Surface structure determinations of crystalline ionic thin films grown on transition metal single crystal surfaces by low energy electron diffraction

Energy Technology Data Exchange (ETDEWEB)

Roberts, Joel Glenn [Univ. of California, Berkeley, CA (United States)

2000-05-01

The surface structures of NaCl(100), LiF(100) and alpha-MgCl2(0001) adsorbed on various metal single crystals have been determined by low energy electron diffraction (LEED). Thin films of these salts were grown on metal substrates by exposing the heated metal surface to a molecular flux of salt emitted from a Knudsen cell. This method of investigating thin films of insulators (ionic salts) on a conducting substrate (metal) circumvents surface charging problems that plagued bulk studies, thereby allowing the use of electron-based techniques to characterize the surface.

Secondary electron emission from textured surfaces

Science.gov (United States)

Huerta, C. E.; Patino, M. I.; Wirz, R. E.

2018-04-01

In this work, a Monte Carlo model is used to investigate electron induced secondary electron emission for varying effects of complex surfaces by using simple geometric constructs. Geometries used in the model include: vertical fibers for velvet-like surfaces, tapered pillars for carpet-like surfaces, and a cage-like configuration of interlaced horizontal and vertical fibers for nano-structured fuzz. The model accurately captures the secondary electron emission yield dependence on incidence angle. The model shows that unlike other structured surfaces previously studied, tungsten fuzz exhibits secondary electron emission yield that is independent of primary electron incidence angle, due to the prevalence of horizontally-oriented fibers in the fuzz geometry. This is confirmed with new data presented herein of the secondary electron emission yield of tungsten fuzz at incidence angles from 0-60°.

[Inelastic electron scattering from surfaces

International Nuclear Information System (INIS)

1993-01-01

This program uses ab-initio and multiple scattering to study surface dynamical processes; high-resolution electron-energy loss spectroscopy is used in particular. Off-specular excitation cross sections are much larger if electron energies are in the LEED range (50--300 eV). The analyses have been extended to surfaces of ordered alloys. Phonon eigenvectors and eigenfrequencies were used as inputs to electron-energy-loss multiple scattering cross section calculations. Work on low-energy electron and positron holography is mentioned

Diamond surface: atomic and electronic structure

International Nuclear Information System (INIS)

Pate, B.B.

1984-01-01

Experimental studies of the diamond surface (with primary emphasis on the (111) surface) are presented. Aspects of the diamond surface which are addressed include (1) the electronic structure, (2) the atomic structure, and (3) the effect of termination of the lattice by foreign atoms. Limited studies of graphite are discussed for comparison with the diamond results. Experimental results from valence band and core level photoemission spectroscopy (PES), Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and carbon 1s near edge x-ray absorption fine structure (NEXAFS) spectroscopy (both the total electron yield (TEY) and Auger electron yield (AEY) techniques) are used to study and characterize both the clean and hydrogenated surface. In addition, the interaction of hydrogen with the diamond surface is examined using results from vibrational high resolution low energy electron loss spectroscopy (in collaboration with Waclawski, Pierce, Swanson, and Celotta at the National Bureau of Standards) and photon stimulated ion desorption (PSID) yield at photon energies near the carbon k-edge (hv greater than or equal to 280 eV). Both EELS and PSID verify that the mechanically polished 1 x 1 surface is hydrogen terminated and also that the reconstructed surface is hydrogen free. The (111) 2 x 2/2 x 1 reconstructed surface is obtained from the hydrogenated (111) 1 x 1:H surface by annealing to approx. = 1000 0 C. We observe occupied intrinsic surface states and a surface chemical shift (0.95 +- 0.1 eV) to lower binding energy of the carbon 1s level on the hydrogen-free reconstructed surface. Atomic hydrogen is found to be reactive with the reconstructed surface, while molecular hydrogen is relatively inert. Exposure of the reconstructed surface to atomic hydrogen results in chemisorption of hydrogen and removal of the intrinsic surface state emission in and near the band gap region

Electrons on the surface of liquid helium

International Nuclear Information System (INIS)

Lambert, D.K.

1979-05-01

Spectroscopic techniques were used to study transitions of electrons between bound states in the potential well near a helium surface. The charge density distribution of electrons on the surface was independently obtained from electrical measurements. From the measurements, information was obtained both about the interaction of the bound state electrons with the surface of liquid helium and about local disorder in the positions of electrons on the surface

Cell surface alteration in Epstein-Barr virus-transformed cells from patients with extreme insulin resistance

International Nuclear Information System (INIS)

Gorden, D.L.; Robert, A.; Moncada, V.Y.; Taylor, S.I.; Muehlhauser, J.C.; Carpentier, J.L.

1990-01-01

An abnormality was detected in the morphology of the cell surface of Epstein-Barr virus-transformed lymphocytes of patients with genetic forms of insulin resistance. In cells from two patients with leprechaunism and two patients with type A extreme insulin resistance, scanning electron microscopy demonstrated a decrease in the percentage of the cell surface occupied by microvilli in cells from the patients with leprechaunism and type A insulin resistance compared with control cells. When cells from a healthy control subject and one of the patients with leprechaunism (Lep/Ark-1) were incubated with 125 I-labeled insulin, there was a decrease in the percentage of 125 I-insulin associated with microvilli on the cell surface. Thus, the decreased localization of insulin receptors with the microvillous region of the cell surface was in proportion to the decrease in microvilli

Surfaces electrons at dielectric plasma walls

International Nuclear Information System (INIS)

Heinisch, Rafael Leslie

2013-01-01

The concept of the electron surface layer introduced in this thesis provides a framework for the description of the microphysics of the surplus electrons immediately at the wall and thereby complements the modelling of the plasma sheath. In this work we have considered from a surface physics perspective the distribution and build-up of an electron adsorbate on the wall as well as the effect of the negative charge on the scattering of light by a spherical particle immersed in a plasma. In our electron surface layer model we treat the wall-bound electrons as a wall-thermalised electron distribution minimising the grand canonical potential and satisfying Poisson's equation. The boundary between the electron surface layer and the plasma sheath is determined by a force balance between the attractive image potential and the repulsive sheath potential and lies in front of the crystallographic interface. Depending on the electron affinity χ, that is the offset of the conduction band minimum to the potential in front of the surface, two scenarios for the wall-bound electrons are realised. For χ 0 electrons penetrate into the conduction band where they form an extended space charge. These different scenarios are also reflected in the electron kinetics at the wall which control the sticking coefficient and the desorption time. If χ -3 . For χ>0 electron physisorption takes place in the conduction band. For this case sticking coefficients and desorption times have not been calculated yet but in view of the more efficient scattering with bulk phonons, responsible for electron energy relaxation in this case, we expect them to be larger than for the case of χ 0 the electrons in the bulk of the particle modify the refractive index through their bulk electrical conductivity. In both cases the conductivity is limited by scattering with surface or bulk phonons. Surplus electrons lead to an increase of absorption at low frequencies and, most notably, to a blue-shift of an

Carrier population control and surface passivation in solar cells

KAUST Repository

Cuevas, Andres

2018-05-02

Controlling the concentration of charge carriers near the surface is essential for solar cells. It permits to form regions with selective conductivity for either electrons or holes and it also helps to reduce the rate at which they recombine. Chemical passivation of the surfaces is equally important, and it can be combined with population control to implement carrier-selective, passivating contacts for solar cells. This paper discusses different approaches to suppress surface recombination and to manipulate the concentration of carriers by means of doping, work function and charge. It also describes some of the many surface-passivating contacts that are being developed for silicon solar cells, restricted to experiments performed by the authors.

Difference of EGCg adhesion on cell surface between Staphylococcus aureus and Escherichia coli visualized by electron microscopy after novel indirect staining with cerium chloride.

Science.gov (United States)

Nakayama, Motokazu; Shigemune, Naofumi; Tsugukuni, Takashi; Tokuda, Hajime; Miyamoto, Takahisa

2011-07-01

We developed a novel method using indirect staining with cerium chloride for visualization of the catechin derivative epigallocatechin gallate (EGCg) on the surface of particles, i.e., polystyrene beads and bacterial cells, by electron microscopy. The staining method is based on the fact that in an alkaline environment, EGCg produces hydrogen peroxide, and then hydrogen peroxide reacts with cerium, resulting in a cerium hydroperoxide precipitate. This precipitate subsequently reacts with EGCg to produce larger deposits. The amount of precipitate is proportional to the amount of EGCg. Highly EGCg-sensitive Staphylococcus aureus and EGCg-resistant Escherichia coli were treated with EGCg under various pH conditions. Transmission electron microscopy observation showed that the amount of deposits on S. aureus increased with an increase in EGCg concentration. After treating bacterial cells with 0.5mg/mL EGCg (pH 6.0), attachment of EGCg was significantly lower to E. coli than to S. aureus. This is the first report that shows differences in affinity of EGCg to the cell surfaces of Gram-positive and -negative bacteria by electron microscopy. Copyright © 2011 Elsevier B.V. All rights reserved.

Cell for studying electron-adsorbed gas interactions; Cellule d'etudes des interactions electron-gaz adsorbe

Energy Technology Data Exchange (ETDEWEB)

Golowacz, H; Degras, D A [Commissariat a l' Energie Atomique, 91 - Saclay (France). Centre d' Etudes Nucleaires, Deptartement de Physique des Plasmas et de la Fusion Controlee, Service de Physique Appliquee, Service de Physique des Interractions Electroniques, Section d' Etude des Interactions Gaz-Solides

1967-07-01

The geometry and the technology of a cell used for investigations on electron-adsorbed gas interactions are described. The resonance frequencies of the surface ions which are created by the electron impact on the adsorbed gas are predicted by simplified calculations. The experimental data relative to carbon monoxide and neon are in good agreement with these predictions. (authors) [French] Les caracteristiques geometriques et technologiques generales d'une cellule d'etude des interactions entre un faisceau d'electrons et un gaz adsorbe sont donnees. Un calcul simplifie permet de prevoir les frequences de resonance des ions de surface crees par l'impact des electrons sur le gaz adsorbe. Les donnees experimentales sur l'oxyde de carbone et le neon confirment les previsions du calcul. (auteurs)

Spin polarized electrons in surface science

International Nuclear Information System (INIS)

Siegmann, H.C.

1983-01-01

The potentialities of spin-polarised electron beams as a probe of surface magnetic properties are outlined. Elastic as well as inelastic scattering of electrons from solid surfaces are considered. (G.Q.)

Surface cell immobilization within perfluoroalkoxy microchannels

Energy Technology Data Exchange (ETDEWEB)

Stojkovič, Gorazd; Krivec, Matic [Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, SI-1000 Ljubljana (Slovenia); Vesel, Alenka [Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana (Slovenia); Marinšek, Marjan [Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, SI-1000 Ljubljana (Slovenia); Žnidaršič-Plazl, Polona, E-mail: polona.znidarsic@fkkt.uni-lj.si [Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, SI-1000 Ljubljana (Slovenia)

2014-11-30

Graphical abstract: - Highlights: • A very efficient approach for immobilization of cells into microreactors is presented. • It is applicable to various materials, including PFA and cyclic olefin (co)polymers. • It was used to immobilize different prokaryotic and eukaryotic microbes. • Cells were immobilized on the surface in high density and showed good stability. • Mechanisms of APTES interactions with target materials are proposed. - Abstract: Perfluoroalkoxy (PFA) is one of the most promising materials for the fabrication of cheap, solvent resistant and reusable microfluidic chips, which have been recently recognized as effective tools for biocatalytic process development. The application of biocatalysts significantly depends on efficient immobilization of enzymes or cells within the reactor enabling long-term biocatalyst use. Functionalization of PFA microchannels by 3-aminopropyltriethoxysilane (ATPES) and glutaraldehyde was used for rapid preparation of microbioreactors with surface-immobilized cells. X-ray photoelectron spectroscopy and scanning electron microscopy were used to accurately monitor individual treatment steps and to select conditions for cell immobilization. The optimized protocol for Saccharomyces cerevisiae immobilization on PFA microchannel walls comprised ethanol surface pretreatment, 4 h contacting with 10% APTES aqueous solution, 10 min treatment with 1% glutaraldehyde and 20 min contacting with cells in deionized water. The same protocol enabled also immobilization of Escherichia coli, Pseudomonas putida and Bacillus subtilis cells on PFA surface in high densities. Furthermore, the developed procedure has been proved to be very efficient also for surface immobilization of tested cells on other materials that are used for microreactor fabrication, including glass, polystyrene, poly (methyl methacrylate), polycarbonate, and two olefin-based polymers, namely Zeonor{sup ®} and Topas{sup ®}.

Electrical properties and surface morphology of electron beam evaporated p-type silicon thin films on polyethylene terephthalate for solar cells applications

Energy Technology Data Exchange (ETDEWEB)

Ang, P. C.; Ibrahim, K.; Pakhuruddin, M. Z. [Nano-Optoelectronics Research and Technology Laboratory, School of Physics, Universiti Sains Malaysia, Minden 11800 Penang (Malaysia)

2015-04-24

One way to realize low-cost thin film silicon (Si) solar cells fabrication is by depositing the films with high-deposition rate and manufacturing-compatible electron beam (e-beam) evaporation onto inexpensive foreign substrates such as glass or plastic. Most of the ongoing research is reported on e-beam evaporation of Si films on glass substrates to make polycrystalline solar cells but works combining both e-beam evaporation and plastic substrates are still scarce in the literature. This paper studies electrical properties and surface morphology of 1 µm electron beam evaporated Al-doped p-type silicon thin films on textured polyethylene terephthalate (PET) substrate for application as an absorber layer in solar cells. In this work, Si thin films with different doping concentrations (including an undoped reference) are prepared by e-beam evaporation. Energy dispersion X-ray (EDX) showed that the Si films are uniformly doped by Al dopant atoms. With increased Al/Si ratio, doping concentration increased while both resistivity and carrier mobility of the films showed opposite relationships. Root mean square (RMS) surface roughness increased. Overall, the Al-doped Si film with Al/Si ratio of 2% (doping concentration = 1.57×10{sup 16} atoms/cm{sup 3}) has been found to provide the optimum properties of a p-type absorber layer for fabrication of thin film Si solar cells on PET substrate.

Electrical properties and surface morphology of electron beam evaporated p-type silicon thin films on polyethylene terephthalate for solar cells applications

Science.gov (United States)

Ang, P. C.; Ibrahim, K.; Pakhuruddin, M. Z.

2015-04-01

One way to realize low-cost thin film silicon (Si) solar cells fabrication is by depositing the films with high-deposition rate and manufacturing-compatible electron beam (e-beam) evaporation onto inexpensive foreign substrates such as glass or plastic. Most of the ongoing research is reported on e-beam evaporation of Si films on glass substrates to make polycrystalline solar cells but works combining both e-beam evaporation and plastic substrates are still scarce in the literature. This paper studies electrical properties and surface morphology of 1 µm electron beam evaporated Al-doped p-type silicon thin films on textured polyethylene terephthalate (PET) substrate for application as an absorber layer in solar cells. In this work, Si thin films with different doping concentrations (including an undoped reference) are prepared by e-beam evaporation. Energy dispersion X-ray (EDX) showed that the Si films are uniformly doped by Al dopant atoms. With increased Al/Si ratio, doping concentration increased while both resistivity and carrier mobility of the films showed opposite relationships. Root mean square (RMS) surface roughness increased. Overall, the Al-doped Si film with Al/Si ratio of 2% (doping concentration = 1.57×1016 atoms/cm3) has been found to provide the optimum properties of a p-type absorber layer for fabrication of thin film Si solar cells on PET substrate.

Auger electron spectroscopy of alloy surfaces

International Nuclear Information System (INIS)

Overbury, S.H.; Somorjai, G.A.

1975-03-01

Regular solution models are used to predict surface segregation of the constituent of lowest surface free energy in homogeneous multicomponent systems. Analysis of the Auger electron emission intensities from alloys yield the surface composition and the depth distribution of the composition near the surface. Auger Electron Spectroscopy (AES) studies of the surface composition of the Ag--Au and Pb--In systems have been carried out as a function of bulk composition and temperature. Although these alloys have very different regular solution parameters their surface compositions are predictable by the regular solution models. (U.S.)

Surface acoustic wave actuated cell sorting (SAWACS).

Science.gov (United States)

Franke, T; Braunmüller, S; Schmid, L; Wixforth, A; Weitz, D A

2010-03-21

We describe a novel microfluidic cell sorter which operates in continuous flow at high sorting rates. The device is based on a surface acoustic wave cell-sorting scheme and combines many advantages of fluorescence activated cell sorting (FACS) and fluorescence activated droplet sorting (FADS) in microfluidic channels. It is fully integrated on a PDMS device, and allows fast electronic control of cell diversion. We direct cells by acoustic streaming excited by a surface acoustic wave which deflects the fluid independently of the contrast in material properties of deflected objects and the continuous phase; thus the device underlying principle works without additional enhancement of the sorting by prior labelling of the cells with responsive markers such as magnetic or polarizable beads. Single cells are sorted directly from bulk media at rates as fast as several kHz without prior encapsulation into liquid droplet compartments as in traditional FACS. We have successfully directed HaCaT cells (human keratinocytes), fibroblasts from mice and MV3 melanoma cells. The low shear forces of this sorting method ensure that cells survive after sorting.

Scanning electron microscopy of cells from periapical lesions.

Science.gov (United States)

Farber, P A

1975-09-01

Examination of lymphocytes from peripheral blood with the scanning electron microscope (SEM) has shown differences between B cells and T cells on the basis of their surface architecture. This study was initiated to determine whether the cellular components of periapical lesions could be identified with the use of similar criteria. Cells were dispersed from lesions by aspiration of fragments of tissue through syringe needles of decreasing diameters. The liberated cells were filtered on silver-coated Flotronic membranes and examined under the SEM. Lymphocytes, macrophages, epithelial cells, and mast cells were observed in granulomas and cysts. Most of the lymphocytes had smooth surfaces similar to that of T cells; others had villous projections similar to that of B cells. Epithelial nests were seen in the cyst linings while the cyst fluid was rich in lymphocytes. These findings suggest that SEM examination of periapical lesions can be a useful adjunct in studying cellular composition and possible immunological reactions in these tissues.

Multi-scale cell/surface interaction on modified titanium aluminum vanadium surfaces

Science.gov (United States)

Chen, Jianbo

This dissertation presents a series of experimental studies of the effects of multi-scale cell/surface interactions on modified Ti-6Al-4V surfaces. These include laser-grooved surfaces; porous structures and RGD-coated laser-grooved surfaces. A nano-second DPSS UV lasers with a Gaussian pulse energy profile was used to introduce the desired micro-groove geometries onto Ti-6Al-4V surfaces. This was done without inducing micro-cracks or significant changes in surface chemistry within the heat affected zones. The desired 8-12 mum groove depths and widths were achieved by the control of pulse frequency, scan speed, and the lens focal length that controls spot size. The interactions between human osteosarcoma (HOS) cells and laser-grooved Ti-6Al-4V surfaces were investigated after 48 hours of cell culture. The cell behavior, including cell spreading, alignment and adhesion, was elucidated using scanning electronic microscopy (SEM), immuno-fluorescence staining and enzymatic detachment. Contact guidance was shown to increase as grooved spacing decreased. For the range of micro-groove geometries studied, micro-grooves with groove spacings of 20 mum provided the best combination of cell orientation and adhesion. Short-term adhesion experiments (15 mins to 1 day) also revealed that there is a positive correlation between cell orientation and cell adhesion. Contact guidance on the micro-grooved surfaces is shown to be enhanced by nano- and micro-scale asperities that provide sites for the attachment of lamellopodia during cell locomotion and spreading. Contact guidance is also promoted by the geometrical confinement provided by laser grooves. An experimental study of initial cell spreading and ingrowth into Ti-6Al-4V porous structures was also carried out on porous structures with different pore sizes and geometries. A combination of SEM, the tetrazolium salt (MTT) colorimetric assay and enzymatic detachment were used to study cell spreading and adhesion. The extent of cell

Nano-diamonds surface modifications: understanding of electron exchange mechanisms and evidence of a therapeutic effect

International Nuclear Information System (INIS)

Petit, Tristan

2013-01-01

In this thesis, a therapeutic effect of nano-diamonds (NDs) has been evidenced by investigating the role of NDs surface chemistry on their electronic properties. More precisely, the generation of reactive oxygen species from detonation NDs under ionizing radiation, which could improve current radiotherapy treatments, has been demonstrated. To this end, surface treatments facilitating electron transfer from NDs to their environment, namely hydrogenation and surface graphitization, were developed. Experimental conditions ensuring an efficient hydrogenation by hydrogen plasma were determined under ultrahigh vacuum, before being used to prepare large quantities of NDs in powder phase. A similar procedure was applied to the surface graphitization of NDs, performed by annealing under vacuum at high temperature. The impact of such surface treatments on the electronic interaction properties of NDs has been investigated under ambient air and after dispersion in water. These surface treatments induce a positive Zeta potential to NDs in water, which origin has been discussed. Finally, their interactions with human tumor cells were observed. Radiosensitization of tumor cells using NDs under gamma irradiation was demonstrated, opening new perspectives for NDs in nano-medicine. (author) [fr

Depletion region surface effects in electron beam induced current measurements

Energy Technology Data Exchange (ETDEWEB)

Haney, Paul M.; Zhitenev, Nikolai B. [Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Yoon, Heayoung P. [Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, Utah 84112 (United States); Gaury, Benoit [Center for Nanoscale Science and Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Maryland NanoCenter, University of Maryland, College Park, Maryland 20742 (United States)

2016-09-07

Electron beam induced current (EBIC) is a powerful characterization technique which offers the high spatial resolution needed to study polycrystalline solar cells. Current models of EBIC assume that excitations in the p-n junction depletion region result in perfect charge collection efficiency. However, we find that in CdTe and Si samples prepared by focused ion beam (FIB) milling, there is a reduced and nonuniform EBIC lineshape for excitations in the depletion region. Motivated by this, we present a model of the EBIC response for excitations in the depletion region which includes the effects of surface recombination from both charge-neutral and charged surfaces. For neutral surfaces, we present a simple analytical formula which describes the numerical data well, while the charged surface response depends qualitatively on the location of the surface Fermi level relative to the bulk Fermi level. We find that the experimental data on FIB-prepared Si solar cells are most consistent with a charged surface and discuss the implications for EBIC experiments on polycrystalline materials.

Surfaces and interfaces of electronic materials

CERN Document Server

Brillson, Leonard J

2012-01-01

An advanced level textbook covering geometric, chemical, and electronic structure of electronic materials, and their applications to devices based on semiconductor surfaces, metal-semiconductor interfaces, and semiconductor heterojunctions. Starting with the fundamentals of electrical measurements on semiconductor interfaces, it then describes the importance of controlling macroscopic electrical properties by atomic-scale techniques. Subsequent chapters present the wide range of surface and interface techniques available to characterize electronic, optical, chemical, and structural propertie

Endothelial cell behaviour on gas-plasma-treated PLA surfaces: the roles of surface chemistry and roughness.

Science.gov (United States)

Shah, Amita; Shah, Sarita; Mani, Gopinath; Wenke, Joseph; Agrawal, Mauli

2011-04-01

Glow-discharge gas-plasma (GP) treatment has been shown to induce surface modifications such that cell adhesion and growth are enhanced. However, it is not known which gas used in GP treatment is optimal for endothelial cell function. Polylactic acid (PLA) films treated oxygen, argon, or nitrogen GP were characterized using contact angles, scanning electron microscopy, atomic force microscopy, optical profilometry, and x-ray photoelectron spectroscopy. All three GP treatments decreased the carbon atomic concentration and surface roughness and increased the oxygen atomic concentration. Human umbilical vein endothelial cells were cultured on the PLA films for up to 7 days. Based on proliferation and live/dead assays, surface chemistry was shown to have the greatest effect on the attachment, proliferation, and viability of these cells, while roughness did not have a significant influence. Of the different gases, endothelial cell viability, attachment and proliferation were most significantly increased on PLA surfaces treated with oxygen and argon gas plasma. Copyright © 2010 John Wiley & Sons, Ltd.

The surface nanostructures of titanium alloy regulate the proliferation of endothelial cells

Directory of Open Access Journals (Sweden)

Min Lai

2014-02-01

Full Text Available To investigate the effect of surface nanostructures on the behaviors of human umbilical vein endothelial cells (HUVECs, surface nanostructured titanium alloy (Ti-3Zr2Sn-3Mo-25Nb, TLM was fabricated by surface mechanical attrition treatment (SMAT technique. Field emission scanning electron microscopy (FE-SEM, atomic force microscopy (AFM, transmission electron microscopy (TEM and X-ray diffraction (XRD were employed to characterize the surface nanostructures of the TLM, respectively. The results demonstrated that nano-crystalline structures with several tens of nanometers were formed on the surface of TLM substrates. The HUVECs grown onto the surface nanostructured TLM spread well and expressed more vinculin around the edges of cells. More importantly, HUVECs grown onto the surface nanostructured TLM displayed significantly higher (p < 0.01 or p < 0.05 cell adhesion and viabilities than those of native titanium alloy. HUVECs cultured on the surface nanostructured titanium alloy displayed significantly higher (p < 0.01 or p < 0.05 productions of nitric oxide (NO and prostacyclin (PGI2 than those of native titanium alloy, respectively. This study provides an alternative for the development of titanium alloy based vascular stents.

Surface electrons of helium films

International Nuclear Information System (INIS)

Studart, N.; Hipolito, O.

1986-01-01

Theoretical calculations of some properties of two-dimensional electrons on a liquid helium film adsorbed on a solid substrate are reviewed. We describe the spectrum of electron bound states on bulk helium as well on helium films. The correlational properties, such as the structure factor and correlation energy, are determined as functions of the film thickness for different types of substrates in the framework of a Generalized Random-Phase Approximation. The collective excitations of this system are also described. The results for electrons on the surface of thin films and bulk helium are easily obtained. we examine the electron interaction with the excitations of the liquid helium surface resulting in a new polaron state, which was observed very recently. The ground state energy and the effective mass of this polaron are determined by using the path-integral formalism and unitary-transformation method. Recent speculations about the phase diagram of electrons on the helium film are also discussed. (Author) [pt

Transmission Electron Microscopy Studies of Electron-Selective Titanium Oxide Contacts in Silicon Solar Cells

KAUST Repository

Ali, Haider

2017-08-15

In this study, the cross-section of electron-selective titanium oxide (TiO2) contacts for n-type crystalline silicon solar cells were investigated by transmission electron microscopy. It was revealed that the excellent cell efficiency of 21.6% obtained on n-type cells, featuring SiO2/TiO2/Al rear contacts and after forming gas annealing (FGA) at 350°C, is due to strong surface passivation of SiO2/TiO2 stack as well as low contact resistivity at the Si/SiO2/TiO2 heterojunction. This can be attributed to the transformation of amorphous TiO2 to a conducting TiO2-x phase. Conversely, the low efficiency (9.8%) obtained on cells featuring an a-Si:H/TiO2/Al rear contact is due to severe degradation of passivation of the a-Si:H upon FGA.

Electron microscopy localization and characterization of functionalized composite organic-inorganic SERS nanoparticles on leukemia cells.

Science.gov (United States)

Koh, Ai Leen; Shachaf, Catherine M; Elchuri, Sailaja; Nolan, Garry P; Sinclair, Robert

2008-12-01

We demonstrate the use of electron microscopy as a powerful characterization tool to identify and locate antibody-conjugated composite organic-inorganic nanoparticle (COINs) surface enhanced Raman scattering (SERS) nanoparticles on cells. U937 leukemia cells labeled with antibody CD54-conjugated COINs were characterized in their native, hydrated state using wet scanning electron microscopy (SEM) and in their dehydrated state using high-resolution SEM. In both cases, the backscattered electron (BSE) detector was used to detect and identify the silver constituents in COINs due to its high sensitivity to atomic number variations within a specimen. The imaging and analytical capabilities in the SEM were further complemented by higher resolution transmission electron microscopy (TEM) images and scanning Auger electron spectroscopy (AES) data to give reliable and high-resolution information about nanoparticles and their binding to cell surface antigens.

Electron microscopy localization and characterization of functionalized composite organic-inorganic SERS nanoparticles on leukemia cells

International Nuclear Information System (INIS)

Koh, Ai Leen; Shachaf, Catherine M.; Elchuri, Sailaja; Nolan, Garry P.; Sinclair, Robert

2008-01-01

We demonstrate the use of electron microscopy as a powerful characterization tool to identify and locate antibody-conjugated composite organic-inorganic nanoparticle (COINs) surface enhanced Raman scattering (SERS) nanoparticles on cells. U937 leukemia cells labeled with antibody CD54-conjugated COINs were characterized in their native, hydrated state using wet scanning electron microscopy (SEM) and in their dehydrated state using high-resolution SEM. In both cases, the backscattered electron (BSE) detector was used to detect and identify the silver constituents in COINs due to its high sensitivity to atomic number variations within a specimen. The imaging and analytical capabilities in the SEM were further complemented by higher resolution transmission electron microscopy (TEM) images and scanning Auger electron spectroscopy (AES) data to give reliable and high-resolution information about nanoparticles and their binding to cell surface antigens.

Surface morphology of the endolymphatic duct in the rat. A scanning electron microscopy study

DEFF Research Database (Denmark)

Qvortrup, K; Rostgaard, Jørgen; Bretlau, P

1995-01-01

microscopy was attained by coating of the specimens with osmium tetroxide and thiocarbohydrazide followed by a continuous dehydration procedure. This technique permitted, for the first time, an investigation of the surface morphology of the epithelial cells in the endolymphatic duct. Three types of cells......Following intracardiac vascular perfusion fixation of 8 rats with glutaraldehyde in a buffered and oxygenated blood substitute, the vestibular aqueduct and endolymphatic duct were opened by microsurgery of the resulting 16 temporal bones. Optimum preservation of the epithelium for scanning electron...... were identified with the scanning electron microscope. A polygonal and oblong epithelial cell was observed in the largest number throughout the duct, and in the juxtasaccular half of the duct, two additional types of epithelial cells were observed. The scanning electron microscopic observations...

Electron emission at the rail surface

International Nuclear Information System (INIS)

Thornhill, L.; Battech, J.

1991-01-01

In this paper the authors examine the processes by which current is transferred from the cathode rail to the plasma armature in an arc-driven railgun. Three electron emission mechanisms are considered, namely thermionic emission, field-enhanced thermionic emission (or Schottky emission), and photoemission. The author's calculations show that the dominant electron emission mechanism depends, to a great extent, on the work function of the rail surface, the rail surface temperature, the electric field at the rail surface, and the effective radiation temperature of the plasma. For conditions that are considered to be typical of a railgun armature, Schottky emission is the dominant electron emission mechanism, providing current densities on the order of 10 9 A/m 2

Electron curing of surface coatings

International Nuclear Information System (INIS)

Nablo, S.V.

1974-01-01

The technical development of electron curing of surface coatings has received great impetus since 1970 from dramatic changes in the economics of the conventional thermal process. The most important of these changes are reviewed, including: the Clear Air Act, increasing cost and restrictive allocation of energy, decreased availability and increased costs of solvents, competitive pressure for higher line productivity. The principles of free-radical initiated curing as they pertain to industrial coatings are reviewed. Although such electron initiated processes have been under active development for at least two decades, high volume production applications on an industrial scale have only recently appeared. These installations are surveyed with emphasis on the developments in machinery and coatings which have made this possible. The most significant economic advantages of electron curing are presented. In particular, the ability of electron curing to eliminate substrate damage and to eliminate the curing station (oven) as the pacing element for most industrial surface coating curing applications is discussed. Examples of several new processes of particular interest in the textile industry are reviewed, including the curing of transfer cast urethane films, flock adhesives, and graftable surface finishes

Carrier population control and surface passivation in solar cells

KAUST Repository

Cuevas, Andres; Wan, Yimao; Yan, Di; Samundsett, Christian; Allen, Thomas; Zhang, Xinyu; Cui, Jie; Bullock, James

2018-01-01

Controlling the concentration of charge carriers near the surface is essential for solar cells. It permits to form regions with selective conductivity for either electrons or holes and it also helps to reduce the rate at which they recombine

Correlative scanning electron and confocal microscopy imaging of labeled cells coated by indium-tin-oxide

KAUST Repository

Rodighiero, Simona

2015-03-22

Confocal microscopy imaging of cells allows to visualize the presence of specific antigens by using fluorescent tags or fluorescent proteins, with resolution of few hundreds of nanometers, providing their localization in a large field-of-view and the understanding of their cellular function. Conversely, in scanning electron microscopy (SEM), the surface morphology of cells is imaged down to nanometer scale using secondary electrons. Combining both imaging techniques have brought to the correlative light and electron microscopy, contributing to investigate the existing relationships between biological surface structures and functions. Furthermore, in SEM, backscattered electrons (BSE) can image local compositional differences, like those due to nanosized gold particles labeling cellular surface antigens. To perform SEM imaging of cells, they could be grown on conducting substrates, but obtaining images of limited quality. Alternatively, they could be rendered electrically conductive, coating them with a thin metal layer. However, when BSE are collected to detect gold-labeled surface antigens, heavy metals cannot be used as coating material, as they would mask the BSE signal produced by the markers. Cell surface could be then coated with a thin layer of chromium, but this results in a loss of conductivity due to the fast chromium oxidation, if the samples come in contact with air. In order to overcome these major limitations, a thin layer of indium-tin-oxide was deposited by ion-sputtering on gold-decorated HeLa cells and neurons. Indium-tin-oxide was able to provide stable electrical conductivity and preservation of the BSE signal coming from the gold-conjugated markers. © 2015 Wiley Periodicals, Inc.

Atomic and electronic structures of novel silicon surface structures

Energy Technology Data Exchange (ETDEWEB)

Terry, J.H. Jr.

1997-03-01

The modification of silicon surfaces is presently of great interest to the semiconductor device community. Three distinct areas are the subject of inquiry: first, modification of the silicon electronic structure; second, passivation of the silicon surface; and third, functionalization of the silicon surface. It is believed that surface modification of these types will lead to useful electronic devices by pairing these modified surfaces with traditional silicon device technology. Therefore, silicon wafers with modified electronic structure (light-emitting porous silicon), passivated surfaces (H-Si(111), Cl-Si(111), Alkyl-Si(111)), and functionalized surfaces (Alkyl-Si(111)) have been studied in order to determine the fundamental properties of surface geometry and electronic structure using synchrotron radiation-based techniques.

High resolution imaging of surface patterns of single bacterial cells

International Nuclear Information System (INIS)

Greif, Dominik; Wesner, Daniel; Regtmeier, Jan; Anselmetti, Dario

2010-01-01

We systematically studied the origin of surface patterns observed on single Sinorhizobium meliloti bacterial cells by comparing the complementary techniques atomic force microscopy (AFM) and scanning electron microscopy (SEM). Conditions ranged from living bacteria in liquid to fixed bacteria in high vacuum. Stepwise, we applied different sample modifications (fixation, drying, metal coating, etc.) and characterized the observed surface patterns. A detailed analysis revealed that the surface structure with wrinkled protrusions in SEM images were not generated de novo but most likely evolved from similar and naturally present structures on the surface of living bacteria. The influence of osmotic stress to the surface structure of living cells was evaluated and also the contribution of exopolysaccharide and lipopolysaccharide (LPS) by imaging two mutant strains of the bacterium under native conditions. AFM images of living bacteria in culture medium exhibited surface structures of the size of single proteins emphasizing the usefulness of AFM for high resolution cell imaging.

Electronic structure of epitaxial chalcopyrite surfaces and interfaces for photovoltaics

International Nuclear Information System (INIS)

Hofmann, Andreas

2012-01-01

electron states was observed, which can be understood as a higher localization of electronic states and lower crystal quality. In addition, a strong rearrangement of the copper partial density of states was shown. The intimate knowledge of the electric structure was then exploited to demonstrate the valence band discontinuity between CuInSe 2 and CuIn 3 Se 5 . The analysis by photoemission yielded a valence band offset of 0.28 eV, again in reasonable agreement with theoretical results. The p-n-junction in chalcopyrite solar cells is situated near the absorber-buffer interface, which is therefore crucial for the device performance. In this thesis, ZnO deposited from metal-organic precursors on epitaxial CuInSe 2 was investigated as cadmium-free buffer material. In the course of contact formation, the interfacial region of the absorber becomes depleted of copper. Additionally, a thin intrinsic ZnSe layer is formed, prior to the growth of ZnO. The derived band alignments show no dependence on the surface orientation of the chalcopyrite substrate and are consistent with theoretical results. The conduction band lineup is favorable for the application in solar cells.

[Inelastic electron scattering from surfaces

International Nuclear Information System (INIS)

1993-01-01

This program is aimed at the quantitative study of surface dynamical processes (vibrational, magnetic excitations) in crystalline slabs, ultrathin-layered materials, and chemisorbed systems on substrates, and of the geometric structure connected to these dynamical excitations. High-resolution electron-energy loss spectroscopy (HREELS) is a powerful probe. Off-specular excitation cross sections are much larger if electron energies are in the LEED range (50-300 eV). The analyses has been used to study surfaces of ordered alloys (NiAl). Ab-initio surface lattice dynamical results were combined with phonon-loss cross sections to achieve a more accurate microscopic description. First-principles phonon eigenvectors and eigenfrequencies were used as inputs to electron-energy-loss multiple scattering cross-section calculations. The combined microscopic approach was used to analyze EELS data of Cu(0001) and Ag(001) at two points. Positron diffraction is discussed as a structural and imaging tool. The relation between geometric structure of a film and its local magnetic properties will be studied in the future, along with other things

Effects of the capping ligands, linkers and oxide surface on the electron injection mechanism of copper sulfide quantum dot-sensitized solar cells.

Science.gov (United States)

Suárez, Javier Amaya; Plata, Jose J; Márquez, Antonio M; Sanz, Javier Fdez

2017-06-07

Quantum dot-sensitized solar cells, QDSCs, are a clean and effective alternative to fossil fuels to reduce CO 2 emissions. However, the different components that constitute the QDSCs and the difficulty of isolating experimentally their effects on the performance of the whole system slow down the development of more efficient devices. In this work, DFT calculations are combined with a bottom-up approach to differentiate the effect of each component on the electronic structure and absorption spectra. First, Cu 2 S QDs were built including a U parameter to effectively describe the localization of electrons. The effect of capping agents is addressed using ligands with different electron-donating/withdrawing groups. The role of linkers and their adsorption on the oxide surface are also examined. Finally, we propose a main indirect electron injection mechanism based on the position of the peaks of the spectra.

Surface characterization by energy distribution measurements of secondary electrons and of ion-induced electrons

International Nuclear Information System (INIS)

Bauer, H.E.; Seiler, H.

1988-01-01

Instruments for surface microanalysis (e.g. scanning electron or ion microprobes, emission electron or ion microscopes) use the current of emitted secondary electrons or of emitted ion-induced electrons for imaging of the analysed surface. These currents, integrating over all energies of the emitted low energy electrons, are however, not well suited to surface analytical purposes. On the contrary, the energy distribution of these electrons is extremely surface-sensitive with respect to shape, size, width, most probable energy, and cut-off energy. The energy distribution measurements were performed with a cylindrical mirror analyser and converted into N(E), if necessary. Presented are energy spectra of electrons released by electrons and argon ions of some contaminated and sputter cleaned metals, the change of the secondary electron energy distribution from oxidized aluminium to clean aluminium, and the change of the cut-off energy due to work function change of oxidized aluminium, and of a silver layer on a platinum sample. The energy distribution of the secondary electrons often shows detailed structures, probably due to low-energy Auger electrons, and is broader than the energy distribution of ion-induced electrons of the same object point. (author)

Hydrophobicity of electron beam modified surface of hydroxyapatite films

Energy Technology Data Exchange (ETDEWEB)

Gregor, M., E-mail: gregor@fmph.uniba.sk [Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University, 84248 Bratislava (Slovakia); Plecenik, T. [Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University, 84248 Bratislava (Slovakia); Tofail, S.A.M. [Materials & Surface Science Institute, University of Limerick, Limerick (Ireland); Zahoran, M.; Truchly, M. [Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University, 84248 Bratislava (Slovakia); Vargova, M. [Department of Inorganic Chemistry, Faculty of Natural Sciences, Comenius University, 84215 Bratislava (Slovakia); Laffir, F. [Materials & Surface Science Institute, University of Limerick, Limerick (Ireland); Plesch, G. [Department of Inorganic Chemistry, Faculty of Natural Sciences, Comenius University, 84215 Bratislava (Slovakia); Kus, P.; Plecenik, A. [Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University, 84248 Bratislava (Slovakia)

2015-05-15

Highlights: • Surface potential of hydroxyapatite films were modified by focused electron beam. • Micron-sized domains of modified surface potential were created. • Wettability and surface free energy of the irradiated areas was studied. • Possible mechanisms of increased surface hydrophobicity are discussed. - Abstract: Arrays of micron-sized domains of modified surface potential were created on hydroxyapatite films by mid-energy (20 keV) electron beam irradiation available in a laboratory scanning electron microscope. The dosage of electron beam was varied between 10{sup −3} and 10{sup 3} μC/cm{sup 2} to inject charge into the film surface. Contrary to the conventional electrowetting theory, the dosage of injected charge used in creating such microdomains caused a gradual increase of the water contact angle from 57° to 93° due to the elimination of the polar component of the surface free energy. Surface contamination by carbonaceous species can be held only partially responsible for such behavior at lower dosage of electron beam. A transfer of free surface charge to water and an electron beam induced disruption of polar orientation of OH ions have been attributed to be influencial factors in the overall dewetting behavior.

Treatment of surfaces with low-energy electrons

Energy Technology Data Exchange (ETDEWEB)

Frank, L., E-mail: ludek@isibrno.cz [Institute of Scientific Instruments of the CAS, v.v.i., Královopolská 147, 61264 Brno (Czech Republic); Mikmeková, E. [Institute of Scientific Instruments of the CAS, v.v.i., Královopolská 147, 61264 Brno (Czech Republic); FEI Company, Achtseweg Noord 5, 5651 GG Eindhoven (Netherlands); Lejeune, M. [LPMC – Faculte des Sciences d’Amiens, Universite de Picardie Jules Verne, 33 rue Saint Leu, 80039 Amiens Cedex 2 (France)

2017-06-15

Highlights: • Using proper irradiation parameters, adsorbed hydrocarbons are released from surfaces. • Slow electrons remove hydrocarbons instead of depositing carbon. • Prolonged irradiation with very slow electrons does not create defects in graphene. - Abstract: Electron-beam-induced deposition of various materials from suitable precursors has represented an established branch of nanotechnology for more than a decade. A specific alternative is carbon deposition on the basis of hydrocarbons as precursors that has been applied to grow various nanostructures including masks for subsequent technological steps. Our area of study was unintentional electron-beam-induced carbon deposition from spontaneously adsorbed hydrocarbon molecules. This process traditionally constitutes a challenge for scanning electron microscopy practice preventing one from performing any true surface studies outside an ultrahigh vacuum and without in-situ cleaning of samples, and also jeopardising other electron-optical devices such as electron beam lithographs. Here we show that when reducing the energy of irradiating electrons sufficiently, the e-beam-induced deposition can be converted to e-beam-induced release causing desorption of hydrocarbons and ultimate cleaning of surfaces in both an ultrahigh and a standard high vacuum. Using series of experiments with graphene samples, we demonstrate fundamental features of e-beam-induced desorption and present results of checks for possible radiation damage using Raman spectroscopy that led to optimisation of the electron energy for damage-free cleaning. The method of preventing carbon contamination described here paves the way for greatly enhanced surface sensitivity of imaging and substantially reduced demands on vacuum systems for nanotechnological applications.

Electron emission during multicharged ion-metal surface interactions

International Nuclear Information System (INIS)

Zeijlmans van Emmichoven, P.A.; Havener, C.C.; Hughes, I.G.; Overbury, S.H.; Robinson, M.T.; Zehner, D.M.; Meyer, F.W.

1992-01-01

The electron emission during multicharged ion-metal surface interactions will be discussed. The interactions lead to the emission of a significant number of electrons. Most of these electrons have energies below 30 eV. For incident ions with innershell vacancies the emission of Auger electrons that fill these vacancies has been found to occur mainly below the surface. We will present recently measured electron energy distributions which will be used to discuss the mechanisms that lead to the emission of Auger and of low-energy electrons

Surface-Plasmon-Driven Hot Electron Photochemistry.

Science.gov (United States)

Zhang, Yuchao; He, Shuai; Guo, Wenxiao; Hu, Yue; Huang, Jiawei; Mulcahy, Justin R; Wei, Wei David

2017-11-30

Visible-light-driven photochemistry has continued to attract heightened interest due to its capacity to efficiently harvest solar energy and its potential to solve the global energy crisis. Plasmonic nanostructures boast broadly tunable optical properties coupled with catalytically active surfaces that offer a unique opportunity for solar photochemistry. Resonant optical excitation of surface plasmons produces energetic hot electrons that can be collected to facilitate chemical reactions. This review sums up recent theoretical and experimental approaches for understanding the underlying photophysical processes in hot electron generation and discusses various electron-transfer models on both plasmonic metal nanostructures and plasmonic metal/semiconductor heterostructures. Following that are highlights of recent examples of plasmon-driven hot electron photochemical reactions within the context of both cases. The review concludes with a discussion about the remaining challenges in the field and future opportunities for addressing the low reaction efficiencies in hot-electron-induced photochemistry.

Modeling the Excess Cell Surface Stored in a Complex Morphology of Bleb-Like Protrusions.

Directory of Open Access Journals (Sweden)

Maryna Kapustina

2016-03-01

Full Text Available Cells transition from spread to rounded morphologies in diverse physiological contexts including mitosis and mesenchymal-to-amoeboid transitions. When these drastic shape changes occur rapidly, cell volume and surface area are approximately conserved. Consequently, the rounded cells are suddenly presented with a several-fold excess of cell surface whose area far exceeds that of a smooth sphere enclosing the cell volume. This excess is stored in a population of bleb-like protrusions (BLiPs, whose size distribution is shown by electron micrographs to be skewed. We introduce three complementary models of rounded cell morphologies with a prescribed excess surface area. A 2D Hamiltonian model provides a mechanistic description of how discrete attachment points between the cell surface and cortex together with surface bending energy can generate a morphology that satisfies a prescribed excess area and BLiP number density. A 3D random seed-and-growth model simulates efficient packing of BLiPs over a primary rounded shape, demonstrating a pathway for skewed BLiP size distributions that recapitulate 3D morphologies. Finally, a phase field model (2D and 3D posits energy-based constitutive laws for the cell membrane, nematic F-actin cortex, interior cytosol, and external aqueous medium. The cell surface is equipped with a spontaneous curvature function, a proxy for the cell surface-cortex couple, that is a priori unknown, which the model "learns" from the thin section transmission electron micrograph image (2D or the "seed and growth" model image (3D. Converged phase field simulations predict self-consistent amplitudes and spatial localization of pressure and stress throughout the cell for any posited stationary morphology target and cell compartment constitutive properties. The models form a general framework for future studies of cell morphological dynamics in a variety of biological contexts.

