bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stress Induced During the Solid-phase Crystallization of Amorphous Silicon Deposited by LPCVD
Authors: Mohammed-Brahim T. , Kis-Sion K. , Briand D. , Sarret M. , Lebihan F. , Fortin B. 
Published: April 2011

AbstractThe Solid Phase Crystallization (SPC) of amorphous silicon films deposited by Low Pressure Chemical Vapor phase Deposition (LPCVD) using pure silane at 550'C was studied by in-situ monitoring the film conductance. The saturation of the conductance at the end of the crystallization process is found transient. The conductance decreases slowly after the onset of the saturation. This degradation is also observed from other analyses such as ellipsometry spectra, optical transmission and Arrhenius plots of the conductivity between 250 and 570K. Hall effect measurements show that the degradation is due to a decrease of the free carrier concentration n and not to a decrease of the mobility. This indicates a constant barrier height at the grain boundaries. The decrease of n is then due to a defect creation in the grain. Hence, whatever the substrate used, an optimum crystallization time exists. It depends on the amorphous quality film which is determined by the deposition techniques and conditions and on the crystallization parameters.
Optical Transmittance of Thin Films of SrFeO2.5+x at Elevated Temperatures and Applications to Gas Sensing
Authors: Post Michael , Yao Jianhua 
Published: April 2011

AbstractNon-stoichiometric perovskites with the general formula SrFeO2.5+x have potential in oxygen sensing applications. Thin films of these compositions have been grown onto various substrates by pulsed laser deposition techniques. At elevated temperatures, (T > 550K), the films react rapidly and reversibly with oxygen and the bulk oxygen content, x, of the films changes. Accompanying the change in oxygen stoichiometry are significant changes in the optical transmittance and reflectance of the films. Transmission spectrophotometry in the uv-vis region has been used to determine the relationship of transmittance with oxygen composition in the gas phase. Spectrophotometric data have been obtained by a batch method and also in-situ in a flow cell at T = 690K. The data show a large variation in transmittance, exceeding 103 for the batch measurements, with SrFeO3 showing the highest opacity. The design of the flow cell is also described.
Structural and Magnetic Properties of γ-Fe2O3 Particles Coated with TiO2
Authors: Borodko Y. G. , Bokhimi  , Acosta D. , Ioffe L. M. , Viveros T. , Bosch P. , Nava N. 
Published: April 2011

AbstractThe surface of single-domain acicular magnetic gamma-Fe203 particles was coated with titania shell and the effect of this coating on the remanent induction and coercive force was measured.
Mechanism of Thermally Assisted Creep Crack Growth
Authors: Golubović Leonardo , Moldovan Dorel 
Published: April 2011

AbstractWe use atomistic Monte-Carlo simulations to investigate the dynamics of cracks which sizes are smaller than the Griffith length. We demonstrate that such cracks can irreversibly grow proviso their size is larger than a certain critical length which is smaller than the Griffith length, as recently suggested [ L. Golubović and A. Peredera, Phys. Rev. E51, 2799 (1995)]. We show here that this thermally assisted creep crack growth is dominated by irreversible changes in the region of the crack tip, primarily in the form of dislocation emissions and nucleation of microcavities and voids. These processes act together during the crack growth: the crack tip region acts as a source for emissions of dislocations which subsequently serve as seeds for creation of vacancy clusters in a region away but still close to the crack tip. Eventually, passages between these vacancy clusters and the mother crack are formed and the crack thus increases in size. As this process repeats, the crack grows.
Spatial Redistribution of Niobium Additives Near Nickel Surfaces
Authors: Muratov Leonid S. , Cooper Bernard R. 
Published: April 2011

AbstractThe spatial redistribution of niobium atoms near the surface of pure nickel has been considered in the low niobium concentration limit. The calculation of free energy includes lattice relaxation around niobium atoms by using molecular dynamics (MD) incorporating atomistic potentials based on ab-initio quantum mechanical calculations and includes vibrational entropy phenomenologically within the local harmonic approximation.
High Toughness Alumina/Aluminate: The Role Of Hetero-Interfaces
Authors: Brito M. E. , Yasuoka M. , Kanzaki S. 
Published: April 2011

