bluuebunny/crossref_metadata_2025 huggingface dataset:
Synchrotron X-ray Absorption Spectroscopy Studies of Pt/Si Systems
Authors: Coulthard I. , Naftel S. J. , Shama T. K.
Published: April 2011

Platinum was deposited onto porous silicon by a reductive deposition technique utilizing the inherent reducing power of porous silicon. The resulting deposits were studied by X-ray Absorption Near Edge Structure (XANES) at the Si-K, Pt-M3, 2, and Pt-L 3 ,2 edges. Samples of varying deposition concentrations were studied and were compared with untreated porous silicon and platinum silicides to determine the nature of the deposits and their effect upon the porous silicon substrate itself.
Exafs characterisation of amorphous GaAs
Authors: Ridgway M. C. , Glover C. J. , Foran G. J. , Yu K. M.
Published: April 2011

The structural parameters of stoichiometric, amorphous GaAs have been determined with extended x-ray absorption fine structure (EXAFS) measurements performed in transmission mode at 10K. Amorphous GaAs samples were fabricated with a combination of epitaxial growth, ion implantation and selective chemical etching. Relative to a crystalline sample, the nearest-neighbor bond length and Debye-Waller factor both increased for amorphous material. In contrast, the coordination numbers about both Ga and As atoms in the amorphous phase decreased to ˜3.85 atoms from the crystalline value of four. All structural parameters were independent of implantation conditions and as a consequence, were considered representative of intrinsic, amorphous GaAs as opposed to an implantation-induced extrinsic structure.
Real time In Situ X-Ray Topographic Observation of Deformation of Single Crystals and Thin Films
Authors: Zhao Z. B. , Hershberger J. , Chiaramonti A. , Rek Z. U. , Bilello J. C.
Published: April 2011

An experimental apparatus, which is capable of performing real time in situ X-ray topographic observation of deformation process via synchrotron white beam topography, has been developed. This device enables both tensile data (load-displacement) and topographic images to be recorded simultaneously. It has been utilized to study the deformation behaviors of crystals of Mo and W.These specimens have been subject to mechanical cycling with increasing load, and their deformation processes have been observed in real time and in situ via x-ray topography. This leads to the observation of several phenomena, which would have been difficult to reveal by other experimental techniques. They include stress concentration, microyielding, reversible variation of contrasts and stress relaxation. In addition, the deformation behaviors of small angle grain boundaries have also been examined. Furthermore, the specimens can be heated through a heating device attached to the tensile stage, which allows high temperature topography to be performed in real time. The technique has been applied to the Ta films on Si (100) substrates. With increasing temperature, the topographic observations have revealed that the Ta films yield, fracture and then proceed to delaminate from their substrates.
Rapid Prototype Fabrication of Smooth Microreactor Channel Systems in PMMA by VUV Laser Ablation at 157 NM for Applications in Genome Analysis and Biotechnology
Authors: Lapczyna Markus , Stuke Michael
Published: April 2011

A rapid prototyping method for the fabrication of microstructures in polymer substrates has been developed, using a combination of laser direct-write patterning of silicon membrane contact masks and vacuum-ultraviolet (VUV) pulsed laser ablation. The process allows the flexible and rapid prototyping of microreactors and microchannel systems with submicrometer resolution. Thanks to the high photon energy of the VUV (7.9 eV) irradiation, PMMA and also other polymers can be ablated without leaving behind carbonated and/or fluorescent surfaces. Fluences of ≅ 100 mJ/cm2 lead to etch rates of ≅ 140 nm/pulse and result in very smooth surfaces with a roughness in the nanometer range on a micrometer lateral scale. The structured substrates are sealed with a PMMA foil by means of a newly developed low temperature technique without adhesives.
Heat Flow Modelling of the Laser Drilling Process as Applied to Unidirectional Carbon Fibre Composites
Authors: Cheng C.F. , Tsui Y.C. , Clyne T.W.
Published: April 2011

Laser drilling has been carried out with a pulsed Nd:YAG laser. The laser has been applied to the drilling of APC-2 (PEEK-61%C fibre), with specimens up to 1 mm in thickness and using both moving and stationary beams. Hole shapes and heat-affected zone (HAZ) microstructures were studied using SEM, optical microscopy of polished sections and optical interferometric surface profilometry. Two prominent microstructural features were noted in the HAZ of the composite. These were (a) swelling of the ends of the carbon fibres (from about 8 microns to about 12 microns in diameter) and (b) an extensive zone around the hole in which the matrix had clearly undergone melting and some flow. The fibre swelling was such that neighbouring fibres were brought into close contact. The degree of swelling was found to remain constant as the laser pulse energy was increased, although the morphology of the fibre ends became more wrinkled and porous. The phenomenon is thought to be caused by internal gas pressure generation and distortion of the turbostratic structure within the fibre.

