bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Properties and Morphology of Gan Grown by MBE on Sapphire Substrates
Authors: Tuncel E. , Oberman D. B. , Lee H. , Ueda T. , Harris J. S. 
Published: April 2011

AbstractA series of GaN films grown by MBE on sapphire substrates with different nitrogen sources are characterized by optical transmission, spectroscopic ellipsometry (SE), photoluminescence (PL) and cross-sectional atomic force microscopy (AFM). The film thicknesses determined from broad spectral range transmission measurements and the AFM images are used in the analysis of the SE spectra. Interface roughnesses between the constituent layers, such as the substrate, the buffer and GaN layers are included in the modelling of the SE spectra and are also imaged by cross-sectional AFM. An effective medium type model is used for the modelling of interface and surface roughnesses in the SE spectra. The optical constants of the films in the band edge spectral range are determined in such a way as to simultaneously satisfy the transmission and the ellipsometry data.
Characterisation of Diamond-like Carbon by Raman Spectroscopy and Optical Constants
Authors: Mölßner C. , Grant P. , Tran H. , Clarke G. , Lockwood D. J. , Labbé H. J. , Mason B. , Berriche R. 
Published: April 2011

AbstractCrystalline diamond coatings and, increasingly, diamond like amorphous carbon (DLC) films are used for tribological and protective layers for their hardness and chemical inertness. They are also under investigation for their electron emitting properties, with possible applications in field emission displays. DLC films were deposited by laser ablation using a KrF excimer laser and fluences between 0.5 and 2 J/cm2. FTIR measurements did not show the presence of hydrogen in the films. Raman spectra allowed for the determination of the nature of the graphitic and diamond bonds (sp2 and sp3) as well as information about the disorder and short range order in the films. For a better determination of the sp3-content, which is often hidden in the Raman spectra, a correlation with optical properties in the near IR to near UV region was established. These values depended strongly on the substrate temperature and the laser fluence. DLC formation could be demonstrated even at substrate temperatures close to room temperature. Vickers hardness values and first measurements on the electron emissivity of the films can be correlated to the diamond character and the preparation method of the films.
Electron Field Emission From Diamond-Like Carbon
Authors: Robertson J , Silva S R P , Amaratunga G A J , Milne W I 
Published: April 2011

AbstractThe low electron affinity of a-C:H is related to that of diamond surfaces and is studied using a chemical bonding model. The electron field emission from hydrogenated amorphous carbon (a-C:H) and nitrogen modified a-C:H showing low turn on fields are described. Nitrogen improves the field emission, apparently by raising the Fermi level.
Characteristics of XeCI Excimer-Laser Annealed Insulator
Authors: Jang Keun-Ho , Choi Hong-Seok , Jun Jae-Hong , Yoo Jhun-Suk , Han Minkoo 
Published: April 2011

AbstractThe laser annealing effects on the TEOS (Tetra-Ethyl-Ortho-Silicate) oxide of MOS (Al/TEOS/n+ Silicon ) structures was investigated with different initial oxide conditions, such as breakdown field. The breakdown field increased upto the 170 mJ/cm2 with increasing laser energy density and decreased at 220 mJ/cm2. It is considered that the increase of breakdown field is originated from the restore of strains which exist mainly at the metal/oxide interface.
Helical Resonator Plasma Oxidation of Amorphous and Polycrystalline Silicon for Flat Panel Displays
Authors: Kaluri Sita R. , Howell Robert S. , Hess Dennis W. , Hatalis Miltiadis K. 
Published: April 2011

AbstractA low temperature process for the oxidation of amorphous and polycrystalline silicon was studied using a helical resonator plasma source. Constant current anodization of amorphous silicon was performed at 350°C and 30 mtorr in an oxygen plasma. Oxidation rate data were analyzed by both parabolic and power law expressions: parabolic rate coefficient B = 23.45 nm2/min and power law rate coefficients α = 0.3807 and C* = 7.3 nm/minα. Oxidation at substrate floating conditions yielded thin oxides; the growth rate saturated after 20 mins, at a thickness of about 10 nm. For TFr fabrication, a two layer oxide was used. The first layer was grown by plasma oxidation to a thickness of about 10 nm to ensure a good interface, and the second layer deposited by PECVD to the final thickness of 35 nm. Electrical properties of control oxides grown on c-Si at the same conditions were promising, with a fixed oxide charge of 1.98 × 1011 charges/cm2 and a mean breakdown field of 5.3 MV/cm after post metallization anneal. The TF's had an average effective electron mobility of 31.1 V/cm2 and an average threshold voltage of 4.6 V.
The Poly-Si Tfts Fabricated by Novel Oxidation Method with Intermediate Oxide
Authors: Park C-M , Yoo J-S , Min B-H , Han M-K 
Published: April 2011