Chemistry of SOFC Cathode Surfaces: Fundamental Investigation and Tailoring of Electronic Behavior

Energy Technology Data Exchange (ETDEWEB)

Yildiz, Bilge; Heski, Clemens

2013-08-31

1) Electron tunneling characteristics on La0.7Sr0.3MnO3 (LSM) thin-film surfaces were studied up to 580oC in 10-3mbar oxygen pressure, using scanning tunneling microscopy/ spectroscopy (STM/STS). A threshold-like drop in the tunneling current was observed at positive bias in STS, which is interpreted as a unique indicator for the activation polarization in cation oxygen bonding on LSM cathodes. Sr-enrichment was found on the surface at high temperature using Auger electron spectroscopy, and was accompanied by a decrease in tunneling conductance in STS. This suggests that Sr-terminated surfaces are less active for electron transfer in oxygen reduction compared to Mn-terminated surfaces on LSM. 2) Effects of strain on the surface cation chemistry and the electronic structure are important to understand and control for attaining fast oxygen reduction kinetics on transition metal oxides. Here, we demonstrate and mechanistically interpret the strain coupling to Sr segregation, oxygen vacancy formation, and electronic structure on the surface of La0.7Sr0.3MnO3 (LSM) thin films as a model system. Our experimental results from x-ray photoelectron spectroscopy and scanning tunneling spectroscopy are discussed in light of our first principles-based calculations. A stronger Sr enrichment tendency and a more facile oxygen vacancy formation prevail for the tensile strained LSM surface. The electronic structure of the tensile strained LSM surface exhibits a larger band gap at room temperature, however, a higher tunneling conductance near the Fermi level than the compressively strained LSM at elevated temperatures in oxygen. Our findings suggest lattice strain as a key parameter to tune the reactivity of perovskite transition metal oxides with oxygen in solid oxide fuel cell cathodes. 3) Cation segregation on perovskite oxide surfaces affects vastly the oxygen reduction activity and stability of solid oxide fuel cell (SOFC) cathodes. A unified theory that explains the physical

Surface electron structure of short-period semiconductor superlattice

International Nuclear Information System (INIS)

Bartos, I.; Czech Academy Science, Prague,; Strasser, T.; Schattke, W.

2004-01-01

Full text: Semiconductor superlattices represent man-made crystals with unique physical properties. By means of the directed layer-by-layer molecular epitaxy growth their electric properties can be tailored (band structure engineering). Longer translational periodicity in the growth direction is responsible for opening of new electron energy gaps (minigaps) with surface states and resonances localized at superlattice surfaces. Similarly as for the electron structure of the bulk, a procedure enabling to modify the surface electron structure of superlattices is desirable. Short-period superlattice (GaAs) 2 (AlAs) 2 with unreconstructed (100) surface is investigated in detail. Theoretical description in terms of full eigenfunctions of individual components has to be used. The changes of electron surface state energies governed by the termination of a periodic crystalline potential, predicted on simple models, are confirmed for this system. Large surface state shifts are found in the lowest minigap of the superlattice when this is terminated in four different topmost layer configurations. The changes should be observable in angle resolved photoelectron spectroscopy as demonstrated in calculations based on the one step model of photoemission. Surface state in the center of the two dimensional Brillouin zone moves from the bottom of the minigap (for the superlattice terminated by two bilayers of GaAs) to its top (for the superlattice terminated by two bilayers of AlAs) where it becomes a resonance. No surface state/resonance is found for a termination with one bilayer of AlAs. The surface state bands behave similarly in the corresponding gaps of the k-resolved section of the electron band structure. The molecular beam epitaxy, which enables to terminate the superlattice growth with atomic layer precision, provides a way of tuning the superlattice surface electron structure by purely geometrical means. The work was supported by the Grant Agency of the Academy of Sciences

Electron-phonon interaction on an Al(001) surface

International Nuclear Information System (INIS)

Sklyadneva, I Yu; Chulkov, E V; Echenique, P M

2008-01-01

We report an ab initio study of the electron-phonon (e-ph) interaction and its contribution to the lifetime broadening of excited hole (electron) surface states on Al(001). The calculations based on density-functional theory were carried out using a linear response approach in the plane-wave pseudopotential representation. The obtained results show that both the electron-phonon coupling and the linewidth experience a weak variation with the energy and momentum position of a hole (electron) surface state in the energy band. An analysis of different contributions to the e-ph coupling reveals that bulk phonon modes turn out to be more involved in the scattering processes of excited electrons and holes than surface phonon modes. It is also shown that the role of the e-ph coupling in the broadening of the Rayleigh surface phonon mode is insignificant compared to anharmonic effects

Physisorption of an electron in deep surface potentials off a dielectric surface

International Nuclear Information System (INIS)

Heinisch, R. L.; Bronold, F. X.; Fehske, H.

2011-01-01

We study phonon-mediated adsorption and desorption of an electron at dielectric surfaces with deep polarization-induced surface potentials where multiphonon transitions are responsible for electron energy relaxation. Focusing on multiphonon processes due to the nonlinearity of the coupling between the external electron and the acoustic bulk phonon triggering the transitions between surface states, we calculate electron desorption times for graphite, MgO, CaO, Al 2 O 3 , and SiO 2 and electron sticking coefficients for Al 2 O 3 , CaO, and SiO 2 . To reveal the kinetic stages of electron physisorption, we moreover study the time evolution of the image-state occupancy and the energy-resolved desorption flux. Depending on the potential depth and the surface temperature, we identify two generic scenarios: (i) adsorption via trapping in shallow image states followed by relaxation to the lowest image state and desorption from that state via a cascade through the second strongly bound image state in not too deep potentials, and (ii) adsorption via trapping in shallow image states but followed by a relaxation bottleneck retarding the transition to the lowest image state and desorption from that state via a one-step process to the continuum in deep potentials.

Surface grafting of carboxylic groups onto thermoplastic polyurethanes to reduce cell adhesion

Energy Technology Data Exchange (ETDEWEB)

Alves, P., E-mail: palves@eq.uc.pt [CIEPQPF, Departamento de Engenharia Química, Universidade de Coimbra, Polo II, Pinhal de Marrocos, 3030-790 Coimbra (Portugal); Ferreira, P. [CIEPQPF, Departamento de Engenharia Química, Universidade de Coimbra, Polo II, Pinhal de Marrocos, 3030-790 Coimbra (Portugal); Kaiser, Jean-Pierre [EMPA, St. Gallen, Lerchenfeldstrasse 5, CH-9014 St. Gallen (Switzerland); Salk, Natalie [Mikrofertigung – Micro Engineering, Fraunhofer IFAM, Wiener Strasse 12, D-288359 Bremen (Germany); Bruinink, Arie [EMPA, St. Gallen, Lerchenfeldstrasse 5, CH-9014 St. Gallen (Switzerland); Sousa, Hermínio C. de; Gil, M.H. [CIEPQPF, Departamento de Engenharia Química, Universidade de Coimbra, Polo II, Pinhal de Marrocos, 3030-790 Coimbra (Portugal)

2013-10-15

The interaction of polymers with other materials is an important issue, being their surface properties clearly crucial. For some important polymer applications, their surfaces have to be modified. Surface modification aims to tailor the surface characteristics of a material for a specific application without affecting its bulk properties. Materials can be surface modified by using biological, chemical or physical methods. The aim of this work was to improve the reactivity of the thermoplastic polyurethane (TPU) material (Elastollan{sup ®}) surface and to make its surface cell repellent by grafting carboxylic groups onto its surface. Two TPU materials were studied: a polyether-based TPU and a polyester-based TPU. The grafting efficiency was evaluated by contact angle measurements and by analytical determination of the COOH groups. Scanning electron microscopy (SEM) of the membranes surface was performed as well as cell adhesion tests. It was proved that the surfaces of the TPUs membranes were successfully modified and that cell adhesion was remarkably reduced.

Rough surface mitigates electron and gas emission

International Nuclear Information System (INIS)

Molvik, A.

2004-01-01

Heavy-ion beams impinging on surfaces near grazing incidence (to simulate the loss of halo ions) generate copious amounts of electrons and gas that can degrade the beam. We measured emission coefficients of η e (le) 130 and η 0 ∼ 10 4 respectively, with 1 MeV K + incident on stainless steel. Electron emission scales as η e ∝ 1/cos(θ), where θ is the ion angle of incidence relative to normal. If we were to roughen a surface by blasting it with glass beads, then ions that were near grazing incidence (90 o ) on smooth surface would strike the rims of the micro-craters at angles closer to normal incidence. This should reduce the electron emission: the factor of 10 reduction, Fig. 1(a), implies an average angle of incidence of 62 o . Gas desorption varies more slowly with θ (Fig. 1(b)) decreasing a factor of ∼2, and along with the electron emission is independent of the angle of incidence on a rough surface. In a quadrupole magnet, electrons emitted by lost primary ions are trapped near the wall by the magnetic field, but grazing incidence ions can backscatter and strike the wall a second time at an azimuth where magnetic field lines intercept the beam. Then, electrons can exist throughout the beam (see the simulations of Cohen, HIF News 1-2/04). The SRIM (TRIM) Monte Carlo code predicts that 60-70% of 1 MeV K + ions backscatter when incident at 88-89 o from normal on a smooth surface. The scattered ions are mostly within ∼10 o of the initial direction but a few scatter by up to 90 o . Ion scattering decreases rapidly away from grazing incidence, Fig. 1(c ). At 62 deg. the predicted ion backscattering (from a rough surface) is 3%, down a factor of 20 from the peak, which should significantly reduce electrons in the beam from lost halo ions. These results are published in Phys. Rev. ST - Accelerators and Beams

Modified titanium surface with gelatin nano gold composite increases osteoblast cell biocompatibility

International Nuclear Information System (INIS)

Lee, Young-Hee; Bhattarai, Govinda; Aryal, Santosh; Lee, Nan-Hee; Lee, Min-Ho; Kim, Tae-Gun; Jhee, Eun-Chung; Kim, Hak-Yong; Yi, Ho-Keun

2010-01-01

This study examined the gelatin nano gold (GnG) composite for surface modification of titanium in addition to insure biocompatibility on dental implants or biomaterials. The GnG composite was constructed by gelatin and hydrogen tetrachloroaurate in presence of reducing agent, sodium borohydrate (NabH 4 ). The GnG composite was confirmed by UV-VIS spectroscopy and transmission electron microscopy (TEM). A dipping method was used to modify the titanium surface by GnG composite. Surface was characterized by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The MC-3T3 E1 cell viability was assessed by trypan blue and the expression of proteins to biocompatibility were analyzed by Western blotting. The GnG composite showed well dispersed character, the strong absorption at 530 nm, roughness, regular crystal and clear C, Na, Cl, P, and Au signals onto titanium. Further, this composite allowed MC-3T3 E1 growth and viability compared to gelatin and pure titanium. It induced ERK activation and the expression of cell adherent molecules, FAK and SPARC, and growth factor, VEGF. However, GnG decreased the level of SAPK/JNK. This shows that GnG composite coated titanium surfaces have a good biocompatibility for osteoblast growth and attachment than in intact by simple and versatile dipping method. Furthermore, it offers good communication between cell and implant surfaces by regulating cell signaling and adherent molecules, which are useful to enhance the biocompatibility of titanium surfaces.

Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA)

Science.gov (United States)

SRD 100 Database for Simulation of Electron Spectra for Surface Analysis (SESSA)Database for Simulation of Electron Spectra for Surface Analysis (SESSA) (PC database for purchase)   This database has been designed to facilitate quantitative interpretation of Auger-electron and X-ray photoelectron spectra and to improve the accuracy of quantitation in routine analysis. The database contains all physical data needed to perform quantitative interpretation of an electron spectrum for a thin-film specimen of given composition. A simulation module provides an estimate of peak intensities as well as the energy and angular distributions of the emitted electron flux.

Few-cycle surface plasmon enhanced electron acceleration

International Nuclear Information System (INIS)

Racz, P.; Lenner, M.; Kroo, N.; Farkas, Gy.; Dombi, P.; Takao Fuji; Krausz, F.; Irvine, S.E.; Elezzabi, A.Y.

2010-01-01

Complete text of publication follows. It is possible to generate high-quality ultrafast electron beams with keV energy based on surface plasmon-enhanced electron acceleration. The beam generated this way can be also used to investigate ultrafast phenomena in the plasmon field. For the better understanding of the temporal behavior of these ultrafast surface processes we carried out time-resolved experiments with 5.5 fs laser pulses for the first time. In this experiment, we executed an autocorrelation measurement with an ultra-broadband interferometer. By generating surface plasmons at the output of the interferometer, we measured the plasmonic photocurrent as a function of the delay between the interferometer arms. Figure (a) shows a typical measured result, and figure (b) shows the fourth order calculated autocorrelation function of the 5.5 fs long laser pulse, corresponding to the fourth order nonlinearity of the electron emission process. According to the correspondence of these two curves, we can also state that the length of the generated surface plasmon pulse is only 2-3 optical cycles. As a further experiment, we executed spectrally resolved measurements of the electron beam at higher intensities. According to these results, it is possible to reach electron beams with keV energy in the few-cycle regime too. It was found that the field strength of the surface plasmons is x 7 to x 30 higher than that of the focused laser pulse.

An AES Study of the Room Temperature Surface Conditioning of Technological Metal Surfaces by Electron Irradiation

CERN Document Server

Scheuerlein, C; Taborelli, M; Brown, A; Baker, M A

2002-01-01

The modifications to technological copper and niobium surfaces induced by 2.5 keV electron irradiation have been investigated in the context of the conditioning process occurring in particle accelerator ultra high vacuum systems. Changes in the elemental surface composition have been found using Scanning Auger Microscopy (SAM) by monitoring the carbon, oxygen and metal Auger peak intensities as a function of electron irradiation in the dose range 10-6 to 10-2 C mm-2. The surface analysis results are compared with electron dose dependent secondary electron and electron stimulated desorption yield measurements. Initially the electron irradiation causes a surface cleaning through electron stimulated desorption, in particular of hydrogen. During this period both the electron stimulated desorption and secondary electron yield decrease as a function of electron dose. When the electron dose exceeds 10-4 C mm-2 electron stimulated desorption yields are reduced by several orders of magnitude and the electron beam indu...

Hot-electron nanoscopy using adiabatic compression of surface plasmons

KAUST Repository

Giugni, Andrea; Torre, Bruno; Toma, Andrea; Francardi, Marco; Malerba, Mario; Alabastri, Alessandro; Proietti Zaccaria, Remo; Stockman, Mark Mark; Di Fabrizio, Enzo M.

2013-01-01

Surface plasmon polaritons are a central concept in nanoplasmonics and have been exploited to develop ultrasensitive chemical detection platforms, as well as imaging and spectroscopic techniques at the nanoscale. Surface plasmons can decay to form highly energetic (or hot) electrons in a process that is usually thought to be parasitic for applications, because it limits the lifetime and propagation length of surface plasmons and therefore has an adverse influence on the functionality of nanoplasmonic devices. Recently, however, it has been shown that hot electrons produced by surface plasmon decay can be harnessed to produce useful work in photodetection, catalysis and solar energy conversion. Nevertheless, the surface-plasmon-to-hot-electron conversion efficiency has been below 1% in all cases. Here we show that adiabatic focusing of surface plasmons on a Schottky diode-terminated tapered tip of nanoscale dimensions allows for a plasmon-to-hot-electron conversion efficiency of ∼30%. We further demonstrate that, with such high efficiency, hot electrons can be used for a new nanoscopy technique based on an atomic force microscopy set-up. We show that this hot-electron nanoscopy preserves the chemical sensitivity of the scanned surface and has a spatial resolution below 50 nm, with margins for improvement.

Hot-electron nanoscopy using adiabatic compression of surface plasmons

KAUST Repository

Giugni, Andrea

2013-10-20

Surface plasmon polaritons are a central concept in nanoplasmonics and have been exploited to develop ultrasensitive chemical detection platforms, as well as imaging and spectroscopic techniques at the nanoscale. Surface plasmons can decay to form highly energetic (or hot) electrons in a process that is usually thought to be parasitic for applications, because it limits the lifetime and propagation length of surface plasmons and therefore has an adverse influence on the functionality of nanoplasmonic devices. Recently, however, it has been shown that hot electrons produced by surface plasmon decay can be harnessed to produce useful work in photodetection, catalysis and solar energy conversion. Nevertheless, the surface-plasmon-to-hot-electron conversion efficiency has been below 1% in all cases. Here we show that adiabatic focusing of surface plasmons on a Schottky diode-terminated tapered tip of nanoscale dimensions allows for a plasmon-to-hot-electron conversion efficiency of ∼30%. We further demonstrate that, with such high efficiency, hot electrons can be used for a new nanoscopy technique based on an atomic force microscopy set-up. We show that this hot-electron nanoscopy preserves the chemical sensitivity of the scanned surface and has a spatial resolution below 50 nm, with margins for improvement.

Electronic Structure of Hydrogenated and Surface-Modified GaAs Nanocrystals: Ab Initio Calculations

Directory of Open Access Journals (Sweden)

Hamsa Naji Nasir

2012-01-01

Full Text Available Two methods are used to simulate electronic structure of gallium arsenide nanocrystals. The cluster full geometrical optimization procedure which is suitable for small nanocrystals and large unit cell that simulates specific parts of larger nanocrystals preferably core part as in the present work. Because of symmetry consideration, large unit cells can reach sizes that are beyond the capabilities of first method. The two methods use ab initio Hartree-Fock and density functional theory, respectively. The results show that both energy gap and lattice constant decrease in their value as the nanocrystals grow in size. The inclusion of surface part in the first method makes valence band width wider than in large unit cell method that simulates the core part only. This is attributed to the broken symmetry and surface passivating atoms that split surface degenerate states and adds new levels inside and around the valence band. Bond length and tetrahedral angle result from full geometrical optimization indicate good convergence to the ideal zincblende structure at the centre of hydrogenated nanocrystal. This convergence supports large unit cell methodology. Existence of oxygen atoms at nanocrystal surface melts down density of states and reduces energy gap.

Surface topography and ultrastructural changes of mucinous carcinoma breast cells.

Science.gov (United States)

Voloudakis, G E; Baltatzis, G E; Agnantis, N J; Arnogianaki, N; Misitzis, J; Voloudakis-Baltatzis, I

2007-01-01

Mucinous carcinoma of the breast (MCB) is histologically classified into 2 groups: (1) pure MCB and (2) mixed MCB. Pure MCB carries a better diagnosis than mixed MCB. This research relates to the cell surface topography and ultrastructure of the cells in the above cases and aims to find the differences between them, by means of two methods: scanning electron microscopy (SEM) and transmission electron microscopy (TEM). For the SEM examination, it was necessary to initially culture the MCB tissues and then proceed with the usual SEM method. In contrast, for the TEM technique, MCB tissues were initially fixed followed by the classic TEM method. The authors found the topography of pure MCB cases to be without nodes. The cell membrane was smooth, with numerous pores and small ruffles that covered the entire cell. The ultrastructural appearance of the same cases was with a normal cell membrane containing abundant collagen fibers. They also had many small vesicles containing mucin as well as secretory droplets. In contrast the mixed MCB had a number of lymph nodes and their cell surface topography showed stronger changes such as microvilli, numerous blebs, ruffles and many long projections. Their ultrastructure showed very long microvilli with large cytoplasmic inclusions and extracellular mucin collections, electron-dense material vacuoles, and many important cytoplasmic organelles. An important fact is that mixed MCB also contains areas of infiltrating ductal carcinoma. These cells of the cytoplasmic organelles are clearly responsible for the synthesis, storage, and secretion of the characteristic mucin of this tumor type. Evidently, this abnormal mucin production and the abundance of secretory granules along with the long projections observed in the topographical structure might be responsible for transferring tumor cells to neighboring organs, thus being responsible for metastatic disease.

Tuning cell adhesion on polymeric and nanocomposite surfaces: Role of topography versus superhydrophobicity

Energy Technology Data Exchange (ETDEWEB)

Zangi, Sepideh [Department of Chemical Engineering, Shahrood Branch, Islamic Azad University, P.O. Box 36155-163, Shahrood (Iran, Islamic Republic of); Hejazi, Iman [Department of Polymer Engineering & Color Technology, Amirkabir University of Technology, Tehran (Iran, Islamic Republic of); Seyfi, Javad, E-mail: Jseyfi@gmail.com [Department of Chemical Engineering, Shahrood Branch, Islamic Azad University, P.O. Box 36155-163, Shahrood (Iran, Islamic Republic of); Hejazi, Ehsan [Department of Clinical Nutrition and Dietetics, Faculty of Nutrition Sciences and Food Technology, Shahid Beheshti University of Medical Sciences, Tehran (Iran, Islamic Republic of); Khonakdar, Hossein Ali [Department of Polymer Engineering, Faculty of Engineering, South Tehran Branch, Islamic Azad University, P.O. Box 19585-466, Tehran (Iran, Islamic Republic of); Davachi, Seyed Mohammad [School of Chemical Engineering, University of Tehran, P.O. Box 11155-4563, Tehran (Iran, Islamic Republic of)

2016-06-01

Development of surface modification procedures which allow tuning the cell adhesion on the surface of biomaterials and devices is of great importance. In this study, the effects of different topographies and wettabilities on cell adhesion behavior of polymeric surfaces are investigated. To this end, an improved phase separation method was proposed to impart various wettabilities (hydrophobic and superhydrophobic) on polypropylene surfaces. Surface morphologies and compositions were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Cell culture was conducted to evaluate the adhesion of 4T1 mouse mammary tumor cells. It was found that processing conditions such as drying temperature is highly influential in cell adhesion behavior due to the formation of an utterly different surface topography. It was concluded that surface topography plays a more significant role in cell adhesion behavior rather than superhydrophobicity since the nano-scale topography highly inhibited the cell adhesion as compared to the micro-scale topography. Such cell repellent behavior could be very useful in many biomedical devices such as those in drug delivery and blood contacting applications as well as biosensors. - Highlights: • A novel method is presented for fabrication of superhydrophobic surfaces. • The presence of nanoparticles in non-solvent bath notably promoted phase separation. • Topography had a more notable impact on cell adhesion than superhydrophobicity. • Nano-scale topographical features highly impeded cell adhesion on polymer surfaces.

Tuning cell adhesion on polymeric and nanocomposite surfaces: Role of topography versus superhydrophobicity

International Nuclear Information System (INIS)

Zangi, Sepideh; Hejazi, Iman; Seyfi, Javad; Hejazi, Ehsan; Khonakdar, Hossein Ali; Davachi, Seyed Mohammad

2016-01-01

Development of surface modification procedures which allow tuning the cell adhesion on the surface of biomaterials and devices is of great importance. In this study, the effects of different topographies and wettabilities on cell adhesion behavior of polymeric surfaces are investigated. To this end, an improved phase separation method was proposed to impart various wettabilities (hydrophobic and superhydrophobic) on polypropylene surfaces. Surface morphologies and compositions were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. Cell culture was conducted to evaluate the adhesion of 4T1 mouse mammary tumor cells. It was found that processing conditions such as drying temperature is highly influential in cell adhesion behavior due to the formation of an utterly different surface topography. It was concluded that surface topography plays a more significant role in cell adhesion behavior rather than superhydrophobicity since the nano-scale topography highly inhibited the cell adhesion as compared to the micro-scale topography. Such cell repellent behavior could be very useful in many biomedical devices such as those in drug delivery and blood contacting applications as well as biosensors. - Highlights: • A novel method is presented for fabrication of superhydrophobic surfaces. • The presence of nanoparticles in non-solvent bath notably promoted phase separation. • Topography had a more notable impact on cell adhesion than superhydrophobicity. • Nano-scale topographical features highly impeded cell adhesion on polymer surfaces.

Electron microscopy study of antioxidant interaction with bacterial cells

Science.gov (United States)

Plotnikov, Oleg P.; Novikova, Olga V.; Konnov, Nikolai P.; Korsukov, Vladimir N.; Gunkin, Ivan F.; Volkov, Uryi P.

2000-10-01

To maintain native microorganisms genotype and phenotype features a lyophylization technique is widely used. However in this case cells are affected by influences of vacuum and low temperature that cause a part of the cells population to be destruction. Another factor reduced microorganisms vitality is formation of reactive oxygen forms that damage certain biological targets (such as DNA, membranes etc.) Recently to raise microorganism's resistance against adverse condition natural and synthetic antioxidants are used. Antioxidant- are antagonists of free radicals. Introduction of antioxidants in protective medium for lyophylization increase bacteria storage life about 2,0-4,8 fold in comparison with reference samples. In the article the main results of our investigation of antioxidants interaction with microorganism cells is described. As bacteria cells we use vaccine strain yersinia pestis EV, that were grown for 48 h at 28 degree(s)C on the Hottinger agar (pH 7,2). Antioxidants are inserted on the agar surface in specimen under test. To investigate a localization of antioxidants for electron microscopy investigation, thallium organic antioxidants were used. The thallium organic compounds have an antioxidant features if thallium is in low concentration (about 1(mu) g/ml). The localization of the thallium organic antioxidants on bacteria Y. pestis EV is visible in electron microscopy images, thallium being heavy metal with high electron density. The negatively stained bacteria and bacteria thin sections with thallium organic compounds were investigated by means of transmission electron microscopy. The localization of the thallium organic compounds is clearly visible in electron micrographs as small dark spots with size about 10-80nm. Probably mechanisms of interaction of antioxidants with bacteria cells are discussed.

Treatment of surfaces with low-energy electrons

Science.gov (United States)

Frank, L.; Mikmeková, E.; Lejeune, M.

2017-06-01

Electron-beam-induced deposition of various materials from suitable precursors has represented an established branch of nanotechnology for more than a decade. A specific alternative is carbon deposition on the basis of hydrocarbons as precursors that has been applied to grow various nanostructures including masks for subsequent technological steps. Our area of study was unintentional electron-beam-induced carbon deposition from spontaneously adsorbed hydrocarbon molecules. This process traditionally constitutes a challenge for scanning electron microscopy practice preventing one from performing any true surface studies outside an ultrahigh vacuum and without in-situ cleaning of samples, and also jeopardising other electron-optical devices such as electron beam lithographs. Here we show that when reducing the energy of irradiating electrons sufficiently, the e-beam-induced deposition can be converted to e-beam-induced release causing desorption of hydrocarbons and ultimate cleaning of surfaces in both an ultrahigh and a standard high vacuum. Using series of experiments with graphene samples, we demonstrate fundamental features of e-beam-induced desorption and present results of checks for possible radiation damage using Raman spectroscopy that led to optimisation of the electron energy for damage-free cleaning. The method of preventing carbon contamination described here paves the way for greatly enhanced surface sensitivity of imaging and substantially reduced demands on vacuum systems for nanotechnological applications.

Influence of laser surface modifying of polyethylene terephthalate on fibroblast cell adhesion

International Nuclear Information System (INIS)

Mirzadeh, H.; Dadsetan, M.

2003-01-01

Attempts have been made to evaluate the changes in physical and chemical properties of the polyethylene terephthalate (PET) surface due to laser irradiation. These changes have been investigated from viewpoints of microstructuring and its effect on fibroblast cell behavior. The surfaces of PET were irradiated using CO 2 and KrF excimer pulsed laser. The changes were characterized by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy (SEM) and contact angle measurements. The data from ATR-FTIR spectra showed that the crystallinity in the surface region decreased due to the CO 2 and excimer laser irradiation. SEM observations showed that specific microstructures were created on the PET surface due to laser irradiation. In order to study biocompatibility and cell behavior, we utilized standard in vitro L929-fibroblast cell culture system. Fibroblast cell adhesion and spreading were significantly correlated to the morphology and wettability of the laser irradiated PET surface

Enhanced Electron-Phonon Coupling at Metal Surfaces

Energy Technology Data Exchange (ETDEWEB)

Plummer, Ward E.

2010-08-04

The Born-Oppenheimer approximation (BOA) decouples electronic from nuclear motion, providing a focal point for most quantum mechanics textbooks. However, a multitude of important chemical, physical and biological phenomena are driven by violations of this approximation. Vibronic interactions are a necessary ingredient in any process that makes or breaks a covalent bond, for example, conventional catalysis or enzymatically delivered biological reactions. Metastable phenomena associated with defects and dopants in semiconductors, oxides, and glasses entail violation of the BOA. Charge exchange in inorganic polymers, organic slats and biological systems involves charge- induced distortions of the local structure. A classic example is conventional superconductivity, which is driven by the electron-lattice interaction. High-resolution angle-resolved photoemission experiments are yielding new insight into the microscopic origin of electron-phonon coupling (EPC) in anisotropic two-dimensional systems. Our recent surface phonon measurement on the surface of a high-Tc material clearly indicates an important momentum dependent EPC in these materials. In the last few years we have shifted our research focus from solely looking at electron phonon coupling to examining the structure/functionality relationship at the surface of complex transition metal compounds. The investigation on electron phonon coupling has allowed us to move to systems where there is coupling between the lattice, the electrons and the spin.

Morphology, surface roughness, electron inelastic and quasi-elastic scattering in elastic peak electron spectroscopy of polymers

International Nuclear Information System (INIS)

Lesiak, B.; Kosinski, A.; Nowakowski, R.; Koever, L.; Toth, J.; Varga, D.; Cserny, I.; Sulyok, A.; Gergely, G.

2006-01-01

Complete text of publication follows. Elastic peak electron spectroscopy (EPES) deals with the interaction of electrons with atoms of a solid surface, studying the distribution of electrons backscattered elastically. The nearest vicinity of the elastic peak, (low kinetic energy region) reflects both, electron inelastic and quasi-elastic processes. The incident electrons produce surface excitations, inducing surface plasmons with the corresponding loss peaks separated by 1 - 20 eV energy from the elastic peak. Quasi-elastic losses result from the recoil of scattering atoms of different atomic number, Z. The respective energy shift and Doppler broadening of the elastic peak depend on Z, the primary electron energy, E, and the measurement geometry. Quantitative surface analytical application of EPES, such as determination of parameters describing electron transport, requires a comparison of experimental data with corresponding data derived from Monte Carlo (MC) simulation. Several problems occur in EPES studies of polymers. The intensity of elastic peak, considered in quantitative surface analysis, is influenced by both, the inelastic and quasi-elastic scattering processes (especially for hydrogen scattering atoms and primary electron energy above 1000 eV). An additional factor affecting the elastic peak intensity is the surface morphology and roughness. The present work compares the effect of these factors on the elastic peak intensity for selected polymers (polyethylene, polyaniline and polythiophenes). X-ray photoelectron spectroscopy (XPS) and helium pycnometry are applied for deriving the surface atomic composition and the bulk density, while scanning electron microscopy (SEM) and atomic force microscopy (AFM) for determining surface morphology and roughness. According to presented results, the influence of surface morphology and roughness is larger than those of surface excitations or recoil of hydrogen atoms. The component due to recoil of hydrogen atoms can be

Polycarbonate surface cell's adhesion examination after Nd:YAG laser irradiation

Energy Technology Data Exchange (ETDEWEB)

Ramazani, S.A. Ahmad, E-mail: Ramazani@sharif.ir [Polymer Group, Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Mousavi, Seyyed Abbas, E-mail: Musavi@che.sharif.ir [Department of Chemistry, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Seyedjafari, Ehsan [Department of Biotechnology, University College of Science, University of Tehran (Iran, Islamic Republic of); Poursalehi, Reza [Department of Physics, University of Shahed, Tehran (Iran, Islamic Republic of); Sareh, Shohreh [Research Center of Iranian Blood Transfusion Organization, Tehran (Iran, Islamic Republic of); Silakhori, Kaveh [Laser Research Center, Atomic Energy Organization, Tehran (Iran, Islamic Republic of); Poorfatollah, Ali Akbar [Research Center of Iranian Blood Transfusion Organization, Tehran (Iran, Islamic Republic of); Shamkhali, Amir Nasser [Department of Chemistry, Sharif University of Technology, Tehran (Iran, Islamic Republic of)

2009-05-05

Nd:YAG laser treatment was used in order to increase surface cell adhesion aspects of polycarbonate (PC) films prepared via melt process. The treatment was carried out under different wavelengths and beam diameters. ATR-FTIR and UV spectra obtained from different samples before and after laser treatment in air showed that laser irradiation has induced some chemical and physical changes in surface properties. The irradiated films were also characterized using scanning electron microscopy (SEM) and contact angle measurements. Effect of pulse numbers on the surface properties was also investigated. Cell culture test was used to evaluate cell adhesion property on the PC films before and after treatment. The results obtained from this test showed that after laser treatment, the cells were attached and proliferated extensively on the Nd:YAG laser treated films in comparison with the unmodified PC. Moreover, it was revealed that a decrease in the laser beam diameter and an increase in the irradiated pulse numbers increased surface wettability and caused a better cell attachment on the polymer surface. The obtained results also showed that a decrease in the laser beam diameter and an increase in the irradiated pulse numbers increased surface wettability and caused a better cell attachment on the polymer surface.

Electron transfer in gas surface collisions

International Nuclear Information System (INIS)

Wunnik, J.N.M. van.

1983-01-01

In this thesis electron transfer between atoms and metal surfaces in general is discussed and the negative ionization of hydrogen by scattering protons at a cesiated crystalline tungsten (110) surface in particular. Experimental results and a novel theoretical analysis are presented. In Chapter I a theoretical overview of resonant electron transitions between atoms and metals is given. In the first part of chapter II atom-metal electron transitions at a fixed atom-metal distance are described on the basis of a model developed by Gadzuk. In the second part the influence of the motion of the atom on the atomic charge state is incorporated. Measurements presented in chapter III show a strong dependence of the fraction of negatively charged H atoms scattered at cesiated tungsten, on the normal as well as the parallel velocity component. In chapter IV the proposed mechanism for the parallel velocity effect is incorporated in the amplitude method. The scattering process of protons incident under grazing angles on a cesium covered surface is studied in chapter V. (Auth.)

Design of a microfluidic cell using microstereolithography for electronic tongue applications

Science.gov (United States)

Jacesko, Stefany L.; Ji, Taeksoo; Abraham, Jose K.; Varadan, Vijay K.; Gardner, Julian W.

2003-07-01

In this paper we present design, fabrication and integration of a micro fluidic cell for use with the electronic tongue. The cell was machined using microstereo lithography on a Hexanediol Diacrylate (HDDA) liquid monomer. The wet cell was designed to confine the liquid under test to the sensing area and insure complete isolation of the interdigital transducers (IDTs). The electronic tongue is a shear horizontal surface acoustic wave (SH-SAW) device. Shear horizontally polarized Love-waves are guided between transmitting and receiving IDTs, over a piezoelectric substrate, which creates an electronic oscillator effect. This device has a dual delay line configuration, which accounts for the measuring of both mechanical and electrical properties of a liquid, simultaneously, with the ability to eliminate environmental factors. The data collected is distinguished using principal components analysis in conjunction with pre-processing parameters. The experiments show that the micro fluidic cell for this electronic tongue does not affect the losses or phase of the device to any extent of concern. Experiments also show that liquids such as Strawberry Hi-C, Teriyaki Sauce, DI Water, Coca Cola, and Pepsi are distinguishable using these methods.

Surface study of liquid 3He using surface state electrons

International Nuclear Information System (INIS)

Shirahama, K.; Ito, S.; Suto, H.; Kono, K.

1995-01-01

We have measured the mobility of surface state electrons (SSE) on liquid 3 He, μ 3 , aiming to study the elementary surface excitations of the Fermi liquid. A gradual increase of μ 3 below 300 mK is attributed to the scattering of electrons by ripplons. Ripplons do exist in 3 He down to 100 mK. We observe an abrupt decrease of μ 3 , due to the transition to the Wigner solid (WS). The dependences of the WS conductivity and mobility on temperature and magnetic field differ from the SSE behavior on liquid 4 He

Effect of the back surface topography on the efficiency in silicon solar cells

International Nuclear Information System (INIS)

Guo Aijuan; Ye Famin; Feng Shimeng; Guo Lihui; Ji Dong

2009-01-01

Different processes are used on the back surface of silicon wafers to form cells falling into three groups: textured, planar, and sawed-off pyramid back surface. The characteristic parameters of the cells, I SC , V OC , FF, Pm, and E ff , are measured. All these parameters of the planar back surface cells are the best. The FF, Pm, and E ff of sawed-off pyramid back surface cells are superior to textured back surface cells, although I SC and V OC are lower. The parasitic resistance is analyzed to explain the higher FF of the sawed-off pyramid back surface cells. The cross-section scanning electron microscopy (SEM) pictures show the uniformity of the aluminum-silicon alloy, which has an important effect on the back surface recombination velocity and the ohmic contact. The measured value of the aluminum back surface field thickness in the SEM picture is in good agreement with the theoretical value deduced from the Al-Si phase diagram. It is shown in an external quantum efficiency (EQE) diagram that the planar back surface has the best response to a wavelength between 440 and 1000 nm and the sawed-off back surface has a better long wavelength response.

Glycoprotein on cell surfaces

International Nuclear Information System (INIS)

Muramatsu, T.

1975-01-01

There are conjugated polysaccharides in cell membranes and outside of animal cells, and they play important role in the control of cell behavior. In this paper, the studies on the glycoprotein on cell surfaces are reported. It was found that the glycoprotein on cell surfaces have both N-glycoside type and O-glycoside type saccharic chains. Therefore it can be concluded that the basic structure of the saccharic chains in the glycoprotein on cell surfaces is similar to that of blood serum and body fluid. The main glycoprotein in the membranes of red blood corpuscles has been studied most in detail, and it also has both types of saccharic chains. The glycoprotein in liver cell membranes was found to have only the saccharic chains of acid type and to be in different pattern from that in endoplasmic reticula and nuclear membranes, which also has the saccharic chains of neutral type. The structure of the saccharic chains of H-2 antigen, i.e. the peculiar glycoprotein on the surfaces of lymph system cells, has been studied, and it is similar to the saccharic chains of glycoprotein in blood serum. The saccharic chain structures of H-2 antigen and TL antigen are different. TL, H-2 (D), Lna and H-2 (K) are the glycoprotein on cell surfaces, and are independent molecules. The analysis of the saccharic chain patterns on cell surfaces was carried out, and it was shown that the acid type saccharic chains were similar to those of ordinary glycoprotein, because the enzyme of pneumococci hydrolyzed most of the acid type saccharic chains. The change of the saccharic chain patterns of glycoprotein on cell surfaces owing to canceration and multiplication is complex matter. (Kako, I.)

Surface Relaxation and Electronic States of Pt(111) Surface with Varying Slab Thickness

International Nuclear Information System (INIS)

Kaushal, Ashok K.; Mullick, Shanta; Ahluwalia, P. K.

2011-01-01

Surface relaxation and electronic DOS's of Pt(111) surface have been studied with varying slab thickness using ab-initio SIESTA method. We found the expansion in the top layer and contraction in the subsurface layers of Pt(111) surface. Our results match with the experimental results. Also observing electronic density of states we found that as we increase the thickness of slab, the PDOS of Pt(111) surface goes towards the bulk density of states and Fermi energy shifts towards the bulk fermi energy.

The surface morphology of retinal breaks and lattice retinal degeneration. A scanning electron microscopic study.

Science.gov (United States)

Robinson, M R; Streeten, B W

1986-02-01

In 14 of 110 eye bank eyes, lesions characteristic of peripheral retinal surface pathology were examined by scanning electron microscopy (SEM). These included operculated and flap tears, trophic round holes, lattice degeneration with holes, and paravascular retinal "pitting" degeneration. By SEM, the edges of the retinal breaks were covered by smooth cellular membranes, merging peripherally with a meshwork of vitreous fibrils. The membrane cells had poorly defined borders, a pitted surface, and variable numbers of microvilli consistent with glia. Lattice surfaces and foci of paravascular retinal degeneration were covered by similar membrane, but showed characteristic differences. It appears that breaks in the internal limiting membrane always stimulate proliferation of preretinal glial membranes. Similar cellular morphology of the membranes associated with breaks is consistent with a common cell of origin. Limited proliferation of these membranes suggests that surface gliosis is normally inhibited when the cells contact either intact basement membrane or vitreous.

Electron acceleration by surface plasma waves in double metal surface structure

Science.gov (United States)

Liu, C. S.; Kumar, Gagan; Singh, D. B.; Tripathi, V. K.

2007-12-01

Two parallel metal sheets, separated by a vacuum region, support a surface plasma wave whose amplitude is maximum on the two parallel interfaces and minimum in the middle. This mode can be excited by a laser using a glass prism. An electron beam launched into the middle region experiences a longitudinal ponderomotive force due to the surface plasma wave and gets accelerated to velocities of the order of phase velocity of the surface wave. The scheme is viable to achieve beams of tens of keV energy. In the case of a surface plasma wave excited on a single metal-vacuum interface, the field gradient normal to the interface pushes the electrons away from the high field region, limiting the acceleration process. The acceleration energy thus achieved is in agreement with the experimental observations.

Improving the Osteoblast Cell Adhesion on Electron Beam Controlled TiO2 Nanotubes

Directory of Open Access Journals (Sweden)

Sung Wook Yoon

2014-01-01

Full Text Available Here we investigate the osteogenesis and synostosis processes on the surface-modified TiO2 nanotubes via electron beam irradiation. The TiO2 nanotubes studied were synthesized by anodization process under different anodizing voltage. For the anodization voltage of 15, 20, and 25 V, TiO2 nanotubes with diameters of 59, 82, and 105 nm and length of 115, 276, and 310 nm were obtained, respectively. MC3T3-E1 osteoblast cell line was incubated on the TiO2 nanotubes to monitor the change in the cell adhesion before and after the electron beam irradiation. We observe that the electron beam irradiation affects the number of surviving osteoblast cells as well as the cultivation time. In particular, the high adhesion rate of 155% was obtained when the osteoblast cells were cultivated for 2 hours on the TiO2 nanotube, anodized under 20 V, and irradiated with 5,000 kGy of electron beam.

Determining surface areas of marine alga cells by acid-base titration method.

Science.gov (United States)

Wang, X; Ma, Y; Su, Y

1997-09-01

A new method for determining the surface area of living marine alga cells was described. The method uses acid-base titration to measure the surface acid/base amount on the surface of alga cells and uses the BET (Brunauer, Emmett, and Teller) equation to estimate the maximum surface acid/base amount, assuming that hydrous cell walls have carbohydrates or other structural compounds which can behave like surface Brönsted acid-base sites due to coordination of environmental H2O molecules. The method was applied to 18 diverse alga species (including 7 diatoms, 2 flagellates, 8 green algae and 1 red alga) maintained in seawater cultures. For the species examined, the surface areas of individual cells ranged from 2.8 x 10(-8) m2 for Nannochloropsis oculata to 690 x 10(-8) m2 for Dunaliella viridis, specific surface areas from 1,030 m2.g-1 for Dunaliella salina to 28,900 m2.g-1 for Pyramidomonas sp. Measurement accuracy was 15.2%. Preliminary studies show that the method may be more promising and accurate than light/electron microscopic measurements for coarse estimation of the surface area of living algae.

Semiconductor interfaces of polycrystalline CdTe thin-film solar cells. Characterization and modification of electronic properties

International Nuclear Information System (INIS)

Fritsche, J.

2003-01-01

In this thesis for the first time the electronic properties of the semiconductor interfaces in polycrystalline CdTe thin-film solar cells, as well as the morphological and electronic properties of the single semiconductor surfaces were systematically characterized by surface-sensitive measuring methods. The morphological surface properties were analyzed by scanning force microscopy. As substrate materials with SnO 2 /ITO covered glass was applied, where the CdS and CdTe layers were deposited. Furthermore the electronic and morphological material properties of differently treated SnO 2 surfaces were characterized. Beside the studies with scanning force microscopy sputtering depth profiles and X-ray photoelectron spectroscopy were measured

Electron beam welding of high-purity copper accelerator cells

International Nuclear Information System (INIS)

Delis, K.; Haas, H.; Schlebusch, P.; Sigismund, E.

1986-01-01

The operating conditions of accelerator cells require high thermal conductivity, low gas release in the ultrahigh vacuum, low content of low-melting metals and an extremely good surface quality. In order to meet these requirements, high-purity copper (OFHC, Grade 1, according to ASTM B 170-82 and extra specifications) is used as structural material. The prefabricated components of the accelerator cells (noses, jackets, flanges) are joined by electron beam welding, the weld seam being assessed on the basis of the same criteria as the base material. The welding procedures required depend, first, on the material and, secondly, on the geometries involved. Therefore experimental welds were made first on standardized specimens in order to study the behaviour of the material during electron beam welding and the influence of parameter variations. The welded joints of the cell design were planned on the basis of these results. Seam configuration, welding procedures and the parameters were optimized on components of original geometry. The experiments have shown that high-quality joints of this grade of copper can be produced by the electron beam welding process, if careful planning and preparation of the seams and adequate containment of the welding pool are assured. (orig.)

Hydration of excess electrons trapped in charge pockets on molecular surfaces

Science.gov (United States)

Jalbout, Abraham F.; Del Castillo, R.; Adamowicz, Ludwik

2007-01-01

In this work we strive to design a novel electron trap located on a molecular surface. The process of electron trapping involves hydration of the trapped electron. Previous calculations on surface electron trapping revealed that clusters of OH groups can form stable hydrogen-bonded networks on one side of a hydrocarbon surface (i.e. cyclohexane sheets), while the hydrogen atoms on the opposite side of the surface form pockets of positive charge that can attract extra negative charge. The excess electron density on such surfaces can be further stabilized by interactions with water molecules. Our calculations show that these anionic systems are stable with respect to vertical electron detachment (VDE).

Electron stimulated desorption of gases at technological surfaces of aluminium

International Nuclear Information System (INIS)

Ding, M.Q.; Williams, E.M.

1989-01-01

The release of gas by electron bombardment at aluminium alloy surfaces in vacuum -9 torr has been investigated for a range of treatments including bakeout and glow discharge cleaning. Particular attention has been given to the role of continuous electron bombardment, with current densities and electron energies of up to 1.5 mA cm -2 and 2.0 keV, respectively, over the 10 cm 2 of surface area under irradiation. The observations of desorption efficiency, defined as the number of desorbed molecules per incident electron, conform to a model involving a dynamic balance between adsorption and desorption, with contributions to adsorption from both surface and sub-surface gas. Continuous electron bombardment promotes a surface with low desorption efficiency, -5 mol/electron, however, the conditioning cycle is accelerated significantly by glow discharge treatment. There is evidence of some short-term memory when the samples are exposed to air. (author)

Surface tailoring of newly developed amorphous Znsbnd Sisbnd O thin films as electron injection/transport layer by plasma treatment: Application to inverted OLEDs and hybrid solar cells

Science.gov (United States)

Yang, Hongsheng; Kim, Junghwan; Yamamoto, Koji; Xing, Xing; Hosono, Hideo

2018-03-01

We report a unique amorphous oxide semiconductor Znsbnd Sisbnd O (a-ZSO) which has a small work function of 3.4 eV for as-deposited films. The surface modification of a-ZSO thin films by plasma treatments is examined to apply it to the electron injection/transport layer of organic devices. It turns out that the energy alignment and exciton dissociation efficiency at a-ZSO/organic semiconductor interface significantly changes by choosing different gas (oxygen or argon) for plasma treatments (after a-ZSO was exposed to atmospheric environment for 5 days). In situ ultraviolet photoelectron spectroscopy (UPS) measurement reveals that the work function of a-ZSO is increased to 4.0 eV after an O2-plasma treatment, while the work function of 3.5 eV is recovered after an Ar-plasma treatment which indicates this treatment is effective for surface cleaning. To study the effects of surface treatments to device performance, OLEDs and hybrid polymer solar cells with O2-plasma or Ar-plasma treated a-ZSO are compared. Effects of these surface treatments on performance of inverted OLEDs and hybrid polymer solar cells are examined. Ar-plasma treated a-ZSO works well as the electron injection layer in inverted OLEDs (Alq3/a-ZSO) because the injection barrier is small (∼ 0.1 eV). On the other hands, O2-plasma treated a-ZSO is more suitable for application to hybrid solar cells which is benefiting from higher exciton dissociation efficiency at polymer (P3HT)/ZSO interface.