A heat flow model has been developed to simulate the drilling process, based on an explicit finite difference formulation and a Cartesian (3-D) mesh. The post-iterative heat accumulation method was used to simulate the effect of latent heat absorption. The explicit approach was found superior to implicit schemes, which tend to exhibit poor stability when handling the phase change algorithm in regions of extremely high thermal gradient. The total solution time was kept within reasonable limits by using a graded mesh, which was fine only in the regions close to the beam axis. Comparisons between predicted and observed hole dimensions showed good agreement over a range of conditions, including variations in beam energy and beam motion. This suggests that effects omitted from the model, such as melt ejection, were not playing a significant role.
Switching Kinetics of Pulsed Laser Deposited Epitaxial PZT Films
Authors: Yamazato M. , Grishin A. M. , Yamagata Y. , Ikegami T. , Ebihara K.
Published: April 2011

We have fabricated epitaxial PbZr0.52Ti0.48O3 (PZT, 40~1200 nm)/YBa2Cu3O7-x (YBCO, 400 nm) film ferroelectric/superconductor heterostructures on the single-crystal neodymium doped yttrium monoaluminate [YAlO3+1%Nd2O3] and MgO substrates by KrF pulsed laser deposition technique. The dielectric constant of 950 and loss tangent δ of 0.04 have been found to be frequency independent in the range 100 Hz to 100 kHz while electric resistivity ρ (150 kV/cm) is of 6×1011 Ω·cm, remnant polarization and coercive field are 32 μC/cm2 and 43 kV/cm, respectively. Fast ferroelectric switching kinetics with characteristic switching time around 50 ns has been observed. Universal electric field and temperature dependencies of switching time as well as film thickness dependence of coercive electric field have been observed and correspond to ferroelectric needle-like domain switching.
A New p-Type Conductive Oxide with Wide Band GAP, SrCu2O2
Authors: Kudo A. , Yanagi H. , Hosono H. , Kawazoe H.
Published: April 2011

SrCu2O2 thin films were prepared onto SiO2 glass substrates by pulsed laser deposition. The film deposited in O2 atmosphere of 7×10-4 Pa at 573 K showed high optical transmission in visible and near infrared regions. The optical band gap of the film was estimated to be -3.3 eV. The dc electrical conductivity of the film was 3.8 × 10-3 Scm-1. Potassium was used for substitutional hole-doping. The dc electrical conductivity of the K-doped film at 300 K increased to 4.8 × 10-2 Scm-1. Positive sign of Seebeck and Hall coefficients demonstrated p-type conduction of the K-doped film. Hole concentration and mobility at 300 K were 6.1 × 1017 cm-3 and 0.46 cm2V-1s-1, respectively.
Growth of High Quality Single Crystal ZnO Films on Sapphire by Pulsed Laser Ablation
Authors: Sharma A.K. , Dovidenko K. , Oktyabrsky S. , Moxey D.E. , Muth J.F. , Kolbas R.M. , Narayan J.
Published: April 2011

The structural and optical characterizations of single crystal zinc oxide films on sapphire have been performed. The ZnO films were deposited by pulsed laser deposition in an oxygen environment. These films were annealed in oxygen for further improvement in the oxygen stoichiometry. Both as-deposited and oxygen annealed films were high quality single crystal as characterized by X-ray diffraction and transmission electron microscopy. The defect density, comprised mainly of dislocations and stacking faults, was low as compared to high quality films of III-nitrides deposited on sapphire. Under these growth conditions, the ZnO films grow two dimensionally on sapphire as opposed to GaN which grows three dimensionally. The band edge photoluminescence was found to be dominant, and an order of magnitude higher in the annealed films. Transmission measurements and the electrical resistivity of the annealed films also show the films were of high quality after annealing. It is envisaged that these improvements in the quality of the ZnO films occur as a result of reduction of oxygen vacancies and the density of point defects.
Tem Characterization of ZnO and AIN/ZnO Thin Films Grown on Sapphire
Authors: Dovidenko K. , Oktyabrsky S. , Sharma A. K. , Narayan J.
Published: April 2011

Thin (~ 250 nm) films of ZnO grown by pulsed laser deposition on basal plane of sapphire were studied by transmission electron microscopy (TEM). Plan-view TEM study proved the films to be single crystal with the following epitaxial relationship with the substrate: (0001)znO || (0001)sap with the 30 30° in-plane rotation - [0110]ZnO || [1210]sap. Dislocations lying mostly in basal plane of ZnO and aligned along both <:1010> and <1120> directions having b=1/3[1120] were found. ZnO films were found to have layered growth morphology contrary to columnar morphology of III-nitrides. Consequently, the threading dislocation density in ZnO films (opposing to the AIN and GaN) drops very fast with the thickness: down to 107cm-2 at ~ 250 nm. The effect of post-annealing (which caused significant improvement in electrical and optical properties) on the microstructure of ZnO films was also studied. Contrary to the atomically sharp and clean interface in the as-deposited films, the post-annealed ZnO/sapphire interface contained reacted layer of 30 - 60 A thickness. The structure of the interlayer was determined to be ZnAl2O4 (spinel). The formation of this single crystal spinel layer did not cause deterioration of the ZnO film structure or properties. We have also explored the possibilities of using ZnO as a buffer for III-nitride growth. The epitaxial AIN films were grown on top of the ZnO layer by pulsed laser deposition. Thin (20 -60 A) interfacial reaction layer (also spinel ZnAm2O4) was observed between AIN and ZnO. Formation of this interlayer is studied in conjunction with the AIN epitaxy and the characteristics of defects and interfaces.
Luminescence Properties of Pulsed Laser Deposited Eu:Y2O3 Thin Film Phosphors on Sapphire Substrates
Authors: Cho K.G. , Kumar D. , Holloway P. H. , Singh R. K.
Published: April 2011

