bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microcrystalline β-SiC Growth on Si by ECR-CVD at 500°C
Authors: Cheng Kuan-Lun , Liu Chih-Chien , Cheng Huang-Chung , Lee Chiapyng , Yew Tri-Rung 
Published: April 2011

ABSTRACTMicrocrystalline β-SiC films were deposited on silicon substrates by electron cyclotron resonance chemical vapor deposition (ECR-CVD) at 500°C utilizing a SiH4-CH4-H2 gas mixture. The effects of two important parameters on film growth, SiH4/CH4 flow ratio and microwave (MW) power, were investigated using X-ray photoelectron spectroscopy (XPS) along with the Fourier transform infrared spectra (FTIR). Results showed that the optimum flow ratio is about 0.5. Under the optimum flow ratio, a large MW power is favorable for the growth of high quality films with an ideal film stoichiometry. Surface morphology inspected by the contact mode atomic force microscopy (AFM) reveals that high MW powers not only improve the film crystallinity but also increase its surface roughness as well.
X-Ray Diffraction Study of Clusters in a-tC Films
Authors: Martínez-Miranda L. J. , Friedmann T. A. , Sullivan J. P. , Siegal M. P. , Mercer T. W. , DiNardo N. J. , Fang F. 
Published: April 2011

ABSTRACTWe performed an X-ray diffraction study of amorphous-tetrahedrally-coordinated carbon (a-tC) films prepared by pulsed laser deposition (PLD). The samples' properties were analyzed as a function of laser energy and thickness. For all thicknesses and laser energies, films were made up of clusters with a basic unit size of 7 -11 nm. Thicker films, as well as films prepared at higher laser densities exhibit larger clusters, in the tens of nanometers. The clusters are not readily observable by AFM, which may indicate the presence of a flat (graphitized) top film surface.
Early Stage of Polycrystalleve Growth of Ge and SiGe by Reactive Thermal Cvd from GeF4 and Si2H6
Authors: Hanna Jun-Ichi , Ohuchi Takayuki , Yamamoto Masaji 
Published: April 2011

ABSTRACTWe have investigated the structure and crystallinity of poly SiGe and Ge films in the early stage of their growth prepared at < 450°C by means of a new type of thermal CVD from GeF4 and Si2H6. Raman study and SEM observation of the films revealed that the nucleation of crystallites took place directly on the substrate, followed by the grain growth in a manner of island growth. Thus, the crystallinity of the films is well established even in the very early stage of the growth, probably < 10 nm in thickness, in contrast to the poly Si growth in the low-temperature CVD precesses.
Thin Film Polycrystalline Si by Cs Solution Growth Technique
Authors: Wallace Richard L. , Anderson Wayne A. , Jones K. M. 
Published: April 2011

ABSTRACTA deposition process has been developed which allows the growth of large grain (20+ μm) polysilicon films on SiO2 substrates at a growth temperature of 650° C. A thin layer of liquid Si-metal solution is formed on the substrate surface as the growth medium. This layer is kept saturated by Si flux from a DC magnetron sputter gun. XRD analysis of the deposited films show a strong (111) preferred orientation, with increasing integrated peak intensities with increasing depositon temperature and solution layer thickness. Films deposited using an In-Si solution are p-type, with carrier concentrations in the mid 1016 cm−3 range. Conductivities of ∼.2 (Ω cm)−1 were measured, with activation energies for both carrier generation and conductivity of about 135meV. The hole mobility was found to be ∼ 30 cm2 V−1s−1. A wetting layer is used which may have a detrimental effect on the minority carrier lifetime.
The Crystalline Quality of Epitaxial Si Layers Solution Grown on Polycrystalline Si Substrates
Authors: Albrecht M. , Steiner B. , Bergmann Th. , Voigt A. , Dorsch W. , Strunk H. P. , Wagner G. 
Published: April 2011

ABSTRACTWe investigate the crystalline and electrical quality of thin layers epitaxially grown on polycrystalline substrates from metallic solution by the method of electron beam induced current, transmission electron microscopy and etching experiments. We observe a reduced recombination strength of dislocations and small angle grain boundaries, i.e. an improved electrical quality of the epitaxial layer compared to the substrate. The improved quality can be attributed (i) to an altered structure of grain boundaries and dislocations and (ii) to a reduced defect density in the epitaxial layer.
High-Quality Polycrystalline Silicon Thin Film Prepared by a Solid Phase Crystallization Method
Authors: Baba T. , Matsuyama T. , Sawada T. , Takahama T. , Wakisaka K. , Tsuda S. 
Published: April 2011

