bluuebunny/crossref_metadata_2025_split huggingface dataset:
Surface defects on MgO thin films: Their detection using metastable impact electron spectroscopy and interaction with probe molecules
Authors: Stultz Jeffrey A. , Kolmakov Andrei , Lai Xiaofeng , Kim Young Dok , Goodman D. Wayne 
Published: April 2011

AbstractMgO thin films having different defect densities are explored in this study using metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS), temperature programmed desorption (TPD), and scanning tunneling microscopy (STM). Surface point defects on MgO exhibit themselves in both the MIES and UPS spectra as a feature approximately 2 eV above the valance band, whereas extended defects are only observed spectroscopically as a broadening of the O 2p band. The interaction of NO and N2O with the MgO surface as a function of surface defect density is explored. Upon adsorption on MgO thin films at 100K, both NO and N2O show the development of three features which coincide with a standard gas phase N2O spectrum. The saturation coverage of N2O from NO adsorption increases with increasing defect density, indicating that defect sites are mainly responsible for N2O formation. STM images confirm the increase of thin film defect density upon thermal quenching.
Synchrotron X-ray Studies of Molecular Ordering in Confined Liquids
Authors: Kim Hyunjung , Seeck O. H. , Lee D. R. , Kaendler I. D. , Shu D. , Basu J. K. , Sinha S. K. 
Published: April 2011

AbstractX-ray specular and off-specular reflectivity studies have been carried out to study the density modulations in liquids confined between two smooth silicon mirrors. The special technique as well as the advantages of using high energy and high brilliance synchrotron x-ray beams for carrying out such experiments will be discussed. Results will be presented on the ordering of octamethyl-cyclotetrasiloxane (OMCTS) as a function of the confining pressure, where we find evidence of layering as the gap is decreased from macroscopic down to a few nanometers.
Spectroscopic Studies of Liquid Crystals Confined in Sol-gel Matrices
Authors: Fehr Carlos , Dieudonne Philippe , Bac Christophe Goze , Gaveau Philippe , Sauvajol Jean-Louis , Anglaret Eric 
Published: April 2011

AbstractThermotropic liquid crystals (5CB and 8CB) were confined in silica porous matrices (xerogels and xero-aerogels) with different pore sizes. The structure and dynamics of confined liquid crystals were studied by Raman spectroscopy and Nuclear Magnetic Resonance. In Raman, the frequency of the CN stretching peak is a good probe of the smectic_A-crystal phase transition. The CN peak is observed to split upon quenching. This suggests a coexistence of crystalline and supercooled liquid phases for confined LC which was not observed in the bulk. In NMR, strong differences in both chemical shifts and linewidths are observed in confinement with respect to the bulk. We present a model which analyses the changes in the spectra in terms of changes of the order parameter and molecular dynamics for the confined LC.
Surface and Volume Diffusion of Water and Oil in Porous Media by Field Cycling Nuclear Relaxation and Pgse NMR
Authors: Godefroy S. , Korb J.-P. , Petit D. , Fleury M. , Bryant R. G. 
Published: April 2011

AbstractThe microdynamics of water and oil in macroporous media with SiO2 or CaCO3 surfaces has been probed at various temperatures by magnetic field-cycling measurements of the spin-lattice relaxation rates. These measurements and an original theory of surface diffusion allowed us to obtain surface dynamical parameters, such as a coefficient of surface affinity of the liquid molecules and the surface diffusion coefficient. The water surface diffusion coefficients are compared to the volume self-diffusion coefficients of water in pores, measured by PGSE method, the latter values being more than an order of magnitude higher than the surface ones. Complementary information on the nature of the solid-liquid interface was given by NMR chemical shift experiments at high magnetic field.
The Formation of Striped Phases by Charge Localization in Vanadium Phosphates
Authors: Bontchev Ranko P. , Do Junghwan , Jacobson Allan J. 
Published: April 2011

ABSTRACTThe compound (H3O)1.5{[VO(H2O)]PO4}3·2.5H2O is a new member of a series of vanadium phosphates containing vanadium in both plus four and five oxidation states. Charge ordering occurs in these mixed vanadium phosphate layered compounds forming striped phases with different periodicities. The VOPO4 layers undulate as a consequence of differences in the O-O atom distances in the ordered V(V)O6 and V(IV)O6 octahedra.
A New Three-dimensional Lanthanide Framework Constructed by Oxalate and 3,5-pyridinedicarboxylate
Authors: Lawandy Michael A. , Pan Long , Huang Xiaoying , Li Jing , Yuen Tan , Lin C. L. 
Published: April 2011