Eu:Y2O3 phosphor films were deposited on (0001) sapphire substrates using 248 nm KrF pulse laser to investigate microstructure-property correlations. A slow film growth (60 nm/min) process results in predominantly (222) orientation while a fast film growth (170 nm/min) process results in predominantly (400) orientation of Eu:Y2O3 film. With an increase in film thickness from 0.6μm to 1.2μm, a 300% increase in brightness has been achieved from Eu:Y2O3 films. An increase in substrate temperature during deposition from 700°C to 800°C resulted in ~40% brighter films. Improvement in brightness from Eu:Y2O3 films with the film thickness may be attributed to an increase in roughness while that from substrate temperature may be attributed to a combined effect of increased roughness and improved crystallinity.
Vacancy Mobility in Nickel Aluminide Versus Composition
Authors: Bai Bin , Fan Jiawen , Collins Gary S.
Published: April 2011

The fractional concentration of Ni-vacancies in NiAl at high temperature has been determined for compositions between 50 and 53 at.% Ni from measurements using perturbed angular correlation of gamma rays (PAC). The vacancies were detected by quadrupole interactions induced at nearby 111In/Cd impurity probes present on the Al sublattice in high dilution. One set of measurements was made at high temperature. A second set made after rapid quenching exhibited an enhancement of Ni-vacancy site fractions that is attributed to diffusion and trapping of vacancies during quenching. The composition dependence of the enhancement was analyzed assuming that the enhancement is proportional to the root-mean-square diffusion length during quenching. The experimental dependence on composition is found to be consistent with bulk diffusion data. The methodology developed clarifies how local environments of impurity probes are modified during rapid quenching. In addition, it is shown that there is an enormous increase in the mobility of vacancies with increasing deviation of the composition from stoichiometry. Diffusion mechanisms that can explain the data trends are discussed.
Determination of the thermodynamic factor for the B2 FeAl phase from X-ray diffuse scattering data
Authors: Liubich Vlad , Dorfman Simon , Fuks David , Mehrert Helmut
Published: April 2011

The interdiffusion coefficient is related via the modified Darken equation to the tracer diffusivities of the constituents. The thermodynamic factor Φ entering the Darken equation for the interdiffusion coefficient is expressed in terms of the energy parameters which describe the ordering process in the binary alloy. Our calculations for Fe-Al alloys yield the dependence of Φ on the long-range order parameter. These calculations are performed with the parameters extracted from diffuse X-ray scattering data on FeAl.
Properties of Iron Atoms at Grain Boundaries in Fe and Fe72Al28
Authors: Schneeweiss O. , Turek I. , Čermák J. , Lejček P.
Published: April 2011

Location of diffused 57Co atoms in single crystals, bicrystals and polycrystals of pure iron and Fe72Al28alloy were investigated by means of emission Mössbauer spectroscopy. To interpret the results, first principles calculations of iron atom magnetic moments and hyper-fine field were carried out. From comparison of M6ssbauer spectra of single crystals with those of bicrystals and polycrystals, an information about grain boundary positions occupied by diffusing atoms is obtained. It is shown that about 5% of the diffusing atoms at the {112} grain boundary of iron are located at the positions either having impurity atoms in the nearest neighbourhood or characterized by larger atomic spacing in comparison with the bulk. In the Fe72Al28 a dominating portion of diffusing atoms have different surrounding than in grain volume. An enrichment of grain boundaries by aluminum could explain their hyperfine parameters.
Defect formation at internal interfaces and grain boundaries of cold-rolled Fe and Ni during heavy ion irradiation
Authors: Aggarwal G. , Sen P.
Published: April 2011

Instabilities arise out of dynamic events and can lead to nonequilibrium (self-organization) processes. Ion irradiation is by nature a nonequilibrium process and hence formation of structures, metastable or otherwise is to be expected. Recently, it has been theoretically predicted that metals under ion irradiation can lead to dissipative structure formation arising out of radiation damage and their subsequent annealing. The possibility of direct observation of such structures in metals, under irradiation, is however reduced due to nonavailability of a large concentration of defects (mainly point defects) at any point of time. In this experimental presentation we show that this can be overcome through the involvement of microstructural imperfections which rearrange during irradiation. Employing microstructurally impure specimens of Fe and Ni, it is shown that heavy ions dissipate their electronic energy to modify atomic arrangements at the microstructure. The increased concentration of defects (atomic rearrangements), amenable to statistical decay is shown to produce structures in the 4-probe resistivity measurements which we assign to dissipative structure formation.
Diffusion in Metals, Quasicrystals, and Intermetallic Compounds
Authors: Mehrer H. , Zumkley Th. , Eggersmann M. , Galler R. , Salamon M.
Published: April 2011

In this paper recent developments of diffusion in three related areas will be reviewed: The first part is devoted to self- and solute diffusion in metals with particular emphasis on Al. Contrary to most other metallic solvents, diffusion of transition elements in Al is anomalous in several respects: diffusion is very slow, activation enthalpies, pre-exponential factors and activation volumes are unusually high. By contrast, non-transition elements in Al show more or less normal solute diffusion behaviour. The anomalous behaviour is attributed to a strong repulsive interaction between transition metal solutes and vacancies. Ab-initio calculations could help to understand this well-documented diffusion problem in detail.

In the second part very recent diffusion studies on single crystals of the Al-base quasicrystalline intermetallic compound Al-Pd-Mn will be discussed. Diffusion of Zn, Ge, Mn, Fe, Co, Pd and Au has been studied by various groups. At least in the high-temperature regime diffusion in the quasicrystal – despite some differences in detail – shows striking similarities to diffusion in Al, for which a vacancy-type mechanism is generally accepted. The activation volumes of +0.67 and +0.74 atomic volumes measured for Mn- and Zn-diffusion in Al-Pd-Mn strongly favour a vacancy mechanism as well. For the low temperature regime of Pd and Au diffusion the possibility of a phason-related mechanism is discussed.