Porous titania surfaces on titanium with hierarchical macro- and mesoporosities for enhancing cell adhesion, proliferation and mineralization

International Nuclear Information System (INIS)

Han, Guang; Müller, Werner E.G.; Wang, Xiaohong; Lilja, Louise; Shen, Zhijian

2015-01-01

Titanium received a macroporous titania surface layer by anodization, which contains open pores with average pore diameter around 5 μm. An additional mesoporous titania top layer following the contour of the macropores, of 100–200 nm thickness and with a pore diameter of 10 nm, was formed by using the evaporation-induced self-assembly (EISA) method with titanium (IV) tetraethoxide as the precursor. A coherent laminar titania surface layer was thus obtained, creating a hierarchical macro- and mesoporous surface that was characterized by high-resolution electron microscopy. The interfacial bonding between the surface layers and the titanium matrix was characterized by the scratch test that confirmed a stable and strong bonding of titania surface layers on titanium. The wettability to water and the effects on the osteosarcoma cell line (SaOS-2) proliferation and mineralization of the formed titania surface layers were studied systematically by cell culture and scanning electron microscopy. The results proved that the porous titania surface with hierarchical macro- and mesoporosities was hydrophilic that significantly promoted cell attachment and spreading. A synergistic role of the hierarchical macro- and mesoporosities was revealed in terms of enhancing cell adhesion, proliferation and mineralization, compared with the titania surface with solo scale topography. - Highlights: • We developed a hierarchical macro- and mesoporous surface layer on titanium. • New surface layer was strong enough to sustain on implant surface. • New surface owned better surface wettability. • New surface can promote SaOS-2 cell adhesion, proliferation and mineralization. • Synergistic effects on cell responses occur when two porous structures coexist

Porous titania surfaces on titanium with hierarchical macro- and mesoporosities for enhancing cell adhesion, proliferation and mineralization

Energy Technology Data Exchange (ETDEWEB)

Han, Guang [Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, 10691 Stockholm (Sweden); Müller, Werner E.G.; Wang, Xiaohong [ERC Advanced Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz, Duesbergweg 6, D-55128 Mainz (Germany); Lilja, Louise [Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, 10691 Stockholm (Sweden); Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping (Sweden); Shen, Zhijian, E-mail: shen@mmk.su.se [Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University, 10691 Stockholm (Sweden)

2015-02-01

Titanium received a macroporous titania surface layer by anodization, which contains open pores with average pore diameter around 5 μm. An additional mesoporous titania top layer following the contour of the macropores, of 100–200 nm thickness and with a pore diameter of 10 nm, was formed by using the evaporation-induced self-assembly (EISA) method with titanium (IV) tetraethoxide as the precursor. A coherent laminar titania surface layer was thus obtained, creating a hierarchical macro- and mesoporous surface that was characterized by high-resolution electron microscopy. The interfacial bonding between the surface layers and the titanium matrix was characterized by the scratch test that confirmed a stable and strong bonding of titania surface layers on titanium. The wettability to water and the effects on the osteosarcoma cell line (SaOS-2) proliferation and mineralization of the formed titania surface layers were studied systematically by cell culture and scanning electron microscopy. The results proved that the porous titania surface with hierarchical macro- and mesoporosities was hydrophilic that significantly promoted cell attachment and spreading. A synergistic role of the hierarchical macro- and mesoporosities was revealed in terms of enhancing cell adhesion, proliferation and mineralization, compared with the titania surface with solo scale topography. - Highlights: • We developed a hierarchical macro- and mesoporous surface layer on titanium. • New surface layer was strong enough to sustain on implant surface. • New surface owned better surface wettability. • New surface can promote SaOS-2 cell adhesion, proliferation and mineralization. • Synergistic effects on cell responses occur when two porous structures coexist.

Generation of attosecond electron packets via conical surface plasmon electron acceleration

Science.gov (United States)

Greig, S. R.; Elezzabi, A. Y.

2016-01-01

We present a method for the generation of high kinetic energy attosecond electron packets via magnetostatic and aperture filtering of conical surface plasmon (SP) accelerated electrons. The conical SP waves are excited by coupling an ultrafast radially polarized laser beam to a conical silica lens coated with an Ag film. Electromagnetic and particle tracking models are employed to characterize the ultrafast electron packets. PMID:26764129

Osteogenesis of bone marrow mesenchymal stem cells on strontium-substituted nano-hydroxyapatite coated roughened titanium surfaces

OpenAIRE

Yang, Hua-Wei; Lin, Mao-Han; Xu, Yuan-Zhi; Shang, Guang-Wei; Wang, Rao-Rao; Chen, Kai

2015-01-01

Objective: To investigate osteogenesis of bone marrow mesenchymal stem cells (BMSCs) on strontium-substituted nano-hydroxyapatite (Sr-HA) coated roughened titanium surfaces. Methods: Sr-HA coating and HA coating were fabricated on roughened titanium surfaces by electrochemical deposition technique and characterized by field emission scanning electron microscope (FESM). BMSCs were cultured on Sr-HA coating, HA coating and roughened titanium surfaces respectively. Cell proliferation, alkaline p...

Diffraction-unlimited optical imaging of unstained living cells in liquid by electron beam scanning of luminescent environmental cells.

Science.gov (United States)

Miyazaki, Hideki T; Kasaya, Takeshi; Takemura, Taro; Hanagata, Nobutaka; Yasuda, Takeshi; Miyazaki, Hiroshi

2013-11-18

An environmental cell with a 50-nm-thick cathodoluminescent window was attached to a scanning electron microscope, and diffraction-unlimited near-field optical imaging of unstained living human lung epithelial cells in liquid was demonstrated. Electrons with energies as low as 0.8 - 1.2 kV are sufficiently blocked by the window without damaging the specimens, and form a sub-wavelength-sized illumination light source. A super-resolved optical image of the specimen adhered to the opposite window surface was acquired by a photomultiplier tube placed below. The cells after the observation were proved to stay alive. The image was formed by enhanced dipole radiation or energy transfer, and features as small as 62 nm were resolved.

Atomic layer deposition in nanostructured photovoltaics: tuning optical, electronic and surface properties

Science.gov (United States)

Palmstrom, Axel F.; Santra, Pralay K.; Bent, Stacey F.

2015-07-01

Nanostructured materials offer key advantages for third-generation photovoltaics, such as the ability to achieve high optical absorption together with enhanced charge carrier collection using low cost components. However, the extensive interfacial areas in nanostructured photovoltaic devices can cause high recombination rates and a high density of surface electronic states. In this feature article, we provide a brief review of some nanostructured photovoltaic technologies including dye-sensitized, quantum dot sensitized and colloidal quantum dot solar cells. We then introduce the technique of atomic layer deposition (ALD), which is a vapor phase deposition method using a sequence of self-limiting surface reaction steps to grow thin, uniform and conformal films. We discuss how ALD has established itself as a promising tool for addressing different aspects of nanostructured photovoltaics. Examples include the use of ALD to synthesize absorber materials for both quantum dot and plasmonic solar cells, to grow barrier layers for dye and quantum dot sensitized solar cells, and to infiltrate coatings into colloidal quantum dot solar cell to improve charge carrier mobilities as well as stability. We also provide an example of monolayer surface modification in which adsorbed ligand molecules on quantum dots are used to tune the band structure of colloidal quantum dot solar cells for improved charge collection. Finally, we comment on the present challenges and future outlook of the use of ALD for nanostructured photovoltaics.

Cell adhesion and spreading on polymer surfaces micropatterned by ion beams

International Nuclear Information System (INIS)

Satriano, C.; Carnazza, S.; Licciardello, A.; Guglielmino, S.; Marletta, G.

2003-01-01

The cell adhesion and spreading behavior on surfaces of poly(ethyleneterephtalate) and poly(hydroxymethylsiloxane) micropatterned by focused 15 keV Ga + beams has been studied. It has been found that while no modification in the cell adhesion process could be observed for unirradiated and irradiated areas on the patterned surfaces, in the case of polyhydroxymethylsiloxane the cell adhesion process is basically confined within the irradiated areas and a clear dependence of the cell ordering on the lateral size of the irradiated areas is observed. The results are discussed in terms of the specific spatially resolved chemical modification induced by Ga + irradiation onto the two different polymers. Thus, the irradiation-induced modification of composition, functional groups concentration, surface free energy, and nanoscale morphology have been studied by means of x-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, contact angle, and atomic force microscopy. The cell adhesion and spreading behavior was found to nicely correlate with the increase of the acid-base component γ AB of the surface free energy and more particularly with the dramatic increase of the Lewis basic electron-donor term

Electron Stimulated Desorption of Condensed Gases on Cryogenic Surfaces

CERN Document Server

Tratnik, H; Hilleret, Noël

2005-01-01

In ultra-high vacuum systems outgassing from vacuum chamber walls and desorption from surface adsorbates are usually the factors which in°uence pressure and residual gas composition. In particular in beam vacuum systems of accelerators like the LHC, where surfaces are exposed to intense synchro- tron radiation and bombardment by energetic ions and electrons, properties like the molecular desorption yield or secondary electron yield can strongly in°uence the performance of the accelerator. In high-energy particle accelerators operating at liquid helium temperature, cold surfaces are exposed to the bombardment of energetic photons, electrons and ions. The gases released by the subsequent desorption are re-condensed on the cold surfaces and can be re-desorbed by the impinging electrons and ions. The equilibrium coverage reached on the surfaces exposed to the impact of energetic particles depends on the desorption yield of the condensed gases and can a®ect the operation of the accelerator by modifying th...

Electronic collective modes and instabilities on semiconductor surfaces. I

International Nuclear Information System (INIS)

Muramatsu, A.; Hanke, W.

1984-01-01

A Green's-function theory of electronic collective modes is presented which leads to a practical scheme for a microscopic determination of surface elementary excitations in conducting as well as nonconducting solids. Particular emphasis is placed on semiconductor surfaces where the jellium approximation is not valid, due to the importance of density fluctuations on a microscopic scale (reflected in the local-field effects). Starting from the Bethe-Salpeter equation for the two-particle Green's function of the surface system, an equation of motion for the electron-hole pair is obtained. Its solutions determine the energy spectra, lifetimes, and amplitudes of the surface elementary excitations, i.e., surface plasmons, excitons, polaritons, and magnons. Exchange and correlation effects are taken into account through the random-phase and time-dependent Hartree-Fock (screened electron-hole attraction) approximations. The formalism is applied to the study of electronic (charge- and spin-density) instabilities at covalent semiconductor surfaces. Quantitative calculations for an eight-layer Si(111) slab display an instability of the ideal paramagnetic surface with respect to spin-density waves with wavelength nearly corresponding to (2 x 1) and (7 x 7) superstructures

Cell-surface proteoglycan in sea urchin primary mesenchyme cell migration

International Nuclear Information System (INIS)

Lane, M.C.

1989-01-01

Early in the development of the sea urchin embryo, the primary mesenchyme cells (PMC) migrate along the basal lamina of the blastocoel. Migration is inhibited in L. pictus embryos cultured in sulfate-free seawater and in S. purpuratus embryos exposed to exogenous β-D-xylosides. An in vitro assay was developed to test the migratory capacity of normal PMC on normal and treated blastocoelic matrix. Sulfate deprivation and exposure to exogenous xyloside render PMC nonmotile on either matrix. Materials removed from the surface of normal PMC by treatment with 1 M urea restored migratory ability to defective cells, whereas a similar preparation isolated from the surface of epithelial cells at the same stage did not. Migration also resumed when cells were removed from the xyloside or returned to normal seawater. The urea extract was partially purified and characterized by radiolabeling, gel electrophoresis, fluorography, ion exchange chromatography, and western blotting. The PMC synthesize a large chondroitin sulfate/dermatan sulfate proteoglycan that is present in an active fraction isolated by chromatography. Chondroitinase ABC digestion of live cells blocked migration reversibly, further supporting the identification of the chondroitin sulfate/dermatan sulfate proteoglycan as the active component in the urea extract. Much of the incorporated sulfate was distributed along the filopodia in 35 SO 4 -labelled PMC by autoradiography. The morphology of normal and treated S. purpuratus PMC was examined by scanning electron microscopy, and differences in spreading, particularly of the extensive filopodia present on the cells, was observed. A model for the role of the chondroitin sulfate/dermatan sulfate proteoglycan in cell detachment during migration is proposed

Transmission electron microscope cells for use with liquid samples

Science.gov (United States)

Khalid, Waqas; Alivisatos, Paul A.; Zettl, Alexander K.

2016-08-09

This disclosure provides systems, methods, and devices related to transmission electron microscopy cells for use with liquids. In one aspect a device includes a substrate, a first graphene layer, and a second graphene layer. The substrate has a first surface and a second surface. The first surface defines a first channel, a second channel, and an outlet channel. The first channel and the second channel are joined to the outlet channel. The outlet channel defines a viewport region forming a though hole in the substrate. The first graphene layer overlays the first surface of the substrate, including an interior area of the first channel, the second channel, and the outlet channel. The second graphene layer overlays the first surface of the substrate, including open regions defined by the first channel, the second channel, and the outlet channel.

Lining cells on normal human vertebral bone surfaces

International Nuclear Information System (INIS)

Henning, C.B.; Lloyd, E.L.

1982-01-01

Thoracic vertebrae from two individuals with no bone disease were studied with the electron microscope to determine cell morphology in relation to bone mineral. The work was undertaken to determine if cell morphology or spatial relationships between the bone lining cells and bone mineral could account for the relative infrequency of bone tumors which arise at this site following radium intake, when compared with other sites, such as the head of the femur. Cells lining the vertebral mineral were found to be generally rounded in appearance with varied numbers of cytoplasmic granules, and they appeared to have a high density per unit of surface area. These features contrasted with the single layer of flattened cells characteristic of the bone lining cells of the femur. A tentative discussion of the reasons for the relative infrequency of tumors in the vertebrae following radium acquisition is presented

Extracellular Electron Uptake: Among Autotrophs and Mediated by Surfaces

DEFF Research Database (Denmark)

Tremblay, Pier-Luc; Angenent, Largus T.; Zhang, Tian

2017-01-01

Autotrophic microbes can acquire electrons from solid donors such as steel, other microbial cells, or electrodes. Based on this feature, bioprocesses are being developed for the microbial electrosynthesis (MES) of useful products from the greenhouse gas CO2. Extracellular electron-transfer mechan......Autotrophic microbes can acquire electrons from solid donors such as steel, other microbial cells, or electrodes. Based on this feature, bioprocesses are being developed for the microbial electrosynthesis (MES) of useful products from the greenhouse gas CO2. Extracellular electron......; or (iii) mediator-generating enzymes detached from cells. This review explores the interactions of autotrophs with solid electron donors and their importance in nature and for biosustainable technologies....

The effect of cell surface components on adhesion ability of Lactobacillus rhamnosus.

Science.gov (United States)

Polak-Berecka, Magdalena; Waśko, Adam; Paduch, Roman; Skrzypek, Tomasz; Sroka-Bartnicka, Anna

2014-10-01

The aim of this study was to analyze the cell envelope components and surface properties of two phenotypes of Lactobacillus rhamnosus isolated from the human gastrointestinal tract. The ability of the bacteria to adhere to human intestinal cells and to aggregate with other bacteria was determined. L. rhamnosus strains E/N and PEN differed with regard to the presence of exopolysaccharides (EPS) and specific surface proteins. Transmission electron microscopy showed differences in the structure of the outer cell surface of the strains tested. Bacterial surface properties were analyzed by Fourier transform infrared spectroscopy, fatty acid methyl esters and hydrophobicity assays. Aggregation capacity and adhesion of the tested strains to the human colon adenocarcinoma cell line HT29 was determined. The results indicated a high adhesion and aggregation ability of L. rhamnosus PEN, which possessed specific surface proteins, had a unique fatty acid content, and did not synthesize EPS. Adherence of L. rhamnosus was dependent on specific interactions and was promoted by surface proteins (42-114 kDa) and specific fatty acids. Polysaccharides likely hindered bacterial adhesion and aggregation by masking protein receptors. This study provides information on the cell envelope constituents of lactobacilli that influence bacterial aggregation and adhesion to intestinal cells. This knowledge will help to understand better their specific contribution in commensal-host interactions and adaptation to this ecological niche.

Surface and Interface Physics of Correlated Electron Materials

Energy Technology Data Exchange (ETDEWEB)

Millis, Andrew [Columbia Univ., New York, NY (United States)

2004-09-01

The {\\it Surface and Interface Physics of Correlated Electron Materials} research program provided conceptual understanding of and theoretical methodologies for understanding the properties of surfaces and interfaces involving materials exhibiting strong electronic correlations. The issues addressed in this research program are important for basic science, because the behavior of correlated electron superlattices is a crucial challenge to and crucial test of our understanding of the grand-challenge problem of correlated electron physics and are important for our nation's energy future because correlated interfaces offer opportunities for the control of phenomena needed for energy and device applications. Results include new physics insights, development of new methods, and new predictions for materials properties.

Method for surface treatment by electron beams

International Nuclear Information System (INIS)

Panzer, S.; Doehler, H.; Bartel, R.; Ardenne, T. von.

1985-01-01

The invention has been aimed at simplifying the technology and saving energy in modifying surfaces with the aid of electron beams. The described beam-object geometry allows to abandon additional heat treatments. It can be used for surface hardening

Suppression secondary electrons from target surface under pulsed ion beams bombardment

International Nuclear Information System (INIS)

Yang Zhen; Peng Yufei; Long Jidong; Lan Chaohui; Dong Pan; Shi Jinshui

2012-01-01

The producing mechanism of secondary electrons from target surface under ion beams bombardment is discussed. Several methods to suppress the secondary electrons in special vacuum devices and their advantages and disadvantages are introduced. The ways of using self-bias and curved surface target are proposed and verified in the experiment. The results show that the secondary electrons can be effectively suppressed when the self-bias is larger than 80 V. The secondary electron yield decreases by using curved surface target instead of flat target. The secondary electron yield calculated from the experimental data is about 0.67, which is slightly larger than the value (0.58) from the literature due to the impurities of the ion beam and target surface. The effect of suppressing the electron countercurrent by the self-bias method is analyzed. The result shows that the self-bias method can not only suppress the secondary electrons from target surface under ion beams bombardment, but also suppress the electron countercurrent resulting from the instability of the pulsed power source. (authors)

Layered insulator hexagonal boron nitride for surface passivation in quantum dot solar cell

International Nuclear Information System (INIS)

Shanmugam, Mariyappan; Jain, Nikhil; Jacobs-Gedrim, Robin; Yu, Bin; Xu, Yang

2013-01-01

Single crystalline, two dimensional (2D) layered insulator hexagonal boron nitride (h-BN), is demonstrated as an emerging material candidate for surface passivation on mesoporous TiO 2 . Cadmium selenide (CdSe) quantum dot based bulk heterojunction (BHJ) solar cell employed h-BN passivated TiO 2 as an electron acceptor exhibits photoconversion efficiency ∼46% more than BHJ employed unpassivated TiO 2 . Dominant interfacial recombination pathways such as electron capture by TiO 2 surface states and recombination with hole at valence band of CdSe are efficiently controlled by h-BN enabled surface passivation, leading to improved photovoltaic performance. Highly crystalline, confirmed by transmission electron microscopy, dangling bond-free 2D layered h-BN with self-terminated atomic planes, achieved by chemical exfoliation, enables efficient passivation on TiO 2 , allowing electronic transport at TiO 2 /h-BN/CdSe interface with much lower recombination rate compared to an unpassivated TiO 2 /CdSe interface

Surface roughness induced electron mobility degradation in InAs nanowires

International Nuclear Information System (INIS)

Wang Fengyun; Yip, Sen Po; Han, Ning; Fok, KitWa; Lin, Hao; Hou, Jared J; Dong, Guofa; Hung, Tak Fu; Chan, K S; Ho, Johnny C

2013-01-01

In this work, we present a study of the surface roughness dependent electron mobility in InAs nanowires grown by the nickel-catalyzed chemical vapor deposition method. These nanowires have good crystallinity, well-controlled surface morphology without any surface coating or tapering and an excellent peak field-effect mobility up to 15 000 cm 2 V −1 s −1 when configured into back-gated field-effect nanowire transistors. Detailed electrical characterizations reveal that the electron mobility degrades monotonically with increasing surface roughness and diameter scaling, while low-temperature measurements further decouple the effects of surface/interface traps and phonon scattering, highlighting the dominant impact of surface roughness scattering on the electron mobility for miniaturized and surface disordered nanowires. All these factors suggest that careful consideration of nanowire geometries and surface condition is required for designing devices with optimal performance. (paper)

Surface modification of the metal plates using continuous electron beam process (CEBP)

International Nuclear Information System (INIS)

Kim, Jisoo; Kim, Jin-Seok; Kang, Eun-Goo; Park, Hyung Wook

2014-01-01

Highlights: • We performed surface modification of SM20C, SUS303, and Al6061 using CEBP. • We analyzed surface properties and microstructure after electron-beam irradiation. • The surface quality was improved after electron-beam irradiation. • The surface hardness for SM20C was increased by ∼50% after CEBP irradiation. - Abstract: The finishing process is an important component of the quality-control procedure for final products in manufacturing applications. In this study, we evaluated the performance of continuous electron-beam process as the final process for finishing SM20C (steel alloy), SUS303 (stainless steel alloy), and Al6061 (aluminum alloy) surfaces both on the initially smooth and rough surfaces. Surface modification of the metals was carried out by varying the feed and frequency of the continuous electron-beam irradiation procedure. The resulting surface roughness was examined with respect to the initial surface roughness of the metals. SM20C and SUS303 experienced an improvement in surface roughness, particularly for initially rough surfaces. Continuous electron-beam process produced craters during the process and the effect of this phenomenon on the resulting surface roughness was relatively large with the initially smooth SM20C and SUS303 alloy surfaces. For Al6061, the continuous electron-beam process was effective at improving its surface roughness even with the initially smooth surface under the optimized conditions of process; this was attributed to its low melting point. Scanning electron microscopy was used to identify metallurgical variation within the thin melted and re-solidification layers of the tested alloys. Changes in the surface contact angle and hardness before and after electron-beam irradiation were also examined

Surface modification of the metal plates using continuous electron beam process (CEBP)

Energy Technology Data Exchange (ETDEWEB)

Kim, Jisoo, E-mail: kimjisu16@unist.ac.kr [School of Mechanical and Advanced Materials Engineering, Ulsan National Institute of Science and Technology, UNIST-gil 50, Eonyang-eup, Ulju-gun, Ulsan Metropolitan City 689-798 (Korea, Republic of); Kim, Jin-Seok, E-mail: totoro22@kitech.re.kr [Korea Institute of Industrial Technology (KITECH), KITECH Cheonan Headquarters 35-3 Hongcheon-ri, Ipjang-myeon, Cheonan-si, Chungcheongnam-do 330-825 (Korea, Republic of); Kang, Eun-Goo, E-mail: egkang@kitech.re.kr [Korea Institute of Industrial Technology (KITECH), KITECH Cheonan Headquarters 35-3 Hongcheon-ri, Ipjang-myeon, Cheonan-si, Chungcheongnam-do 330-825 (Korea, Republic of); Park, Hyung Wook, E-mail: hwpark@unist.ac.kr [School of Mechanical and Advanced Materials Engineering, Ulsan National Institute of Science and Technology, UNIST-gil 50, Eonyang-eup, Ulju-gun, Ulsan Metropolitan City 689-798 (Korea, Republic of)

2014-08-30

Highlights: • We performed surface modification of SM20C, SUS303, and Al6061 using CEBP. • We analyzed surface properties and microstructure after electron-beam irradiation. • The surface quality was improved after electron-beam irradiation. • The surface hardness for SM20C was increased by ∼50% after CEBP irradiation. - Abstract: The finishing process is an important component of the quality-control procedure for final products in manufacturing applications. In this study, we evaluated the performance of continuous electron-beam process as the final process for finishing SM20C (steel alloy), SUS303 (stainless steel alloy), and Al6061 (aluminum alloy) surfaces both on the initially smooth and rough surfaces. Surface modification of the metals was carried out by varying the feed and frequency of the continuous electron-beam irradiation procedure. The resulting surface roughness was examined with respect to the initial surface roughness of the metals. SM20C and SUS303 experienced an improvement in surface roughness, particularly for initially rough surfaces. Continuous electron-beam process produced craters during the process and the effect of this phenomenon on the resulting surface roughness was relatively large with the initially smooth SM20C and SUS303 alloy surfaces. For Al6061, the continuous electron-beam process was effective at improving its surface roughness even with the initially smooth surface under the optimized conditions of process; this was attributed to its low melting point. Scanning electron microscopy was used to identify metallurgical variation within the thin melted and re-solidification layers of the tested alloys. Changes in the surface contact angle and hardness before and after electron-beam irradiation were also examined.

Nonplasmonic Hot-Electron Photocurrents from Mn-Doped Quantum Dots in Photoelectrochemical Cells.

Science.gov (United States)

Dong, Yitong; Rossi, Daniel; Parobek, David; Son, Dong Hee

2016-03-03

We report the measurement of the hot-electron current in a photoelectrochemical cell constructed from a glass/ITO/Al2 O3 (ITO=indium tin oxide) electrode coated with Mn-doped quantum dots, where hot electrons with a large excess kinetic energy were produced through upconversion of the excitons into hot electron hole pairs under photoexcitation at 3 eV. In our recent study (J. Am. Chem. Soc. 2015, 137, 5549), we demonstrated the generation of hot electrons in Mn-doped II-VI semiconductor quantum dots and their usefulness in photocatalytic H2 production reaction, taking advantage of the more efficient charge transfer of hot electrons compared with band-edge electrons. Here, we show that hot electrons produced in Mn-doped CdS/ZnS quantum dots possess sufficient kinetic energy to overcome the energy barrier from a 5.4-7.5 nm thick Al2 O3 layer producing a hot-electron current in photoelectrochemical cell. This work demonstrates the possibility of harvesting hot electrons not only at the interface of the doped quantum dot surface, but also far away from it, thus taking advantage of the capability of hot electrons for long-range electron transfer across a thick energy barrier. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Surface flashover performance of epoxy resin microcomposites improved by electron beam irradiation

Energy Technology Data Exchange (ETDEWEB)

Huang, Yin; Min, Daomin [State Key Laboratory of Electrical Insulation and Power Equipment, Xi' an Jiaotong University, Xi' an 710049 (China); Li, Shengtao, E-mail: stli@mail.xjtu.edu.cn [State Key Laboratory of Electrical Insulation and Power Equipment, Xi' an Jiaotong University, Xi' an 710049 (China); Li, Zhen; Xie, Dongri [State Key Laboratory of Electrical Insulation and Power Equipment, Xi' an Jiaotong University, Xi' an 710049 (China); Wang, Xuan [Key Laboratory of Engineering Dielectric and its Application, Ministry of Education, Harbin University of Science and Technology, Harbin 150040 (China); Lin, Shengjun [State Key Laboratory of Electrical Insulation and Power Equipment, Xi' an Jiaotong University, Xi' an 710049 (China); Pinggao Group Company Ltd., State Grid High Voltage Switchgear Insulation Materials Laboratory, Pingdingshan 467001 (China)

2017-06-01

Highlights: • Epoxy resin microcomposites were irradiated by electron beam with energies of 10 and 20 keV. • Surface flashover voltage increase with the increase of electron beam energy. • Both the untreated and irradiated samples have two trap centers, which are labeled as shallow and deep traps. • Deposition energy in epoxy resin microcomposites increases with electron beam energy, and surface trap properties are determined by deposition energy. • The influence of surface conductivity and trap distribution on flashover voltage is discussed. - Abstract: The influencing mechanism of electron beam irradiation on surface flashover of epoxy resin/Al{sub 2}O{sub 3} microcomposite was investigated. Epoxy resin/Al{sub 2}O{sub 3} microcomposite samples with a diameter of 50 mm and a thickness of 1 mm were prepared. The samples were irradiated by electron beam with energies of 10 and 20 keV and a beam current of 5 μA for 5 min. Surface potential decay, surface conduction, and surface flashover properties of untreated and irradiated samples were measured. Both the decay rate of surface potential and surface conductivity decrease with an increase in the energy of electron beam. Meanwhile, surface flashover voltage increase. It was found that both the untreated and irradiated samples have two trap centers, which are labeled as shallow and deep traps. The increase in the energy and density of deep surface traps enhance the ability to capture primary emitted electrons. In addition, the decrease in surface conductivity blocks electron emission at the cathode triple junction. Therefore, electron avalanche at the interface between gas and an insulating material would be suppressed, eventually improving surface flashover voltage of epoxy resin microcomposites.

The effect of hot electrons and surface plasmons on heterogeneous catalysis

International Nuclear Information System (INIS)

Kim, Sun Mi; Lee, Si Woo; Moon, Song Yi; Park, Jeong Young

2016-01-01

Hot electrons and surface-plasmon-driven chemistry are amongst the most actively studied research subjects because they are deeply associated with energy dissipation and the conversion processes at the surface and interfaces, which are still open questions and key issues in the surface science community. In this topical review, we give an overview of the concept of hot electrons or surface-plasmon-mediated hot electrons generated under various structural schemes (i.e. metals, metal–semiconductor, and metal–insulator–metal) and their role affecting catalytic activity in chemical reactions. We highlight recent studies on the relation between hot electrons and catalytic activity on metallic surfaces. We discuss possible mechanisms for how hot electrons participate in chemical reactions. We also introduce controlled chemistry to describe specific pathways for selectivity control in catalysis on metal nanoparticles. (topical review)

Electronic properties of adsorbates and clean surfaces of metals and semiconductors

International Nuclear Information System (INIS)

Lecante, J.

1980-01-01

This paper surveys recent progress in experimental studies on electronic properties of adsorbates and clean metal surfaces. Electron spectroscopy and particularly angle resolved photoelectron spectroscopy appears to be a very powerful tool to get informations on electronic levels of adsorbates or clean surfaces. Moreover this technique may also give informations about the atomic geometry of the surface. Experimental investigation about surface plasmons, surface states, core level shifts are presented for clean surfaces. As examples of adsorbate covered surfaces two typical cases are chosen: two dimensional band structure and oriented molecules. Finally the photoelectron diffraction may be used for surface structure determination either in the case of an adsorbate or a clean metal surface [fr

Cardiomyocyte differentiation of embryonic stem cells on the surface of organic semiconductors.

Science.gov (United States)

Caserta, Sergio; Barra, Mario; Manganelli, Genesia; Tomaiuolo, Giovanna; Filosa, Stefania; Cassinese, Antonio; Guido, Stefano

2013-06-25

Electrically active supports provide new horizons for bio-sensing and artificial organ design. Cell-based electrochemical biosensors can be used as bio-microactuators, applied to the biorobotics. Microchip-based bioassay systems can provide real-time cell analysis for preclinical drug design or for intelligent drug delivery devices. In regenerative medicine, electrically active supports can be used as bio-reactors to monitor cell activity, optimize the stem cell differentiation and control cell and tissue morphology. Biocompatibility and direct interaction of the electrically active surface with the cell surface is a critical aspect of this technology.
 In this work embryonic stem cells (AK7 ES) have been cultivated on the surface of thin films achieved through the evaporation of two aromatic compounds (T6 and PDI-8CN2 ) of particular interest for the fabrication of organic field-effect transistors (OFET). One of the potential advantages offered by the application of OFETs as bio-electronic supports is that they represent a powerful tool for the detection of bio-signals because their electrically active surface is an organic film.
 The cell morphology on T6 and PDI-8CN2 surface shows to be similar to the usual cell appearance, as obtained when standard culture support (petri dish) are employed. Moreover, our experimental results demonstrate that stem cells can be lead to differentiation up to "beating" cardiomyocytes even on these electrically-active organic films.
 This investigation encourages the perspective to develop OFET-based biosensors in order to accurately characterize stem cells during the cardiac differentiation process and eventually increase their differentiation efficiency.

Electron emission during multicharged ion-surface interactions

International Nuclear Information System (INIS)

Zeijlmans van Emmichoven, P.A.; Havener, C.C.; Meyer, F.W.; Zehner, D.M.

1990-01-01

Recent measurements of electron spectra for slow multicharged N ion-surface collisions are presented. The emphasis is on potential emission, i.e. the electron emission related to the neutralization of the ions. When using N ions that carry a K shell vacancy into the collision, characteristic K Auger electron emission from the projectiles is observed, as well as, for specific surfaces, target atom Auger transitions (resulting from vacancy transfer). Measurements of the intensity of these Auger transitions as a function of the time the ions spend above the surface can serve as a useful probe of the timescales characterizing the relevant neutralization processes. This technique is elucidated with the help of some computer simulations. It is shown that neutralization timescales required in the atomic ladder picture, in which neutralization takes place by resonant capture followed by purely intra-atomic Auger transitions, are too long to explain our experimental results. The introduction of additional neutralization/de-excitation mechanisms in the simulations leads to much better agreement with the experiments

Surface influence on convoy electron emission at low energies

International Nuclear Information System (INIS)

Sanchez, E.A.

1988-01-01

It is studied the dependence of the production of convoy electrons induced by H + - 60 KeV with surface conditions of Al targets by in situ deposition of Na and O. The conclusion is that convoy electron production increases with the work function of the surface. (A.C.A.S.) [pt

Tumor suppressor protein SMAR1 modulates the roughness of cell surface: combined AFM and SEM study

Directory of Open Access Journals (Sweden)

Mamgain Hitesh

2009-10-01

Full Text Available Abstract Background Imaging tools such as scanning electron microscope (SEM and atomic force microscope (AFM can be used to produce high-resolution topographic images of biomedical specimens and hence are well suited for imaging alterations in cell morphology. We have studied the correlation of SMAR1 expression with cell surface smoothness in cell lines as well as in different grades of human breast cancer and mouse tumor sections. Methods We validated knockdown and overexpression of SMAR1 using RT-PCR as well as Western blotting in human embryonic kidney (HEK 293, human breast cancer (MCF-7 and mouse melanoma (B16F1 cell lines. The samples were then processed for cell surface roughness studies using atomic force microscopy (AFM and scanning electron microscopy (SEM. The same samples were used for microarray analysis as well. Tumors sections from control and SMAR1 treated mice as well as tissues sections from different grades of human breast cancer on poly L-lysine coated slides were used for AFM and SEM studies. Results Tumor sections from mice injected with melanoma cells showed pronounced surface roughness. In contrast, tumor sections obtained from nude mice that were first injected with melanoma cells followed by repeated injections of SMAR1-P44 peptide, exhibited relatively smoother surface profile. Interestingly, human breast cancer tissue sections that showed reduced SMAR1 expression exhibited increased surface roughness compared to the adjacent normal breast tissue. Our AFM data establishes that treatment of cells with SMAR1-P44 results into increase in cytoskeletal volume that is supported by comparative gene expression data showing an increase in the expression of specific cytoskeletal proteins compared to the control cells. Altogether, these findings indicate that tumor suppressor function of SMAR1 might be exhibited through smoothening of cell surface by regulating expression of cell surface proteins. Conclusion Tumor suppressor

Improving polymer/nanocrystal hybrid solar cell performance via tuning ligand orientation at CdSe quantum dot surface.

Science.gov (United States)

Fu, Weifei; Wang, Ling; Zhang, Yanfang; Ma, Ruisong; Zuo, Lijian; Mai, Jiangquan; Lau, Tsz-Ki; Du, Shixuan; Lu, Xinhui; Shi, Minmin; Li, Hanying; Chen, Hongzheng

2014-11-12

Achieving superior solar cell performance based on the colloidal nanocrystals remains challenging due to their complex surface composition. Much attention has been devoted to the development of effective surface modification strategies to enhance electronic coupling between the nanocrystals to promote charge carrier transport. Herein, we aim to attach benzenedithiol ligands onto the surface of CdSe nanocrystals in the "face-on" geometry to minimize the nanocrystal-nanocrystal or polymer-nanocrystal distance. Furthermore, the "electroactive" π-orbitals of the benzenedithiol are expected to further enhance the electronic coupling, which facilitates charge carrier dissociation and transport. The electron mobility of CdSe QD films was improved 20 times by tuning the ligand orientation, and high performance poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT):CdSe nanocrystal hybrid solar cells were also achieved, showing a highest power conversion efficiency of 4.18%. This research could open up a new pathway to improve further the performance of colloidal nanocrystal based solar cells.

Visualizing Surface Plasmons with Photons, Photoelectrons, and Electrons

Energy Technology Data Exchange (ETDEWEB)

El-Khoury, Patrick Z.; Abellan Baeza, Patricia; Gong, Yu; Hage, F. S.; Cottom, J.; Joly, Alan G.; Brydson, R.; Ramasse, Q. M.; Hess, Wayne P.

2016-06-21

Both photons and electrons may be used to excite surface plasmon polaritons, the collective charge density fluctuations at the surface of metal nanostructures. By virtue of their nanoscopic and dissipative nature, a detailed characterization of surface plasmon (SP) eigenmodes in real space-time ultimately requires joint sub-nanometer spatial and sub-femtosecond temporal resolution. The latter realization has driven significant developments in the past few years, aimed at interrogating both localized and propagating SP modes over the relevant length and time scales. In this mini-review, we briefly highlight different techniques we employ to visualize the enhanced electric fields associated with SPs. Specifically, we discuss recent hyperspectral optical microscopy, tip-enhanced Raman nano-spectroscopy, nonlinear photoemission electron microscopy, as well as correlated scanning transmission electron microscopy-electron energy loss spectroscopy measurements targeting prototypical plasmonic nanostructures and constructs. Through selected practical examples, we examine the information content in multidimensional images recorded by taking advantage of each of the aforementioned techniques. In effect, we illustrate how SPs can be visualized at the ultimate limits of space and time.

Tumor cell surface proteins

International Nuclear Information System (INIS)

Kennel, S.J.; Braslawsky, G.R.; Flynn, K.; Foote, L.J.; Friedman, E.; Hotchkiss, J.A.; Huang, A.H.L.; Lankford, P.K.

1982-01-01

Cell surface proteins mediate interaction between cells and their environment. Unique tumor cell surface proteins are being identified and quantified in several tumor systems to address the following questions: (i) how do tumor-specific proteins arise during cell transformation; (ii) can these proteins be used as markers of tumor cell distribution in vivo; (iii) can cytotoxic drugs be targeted specifically to tumor cells using antibody; and (iv) can solid state radioimmunoassay of these proteins provide a means to quantify transformation frequencies. A tumor surface protein of 180,000 M/sub r/ (TSP-180) has been identified on cells of several lung carcinomas of BALB/c mice. TSP-180 was not detected on normal lung tissue, embryonic tissue, or other epithelial or sarcoma tumors, but it was found on lung carcinomas of other strains of mice. Considerable amino acid sequence homology exists among TSP-180's from several cell sources, indicating that TSP-180 synthesis is directed by normal cellular genes although it is not expressed in normal cells. The regulation of synthesis of TSP-180 and its relationship to normal cell surface proteins are being studied. Monoclonal antibodies (MoAb) to TSP-180 have been developed. The antibodies have been used in immunoaffinity chromatography to isolate TSP-180 from tumor cell sources. This purified tumor antigen was used to immunize rats. Antibody produced by these animals reacted at different sites (epitopes) on the TSP-180 molecule than did the original MoAb. These sera and MoAb from these animals are being used to identify normal cell components related to the TSP-180 molecule

Neutralizing trapped electrons on the hydrogenated surface of a diamond amplifier

Directory of Open Access Journals (Sweden)

Xiangyun Chang

2012-01-01

Full Text Available We discuss our investigation of electron trapping in a diamond amplifier (DA. Our previous work demonstrated that some electrons reaching the DA’s hydrogenated surface are not emitted. The state and the removal of these electrons is important for DA applications. We found that these stopped electrons are trapped, and cannot be removed by a strong reversed-polarity electric field; to neutralize this surface charge, holes must be sent to the hydrogenated surface to recombine with the trapped electrons through the Shockley-Read-Hall surface-recombination mechanism. We measured the time taken for such recombination on the hydrogenated surface, viz. the recombination time, as less than 5 ns, limited by the resolution of our test system. With this measurement, we demonstrated that DA could be operated in an rf cavity with frequency of a few hundred megahertz.

Contact lens surface by electron beam

International Nuclear Information System (INIS)

Shin, Jung Hyuck; Lee, Suk Ju; Hwang, Kwang Ha; Jeon Jin

2011-01-01

Contact lens materials needs good biocompatibility, high refractive index, high optical transparency, high water content etc. Surface treat method by using plasma and radiation can modify the physical and/or chemical properties of the contact lens surface. Radiation technology such as electron beam irradiation can apply to polymerization reaction and enhance the functionality of the polymer.The purpose of this study is to modify of contact lens surface by using Eb irradiation technology. Electron beam was irradiated to the contact lens surface which was synthesized thermal polymerization method and commercial contact lens to modify physical and chemical properties. Ft-IR, XP, UV-vis spectrophotometer, water content, oxygen trans-metastability were used to characterize the surface state, physicochemical, and optical property of the contact lens treated with Eb. The water content and oxygen transmissibility of the contact lens treated with Eb were increased due to increase in the hydrophilic group such as O-C=O and OH group on the contact lens surface which could be produced by possible reaction between carbon and oxygen during the Eb irradiation. All of the lenses showed the high optical transmittance above 90%. In this case of B/Es, TES, Ti contact lens, the optical transmittance decreased about 5% with increasing Eb dose in the wavelength of UV-B region. The contact lens modified by Eb irradiation could improve the physical properties of the contact lens such as water content and oxygen transmissibility

Warm electrons on the liquid 4He surface

International Nuclear Information System (INIS)

Saitoh, Motohiko

1977-01-01

Detailed theoretical analysis of non-Ohmic transport of electrons on the liquid 4 He surface is given. The correct form of the electron-ripplon scattering as well as the electron- 4 He gas scattering is taken into account. A characteristic electric field at which electron mobility deviates from the Ohmic value is estimated as a function of temperature and the holding field on the basis of the electron effective temperature approximation. (auth.)

Inelastic electron scattering from surfaces

International Nuclear Information System (INIS)

Tong, S.Y.; Mills, D.L.

1992-01-01

This report contains highlights of accomplishments of the past year, for the University of California, Irvine and the University of Wisconsin, Milwaukee collaboration on surface excitations, and their interactions with low energy electrons. In addition, we present a summary of future research to be carried out in the coming grant year

Treatment of surfaces with low-energy electrons

Czech Academy of Sciences Publication Activity Database

Frank, Luděk; Mikmeková, Eliška; Lejeune, M.

2017-01-01

Roč. 407, JUN 15 (2017), s. 105-108 ISSN 0169-4332 R&D Projects: GA TA ČR(CZ) TE01020118; GA MŠk(CZ) LO1212; GA MŠk ED0017/01/01 Institutional support: RVO:68081731 Keywords : Low- energy electrons * Electron beam induced release * Graphene * Ultimate cleaning of surfaces Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering OBOR OECD: Nano-processes (applications on nano-scale) Impact factor: 3.387, year: 2016

Low-energy electron irradiation induced top-surface nanocrystallization of amorphous carbon film

Science.gov (United States)

Chen, Cheng; Fan, Xue; Diao, Dongfeng

2016-10-01

We report a low-energy electron irradiation method to nanocrystallize the top-surface of amorphous carbon film in electron cyclotron resonance plasma system. The nanostructure evolution of the carbon film as a function of electron irradiation density and time was examined by transmission electron microscope (TEM) and Raman spectroscopy. The results showed that the electron irradiation gave rise to the formation of sp2 nanocrystallites in the film top-surface within 4 nm thickness. The formation of sp2 nanocrystallite was ascribed to the inelastic electron scattering in the top-surface of carbon film. The frictional property of low-energy electron irradiated film was measured by a pin-on-disk tribometer. The sp2 nanocrystallized top-surface induced a lower friction coefficient than that of the original pure amorphous film. This method enables a convenient nanocrystallization of amorphous surface.

Cells behaviors and genotoxicity on topological surface

International Nuclear Information System (INIS)

Yang, N.; Yang, M.K.; Bi, S.X.; Chen, L.; Zhu, Z.Y.; Gao, Y.T.; Du, Z.

2013-01-01

To investigate different cells behaviors and genotoxicity, which were driven by specific microenvironments, three patterned surfaces (pillars, wide grooves and narrow grooves) and one smooth surface were prepared by template-based technique. Vinculin is a membrane-cytoskeletal protein in focal adhesion plaques and associates with cell–cell and cell–matrix junctions, which can promote cell adhesion and spreading. The immunofluorescence staining of vinculin revealed that the narrow grooves patterned substrate was favorable for L929 cell adhesion. For cell multiplication, the narrow grooves surface was fitted for the proliferation of L929, L02 and MSC cells, the pillars surface was only in favor of L929 cells to proliferate during 7 days of cell cultivation. Cell genetic toxicity was evaluated by cellular micronuclei test (MNT). The results indicated that topological surfaces were more suitable for L929 cells to proliferate and maintain the stability of genome. On the contrary, the narrow grooves surface induced higher micronuclei ratio of L02 and MSC cells than other surfaces. With the comprehensive results of cell multiplication and MNT, it was concluded that the wide grooves surface was best fitted for L02 cells to proliferate and have less DNA damages, and the smooth surface was optimum for the research of MSC cells in vitro. - Highlights: • Different cells behaviors on microstructure surfaces were discussed in this paper. • The expression of cell protein of Vinculin was studied in this research. • Cellular micronuclei test was applied to evaluate cells' genotoxicity. • Cell genotoxicity was first studied in the research field of topological surfaces

Superior MR images with electronically tuned and decoupled surface coils

International Nuclear Information System (INIS)

Ingwersen, H.; Freisen, L.; Friedrich, A.; Kess, H.; Krause, N.; Meissner, R.; Popp, W.

1987-01-01

In order to gain free positioning of surface coils in linearly polarized transmitting coils, it is absolutely necessary to electronically decouple both coils. For circularly polarized transmitting coils, decoupling is necessary in any case. In addition to the decoupling circuit automatic electronic tuning of the surface coils is used to gain the bast ratio of signal to noise. This combination of electronically decoupling and tuning of the surface coils yields intrinsic patient safety concerning local power deposition as well as free positioning and easy handling at the same time. Block diagrams, circuit schemes, and MR images obtained with several different surface coils are shown

Surface nanotopography of an anodized Ti–6Al–7Nb alloy enhances cell growth

Energy Technology Data Exchange (ETDEWEB)

Huang, Her-Hsiung [Department of Dentistry, National Yang-Ming University, Taipei 112, Taiwan (China); Graduate Institute of Basic Medical Science, China Medical University, Taichung 404, Taiwan (China); Department of Biomedical Informatics, Asia University, Taichung 413, Taiwan (China); Department of Stomatology, Taipei Veterans General Hospital, Taipei 112, Taiwan (China); Wu, Chia-Ping [Institute of Oral Biology, National Yang-Ming University, Taipei 112, Taiwan (China); Sun, Ying-Sui [Department of Dentistry, National Yang-Ming University, Taipei 112, Taiwan (China); Yang, Wei-En [Institute of Oral Biology, National Yang-Ming University, Taipei 112, Taiwan (China); Lee, Tzu-Hsin, E-mail: biomaterials@hotmail.com [School of Dentistry, Chung Shan Medical University, Taichung 402, Taiwan (China); Oral Medicine Center, Chung Shan Medical University Hospital, Taichung 402, Taiwan (China)

2014-12-05

Highlights: • An electrochemical anodization was applied to α/β-type Ti–6Al–7Nb alloy surface. • Anodized surface had a nontoxic nanoporous topography. • Anodized surface increased proteins adsorption due to nanotopography. • Anodized surface enhanced cell growth due to nanotopography. • Electrochemical anodization has potential as implant surface treatment. - Abstract: The α/β-type Ti–6Al–7Nb alloy is a potential replacement for α/β-type Ti–6Al–4V alloy, which is widely used in biomedical implant applications. The biological response to implant material is dependent on the surface characteristics of the material. In the present study, a simple and fast process was developed to perform an electrochemical anodization treatment on Ti–6Al–7Nb alloy. The proposed process yielded a thin surface nanotopography, which enhanced cell growth on the Ti–6Al–7Nb alloy. The surface characteristics, including the morphology, wettability, and protein adsorption, were investigated, and the cytotoxicity was evaluated according to International Organization for Standardization 10993-5 specifications. Cell adhesion of human bone marrow mesenchymal stem cells on the test specimens was observed via fluorescence microscopy and scanning electron microscopy. The anodization process produced a surface nanotopography (pore size <100 nm) on anodized Ti–6Al–7Nb alloy, which enhanced the wettability, protein adsorption, cell adhesion, cell migration, and cell mineralization. The results showed that the surface nanotopography produced using the proposed electrochemical anodization process enhanced cell growth on anodized Ti–6Al–7Nb alloy for implant applications.

