. Here, we present a general framework for high-order Lagrangian discretization of these compressible shock hydrodynamics equations using curvilinear finite elements. This method is an extension of the approach outlined in [Dobrev et al., Internat. J. Numer. Methods Fluids, 65 (2010), pp. 1295--1310] and can be formulated for any finite dimensional approximation of the kinematic and thermodynamic fields, including generic finite elements on two- and three-dimensional meshes with triangular, quadrilateral, tetrahedral, or hexahedral zones. We discretize the kinematic variables of position and velocity using a continuous high-order basis function expansion of arbitrary polynomial degree which is obtained via a corresponding high-order parametric mapping from a standard reference element. This enables the use of curvilinear zone geometry, higher-order approximations for fields within a zone, and a pointwise definition of mass conservation which we refer to as strong mass conservation. Moreover, we discretize the internal energy using a piecewise discontinuous high-order basis function expansion which is also of arbitrary polynomial degree. This facilitates multimaterial hydrodynamics by treating material properties, such as equations of state and constitutive models, as piecewise discontinuous functions which vary within a zone. To satisfy the Rankine--Hugoniot jump conditions at a shock boundary and generate the appropriate entropy, we introduce a general tensor artificial viscosity which takes advantage of the high-order kinematic and thermodynamic information available in each zone. Finally, we apply a generic high-order time discretization process to the semidiscrete equations to develop the fully discrete numerical algorithm. Our method can be viewed as the high-order generalization of the so-called staggered

Interaction of toremifene with dipalmitoyl-phosphatidyl-glycerol in monolayers at the air–water interface followed by fluorescence microscopy in Langmuir–Blodgett films

International Nuclear Information System (INIS)

Romão, Rute I.S.; Maçôas, Ermelinda; Martinho, José M.G.; Gonçalves da Silva, Amélia M.P.S.

2013-01-01

Langmuir monolayers of dipalmitoyl-phosphatidyl-glycerol (DPPG) containing toremifene (TOR), an antiestrogen drug derivative of tamoxifen, were prepared in order to study the interaction of the drug with the cell membrane. TOR is not surface active but it remains at the interface in DPPG rich monolayers anchored by electrostatic interaction with the anionic DPPG up to the equimolar composition. The fluidity of mixed monolayers increases up to the TOR mole fraction X TOR = 0.3, remaining practically invariant for higher compositions. Brewster angle microscopy shows that the TOR disturbs the DPPG organization and the liquid condensed (LC) domains of DPPG become undetectable for X TOR ≥ 0.4. Laser scanning confocal fluorescence microscopy images of the LB films doped with rhodamine B-piperazine amide dye confirm the progressive reduction in size of LC domains, from which TOR and rhodamine are excluded. The incorporation of TOR in DPPG monolayers up to the equimolar composition supports the formation of a TOR:DPPG complex (1:1) due to electrostatic interactions between the negatively charged polar groups of DPPG and protonated TOR. - Highlights: • Toremifene (TOR) in dipalmitoyl-phosphatidyl-glycerol (DPPG) monolayers • Electrostatic interactions between DPPG and TOR form a 1:1 complex. • TOR increases the fluidity of DPPG monolayers. • Incorporation of TOR in the fluid phase of DPPG followed by fluorescence imaging

Interaction of toremifene with dipalmitoyl-phosphatidyl-glycerol in monolayers at the air–water interface followed by fluorescence microscopy in Langmuir–Blodgett films

Energy Technology Data Exchange (ETDEWEB)

Romão, Rute I.S. [Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, P-1049-001 Lisboa (Portugal); Maçôas, Ermelinda [Centro de Química-Física Molecular and IN — Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, P-1049-001 Lisboa (Portugal); Martinho, José M.G. [Centro de Química-Física Molecular and IN — Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, P-1049-001 Lisboa (Portugal); Departamento de Engenharia Química, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, P-1049-001 Lisboa (Portugal); Gonçalves da Silva, Amélia M.P.S., E-mail: ameliags@ist.utl.pt [Centro de Química Estrutural, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, P-1049-001 Lisboa (Portugal); Departamento de Engenharia Química, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, P-1049-001 Lisboa (Portugal)

2013-05-01

Langmuir monolayers of dipalmitoyl-phosphatidyl-glycerol (DPPG) containing toremifene (TOR), an antiestrogen drug derivative of tamoxifen, were prepared in order to study the interaction of the drug with the cell membrane. TOR is not surface active but it remains at the interface in DPPG rich monolayers anchored by electrostatic interaction with the anionic DPPG up to the equimolar composition. The fluidity of mixed monolayers increases up to the TOR mole fraction X{sub TOR} = 0.3, remaining practically invariant for higher compositions. Brewster angle microscopy shows that the TOR disturbs the DPPG organization and the liquid condensed (LC) domains of DPPG become undetectable for X{sub TOR} ≥ 0.4. Laser scanning confocal fluorescence microscopy images of the LB films doped with rhodamine B-piperazine amide dye confirm the progressive reduction in size of LC domains, from which TOR and rhodamine are excluded. The incorporation of TOR in DPPG monolayers up to the equimolar composition supports the formation of a TOR:DPPG complex (1:1) due to electrostatic interactions between the negatively charged polar groups of DPPG and protonated TOR. - Highlights: • Toremifene (TOR) in dipalmitoyl-phosphatidyl-glycerol (DPPG) monolayers • Electrostatic interactions between DPPG and TOR form a 1:1 complex. • TOR increases the fluidity of DPPG monolayers. • Incorporation of TOR in the fluid phase of DPPG followed by fluorescence imaging.

Tuning the Electronic, Optical, and Magnetic Properties of Monolayer GaSe with a Vertical Electric Field

Science.gov (United States)

Ke, Congming; Wu, Yaping; Guo, Guang-Yu; Lin, Wei; Wu, Zhiming; Zhou, Changjie; Kang, Junyong

2018-04-01

Inspired by two-dimensional material with their unique physical properties and innovative device applications, here we report a design framework on monolayer GaSe, an important member of the two-dimensional material family, in an effort to tune the electronic, optical, and magnetic properties through a vertical electric field. A transition from indirect to direct band gap in monolayer GaSe is found with an electric field of 0.09 V /Å . The giant Stark effect results in a reduction of the band gap with a Stark coefficient of 3.54 Å. Optical and dielectric properties of monolayer GaSe are dependent on the vertical electric field. A large regulation range for polarization E ∥c ^ is found for the static dielectric constant. The optical anisotropy with the dipole transition from E ∥c ^ to E ⊥c ^ is achieved. Induced by the spin-orbit coupling, spin-splitting energy at the valence band maximum increases linearly with the electric field. The effective mass of holes is highly susceptible to the vertical electric field. Switchable spin-polarization features in spin texture of monolayer GaSe are predicted. The tunable electronic, optical, and magnetic properties of monolayer GaSe hold great promise for applications in both the optoelectronic and spintronic devices.

Performance of monolayer graphene nanomechanical resonators with electrical readout.

Science.gov (United States)

Chen, Changyao; Rosenblatt, Sami; Bolotin, Kirill I; Kalb, William; Kim, Philip; Kymissis, Ioannis; Stormer, Horst L; Heinz, Tony F; Hone, James

2009-12-01

The enormous stiffness and low density of graphene make it an ideal material for nanoelectromechanical applications. Here, we demonstrate the fabrication and electrical readout of monolayer graphene resonators, and test their response to changes in mass and temperature. The devices show resonances in the megahertz range, and the strong dependence of resonant frequency on applied gate voltage can be fitted to a membrane model to yield the mass density and built-in strain of the graphene. Following the removal and addition of mass, changes in both density and strain are observed, indicating that adsorbates impart tension to the graphene. On cooling, the frequency increases, and the shift rate can be used to measure the unusual negative thermal expansion coefficient of graphene. The quality factor increases with decreasing temperature, reaching approximately 1 x 10(4) at 5 K. By establishing many of the basic attributes of monolayer graphene resonators, the groundwork for applications of these devices, including high-sensitivity mass detectors, is put in place.

Gas-exfoliated porous monolayer boron nitride for enhanced aerobic oxidative desulfurization performance

Science.gov (United States)

Wu, Yingcheng; Wu, Peiwen; Chao, Yanhong; He, Jing; Li, Hongping; Lu, Linjie; Jiang, Wei; Zhang, Beibei; Li, Huaming; Zhu, Wenshuai

2018-01-01

Hexagonal boron nitride has been regarded to be an efficient catalyst in aerobic oxidation fields, but limited by the less-exposed active sites. In this contribution, we proposed a simple green liquid nitrogen gas exfoliation strategy for preparation of porous monolayer nanosheets (BN-1). Owing to the reduced layer numbers, decreased lateral sizes and artificially-constructed pores, increased exposure of active sites was expected, further contributed to an enhanced aerobic oxidative desulfurization (ODS) performance up to ˜98% of sulfur removal, achieving ultra-deep desulfurization. This work not only introduced an excellent catalyst for aerobic ODS, but also provided a strategy for construction of some other highly-efficient monolayer two-dimensional materials for enhanced catalytic performance.

Oxygen adsorption and dissociation during the oxidation of monolayer Ti2C

KAUST Repository

Gan, Liyong

2013-08-20

Exfoliated two-dimensional early transition metal carbides and carbonitrides are usually not terminated by metal atoms but saturated by O, OH, and/or F, thus making it difficult to understand the surface structure evolution and the induced electronic modifications. To fill this gap, density functional theory and molecular dynamics simulations are performed to capture the initial stage of the oxidation process of Ti2C, a prototypical example from the recently fabricated class of two-dimensional carbides and carbonitrides. It is shown that the unsaturated Ti 3d orbitals of the pristine Ti2C surface interact strongly with the approaching O2 molecules, resulting in barrierless O2 dissociation. The diffusion of the dissociated O atoms is also found to be very facile. Molecular dynamics simulations suggest that both dissociation and diffusion are enhanced as the O2 coverage increases to 0.25 monolayer. For a coverage of less than 0.11 monolayer, the adsorbates lead to a minor modification of the electronic properties of Ti2C, while the modification is remarkable at 0.25 monolayer. The formed Ti2CO2 after O saturation is an indirect narrow gap semiconductor (0.33 eV) with high intrinsic carrier concentration at room temperature and high thermodynamic stability at intermediate temperature (e.g., 550 °C).

Oxygen adsorption and dissociation during the oxidation of monolayer Ti2C

KAUST Repository

Gan, Liyong; Huang, Dan; Schwingenschlö gl, Udo

2013-01-01

Exfoliated two-dimensional early transition metal carbides and carbonitrides are usually not terminated by metal atoms but saturated by O, OH, and/or F, thus making it difficult to understand the surface structure evolution and the induced electronic modifications. To fill this gap, density functional theory and molecular dynamics simulations are performed to capture the initial stage of the oxidation process of Ti2C, a prototypical example from the recently fabricated class of two-dimensional carbides and carbonitrides. It is shown that the unsaturated Ti 3d orbitals of the pristine Ti2C surface interact strongly with the approaching O2 molecules, resulting in barrierless O2 dissociation. The diffusion of the dissociated O atoms is also found to be very facile. Molecular dynamics simulations suggest that both dissociation and diffusion are enhanced as the O2 coverage increases to 0.25 monolayer. For a coverage of less than 0.11 monolayer, the adsorbates lead to a minor modification of the electronic properties of Ti2C, while the modification is remarkable at 0.25 monolayer. The formed Ti2CO2 after O saturation is an indirect narrow gap semiconductor (0.33 eV) with high intrinsic carrier concentration at room temperature and high thermodynamic stability at intermediate temperature (e.g., 550 °C).

Neutrophil-endothelial cell interactions on endothelial monolayers grown on micropore filters.

Science.gov (United States)

Taylor, R F; Price, T H; Schwartz, S M; Dale, D C

1981-01-01

We have developed a technique for growing endothelial monolayers on micropore filters. These monolayers demonstrate confluence by phase and electron microscopy and provide a functional barrier to passage of radiolabeled albumin. Neutrophils readily penetrate the monolayer in response to chemotaxin, whereas there is little movement in the absence of chemotaxin. This system offers unique advantages over available chemotaxis assays and may have wider applications in the study of endothelial function. Images PMID:7007441

Studies of the structure and properties of organic monolayers, multilayers and superlattices

International Nuclear Information System (INIS)

Dutta, P.; Ketterson, J.B.

1990-01-01

Organic monolayers and multilayers are both scientifically fascinating and technologically promising; they are, however, both complex systems and relatively inaccessible to experimental probes. In this progress report, we describe our x-ray diffraction studies, which have given us substantial new information about the structures and phase transitions in monolayers on the surface of water; our use of these monolayers as a unique probe of the dynamics of wetting and spreading; and our studies of monolayer mechanical properties using a simple but effective technique available to anyone using the Wilhelmy method to measure surface tension. 20 refs., 11 figs

Langmuir monolayer formation of metal complexes from polymerizable amphiphilic ligands

NARCIS (Netherlands)

Werkman, P.J; Schouten, A.J.

1996-01-01

The monolayer behaviour of 4-(10,12-pentacosadiynoicamidomethyl)-pyridine at the air-water interface was studied by measuring the surface pressure-area isotherms. The amphiphile formed stable monolayers with a clear liquid-expanded (LE) to liquid-condensed phase transition at various temperatures.

Displacive phase transition at the 5/3 monolayer of Pb on Ge(001)

Science.gov (United States)

Cvetko, D.; Ratto, F.; Cossaro, A.; Bavdek, G.; Morgante, A.; Floreano, L.

2005-07-01

At a coverage of 5/3 monolayer (ML), Pb adsorbed on Ge(001) forms a ground phase displaying a ((21)/(06)) symmetry. This phase undergoes two reversible phase transitions ((21)/(06))↔((21)/(03))↔(2×1) at the critical temperatures Tc1˜178K and Tc2˜375K , respectively. We investigated the behavior of the relevant order parameters at the critical temperatures by means of He and in-plane x-ray diffraction (HAS and XRD, respectively). Both phase transitions at the critical temperature put in evidence a clear order-disorder behavior, in agreement with the universality class expected for the corresponding symmetry group transformation. The low-temperature transition yields the critical exponent of the two-dimensional (2-D) Ising universality class, whereas the three-state Potts’ critical exponents are found for the high-temperature transition. By out-of-plane XRD measurements, the low-temperature phase transition is observed to be accompanied by a static surface distortion at room temperature. A complementary HAS study of the temperature evolution of the surface charge corrugation reveals that the complete ((21)/(06))↔((21)/(03)) transition is of the displacive type. On the contrary, the high-temperature phase transition does not show any change of the surface corrugation up to its irreversible decomposition, thus pointing to a pure order-disorder character.

Wavepacket revivals in monolayer and bilayer graphene rings.

Science.gov (United States)

García, Trinidad; Rodríguez-Bolívar, Salvador; Cordero, Nicolás A; Romera, Elvira

2013-06-12

We have studied the existence of quantum revivals in graphene quantum rings within a simplified model. The time evolution of a Gaussian-populated wavepacket shows revivals in monolayer and bilayer graphene rings. We have also studied this behavior for quantum rings in a perpendicular magnetic field. We have found that revival time is an observable that shows different values for monolayer and bilayer graphene quantum rings. In addition, the revival time shows valley degeneracy breaking.

Lower lattice thermal conductivity in SbAs than As or Sb monolayers: a first-principles study.

Science.gov (United States)

Guo, San-Dong; Liu, Jiang-Tao

2017-12-06

Phonon transport in group-VA element (As, Sb and Bi) monolayer semiconductors has been widely investigated in theory, and, of them, monolayer Sb (antimonene) has recently been synthesized. In this work, phonon transport in monolayer SbAs is investigated with a combination of first-principles calculations and the linearized phonon Boltzmann equation. It is found that the lattice thermal conductivity of monolayer SbAs is lower than those of both monolayer As and Sb, and the corresponding sheet thermal conductance is 28.8 W K -1 at room temperature. To understand the lower lattice thermal conductivity in monolayer SbAs than those in monolayer As and Sb, the group velocities and phonon lifetimes of monolayer As, SbAs and Sb are calculated. The calculated results show that the group velocities of monolayer SbAs are between those of monolayer As and Sb, but that the phonon lifetimes of SbAs are smaller than those of both monolayer As and Sb. Hence, the low lattice thermal conductivity in monolayer SbAs is attributed to very small phonon lifetimes. Unexpectedly, the ZA branch has very little contribution to the total thermal conductivity, only 2.4%, which is obviously different from those of monolayer As and Sb with very large contributions. This can be explained by very small phonon lifetimes for the ZA branch of monolayer SbAs. The lower lattice thermal conductivity of monolayer SbAs compared to that of monolayer As or Sb can be understood by the alloying of As (Sb) with Sb (As), which should introduce phonon point defect scattering. We also consider the isotope and size effects on the lattice thermal conductivity. It is found that isotope scattering produces a neglectful effect, and the lattice thermal conductivity with a characteristic length smaller than 30 nm can reach a decrease of about 47%. These results may offer perspectives on tuning the lattice thermal conductivity by the mixture of multiple elements for applications of thermal management and

Emergence of Dirac and quantum spin Hall states in fluorinated monolayer As and AsSb

KAUST Repository

Zhang, Qingyun

2016-01-21

Using first-principles calculations, we investigate the electronic and vibrational properties of monolayer As and AsSb. While the pristine monolayers are semiconductors (direct band gap at the Γ point), fluorination results in Dirac cones at the K points. Fluorinated monolayer As shows a band gap of 0.16 eV due to spin-orbit coupling, and fluorinated monolayer AsSb a larger band gap of 0.37 eV due to inversion symmetry breaking. Spin-orbit coupling induces spin splitting similar to monolayer MoS2. Phonon calculations confirm that both materials are dynamically stable. Calculations of the edge states of nanoribbons by the tight-binding method demonstrate that fluorinated monolayer As is topologically nontrivial in contrast to fluorinated monolayer AsSb.

Fluorinated alkyne-derived monolayers on oxide-free silicon nanowires via one-step hydrosilylation

Energy Technology Data Exchange (ETDEWEB)

Nguyen Minh, Quyen [Laboratory of Organic Chemistry, Wageningen University, Stippeneng 4, 6708 WE Wageningen (Netherlands); Nanosens, IJsselkade 7, 7201 HB Zutphen (Netherlands); Pujari, Sidharam P. [Laboratory of Organic Chemistry, Wageningen University, Stippeneng 4, 6708 WE Wageningen (Netherlands); Wang, Bin [The Department of Chemical Engineering and Russell Berrie Nanotechnology Institute, Technion – Israel Institute of Technology, Haifa 3200003 (Israel); Wang, Zhanhua [Laboratory of Organic Chemistry, Wageningen University, Stippeneng 4, 6708 WE Wageningen (Netherlands); Haick, Hossam [The Department of Chemical Engineering and Russell Berrie Nanotechnology Institute, Technion – Israel Institute of Technology, Haifa 3200003 (Israel); Zuilhof, Han [Laboratory of Organic Chemistry, Wageningen University, Stippeneng 4, 6708 WE Wageningen (Netherlands); Rijn, Cees J.M. van, E-mail: cees.vanrijn@wur.nl [Laboratory of Organic Chemistry, Wageningen University, Stippeneng 4, 6708 WE Wageningen (Netherlands)

2016-11-30

Highlights: • Oxide-free H-terminated silicon nanowires undergo efficient surface modification by reaction with fluorinated 1-alkynes (HC≡C−(CH{sub 2}){sub 6}C{sub 8}H{sub 17−x}F{sub x}; x = 0–17). • These surface-modified Si NWs are chemically stable under range of conditions (including acid, base). • The surface coating yields efficient electrical passivation as demonstrated by a near-zero electrochemical activity of the surface. - Abstract: Passivation of oxide-free silicon nanowires (Si NWs) by the formation of high-quality fluorinated 1-hexadecyne-derived monolayers with varying fluorine content has been investigated. Alkyl chain monolayers (C{sub 16}H{sub 30−x}F{sub x}) with a varying number of fluorine substituents (x = 0, 1, 3, 9, 17) were attached onto hydrogen-terminated silicon (Si−H) surfaces with an effective one-step hydrosilylation. This surface chemistry gives well-defined monolayers on nanowires that have a cylindrical core–shell structure, as characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and static contact angle (SCA) analysis. The monolayers were stable under acidic and basic conditions, as well as under extreme conditions (such as UV exposure), and provide excellent surface passivation, which opens up applications in the fields of field effect transistors, optoelectronics and especially for disease diagnosis.

Electrochemical Properties of Alkanethiol Monolayers Adsorbed on Nanoporous Au Surfaces

International Nuclear Information System (INIS)

Chu, Yeon Yi; Seo, Bora; Kim, Jong Won

2010-01-01

We investigated the electrochemical properties of alkanethiol monolayers adsorbed on NPG surfaces by cyclic voltammetry and electrochemical impedance spectroscopy, and the results are compared to those on flat Au surfaces. The reductive desorption of alkanethiols on NPG surfaces is observed in more negative potential regions than that on flat Au surfaces due the stronger S-Au interaction on NPG surfaces. While the electron transfer through alkanethiol monolayers on flat Au surfaces occurs via a tunneling process through the monolayer films, the redox species can permeate through the monolayers on NPG surfaces to transfer the electrons to the Au surfaces. The results presented here will help to elucidate the intrinsic electrochemical properties of alkanethiol monolayers adsorbed on curved Au surfaces, particularly on the surface of AuNPs. Self-assembled monolayers (SAMs) of thiolate molecules on Au surfaces have been the subject of intensive research for the last few decades due to their unique physical and chemical properties. The well-organized surface structures of thiolate SAMs with various end-group functionalities can be further utilized for many applications in biology and nanotechnology. In addition to the practical applications, SAMs of thiolate molecules on Au surfaces also provide unique opportunities to address fundamental issues in surface chemistry such as self-organized surface structures, electron transfer behaviors, and moleculesubstrate interactions. Although there have been numerous reports on the fundamental physical and chemical properties of thiolate SAMs on Au surfaces, most of them were investigated on flat Au surfaces, typically on well-defined Au(111) surfaces

Detection of the adsorption of water monolayers through the ion oscillation frequency in the magnesium oxide lattice by means of low energy electron diffraction

Directory of Open Access Journals (Sweden)

M. Guevara-Bertsch

2016-03-01

Full Text Available We investigate the variation of the oscillation frequency of the Mg2+ and O2− ions in the magnesium oxide lattice due to the interactions of the surface with water monolayers by means of Low Energy Electron Diffraction. Our key result is a new technique to determine the adsorbate vibrations produced by the water monolayers on the surface lattice as a consequence of their change in the surface Debye temperature and its chemical shift. The latter was systematically investigated for different annealing times and for a constant external thermal perturbation in the range of 110–300 K in order to accomplish adsorption or desorption of water monolayers in the surface lattice.

