bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties And Prevention of Adhesions Applications of Bioelastic Materials
Authors: Urry D. W. , Gowda D. Channe , Cox Betty A. , Hoban Lynne D. , Mckee Adam , Williams Taffy
Published: March 2011

The origins, syntheses, variable composition and physical properties of bioelastic materials are discussed. The latter includes their capacity to undergo inverse temperature transitions to increased order on raising the temperature and to be designable to interconvert free energies involving the intensive variables of mechanical force, temperature, pressure, chemical potential, electrochemical potential and light.

Bioelastic materials include analogues and other chemical variations of the viscoelastic polypeptide, poly(Val-Pro-Gly-Val-Gly), and cross-linked elastomeric matrices thereof. This parent material has been shown to be remarkably biocompatible; it can be minimally modified to vary the rate of hydrolytic breakdown; it can contain enzymatically reactive sites; and it can have cell attachment sites included which promote excellent cell adhesion, spreading and growth to confluence.

One specific application is in the prevention of postoperative adhesion. There are some 30,000,000 per year surgical procedures in this country and a large portion of these would benefit if a suitable material were available for preventing adhesions. Bioelastic materials have been tested in a contaminated peritoneal model, and promising preliminary studies have been carried out in the rabbit eye model for strabismus surgery. In the peritoneal model, 90% of the 29 control animals exhibited significant adhesions; whereas, only 20% of the 29 animals using gas sterilized matrices had significant adhesions. On the basis of this data, it appears that cross-linked poly(VPGVG) is an effective physical barrier to adhesion formation in a trauma model with resulting hemorrhage and contamination.

The potential use of bioelastic materials as a pericardial substitute following the more than 400,000 open heart surgeries per year in the U.S. is under development beginning with the use of bioelastic matrices to prevent adhesions to the total artificial heart being used as a bridge to heart transplantation such that the site will be less compromised when receiving the donor heart.
Nuts
Authors: Vincent Julian F. V.
Published: March 2011

The shell (pericarp) of nuts protects the seed from being eaten before it can germinate. It is presumably designed to resist fracture by external forces, and evolution will have optimised its design for this purpose. It appears that the material of larger shells, which will tend to be structurally more brittle, is tougher. However, the fracture mechanics theory for shells in compression is not available, nor the information on the biological selection pressures.
Structure and Composition of Rhinoceros Horn
Authors: Orden Ann Chidester Van , Daniel Joseph C.
Published: March 2011

Rhinoceros horn has been used medicinally and as a talisman in many cultures and animals are slaughtered to obtain the horn. With the dwindling populations of rhinos, and the limited number and breeding success of captive rhinos, there is a critical need to learn as much as is possible about their horns to find an adequate substitute. Examination of rhino horn was made using optical microscopy, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD). The structure of the horn is unusual and consists of two separate phases, one of hair-like filaments, built around a central core in circumferential layers and the other surrounding and filling in the spaces between the filaments as a matrix. Together, these two structures make up a biological composite, structurally similar to metal, ceramic or polymer based composites. The structural morphology, the dimensions of the structures, and the chemistry of the horn are discussed. Comparisons are made between horn, hoof, and hair of rhinos and hoof and hair from horses, their nearest living relatives.
Is the Tyrosine Rich Eggshell Protein of Schistosoma Mansoni an Electron Transport Chain?
Authors: Cordingley John S. , Thomson John A. , Middaugh C. Russell
Published: March 2011

The schistosome eggshell is composed of two kinds of cross-linked proteins. One is glycine rich and the other is extremely tyrosine rich and highly repetitive. The highly conserved sequence of the tyrosine residues in the tyrosine rich protein suggests that it may play a role as an electron transport chain during eggshell cross-linking. Studies using model synthetic peptides suggest that the tyrosine rich protein may adopt a left-handed structure, possibly a left-handed alpha-helix.
Self-Assembling Nanostructures: Recognition and Ordered Assembly in Protein-Based Materials
Authors: McGrath Kevin P. , Kaplan David L.
Published: March 2011

A new approach to materials design is presented, utilizing specific recognition and assembly at the molecular level. The approach described exploits the control over polymer chain microstructure afforded by biosynthesis to produce proteinbased materials with precisely defined physical properties. Incorporated into these materials are recognition elements that stringently control the placement and organization of each chain within higher order superstructures. The proteins, designated Recognin A2 through Recognin E2, are recombinant polypeptides designed de novo from both natural consensus sequences and an appreciation of the physical principles governing biological recognition. These materials are designed to examine the forces involved in specific recognition and complexation. through control of charge identity and placement, a pattern for specific interaction can be introduced. A subset of these materials are programmed to spontaneously assemble into complex, multicomponent structures and represent the first step in a rational approach to nanometer-scale structural design.
Over-Expression of a Core Repeat from an Insect Silk Protein that forms Intramolecular Disulfide Bonds
Authors: Smith Stanley V. , Case Steven T.
Published: March 2011

A gene encoding one complete [C+SR] core repeat from spIa, a 1000-kDa silk protein from Chironomus tentans, was synthesized and its recombinant protein expressed to high levels in bacterial cells. We observed that reducing agents significantly alter the electrophoretic mobility of this protein. A variety of data indicate that the purified recombinant protein is folded and its structure stabilized by two intramolecular disulfide bonds.
Cloning and Expression of a Synthetic Mussel Adhesive Protein inEscherichia Coli
Authors: Salerno Anthony J. , Goldberg Ina
Published: March 2011

Repetitious gene cassettes that encode the consensus decapeptide repeat ofMytilus edulisbioadhesive protein were cloned and expressed inEscherichia coli. The bioadhesive precursor (BP, Mx−25,000) was expressed from one 600-bp gene comprised of a 30-bp unit repeat. The repetitious gene appeared stable in a T7-based host/vector system.