Surface nanotopography of an anodized Ti–6Al–7Nb alloy enhances cell growth

International Nuclear Information System (INIS)

Huang, Her-Hsiung; Wu, Chia-Ping; Sun, Ying-Sui; Yang, Wei-En; Lee, Tzu-Hsin

2014-01-01

Highlights: • An electrochemical anodization was applied to α/β-type Ti–6Al–7Nb alloy surface. • Anodized surface had a nontoxic nanoporous topography. • Anodized surface increased proteins adsorption due to nanotopography. • Anodized surface enhanced cell growth due to nanotopography. • Electrochemical anodization has potential as implant surface treatment. - Abstract: The α/β-type Ti–6Al–7Nb alloy is a potential replacement for α/β-type Ti–6Al–4V alloy, which is widely used in biomedical implant applications. The biological response to implant material is dependent on the surface characteristics of the material. In the present study, a simple and fast process was developed to perform an electrochemical anodization treatment on Ti–6Al–7Nb alloy. The proposed process yielded a thin surface nanotopography, which enhanced cell growth on the Ti–6Al–7Nb alloy. The surface characteristics, including the morphology, wettability, and protein adsorption, were investigated, and the cytotoxicity was evaluated according to International Organization for Standardization 10993-5 specifications. Cell adhesion of human bone marrow mesenchymal stem cells on the test specimens was observed via fluorescence microscopy and scanning electron microscopy. The anodization process produced a surface nanotopography (pore size <100 nm) on anodized Ti–6Al–7Nb alloy, which enhanced the wettability, protein adsorption, cell adhesion, cell migration, and cell mineralization. The results showed that the surface nanotopography produced using the proposed electrochemical anodization process enhanced cell growth on anodized Ti–6Al–7Nb alloy for implant applications

Unoccupied surface electronic structure of Gd(0001)

International Nuclear Information System (INIS)

Li, D.; Dowben, P.A.; Ortega, J.E.; Himpsel, F.J.

1994-01-01

The unoccupied surface electronic structure of Gd(0001) was investigated with high-resolution inverse-photoemission spectroscopy. An empty surface state near E F is observed at bar Γ. Two other surface-sensitive features are also revealed at 1.2 and 3.1 eV above the Fermi level. Hydrogen adsorption on Gd surfaces was used to distinguish the surface-sensitive features from the bulk features. The unoccupied bulk-band critical points are determined to be Γ 3 + at 1.9 eV and A 1 at 0.8 eV

Tantalum surface oxidation: Bond relaxation, energy entrapment, and electron polarization

Energy Technology Data Exchange (ETDEWEB)

Guo, Yongling [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Bo, Maolin [Yangtze Normal University, College of Mechanical and Electrical Engineering, Chongqing 408100 (China); Wang, Yan [School of Information and Electronic Engineering, Hunan University of Science and Technology, Hunan 411201 (China); Liu, Yonghui [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Sun, Chang Q. [NOVITAS, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Huang, Yongli, E-mail: huangyongli@xtu.edu.cn [Key Laboratory of Low-Dimensional Materials and Application Technologies (Ministry of Education), Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China)

2017-02-28

Graphical abstract: The bond, electron and energy relaxation result in core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Highlights: • Increasing the oxygen coverage lowers the adsorption energy associated with lattice reconstruction. • Electrons transfer from Ta surface atoms to sp-hydrated oxygen, creating dipole moment that decreases the work function. • Oxygen chemisorption modified valence density-of-state (DOS) for Ta with four excessive DOS features: O−Ta bonding, O{sup 2−} lone pairs, Ta+ electron holes, and the lone-pair polarized Ta dipoles. • The bond, electron and energy relaxation between surface undercoordinated atoms are responsible for core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Abstract: A combination of photoelectron spectrometric analysis and density functional theory calculations has enabled reconciliation of the bond-energy-electron relaxation for the Ta(100, 110, 111) surfaces chemisorbed with oxygen at different coverages. Results show that increasing oxygen coverage lowers the adsorption energy associated with lattice reconstruction. Valence electrons transfer from Ta surface atoms to oxygen to create four excessive DOS features in terms of O−Ta bonding, lone pairs of oxygen, Ta{sup +} electron holes, and polarized Ta dipoles. Oxidation proceeds in the following dynamics: oxygen gets electrons from two neighboring Ta atoms left behind Ta{sup +}; the sp{sup 3}-orbital hybridization takes place with additional two electron lone pairs, the lone pairs polarize the other two Ta neighbors becoming dipoles. X-ray photoelectron spectral analysis results in the 4f binding energy of an isolated Ta atom and its shift upon bond formation and oxidation. Exercises provide not only a promising numerical approach for the quantitative information about the bond and electronic behavior but also consistent

Tantalum surface oxidation: Bond relaxation, energy entrapment, and electron polarization

International Nuclear Information System (INIS)

Guo, Yongling; Bo, Maolin; Wang, Yan; Liu, Yonghui; Sun, Chang Q.; Huang, Yongli

2017-01-01

Graphical abstract: The bond, electron and energy relaxation result in core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Highlights: • Increasing the oxygen coverage lowers the adsorption energy associated with lattice reconstruction. • Electrons transfer from Ta surface atoms to sp-hydrated oxygen, creating dipole moment that decreases the work function. • Oxygen chemisorption modified valence density-of-state (DOS) for Ta with four excessive DOS features: O−Ta bonding, O"2"− lone pairs, Ta+ electron holes, and the lone-pair polarized Ta dipoles. • The bond, electron and energy relaxation between surface undercoordinated atoms are responsible for core level energy shift, local densification, quantum entrapment and electron polarization of bonding electrons. - Abstract: A combination of photoelectron spectrometric analysis and density functional theory calculations has enabled reconciliation of the bond-energy-electron relaxation for the Ta(100, 110, 111) surfaces chemisorbed with oxygen at different coverages. Results show that increasing oxygen coverage lowers the adsorption energy associated with lattice reconstruction. Valence electrons transfer from Ta surface atoms to oxygen to create four excessive DOS features in terms of O−Ta bonding, lone pairs of oxygen, Ta"+ electron holes, and polarized Ta dipoles. Oxidation proceeds in the following dynamics: oxygen gets electrons from two neighboring Ta atoms left behind Ta"+; the sp"3-orbital hybridization takes place with additional two electron lone pairs, the lone pairs polarize the other two Ta neighbors becoming dipoles. X-ray photoelectron spectral analysis results in the 4f binding energy of an isolated Ta atom and its shift upon bond formation and oxidation. Exercises provide not only a promising numerical approach for the quantitative information about the bond and electronic behavior but also consistent insight into the

Adhesion and endothelialization of endothelial cells on the surface of endovascular stents by the novel rotational culture of cells

International Nuclear Information System (INIS)

Tang Chaojun; Wang Guixue; Cao Yi; Wu Xue; Xie Xiang; Xiao Li

2008-01-01

Recent researches indicate that the initial event in the implantation of endovascular stents involves mechanical injury to the vessel wall. Confluent endothelialization of vascular grafts in vitro before implantation has been suggested as a way to reduce injury of the blood vessel. The purpose of this study is to establish a useful way to improve the adhesion of endothelial cells and accelerate endothelialization on the surface of endovascular stents by a novel rotational culture device. Numerical simulation was used to predict the shear stress on the surface of stents. The number of cellular adhesion was calculated by cell counting, the cell growth was observed by scanning electron microscope and fluorescence microscope. Numerical simulation results showed that the stents was exposed to shear stress of 2.66 x 10 -3 to 8.88 x 10 -2 Pa. Rotational culture of human umbilical vein endothelial cells could enhance the adhesion of cells and accelerate endothelialization on the surface of stents when the culture conditions for EC adhesion were intermediate rotation speed, higher dynamic incubation times, lower cell densities

Mineralization of bacterial cell mass on a photocatalytic surface in air

International Nuclear Information System (INIS)

Jacoby, W.A.; Maness, P.C.; Wolfrum, E.J.; Blake, D.M.; Fennell, J.A.

1998-01-01

Whole cells deposited on a titanium dioxide-coated surface have been oxidized in air to carbon dioxide via photocatalysis. This paper provides the first evidence that the organic matter in whole cells can be completely oxidized. Three experimental techniques were employed to monitor this reaction: scanning electron microscopy, 14 C radioisotope labeling experiments establish that the carbon content of E. coli is oxidized to form carbon dioxide with substantial closure of the mass balance. The batch reactor experiments corroborate the mass balance and provide a preliminary indication of the rate of the oxidation reaction. These results provide evidence that a photocatalytic surface used for disinfection can also be self-cleaning in an air-solid system

Surface and volume photoemission of hot electrons from plasmonic nanoantennas

DEFF Research Database (Denmark)

Uskov, Alexander V.; Protsenko, Igor E.; Ikhsanov, Renat S.

2014-01-01

We theoretically compare surface- and volume-based photoelectron emission from spherical nanoparticles, obtaining analytical expressions for the emission rate in both mechanisms. We show that the surface mechanism prevails, being unaffected by detrimental hot electron collisions.......We theoretically compare surface- and volume-based photoelectron emission from spherical nanoparticles, obtaining analytical expressions for the emission rate in both mechanisms. We show that the surface mechanism prevails, being unaffected by detrimental hot electron collisions....

Electron backscatter diffraction characterization of laser-induced periodic surface structures on nickel surface

Energy Technology Data Exchange (ETDEWEB)

Sedao, Xxx, E-mail: sedao.xxx@gmail.com [Laboratoire Hubert Curien, Université Jean Monnet, 42000 St-Etienne (France); Maurice, Claire [Laboratoire Georges Friedel, Ecole Nationale Supérieure des Mines, 42023 St-Etienne (France); Garrelie, Florence; Colombier, Jean-Philippe; Reynaud, Stéphanie [Laboratoire Hubert Curien, Université Jean Monnet, 42000 St-Etienne (France); Quey, Romain; Blanc, Gilles [Laboratoire Georges Friedel, Ecole Nationale Supérieure des Mines, 42023 St-Etienne (France); Pigeon, Florent [Laboratoire Hubert Curien, Université Jean Monnet, 42000 St-Etienne (France)

2014-05-01

Graphical abstract: -- Highlight: •Lattice rotation and its distribution in laser-induced periodic surface structures (LIPSS) and the subsurface region on a nickel substrate are revealed using electron backscatter diffraction (EBSD). -- Abstract: We report on the structural investigation of laser-induced periodic surface structures (LIPSS) generated in polycrystalline nickel target after multi-shot irradiation by femtosecond laser pulses. Electron backscatter diffraction (EBSD) is used to reveal lattice rotation caused by dislocation storage during LIPSS formation. Localized crystallographic damages in the LIPSS are detected from both surface and cross-sectional EBSD studies. A surface region (up to 200 nm) with 1–3° grain disorientation is observed in localized areas from the cross-section of the LIPSS. The distribution of the local disorientation is inhomogeneous across the LIPSS and the subsurface region.

Solvation of excess electrons trapped in charge pockets on molecular surfaces

Science.gov (United States)

Jalbout, Abraham F.

This work considers the ability of hydrogen fluoride (HF) to solvate excess electrons located on cyclic hydrocarbon surfaces. The principle applied involves the formation of systems in which excess electrons can be stabilized not only on concentrated molecular surface charge pockets but also by HF. Recent studies have shown that OH groups can form stable hydrogen-bonded networks on one side of a hydrocarbon surface (i.e. cyclohexane sheets), at the same time, the hydrogen atoms on the opposite side of this surface form a pocket of positive charge can attract the excess electron. This density can be further stabilized by the addition of an HF molecule that can form an 'anion with an internally solvated electron' (AISE) state. These systems are shown to be stable with respect to vertical electron detachment (VDE).

A surface-electrode quadrupole guide for electrons

Energy Technology Data Exchange (ETDEWEB)

Hoffrogge, Johannes Philipp

2012-12-19

This thesis reports on the design and first experimental realization of a surface-electrode quadrupole guide for free electrons. The guide is based on a miniaturized, planar electrode layout and is driven at microwave frequencies. It confines electrons in the near-field of the microwave excitation, where strong electric field gradients can be generated without resorting to resonating structures or exceptionally high drive powers. The use of chip-based electrode geometries allows the realization of versatile, microstructured potentials with the perspective of novel quantum experiments with guided electrons. I present the design, construction and operation of an experiment that demonstrates electron confinement in a planar quadrupole guide for the first time. To this end, electrons with kinetic energies from one to ten electron-volts are guided along a curved electrode geometry. The stability of electron guiding as a function of drive parameters and electron energy has been studied. A comparison with numerical particle tracking simulations yields good qualitative agreement and provides a deeper understanding of the electron dynamics in the guiding potential. Furthermore, this thesis gives a detailed description of the design of the surface-electrode layout. This includes the development of an optimized coupling structure to inject electrons into the guide with minimum transverse excitation. I also discuss the extension of the current setup to longitudinal guide dimensions that are comparable to or larger than the wavelength of the drive signal. This is possible with a modified electrode layout featuring elevated signal conductors. Electron guiding in the field of a planar, microfabricated electrode layout allows the generation of versatile and finely structured guiding potentials. One example would be the realization of junctions that split and recombine a guided electron beam. Furthermore, it should be possible to prepare electrons in low-lying quantum mechanical

A surface-electrode quadrupole guide for electrons

International Nuclear Information System (INIS)

Hoffrogge, Johannes Philipp

2012-01-01

This thesis reports on the design and first experimental realization of a surface-electrode quadrupole guide for free electrons. The guide is based on a miniaturized, planar electrode layout and is driven at microwave frequencies. It confines electrons in the near-field of the microwave excitation, where strong electric field gradients can be generated without resorting to resonating structures or exceptionally high drive powers. The use of chip-based electrode geometries allows the realization of versatile, microstructured potentials with the perspective of novel quantum experiments with guided electrons. I present the design, construction and operation of an experiment that demonstrates electron confinement in a planar quadrupole guide for the first time. To this end, electrons with kinetic energies from one to ten electron-volts are guided along a curved electrode geometry. The stability of electron guiding as a function of drive parameters and electron energy has been studied. A comparison with numerical particle tracking simulations yields good qualitative agreement and provides a deeper understanding of the electron dynamics in the guiding potential. Furthermore, this thesis gives a detailed description of the design of the surface-electrode layout. This includes the development of an optimized coupling structure to inject electrons into the guide with minimum transverse excitation. I also discuss the extension of the current setup to longitudinal guide dimensions that are comparable to or larger than the wavelength of the drive signal. This is possible with a modified electrode layout featuring elevated signal conductors. Electron guiding in the field of a planar, microfabricated electrode layout allows the generation of versatile and finely structured guiding potentials. One example would be the realization of junctions that split and recombine a guided electron beam. Furthermore, it should be possible to prepare electrons in low-lying quantum mechanical

Effect of plasma surface functionalization on preosteoblast cells spreading and adhesion on a biomimetic hydroxyapatite layer formed on a titanium surface

International Nuclear Information System (INIS)

Myung, Sung Woon; Ko, Yeong Mu; Kim, Byung Hoon

2013-01-01

This study examined the plasma surface modification of biomimetic hydroxyapatite (HAp) formed on a titanium (Ti) surface as well as its influence on the behavior of preosteoblast cells. Ti substrates pre-treated with a plasma-polymerized thin film rich in carboxyl groups were subjected to a biomimetic process in a simulated body fluid solution to synthesize the HAp. The HAp layer grown on Ti substrate was then coated with two types of plasma polymerized acrylic acid and allyl amine thin film. The different types of Ti substrates were characterized by attenuated total reflection Fourier transform infrared spectroscopy, energy dispersive spectroscopy and X-ray diffraction. HAp with a Ca/P ratio from 1.25 to 1.38 was obtained on the Ti substrate and hydrophilic carboxyl (-COOH) and amine (-NH 2 ) functional groups were introduced to its surface. Scanning electron microscopy was used to observe the surface of the HAp coatings and the morphology of MC3T3-E1 cells. These results showed that the -COOH-modified HAp surfaces promoted the cell spreading synergistically by changing the surface morphology and chemical state.-NH 2 modified HAp had the lowest cell spreading and proliferation compared to HAp and -COOH-modified HAp. These results correspond to fluorescein analysis, which showed many more cell spreading of COOH/HAp/Ti surface compared to HAp and NH 2 modified HAp. A MTT assay was used to evaluate cell proliferation. The results showed that the proliferation of MC3T3-E1 cells increased in the order of COOH/HAp/Ti > HAp/Ti > NH 2 /Ti > Ti, corresponding to the effect of cell spreading for 6 days. The change in morphology and the chemical surface properties of the biomaterial via plasma polymerization can affect the behavior of MC3T3-E1 cells.

Effect of plasma surface functionalization on preosteoblast cells spreading and adhesion on a biomimetic hydroxyapatite layer formed on a titanium surface

Energy Technology Data Exchange (ETDEWEB)

Myung, Sung Woon; Ko, Yeong Mu; Kim, Byung Hoon, E-mail: kim5055@chosun.ac.kr

2013-12-15

This study examined the plasma surface modification of biomimetic hydroxyapatite (HAp) formed on a titanium (Ti) surface as well as its influence on the behavior of preosteoblast cells. Ti substrates pre-treated with a plasma-polymerized thin film rich in carboxyl groups were subjected to a biomimetic process in a simulated body fluid solution to synthesize the HAp. The HAp layer grown on Ti substrate was then coated with two types of plasma polymerized acrylic acid and allyl amine thin film. The different types of Ti substrates were characterized by attenuated total reflection Fourier transform infrared spectroscopy, energy dispersive spectroscopy and X-ray diffraction. HAp with a Ca/P ratio from 1.25 to 1.38 was obtained on the Ti substrate and hydrophilic carboxyl (-COOH) and amine (-NH{sub 2}) functional groups were introduced to its surface. Scanning electron microscopy was used to observe the surface of the HAp coatings and the morphology of MC3T3-E1 cells. These results showed that the -COOH-modified HAp surfaces promoted the cell spreading synergistically by changing the surface morphology and chemical state.-NH{sub 2} modified HAp had the lowest cell spreading and proliferation compared to HAp and -COOH-modified HAp. These results correspond to fluorescein analysis, which showed many more cell spreading of COOH/HAp/Ti surface compared to HAp and NH{sub 2} modified HAp. A MTT assay was used to evaluate cell proliferation. The results showed that the proliferation of MC3T3-E1 cells increased in the order of COOH/HAp/Ti > HAp/Ti > NH{sub 2}/Ti > Ti, corresponding to the effect of cell spreading for 6 days. The change in morphology and the chemical surface properties of the biomaterial via plasma polymerization can affect the behavior of MC3T3-E1 cells.

Surface chemical functionalities affect the behavior of human adipose-derived stem cells in vitro

International Nuclear Information System (INIS)

Liu, Xujie; Feng, Qingling; Bachhuka, Akash; Vasilev, Krasimir

2013-01-01

This study examines the effect of surface chemical functionalities on the behavior of human adipose-derived stem cells (hASCs) in vitro. Plasma polymerized films rich in amine (-NH 2 ), carboxyl (-COOH) and methyl (-CH 3 ), were generated on hydroxyapatite (HAp) substrates. The surface chemical functionalities were characterized by X-ray photoelectron spectroscopy (XPS). The ability of different substrates to absorb proteins was evaluated. The results showed that substrates modified with hydrophilic functional group (-COOH and -NH 2 ) can absorb more proteins than these modified with more hydrophobic functional group (-CH 3 ). The behavior of human adipose-derived stem cells (hASCs) cultured on different substrates was investigated in vitro: cell counting kit-8 (CCK-8) analysis was used to characterize cell proliferation, scanning electronic microscopy (SEM) analysis was used to characterize cell morphology and alkaline phosphatase (ALP) activity analysis was used to account for differentiation. The results of this study demonstrated that the -NH 2 modified surfaces encourage osteogenic differentiation; the -COOH modified surfaces promote cell adhesion and spreading and the -CH 3 modified surfaces have the lowest ability to induce osteogenic differentiation. These findings confirmed that the surface chemical states of biomaterials can affect the behavior of hASCs in vitro.

Surface chemical functionalities affect the behavior of human adipose-derived stem cells in vitro

Energy Technology Data Exchange (ETDEWEB)

Liu, Xujie [State key laboratory of new ceramics and fine processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Feng, Qingling, E-mail: biomater@mail.tsinghua.edu.cn [State key laboratory of new ceramics and fine processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Bachhuka, Akash [Mawson Institute, University of South Australia, Mawson Lakes 5095 (Australia); Vasilev, Krasimir [Mawson Institute, University of South Australia, Mawson Lakes 5095 (Australia); School of Advanced Manufacturing, University of South Australia, Mawson Lakes 5095 (Australia)

2013-04-01

This study examines the effect of surface chemical functionalities on the behavior of human adipose-derived stem cells (hASCs) in vitro. Plasma polymerized films rich in amine (-NH{sub 2}), carboxyl (-COOH) and methyl (-CH{sub 3}), were generated on hydroxyapatite (HAp) substrates. The surface chemical functionalities were characterized by X-ray photoelectron spectroscopy (XPS). The ability of different substrates to absorb proteins was evaluated. The results showed that substrates modified with hydrophilic functional group (-COOH and -NH{sub 2}) can absorb more proteins than these modified with more hydrophobic functional group (-CH{sub 3}). The behavior of human adipose-derived stem cells (hASCs) cultured on different substrates was investigated in vitro: cell counting kit-8 (CCK-8) analysis was used to characterize cell proliferation, scanning electronic microscopy (SEM) analysis was used to characterize cell morphology and alkaline phosphatase (ALP) activity analysis was used to account for differentiation. The results of this study demonstrated that the -NH{sub 2} modified surfaces encourage osteogenic differentiation; the -COOH modified surfaces promote cell adhesion and spreading and the -CH{sub 3} modified surfaces have the lowest ability to induce osteogenic differentiation. These findings confirmed that the surface chemical states of biomaterials can affect the behavior of hASCs in vitro.

Endothelial cell labeling with indium-111-oxine as a marker of cell attachment to bioprosthetic surfaces

International Nuclear Information System (INIS)

Sharefkin, J.B.; Lather, C.; Smith, M.; Rich, N.M.

1983-01-01

Canine vascular endothelium labeled with indium-111-oxine was used as a marker of cell attachment to vascular prosthetic surfaces with complex textures. Primarily cultured and freshly harvested endothelial cells both took up the label rapidly. An average of 72% of a 32 micro Ci labeling dose was taken up by 1.5 X 10(6) cells in 10 min in serum-free medium. Over 95% of freshly labeled cells were viable by trypan blue tests and only 5% of the label was released after 1 h incubations at 37 degrees C. Labeled and unlabeled cells had similar rates of attachment to plastic dishes. Scanning electron microscopic studies showed that labeled cells retained their ability to spread on tissue culture dishes even at low (1%) serum levels. Labeled endothelial cells seeded onto Dacron or expanded polytetrafluoroethylene vascular prostheses by methods used in current surgical models could be identified by autoradiography of microscopic sections of the prostheses, and the efficiency of cell attachment to the prosthesis could be measured by gamma counting. Indium-111 labeling affords a simple and rapid way to measure initial cell attachment to, and distribution on, vascular prosthetic materials. The method could also allow measurement of early cell loss from a flow surface in vivo by using external gamma imaging

Analysis of Field Emission of Fabricated Nanogap in Pd Strips for Surface Conduction Electron-Emitter Displays

Science.gov (United States)

Lo, Hsiang-Yu; Li, Yiming; Tsai, Chih-Hao; Pan, Fu-Ming

2008-04-01

We study the field emission (FE) property of a nanometer-scale gap structure in a palladium strip, which was fabricated by hydrogen absorption under high-pressure treatment. A vigorous cracking process could be accompanied by extensive atomic migration during the hydrogen treatment. A three-dimensional finite-difference time-domain particle-in-cell method is adopted to simulate the electron emission in a surface-conduction electron-emitter display (SED) device. Examinations of conducting characteristics, FE efficiency, the local field around the emitter, and the current density on the anode plate with one FE emitter are conducted. The image of a light spot is successfully produced on a phosphor plate, which implies that the explored electrode with nanometer separation possesses a potential SED application. Experimental observation and numerical simulation show that the proposed structure can be used as a surface conduction electron emitter and has a high FE efficiency with low turn-on voltage and a different electron emission mechanism. This study benefits the advanced SED design for a new type of electron source.

Solving complex and disordered surface structures with electron diffraction

International Nuclear Information System (INIS)

Van Hove, M.A.

1987-10-01

The past of surface structure determination with low-energy electron diffraction (LEED) will be briefly reviewed, setting the stage for a discussion of recent and future developments. The aim of these developments is to solve complex and disordered surface structures. Some efficient solutions to the theoretical and experimental problems will be presented. Since the theoretical problems dominate, the emphasis will be on theoretical approaches to the calculation of the multiple scattering of electrons through complex and disordered surfaces. 49 refs., 13 figs., 1 tab

Electronic structures near surfaces of perovskite type oxides

International Nuclear Information System (INIS)

Hara, Toru

2005-01-01

This work is intended to draw attention to the origin of the electronic structures near surfaces of perovskite type oxides. Deep states were observed by ultraviolet photoelectron spectroscopic measurements. The film thickness dependent electronic structures near surfaces of (Ba 0.5 Sr 0.5 )TiO 3 thin films were observed. As for the 117-308 nm thick (Ba 0.5 Sr 0.5 )TiO 3 films, deep states were lying at 0.20, 0.55, and 0.85 eV below the quasi-fermi level, respectively. However, as for the 40 nm thick (Ba 0.5 Sr 0.5 )TiO 3 film, the states were overlapped. The A-site doping affected electronic structures near surfaces of SrTiO 3 single crystals. No evolution of deep states in non-doped SrTiO 3 single crystal was observed. However, the evolution of deep states in La-doped SrTiO 3 single crystal was observed

Traversal of cells by radiation and absorbed fraction estimates for electrons and alpha particles

International Nuclear Information System (INIS)

Eckerman, K.F.; Ryman, J.C.; Taner, A.C.; Kerr, G.D.

1986-01-01

Consideration of the pathlength which radiation traverses in a cell is central to algorithms for estimating energy deposition on a cellular level. Distinct pathlength distributions occur for radionuclides: (1) uniformly distributed in space about the cell (referred to as μ-randomness); (2) uniformly distributed on the surface of the cell (S-randomness); and (3) uniformly distributed within the cell volume (I-randomness). For a spherical cell of diameter d, the mean pathlengths are 2/3d, and 3/4d, respectively, for these distributions. Algorithms for simulating the path of radiation through a cell are presented and the absorbed fraction in the cell and its nucleus are tabulated for low energy electrons and alpha particles emitted on the surface of spherical cells. The algorithms and absorbed fraction data should be of interest to those concerned with the dosimetry of radionuclide-labeled monoclonal antibodies. 8 references, 3 figures, 2 tables

Surface modification of a proton exchange membrane and hydrogen storage in a metal hydride for fuel cells

Science.gov (United States)

Andrews, Lisa

Interest in fuel cell technology is rising as a result of the need for more affordable and available fuel sources. Proton exchange membrane fuel cells involve the catalysis of a fuel to release protons and electrons. It requires the use of a polymer electrolyte membrane to transfer protons through the cell, while the electrons pass through an external circuit, producing electricity. The surface modification of the polymer, NafionRTM, commonly researched as a proton exchange membrane, may improve efficiency of a fuel cell. Surface modification can change the chemistry of the surface of a polymer while maintaining bulk properties. Plasma modification techniques such as microwave discharge of an argon and oxygen gas mixture as well as vacuum-ultraviolet (VUV) photolysis may cause favorable chemical and physical changes on the surface of Nafion for improved fuel cell function. A possible increase in hydrophilicity as a result of microwave discharge experiments may increase proton conductivity. Grafting of acrylic acid from the surface of modified Nafion may decrease the permeation of methanol in a direct methanol fuel cell, a process which can decrease efficiency. Modification of the surface of Nafion samples were carried out using: 1) An indirect Ar/O2 gas mixture plasma investigating the reaction of oxygen radicals with the surface, 2) A direct Ar/O2 gas mixture plasma investigating the reaction of oxygen radicals and VUV radiation with the surface and, 3) VUV photolysis investigating exclusively the interaction of VUV radiation with the surface and any possible oxidation upon exposure to air. Acrylic acid was grafted from the VUV photolysed Nafion samples. All treated surfaces were analyzed using X-ray photoelectron spectroscopy (XPS). Fourier transform infrared spectroscopy (FTIR) was used to analyze the grafted Nafion samples. Scanning electron microscopy (SEM) and contact angle measurements were used to analyze experiments 2 and 3. Using hydrogen as fuel is a

Positron annihilation induced Auger electron spectroscopic studies of oxide surfaces

Science.gov (United States)

Nadesalingam, Manori

2005-03-01

Defects on oxide surfaces are well known to play a key role in catalysis. TiO2, MgO, SiO2 surfaces were investigated using Time-Of-Flight Positron induced Auger Electron Spectroscopy (TOF-PAES). Previous work in bulk materials has demonstrated that positrons are particularly sensitive to charged defects. In PAES energetic electron emission results from Auger transitions initiated by annihilation of core electrons with positrons trapped in an image-potential well at the surface. Annealed samples in O2 environment show a strong Auger peak of Oxygen. The implication of these results will be discussed

SiGe Based Low Temperature Electronics for Lunar Surface Applications

Science.gov (United States)

Mojarradi, Mohammad M.; Kolawa, Elizabeth; Blalock, Benjamin; Cressler, John

2012-01-01

The temperature at the permanently shadowed regions of the moon's surface is approximately -240 C. Other areas of the lunar surface experience temperatures that vary between 120 C and -180 C during the day and night respectively. To protect against the large temperature variations of the moon surface, traditional electronics used in lunar robotics systems are placed inside a thermally controlled housing which is bulky, consumes power and adds complexity to the integration and test. SiGe Based electronics have the capability to operate over wide temperature range like that of the lunar surface. Deploying low temperature SiGe electronics in a lander platform can minimize the need for the central thermal protection system and enable the development of a new generation of landers and mobility platforms with highly efficient distributed architecture. For the past five years a team consisting of NASA, university and industry researchers has been examining the low temperature and wide temperature characteristic of SiGe based transistors for developing electronics for wide temperature needs of NASA environments such as the Moon, Titan, Mars and Europa. This presentation reports on the status of the development of wide temperature SiGe based electronics for the landers and lunar surface mobility systems.

Structural and electronic properties of hydrosilylated silicon surfaces

Energy Technology Data Exchange (ETDEWEB)

Baumer, A.

2005-11-15

The structural and electronic properties of alkyl-terminated Si surfaces prepared by thermallyinduced hydrosilylation have been studied in detail in the preceding chapters. Various surfaces have been used for the functionalization ranging from crystalline Si over amorphous hydrogenated Si to nanoscaled materials such as Si nanowires and nanoparticles. In each case, the alkyl-terminated surfaces have been compared to the native oxidized and H-terminated surfaces. (orig.)

Silver nanoparticles-incorporated Nb2O5 surface passivation layer for efficiency enhancement in dye-sensitized solar cells.

Science.gov (United States)

Suresh, S; Unni, Gautam E; Satyanarayana, M; Sreekumaran Nair, A; Mahadevan Pillai, V P

2018-08-15

Guiding and capturing photons at the nanoscale by means of metal nanoparticles and interfacial engineering for preventing back-electron transfer are well documented techniques for performance enhancement in excitonic solar cells. Drifting from the conventional route, we propose a simple one-step process to integrate both metal nanoparticles and surface passivation layer in the porous photoanode matrix of a dye-sensitized solar cell. Silver nanoparticles and Nb 2 O 5 surface passivation layer are simultaneously deposited on the surface of a highly porous nanocrystalline TiO 2 photoanode, facilitating an absorption enhancement in the 465 nm and 570 nm wavelength region and a reduction in back-electron transfer in the fabricated dye-sensitized solar cells together. The TiO 2 photoanodes were prepared by spray pyrolysis deposition method from a colloidal solution of TiO 2 nanoparticles. An impressive 43% enhancement in device performance was accomplished in photoanodes having an Ag-incorporated Nb 2 O 5 passivation layer as against a cell without Ag nanoparticles. By introducing this idea, we were able to record two benefits - the metal nanoparticles function as the absorption enhancement agent, and the Nb 2 O 5 layer as surface passivation for TiO 2 nanoparticles and as an energy barrier layer for preventing back-electron transfer - in a single step. Copyright © 2018 Elsevier Inc. All rights reserved.

Magnetoresistance oscillations of two-dimensional electron systems in lateral superlattices with structured unit cells

Science.gov (United States)

Gerhardts, Rolf R.

2015-11-01

Model calculations for commensurability oscillations of the low-field magnetoresistance of two-dimensional electron systems (2DES) in lateral superlattices, consisting of unit cells with an internal structure, are compared with recent experiments. The relevant harmonics of the effective modulation potential depend not only on the geometrical structure of the modulated unit cell, but also strongly on the nature of the modulation. While higher harmonics of an electrostatically generated surface modulation are exponentially damped at the position of the 2DES about 90 nm below the surface, no such damping appears for strain-induced modulation generated, e.g., by the deposition of stripes of calixarene resist on the surface before cooling down the sample.

Multilamellar structures and filament bundles are found on the cell surface during bunyavirus egress.

Directory of Open Access Journals (Sweden)

Laura Sanz-Sánchez

Full Text Available Inside cells, viruses build specialized compartments for replication and morphogenesis. We observed that virus release associates with specific structures found on the surface of mammalian cells. Cultured adherent cells were infected with a bunyavirus and processed for oriented sectioning and transmission electron microscopy. Imaging of cell basal regions showed sophisticated multilamellar structures (MLS and extracellular filament bundles with attached viruses. Correlative light and electron microscopy confirmed that both MLS and filaments proliferated during the maximum egress of new viruses. MLS dimensions and structure were reminiscent of those reported for the nanostructures on gecko fingertips, which are responsible for the extraordinary attachment capacity of these lizards. As infected cells with MLS were more resistant to detachment than control cells, we propose an adhesive function for these structures, which would compensate for the loss of adherence during release of new virus progeny.

Investigation on cell biocompatible behaviors of polyaniline film fabricated via electroless surface polymerization

International Nuclear Information System (INIS)

Liu Sheng; Wang Jinqing; Zhang Dong; Zhang Puliang; Ou Junfei; Liu Bin; Yang Shengrong

2010-01-01

Considering for the potential application in tissue engineering, polyaniline (PANi) film was fabricated via a two-step route: a self-assembled monolayer of C 6 H 5 NHC 3 H 6 Si(OMe) 3 was firstly formed on the single-crystal Si substrate; the conducting PANi film was then prepared through electroless surface polymerization of the aniline molecules on the aniline monolayer-bearing silane surface in an acidic aqueous solution. The formation of PANi film on Si surface was confirmed by characterizations of X-ray photoelectron spectroscope (XPS) and specular reflectance Fourier transform infrared (SR-FTIR) spectrum, etc. At last, the proliferation behaviors of PC-12 cells on the PANi film surface were studied by the [3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyl tetrazolium bromide] (MTT) colorimetric assays, acridine orange fluorometric staining, and scanning electron microscope (SEM) observation, etc. The results demonstrate that the as-prepared PANi film provides high ability for cell proliferation, exhibiting promising potentials as surface coating to cultivate neuronal cells for applications in the tissue engineering.

Conditioning of Si-interfaces by wet-chemical oxidation: Electronic interface properties study by surface photovoltage measurements

Energy Technology Data Exchange (ETDEWEB)

Angermann, Heike, E-mail: angermann@helmholtz-berlin.de

2014-09-01

Highlights: • Determination of electronic interface properties by contact-less surface photovoltage (SPV) technique. • Systematic correlations of substrate morphology and surface electronic properties. • Optimization of surface pre-treatment for flat, saw damage etched, and textured Si solar cell substrates. • Ultra-thin passivating Si oxide layers with low densities of rechargeable states by wet-chemical oxidation and subsequent annealing. • Environmentally acceptable processes, utilizing hot water, diluted HCl, or ozone low cost alternative to current approaches with concentrated chemicals. • The effect of optimized wet-chemical pre-treatments can be preserved during subsequent layer deposition. - Abstract: The field-modulated surface photovoltage (SPV) method, a very surface sensitive technique, was utilized to determine electronic interface properties on wet-chemically oxidized and etched silicon (Si) interfaces. The influence of preparation-induced surface micro-roughness and un-stoichiometric oxides on the resulting the surface charge, energetic distribution D{sub it}(E), and density D{sub it,min} of rechargeable states was studied by simultaneous, spectroscopic ellipsometry (SE) measurements on polished Si(111) and Si(100) substrates. Based on previous findings and new research, a study of conventional and newly developed wet-chemical oxidation methods was established, correlating the interactions between involved oxidizing and etching solutions and the initial substrate morphology to the final surface conditioning. It is shown, which sequences of wet-chemical oxidation and oxide removal, have to be combined in order to achieve atomically smooth, hydrogen terminated surfaces, as well as ultra-thin oxide layers with low densities of rechargeable states on flat, saw damage etched, and textured Si substrates, as commonly applied in silicon device and solar cell manufacturing. These conventional strategies for wet-chemical pre-treatment are mainly

Conditioning of Si-interfaces by wet-chemical oxidation: Electronic interface properties study by surface photovoltage measurements

International Nuclear Information System (INIS)

Angermann, Heike

2014-01-01

Highlights: • Determination of electronic interface properties by contact-less surface photovoltage (SPV) technique. • Systematic correlations of substrate morphology and surface electronic properties. • Optimization of surface pre-treatment for flat, saw damage etched, and textured Si solar cell substrates. • Ultra-thin passivating Si oxide layers with low densities of rechargeable states by wet-chemical oxidation and subsequent annealing. • Environmentally acceptable processes, utilizing hot water, diluted HCl, or ozone low cost alternative to current approaches with concentrated chemicals. • The effect of optimized wet-chemical pre-treatments can be preserved during subsequent layer deposition. - Abstract: The field-modulated surface photovoltage (SPV) method, a very surface sensitive technique, was utilized to determine electronic interface properties on wet-chemically oxidized and etched silicon (Si) interfaces. The influence of preparation-induced surface micro-roughness and un-stoichiometric oxides on the resulting the surface charge, energetic distribution D it (E), and density D it,min of rechargeable states was studied by simultaneous, spectroscopic ellipsometry (SE) measurements on polished Si(111) and Si(100) substrates. Based on previous findings and new research, a study of conventional and newly developed wet-chemical oxidation methods was established, correlating the interactions between involved oxidizing and etching solutions and the initial substrate morphology to the final surface conditioning. It is shown, which sequences of wet-chemical oxidation and oxide removal, have to be combined in order to achieve atomically smooth, hydrogen terminated surfaces, as well as ultra-thin oxide layers with low densities of rechargeable states on flat, saw damage etched, and textured Si substrates, as commonly applied in silicon device and solar cell manufacturing. These conventional strategies for wet-chemical pre-treatment are mainly based on

The impact of surface coverage on the kinetics of electron transfer through redox monolayers on a silicon electrode surface

International Nuclear Information System (INIS)

Ciampi, Simone; Choudhury, Moinul H.; Ahmad, Shahrul Ainliah Binti Alang; Darwish, Nadim; Brun, Anton Le; Gooding, J.Justin

2015-01-01

Graphical abstract: The impact of surface coverage on the kinetics of electron transfer through redox monolayers on a silicon electrode surface. ABSTRACT: The impact of the coverage of ferrocene moieties, attached to a silicon electrode modified via hydrosilylation of a dialkyne, on the kinetics of electron transfer between the redox species and the electrode is explored. The coverage of ferrocene is controlled by varying the coupling time between azidomethylferrocene and the distal alkyne of the monolayer via the copper assisted azide-alkyne cycloaddition reaction. All other variables in the surface preparation are maintained identical. What is observed is that the higher the surface coverage of the ferrocene moieties the faster the apparent rates of electron transfer. This surface coverage-dependent kinetic effect is attributed to electrons hopping between ferrocene moieties across the redox film toward hotspots for the electron transfer event. The origin of these hotspots is tentatively suggested to result from minor amounts of oxide on the underlying silicon surface that reduce the barrier for the electron transfer.

Photon- and electron-induced surface voltage in electron spectroscopies on ZnSe(0 0 1)

International Nuclear Information System (INIS)

Cantoni, M.; Bertacco, R.; Brambilla, A.; Ciccacci, F.

2009-01-01

The surface band bending in ZnSe(0 0 1), as a function of the temperature, is investigated both in the valence band (by photoemission) and in the conduction band (by inverse photoemission and absorbed current spectroscopies). Two different mechanisms are invoked for interpreting the experimental data: the band bending due to surface states, and the surface voltage induced by the incident beam. While the latter is well known in photoemission (surface photovoltage), we demonstrate the existence of a similar effect in inverse photoemission and absorbed current spectroscopies, induced by the incident electrons instead of photons. These results point to the importance of considering the surface voltage effect even in electron-in techniques for a correct evaluation of the band bending.

Enhanced charge carrier transport properties in colloidal quantum dot solar cells via organic and inorganic hybrid surface passivation† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c6ta06835a Click here for additional data file.

Science.gov (United States)

Hong, John; Hou, Bo; Lim, Jongchul; Pak, Sangyeon; Kim, Byung-Sung; Cho, Yuljae; Lee, Juwon; Lee, Young-Woo; Giraud, Paul; Lee, Sanghyo; Park, Jong Bae; Morris, Stephen M.; Snaith, Henry J.; Kim, Jong Min

2016-01-01

Colloidal quantum dots (CQDs) are extremely promising as photovoltaic materials. In particular, the tunability of their electronic band gap and cost effective synthetic procedures allow for the versatile fabrication of solar energy harvesting cells, resulting in optimal device performance. However, one of the main challenges in developing high performance quantum dot solar cells (QDSCs) is the improvement of the photo-generated charge transport and collection, which is mainly hindered by imperfect surface functionalization, such as the presence of surface electronic trap sites and the initial bulky surface ligands. Therefore, for these reasons, finding effective methods to efficiently decorate the surface of the as-prepared CQDs with new short molecular length chemical structures so as to enhance the performance of QDSCs is highly desirable. Here, we suggest employing hybrid halide ions along with the shortest heterocyclic molecule as a robust passivation structure to eliminate surface trap sites while decreasing the charge trapping dynamics and increasing the charge extraction efficiency in CQD active layers. This hybrid ligand treatment shows a better coordination with Pb atoms within the crystal, resulting in low trap sites and a near perfect removal of the pristine initial bulky ligands, thereby achieving better conductivity and film structure. Compared to halide ion-only treated cells, solar cells fabricated through this hybrid passivation method show an increase in the power conversion efficiency from 5.3% for the halide ion-treated cells to 6.8% for the hybrid-treated solar cells. PMID:29308200

Electron Debye scale Kelvin-Helmholtz instability: Electrostatic particle-in-cell simulations

International Nuclear Information System (INIS)

Lee, Sang-Yun; Lee, Ensang; Kim, Khan-Hyuk; Lee, Dong-Hun; Seon, Jongho; Jin, Ho

2015-01-01

In this paper, we investigated the electron Debye scale Kelvin-Helmholtz (KH) instability using two-dimensional electrostatic particle-in-cell simulations. We introduced a velocity shear layer with a thickness comparable to the electron Debye length and examined the generation of the KH instability. The KH instability occurs in a similar manner as observed in the KH instabilities in fluid or ion scales producing surface waves and rolled-up vortices. The strength and growth rate of the electron Debye scale KH instability is affected by the structure of the velocity shear layer. The strength depends on the magnitude of the velocity and the growth rate on the velocity gradient of the shear layer. However, the development of the electron Debye scale KH instability is mainly determined by the electric field generated by charge separation. Significant mixing of electrons occurs across the shear layer, and a fraction of electrons can penetrate deeply into the opposite side fairly far from the vortices across the shear layer

Electron microbeam specifications for use in cell irradiation experiments

International Nuclear Information System (INIS)

Kim, E.-H.; Choi, M.-C.; Lee, D.-H.; Chang, M.; Kang, C.-S.

2003-01-01

The microbeam irradiation system was devised originally to identify the hit and unhit cells by confining the beam within the target cell. The major achievement through the microbeam experiment studies has turned out to be the discovery of the 'bystander effect'. Microbeam experiments have been performed with alpha and proton beams in major and with soft x-rays in minor. The study with electron microbeam has been deferred mainly due to the difficulty in confining the electron tracks within a single target cell. In this paper, the electron microbeam irradiation system under development in Korea is introduced in terms of the beam specifications. The KIRAMS electron microbeam irradiation system consists of an electron gun, a vacuum chamber for beam collimation into 5 μm in diameter and a biology stage. The beam characteristics in terms of current and energy spectrum of the electrons entering a target cell and its neighbor cells were investigated by Monte Carlo simulation for the electron source energies of 25, 50, 75 and 100 keV. Energy depositions in the target cell and the neighbor cells were also calculated. The beam attenuation in current and energy occurs while electrons pass through the 2 μm-thick Mylar vacuum window, 100 μm-thick air gap and the 2 μm-thick Mylar bottom of cell dish. With 25 keV electron source, 80 % of decrease in current and 30 % of decrease in average energy were estimated before entering the target cell. With 75 keV electron source, on the other hand, 55 % of decrease in current and less than 1 % of decrease in average energy were estimated. Average dose per single collimated electron emission was 0.067 cGy to the target cell nucleus of 5 μm in diameter and 0.030 cGy to the cytoplasm of 2.5 μm in thickness with 25 keV electron source while they were 0.15 cGy and 0.019 cGy, respectively, with 75 keV electron source. The multiple scattering of electrons resulted in energy deposition in the neighbor cells as well. Dose to the first

Traversal of cells by radiation and absorbed fraction estimates for electrons and alpha particles

International Nuclear Information System (INIS)

Eckerman, K.F.; Ryman, J.C.; Taner, A.C.; Kerr, G.D.

1985-01-01

Consideration of the pathlength which radiation traverses in a cell is central to algorithms for estimating energy deposition on a cellular level. Distinct pathlength distributions occur for radionuclides: (1) uniformly distributed in space about the cell (referred to as μ-randomness); (2) uniformly distributed on the surface of the cell (S-randomness); and (3) uniformly distributed within the cell volume (I-randomness). For a spherical cell of diameter d, the mean pathlengths are 2/3d, 1/2d, and 3/4d, respectively, for these distributions. Algorithms for simulating the path of radiation through a cell are presented and the absorbed fraction in the cell and its nucleus are tabulated for low energy electrons and alpha particles emitted on the surface of spherical cells. The algorithms and absorbed fraction data should be of interest to those concerned with the dosimetry of radionuclide-labeled monoclonal antibodies. 8 refs., 3 figs., 2 tabs

Tantalum Nitride Electron-Selective Contact for Crystalline Silicon Solar Cells

KAUST Repository

Yang, Xinbo

2018-04-19

Minimizing carrier recombination at contact regions by using carrier‐selective contact materials, instead of heavily doping the silicon, has attracted considerable attention for high‐efficiency, low‐cost crystalline silicon (c‐Si) solar cells. A novel electron‐selective, passivating contact for c‐Si solar cells is presented. Tantalum nitride (TaN x ) thin films deposited by atomic layer deposition are demonstrated to provide excellent electron‐transporting and hole‐blocking properties to the silicon surface, due to their small conduction band offset and large valence band offset. Thin TaNx interlayers provide moderate passivation of the silicon surfaces while simultaneously allowing a low contact resistivity to n‐type silicon. A power conversion efficiency (PCE) of over 20% is demonstrated with c‐Si solar cells featuring a simple full‐area electron‐selective TaNx contact, which significantly improves the fill factor and the open circuit voltage (Voc) and hence provides the higher PCE. The work opens up the possibility of using metal nitrides, instead of metal oxides, as carrier‐selective contacts or electron transport layers for photovoltaic devices.