Detection of the adsorption of water monolayers through the ion oscillation frequency in the magnesium oxide lattice by means of low energy electron diffraction

Energy Technology Data Exchange (ETDEWEB)

Guevara-Bertsch, M.; Avendaño, E. [Escuela de Física, Universidad de Costa Rica, 2060 San Pedro, San José (Costa Rica); Centro de Investigación en Ciencia e Ingeniería de Materiales, Universidad de Costa Rica, 2060 San Pedro, San José (Costa Rica); Ramírez-Hidalgo, G. [Centro de Investigación en Ciencia e Ingeniería de Materiales, Universidad de Costa Rica, 2060 San Pedro, San José (Costa Rica); Sección de Física Teórica, Universidad de Costa Rica, 2060 San Pedro, San José (Costa Rica); Chavarría-Sibaja, A.; Araya-Pochet, J. A. [Centro de Investigación en Ciencia e Ingeniería de Materiales, Universidad de Costa Rica, 2060 San Pedro, San José (Costa Rica); Herrera-Sancho, O. A., E-mail: oscar-andrey.herrera@uibk.ac.at [Escuela de Física, Universidad de Costa Rica, 2060 San Pedro, San José (Costa Rica); Centro de Investigación en Ciencia e Ingeniería de Materiales, Universidad de Costa Rica, 2060 San Pedro, San José (Costa Rica); Institut für Quantenoptik und Quanteninformation, Österreichische Akademie der Wissenschaften, Technikerstr. 21a, 6020 Innsbruck (Austria)

2016-03-15

We investigate the variation of the oscillation frequency of the Mg{sup 2+} and O{sup 2−} ions in the magnesium oxide lattice due to the interactions of the surface with water monolayers by means of Low Energy Electron Diffraction. Our key result is a new technique to determine the adsorbate vibrations produced by the water monolayers on the surface lattice as a consequence of their change in the surface Debye temperature and its chemical shift. The latter was systematically investigated for different annealing times and for a constant external thermal perturbation in the range of 110–300 K in order to accomplish adsorption or desorption of water monolayers in the surface lattice.

High order depletion sensitivity analysis

International Nuclear Information System (INIS)

Naguib, K.; Adib, M.; Morcos, H.N.

2002-01-01

A high order depletion sensitivity method was applied to calculate the sensitivities of build-up of actinides in the irradiated fuel due to cross-section uncertainties. An iteration method based on Taylor series expansion was applied to construct stationary principle, from which all orders of perturbations were calculated. The irradiated EK-10 and MTR-20 fuels at their maximum burn-up of 25% and 65% respectively were considered for sensitivity analysis. The results of calculation show that, in case of EK-10 fuel (low burn-up), the first order sensitivity was found to be enough to perform an accuracy of 1%. While in case of MTR-20 (high burn-up) the fifth order was found to provide 3% accuracy. A computer code SENS was developed to provide the required calculations

Generation of intense high-order vortex harmonics.

Science.gov (United States)

Zhang, Xiaomei; Shen, Baifei; Shi, Yin; Wang, Xiaofeng; Zhang, Lingang; Wang, Wenpeng; Xu, Jiancai; Yi, Longqiong; Xu, Zhizhan

2015-05-01

This Letter presents for the first time a scheme to generate intense high-order optical vortices that carry orbital angular momentum in the extreme ultraviolet region based on relativistic harmonics from the surface of a solid target. In the three-dimensional particle-in-cell simulation, the high-order harmonics of the high-order vortex mode is generated in both reflected and transmitted light beams when a linearly polarized Laguerre-Gaussian laser pulse impinges on a solid foil. The azimuthal mode of the harmonics scales with its order. The intensity of the high-order vortex harmonics is close to the relativistic region, with the pulse duration down to attosecond scale. The obtained intense vortex beam possesses the combined properties of fine transversal structure due to the high-order mode and the fine longitudinal structure due to the short wavelength of the high-order harmonics. In addition to the application in high-resolution detection in both spatial and temporal scales, it also presents new opportunities in the intense vortex required fields, such as the inner shell ionization process and high energy twisted photons generation by Thomson scattering of such an intense vortex beam off relativistic electrons.

High-order beam optics - an overview

International Nuclear Information System (INIS)

Heighway, E.A.

1989-01-01

Beam-transport codes have been around for as long as thirty years and high order codes, second-order at least, for close to twenty years. Before this period of design-code development, there was considerable high-order treatment, but it was almost entirely analytical. History has a way of repeating itself, and the current excitement in the field of high-order optics is based on the application of Lie algebra and the so-called differential algebra to beam-transport codes, both of which are highly analytical in foundation. The author will describe some of the main design tools available today, giving a little of their history, and will conclude by trying to convey some of the excitement in the field through a brief description of Lie and differential algebra. 30 refs., 7 figs., 1 tab

Thermal stability of thiol and silane monolayers: A comparative study

International Nuclear Information System (INIS)

Chandekar, Amol; Sengupta, Sandip K.; Whitten, James E.

2010-01-01

The stability of self-assembled monolayers (SAMs) at elevated temperatures is of considerable technological importance. The thermal stability of 1-octadecanethiol (ODT), 16-mercaptohexadecanoic acid (MHDA) and 1H,1H,2H,2H-perfluorodecanethiol (PFDT) SAMs on gold surfaces, and of 4-aminobutyltriethoxysilane (ABTES) and 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane (PFDS) assembled on hydroxylated silicon surfaces, was studied by X-ray photoelectron spectroscopy (XPS). The samples were heated in ultrahigh vacuum to temperatures in excess of that required for SAM degradation. ODT monolayers were stable to ca. 110 deg. C, while MHDA and PFDT SAMs were stable to ca. 145 deg. C. ABTES SAMs were found to be indefinitely stable to 250 deg. C, while PFDS SAMs were stable to 350 deg. C. These studies demonstrate the advantages of using silane monolayers for moderate to high temperature applications and illustrate differences that arise due to the nature of the tail group. To demonstrate the feasibility of silanes for template-directed patterning, a hydroxylated silicon oxide surface containing microcontact-printed PFDS patterns was spin-coated with a mainly hydrophilic block copolymer. Annealing the surface at 90 deg. C for 2 h caused the block copolymer to dewet the hydrophobic PFDS-patterned regions and adsorb exclusively on the unpatterned regions of the surface.

Wafer-scaled monolayer WO{sub 3} windows ultra-sensitive, extremely-fast and stable UV-A photodetection

Energy Technology Data Exchange (ETDEWEB)

Hai, Zhenyin; Akbari, Mohammad Karbalaei [Ghent University Global Campus, Department of Applied Analytical & Physical Chemistry, Faculty of Bioscience Engineering, 119 Songdomunhwa-ro, Yeonsu-gu, Incheon 21985 (Korea, Republic of); Xue, Chenyang [Key Laboratory of Instrumentation Science and Dynamic Measurement of Ministry of Education, North University of China, Taiyuan, Shanxi 030051 (China); Xu, Hongyan [School of Materials Science and Engineering, North University of China, Taiyuan, Shanxi 030051 (China); Hyde, Lachlan [Melbourne Centre for Nanofabrication, Clayton, Victoria 3168 (Australia); Zhuiykov, Serge, E-mail: serge.zhuiykov@ugent.be [Ghent University Global Campus, Department of Applied Analytical & Physical Chemistry, Faculty of Bioscience Engineering, 119 Songdomunhwa-ro, Yeonsu-gu, Incheon 21985 (Korea, Republic of)

2017-05-31

Highlights: • Monolayer WO{sub 3}-based photodetectors were fabricated for the first time. • The device has ultrafast response time of ∼40 μs and responsivity of ∼0.329 A W{sup −1}. • The response time is 400-fold improvement over any other WO{sub 3} UV photodetectors. • The device has better characteristics than many 2D materials-based photodetectors. • This proposed strategy has great potential for commercialization of photodetectors. - Abstract: The monolayer WO{sub 3}-based UV-A photodetectors, fabricated by atomic layer deposition (ALD) technique at the large area of SiO{sub 2}/Si wafer, have demonstrated vastly improved functional capabilities: extremely fast response time of less than 40 μs and photoresponsivity reaching of ∼0.329 A W{sup −1}. Their ultrafast photoresponse time is at least 400-fold improvement over the previous reports for any other WO{sub 3}-based UV photodetectors that have ever been fabricated, and significantly faster than most of other photodetectors based on two-dimensional (2D) nanomaterials reported-to-date. Moreover, their measured long-term stability exceeds more than 200 cycles without any visible degradation. The ALD-deposited WO{sub 3} monolayer has also exhibited wider bandgap of 3.53 eV and the UV-A photodetector based on it is environmentally friendly, highly reliable, with excellent reproducibility and long-term stability. Thus, the shift to mono-layered semiconductors, which possess completely new quantum-confined effects, has the greatest potential in creating a new class of nano-materials, which in return windows new functional opportunities for various opto-electronic instruments built on semiconductor monolayer and, more importantly, can result in new strategy for fabrication highly-flexible, inexpensive and extremely-sensitive devices. This strategy also opens up the great opportunities for industrialization and commercialization of the photodetectors and other optoelectronic devices based on

Landau levels in biased graphene structures with monolayer-bilayer interfaces

Science.gov (United States)

Mirzakhani, M.; Zarenia, M.; Vasilopoulos, P.; Ketabi, S. A.; Peeters, F. M.

2017-09-01

The electron energy spectrum in monolayer-bilayer-monolayer and in bilayer-monolayer-bilayer graphene structures is investigated and the effects of a perpendicular magnetic field and electric bias are studied. Different types of monolayer-bilayer interfaces are considered as zigzag (ZZ) or armchair (AC) junctions which modify considerably the bulk Landau levels (LLs) when the spectra are plotted as a function of the center coordinate of the cyclotron orbit. Far away from the two interfaces, one obtains the well-known LLs for extended monolayer or bilayer graphene. The LL structure changes significantly at the two interfaces or junctions where the valley degeneracy is lifted for both types of junctions, especially when the distance between them is approximately equal to the magnetic length. Varying the nonuniform bias and the width of this junction-to-junction region in either structure strongly influence the resulting spectra. Significant differences exist between ZZ and AC junctions in both structures. The densities of states (DOSs) for unbiased structures are symmetric in energy whereas those for biased structures are asymmetric. An external bias creates interface LLs in the gaps between the LLs of the unbiased system in which the DOS can be quite small. Such a pattern of LLs can be probed by scanning tunneling microscopy.

Characterizing interstate vibrational coherent dynamics of surface adsorbed catalysts by fourth-order 3D SFG spectroscopy

Science.gov (United States)

Li, Yingmin; Wang, Jiaxi; Clark, Melissa L.; Kubiak, Clifford P.; Xiong, Wei

2016-04-01

We report the first fourth-order 3D SFG spectroscopy of a monolayer of the catalyst Re(diCN-bpy)(CO)3Cl on a gold surface. Besides measuring the vibrational coherences of single vibrational modes, the fourth-order 3D SFG spectrum also measures the dynamics of interstate coherences and vibrational coherences states between two vibrational modes. By comparing the 3D SFG to the corresponding 2D and third-order 3D IR spectroscopy of the same molecules in solution, we found that the interstate coherences exist in both liquid and surface systems, suggesting that the interstate coherence is not disrupted by surface interactions. However, by analyzing the 3D spectral lineshape, we found that the interstate coherences also experience non-negligible homogenous dephasing dynamics that originate from surface interactions. This unique ability of determining interstate vibrational coherence dynamics of the molecular monolayer can help in understanding of how energy flows within surface catalysts and other molecular monolayers.

Effect of single vacancy on the structural, electronic structure and magnetic properties of monolayer graphyne by first-principles

Energy Technology Data Exchange (ETDEWEB)

Yun, Jiangni, E-mail: niniyun@nwu.edu.cn; Zhang, Yanni; Xu, Manzhang; Wang, Keyun; Zhang, Zhiyong

2016-10-01

The effect of single vacancy on the structural, electronic and magnetic properties of monolayer graphyne is investigated by the first-principles calculations. The calculated results reveal that single vacancy can result in the spin polarization in monolayer graphyne and the spin polarization is sensitive to local geometric structure of the vacancy. In the case of monolayer graphyne with one single vacancy at the sp{sup 2} hybridized C site, the vacancy introduces rather weakly spin-polarized, flat bands in the band gap. Due to the localization nature of the defect-induced bands, the magnetic moment is mainly localized at the vacancy site. As for the monolayer graphyne with one single vacancy at the sp hybridized C site, one defect-induced state which is highly split appears in the band gap. The spin-up band of the defect-induced state is highly dispersive and shows considerable delocalization, suggesting that the magnetic moment is dispersed around the vacancy site. The above magnetization in monolayer graphyne with one single vacancy is possibly explained in terms of the valence-bond theory. - Graphical abstract: Calculated band structure of the monolayer graphyne without (a) and with one single vacancy at Vb site (b) and at Vr site(c), respectively. Blue and red lines represent the spin-up and spin-down bands, respectively. For the sake of clarity, the band structure near the Fermi energy is also presented on the right panel. The Fermi level is set to zero on the energy scale. - Highlights: • A Jahn-Teller distortion occurs in monolayer graphyne with single vacancy. • The spin polarization is sensitive to local geometric structure of the vacancy. • Vacancy lying at sp{sup 2} hybridized C site introduces weakly spin-polarized defect bands. • A strong spin splitting occurs when the vacancy lies at sp hybridized C site. • The magnetization is explained in terms of the valence-bond theory.

A first-principles study on the magnetic properties of nonmetal atom doped phosphorene monolayers.

Science.gov (United States)

Zheng, Huiling; Zhang, Jianmin; Yang, Baishun; Du, Xiaobo; Yan, Yu

2015-07-07

In order to induce magnetism in two-dimensional semiconductors for their applications in spintronic devices and novel chemical and electronic properties of semiconducting phosphorene, the geometrical structure, electronic and magnetic properties of doped phosphorene monolayers with a series of nonmetal atoms, including H, F, Cl, Br, I, B, C, Si, N, As, O, S and Se, were systematically investigated using first-principles calculations. The results show that although the substitutional doping of H, F, Cl, Br, I, B, N, O, S or Se results in large structural deformation at the doping sites of phosphorene monolayers, all neutral nonmetal atom doped systems are stable. The calculated formation energies reveal that the substitutional doping of numerous nonmetal atoms in phosphorene monolayer are possible under appropriate experimental conditions, and the charged dopants C(-), Si(-), S(+) and Se(+) are stable. Moreover, the substitutional doping of H, F, Cl, Br, I, B, N, As, C(-), Si(-), S(+) or Se(+) cannot induce magnetism in phosphorene monolayer due to the saturation or pairing of valence electrons of dopant and its neighboring P atoms, whereas ground states of neutral C, Si, O, S or Se doped systems are magnetic due to the appearance of an unpaired valence electron of C and Si or the formation of a nonbonding 3p electron of a neighboring P atom around O, S and Se. Furthermore, the magnetic coupling between the moments induced by two Si, O, S or Se are long-range anti-ferromagnetic and the coupling can be attributed to the hybridization interaction involving polarized electrons, whereas the coupling between the moments induced by two C is weak.

Wavepacket revivals in monolayer and bilayer graphene rings

International Nuclear Information System (INIS)

García, Trinidad; Rodríguez-Bolívar, Salvador; Cordero, Nicolás A; Romera, Elvira

2013-01-01

We have studied the existence of quantum revivals in graphene quantum rings within a simplified model. The time evolution of a Gaussian-populated wavepacket shows revivals in monolayer and bilayer graphene rings. We have also studied this behavior for quantum rings in a perpendicular magnetic field. We have found that revival time is an observable that shows different values for monolayer and bilayer graphene quantum rings. In addition, the revival time shows valley degeneracy breaking. (paper)

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

Energy Technology Data Exchange (ETDEWEB)

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: tomasz.martynski@put.poznan.pl [Faculty of Technical Physics, Poznan University of Technology, 60-965 Poznan (Poland)

2016-10-01

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.

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

NARCIS (Netherlands)

Kim, B.J.; Liebau, M.; Huskens, Jurriaan; Reinhoudt, David; Brugger, J.P.

2001-01-01

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

Active cell-matrix coupling regulates cellular force landscapes of cohesive epithelial monolayers

Science.gov (United States)

Zhao, Tiankai; Zhang, Yao; Wei, Qiong; Shi, Xuechen; Zhao, Peng; Chen, Long-Qing; Zhang, Sulin

2018-03-01

Epithelial cells can assemble into cohesive monolayers with rich morphologies on substrates due to competition between elastic, edge, and interfacial effects. Here we present a molecularly based thermodynamic model, integrating monolayer and substrate elasticity, and force-mediated focal adhesion formation, to elucidate the active biochemical regulation over the cellular force landscapes in cohesive epithelial monolayers, corroborated by microscopy and immunofluorescence studies. The predicted extracellular traction and intercellular tension are both monolayer size and substrate stiffness dependent, suggestive of cross-talks between intercellular and extracellular activities. Our model sets a firm ground toward a versatile computational framework to uncover the molecular origins of morphogenesis and disease in multicellular epithelia.

Modeling mechanical inhomogeneities in small populations of proliferating monolayers and spheroids.

Science.gov (United States)

Lejeune, Emma; Linder, Christian

2018-06-01

Understanding the mechanical behavior of multicellular monolayers and spheroids is fundamental to tissue culture, organism development, and the early stages of tumor growth. Proliferating cells in monolayers and spheroids experience mechanical forces as they grow and divide and local inhomogeneities in the mechanical microenvironment can cause individual cells within the multicellular system to grow and divide at different rates. This differential growth, combined with cell division and reorganization, leads to residual stress. Multiple different modeling approaches have been taken to understand and predict the residual stresses that arise in growing multicellular systems, particularly tumor spheroids. Here, we show that by using a mechanically robust agent-based model constructed with the peridynamic framework, we gain a better understanding of residual stresses in multicellular systems as they grow from a single cell. In particular, we focus on small populations of cells (1-100 s) where population behavior is highly stochastic and prior investigation has been limited. We compare the average strain energy density of cells in monolayers and spheroids using different growth and division rules and find that, on average, cells in spheroids have a higher strain energy density than cells in monolayers. We also find that cells in the interior of a growing spheroid are, on average, in compression. Finally, we demonstrate the importance of accounting for stochastic fluctuations in the mechanical environment, particularly when the cellular response to mechanical cues is nonlinear. The results presented here serve as a starting point for both further investigation with agent-based models, and for the incorporation of major findings from agent-based models into continuum scale models when explicit representation of individual cells is not computationally feasible.

Ultrahigh mobility and efficient charge injection in monolayer organic thin-film transistors on boron nitride.

Science.gov (United States)

He, Daowei; Qiao, Jingsi; Zhang, Linglong; Wang, Junya; Lan, Tu; Qian, Jun; Li, Yun; Shi, Yi; Chai, Yang; Lan, Wei; Ono, Luis K; Qi, Yabing; Xu, Jian-Bin; Ji, Wei; Wang, Xinran

2017-09-01

Organic thin-film transistors (OTFTs) with high mobility and low contact resistance have been actively pursued as building blocks for low-cost organic electronics. In conventional solution-processed or vacuum-deposited OTFTs, due to interfacial defects and traps, the organic film has to reach a certain thickness for efficient charge transport. Using an ultimate monolayer of 2,7-dioctyl[1]benzothieno[3,2- b ][1]benzothiophene (C 8 -BTBT) molecules as an OTFT channel, we demonstrate remarkable electrical characteristics, including intrinsic hole mobility over 30 cm 2 /Vs, Ohmic contact with 100 Ω · cm resistance, and band-like transport down to 150 K. Compared to conventional OTFTs, the main advantage of a monolayer channel is the direct, nondisruptive contact between the charge transport layer and metal leads, a feature that is vital for achieving low contact resistance and current saturation voltage. On the other hand, bilayer and thicker C 8 -BTBT OTFTs exhibit strong Schottky contact and much higher contact resistance but can be improved by inserting a doped graphene buffer layer. Our results suggest that highly crystalline molecular monolayers are promising form factors to build high-performance OTFTs and investigate device physics. They also allow us to precisely model how the molecular packing changes the transport and contact properties.

