bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural Changes in Iron(II) Polymeric Complexes upon Thermally and Optically Induced Spin Transition Determined by EXAFS Spectroscopy
Authors: Erenburg S. B. , Bausk N. V. , Lavrenova L. G. , Shvedenkov Yu. G. , Mazalov L. N.
Published: April 2011

Changes in the electronic and spatial structure of polymeric Fe(II) complexes with 1,2,4- triazoles and various anions upon spin transition was studied using EXAFS and XANES spectroscopy. Spin transition and structural changes were induced by variations of the anion, dilution with Zn, under heating or the action of light. In all complexes, the spin transition is accompanied by drastic changes in the local environment of Fe atoms. The increase in spin transition temperature for the complexes with variable anions CIO4-, I-, Br-, BF4-, NO3- was found to correlate with changes in the Fe-N distances and changes in bond covalence determined from the chemical shifts in Mössbauer spectra. High spin metastable long life states were detected and studied in the polymeric complex Fe(atrz)3(ClO4)2. It was established that the changes in structure of polymeric complexes upon the transition to a metastable high spin state under the action of light differ from those in the thermally induced spin transition. Such differences are determined by mutual influence of Fe atoms in high spin and low spin states in polymeric chains.
Automated Indexing of Laue Images from Polycrystalline Materials
Authors: Chung Jin-Seok , Ice Gene E.
Published: April 2011

Third generation hard x-ray synchrotron sources and new x-ray optics have revolutionized x-ray microbeams. Now intense sub-micron x-ray beams are routinely available for x-ray diffraction measurement. An important application of sub-micron xray beams is analyzing polycrystalline material by measuring the diffraction of individual grains. For these measurements, conventional analysis methods will not work. The most suitable method for microdiffraction on polycrystalline samples is taking broad-bandpass or white-beam Laue images. With this method, the crystal orientation and non-isostatic strain can be measured rapidly without rotation of sample or detector. The essential step is indexing the reflections from more than one grain. An algorithm has recently been developed to index broad bandpass Laue images from multi-grain samples. For a single grain, a unique set of indices is found by comparing measured angles between Laue reflections and angles between possible indices derived from the x-ray energy bandpass and the scattering angle 2 theta. This method has been extended to multigrain diffraction by successively indexing points not recognized in preceding indexing iterations. This automated indexing method can be used in a wide range of applications.
The Mechanism of Twinning in Zincblende Structure Crystals: New Insights on Polarity Effects From a Study of Magnetic Liquid Encapsulated Czochralski Grown Inp Single Crystals
Authors: Dudley M. , Raghothamachar B. , Guo Y. , Huang X. R. , Chung H. , Larson D. J. , Hurle D. T. J. , Bliss D. F. , Prasad V. , Huang Z.
Published: April 2011

Synchrotron White Beam X-ray Topography (SWBXT) and synchrotron X-ray anomalous scattering have been employed to determine the polarity of {111} edge facets, anchored to the three phase boundary (TPB) on which twinning is observed to nucleate in Magnetic Liquid Encapsulated Czochralski (MLEC) grown sulfur doped, <001> InP single crystals. Analysis of the results indicates that both the formation of edge facets and the nucleation of twins occur preferentially on {111}P faces. Of the four possible sets of edge facets, belonging to the {111}P form, which are oriented so as to be thermodynamically favored to be anchored to the TPB, two can give rise to a {115} to {111}P external shoulder facet conversion upon twinning, while the other two can give rise to a {114} to {110} conversion. For these cases, twinning is only observed when the {111}P edge facets are anchored to the TPB in a region where the shoulder angle is close to 74.21° or 70.53°, facilitating the production of the {115} and {114} external shoulder facets, respectively, prior to twinning. These observations are discussed in light of calculated surface energies of the various internal and external facets.
Twin and Grain Boundary in InP :A Synchrotron Radiation Study
Authors: Han Yujie , Jiang Jianhua , Wang Zhouguang , Liu Xunlang , Jiao Jinghua , Tian Yulian , Lin Lanying
Published: April 2011