AbstractSilica doped alumina/aluminate materials present a combination of high strength and high toughness not achieved before in other alumina systems, except for transformation toughened alumina. We have associated the increase in toughness to crack bridging by anisotropically grown alumina grains with concurrent interfacial debonding of these grains. A HREM study of grain boundaries and hetero-interface structures in this material shows the absence of amorphous phases at grain boundaries. Local Auger electron analysis of fractured surfaces revealed the coexistence of Si and La at the grain facets exposed by the noticeable intergranular fracture mode of this material. It is concluded that a certain and important degree of boundaries weakness is related to both, presence of Si at the interfaces and existence of alumina/aluminate hetero-interfaces.
Scaling Of Fracture In Quasibrittle Materials And The Question Of Possible Influence Of Fractal Morphology
Authors: Bažant Zdeněk P. 
Published: April 2011

AbstractThe paper presents a review of recent results on the problem of size effect (or the scaling problem) in nonlinear fracture mechanics of quasibrittle materials and on the validity or recent claims that the observed size effect may be caused by the fractal nature of crack surfaces. The problem of scaling is approached through dimensional analysis and asymptotic matching. Large-size and small-size asymptotic expansions of the size effect on the nominal strength of structures are presented, considering not only specimens with large notches (or traction-free cracks) but also structures with no notches. Simple size effect formulas matching the required asymptotic properties are given. Regarding the fractal nature of crack surfaces, it is concluded that it cannot be the cause of the observed size effect.
Crack Growth and Propagation in Metallic Alloys
Authors: Morrey W. C. , Wille L. T. 
Published: April 2011

AbstractUsing large-scale molecular dynamics simulation on a massively parallel computer, we have studied the initiation of cracking in a Monel-like alloy of Cu-Ni. In a low temperature 2D sample, fracture from a notch starts at a little beyond 2.5% critical strain when the propagation direction is perpendicular to a cleavage plane. We discuss a method of characterizing crack tip position using a measure of area around the crack tip.
New Polymer Precursors To SiNCB Materials
Authors: Wideman T. , SU K. , Remsen E. E. , Zank G. A. , Sneddon L. G. 
Published: April 2011

ABSTRACTThe first borazine/silazane backbone copolymers derived from the parent borazine, B3N3H6, have been obtained by the thermal condensation of borazine with either of two silazanes, tris(trimethylsilylamino)silane (TTS) or 1,1,3,3,5,5- hexamethylcyclotrisilazane (HCT), to yield copolymers of typical composition (B3N3H4)1.00(N)1.17(SiMe 3)1.16 (SiH)0.34 and (B3N3H4) 1.00(N) 1.67(SiMe 2)1.49(H) 1.5, respectively. Despite their similar compositions, upon pyrolysis the TTS copolymers yield B1.0N1.0Si<0.2 ceramics, while the ceramics derived from the HCT copolymers showed greater retention of silicon and carbon with typical compositions of B1.0N1.5Si0.4C0.2 The XRD spectra show the materials are amorphous to 1400 °C, but show crystalline phases of β-Si3N4, °C, with no diffraction from any boron-containing species. The DRIFT spectra of the ceramics, however, indicate the presence of boron nitride.
Qualitative and Quantitative Analysis of Stacking Disorder in α-and β-SiC by X-ray Diffraction and Structure Modeling
Authors: Palosz Bogdan , Stel'makh Svetlana , Gierlotka Stanislaw 
Published: April 2011

ABSTRACTA method of analysis of disordering in α- and β-SiC polycrystals by numerical modeling, and a simulation of X-ray diffraction profiles are presented. The diffraction patterns of nonperiodic structures were simulated for models of 2000 layer fragments of the structure. Computer generation of the models was based on the Poisson function describing the size distribution of the domains of basic polytypes and faults. The models were quantified by a set of input probability parameters describing relative frequencies of the occurrence of the domains of polytypes and faults. Implementation of a correlation parameter that characterizes coherence of sequential domains of a given polytype assures a good reproducibility of the simulated diffraction profiles obtained for the same set of the model parameters. Based on this method, a quantitative analysis of disordering in polycrystals of SiC annealed in the temperature range 1100–2200 °C was performed.
Plasma Enhanced Chemical Vapor Deposition of Zirconium Nitride Thin Films
Authors: Atagi Lauren M. , Samuels John A. , Smith David C. , Hoffman David M. 
Published: April 2011