Multicellular automaticity of cardiac cell monolayers: effects of density and spatial distribution of pacemaker cells

International Nuclear Information System (INIS)

Duverger, James Elber; Boudreau-Béland, Jonathan; Le, Minh Duc; Comtois, Philippe

2014-01-01

Self-organization of pacemaker (PM) activity of interconnected elements is important to the general theory of reaction–diffusion systems as well as for applications such as PM activity in cardiac tissue to initiate beating of the heart. Monolayer cultures of neonatal rat ventricular myocytes (NRVMs) are often used as experimental models in studies on cardiac electrophysiology. These monolayers exhibit automaticity (spontaneous activation) of their electrical activity. At low plated density, cells usually show a heterogeneous population consisting of PM and quiescent excitable cells (QECs). It is therefore highly probable that monolayers of NRVMs consist of a heterogeneous network of the two cell types. However, the effects of density and spatial distribution of the PM cells on spontaneous activity of monolayers remain unknown. Thus, a simple stochastic pattern formation algorithm was implemented to distribute PM and QECs in a binary-like 2D network. A FitzHugh–Nagumo excitable medium was used to simulate electrical spontaneous and propagating activity. Simulations showed a clear nonlinear dependency of spontaneous activity (occurrence and amplitude of spontaneous period) on the spatial patterns of PM cells. In most simulations, the first initiation sites were found to be located near the substrate boundaries. Comparison with experimental data obtained from cardiomyocyte monolayers shows important similarities in the position of initiation site activity. However, limitations in the model that do not reflect the complex beat-to-beat variation found in experiments indicate the need for a more realistic cardiomyocyte representation. (paper)

Multicellular automaticity of cardiac cell monolayers: effects of density and spatial distribution of pacemaker cells

Science.gov (United States)

Elber Duverger, James; Boudreau-Béland, Jonathan; Le, Minh Duc; Comtois, Philippe

2014-11-01

Self-organization of pacemaker (PM) activity of interconnected elements is important to the general theory of reaction-diffusion systems as well as for applications such as PM activity in cardiac tissue to initiate beating of the heart. Monolayer cultures of neonatal rat ventricular myocytes (NRVMs) are often used as experimental models in studies on cardiac electrophysiology. These monolayers exhibit automaticity (spontaneous activation) of their electrical activity. At low plated density, cells usually show a heterogeneous population consisting of PM and quiescent excitable cells (QECs). It is therefore highly probable that monolayers of NRVMs consist of a heterogeneous network of the two cell types. However, the effects of density and spatial distribution of the PM cells on spontaneous activity of monolayers remain unknown. Thus, a simple stochastic pattern formation algorithm was implemented to distribute PM and QECs in a binary-like 2D network. A FitzHugh-Nagumo excitable medium was used to simulate electrical spontaneous and propagating activity. Simulations showed a clear nonlinear dependency of spontaneous activity (occurrence and amplitude of spontaneous period) on the spatial patterns of PM cells. In most simulations, the first initiation sites were found to be located near the substrate boundaries. Comparison with experimental data obtained from cardiomyocyte monolayers shows important similarities in the position of initiation site activity. However, limitations in the model that do not reflect the complex beat-to-beat variation found in experiments indicate the need for a more realistic cardiomyocyte representation.

Electrical passivation of the silicon surface by organic monolayers of 1-octadecene

International Nuclear Information System (INIS)

Antonova, I. V.; Soots, R. A.; Seleznev, V. A.; Prints, V. Ya.

2007-01-01

The electrical properties of structures consisting of a monolayer of 1-octadecene deposited on the Si surface are investigated depending on the method of passivation of the surface prior to the deposition of the film (hydrogen and ion passivation) and the intensity of illumination which activates the addition reaction of molecules of 1-octadecene to the Si atoms. The monolayer of 1-octadecene on the Si surface is stable and provides the chemical passivation of the surface. Two types of traps are found, namely, traps for holes and electrons, whose density can be varied during deposition of the monolayer by the choice of intensity of illumination and by the method of passivation of the surface. In the case of a low level of illumination and/or the use of the iodine passivation of the surface, the electron traps prevail, and, in the case of high intensity of illumination and/or hydrogen passivation of the surface, the hole traps prevail. It is shown that the use of these films provides conductivity in thin near-surface layers of Si due to providing the mode of flat bands or accumulation of carriers near the surface

Tribology and stability of organic monolayers on CrN: a comparison among silane, phosphonate, alkene, and alkyne chemistries.

Science.gov (United States)

Pujari, Sidharam P; Li, Yan; Regeling, Remco; Zuilhof, Han

2013-08-20

The fabrication of chemically and mechanically stable monolayers on the surfaces of various inorganic hard materials is crucial to the development of biomedical/electronic devices. In this Article, monolayers based on the reactivity of silane, phosphonate, 1-alkene, and 1-alkyne moieties were obtained on the hydroxyl-terminated chromium nitride surface. Their chemical stability and tribology were systematically investigated. The chemical stability of the modified CrN surfaces was tested in aqueous media at 60 °C at pH 3, 7, and 11 and monitored by static water contact angle measurements, X-ray photoelectron spectroscopy (XPS), ellipsometry, and Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS). The tribological properties of the resulting organic monolayers with different end groups (fluorinated or nonfluorinated) were studied using atomic force microscopy (AFM). It was found that the fluorinated monolayers exhibit a dramatic reduction of adhesion and friction force as well as excellent wear resistance compared to those of nonfluorinated coatings and bare CrN substrates. The combination of remarkable chemical stability and superior tribological properties makes these fluorinated monolayers promising candidates for the development of robust high-performance devices.

X-ray reflectivity investgation of structure and kinetics of photoswitchable lipid monolayers

DEFF Research Database (Denmark)

Chatterjee, Kuntal; Haushahn, Björn; Shen, Chen

The mechanical and dynamic properties of phospholipid membranes are of importance for important biological functions, such as switching of embedded proteins. In order to investigate these properties we study model systems in which amphiphilic photoswitchable molecules are integrated into Langmuir...... films of phospholipids. we have modified glycolipids to contain an azobenzene photoswitch between the chain and the head group and successfully embedded those in a monolayer of dipalmitoylphosphatidylcholine (DPPC). This allows us to reversibly change the azobenzene-glycolipid orientation between...

Controlled modification of octadecyltrichlorosilane self-assembled monolayer by CO2 plasma

International Nuclear Information System (INIS)

Delorme, Nicolas; Bardeau, Jean-Francois; Bulou, Alain; Poncin-Epaillard, Fabienne

2006-01-01

CO 2 -plasma is used to introduce functional groups on the uppermost surface of an alkoxy silane self-assembled monolayer (Sam). The structural and chemical modifications of the material surface were monitored by X-ray reflectometry, atomic force microscopy, X-ray photoelectrons spectroscopy and water contact angle measurements. Optimization of the plasma parameters is performed in order to achieve a maximum functionalization and to prevent degradation of the SAM. Finally, the ability of grafting organic compounds onto the plasma modified SAMS was demonstrated by the formation of an alkoxysilane bilayer

A first-principles study of NbSe2 monolayer as anode materials for rechargeable lithium-ion and sodium-ion batteries

Science.gov (United States)

Lv, Xingshuai; Wei, Wei; Sun, Qilong; Huang, Baibiao; Dai, Ying

2017-06-01

There is a great desire to search for suitable anodes with good performance for rechargeable metal-ion batteries, which require not only large capacity but excellent rate performance and cycling stability. In this work, the electronic properties of NbSe2 monolayer were explored based on first-principles calculations. We performed a full geometry optimization for Li/Na-adsorbed structures and obtained favorable adsorption sites. The metallic character for both pristine NbSe2 monolayer and the Li/Na-adsorbed NbSe2 ensures good electrical conduction. In addition, we find that NbSe2 monolayer is more inclined to adsorb Li and Na atoms with smaller adsorption energy under Li/Na-rich condition, indicating the superiority of NbSe2 monolayer as an electrode. Then, we obtained a relatively low diffusion barrier of approximately 0.205 eV for Li and, in particular, a significantly small diffusion barrier of about 0.086 eV for Na, which ensures excellent cycling performance of NbSe2 monolayer as a battery electrode. Most importantly, the Li and Na adsorption density in NbSe2 monolayer can be as high as Li2NbSe2 and Na4NbSe2, corresponding to theoretical specific capacities of 203 and 312 mAh·g-1, respectively. And the average electrode potentials were predicted to be 0.51 V for the chemical stoichiometry of Li2NbSe2 and 0.22 V for Na4NbSe2. In view of these excellent properties, our work predicts that NbSe2 monolayer can be a promising anode material for the development of low-cost high-performance Li- and Na-ion batteries.

Diverse carrier mobility of monolayer BNC x : a combined density functional theory and Boltzmann transport theory study.

Science.gov (United States)

Wu, Tao; Deng, Kaiming; Deng, Weiqiao; Lu, Ruifeng

2017-10-19

BNC x monolayer as a kind of two-dimensional material has numerous chemical atomic ratios and arrangements with different electronic structures. Via calculations on the basis of density functional theory and Boltzmann transport theory under deformation potential approximation, the band structures and carrier mobilities of BNC x (x  =  1,2,3,4) nanosheets are systematically investigated. The calculated results show that BNC 2 -1 is a material with very small band gap (0.02 eV) among all the structures while other BNC x monolayers are semiconductors with band gap ranging from 0.51 eV to 1.32 eV. The carrier mobility of BNC x varies considerably from tens to millions of cm 2 V -1 s -1 . For BNC 2 -1, the hole mobility and electron mobility along both x and y directions can reach 10 5 orders of magnitude, which is similar to the carrier mobility of graphene. Besides, all studied BNC x monolayers obviously have anisotropic hole mobility and electron mobility. In particular, for semiconductor BNC 4 , its hole mobility along the y direction and electron mobility along the x direction unexpectedly reach 10 6 orders of magnitude, even higher than that of graphene. Our findings suggest that BNC x layered materials with the proper ratio and arrangement of carbon atoms will possess desirable charge transport properties, exhibiting potential applications in nanoelectronic devices.

Monolayer II-VI semiconductors: A first-principles prediction

Science.gov (United States)

Zheng, Hui; Chen, Nian-Ke; Zhang, S. B.; Li, Xian-Bin

A systematic study of 32 honeycomb monolayer II-VI semiconductors is carried out by first-principles methods. It appears that BeO, MgO, CaO, ZnO, CdO, CaS, SrS, SrSe, BaTe, and HgTe honeycomb monolayers have a good dynamic stability which is revealed by phonon calculations. In addition, from the molecular dynamic (MD) simulation of other unstable candidates, we also find two extra monolayers dynamically stable, which are tetragonal BaS and orthorhombic HgS. The honeycomb monolayers exist in form of either a planar perfect honeycomb or a low-buckled 2D layer, all of which possess a band gap and most of them are in the ultraviolet region. Interestingly, the dynamically stable SrSe has a gap near visible light, and displays exotic electronic properties with a flat top of the valence band, and hence has a strong spin polarization upon hole doping. The honeycomb HgTe has been reported to achieve a topological nontrivial phase under appropriate in-plane tensile strain and spin-orbital coupling (SOC). Some II-VI partners with less than 5% lattice mismatch may be used to design novel 2D heterojunction devices. If synthesized, potential applications of these 2D II-VI families could include optoelectronics, spintronics, and strong correlated electronics. Distinguished Student (DS) Program of APS FIP travel funds.

Mixed carboranethiol self-assembled monolayers on gold surfaces

Science.gov (United States)

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

2017-08-01

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.

Modeling of monolayer charge-stabilized colloidal crystals with static hexagonal crystal lattice

Science.gov (United States)

Nagatkin, A. N.; Dyshlovenko, P. E.

2018-01-01

The mathematical model of monolayer colloidal crystals of charged hard spheres in liquid electrolyte is proposed. The particles in the monolayer are arranged into the two-dimensional hexagonal crystal lattice. The model enables finding elastic constants of the crystals from the stress-strain dependencies. The model is based on the nonlinear Poisson-Boltzmann differential equation. The Poisson-Boltzmann equation is solved numerically by the finite element method for any spatial configuration. The model has five geometrical and electrical parameters. The model is used to study the crystal with particles comparable in size with the Debye length of the electrolyte. The first- and second-order elastic constants are found for a broad range of densities. The model crystal turns out to be stable relative to small uniform stretching and shearing. It is also demonstrated that the Cauchy relation is not fulfilled in the crystal. This means that the pair effective interaction of any kind is not sufficient to proper model the elasticity of colloids within the one-component approach.

Enhanced valley splitting in monolayer WSe2 due to magnetic exchange field.

Science.gov (United States)

Zhao, Chuan; Norden, Tenzin; Zhang, Peiyao; Zhao, Puqin; Cheng, Yingchun; Sun, Fan; Parry, James P; Taheri, Payam; Wang, Jieqiong; Yang, Yihang; Scrace, Thomas; Kang, Kaifei; Yang, Sen; Miao, Guo-Xing; Sabirianov, Renat; Kioseoglou, George; Huang, Wei; Petrou, Athos; Zeng, Hao

2017-08-01

Exploiting the valley degree of freedom to store and manipulate information provides a novel paradigm for future electronics. A monolayer transition-metal dichalcogenide (TMDC) with a broken inversion symmetry possesses two degenerate yet inequivalent valleys, which offers unique opportunities for valley control through the helicity of light. Lifting the valley degeneracy by Zeeman splitting has been demonstrated recently, which may enable valley control by a magnetic field. However, the realized valley splitting is modest (∼0.2 meV T -1 ). Here we show greatly enhanced valley spitting in monolayer WSe 2 , utilizing the interfacial magnetic exchange field (MEF) from a ferromagnetic EuS substrate. A valley splitting of 2.5 meV is demonstrated at 1 T by magnetoreflectance measurements and corresponds to an effective exchange field of ∼12 T. Moreover, the splitting follows the magnetization of EuS, a hallmark of the MEF. Utilizing the MEF of a magnetic insulator can induce magnetic order and valley and spin polarization in TMDCs, which may enable valleytronic and quantum-computing applications.

Elastically frustrated rehybridization: Origin of chemical order and compositional limits in InGaN quantum wells

Science.gov (United States)

Lymperakis, L.; Schulz, T.; Freysoldt, C.; Anikeeva, M.; Chen, Z.; Zheng, X.; Shen, B.; Chèze, C.; Siekacz, M.; Wang, X. Q.; Albrecht, M.; Neugebauer, J.

2018-01-01

Nominal InN monolayers grown by molecular beam epitaxy on GaN(0001) are investigated combining in situ reflection high-energy electron diffraction (RHEED), transmission electron microscopy (TEM), and density functional theory (DFT). TEM reveals a chemical intraplane ordering never observed before. Employing DFT, we identify a novel surface stabilization mechanism elastically frustrated rehybridization, which is responsible for the observed chemical ordering. The mechanism also sets an incorporation barrier for indium concentrations above 25% and thus fundamentally limits the indium content in coherently strained layers.

High-Performance n-Channel Organic Transistors Using High-Molecular-Weight Electron-Deficient Copolymers and Amine-Tailed Self-Assembled Monolayers.

Science.gov (United States)

Wang, Yang; Hasegawa, Tsukasa; Matsumoto, Hidetoshi; Mori, Takehiko; Michinobu, Tsuyoshi

2018-03-01

While high-performance p-type semiconducting polymers are widely reported, their n-type counterparts are still rare in terms of quantity and quality. Here, an improved Stille polymerization protocol using chlorobenzene as the solvent and palladium(0)/copper(I) as the catalyst is developed to synthesize high-quality n-type polymers with number-average molecular weight up to 10 5 g mol -1 . Furthermore, by sp 2 -nitrogen atoms (sp 2 -N) substitution, three new n-type polymers, namely, pBTTz, pPPT, and pSNT, are synthesized, and the effect of different sp 2 -N substitution positions on the device performances is studied for the first time. It is found that the incorporation of sp 2 -N into the acceptor units rather than the donor units results in superior crystalline microstructures and higher electron mobilities. Furthermore, an amine-tailed self-assembled monolayer (SAM) is smoothly formed on a Si/SiO 2 substrate by a simple spin-coating technique, which can facilitate the accumulation of electrons and lead to more perfect unipolar n-type transistor performances. Therefore, a remarkably high unipolar electron mobility up to 5.35 cm 2 V -1 s -1 with a low threshold voltage (≈1 V) and high on/off current ratio of ≈10 7 is demonstrated for the pSNT-based devices, which are among the highest values for unipolar n-type semiconducting polymers. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Strongly bound excitons in monolayer PtS2 and PtSe2

KAUST Repository

Sajjad, M.

2018-01-22

Based on first-principles calculations, the structural, electronic, and optical properties of monolayers PtS2 and PtSe2 are investigated. The bond stiffnesses and elastic moduli are determined by means of the spring constants and strain-energy relations, respectively. Dynamic stability is confirmed by calculating the phonon spectra, which shows excellent agreement with experimental reports for the frequencies of the Raman-active modes. The Heyd-Scuseria-Ernzerhof functional results in electronic bandgaps of 2.66 eV for monolayer PtS2 and 1.74 eV for monolayer PtSe2. G0W0 calculations combined with the Bethe-Salpeter equation are used to predict the optical spectra and exciton binding energies (0.78 eV for monolayer PtS2 and 0.60 eV for monolayer PtSe2). It turns out that the excitons are strongly bound and therefore very stable against external perturbations.

Defect Structure of Localized Excitons in a WSe2 Monolayer

KAUST Repository

Zhang, Shuai

2017-07-26

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.

Methods for top-down fabrication of wafer scale TMDC monolayers

Science.gov (United States)

Das, Saptarshi; Bera, Mrinal K.; Roelofs, Andreas K; Antonio, Mark

2017-11-07

A method of forming a TMDC monolayer comprises providing a multi-layer transition metal dichalcogenide (TMDC) film. The multi-layer TMDC film comprises a plurality of layers of the TMDC. The multi-layer TMDC film is positioned on a conducting substrate. The conducting substrate is contacted with an electrolyte solution. A predetermined electrode potential is applied on the conducting substrate and the TMDC monolayer for a predetermined time. A portion of the plurality of layers of the TMDC included in the multi-layer TMDC film is removed by application of the predetermined electrode potential, thereby leaving a TMDC monolayer film positioned on the conducting substrate.

Differential binding of 125I-IGF-I preparations to human fibroblast monolayers

International Nuclear Information System (INIS)

Conover, C.A.; Misra, P.; Hintz, R.L.; Rosenfeld, R.G.

1988-01-01

Specific, high affinity binding of 125 I-IGF-I to the type IIGF receptor on human fibroblast monolyaers was not altered by varying feeding schedules, serum lots, washing procedures, or incubation times and temperatures. However, markedly different competitive binding curves were obtained when different iodinated IGF-I preparations were used. Five of six radioligands bound preferentially to the type IIGF receptor on human fibroblast monolayers, with 50% displacement at 4-8 μg/l unlabelled IGF-I; with one radioligand a paradoxical 20-200% increase in 125 I-IGF-I binding was observed at low concentrations of unlabelled IGF-I, while concentrations as high as 100 μg/l IGF-I failed to displace this radioligand. The latter binding pattern cannot be accounted for by 125 -I-IGF-I binding to the type II IGF receptor. These data indicate that various radioligands may have preferential affinities for different IGF-I binding sites on human fibroblast monolayers. (author)

Reaction kinetics of metal deposition via surface limited red-ox replacement of underpotentially deposited metal monolayers

International Nuclear Information System (INIS)

Gokcen, Dincer; Bae, Sang-Eun; Brankovic, Stanko R.

2011-01-01

The study of the kinetics of metal deposition via surface limited red-ox replacement of underpotentially deposited metal monolayers is presented. The model system was Pt submonolayer deposition on Au(1 1 1) via red-ox replacement of Pb and Cu UPD monolayers on Au(1 1 1). The kinetics of a single replacement reaction was studied using the formalism of the comprehensive analytical model developed to fit the open circuit potential transients from deposition experiments. The practical reaction kinetics parameters like reaction half life, reaction order and reaction rate constant are determined and discussed with their relevance to design and control of deposition experiments. The effects of transport limitation and the role of the anions/electrolyte on deposition kinetics are investigated and their significance to design of effective deposition process is discussed.

SYNCHROTRON X-RAY OBSERVATIONS OF A MONOLAYER TEMPLATE FOR MINERALIZATION

International Nuclear Information System (INIS)

Dimasi, E.; Gower, L.B.

2000-01-01

Mineral nucleation at a Langmuir film interface has been studied by synchrotron x-ray scattering. Diluted calcium bicarbonate solutions were used as subphases for arachidic and stearic acid monolayers, compressed in a Langmuir trough. Self-assembly of the monolayer template is observed directly, and subsequent crystal growth monitored in-situ

Self-renewing Monolayer of Primary Colonic or Rectal Epithelial CellsSummary

Directory of Open Access Journals (Sweden)

Yuli Wang

2017-07-01

Full Text Available Background & Aims: Three-dimensional organoid culture has fundamentally changed the in vitro study of intestinal biology enabling novel assays; however, its use is limited because of an inaccessible luminal compartment and challenges to data gathering in a three-dimensional hydrogel matrix. Long-lived, self-renewing 2-dimensional (2-D tissue cultured from primary colon cells has not been accomplished. Methods: The surface matrix and chemical factors that sustain 2-D mouse colonic and human rectal epithelial cell monolayers with cell repertoires comparable to that in vivo were identified. Results: The monolayers formed organoids or colonoids when placed in standard Matrigel culture. As with the colonoids, the monolayers exhibited compartmentalization of proliferative and differentiated cells, with proliferative cells located near the peripheral edges of growing monolayers and differentiated cells predominated in the central regions. Screening of 77 dietary compounds and metabolites revealed altered proliferation or differentiation of the murine colonic epithelium. When exposed to a subset of the compound library, murine organoids exhibited similar responses to that of the monolayer but with differences that were likely attributable to the inaccessible organoid lumen. The response of the human primary epithelium to a compound subset was distinct from that of both the murine primary epithelium and human tumor cells. Conclusions: This study demonstrates that a self-renewing 2-D murine and human monolayer derived from primary cells can serve as a physiologically relevant assay system for study of stem cell renewal and differentiation and for compound screening. The platform holds transformative potential for personalized and precision medicine and can be applied to emerging areas of disease modeling and microbiome studies. Keywords: Colonic Epithelial Cells, Monolayer, Organoids, Compound Screening

Failure mechanism of monolayer graphene under hypervelocity impact of spherical projectile

Science.gov (United States)

Xia, Kang; Zhan, Haifei; Hu, De'An; Gu, Yuantong

2016-09-01

The excellent mechanical properties of graphene have enabled it as appealing candidate in the field of impact protection or protective shield. By considering a monolayer graphene membrane, in this work, we assessed its deformation mechanisms under hypervelocity impact (from 2 to 6 km/s), based on a serial of in silico studies. It is found that the cracks are formed preferentially in the zigzag directions which are consistent with that observed from tensile deformation. Specifically, the boundary condition is found to exert an obvious influence on the stress distribution and transmission during the impact process, which eventually influences the penetration energy and crack growth. For similar sample size, the circular shape graphene possesses the best impact resistance, followed by hexagonal graphene membrane. Moreover, it is found the failure shape of graphene membrane has a strong relationship with the initial kinetic energy of the projectile. The higher kinetic energy, the more number the cracks. This study provides a fundamental understanding of the deformation mechanisms of monolayer graphene under impact, which is crucial in order to facilitate their emerging future applications for impact protection, such as protective shield from orbital debris for spacecraft.