The third part deals with recent investigations of iron-aluminides and iron-silicides for which Fe self-diffusion and diffusion of selected foreign elements (Ge in Fe–Si, In and Zn in Fe–Al) has been investigated. There is no doubt that vacancies mediate the diffusion process. Within this general mechanism a number of factors like the crystal structure, the state of order, the composition, and the type of bonding have strong influence on diffusion. Such factors are discussed also in connection with results from positron annihilation and M6ssbauer spectroscopy.
Self and Impurity Diffusion in Icosahedral Al-Pd-Mn Quasicrystals
Authors: Sprengel W. , Nakajima H. , Lograsso T.A.
Published: April 2011

Diffusivities of Cr in icosahedral quasicrystals of Al-Pd-Mn system have been measured by the radioactive tracer method in combination with a precision grinding technique. The temperature dependence of the diffusivities follows the Arrhenius equation in the investigated temperature range from 850 to 1107 K. The activation energy Q = 235.5 ± 7.8 kJmol-1 and pre-exponential factor D0 = 1.2 × 10-2 m2s-1 were evaluated. The diffusion behavior is discussed in terms of a vacancy diffusion mechanism.
Self-Diffusion in Isotopically Controlled Heterostructures of Elemental and Compound Semiconductors
Authors: Bracht H. , Haller E. E. , Eberl K. , Cardona M. , Clark-Phelps R.
Published: April 2011

We report self-diffusion studies of silicon between 855 and 1388°C in highly enriched epitaxial 28Si layers. Diffusion profiles of 30Si and 29Si are determined with high resolution secondary ion mass spectrometry (SIMS). The temperature dependence of the Si self-diffusion coefficients is accurately described with an activation enthalpy of 4.76 eV and a pre-exponential factor of 560 cm2s-1. The single activation enthalpy indicates that Si self-interstitials dominate self-diffusion over the whole temperature range investigated. Self- and interdiffusion in buried Al71GaAs/Al69GaAs/71GaAs isotope heterostructures with different Al composition is measured between 800 and 1160°C. Ga self-diffusion in AlGaAs and interdiffusion of Al and Ga at the AlGaAs/GaAs interface show that Ga diffusion decreases with increasing Al composition and that the interdiffusion coefficient depends linearly on Al concentration. Furthermore Al is found to diffuse more rapidly into GaAs than Ga diffuses in GaAs. The temperature dependence of Ga and Al diffusion in GaAs and of Ga diffusion in AlGaAs is described by a single activation enthalpy in the range of 3.6±0.1 eV, but by different pre-exponential factors. Differences found for Ga and Al diffusion in GaAs and for Ga diffusion in AlGaAs with different Al concentrations are discussed.
Ionic Conductivity Study on the New High Oxide Conducting Perovskite LaGaO3
Authors: Kiruthika G.V.M. , Varadaraju U.V.
Published: April 2011

Oxide ion conductivity studies have been done on the Lanthanum Gallate based compounds. Yttrium substitution at the Ga site has been attempted to increase the unit cell size. Single phase was obtained for limited Y substituion i.e., La0.9Sr0.1Ga0.7Y0.1Mg0.2O3-x. It is found that the activation energy for the oxide ion conductivity has decreased for this composition. Based on the tolerance factor and B-site radius values, the migration energies were obtained for the LaGaO3 based perovskites. It is observed that migration energy has been significantly reduced upon substitution at the B-site. Absence of an enhancement in the conductivity with Yttrium substitution could be due to the vaccancy ordering inhibiting the oxide ion migration.
Enhancement of Ionic Diffusion by Microwave-Field-Induced Ponderomotive Forces at Physical Interfaces
Authors: Booske J. H. , Cooper R. F. , Freeman S. A. , Binger K. R.
Published: April 2011

Numerous observations have been reported in the literature of enhanced mass transport and solid-state reaction rates during microwave heating or processing of a variety of ceramic, glass, and polymer materials. Recent research reveals that these phenomena are probably the result of a previously-unknown driving force for ionic mass transport. The driving force--termed a “ponderomotive” (mass-moving) force--results from the application of intense, high-frequency electric fields near physical interfaces (e.g., free surfaces, grain boundaries). Experiments, theory, and numerical simulations all demonstrate that this driving force can influence solid state reaction kinetics by enhancing mass transport rates.
A Controlled Solid State Diffusion Process to form Cermet Anodes for Solid Oxide Fuel Cells
Authors: Tang Eric Z. , Ivey Douglas G. , Etsell Thomas H.
Published: April 2011

The interfacing of thin film vapor deposition technologies and solid state electrochemistry has led to the recent development of polarized electrochemical vapor deposition (PEVD). In this study, PEVD was applied to deposit a thin layer of yttria stabilized zirconia (YSZ) over a porous metallic electrode to form the cermet anode of a solid oxide fuel cell (SOFC). During PEVD, oxygen ions are transported through the solid electrolyte of an SOFC under an electrical potential gradient provided by an external dc source. At the metallic electrode (anode) surface, oxygen ions react electrochemically with ZrCl4and YCl3 in the vapor phase to deposit YSZ. The growth of YSZ resembles the mechanisms illustrated in Wagner's tarnishing theory. However, modification has been made to the initial growth of YSZ at both electronically and ionically shorted paths along the metallic electrode and solid electrolyte surfaces, respectively. The initial experimental results in the present study showed that PEVD is capable of depositing a thin layer of YSZ on a porous metallic electrode to form a cermet anode. This layer not only provides a continuous ionic conducting path in the anode to reduce the overpotential loss, but also protects the metallic electrode from further sintering, vapor loss and poisoning in the harsh SOFC operating conditions.
Mobility of Self-Interstitial Clusters in FE and CU
Authors: Osetsky Yu.N. , Serra A. , Priego V.
Published: April 2011