Experimentally observed X-ray reflectivity curves show bi-crystal(twin) characteristics. The study revealed that there was defect segregation at the twin boundary. Stress was relaxed at the edge of the boundary. Relaxation of the stress resulted in formation of twin and other defects. As a result of formation of such defects, a defect-free and stress-free zone or low defect density and small stress zone is created around the defects. So a twin model was proposed to explain the experimental results. Stress(mainly thermal stress), chemical stoichiometry deviation and impurities nonhomogeneous distributions are the key factors that cause twins in LEC InP crystal growth. Twins on (111) face in LEC InP crystal were studied. Experimental evidence of above mentioned twin model and suggestions on how to get twin-free LEC InP single crystals will be discussed.
Pulsed Femtosecond Excimer Laser-Induced Chemically Clean Etching of Diamond
Authors: Malshe A.P. , Ozkan A.M. , Railkar T.A. , Molian P.A. , Brown W.D.
Published: April 2011

Chemically clean etching of thermodynamically metastable diamond using a 500 femtosecond (fs), 248 nm KrF excimer laser is reported. The experimental results, characterized by micro-Raman spectroscopy indicate that unlike nanosecond (ns) pulsed laser processing of diamond, fs laser irradiation of the surface does not generate any graphite or amorphous carbon residues. Microstructural analysis of the fs pulsed laser etched surface indicates streaks.
Crystal Quality and Orientation of Pulsed Laser Deposited Barium Titanate Thin Films
Authors: Gottmann J. , Klotzbücher T. , Vosseler B. , Kreutz E. W.
Published: April 2011

KrF excimer laser radiation (λ=248 nm, τ=25 ns) is used for pulsed laser deposition of BaTiO3 thin films on Pt/Ti/Si multilayer substrates. The processing gas atmosphere consists of O2 at typical pressures of p=10-3-5·10-1 mbar. The investigations concentrate on the influence of the substrate temperature and the kinetic energy of the film forming particles on the crystalline structure and orientation of the growing films.

X-ray diffraction measurements and polarization dependent micro Raman spectroscopy reveal oriented growth of the films with c-axis orientation normal to the substrate surface and [100] texture if the energy of the particles is > 60 eV, while at lower kinetic energies a [110] or [111] texture with partly a-axis orientation is preferred. The ferroelectricity and the dielectric constant of the films, as determined by polarization versus voltage (P-V) and capacitance versus voltage (C-V) impedance measurements, decreases with increasing kinetic energy of the film forming particles. This decrease of the dielectric properties correlates with the change of the preferred orientation and the crystalline quality of the films.
Preparation and Characterization of (Ba1-xSrx)TiO3 Thin Films for Infrared Detection by Pulsed Iaserdeposion Method
Authors: Kubo R. , Xu H. , Yoshino Y. , Okuyama M.
Published: April 2011

Ba1-xSrxTiO3 thin films have been deposited on Pt/Ti/SiO2/Si substra by the pulsed ArF laser deposition method. Deposition conditions, such as ambient gas and substrt temperatze, have been optmized to rrxove crystallinepropesty. Fe oelectric p e phasehasbeenobtainod ithe BSTthin filns deposited above 500°C in Q2 gas havingpressure ofabout 13Pa. Using N2O gas instead of O2 gas improved the crystallinity, because highly chemical active oxygen radicals produced due to ultraviolet inadiation of the laser. Doping of Bi ranging around 2% fills of the role of decrease leakage current of BST thin films. Temperature dependence of the dielectric constant (εr) shows a sharp change, peaking aroumd room temperature. The peak point exists below 25°C in the ratio of Ba/Sr=1.1 film, and shills above 50°C in Ba/Sr=5.7 film. When the Ba/Sr ratio is 1.4 the dielectric peak exists near 27°C and is very sharp. The maxinium differentW rate of dielectric constanttversus temperature is the largest in Ba/Sr=1.4 film and is about 100K-1. This value is equivalent to apyroelectric coefficient of 1.8 × 10-7 C/cm2K, which is almost the same as that of LiTaO3 single crystl, a typical pyroelectric material.
Pulsed Laser Deposition of BaxSr1-xTiO3 Thin Films for Frequency Agile Microwave Electronics
Authors: Chang W. , Horwitz J. S. , Pond J. M. , Kirchoefer S. W. , Chrisey D B.
Published: April 2011