ABSTRACTHydrothermal reactions of rare-earth metal acetates and nitrates with oxalic acid (H2C2O4) and 3,5-pyridinedicarboxylic acid (H2pddc) in triethylamine/water solutions have yielded five isostructural polymers with the general formula: [Ln(pddc)(C2O4)1/2(H2O)2]·H2O. [Ln = La(1), Pr(2), Nd(3), Eu(4) and Er(5)]. These compounds crystallize in monoclinic crystal system, space group P21/n, Z = 4, with only slight variations in their unit cell parameters: 1 a = 7.747(2), b = 9.954(2), c = 15.134(3) Å, = 98.64(3)°, V = 1153.8(4) Å3; 2 a = 7.707(2), b = 9.895(2), c = 15.006(3) Å, β = 98.54(3)°, V = 1131.7(4) Å3; 3 a = 7.688(2), b = 9.897(2), c = 14.955(3) Å, β = 98.43(3)°, V = 112 5.6(4) Å3; 4 a = 7.638(2), b = 9.842(2), c = 14.809(3) Å, β = 98.42(3)°, V = 1101.2(4) Å3; 5 a = 7.573(2), b = 9.761(2) Å, c = 14.630(3) Å, β = 98.10(3)°, V = 1070.7(4) Å3. The structure of these compounds is composed of 2D Ln(pddc) layers that are interconnected by chelating oxalate. Within the layer, each rare-earth metal forms a monodentate bond with each of the four pddc groups. The metal centers in the neighboring layers are bridged through µ4-oxalate, resulting in a three-dimensional framework. The remaining two sites around the eight-coordinate Ln are occupied by water molecules. Compounds 2, 3, and 5 exhibit paramagnetic behavior and 1 is diamagnetic. They are thermally stable up to 250°C.
Two Pillared Three-Dimensional Inorganic/Organic Hybrid Structures Composed of Bimetallic Layers Bridged by Exo-bidentate Ligands
Authors: Pan Long , Huang Xiaoying , Li Jing 
Published: April 2011

ABSTRACTThe hydrothermal reactions of Cu(NO3)2.3H2O, K2CrO4 and exo-bidentate ligand bpy/bpe, (bpy = 4,4'-bipyridine, bpe = trans-1,2-bis(4-pyridyl)ethylene) result in two pillared 3D organic-inorganic hybrid compounds. Both contain bimetallic layers of copper(II) cations and chromate anions, which are directly connected by different organic ligands, leading to pillared structures with varying pillar length and thickness of layers. Crystal data for [Cu3(CrO4)2(OH)2(bpy)2] (1): triclinic, P1, a = 5.358(1), b = 5.603(1), c = 13.515(3) Å, α = 81.78(3), γ = 86.56(3), Å3 = 79.75(3)°, V = 394.91(13) Å3, Z = 1; [CuCrO4(bpe)] (2): monoclinic, C2/c, a = 23.282(5), b = 11.917(2), c = 9.726(2) Å, β = 112.99(3)°, V = 2484.2(8) Å3, Z = 8.
ESCA and Vibrational Spectroscopy of Alkali Cation Exchanged Manganic Acids with the 2×2 type Tunnel Structure Synthesized via Different Chemical Routes
Authors: Tsuji Masamichi , Kanoh Hirofumi , Ooi Kenta 
Published: April 2011

ABSTRACTManganese dioxides have received much attention over the last two decades as ion exchangers. Actually these are typically mixed-valence compounds and the terminology of ‘dioxide’ is not appropriate. The mechanisms for their variety of chemical reactivities are still open for study. On the cation uptake mechanism there are strong claims that a redox process is involved in cation uptakes by manganic acids synthesized by substituting H+ for alkali cations incorporated in ‘hydrous manganese dioxides’. The present work was carried out to physically demonstrate the alkali cation exchange mechanism on tunnel-structured manganic acids and to study the ion exchange with lattice vibrational spectroscopy. Manganic acids were prepared through the redox process using KMnO4 and MnSO4, and thermal decomposition of (CH3)3COK and MnCO3 at 530°C. ESCA spectra of their alkali cation exchanged forms indicated no evidence of redox process and supported the ion exchange mechanism on these materials. Their infrared absorption spectra strongly depended on their preparation routes and are closely related to their ion-exchange selectivity of each material. Thus, the vibrational spectra of manganic acids take an important role as a synthesis index together with XRD patterns.
Study of Calcium/Lead Apatite Structure Type for Stabilising Heavy Metals
Authors: Dong Z.L. , Wei B. , White T.J. 
Published: April 2011