Molecular dynamics (MD) simulation has been used to study the thermally activated mobility of clusters of self-interstitial atoms (SIAs) in Fe and Cu. Such clusters are formed in metals during irradiation with energetical particles and, according to the cascade production bias model, they play an important role in the microstructure evolution of metals under irradiation. An extensive simulation of clusters from 2 to 30 interstitials has been carried out for the temperature range ≍360-1200K using long-range interatomic pair potentials. The results show that clusters bigger than two SIAs are one-dimensionally mobile. Di-interstitials have two migration mechanisms depending on the temperature. At low temperature the mechanism is one-dimensional whereas at high temperature the probability of rotation and three-dimensional migration increases. It was found that in both metals the effective migration energy of clusters estimated via their jump frequency does not depend on the cluster size, although the cluster jump frequency decreases as the cluster size increases. The mechanism of cluster migration and problems of the treatment of one-dimensional mobility are discussed.
Simulations of Defect and Diffusion Properties in The Interstitial CU-C Solid Solutions
Authors: Ellis D.E. , Mundim K.C. , Fuks D. , Dorfman S. , Berner A.
Published: April 2011

HRSEM analyses of copper/graphite interfaces are presented, showing a narrow solid solution zone. Atomistic simulations in the framework of the Generalized Simulated Annealing approach lead to very reasonable relaxed geometries around carbon interstitials and vacancy complexes of a Cu host, and for a Cu/graphite interface. Embedded Cluster Density Functional results indicate a charge transfer of ~1 e to carbon, mostly from the first neighbor shell, in all relaxed environments studied.
Comparison of Release Profiles of Various Growth Factors from Biodegradable Carriers
Authors: Tabata Y. , Yamamoto M. , Ikada Y.
Published: April 2011

A biodegradable hydrogel was prepared by glutaraldehyde crosslinking of acidic gelatin with an isoelectric point (IEP) of 5.0 as a carrier to release basic growth factors on the basis of polyion complexation. Basic fibroblast growth factor (bFGF), transforming growth factor β1 (TGF-β1), and bone morphogenetic protein-2 (BMP-2) were sorbed from their aqueous solution into the dried gelatin hydrogels to prepare respective growth factor-incorporating hydrogels. Under an in vitro non-degradation condition, approximately 20 % of incorporated bFGF and TGF-β1 was released from the hydrogels within initial 40 min, followed by no further release, whereas a large initial release of BMP-2 was observed. After subcutaneous implantation of the gelatin hydrogels incorporating 125I-labeled growth factor in the mouse back, the remaining radioactivity was measured to estimate the in vivo release profile of growth factors. Incorporation into gelatin hydrogels enabled bFGF and TGF-β1 to retain in the body for about 15 days and the retention period well correlated with that of the gelatin hydrogel. Taken together, it is likely that the growth factors ionically complexed with acidic gelatin were released in vivo as a result of hydrogel biodegradation. On the contrary, basic BMP-2 did not ionically interact with acidic gelatin, resulting in no sustained released by the present biodegradable carrier system.
A New Approach to Cartilage Tissue Engineering Using Human Dermal Fibroblasts Seeded on Three-Dimensional Polymer Scaffolds
Authors: Nicoll S. B. , Wedrychowska A. , Smith N. R. , Bhatnagar R. S.
Published: April 2011

Current methods for correcting articular cartilage defects are limited by a scarcity of cartilage cells. Here we describe a novel method for the conversion of human dermal fibroblasts to chondrocyte-like cells and the potential application of this methodology to cartilage tissue engineering. Human neonatal foreskin fibroblasts were seeded on two-dimensional, tissue culture polystyrene (TCPS) in high density micromass cultures in the presence of staurosporine (50-200 nM), a protein kinase C (PKC) inhibitor, and lactic acid (40 mM) to induce functional hypoxia. Dermal fibroblasts were similarly cultured on three-dimensional polymer scaffolds composed of a non-woven polyglycolic acid (PGA) fiber mesh reinforced in a dilute solution of poly(L-lactic acid) (PLLA). At 24 hours, northern analysis revealed a staurosporine dose-dependent increase in aggrecan core protein expression in lactate-treated micromass cultures on TCPS, while type I collagen gene expression was virtually abolished in all cultures supplemented with staurosporine. The cells in these cultures displayed a rounded, cobblestone-shaped morphology typical of differentiated chondrocytes (most pronounced at 200 n.M staurosporine and 40 mM lactate), and were organized into nodules which stained positively with Alcian blue. When seeded on PGA/PLLA matrices under identical conditions as described for TCPS, a chondrocyte-like morphology was observed in cultures treated with lactate and staurosporine in contrast to the flattened sheets of fibroblast-like cells seen in untreated controls. Taken together, the above findings suggest that staurosporine treatment coupled with high density micromass culture in the presence of lactate induces chondrogenic differentiation in human dermal fibroblasts, and that these cells may be used in concert with three-dimensional polymer scaffolds for the repair of articular cartilage lesions.
Materials Designed to Control and Examine The Function of Single Cells
Authors: Thomas C.H. , Lhoest J.B. , Castner D.G. , Mcfarland C.D. , Healy K.E.
Published: April 2011