ABSTRACTDepositions of high quality zirconium nitride, (Zr3N4), films using the metal-organic precursor Zr(Net2)4 were carried out in a microwave argon/ammonia plasma (2.45 GHz). The films were deposited on crystalline silicon wafers and quartz substrates at temperatures of 200–400 °C. The transparent yellow films have resistivity values greater than MΩ cm. The stoichiometry is N/Zr = 1.3, with less than 5 atom % carbon and little of no oxygen. The hydrogen content is less than 9 atom %, and it does not vary with deposition temperature. The growth rates range from 600 to 1200 Å/min, depending on the flow rates and precursor bubbler temperature. X-ray diffraction studies show a Zr3N4 film deposited at 400 °C is polycrystalline with some (220) orientation. The crystallite size is approximately 30 Å. The band gap, as estimated from transmission spectra, is 3.1 eV.
Ternary Bismuth Chalcogenides for Thermoelectric Applications. Synthesis and Charge Transport Properties of New Compounds in the K-BI-S System.
Authors: Kanatzidis Mercouri G. , McCarthy Timothy J. , Tanzer Troy A. , Chen Li-H. , Hogan Tim , Kannewurf Carl R. , Iordanidis Lykourgos 
Published: April 2011

ABSTRACTKBi6.33S10 and K2Bi8S13 were synthesized by the direct combination of K2S/Bi2S3 at high temperature (>700°C). The reaction of K2S/3.3Bi2S3 at 800°C revealed the presence of a new ternary sulfide KBi6.33S10 (I) (92% yield). The structure consists of blocks of Bi2Te3 and Cdl2-type units that are connected to form a three-dimensional network with K+ ions located in the channels that run along the b-axis. The same reaction but with a different ratio, at 750°C, gave the new ternary sulfide K2Bi8S13 (II) (94% yield). The structure of the shiny rod-like crystals is closely related to that of I. As in I, it also consists of Bi2Te3 and Cdl2-type fragments that connect to form K+-filled channels. The two potassium atoms and one bismuth atom are disordered over three sites. Some preliminary electrical and optical properties of these materials are discussed.
Kinetics of Reactions Between Silica and Carbon and the Formation of Silicon Carbide
Authors: Wiik Kjell , Motzfeldt Ketil 
Published: April 2011

ABSTRACTThe reactions taking place between coarse grained mixtures of silica (cristobalite) and carbon (graphite) at 1558°C in pure CO as well as mixtures of CO and Ar, have been subjected to a thermogravimetric investigation. A model is developed in the regime where the formation of SiC does not take place. The primary steps are assumed to be: Reaction betweefn SiO2 and CO to give SiO(g) and CO2 followed by the reaction between CO2 and C to give CO. The model predicts the prevailing partial pressure of SiO throughout the charge, and the correlation between observations and model strongly supports the above given reaction mechanism.Enhanced and accelerating reaction rates were observed when the formation of β-SiC took place. It is suggested that this is due to the continuous formation of stable SiC-nucleus on the Csurface and the subsequent shortening of the diffusion path for SiO.
Silicon Nanotechnology for Biofiltration and Immunoisolated Cell Xenografts
Authors: Ferrari M. , Chu IW. , Desai IT. , Hansford D. , Mazzoni G. , Huen T. , Zhang M. 
Published: April 2011

AbstractSilicon-based clean-room technology is employed for the microfabrication of a particle filter with uniform pore dimensions in the 20-40-nm range. Surface and bulk micromachining are integrated in the fabrication process, resulting in a filtering membrane with large active area, flow rate and resistance to pressure. The microfabricated membrane is especially suitable for biofluid purification, including viral elimination. The nanofilter is a technological precursor for a microfabricated, silicon-based capsule to be employed in the reaction-free xenotransplantation of cells. Results are presented below that address the issue of biocompatibility of the microfabricated capsule components and materials.
Osteoconduction on, and Bonding to, Calcium Phosphate Ceramic Implants
Authors: Dziedzic D. M. , Savva I. H. , Wilkinson D. S. , Davies J. E. 
Published: April 2011

AbstractCalcium phosphate ceramic blocks of three different densities, porous, intermediate and dense, were prepared by tape casting (total = 18), and implanted in the femora of 9 Wistar rats for 1 to 3 weeks. Following fixation, the tissue was prepared for examination by scanning electron microscopy (SEM) of freeze fractured specimens, or back-scattered electron imaging (BSEI) of polymethylmethacrylate (PMMA) embedded, undecalcified, sections. The results demonstrated that while all ceramics were osteoconductive, the 93 % dense implants showed no evidence of bone bonding as judged by the plane at which specimens separated or cracked during preparation for microscopy. The porous ceramics, on whose surfaces both multinucleated cells and osteoid tissue were observed at all implantation times, exhibited less bone contact than the other two groups. Both SEM and BSEI showed that there was bone growth into the microporosity of both intermediate and porous ceramics, pore size range 1−2μ m, to a depth of about 6μm. The latter corresponds to the thickness of natural bone lamellae. In all implants examined,de novobone formed on the ceramic surface by the initial production of a biological cement-line like interfacial extracellular matrix. The results clearly show that osteoconduction and bone-bonding are distinct mechanistic phenomena. While we assume the former to be a consequence of protein adsorption events culminating in anchorage of osteoblasts to the implant surface, the latter is the result of mechanical interdigitation of the extracellular matrix, produced by osteoblasts, with the microtopography of the implant surface.
Self-Assembling Peptide Monolayers: Endothelial Cell Behavior on Functionalized Metal Substrates
Authors: Chaikof E.L. , Wang H. S. , Wingert T. M. , Stephens S. , Dluhy R. A. 
Published: April 2011