AbstractWe have fabricated a poly-Si TFT using a novel oxidation method, which improves the surface roughness at the interface between the poly-Si layer and the gate oxide layer. Compared with the poly-Si TFTs fabricated by the conventional oxidation method, the proposed poly-Si TFT exhibits the remarkable enhancement of the electrical parameters, such as the subthreshold swing and the threshold voltage. It is observed that the proposed poly-Si TFT has a higher dielectric strength and the device characteristics are not degraded significantly after an electrical stress. The improvement of the surface roughness at oxide/poly-Si interface is found to be critical to enhance the device performance.
Improvement of Poly-Silicon Thin Films and Thin Film Transistors Using Ultrasound Treatment
Authors: Ostapenko S. , Jastrzebski L. , Lagowski J. , Smeltzer R. K. 
Published: April 2011

AbstractUltrasound treatment (UST) was applied to improve electronic properties of polycrystalline silicon films on silica-based substrates. A strong decrease of sheet resistance by a factor of two orders of magnitude was observed in hydrogenated films at UST temperatures lower than 100°C. This is accompanied by improvement of a film homogeneity as confirmed by spatially resolved photoluminescence study. The UST effect on sheet resistance demonstrates both stable and metastable behavior. A stable UST effect can be accomplished using consecutive cycles of UST and relaxation. An enhanced passivation of grain boundary defects after UST was directly measured by nano-scale contact potential difference with atomic force microscope. Two specific UST processes based on interaction between ultrasound and atomic hydrogen are suggested: enhanced passivation of grain boundary states and UST induced metastability of hydrogen related defects. We also demonstrate a utility of UST for improvement of leakage current and threshold voltage in hydrogenated poly-Si thin film transistors.
Solid-Phase Crystallization of Amorphous Si0.7Ge0.3/Si and Si/Si0.7Ge0.3 Bilayer Films on SiO2
Authors: Kim Tae-Hoon , Ryu Myung-Kwan , Kim Jin-Won , Kim Chang-Soo , Kim Ki-Bum 
Published: April 2011

AbstractWe have investigated the solid phase crystallization of a-(Si/Si0.7Ge0.3) and a-(Si0.7Ge0.3/Si) bilayer films deposited on SiO2 for an annealing temperature of 550 °C. It was found that, in case of a-(Si0.7Ge0 3/Si), nucleation of crystalline phases occurred at the free surface, while in a-(Si/Si0.7Ge0.3) crystalline phase nucleated at Si0.7Ge0.3/SiO2 interface. The crystallization rate of an a-(Si0.7Ge0.3/Si) is much slower than that of an a-(Si/Si0.7Ge0.3) films. After full crystallization, poly-(Si0.7Ge0.3/Si) has many equiaxed grains and the defect density of the upper Si0.7Ge0.3 was much lower than that of lower Si0.7 Ge0.3 in a poly-(Si/Si0.7Ge0.3) film whose grain morphology was elliptical. The average grain size of poly-(Si0.7Ge0.3/Si) was ˜7 μm and this film had strong (111) preferential orientation, while poly-(Si/Si0.7Ge0.3) had weak (311) or random oriented grains with the average size of˜0.3 μm.
The effect of phenyl benzoate self-assembled monolayers on liquid crystal alignment
Authors: Ondris-Crawford R. J. , Lander L. M. , Frank C. W. , Twjeg R. J. 
Published: April 2011

AbstractWe have synthesized compounds of the form M-R-SiCl3where M is a mesogen based on octyloxy phenyl benzoate, and R is an alkyl chain (tether) that connects M to the silane head group. Tethering lengths from the mesogenic unit to the silane moiety involved 3, 6, or 10 methylene units. These compounds were used to form self-assembled monolayers (SAMs) on silicon wafers, fused silica, and SiO2coated indium tin oxide (ITO) coated glass. Characterization of these systems includes contact angle measurements, ellipsometry, and atomic force microscopy. Results suggest that the monolayer packing is governed by the lateral interactions between the mesogenic units and not by the tethering length to the solid surface. We have investigated the utility of these chemically-tuned surfaces for liquid crystal alignment. The octyloxy phenyl benzoate self-assembled monolayers induce homeotropic alignment of a nematic liquid crystal.
The Effect of Technology and Materials Choice on Field Emission Display Performance
Authors: Slusarczuk Marko M. G. 
Published: April 2011