Oriented, single phase thin films (~5000Å thick) of BaxSr1-xTiO3 (BST) have been deposited on to (100) MgO and LaAlO3 (LAO) single crystal substrates using pulsed laser deposition (PLD). A strong correlation is observed between the microstructure of the deposited film and the dielectric tuning and loss at microwave frequencies. Microstructural defects observed in as deposited films include strain, due to film substrate lattice mismatch and oxygen and cation vacancies. Compensation of the ablation target with excess Ba and Sr is observed to increase the dielectric constant and to reduce the dielectric loss. Post-deposition, bomb annealing of films at high temperatures (1250°C) is observed to fill oxygen vacancies and increase grain size. The difference in the dielectric behavior for as-deposited and low temperature annealed BST films on MgO and BST films on LAO is observed and may be attributed to the differences in film stress. A further improvement in the dielectric behavior is observed by the addition of donor/acceptor dopants such as Mn. The data shows that ferroelectric thin films can be used to build tunable microwave circuits that offer significant performance advantages over devices made from conventional semiconducting materials.
Microstructure and Temperature Dependence of Microwave Penetration Depth of Ag-YBa2Cu3O7-δ Thin Films
Authors: Kaur Davinder , Pinto R.
Published: April 2011

We report the measurements of the magnetic penetration depth λ(T) of Ag-doped YBa2Cu3O7-δ (YBCO) thin films in the film thickness range 1500-4000A and temperature range 18-88K. The films are insitu grown by laser ablation on LaAlO3 <100> single crystal substrates. The penetration depth measurements are performed by microstrip resonator technique. A correlation of λ(T) with the film microstructure observed with Atomic Force Microscopy has shown that λ(T) depends critically on the film microstructure. Temperature dependence of λ(T) has also been studied for best quality films.The experimental results are discussed in terms of BCS theory (s-wave pairing) and d-wave Pairing with and without impurity scattering. The results are found to be best fitted to the d-wave model in dirty limit with impurity scattering. Near Tc, we have also compare the (3D) XY critical regime and the Ginzburg-Landau (GL) behaviour.
Amorphous Diamond Films Deposited by Pulsed-Laser Ablation: the Optimum Carbon-Ion Kinetic Energy and Effects of Laser Wavelength
Authors: Lowndes Douglas H. , Merkulov Vladimir I. , Puretzky A. A. , Geohegan D. B. , Jellison G. E. , Rouleau C. M. , Thundat T.
Published: April 2011

A systematic study has been made of changes in the bonding and optical properties of hydrogen-free tetrahedral amorphous carbon (ta-C) films, as a function of the kinetic energy of the incident carbon ions measured under film-deposition conditions. Ion probe measurements of the carbon ion kinetic energies produced by ArF and KrF laser ablation of graphite are compared under identical beam-focusing conditions. Much higher C+ kinetic energies are produced by ArF-laser ablation than by KrF for any given fluence and spot size. Electron energy loss spectroscopy and scanning ellipsometry measurements of the sp3 bonding fraction, plasmon energy, and optical properties reveal a well-defined optimum kinetic energy of 90 eV to deposit ta-C films having the largest sp3 fraction and the widest optical (Tauc) energy gap (equivalent to minimum near-gap optical absorption). Tapping-mode atomic force microscope measurements show that films deposited at near-optimum kinetic energy are extremely smooth, with rms roughness of only ~ 1 Å over distances of several hundred nm, and are relatively free of particulates.
Matrix Assisted Pulsed Laser Evaporation (Maple) of Polymeric Materials: Methodology and Mechanistic Studies
Authors: Piqué A. , McGill R. C. R. A. , Chrisey D. B. , Callahan J. , Mlsna T. E.
Published: April 2011