AbstractDespite the high initial success rate with metallic stents for the treatment of a variety of vascular lesions, problems have included occlusion due to thrombus formation or intimal proliferation. Improving the biological behavior of these and other other implantable metallic devices may require the use of biomimetic peptide coatings which promote specific cellular responses at the biological-materials interface.Thiol-terminated peptides, without the addition of a cysteine residue, were synthesized by a modification of standard solid phase methodology. Gold/mica or gold/glass surfaces were exposed for 6 hours at 23 °C to one of three peptide solutions: GRGD(βA)3YNH(CH2)2SH (RGD); (βA)6NH (CH2)2SH (bAla); or a 1:1 mix of both peptides. Peptide films were examined by external reflectance infrared (IR) spectroscopy and atomic force microscopy (AFM) which confirmed the presence of unique close-packed structures for bAla and the 1:1 mix. Endothelial cell proliferative, migratory, and adhesive behavior were evaluated using 3H-thymidine and 51Cr labeling techniques, respectively. Cell proliferation, migration, and adhesion were significantly higher on RGD containing peptide films.Well-ordered protein assemblies on metallic substrates can be produced with the proper choice of peptide chain structure and terminal residues. Biological activity is a function of film composition and oligopeptide pendant structure.
Apatite Nucleation on Low Porosity Silicon in Acellular Simulated Body Fluids
Authors: Canham L T , Reeves C L 
Published: April 2011

AbstractThe response of a range of porous Si films to acellular simulated body fluids has been monitored by SEM, EDX and FTIR analyses. Quite low levels of porosity are shown here to induce hydroxyapatite growth both on top of the film, and even on neighbouring areas of bulk Si, which in isolation have no such effect. The in-vitro demonstration of hydroxyapatite nucleation by a porous semiconductor could provide further insight into the phenomenon of bioactivity and help realise a broader range of bioactive materials.
Method for Calculation of Dielectric Properties of Modulated Semiconducting Structures
Authors: Mirovitskii V. Yu. , Mashtakov O. Yu. 
Published: April 2011

AbstractA new method for calculation the effects of composition modulation upon the dielectric properties of semiconductors is proposed. Specific consideration is carried out for ultrathin [001] oriented (AIIICV)m(BIIICV)n superlattices (SL). These SL are formally considered to result from complete A(B) atoms orderiig over a-sublattice in a hypothetical initial structure –bulk mixed crystal (AxB1−x)C with zincblende lattice and x = m/(m + n). From this point of view a variation in dielectric constants tensor (DCT) induced by the ordering can be calculated nearly in a spirit of the phenomenological Landau theory of second-order phase transitions. It is shown that the changes in spatial dispersion of the DCT are expressed through the coefficients at invariants in the expansion of SL thermodynamic potential in a power series of the order parameter components. The way is described for numerical estimation of the thermodynamic potential coefficients from microscopic model of the initial alloy which take account of spatial correlations in A(B) atoms distribution.
Growth of Uniform InGaAs Bulk Crystal by Multi-Component Zone Melting Method
Authors: Kusunoki T. , Nakajima K. , Shoji H. , Suzuki T. 
Published: April 2011

AbstractWe have developed a Multi-component Zone Melting method to grow a ternary compound crystal which has a uniform composition. A 4.5 mm long InGaAs bulk crystal with a uniform InAs composition of 0.3 has been successfully grown using this method. InGaAlAs/InGaAs strained quantum well lasers were fabricated on an In0. 2Ga0.8As substrate which was grown by this method. A minimum threshold current density of 280 A/cm2 was achieved.
A New Structure Design “Multiple-Quantum Barrier in Active Region” for High Temperature Operation of AlGaAs Superluminescent Diode
Authors: Kumar Rajesh , Kuno Hironari , Tomita Kazuyoshi , Hara Kunihiko 
Published: April 2011