Surface sensitization mechanism on negative electron affinity p-GaN nanowires

Science.gov (United States)

Diao, Yu; Liu, Lei; Xia, Sihao; Feng, Shu; Lu, Feifei

2018-03-01

The surface sensitization is the key to prepare negative electron affinity photocathode. The thesis emphasizes on the study of surface sensitization mechanism of p-type doping GaN nanowires utilizing first principles based on density function theory. The adsorption energy, work function, dipole moment, geometry structure, electronic structure and optical properties of Mg-doped GaN nanowires surfaces with various coverages of Cs atoms are investigated. The GaN nanowire with Mg doped in core position is taken as the sensitization base. At the initial stage of sensitization, the best adsorption site for Cs atom on GaN nanowire surface is BN, the bridge site of two adjacent N atoms. Surface sensitization generates a p-type internal surface with an n-type surface state, introducing a band bending region which can help reduce surface barrier and work function. With increasing Cs coverage, work functions decrease monotonously and the "Cs-kill" phenomenon disappears. For Cs coverage of 0.75 ML and 1 ML, the corresponding sensitization systems reach negative electron affinity state. Through surface sensitization, the absorption curves are red shifted and the absorption coefficient is cut down. All theoretical calculations can guide the design of negative electron affinity Mg doped GaN nanowires photocathode.

Electronic structure of incident carbon ions on a graphite surface

International Nuclear Information System (INIS)

Kiuchi, Masato; Takeuchi, Takae; Yamamoto, Masao.

1997-01-01

The electronic structure of an incident carbon ion on a graphite surface is discussed on the basis of ab initio molecular orbital calculations. A carbon cation forms a covalent bond with the graphite, and a carbon nonion is attracted to the graphite surface through van der Waals interaction. A carbon anion has no stable state on a graphite surface. The charge effects of incident ions become clear upon detailed examination of the electronic structure. (author)

Electron-Beam Induced Grafting of Isopropylacrylamide to a Poly(Ethylene-Terephthalate) Membrane for Cell Sheet Detachment, and Fuel Cell Membrane

Energy Technology Data Exchange (ETDEWEB)

Shahamat, L; Al-Sheikhly, M [Department of Materials Science and Engineering, College Park, MD (United States)

2012-09-15

Using high-energy irradiation initiation, isopropylacrylamide (IPAA) was grafted to a porous membrane dish composed of poly(ethylene terephthalate) (PET). IPPA demonstrates a transition from a hydrophobic to a hydrophilic structure with a simple change in temperature. The dishes were used for cell grow. Cells generally grow in an environment set at 37 deg. C, at which the IPAA polymer exhibits its hydrophobic structure. IPAA was attached uniformly to a cell culture surface, and cells were able to grow on top of the IPAA while it was in its hydrophobic state. Cells were easily removed from the surface of the dishes after changing the temperature below the LCST of IPAA. By changing the temperature polymer altered its structure to a hydrophilic state and no longer provided a suitable surface for the cells to adhere to. This caused the cells to lift off the culture surface without the use of a destructive enzyme such as trypsin or dispase. These cell sheets are useful to cell sheet engineering because the cells will retain both their extracellular matrix (ECM) and cell-to-cell junctions, which are normally lost in the harvest of cells. Poly(tetrafluoroethylene-co-hexefluoropropylene) (FEP) is a material under investigation as a polymer electrolyte membrane for fuel cells. In order to make it ionically conductive, styrene was grafted to it and then subsequently sulfonated. Grafting of styrene to FEP was performed by simultaneous irradiation of the monomer and substrate to initiate the reaction, followed by a heat treatment to allow the reaction to undergo propagation. The effects of dose rate and heat treatment time on the weight percent yield of grafting and uniformity as a function of depth in the substrate was investigated. A 38.5 wt% graft was obtained after a 50 kGy dose of electron irradiation at a dose rate of 2,8 Gy/pulse and post-irradiation heat treatment of 60 deg. C for three hours. FTIR analysis of 10 {mu}m sections of material grafted under these

One-dimensional versus two-dimensional electronic states in vicinal surfaces

International Nuclear Information System (INIS)

Ortega, J E; Ruiz-Oses, M; Cordon, J; Mugarza, A; Kuntze, J; Schiller, F

2005-01-01

Vicinal surfaces with periodic arrays of steps are among the simplest lateral nanostructures. In particular, noble metal surfaces vicinal to the (1 1 1) plane are excellent test systems to explore the basic electronic properties in one-dimensional superlattices by means of angular photoemission. These surfaces are characterized by strong emissions from free-electron-like surface states that scatter at step edges. Thereby, the two-dimensional surface state displays superlattice band folding and, depending on the step lattice constant d, it splits into one-dimensional quantum well levels. Here we use high-resolution, angle-resolved photoemission to analyse surface states in a variety of samples, in trying to illustrate the changes in surface state bands as a function of d

Surface and protein analyses of normal human cell attachment on PIII-modified chitosan membranes

International Nuclear Information System (INIS)

Saranwong, N.; Inthanon, K.; Wongkham, W.; Wanichapichart, P.; Suwannakachorn, D.; Yu, L.D.

2012-01-01

Surface of chitosan membrane was modified with argon (Ar) and nitrogen (N) plasma immersion ion implantation (PIII) for human skin fibroblasts F1544 cell attachment. The modified surfaces were characterized by Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). Cell attachment patterns were evaluated by scanning electron microscopy (SEM). The enzyme-linked immunosorbent assay (ELISA) was used to quantify levels of focal adhesion kinase (FAK). The results showed that Ar PIII had an enhancement effect on the cell attachment while N-PIII had an inhibition effect. Filopodial analysis revealed more microfilament cytoplasmic spreading on the edge of cells attached on the Ar-treated membranes than N-treated membranes. Higher level FAK was found in Ar-treated membranes than that in N-treated membranes.

Electron Emission by N6+ Ions Scattered at a Magnetized Iron Surface

International Nuclear Information System (INIS)

Solleder, B.; Lemell, C.; Burgdoerfer, J.; Tokesi, K.

2006-01-01

Complete text of publication follows. Magnetized materials are of considerable interest in the electronics industry (hard discs, spintronics, etc.). A detailed understanding of the properties of magnetized surfaces is therefore important to optimize technical applications. In the last decades, different experimental techniques have been developed to probe spin effects in magnetized materials. In this work the spin polarization of electrons emitted during the impact of N 6+ ions on a magnetized Fe surface is investigated. We study potential emission (PE) of electrons as well as secondary electron (SE) production and transport in the target with the help of Monte Carlo (MC) simulations. Spin dependence of electron transfer processes and of transport in the solid are included. Fig. 1 shows the results of our simulation for the energy distribution and spin polarization of emitted electrons in comparison with experimental data of Pfandzelter et al. [1] for the interaction of N 6+ ions with magnetized Fe. Electrons with energies higher than 200 eV are predominantly PE electrons, emitted close to the surface via autoionization (AI), Auger capture (AC) and Auger deexcitation (AD) channels. Low energy electrons are dominated by promoted, autoionized, and secondary electrons. The polarization of above surface electrons is determined by the high of the potential barrier separating projectile and target. At large distances, the barrier drops only slightly below the Fermi edge and enables transitions of electrons from this part of the band structure which has about 50% polarization. These electrons are transferred to high n states feeding promotion and AI processes between high lying states. Electrons emitted by these processes therefore reflect the polarization near the Fermi edge. Close to the surface, the barrier is low enough to allow for electron capture from the entire conduction band. K-Auger electrons are emitted in immediate vicinity of the surface and therefore mirror

Electron Microscopy of Ebola Virus-Infected Cells.

Science.gov (United States)

Noda, Takeshi

2017-01-01

Ebola virus (EBOV) replicates in host cells, where both viral and cellular components show morphological changes during the process of viral replication from entry to budding. These steps in the replication cycle can be studied using electron microscopy (EM), including transmission electron microscopy (TEM) and scanning electron microscopy (SEM), which is one of the most useful methods for visualizing EBOV particles and EBOV-infected cells at the ultrastructural level. This chapter describes conventional methods for EM sample preparation of cultured cells infected with EBOV.

Targeting and molecular imaging of HepG2 cells using surface-functionalized gold nanoparticles

International Nuclear Information System (INIS)

Rathinaraj, Pierson; Lee, Kyubae; Choi, Yuri; Park, Soo-Young; Kwon, Oh Hyeong; Kang, Inn-Kyu

2015-01-01

Mercaptosuccinic acid (M)-conjugated gold nanoparticles (GM) were prepared and characterized by transmission electron microscope and dynamic light scattering. M was used to improve the monodispersity and non-specific intracellular uptake of nanoparticles. Lactobionic acid (L) was subsequently conjugated to the GM to target preferentially HepG2 cells (liver cancer cells) that express asialoglycoprotein receptors (ASGPR) on their membrane surfaces and facilitate the transit of nanoparticles across the cell membrane. The mean size of lactobionic acid-conjugated gold nanoparticle (GL) was approximately 10 ± 0.2 nm. Finally, the Atto 680 dye (A6) was coupled to the nanoparticles to visualize their internalization into HepG2 cells. The interaction of surface-modified gold nanoparticles with HepG2 cells was studied after culturing cells in media containing the GM or L-conjugated GM (GL)

Targeting and molecular imaging of HepG2 cells using surface-functionalized gold nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Rathinaraj, Pierson [Auckland University of Technology, Institute of Biomedical Technologies (New Zealand); Lee, Kyubae; Choi, Yuri; Park, Soo-Young [Kyungpook National University, School of Applied Chemical Engineering, Graduate School (Korea, Republic of); Kwon, Oh Hyeong [Kumoh National Institute of Technology, Department of Polymer Science and Engineering (Korea, Republic of); Kang, Inn-Kyu, E-mail: ikkang@knu.ac.kr [Kyungpook National University, School of Applied Chemical Engineering, Graduate School (Korea, Republic of)

2015-07-15

Mercaptosuccinic acid (M)-conjugated gold nanoparticles (GM) were prepared and characterized by transmission electron microscope and dynamic light scattering. M was used to improve the monodispersity and non-specific intracellular uptake of nanoparticles. Lactobionic acid (L) was subsequently conjugated to the GM to target preferentially HepG2 cells (liver cancer cells) that express asialoglycoprotein receptors (ASGPR) on their membrane surfaces and facilitate the transit of nanoparticles across the cell membrane. The mean size of lactobionic acid-conjugated gold nanoparticle (GL) was approximately 10 ± 0.2 nm. Finally, the Atto 680 dye (A6) was coupled to the nanoparticles to visualize their internalization into HepG2 cells. The interaction of surface-modified gold nanoparticles with HepG2 cells was studied after culturing cells in media containing the GM or L-conjugated GM (GL)

Electronically controllable spoof localized surface plasmons

Science.gov (United States)

Zhou, Yong Jin; Zhang, Chao; Yang, Liu; Xun Xiao, Qian

2017-10-01

Electronically controllable multipolar spoof localized surface plasmons (LSPs) are experimentally demonstrated in the microwave frequencies. It has been shown that half integer order LSPs modes exist on the corrugated ring loaded with a slit, which actually arise from the Fabry-Perot-like resonances. By mounting active components across the slit in the corrugated rings, electronic switchability and tunability of spoof LSPs modes have been accomplished. Both simulated and measured results demonstrate efficient dynamic control of the spoof LSPs. These elements may form the basis of highly integrated programmable plasmonic circuits in microwave and terahertz regimes.

Mapping Carrier Dynamics on Material Surfaces in Space and Time using Scanning Ultrafast Electron Microscopy

KAUST Repository

Sun, Jingya; Adhikari, Aniruddha; Shaheen, Basamat; Yang, Haoze; Mohammed, Omar F.

2016-01-01

Selectively capturing the ultrafast dynamics of charge carriers on materials surfaces and at interfaces is crucial to the design of solar cells and optoelectronic devices. Despite extensive research efforts over the past few decades, information and understanding about surface-dynamical processes, including carrier trapping and recombination remains extremely limited. A key challenge is to selectively map such dynamic processes, a capability that is hitherto impractical by time-resolved laser techniques, which are limited by the laser’s relatively large penetration depth and consequently they record mainly bulk information. Such surface dynamics can only be mapped in real space and time by applying four-dimensional (4D) scanning ultrafast electron microscopy (S-UEM), which records snapshots of materials surfaces with nanometer spatial and sub-picosecond temporal resolutions. In this method, the secondary electron (SE) signal emitted from the sample’s surface is extremely sensitive to the surface dynamics and is detected in real time. In several unique applications, we spatially and temporally visualize the SE energy gain and loss, the charge carrier dynamics on the surface of InGaN nanowires and CdSe single crystals and its powder film. We also provide the mechanisms for the observed dynamics, which will be the foundation for future potential applications of S-UEM to a wide range of studies on material surfaces and device interfaces.

Mapping Carrier Dynamics on Material Surfaces in Space and Time using Scanning Ultrafast Electron Microscopy

KAUST Repository

Sun, Jingya

2016-02-25

Selectively capturing the ultrafast dynamics of charge carriers on materials surfaces and at interfaces is crucial to the design of solar cells and optoelectronic devices. Despite extensive research efforts over the past few decades, information and understanding about surface-dynamical processes, including carrier trapping and recombination remains extremely limited. A key challenge is to selectively map such dynamic processes, a capability that is hitherto impractical by time-resolved laser techniques, which are limited by the laser’s relatively large penetration depth and consequently they record mainly bulk information. Such surface dynamics can only be mapped in real space and time by applying four-dimensional (4D) scanning ultrafast electron microscopy (S-UEM), which records snapshots of materials surfaces with nanometer spatial and sub-picosecond temporal resolutions. In this method, the secondary electron (SE) signal emitted from the sample’s surface is extremely sensitive to the surface dynamics and is detected in real time. In several unique applications, we spatially and temporally visualize the SE energy gain and loss, the charge carrier dynamics on the surface of InGaN nanowires and CdSe single crystals and its powder film. We also provide the mechanisms for the observed dynamics, which will be the foundation for future potential applications of S-UEM to a wide range of studies on material surfaces and device interfaces.

Electron scattering at surfaces and grain boundaries in thin Au films

International Nuclear Information System (INIS)

Henriquez, Ricardo; Flores, Marcos; Moraga, Luis; Kremer, German; González-Fuentes, Claudio; Munoz, Raul C.

2013-01-01

The electron scattering at surfaces and grain boundaries is investigated using polycrystalline Au films deposited onto mica substrates. We vary the three length scales associated with: (i) electron scattering in the bulk, that at temperature T is characterized by the electronic mean free path in the bulk ℓ 0 (T); (ii) electron-surface scattering, that is characterized by the film thickness t; (iii) electron-grain boundary scattering, that is characterized by the mean grain diameter D. We varied independently the film thickness from approximately 50 nm to about 100 nm, and the typical grain size making up the samples from 12 nm to 160 nm. We also varied the scale of length associated with electron scattering in the bulk by measuring the resistivity of each specimen at temperatures T, 4 K 0 (T) by approximately 2 orders of magnitude. Detailed measurements of the grain size distribution as well as surface roughness of each sample were performed with a Scanning Tunnelling Microscope (STM). We compare, for the first time, theoretical predictions with resistivity data employing the two theories available that incorporate the effect of both electron-surface as well as electron-grain boundary scattering acting simultaneously: the theory of A.F. Mayadas and M. Shatzkes, Phys. Rev. 1 1382 (1970) (MS), and that of G. Palasantzas, Phys. Rev. B 58 9685 (1998). We eliminate adjustable parameters from the resistivity data analysis, by using as input the grain size distribution as well as the surface roughness measured with the STM on each sample. The outcome is that both theories provide a fair representation of both the temperature as well as the thickness dependence of the resistivity data, but yet there are marked differences between the resistivity predicted by these theories. In the case of the MS theory, when the average grain diameter D is significantly smaller than ℓ 0 (300) = 37 nm, the electron mean free path in the bulk at 300 K, the effect of electron

Surface sterilization by low energy electron beams

International Nuclear Information System (INIS)

Sekiguchi, Masayuki; Tabei, Masae

1989-01-01

The germicidal effectiveness of low energy electron beams (175 KV) against bacterial cells was investigated. The dry spores of Bacillus pumilus ATCC 27142 and Bacillus globigii ATCC 9372 inoculated on carrier materials and irradiated by gamma rays showed the exponential type of survival curves whereas they showed sigmoidal ones when exposed to low energy electron beams. When similarly irradiated, the wet spores inoculated on membrane filter showed the same survival curves as the dry spores inoculated on carrier materials. The wet vegetative cells of Escherichia coli ATCC 25922 showed exponential curves when exposed to gamma and electron beam irradiation. Low energy electron beams in air showed little differences from nitrogen stream in their germicidal effectiveness against dry spores of B. pumilus. The D values of B. pumilus spores inoculated on metal plates decreased as the amounts of backscattering electrons from the plates increased. There was adequate correlation between the D value (linear region of survival curve), average D value (6D/6) and 1% survival dose and backscattering factor. Depth dose profile and backscatterig dose of low energy electron beams were measured by radiochromic dye film dosimeter (RCD). These figures were not always in accord with the observed germicidal effectiveness against B. pumilus spores because of varying thickness of RCD and spores inoculated on carrier material. The dry spores were very thin and this thinness was useful in evaluating the behavior of low energy electrons. (author)

Cell wall and DNA cosegregation in Bacillus subtilis studied by electron microscope autoradiography

International Nuclear Information System (INIS)

Schlaeppi, J.M.; Schaefer, O.; Karamata, D.

1985-01-01

Cells of a Bacillus subtilis mutant deficient in both major autolytic enzyme activities were continuously labeled in either cell wall or DNA or both cell wall and DNA. After appropriate periods of chase in minimal as well as in rich medium, thin sections of cells were autoradiographed and examined by electron microscopy. The resolution of the method was adequate to distinguish labeled DNA units from cell wall units. The latter, which could be easily identified, were shown to segregate symmetrically, suggesting a zonal mode of new wall insertion. DNA units could also be clearly recognized despite a limited fragmentation; they segregated asymmetrically with respect to the nearest septum. Analysis of cells simultaneously labeled in cell wall and DNA provided clear visual evidence of their regular but asymmetrical cosegregation, confirming a previous report obtained by light microscope autoradiography. In addition to labeled wall units, electron microscopy of thin sections of aligned cells has revealed fibrillar networks of wall material which are frequently associated with the cell surface. Most likely, these structures correspond to wall sloughed off by the turnover mechanism but not yet degraded to filterable or acid-soluble components

Surface properties and microporosity of polyhydroxybutyrate under scanning electron microscopy

International Nuclear Information System (INIS)

Raouf, A.A.; Samsudin, A.R.; Samian, R.; Akool, K.; Abdullah, N.

2004-01-01

This study was designed to investigate the surface properties especially surface porosity of polyhydroxybutyrate (PHB) using scanning electron microscopy. PHB granules were sprinkled on the double-sided sticky tape attached on a SEM aluminium stub and sputtered with gold (10nm thickness) in a Polaron SC515 Coater, following which the samples were placed into the SEM specimen chamber for viewing and recording. Scanning electron micrographs with different magnification of PHB surface revealed multiple pores with different sizes. (Author)

Is there an optimal topographical surface in nano-scale affecting protein adsorption and cell behaviors? Part II

Energy Technology Data Exchange (ETDEWEB)

Wang Huajie, E-mail: wanghuajie972001@163.com; Sun Yuanyuan; Cao Ying, E-mail: caoying1130@sina.com; Wang Kui; Yang Lin [Henan Normal University, College of Chemistry and Environmental Science (China); Zhang Yidong; Zheng Zhi [Xuchang University, Institute of Surface Micro and Nano Materials (China)

2012-05-15

Although nano-structured surfaces exhibit superior biological activities to the smooth or micro-structured surfaces, whether there is an optimal topographical surface in nano-scale affecting protein adsorption and cell behaviors is still controversial. In this study, porous aluminum oxide membranes with different pore sizes ranging from 25 to 120 nm were prepared by the anodic oxidation technique. The surface morphology, topography and wettability were analyzed by scanning electron microscope, atomic force microscope and water contact angle measurement, respectively. The results indicated that the synergistic action of the nano-topography structure and hydrophilic/hydrophobic properties resulted in a highest protein adsorption on the aluminum oxide membrane with 80 nm pore size. Additionally, the morphological, metabolic and cell counting methods showed that cells had different sensitivity to porous aluminum oxide membranes with different surface features. Furthermore, this sensitivity was cell type dependent. The optimal pore size of aluminum oxide membranes for cell growth was 80 nm for PC12 cells and 50 nm for NIH 3T3 cells.

Surface morphology and electronic structure of Ni/Ag(100)

International Nuclear Information System (INIS)

Hite, D. A.; Kizilkaya, O.; Sprunger, P. T.; Howard, M. M.; Ventrice, C. A. Jr.; Geisler, H.; Zehner, D. M.

2000-01-01

The growth morphology and electronic structure of Ni on Ag(100) has been studied with scanning tunneling microscopy (STM) and synchrotron based angle resolved photoemission spectroscopy. At deposition temperatures at or below 300 K, STM reveals Ni cluster growth on the surface along with some subsurface growth. Upon annealing to 420 K, virtually all Ni segregates into the subsurface region forming embedded nanoclusters. The electronic structure of Ni d bands in the unannealed surface shows dispersion only perpendicular to the surface whereas the annealed surface has Ni d bands that exhibit a three-dimensional-like structure. This is a result of the increased Ni d-Ag sp hybridization bonding and increased coordination of the embedded Ni nanoclusters. (c) 2000 American Vacuum Society

Surface plasmon enhanced interfacial electron transfer and resonance Raman, surface-enhanced resonance Raman studies of cytochrome C mutants

Energy Technology Data Exchange (ETDEWEB)

Zheng, Junwei [Iowa State Univ., Ames, IA (United States)

1999-11-08

Surface plasmon resonance was utilized to enhance the electron transfer at silver/solution interfaces. Photoelectrochemical reductions of nitrite, nitrate, and CO₂ were studied on electrochemically roughened silver electrode surfaces. The dependence of the photocurrent on photon energy, applied potential and concentration of nitrite demonstrates that the photoelectrochemical reduction proceeds via photoemission process followed by the capture of hydrated electrons. The excitation of plasmon resonances in nanosized metal structures resulted in the enhancement of the photoemission process. In the case of photoelectrocatalytic reduction of CO₂, large photoelectrocatalytic effect for the reduction of CO₂ was observed in the presence of surface adsorbed methylviologen, which functions as a mediator for the photoexcited electron transfer from silver metal to CO₂ in solution. Photoinduced reduction of microperoxidase-11 adsorbed on roughened silver electrode was also observed and attributed to the direct photoejection of free electrons of silver metal. Surface plasmon assisted electron transfer at nanostructured silver particle surfaces was further determined by EPR method.

Surface electronic transport measurements: A micro multi-point probe approach

DEFF Research Database (Denmark)

Barreto, Lucas

2014-01-01

This work is mostly focused on the study of electronic transport properties of two-dimensional materials, in particular graphene and topological insulators. To study these, we have improved a unique micro multi-point probe instrument used to perform transport measurements. Not only the experimental...... quantities are extracted, such as conductivity, carrier density and carrier mobility. • A method to insulate electrically epitaxial graphene grown on metals, based on a stepwise intercalation methodology, is developed and transport measurements are performed in order to test the insulation. • We show...... a direct measurement of the surface electronic transport on a bulk topological insulator. The surface state conductivity and mobility are obtained. Apart from transport properties, we also investigate the atomic structure of the Bi2Se3(111) surface via surface x-ray diraction and low-energy electron...

Morphology and Differentiation of MG63 Osteoblast Cells on Saliva Contaminated Implant Surfaces

Directory of Open Access Journals (Sweden)

Neda Shams

2015-11-01

Full Text Available Objectives: Osteoblasts are the most important cells in the osseointegration process. Despite years of study on dental Implants, limited studies have discussed the effect of saliva on the adhesion process of osteoblasts to implant surfaces. The aim of this in vitro study was to evaluate the effect of saliva on morphology and differentiation of osteoblasts attached to implant surfaces.Materials and Methods: Twelve Axiom dental implants were divided into two groups. Implants of the case group were placed in containers, containing saliva, for 40 minutes. Then, all the implants were separately stored in a medium containing MG63 human osteoblasts for a week. Cell morphology and differentiation were assessed using a scanning electron microscope and their alkaline phosphatase (ALP activity was determined. The t-test was used to compare the two groups.Results: Scanning electron microscopic observation of osteoblasts revealed round or square cells with fewer and shorter cellular processes in saliva contaminated samples, whereas elongated, fusiform and well-defined cell processes were seen in the control group. ALP level was significantly lower in case compared to control group (P<0.05.Conclusion: Saliva contamination alters osteoblast morphology and differentiation and may subsequently interfere with successful osseointegration. Thus, saliva contamination of bone and implant must be prevented or minimized.

Electronic structure of disordered alloys, surfaces and interfaces

CERN Document Server

Turek, Ilja; Kudrnovský, Josef; Šob, Mojmír; Weinberger, Peter

1997-01-01

At present, there is an increasing interest in the prediction of properties of classical and new materials such as substitutional alloys, their surfaces, and metallic or semiconductor multilayers. A detailed understanding based on a thus of the utmost importance for fu­ microscopic, parameter-free approach is ture developments in solid state physics and materials science. The interrela­ tion between electronic and structural properties at surfaces plays a key role for a microscopic understanding of phenomena as diverse as catalysis, corrosion, chemisorption and crystal growth. Remarkable progress has been made in the past 10-15 years in the understand­ ing of behavior of ideal crystals and their surfaces by relating their properties to the underlying electronic structure as determined from the first principles. Similar studies of complex systems like imperfect surfaces, interfaces, and mul­ tilayered structures seem to be accessible by now. Conventional band-structure methods, however, are of limited use ...

Application of a sawtooth surface to accelerator beam chambers with low electron emission rate

International Nuclear Information System (INIS)

Suetsugu, Y.; Tsuchiya, M.; Nishidono, T.; Kato, N.; Satoh, N.; Endo, S.; Yokoyama, T.

2003-01-01

One of the latest problems in positron or proton accelerators is a single-beam instability due to an electron cloud around the beam. The instability, for an example, causes a beam size blow up of the positron beam and deteriorates the performance of the electron-positron collider. the seed of the electron cloud is the electrons emitted from the surface of the beam chamber, which consists of electrons due to the synchrotron radiation (photoelectrons) and sometimes those multiplied by the multipactoring. Suppressing the electron emission from the surface is, therefore, an essential way to cure the instability. Here a rough surface with a sawtooth structure (sawtooth surface) is proposed to reduce the electron emission from the surface of the beam chamber. A new rolling-tap method is developed for this study to make the sawtooth surface in a circular beam chamber with a length of several meters. The first experiment using a test chamber at a photon beam line of the KEK Photon Factory verifies its validity. The photoelectron emission from the sawtooth surface reduces by one order of magnitude compared to the usual smooth surface. In the second experiment under a bunched positron beam in the KEK B-Factory, however, the electron emission is comparable to that of a smooth surface and the behavior is quite different from the previous one. The reason is that the beam field excites the multipactoring of electrons and the decrease of the photoelectron emission by the sawtooth surface is wiped out. The sawtooth surface will be effective to reduce the electron emission under the situation with external magnetic fields or without strong beam fields where the electron multipactoring hardly occurs

An AES Study of the Room Temperature Surface Conditioning of Technological Metal Surfaces by Electron Irradiation

OpenAIRE

Scheuerlein, C; Hilleret, Noël; Taborelli, M; Brown, A; Baker, M A

2002-01-01

The modifications to technological copper and niobium surfaces induced by 2.5 keV electron irradiation have been investigated in the context of the conditioning process occurring in particle accelerator ultra high vacuum systems. Changes in the elemental surface composition have been found using Scanning Auger Microscopy (SAM) by monitoring the carbon, oxygen and metal Auger peak intensities as a function of electron irradiation in the dose range 10-6 to 10-2 C mm-2. The surface analysis resu...

Using continuous porous silicon gradients to study the influence of surface topography on the behaviour of neuroblastoma cells

International Nuclear Information System (INIS)

Khung, Y.L.; Barritt, G.; Voelcker, N.H.

2008-01-01

The effects of surface topography on cell behaviour are the subject of intense research in cell biology. These effects have so far only been studied using substrate surfaces of discretely different topography. In this paper, we present a new approach to characterise cell growth on porous silicon gradients displaying pore sizes from several thousands to a few nanometers. This widely applicable format has the potential to significantly reduce sample numbers and hence analysis time and cost. Our gradient format was applied here to the culture of neuroblastoma cells in order to determine the effects of topography on cell growth parameters. Cell viability, morphology, length and area were characterised by fluorescence and scanning electron microscopy. We observed a dramatic influence of changes in surface topography on the density and morphology of adherent neuroblastoma cells. For example, pore size regimes where cell attachment is strongly discouraged were identified providing cues for the design of low-fouling surfaces. On pore size regimes more conducive to cell attachment, lateral cell-cell interactions crosslinked the cell layer to the substratum surface, while direct substrate-cell interactions were scarce. Finally, our study revealed that cells were sensitive to nanoscale surface topography with feature sizes of < 20 nm

Electron scattering at surfaces and grain boundaries in thin Au films

Energy Technology Data Exchange (ETDEWEB)

Henriquez, Ricardo [Departamento de Física, Universidad Técnica Federico Santa María, Av. España 1680, Casilla 110-V, Valparaíso (Chile); Flores, Marcos; Moraga, Luis [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Blanco Encalada 2008, Casilla 487-3, Santiago 8370449 (Chile); Kremer, German [Bachillerato, Universidad de Chile, Las Palmeras 3425, Santiago 7800024 (Chile); González-Fuentes, Claudio [Departamento de Física, Universidad Técnica Federico Santa María, Av. España 1680, Casilla 110-V, Valparaíso (Chile); Munoz, Raul C., E-mail: ramunoz@ing.uchile.cl [Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Blanco Encalada 2008, Casilla 487-3, Santiago 8370449 (Chile)

2013-05-15

The electron scattering at surfaces and grain boundaries is investigated using polycrystalline Au films deposited onto mica substrates. We vary the three length scales associated with: (i) electron scattering in the bulk, that at temperature T is characterized by the electronic mean free path in the bulk ℓ{sub 0}(T); (ii) electron-surface scattering, that is characterized by the film thickness t; (iii) electron-grain boundary scattering, that is characterized by the mean grain diameter D. We varied independently the film thickness from approximately 50 nm to about 100 nm, and the typical grain size making up the samples from 12 nm to 160 nm. We also varied the scale of length associated with electron scattering in the bulk by measuring the resistivity of each specimen at temperatures T, 4 K < T < 300 K. Cooling the samples to 4 K increases ℓ{sub 0}(T) by approximately 2 orders of magnitude. Detailed measurements of the grain size distribution as well as surface roughness of each sample were performed with a Scanning Tunnelling Microscope (STM). We compare, for the first time, theoretical predictions with resistivity data employing the two theories available that incorporate the effect of both electron-surface as well as electron-grain boundary scattering acting simultaneously: the theory of A.F. Mayadas and M. Shatzkes, Phys. Rev. 1 1382 (1970) (MS), and that of G. Palasantzas, Phys. Rev. B 58 9685 (1998). We eliminate adjustable parameters from the resistivity data analysis, by using as input the grain size distribution as well as the surface roughness measured with the STM on each sample. The outcome is that both theories provide a fair representation of both the temperature as well as the thickness dependence of the resistivity data, but yet there are marked differences between the resistivity predicted by these theories. In the case of the MS theory, when the average grain diameter D is significantly smaller than ℓ{sub 0}(300) = 37 nm, the electron mean

Ionic liquids influence on the surface properties of electron beam irradiated wood

Energy Technology Data Exchange (ETDEWEB)

Croitoru, Catalin [“Transilvania” University of Brasov, Product Design and Environment Department, 29 Eroilor Str., 500036, Brasov (Romania); Patachia, Silvia, E-mail: st.patachia@unitbv.ro [“Transilvania” University of Brasov, Product Design and Environment Department, 29 Eroilor Str., 500036, Brasov (Romania); Doroftei, Florica; Parparita, Elena; Vasile, Cornelia [“Petru Poni” Institute of Macromolecular Chemistry, Physical Chemistry of Polymers Department, 41A Gr. Ghica Voda Alley, Iasi (Romania)

2014-09-30

Highlights: • Wood veneers impregnated with three imidazolium-based ionic liquids and irradiated with electron beam were studied by FTIR-ATR, SEM/EDX, AFM, contact angle and image analysis. • ILs preserve the surface properties of the wood (surface energy, roughness, color) upon irradiation, in comparison with the reference wood, but the surface composition is changed by treatment with IL-s, mainly with 1-butyl-3-methylimidazolium tetrafluoroborate. • Under electron beam irradiation covalent bonding of the imidazolium moiety to wood determines a higher resistance to water penetration and spreading on the surface. - Abstract: In this paper, the influence of three imidazolium-based ionic liquids (1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate and 1-hexyl-3-methylimidazolium chloride) on the structure and surface properties of sycamore maple (Acer pseudoplatanus) veneers submitted to electron beam irradiation with a dose of 50 kGy has been studied by using Fourier transform infrared spectroscopy, as well as image, scanning electron microscopy/SEM/EDX, atomic force microscopy and contact angle analysis. The experimental results have proven that the studied ionic liquids determine a better preservation of the structural features of wood (cellulose crystallinity index and lignin concentration on the surface) as well as some of surface properties such as surface energy, roughness, color upon irradiation with electron beam, in comparison with the reference wood, but surface composition is changed by treatment with imidazolium-based ionic liquids mainly with 1-butyl-3-methylimidazolium tetrafluoroborate. Also, under electron beam irradiation covalent bonding of the imidazolium moiety to wood determines a higher resistance to water penetration and spreading on the surface.

Controlling the surface photovoltage on WSe2 by surface chemical modification

Science.gov (United States)

Liu, Ro-Ya; Ozawa, Kenichi; Terashima, Naoya; Natsui, Yuto; Feng, Baojie; Ito, Suguru; Chen, Wei-Chuan; Cheng, Cheng-Maw; Yamamoto, Susumu; Kato, Hiroo; Chiang, Tai-Chang; Matsuda, Iwao

2018-05-01

The surface photovoltage (SPV) effect is key to the development of opto-electronic devices such as solar-cells and photo-detectors. For the prototypical transition metal dichalcogenide WSe2, core level and valence band photoemission measurements show that the surface band bending of pristine cleaved surfaces can be readily modified by adsorption with K (an electron donor) or C60 (an electron acceptor). Time-resolved pump-probe photoemission measurements reveal that the SPV for pristine cleaved surfaces is enhanced by K adsorption, but suppressed by C60 adsorption, and yet the SPV relaxation time is substantially shortened in both cases. Evidently, adsorbate-induced electronic states act as electron-hole recombination centers that shorten the carrier lifetime.

Ab initio study of the electron-phonon coupling at the Cr(001) surface

Science.gov (United States)

Peters, L.; Rudenko, A. N.; Katsnelson, M. I.

2018-04-01

It is experimentally well established that the Cr(001) surface exhibits a sharp resonance around the Fermi level. However, there is no consensus about its physical origin. It is proposed to be either due to a single particle dz2 surface state renormalized by electron-phonon coupling or the orbital Kondo effect involving the degenerate dx z/ dy z states. In this paper we examine the electron-phonon coupling of the Cr(001) surface by means of ab-initio calculations in the form of density functional perturbation theory. More precisely, the electron-phonon mass-enhancement factor of the surface layer is investigated for the 3d states. For the majority and minority spin dz2 surface states we find values of 0.19 and 0.16. We show that these calculated electron-phonon mass-enhancement factors are not in agreement with the experimental data even if we use realistic values for the temperature range and surface Debye frequency for the fit of the experimental data. More precisely, then experimentally an electron-phonon mass-enhancement factor of 0.70 ±0.10 is obtained, which is not in agreement with our calculated values of 0.19 and 0.16. Our findings suggest that the experimentally observed resonance at the Cr(001) surface is not due to electron-phonon effects but due to electron-electron correlation effects.

Association of intracellular and synaptic organization in cochlear inner hair cells revealed by 3D electron microscopy

OpenAIRE

Bullen, Anwen; West, Timothy; Moores, Carolyn; Ashmore, Jonathan; Fleck, Roland A.; MacLellan-Gibson, Kirsty; Forge, Andrew

2015-01-01

ABSTRACT The ways in which cell architecture is modelled to meet cell function is a poorly understood facet of cell biology. To address this question, we have studied the cytoarchitecture of a cell with highly specialised organisation, the cochlear inner hair cell (IHC), using multiple hierarchies of three-dimensional (3D) electron microscopy analyses. We show that synaptic terminal distribution on the IHC surface correlates with cell shape, and the distribution of a highly organised network ...

Quasi-one-dimensional electron transport over the surface of a liquid-helium film

International Nuclear Information System (INIS)

Sokolov, Sviatoslav; Studart, Nelson

2003-01-01

Quasi-one-dimensional mobility of surface electrons over a liquid-helium suspended film is studied for a conducting channel. The electron mobility is calculated taking into account the electron scattering by helium atoms in the vapor phase, ripplons, and surface defects of the film substrate both in one-electron regime and in the so-called complete-control limit where the influence of inter-electron collisions on the electron distribution function is taken into account. It is shown that the mobility for low temperatures is dominated by the surface-defect scattering and its temperature dependence is essentially different from that of the electron-ripplon scattering

Theoretical study of the localization of excess electrons at the surface of ice

International Nuclear Information System (INIS)

Hermann, A; Schwerdtfeger, P; Schmidt, W G

2008-01-01

The localization of excess electrons at the basal plane surface of hexagonal ice Ih is investigated theoretically, combining density functional theory (DFT) with a partial self-interaction correction (SIC) scheme, to account for spurious self-interaction effects that artificially delocalize the excess electrons. Starting from energetically favored surface geometries, we find strong localization of excess electrons at surface dangling bonds, in particular for surface adsorbed water monomers and dimers

Investigation of the near-surface electronic structure of Cr(001)

International Nuclear Information System (INIS)

Klebanoff, L.E.; Robey, S.W.; Liu, G.; Shirley, D.A.

1985-01-01

An angle-resolved photoelectron spectroscopy (ARPES) study of Cr(001) near-surface electronic structure is presented. Measurements are reported for energy-band dispersions along the [010] direction parallel to the crystal surface. The periodicity of these band dispersions indicates that the valence electrons experience and self-consistently establish antiferromagnetism in the near-surface layers of Cr(001). We also present highly-surface-sensitive ARPES measurements of the energy-band dispersions along the [001] direction normal to the surface. The results suggest that the surface magnetic moments, which couple ferromagnetically to each other within the surface layer, couple antiferromagnetically to the moments of the atoms in the second layer. Temperature-dependent studies are presented that reveal the persistence of near-surface antiferromagnetic order for temperatures up to 2.5 times the bulk Neel temperature. The temperature dependence of this antiferromagnetic order suggests that its thermal stability derives in part from the stability of the Cr(001) ferromagnetic surface phase

Cell adhesive ability of a biological foam ceramic with surface modification

International Nuclear Information System (INIS)

Zhang Yong; Li Xiaoyu; Feng Fan; Lin Yunfeng; Liao Yunmao; Tian, Weidong; Liu Lei

2008-01-01

Biological foam ceramic is a promising material for tissue engineering scaffold because of its biocompatibility, biodegradation and adequate pores measured from micrometer to nanometers. The aim of this study was to evaluate the adhesion and proliferation of adipose-derived stromal cells (ADSCs) on the biological foam ceramic coated with fibronectin. ADSCs were harvested from SD rats and passaged three times prior to seeding onto biological foam surface modified with fibronectin (50 μg/ml). Scaffold without surface modification served as control. To characterize cellular attachment, cells were incubated on the scaffold for 1 h and 3 h and then the cells attached onto the scaffold were counted. The difference of proliferation was appraised using MTT assay at day 1, 3, 5 and 7 before the cells reached confluence. After 7 days of culture, scanning electron microscope (SEM) was chosen to assess cell morphology and attachment of ADSCs on the biological foam ceramic. Attachment of ADSCs on the biological foam ceramic surface modified with fibronectin at 1 h or 3 h was substantially greater than that in control. MTT assay revealed that ADSCs proliferation tendency of the experimental group was nearly parallel to that of control. SEM view showed that ADSCs in the experimental groups connected more tightly and excreted more collagen than that in control. The coating of fibronectin could improve the cell adhesive ability of biological foam ceramics without evident effect on proliferation

High surface conductivity of Fermi-arc electrons in Weyl semimetals

Science.gov (United States)

Resta, Giacomo; Pi, Shu-Ting; Wan, Xiangang; Savrasov, Sergey Y.

2018-02-01

Weyl semimetals (WSMs), a new type of topological condensed matter, are currently attracting great interest due to their unusual electronic states and intriguing transport properties such as chiral anomaly induced negative magnetoresistance, a semiquantized anomalous Hall effect, and the debated chiral magnetic effect. These systems are close cousins of topological insulators (TIs) which are known for their disorder-tolerant surface states. Similarly, WSMs exhibit unique topologically protected Fermi-arc surface states. Here, we analyze electron-phonon scattering, a primary source of resistivity in metals at finite temperatures, as a function of the shape of the Fermi arc where we find that the impact on surface transport is significantly dependent on the arc curvature and disappears in the limit of a straight arc. Next, we discuss the effect of strong surface disorder on the resistivity by numerically simulating a tight-binding model with the presence of quenched surface vacancies using the coherent potential approximation and Kubo-Greenwood formalism. We find that the limit of a straight arc geometry is remarkably disorder tolerant, producing surface conductivity that is one to two orders of magnitude larger than a comparable setup with surface states of TI. This is primarily attributed to a significantly different hybridization strength of the surface states with the remaining electrons in two systems. Finally, a simulation of the effects of surface vacancies on TaAs is presented, illustrating the disorder tolerance of the topological surface states in a recently discovered WSM material.

Optical and electrical properties of electron-irradiated Cu(In,Ga)Se{sub 2} solar cells

Energy Technology Data Exchange (ETDEWEB)

Hirose, Y.; Warasawa, M. [Department of Electrical Engineering, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda 278-8510 (Japan); Takakura, K. [Department of Information, Communication and Electrical Engineering, Kumamoto National College of Technology, 2659-2 Suya, Koshi, Kumamoto 861-1102 (Japan); Kimura, S. [Department of Electrical Engineering, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda 278-8510 (Japan); Chichibu, S.F. [CANTech, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577 (Japan); Ohyama, H. [Department of Information, Communication and Electrical Engineering, Kumamoto National College of Technology, 2659-2 Suya, Koshi, Kumamoto 861-1102 (Japan); Sugiyama, M., E-mail: mutsumi@rs.noda.tus.ac.jp [Department of Electrical Engineering, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda 278-8510 (Japan)

2011-08-31

The optical and electrical properties of electron-irradiated Cu(In,Ga)Se{sub 2} (CIGS) solar cells and the thin films that composed the CIGS solar cell structure were investigated. The transmittance of indium tin oxide (ITO), ZnO:Al, ZnO:Ga, undoped ZnO, and CdS thin films did not change for a fluence of up to 1.5 x 10{sup 18} cm{sup -2}. However, the resistivity of ZnO:Al and ZnO:Ga, which are generally used as window layers for CIGS solar cells, increased with increasing irradiation fluence. For CIGS thin films, the photoluminescence peak intensity due to Cu-related point defects, which do not significantly affect solar cell performance, increased with increasing electron irradiation. In CIGS solar cells, decreasing J{sub SC} and increasing R{sub s} reflected the influence of irradiated ZnO:Al, and decreasing V{sub OC} and increasing R{sub sh} mainly tended to reflect the pn-interface properties. These results may indicate that the surface ZnO:Al thin film and several heterojunctions tend to degrade easily by electron irradiation as compared with the bulk of semiconductor-composed solar cells.

Dedicated Tool for Irradiation and Electrical Measurement of Large Surface Samples on the Beamline of a 2.5 Mev Pelletron Electron Accelerator: Application to Solar Cells

OpenAIRE

Lefèvre Jérémie; Le Houedec Patrice; Losco Jérôme; Cavani Olivier; Boizot Bruno

2017-01-01

We designed a tool allowing irradiation of large samples over a surface of A5 size dimension by means of a 2.5 MeV Pelletron electron accelerator. in situ electrical measurements (I-V, conductivity, etc.) can also be performed, in the dark or under illumination, to study radiation effects in materials. Irradiations and electrical measurements are achievable over a temperature range from 100 K to 300 K. The setup was initially developed to test real-size triple junction solar cells at low t...

Effects of Titanium Surface Microtopography and Simvastatin on Growth and Osteogenic Differentiation of Human Mesenchymal Stem Cells in Estrogen-Deprived Cell Culture.

Science.gov (United States)

Arpornmaeklong, Premjit; Pripatnanont, Prisana; Chookiatsiri, Chonticha; Tangtrakulwanich, Boonsin

This study aimed to investigate the effects of titanium surface topography and simvastatin on growth and osteogenic differentiation of human bone marrow stromal cells (hBMSCs) in estrogen-deprived (ED) cell culture. Human BMSCs were seeded on cell culture plates, smooth-surface titanium (Ti) disks, and sandblasted with large grits and acid etched (SLA)-surface Ti disks; and subsequently cultured in regular (fetal bovine serum [FBS]), ED, and ED-with 100 nM simvastatin (ED-SIM) culture media for 14 to 21 days. Live/dead cell staining, scanning electron microscope examination, and cell viability assay were performed to determine cell attachment, morphology, and growth. Expression levels of osteoblast-associated genes, Runx2 and bone sialoprotein and levels of alkaline phosphatase (ALP) activity, calcium content, and osteocalcin in culture media were measured to determine osteoblastic differentiation. Expression levels of bone morphogenetic protein-2 (BMP-2) were investigated to examine stimulating effects of simvastatin (n = 4 to 5, mean ± SD). In vitro mineralization was verified by calcein staining. Human BMSCs exhibited different attachment and shapes on smooth and SLA titanium surfaces. Estrogen-deprived cell culture decreased cell attachment and growth, particularly on the SLA titanium surface, but cells were able to grow to reach confluence on day 21 in the ED-osteogenic (OS) culture medium. Promoting effects of the SLA titanium surface in ED-OS were significantly decreased. Simvastatin significantly increased osteogenic differentiation of human BMSCs on the SLA titanium surface in the ED-OS medium, and the promoting effects of simvastatin corresponded with the increasing of BMP-2 gene expression on the SLA titanium surface in ED-OS-SIM culture medium. The ED cell culture model provided a well-defined platform for investigating the effects of hormones and growth factors on cells and titanium surface interaction. Titanium, the SLA surface, and simvastatin

Nonadiabaticity and single-electron transport driven by surface acoustic waves

DEFF Research Database (Denmark)

Flensberg, Karsten; Niu, Q.; Pustilnik, M.

1999-01-01

Single-electron transport driven by surface acoustic waves (SAW) through a narrow constriction, formed in a two-dimensional electron gas, is studied theoretically. Due to long-range Coulomb interaction, the tunneling coupling between the electron gas and the moving minimum of the SAW...

Electron Microscopy of Nanostructures in Cells

DEFF Research Database (Denmark)

Købler, Carsten

with cells is therefore increasingly more relevant from both an engineering and a toxicological viewpoint. My work involves developing and exploring electron microscopy (EM) for imaging nanostructures in cells, for the purpose of understanding nanostructure-cell interactions in terms of their possibilities...... in science and concerns in toxicology. In the present work, EM methods for imaging nanostructure-cell interactions have been explored, and the complex interactions documented and ordered. In particular the usability of the focused ion beam scanning electron microscope (FIB-SEM) was explored. Using EM...... in literature. Furthermore, EM proved valuable as it revealed an unnoticed CNT effect. FIB-SEM helped establish that the effect was linked to eosionophilic crystalline pneumonia (ECP)....