ABSTRACTWe succeeded, for the first time, in depositing a silicon film which features 1000Å-wide single-crystalline grains embedded in a matrix of amorphous tissue. The deposition was done by plasma-enhanced CVD from silane diluted with hydrogen at a considerably high temperature (550°C). 5pm-thick undoped amorphous silicon film was deposited on the above film and was crystallized by a solid phase crystallization method. The polycrystalline silicon film which was obtained has a columnar structure and shows an extremely high electron mobility of 808 cm2/Vs.
Effect of Deposition Temperature on the Photoresponse of Crystallized Hydrogenated Amorphous Silicon Films
Authors: Sridhar Nagarajan , Chung D. D. L. , Anderson W. A. , Coleman J. 
Published: April 2011

ABSTRACTThe deposition temperature of hydrogenated amorphous silicon films deposited by dc glow discharge was found to affect the photoresponse (ratio of the photo to dark conductivity) after crystallization of the film. This effect depended on the crystallization technique. For crystallization by laser annealing, the photoresponse (0.15 - 1.5) increased with increasing deposition temperature (150 - 300 °C) due to the increase in SiH and SiH2 bonding, as shown by infrared spectroscopy. For crystallization by furnace annealing (e.g. 650 °C, 50 h), the photoresponse (0.08 - 0) decreased with increasing deposition temperature (150 - 300 °C) due to the decrease in grain size and crystallinity as shown by x-ray diffraction; the complete loss in hydrogen during furnace annealing made the photoresponse low and the silicon-hydrogen bonding effect immaterial. Thus, laser crystallization at the highest deposition temperature gave the highest photoresponse.
Diffusion Behavior of B-, As- and Sb-Dopants in Thin Epitaxial Layers
Authors: Krautschneider W.H. , Lau F. , Gossner H. , Schaefer H. 
Published: April 2011

ABSTRACTAdvanced CVD- and MBE-epitaxy allows processing of very thin epitaxial layers with extremely steep dopant gradients. As steep dopant profiles are very sensitive to temperature treatments, the impact of thermal processing from 800°C to 1000°C on the dopant redistribution in epitaxial layers was investigated.
Inorganic Fullerenes of MX2 (M=W,Mo;X=S,Se)
Authors: Tenne R. , Margulis L. , Feldman Y. , Homyonfer M. 
Published: April 2011

ABSTRACTThe gas-phase reaction between MoO3-x and H2S in a reducing atmosphere and at elevated temperatures (800° to 950°C) has been used to synthesize large quantities of an almost pure nested inorganic fullerenes (IFs) phase of MoS2. A uniform IF phase with a relatively narrow size distribution was obtained. The x-ray spectra of the different samples show that as the average size of the IF decreases the van der Waals gap along the c axis increases, largely because of the strain involved in folding of the lamella. Large amount of quite uniform nanotubes were obtained under modified preparation conditions.In the second part of this work MoS2 nested fullerenes were grown on Ti and Nb and Mo oxide substrates. In one set of conditions hollow nested fullerenes of MoS2 were collected on a titanium oxide matrix, and analyzed by local area energy dispersive analysis. Under different flow conditions of the reacting gasses nested fullerenes with endohedral metal oxides were obtained and analyzed by electron diffraction.
Inter-Cage Orbital Interactions in [2+2] and [4+4] Dimers of Buckminsterfullerene
Authors: Ōsawa Shūichi , Ōsawa Eiji 
Published: April 2011

ABSTRACTGeometry optimization of [2+2]- and [4+4]-dimers of C60 by semiempirical AMI MO method reveals usual length for the bridge bonds of the former but unusually long bonds for the latter. Perturbational analysis of molecular orbitals confirm the presence of orbital interaction through bond (OITB) between the cages in the [2+2] dimer but no interaction in the [4+4] dimer. These results contradict with previous examples of OITB wherein elongation of the mediating σ bond is usually observed.
Combustion Synthesis of Fullerenes
Authors: Richter H. , Fonseca A. , Thiry P. A. , Gilles J. M. , Nagy J. B. , Lucas A. A. 
Published: April 2011

ABSTRACTThe formation of fullerenes by combustion was investigated for nine benzene/oxygen/argon flames, one acetylene/oxygen/argon- and one toluene/oxygen/argon flame burning at 75 mbar. The flame-generated soot was Soxhlet extracted with toluene and the extract analyzed by HPLC. It was shown that the C60/C70ratio depends on the percentage of argon in the fresh gas mixture, which is directly related to the flame temperature. The use of acetylene and toluene as combustible led also to the formation of fullerenes, the yield in the toluene flame being 3.71% of the generated soot, so that toluene represents a serious alternative to benzene for fullerene fabrication in flames.
Qualitative Model for Fullerene Formation
Authors: Astakhova Tanya Yu. , Shaginyan Shagen A. , Vinogradov George A. 
Published: April 2011