Photo-induced travelling waves in condensed Langmuir monolayers

Energy Technology Data Exchange (ETDEWEB)

Tabe, Y [Yokoyama Nano-Structured Liquid Crystal Project, ERATO, Japan Science and Technology Corporation, 5-9-9 Tokodai, Tsukuba, Ibaraki 300-2635, Japan (Japan); Yamamoto, T [Yokoyama Nano-Structured Liquid Crystal Project, ERATO, Japan Science and Technology Corporation, 5-9-9 Tokodai, Tsukuba, Ibaraki 300-2635, Japan (Japan); Yokoyama, H [Yokoyama Nano-Structured Liquid Crystal Project, ERATO, Japan Science and Technology Corporation, 5-9-9 Tokodai, Tsukuba, Ibaraki 300-2635, Japan (Japan)

2003-06-01

We report the detailed properties of photo-induced travelling waves in liquid crystalline Langmuir monolayers composed of azobenzene derivatives. When the monolayer, in which the constituent rodlike molecules are coherently tilted from the layer normal, is weakly illuminated to undergo the trans-cis photo-isomerization, spatio-temporal periodic oscillations of the molecular azimuth begin over the entire excited area and propagate as a two-dimensional orientational wave. The wave formation takes place only when the film is formed at an asymmetric interface with broken up-down symmetry and when the chromophores are continuously excited near the long-wavelength edge of absorption to induce repeated photo-isomerizations between the trans and cis forms. Under proper illumination conditions, Langmuir monolayers composed of a wide variety of azobenzene derivatives have been confirmed to exhibit similar travelling waves with velocity proportional to the excitation power irrespective of the degree of amphiphilicity. The dynamics can be qualitatively explained by the modified reaction-diffusion model proposed by Reigada, Sagues and Mikhailov.

Growth of cells superinoculated onto irradiated and nonirradiated confluent monolayers

International Nuclear Information System (INIS)

Matsuoka, H.; Ueo, H.; Sugimachi, K.

1990-01-01

We prepared confluent monolayers of normal BALB/c 3T3 cells and compared differences in the growth of four types of cells superinoculated onto these nonirradiated and irradiated monolayers. The test cells were normal BALB/c 3T3 A31 cells, a squamous cell carcinoma from a human esophageal cancer (KSE-1), human fetal fibroblasts, and V-79 cells from Chinese hamster lung fibroblasts. Cell growth was checked by counting the cell number, determining [3H]thymidine incorporation and assessing colony formation. We found that on nonirradiated monolayers, colony formation of human fetal fibroblasts and normal BALB/c 3T3 cells was completely inhibited. On irradiated cells, test cells did exhibit some growth. KSE-1 cells, which had a low clonogenic efficiency on plastic surfaces, formed colonies on both irradiated and nonirradiated cells. On these monolayers, the clonogenic efficiency of V-79 cells was also higher than that on plastic surfaces. We conclude that the nonirradiated monolayer of BALB/c 3T3 cells completely inhibits the growth of superinoculated normal BALB/c 3T3 and human fetal fibroblasts, while on the other hand, they facilitate the growth of neoplastic KSE-1 and V-79 cells by providing a surface for cell adherence and growth, without affecting the presence of normal cells in co-cultures

LDL-Cholesterol Increases the Transcytosis of Molecules through Endothelial Monolayers.

Science.gov (United States)

Magalhaes, Ana; Matias, Inês; Palmela, Inês; Brito, Maria Alexandra; Dias, Sérgio

2016-01-01

Cholesterol has been identified as a causative factor in numerous pathologies including atherosclerosis and cancer. One of the frequent effects of elevated cholesterol levels in humans is the compromise of endothelial function due to activation of pro-inflammatory signalling pathways. While the mechanisms involved in endothelial activation by cholesterol during an inflammatory response are well established, less is known about the mechanisms by which cholesterol may affect endothelial barrier function, which were the subject of the present study. Here we show that low density lipoprotein (LDL) increases the permeability of endothelial monolayers to high molecular weight dextrans in an LDL receptor and cholesterol-dependent manner. The increased permeability seen upon LDL treatment was not caused by disruption of cell-to-cell junctions as determined by a normal localization of VE-Cadherin and ZO-1 proteins, and no major alterations in transendothelial electrical resistance or permeability to fluorescein. We show instead that LDL increases the level of high molecular weight transcytosis and that this occurs in an LDL receptor, cholesterol and caveolae-dependent way. Our findings contribute to our understanding of the systemic pathological effects of elevated cholesterol and the transport of cargo through endothelial monolayers.

Contrasting suspended covers reveal the impact of an artificial monolayer on heat transfer processes at the interfacial boundary layer.

Science.gov (United States)

Pittaway, P; Martínez-Alvarez, V; Hancock, N

2015-01-01

The highly variable performance of artificial monolayers in reducing evaporation from water storages has been attributed to wind speed and wave turbulence. Other factors operating at the interfacial boundary layer have seldom been considered. In this paper, two physical shade covers differing in porosity and reflectivity were suspended over 10 m diameter water tanks to attenuate wind and wave turbulence. The monolayer octadecanol was applied to one of the covered tanks, and micrometeorological conditions above and below the covers were monitored to characterise diurnal variation in the energy balance. A high downward (air-to-water) convective heat flux developed under the black cover during the day, whereas diurnal variation in the heat flux under the more reflective, wind-permeable white cover was much less. Hourly air and water temperature profiles under the covers over 3 days when forced convection was minimal (low wind speed) were selected for analysis. Monolayer application reduced temperature gain in surface water under a downward convective heat flux, and conversely reduced temperature loss under an upward convective heat flux. This 'dual property' may explain why repeat application of an artificial monolayer to retard evaporative loss (reducing latent heat loss) does not inevitably increase water temperature.

Linear and Star Poly(ionic liquid) Assemblies: Surface Monolayers and Multilayers.

Science.gov (United States)

Erwin, Andrew J; Xu, Weinan; He, Hongkun; Matyjaszewski, Krzysztof; Tsukruk, Vladimir V

2017-04-04

The surface morphology and organization of poly(ionic liquid)s (PILs), poly[1-(4-vinylbenzyl)-3-butylimidazolium bis(trifluoromethylsulfonyl)imide] are explored in conjunction with their molecular architecture, adsorption conditions, and postassembly treatments. The formation of stable PIL Langmuir and Langmuir-Blodgett (LB) monolayers at the air-water and air-solid interfaces is demonstrated. The hydrophobic bis(trifluoromethylsulfonyl)imide (Tf 2 N - ) is shown to be a critical agent governing the assembly morphology, as observed in the reversible condensation of LB monolayers into dense nanodroplets. The PIL is then incorporated as an unconventional polyelectrolyte component in the layer-by-layer (LbL) films of hydrophobic character. We demonstrate that the interplay of capillary forces, macromolecular mobility, and structural relaxation of the polymer chains influence the dewetting mechanisms in the PIL multilayers, thereby enabling access to a diverse set of highly textured, porous, and interconnected network morphologies for PIL LbL films that would otherwise be absent in conventional LbL films. Their compartmentalized internal structure is relevant to molecular separation membranes, ultrathin hydrophobic coatings, targeted cargo delivery, and highly conductive films.

A family of high-order gas-kinetic schemes and its comparison with Riemann solver based high-order methods

Science.gov (United States)

Ji, Xing; Zhao, Fengxiang; Shyy, Wei; Xu, Kun

2018-03-01

Most high order computational fluid dynamics (CFD) methods for compressible flows are based on Riemann solver for the flux evaluation and Runge-Kutta (RK) time stepping technique for temporal accuracy. The advantage of this kind of space-time separation approach is the easy implementation and stability enhancement by introducing more middle stages. However, the nth-order time accuracy needs no less than n stages for the RK method, which can be very time and memory consuming due to the reconstruction at each stage for a high order method. On the other hand, the multi-stage multi-derivative (MSMD) method can be used to achieve the same order of time accuracy using less middle stages with the use of the time derivatives of the flux function. For traditional Riemann solver based CFD methods, the lack of time derivatives in the flux function prevents its direct implementation of the MSMD method. However, the gas kinetic scheme (GKS) provides such a time accurate evolution model. By combining the second-order or third-order GKS flux functions with the MSMD technique, a family of high order gas kinetic methods can be constructed. As an extension of the previous 2-stage 4th-order GKS, the 5th-order schemes with 2 and 3 stages will be developed in this paper. Based on the same 5th-order WENO reconstruction, the performance of gas kinetic schemes from the 2nd- to the 5th-order time accurate methods will be evaluated. The results show that the 5th-order scheme can achieve the theoretical order of accuracy for the Euler equations, and present accurate Navier-Stokes solutions as well due to the coupling of inviscid and viscous terms in the GKS formulation. In comparison with Riemann solver based 5th-order RK method, the high order GKS has advantages in terms of efficiency, accuracy, and robustness, for all test cases. The 4th- and 5th-order GKS have the same robustness as the 2nd-order scheme for the capturing of discontinuous solutions. The current high order MSMD GKS is a

A simple method to tune graphene growth between monolayer and bilayer

Directory of Open Access Journals (Sweden)

Xiaozhi Xu

2016-02-01

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.

Penetration of Milk-Derived Antimicrobial Peptides into Phospholipid Monolayers as Model Biomembranes

Directory of Open Access Journals (Sweden)

Wanda Barzyk

2013-01-01

Full Text Available Three antimicrobial peptides derived from bovine milk proteins were examined with regard to penetration into insoluble monolayers formed with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC or 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol sodium salt (DPPG. Effects on surface pressure (Π and electric surface potential (ΔV were measured, Π with a platinum Wilhelmy plate and ΔV with a vibrating plate. The penetration measurements were performed under stationary diffusion conditions and upon the compression of the monolayers. The two type measurements showed greatly different effects of the peptide-lipid interactions. Results of the stationary penetration show that the peptide interactions with DPPC monolayer are weak, repulsive, and nonspecific while the interactions with DPPG monolayer are significant, attractive, and specific. These results are in accord with the fact that antimicrobial peptides disrupt bacteria membranes (negative while no significant effect on the host membranes (neutral is observed. No such discrimination was revealed from the compression isotherms. The latter indicate that squeezing the penetrant out of the monolayer upon compression does not allow for establishing the penetration equilibrium, so the monolayer remains supersaturated with the penetrant and shows an under-equilibrium orientation within the entire compression range, practically.

Pressure-area isotherm of a lipid monolayer from molecular dynamics simulations

NARCIS (Netherlands)

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

2007-01-01

We calculated the pressure-area isotherm of a dipalmitoyl-phosphatidylcholine (DPPC) lipid monolayer from molecular dynamics simulations using a coarse-grained molecular model. We characterized the monolayer structure, geometry, and phases directly from the simulations and compared the calculated

Comparative proteome analysis of monolayer and spheroid culture of canine osteosarcoma cells.

Science.gov (United States)

Gebhard, Christiane; Miller, Ingrid; Hummel, Karin; Neschi Née Ondrovics, Martina; Schlosser, Sarah; Walter, Ingrid

2018-04-15

Osteosarcoma is an aggressive bone tumor with high metastasis rate in the lungs and affects both humans and dogs in a similar way. Three-dimensional tumor cell cultures mimic the in vivo situation of micro-tumors and metastases and are therefore better experimental in vitro models than the often applied two-dimensional monolayer cultures. The aim of the present study was to perform comparative proteomics of standard monolayer cultures of canine osteosarcoma cells (D17) and three-dimensional spheroid cultures, to better characterize the 3D model before starting with experiments like migration assays. Using DIGE in combination with MALDI-TOF/TOF we found 27 unique canine proteins differently represented between these two culture systems, most of them being part of a functional network including mainly chaperones, structural proteins, stress-related proteins, proteins of the glycolysis/gluconeogenesis pathway and oxidoreductases. In monolayer cells, a noticeable shift to more acidic pI values was noticed for several proteins of medium to high abundance; two proteins (protein disulfide isomerase A3, stress-induced-phosphoprotein 1) showed an increase of phosphorylated protein species. Protein distribution within the cells, as detected by immunohistochemistry, displayed a switch of stress-induced-phosphoprotein 1 from the cytoplasm (in monolayer cultures) to the nucleus (in spheroid cultures). Additionally, Western blot testing revealed upregulated concentrations of metastasin (S100A4), triosephosphate isomerase 1 and septin 2 in spheroid cultures, in contrast to decreased concentrations of CCT2, a subunit of the T-complex. Results indicate regulation of stress proteins in the process of three-dimensional organization characterized by a hypoxic and nutrient-deficient environment comparable to tumor micro-metastases. Osteosarcoma is an aggressive bone tumor that early spreads to the lungs. Three-dimensional tumor cell cultures represent the avascular stage of micro

Generation of high order modes

CSIR Research Space (South Africa)

Ngcobo, S

2012-07-01

Full Text Available with the location of the Laguerre polynomial zeros. The Diffractive optical element is used to shape the TEM00 Gassian beam and force the laser to operate on a higher order TEMp0 Laguerre-Gaussian modes or high order superposition of Laguerre-Gaussian modes...

Atomic defects and doping of monolayer NbSe2

OpenAIRE

Nguyen, Lan; Komsa, Hannu-Pekka; Khestanova, Ekaterina; Kashtiban, Reza J; Peters, Jonathan J.P.; Lawlor, Sean; Sanchez, Ana M.; Sloan, Jeremy; Gorbachev, Roman; Grigorieva, Irina; Krasheninnikov, Arkady V.; Haigh, Sarah

2017-01-01

We have investigated the structure of atomic defects within monolayer NbSe2 encapsulated in graphene by combining atomic resolution transmission electron microscope imaging, density functional theory (DFT) calculations, and strain mapping using geometric phase analysis. We demonstrate the presence of stable Nb and Se monovacancies in monolayer material and reveal that Se monovacancies are the most frequently observed defects, consistent with DFT calculations of their formation energy. We reve...

Effect of lipid composition and packing on the adsorption of apolipoproteins to lipid monolayers

International Nuclear Information System (INIS)

Ibdah, J.A.; Lund-Katz, S.; Phillips, M.C.

1987-01-01

The monolayer system has been used to study the effects of lipoprotein surface lipid composition and packing on the affinities of apolipoproteins for the surfaces of lipoprotein particles. The adsorption of apolipoproteins injected beneath lipid monolayers prepared with pure lipids or lipoprotein surface lipids is evaluated by monitoring the surface pressure of the film and the surface concentration (Gamma) of 14 C-labelled apolipoprotein. At a given initial film pressure (π/sub i/) there is a higher adsorption of human apo A-I to unsaturated phosphatidylcholine (PC) monolayers compared to saturated PC monolayers (e.g., at π/sub i/ = 10 mN/m, Gamma = 0.35 and 0.06 mg/m 2 for egg PC and distearoyl PC, respectively, with 3 x 10 -4 mg/ml apo A-I in the subphase). In addition, adsorption of apo A-I is less to an egg sphingomyelin monolayer than to an egg PC monolayer. The adsorption of apo A-I to PC monolayers is decreased by addition of cholesterol. Generally, apo A-I adsorption diminishes as the lipid molecular area decreases. Apo A-I adsorbs more to monolayers prepared with HDL 3 surface lipids than with LDL surface lipids. These studies suggest that lipoprotein surface lipid composition and packing are crucial factors influencing the transfer and exchange of apolipoproteins among various lipoprotein classes during metabolism of lipoprotein particles

Sub-monolayer dot vertical-cavity surface-emitting lasers

International Nuclear Information System (INIS)

Blokhin, S.A.; Maleev, N.A.; Kuz'menkov, A.G.

2006-01-01

Vertical-cavity surface-emitting lasers (VCSELs) based on submonolayer InGaAs quantum-dot active region and doped with AlGaAs/GaAs distributed Bragg reflectors were grown by molecular beam epitaxy. 3 μm aperture single-mode VCSELs demonstrate lasing at 980 nm with threshold current of 0.6 mA, maximum output power of 4 mW and external differential efficiency as high as 68%. Ultimately low internal optical losses were measured for these multimode sub-monolayer quantum dot VCSELs [ru

Shear thinning behavior of monolayer liquid lubricant films measured by fiber wobbling method

International Nuclear Information System (INIS)

Hamamoto, Y; Itoh, S; Fukuzawa, K; Zhang, H

2010-01-01

It is essential to clarify mechanical properties of monolayer lubricant films coated on magnetic disks under shearing motion for designing future hard disk drives with ultra-low flying height. Many of previous researchers reported that strong shear rate dependence of viscoelasticity was one of the typical phenomena observed with molecularly thin liquid films. However, it has not been clarified whether or not perfluoropolyether (PFPE) lubricant films, which are used for the head-disk interface (HDI) lubrication, show shear thinning behavior under actual HDI conditions. In this study, we used the fiber wobbling method that can achieve both highly-sensitive shear force measurement and precise gap control and measured shear rate dependence of viscoelastic properties of monolayer PFPE films coated on the magnetic disk. Our experimental results showed that shear thinning does occur at high shear rate ranged from 10 2 to 10 6 s -1 .

Synthesis, electrochemistry, STM investigation of oligothiophene self-assemblies with superior structural order and electronic properties

Energy Technology Data Exchange (ETDEWEB)

Kuo, Cheng-Yu [C-PCS, Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Liu, Yinghao; Yarotski, Dmitry [Center of Integrated Nanotechnologies, Materials Physics and Application Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Li, Hao [Theory Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Xu, Ping; Yen, Hung-Ju [C-PCS, Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Tretiak, Sergei, E-mail: serg@lanl.gov [Theory Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Wang, Hsing-Lin, E-mail: hwang@lanl.gov [C-PCS, Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

2016-12-20

Graphical abstract: STM imaging reveals differently oriented domains of self-assembled tetrathiophene molecules. - Highlights: • Optical and redox properties of oligothiophene derivatives are studied. • Packing pattern of self-assembly monolayer depends on the conjugation length. • Strong electronic coupling and three redox couples in cyclic voltamogram are observed in the hierarchical self-assembly. - Abstract: Three oligothiophene (terthiophene, tetrathiophene and pentathiophene) derivatives are synthesized and their monolayer self-assemblies on gold (Au) are prepared via Au–S covalent bond. Our UV–Vis experimental characterization of solution reveals the dependence of the optical properties on the conjugation length of the oligothiophenes, which compares well with Time-Dependent Density Functional Theory (TDDFT) simulations of spectra of individual chromophores. Photoluminescent spectra of thin films show pronounced red shifts compared to that of solutions, suggesting strong inter-oligomer interactions. The comparative studies of cyclic voltammograms of tetrathiophene from solution, cast film and self-assembled monolayer (SAM) indicate presence of one, two, and three oxidized species in these samples, respectively, suggesting a very strong electronic coupling between tetrathiophene molecules in the SAM. Scanning tunneling microscopy (STM) imaging of SAMs of the tetrathiophene on an atomically flat Au surface exhibits formation of monolayer assemblies with molecular order, and the molecular packing appears to show an overlay of oligothiophene molecules on top of another one. In contrast, the trimer and pentamer images show only aggregated species lacking long-range order on the molecular level. Such trends in going from disordered–ordered–disordered monolayer assemblies are mainly due to a delicate balance between inter-chromophore π–π couplings, hydrophobic interaction and the propensity to form Au–S covalent bond. Such hypothesis has been

High spectral selectivity for solar absorbers using a monolayer transparent conductive oxide coated on a metal substrate

Science.gov (United States)

Shimizu, Makoto; Suzuki, Mari; Iguchi, Fumitada; Yugami, Hiroo

2017-05-01

A spectrally selective absorber composed of a monolayer transparent conductive oxide (TCO) coated on a metal substrate is investigated for use in solar systems operating at temperatures higher (>973 K) than the operation temperature of conventional systems ( ˜ 673 K). This method is different from the currently used solar-selective coating technologies, such as those using multilayered and cermet materials. The spectral selective absorption property can be attributed to the inherent optical property of TCO owing to the plasma frequency and interferences between the substrates. Since spectral selectivity can be achieved using monolayered materials, the effect of atomic diffusion occurring at each layer boundary in a multilayer or cermet coatings under high-temperature conditions can be reduced. In addition, since this property is attributed to the inherent property of TCO, the precise control of the layer thickness can be omitted if the layer is sufficiently thick (>0.5 μm). The optimum TCO properties, namely, carrier density and mobility, required for solar-selective absorbers are analyzed to determine the cutoff wavelength and emittance in the infrared range. A solar absorptance of 0.95 and hemispherical emittance of 0.10 at 973 K are needed for achieving the optimum TCO properties, i.e., a carrier density of 5.5 × 1020 cm-3 and mobility of 90 cm2 V-1 s-1 are required. Optical simulations indicate that the spectrally selective absorption weakly depends on the incident angle and film thickness. The thermal stability of the fabricated absorber treated at temperatures up to 973 K for 10 h is verified in vacuum by introducing a SiO2 interlayer, which plays an important role as a diffusion barrier.

Electrically tunable magnetic configuration on vacancy-doped GaSe monolayer

Science.gov (United States)

Tang, Weiqing; Ke, Congming; Fu, Mingming; Wu, Yaping; Zhang, Chunmiao; Lin, Wei; Lu, Shiqiang; Wu, Zhiming; Yang, Weihuang; Kang, Junyong

2018-03-01

Group-IIIA metal-monochalcogenides with the enticing properties have attracted tremendous attention across various scientific disciplines. With the aim to satisfy the multiple demands of device applications, here we report a design framework on GaSe monolayer in an effort to tune the electronic and magnetic properties through a dual modulation of vacancy doping and electric field. A half-metallicity with a 100% spin polarization is generated in a Ga vacancy doped GaSe monolayer due to the nonbonding 4p electronic orbital of the surrounding Se atoms. The stability of magnetic moment is found to be determined by the direction of applied electric field. A switchable magnetic configuration in Ga vacancy doped GaSe monolayer is achieved under a critical electric field of 0.6 V/Å. Electric field induces redistribution of the electronic states. Finally, charge transfers are found to be responsible for the controllable magnetic structure in this system. The magnetic modulation on GaSe monolayer in this work offers some references for the design and fabrication of tunable two-dimensional spintronic device.