A new matrix assisted pulsed laser evaporation (MAPLE) technique has been developed at the Naval Research Laboratory, to deposit superior quality ultra thin, and uniform films for a range of highly functionalized polymeric materials. The MAPLE technique is carried out in a vacuum chamber, and involves directing a pulsed laser beam onto a frozen target, consisting of a polymer dissolved in a solvent matrix. The laser beam evaporates the surface layers of the target, where both solvent and polymer molecules are lifted into the evacuated gas phase. A solvent and polymer plume are generated incident to the substrate being coated. Si(111), and NaCl substrates coated with thin layers of polymer have been examined by a range of techniques including: optical microscopy, scanning electron microscopy and Fourier transform infra-red spectroscopy. Under optimum conditions the native polymer was transferred to the substrate without chemical modification as a highly uniform film.

The MAPLE technique offers a number of advantages over conventional polymer deposition techniques, including the ability to precisely and accurately coat a relatively large or small targeted area with an ultrathin, and uniform coating with sub monolayer thickness control. Conventional pulsed laser ablation techniques can be utilized for coating a limited number of polymers, but we have found that for highly functionalized materials the native polymer structure is almost completely lost in the process. In contrast, when the MAPLE conditions are optimized the deposition of even highly functionalized polymeric materials proceeds with little effect on the intrinsic polymer structure.
A Comparison of Single-Wall Carbon Nanotube Production Using Continuous Wave and Pulsed Laser Vaporization
Authors: Dillon A.C. , Parilla P.A. , Jones K.M. , Riker G. , Heben M.J.
Published: April 2011

We have produced single-wall carbon nanotubes (SWNTs) by Nd:Yag laser vaporization of porous cobalt-nickel/graphite targets for the first time without applying external heat to the target. Both continuous wave (c.w.) and pulsed laser-techniques were explored. In the pulsed experiments, the energy density per pulse was varied between 0.12 and 0.62 J/cm2 and pulse rates ranged from 24 kHz down to 3 kHz corresponding to average powers of 25.5 to 16 W. Continuous wave experiments were conducted at average powers which corresponded to those measured for each of the pulsed runs. An additional run at 30 W was also performed. A rigorous method developed for the analysis of transmission electron microscopy (TEM) images was used to estimate SWNT content in the laser-generated carbon samples. The pulsed and continuous wave processes both produced a linear increase in SWNT content with increasing average power. These results are not intuitive for the pulsed laser-production since a higher average power corresponds to a lower peak pulse power. In fact, a pulsed run with the maximum pulse energy of 0.62 J/cm2 (3 kHz, 16 W), produced no detectable SWNTs. A maximum SWNT content of 78% was observed for c.w. experiments at a power of 30 W. Additional laser experiments performed on dense cobalt-nickel / graphite targets at room temperature enabled a better understanding of the carbon removal mechanisms for the pulsed versus c.w. processes. Cumulatively, these investigations indicate that high energy laser pulses produce particles from highly porous targets by ablation which are too large to readily be incorporated into growing nanotubes. Successful high-yield production of SWNTs relies upon remaining in a vaporization regime during synthesis.
Use of Matrix Assisted Pulsed Laser Evaporation (Maple) for the Growth of Organic Thin Films
Authors: Piqué A. , Chrisey D.B. , Spargo B.J. , Bucaro M.A. , Vachet R.W. , Callahan J.H. , McGill R.A. , Leonhardt D. , Mlsna T.E.
Published: April 2011