Using the T7 expression system for induction, BP was produced at levels approaching 60% of total cell protein. BP was found both in intracellular inclusions and in the soluble fraction. Interestingly, methionine was processed from the N-terminus of the purified protein to give an authentic consensus precursor protein.
Development of Electrically Conductive Poly(3-Hexylthiophene) as a thin Film Sensor for Hydrazine Vapor
Authors: Ellis D. L. , Zakin M. R. , Bernstein L. S. , Rubner M. F.
Published: March 2011

Thin films of the electrically conducting polymer, poly(3-hexylthiophene) (P3HT), were developed as sensors for hydrazine vapor at the part-per-billion level. The P3HT films were fabricated by a spin coating technique onto quartz substrates incorporating gold interdigitated electrodes, and were rendered conductive by doping with an NOPF6 solution. The sensors respond strongly and instantaneously to hydrazine concentrations as low as 1 part-per-billion with a measurement accuracy of ±20%. In addition, the sensors exhibited excellent environmental stability, long shelf life, and good interference rejection.
Core Level Orbital Interactions and Fast Ion Conduction
Authors: Oliveria M. , Johnson K. H.
Published: March 2011

Although there has been much success in theoretical modelling of fast ion conductors with molecular dynamics simulations, there has been less attention paid to development of a chemical understanding of fast ion conduction. In this paper we explore the importance of core level interactions and the role that they play in constructing high diffusivity paths in solids. In particular, we have carried out molecular orbital calculations (using the self-consistent-field X-alpha scattered-wave method) on AgI clusters to examine the orbital interactions of the filled Ag 4d level. We hypothesize that it is the interaction of the d electrons that is responsible for fast ion conduction in AgI and other Ag and Cu binary fast ion conductors. The results of these calculations will be compared with other electronic structure calculations and XPS data.
Non-Debye Relaxation Process of Hopping Ionic Conduction in Lattice Gas Models
Authors: Sato Hiroshi , Datta Anuradha
Published: March 2011

Based on the examination of the relaxation process of the motion of a single particle in the assembly of particles of the same species, it is shown that the relaxation process of the motion of a particle in a lattice gas model is intrinsically non-Debye. The origin of this effect is traced to the deviation of the motion of particles from equilibrium immediately after their jumps.
Structure, Fragmentation, and Phonons in Silicon Microclusters
Authors: Li Wei , Kalia Rajiv K. , Vashishta Priya
Published: March 2011

Molecular-dynamics simulations are performed to investigate structures, vibrational spectra, and fragmentation channels of silicon microclusters ranging in size from 32 to 52 atoms. Structural information is derived from pair-distribution functions, bond-angle distributions, and the structure and statistics of rings. Molecular-dynamics simulation results for energetics suggest that 33, 39, 45 and 51 atom clusters are highly stable. These magic-number clusters have predominantly five and six membered rings. With an increase in “temperature”, most clusters tend to fragment by loosing one atom at a time. Vibrational densities of states of 32-52 atom silicon clusters show only minor deviations from the bulk behavior.
Oxygen Ion Conductivity in a New Class of Layered Bismuth Oxide Compounds
Authors: Thomas Julie K. , Anderson Mairin E. , Krause Wendy E. , Loye Hansconrad Zur
Published: March 2011

Compounds that consist of intergrowths between the Aurivillius phase Bi4Ti3O12 and brownmillerite-like slabs of BaMO2.5were synthesized and their oxygen ion conductivities investigated. Both BaBi4Ti3ScO14.5 and BaBi4Ti3InO14.5 display a discontinuity in their Arrhenius plots that appears to be caused by an oxygen vacancy order-disorder transition. Conductivity data for two Aurivillius phases BaBi4Ti4O15 and BaBi2Nb2O9 are included for comparison.
Ruthenium Doped Gadolinium Titanate: Effects of a Variable Valent Acceptor on Ionic and Electronic Conduction
Authors: Spears M.A. , Tuller H.L.
Published: March 2011

We have investigated ruthenium doped gadolinium titanate, Gd2(RuxTi1-x)2O7-δ with 0 ≤ x ≤ 0.2, to determine the role of variable valent Ru in influencing the defect structure and transport properties of the pyrochlore host. We have developed a defect chemical model to interpret electrical conductivity, thermoelectric power, and thermogravimetry data. We have found that Ru acts as an acceptor compensated in large part by oxygen vacancies, resulting in enhanced ionic conduction at low values of x. For larger values (x ≈ 0.05), electronic conductivity predominates which we attribute to electron migration by hopping through a Ru-derived defect band.
A Study of the Electrical Behavior of UO2(O3PC6H5) Supported Film
Authors: Benavente J. , Barrado J.R. Ramos , Bruque S. , Martinez M.
Published: March 2011