Cell behavior on microparticles with different surface morphology

International Nuclear Information System (INIS)

Huang Sha; Fu Xiaobing

2010-01-01

Microparticles can serve as substrates for cell amplification and deliver the cell aggregation to the site of the defect for tissue regeneration. To develop favorable microparticles for cell delivery application, we fabricated and evaluated three types of microparticles that differ in surface properties. The microparticles with varied surface morphology (smooth, pitted and multicavity) were created from chemically crosslinked gelatin particles that underwent various drying treatments. Three types of microparticles were characterized and assessed in terms of the cell behavior of human keratinocytes and fibroblasts seeded on them. The cells could attach, spread and proliferate on all types of microparticles but spread and populated more slowly on the microparticles with smooth surfaces than on those with pitted or multicavity surfaces. Microparticles with a multicavity surface demonstrated the highest cell attachment and growth rate. Furthermore, cells tested on microparticles with a multicavity surface exhibited better morphology and induced the earlier formation of extracellular-based cell-microparticle aggregation than those on microparticles with other surface morphology (smooth and pitted). Thus, microparticles with a multicavity surface show promise for attachment and proliferation of cells in tissue engineering.

Adsorption and Electronic Structure of Sr and Ag Atoms on Graphite Surfaces: a First-Principles Study

Science.gov (United States)

Luo, Xiao-Feng; Fang, Chao; Li, Xin; Lai, Wen-Sheng; Sun, Li-Feng; Liang, Tong-Xiang

2013-06-01

The adsorption behaviors of radioactive strontium and silver nuclides on the graphite surface in a high-temperature gas-cooled reactor are studied by first-principles theory using generalized gradient approximation (GGA) and local density approximation (LDA) pseudo-potentials. It turns out that Sr prefers to be absorbed at the hollow of the carbon hexagonal cell by 0.54 eV (GGA), while Ag likes to sit right above the carbon atom with an adsorption energy of almost zero (GGA) and 0.45 eV (LDA). Electronic structure analysis reveals that Sr donates its partial electrons of the 4p and 5s states to the graphite substrate, while Ag on graphite is a physical adsorption without any electron transfer.

Magnetoresistance of tungsten thin wafer at the multichannel surface scattering of conduction electrons

International Nuclear Information System (INIS)

Lutsishin, P.P.; Nakhodkin, T.N.

1982-01-01

The magnetoresistance of tungsten thin wafer with the (110) surface was studied at the adsorption of tungsten dioxide. The method of low-energy electron diffraction was used to study the symmetry of ordered surface structures. Using the method of the magnetoresistance measurement the character of the scattering of conduction electrons was investigated. THe dependence of magnetoresistance on the surface concentration of tungsten dioxide correlated w1th the structure of the surface layer of atoms, what was explained with allowance for diffraction of conduction electrons at the metal boundary. The magnetoresistance maximum for the (2x2) structure, which characterised decrease in surface conduction under the conditions of static skin effect, was explained by multichannel mirror reflection with the recombinations of electron and ho.le sections of Fermi Surface

Direct Electron Transfer of Dehydrogenases for Development of 3rd Generation Biosensors and Enzymatic Fuel Cells

Directory of Open Access Journals (Sweden)

Paolo Bollella

2018-04-01

Full Text Available Dehydrogenase based bioelectrocatalysis has been increasingly exploited in recent years in order to develop new bioelectrochemical devices, such as biosensors and biofuel cells, with improved performances. In some cases, dehydrogeases are able to directly exchange electrons with an appropriately designed electrode surface, without the need for an added redox mediator, allowing bioelectrocatalysis based on a direct electron transfer process. In this review we briefly describe the electron transfer mechanism of dehydrogenase enzymes and some of the characteristics required for bioelectrocatalysis reactions via a direct electron transfer mechanism. Special attention is given to cellobiose dehydrogenase and fructose dehydrogenase, which showed efficient direct electron transfer reactions. An overview of the most recent biosensors and biofuel cells based on the two dehydrogenases will be presented. The various strategies to prepare modified electrodes in order to improve the electron transfer properties of the device will be carefully investigated and all analytical parameters will be presented, discussed and compared.

The influence of surface chemistry and topography on the contact guidance of MG63 osteoblast cells.

Science.gov (United States)

Ismail, F S Magdon; Rohanizadeh, R; Atwa, S; Mason, R S; Ruys, A J; Martin, P J; Bendavid, A

2007-05-01

The purpose of the present study was to determine in vitro the effects of different surface topographies and chemistries of commercially pure titanium (cpTi) and diamond-like carbon (DLC) surfaces on osteoblast growth and attachment. Microgrooves (widths of 2, 4, 8 and 10 microm and a depth of 1.5-2 microm) were patterned onto silicon (Si) substrates using microlithography and reactive ion etching. The Si substrates were subsequently vapor coated with either cpTi or DLC coatings. All surfaces were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements. Using the MG63 Osteoblast-Like cell line, we determined cell viability, adhesion, and morphology on different substrates over a 3 day culture period. The results showed cpTi surfaces to be significantly more hydrophilic than DLC for groove sizes larger than 2 microm. Cell contact guidance was observed for all grooved samples in comparison to the unpatterned controls. The cell viability tests indicated a significantly greater cell number for 8 and 10 microm grooves on cpTi surfaces compared to other groove sizes. The cell adhesion study showed that the smaller groove sizes, as well as the unpatterned control groups, displayed better cell adhesion to the substrate.

Backscattering of projectile-bound electrons from solid surfaces

International Nuclear Information System (INIS)

Tobisch, M.; Schosnig, M.; Kroneberger, K.; Kuzel, M.; Maier, R.; Jung, M.; Fiedler, C.; Rothard, H.; Clouvas, A.; Suarez, S.; Groeneveld, K.O.

1994-01-01

The contribution of projectile ionization (PI) to secondary electron emission is studied by collision of H 2 + and H 3 + ions (400 keV/u and 700 keV/u) with carbon, copper and gold targets (600 A). The measured doubly differential intensity distribution shows a peak of lost projectile electrons near - v p . We describe the subtraction of the contribution of target ionization (TI), and compare the remaining electron intensities with a BEA calculation. For solids we observe a strong energy shift of the electron loss peak, which is compared with the influence of electron transport and binding energy. Furthermore, the low energy tail of the electron loss peak indicates the simultaneous occurrence of PI and TI. Finally we discuss the influence of surface conditions and the dependence of the observation angles on the measured electron intensities. (orig.)

Endocytosis of wheat germ agglutinin binding sites from the cell surface into a tubular endosomal network.

Science.gov (United States)

Raub, T J; Koroly, M J; Roberts, R M

1990-04-01

By using fluorescence and electron microscopy, the endocytic pathway encountered by cell surface components after they had bound wheat germ agglutinin (WGA) was visualized. The majority of these components are thought to consist of sialylated glycoproteins (HMWAG) that represent a subpopulation of the total cell surface proteins but most of the externally disposed plasma membrane proteins of the cell. Examination of semi-thin sections by medium- and high-voltage electron microscopy revealed the three-dimensional organization of vesicular and tubular endosomes. Binding of either fluorescein isothiocyanate-, horseradish peroxidase-, or ferritin-conjugated WGA to cells at 4 degrees C showed that the HMWAG were distributed uniformly over the cell surface. Warming of surface-labeled cells to 37 degrees C resulted in the endocytosis of WGA into peripheral endosomes via invagination of regions of both coated and uncoated membrane. The peripheral endosome appeared as isolated complexes comprising a vesicular element (300-400 nm diam.) surrounded by and continuous with tubular cisternae (45-60 nm diam.), which did not interconnect the endosomes. After 30 min or more label also became localized in a network of anastomosing tubules (45-60 nm diam.) that were located in the centrosomal region of the cell. Endocytosed WGA-HMWAG complexes did not become associated with cisternae of the Golgi apparatus, although tubular and vesicular endosomes were noted in the vicinity of the trans-Golgi region. The accumulation of WGA-HMWAG in the endosomes within the centrosomal region was inhibited when cells were incubated at 18 degrees C. None of these compartments contained acid phosphatase activity, a result that is consistent with other data that the HMWAG do not pass through lysosomes initially. The kinetics of labeling were consistent with the interpretation that recycling of most of the WGA binding surface glycoproteins occurred rapidly from early peripheral endosomes followed by the

Electron microscopy study of the microstructure of Ni–W substrate surface

Energy Technology Data Exchange (ETDEWEB)

Ovcharov, A. V.; Karateev, I. A.; Mikhutkin, A. A. [National Research Centre “Kurchatov Institute,” (Russian Federation); Orekhov, A. S. [Russian Academy of Sciences, Shubnikov Institute of Crystallography, Federal Scientific Research Centre “Crystallography and Photonics,” (Russian Federation); Presniakov, M. Yu.; Chernykh, I. A.; Zanaveskin, M. L.; Kovalchuk, M. V.; Vasiliev, A. L., E-mail: a.vasiliev56@gmail.com [National Research Centre “Kurchatov Institute,” (Russian Federation)

2016-11-15

The surface microstructure of Ni–W alloy tapes, which are used as substrates to form films of high-temperature superconductors and photovoltaic devices, has been studied. Several samples of a Ni{sub 95}W{sub 5} tape (Evico) annealed under different conditions were analyzed using scanning electron microscopy, energy-dispersive X-ray microanalysis, electron diffraction, and electron energy-loss spectroscopy. NiWO{sub 4} precipitates are found on the surface of annealed samples. The growth of precipitates at a temperature of 950°C is accompanied by the formation of pores on the surface or under an oxide film. Depressions with a wedge-shaped profile are found at the grain boundaries. Annealing in a reducing atmosphere using a specially prepared chamber allows one to form a surface free of nickel tungstate precipitates.

The role of electron irradiation history in liquid cell transmission electron microscopy

Energy Technology Data Exchange (ETDEWEB)

Moser, Trevor H.; Mehta, Hardeep S.; Park, Chiwoo; Kelly, Ryan T.; Shokuhfar, Tolou; Evans, James E.

2018-04-20

In situ liquid cell transmission electron microscopy (LC-TEM) allows dynamic nanoscale characterization of systems in a hydrated state. Although powerful, this technique remains impaired by issues of repeatability that limit experimental fidelity and hinder the identification and control of some variables underlying observed dynamics. We detail new LC- TEM devices that improve experimental reproducibility by expanding available imaging area and providing a platform for investigating electron flux history on the sample. Irradiation history is an important factor influencing LC-TEM results that has, to this point, been largely qualitatively and not quantitatively described. We use these devices to highlight the role of cumulative electron flux history on samples from both nanoparticle growth and biological imaging experiments and demonstrate capture of time zero, low-dose images on beam-sensitive samples. In particular, the ability to capture pristine images of biological samples, where the acquired image is the first time that the cell experiences significant electron flux, allowed us to determine that nanoparticle movement compared to the cell membrane was a function of cell damage and therefore an artifact rather than visualizing cell dynamics in action. These results highlight just a subset of the new science that is accessible with LC-TEM through the new multiwindow devices with patterned focusing aides.

Diffuse Surface Scattering in the Plasmonic Resonances of Ultralow Electron Density Nanospheres.

Science.gov (United States)

Monreal, R Carmina; Antosiewicz, Tomasz J; Apell, S Peter

2015-05-21

Localized surface plasmon resonances (LSPRs) have recently been identified in extremely diluted electron systems obtained by doping semiconductor quantum dots. Here, we investigate the role that different surface effects, namely, electronic spill-out and diffuse surface scattering, play in the optical properties of these ultralow electron density nanosystems. Diffuse scattering originates from imperfections or roughness at a microscopic scale on the surface. Using an electromagnetic theory that describes this mechanism in conjunction with a dielectric function including the quantum size effect, we find that the LSPRs show an oscillatory behavior in both position and width for large particles and a strong blue shift in energy and an increased width for smaller radii, consistent with recent experimental results for photodoped ZnO nanocrystals. We thus show that the commonly ignored process of diffuse surface scattering is a more important mechanism affecting the plasmonic properties of ultralow electron density nanoparticles than the spill-out effect.

Dissociative electron attachment on surfaces and in bulk media

International Nuclear Information System (INIS)

Fabrikant, Ilya I.

2007-01-01

A theory of dissociative electron attachment to molecules condensed at surfaces and embedded within bulk media is developed. The theory of low-energy electron diffraction is used to obtain the width for electron-molecule resonance scattering in the condensed phase from the width for the gas phase. It is then employed for the calculation of dissociative attachment in the framework of the nonlocal complex potential theory. Specific calculations using the effective mass approximation are carried out for electron attachment to CH 3 Cl and CF 3 Cl molecules physisorbed on the surface of a Kr film. The role of image states and image-potential resonances is analyzed. The results show an increase by several orders of magnitude in the cross section for physisorbed molecules as compared with gas-phase molecules. This is in general agreement with the measured cross sections. However, the position of the peak in the cross section for CH 3 Cl is significantly shifted towards higher energies as compared to experiment [K. Nagesha et al., J. Chem. Phys. 114, 4934 (2001)], and the magnitude of the calculated cross section for CF 3 Cl at the surface is significantly higher than the measured value. Possible reasons for disagreements are analyzed

A surface diffuse scattering model for the mobility of electrons in surface charge coupled devices

International Nuclear Information System (INIS)

Ionescu, M.

1977-01-01

An analytical model for the mobility of electrons in surface charge coupled devices is studied on the basis of the results previously obtained, considering a surface diffuse scattering; the importance of the results obtained for a better understanding of the influence of the fringing field in surface charge coupled devices is discussed. (author)

Biomolecular strategies for cell surface engineering

Science.gov (United States)

Wilson, John Tanner

Islet transplantation has emerged as a promising cell-based therapy for the treatment of diabetes, but its clinical efficacy remains limited by deleterious host responses that underlie islet destruction. In this dissertation, we describe the assembly of ultrathin conformal coatings that confer molecular-level control over the composition and biophysicochemical properties of the islet surface with implications for improving islet engraftment. Significantly, this work provides novel biomolecular strategies for cell surface engineering with broad biomedical and biotechnological applications in cell-based therapeutics and beyond. Encapsulation of cells and tissue offers a rational approach for attenuating deleterious host responses towards transplanted cells, but a need exists to develop cell encapsulation strategies that minimize transplant volume. Towards this end, we endeavored to generate nanothin films of diverse architecture with tunable properties on the extracellular surface of individual pancreatic islets through a process of layer-by-layer (LbL) self assembly. We first describe the formation of poly(ethylene glycol) (PEG)-rich conformal coatings on islets via LbL self assembly of poly(L-lysine)-g-PEG(biotin) and streptavidin. Multilayer thin films conformed to the geometrically and chemically heterogeneous islet surface, and could be assembled without loss of islet viability or function. Significantly, coated islets performed comparably to untreated controls in a murine model of allogenic intraportal islet transplantation, and, to our knowledge, this is the first study to report in vivo survival and function of nanoencapsulated cells or cell aggregates. Based on these findings, we next postulated that structurally similar PLL-g-PEG copolymers comprised of shorter PEG grafts might be used to initiate and propagate the assembly of polyelectrolyte multilayer (PEM) films on pancreatic islets, while simultaneously preserving islet viability. Through control of PLL

A nucleation theory of cell surface capping

International Nuclear Information System (INIS)

Coutsias, E.A.; Wester, M.J.; Perelson, A.S.

1997-01-01

We propose a new theory of cell surface capping based on the principles of nucleation. When antibody interacts with cell surface molecules, the molecules initially form small aggregates called patches that later coalesce into a large aggregate called a cap. While a cap can form by patches being pulled together by action of the cell''s cytoskeleton, in the case of some molecules, disruption of the cytoskeleton does not prevent cap formation. Diffusion of large aggregates on a cell surface is slow, and thus we propose that a cap can form solely through the diffusion of small aggregates containing just one or a few cell surface molecules. Here we consider the extreme case in which single molecules are mobile, but aggregates of all larger sizes are immobile. We show that a set of patches in equilibrium with a open-quotes seaclose quotes of free cell surface molecules can undergo a nucleation-type phase transition in which the largest patch will bind free cell surface molecules, deplete the concentration of such molecules in the open-quotes seaclose quotes and thus cause the other patches to shrink in size. We therefore show that a cap can form without patches having to move, collide with each other, and aggregate

Electron mobility on the surface of liquid Helium: influence of surface level atoms and depopulation of lowest subbands

International Nuclear Information System (INIS)

Grigoriev, P. D.; Dyugaev, A. M.; Lebedeva, E. V.

2008-01-01

The temperature dependence of electron mobility is examined. We calculate the contribution to the electron scattering rate from the surface level atoms (SLAs), proposed in [10]. This contribution is substantial at low temperatures T < 0.5, when the He vapor concentration is exponentially small. We also study the effect of depopulation of the lowest energy subband, which leads to an increase in the electron mobility at high temperature. The results explain certain long-standing discrepancies between the existing theory and experiment on electron mobility on the surface of liquid helium

Pancreatic hormones are expressed on the surfaces of human and rat islet cells through exocytotic sites

DEFF Research Database (Denmark)

Larsson, L I; Hutton, J C; Madsen, O D

1989-01-01

. Electron microscopy reveals the labeling to occur at sites of exocytotic granule release, involving the surfaces of extruded granule cores. The surfaces of islet cells were labeled both by polyclonal and monoclonal antibodies, excluding that receptor-interacting, anti-idiotypic hormone antibodies were...... for these results. It is concluded that the staining reflects interactions between the appropriate antibodies and exocytotic sites of hormone release....

Cell Adhesion on Surface-Functionalized Magnesium.

Science.gov (United States)

Wagener, Victoria; Schilling, Achim; Mainka, Astrid; Hennig, Diana; Gerum, Richard; Kelch, Marie-Luise; Keim, Simon; Fabry, Ben; Virtanen, Sannakaisa

2016-05-18

The biocompatibility of commercially pure magnesium-based (cp Mg) biodegradable implants is compromised of strong hydrogen evolution and surface alkalization due to high initial corrosion rates of cp Mg in the physiological environment. To mitigate this problem, the addition of corrosion-retarding alloying elements or coating of implant surfaces has been suggested. In the following work, we explored the effect of organic coatings on long-term cell growth. cp Mg was coated with aminopropyltriehtoxysilane + vitamin C (AV), carbonyldiimidazole (CDI), or stearic acid (SA). All three coatings have been previously suggested to reduce initial corrosion and to enhance protein adsorption and hence cell adhesion on magnesium surfaces. Endothelial cells (DH1+/+) and osteosarcoma cells (MG63) were cultured on coated samples for up to 20 days. To quantify Mg corrosion, electrochemical impedance spectroscopy (EIS) was measured after 1, 3, and 5 days of cell culture. We also investigated the speed of initial cell spreading after seeding using fluorescently labeled fibroblasts (NIH/3T3). Hydrogen evolution after contact with cell culture medium was markedly decreased on AV- and SA-coated Mg compared to uncoated Mg. These coatings also showed improved cell adhesion and spreading after 24 h of culture comparable to tissue-treated plastic surfaces. On AV-coated cp Mg, a confluent layer of endothelial cells formed after 5 days and remained intact for up to 20 days. Together, these data demonstrate that surface coating with AV is a viable strategy for improving long-term biocompatibility of cp Mg-based implants. EIS measurements confirmed that the presence of a confluent cell layer increased the corrosion resistance.

Electron emission from tungsten surface induced by neon ions

Science.gov (United States)

Xu, Zhongfeng; Zeng, Lixia; Zhao, Yongtao; Cheng, Rui; Zhang, Xiaoan; Ren, Jieru; Zhou, Xianming; Wang, Xing; Lei, Yu; Li, Yongfeng; Yu, Yang; Liu, Xueliang; Xiao, Guoqing; Li, Fuli

2014-04-01

The electron emission from W surface induced by Neq+ has been measured. For the same charge state, the electron yield gradually increases with the projectile velocity. Meanwhile, the effect of the potential energy of projectile has been found obviously. Our results give the critical condition for "trampoline effect".

A scanning Auger electron spectrometer for internal surface analysis of Large Electron Positron 2 superconducting radio-frequency cavities

Science.gov (United States)

Benvenuti, C.; Cosso, R.; Genest, J.; Hauer, M.; Lacarrère, D.; Rijllart, A.; Saban, R.

1996-08-01

A computer-controlled surface analysis instrument, incorporating static Auger electron spectroscopy, scanning Auger mapping, and secondary electron imaging, has been designed and built at CERN to study and characterize the inner surface of superconducting radio-frequency cavities to be installed in the Large Electron Positron collider. A detailed description of the instrument, including the analytical head, the control system, and the vacuum system is presented. Some recent results obtained from the cavities provide examples of the instrument's capabilities.

Cell behavior related to implant surfaces with different microstructure and chemical composition: an in vitro analysis.

Science.gov (United States)

Conserva, Enrico; Lanuti, Anna; Menini, Maria

2010-01-01

This paper reports on an in vitro comparison of osteoblast and mesenchymal stem cell (MSC) adhesion, proliferation, and differentiation related to two different surface treatments applied to the same implant design to determine whether the interaction between cells and implants is influenced by surface structure and chemical composition of the implants. Thirty-nine implants with a sandblasted (SB) surface and 39 implants with a grit-blasted and high-temperature acid-etched (GBAE) surface were used. The implant macrostructures and microstructures were analyzed by high- and low-voltage scanning electron microscopy (SEM) and by stereo-SEM. The surface chemical composition was investigated by energy dispersive analysis and x-ray photoemission spectroscopy. SaOS-2 osteoblasts and human MSCs were used for the evaluation of cell proliferation and alkaline phosphatase enzymatic activity in contact with the two surfaces. The GBAE surface showed fewer contaminants and a very high percentage of titanium (19.7%) compared to the SB surface (14.2%). The two surfaces showed similar mean roughness (Ra), but the depth (Rz) and density (RSm) of the porosity were significantly increased in the GBAE surface. The GBAE surface presented more osteoblast and MSC proliferation than the SB surface. No statistically significant differences in alkaline phosphatase activity were found between surfaces for either cellular line. The GBAE surface showed less surface contaminants and a higher percentage of titanium (19.7%) than the SB surface. The macro/micropore structured design and chemical composition of the GBAE surface allowed greater cell adhesion and proliferation and an earlier cell spreading but did not play an obvious role in in vitro cellular differentiation.

The powerful pulsed electron beam effect on the metallic surfaces

International Nuclear Information System (INIS)

Neklyudov, I.M.; Yuferov, V.B.; Kosik, N.A.; Druj, O.S.; Skibenko, E.I.

2001-01-01

Experimental results of the influence of powerful pulsed electron beams on the surface structure,hardness and corrosion resistance of the Cr18ni10ti steel are presented. The experiments were carried out in the powerful electron accelerators of directional effect VGIK-1 and DIN-2K with an energy up to approx 300 KeV and a power density of 10 9 - 10 11 W/cm 2 for micro- and nanosecond range. The essential influence of the irradiation power density on the material structure was established. Pulsed powerful beam action on metallic surface leads to surface melting,modification of the structure and structure-dependent material properties. The gas emission and mass-spectrometer analysis of the beam-surface interaction were defined

Transmission Electron Microscopy Studies of Electron-Selective Titanium Oxide Contacts in Silicon Solar Cells

KAUST Repository

Ali, Haider; Yang, Xinbo; Weber, Klaus; Schoenfeld, Winston V.; Davis, Kristopher O.

2017-01-01

In this study, the cross-section of electron-selective titanium oxide (TiO2) contacts for n-type crystalline silicon solar cells were investigated by transmission electron microscopy. It was revealed that the excellent cell efficiency of 21

Electronic structure at metal-smiconductor surfaces and interfaces: effects of disorder

International Nuclear Information System (INIS)

Rodrigues, D.E.

1988-01-01

The main concern of this work is the study of the electronic structure at metal and semiconductor surfaces or interfaces, with special emphasis in the effects of disorder and local microstructure upon them. Various factors which determine this structure are presented and those of central importance are identified. A model that allows the efficient and exact calculation of the local density of states at disordered interfaces is described. This model is based on a tight-binding hamiltonian that has enough flexibility so as to allow an adequate description of real solids. The disorder is taken into account by including stochastic perturbations in the diagonal elements of the hamiltonian in a site orbital basis. These perturbations are taken at each layer from a lorentzian probability distribution. An exact expression for the calculation of the local density of states is derived and applied to a model surface built up from a type orbitals arranged in a simple cubic lattice. The effects of disorder on the local densities of states and on the existence of surface Tamm states are studied. The properties of the electronic states with this kind of model of disorder are considered. The self-consistent calculation of the electronic structure of the Si(111) - (1x1) surface is presented. The effects of disorder on the electronic properties such as the work function or the position of surface states within the gap are evaluated. The surface of the metallic compound NiSi 2 is also treated. The first self-consistent calculation of the electronic structure of its (111) surface is presented. The electronic structure of the Si/NiSi 2 (111) interfaces is calculated for the two types of junctions that can be grown experimentally. The origin of the difference between the Schottky barrier heights at both interfaces is discussed. The results are compared with available experimental data. The implications of this calculation on existing theories about the microscopic mechanism that causes

A Particle-In-Cell approach to particle flux shaping with a surface mask

Directory of Open Access Journals (Sweden)

G. Kawamura

2017-08-01

Full Text Available The Particle-In-Cell simulation code PICS has been developed to study plasma in front of a surface with two types of masks, step-type and roof-type. Parameter scans with regard to magnetic field angle, electron density, and mask height were carried out to understand their influence on ion particle flux distribution on a surface. A roof-type mask with a small mask height yields short decay length in the flux distribution which is consistent with that estimated experimentally. A roof-type mask with a large height yields very long decay length and the flux value does not depend on a mask height or an electron density, but rather on a mask length and a biasing voltage of the surface. Mask height also changes the flux distribution apart from the mask because of the shading effect of the mask. Electron density changes the distribution near the mask edge according to the Debye length. Dependence of distribution on parameters are complicated especially for a roof-type mask, and simulation study with various parameters are useful to understand the physical reasons of dependence and also is useful as a tool for experiment studies.

New electron-ion-plasma equipment for modification of materials and products surface

International Nuclear Information System (INIS)

Koval', N.N.

2013-01-01

Electron-ion-plasma treatment of materials and products, including surface clearing and activation, formation surface layers with changed chemical and phase structure, increased hardness and corrosion resistance; deposition of various functional coatings, has received a wide distribution in a science and industry. Widespread methods of ion-plasma modification of material and product surfaces are ion etching and activation, ion-plasma nitriding, arc or magnetron deposition of functional coatings, including nanostructured. The combination of above methods of surface modification allows essentially to improve exploitation properties of treated products and to optimize the characteristics of modified surfaces for concrete final requirements. For the purpose of a combination of various methods of ion-plasma treatment in a single work cycle at Institute of High Current Electronics of SB RAS (IHCE SB RAS) specialized technological equipment 'DUET', 'TRIO' and 'QUADRO' and 'KVINTA' have been developed. This equipment allow generating uniform low-temperature gas plasma at pressures of (0.1-1) Pa with concentration of (10 9 -10 11 ) cm -3 in volume of (0.1-1) m 3 . In the installations consistent realization of several various operations of materials and products treatment in a single work cycle is possible. The operations are preliminary heating and degassing, ion clearing, etching and activation of materials and products surface by plasma of arc discharges; chemicothermal treatment (nitriding) for formation of diffusion layer on a surface of treated sample using plasma of nonself-sustained low-pressure arc discharge; deposition of single- or multilayered superhard (≥40 GPa) nanocrystalline coatings on the basis of pure metals or their compounds (nitrides, carbides, carbonitrides) by the arc plasma-assisted method. For realization of the modes all installations are equipped by original sources of gas and metal plasma. Besides, in

Work function and surface stability of tungsten-based thermionic electron emission cathodes

Science.gov (United States)

Jacobs, Ryan; Morgan, Dane; Booske, John

2017-11-01

Materials that exhibit a low work function and therefore easily emit electrons into vacuum form the basis of electronic devices used in applications ranging from satellite communications to thermionic energy conversion. W-Ba-O is the canonical materials system that functions as the thermionic electron emitter commercially used in a range of high-power electron devices. However, the work functions, surface stability, and kinetic characteristics of a polycrystalline W emitter surface are still not well understood or characterized. In this study, we examined the work function and surface stability of the eight lowest index surfaces of the W-Ba-O system using density functional theory methods. We found that under the typical thermionic cathode operating conditions of high temperature and low oxygen partial pressure, the most stable surface adsorbates are Ba-O species with compositions in the range of Ba0.125O-Ba0.25O per surface W atom, with O passivating all dangling W bonds and Ba creating work function-lowering surface dipoles. Wulff construction analysis reveals that the presence of O and Ba significantly alters the surface energetics and changes the proportions of surface facets present under equilibrium conditions. Analysis of previously published data on W sintering kinetics suggests that fine W particles in the size range of 100-500 nm may be at or near equilibrium during cathode synthesis and thus may exhibit surface orientation fractions well described by the calculated Wulff construction.

Laser surface treatment of polyamide and NiTi alloy and the effects on mesenchymal stem cell response

Science.gov (United States)

Waugh, D. G.; Lawrence, J.; Shukla, P.; Chan, C.; Hussain, I.; Man, H. C.; Smith, G. C.

2015-07-01

Mesenchymal stem cells (MSCs) are known to play important roles in development, post-natal growth, repair, and regeneration of mesenchymal tissues. What is more, surface treatments are widely reported to affect the biomimetic nature of materials. This paper will detail, discuss and compare laser surface treatment of polyamide (Polyamide 6,6), using a 60 W CO2 laser, and NiTi alloy, using a 100 W fiber laser, and the effects of these treatments on mesenchymal stem cell response. The surface morphology and composition of the polyamide and NiTi alloy were studied by scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS), respectively. MSC cell morphology cell counting and viability measurements were done by employing a haemocytometer and MTT colorimetric assay. The success of enhanced adhesion and spreading of the MSCs on each of the laser surface treated samples, when compared to as-received samples, is evidenced in this work.

Investigating the use of in situ liquid cell scanning transmission electron microscopy

Energy Technology Data Exchange (ETDEWEB)

Nguy, Amanda [Iowa State Univ., Ames, IA (United States)

2016-02-19

Engineering nanoparticles with desired shape-dependent properties is the key to many applications in nanotechnology. Although many synthetic procedures exist to produce anisotropic gold nanoparticles, the dynamics of growth are typically unknown or hypothetical. In the case of seed-mediated growth in the presence of DNA into anisotropic nanoparticles, it is not known exactly how DNA directs growth into specific morphologies. A series of preliminary experiments were carried out to contribute to the investigation of the possible mechanism of DNA-mediated growth of gold nanoprisms into gold nanostars using liquid cell scanning transmission electron microscopy (STEM). Imaging in the liquid phase was achieved through the use of a liquid cell platform and liquid cell holder that allow the sample to be contained within a “chip sandwich” between two electron transparent windows. Ex situ growth experiments were performed using Au-T30 NPrisms (30-base thymine oligonucleotide-coated gold nanoprisms) that are expected to grow into gold nanostars. Growth to form these nanostars were imaged using TEM (transmission electron microscopy) and liquid cell STEM (scanning transmission electron microscopy). An attempt to perform in situ growth experiments with the same Au-T30 nanoprisms revealed challenges in obtaining desired morphology results due to the environmental differences within the liquid cell compared to the ex situ environment. Different parameters in the experimental method were explored including fluid line set up, simultaneous and alternating reagent addition, and the effect of different liquid cell volumes to ensure adequate flow of reagents into the liquid cell. Lastly, the binding affinities were compared for T30 and A30 DNA incubated with gold nanoparticles using zeta potential measurements, absorption spectroscopy, and isothermal titration calorimetry (ITC). It was previously reported thymine bases have a lower binding affinity to gold surfaces than adenine

Investigation of the surface current excitation by a relativistic electron electromagnetic field

International Nuclear Information System (INIS)

Naumenko, G; Shevelev, M; Potylitsyn, A; Popov, Yu; Sukhikh, L

2010-01-01

Surface current method and pseudo-photon ones are widely used in the problems of diffraction and transition radiation of relativistic electron in conductive targets. The simple analysis disclosed the contradiction between these methods in respect to the surface current excitation on target surfaces. This contradiction was resolved experimentally by the measurement of a surface current on the upstream and downstream target surfaces in diffraction radiation geometry. The experimental test showed, that no surface current is induced on the target downstream surface under the influence of a relativistic electron electromagnetic field in contrast to the upstream surface. This is important for the understanding of a forward transition and diffraction radiation nature and electromagnetic field evolution in interaction processes.

Electron emission from tungsten surface induced by neon ions

International Nuclear Information System (INIS)

Xu, Zhongfeng; Zeng, Lixia; Zhao, Yongtao; Liu, Xueliang; Xiao, Guoqing; Li, Fuli; Cheng, Rui; Zhang, Xiaoan; Ren, Jieru; Zhou, Xianming; Wang, Xing; Lei, Yu; Li, Yongfeng; Yu, Yang

2014-01-01

The electron emission from W surface induced by Ne q+ has been measured. For the same charge state, the electron yield gradually increases with the projectile velocity. Meanwhile, the effect of the potential energy of projectile has been found obviously. Our results give the critical condition for ''trampoline effect''

Electron emission induced by resonant coherent ion-surface interaction at grazing incidence

International Nuclear Information System (INIS)

Garcia de Abajo, F.J.; Ponce, V.H.; Echenique, P.M.

1992-01-01

A new spectroscopy based on the resonant coherently induced electron loss to the continuum in ion-surface scattering under grazing incidence is proposed. A series of peaks, corresponding to the energy differences determined by the resonant interaction with the rows of atoms in the surface, is predicted to appear in the energy distribution of electrons emitted from electronic states bound to the probe. Calculations for MeV He + ions scattered at a W(001) surface along the left-angle 100 right-angle direction with a glancing angle of 0--2 mrad show a total yield close to 1

Long helical filaments are not seen encircling cells in electron cryotomograms of rod-shaped bacteria

International Nuclear Information System (INIS)

Swulius, Matthew T.; Chen, Songye; Jane Ding, H.; Li, Zhuo; Briegel, Ariane; Pilhofer, Martin; Tocheva, Elitza I.; Lybarger, Suzanne R.; Johnson, Tanya L.; Sandkvist, Maria; Jensen, Grant J.

2011-01-01

Highlights: → No long helical filaments are seen near or along rod-shaped bacterial inner membranes by electron cryo-tomography. → Electron cryo-tomography has the resolution to detect single filaments in vivo. -- Abstract: How rod-shaped bacteria form and maintain their shape is an important question in bacterial cell biology. Results from fluorescent light microscopy have led many to believe that the actin homolog MreB and a number of other proteins form long helical filaments along the inner membrane of the cell. Here we show using electron cryotomography of six different rod-shaped bacterial species, at macromolecular resolution, that no long (>80 nm) helical filaments exist near or along either surface of the inner membrane. We also use correlated cryo-fluorescent light microscopy (cryo-fLM) and electron cryo-tomography (ECT) to identify cytoplasmic bundles of MreB, showing that MreB filaments are detectable by ECT. In light of these results, the structure and function of MreB must be reconsidered: instead of acting as a large, rigid scaffold that localizes cell-wall synthetic machinery, moving MreB complexes may apply tension to growing peptidoglycan strands to ensure their orderly, linear insertion.

Studies on electronic structure of GaN(0001) surface

CERN Document Server

Xie Chang Kun; Xu Fa Qiang; Deng Rui; Liu Feng; Yibulaxin, K

2002-01-01

An electronic structure investigation on GaN(0001) is reported. The authors employ a full-potential linearized augmented plane-wave (FPLAPW) approach to calculate the partial density of state, which is in agreement with previous experimental results. The effects of the Ga3d semi-core levels on the electronic structure of GaN are discussed. The valence-electronic structure of the wurtzite GaN(0001) surface is investigated using synchrotron radiation excited angle-resolved photoemission spectroscopy. The bulk bands dispersion along GAMMA A direction in the Brillouin zones is measured using normal-emission spectra by changing photon-energy. The band structure derived from authors' experimental data is compared well with the results of authors' FPLAPW calculation. Furthermore, off-normal emission spectra are also measured along the GAMMA K and GAMMA M directions. Two surface states are identified, and their dispersions are characterized

The near-surface electron radiation environment of Saturn's moon Mimas

Science.gov (United States)

Nordheim, T. A.; Hand, K. P.; Paranicas, C.; Howett, C. J. A.; Hendrix, A. R.; Jones, G. H.; Coates, A. J.

2017-04-01

Saturn's inner mid-size moons are exposed to a number of external weathering processes, including charged particle bombardment and UV photolysis, as well as deposition of E-ring grains and interplanetary dust. While optical remote sensing observations by several instruments onboard the Cassini spacecraft have revealed a number of weathering patterns across the surfaces of these moons, it is not entirely clear which external process is responsible for which observed weathering pattern. Here we focus on Saturn's moon Mimas and model the effect of energetic electron bombardment across its surface. By using a combination of a guiding center, bounce-averaged charged particle tracing approach and a particle physics code, we investigate how the radiation dose due to energetic electrons is deposited with depth at different locations. We predict a lens-shaped electron energy deposition pattern that extends down to ∼cm depths at low latitudes centered around the apex of the leading hemisphere (90° W). These results are consistent with previous remote sensing observations of a lens-shaped color anomaly observed by the Imaging Science Subsystem (ISS) instrument as well as a thermal inertia anomaly observed by the Visual and Infrared Mapping Spectrometer (VIMS) and the Composite Infrared Spectrometer (CIRS). Our results confirm that these features are produced by MeV electrons that have a penetration depth into the surface comparable to the effective sampling depths of these instruments. On the trailing hemisphere we predict a similar lens-shaped electron energy deposition pattern, whose effects have to date not been observed by the Cassini remote sensing instruments. We suggest that no corresponding lens-shaped weathering pattern has been observed on the trailing hemisphere because of the comparatively short range of lower energy (<1 MeV) electrons into surface ice, as well as competing effects from cold plasma, neutral, and dust bombardment.

Plasma surface modification of poly (L-lactic acid) and poly (lactic-co-glycolic acid) films for improvement of nerve cells adhesion

International Nuclear Information System (INIS)

Khorasani, M.T.; Mirzadeh, H.; Irani, S.

2008-01-01

Radio frequency (RF) plasma treatment in O 2 was applied to modify the surface of poly (L-lactic acid) (PLLA) and poly (D,L-lactic acid-coglycolic acid) (PLGA) as biodegradable polymers. The surface structure, morphology, wettability and surface chemistry of treated films were characterized by water drop contact angle measurement, scanning electron microscope (SEM), optical invert microscope, differential scanning calorimetry (DSC) and ATIR-FTIR spectroscopy. The cell affinity of the oxygen plasma treated film was evaluated by nervous tissue B65 cell culture in stationary conditions. The results showed that the hydrophilicity increased greatly after O 2 plasma treatment. The results showed that improved cell adhesion was attributed to the combination of surface chemistry and surface wettability during plasma treatment. Cell culture results showed that B65 nervous cell attachment and growth on the plasma treated PLLA was much higher than an unmodified sample and PLGA. Surface hydrophilicity and chemical functional groups with high polar component play an important role in enhancing cell attachment and growth

Electronic Structure of the Perylene / Zinc Oxide Interface: A Computational Study of Photoinduced Electron Transfer and Impact of Surface Defects

KAUST Repository

Li, Jingrui

2015-07-29

The electronic properties of dye-sensitized semiconductor surfaces consisting of pery- lene chromophores chemisorbed on zinc oxide via different spacer-anchor groups, have been studied at the density-functional-theory level. The energy distributions of the donor states and the rates of photoinduced electron transfer from dye to surface are predicted. We evaluate in particular the impact of saturated versus unsaturated aliphatic spacer groups inserted between the perylene chromophore and the semiconductor as well as the influence of surface defects on the electron-injection rates.

Electronic Structure of the Perylene / Zinc Oxide Interface: A Computational Study of Photoinduced Electron Transfer and Impact of Surface Defects

KAUST Repository

Li, Jingrui; Li, Hong; Winget, Paul; Bredas, Jean-Luc

2015-01-01

The electronic properties of dye-sensitized semiconductor surfaces consisting of pery- lene chromophores chemisorbed on zinc oxide via different spacer-anchor groups, have been studied at the density-functional-theory level. The energy distributions of the donor states and the rates of photoinduced electron transfer from dye to surface are predicted. We evaluate in particular the impact of saturated versus unsaturated aliphatic spacer groups inserted between the perylene chromophore and the semiconductor as well as the influence of surface defects on the electron-injection rates.

The Effects of Surface Reconstruction and Electron-Positron Correlation on the Annihilation Characteristics of Positrons Trapped at Semiconductor Surfaces

International Nuclear Information System (INIS)

Fazleev, N. G.; Jung, E.; Weiss, A. H.

2009-01-01

Experimental positron annihilation induced Auger electron spectroscopy (PAES) data from Ge(100) and Ge(111) surfaces display several strong Auger peaks corresponding to M 4,5 N 1 N 2,3 , M 2,3 M 4,5 M 4,5 , M 2,3 M 4,5 V, and M 1 M 4,5 M 4,5 Auger transitions. The integrated peak intensities of Auger transitions have been used to obtain experimental annihilation probabilities for the Ge 3d and 3p core electrons. The experimental data were analyzed by performing theoretical studies of the effects of surface reconstructions and electron-positron correlations on image potential induced surface states and annihilation characteristics of positrons trapped at the reconstructed Ge(100) and Ge(111) surfaces. Calculations of positron surface states and annihilation characteristics have been performed for Ge(100) surface with (2x1), (2x2), and (4x2) reconstructions, and for Ge(111) surface with c(2x8) reconstruction. Estimates of the positron binding energy and annihilation characteristics reveal their sensitivity to the specific atomic structure of the topmost layers of the semiconductor and to the approximations used to describe electron-positron correlations. The results of these theoretical studies are compared with the ones obtained for the reconstructed Si(100)-(2x1) and Si(111)-(7x7) surfaces.

Basic Surface Properties of Mononuclear Cells from Didelphis marsupialis

Directory of Open Access Journals (Sweden)

Nacife Valéria Pereira

1998-01-01

Full Text Available The electrostatic surface charge and surface tension of mononuclear cells/monocytes obtained from young and adult marsupials (Didelphis marsupialis were investigated by using cationized ferritin and colloidal iron hydroxyde, whole cell electrophoresis, and measurements of contact angles. Anionic sites were found distributed throughout the entire investigated cell surfaces. The results revealed that the anionic character of the cells is given by electrostatic charges corresponding to -18.8 mV (cells from young animals and -29.3 mV (cells from adult animals. The surface electrostatic charge decreased from 10 to 65.2% after treatment of the cells with each one of trypsin, neuraminidase and phospholipase C. The hydrophobic nature of the mononuclear cell surfaces studied by using the contact angle method revealed that both young and adult cells possess cell surfaces of high hidrofilicity since the angles formed with drops of saline water were 42.5°and 40.8°, respectively. Treatment of the cells with trypsin or neuraminidase rendered their surfaces more hydrophobic, suggesting that sialic acid-containing glycoproteins are responsible for most of the hydrophilicity observed in the mononuclear cell surfaces from D. marsupialis.

Dynamics of electrons and holes at surfaces

International Nuclear Information System (INIS)

Chulkov, E.V.; Leonardo, A.; Sklyadneva, I.Yu.; Silkin, V.M.

2007-01-01

We present ab initio calculation results for electron-phonon (e-ph) contribution to hole lifetime broadening of the X-bar surface state on Al(0 0 1). We show that e-ph coupling in this state is significantly stronger than in bulk Al at the Fermi level. It makes the e-ph decay channel very important in the formation of the hole decay in the surface state at X-bar. We also present the results for e-e lifetime broadening in a quantum-well state in 1 ML K/Cu(1 1 1). We show that this contribution is not negligible and is much larger than that in a surface state on Ag(1 1 1)

Lactoperoxidase catalyzed radioiodination of cell surface immunoglobulin: incorporated radioactivity may not reflect relative cell surface Ig density

International Nuclear Information System (INIS)

Wilder, R.L.; Yuen, C.C.; Mage, R.G.

1979-01-01

Rabbit and mouse splenic lymphocytes were radioiodinated by the lactoperoxidase technique, extracted with non-ionic detergent, immunoprecipitated with high titered rabbit anti-kappa antisera, and compared by SDS-PAGE. Mouse sIg peaks were reproducibly larger in size than rabbit sIg peaks (often greater than 10 times). Neither differences in incorporation of label into the rabbit cell surface, nor differences in average sIg density explain this result. Total TCA-precipitable radioactivity was similar in each species. Estimation of the relative amounts of sIg in the mouse and rabbit showed similar average sIg densities. Differences in detergent solubility, proteolytic lability, or antisera used also do not adequately account for this difference. Thus, these data indicate that radioactivity incorporated after lactoperoxidase catalyzed cell surface radioiodination may not reflect cell surface Ig density. Conclusions about cell surface density based upon relative incorporation of radioactivity should be confirmed by other approaches

Multijunction Solar Cell Technology for Mars Surface Applications

Science.gov (United States)

Stella, Paul M.; Mardesich, Nick; Ewell, Richard C.; Mueller, Robert L.; Endicter, Scott; Aiken, Daniel; Edmondson, Kenneth; Fetze, Chris

2006-01-01

Solar cells used for Mars surface applications have been commercial space qualified AM0 optimized devices. Due to the Martian atmosphere, these cells are not optimized for the Mars surface and as a result operate at a reduced efficiency. A multi-year program, MOST (Mars Optimized Solar Cell Technology), managed by JPL and funded by NASA Code S, was initiated in 2004, to develop tools to modify commercial AM0 cells for the Mars surface solar spectrum and to fabricate Mars optimized devices for verification. This effort required defining the surface incident spectrum, developing an appropriate laboratory solar simulator measurement capability, and to develop and test commercial cells modified for the Mars surface spectrum. This paper discusses the program, including results for the initial modified cells. Simulated Mars surface measurements of MER cells and Phoenix Lander cells (2007 launch) are provided to characterize the performance loss for those missions. In addition, the performance of the MER rover solar arrays is updated to reflect their more than two (2) year operation.

Bio-active molecules modified surfaces enhanced mesenchymal stem cell adhesion and proliferation

International Nuclear Information System (INIS)

Mobasseri, Rezvan; Tian, Lingling; Soleimani, Masoud; Ramakrishna, Seeram; Naderi-Manesh, Hossein

2017-01-01

Surface modification of the substrate as a component of in vitro cell culture and tissue engineering, using bio-active molecules including extracellular matrix (ECM) proteins or peptides derived ECM proteins can modulate the surface properties and thereby induce the desired signaling pathways in cells. The aim of this study was to evaluate the behavior of human bone marrow mesenchymal stem cells (hBM-MSCs) on glass substrates modified with fibronectin (Fn), collagen (Coll), RGD peptides (RGD) and designed peptide (R-pept) as bio-active molecules. The glass coverslips were coated with fibronectin, collagen, RGD peptide and R-peptide. Bone marrow mesenchymal stem cells were cultured on different substrates and the adhesion behavior in early incubation times was investigated using scanning electron microscopy (SEM) and confocal microscopy. The MTT assay was performed to evaluate the effect of different bio-active molecules on MSCs proliferation rate during 24 and 72 h. Formation of filopodia and focal adhesion (FA) complexes, two steps of cell adhesion process, were observed in MSCs cultured on bio-active molecules modified coverslips, specifically in Fn coated and R-pept coated groups. SEM image showed well adhesion pattern for MSCs cultured on Fn and R-pept after 2 h incubation, while the shape of cells cultured on Coll and RGD substrates indicated that they might experience stress condition in early hours of culture. Investigation of adhesion behavior, as well as proliferation pattern, suggests R-peptide as a promising bio-active molecule to be used for surface modification of substrate in supporting and inducing cell adhesion and proliferation. - Highlights: • Bioactive molecules modified surface is a strategy to design biomimicry scaffold. • Bi-functional Tat-derived peptide (R-pept) enhanced MSCs adhesion and proliferation. • R-pept showed similar influences to fibronectin on FA formation and attachment.