AbstractThe Field Emission Display (FED) is often portrayed as the emerging alternative to the Active Matrix Liquid Crystal Display (AMLCD). FED displays are based on cold cathodes that emit electrons which are accelerated across a potential in a vacuum to strike a phosphor and emit light. There are numerous material and technology choices at each point of the display system design. Each alternative is characterized by advantages and consequences that affect subsequent choices and system performance. This paper discusses the alternative approaches to cathode material and structure, electron beam focusing, support structure, phosphor and system integration. These choices are related to ultimate display performance and cost.
Investigation Of The Nucleation And Growth Of Thin-Film Phosphors
Authors: Moss T. S. , Springer R. W. , Peachey N. M. , Dye R. C. 
Published: April 2011

AbstractThe deposition of CaGa2S4:Ce has been accomplished using a commercial liquid delivery system on two substrate surfaces: ZnS and SrS. However, the film deposited on ZnS was not of satisfactory quality because of the formation of an amorphous layer and a high amount of residual porosity within the deposition. The use of a SrS layer on top of the ZnS improved the nucleation by reducing the interfacial energy between the substrate and deposition. It greatly reduced the porosity in the coating and reduced the formation of the amorphous layer. The crystallinity of the CaGa2S4 400 peak was also increased by a factor of ten when a layer of SrS was used. Further, the FWHM of the 400 peaks from the two depositions was not significantly different, indicating that the crystallite size and strain was approximately the same. The B40 was increased by a factor of two, from 1.84 cd/m2 for ZnS to 3.67 cd/m2 for SrS. This increase is an improvement in the performance of the films and is attributable to the increase in the crystallinity.
Influence Of The Density of States and Series Resistance on the Field-Effect Activation Energy in a-Si:H TFT
Authors: Chen Chun-Ying , Kanicki Jerzy 
Published: April 2011

AbstractWe have proposed a new two-dimensional simulation model, which takes into account the density of states of hydrogenated amorphous silicon (a-Si:H) and temperature-dependence of the source/drain series resistances (Rs), to explain the dependence of the activation energy (Eact) of drain-source current (IDs) on gate-source bias (VGs) in a-Si:H thin-film transistors (TFTs). We found that the influence of series resistance cannot be ignored, else an overestimated Eact will result. The results of our simulation are in agreement with experimentally observed saturation of the Eact at higher VGs.
Investigation of the off-current in amorphous silicon thin film transistors for SiO2 and SiNx. gate insulators
Authors: Kim Jeong Hyun , Choi Woong Sik , Hong Chan Hee , Soh Hoe Sup 
Published: April 2011

AbstractThe off current behavior of hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) with an atmospheric pressure chemical vapor deposition (APCVD) silicon dioxide (SiO2) gate insulator were investigated at negative gate voltages. The a-Si:H TFT with SiO2 gate insulator has small off currents and large activation energy (Ea) of the off current compared to the a-Si:H TFT with SiNx gate insulator. The holes induced in the channel by negative gate voltage seem to be trapped in the defect states near the a-Si:H/SiO2 interface. The interface state density in the lower half of the band gap of a-Si:H/SiO2 appears to be much higher than that for a-Si:H/SiNx.
Physics of Below Threshold Current Distribution in a-Si:H TFTs
Authors: Slade H. C. , Shur M. S. , Deane S. C. , Hack M. 
Published: April 2011

AbstractWe have examined the material properties and operation of bottom-gate amorphous silicon thin film transistors (TFTs) using temperature measurements of the subthreshold current. From the derivative of current activation energy with respect to gate bias, we have deduced information about the density of states for several different transistor types. We have demonstrated that, in TFTs with thin active layers and top nitride passivation, the current conduction channel moves from the gate insulator interface to the passivation insulator interface as the transistor switches off. Our 2D simulations clarify these experimental results. We have examined the effect of bias stress on the transistors and analyzed the resulting reduction in the subthreshold slope. Based on these results, we have extended our analytic amorphous silicon TFI SPICE model to include the effect of bias stress.
Statistical Theory on Polymer Liquid Crystals
Authors: Kimura Hatsuo 
Published: April 2011