AbstractA multiple-quantum barrier (MQB) structure has been applied to AlGaAs superluminescent diode (SLD) to suppress the electron overflow from active to cladding region at elevated temperatures. It was found that the presence of MQB in the p-cladding region leads to stagnant hole transport to the active region. To improve the hole transportation, we propose a new quantum structure for active region. In this design, the superlattice structure MQB is located in the middle of active region which allows smooth hole injection to the active from the cladding region. Carriers can reach both side of the MQB structure in the active region by tunneling phenomenon which critically depends on the barrier thickness. Simulation results show that low energy electrons can tunnel through the MQB barriers, while high energy electrons are reflected back by effective barrier. Finally, multiple-quantum well (MQW) structure is integrated at each side of MQB to minimize the possible over-flow of tunneled electrons and to improve the radiative efficiency of the SLD device. Experimental data support the visibility of the proposed ‘MQB+MQW in Active’ structure at elevated temperatures.
Sputtered SiO2:C Films Showing Visible Photoluminescence
Authors: Sendova-Vassileva M. , Tzenov N. , Dimova-Malinovska D. , Josepovits K. V. 
Published: April 2011

AbstractLuminescent a-Si:O:C layers were obtained by magnetron co-sputtering and annealing. Maximum photoluminescence intensity is comparable to that of porous silicon. Luminescence maximum is between 1.8 eV and 2.2 eV. X-ray photoelectron spectroscopy (XPS) finds Si-O, C-Si and C-C bonding. Secondary ion mass spectrometry(SIMS) data are presented.
New Technique for Ohmic Formation
Authors: Hara S. , Teraji T. , Okushi H. , Kajimura K. 
Published: April 2011

AbstractWe propose a new systematical method to control Schottky barrier heights of metal/semiconductor interfaces by controlling the density of interface electronic states and the number of charges in the states. The density of interface states is controlled by changing the density of surface electronic states, which is controlled by surface hydrogenation and flattening the surface atomically. We apply establishing hydrogen termination techniques using a chemical solution, pH controlled buffered HF or hot water. Also, slow oxidation by oxygen gas was used to flatten resultant semiconductor surfaces. The density of interface charges is changeable by controlling a metal work function. When the density of surface states is reduced enough to unpin the Fermi level, the barrier height is determined simply by the difference between the work function of a metal φm and the flat-band semiconductor ØsFB. In such an interface with the low density of interface states, an Ohmic contact with a zero barrier height is formed when we select a metal with φm < φsFB. We have already demonstrated controlling Schottky and Ohmic properties by changing the pinning degree on silicon carbide (0001) surfaces. Further, on an atomically-flat Si(111) surface with monohydride termination, we have observed the lowering of an Al barrier height.
Comparison of TiN films produced by TDEAT (Ti[N(C2H5)2]4), TDMAT (Ti[N(CH3)2]4), and a new precursor TEMAT (Ti[N(CH3)C2H5]4)
Authors: Lee J-G , Kim J-H , Shin H-K , Park S-J , Yun S-J , Kim G-H 
Published: April 2011

AbstractTiN films have been deposited by chemical vapor deposition (CVD) from a new TiN precursor, tetrakis(ethylmethylamino)titanium (TEMAT), and compared with those from tetrakis(diethylamino)titanium (TDEAT) and tetrakis(dimethylamino)titanium (TDMAT) in terms of film quality and conformality. The TDEAT process at 350°C provides films with low resistivity of ˜2500μΩ-cm and 30% carbon. In addition, films deposited from TDEAT contain no oxygen and show good stability in resistivity with time. Furthermore, this process provides bottom-coverage ranging from 65% at 275°C to 30% at 350°C. In contrast, excellent bottom-coverage of ˜90% over 0.5μΩ contact holes is obtained by the TDMAT process. However, films deposited from TDMAT are air-reactive upon air-exposure, resulting in a large increase in resistivity when exposed to air. The use of TEMAT, possessing physical properties between those of TDMAT and TDEAT, allows less air-reactive and better crystalline films, compared with TiN films from TDMAT. It is also observed that the carbon level is ˜2x lower than that in TiN films from TDEAT. Futhermore, this process provides good step-coverage in 0.35μΩ contacts with an aspect ratio of 2.9. Consequently, the TEMAT process can be an attractive choice for sub-0.5 μΩ application.