A novel variation of conventional pulsed laser deposition, called matrix assisted pulsed laser evaporation, or MAPLE, has been utilized for growing organic thin films. The MAPLE technique is carried out in a vacuum chamber and involves directing a pulsed laser beam) onto a frozen target consisting of an organic compound dissolved in a solvent matrix. The laser beam evaporates the surface layers of the target with both solvent and organic molecules being released into the chamber. The volatile solvent is pumped away, whereas the organic molecules coat the surface of a substrate. Very thin and uniform films (50 to 100 nm) of various organic materials, such as carbohydrates, have been deposited on Si(111) and NaCl substrates. The films prepared using this method have been examined by optical microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and electrospray mass spectrometry. Careful control of the processing conditions allowed carbohydrates such as sucrose and glucose, in addition to high molecular weight polymers such as dextran, to be transferred to the substrate as uniform films, without significant chemical decomposition. The use of MAPLE films for chemical and biological sensor applications is being investigated and the potential of this technique for producing high quality thin films of other organic compounds will be discussed.
Large Scale Synthesis of Silicon Nanowires by Laser Ablation
Authors: Tang Y.H. , Zhang Y.F. , Lee C.S. , Wang N. , Yu D.P. , Bello I. , Lee S.T.
Published: April 2011

Quasi one-dimensional materials have attracted considerable attention in recent years because of its potential to both fundamental physics and nanoelectronic applications. More recently, we have achieved large scale synthesis of silicon nanowires (SINW) at a high growth rate by laser ablation of Si target at 1200 °C. The laser source was a pulsed KrF excimer laser and the Si targets were made by pressing Si powder of 5 microns in size. 50 sccm Ar was used as a carrying gas flowing from the side near the Si target towards a water-cooled copper finger. Si nanowires have been grown with diameters ranging from 3 to 43 nm and several hundreds microns in length after 2 hours of laser ablation of Si target. The SLNWs were analyzed by XRD, Raman, EDS, TEM and HRTEM. Successful large scale synthesis of SINW by laser ablation extends the pulsed laser ablation method from depositing thin films to synthesis of nanowires.
Diffusion of Strain Induced Defects after Heavy Ion Irradiation
Authors: Aggarwal G. , Sen P.
Published: April 2011

We report study of recovery dynamics, followed by in-situ resistivity measurement, after 100 MeV oxygen ion irradiation in cold rolled Fe at 300K. Scaling behavior with microstructural density and temperature of sample has been used to establish stress induced defects formed during irradiation as a new type of sink. The dynamics after irradiation has been shown to be due to migration of defects to two types of sinks i.e. stress induced defect as variable sinks and internal surfaces as fixed sinks.
The Volume Diffusion of Interstitial Atoms in Ordered Magnetic Alloys Under Pressure
Authors: Zaginaichenko S.Yu. , Matysina Z.A.
Published: April 2011

Theoretical investigation of interstitial atom diffusion in a binary alloy A-B with crystal lattice of CsCl type with atomic and magnetic (ferromagnetic or antiferromagnetic) order has been performed. The influence of external pressure on diffusion of hydrogen atoms has been defined. Calculations has been carried out by methods of statistical physics with application of thermodynamic functions.
Calculation of The Diffusion Parameters in an Ordered Ni3Al-Alloy for A Relaxed Lattice
Authors: Schmidt C. , Bocquet J.L.
Published: April 2011

Using atomistic computer simulations, we calculate the diffusion parameters of an Ll2-ordered Ni3Al-alloy. A conjugate gradient algorithm under constant zero pressure and a semi-empirical N-body potential are applied to evaluate potential barrier heights and pre-exponential factors. We focus our investigation on those diffusion mechanisms that have been proposed to account for the experimentally observed but theoretically still disputed fast self-diffusion of Al in Ni3Al: antisite bridge mechanisms and correlated six-jump cycles. Our results demonstrate that the most competitive jumps or jump sequences involve AlNJ-antistructure atoms which are shown to play a key role in the diffusion process by either actively or passively lowering the activation energy of migration.
Monte Carlo Simulation of the Initial Disordering Rate of Cu3Au Under Ion Irradiation
Authors: Wei L.C. , Lang E. , Ghaly M. , Bellon P. , Averback R. S.
Published: April 2011