Stress levels imparted on a cell have been shown to alter cell organization and function, presumably as a result of morphological cues affecting cytoskeletal organization. Materials with spatially resolved surface chemistry were designed to isolate individual mammalian cells to determine the influence of projected area on cell proliferation and cytoskeletal organization. Surfaces were fabricated using a photolithographic process resulting in islands of cell binding N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (EDS) separated by a non-adhesive interpenetrating polymer network [poly acrylamide-co-ethylene glycol; P(AAm-co-EG)]. The surfaces contained over 3800 adhesive islands/cm2, allowing for isolation of single cells with projected areas ranging from 100µm2to 10,000µm2. These surfaces provide a useful tool for researching how cell morphology and mechanical forces affect cell function.
Impact of Silicon Wafer Material on Dislocation Generation in Local Oxidation
Authors: Peidous I. V. , Sundaresan R. , Quek E. , Leung Y. K. , Beh M.
Published: April 2011

Crystalline quality of locally oxidized silicon wafers has been studied. Wafers from different supply sources were found to be differently susceptible to stress-induced dislocation generation, although they had been produced to the same specification. On the basis of the analysis of a depth distribution of the dislocations, critical resolved shear stress of dislocation movement in the bulk areas of the wafers was determined. It varied from about 1.65 to 5.12 MPa and correlated positively to the surface defect density. The results show that uncontrollable variations of bulk silicon properties may significantly influence the stress-induced defect nucleation on the surface of wafers during processing.
Ultra Shallow Junction Formation by Cluster Ion Implantation
Authors: Matsuo Jiro , Aoki Takaaki , Goto Ken-ichi , Sugii Toshihiro , Yamada Isao
Published: April 2011

Implantation of B cluster ions into Si using decaborane (B10H14) has been demonstrated. SIMS measurements show that the depth distribution of boron atoms implanted with a monomer ion is exactly matched by that of boron atoms implanted from decaborane ions, if the cluster ion has an order of magnitude larger acceleration energy. According to the Langmuir-Child equation, two orders of magnitude larger space-charge limited ion beam current is possible when decaborane ions are used. Implanted boron atoms from decaborane ions are electrically activated after annealing. Junction depth of the implanted layer with 3 keV decaborane ions is approximately 20nm after annealing at 900°C. Molecular dynamic caluculations show that implantation efficency of boron monomer ions and decaborane ions are the same. However, the number of displaced silicon atoms per implanted boron atom from a decaborane ion impact is 4 times larger than that by boron monomer impact so that a heavily damaged region is created near the impact zone by decaborane ion penetration.
Formation of Subthreshold Defects in Erbium Implanted Silicon
Authors: Flink C. , Mui S. , Gottschalk H. , Palm J. , Weber E. R.
Published: April 2011

In this work we present the first quantitative approach to model subthreshold defects. Using cross-sectional Transmission Electron Microscopy (XTEM) and Convergent Beam Electron Diffraction (CBED), we studied subthreshold defects in Cz-silicon that followed a deep implantation of erbium, and their interaction with co-implantations. The analyzed Frank loops show an increasing size by a factor of five with increasing depth in the wafer. The ratios of the number of condensed silicon atoms to the implant doses support a “+0.4 model” for the erbium and a “+0.07 model” for the oxygen as a co-implant. Our results indicate that a “push away” mechanism produces the excess silicon atoms in the case of interstitial implant atoms. The observed loop size depth distributions helped to reveal the condensation mechanism of subthreshold defects. This mechanism is described by the relaxation of excess silicon atoms on primary defect clusters. The decreasing concentration profiles of the primary defect clusters together with the high diffusivity of silicon interstitials results in a number of condensed silicon atoms per loop that increases with the depth in the wafer.
Point-Defect Migration in Crystalline Si: Impurity Content, Surface and Stress Effects
Authors: Coffa S. , Libertino S. , La Magna A. , Privitera V. , Mannino G. , Priolo F.
Published: April 2011

The results of several recent experiments aimed at assessing the room temperature migration properties of interstitials (D) and vacancies (V) in ion implanted crystalline Si are reviewed. We show that combining the results of ex-situ techniques (deep level transient spectroscopy and spreading resistance profilometry) and in-situ leakage current measurements new and interesting information can be achieved. It has been found that at room temperature I and V, generated by an ion beam, undergo fast long range migration (with diffusivities higher than 10−1 cm2/sec) which is interrupted by trapping at impurities (C, O) or dopant atoms and by recombination at surface. Analysis of two-dimensional migration of point defects injected through a photolithographically defined mask shows that a strong I recombination (characterized by a coefficient of 30 μm−1) occurs at the sample surface. Moreover, we have found that the strain field induced by an oxide or a nitride mask significantly affects defect migration and produces a strong anisotropy of the defect diffusivity tensor. Finally, using in-situ leakage current measuremens, performed both during and just after ion irradiation, the time scale of point defect evolution at room temperature has been determined and defect diffusivities evaluated. The implications of these results on our current understanding of defect and diffusion phenomena in Si are discussed.
Epitaxially Grown N+ Phosphorus Collector Peaks In Highfrequency hbt's with Implanted Emitters
Authors: Visser C. C. G , Nanver L. K. , Bogaard A. Van Den
Published: April 2011