AbstractBased on common molecular model, polymer liquid crystals of hard-rod and flexible main-chain are studied statistical mechanically. The hard-core repulsion and also the attractive potentials are assumed between molecules. The nematic-isotropic phase transitions, and molecular orientations at interfaces in polymers and polymer-liquid crystal composite systems are discussed.
Molecular Dynamics of Side Chain Liquid Crystalline Polysiloxanes
Authors: Podojil G. M. , Farmer B. L. , Bunning T. J. , Pachter R. , Adams W. W. 
Published: April 2011

AbstractMolecular dynamics simulations have been used to characterize the development and longevity of associations between cholesterol and biphenyl mesogens when attached to linear siloxane oligomers by flexible spacer groups. Single substituents, alternating substituents, and diblock and triblock arrangements of the substituents were considered. The backbone and spacer groups allow sufficient flexibility that long-lived associations between cholesterol mesogens form quite rapidly, as do more fluid associations between biphenyl and cholesterol mesogens. The study of the individual mesogen interactions and how these lead to larger scale aligned structures has provided insight into the nature of the liquid crystalline state in these materials.
A Novel Rheological Microscope for Flow Studies of Thermotropic Polymers and Polymer Blends: Droplet Deformation
Authors: Mather P. T. , Stüber H. R. , Chaffee K. P. , Haddad T. S. , Romo-Uribe A. , Lichtenhan J. D. 
Published: April 2011

AbstractWe have recently begun investigating the rheological behavior of blends containing thermotropic liquid crystalline polymers (LCPs) and isotropic polymers. To aid us in our studies, we have designed a unique instrument for simultaneous visualization of morphology evolution and rheological measurements. Rectilinear shear is used, with a top glass bar being translated relative to a fixed bottom glass bar. The sample is heated by conduction from mica heaters embedded in the substrate materials supporting the bounding glass bars. Shear forces are obtained by measuring the (small) deflection of the bottom glass bar and heating assembly which is designed to be slightly compliant in the flow direction while rigid in direction normal to the sample.
Highly Uniform Oriented Liquid Crystalline Thermosets
Authors: Amendola E. , Carfagna C. , Giamberini M. , Komitov L. 
Published: April 2011

AbstractCuring of mesogenic epoxy monomer p-Bis(2, 3-epoxypropoxy)-cz-methylstilbene (DOMS) with aromatic amines is discussed. The crosslinking density is controlled using a mixture of biand tetra-functional hardener. The unidirectional alignment of the molecules was achieved during the curing process by external factors such as surface-liquid crystal interactions.
Liquid Crystals in Ternary Polyoxyethylene Trisiloxane Surfactant - Silicone Oil - H2O System
Authors: Li X. , Hill R. M. , Scriven L. E. , Davis H. T. 
Published: April 2011

AbstractPolyethylene trisiloxane surfactants M(D′En)M (n=6, 8, 10, 12) self assemble into sheet-like structure and form various lyotropic cubic, hexagonal and lamellar liquid crystal phases in ternary trisiloxane surfactant - silicone oil - water systems. Small angle X-ray scattering (SAXS) was used to identify and characterize the liquid crystal phases. Cyclic octamethylcyclotetrasiloxane (D4), decamethyl-cyclopentasiloxane(D5) and short linear decamethyltetrasiloxane (MD2M) silicone oils facilitate the formation of liquid crystals. The structures in liquid crystals (LC) progress from zero curvature lamellar liquid crystals to higher curvature cubic liquid crystals with increasing the surfactant hydrophilic head group size. The effects of surfactant and oil concentration on the lamellar bilayer thickness and molecular packing were studied with small angle X-ray scattering.
Polarized Fluorescence from Vitrified Liquid Crystalline Films
Authors: Conger Brooke M. , Shi H. , Chen S. H. , Tsutsui T. 
Published: April 2011

AbstractLinearly and circularly polarized photoluminescence (PL) were observed from neat vitrified liquid crystal (LC) films. Electronic properties of the compounds were investigated through measurement of absorption and emission spectra in solution and in film. The nematic film exhibited a polarization factor (linear polarization) of 2.8 at an order parameter of 0.70, whereas the chiral nematic film gave rise to an absolute dissymmetry factor (circular polarization) of 0.27 at an order parameter of 0.54.
Dynamics of Defect Annihilation in Vitrified Liquid Crystalline (VLC) Thin Films Upon Thermal Annealing
Authors: Shi H. , Katsis D. , Chen S. H. , De Rosa M. E. , Adams W. W. , Bunning T. J. 
Published: April 2011