ABSTRACT(CaxPb10−x)(VO4)6F2 apatites were synthesised and their microstructures were studied using powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy before and after leach testing. X-ray diffraction showed that the apatites were hexagonal with a ≍ 10Å and c ≍ 7Å. During the leach test, Pb was released into the solution more slowly than Ca, which is desirable as the immobilisation of Pb is of importance. The experimental results also showed that V was almost undetectable in the leaching test solutions. In the (Ca7Pb3)(VO4)6F2 pellet, Ca and Pb distributions were not homogenous from one grain to another. Microstructural evidence from scanning electron microscopy revealed that the dissolution via development of etch pits began at grain boundaries and inside grains, and progressed faster in Ca rich regions. These results suggest that apatites of high Pb to Ca ratio are more durable.
Nickel Determination by Complexation Utilizing a Functionalized Optical Waveguide Sensor
Authors: Carter Erin S. , Dahmen Klaus-H. 
Published: April 2011

ABSTRACTThis research focuses on the design of chemically functionalized optical waveguide sensors. The waveguide is an optically transparent sol-gel coated onto a glass substrate chip. By having a higher refractive index than the substrate, the waveguide internally reflects a laser beam to photodetectors at both ends of the chip. The adsorption of any species onto the waveguide surface changes the light propagation, and therefore its effective refractive index, N. The change in N is dependent upon the amount of analyte present. By covalently bonding specific chemical receptors onto its surface, it can be designed to target a particular analyte. This research involves functionalizing the surface of the waveguide with ED3A in order to complex out of solution Ni2+. The change in N and the thickness of the adlayer will allow the concentration to be determined.
In situ XAFS study on cathode materials for lithium-ion batteries
Authors: Nonaka Takamasa , Okuda Chikaaki , Ukyo Yoshio , Okamoto Tokuhiko 
Published: April 2011

ABSTRACTNi and Co K-edge X-ray absorption spectra of LiNi0.8Co0.2O2 have been collected using in situ coin cells. To investigate the electronic and structural changes accompanied by the capacity fading during electrochemical cycling and keeping batteries at high temperatures, the cells with different cycling states and keeping conditions (temperature, time) were prepared. Upon charging the cell, the Ni and Co K absorption edge shifted towards higher energy, and the good correlation between the range of chemical shifts upon charging and the capacity of the cell was observed. From quantitative analysis of EXAFS data, it was revealed that the capacity fading is closely related to the Jahn-Teller distortion of the NiO6 octahedron.
Relation between Erbium Photoluminescence and Dangling-Bond Defects in a-Si:H
Authors: Kumeda Minoru , Itoh Hiroshi , Shitakata Norio , Shimizu Tatsuo 
Published: April 2011

ABSTRACTIn order to study a role of Si dangling bonds in the Er photoluminescence mechanism in a-Si:H, we prepared Er-doped a-Si:H films with various densities of Si dangling bonds using rf magnetron sputtering method. The density of Si dangling bonds was changed by three ways: (1) change of Ar-to-H2 gas ratio in the sputtering ambient, (2) light soaking and (3) annealing. The intensity of the Er photoluminescence at 1540 nm tends to decrease with increasing the density of Si dangling bonds in the first two cases. In the case of annealing, the intensity of the Er photoluminescence first increases with a decrease in the density of Si dangling bonds due to the structural relaxation up to 250 °C and continues to increase up to 350 °C even though the density of Si dangling bonds increases due to hydrogen evolution. This increase in the photoluminescence intensity is probably caused by a change of the environment of Er ions.
Light-induced Annealing of Deep Defects in Low Ge Fraction a-Si,Ge:H Alloys: Further Insights into the Fundamentals of Light-induced Degradation
Authors: Cohen J.David , Heath Jennifer , Palinginis Kimon C. , Yang Jeffrey C. , Guha Subhendu 
Published: April 2011

ABSTRACTModulated photocurrent (MPC) was employed to study metastable deep defect creation and annealing in low Ge fraction a-Si,Ge:H alloys (Ge fractions below 10at.%). These MPC spectra reveal two distinct bands of deep defects identified as neutral Si and neutral Ge dangling bonds. Upon heating in the dark from a strongly light degraded state, these are reduced in direct competition to each other, therefore implying a global reconfiguration mechanism. We have extended our studies to compare purely thermal annealing with light-induced annealing in these alloys. We have found that the relative anneal rate for the two types of defects differs from the case of purely thermal annealing. This therefore tends to rule out models in which the rate limiting step during annealing comes from the release of the mediating entity from a remote site.
Network Rebonding Model for Metastability in Amorphous Silicon
Authors: Biswas R. , Pan B.C. , Ye Y. 
Published: April 2011