The electrochemical behaviour of a polymeric supported uranyl phophonate film, when it is placed in contact with solutions of two generating electrolytes, (H2PO3C6H5 and UO2(NO3)2) at different concentrations, is studied by AC impedance spectroscopy and diffusion potential measurements. The equivalent circuit associated to the film and some of its characteristic electrical parameters (Rf and Qf) are determined. The cation transport numbers in the film (t+ = I+/I) with both electrolytes as well as their variation with concentration are also obtained. Differences found in the Qf parameter for both film/electrolyte systems are attributed to the different values of the transport numbers.
Characterization of I.T.O. Thin Film Electrodes in Li-Based Systems and their Use in Electrochromic Windows
Authors: Golden S. J. , Steele B.C.H.
Published: March 2011

Thin films of tin-doped indium oxide (I.T.O.) were produced by r.f. sputtering and lithiated electrochemically in LiClO4-PC. X-ray diffraction studies showed a cubic structure with a small increase in the cubic lattice parameter with x up to unity (LixITO). Electrochemical studies indicated that Li insertion is reversible, at least over a small number of cycles. Spectral transmittance decreased slightly with considerable levels of insertion indicating low electrochromic colouration efficiencies and making thin film I.T.O. a suitable counter-electrode material for electrochromic window systems.
Kinetics Study of Hydrogen Discharge from A Lani4.5AL0.5Dy Electrode by in Situ Real Time Neutron Diffraction
Authors: Poinsignon Christiane , Dalphrase Nicole , Latroche Michel , Pannetier Jean , Percheron Annick
Published: March 2011

Electrochemical studies performed by linear potential scan voltamperometry on the monosubstituted intermetallic hydrides LaNi4.5M0.5, with M=AI, Mn or Co, confirm previous observations [ 14, 16, 20] of the influence of the nickel substitute on the rate of hydrogen insertion/desinsertion in solid gaz : the rate of discharge is faster for the Co and Mn substituted hydrides than for the Al one : during a controled discharge process by potential step of 20mV during 10 hours, hydrogen full capacity is desinserted over a potential range of 200mV in 80 hours for LaNi4.5AI0.5, over 130mV in 40 hours for LaNi4.5Mn0.5 and over 50mV in 30 hours for LaNi4.5Co0.5

Coupled techniques of real time neutron diffraction and linear potential scan voltammetry applied to the in situ study of the charge/discharge of a LaNi4.5A10.5Dx electrode in a KOD 7N electrolyte gives account for the respective variation of the cell parameters of the α and β phases[ 11] and provides access to the hydogen desinsertion kinetics from both phases. The decrease rate of the unit cell volume of the α phase is found to be 4.8 10−3 A3/hour whereas that of the β phase is 61 10−3 A3/hour. At the end of the discharge process occurence of isolated 13ph ase domains is attributed to the faster rate of hydrogen desinsertion in the β phase than in the (β phase, which is in all likelihood at the origin of the loss of capacity observed during cycling for this electrode.
Fourier Transform Infrared (FTIR) Analysis of Copper Oxide Thin Films Prepared by Metal Organic Chemical Vapor Deposition (MOCVD)
Authors: Chang Yu-Neng
Published: March 2011

FTIR results from cuprous oxide (Cu2O) and cupric oxide (CuO) films prepared by MOCVDtechnique were presented. According to FTIR and XRD results, Cu2O films can be prepared by MOCVD using 0.20 tort of copper acetylacetonate (Cu(acac)2) vapor and 150 torn of oxygen, at a deposition temperature of 340°C. The strong reductive tendency of Cu(acac)2 vapor in the MOCVD process is noted, as the oxidation state of copper was reduced from 2+ in Cu(acac)2 to 1+ in the Cu2O film. Cu2O films have a strong IR absorption band at 610 cm−1. CuO films were prepared at 0.20 tort of Cu(acac)2 vapor and 190 torr of oxygen, at a deposition temperature of 420°C. The IR bands of CuO films located at 440 cm−1, 480cm−1, and 540cm−1. The XRD results indicated that Cu2O films have a preferential orientation at (111) plane. From IR study, it appears that the MOCVD processing condition has an impact on the film microstructure, which in term influenced the band position and band shape of corresponding IR bands.
The Lithium Electrode Interface: A Crucial Aspect in Polymer Batteries
Authors: Scrosati Bruno , Croce Fausto
Published: March 2011

Rechargeable, polymer lithium batteries are today considered as very promising advanced power sources for electric vehicle and/or consumer electronics. Many polymer electrolytes, some of which having very high ambient temperature conductivity, have been developed and characterized. However, very little attention has been so far dedicated to the study of the characteristics of the lithium electrode interface. Since the clarification of the interfacial phenomena is crucial in assessing the effective impact of polymer batteries, we have undertaken a detailed investigation of the Li passivation processes in most relevant electrolyte media and in this work we report results obtained in highly conductive cells using electrolytes formed by the immobilization of lithium solvates in polymer networks.
In Situ X-RAY Diffraction Studies of Li+ Insertion into V6O13
Authors: Lampe-Önnerud C. , Gustafsson T. , Thomas J.O.
Published: March 2011

A fast in situ X-ray powder diffraction set-up working in transmission mode is used to explore the structural changes occurring on Li+ insertion into the active V6O13 component of the cathode in a thin-film < Li I polymer electrolyte | V6O13 > battery. It is confirmed that the V6O13 is indeed converted reversibly into three discrete phases, LixV6O13 for x = 1, 4 and 8, as the fully charged cell (ca. 3.OV) is discharged to 1.8V. The effect on the insertion process of repeated cycling with different currents has been studied. Cell collapse was induced after ca. 35 cycles for 0.2 mA/cm2. This was not reflected, however, in any significant change in the diffraction pattern from the battery. Moreover, the battery returned to normal functioning after lying on open circuit for 7 days. A gradual loss of reflection intensity is observed, but no particle line-broadening. The implications of these results are discussed as they relate to the nature of the solid-state insertion process of Li+ into V6O13.
Dehydration and Lithium Insertion Studies in Phyllomanganates
Authors: Strobel Pierre
Published: March 2011