The boron out-diffusion into the Si collector of SiGe HBT's with implanted emitters is compensated by an epitaxially grown n+ phosphorus peak effectively positioned adjacent to the as-grown boron peak. Detrimental barrier formation is suppressed in devices with base sheet resistance 3.3 k.Ω and cut-off frequency of 31 GHz.
Characterization of SiGeC Using Pt(SiGeC) Silicide Schottky Contacts
Authors: Peterson Jeff J. , Hunt Charles E. , Robinson McDonald , SCott Robin
Published: April 2011

Material and electrical characterization of n-type and p-type Si1-x-yGex Cy epitaxial layers on Si(100) was performed using silicided platinum Schottky contacts. XRD studies show Pt silcidation of SiGeC proceeds from non-reacted Pt to Pt2(SiGeC) and completes with the Pt(SiGeC) phase similar to Pt/Si silicides, but Pt silicide reactions with SiGeC are shown to require higher temperatures than Pt reactions with Si. Electrical characterization of Pt(SiGeC) contacts to n-type Sil1-x-yGexCx/Si shows rectifying behavior with constant barrier heights of 0.67eV independent of composition, indicating Fermi level pinning relative to the SiGeC conduction band is occurring. Pt(SiGeC) contacts to p-type Si1-x-yGexCy/Si are also rectifying with barrier heights that track the variation of the SiGeC energy bandgap.
Ellipsometry Studies, Optical Properties, And Band Structure of Gel.1-yCy, Ge-RICH Si1-x-yGexCy, And Boron-Doped Si1-xGexAlloys
Authors: Junge Kelly E. , Lange Ruidiger , Dolan Jennifer M. , Zollner Stefan , Humlfcek Josef , Dashiell M. W. , Hits D. A. , Orner B. A. , Kolodzey James
Published: April 2011

We measured the pseudodielectric function (PDF) of Ge1-yCy and Ge-rich Si1-x-yGexCy alloys from 1.1 to 5.2 eV using spectroscopic ellipsometry. These alloys were grown by molecular beam epitaxy at 6000C on (001) Si substrates. Analytical lineshapes fitted to numerically calculated derivatives of their PDFs determined the critical-point parameters of the E1, E1+Δ1, E0', and E2 transitions. The critical-point energies of the Ge1-yCy alloys were found to be similar to bulk Ge. This indicates that the presence of C in these alloys only has a small influence on the band structure. For some samples, the amplitude of the PDF is much lower than in bulk Ge, which can be attributed to surface roughness and explained within the framework of the Kirchhoff theory of diffraction or using effective medium theory. The degree of surface roughness indicated by optical measurements was confirmed by atomic force microscopy. We also studied bulk Czochralski-grown Si1-xGex alloys (0<x<0.28) doped with boron. Due to doping, the critical points shift to lower energies as reported previously for bulk Si and Ge.
Light Emission From Erbium Doped Si1-x XGe1Heterostructures
Authors: Evans-Freeman J H , Naveed A T , Huda M Q , eaker A R , oughton D C , right A C
Published: April 2011

UHVCVD-grown SiO.s 7Ge0.13/Si heterostructures have been implanted with erbium, and photoluminescence and electroluminescence centred on 1.54ýim have been studied. Implantation conditions were chosen so that the erbium concentration profile was flat over the spatial location of the SiGe quantum well region. We demonstrate that the technology of implantation and regrowth is feasible even when Si/SiGe interfaces are present. We have obtained more intense photoluminescence from erbium implanted SiGe heterostructures than that from a silicon layer implanted with a higher erbium dose. We report forward bias electroluminescence from the Er doped SiGe/Si heterostructures; the photoluminescence and electroluminescence from these structures demonstrates that the detailed mechanism of excitation is different from the Er:Si case.
Effect of Interface-Related Deep Levels on high Sensitivity of Schottky Diode Photodetector Based on Ultrathin InGaAs Film on Si
Authors: Kvit A. V. , Yakimov M. V. , Konstantinov P. L. , Naidenkov M. N.
Published: April 2011

Recently, the Fermi level has been demonstrated to be pinned in GaAs semiinsulating ultrathin (<100 A) films grown at low temperatures [1]. This allows one to construct a detector with “internal” photocurrent amplification. The amplification effect compensates losses in sensitivity due to the small width of light-sensitive layer which absorbs 10 — 50 % of incident radiation. We fabricate photodetector structures with external quantum efficiency more than 1 for visible region. Photogenerated carriers in the GaAs layer are effectively separated by the built-in electric fields formed by the Schottky barrier and by the charge at the GaAs/Si interface. In this work, we show the relationships between spectral sensitivity of the metal-InGaAs/Si structures and In content. We observed the red shift in the photocurrent spectra with increasing In concentration, although photosensitivity of such structures dropped drastically. This shift demonstrates that the thin InGaAs film is actually responsible for photosensitivity. Despite the low photoluminescence intensity, the lowtemperature PL spectra indicate that band gap decreases with indium flux rising during MEE growth. The surprise was that the decrease of the film thickness caused the increase of photosensitivity. The GaAs(20 A)-InGaAs (20 A)/Si structure was the most sensitive one. We also observed high quantum efficiency in near-UV region (up to 0.8). We determined activation energy of elctron and hole traps and their concentration profiles by DLTS. The centers localized on interface between polar and nonpolar semiconductors are responsible for Fermi-level pinning in III-V semiinsulating materials and act as an electron trap with activation energy 0.59 eV. The origin of deep levels is discussed.
Using Growth Kinetics for Nanoengineering of Si-Ge Surfaces
Authors: Goldfarb I. , Briggs G. A. D.
Published: April 2011