ABSTRACTA new mechanism of fullerene formation is presented. The ”gas-liquid” transition in the expanding flux of carbon atoms is considered as a necessary initial stage. The transition is not terminated at the liquid phase formation as the more powerful processes of network formation predominate. The process of clusters formation starts with the transformation of three-contact structures to stable two-dimensional networks and is governed by the carbon atoms specificity: three-functionality and high rate of chemical reactions. The resulting network is a flat hexagonal lattice with pentagonal ”defects” bending the surface, the free energy minimum structures being fullerenes.
Controlling the Reactivity of C60: A Theoretical Analysis of the Electronic States Modulated by Substitutional Chemistry
Authors: Wang S.-H. , Kashani M. , Jansen S. 
Published: April 2011

ABSTRACTThe availability of large amounts of Buckminsterfullerene has allowed a plethora of experimental investigations on fullerenes. The chemical and physical studies have focussed on synthesis, isomerism, magnetism, spectroscopy and high temperature superconductivity in doped materials. The chemical reactivities of fullerenes have been defined and most of the studies are dominated by C60 isomers. Some of the observed activities of fullerenes parlled those of alkeies. In our previous studies, the reactivity of the 6-6' bond with respect to eco- addition was described. Current studies have exploited the olefinic nature of the 6-6' bond and analyzed the effect of the addition on cluster stability and frontier character. In this work, we describe the mechanisms of simple substitution and analyze stability and orbital effects for the addition chemistry of C60 with multiple species. Evolving changes in orbital frontier character are analyzed with respect to site directed chemistry exhibited by C60.
Fullerenes Under Pressure Studied by 13C-NMR
Authors: Auban-Senzier Pascale , Kerkoud R. , Jerome D. , Rachdi F. , Bernier P. 
Published: April 2011

ABSTRACTHigh pressure is an important parameter for the study of C60 and doped fullerenes as these molecular crystals are very compressible. 13C-NMR experiments under pressure in K3C60 have given access to the determination of the 13C Knight shift and the chemical shift of this superconducting compound. These NMR data do not reveal significant effects of Coulomb correlations in K3C60 and support a pairing mechanism for superconductivity mediated by intramolecular vibrations.We report also a 13C-NMR investigation of Rb4C60 under pressure and temperature. The temperature dependence of the spin-lattice relaxation rate clearly shows, under pressure, the increase of a linear contribution which gradually substitutes to the exponential behaviour present at ambient pressure. The activated relaxation is attributed to intrinsic spin excitations through the direct Jahn-Teller gap whereas the closing of a small indirect gap under pressure gives rise to a semimetal and a Korringa like relaxation.
The Superconducting Energy Gap of Rb3C60 as measured by IR Transmission in Thin Films
Authors: Koller Daniel , Martin Michael C. , Mihaly Laszlo 
Published: April 2011

ABSTRACTThe superconducting energy gap of Rb3C60 has been measured by infrared transmission through a thin film. Resistivity measurements on the same samples in situ indicate a transition to superconductivity at the expected temperature, ∼30K, with distinct gap features appearing in the transmission below this temperature. The results are interpreted in terms of the BCS theory.
Structural Characterization of a Polymer Substituted Fullerene (Flagellene) by Small Angle Neutron Scattering
Authors: Affholter K.A. , Bunick G.J. , Desimone J.M. , Hunt M.O. , Menceloglu Y.Z. , Samulski E.T. , Wignall G.D. 
Published: April 2011

ABSTRACTSmall-angle neutron scattering (SANS) can structurally characterize fullerenes1in solvents with strong SANS contrast (e.g. CS2). Deuterated solvents (e.g. toluene-d8) have a high scattering length density (SLD), which is close to that of C60and C70moieties. Hence, there is virtually no SANS contrast with the solvent and these particles are practically “invisible” in such media. On the other hand, the negative scattering length of hydrogen means that the SLD of H1-containing materials is much lower, so they have strong contrast with toluene-d8. Thus, SANS makes it possible to study the size and shapes of modified buckyballs such as the polymer-substituted fullerenes, or flagellenes2. These consist of C60cores to which 1-4 polystyrene chains (with a molecular weight, MW ≃ 2000) are attached. The extrapolated cross section at zero angle of scatter [dΣ/dΩ(0)]s is a function of the number of pendant chains, so SANS can be used to assess the number of “arms” which are covalently attached to the fullerene “sphere”. Close agreement (± 4%) between the measured and calculated values of dΣ/dΩ(0) along with independent estimates of the radius of gyration (Rg) and second virial coefficient (A2) for a calibration linear polystyrene sample serves as a cross check on the validity of this methodology.
Microdielectric Measurements of Pristine and Modified thin Fullerene (C60) Films
Authors: Pevznert B. , Hebard A. F. , Haddon R. C. , Senturiat S. D. , Dresselhaus M. S. 
Published: April 2011