Layered oxides AxMnO≈2,yH20 (A = Na, K, NH4, Cs or Mn2+) have been dehydrated and intercalated by lithium. Dehydration is accompanied by a shrinking of the interlayer space height depending on the size of A. The valence of Mn is reduced to +2 by reaction with n-butyllithium. Electrochemical studies of cells AxMnO≈2-graphite | LiClO4-PC|I Li showed two main reaction peaks at ca. 3V and below 2 V. The first reaction is a reversible reduction to a disordered Mn3+ phased. Capacities at the third cycle are ca. 300 Wh/kg. No marked difference was found as a function of A or of the degree of order of the starting compound.
Electron Microscopy Characterization Of Epitaxial Growth Of Ag Deposited On Mgo Microcubes
Authors: Liu J. , Pan M. , Spinnler G. E.
Published: March 2011

The crystalline structure, the morphology and the chemistry of small Ag particles vacuum-deposited on preheated MgO microcubes were characterized by in situ and ex situ electron microscopy and surface analysis techniques. Observations were made of the nucleation and growth of Ag clusters on MgO surfaces and along surface steps. It is found that Ag particles deposited onto clean MgO crystals have an epitaxial orientation relationship of (100)Agll(100)MgO with [100]Agll[00]MgO. Prior to air exposure Ag particles are stable under the electron beam but they become unstable upon exposure to air. During electron irradiation on air-exposed samples terraces are formed on the surfaces of MgO cubes, preferentially near Ag particles and at their interfaces with the substrate. The stability of vacuum-deposited Ag particles and the growth of the terraces on MgO microcubes seem to depend on air exposure of the sample.
Artifacts in Atomic Force Microscopy of Nanoporous and Mesoporous Fiducial Samples
Authors: Deckman H. W. , Plano R. J.
Published: March 2011

Artifacts dominate atomic force microscope (AFM) images of nanoporous and mesoporous inorganic oxide materials taken under ambient atmospheric conditions with currently available tips. Artifacts in these AFM images are attributed to tip-sample interactions and the sharpness of tips on currently available cantilevers. We show that by modifying currently available AFM tips with carbonaceous materials, many image artifacts are eliminated. To characterize image artifacts, a variety of fiducial samples with feature sizes between ∼100 Å and 2,000 Å are used. One of the most useful fiducial samples is a close packed array of holes in a commercially available alumina membrane and we suggest that it be adopted as a standard fiducial sample.
High Resolution Electron Microscopy of ∑ =3 NiSi2 (111)(115) Si And NiSi2(221)/(001)Si Interfaces
Authors: Chen Wen-Jauh , Chen Fu-Rong
Published: March 2011

High resolution imaging technique is applied to systematically study the ∑ =3 NiSi2(111)/(115)Si and NiSi2(221)/(001)Si interfaces. The long-period boundaries of ∑ =3 NiSi2 (111)/(115)Si and NiSi2(221)/(001)Si have been shown to decompose into short period of symmetrical NiSi2 (111)/(111)Si and NiSi2 (112)/(112)Si atomic facets which are similar to the case of asymmetrical twin boundaries in NiSi2 crystal. This result is consistent with the computer simulation in grain boundary case that asymmetrical tilt boundaries which are generally of longer periods may facet on an atomic scale into short period symmetrical boundaries.

The domain-related atomic faceting interfaces have been found in both of.∑ =3 NiSi2(111)/(115)Si and NiSi2(221)/(001)Si interfaces. The coexistence of two domain-related atomic faceting interfaces in the ∑ =3 NiSi2(111)/(115)Si has also been observed in different area of an interface which are separated by a 1/4<111> type of dislocation associated with a ‘demi-step’. The Burgers vector and step of a dislocation required to separate two domain structures in the ∑ =3 NiSi2/Si interface can be derived from the CCSL model.
Experimental Optimization for Imaging with Photoelectron Diffraction
Authors: Tobin J. G. , Waddill G. D. , Li Hua , Tong S. Y.
Published: March 2011

The experimental apparatus and its optimization for holographic imaging with energy dependent photoelectron diffraction are described. A substantial improvement in data taking efficiency has resulted, allowing total data collection time to be reduced to about twelve hours for a single image-map.
Design of Ultra High Vacuum Scanning Electron Microscope Combined with Scanning Tunneling Microscope
Authors: Takai Mikio , Yokoi Naoki , Mimura Ryou , Sawaragi Hiroshi , Aihara Ryuso
Published: March 2011

An ultra high vacuum (UHV) scanning electron microscope (SEM) combined with a scanning tunneling microscope (STM) has been designed and constructed to solve problems, arising from STM surface imaging and nanofabrication using STM tips, such as difficulty in probe tip location and change in tip shape. The system facilitates to image and/or to modify a wide range of area from submicron down to subnanometer. A ZrO/W thermal emitter in a Schottky mode has been used for an electron gun to obtain a low energy spread with a high angular current density. Minimum beam spot diameters of 6 and 12 nm with currents of 100 pA and 4 nA are estimated by optical property calculation for high resolution (SEM) and high current (fabrication) modes, respectively.
The Surface Structure of Oxides Studied with Reflected High Energy Electrons
Authors: Hsu Tung
Published: March 2011