ABSTRACTWe propose a new network rebonding model to describe light-induced metastability in hydrogenated amorphous silicon. This model involves global changes in both the silicon and hydrogen bonding sites. The first step in the process is the breaking of a weak silicon bond generating a dangling bond and floating bond pair. The mobile floating bond diffuses away leaving behind an isolated dangling bond in agreement with ESR measurements. Tight-binding molecular dynamics simulations show clear evidence for each of these processes. Floating bonds are an intermediate transient species that do not remain in the light-soaked steady state. Floating bonds annihilate by reacting with SiH bonds and locally displacing hydrogen atoms. This model provides a new explanation for several major experimental features of the Staebler-Wronski effect, including the t1/3 kinetics for the growth of defects, and the anticorrelation of dangling bonds with H. This new model provides a new platform for understanding the atomistic origins of light-induced degradation.
Tailoring the Structure of Low-Temperature-Deposited Microcrystalline Silicon Films by Biasing the Substrate
Authors: Birkholz Mario , Selle Burkhardt , Fuhs Walther , Williamson Don L. 
Published: April 2011

ABSTRACTBiasing the substrate during deposition and the substrate's surface morphology may both have major effects on the structural properties of thin films. We present the results of structural investigations (Raman and FTIR spectroscopy, XRD, SAXS) of thin silicon films that were prepared at low temperatures by electron-cyclotron resonance (ECR) chemical-vapor deposition. The effect of substrate bias during the deposition was investigated for positive DC susceptor biases VB ranging from 0 to 45 V. For stainless steel substrates with an artificially enlarged surface roughness (smart substrates), an increase of the crystallinity could be observed with Raman spectroscopy. Films prepared under a susceptor bias of +15 V exhibited a texture inversion of preferential (220)- to (111)- oriented grains, which was accompanied by an increase in grain size from 18 to 42 nm. Small-angle X-ray scattering (SAXS) revealed the films as deposited on Al foil to exhibit significant free volume fractions (microvoids). The ability of tailoring the structure of thin Si films by applying a bias is discussed in terms of controlling the energy and intensity of ion flux to the surface of the growing film. This can efficiently be achieved in an ECR system, where the mean free path of gas particles exceeds the thickness of the plasma sheath.
Microscopic Aspects Of Charge Transport In Hydrogenated Microcrystalline Silicon
Authors: Fejfar Antonín , Mates Tomáš , Koch Christian , Rezek Bohuslav , Švřek Vladimír , Fojtík Petr , Stuchlíková Ha , Stuchlík Jiř́ , Kočka Jan 
Published: April 2011

ABSTRACTCharge transport in hydrogenated microcrystalline silicon (µc-Si:H) is determined by structure on several size scales: i) local atomic arrangement (<1 nm), ii) crystalline grains and their boundaries (1-10 nm), iii) grain aggregates or columns (0.1-1 µm) and finally iv) features comparable to layer thickness (0.1-10 µm). We first summarize our experimental results concerning these effects: differences of conductivities of grains and amorphous tissue measured locally by conductive AFM, transport anisotropy observed by comparing dark conductivity and ambipolar diffusion length parallel and perpendicular to the substrate, and finally thickness dependence of transport parameters (e.g. dark conductivity activation energy and prefactor). Most of these phenomena can be described by using a novel model of the µc-Si:H growth leading to a structure known as Voronoi adjacency network. The model is based on the nearest neighbor constrained growth. To our knowledge, the Voronoi structure is the first structural model able to predict structure and transport properties of the µc-Si:H and it may become a basis for the future predictive model of µc-Si:H based solar cells.
P-channel Polycrystalline Silicon Thin Film Transistors on Steel Foil Substrates
Authors: Wu Ming , Wagner Sigurd 
Published: April 2011

ABSTRACTWe fabricated self-aligned polycrystalline silicon (polysilicon) thin film transistors on flexible steel substrates. The polysilicon was formed by furnace crystallization of hydrogenated amorphous silicon at 950°C/20sec or 750°C/2min. The TFTs made from these polysilicon films have hole field effect mobilities in the linear regime of 22 cm2·V−1s−1 (950°C) and 14 cm2·V−1s−1 (750°C). The OFF current at 10 V drain-source voltage is 10−10A and the drain current ON/OFF ratio is ∼106.
Microcrystalline silicon solar cells prepared by 13.56 MHz PECVD at high growth rates: Solar cell and material properties
Authors: Roschek Tobias , Rech Bernd , Beyer Wolfhard , Werner Peter , Edelman Felix , Chack Albert , Weil Raoul , Beserman Robert 
Published: April 2011