In this work we explore how various growth characteristics of Ge on Si(001) can be used to fabricate structures for potential nanodevices. In the first example, the self-assembling tendency of germanium for three-dimensional islanding on Si(001) is considered, e.g. for application in devices based on quantum dots and wires. We aimed at achieving a detailed understanding of dot nucleation and growth mechanisms from germane. By controlling the deposition parameters, such as the germane pressure and substrate temperature, arrays of dots and antidots can be created on the grown surface, and further modified by post-deposition anneals. While lower temperature deposition leads to randomly distributed dots (i.e. small and coherent three-dimensional clusters with pyramidal shapes), a higher temperature deposition results in formation of antidots (i.e. pyramidal pits), which, in turn, are gradually replaced by the clusters, if the deposition is allowed to continue. The difference is caused by the different hydrogen behaviour at the respective temperature ranges. The germanium tendency to incorporate preferentially at the step and island edges is another beneficial property, which can be used to align the dots along step edges, creating wires rather than dots, or to fabricate ultrasmall Si-Ge heterojunctions, of a less than 10 nanometer size.
Toward RF System-Level Integration: Process Integration Issues in Sige BICMOS
Authors: Freeman G. , Schonenberg K. , Ahlgren D. , Jeng S-J. , Nguyen-Ngoc D. , Stein K. , Colavito D. , Subbanna S. , Harame D. , Meyerson B.
Published: April 2011

The SiGe HBT, integrated with CMOS devices on the same chip, will be the first integrated device combination to realize the long-standing technology goal of fabricating RF systems on a chip. It has been demonstrated that the HBT device can replace the standard GaAs front-end of RF systems and take advantage of the reduced cost available from Si technologies in 200–300mm wafers. However, the SiGe HBT can only be part of a large-scale RF system on a chip when, in the same technology, NFETs and PFETs are provided for low power, low frequency digital logic, and a suite of resistors, capacitors, diodes, and inductor passive elements are provided for the high frequency analog circuitry. Furthermore, all these elements must be manufacturable defect-free at medium and high levels of integration.

This paper covers keyprocess integration issues confronting technologists when integrating a SiGe HBT device with the requisite CMOS and passive elements and at the same time maintaining very high GaAs-like performance. Topics to be discussed are 1) a review of high-performance HBT device integration schemes employed to date and integration issues with each scheme, 2)integration issues in epitaxial cleaning and growth techniques, 3) integration issues influencing crystal defects, and 4) integration issues with passive elements. Status of the IBM SiGe BiCMOS technology will be presented to illustrate the first successful integration of this set of devices into
a manufacturable process.
The Application of Novel Chemical Precursors for the Preparation of Si-Ge-C Heterostructures and Superlattices
Authors: Nesting David C. , Kouvetakis John , Lorentzen Julie , Menéndez José
Published: April 2011

We have investigated new synthetic methods to Si-Ge-C materials by UHV-CVD and novel chemical precursors. The reactions of (SiH3)4C and (GeH3)4C with GeH4 and SiH4 produce diamond structured materials with the general formula (CSi4)xGey and (CGe4)xSiy respectively. These reactions demonstrate the application of novel C-H free precursors that incorporate Si4C and Ge4C building blocks to prepare single phase materials containing a significant amount of carbon (5–6 at.%). They also indicate the remarkable degree of compositional control provided by the precursor to incorporate the Si4C and Ge4C molecular framework into the solid state. A range of Si1-x-yGexCy compositions were also prepared pseudomorphically on [1 0 0] Si at 450–500 °C via reactions of (SiH3)4C with mixtures of GeH4 and Si4. The (Si2Ge)31C6 composition appears to display ordering of the Ge and Si atoms in the structure. The incorporation of C in the Si planes seems to provide local strain centers which facilitate the formation of this ordered phase.
Limitations to the use of Sb as a Surfactant During SiGe MBE
Authors: Jernigan Glenn G. , Silvestre Conrad L. , Fatemi Mohammad , Twigg Mark E. , Thompson Phillip E.
Published: April 2011

The use of Sb as a surfactant in suppressing Ge segregation during SiGe alloy growth was investigated as a function of Sb surface coverage, Ge alloy concentration, and alloy thickness using xray photoelectron spectroscopy, x-ray diffraction, and transmission electron microscopy. Unlike previous studies where Sb was found to completely quench Ge segregation into a Si capping layer, we find that Sb can not completely prevent Ge segregation while Si and Ge are being co-deposited. This results in the production of a non-square quantum well with missing Ge at the beginning and extra Ge at the end of the alloy. We also found that Sb does not relieve strain in thin films but does result in compositional or strain variations within thick alloy layers.
Carrier Transport and Velocity Overshoot in Strained Si On Sige Heterostructures
Authors: Ferry David K. , Formicone Gabriele , Vasileska Dragica
Published: April 2011

We examine the velocity overshoot effect in strained Six on Six-Ge1-x heterostructures. We also investigate the performance of surface-channel strained-Si MOSFETs for devices with gate lengths representative of the state-of-the-art technology. The Ensemble Monte Carlo method, self-consistently coupled with the 2D Poisson equation solver, is used in the investigation of the device performance. Our simulations suggest that, in short-channel devices, velocity overshoot is very important. In fact, when velocity overshoot occurs, it greatly affects the carrier dynamics and the current enhancement factor of both surface-channel strained-Si and conventional Si MOSFETs.