Theory of lithium islands and monolayers: Electronic structure and stability

International Nuclear Information System (INIS)

Quassowski, S.; Hermann, K.

1995-01-01

Systematic calculations on planar clusters and monolayers of lithium are performed to study geometries and stabilities of the clusters as well as their convergence behavior with increasing cluster size. The calculations are based on ab initio methods using density-functional theory within the local-spin-density approximation for exchange and correlation. The optimized nearest-neighbor distances d NN of the Li n clusters, n=1,...,25, of both hexagonal and square geometry increase with cluster size, converging quite rapidly towards the monolayer results. Further, the cluster cohesive energies E c increase with cluster size and converge towards the respective monolayer values that form upper bounds. Clusters of hexagonal geometry are found to be more stable than square clusters of comparable size, consistent with the monolayer results. The size dependence of the cluster cohesive energies can be described approximately by a coordination model based on the concept of pairwise additive nearest-neighbor binding. This indicates that the average binding in the Li n clusters and their relative stabilities can be explained by simple geometric effects which derive from the nearest-neighbor coordination

One-pot reaction for the preparation of biofunctionalized self-assembled monolayers on gold surfaces

Energy Technology Data Exchange (ETDEWEB)

Raigoza, Annette F.; Fies, Whitney; Lim, Amber; Onyirioha, Kristeen; Webb, Lauren J., E-mail: lwebb@cm.utexas.edu

2017-02-01

Highlights: • One-pot synthesis of α-helical-terminated self-assembled monolayers on Au(111). • Synthesis of high density, structured, and covalently bound α-helices on Au(111). • Characterization by surface-averaged and single molecule techniques. • Peptide-terminated surfaces for fabrication of biomaterials and sensors. - Abstract: The Huisgen cycloaddition reaction (“click” chemistry) has been used extensively to functionalize surfaces with macromolecules in a straightforward manner. We have previously developed a procedure using the copper(I)-catalyzed click reaction to tether synthetic α-helical peptides carrying two alkyne groups to a well-ordered azide-terminated alkanethiol self-assembled monolayer (SAM) on a Au(111) surface. While convenient, click-based strategies potentially pose significant problems from reagents, solvents, and reaction temperatures that may irreversibly damage some molecules or substrates. Tuning click chemistry conditions would allow individual optimization of reaction conditions for a wide variety of biomolecules and substrate materials. Here, we explore the utility of simultaneous SAM formation and peptide-attachment chemistry in a one-pot reaction. We demonstrate that a formerly multistep reaction can be successfully carried out concurrently by mixing azide-terminated alkanethiols, CuCl, and a propargylglycine-containing peptide over a bare gold surface in ethanol and reacting at 70 °C. X-ray photoelectron spectroscopy (XPS), surface infrared spectroscopy, surface circular dichroic (CD) spectroscopy, and scanning tunneling microscopy (STM) were used to determine that this one-pot reaction strategy resulted in a high density of surface-bound α-helices without aggregation. This work demonstrates the simplicity and versatility of a SAM-plus-click chemistry strategy for functionalizing Au surfaces with structured biomolecules.

Nanotubes based on monolayer blue phosphorus

KAUST Repository

Montes Muñ oz, Enrique; Schwingenschlö gl, Udo

2016-01-01

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

The structure of a lipid-water lamellar phase containing two types of lipid monolayers

International Nuclear Information System (INIS)

Ranck, J.L.; Luzzati, V.; Zaccai, G.

1980-01-01

One lamellar phase, observed in the mitochondrial lipids-water system at low temperature (ca 253 K) and at low water content (ca 15%), contains four lipid monolayers in its unit cell, two of type α and two of type β. Previous X-ray scattering studies of this phase led to an ambiguity: the phase could contain either two homogeneous bilayers, one α and one β, or two mixed bilayers, each formed by an α and a β monolayer. A solution to this problem was sought in a neutron scattering study as a function of the D 2 O/H 2 O ratio. Because of limited resolution, straightforward analysis of the neutron scattering data leads also to ambiguous results. Using a more sophisticated analysis based upon the zeroth- and second-order moments of the Patterson peaks relevant to the exchangeable components, it is shown that the weight of the evidence is in favour of a structure containing mixed bilayers. (Auth.)

Supramolecular domains in mixed peptide self-assembled monolayers on gold nanoparticles.

Science.gov (United States)

Duchesne, Laurence; Wells, Geoff; Fernig, David G; Harris, Sarah A; Lévy, Raphaël

2008-09-01

Self-organization in mixed self-assembled monolayers of small molecules provides a route towards nanoparticles with complex molecular structures. Inspired by structural biology, a strategy based on chemical cross-linking is introduced to probe proximity between functional peptides embedded in a mixed self-assembled monolayer at the surface of a nanoparticle. The physical basis of the proximity measurement is a transition from intramolecular to intermolecular cross-linking as the functional peptides get closer. Experimental investigations of a binary peptide self-assembled monolayer show that this transition happens at an extremely low molar ratio of the functional versus matrix peptide. Molecular dynamics simulations of the peptide self-assembled monolayer are used to calculate the volume explored by the reactive groups. Comparison of the experimental results with a probabilistic model demonstrates that the peptides are not randomly distributed at the surface of the nanoparticle, but rather self-organize into supramolecular domains.

Ultrasensitive electrochemical biosensor based on the oligonucleotide self-assembled monolayer-mediated immunosensing interface

Energy Technology Data Exchange (ETDEWEB)

Liu, Dengyou; Luo, Qimei [Science College of Hunan Agricultural University, Changsha 410128 (China); Deng, Fawen [The Fourth Hospital of Chansha, Changsha 410006 (China); Li, Zhen [Science College of Hunan Agricultural University, Changsha 410128 (China); Li, Benxiang, E-mail: 172170960@qq.com [Science College of Hunan Agricultural University, Changsha 410128 (China); Shen, Zhifa, E-mail: shenzhifa@wmu.edu.cn [Key Laboratory of Laboratory Medicine, Ministry of Education, Zhejiang Provincial Key Laboratory of Medical Genetics, College of Laboratory Medicine and Life Sciences, Wenzhou Medical University, Wenzhou 325035 (China)

2017-06-08

Highly sensitive and selective quantitation of a variety of proteins over a wide concentration range is highly desirable for increased accuracy of biomarker detection or for multidisease diagnostics. In the present contribution, using human immunoglobulin G (HIgG) as the model target protein, an electrochemical ultrasensitive immunosensing platform was developed based on the oligonucleotide self-assembled monolayer-mediated (OSAM) sensing interface. For this immunosensor, the “signal-on” signaling mechanism and enzymatic signal amplification effect were integrated into one sensing architecture. Moreover, the thiolated flexible single-stranded DNAs immobilized onto gold electrode surface not only performs the wobbling motion to facilitate the electron transfer between the electrode surface and biosensing layer but also fundamentally prohibiting the direct interaction of proteins with gold substrate. Thus, the electrochemical signal could be efficiently enhanced and the unspecific adsorption or cross-reaction might be eliminated. As a result, utilizing the newly-proposed immunosensor, the HIgG can be detected down to 0.5 ng/mL, and the high detection specificity is offered. The successful design of OSAM and the highly desirable detection capability of new immunosensor are expected to provide a perspective for fabricating new robust immunosensing platform and for promising potential of oligonucleotide probe in biological research and biomedical diagnosis. - Highlights: • An electrochemical ultrasensitive immunosensing platform was developed based on the oligonucleotide self-assembled monolayer (OASM). • OASM severs as a flexible monolayer to promote electron transfer and prohibits the direct interaction of proteins with gold substrate. • The electrochemical signal is efficiently enhanced and the unspecific adsorption or cross-reaction is eliminated. • Target protein can be detected down to 0.5 ng/mL, and the high detection specificity can be obtained. �

Vertical uniformity of cells and nuclei in epithelial monolayers.

Science.gov (United States)

Neelam, Srujana; Hayes, Peter Robert; Zhang, Qiao; Dickinson, Richard B; Lele, Tanmay P

2016-01-22

Morphological variability in cytoskeletal organization, organelle position and cell boundaries is a common feature of cultured cells. Remarkable uniformity and reproducibility in structure can be accomplished by providing cells with defined geometric cues. Cells in tissues can also self-organize in the absence of directing extracellular cues; however the mechanical principles for such self-organization are not understood. We report that unlike horizontal shapes, the vertical shapes of the cell and nucleus in the z-dimension are uniform in cells in cultured monolayers compared to isolated cells. Apical surfaces of cells and their nuclei in monolayers were flat and heights were uniform. In contrast, isolated cells, or cells with disrupted cell-cell adhesions had nuclei with curved apical surfaces and variable heights. Isolated cells cultured within micron-sized square wells displayed flat cell and nuclear shapes similar to cells in monolayers. Local disruption of nuclear-cytoskeletal linkages resulted in spatial variation in vertical uniformity. These results suggest that competition between cell-cell pulling forces that expand and shorten the vertical cell cross-section, thereby widening and flattening the nucleus, and the resistance of the nucleus to further flattening results in uniform cell and nuclear cross-sections. Our results reveal the mechanical principles of self-organized vertical uniformity in cell monolayers.

Photocarrier dynamics in monolayer phosphorene and bulk black phosphorus.

Science.gov (United States)

Zereshki, Peymon; Wei, Yaqing; Ceballos, Frank; Bellus, Matthew Z; Lane, Samuel D; Pan, Shudi; Long, Run; Zhao, Hui

2018-06-13

We report a combined theoretical and experimental study on photocarrier dynamics in monolayer phosphorene and bulk black phosphorus. Samples of monolayer phosphorene and bulk black phosphorus were fabricated by mechanical exfoliation, identified according to their reflective contrasts, and protected by covering them with hexagonal boron nitride layers. Photocarrier dynamics in these samples was studied by an ultrafast pump-probe technique. The photocarrier lifetime of monolayer phosphorene was found to be about 700 ps, which is about 9 times longer than that of bulk black phosphorus. This trend was reproduced in our calculations based on ab initio nonadiabatic molecular dynamics combined with time-domain density functional theory in the Kohn-Sham representation, and can be attributed to the smaller bandgap and stronger nonadiabatic coupling in bulk. The transient absorption response was also found to be dependent on the sample orientation with respect to the pump polarization, which is consistent with the previously reported anisotropic absorption of phosphorene. In addition, an oscillating component of the differential reflection signal at early probe delays was observed in the bulk sample and was attributed to the layer-breathing phonon mode with an energy of about 1 meV and a decay time of about 1.35 ps. These results provide valuable information for application of monolayer phosphorene in optoelectronics.

Topography-specific isotropic tunneling in nanoparticle monolayer with sub-nm scale crevices.

Science.gov (United States)

Wang, Guisheng; Jiao, Weihong; Yi, Lizhi; Zhang, Yuejiao; Wu, Ke; Zhang, Chao; Lv, Xianglong; Qian, Lihua; Li, Jianfeng; Yuan, Songliu; Chen, Liang

2016-10-07

Material used in flexible devices may experience anisotropic strain with identical magnitude, outputting coherent signals that tend to have a serious impact on device reliability. In this work, the surface topography of the nanoparticles (NPs) is proposed to be a parameter to control the performance of strain gauge based on tunneling behavior. In contrast to anisotropic tunneling in a monolayer of spherical NPs, electron tunneling in a monolayer of urchin-like NPs actually exhibits a nearly isotropic response to strain with different loading orientations. Isotropic tunneling of the urchin-like NPs is caused by the interlocked pikes of these urchin-like NPs in a random manner during external mechanical stimulus. Topography-dependent isotropic tunneling in two dimensions reported here opens a new opportunity to create highly reliable electronics with superior performance.

Phase transitions in polymer monolayers

NARCIS (Netherlands)

Deschênes, Louise; Lyklema, J.; Danis, Claude; Saint-Germain, François

2015-01-01

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.

Displacive phase transition at the 5/3 monolayer of Pb on Ge(001)

International Nuclear Information System (INIS)

Cvetko, D.; Ratto, F.; Cossaro, A.; Floreano, L.; Bavdek, G.; Morgante, A.

2005-01-01

At a coverage of 5/3 monolayer (ML), Pb adsorbed on Ge(001) forms a ground phase displaying a ((2 1/0 6)) symmetry. This phase undergoes two reversible phase transitions ((2 1/0 6))↔((2 1/0 3))↔(2x1) at the critical temperatures T c 1 ∼178 K and T c 2 ∼375 K, respectively. We investigated the behavior of the relevant order parameters at the critical temperatures by means of He and in-plane x-ray diffraction (HAS and XRD, respectively). Both phase transitions at the critical temperature put in evidence a clear order-disorder behavior, in agreement with the universality class expected for the corresponding symmetry group transformation. The low-temperature transition yields the critical exponent of the two-dimensional (2-D) Ising universality class, whereas the three-state Potts' critical exponents are found for the high-temperature transition. By out-of-plane XRD measurements, the low-temperature phase transition is observed to be accompanied by a static surface distortion at room temperature. A complementary HAS study of the temperature evolution of the surface charge corrugation reveals that the complete ((2 1/0 6))↔((2 1/0 3)) transition is of the displacive type. On the contrary, the high-temperature phase transition does not show any change of the surface corrugation up to its irreversible decomposition, thus pointing to a pure order-disorder character

Anomalously temperature-dependent thermal conductivity of monolayer GaN with large deviations from the traditional 1 /T law

Science.gov (United States)

Qin, Guangzhao; Qin, Zhenzhen; Wang, Huimin; Hu, Ming

2017-05-01

Efficient heat dissipation, which is featured by high thermal conductivity, is one of the crucial issues for the reliability and stability of nanodevices. However, due to the generally fast 1 /T decrease of thermal conductivity with temperature increase, the efficiency of heat dissipation quickly drops down at an elevated temperature caused by the increase of work load in electronic devices. To this end, pursuing semiconductor materials that possess large thermal conductivity at high temperature, i.e., slower decrease of thermal conductivity with temperature increase than the traditional κ ˜1 /T relation, is extremely important to the development of disruptive nanoelectronics. Recently, monolayer gallium nitride (GaN) with a planar honeycomb structure emerges as a promising new two-dimensional material with great potential for applications in nano- and optoelectronics. Here, we report that, despite the commonly established 1 /T relation of thermal conductivity in plenty of materials, monolayer GaN exhibits anomalous behavior that the thermal conductivity almost decreases linearly over a wide temperature range above 300 K, deviating largely from the traditional κ ˜1 /T law. The thermal conductivity at high temperature is much larger than the expected thermal conductivity that follows the general κ ˜1 /T trend, which would be beneficial for applications of monolayer GaN in nano- and optoelectronics in terms of efficient heat dissipation. We perform detailed analysis on the mechanisms underlying the anomalously temperature-dependent thermal conductivity of monolayer GaN in the framework of Boltzmann transport theory and further get insight from the view of electronic structure. Beyond that, we also propose two required conditions for materials that would exhibit similar anomalous temperature dependence of thermal conductivity: large difference in atom mass (huge phonon band gap) and electronegativity (LO-TO splitting due to strong polarization of bond). Our

Role of defects in tuning the electronic properties of monolayer WS{sub 2} grown by chemical vapor deposition

Energy Technology Data Exchange (ETDEWEB)

Yang, Jie; Zheliuk, Oleksandr; Lu, Jianming; Ye, Jianting [Zernike Institute for Advanced Materials, University of Groningen, Groningen (Netherlands); Gordiichuk, Pavlo [Zernike Institute for Advanced Materials, University of Groningen, Groningen (Netherlands); Department of Chemistry, Northwestern University, Evanston, IL (United States); Herrmann, Andreas [Zernike Institute for Advanced Materials, University of Groningen, Groningen (Netherlands); Molecular Biophysics, Department of Biology, Humboldt-Universitaet Berlin (Germany)

2017-10-15

Two-dimensional transition metal dichalcogenides have already attracted enormous research interest. To understand the dependence of electronic properties on the quality and defect morphology is vital for synthesizing high quality materials and the realization of functional devices. Here, we demonstrate the mapping of the conductive variations by conducting atomic force microscopy (C-AFM) in the monolayer tungsten disulfide (WS{sub 2}) grown by chemical vapor deposition. The electronic properties are strongly affected by the formation of vacancies in monolayer WS{sub 2} during growth, which is also verified by the photoluminescence. This spatial study of defects provides opportunities for optimization of the growth process for enhancing devices performance of TMDs monolayers. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Robust tunable excitonic features in monolayer transition metal dichalcogenide quantum dots

Science.gov (United States)

Fouladi-Oskouei, J.; Shojaei, S.; Liu, Z.

2018-04-01

The effects of quantum confinement on excitons in parabolic quantum dots of monolayer transition metal dichalcogenides (TMDC QDs) are investigated within a massive Dirac fermion model. A giant spin-valley coupling of the TMDC QDs is obtained, larger than that of monolayer TMDC sheets and consistent with recent experimental measurements. The exciton transition energy and the binding energy are calculated, and it is found that the strong quantum confinement results in extremely high exciton binding energies. The enormously large exciton binding energy in TMDC QDs (({{E}{{B2D}}}∼ 500 meV)different kinds of TMDC QDs) ensures that the many body interactions play a significant role in the investigation of the optical properties of these novel nanostructures. The estimated oscillator strength and radiative lifetime of excitons are strongly size-dependent and indicate a giant oscillator strength enhancement and ultrafast radiative annihilation of excitons, varying from a few tens of femtoseconds to a few picoseconds. We found that the spin-dependent band gap, spin-valley coupling, binding energy and excitonic effects can be tuned by quantum confinements, leading to tunable quantum dots in monolayer TMDCs. This finding offers new functionality in engineering the interaction of a 2D material with light and creates promise for the quantum manipulation of spin and valley degrees of freedom in TMDC nanostructures, enabling versatile novel 2D quantum photonic and optoelectronic nanodevices.

Interactions of phospholipid monolayer with single-walled carbon nanotube wrapped by lysophospholipid

Energy Technology Data Exchange (ETDEWEB)

Lim, Siwool; Kim, Hyungsu, E-mail: hkim@dku.edu

2012-10-01

In this study, we prepared single-walled carbon nanotubes (SWNTs) wrapped by 1-stearoyl-2-hydroxy-sn-glycero-3-phospho-(1 Prime -rac-glycerol) (LPG), leading to a complex of SWNT-LPG. In an attempt to investigate the interactions of SWNT-LPG with a mimicked cell surface, SWNT-LPG solution was injected into the sub-phase of Langmuir trough to form a mixed monolayer with dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG), respectively. In addition to the measurement of typical surface pressure-area isotherms under compression mode, area changes occurring during insertion of SWNT-LPG into the monolayer were recorded at various surface pressures. Changes in surface potential were also measured for evident tracing of the degree of interactions between sub-phase and monolayer. A systematic comparison of relaxation patterns and insertion behavior along with surface potential data provided a rational basis to distinguish the degree of interactions between SWNT-LPG and the designated monolayer. The observed tendencies were found to be in accordance with the surface topography as revealed by the tapping mode atomic force microscopy. It was consistently observed that SWNT-LPG interacted with DPPC to a greater extent than with DPPG, when the sufficient coverage of nanotube surface by LPG molecules was assured. - Highlights: Black-Right-Pointing-Pointer Complex of single-walled carbon nanotubes and lysophospholipid (SWNT-LPG) is formed. Black-Right-Pointing-Pointer Composite monolayer is formed by inserting SWNT-LPG into the phospholipid monolayer. Black-Right-Pointing-Pointer We measure area-pressure responses and dipole potentials during the insertion process. Black-Right-Pointing-Pointer Properties of composite monolayer depend on the kind of phospholipid and LPG content.

Synthesis of organosilicon derivatives of [1]benzothieno[3,2-b][1]-benzothiophene for efficient monolayer Langmuir-Blodgett organic field effect transistors.

Science.gov (United States)

Borshchev, O V; Sizov, A S; Agina, E V; Bessonov, A A; Ponomarenko, S A

2017-01-16

For the first time, the synthesis of organosilicon derivatives of dialkyl[1]benzothieno[3,2-b][1]-benzothiophene (BTBT) capable of forming a semiconducting monolayer at the water-air interface is reported. Self-assembled monolayer organic field-effect transistors prepared from these materials using the Langmuir-Blodgett technique showed high hole mobilities and excellent air stability.

Quantification of stromal vascular cell mechanics with a linear cell monolayer rheometer

Energy Technology Data Exchange (ETDEWEB)

Elkins, Claire M., E-mail: cma9@stanford.edu; Fuller, Gerald G. [Department of Chemical Engineering, Stanford University, Stanford, California 94305 (United States); Shen, Wen-Jun; Khor, Victor K.; Kraemer, Fredric B. [Division of Endocrinology, Gerontology and Metabolism, Stanford University, Stanford, California 94305 and Veterans Affairs Palo Alto Health Care System, Palo Alto, California 94304 (United States)

2015-01-15

Over the past few decades researchers have developed a variety of methods for measuring the mechanical properties of whole cells, including traction force microscopy, atomic force microscopy (AFM), and single-cell tensile testing. Though each of these techniques provides insight into cell mechanics, most also involve some nonideal conditions for acquiring live cell data, such as probing only one portion of a cell at a time, or placing the cell in a nonrepresentative geometry during testing. In the present work, we describe the development of a linear cell monolayer rheometer (LCMR) and its application to measure the mechanics of a live, confluent monolayer of stromal vascular cells. In the LCMR, a monolayer of cells is contacted on both top and bottom by two collagen-coated plates and allowed to adhere. The top plate then shears the monolayer by stepping forward to induce a predetermined step strain, while a force transducer attached to the top plate collects stress information. The stress and strain data are then used to determine the maximum relaxation modulus recorded after step-strain, G{sub r}{sup 0}, referred to as the zero-time relaxation modulus of the cell monolayer. The present study validates the ability of the LCMR to quantify cell mechanics by measuring the change in G{sub r}{sup 0} of a confluent cell monolayer upon the selective inhibition of three major cytoskeletal components (actin microfilaments, vimentin intermediate filaments, and microtubules). The LCMR results indicate that both actin- and vimentin-deficient cells had ∼50% lower G{sub r}{sup 0} values than wild-type, whereas tubulin deficiency resulted in ∼100% higher G{sub r}{sup 0} values. These findings constitute the first use of a cell monolayer rheometer to quantitatively distinguish the roles of different cytoskeletal elements in maintaining cell stiffness and structure. Significantly, they are consistent with results obtained using single-cell mechanical testing methods

Hybrid nanostructures of well-organized arrays of colloidal quantum dots and a self-assembled monolayer of gold nanoparticles for enhanced fluorescence

Science.gov (United States)

Liu, Xiaoying; McBride, Sean P.; Jaeger, Heinrich M.; Nealey, Paul F.