The temperature dependence of disordering of Cu3Au during ion irradiation has been investigated by computer simulations using MONTE CARLO methods. The investigation was motivated by peculiar experimental observations that the initial disordering rate begins to decrease above ~300 K, which can be explained by vacancies just becoming mobile at that temperature, but then at ~ 475 K, it reaches a minimum and then increases rapidly as the temperature is further increased, up to the order-disorder temperature. The present simulation shows that this behavior can be understood in terms of temperatures dependencies in both atomic mixing in the cascade and the efficiency of vacancy annealing of disorder as the vacancies diffuse out of the cascade.
Stochastic Vacancy Motion in B2 Intermetallics Detected by PAC
Authors: Bai Bin , Collins Gary S. , Nieuwenhuis Harmen Thys , Wei Mingzhong , Evenson William E.
Published: April 2011

Using perturbed angular correlation of gamma rays (PAC), nuclear relaxation has been detected at high temperature in highly ordered B2 intermetallics that is attributed to stochastic motion of vacancies near 111In/Cd probe atoms. The relaxation is of quadrupole interaction signals due to transition-metal vacancies in the first atomic shells of the probes. Possible relaxation mechanisms are reorientation of the vacancy with respect to the probe, detrapping of the vacancy, or trapping of a second vacancy. The relaxation reaches values of 10 MHz at temperatures of 1500K, 1200 K and 1170 K, respectively, for NiAI, FeAl and PdIn. For NiAl and FeAI, the onset of relaxation is abrupt, suggesting an activation enthalpy for the associated vacancy motion of several electron-volts. For PdIn, the relaxation has an activation enthalpy of 1.00(19) eV, a value significantly lower than might be expected naively on the basis of diffusion data. This difference gives insight into vacancy motion and diffusion mechanisms in PdIn.
Modeling of Diffusion in Ordered Structures of B2-Type
Authors: Ganchenkova M.G. , Nazarov A.V.
Published: April 2011

Using Monte Carlo simulation, we model the effect of interaction of vacancies on their diffusivities in ordered structures of B2-type. The activation barriers of atom jumps to vacancy are calculated by the static relaxation technique using interatomic potentials for both vacancy exchanges: with nearest-neighbour atoms and next-nearest-neighbour atoms. This is done for all possible positions of the second vacancy. Knowing these barriers it is possible to calculate the jump rates and to model the vacancy migration. The calculations were done for a system with parameters similar to NiAl. The modeling allows to inter the existence of a new diffusion mechanism in ordered structures of B2-type, which could be attributable to dynamic pair of vacancies and vacancy exchanges with next-nearest-neighbor atoms.
Kinetics and Mechanisms of Intermetallic Growth by Bulk Interdiffusion
Authors: Paritskaya L.N. , Kaganovskii Yu.S. , Bogdanov V.V.
Published: April 2011

Kinetic properties of γ-phase (Cu5Zn8) growth in the binary system Cu-Zn were studied at 160-270°C. It has been found that γ-phase grows in diffusional-kinetic regime. Both kinetic coefficients of interfacial reaction rate β and diffusion coefficients D have been determined taking into account Kirkendall effect. Arrhenius equations for the kinetic and diffusion coefficients have been obtained, with the high values of “dynamic” diffusion coefficients and low activation energies for both diffusion (QD) and interfacial reaction (Qβ). The mechanism of Zn diffusion in non-stoichiometric Cu5Zn8 phase is discussed.
Effect of Atomic Order on Iron and Cobalt Grain Boundary Diffusion in the FeCo Equiatomic Compound
Authors: Tôkei Zs. , Bernardini J. , Beke D. L.
Published: April 2011