ABSTRACTAs developed by Senturia and co-workers [1], microdielectrometry is a technique for measuring complex permittivity utilizing microfabrication technology to incorporate both the interdigital sensing electrodes and associated circuitry on the same microchip. By covering a microdielectrometer chip with a thin layer of C60, it is possible to dynamically monitor the film's frequency response and dielectric properties as a function of doping with selected gases and other species.It is known that solid C60 has a substantial amount of interstitial volume. The presence of mobile ions in these spaces compromises the breakdown voltage and makes pure C60 unsuitable for applications requiring high-quality dielectric films. However, various immobile ions or neutral species (e.g. oxygen) can be made to fill the interstitial volume, changing the characteristics of the C60 films and, in some cases, improving the dielectric properties. In-situ microdielectric measurements of pristine and modified C60 films were performed for frequencies ranging from 0.005 Hz to 100 kHz. Based on the low-frequency behavior of the dielectric constant, a model is proposed for the mechanism of oxygen diffusion into the interstitial spaces of the fullerene material.
Fragmentation of C60 Molecules in Partially Ionized Fullerene Beam Deposition
Authors: Ren Zhong-Min , Xiong Xia-Xing , Du Yuan-Cheng , Ying Zhi-Feng , Chen Liang-Yao , Li Fu-Ming 
Published: April 2011

ABSTRACTC60 films have been deposited using a partially ionized cluster beam deposition (PIBD) technique. The experimental results show that as Va. exceeds about 400 V almost all the C60 molecules fragmentate at collision with the substrate and the obtained films turn to be amorphous carbon layers at elevated Va, indicated by measurements of Raman spectra, X-ray diffraction, and ellipsometry.
Doping of C60 Films Using High Energy Boron Ion Implantation
Authors: Ren Zhong-Min , Du Yuan-Cheng , Xiong Xia-Xing , Ying Zhi-Feng , Li Fu-Ming , Xu Xing-Long 
Published: April 2011

ABSTRACTC60 films, which are deposited by partially ionized beam deposition (PIBD), are doped by 100 keV boron ion implantation at dose ranging from 3*1014 to 1*1016 cm2 The implantation process has been studied using Fourier transform infrared spectroscopy (FTIR), Raman spectra and X-ray diffraction (XRD) analyses. Almost all C60 soccer-balls in the doped region in the films are found to be broken at dose of 1*1016 cm2, while at dose less than 6*1014 cm2 a few C60 molecules remain undestroyed and maintain the original structural properties.
Structural and Electronic Properties of Damaged Fullerite Crystals
Authors: Manfredini M. , Serra S. , Colombo L. , Milani P. 
Published: April 2011

ABSTRACTA structural tranfsormation of C60 crystals has been induced by high fluence laser irradiation under various chemical environments. The role of oxygen in driving fullerene cage opening reactions is investigated. The resulting material, showing features typical of low density amorphous carbon, has been characterized by Raman spectroscopy. In order to provide an atomistic model of the damaged sample, we have simulated the irradiation process by a tight binding molecular dynamics calculation on a 240-atoms system. We have carefully investigated the structural and electronic properties. In particular, the short- and medium-range features have been related to the cage opening, which is here modeled as a sequence of bond breakings.
Multiphoton Ionization Mass Spectroscopy of Fullerenes in Methane Diffusion Flames
Authors: Hepp H. , Siegmann K. , Sattler K. 
Published: April 2011

ABSTRACTMultiphoton ionization time-of-flight mass spectrosocopy is used as an on-line technique to investigate polycyclic aromatic hydrocarbons (PAH) and fullerenes in atmospheric pressure flames. We have recorded height profiles of neutral PAH and fullerenes in methane/argon diffusion flames. Fullerenes ranging from C32 to at least C150 are found in a region where PAH concentration starts to decrease. Uniformity of the profiles indicates that the fullerenes do not grow from smaller to larger ones. The influence of the amount of argon additive is discussed.
Physical Phenomena in Ferroelectric Thin Films: Study and Modeling
Authors: Petrovsky Vladimir I. , Pevtsov Eugeniy Ph. , Sigov Alexsander S. 
Published: April 2011