Scanning electron microscopic evaluation of root canal surfaces ...

African Journals Online (AJOL)

Scanning electron microscopic evaluation of root canal surfaces prepared with three rotary endodontic systems: Lightspeed, ProTaper and EndoWave. ... fracture with LightSpeed (LS), ProTaper (PT) and EndoWave (Ew) rotary instruments.

Note: Electron energy spectroscopy mapping of surface with scanning tunneling microscope.

Science.gov (United States)

Li, Meng; Xu, Chunkai; Zhang, Panke; Li, Zhean; Chen, Xiangjun

2016-08-01

We report a novel scanning probe electron energy spectrometer (SPEES) which combines a double toroidal analyzer with a scanning tunneling microscope to achieve both topography imaging and electron energy spectroscopy mapping of surface in situ. The spatial resolution of spectroscopy mapping is determined to be better than 0.7 ± 0.2 μm at a tip sample distance of 7 μm. Meanwhile, the size of the field emission electron beam spot on the surface is also measured, and is about 3.6 ± 0.8 μm in diameter. This unambiguously demonstrates that the spatial resolution of SPEES technique can be much better than the size of the incident electron beam.

Note: Electron energy spectroscopy mapping of surface with scanning tunneling microscope

Energy Technology Data Exchange (ETDEWEB)

Li, Meng; Xu, Chunkai, E-mail: xuck@ustc.edu.cn, E-mail: xjun@ustc.edu.cn; Zhang, Panke; Li, Zhean; Chen, Xiangjun, E-mail: xuck@ustc.edu.cn, E-mail: xjun@ustc.edu.cn [Hefei National Laboratory for Physical Science at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026 (China)

2016-08-15

We report a novel scanning probe electron energy spectrometer (SPEES) which combines a double toroidal analyzer with a scanning tunneling microscope to achieve both topography imaging and electron energy spectroscopy mapping of surface in situ. The spatial resolution of spectroscopy mapping is determined to be better than 0.7 ± 0.2 μm at a tip sample distance of 7 μm. Meanwhile, the size of the field emission electron beam spot on the surface is also measured, and is about 3.6 ± 0.8 μm in diameter. This unambiguously demonstrates that the spatial resolution of SPEES technique can be much better than the size of the incident electron beam.

Note: Electron energy spectroscopy mapping of surface with scanning tunneling microscope

International Nuclear Information System (INIS)

Li, Meng; Xu, Chunkai; Zhang, Panke; Li, Zhean; Chen, Xiangjun

2016-01-01

We report a novel scanning probe electron energy spectrometer (SPEES) which combines a double toroidal analyzer with a scanning tunneling microscope to achieve both topography imaging and electron energy spectroscopy mapping of surface in situ. The spatial resolution of spectroscopy mapping is determined to be better than 0.7 ± 0.2 μm at a tip sample distance of 7 μm. Meanwhile, the size of the field emission electron beam spot on the surface is also measured, and is about 3.6 ± 0.8 μm in diameter. This unambiguously demonstrates that the spatial resolution of SPEES technique can be much better than the size of the incident electron beam.

An experimental study of electron transfer and emission during particle-surface interactions

International Nuclear Information System (INIS)

McGrath, C.T.

2000-09-01

A new coincidence technique has been developed and used to study the secondary electron emission that arises during the interaction of ions with surfaces. This coincidence technique allows the secondary electron emission statistics due to the impact of singly, doubly and multiply charged ions on surfaces to be measured in coincidence with reflected particles, in specific charge states and with specific post-collision trajectories. This system has been used to study the impact of 8 keV H + ions on polycrystalline copper and aluminium targets. Under these conditions the potential emission contribution is negligible and the electron emission is almost entirely due to kinetic emission processes. The sub-surface contribution to the observed electron emission has been isolated using two newly developed models. These models provide valuable information about the depth and amount of surface penetration and on the probability for subsequent electron transport to the surface. The impact of 2 - 100 keV Xe q+ (q = 1 - 10) ions on polycrystalline copper has also been studied using this system. From the subsequent data the potential and kinetic contributions to secondary electron emission have been separated using a previously established model for potential emission. The resulting kinetic emission yield increases with increasing ion impact energy, consistent with current concepts on quasimolecular ionisation. For ions impacting at large incident angles evidence for sub-surface emission has also been observed. The degree of penetration increases with ion impact energy, consistent with current concepts on this effect. The formation of H - ions from incident H + ions has also been studied by measuring the secondary electron emission statistics in coincidence with reflected particles in specific final charge states. This preliminary data is consistent with a two-step process of Auger neutralisation followed by resonant electron capture to the affinity level. However this mechanism

Fermi surface properties of paramagnetic NpCd11 with a large unit cell

Science.gov (United States)

Homma, Yoshiya; Aoki, Dai; Haga, Yoshinori; Settai, Rikio; Sakai, Hironori; Ikeda, Shugo; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu; Takeuchi, Tetsuya; Yamagami, Hiroshi; Ōnuki, Yoshichika

2010-03-01

We succeeded in growing a high-quality single crystal of NpCd11 with the cubic BaHg11-type structure by the Cd-self flux method. The lattice parameter of a = 9.2968(2) Å and crystallographic positions of the atoms were determined by x-ray single-crystal structure analysis. From the results of the magnetic susceptibility and specific heat experiments, this compound is found to be a 5f-localized paramagnet with the singlet ground state in the crystalline electric field (CEF) scheme. Fermi surface properties were measured using the de Haas-van Alphen (dHvA) technique. Long-period oscillations were observed in the dHvA frequency range of 9.1 x 105 to 1.9 x 107 Oe, indicating small cross-sectional areas of Fermi surfaces, which is consistent with a small Brillouin zone based on a large unit cell. From the results of dHvA and magnetoresistance experiments, the Fermi surface of NpCd11 is found to consist of many kinds of closed Fermi surfaces and a multiply-connected-like Fermi surface, although the result of energy band calculations based on the 5f-localized Np3+(5f4) configuration reveals the existence of only closed Fermi surfaces. The corresponding cyclotron effective mass is small, ranging from 0.1 to 0.7 m0, which is consistent with a small electronic specific heat coefficient γ ≅ 10mJ/K2·mol, revealing no hybridization between the 5f electrons and conduction electrons.

One-Dimensional Electron Transport Layers for Perovskite Solar Cells

Directory of Open Access Journals (Sweden)

Ujwal K. Thakur

2017-04-01

Full Text Available The electron diffusion length (Ln is smaller than the hole diffusion length (Lp in many halide perovskite semiconductors meaning that the use of ordered one-dimensional (1D structures such as nanowires (NWs and nanotubes (NTs as electron transport layers (ETLs is a promising method of achieving high performance halide perovskite solar cells (HPSCs. ETLs consisting of oriented and aligned NWs and NTs offer the potential not merely for improved directional charge transport but also for the enhanced absorption of incoming light and thermodynamically efficient management of photogenerated carrier populations. The ordered architecture of NW/NT arrays affords superior infiltration of a deposited material making them ideal for use in HPSCs. Photoconversion efficiencies (PCEs as high as 18% have been demonstrated for HPSCs using 1D ETLs. Despite the advantages of 1D ETLs, there are still challenges that need to be overcome to achieve even higher PCEs, such as better methods to eliminate or passivate surface traps, improved understanding of the hetero-interface and optimization of the morphology (i.e., length, diameter, and spacing of NWs/NTs. This review introduces the general considerations of ETLs for HPSCs, deposition techniques used, and the current research and challenges in the field of 1D ETLs for perovskite solar cells.

One-Dimensional Electron Transport Layers for Perovskite Solar Cells

Science.gov (United States)

Thakur, Ujwal K.; Kisslinger, Ryan; Shankar, Karthik

2017-01-01

The electron diffusion length (Ln) is smaller than the hole diffusion length (Lp) in many halide perovskite semiconductors meaning that the use of ordered one-dimensional (1D) structures such as nanowires (NWs) and nanotubes (NTs) as electron transport layers (ETLs) is a promising method of achieving high performance halide perovskite solar cells (HPSCs). ETLs consisting of oriented and aligned NWs and NTs offer the potential not merely for improved directional charge transport but also for the enhanced absorption of incoming light and thermodynamically efficient management of photogenerated carrier populations. The ordered architecture of NW/NT arrays affords superior infiltration of a deposited material making them ideal for use in HPSCs. Photoconversion efficiencies (PCEs) as high as 18% have been demonstrated for HPSCs using 1D ETLs. Despite the advantages of 1D ETLs, there are still challenges that need to be overcome to achieve even higher PCEs, such as better methods to eliminate or passivate surface traps, improved understanding of the hetero-interface and optimization of the morphology (i.e., length, diameter, and spacing of NWs/NTs). This review introduces the general considerations of ETLs for HPSCs, deposition techniques used, and the current research and challenges in the field of 1D ETLs for perovskite solar cells. PMID:28468280

A study of charge transfer kinetics in dye-sensitized surface conductivity solar cells

Energy Technology Data Exchange (ETDEWEB)

Friedrich, Dennis

2011-05-15

The efficiency of the quasi-solid-state dye-sensitized solar cell developed by Junghaenel and Tributsch, the so-called Nano Surface Conductivity Solar Cell (NSCSC), was improved from 2% to 3.5% introducing a compact TiO{sub 2} underlayer, modifying the surface of the mesoporous TiO{sub 2} electrode, optimizing the deposition process of the electrolyte film, and replacing the platinum counter electrode by a carbon layer. Space-resolved photocurrent images revealed the importance of a homogeneous distribution of the electrolyte film. An uneven dispersion led to localized areas of high and low photocurrents, whereas the latter were attributed to an insufficient concentration of the redox couple. Impedance spectroscopy was performed on cells containing different concentrations of the redox couple. By modeling the spectra using an equivalent circuit with a transmission line of resistive and capacitive elements, the characteristic parameters of electron transport in the TiO{sub 2}, such as diffusion length and electron lifetime were obtained. The measurements indicated that the transport of the positive charge to the counter electrode is the main process limiting the efficiency of the cells. Excess charge carrier decay in functioning devices was analyzed by contactless transient photoconductance measurements in the microwave frequency range (TRMC). The lifetime of the photogenerated charge carriers was observed to decrease with increasing applied potential, reaching its maximum close to the opencircuit potential of the cell, where the photocurrent density was minimal, i.e. the potential dependent decay observed was limited by the injection of electrons into the front contact. The functioning of this NSCSC indicated that the transport of the positive charge occurs by solid-state diffusion at the surface of the TiO{sub 2} particles. TRMC measurements on subset devices in the form of sensitized TiO{sub 2} layers revealed charge carrier kinetics strongly dependent on the

Application of positron annihilation induced auger electron spectroscopy to the study of surface chemistry

International Nuclear Information System (INIS)

Weiss, A.H.; Yang, G.; Nangia, A.; Kim, J.H.; Fazleev, N.G.

1996-01-01

Positron annihilation induced Auger Electron Spectroscopy (PAES), makes use a beam of low energy positrons to excite Auger transitions by annihilating core electrons. This novel mechanism provides PAES with a number of unique features which distinguishes it from other methods of surface analysis. In PAES the very large collisionally induced secondary electron background which is present under the low energy Auger peaks using conventional techniques can be eliminated by using a positron beam whose energy is below the range of Auger electron energies. In addition, PAES is more surface selective than conventional Auger Spectroscopy because the PAES signal originates almost exclusively from the topmost atomic layer due to the fact that the positrons annihilating with the core electrons are trapped in an image correlation well just outside the surface. In this paper, recent applications of Positron Annihilation Induced Auger Electron Spectroscopy (PAES) to the study of surface structure and surface chemistry will be discussed including studies of the growth, alloying and inter-diffusion of ultrathin layers of metals, metals on semiconductors, and semiconductors on semiconductors. In addition, the possibilities for future application of PAES to the study of catalysis and surface chemistry will be outlined. (author)

Electron emission from MOS electron emitters with clean and cesium covered gold surface

DEFF Research Database (Denmark)

Nielsen, Gunver; Thomsen, Lasse Bjørchmar; Johansson, Martin

2009-01-01

MOS (metal-oxide-semiconductor) electron emitters consisting of a Si substrate, a SiO2 tunnel barrier and a Ti (1 nm)/Au(7 nm) top-electrode, with an active area of 1 cm(2) have been produced and studied with surface science techniques under UHV (ultra high vacuum) conditions and their emission...... characteristics have been investigated. It is known, that deposition of an alkali metal on the emitting surface lowers the work function and increases the emission efficiency. For increasing Cs coverages the surface has been characterized by X-ray Photoelectron Spectroscopy (XPS), Ion Scattering Spectroscopy (ISS...

Cell Surface Proteome of Dental Pulp Stem Cells Identified by Label-Free Mass Spectrometry.

Directory of Open Access Journals (Sweden)

Christian Niehage

Full Text Available Multipotent mesenchymal stromal cells (MSCs are promising tools for regenerative medicine. They can be isolated from different sources based on their plastic-adherence property. The identification of reliable cell surface markers thus becomes the Holy Grail for their prospective isolation. Here, we determine the cell surface proteomes of human dental pulp-derived MSCs isolated from single donors after culture expansion in low (2% or high (10% serum-containing media. Cell surface proteins were tagged on intact cells using cell impermeable, cleavable sulfo-NHS-SS-biotin, which allows their enrichment by streptavidin pull-down. For the proteomic analyses, we first compared label-free methods to analyze cell surface proteomes i.e. composition, enrichment and proteomic differences, and we developed a new mathematical model to determine cell surface protein enrichment using a combinatorial gene ontology query. Using this workflow, we identified 101 cluster of differentiation (CD markers and 286 non-CD cell surface proteins. Based on this proteome profiling, we identified 14 cell surface proteins, which varied consistently in abundance when cells were cultured under low or high serum conditions. Collectively, our analytical methods provide a basis for identifying the cell surface proteome of dental pulp stem cells isolated from single donors and its evolution during culture or differentiation. Our data provide a comprehensive cell surface proteome for the precise identification of dental pulp-derived MSC populations and their isolation for potential therapeutic intervention.

Motion of cells sedimenting on a solid surface in a laminar shear flow.

Science.gov (United States)

Tissot, O; Pierres, A; Foa, C; Delaage, M; Bongrand, P

1992-01-01

Cell adhesion often occurs under dynamic conditions, as in flowing blood. A quantitative understanding of this process requires accurate knowledge of the topographical relationships between the cell membrane and potentially adhesive surfaces. This report describes an experimental study made on both the translational and rotational velocities of leukocytes sedimenting of a flat surface under laminar shear flow. The main conclusions are as follows: (a) Cells move close to the wall with constant velocity for several tens of seconds. (b) The numerical values of translational and rotational velocities are inconsistent with Goldman's model of a neutrally buoyant sphere in a laminar shear flow, unless a drag force corresponding to contact friction between cells and the chamber floor is added. The phenomenological friction coefficient was 7.4 millinewton.s/m. (c) Using a modified Goldman's theory, the width of the gap separating cells (6 microns radius) from the chamber floor was estimated at 1.4 micron. (d) It is shown that a high value of the cell-to-substrate gap may be accounted for by the presence of cell surface protrusions of a few micrometer length, in accordance with electron microscope observations performed on the same cell population. (e) In association with previously reported data (Tissot, O., C. Foa, C. Capo, H. Brailly, M. Delaage, and P. Bongrand. 1991. Biocolloids and Biosurfaces. In press), these results are consistent with the possibility that cell-substrate attachment be initiated by the formation of a single molecular bond, which might be considered as the rate limiting step.

Interdomain electron transfer in cellobiose dehydrogenase is governed by surface electrostatics.

Science.gov (United States)

Kadek, Alan; Kavan, Daniel; Marcoux, Julien; Stojko, Johann; Felice, Alfons K G; Cianférani, Sarah; Ludwig, Roland; Halada, Petr; Man, Petr

2017-02-01

Cellobiose dehydrogenase (CDH) is a fungal extracellular oxidoreductase which fuels lytic polysaccharide monooxygenase with electrons during cellulose degradation. Interdomain electron transfer between the flavin and cytochrome domain in CDH, preceding the electron flow to lytic polysaccharide monooxygenase, is known to be pH dependent, but the exact mechanism of this regulation has not been experimentally proven so far. To investigate the structural aspects underlying the domain interaction in CDH, hydrogen/deuterium exchange (HDX-MS) with improved proteolytic setup (combination of nepenthesin-1 with rhizopuspepsin), native mass spectrometry with ion mobility and electrostatics calculations were used. HDX-MS revealed pH-dependent changes in solvent accessibility and hydrogen bonding at the interdomain interface. Electrostatics calculations identified these differences to result from charge neutralization by protonation and together with ion mobility pointed at higher electrostatic repulsion between CDH domains at neutral pH. In addition, we uncovered extensive O-glycosylation in the linker region and identified the long-unknown exact cleavage point in papain-mediated domain separation. Transition of CDH between its inactive (open) and interdomain electron transfer-capable (closed) state is shown to be governed by changes in the protein surface electrostatics at the domain interface. Our study confirms that the interdomain electrostatic repulsion is the key factor modulating the functioning of CDH. The results presented in this paper provide experimental evidence for the role of charge repulsion in the interdomain electron transfer in cellobiose dehydrogenases, which is relevant for exploiting their biotechnological potential in biosensors and biofuel cells. Copyright © 2016 Elsevier B.V. All rights reserved.

6 MeV pulsed electron beam induced surface and structural changes in polyimide

Energy Technology Data Exchange (ETDEWEB)

Mathakari, Narendra L.; Bhoraskar, Vasant N. [Microtron Accelerator Laboratory, Department of Physics, University of Pune, Ganeshkhind, Pune 411007, Maharashtra (India); Dhole, Sanjay D., E-mail: sanjay@physics.unipune.ernet.i [Microtron Accelerator Laboratory, Department of Physics, University of Pune, Ganeshkhind, Pune 411007, Maharashtra (India)

2010-04-15

Thin films of polyimide (PMDA-ODA, Kapton) having 50 mum thickness were irradiated with 6 MeV pulsed electron beam. The bulk and surface properties of pristine and irradiated samples were characterized by several techniques such as stress-strain measurements, Fourier Transform Infrared (FTIR), UV-vis spectroscopy, contact angle, atomic force microscopy (AFM) and profilometry. The tensile strength, percentage elongation and strain energy show an enhancement from pristine value of 73-89 MPa, 10-22% and 4.75-14.2 MJ/m{sup 3} respectively at the maximum fluence of 4 x 10{sup 15} electrons/cm{sup 2}. This signifies that polyimide being an excessively aromatic polymer is crosslinked due to high-energy electron irradiation. In surface properties, the contact angle shows a significant decrease from 59 deg. to 32 deg. indicating enhancement in hydrophilicity. This mainly attributes to surface roughening, which is due to the electron beam induced sputtering. The surface roughening is confirmed in AFM and profilometry measurements. The AFM images clearly show that surface roughness increases after electron irradiation. Moreover, the roughness average (R{sub a}) as measured from surface profilograms is found to increase from 0.06 to 0.1. The FTIR and UV-vis spectra do not show noticeable changes as regards to scissioning of bonds and the oxidation. This work leads to a definite conclusion that 6 MeV pulsed electron beam can be used to bring about desired changes in surface as well as bulk properties of polyimide, which is considered to be a high performance space quality polymer.

Copper plasmonics and catalysis: role of electron-phonon interactions in dephasing localized surface plasmons

Science.gov (United States)

Sun, Qi-C.; Ding, Yuchen; Goodman, Samuel M.; H. Funke, Hans; Nagpal, Prashant

2014-10-01

Copper metal can provide an important alternative for the development of efficient, low-cost and low-loss plasmonic nanoparticles, and selective nanocatalysts. However, poor chemical stability and lack of insight into photophysics and plasmon decay mechanisms has impeded study. Here, we use smooth conformal ALD coating on copper nanoparticles to prevent surface oxidation, and study dephasing time for localized surface plasmons on different sized copper nanoparticles. Using dephasing time as a figure of merit, we elucidate the role of electron-electron, electron-phonon, impurity, surface and grain boundary scattering on the decay of localized surface plasmon waves. Using our quantitative analysis and different temperature dependent measurements, we show that electron-phonon interactions dominate over other scattering mechanisms in dephasing plasmon waves. While interband transitions in copper metal contributes substantially to plasmon losses, tuning surface plasmon modes to infrared frequencies leads to a five-fold enhancement in the quality factor. These findings demonstrate that conformal ALD coatings can improve the chemical stability for copper nanoparticles, even at high temperatures (>300 °C) in ambient atmosphere, and nanoscaled copper is a good alternative material for many potential applications in nanophotonics, plasmonics, catalysis and nanoscale electronics.Copper metal can provide an important alternative for the development of efficient, low-cost and low-loss plasmonic nanoparticles, and selective nanocatalysts. However, poor chemical stability and lack of insight into photophysics and plasmon decay mechanisms has impeded study. Here, we use smooth conformal ALD coating on copper nanoparticles to prevent surface oxidation, and study dephasing time for localized surface plasmons on different sized copper nanoparticles. Using dephasing time as a figure of merit, we elucidate the role of electron-electron, electron-phonon, impurity, surface and grain

Effects of QD surface coverage in solid-state PbS quantum dot-sensitized solar cells

KAUST Repository

Roelofs, Katherine E.; Brennan, Thomas P.; Trejo, Orlando; Xu, John; Prinz, Fritz B.; Bent, Stacey F.

2013-01-01

Lead sulfide quantum dots (QDs) were grown in situ on nanoporous TiO 2 by successive ion layer adsorption and reaction (SILAR) and by atomic layer deposition (ALD), to fabricate solid-state quantum-dot sensitized solar cells (QDSSCs). With the ultimate goal of increasing QD surface coverage, this work compares the impact of these two synthetic routes on the light absorption and electrical properties of devices. A higher current density was observed in the SILAR-grown QD devices under reverse bias, as compared to ALD-grown QD devices, attributed to injection problems of the lower-band-gap QDs present in the SILAR-grown QD device. To understand the effects of QD surface coverage on device performance, particularly interfacial recombination, electron lifetimes were measured for varying QD deposition cycles. Electron lifetimes were found to decrease with increasing SILAR cycles, indicating that the expected decrease in recombination between electrons in the TiO2 and holes in the hole-transport material, due to increased QD surface coverage, is not the dominant effect of increased deposition cycles. © 2013 IEEE.

Effects of QD surface coverage in solid-state PbS quantum dot-sensitized solar cells

KAUST Repository

Roelofs, Katherine E.

2013-06-01

Lead sulfide quantum dots (QDs) were grown in situ on nanoporous TiO 2 by successive ion layer adsorption and reaction (SILAR) and by atomic layer deposition (ALD), to fabricate solid-state quantum-dot sensitized solar cells (QDSSCs). With the ultimate goal of increasing QD surface coverage, this work compares the impact of these two synthetic routes on the light absorption and electrical properties of devices. A higher current density was observed in the SILAR-grown QD devices under reverse bias, as compared to ALD-grown QD devices, attributed to injection problems of the lower-band-gap QDs present in the SILAR-grown QD device. To understand the effects of QD surface coverage on device performance, particularly interfacial recombination, electron lifetimes were measured for varying QD deposition cycles. Electron lifetimes were found to decrease with increasing SILAR cycles, indicating that the expected decrease in recombination between electrons in the TiO2 and holes in the hole-transport material, due to increased QD surface coverage, is not the dominant effect of increased deposition cycles. © 2013 IEEE.

Electromagnetic surface waves at the interface of a relativistic electron beam with vacuum

International Nuclear Information System (INIS)

Shoucri, M.M.; Gagne, R.R.J.

1977-01-01

The dispersion relation for electromagnetic surface waves propagating at the interface between a relativistic electron beam and vacuum is derived. The excitation of surface modes in a plasma at rest by a relativistic electron beam is discussed

Surface hardening of 30CrMnSiA steel using continuous electron beam

Science.gov (United States)

Fu, Yulei; Hu, Jing; Shen, Xianfeng; Wang, Yingying; Zhao, Wansheng

2017-11-01

30CrMnSiA high strength low alloy (HSLA) carbon structural steel is typically applied in equipment manufacturing and aerospace industries. In this work, the effects of continuous electron beam treatment on the surface hardening and microstructure modifications of 30CrMnSiA are investigated experimentally via a multi-purpose electron beam machine Pro-beam system. Micro hardness value in the electron beam treated area shows a double to triple increase, from 208 HV0.2 on the base metal to 520 HV0.2 on the irradiated area, while the surface roughness is relatively unchanged. Surface hardening parameters and mechanisms are clarified by investigation of the microstructural modification and the phase transformation both pre and post irradiation. The base metal is composed of ferrite and troostite. After continuous electron beam irradiation, the micro structure of the electron beam hardened area is composed of acicular lower bainite, feathered upper bainite and part of lath martensite. The optimal input energy density for 30CrMnSiA steel in this study is of 2.5 kJ/cm2 to attain the proper hardened depth and peak hardness without the surface quality deterioration. When the input irradiation energy exceeds 2.5 kJ/cm2 the convective mixing of the melted zone will become dominant. In the area with convective mixing, the cooling rate is relatively lower, thus the micro hardness is lower. The surface quality will deteriorate. Chemical composition and surface roughness pre and post electron beam treatment are also compared. The technology discussed give a picture of the potential of electron beam surface treatment for improving service life and reliability of the 30CrMnSiA steel.

Study of Textile Surface Characteristic Modification by Using Electron Beam Radiation

International Nuclear Information System (INIS)

Iswani Gitawati; Rany Saptaaji

2007-01-01

The success of accelerator technology application in various field of industry, medical and pharmacy, environment, agricultural, food increase each year as the increasing of people needs, not excepted for surface treatment of fibers and textiles in textile industry. This writing aim is to asses the application of electron beam accelerator for textile surface treatment on finishing step. Surface treatment was done with electron beam low energy (100 - 500 keV), and because of its low penetration it was suitable used to gain the improvement of chemical, physical and mechanical properties of textile surface such as adhesion, wettability, printability, dyes-intake, crease recovery, wrinkle-resistance, flammability, abrasion resistance, soil and stain release to get better result. Modification of fibers and textiles surface properties on finishing process can be caused by crosslinking, grafting and degradation reactions. The assesment results showed that the greatest impact on commercial application of radiation in textiles were crease recovery and surface modification of wetting properties (soil and stain release). The radiation dose used for those purposes were 5 - 50 kGy. The bach process of graft textiles surface modification before and after irradiation by Co-60 source (gamma energies of 1.33 and 1.17 MeV) and continue process by electron beam were presented. The assesment results were reported in this paper. (author)

Surface analysis by electron spectroscopy. General concepts and applications

International Nuclear Information System (INIS)

Feliu, S.

1993-01-01

An introduction is made to the techniques of electron spectroscopy (XPS and AES) used in the study of surface phenomena. Their theoretical principles, the singular information supplied by these techniques and their basic instrumentation (vacuum systems, excitation sources and electron analysers) are described. A revision of their applications to the Materials Science and the Corrosion Sciences is also made. Author. 44 refs

Enhancing Efficiency of Perovskite Solar Cells via Surface Passivation with Graphene Oxide Interlayer.

Science.gov (United States)

Li, Hao; Tao, Leiming; Huang, Feihong; Sun, Qiang; Zhao, Xiaojuan; Han, Junbo; Shen, Yan; Wang, Mingkui

2017-11-08

Perovskite solar cells have been demonstrated as promising low-cost and highly efficient next-generation solar cells. Enhancing V OC by minimization the interfacial recombination kinetics can further improve device performance. In this work, we for the first time reported on surface passivation of perovskite layers with chemical modified graphene oxides, which act as efficient interlayer to reduce interfacial recombination and enhance hole extraction as well. Our modeling points out that the passivation effect mainly comes from the interaction between functional group (4-fluorophenyl) and under-coordinated Pb ions. The resulting perovskite solar cells achieved high efficient power conversion efficiency of 18.75% with enhanced high open circuit V OC of 1.11 V. Ultrafast spectroscopy, photovoltage/photocurrent transient decay, and electronic impedance spectroscopy characterizations reveal the effective passivation effect and the energy loss mechanism. This work sheds light on the importance of interfacial engineering on the surface of perovskite layers and provides possible ways to improve device efficiency.

Surface Alloying of SUS 321 Chromium-Nickel Steel by an Electron-Plasma Process

Science.gov (United States)

Ivanov, Yu. F.; Teresov, A. D.; Petrikova, E. A.; Krysina, O. V.; Ivanova, O. V.; Shugurov, V. V.; Moskvin, P. V.

2017-07-01

The mechanisms of forming nanostructured, nanophase layers are revealed and analyzed in austenitic steel subjected to surface alloying using an electron-plasma process. Nanostructured, nanophase layers up to 30 μm in thickness were formed by melting of the film/substrate system with an electron beam generated by a SOLO facility (Institute of High Current Electronics, SB RAS), Tomsk), which ensured crystallization and subsequent quenching at the cooling rates within the range 105-108 K/s. The surface was modified with structural stainless steel specimens (SUS 321 steel). The film/substrate system (film thickness 0.5 μm) was formed by a plasma-assisted vacuum-arc process by evaporating a cathode made from a sintered pseudoalloy of the following composition: Zr - 6 at.% Ti - 6 at.% Cu. The film deposition was performed in a QUINTA facility equipped with a PINK hot-cathode plasma source and DI-100 arc evaporators with accelerated cooling of the process cathode, which allowed reducing the size and fraction of the droplet phase in the deposited film. It is found that melting of the film/substrate system (Zr-Ti-Cu)/(SUS 321 steel) using a high-intensity pulsed electron beam followed by the high-rate crystallization is accompanied by the formation of α-iron cellular crystallization structure and precipitation of Cr2Zr, Cr3C2 and TiC particles on the cell boundaries, which as a whole allowed increasing microhardness by a factor of 1.3, Young's modulus - by a factor of 1.2, wear resistance - by a factor of 2.7, while achieving a three-fold reduction in the friction coefficient.

Cell surface of sea urchin micromeres and primary mesenchyme

International Nuclear Information System (INIS)

DeSimone, D.W.

1985-01-01

The cell surface and extracellular matrix (ECM) of the sea urchin embryo were studied during the early morphogenetic events involved in the differentiation of the micromere cell lineage. Sixteen-cell and early cleavage stage blastomeres were isolated and the protein composition of their cell surfaces examined by 125 I-labelling followed by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Micromere-specific cell surface proteins are reported for Arbacia punctulata, Strongylocentrotus droebachiensis, and Strongylocentrotus purpuratus. Cell surface glycoproteins were characterized on the basis of lectin binding specificity with a novel lectin affinity transfer technique. Using this procedure, cell-type specific surface proteins, which are also lectin-binding specific, can be detected. In addition, fluorescein conjugated lectins were microinjected into the blastocoels of living S. drobachiensis and Lytechinus pictus embryos and the patterns of lectin bindings observed by fluorescence microscopy. The evidence presented in this thesis suggests that the differentiation of the primary mesenchyme cells is correlated with changes in the molecular composition of the cell-surface and the ECM

Extremely confined gap surface-plasmon modes excited by electrons

DEFF Research Database (Denmark)

Raza, Søren; Stenger, Nicolas; Pors, Anders Lambertus

2014-01-01

High-spatial and energy resolution electron energy-loss spectroscopy (EELS) can be used for detailed characterization of localized and propagating surface-plasmon excitations in metal nanostructures, giving insight into fundamental physical phenomena and various plasmonic effects. Here, applying...... EELS to ultra-sharp convex grooves in gold, we directly probe extremely confined gap surface-plasmon (GSP) modes excited by swift electrons in nanometre-wide gaps. We reveal the resonance behaviour associated with the excitation of the antisymmetric GSP mode for extremely small gap widths, down to ~5...... mode exploited in plasmonic waveguides with extreme light confinement is a very important factor that should be taken into account in the design of nanoplasmonic circuits and devices....

A theoretical model on surface electronic behavior: Strain effect

International Nuclear Information System (INIS)

Qin, W.G.; Shaw, D.

2009-01-01

Deformation from mechanical loading can affect surface electronic behavior. Surface deformation and electronic behavior can be quantitatively expressed using strain and work function, respectively, and their experimental relationship can be readily determined using the Kelvin probing technique. However, the theoretical correlation between work function and strain has been unclear. This study reports our theoretical exploration, for the first time, of the effect of strain on work function. We propose a simple electrostatic action model by considering the effect of a dislocation on work function of a one-dimensional lattice and further extend this model to the complex conditions for the effect of dislocation density. Based on this model, we established successfully a theoretical correlation between work function and strain.

Measuring surface topography by scanning electron microscopy. II. Analysis of three estimators of surface roughness in second dimension and third dimension.

Science.gov (United States)

Bonetto, Rita Dominga; Ladaga, Juan Luis; Ponz, Ezequiel

2006-04-01

Scanning electron microscopy (SEM) is widely used in surface studies and continuous efforts are carried out in the search of estimators of different surface characteristics. By using the variogram, we developed two of these estimators that were used to characterize the surface roughness from the SEM image texture. One of the estimators is related to the crossover between fractal region at low scale and the periodic region at high scale, whereas the other estimator characterizes the periodic region. In this work, a full study of these estimators and the fractal dimension in two dimensions (2D) and three dimensions (3D) was carried out for emery papers. We show that the obtained fractal dimension with only one image is good enough to characterize the roughness surface because its behavior is similar to those obtained with 3D height data. We show also that the estimator that indicates the crossover is related to the minimum cell size in 2D and to the average particle size in 3D. The other estimator has different values for the three studied emery papers in 2D but it does not have a clear meaning, and these values are similar for those studied samples in 3D. Nevertheless, it indicates the formation tendency of compound cells. The fractal dimension values from the variogram and from an area versus step log-log graph were studied with 3D data. Both methods yield different values corresponding to different information from the samples.

Studies on the polycrystalline silicon/SiO2 stack as front surface field for IBC solar cells by two-dimensional simulations

International Nuclear Information System (INIS)

Jiang Shuai; Jia Rui; Tao Ke; Hou Caixia; Sun Hengchao; Li Yongtao; Yu Zhiyong

2017-01-01

Interdigitated back contact (IBC) solar cells can achieve a very high efficiency due to its less optical losses. But IBC solar cells demand for high quality passivation of the front surface. In this paper, a polycrystalline silicon/SiO 2 stack structure as front surface field to passivate the front surface of IBC solar cells is proposed. The passivation quality of this structure is investigated by two dimensional simulations. Polycrystalline silicon layer and SiO 2 layer are optimized to get the best passivation quality of the IBC solar cell. Simulation results indicate that the doping level of polycrystalline silicon should be high enough to allow a very thin polycrystalline silicon layer to ensure an effective passivation and small optical losses at the same time. The thickness of SiO 2 should be neither too thin nor too thick, and the optimal thickness is 1.2 nm. Furthermore, the lateral transport properties of electrons are investigated, and the simulation results indicate that a high doping level and conductivity of polycrystalline silicon can improve the lateral transportation of electrons and then the cell performance. (paper)

Osteoblast cell response to surface-modified carbon nanotubes

International Nuclear Information System (INIS)

Zhang Faming; Weidmann, Arne; Nebe, J. Barbara; Burkel, Eberhard

2012-01-01

In order to investigate the interaction of cells with modified multi-walled carbon nanotubes (MWCNTs) for their potential biomedical applications, the MWCNTs were chemically modified with carboxylic acid groups (–COOH), polyvinyl alcohol (PVA) polymer and biomimetic apatite on their surfaces. Additionally, human osteoblast MG-63 cells were cultured in the presence of the surface-modified MWCNTs. The metabolic activities of osteoblastic cells, cell proliferation properties, as well as cell morphology were studied. The surface modification of MWCNTs with biomimetic apatite exhibited a significant increase in the cell viability of osteoblasts, up to 67.23%. In the proliferation phases, there were many more cells in the biomimetic apatite-modified MWCNT samples than in the MWCNTs–COOH. There were no obvious changes in cell morphology in osteoblastic MG-63 cells cultured in the presence of these chemically-modified MWCNTs. The surface modification of MWCNTs with apatite achieves an effective enhancement of their biocompatibility.

Photoelectric emission from negative-electron-affinity diamond (111) surfaces: Exciton breakup versus conduction-band emission

International Nuclear Information System (INIS)

Bandis, C.; Pate, B.B.

1995-01-01

We have recently reported that bound electron-hole pairs (Mott-Wannier excitons) are the dominant source of photoelectron emission from specially prepared [''as-polished'' C(111)-(1x1):H] negative-electron-affinity diamond surfaces for near-band-gap excitation up to 0.5 eV above threshold [C. Bandis and B. B. Pate, Phys. Rev. Lett. 74, 777 (1995)]. It was found that photoexcited excitons transport to the surface, break up, and emit their electron. In this paper, we extend the study of exciton-derived emission to include partial yield (constant final-state) analysis as well as angular distribution measurements of the photoelectric emission. In addition, we find that exciton-derived emission does not always dominate. Photoelectric emission properties of the in situ ''rehydrogenated'' (111)-(1x1):H diamond surface are characteristically different than emission observed from the as-polished (111)-(1x1):H surface. The rehydrogenated surface has additional downward band bending as compared to the as-polished surface. In confirmation of the assignment of photoelectric yield to exciton breakup emission, we find a significant enhancement of the total electron yield when the downward band bending of the hydrogenated surface is increased. The functional form of the observed total electron yield demonstrates that, in contrast to the as-polished surface, conduction-band electrons are a significant component of the observed photoelectric yield from the in situ hydrogenated (111)-(1x1):H surface. Furthermore, electron emission characteristics of the rehydrogenated surface confirms our assignment of a Fan phonon-cascade mechanism for thermalization of excitons

A micromachined surface stress sensor with electronic readout

NARCIS (Netherlands)

Carlen, Edwin; Weinberg, M.S.; Zapata, A.M.; Borenstein, J.T.

2008-01-01

A micromachined surface stress sensor has been fabricated and integrated off chip with a low-noise, differential capacitance, electronic readout circuit. The differential capacitance signal is modulated with a high frequency carrier signal, and the output signal is synchronously demodulated and

Effect of MeV Electron Radiation on Europa’s Surface Ice Analogs

Science.gov (United States)

Gudipati, Murthy; Henderson, Bryana; Bateman, Fred

2017-10-01

MeV electrons that impact Europa’s trailing hemisphere and cause both physical and chemical alteration of the surface and near-surface. The trailing hemisphere receives far lower fluxes above 25 MeV as compared with lower energy particles, but can cause significant chemical and physical modifications at these energies. With NASA's planned Europa Clipper mission and a Europa Lander Concept on the horizon, it is critical to understand and quantify the effect of Europa’s radiation environment on the surface and near surface.Electrons penetrate through ice by far the deepest at any given energy compared to protons and ions, making the role of electrons very important to understand. In addition, secondary radiation - Bremsstrahlung, in X-ray wavelengths - is generated during high-energy particle penetration through solids. Secondary X-rays are equally lethal to life and penetrate even deeper than electrons, making the cumulative effect of radiation on damaging organic matter on the near surface of Europa a complex process that could have effects several meters below Europa’s surface. Other physical properties such as coloration could be caused by radiation.In order to quantify this effect under realistic Europa trailing hemisphere conditions, we devised, built, tested, and obtained preliminary results using our ICE-HEART instrument prototype totally funded by JPL’s internal competition funding for Research and Technology Development. Our Ice Chamber for Europa High-Energy Electron And Radiation-Environment Testing (ICE-HEART) operates at ~100 K. We have also implemented a magnet that is used to remove primary electrons subsequent to passing through an ice column, in order to determine the flux of secondary X-radiation and its penetration through ice.Some of the first results from these studies will be presented and their relevance to understand physical and chemical properties of Europa’s trailing hemisphere surface.This work has been carried out at Jet

Mechanobiological Assessment of TMJ Disc Surfaces: Nanoindentation and Transmission Electron Microscopy

Directory of Open Access Journals (Sweden)

Cassandra M. Juran

2015-12-01

Full Text Available Objectives: Temporomandibular disc is a mechanically robust fibrocartilage tissue exhibiting highly elastic compressive, shear, and tensile moduli with structurally dense extracellular matrix that supports functional loading of the joint. The aim of this study was to illustrate structural complexities of the superior and inferior disc surfaces, to demonstrate the robust mechanical ability of the disc as a whole may be due to depth-dependent regional/layered variation, and also to provide characterization data imperative for future tissue engineering efforts focused on restoring function to the joint. Material and Methods: Nanoindentation was used to assess tissue zones in conjunction with detailed Transmission Electron Microscopy to define structural attributes that influence the temporomandibular disc function. Results: The disc architecture adjacent to the superior surface was shown to have three distinct regional segments within the interface layer: 1-a surface peripheral layer; 2-subsurface region; and 3-a layer of helical matrix bundles. The inferior surface displayed an interface layer (20 µm that showed limited cell populations with little depth-dependent structural variation, a stiffer elastic modulus and reduced energy dissipation compared to the superior surface. These data indicate that the primary function of the inferior surface is resistance to compression rather than load distribution during joint motion. Conclusions: These are the first works that demonstrate that the superior central surface of the he temporomandibular disc is structured in depth-dependent isometric layers, each of which provides different mechanical function supporting the bulk tissue’s properties. From a clinical perspective these data have potential to define regions susceptible to fatigue that may translate to diagnostic criteria to better define the stages of dysfunction.

Interaction of Uranium with Bacterial Cell Surfaces: Inferences from Phosphatase-Mediated Uranium Precipitation

Science.gov (United States)

Kulkarni, Sayali; Misra, Chitra Seetharam; Gupta, Alka; Ballal, Anand

2016-01-01

ABSTRACT Deinococcus radiodurans and Escherichia coli expressing either PhoN, a periplasmic acid phosphatase, or PhoK, an extracellular alkaline phosphatase, were evaluated for uranium (U) bioprecipitation under two specific geochemical conditions (GCs): (i) a carbonate-deficient condition at near-neutral pH (GC1), and (ii) a carbonate-abundant condition at alkaline pH (GC2). Transmission electron microscopy revealed that recombinant cells expressing PhoN/PhoK formed cell-associated uranyl phosphate precipitate under GC1, whereas the same cells displayed extracellular precipitation under GC2. These results implied that the cell-bound or extracellular location of the precipitate was governed by the uranyl species prevalent at that particular GC, rather than the location of phosphatase. MINTEQ modeling predicted the formation of predominantly positively charged uranium hydroxide ions under GC1 and negatively charged uranyl carbonate-hydroxide complexes under GC2. Both microbes adsorbed 6- to 10-fold more U under GC1 than under GC2, suggesting that higher biosorption of U to the bacterial cell surface under GC1 may lead to cell-associated U precipitation. In contrast, at alkaline pH and in the presence of excess carbonate under GC2, poor biosorption of negatively charged uranyl carbonate complexes on the cell surface might have resulted in extracellular precipitation. The toxicity of U observed under GC1 being higher than that under GC2 could also be attributed to the preferential adsorption of U on cell surfaces under GC1. This work provides a vivid description of the interaction of U complexes with bacterial cells. The findings have implications for the toxicity of various U species and for developing biological aqueous effluent waste treatment strategies. IMPORTANCE The present study provides illustrative insights into the interaction of uranium (U) complexes with recombinant bacterial cells overexpressing phosphatases. This work demonstrates the effects of aqueous

Surface modification of steels and magnesium alloy by high current pulsed electron beam

Science.gov (United States)

Hao, Shengzhi; Gao, Bo; Wu, Aimin; Zou, Jianxin; Qin, Ying; Dong, Chuang; An, Jian; Guan, Qingfeng

2005-11-01

High current pulsed electron beam (HCPEB) is now developing as a useful tool for surface modification of materials. When concentrated electron flux transferring its energy into a very thin surface layer within a short pulse time, superfast processes such as heating, melting, evaporation and consequent solidification, as well as dynamic stress induced may impart the surface layer with improved physico-chemical and mechanical properties. This paper presents our research work on surface modification of steels and magnesium alloy with HCPEB of working parameters as electron energy 27 keV, pulse duration ∼1 μs and energy density ∼2.2 J/cm2 per pulse. Investigations performed on carbon steel T8, mold steel D2 and magnesium alloy AZ91HP have shown that the most pronounced changes of phase-structure state and properties occurring in the near-surface layers, while the thickness of the modified layer with improved microhardness (several hundreds of micrometers) is significantly greater than that of the heat-affected zone. The formation mechanisms of surface cratering and non-stationary hardening effect in depth are discussed based on the elucidation of non-equilibrium temperature filed and different kinds of stresses formed during pulsed electron beam melting treatment. After the pulsed electron beam treatments, samples show significant improvements in measurements of wear and corrosion resistance.

Surface modification of steels and magnesium alloy by high current pulsed electron beam

International Nuclear Information System (INIS)

Hao, Shengzhi; Gao, Bo; Wu, Aimin; Zou, Jianxin; Qin, Ying; Dong, Chuang; An, Jian; Guan, Qingfeng

2005-01-01

High current pulsed electron beam (HCPEB) is now developing as a useful tool for surface modification of materials. When concentrated electron flux transferring its energy into a very thin surface layer within a short pulse time, superfast processes such as heating, melting, evaporation and consequent solidification, as well as dynamic stress induced may impart the surface layer with improved physico-chemical and mechanical properties. This paper presents our research work on surface modification of steels and magnesium alloy with HCPEB of working parameters as electron energy 27 keV, pulse duration ∼1 μs and energy density ∼2.2 J/cm 2 per pulse. Investigations performed on carbon steel T8, mold steel D2 and magnesium alloy AZ91HP have shown that the most pronounced changes of phase-structure state and properties occurring in the near-surface layers, while the thickness of the modified layer with improved microhardness (several hundreds of micrometers) is significantly greater than that of the heat-affected zone. The formation mechanisms of surface cratering and non-stationary hardening effect in depth are discussed based on the elucidation of non-equilibrium temperature filed and different kinds of stresses formed during pulsed electron beam melting treatment. After the pulsed electron beam treatments, samples show significant improvements in measurements of wear and corrosion resistance

Dye-Sensitized Solar Cells Based on High Surface Area Nanocrystalline Zinc Oxide Spheres

Directory of Open Access Journals (Sweden)

Pavuluri Srinivasu

2011-01-01

Full Text Available High surface area nanocrystalline zinc oxide material is fabricated using mesoporous nanostructured carbon as a sacrificial template through combustion process. The resulting material is characterized by XRD, N2 adsorption, HR-SEM, and HR-TEM. The nitrogen adsorption measurement indicates that the materials possess BET specific surface area ca. 30 m2/g. Electron microscopy images prove that the zinc oxide spheres possess particle size in the range of 0.12 μm–0.17 μm. The nanocrystalline zinc oxide spheres show 1.0% of energy conversion efficiency for dye-sensitized solar cells.

Lateral propagation of fast electrons at the laser-irradiated target surfaces

International Nuclear Information System (INIS)

Li, Y T; Lin, X X; Liu, B C; Du, F; Wang, S J; Li, C; Zhou, M L; Zhang, L; Liu, X; Wang, J; Liu, X L; Chen, L M; Wang, Z H; Ma, J L; Wei, Z Y; Zhang, J; Liu, F; Liu, F

2010-01-01

Lateral propagation of fast electrons at the target surfaces irradiated by femtosecond intense laser pulses is measured by k α x-ray imaging technique when a preplasma is presented. An annular halo surrounding a bright spot is observed in the x-ray images when the scale length of the electron density is large. For an incidence angle of 70 0 the x-ray images show a non-symmetrical distribution peaked to the laser propagation direction. The x-ray photons in the halo are mainly excited by the fast electrons that flow in the preplasma when their paths intersect the high density regions near the target surface.