AbstractBased on a series of model nematic and chiral-nematic compounds as well as a polymer analog, it was found that the annihilation of defects in a VLC system occurs at a much faster rate than its polymer analog. In chiral-nematic blends, the degree of structural similarity between the nematic host and the chiral dopant plays an important role; a wider biphasic region contributes to a slower annihilation process.
Cyclic Liquid Crystalline Siloxanes - Chemistry and Applications
Authors: Kreuzer F.-H. , Maurer R. , Stohrer J. 
Published: April 2011

AbstractCyclic Siloxanes, bearing mesogenic groups, connected with the backbone via aliphatic spacers exhibit phases analogue to the classic calamitics. Bearing two different mesogenic groups, these materials can be considered as cooligomers, whose degree of polymerization is given by the H-siloxanes used. These cooligomers consist of a mixture of molecules with substitution patterns determined by the statistics of the addition reaction of the mesogenic groups to the H-siloxane. Two types of materials are available, crosslinkable and non crosslinkable. As most important applications may be mentioned: Cholesteric reflectors and filters, storage materials for optical informations, retardation plates and pigments for iridescent or polarizing coatings.
Morphology and Mechanical Properties of Pc/Lcp in Situ Composites With Compatibilizer
Authors: Leng Y. , Zheng W. G. 
Published: April 2011

AbstractA bisphenol A epoxy resin is used to modify compatibility between PC and LCP (Vectra B950, a wholly aromatic liquid crystalline polymer) during injection molding. LCP can effectively reinforce PC, since it forms in situ micro-fibrils in the thermoplastic PC matrix during melt flow. However, the immiscibility of PC and LCP affects the mechanical performance of the LCP in situ composite. Preliminary results of this work indicate that epoxy might improve the interfacial bonding between PC and LCP fibrils, and also modify the tensile properties of the PC/LCP system.
Peculiarities of the Structure and Properties of Liquid-Crystal Composites Based on Polymer Complexes
Authors: Lazareva T. G. , Vashuk E. V. , Yakovleva O. V. , Prodan S. A. 
Published: April 2011

AbstractSome features of the: formation of liquid-crystal structures based on polymer complexes are discussed for composites of polyvinyl alcohol with cellulose esters, polyacids, inorganic acids and variable-valence metals. Rheological and optical methods of research as well as a dielectric relaxation method have revealed the formation of several types of interpolymer complexes in liquid flowable media. This leads to formation of associates and results in an increase of the molecular mobility of macromolecules and their fragments. The structure and properties of the complexes depend on the media compositions and on the method of additive introduction. The composites obtained -can be used for producing light-, electric- and heat-sensitive film materials and sensors of various types.
Switchable Bragg Gratings Formed in Situ Within a Polymer-Dispersed Liquid Crystal Composite Medium
Authors: Sutherland R. L. , Natarajan L. V. , Bunning T. J. , Tondiglia V. P. , Adams W. W. 
Published: April 2011

AbstractHolographic photo-curing of a penta-acrylate monomer-liquid crystal mixture forms a unique system of liquid crystal microdomains confined to Bragg planes. We examine the physics of this structure as it relates to the formation of electrically switchable holograms, for which many potential applications exist. The results of scanning electron microscopy and laser characterization studies lead to the development of concepts and models for explaining the microscopic morphology and electro-optical properties of these holograms. We find that a model incorporating a shaped-droplet analysis of the electro-mechanical properties of LC domains combined with standard coupled-wave theory of holography offers good numerical agreement with diffraction efficiency data for ppolarized probe light.
Investigations of Silicon Nitride Films for Silicon Solar Cells
Authors: Elmiger J. R. , Kunst M. 
Published: April 2011

AbstractSilicon nitride films on crystalline silicon were deposited in a low-temperature (< 400 °C ) Plasma Enhanced Chemical Vapour Deposition process. The deposition process is monitored with in situ Time Resolved Microwave Conductivity measurements leading to an on-line quality control of the deposited films. It is shown that at the start of the deposition there is a strong decrease of the lifetime of the measured transient signal due to plasma induced damage at the silicon surface. Afterwards an increase of the lifetime is observed due to passivation of the interface. For thin films (< 30 nm), the lifetime and the film composition depend on the film thickness. Furthermore, the film composition has a strong impact on the passivation of thick (100 nm ) silicon nitride films. The best passivation is obtained for almost stoichiometric films characterized by a refractive index of 1.95.