Reflected high energy electrons have been employed for studying surfaces of single crystal oxides in real and reciprocal space. The techniques used include reflection high energy electron diffraction (RHEED), reflection electron microscopy (REM), scanning reflection electron microscopy (SREM), and reflection electron energy loss spectroscopy (REELS). These methods have provided much information on surface morphology as well as the atomic and electronic structure of MgO, ∝-Al2O3, ∝ -Fe2O3, SiO2, TiO2(rutile), and ZnO single crystals. Analyses for chemical composition and electronic states are possible using SREM and REELS. Surfaces terminating at different atomic layers of large-unit-cell materials have been determined in REM images and also in REELS data obtained under REM and SREM. Surface modification due to bombardment with the incident electron beam is pronounced on some oxide surfaces. These processes have been investigated with the REM imaging and REELS techniques.
Scanning Tunneling Microscopy Perspective of Structures on Reduced SrTiO3 (001) Surfaces
Authors: Liang Yong , Bonnell Dawn A.
Published: March 2011

Scanning tunneling microscopy has been used in ultra high vacuum to provide atomic scale structural information on reduced SrTiO3(001) surfaces. Our tunneling images exhibit row-like features with 12 Å and 20 Å periodicities on the reduced surface. A local 2×1 reconstruction was also revealed on some regions of the surface. The experimental results are discussed in terms of the different sublimation rates of surface constituents and formation of lamella structures of Srn+lTinO3n+l.
Surface Structure and Electronic Property of Reduced SrTiO3 (100) Surface Observed by STM/STS
Authors: Matsumoto Takuya , Tanaka Hiroyuki , Kawai Tomoji , Kawai Shichio
Published: March 2011

We have obtained STM images and STS data with atomic-scale resolution for SrTIO3 (100) surface annealed in UHV at 1200 °C. A √5×√5-R26.6° surface superstructure indicating oxygen vacancy ordering has been observed. The STS data provide evidence for a localized surface state arising from oxygen vacancies at 1.35 eV below the Fermi level. STM images of the √5×√5 structure correspond to the surface orbital of the ordered Ti-oxygen vacancy.
Mechanisms and Energetics of Surface Atomic Processes, an Atom-Probe Field Ion Microscope Study
Authors: Tsong Tien T.
Published: March 2011

Atom-probe field ion microscopy is capable of imaging solid surfaces with atomic resolution, and at the same time chemically analyzing atoms selected by the observer from the atomic image. The samples are restricted to those having a tip shape, but in many cases this is no longer a drawback since structures in high-tech materials are reducing in size to that comparable to or smaller than the field ion emitter tip. This technique is finding many applications in different areas. Our recent applications of this technique to the study of the dynamical behavior of surfaces and surface atoms and their mechanisms and energetics, and the atomic scale chemical and composition analysis will be briefly described.
Growth and Surface Morphology of Thin Silicon Films Using an atomic Force Microscope
Authors: Hegde Rama I. , Chonko Mark A. , Tobin Philip J.
Published: March 2011

The growth and surface morphology of thin LPCVD silicon films were investigated with an atomic force microscope (AFM). Silicon films of 30 nm thicknesses were deposited on SiO2 using SiH4 at four different temperatures between 550 °C and 625 °C. These AFM results permitted visualization of silicon surface granularity, roughness, and the transition with temperature from amorphous to crystalline structure between 550 °C and 580 °C. The surface of the amorphous film deposited at 550 °C is very smooth and the film is continuous physically, while the film formed at 580 °C appears crystalline, rough and porous. At 600 °C and 625 °C the films are fully crystalline. For these higher temperature films surface roughness and the average grain size decreased significantly compared to 580 °C film. Crystallinity and film continuity were further examined by x-ray diffraction (XRD) and cross-sectional TEM measurements.
Solving Interface Structures by Combined Electron Microscopy and X-Ray Diffraction
Authors: Bourret A. , Feuillet G.
Published: March 2011

By a combination of high resolution imaging (HREM) and grazing incidence X-ray scattering (GIXS), periodic interfaces with large unit cell can be solved at an atomic scale. The advantage of recording information in the real space is that phases are directly encoded in the image. On the other hand the X-ray diffraction gives quantitative information at a resolution level better than with HREM. This combined analysis is illustrated on GaAs (001)-CdTe (111) and on GaAs(001)-GaSb(001) interfaces. In both cases the structure at the interface is obtained and some mechanisms for the strain relaxation at heterostructures with large misfit are proposed.
Quantitative Hrem Study of the Atomic Structure of the Σ(310)/[001] Symmetric Tilt Grain Boundary in Nb
Authors: King Wayne E. , Campbell Geoffrey H.
Published: March 2011

We have used a non-linear least squares optimization method to deduce a model for the atomic structure of the Σ(310)/[001] symmetric tilt grain boundary in Nb from high resolution electron micrographs (HREM) of a bicrystal prepared by diffusion bonding. The resultant model is similar to, but differs in detail from a theoretical prediction based on interatomic potentials which included angular forces thought to be important in the prediction of defect structures in body centered cubic metals. Results validate this approach as a step towards making HREM a quantitative technique.
Visible-Light Amorphous Silicon-Nitride Thin Film Light Emitting Diode
Authors: Boonkosum Wirote , Kruangam Dusit , Panyakeow Somsak
Published: March 2011