2016-07-01

Hybrid nanomaterials comprised of well-organized arrays of colloidal semiconductor quantum dots (QDs) in close proximity to metal nanoparticles (NPs) represent an appealing system for high-performance, spectrum-tunable photon sources with controlled photoluminescence. Experimental realization of such materials requires well-defined QD arrays and precisely controlled QD-metal interspacing. This long-standing challenge is tackled through a strategy that synergistically combines lateral confinement and vertical stacking. Lithographically generated nanoscale patterns with tailored surface chemistry confine the QDs into well-organized arrays with high selectivity through chemical pattern directed assembly, while subsequent coating with a monolayer of close-packed Au NPs introduces the plasmonic component for fluorescence enhancement. The results show uniform fluorescence emission in large-area ordered arrays for the fabricated QD structures and demonstrate five-fold fluorescence amplification for red, yellow, and green QDs in the presence of the Au NP monolayer. Encapsulation of QDs with a silica shell is shown to extend the design space for reliable QD/metal coupling with stronger enhancement of 11 times through the tuning of QD-metal spatial separation. This approach provides new opportunities for designing hybrid nanomaterials with tailored array structures and multiple functionalities for applications such as multiplexed optical coding, color display, and quantum transduction.

Growth and time dependent alignment of KCl crystals in Hemoglobin LB monolayer

International Nuclear Information System (INIS)

Mahato, Mrityunjoy; Pal, Prabir; Tah, Bidisha; Kamilya, Tapanendu; Talapatra, G.B.

2012-01-01

Nature and organism often use the biomineralization technique to build up various highly regular structures such as bone, teeth, kidney stone etc., and recently this becomes the strategy to design and synthesis of novel biocomposite materials. We report here the controlled crystallization of KCl in Langmuir and Langmuir Blodgett (LB) monolayer of Hemoglobin (Hb) at ambient condition. The nucleation and growth of KCl crystals in Hb monolayer has temporal and KCl concentration dependency. The growth of KCl crystals in LB film of Hb has distinct behavior in the alignment of crystals from linear to fractal like structures depending on growth time. The crystallographic identity of the biomineralized KCl crystal is confirmed from HR-TEM, XRD, and from powder diffraction simulation. Our results substantiated that the template of Langmuir monolayer of proteins plays a crucial role in biomineralization as well as in designing and synthesizing of novel biocomposite materials. Highlights: ► Biomineralization of KCl crystal has been studied in Hemoglobin LB film. ► KCl crystal growth is time and concentration of KCl dependent. ► The alignment of KCl crystal growth is fractal nature with time. ► The unfolding of Hb and evaporation factor has some role in crystallization and fractal growth.

Monolayer-Mediated Growth of Organic Semiconductor Films with Improved Device Performance.

Science.gov (United States)

Huang, Lizhen; Hu, Xiaorong; Chi, Lifeng

2015-09-15

Increased interest in wearable and smart electronics is driving numerous research works on organic electronics. The control of film growth and patterning is of great importance when targeting high-performance organic semiconductor devices. In this Feature Article, we summarize our recent work focusing on the growth, crystallization, and device operation of organic semiconductors intermediated by ultrathin organic films (in most cases, only a monolayer). The site-selective growth, modified crystallization and morphology, and improved device performance of organic semiconductor films are demonstrated with the help of the inducing layers, including patterned and uniform Langmuir-Blodgett monolayers, crystalline ultrathin organic films, and self-assembled polymer brush films. The introduction of the inducing layers could dramatically change the diffusion of the organic semiconductors on the surface and the interactions between the active layer with the inducing layer, leading to improved aggregation/crystallization behavior and device performance.

Monolayer graphene-insulator-semiconductor emitter for large-area electron lithography

Science.gov (United States)

Kirley, Matthew P.; Aloui, Tanouir; Glass, Jeffrey T.

2017-06-01

The rapid adoption of nanotechnology in fields as varied as semiconductors, energy, and medicine requires the continual improvement of nanopatterning tools. Lithography is central to this evolving nanotechnology landscape, but current production systems are subject to high costs, low throughput, or low resolution. Herein, we present a solution to these problems with the use of monolayer graphene in a graphene-insulator-semiconductor (GIS) electron emitter device for large-area electron lithography. Our GIS device displayed high emission efficiency (up to 13%) and transferred large patterns (500 × 500 μm) with high fidelity (industries and opening opportunities in nanomanufacturing.

Valley–spin Seebeck effect in heavy group-IV monolayers

International Nuclear Information System (INIS)

Zhai, Xuechao; Wang, Shengdong; Zhang, Yan

2017-01-01

Akin to electron spin, the valley has become another highly valued degree of freedom in modern electronics, specifically after tremendous studies on monolayers of group-IV materials, i.e. graphene, silicene, germanene and stanene. Except for graphene, the other heavy group-IV monolayers have observable intrinsic spin–orbit interactions due to their buckled structures. Distinct from the usual electric or optical control of valley and spin, we here employ a temperature difference to drive electron motion in ferromagnetic heavy group-IV monolayers via designing a caloritronic device locally modulated by an interlayer electric (E z ) field. A unique valley–spin Seebeck (VSS) effect is discovered, with the current contributed only by one (the other) valley and one (the other) spin moving along one (the opposite) direction. This effect is suggested to be detected below the critical temperature about 18 K for silicene, 200 K for germanene and 400 K for stanene, arising from the characteristic valley–spin nondegenerate band structures tuned by the E z field, but cannot be driven in graphene without spin–orbit interaction. Above the critical temperature, the VSS effect is broken by overlarge temperature broadening. Besides the temperature, it is also found that the E z field can drive a transition between the VSS effect and the normal spin Seebeck effect. Further calculations indicate that the VSS effect is robust against many realistic perturbations. Our research represents a conceptually but substantially major step towards the study of the Seebeck effect. These findings provide a platform for encoding information simultaneously by the valley and spin quantum numbers of electrons in future thermal-logic circuits and energy-saving devices. (paper)

Bioinspired Nanocomposite Hydrogels with Highly Ordered Structures.

Science.gov (United States)

Zhao, Ziguang; Fang, Ruochen; Rong, Qinfeng; Liu, Mingjie

2017-12-01

In the human body, many soft tissues with hierarchically ordered composite structures, such as cartilage, skeletal muscle, the corneas, and blood vessels, exhibit highly anisotropic mechanical strength and functionality to adapt to complex environments. In artificial soft materials, hydrogels are analogous to these biological soft tissues due to their "soft and wet" properties, their biocompatibility, and their elastic performance. However, conventional hydrogel materials with unordered homogeneous structures inevitably lack high mechanical properties and anisotropic functional performances; thus, their further application is limited. Inspired by biological soft tissues with well-ordered structures, researchers have increasingly investigated highly ordered nanocomposite hydrogels as functional biological engineering soft materials with unique mechanical, optical, and biological properties. These hydrogels incorporate long-range ordered nanocomposite structures within hydrogel network matrixes. Here, the critical design criteria and the state-of-the-art fabrication strategies of nanocomposite hydrogels with highly ordered structures are systemically reviewed. Then, recent progress in applications in the fields of soft actuators, tissue engineering, and sensors is highlighted. The future development and prospective application of highly ordered nanocomposite hydrogels are also discussed. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A fast transfer-free synthesis of high-quality monolayer graphene on insulating substrates by a simple rapid thermal treatment.

Science.gov (United States)

Wu, Zefei; Guo, Yanqing; Guo, Yuzheng; Huang, Rui; Xu, Shuigang; Song, Jie; Lu, Huanhuan; Lin, Zhenxu; Han, Yu; Li, Hongliang; Han, Tianyi; Lin, Jiangxiazi; Wu, Yingying; Long, Gen; Cai, Yuan; Cheng, Chun; Su, Dangsheng; Robertson, John; Wang, Ning

2016-02-07

The transfer-free synthesis of high-quality, large-area graphene on a given dielectric substrate, which is highly desirable for device applications, remains a significant challenge. In this paper, we report on a simple rapid thermal treatment (RTT) method for the fast and direct growth of high-quality, large-scale monolayer graphene on a SiO2/Si substrate from solid carbon sources. The stack structure of a solid carbon layer/copper film/SiO2 is adopted in the RTT process. The inserted copper film does not only act as an active catalyst for the carbon precursor but also serves as a "filter" that prevents premature carbon dissolution, and thus, contributes to graphene growth on SiO2/Si. The produced graphene exhibits a high carrier mobility of up to 3000 cm(2) V(-1) s(-1) at room temperature and standard half-integer quantum oscillations. Our work provides a promising simple transfer-free approach using solid carbon sources to obtain high-quality graphene for practical applications.

A high-coverage nanoparticle monolayer for the fabrication of a subwavelength structure on InP substrates.

Science.gov (United States)

Kim, Dae-Seon; Park, Min-Su; Jang, Jae-Hyung

2011-08-01

Subwavelength structures (SWSs) were fabricated on the Indium Phosphide (InP) substrate by utilizing the confined convective self-assembly (CCSA) method followed by reactive ion etching (RIE). The surface condition of the InP substrate was changed by depositing a 30-nm-thick SiO2 layer and subsequently treating the surface with O2 plasma to achieve better surface coverage. The surface coverage of nanoparticle monolayer reached 90% by using O2 plasma-treated SiO2/InP substrate among three kinds of starting substrates such as the bare InP, SiO2/InP and O2 plasma-treated SiO2/InP substrate. A nanoparticle monolayer consisting of polystyrene spheres with diameter of 300 nm was used as an etch mask for transferring a two-dimensional periodic pattern onto the InP substrate. The fabricated conical SWS with an aspect ratio of 1.25 on the O2 plasma-treated SiO2/InP substrate exhibited the lowest reflectance. The average reflectance of the conical SWS was 5.84% in a spectral range between 200 and 900 nm under the normal incident angle.

The Rheological Properties of Lipid Monolayers Modulate the Incorporation of l-Ascorbic Acid Alkyl Esters.

Science.gov (United States)

Díaz, Yenisleidy de Las Mercedes Zulueta; Mottola, Milagro; Vico, Raquel V; Wilke, Natalia; Fanani, María Laura

2016-01-19

In this work, we tested the hypothesis that the incorporation of amphiphilic drugs into lipid membranes may be regulated by their rheological properties. For this purpose, two members of the l-ascorbic acid alkyl esters family (ASCn) were selected, ASC16 and ASC14, which have different rheological properties when organized at the air/water interface. They are lipophilic forms of vitamin C used in topical pharmacological preparations. The effect of the phase state of the host lipid membranes on ASCn incorporation was explored using Langmuir monolayers. Films of pure lipids with known phase states have been selected, showing liquid-expanded, liquid-condensed, and solid phases as well as pure cholesterol films in liquid-ordered state. We also tested ternary and quaternary mixed films that mimic the properties of cholesterol containing membranes and of the stratum corneum. The compressibility and shear properties of those monolayers were assessed in order to define its phase character. We found that the length of the acyl chain of the ASCn compounds induces differential changes in the rheological properties of the host membrane and subtly regulates the kinetics and extent of the penetration process. The capacity for ASCn uptake was found to depend on the phase state of the host film. The increase in surface pressure resultant after amphiphile incorporation appears to be a function of the capacity of the host membrane to incorporate such amphiphile as well as the rheological response of the film. Hence, monolayers that show a solid phase state responded with a larger surface pressure increase to the incorporation of a comparable amount of amphiphile than liquid-expanded ones. The cholesterol-containing films, including the mixture that mimics stratum corneum, allowed a very scarce ASCn uptake independently of the membrane diffusional properties. This suggests an important contribution of Cho on the maintenance of the barrier function of stratum corneum.

Interferon induction in bovine and feline monolayer cultures by four bluetongue virus serotypes.

OpenAIRE

Fulton, R W; Pearson, N J

1982-01-01

The interferon inducing ability of bluetongue viruses was studied in bovine and feline monolayer cultures inoculated with each of four bluetongue virus serotypes. Interferon was assayed by a plaque reduction method in monolayer cultures with vesicular stomatitis virus as challenge virus. Interferon was produced by bovine turbinate, Georgia bovine kidney, and Crandell feline kidney monolayer cultures in response to bluetongue virus serotypes 10, 11, 13 and 17. The antiviral substances produced...

Investigation on gallium ions impacting monolayer graphene

Energy Technology Data Exchange (ETDEWEB)

Wu, Xin; Zhao, Haiyan, E-mail: hyzhao@tsinghua.edu.cn; 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)

2015-06-15

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.

Packing stress reduction in polymer-lipid monolayers at the air-water interface: An X-ray grazing-incidence diffraction and reflectivity study

Energy Technology Data Exchange (ETDEWEB)

Kuhl, T.L.; Majewski, J.; Howes, P.B.; Kjaer, K.; Nahmen, A. von; Lee, K.Y.C.; Ocko, B.; Israelachvili, J.N.; Smith, G.S.

1999-08-25

Using synchrotron grazing-incidence X-ray diffraction (GIXD) and reflectivity (XR), the authors have determined the in-plane and out-of-plane structure of phospholipid monolayers at the air-water interface as a function of hydrophilic lipid headgroup size. Di-stearoyl-phosphatidyl-ethanolamine (DSPE) lipid monolayers were systematically modified by chemically grafting hydrophilic poly(ethylene glycol) (PEG) chains of MW = 90 g/mol (2 ethylene oxide, EO, units), MW = 350 g/mol (8 EO units), and MW = 750 g/mol (17 EO units) to the lipid headgroups. The monolayers were studied in the solid phase at a surface pressure of 42 mN/m. At these high lipid packing densities, the PEG chains are submerged in the water subphase. The increased packing stresses from these bulky polymer headgroups distort the unit cell and the in-plane packing modes of the monolayers, leading to large out-of-plane alterations and staggering of the lipid molecules. Surprisingly, a change in the molecular packing of the monolayer toward higher packing densities (lower area per molecule) was observed on increasing the PEG MW to 750 g/mol (17 EO units). This rearrangement of the monolayer structure may be due to a conformational change in the PEG chains.

Electric field effect of GaAs monolayer from first principles

Directory of Open Access Journals (Sweden)

Jiongyao Wu

2017-03-01

Full Text Available Using first-principle calculations, we investigate two-dimensional (2D honeycomb monolayer structures composed of group III-V binary elements. It is found that such compound like GaAs should have a buckled structure which is more stable than graphene-like flat structure. This results a polar system with out-of-plane dipoles arising from the non-planar structure. Here, we optimized GaAs monolayer structure, then calculated the electronic band structure and the change of buckling height under external electric field within density functional theory using generalized gradient approximation method. We found that the band gap would change proportionally with the electric field magnitude. When the spin-orbit coupling (SOC is considered, we revealed fine spin-splitting at different points in the reciprocal space. Furthermore, the valence and conduction bands spin-splitting energies due to SOC at the K point of buckled GaAs monolayers are found to be weakly dependent on the electric field strength. Finally electric field effects on the spin texture and second harmonic generation are discussed. The present work sheds light on the control of physical properties of GaAs monolayer by the applied electric field.

Large valley splitting in monolayer WS2 by proximity coupling to an insulating antiferromagnetic substrate

Science.gov (United States)

Xu, Lei; Yang, Ming; Shen, Lei; Zhou, Jun; Zhu, Tao; Feng, Yuan Ping

2018-01-01

Lifting the valley degeneracy is an efficient way to achieve valley polarization for further valleytronics operations. In this Rapid Communication, we demonstrate that a large valley splitting can be obtained in monolayer transition metal dichalcogenides by magnetic proximity coupling to an insulating antiferromagnetic substrate. As an example, we perform first-principles calculations to investigate the electronic structures of monolayer WS2 on the MnO(111) surface. Our calculation results suggest that a large valley splitting of 214 meV, which corresponds to a Zeeman magnetic field of 1516 T, is induced in the valence band of monolayer WS2. The magnitude of valley splitting relies on the strength of interfacial orbital hybridization and can be tuned continually by applying an external out-of-plane pressure and in-plane strain. More interestingly, we find that both spin and valley index will flip when the magnetic ordering of MnO is reversed. Besides, owing to the sizable Berry curvature and time-reversal symmetry breaking in the WS2/MnO heterostructure, a spin- and valley-polarized anomalous Hall current can be generated in the presence of an in-plane electric field, which allows one to detect valleys by the electrical approach. Our results shed light on the realization of valleytronic devices using the antiferromagnetic insulator as the substrate.

Ordering transitions of weakly anisotropic hard rods in narrow slitlike pores.

Science.gov (United States)

Aliabadi, Roohollah; Gurin, Péter; Velasco, Enrique; Varga, Szabolcs

2018-01-01

The effect of strong confinement on the positional and orientational ordering is examined in a system of hard rectangular rods with length L and diameter D (L>D) using the Parsons-Lee modification of the second virial density-functional theory. The rods are nonmesogenic (L/Dlayers is allowed to form in the pore. In the extreme confinement limit of H≤2D, where only one-layer structures appear, we observe a structural transition from a planar to a homeotropic fluid layer with increasing density, which becomes sharper as L→H. In wider pores (2Dlayers, homeotropic order, and even combined bilayer structures (one layer is homeotropic, while the other is planar) can be stabilized at high densities. Moreover, first-order phase transitions can be seen between different structures. One of them emerges between a monolayer and a bilayer with planar orders at relatively low packing fractions.

Regulation of endothelial cell shape and monolayer permeability by atrial natriuretic peptide

International Nuclear Information System (INIS)

Lofton-Day, C.E.

1989-01-01

Atrial natriuretic peptide (ANP), considered to be an important regulator of intravascular fluid volume, binds specifically to receptors on endothelial cells. In this study, the role of ANP-specific binding was investigated by examining the effect of ANP on the morphology and macromolecular permeability of monolayer cultures of bovine aortic endothelial cells. ANP alone had no observable effect on the monolayers. However, incubation of monolayers with ANP antagonized thrombin- or glucose oxidase-induced cell shape changes and intercellular gap formation. ANP pretreatment also opposed the effect of thrombin and glucose oxidase on actin filament distribution as observed by rhodamine-phalloidin staining and digital image analysis of F0actin staining. In addition, ANP reversed cell shape changes and cytoskeletal alterations induced by thrombin treatment but did not reverse alternations induced by glucose oxidase treatment. ANP significantly reduced increases in monolayer permeability to albumin resulting from thrombin or glucose oxidases treatment. Thrombin caused a 2-fold increase in monolayer permeability to 125 I-labeled albumin, which was abolished by 10 -8 -10 -6 M ANP pretreatment. Glucose oxidase caused similar increases in permeability and was inhibited by ANP at slightly shorter time periods

Photoluminescence Enhancement and Structure Repairing of Monolayer MoSe 2 by Hydrohalic Acid Treatment

KAUST Repository

Han, Hau-Vei

2015-12-30

Atomically thin two-dimensional transition-metal dichalcogenides (TMDCs) have attracted much attention recently due to their unique electronic and optical properties for future optoelectronic devices. The chemical vapor deposition (CVD) method is able to generate TMDCs layers with a scalable size and a controllable thickness. However, the TMDC monolayers grown by CVD may incorporate structural defects, and it is fundamentally important to understand the relation between photoluminescence and structural defects. In this report, point defects (Se vacancies) and oxidized Se defects in CVD-grown MoSe2 monolayers are identified by transmission electron microscopy and X-ray photoelectron spectroscopy. These defects can significantly trap free charge carriers and localize excitons, leading to the smearing of free band-to-band exciton emission. Here, we report that the simple hydrohalic acid treatment (such as HBr) is able to efficiently suppress the trap-state emission and promote the neutral exciton and trion emission in defective MoSe2 monolayers through the p-doping process, where the overall photoluminescence intensity at room temperature can be enhanced by a factor of 30. We show that HBr treatment is able to activate distinctive trion and free exciton emissions even from highly defective MoSe2 layers. Our results suggest that the HBr treatment not only reduces the n-doping in MoSe2 but also reduces the structural defects. The results provide further insights of the control and tailoring the exciton emission from CVD-grown monolayer TMDCs.

The titration of carboxyl-terminated monolayers revisited: in situ calibrated fourier transform infrared study of well-defined monolayers on silicon.

Science.gov (United States)

Aureau, D; Ozanam, F; Allongue, P; Chazalviel, J-N

2008-09-02

The acid-base equilibrium at the surface of well-defined mixed carboxyl-terminated/methyl-terminated monolayers grafted on silicon (111) has been investigated using in situ calibrated infrared spectroscopy (attenuated total reflectance (ATR)) in the range of 900-4000 cm (-1). Spectra of surfaces in contact with electrolytes of various pH provide a direct observation of the COOH COO (-) conversion process. Quantitative analysis of the spectra shows that ionization of the carboxyl groups starts around pH 6 and extends over more than 6 pH units: approximately 85% ionization is measured at pH 11 (at higher pH, the layers become damaged). Observations are consistently accounted for by a single acid-base equilibrium and discussed in terms of change in ion solvation at the surface and electrostatic interactions between surface charges. The latter effect, which appears to be the main limitation, is qualitatively accounted for by a simple model taking into account the change in the Helmholtz potential associated with the surface charge. Furthermore, comparison of calculated curves with experimental titration curves of mixed monolayers suggests that acid and alkyl chains are segregated in the monolayer.