ABSTRACTAn impact of different factors on the shape of dielectric hysteresis loop in ferroelectric thin films is discussed. They include: polycrystallinity and disorientation of polarization axis, polarization nonuniformity and depolarization fields, interface contact layer and series capacity, contact potential difference and interaction of volume impurity centers with polarization field. A comparison between models and experiment show that compromise of interface layer and space charge permits to explain all main distortions of dielectric hysteresis loop in thin films at realistic parameters of the layers. The obtained results permit to explaine the distortions of real hysteresis loop and also to obtain quality parameters of samples, which are important for improving of film preparation techniques.
Ferroelectric Film Self-Polarization
Authors: Sviridov E. , Sem I. , Alyoshih V. , Biryukov S. , Dudkevich V. 
Published: April 2011

ABSTRACTIn the present paper three mechanisms of self-polarization of ferroelectric crystals are discussed: polarization by the crystal bending, that by the “organized” Phase transition and that by the internal field. It is shown that these mechanisms operate also in the case of films. However, the using of cathode sputtering leads to the appearance of two new mechanisms: polarization by the field biasing the substrate with respect to the gas discharge at the film deposition temperature Ts below the Curie point temperature Tc (Ts < TO; and polarization by the field captured by the traps of the negative charge having no time to relax for the time of cooling the film to Tc (Ts > Tc).
Deposition of Strontium Barium Niobate Thin Films by Metal-Organic Chemical Vapor Deposition and Their Nonlinear Optical Properties
Authors: Nystrom M.J. , Wessels B.W. , Neumayer D.A. , Marks T.J. , Lin W.P. , Wong G.K. 
Published: April 2011

ABSTRACTSingle phase, highly textured strontium barium niobate (SBN) thin films were deposited by low pressure metal-organic chemical vapor deposition on both crystalline and amorphous substrates. The metal precursors employed were niobium pentaethoxide as well as barium and strontium (hexafluoroacetylacetonate)2•tetraglyme. SBN thin films with compositions across the entire solid solution range were deposited. The nonlinear optical properties of the SBN films were also measured. Nonlinear optical coefficients approaching bulk values were obtained for as-deposited oriented films. The room temperature, effective second-order nonlinear coefficient was 3.0 pm/V. Films with the highest degree of crystalline perfection had the largest effective nonlinear coefficient. The second harmonic intensity was strongly temperature dependent with a maximum at the ferroelectric transition.
Light Influence on Fatigue in PZT Films with Planar Electrodes
Authors: Dudkevich V.P. , Sem I.M. , Sviridov E.V. , Surowiak Z. 
Published: April 2011

ABSTRACTA set of fatigue measurements has been performed on RF-sputtered PZT films of about 2 urn in thickness. Polarization switching characteristics with the sinusoidal ac electric field applied were studied both with sandwich and planar electrodes. Planar structure has allowed one to study the influence of the free charge carriers induced by UV -illumination in the planar capacitor gap. The fatigue became noticeable after 106 switching cycles for a sandwich structure and after 109 cycles for the films with planar electrodes. Illuminating the film during polarization switching greatly accelerates the fatigue process. The additional fatigue induced by the photoactive light was completely reversible.
Photoferroelectric Phenomena in Sn2P2S6 Single Crystals and Thin Films
Authors: Arnautova E. , Kosonogov N. , Rogach E. , Pavlov A. , Protsenko N. , Grekov A. 
Published: April 2011

ABSTRACTTne present paper is devoted to the experimental study and the analysis of photoferroelectric phenomena in ferroelectric-semiconductor Sn2P2S6 crystals and films. These photoactive light-induced phenomena observed in polarized Sn2P2S6 samples are described by the model of screening the depoling field of remanent polarisation by free charge carriers fixed at the deep energy levels.
Structural and Ferroelectric Properties of SrBi2Ta2O9 Thin Films
Authors: Amanuma Kazushi , Hase Takashi , Mtyasaka Yoicht 
Published: April 2011

ABSTRACTStructural and electrical properties were investigated for chemically prepared SrBi2Ta2O9(SBT) thin films on Pt/Ti/SiO2/Si substrates. Good ferroelectric properties were obtained with a Pt top electrode: Pr=10.0μC/cm2 and Ec-34kV/cm. Au top electrodes resulted in smaller Pr. However, no fatigue was observed up to 109 switching cycles regardless of the top electrode material. Grains were spherical, not columnar, and the average grain size was 200nm. A marked structural change took place in the bottom Pt/Ti electrode during film preparation. The SIMS analysis indicates the reaction between Bi and Pt