A visible-light Thin Film Light Emitting Diode (TFLED) having a-SiN:H as a luminescent active layer has been developed. The TFLED has a structure of glass substrate/ITO/p a-SiC:H/i a-SiN:H/n a-SiC:H/Al. The emission color could be changed from red to orange, yellow, green and white-blue by varying the optical energy gap of the i a-SiN:H layer in the TFLED. The brightness was in the order of 0.1-1 cd/m2 . A series of systematic investigations on the basic properties of a-SiN:H films carrier injection and recombination mechanism in TFLEDs is described.
First Principles Molecular Dynamics Studies of a-Si and a-Si:H
Authors: Fedders P.A.
Published: March 2011

We give a brief description of the various classes of molecular dynamics simulations and then describe what we have learned from our simulations recently. This includes information on the nature of defects in a-Si:H including positions in the energy gap and localization, relaxation and rearrangement effects, light induced defects, and the motion of H atoms and Si dangling bonds.
Effects of Structural Disorder on the Electronic Properties of Silicon: Tight-Binding Calculations of Grain Boundaries
Authors: Kohyama M. , Yamamoto R.
Published: March 2011

The atomic and electronic structures of tilt and twist boundaries in Si have been calculated by using the transferable semi-empirical tight-binding (SETB) method, and the relations between the local structural disorder and the electronic properties of Si have been obtained clearly. The odd-membered rings and the four-membered rings induce the changes of the shape of the local density of states (LDOS). The bond distortions generate the peaks at the band edges in the LDOS, and greatly distorted bonds induce the weak-bond states inside the band gap. The three-coordinated defect generates a deep state in the band gap, which is much localized at the three-coordinated atom. The five-coordinated defect generates both deep and shallow states. The deep state is localized in the neighboring atoms except the five-coordinated atom, although the shallow states exist among the five-coordinated atom and the neighboring atoms. Configurations of boundaries are very effective in order to clarify the effects of the local structural disorder in amorphous SI.
Defect Relaxation Dynamics in Amorphous Silicon
Authors: Cohen J. David , Leen Thomas M. , Zhong Fan , Rasmussen R.J.
Published: March 2011

Using transient capacitance and transient spin techniques, we have the determined the manner in which the mobility gap energy of the D defect is altered following a change in its charge state. This relaxation process gives rise to a power law rather an exponential thermal release of defect electrons with time and also causes the charge emission and spin transients to obey a scaling law. We also deduce that the D°/D+ transition rate depends on the tenure of the proceeding D-/D° transition. This last aspect of the D defect emission behavior implies that it must be treated as a non-Markovian process. Such relaxation dynamics have profound consequences for the steady state distribution of D defect energies. Using the relaxation parameters determined by the transient measurements we have been able to solve a set of coupled differential equations under steady-state conditions to provide the energy distributions of both the D° and DD+ defect sub-bands. The results of these calculations agree remarkably well with the experimental distributions determined by modulated photocurrent and steady-state capacitance measurements. This implies that the statistical variations in the occupation history of the defect may be the dominant factor determining both distributions.
Hydrogen Diffusion Mechanism in Amorphous Silicon From D Tracer Diffusion: Theory and Experiment
Authors: Branz Howard M. , Asher Sally , Nelson Brent P. , Kemp Mathieu
Published: March 2011

We compare experimental diffusion studies to the results of a theoretical study of diffusion controlled by a single deep trap level. Analytic solutions for the D profiles after annealing depend on the characteristic H release time, τ, from the deep trap. At times much shorter than τ, the D profile develops exponential wings whose decay length is the mean D displacement between trapping events. The long-time D profile is a solution to the ideal diffusion equation, but with an effective diffusion coefficient that can be calculated from features of the early-time profiles. New experimental data establish the validity of the model at a range of anneal times and temperatures. We also find that the mean displacement of free H before retrapping decreases with both increased illumination and increasing anneal temperature.
Effect of Gas Phase Hydrogen-Dilution on the Nucleation, Growth, and Interfaces Of a-Si1-xCx:H
Authors: Lu Yiwei , An Ilsin , Gunes M. , Wakagi M. , Wronski C.R. , Collins R.W.
Published: March 2011

The microstructural evolution of a-Si1-xCx:H with an optical gap of 1.95 eV, prepared by plasma-enhanced chemical vapor deposition (PECVD), has been studied versus gas phase H2- dilution by real time spectroscopic ellipsometry. As the H2/(CH4+SiH4) flow ratio is increased to 24, the monolayer-scale features of the growth process suggest an enhancement in precursor diffusion on substrate and film surfaces. Such features include a reduction in nucleation density, extensive surface smoothening during coalescence, and an increase the structural stability and density of the final film. We suggest a causal connection between these characteristics, and the photoelectronic properties of the film, which also improve with H2-dilution. Potentially detrimental effects of H2 dilution when a-Si1-xCx:H is deposited on TCO’s, including metal contamination at interfaces with Sn02 and H-diffusion into ZnO, are also characterized.
Defect Relaxation in a-Si:H Studied by Defect Absorption and Luminescence
Authors: Han Daxing , Xiao Yang
Published: March 2011

The experimental results about defect relaxation in a-Si:H have been reported recently on several transient measurements, such as forward-bias-transient-current,1 optical bias effect on electron drift,2 and photo-capacitance transient.3 In this paper we report the steady state results of the bias effect on sub-band-gap absorption and photon-emission spectra measurements in undoped samples.