GaAs monolayer: Excellent SHG responses and semi metallic to metallic transition modulated by vacancy effect

Science.gov (United States)

Rozahun, Ilmira; Bahti, Tohtiaji; He, Guijie; Ghupur, Yasenjan; Ablat, Abduleziz; Mamat, Mamatrishat

2018-05-01

Monolayer materials are considered as a promising candidate for novel applications due to their attractive magnetic, electronic and optical properties. Investigation on nonlinear optical (NLO) properties and effect of vacancy on monolayer materials are vital to property modulations of monolayers and extending their applications. In this work, with the aid of first-principles calculations, the crystal structure, electronic, magnetic, and optical properties of GaAs monolayers with the vacancy were investigated. The result shows gallium arsenic (GaAs) monolayer produces a strong second harmonic generation (SHG) response. Meanwhile, the vacancy strongly affects structural, electronic, magnetic and optical properties of GaAs monolayers. Furthermore, arsenic vacancy (VAs) brings semi metallic to metallic transition, while gallium vacancy (VGa) causes nonmagnetic to magnetic conversion. Our result reveals that GaAs monolayer possesses application potentials in Nano-amplifying modulator and Nano-optoelectronic devices, and may provide useful guidance in designing new generation of Nano-electronic devices.

Strain and electric field induced metallization in the GaX (X = N, P, As & Sb) monolayer

Science.gov (United States)

Bahuguna, Bhagwati Prasad; Saini, L. K.; Sharma, Rajesh O.; Tiwari, Brajesh

2018-05-01

We investigate the strain and electric field dependent electronic properties of two dimensional Ga-based group III-V monolayer from the first-principles approach within density functional theory. The energy bandgap of GaX monolayer increases upto the certain value of compressive strain and then decreases. On the other hand, the energy bandgap of GaX monolayer is monotonically decreased with increasing tensile strain and become metallic at the higher value. Furthermore, the perpendicular electric field decreases the energy band gap of unstrained GaX monolayer and shows semiconductor to metal transition. These results suggest that the nature of energy bands and value of energy bandgap in GaX monolayer can be tuned by the biaxial mechanical strain or perpendicular electrical field. Additionally, we have also studied the optical response of unstrained GaX monolayer in term of optical conductivity. These findings may provide valuable information to develop the Ga-based optoelectronic devices and further the understanding of the GaX monolayer.

Preparation of porous monolayer film by immersing the stearic acid Langmuir-Blodgett monolayer on mica in salt solution

Energy Technology Data Exchange (ETDEWEB)

Wang, S. [Institute of Near-Field Optics and Nano Technology, School of Physics and Optoelectronic Technology, Dalian University of Technology, Street No. 2 Linggong Road, Dalian 116024 (China); Li, Y.L.; Zhao, H.L.; Liang, H. [Institute of Photo-Biophysics, School of Physics and Electronic, Henan University, Jinming, Kaifeng 475004, Henan (China); Liu, B., E-mail: boliu@henu.edu.cn [Institute of Photo-Biophysics, School of Physics and Electronic, Henan University, Jinming, Kaifeng 475004, Henan (China); Pan, S., E-mail: span@dlut.edu.cn [Institute of Near-Field Optics and Nano Technology, School of Physics and Optoelectronic Technology, Dalian University of Technology, Street No. 2 Linggong Road, Dalian 116024 (China)

2012-11-15

Highlights: Black-Right-Pointing-Pointer Porous film has been prepared by immersing the stearic acid Langmuir-Blodgett monolayer on mica in salt solution. Black-Right-Pointing-Pointer The mechanism relies on the electrostatic screening effect of the cations in salt solution. Black-Right-Pointing-Pointer The factors influencing the size and area of the pores were investigated. - Abstract: Porous materials have drawn attention from scientists in many fields such as life sciences, catalysis and photonics since they can be used to induce some materials growth as expected. Especially, porous Langmuir-Blodgett (LB) film is an ideal material with controlled thickness and flat surface. In this paper, stearic acid (SA), which has been extensively explored in LB film technique, is chosen as the template material with known parameters to prepare the LB film, and then the porous SA monolayer film is obtained by means of etching in salt solution. The main etching mechanism is suggested that the cations in the solution block the electrostatic interaction between the polar carboxyl group of SA and the electronegative mica surface. The influencing factors (such as concentration of salt solution, valence of cation and surface pressure) of the porous SA film are systematically studied in this work. The novel method proposed in this paper makes it convenient to prepare porous monolayer film for designed material growth or cell culture.

Scanning Tunneling Microscopic Observation of Adatom-Mediated Motifs on Gold-Thiol Self-assembled Monolayers at High Coverage

DEFF Research Database (Denmark)

Wang, Yun; Chi, Qijin; Hush, Noel S.

2009-01-01

the structural motifs observed on surfaces at low coverage and on gold nanoparticles to the observed spectroscopic properties of high-coverage SAMs formed by methanethiol. However, the significant role attributed to intermolecular steric packing effects suggests a lack of generality for the adatom-mediated motif......Self-assembled monolayers (SAMs) formed by chemisorption of a branched-chain alkanethiol, 2-methyl-1-propanethiol, on Au(111) surfaces were studied by in situ scanning tunneling microscopy (STM) under electrochemical potential control and analyzed using extensive density functional theory (DFT...... two R−S−Au−S−R adatom-mediated motifs per surface cell, with steric-induced variations in the adsorbate alignment inducing the observed STM image contrasts. Observed pits covering 5.6 ± 0.5% of the SAM surface are consistent with this structure. These results provide the missing link from...

Activating basal-plane catalytic activity of two-dimensional MoS2 monolayer with remote hydrogen plasma

KAUST Repository

Cheng, Chia-Chin

2016-09-10

Two-dimensional layered transition metal dichalcogenide (TMD) materials such as Molybdenum disufide (MoS2) have been recognized as one of the low-cost and efficient electrocatalysts for hydrogen evolution reaction (HER). The crystal edges that account for a small percentage of the surface area, rather than the basal planes, of MoS2 monolayer have been confirmed as their active catalytic sites. As a result, extensive efforts have been developing in activating the basal planes of MoS2 for enhancing their HER activity. Here, we report a simple and efficient approach-using a remote hydrogen-plasma process-to creating S-vacancies on the basal plane of monolayer crystalline MoS2; this process can generate high density of S-vacancies while mainly maintaining the morphology and structure of MoS2 monolayer. The density of S-vacancies (defects) on MoS2 monolayers resulted from the remote hydrogen-plasma process can be tuned and play a critical role in HER, as evidenced in the results of our spectroscopic and electrical measurements. The H2-plasma treated MoS2 also provides an excellent platform for systematic and fundamental study of defect-property relationships in TMDs, which provides insights for future applications including electrical, optical and magnetic devices. © 2016 Elsevier Ltd.

Electrical control of truly two-dimensional neutral and charged excitons in monolayer MoSe2

Science.gov (United States)

Ross, Jason; Wu, Sanfeng; Yu, Hongyi; Ghimire, Nirmal; Jones, Aaron; Aivazian, Grant; Yan, Jiaqiang; Mandrus, David; Xiao, Di; Xiao, Di; Xu, Xiaodong

2013-03-01

Monolayer transition metal dichalcogenides (TMDs) have emerged as ideal 2D semiconductors with valley and spin polarized excitations expected to enable true valley-tronics. Here we investigate MoSe2, a TMD which has yet to be characterized in the monolayer limit. Specifically, we examine excitons and trions (their singly charged counterparts) in the ultimate 2D limit. Utilizing high quality exfoliated MoSe2 monolayers, we report the observation and electrostatic tunability of positively charged (X +) , neutral (Xo), and negatively charged (X-) excitons via photoluminescence in FETs. The trion charging energy is large (30 meV), enhanced by strong confinement and heavy effective masses, while the linewidth is narrow (5 meV) at temperatures below 55 K. This is greater spectral contrast than in any known quasi-2D system. Further, the charging energies for X + and X- to are nearly identical implying the same effective mass for electrons and holes, which supports their recent description as massive Dirac fermions. This work demonstrates that monolayer MoSe2 is an ultimate 2D semiconductor opening the door for the investigation of truly 2D exciton physics while laying the ground work necessary to begin valley-spin polarization studies. Support: US DoE, BES, Division of MSE. HY and WY supported by Research Grant Council of Hong Kong

Solar cells based on particulate structure of active layer: Investigation of light absorption by an ordered system of spherical submicron silicon particles

Science.gov (United States)

Miskevich, Alexander A.; Loiko, Valery A.

2015-12-01

Enhancement of the performance of photovoltaic cells through increasing light absorption due to optimization of an active layer is considered. The optimization consists in creation of particulate structure of active layer. The ordered monolayers and multilayers of submicron crystalline silicon (c-Si) spherical particles are examined. The quasicrystalline approximation (QCA) and the transfer matrix method (TMM) are used to calculate light absorption in the wavelength range from 0.28 μm to 1.12 μm. The integrated over the terrestial solar spectral irradiance "Global tilt" ASTM G173-03 absorption coefficient is calculated. In the wavelength range of small absorption index of c-Si (0.8-1.12 μm) the integral absorption coefficient of monolayer can be more than 20 times higher than the one of the plane-parallel plate of the equivalent volume of material. In the overall considered range (0.28-1.12 μm) the enhancement factor up to ~1.45 for individual monolayer is observed. Maximum value of the spectral absorption coefficient approaches unity for multilayers consisting of large amount of sparse monolayers of small particles. Multilayers with variable concentration and size of particles in the monolayer sequences are considered. Absorption increasing by such gradient multilayers as compared to the non-gradient ones is illustrated. The considered structures are promising for creation of high efficiency thin-film solar cells.

Chiral hierarchical self-assembly in Langmuir monolayers of diacetylenic lipids

KAUST Repository

Basnet, Prem B.

2013-01-01

When compressed in the intermediate temperature range below the chain-melting transition yet in the low-pressure liquid phase, Langmuir monolayers made of chiral lipid molecules form hierarchical structures. Using Brewster angle microscopy to reveal this structure, we found that as the liquid monolayer is compressed, an optically anisotropic condensed phase nucleates in the form of long, thin claws. These claws pack closely to form stripes. This appears to be a new mechanism for forming stripes in Langmuir monolayers. In the lower temperature range, these stripes arrange into spirals within overall circular domains, while near the chain-melting transition, the stripes arrange into target patterns. We attributed this transition to a change in boundary conditions at the core of the largest-scale circular domains. © 2013 The Royal Society of Chemistry.

Chirality-dependent anisotropic elastic properties of a monolayer graphene nanosheet.

Science.gov (United States)

Guo, Jian-Gang; Zhou, Li-Jun; Kang, Yi-Lan

2012-04-01

An analytical approach is presented to predict the elastic properties of a monolayer graphene nanosheet based on interatomic potential energy and continuum mechanics. The elastic extension and torsional springs are utilized to simulate the stretching and angle variation of carbon-carbon bond, respectively. The constitutive equation of the graphene nanosheet is derived by using the strain energy density, and the analytical formulations for nonzero elastic constants are obtained. The in-plane elastic properties of the monolayer graphene nanosheet are proved to be anisotropic. In addition, Young's moduli, Poisson's ratios and shear modulus of the monolayer graphene nanosheet are calculated according to the force constants derived from Morse potential and AMBER force field, respectively, and they were proved to be chirality-dependent. The comparison with experimental results shows a very agreement.

Photoluminescence inhomogeneity and excitons in CVD-grown monolayer WS2

Science.gov (United States)

Ren, Dan-Dan; Qin, Jing-Kai; Li, Yang; Miao, Peng; Sun, Zhao-Yuan; Xu, Ping; Zhen, Liang; Xu, Cheng-Yan

2018-06-01

Transition metal dichalcogenides two-dimensional materials are of great importance for future electronic and optoelectronic applications. In this work, triangular WS2 monolayers with size up to 130 μm were prepared via chemical vapor deposition method. WS2 monolayers presented uniform Raman intensity, while quenched photoluminescence (PL) was observed in the center. The PL quenching in the central part of WS2 monolayer flakes was attributed to the gradually increasing sulfur vacancies toward the center. The proportion of negative trion (X-) in PL spectrum increases with increasing sulfur vacancies in WS2. The enhanced binding energy of X- suggests higher Fermi level and n-doping level with larger sulfur vacancy concentration. Our findings may be beneficial to the development of integrated devices, and also explore the defect-induced optical and electrical properties for nanophotonics.

Characterization of 10,12-pentacosadiynoic acid Langmuir–Blodgett monolayers and their use in metal–insulator–metal tunnel devices

Directory of Open Access Journals (Sweden)

Saumya Sharma

2014-11-01

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.

Self-assembled monolayers of a disulphide-derivatised cobalt-porphyrin on gold

International Nuclear Information System (INIS)

Viana, A.S.; Leupold, S.; Montforts, F.-P.; Abrantes, L.M.

2005-01-01

A self-assembled monolayer (SAM) of a novel cobalt(II)porphyrin disulphide derivative was prepared on flat gold(1 1 1) electrode. Evidence for surface modification was provided by electrochemical reductive desorption of the monolayer and ellipsometry, consistent with a coverage of 2.5 x 10 -10 mol cm -2 and a thickness of 13 A, respectively. Both results support the presence of SAMs where the molecules share an intermediate position between perpendicular and flat orientation. Scanning tunnelling microscopy have also proven the formation of CoPSS SAMs, however high-resolution images could only be obtained when the CoPSS molecules were diluted in an hexanethiol SAM. The electrocatalytic activity of the surface confined Co-porphyrin was evaluated for the oxygen reduction. Voltammetric data indicate that reaction involves two electrons consistent with the formation of hydrogen peroxide. Under similar experimental conditions the data obtained for an iron-porphyrin analogue points for a full reduction of dioxygen to water

Enhanced photoresponse of monolayer molybdenum disulfide (MoS2) based on microcavity structure

Science.gov (United States)

Lu, Yanan; Yang, Guofeng; Wang, Fuxue; Lu, Naiyan

2018-05-01

There is an increasing interest in using monolayer molybdenum disulfide (MoS2) for optoelectronic devices because of its inherent direct band gap characteristics. However, the weak absorption of monolayer MoS2 restricts its applications, novel concepts need to be developed to address the weakness. In this work, monolayer MoS2 monolithically integrates with plane microcavity structure, which is formed by the top and bottom chirped distributed Bragg reflector (DBR), is demonstrated to improve the absorption of MoS2. The optical absorption is 17-fold enhanced, reaching values over 70% at work wavelength. Moreover, the monolayer MoS2-based photodetector device with microcavity presents a significantly increased photoresponse, demonstrating its promising prospects in MoS2-based optoelectronic devices.

Ultralow lattice thermal conductivity in monolayer C3N as compared to graphene

KAUST Repository

Sarath Kumar, S. R.

2017-09-21

Using density functional theory and the Boltzmann transport equation for phonons, we demonstrate that the thermal conductivity is massively reduced in monolayer CN as compared to isostructural graphene. We show that larger phase space for three-phonon scattering processes is available in monolayer CN, which results in much shorter phonon life-times. Although both materials are characterized by sp hybridisation, anharmonicity effects are found to be enhanced for the C-N and C-C bonds in monolayer CN, reflected by a Grüneisen parameter of -8.5 as compared to -2.2 in graphene. The combination of these properties with the fact that monolayer CN is organic, non-toxic, and built of earth abundant elements gives rise to great potential in thermoelectric applications.

Fullerene monolayer formation by spray coating

NARCIS (Netherlands)

Cervenka, J.; Flipse, C.F.J.

2010-01-01

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

Molecular tilt on monolayer-protected nanoparticles

KAUST Repository

Giomi, L.

2012-02-01

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.

Molecular tilt on monolayer-protected nanoparticles

KAUST Repository

Giomi, L.; Bowick, M. J.; Ma, X.; Majumdar, A.

2012-01-01

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.

Morphology, defect evolutions and nano-mechanical anisotropy of behenic acid monolayer

International Nuclear Information System (INIS)

Yang Guanghong; Jiang Xiaohong; Dai Shuxi; Cheng Gang; Zhang Xingtang; Du Zuliang

2010-01-01

Langmuir-Blodgett monolayers of behenic acid (BA) were prepared by the vertical deposition method and their morphological evolutions and nano-mechanical anisotropy were studied by atomic force microscopy (AFM) and lateral force microscopy. Results show that there are platforms in the differential surface pressure-area (π-A) isotherm presenting linear relations between the chain tilting angles and surface pressures. The reorganization, appearance and disappearance of defects such as pinholes and holes can strongly affect the profile of π-A isotherm; AFM images reflect evolution rules from pinholes to holes, and from monolayer to bilayers along with compression and relaxation of structures in BA monolayer. Due to higher molecule density and larger real contact area, the tip-monolayer contacts at 15 and 25 mN/m correspond to the Derjaguin-Muller-Toporov (DMT) model showing long-ranged interaction forces. But owing to more easily-deformed conformations, contacts at 5 and 35 mN/m accord with the Johnson-Kendall-Robert and DMT transition cases exhibiting short-ranged interface interactions. A little higher friction is proved in the direction perpendicular to the deposition.

Al-Doped ZnO Monolayer as a Promising Transparent Electrode Material: A First-Principles Study

Directory of Open Access Journals (Sweden)

Mingyang Wu

2017-03-01

Full Text Available Al-doped ZnO has attracted much attention as a transparent electrode. The graphene-like ZnO monolayer as a two-dimensional nanostructure material shows exceptional properties compared to bulk ZnO. Here, through first-principle calculations, we found that the transparency in the visible light region of Al-doped ZnO monolayer is significantly enhanced compared to the bulk counterpart. In particular, the 12.5 at% Al-doped ZnO monolayer exhibits the highest visible transmittance of above 99%. Further, the electrical conductivity of the ZnO monolayer is enhanced as a result of Al doping, which also occurred in the bulk system. Our results suggest that Al-doped ZnO monolayer is a promising transparent conducting electrode for nanoscale optoelectronic device applications.

A novel serum-free monolayer culture for orderly hematopoietic differentiation of human pluripotent cells via mesodermal progenitors.

Directory of Open Access Journals (Sweden)

Akira Niwa

Full Text Available Elucidating the in vitro differentiation of human embryonic stem (ES and induced pluripotent stem (iPS cells is important for understanding both normal and pathological hematopoietic development in vivo. For this purpose, a robust and simple hematopoietic differentiation system that can faithfully trace in vivo hematopoiesis is necessary. In this study, we established a novel serum-free monolayer culture that can trace the in vivo hematopoietic pathway from ES/iPS cells to functional definitive blood cells via mesodermal progenitors. Stepwise tuning of exogenous cytokine cocktails induced the hematopoietic mesodermal progenitors via primitive streak cells. These progenitors were then differentiated into various cell lineages depending on the hematopoietic cytokines present. Moreover, single cell deposition assay revealed that common bipotential hemoangiogenic progenitors were induced in our culture. Our system provides a new, robust, and simple method for investigating the mechanisms of mesodermal and hematopoietic differentiation.

NO2 decreases paracellular resistance to ion and solute flow in alveolar epithelial monolayers

International Nuclear Information System (INIS)

Cheek, J.M.; Kim, K.J.; Crandall, E.D.

1990-01-01

Primary cultured monolayers of rat alveolar epithelial cells grown on tissue culture-treated Nuclepore filters were exposed to 2.5 ppm nitrogen dioxide NO 2 for 2-20 min. Changes in monolayer bioelectric properties and solute permeabilities were subsequently measured. Exposure to NO 2 produced a dose-dependent decrease in monolayer transepithelial electrical resistance (Rt), whereas monolayer short-circuit current was unaffected. Post-exposure monolayer permeability to 14 C-sucrose (which primarily crosses alveolar epithelium via the paracellular pathway) increased markedly. That for 3 H-glycerol (which permeates through both paracellular and transcellular pathways) increased to a lesser extent. Partial recovery of Rt and solute permeabilities was noted by 48-h post-exposure. The time courses of the decrease in Rt and increase in solute permeabilities were similar. These results suggest that NO 2 primarily impairs passive alveolar epithelial barrier functions in vitro, probably by altering intercellular junctions, and does not appear to directly affect cell membrane active ion transport processes. When correlated with results obtained from experimental approaches, studies of in vitro alveolar epithelial monolayers may facilitate investigations of dosimetry, sites, and mechanisms of oxidant injury in the lung

Nanostructure of polymer monolayer and polyelectrolyte brush at air/water interface by X-ray and neutron reflectometry

CERN Document Server

Matsuoka, H; Matsumoto, K

2003-01-01

The nanostructure of amphiphilic diblock copolymer monolayer on water was directly investigated by in situ X-ray and neutron reflectivity techniques. The diblock copolymer consists of polysilacyclobutane, which is very flexible, as a hydrophobic block and polymethacrylic acid, an anionic polymer, as a hydrophilic block. The polymers with shorter hydrophilic segment formed a very smooth and uniform monolayer with hydrophobic layer on water and dense hydrophilic layer under the water. But the longer hydrophilic segment polymer formed three-layered monolayer with polyelectrolyte brush in addition to hydrophobic and dense hydrophilic layers. The dense hydrophilic layer is thought to be formed to avoid a contact between hydrophobic polymer layer and water. Its role is something like a 'carpet'. An additional interesting information is that the thickness of the 'carpet layer' is almost 15A, independent the surface pressure and hydrophilic polymer length. Highly quantitative information was obtained about the nanost...