Simultaneous grain boundary self-diffusion of iron and cobalt in FeCo was investigated in the B-kinetic regime by the radiotracer method combined with a serial sectioning technique over the temperature range 873-1133 K, which includes the A2-B2 bulk order-disorder transition temperature. This transition leads to a decrease in both iron and cobalt mass transport mainly owing to a change in the pre-exponential factor, but not in the diffusion activation energy. Moreover, the breaking point in the Arrhenius plots is observed below the bulk order-disorder transition temperature. In view of recent surface segregation studies on Fe-Co, and according to the Fe-Co phase diagram, the results are discussed assuming an iron segregation, which decreases the A2-B2 transition temperature in grain boundaries.
Out Diffusion of Oxygen in Czochralski Silicon at Low Temperatures
Authors: McQuaid S.A. , Johnson B.K. , Gambaro D. , Falster R. , Ashwin M. , Newman R.C.
Published: April 2011

Previously reported measurements of anomalously high rates of oxygen out-diffusion in Czochralski silicon at low temperatures (T≤450°C) are confirmed. The surface concentration is shown to decrease with increasing time while the depth to which the concentration is depleted remains constant. Exposure to a hydrogen plasma under conditions known to catalyse the diffusion of isolated oxygen atoms causes an increased rate of decrease of the surface concentration without significantly affecting the depth to which the concentration is depleted. The evolution of the out-diffusion profiles cannot be explained by a catalytic mechanism operating on the isolated oxygen atoms. A slow conversion of Oi to a complex containing oxygen which can diffuse rapidly over long distances before being trapped either on the surface or in the bulk of the sample can account for both out-diffusion and simultaneous loss of [Oi] in the bulk. The conversion rate is enhanced by exposure to a hydrogen plasma, indicating that it is controlled by the diffusion rate of isolated atoms.
Threshold Character of Zn Diffusion into InP
Authors: Kamanin A.V. , Kudryavtsev Yu.A. , Shmidt N.M.
Published: April 2011

The initial diffusion stage (lIDS) of Zn in InP from polymer spin-on films has been investigated. The threshold diffusion temperature of 375°C has been established. It has been found that the heavily-doped near-surface layer, that consisted of electrically neutral zinc-containing complexes, was formed at IDS, while a low part of Zn was electrically active. The Zn diffusivity during IDS has been found to be at least two orders of magnitude more than the Zn diffusivity obtained after an isothermal diffusion.
Quantitative Measurement of Reduction of Boron Diffusion by Substitutional Carbon Incorporation
Authors: Carroll M. S. , Lanzerotti L. D. , Sturm J. C.
Published: April 2011

Recently, the suppression of boron diffusion due to both thermal and transient enhanced diffusion (TED) has been demonstrated through the incorporation of 0.5% substitutional carbon in the base of Si/SiGe/Si heterojunction transistor's (HBT)[1,2]. Because the devices are sensitive to diffusion on a scale less than that we can detect with SIMS, in this paper combined process and device modeling (TMA TSUPREM4 and MEDICI) are used to relate observed electrical characteristics (collector saturation currents and Early voltages) of the HBT's to boron diffusion, with a sensitivity of 20-30Å. Boron diffusivity in the SiGeC base is ~8 times slower than that of the boron diffusivity in the SiGe base without implant damage (no TED). In the case of ion implant damage in an overlying layer to cause TED the excess interstitial concentration due to ion implant damage is reduced by approximately 99% through incorporation of 0.5% substitutional carbon in the HBT SiGe bases. This demonstrates that carbon incorporation acts as an effective sink for interstitials.
Molecular Diffusion Processes in Crystalline Microporous Materials
Authors: Sastre G. , Corma A. , Catlow C. R. A.
Published: April 2011

Atomistic Molecular Dynamics are used to simulate diffusion of hydrocarbons inside the microporous structure of siliceous zeolite CIT-I, with chemical composition SiO2. CIT-1 is a crystalline microporous material containing channels formed by rings containing 12 and 10 Si atoms (Figure 1). The dimensions of these two channel systems are sufficient to cause substantial differences in the diffusion of para-xylene and ortho-xylene. Diffusion coefficients as a function of loading of each isomer, and activation energies have been calculated from the simulations. The effect of the isomer size in the diffusion path is also analysed.
An Oxygen Potential Gradient as a Possible Diffusion Driving Force
Authors: Pint B. A. , Alexander K. B. , Monteiro O. R. , Brown I. G.
Published: April 2011