The optical bias effects the sub-band absorption. In additional to an enhancement of the sub-band gap absorption, the absorption threshold moved from 0.8 eV to 0.6 eV for undoped samples under optical bias at room temperature. The effects are larger in the light-soaked-state than in the annealed-state.

We also report on the generation rate dependence on photoluminescence (PL) spectra line shape. We found that the energy position of the defect PL band shifted from 1.1 eV to 0.9 eV when the excitation level increased 4,000 times.

While motion of the quasi-Fermi level as a explanation cannot be eliminated, defect relaxation seems more plausible.
A New Pds Study on PECVD a-Si:H
Authors: Manfredotti C. , Fizzotti F. , Boero M. , Vittone E. , Amato G. , Boarino L.
Published: March 2011

The effect of incorporation of SiH2 on a-Si:H matrix on the optical properties has been investigated on some details. It is shown that SiH2 incorporation is responsible for a further increase of the optical gap, and also for an increase in disorder. For concentrations larger than 15% approximately, microvoids are probably created and SiH2, which is covering their inner surfaces, seems not to affect the optical properties further on. The results indicate also clearly that the effect of autoannealing of the film during its growth cannot be neglected and that a new parameter should be retained, i.e. the total deposition time.
Structural Nature of Nanocrystalline Silicon
Authors: Han Weiqiang , Han Gaorong , Qiao Jianmin , Du Piyi , Ding Zhishang , Xu Jing , Shen Zhijian
Published: March 2011

Nanocrystalline silicon (nc-Si:H) films with an average grain size ranging between 2 and 10 nm are prepared in a modified plasma chemical vapor deposition system. X-ray diffraction, transmission electron diffraction, and high resolution electron microscope are used to elucidate the structural nature in the deposited nc-Si:H films. The lattice network of the deposited silicon films changes from disordered structure to ordered structure with the increasing of plasma energy. The results also show that the crystal lattice of the nc-Si:H film is distorted from those of microcrystalline silicon and crystalline silicon. In the observed x-ray diffraction, there are two anomalous peaks at 2θ = 29.5°and 32.5°of Si besides the normal peaks at 2θ = 28.5°of Si(111) and 2θ = 47.3°of Si(220). By the high resolution electron microscopy study, a new crystallography structure with distorted Si(111) crystallites in nc- Si:H films is found. Based on our results, a structure model of nc-Si:H films is proposed.
Determination of Drift, Extended State Mobility and Recombination Lifetime in Compensated a-Si:H by Photomixing
Authors: Tang Yi , Braunstein R. , Von Roedern Bolko , Shapiro F.R.
Published: March 2011

Mobilities of a series of compensated a-Si:H samples, measured earlier by the time-of-flight technique [1], were determined by the technique of photomixing. We have found that both the extended state and the drift mobilities decrease as the compensation increases. Modelling these transport processes in the context of the photomixing technique, it is shown that long-range potential fluctuations can account for the decrease in the extended state mobility in compensated samples.
Correlation Between Minority Carrier Diffusion Length and Microstructure in a-Si:H Thin Films
Authors: Conte G. , Fameli G. , Rubino A. , Terzini E. , Villani F. , Caputo D. , Cesare G. De , Irrera F. , Palma F. , Rossi M.C.
Published: March 2011

Aim of this work is to investigate the opto-electronic properties of amorphous hydrogenated silicon (a-Si:H). The deposition temperature nas been used as a driving force to modify the morphology and bonded hydrogen distribution. The influence of the hydrogen microstructure on the carriers μτ product has been examined. The majority and minority carrier μτ have been evaluated from the diffusion length measurement, by using the Steady State Photocarrier Grating (SSPG) technique, and from the photoconductivity in the steady state condition (SSPC). The μτ values have been correlated with the defect density and the Fermi level position. Some considerations are proposed to explain the carrier transport in terms of the compositional inhomogeneities in Si:H alloys due to the morphological variations.
Physical Properties of P and B Doped Microcrystalline Si:H Deposited by PECVD
Authors: Rubino A. , Addonizio M.L. , Conte G. , Nobile G. , Terzini E. , Madan A.
Published: March 2011

Boron and phosphorus doped high conductivity microcrystalline thin films were deposited in a PECVD reactor. We report conductivities as high as 3 and 41 S/cm for B and P doped materials respectively on films deposited at 210 °C. The conductivity as well as the microcrystalline fraction increase for the n layer with decreasing RF power, while, for the p material, an increase of power is needed to improve the film characteristics. The conductivity prefactor (σo) as well as the conductivity (σ) itself as a function of the activation energy (Ea) show a slope inversion for both n and p materials at an activation energy or about 40 meV and 80 meV respectively. Different possible transport mechanisms are examined in order to explain the experimental data.
A Spectroscopic Investigation of the Amorphous to Microcrystalline Transition in Silicon Prepared by Reactive Magnetron Sputtering
Authors: Turner W.A. , Lucovsky G.
Published: March 2011