Development and Characterization of a Human and Mouse Intestinal Epithelial Cell Monolayer Platform

Directory of Open Access Journals (Sweden)

Kenji Kozuka

2017-12-01

Full Text Available Summary: We describe the development and characterization of a mouse and human epithelial cell monolayer platform of the small and large intestines, with a broad range of potential applications including the discovery and development of minimally systemic drug candidates. Culture conditions for each intestinal segment were optimized by correlating monolayer global gene expression with the corresponding tissue segment. The monolayers polarized, formed tight junctions, and contained a diversity of intestinal epithelial cell lineages. Ion transport phenotypes of monolayers from the proximal and distal colon and small intestine matched the known and unique physiology of these intestinal segments. The cultures secreted serotonin, GLP-1, and FGF19 and upregulated the epithelial sodium channel in response to known biologically active agents, suggesting intact secretory and absorptive functions. A screen of over 2,000 pharmacologically active compounds for inhibition of potassium ion transport in the mouse distal colon cultures led to the identification of a tool compound. : Siegel and colleagues describe their development of a human and mouse intestinal epithelial cell monolayer platform that maintains the cellular, molecular, and functional characteristics of tissue for each intestinal segment. They demonstrate the platform's application to drug discovery by screening a library of over 2,000 compounds to identify an inhibitor of potassium ion transport in the mouse distal colon. Keywords: intestinal epithelium, organoids, monolayer, colon, small intestine, phenotype screening assays, enteroid, colonoid

A Route to Permanent Valley Polarization in Monolayer MoS2

KAUST Repository

Singh, Nirpendra

2016-10-24

Realization of permanent valley polarization in Cr-doped monolayer MoS2 is found to be unfeasible because of extended moment formation. Introduction of an additional hole is suggested as a viable solution. V-doped monolayer MoS2 is demonstrated to sustain permanent valley polarization and therefore can serve as a prototype material for valleytronics.

Biomimetic nanoparticles with polynucleotide and PEG mixed-monolayers enhance calcium phosphate mineralization

Science.gov (United States)

Vasconcellos, Kayla B.; McHugh, Sean M.; Dapsis, Katherine J.; Petty, Alexander R.; Gerdon, Aren E.

2013-09-01

Biomineralization of hydroxyapatite (Ca10(PO4)6(OH)2) is of significant importance in biomedical applications such as bone and dental repair, and biomimetic control of mineral formation may lead to more effective restorative procedures. Gold nanoparticles are functional scaffolds on which to assemble multi-component monolayers capable of mimicking protein activity in the templated synthesis of calcium phosphate. The goal of this research was to explore nanoparticle templates with mixed-monolayers of uncharged polar polyethylene glycol (PEG) molecules and highly charged polynucleotide and amino acid molecules in their ability to influence mineralization rates and mineral particle size and morphology. This research demonstrates through time-resolved optical density and dynamic light scattering measurements that the combination of tiopronin, PEG, and DNA presented on a nanoparticle surface decreases nanoparticle aggregation from 59 to 21 nm solvated radius, increases mineralization kinetics from 1.5 × 10-3 to 3.1 × 10-3 OD/min, and decreases mineral particle size from 685 to 442 nm average radius. FT-IR and TEM data demonstrate that mineralized material, while initially amorphous, transforms to a semi-crystalline material when guided by template interactions. This demonstrates that surface-tailored monolayer protected cluster scaffolds are successful and controllable mineralization templates with further potential for biomedical applications involving calcium phosphate and other biomaterials.

Biomimetic nanoparticles with polynucleotide and PEG mixed-monolayers enhance calcium phosphate mineralization

Energy Technology Data Exchange (ETDEWEB)

Vasconcellos, Kayla B.; McHugh, Sean M.; Dapsis, Katherine J.; Petty, Alexander R.; Gerdon, Aren E., E-mail: gerdoar@emmanuel.edu [Emmanuel College (United States)

2013-09-15

Biomineralization of hydroxyapatite (Ca{sub 10}(PO{sub 4}){sub 6}(OH){sub 2}) is of significant importance in biomedical applications such as bone and dental repair, and biomimetic control of mineral formation may lead to more effective restorative procedures. Gold nanoparticles are functional scaffolds on which to assemble multi-component monolayers capable of mimicking protein activity in the templated synthesis of calcium phosphate. The goal of this research was to explore nanoparticle templates with mixed-monolayers of uncharged polar polyethylene glycol (PEG) molecules and highly charged polynucleotide and amino acid molecules in their ability to influence mineralization rates and mineral particle size and morphology. This research demonstrates through time-resolved optical density and dynamic light scattering measurements that the combination of tiopronin, PEG, and DNA presented on a nanoparticle surface decreases nanoparticle aggregation from 59 to 21 nm solvated radius, increases mineralization kinetics from 1.5 Multiplication-Sign 10{sup -3} to 3.1 Multiplication-Sign 10{sup -3} OD/min, and decreases mineral particle size from 685 to 442 nm average radius. FT-IR and TEM data demonstrate that mineralized material, while initially amorphous, transforms to a semi-crystalline material when guided by template interactions. This demonstrates that surface-tailored monolayer protected cluster scaffolds are successful and controllable mineralization templates with further potential for biomedical applications involving calcium phosphate and other biomaterials.

N-Type self-assembled monolayer field-effect transistors for flexible organic electronics

NARCIS (Netherlands)

Ringk, A.; Roelofs, Christian; Smits, E.C.P.; van der Marel, C.; Salzmann, I.; Neuhold, A.; Gelinck, G.H.; Resel, R.; de Leeuw, D.M.; Strohriegl, P.

Within this work we present n-type self-assembled monolayer field-effect transistors (SAMFETs) based on a novel perylene bisimide. The molecule spontaneously forms a covalently fixed monolayer on top of an aluminium oxide dielectric via a phosphonic acid anchor group. Detailed studies revealed an

Complexation of phospholipids and cholesterol by triterpenic saponins in bulk and in monolayers.

Science.gov (United States)

Wojciechowski, Kamil; Orczyk, Marta; Gutberlet, Thomas; Geue, Thomas

2016-02-01

The interactions between three triterpene saponins: α-hederin, hederacoside C and ammonium glycyrrhizate with model lipids: cholesterol and dipalmitoylphosphatidylcholine (DPPC) are described. The oleanolic acid-type saponins (α-hederin and hederacoside C) were shown to form 1:1 complexes with lipids in bulk, characterized by stability constants in the range (4.0±0.2)·10(3)-(5.0±0.4)·10(4) M(-1). The complexes with cholesterol are generally stronger than those with DPPC. On the contrary, ammonium glycyrrhizate does not form complexes with any of the lipids in solution. The saponin-lipid interactions were also studied in a confined environment of Langmuir monolayers of DPPC and DPPC/cholesterol with the saponins present in the subphase. A combined monolayer relaxation, surface dilational rheology, fluorescence microscopy and neutron reflectivity (NR) study showed that all three saponins are able to penetrate pure DPPC and mixed DPPC/cholesterol monolayers. Overall, the effect of the saponins on the model lipid monolayers does not fully correlate with the lipid-saponin complex formation in the homogeneous solution. The best correlation was found for α-hederin, for which even the preference for cholesterol over DPPC observed in bulk is well reflected in the monolayer studies and the literature data on its membranolytic activity. Similarly, the lack of interaction of ammonium glycyrrhizate with both lipids is evident equally in bulk and monolayer experiments, as well as in its weak membranolytic activity. The combined bulk and monolayer results are discussed in view of the role of confinement in modulating the saponin-lipid interactions and possible mechanism of membranolytic activity of saponins. Copyright © 2015 Elsevier B.V. All rights reserved.

Substoichiometric cobalt oxide monolayer on Ir(100)-(1 x 1)

International Nuclear Information System (INIS)

Gubo, M; Ebensperger, C; Meyer, W; Hammer, L; Heinz, K

2009-01-01

A substoichiometric monolayer of cobalt oxide has been prepared by deposition and oxidation of slightly less than one monolayer of cobalt on the unreconstructed surface of Ir(100). The ultrathin film was investigated by scanning tunnelling microscopy (STM) and quantitative low-energy electron diffraction (LEED). The cobalt species of the film reside in or near hollow positions of the substrate with, however, unoccupied sites (vacancies) in a 3 x 3 arrangement. In the so-formed 3 x 3 supercell the oxide's oxygen species are both threefold and fourfold coordinated to cobalt, forming pyramids with a triangular and square cobalt basis, respectively. These pyramids are the building blocks of the oxide. Due to the reduced coordination as compared to the sixfold one in the bulk of rock-salt-type CoO, the Co-O bond lengths are smaller than in the latter. For the threefold coordination they compare very well with the bond length in oxygen terminated CoO(111) films investigated recently. The substoichiometric 3 x 3 oxide monolayer phase transforms to a stoichiometric c(10 x 2)-periodic oxide monolayer under oxygen exposure, in which, however, cobalt and oxygen species are in (111) orientation and so form a CoO(111) layer.

Thermodynamic and real-space structural evidence of a 2D critical point in phospholipid monolayers

DEFF Research Database (Denmark)

Nielsen, Lars K.; Bjørnholm, Thomas; Mouritsen, Ole G.

2007-01-01

The two-dimensional phase diagram of phospholipid monolayers at air-water interfaces has been constructed from Langmuir compression isotherms. The coexistence region between the solid and fluid phases of the monolayer ends at the critical temperature of the transition. The small-scale lateral...... structure of the monolayers has been imaged by atomic force microscopy in the nm to mu m range at distinct points in the phase diagram. The lateral structure is immobilized by transferring the monolayer from an air-water interface to a solid mica support using Langmuir-Blodgett techniques. A transfer...

Disorder-dependent valley properties in monolayer WSe2

KAUST Repository

Tran, Kha

2017-07-19

We investigate the effect of disorder on exciton valley polarization and valley coherence in monolayer WSe2. By analyzing the polarization properties of photoluminescence, the valley coherence (VC) and valley polarization (VP) are quantified across the inhomogeneously broadened exciton resonance. We find that disorder plays a critical role in the exciton VC, while affecting VP less. For different monolayer samples with disorder characterized by their Stokes shift (SS), VC decreases in samples with higher SS while VP does not follow a simple trend. These two methods consistently demonstrate that VC as defined by the degree of linearly polarized photoluminescence is more sensitive to disorder, motivating further theoretical studies.

Transient impedance changes in venous endothelial monolayers as a biological radiation dosimetry response

Directory of Open Access Journals (Sweden)

Erik Fossum Young

2012-10-01

Full Text Available In March of 2011, a magnitude 9.0 earthquake and subsequent 14 m-high tsunami caused major damage to the Fukushima Daiichi nuclear power plant in Japan.  While cancer incidence in the radiation-exposed population is a logical concern, the complex effects of radiation on the heart and cardiovascular system are also of interest.  Immediate and early vascular radiation effects could be exploited as a dosimetry modality.  To test whether non-coronary vasculature exhibited transient perturbation in barrier function, video microscopy studies and Electric Cell Substrate Impedance Sensing technology were used to probe very subtle changes in primary human vascular endothelium.  Human umbilical vein endothelial cell (HUVEC monolayers exhibit a transient, statistically significant decrease (P = 0.017 in monolayer resistance 3 h after irradiation with 5.0 Gy of g rays.  Radiation induced perturbations in HUVEC monolayer permeability are similar in magnitude and kinetics to those observed in coronary arterial endothelium.  Therefore, at least two types of vasculature respond to radiation on ECIS arrays with an early transient disruption in permeability.  The finding supports the use of early passage HUVECs for use in bioelectric dosimetry studies of vasculature and suggests that permeability of vessels could potentially serve as a biological dosimetry tool.

Chemical surface reactions by click chemistry: coumarin dye modification of 11-bromoundecyltrichlorosilane monolayers

International Nuclear Information System (INIS)

Haensch, Claudia; Hoeppener, Stephanie; Schubert, Ulrich S

2008-01-01

The functionalization of surfaces and the ability to tailor their properties with desired physico-chemical functions is an important field of research with a broad spectrum of applications. These applications range from the modification of wetting properties, over the alteration of optical properties, to the fabrication of molecular electronic devices. In each of these fields, it is of specific importance to be able to control the quality of the layers with high precision. The present study demonstrates an approach that utilizes the 1,3-dipolar cycloaddition of terminal acetylenes to prepare triazole-terminated monolayers on different substrates. The characterization of the precursor monolayers, the optimization of the chemical surface reactions as well as the clicking of a fluorescent dye molecule on such azide-terminated monolayers was carried out. A coumarin 343 derivative was utilized to discuss the aspects of the functionalization approach. Based on this approach, a number of potential surface reactions, facilitated via the acetylene-substituted functional molecules, for a broad range of applications is at hand, thus leading to numerous possibilities where surface modifications are concerned. These modifications can be applied on non-structured surfaces of silicon or glass or can be used on structured surfaces. Various possibilities are discussed

A class of monolayer metal halogenides MX{sub 2}: Electronic structures and band alignments

Energy Technology Data Exchange (ETDEWEB)

Lu, Feng; Wang, Weichao; Luo, Xiaoguang; Cheng, Yahui; Dong, Hong; Liu, Hui; Wang, Wei-Hua, E-mail: whwangnk@nankai.edu.cn [Department of Electronics and Tianjin Key Laboratory of Photo-Electronic Thin Film Device and Technology, Nankai University, Tianjin 300071 (China); Xie, Xinjian [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China)

2016-03-28

With systematic first principles calculations, a class of monolayer metal halogenides MX{sub 2} (M = Mg, Ca, Zn, Cd, Ge, Pb; M = Cl, Br, I) has been proposed. Our study indicates that these monolayer materials are semiconductors with the band gaps ranging from 2.03 eV of ZnI{sub 2} to 6.08 eV of MgCl{sub 2}. Overall, the band gap increases with the increase of the electronegativity of the X atom or the atomic number of the metal M. Meanwhile, the band gaps of monolayer MgX{sub 2} (X = Cl, Br) are direct while those of other monolayers are indirect. Based on the band edge curvatures, the derived electron (m{sub e}) and hole (m{sub h}) effective masses of MX{sub 2} monolayers are close to their corresponding bulk values except that the m{sub e} of CdI{sub 2} is three times larger and the m{sub h} for PbI{sub 2} is twice larger. Finally, the band alignments of all the studied MX{sub 2} monolayers are provided using the vacuum level as energy reference. These theoretical results may not only introduce the monolayer metal halogenides family MX{sub 2} into the emerging two-dimensional materials, but also provide insights into the applications of MX{sub 2} in future electronic, visible and ultraviolet optoelectronic devices.

Method to synthesize metal chalcogenide monolayer nanomaterials

Science.gov (United States)

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

2016-12-13

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.

Magnetism in the p-type Monolayer II-VI semiconductors SrS and SrSe

Science.gov (United States)

Lin, Heng-Fu; Lau, Woon-Ming; Zhao, Jijun

2017-01-01

Using density functional theory calculations, we study the electronic and magnetic properties of the p-type monolayer II-VI semiconductors SrX (X = S,Se). The pristine SrS and SrSe monolayers are large band gap semiconductor with a very flat band in the top valence band. Upon injecting hole uniformly, ferromagnetism emerges in those system in a large range of hole density. By varying hole density, the systems also show complicated phases transition among nonmagnetic semiconductor, half metal, magnetic semiconductor, and nonmagnetic metal. Furthermore, after introducing p-type dopants in SrS and SrSe via substitutionary inserting P (or As) dopants at the S (or Se) sites, local magnetic moments are formed around the substitutional sites. The local magnetic moments are stable with the ferromagnetic order with appreciable Curie temperature. The ferromagnetism originates from the instability of the electronic states in SrS and SrSe with the large density of states at the valence band edge, which demonstrates a useful strategy for realizing the ferromagnetism in the two dimensional semiconductors. PMID:28378761

Monolayer MoSe 2 Grown by Chemical Vapor Deposition for Fast Photodetection

KAUST Repository

Chang, Yung-Huang; Zhang, Wenjing; Zhu, Yihan; Han, Yu; Pu, Jiang; Chang, Jan-Kai; Hsu, Wei-Ting; Huang, Jing-Kai; Hsu, Chang-Lung; Chiu, Ming-Hui; Takenobu, Taishi; Li, Henan; Wu, Chih-I; Chang, Wen-Hao; Wee, Andrew Thye Shen; Li, Lain-Jong

2014-01-01

that the MoSe2 monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe2 presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS2 monolayer at room temperature in ambient conditions

Electronic transport through organophosphonate monolayers on silicon/silicon dioxide substrates

Energy Technology Data Exchange (ETDEWEB)

Bora, Achyut; Pathak, Anshuma; Tornow, Marc [Institut fuer Halbleitertechnik, TU Braunschweig (Germany); Liao, Kung-Ching; Schwartz, Jeffrey [Department of Chemistry, Princeton University, NJ (United States); Cattani-Scholz, Anna; Abstreiter, Gerhard [Walter Schottky Institut, TU Muenchen (Germany)

2011-07-01

Understanding the electronic transport through layered systems of organic functional layers on semiconductor surfaces is of major importance for future applications in nanoelectronics, photovoltaics and sensors. We have prepared self-assembled monolayers (SAMs) of 9,10-diphenyl-2,6-diphosphono-anthracene and 11-hydroxyundecyl phosphonic acid precursors on highly p-doped silicon surfaces coated with a 1 nm SiO{sub 2} layer. Contact angle, AFM and ellipsometry evidenced the homogeneity of the formed SAMs, and their thickness was determined to be 0.82{+-}0.07 nm and 1.13{+-}0.09 nm, respectively. We provided large area electrical contacts on top of the SAMs by a hanging Hg drop electrode. The measured I-V characteristics revealed an enhanced conductance of the aromatic vs. the aliphatic compounds, with current densities of the order of 10 A/m{sup 2} and 0.01 A/m{sup 2}, at 0.5 V, respectively. We analyzed the data in terms of non-resonant tunneling through the combined oxide-SAM barrier and found good qualitative agreement up to 0.2 V bias. Preliminary measurements on organized bilayers of anthracene bisphosphonates that were grown using techniques of coordination chemistry are discussed, too.

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

Directory of Open Access Journals (Sweden)

Wei Zhao

2014-01-01

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.

High-order passive photonic temporal integrators.

Science.gov (United States)

Asghari, Mohammad H; Wang, Chao; Yao, Jianping; Azaña, José

2010-04-15

We experimentally demonstrate, for the first time to our knowledge, an ultrafast photonic high-order (second-order) complex-field temporal integrator. The demonstrated device uses a single apodized uniform-period fiber Bragg grating (FBG), and it is based on a general FBG design approach for implementing optimized arbitrary-order photonic passive temporal integrators. Using this same design approach, we also fabricate and test a first-order passive temporal integrator offering an energetic-efficiency improvement of more than 1 order of magnitude as compared with previously reported passive first-order temporal integrators. Accurate and efficient first- and second-order temporal integrations of ultrafast complex-field optical signals (with temporal features as fast as approximately 2.5ps) are successfully demonstrated using the fabricated FBG devices.

Monolayered Bi2WO6 nanosheets mimicking heterojunction interface with open surfaces for photocatalysis

Science.gov (United States)

Zhou, Yangen; Zhang, Yongfan; Lin, Mousheng; Long, Jinlin; Zhang, Zizhong; Lin, Huaxiang; Wu, Jeffrey C.-S.; Wang, Xuxu

2015-09-01

Two-dimensional-layered heterojunctions have attracted extensive interest recently due to their exciting behaviours in electronic/optoelectronic devices as well as solar energy conversion systems. However, layered heterojunction materials, especially those made by stacking different monolayers together by strong chemical bonds rather than by weak van der Waal interactions, are still challenging to fabricate. Here the monolayer Bi2WO6 with a sandwich substructure of [BiO]+-[WO4]2--[BiO]+ is reported. This material may be characterized as a layered heterojunction with different monolayer oxides held together by chemical bonds. Coordinatively unsaturated Bi atoms are present as active sites on the surface. On irradiation, holes are generated directly on the active surface layer and electrons in the middle layer, which leads to the outstanding performances of the monolayer material in solar energy conversion. Our work provides a general bottom-up route for designing and preparing novel monolayer materials with ultrafast charge separation and active surface.

The surface pressure dynamics and appearance of mixed monolayers of cholesterol and different sized polystyrenes at an air-water interface.

Science.gov (United States)

Mudgil, Poonam; Dennis, Gary R; Millar, Thomas J

2005-02-15

Synthetic polymers are increasingly being used in situations where they are designed to interact with biological systems. As a result, it is important to investigate the interactions of the polymers with biochemicals. We have used cholesterol, as an example of an important biological surfactant component, to study its interactions with polystyrene. Mixed monolayers of cholesterol and one of two different molecular weight polystyrenes were formed at an air-water interface to investigate their interactions and to determine whether the size of the polystyrene affected the interaction. The pressure-area (pi-A) isocycles of mixed monolayers of cholesterol and polystyrene MW 2700 or polystyrene MW32700 showed that strongest attractive interactions occur at high surface pressures and in polystyrene rich films. The excess area and excess free energy of mixing were most negative at high surface pressures and at high mole fraction of polystyrene. The most stable mixed monolayers were formed with X(PS2700) = 0.9 and X(PS32700) = 0.09. Microscopic observation of the mixed monolayers of cholesterol and polystyrene showed the formation of stable islands in the cholesterol/polystyrene mixtures. These observations, the nature of the inflection points in the isocycles, and the anomalous changes in free energy lead us to conclude that there is a stable rearrangement of polystyrene into compact islands when it is mixed with cholesterol. Any excess cholesterol is excluded from these islands and remains as a separate film surrounding the islands.

Optimal explicit strong stability preserving Runge–Kutta methods with high linear order and optimal nonlinear order

KAUST Repository

Gottlieb, Sigal

2015-04-10

High order spatial discretizations with monotonicity properties are often desirable for the solution of hyperbolic PDEs. These methods can advantageously be coupled with high order strong stability preserving time discretizations. The search for high order strong stability time-stepping methods with large allowable strong stability coefficient has been an active area of research over the last two decades. This research has shown that explicit SSP Runge-Kutta methods exist only up to fourth order. However, if we restrict ourselves to solving only linear autonomous problems, the order conditions simplify and this order barrier is lifted: explicit SSP Runge-Kutta methods of any linear order exist. These methods reduce to second order when applied to nonlinear problems. In the current work we aim to find explicit SSP Runge-Kutta methods with large allowable time-step, that feature high linear order and simultaneously have the optimal fourth order nonlinear order. These methods have strong stability coefficients that approach those of the linear methods as the number of stages and the linear order is increased. This work shows that when a high linear order method is desired, it may still be worthwhile to use methods with higher nonlinear order.