The role of surface charge on the uptake and biocompatibility of hydroxyapatite nanoparticles with osteoblast cells

Energy Technology Data Exchange (ETDEWEB)

Chen Liang; Mccrate, Joseph M; Li Hao [Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO 65211 (United States); Lee, James C-M, E-mail: liha@missouri.edu [Department of Biological Engineering, University of Missouri, Columbia, MO 65211 (United States)

2011-03-11

The objective of this study is to evaluate the effect of hydroxyapatite (HAP) nanoparticles with different surface charges on the cellular uptake behavior and in vitro cell viability and proliferation of MC3T3-E1 cell lines (osteoblast). The nanoparticles' surface charge was varied by surface modification with two carboxylic acids: 12-aminododecanoic acid (positive) and dodecanedioic acid (negative). The untreated HAP nanoparticles and dodecanoic acid modified HAP nanoparticles (neutral) were used as the control. X-ray diffraction (XRD) revealed that surface modifications by the three carboxylic acids did not change the crystal structure of HAP nanoparticles; Fourier transform infrared spectroscopy (FT-IR) confirmed the adsorption and binding of the carboxylic acids on the HAP nanoparticles' surfaces; and zeta potential measurement confirmed that the chemicals successfully modified the surface charge of HAP nanoparticles in water based solution. Transmission electron microscopy (TEM) images showed that positively charged, negatively charged and untreated HAP nanoparticles, with similar size and shape, all penetrated into the cells and cells had more uptake of HAP nanoparticles with positive charge compared to those with negative charge, which might be attributed to the attractive or repulsive interaction between the negatively charged cell membrane and positively/negatively charged HAP nanoparticles. The neutral HAP nanoparticles could not penetrate the cell membrane due to their larger size. MTT assay and LDH assay results indicated that as compared with the polystyrene control, greater cell viability and cell proliferation were measured on MC3T3-E1 cells treated with the three kinds of HAP nanoparticles (neutral, positive, and untreated), among which positively charged HAP nanoparticles showed the strongest improvement for cell viability and cell proliferation. In summary, the surface charge of HAP nanoparticles can be modified to influence the cellular

The role of surface charge on the uptake and biocompatibility of hydroxyapatite nanoparticles with osteoblast cells

International Nuclear Information System (INIS)

Chen Liang; Mccrate, Joseph M; Li Hao; Lee, James C-M

2011-01-01

The objective of this study is to evaluate the effect of hydroxyapatite (HAP) nanoparticles with different surface charges on the cellular uptake behavior and in vitro cell viability and proliferation of MC3T3-E1 cell lines (osteoblast). The nanoparticles' surface charge was varied by surface modification with two carboxylic acids: 12-aminododecanoic acid (positive) and dodecanedioic acid (negative). The untreated HAP nanoparticles and dodecanoic acid modified HAP nanoparticles (neutral) were used as the control. X-ray diffraction (XRD) revealed that surface modifications by the three carboxylic acids did not change the crystal structure of HAP nanoparticles; Fourier transform infrared spectroscopy (FT-IR) confirmed the adsorption and binding of the carboxylic acids on the HAP nanoparticles' surfaces; and zeta potential measurement confirmed that the chemicals successfully modified the surface charge of HAP nanoparticles in water based solution. Transmission electron microscopy (TEM) images showed that positively charged, negatively charged and untreated HAP nanoparticles, with similar size and shape, all penetrated into the cells and cells had more uptake of HAP nanoparticles with positive charge compared to those with negative charge, which might be attributed to the attractive or repulsive interaction between the negatively charged cell membrane and positively/negatively charged HAP nanoparticles. The neutral HAP nanoparticles could not penetrate the cell membrane due to their larger size. MTT assay and LDH assay results indicated that as compared with the polystyrene control, greater cell viability and cell proliferation were measured on MC3T3-E1 cells treated with the three kinds of HAP nanoparticles (neutral, positive, and untreated), among which positively charged HAP nanoparticles showed the strongest improvement for cell viability and cell proliferation. In summary, the surface charge of HAP nanoparticles can be modified to influence the cellular uptake of

Surface chemistry and electronic structure of nonpolar and polar GaN films

Energy Technology Data Exchange (ETDEWEB)

Mishra, Monu; Krishna, T.C. Shibin; Aggarwal, Neha; Gupta, Govind, E-mail: govind@nplindia.org

2015-08-01

Highlights: • Surface chemistry and electronic structure of polar and nonpolar GaN is reported. • Influence of polarization on electron affinity of p & np GaN films is investigated. • Correlation between surface morphology and polarity has been deduced. - Abstract: Photoemission and microscopic analysis of nonpolar (a-GaN/r-Sapphire) and polar (c-GaN/c-Sapphire) epitaxial gallium nitride (GaN) films grown via RF-Molecular Beam Epitaxy is reported. The effect of polarization on surface properties like surface states, electronic structure, chemical bonding and morphology has been investigated and correlated. It was observed that polarization lead to shifts in core level (CL) as well as valence band (VB) spectra. Angle dependent X-ray Photoelectron Spectroscopic analysis revealed higher surface oxide in polar GaN film compared to nonpolar GaN film. On varying the take off angle (TOA) from 0° to 60°, the Ga−O/Ga−N ratio varied from 0.11–0.23 for nonpolar and 0.17–0.36 for polar GaN film. The nonpolar film exhibited N-face polarity while Ga-face polarity was perceived in polar GaN film due to the inherent polarization effect. Polarization charge compensated surface states were observed on the polar GaN film and resulted in downward band bending. Ultraviolet photoelectron spectroscopic measurements revealed electron affinity and ionization energy of 3.4 ± 0.1 eV and 6.8 ± 0.1 eV for nonpolar GaN film and 3.8 ± 0.1 eV and 7.2 ± 0.1 eV for polar GaN film respectively. Field Emission Scanning Electron Microscopy measurements divulged smooth morphology with pits on polar GaN film. The nonpolar film on the other hand showed pyramidal structures having facets all over the surface.

Scanning tunnelling microscope imaging of nanoscale electron density gradients on the surface of GaAs

International Nuclear Information System (INIS)

Hamilton, B; Jacobs, J; Missous, M

2003-01-01

This paper is concerned with the scanning tunnelling microscope tunnelling conditions needed to produce constant current images dominated either by surface topology or by electronic effects. A model experimental structure was produced by cleaving a GaAs multiδ-doped layer in UHV and so projecting a spatially varying electron gas density onto the (110) surface. This cross sectional electron density varies on a nanometre scale in the [100] growth direction. The electronic structure and tunnelling properties of this system were modelled, and the tunnelling conditions favouring sensitivity to the surface electron gas density determined

Electron beam induced Hg desorption and the electronic structure of the Hg depleted surface of Hg1/sub -//sub x/Cd/sub x/Te

International Nuclear Information System (INIS)

Shih, C.K.; Friedman, D.J.; Bertness, K.A.; Lindau, I.; Spicer, W.E.; Wilson, J.A.

1986-01-01

Auger electron spectroscopy (AES), x-ray photoemission spectroscopy (XPS), low energy electron diffraction (LEED), and angle-resolved ultraviolet photoemission spectroscopy (ARPES) were used to study the electron beam induced Hg desorption from a cleaved (110)Hg/sub 1-//sub x/Cd/sub x/Te surface and the electronic structure of the Hg depleted surface. Solid state recrystallized Hg/sub 1-//sub x/Cd/sub x/Te single crystals were used. It was found that the electron beam heating dominated the electron beam induced Hg desorption on Hg/sub 1-//sub x/Cd/sub x/Te. At the electron beam energy used, the electron beam heating extended several thousand angstroms deep. However, the Hg depletion saturated after a few monolayers were depleted of Hg atoms. At the initial stage of Hg loss (only 3%), the surface band bends upward (more p type). The ARPES spectrum showed the loss of some E vs k dispersion after 22% Hg atoms were removed from the surface region, and no dispersion was observed after 43% Hg atoms were removed. These results have important implications on the electronic structure of the surfaces and interfaces of which the stoichiometry is altered

Response of cells on surface-induced nanopatterns: fibroblasts and mesenchymal progenitor cells.

Science.gov (United States)

Khor, Hwei Ling; Kuan, Yujun; Kukula, Hildegard; Tamada, Kaoru; Knoll, Wolfgang; Moeller, Martin; Hutmacher, Dietmar W

2007-05-01

Ultrathin films of a poly(styrene)-block-poly(2-vinylpyrindine) diblock copolymer (PS-b-P2VP) and poly(styrene)-block-poly(4-vinylpyrindine) diblock copolymer (PS-b-P4VP) were used to form surface-induced nanopattern (SINPAT) on mica. Surface interaction controlled microphase separation led to the formation of chemically heterogeneous surface nanopatterns on dry ultrathin films. Two distinct nanopatterned surfaces, namely, wormlike and dotlike patterns, were used to investigate the influence of topography in the nanometer range on cell adhesion, proliferation, and migration. Atomic force microscopy was used to confirm that SINPAT was stable under cell culture conditions. Fibroblasts and mesenchymal progenitor cells were cultured on the nanopatterned surfaces. Phase contrast and confocal laser microscopy showed that fibroblasts and mesenchymal progenitor cells preferred the densely spaced wormlike patterns. Atomic force microscopy showed that the cells remodelled the extracellular matrix differently as they migrate over the two distinctly different nanopatterns.

Defect and structural imperfection effects on the electronic properties of BiTeI surfaces

International Nuclear Information System (INIS)

Fiedler, Sebastian; Seibel, Christoph; Lutz, Peter; Bentmann, Hendrik; Reinert, Friedrich; El-Kareh, Lydia; Bode, Matthias; Eremeev, Sergey V; Tereshchenko, Oleg E; Kokh, Konstantin A; Chulkov, Evgueni V; Kuznetsova, Tatyana V; Grebennikov, Vladimir I

2014-01-01

The surface electronic structure of the narrow-gap seminconductor BiTeI exhibits a large Rashba-splitting which strongly depends on the surface termination. Here we report on a detailed investigation of the surface morphology and electronic properties of cleaved BiTeI single crystals by scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), electron diffraction (SPA-LEED) and density functional theory calculations. Our measurements confirm a previously reported coexistence of Te- and I-terminated surface areas originating from bulk stacking faults and find a characteristic length scale of ∼100 nm for these areas. We show that the two terminations exhibit distinct types of atomic defects in the surface and subsurface layers. For electronic states resided on the I terminations we observe an energy shift depending on the time after cleavage. This aging effect is successfully mimicked by depositon of Cs adatoms found to accumulate on top of the I terminations. As shown theoretically on a microscopic scale, this preferential adsorbing behaviour results from considerably different energetics and surface diffusion lengths at the two terminations. Our investigations provide insight into the importance of structural imperfections as well as intrinsic and extrinsic defects on the electronic properties of BiTeI surfaces and their temporal stability. (paper)

Energy filtering transmission electron microscopy immunocytochemistry and antigen retrieval of surface layer proteins from Tannerella forsythensis using microwave or autoclave heating with citraconic anhydride

Science.gov (United States)

2012-01-01

Tannerella forsythensis (Bacteroides forsythus), an anaerobic Gram-negative species of bacteria that plays a role in the progression of periodontal disease, has a unique bacterial protein profile. It is characterized by two unique protein bands with molecular weights of more than 200 kDa. It also is known to have a typical surface layer (S-layer) consisting of regularly arrayed subunits outside the outer membrane. We examined the relationship between high molecular weight proteins and the S-layer using electron microscopic immunolabeling with chemical fixation and an antigen retrieval procedure consisting of heating in a microwave oven or autoclave with citraconic anhydride. Immunogold particles were localized clearly at the outermost cell surface. We also used energy-filtering transmission electron microscopy (EFTEM) to visualize 3, 3′-diaminobenzidine tetrahydrochloride (DAB) reaction products after microwave antigen retrieval with 1% citraconic anhydride. The three-window method for electron spectroscopic images (ESI) of nitrogen by the EFTEM reflected the presence of moieties demonstrated by the DAB reaction with horseradish peroxidase (HRP)-conjugated secondary antibodies instead of immunogold particles. The mapping patterns of net nitrogen were restricted to the outermost cell surface. PMID:22984898

Electron emission and energy loss in grazing collisions of protons with insulator surfaces

International Nuclear Information System (INIS)

Gravielle, M. S.; Miraglia, J. E.; Aldazabal, I.; Arnau, A.; Ponce, V. H.; Aumayr, F.; Lederer, S.; Winter, H.

2007-01-01

Electron emission from LiF, KCl, and KI crystal surfaces during grazing collisions of swift protons is studied using a first-order distorted-wave formalism. Owing to the localized character of the electronic structure of these surfaces, we propose a model that allows us to describe the process as a sequence of atomic transitions from different target ions. Experimental results are presented for electron emission from LiF and KI and energy loss from KI surfaces. Calculations show reasonable agreement with these experimental data. The role played by the charge of the incident particle is also investigated

Pheochromocytoma (PC12 Cell Response on Mechanobactericidal Titanium Surfaces

Directory of Open Access Journals (Sweden)

Jason V. Wandiyanto

2018-04-01

Full Text Available Titanium is a biocompatible material that is frequently used for making implantable medical devices. Nanoengineering of the surface is the common method for increasing material biocompatibility, and while the nanostructured materials are well-known to represent attractive substrata for eukaryotic cells, very little information has been documented about the interaction between mammalian cells and bactericidal nanostructured surfaces. In this study, we investigated the effect of bactericidal titanium nanostructures on PC12 cell attachment and differentiation—a cell line which has become a widely used in vitro model to study neuronal differentiation. The effects of the nanostructures on the cells were then compared to effects observed when the cells were placed in contact with non-structured titanium. It was found that bactericidal nanostructured surfaces enhanced the attachment of neuron-like cells. In addition, the PC12 cells were able to differentiate on nanostructured surfaces, while the cells on non-structured surfaces were not able to do so. These promising results demonstrate the potential application of bactericidal nanostructured surfaces in biomedical applications such as cochlear and neuronal implants.

High resolution surface scanning of Thick-GEM for single photo-electron detection

International Nuclear Information System (INIS)

Hamar, G.; Varga, D.

2012-01-01

An optical system for high resolution scanning of TGEM UV photon detection systems is introduced. The structure exploits the combination of a single Au-coated TGEM under study, and an asymmetric MWPC (Close Cathode Chamber) as post-amplification stage. A pulsed UV LED source with emission down to 240 nm has been focused to a spot of 0.07 mm on the TGEM surface, and single photo-electron charge spectra has been recorded over selected two dimensional regions. This way, the TGEM gain (order of 10–100) and TGEM photo-electron detection efficiency is clearly separated, unlike in case of continuous illumination. The surface structure connected to the TGEM photon detection is well observable, including inefficiencies in the holes and at the symmetry points between holes. The detection efficiency as well as the gas gain are fluctuating from hole to hole. The gain is constant in the hexagon around any hole, pointing to the fact that the gain depends on hole geometry, and less on the position where the electron enters. The detection probability map strongly changes with the field strength above the TGEM surface, in relation to the change of the actual surface field configuration. The results can be confronted with position-dependent simulations of TGEM electron transfer and gas multiplication. -- Highlights: ► First demonstration of Thick GEM surface scanning with single photo-electrons. ► Resolution of 0.1 mm is sufficient to identify structures connected to TGEM surface field structure. ► Gain and detection efficiency and separately measurable. ► Detection efficiency is high in a ring around the holes, and gain is constant in the hexagonal collection regions.

Surface science analysis of GaAs photocathodes following sustained electron beam delivery

Directory of Open Access Journals (Sweden)

V. Shutthanandan

2012-06-01

Full Text Available Degradation of the photocathode materials employed in photoinjectors represents a challenge for sustained operation of nuclear physics accelerators and high power free electron lasers (FEL. Photocathode quantum efficiency degradation is due to residual gases in the electron source vacuum system being ionized and accelerated back to the photocathode. These investigations are a first attempt to characterize the nature of the photocathode degradation, and employ multiple surface and bulk analysis techniques to investigate damage mechanisms including sputtering of the Cs-oxidant surface monolayer, other surface chemistry effects, and ion implantation. Surface and bulk analysis studies were conducted on two GaAs photocathodes, which were removed from the JLab FEL DC photoemission gun after delivering electron beam, and two control samples. The analysis techniques include helium ion microscopy, Rutherford backscattering spectrometry (RBS, atomic force microscopy, and secondary ion mass spectrometry (SIMS. In addition, two high-polarization strained superlattice GaAs photocathode samples, one removed from the continuous electron beam accelerator facility (CEBAF photoinjector and one unused, were also analyzed using transmission electron microscopy (TEM and SIMS. It was found that heat cleaning the FEL GaAs wafer introduces surface roughness, which seems to be reduced by prolonged use. The bulk GaAs samples retained a fairly well organized crystalline structure after delivering beam but show evidence of Cs depletion on the surface. Within the precision of the SIMS and RBS measurements, the data showed no indication of hydrogen implantation or lattice damage from ion back bombardment in the bulk GaAs wafers. In contrast, SIMS and TEM measurements of the strained superlattice photocathode show clear crystal damage in the wafer from ion back bombardment.

Chemical formation of palladium-free surface-nickelized polyimide film for flexible electronics

International Nuclear Information System (INIS)

Hsiao, Y.-S.; Whang, W.-T.; Wu, S.-C.; Chuang, Kuen-Ru

2008-01-01

Flexible polyimide (PI) films for flexible electronics were surface-nickelized using a fully solution-based process and excellent adhesion between the nickel and polyimide phases was observed. Polyimide substrates were modified by alkaline hydrolysis, ion exchange, reduction and nickel electroless deposition without palladium. Atomic force microscopy and field emission scanning electron microscopy were used to follow the growth of nickel nanoparticles (Ni-NPs) and nickel layers on the polyimide surface. The surface resistances of the Ni-NPs/PI films and Ni/PI films, measured using a four-point probe, were 1.6 x 10 7 and 0.83 Ω/cm 2 , respectively. The thicknesses of Ni-NPs and the Ni layer on the polyimide surface were 82 nm and 382 nm, respectively, as determined by transmission electron microscopy, and the Ni layer adhered well to PI, as determined by the adhesive tape testing method

Polymer Solar Cells with Efficiency >10% Enabled via a Facile Solution-Processed Al-Doped ZnO Electron Transporting Layer

KAUST Repository

Jagadamma, Lethy Krishnan; Al-Senani, Mohammed; El Labban, Abdulrahman; Gereige, Issam; Ngongang Ndjawa, Guy Olivier; Faria, Jorge C D; Kim, Taesoo; Zhao, Kui; Cruciani, Federico; Anjum, Dalaver H.; McLachlan, Martyn A.; Beaujuge, Pierre; Amassian, Aram

2015-01-01

/reduces the native defects by nitrogen incorporation, making them good electron transporters and energetically matched with the fullerene acceptor. It is demonstrated that highly efficient solar cells can be achieved without the need for additional surface chemical

Mechanisms of electron transport and recombination in ZnO nanostructures for dye-sensitized solar cells.

Science.gov (United States)

Vega-Poot, Alberto G; Macías-Montero, Manuel; Idígoras, Jesus; Borrás, Ana; Barranco, Angel; Gonzalez-Elipe, Agustín R; Lizama-Tzec, Francisco I; Oskam, Gerko; Anta, Juan A

2014-04-14

ZnO is an attractive material for applications in dye-sensitized solar cells and related devices. This material has excellent electron-transport properties in the bulk but its electron diffusion coefficient is much smaller in mesoporous films. In this work the electron-transport properties of two different kinds of dye-sensitized ZnO nanostructures are investigated by small-perturbation electrochemical techniques. For nanoparticulate ZnO photoanodes prepared via a wet-chemistry technique, the diffusion coefficient is found to reproduce the typical behavior predicted by the multiple-trapping and the hopping models, with an exponential increase with respect to the applied bias. In contrast, in ZnO nanostructured thin films of controlled texture and crystallinity prepared via a plasma chemical vapor deposition method, the diffusion coefficient is found to be independent of the electrochemical bias. This observation suggests a different transport mechanism not controlled by trapping and electron accumulation. In spite of the quite different transport features, the recombination kinetics, the electron-collection efficiency and the photoconversion efficiency are very similar for both kinds of photoanodes, an observation that indicates that surface properties rather than electron transport is the main efficiency-determining factor in solar cells based on ZnO nanostructured photoanodes. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Separating Bulk and Surface Contributions to Electronic Excited-State Processes in Hybrid Mixed Perovskite Thin Films via Multimodal All-Optical Imaging.

Science.gov (United States)

Simpson, Mary Jane; Doughty, Benjamin; Das, Sanjib; Xiao, Kai; Ma, Ying-Zhong

2017-07-20

A comprehensive understanding of electronic excited-state phenomena underlying the impressive performance of solution-processed hybrid halide perovskite solar cells requires access to both spatially resolved electronic processes and corresponding sample morphological characteristics. Here, we demonstrate an all-optical multimodal imaging approach that enables us to obtain both electronic excited-state and morphological information on a single optical microscope platform with simultaneous high temporal and spatial resolution. Specifically, images were acquired for the same region of interest in thin films of chloride containing mixed lead halide perovskites (CH 3 NH 3 PbI 3-x Cl x ) using femtosecond transient absorption, time-integrated photoluminescence, confocal reflectance, and transmission microscopies. Comprehensive image analysis revealed the presence of surface- and bulk-dominated contributions to the various images, which describe either spatially dependent electronic excited-state properties or morphological variations across the probed region of the thin films. These results show that PL probes effectively the species near or at the film surface.

Surface morphology and electronic structure of halogen etched InAs (1 1 1)

Energy Technology Data Exchange (ETDEWEB)

Eassa, N., E-mail: nashwa.eassa@nmmu.ac.za [Department of Physics, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031 (South Africa); Murape, D.M. [Department of Physics, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031 (South Africa); Betz, R. [Department of Chemistry, Nelson Mandela Metropolitan University (South Africa); Neethling, J.H.; Venter, A.; Botha, J.R. [Department of Physics, Nelson Mandela Metropolitan University, P.O. Box 77000, Port Elizabeth 6031 (South Africa)

2012-05-15

The reaction of halogen-based etchants with n-InAs (1 1 1)A and the resulting surface morphology and surface electronic structure are investigated using field emission scanning electron microscopy and Raman spectroscopy. Using the intensity ratio of the unscreened longitudinal optical (LO) phonon to the transverse optical (TO) phonon in the Raman spectrum, a significant reduction in band bending is deduced after exposure of the InAs surface to HCl:H{sub 2}O, Br-methanol and I-ethanol for moderate times and concentrations. These procedures also lead to smooth and defect-free InAs surfaces. The improvements in surface properties are reversed, however, if the concentrations of the etchants are increased or the etch time is too long. In the worst cases, pit formation and inverted pyramids with {l_brace}1 1 1{r_brace} side facets are observed. The influence of the etchant concentration and etch time on the morphological and electronic properties of the etched surfaces is reported.

Surface morphology and electronic structure of halogen etched InAs (1 1 1)

International Nuclear Information System (INIS)

Eassa, N.; Murape, D.M.; Betz, R.; Neethling, J.H.; Venter, A.; Botha, J.R.

2012-01-01

The reaction of halogen-based etchants with n-InAs (1 1 1)A and the resulting surface morphology and surface electronic structure are investigated using field emission scanning electron microscopy and Raman spectroscopy. Using the intensity ratio of the unscreened longitudinal optical (LO) phonon to the transverse optical (TO) phonon in the Raman spectrum, a significant reduction in band bending is deduced after exposure of the InAs surface to HCl:H 2 O, Br–methanol and I–ethanol for moderate times and concentrations. These procedures also lead to smooth and defect-free InAs surfaces. The improvements in surface properties are reversed, however, if the concentrations of the etchants are increased or the etch time is too long. In the worst cases, pit formation and inverted pyramids with {1 1 1} side facets are observed. The influence of the etchant concentration and etch time on the morphological and electronic properties of the etched surfaces is reported.

Correlation properties of surface and percolation transfer of electrons

International Nuclear Information System (INIS)

Bakunin, O.G.

2002-01-01

In this work was received equation, connecting correlatively properties of surface with electrons distribution function. Usually for equilibrium is necessary a large number of collisions. Collisions are 'destroying' correlations. In case rare collisions large importance have correlations and 'memory' effects. Non-Markov's character of emitting particles by surface lead to strongly nonequilibrium condition of 'gas'. Here kinetic equation of diffusive form does not apply. Classical kinetic equation are described only conditions near to equilibrium. This work offers to use ideas anomal diffusion in phase-space. The correlation properties of surface describe by correlations of velocities of emitting electrons: B(t). We offer to use functional equation for probability collision instead of kinetic equation: ∫ 0 ν 0 W noncoll F(ν) dv = 1 - B(t). This functional allow to consider 'memory' effects. It is important for consideration of electrons and clusters near surfaces. Distribution function become direct connected with correlations. In classical Kubo-Mory theory of transfer is necessary to get nondivergences integral: D ∝ ∫ 0 ∞ B(t). In considering case we can use even 'power function'. It was used 'slow' correlation function as Kohlraush in calculations. The information about kinetics and correlations properties are containing in one functional equation. It was received solution of this equation in form Levy function: F(ν) ∝ 1/ν α exp(-1/ν). The solution of this form can not be get with help asymptotic methods of kinetic theory. Asymptotics of solution have scale-invariant character F(V) ∝ 1/V α . This indicate on fractal properties phase-space. (author)

Interfacial Energy Alignment at the ITO/Ultra-Thin Electron Selective Dielectric Layer Interface and Its Effect on the Efficiency of Bulk-Heterojunction Organic Solar Cells.

Science.gov (United States)

Itoh, Eiji; Goto, Yoshinori; Saka, Yusuke; Fukuda, Katsutoshi

2016-04-01

We have investigated the photovoltaic properties of an inverted bulk heterojunction (BHJ) cell in a device with an indium-tin-oxide (ITO)/electron selective layer (ESL)/P3HT:PCBM active layer/MoOx/Ag multilayered structure. The insertion of only single layer of poly(diallyl-dimethyl-ammonium chloride) (PDDA) cationic polymer film (or poly(ethyleneimine) (PEI) polymeric interfacial dipole layer) and titanium oxide nanosheet (TN) films as an ESL effectively improved cell performance. Abnormal S-shaped curves were observed in the inverted BHJ cells owing to the contact resistance across the ITO/active layer interface and the ITO/PDDA/TN/active layer interface. The series resistance across the ITO/ESL interface in the inverted BHJ cell was successfully reduced using an interfacial layer with a positively charged surface potential with respect to ITO base electrode. The positive dipole in PEI and the electronic charge phenomena at the electrophoretic deposited TN (ED-TN) films on ITO contributed to the reduction of the contact resistance at the electrode interface. The surface potential measurement revealed that the energy alignment by the transfer of electronic charges from the ED-TN to the base electrodes. The insertion of the ESL with a large positive surface potential reduced the potential barrier for the electron injection at ITO/TN interface and it improved the photovoltaic properties of the inverted cell with an ITO/TN/active layer/MoOx/Ag structure.

Ru-decorated Pt surfaces as model fuel cell electrocatalysts for CO electrooxidation.

Science.gov (United States)

Maillard, F; Lu, G-Q; Wieckowski, A; Stimming, U

2005-09-01

This feature article concerns Pt surfaces modified (decorated) by ruthenium as model fuel cell electrocatalysts for electrooxidation processes. This work reveals the role of ruthenium promoters in enhancing electrocatalytic activity toward organic fuels for fuel cells, and it particularly concerns the methanol decomposition product, surface CO. A special focus is on surface mobility of the CO as it is catalytically oxidized to CO(2). Different methods used to prepare Ru-decorated Pt single crystal surfaces as well as Ru-decorated Pt nanoparticles are reviewed, and the methods of characterization and testing of their activity are discussed. The focus is on the origin of peak splitting involved in the voltammetric electrooxidation of CO on Ru-decorated Pt surfaces, and on the interpretative consequences of the splitting for single crystal and nanoparticle Pt/Ru bimetallic surfaces. Apparently, screening through the literature allows formulating several models of the CO stripping reaction, and the validity of these models is discussed. Major efforts are made in this article to compare the results reported by the Urbana-Champaign group and the Munich group, but also by other groups. As electrocatalysis is progressively more and more driven by theory, our review of the experimental findings may serve to summarize the state of the art and clarify the roads ahead. Future studies will deal with highly dispersed and reactive nanoscale surfaces and other more advanced catalytic materials for fuel cell catalysis and related energy applications. It is expected that the metal/metal and metal/substrate interactions will be increasingly investigated on atomic and electronic levels, with likewise increasing participation of theory, and the structure and reactivity of various monolayer catalytic systems involving more than two metals (that is ternary and quaternary systems) will be interrogated.

Comparison of biological characteristics of mesenchymal stem cells grown on two different titanium implant surfaces

International Nuclear Information System (INIS)

Wang Chengyue; Zhao Baohong; Ai Hongjun; Wang Yiwei

2008-01-01

This study examined the biological characteristics of mesenchymal stem cells (MSCs) grown on sand-blasted, large-grit, acid-etched (SLA) surface and hydroxyapatite (HA) coating on the SLA (HA/SLA) surface of titanium dental implants. The HA/SLA surfaces of titanium dental implants were formed by the ion beam assisted deposition (IBAD) method. Rabbit bone marrow derived mesenchymal stem cells cultured in vitro were seeded onto the surface of SLA and HA/SLA; the growth states of MSCs on the two samples were observed by a scanning electron microscope; the proliferation index, alkaline phosphatase (ALP) activity, osteocalcin (OCN) content of MSCs and mRNA relative expression level of osteopontin (opn) were compared between two groups. MSCs were found to be easier to adhere to the HA/SLA surface compared to the SLA surface. At the same time, the ALP activity and the OCN content of MSCs grown on the HA/SLA surface were obviously higher, and the relative expression level of opn mRNA was 4.78 times higher than that on the SLA surface. The HA coating formed by the IBAD method on the SLA surface of titanium dental implants significantly improves proliferation and well-differentiated osteoblastic phenotype of MSCs, which indicates a promising method for the surface modification of titanium dental implants

A solution-processed binary cathode interfacial layer facilitates electron extraction for inverted polymer solar cells.

Science.gov (United States)

Zhang, Xinyuan; Li, Zhiqi; Liu, Chunyu; Guo, Jiaxin; Shen, Liang; Guo, Wenbin

2018-03-15

The charge transfer and separation are significantly affected by the electron properties of the interface between the electron-donor layer and the carrier-transporting layer in polymer solar cells (PSCs). In this study, we investigate the electron extraction mechanism of PSCs with a low temperature solution-processed ZnO/PEI as electron transport layer. The incorporation of PEI layer can decrease the work function of ZnO and reduce interfacial barrier, which facilitates electron extraction and suppresses bimolecular recombination, leading to a significant performance enhancement. Furthermore, PEI layer can induce phase separation and passivite inorganic surface trap states as well as shift the interfacial energy offset between metal oxide and organic materials. This work offers a simple and effective way to improve the charge transporting property of organic photovoltaic devices. Copyright © 2017 Elsevier Inc. All rights reserved.

Molecular surface mesh generation by filtering electron density map.

Science.gov (United States)

Giard, Joachim; Macq, Benoît

2010-01-01

Bioinformatics applied to macromolecules are now widely spread and in continuous expansion. In this context, representing external molecular surface such as the Van der Waals Surface or the Solvent Excluded Surface can be useful for several applications. We propose a fast and parameterizable algorithm giving good visual quality meshes representing molecular surfaces. It is obtained by isosurfacing a filtered electron density map. The density map is the result of the maximum of Gaussian functions placed around atom centers. This map is filtered by an ideal low-pass filter applied on the Fourier Transform of the density map. Applying the marching cubes algorithm on the inverse transform provides a mesh representation of the molecular surface.

Molecular Surface Mesh Generation by Filtering Electron Density Map

Directory of Open Access Journals (Sweden)

Joachim Giard

2010-01-01

Full Text Available Bioinformatics applied to macromolecules are now widely spread and in continuous expansion. In this context, representing external molecular surface such as the Van der Waals Surface or the Solvent Excluded Surface can be useful for several applications. We propose a fast and parameterizable algorithm giving good visual quality meshes representing molecular surfaces. It is obtained by isosurfacing a filtered electron density map. The density map is the result of the maximum of Gaussian functions placed around atom centers. This map is filtered by an ideal low-pass filter applied on the Fourier Transform of the density map. Applying the marching cubes algorithm on the inverse transform provides a mesh representation of the molecular surface.

Nanoparticle growth and surface chemistry changes in cell-conditioned culture medium.

Science.gov (United States)

Kendall, Michaela; Hodges, Nikolas J; Whitwell, Harry; Tyrrell, Jess; Cangul, Hakan

2015-02-05

When biomolecules attach to engineered nanoparticle (ENP) surfaces, they confer the particles with a new biological identity. Physical format may also radically alter, changing ENP stability and agglomeration state within seconds. In order to measure which biomolecules are associated with early ENP growth, we studied ENPs in conditioned medium from A549 cell culture, using dynamic light scattering (DLS) and linear trap quadrupole electron transfer dissociation mass spectrometry. Two types of 100 nm polystyrene particles (one uncoated and one with an amine functionalized surface) were used to measure the influence of surface type. In identically prepared conditioned medium, agglomeration was visible in all samples after 1 h, but was variable, indicating inter-sample variability in secretion rates and extracellular medium conditions. In samples conditioned for 1 h or more, ENP agglomeration rates varied significantly. Agglomerate size measured by DLS was well correlated with surface sequestered peptide number for uncoated but not for amine coated polystyrene ENPs. Amine-coated ENPs grew much faster and into larger agglomerates associated with fewer sequestered peptides, but including significant sequestered lactose dehydrogenase. We conclude that interference with extracellular peptide balance and oxidoreductase activity via sequestration is worthy of further study, as increased oxidative stress via this new mechanism may be important for cell toxicity. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Self-consistent electronic structure of the contracted tungsten (001) surface

International Nuclear Information System (INIS)

Posternak, M.; Krakauer, H.; Freeman, A.J.

1982-01-01

Self-consistent linearized-augmented-plane-wave energy-band studies using the warped muffin-tin approximation for a seven-layer W(001) single slab with the surface-layer separation contracted by 6% of the bulk interlayer spacing are reported. Surface electronic structure, local densities of states, generalized susceptibility for the surface, work function, and core-level shifts are found to have insignificant differences with corresponding results for the unrelaxed surface. Several differences in surface states between theory and recent angle-resolved photoemission experiments are discussed in the light of new proposed models of the actual unreconstructed surface structure at high temperatures

Asymptotic theory of dissipative trapped electron mode overlapping many rational surfaces

International Nuclear Information System (INIS)

Rogister, A.; Hasselberg, G.

1978-01-01

The two dimensional eigenvalue equation describing the dissipative trapped electron mode is solved exactly in the limit of the mode overlapping many rational surfaces using the Pogutse model for the magnetic field and the pitch angle collision operator. The trapped electron contribution to the growth rate decreases, with respect to the standard theory, by a factor of order Δ/chi sub(T) << 1 where chi sub(T) is the position of the turning point and Δ the distance between rational surfaces

New electronics for the surface detectors of the Pierre Auger Observatory

Energy Technology Data Exchange (ETDEWEB)

Kleifges, M., E-mail: Matthias.Kleifges@kit.edu [Karlsruhe Institute of Technology – Institute for Data Processing and Electronics, Karlsruhe (Germany)

2016-07-11

The Pierre Auger Observatory is the largest installation worldwide for the investigation of ultra-high energy cosmic rays. Air showers are detected using a hybrid technique with 27 fluorescence telescopes and 1660 water-Cherenkov detectors (WCD) distributed over about 3000 km{sup 2}. The Auger Collaboration has decided to upgrade the electronics of the WCD and complement the surface detector with scintillators (SSD). The objective is to improve the separation between the muonic and the electron/photon shower component for better mass composition determination during an extended operation period of 8–10 years. The surface detector electronics records data locally and generates time stamps based on the GPS timing. The performance of the detectors is significantly improved with a higher sampling rate, an increased dynamic range, new generation of GPS receivers, and FPGA integrated CPU power. The number of analog channels will be increased to integrate the new SSD, but the power consumption needs to stay below 10 W to be able to use the existing photovoltaic system. In this paper, the concept of the additional SSD is presented with a focus on the design and performance of the new surface detector electronics.

The role of substrate electrons in the wetting of a metal surface

DEFF Research Database (Denmark)

Schiros, T.; Takahashi, O.; Andersson, Klas Jerker

2010-01-01

We address how the electronic and geometric structures of metal surfaces determine water-metal bonding by affecting the balance between Pauli repulsion and electrostatic attraction. We show how the rigid d-electrons and the softer s-electrons utilize different mechanisms for the redistribution...

A Simple Hydrophilic Treatment of SU-8 Surfaces for Cell Culturing and Cell Patterning

DEFF Research Database (Denmark)

Wang, Zhenyu; Stangegaard, Michael; Dufva, Hans Martin

2005-01-01

SU-8, an epoxy-based photoresist, widely used in constitution different mTAS systems, is incompatible with mammalian cell adhesion and culture in its native form. Here, we demonstrate a simple, cheap and robust two-step method to render a SU-8 surface hydrophilic and compatible with cell culture........ The contact angle of SU-8 surface was significantly reduced from 90° to 25° after the surface modification. The treated SU-8 surfaces provided a cell culture environment that was comparable with cell culture flask surface in terms of generation time and morphology....

Effect of pulsed electron beam on cell killing

International Nuclear Information System (INIS)

Acharya, Santhosh; Joseph, Praveen; Sanjeev, Ganesh; Narayana, Y.; Bhat, N.N.

2009-01-01

The extent of repairable and irreparable damage in a living cell produced by ionizing radiation depends on the quality of the radiation. In the case of sparsely ionizing radiation, the dose rate and the pattern of energy deposition of the radiation are the important physical factors which can affect the amount of damage in living cells. In the present study, radio-sensitive and radioresistive bacteria cells were exposed to 8 MeV pulsed electron beam and the efficiency of cell-killing was investigated to evaluate the Do, the mean lethal dose. The dose to the cell was delivered in micro-second pulses at an instantaneous dose rate of 2.6 x 10 5 Gy s -1 . Fricke dosimeter was used to measure the absorbed dose of electron beam. The results were compared with those of gamma rays. The survival curve of radio-resistive Deinococcus-radiodurans (DR) is found to be sigmoidal and the survival response for radio-sensitive Escherichia-coli (E-coli) is found to be exponential without any shoulder. Comparison of Do values indicate that irradiation with pulsed electron beam resulted in more cell-killing than was observed for gamma irradiation. (author)

MEMS-based dynamic cell-to-cell culture platforms using electrochemical surface modifications

International Nuclear Information System (INIS)

Chang, Jiyoung; Lin, Liwei; Yoon, Sang-Hee; Mofrad, Mohammad R K

2011-01-01

MEMS-based biological platforms with the capability of both spatial placements and time releases of living cells for cell-to-cell culture experiments have been designed and demonstrated utilizing electrochemical surface modification effects. The spatial placement is accomplished by electrochemical surface modification of substrate surfaces to be either adhesive or non-adhesive for living cells. The time control is achieved by the electrical activation of the selective indium tin oxide co-culture electrode to allow the migration of living cells onto the electrode to start the cell-to-cell culture studies. Prototype devices have a three-electrode design with an electrode size of 50 × 50 µm 2 and the separation gaps of 2 µm between them. An electrical voltage of −1.5 V has been used to activate the electrodes independently and sequentially to demonstrate the dynamic cell-to-cell culture experiments of NIH 3T3 fibroblast and Madin Darby canine kidney cells. As such, this MEMS platform could be a basic yet versatile tool to characterize transient cell-to-cell interactions

Extracellular enzymes facilitate electron uptake in biocorrosion and bioelectrosynthesis.

Science.gov (United States)

Deutzmann, Jörg S; Sahin, Merve; Spormann, Alfred M

2015-04-21

Direct, mediator-free transfer of electrons between a microbial cell and a solid phase in its surrounding environment has been suggested to be a widespread and ecologically significant process. The high rates of microbial electron uptake observed during microbially influenced corrosion of iron [Fe(0)] and during microbial electrosynthesis have been considered support for a direct electron uptake in these microbial processes. However, the underlying molecular mechanisms of direct electron uptake are unknown. We investigated the electron uptake characteristics of the Fe(0)-corroding and electromethanogenic archaeon Methanococcus maripaludis and discovered that free, surface-associated redox enzymes, such as hydrogenases and presumably formate dehydrogenases, are sufficient to mediate an apparent direct electron uptake. In genetic and biochemical experiments, we showed that these enzymes, which are released from cells during routine culturing, catalyze the formation of H2 or formate when sorbed to an appropriate redox-active surface. These low-molecular-weight products are rapidly consumed by M. maripaludis cells when present, thereby preventing their accumulation to any appreciable or even detectable level. Rates of H2 and formate formation by cell-free spent culture medium were sufficient to explain the observed rates of methane formation from Fe(0) and cathode-derived electrons by wild-type M. maripaludis as well as by a mutant strain carrying deletions in all catabolic hydrogenases. Our data collectively show that cell-derived free enzymes can mimic direct extracellular electron transfer during Fe(0) corrosion and microbial electrosynthesis and may represent an ecologically important but so far overlooked mechanism in biological electron transfer. The intriguing trait of some microbial organisms to engage in direct electron transfer is thought to be widespread in nature. Consequently, direct uptake of electrons into microbial cells from solid surfaces is assumed

An ultrafast nanotip electron gun triggered by grating-coupled surface plasmons

Energy Technology Data Exchange (ETDEWEB)

Schröder, Benjamin; Sivis, Murat; Bormann, Reiner; Schäfer, Sascha; Ropers, Claus, E-mail: cropers@gwdg.de [4th Physical Institute - Solids and Nanostructures, University of Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen (Germany)

2015-12-07

We demonstrate multiphoton photoelectron emission from gold nanotips induced by nanofocusing surface plasmons, resonantly excited on the tip shaft by a grating coupler. The tip is integrated into an electron gun assembly, which facilitates control over the spatial emission sites and allows us to disentangle direct grating emission from plasmon-triggered apex emission. The nanoscale source size of this electron gun concept enables highly coherent electron pulses with applications in ultrafast electron imaging and diffraction.

Band-structure-based collisional model for electronic excitations in ion-surface collisions

International Nuclear Information System (INIS)

Faraggi, M.N.; Gravielle, M.S.; Alducin, M.; Silkin, V.M.; Juaristi, J.I.

2005-01-01

Energy loss per unit path in grazing collisions with metal surfaces is studied by using the collisional and dielectric formalisms. Within both theories we make use of the band-structure-based (BSB) model to represent the surface interaction. The BSB approach is based on a model potential and provides a precise description of the one-electron states and the surface-induced potential. The method is applied to evaluate the energy lost by 100 keV protons impinging on aluminum surfaces at glancing angles. We found that when the realistic BSB description of the surface is used, the energy loss obtained from the collisional formalism agrees with the dielectric one, which includes not only binary but also plasmon excitations. The distance-dependent stopping power derived from the BSB model is in good agreement with available experimental data. We have also investigated the influence of the surface band structure in collisions with the Al(100) surface. Surface-state contributions to the energy loss and electron emission probability are analyzed

The role of (sub)-surface oxygen on the surface electronic structure of hydrogen terminated (100) CVD diamond

NARCIS (Netherlands)

Deferme, W.; Tanasa, G.; Amir, J.; Haenen, K.; Nesladek, M.; Flipse, C.F.J.

2006-01-01

In this work, scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS) were applied to investigate the surface morphol. and the surface electronic structure of plasma-treated (100)-oriented CVD diamond films. These films were hydrogenated using a conventional MWPE-CVD

High resolution surface scanning of Thick-GEM for single photo-electron detection

Energy Technology Data Exchange (ETDEWEB)

Hamar, G., E-mail: hamar.gergo@wigner.mta.hu [Wigner Research Centre for Physics, Budapest (Hungary); Varga, D., E-mail: vdezso@mail.cern.ch [Eoetvoes Lorand University, Budapest (Hungary)

2012-12-01

An optical system for high resolution scanning of TGEM UV photon detection systems is introduced. The structure exploits the combination of a single Au-coated TGEM under study, and an asymmetric MWPC (Close Cathode Chamber) as post-amplification stage. A pulsed UV LED source with emission down to 240 nm has been focused to a spot of 0.07 mm on the TGEM surface, and single photo-electron charge spectra has been recorded over selected two dimensional regions. This way, the TGEM gain (order of 10-100) and TGEM photo-electron detection efficiency is clearly separated, unlike in case of continuous illumination. The surface structure connected to the TGEM photon detection is well observable, including inefficiencies in the holes and at the symmetry points between holes. The detection efficiency as well as the gas gain are fluctuating from hole to hole. The gain is constant in the hexagon around any hole, pointing to the fact that the gain depends on hole geometry, and less on the position where the electron enters. The detection probability map strongly changes with the field strength above the TGEM surface, in relation to the change of the actual surface field configuration. The results can be confronted with position-dependent simulations of TGEM electron transfer and gas multiplication. -- Highlights: Black-Right-Pointing-Pointer First demonstration of Thick GEM surface scanning with single photo-electrons. Black-Right-Pointing-Pointer Resolution of 0.1 mm is sufficient to identify structures connected to TGEM surface field structure. Black-Right-Pointing-Pointer Gain and detection efficiency and separately measurable. Black-Right-Pointing-Pointer Detection efficiency is high in a ring around the holes, and gain is constant in the hexagonal collection regions.

Theory of hot electrons on the liquid 4He surface, 2

International Nuclear Information System (INIS)

Aoki, Takayuki; Saitoh, Motohiko

1979-01-01

Theoretical study is given of the high field transport of surface state electrons on the liquid 4 He. The explicit form of the electron distribution function is solved by the use of the Boltzmann transport equation where the electron-ripplon and electron-He gas interactions are considered as dominant scattering mechanisms, and the electron-electron interactions are completely neglected. Inter-subband and intra-subband transitions are treated equally. The S-shaped non-linear behaviors predicted to occur at low temperature region in the electron temperature approximation have been removed. Experimentally observed hysteresis, if any, in the widths of the plasmon resonance and cyclotron resonance may thus be attributed to the electron-electron interaction. (author)

Mpl traffics to the cell surface through conventional and unconventional routes.

Science.gov (United States)

Cleyrat, Cédric; Darehshouri, Anza; Steinkamp, Mara P; Vilaine, Mathias; Boassa, Daniela; Ellisman, Mark H; Hermouet, Sylvie; Wilson, Bridget S

2014-09-01

Myeloproliferative neoplasms (MPNs) are often characterized by JAK2 or calreticulin (CALR) mutations, indicating aberrant trafficking in pathogenesis. This study focuses on Mpl trafficking and Jak2 association using two model systems: human erythroleukemia cells (HEL; JAK2V617F) and K562 myeloid leukemia cells (JAK2WT). Consistent with a putative chaperone role for Jak2, Mpl and Jak2 associate on both intracellular and plasma membranes (shown by proximity ligation assay) and siRNA-mediated knockdown of Jak2 led to Mpl trapping in the endoplasmic reticulum (ER). Even in Jak2 sufficient cells, Mpl accumulates in punctate structures that partially colocalize with ER-tracker, the ER exit site marker (ERES) Sec31a, the autophagy marker LC3 and LAMP1. Mpl was fused to miniSOG, a genetically encoded tag for correlated light and electron microscopy. Results suggest that a fraction of Mpl is taken up into autophagic structures from the ER and routed to autolyososomes. Surface biotinylation shows that both immature and mature Mpl reach the cell surface; in K562 cells Mpl is also released in exosomes. Both forms rapidly internalize upon ligand addition, while recovery is primarily attributed to immature Mpl. Mpl appears to reach the plasma membrane via both conventional ER-Golgi and autolysosome secretory pathways, as well as recycling. © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Photoelectron spectroscopy bulk and surface electronic structures