Reactive magnetron sputtering of a c-Si target in an atmosphere containing argon and a varying partial pressure of hydrogen has been used to prepared a series of samples which span the transition from amorphous to microcrystalline silicon. Samples prepared at a substrate temperature of 200 °C, power of 100 W, and Ar partial pressure of 2.10 mtorr can be divided according to the partial pressure of H2, PH2, used in the deposition. Samples deposited using PH2 ≤ 1.00 mtorr are amorphous, those deposited using P H2≥ 1.25 mtorr are microcrystalline. Raman scattering is used to confirm amorphousity/microcrystallinity. Two types of changes are observed using infrared, IR, spectroscopy. First, the IR absorption spectrum changes at the onset of microcrystallinity. The absorption centered at 630 cm-1 changes shape while the feature at 2000 cm-1 appears to shift upward to 2090 cm-1. Second, microcrystalline samples deposited using PH2 ≥ 1.50 mtorr show significant post-deposition contamination upon atmospheric exposure. This is most clearly noted by the strengthening, over time, of Si02 related absorption features which appear at 1050 and 1150 cm-1, and a weakening of a narrow component of the 630 cm-1 absorption. This narrow component is not observed in amorphous material. The strength of the O-related absorption suggests that the oxide is a bulk property. The porous, low density network which is necessary for this contamination to occur is confirmed using HRTEM.
Thermodynamic Predictions of Phase Stability and Crystallization Temperature of Silicon-Based Amorphous Alloys
Authors: Carlsson J.R.A. , Li X.H. , Gong S.F. , Hentzell H.T.G.
Published: March 2011

A thermodynamic calculation of Si-X alloys has been carried out, where X is any element from group III or V. Free-energy diagrams for those systems have been established. A comparison between thermodynamic predictions and experimental results is carried out for the Si-B and the Si-Sb alloys. It is found that the agreement between theory and experimental results for the free- energy diagrams and for the crystallization temperature predictions are good. The model and the different features for the various elements are described in detail.
Effect of Deposition-Induced Annealable Defects on Light-Induced Defect Generation in a-Si:H
Authors: Yoon Jong-Hwan
Published: March 2011

In this paper we present a method to determine the annealable defect density(ΔNann) present in hydrogenated amorphous silicon(a-Si:H). The effects of the annealable defects on the light-induced defect generation rate, saturated defect density (Nsat) and the change of defect density in the light-induced saturated state(ΔNsat) have been studied. Annealable defect density was varied by depositing samples at various substrate temperatures or by post-growth anneals of samples grown at low substrate temperatures. It is found that the generation rate, N satand ΔNsat are well correlated with ΔNann. In particular, the ΔNsat is found to follow a relation ΔNsat ≈ ΔNann. These results suggest that defect-related microscopic models are appropriate for light-induced metastability.
Annealing the Defects in a-Si:H Under Illumination
Authors: Gleskova Helena , Morin P.A. , Wagner S.
Published: March 2011

The results of a study of the kinetics of the light-induced annealing of the deep-level defects in hydrogenated amorphous silicon (a-Si:H) are presented. They show that at elevated temperatures illumination increases the rate of annealing compared to annealing in the dark. We also detected light-induced annealing at room temperature. On the basis of a model in which the defects are generated by electron-hole recombination and annealing occurs through the action of a single carrier, we found values of 0.86 eV for the activation energy of the light-induced
generation coefficient γ-1, and 1.23 eV for the light-induced annealing prefactor λ
Effects of Electrode Spacing and Hydrogen Dilution on a-SiC:H and a-Si:H Layers
Authors: Ouwens J. Daey , Schropp R.E.I. , Van Der Werf C.H.M. , Von Der Linden M.B. , Maree C.H.M. , Van Der Weg W.F. , Rava P. , Demichelis F. , Pirri C.F. , Tresso E.
Published: March 2011

A series of hydrogenated amorphous silicon carbide (a-Si1–xCx:H) films was deposited by rf glow discharge deposition using various pressures, electrode spacings and hydrogen dilution ratios. We found that improvement of the structure by hydrogen dilution is more effective when a large electrode spacing is applied. In the case of undiluted a-SiC:H, the product of pressure and electrode spacing appears to be the important parameter. Dilution causes an increase of the photoconductivity. The band gap decreases but increases again for highly diluted samples. A striking result is that the Fourier transform infra-red spectroscopy (FTIR) bands assigned to CHX and SiHx increase upon dilution when a small electrode spacing is applied, although the hydrogen content is reduced. It is shown that this is due to an increase of the density of the films and to an increase of the amount of carbon built into the bulk instead of into voids. The combination of decreasing hydrogen content, void fraction and increasing amount of carbon atoms into the bulk explains the behaviour of the photoconductivity and band gap as a function of H2 dilution.
Fast Degradation with Pulsed Light of a-Si:H P-I-N Photodiodes
Authors: Puigdollers J. , Bertomeu J. , Asensi J.M. , Andreu J. , Delgado J.C.
Published: March 2011

Amorphous Silicon p-i-nphotodiodes were obtained by PECVD in a reactor with a rotating substrate holder. Reverse currents as low as 5 × 10−11 A/cm2 at a bias of − 2V were measured using a guard ring electrode to minimize lateral edge currents. The devices were degraded by a Xenon flash lamp in open circuit conditions. The kinetics of the degradation process was evaluated by studying the long time dark current transient under reverse bias.
“Fast” and “Slow” Metastable Defects in a-Si:H
Authors: Yang Liyou , Chen Liang-Fan
Published: March 2011

A two-step light soaking experiment at high and low intensities provided convincing evidence that defect generation and annealing in a-Si:H are controlled by defect states of different characteristics. We point out that the total defect density by itself cannot uniquely determine the state of material or be described by a single rate equation, even though it might be the only quantity that is experimentally measurable. A system of rate equations for all defect components, therefore, must be established in order to accurately describe the defect kinetics. A simple two-component model in which defects are categorized as “fast” or “slow” is shown to be adequate to explain a variety of experimental results in a consistent fashion.