ABSTRACTMicrocrystalline silicon (μc-Si:H) solar cells were prepared in a wide range of deposition parameters using 13.56 MHz plasma-enhanced chemical vapour deposition (PECVD). The best μc-Si:H solar cells were prepared close to the transition to amorphous silicon (a-Si:H) growth at very high deposition pressures (∼10 Torr) showing solar cell efficiencies up to 8.0 % at a deposition rate of 5ÊÅ/s. Investigations of the solar cells were performed by Raman spectroscopy and transmission electron microscopy (TEM). TEM measurements revealed similar structural properties with similar high crystalline volume fractions for these cells although they showed distinctly different efficiencies. However, an increased amorphous volume fraction was detected by Raman spectroscopy for the low efficiency cells prepared at low deposition pressures. This result is attributed to an increased ion bombardment at low pressures.
Solar Cell Performance Under Different Illumination Conditions
Authors: Gemmer Christian , Schubert Markus B. 
Published: April 2011

ABSTRACTWe numerically simulate performance data of hydrogenated amorphous silicon (a-Si:H) and copper indium gallium diselenide (CIGS) based solar cells for various illumination conditions. For ease of comparison, we model typical single junctions with the very same software. The study allows us to evaluate the cell feasibility in different hybrid electronic systems like smart cards, wrist watches, transponder systems, and mobile sensors. At an illumination intensity of 1 sun, the optical bandgap of the absorber material and the series resistances determine the spectral sensitivity of the solar cell to particular illumination spectra. For intensities of 10-2 suns and so-called D65 spectrum, which represents daylight under cloudy skies, the efficiency of a-Si:H solar cells nearly equates the CIGS cell performance although the AM 1.5 efficiency of the CIGS diode exceeds the one of our a-Si:H cell by more than a factorof two. Infrared-weighted black body radiation leads to superior performance of the CIGS type, whereas for ultraviolet-weighted illumination the a-Si:H cell shows better performance. For intensities below 10-4 suns theexternal shunt resistance dominates the current-voltage characteristics of both cell types, resulting in poor performance independent of the incident spectrum. We complete our study by simulating the solar-powered charging process of a gold capacitor, which serves us as a model for the energy storage within a hybrid electronic system. The charging behavior under various realistic illumination conditions shows particular cellcharacteristics: high open circuit voltages qualify a-Si:H solar cells for electronic systems that require increased voltages and CIGS cells are suited for applications with higher current need.
Hydrogenated Amorphous Silicon / ZnO Shottky Heterojunction for Position Sensitive Detectors
Authors: ǵuas H. , Nunes P. , Fortunato E. , Silva R. , Silva V. , Figueiredo J. , Soares F. , Martins R. 
Published: April 2011

ABSTRACTIn this work a new structure is proposed for position sensitive detectors consisting of glass/Cr/a-Si:H(n+)/a-Si:H(i)/ZnO, where the ZnO forms an heterojunction with the a-Si:H(i). The results show that this structure works with success in the fabrication of linear position sensitive detectors. The devices present a good nonlinearity of ͌ 2% and a good sensitivity tothe light intensity. The main advantages of this structure over the classical p-i-n are an easier to built topology and a higher yield due to a better immunity to the a-Si:H pinholes, since the ZnO does not diffuse so easily into a-Si:H as the metal does, which are the cause of frequent failure in the p-i-n devices due to short-circuits caused by the deposition of the metal over the a-Si:H. In this structure the illumination is made directly on the ZnO, so a transparent substrate is not needed and a larger range of substrates can be used.
Basic mechanisms of structural relaxation and diffusion in amorphous silicon
Authors: Barkema G. T. , Mousseau Normand , Vink R.L.C. , Biswas Parthapratim 
Published: April 2011

ABSTRACTThe low-temperature dynamics in amorphous silicon occurs through a sequence of discrete, activated events that reorganize the topology of the network. In this review, we present some recent work done to understand better the nature of these events and the associated dynamics ina-Si. Using the activation-relaxation technique (ART), we generated more than 8000 events in a 1000-atom model ofa-Si, providing an extensive database of relaxation and diffusion mechanisms. The generic properties of these events, such as the number of involved atoms and the activation energies, were investigated and foundto be in agreement with experimental data. As it turns out, the bond-transposition mechanism proposed by Wooten, Winer and Weaire (WWW) some time ago plays an important role in the events generated by ART. We have therefore turned to an optimized version of the WWW algorithm to generate the best overall configurations ofa-Si available today. We discuss the details of the optimization and present the structural and electronic properties of the resulting models.