Oxygen-active elements such as Y, Zr and Hf are added to alumina-forming alloys to improve the adhesion of the external α-Al2O3 scale formed during high temperature oxidation. During oxidation at 1000°-1500°C, many such elements are observed to diffuse from the alloy through the scale and form oxide particles at the scale-gas interface. Once nucleated, the volume fraction of these particles increases with oxidation temperature and time. The continued increase in volume fraction with time suggests that diffusion is not merely driven by a concentration gradient of the oxygen-active elements. Pre-coating with a dense, 1 μm-thick, plasma-deposited alumina layer prior to oxidation did not prevent the nucleation and growth of these types of particles at the gas interface of the coating. The driving force for this diffusion phenomenon is attributed to the oxygen potential gradient across the metal-oxide-gas system and the high oxygen affinity of these elements.
Chromium Diffusion in Sapphire Crystals: Influence of Preannealing Conditions
Authors: Gontier-Moya E. G. , Moya F. , Bigarre J. , Juve D. , Treheux D. , Grattepain C.
Published: April 2011

Chromium diffusion coefficients in alumina single crystals were evaluated from penetration profiles determined by the SIMS technique. The samples were previously annealed at 1000°C (1 hour), 1500°C (4 hours), and 1700°C (24 hours). Diffusion experiments were carried out at 1400°C during 10 hours.

The results show that bulk diffusion coefficients are strongly dependent on preannealing conditions (temperature and time): they decrease by more than an order of magnitude when the preannealing temperature is increased from 1000°C to 1700°C.

These results are discussed taking into account the dislocations and point defects in alumina. We consider the role played by the linear defects resulting from surface polishing, as well as point defects associated with impurities. It is found that the lowest defect concentration is achieved after an annealing treatment at 1700°C during 24 hours. The conditions for obtaining a, «reference material» are proposed.
Proliferation of Human Osteoblastic Cells and Synthesis of Extracellular Bone Matrix on Biomaterials
Authors: Schaefer D. J. , Munder B. , Voigt M. , Stark G. B.
Published: April 2011

Primary human osteoblasts were cultered on biomaterials to develop living bone substitutes by Tissue Engineering. Monolayer cultures were established from iliac crest biopsies. Single cell suspensions were then seeded onto tricalciumphosphate (TCP) BIOBASE®, hydroxyapatitecollagen(HAC), autoclaved cancellous bone (CB) and fibrin glue (FG) Tissucol® The constructs were analyzed by electronmicroscopy, Cell proliferation assay (XTT) and histology to assess adhesion, proliferation and extracellular matrix formation on the biomaterial.

The osteoblastic cells survived in the fibrin glue and established a mesenchymal phenotype. They adhered to the HAC-sponges, TCP and CB. Prolifertion was seen on TCP and CB. HAC had a suppressive effect on the cells. An inmature matrix was found on TCP and a bone neomatrix on CB after 4 weeks in vitro.
PEG Cross-Linked Alginate Hydrogels with Controlled Mechanical Properties
Authors: Eiselt Petra , Rowley Jon A. , Mooney David J.
Published: April 2011

Reconstruction of tissues and organs utilizing cell transplantation offers an attractive approach for the treatment of patients suffering from organ failure or loss. Highly porous synthetic materials are often used to mimic the function of the extracellular matrix (ECM) in tissue engineering, and serve as a cell delivery vehicle for the formation of tissues in vivo. Alginate, a linear copolysaccharide composed of D-mannuronic acid (M) and L-guluronic acid (G) units is widely used as a cell transplantation matrix. Alginate is considered to be biocompatible, and hydrogels are formed in the presence of divalent cations such as Ca2+, Ba2+and Sr2+. However, ionically cross-linked alginate gels continuously lose their mechanical properties over time with uncontrollable degradation behavior. We have modified alginate via covalent coupling of cross-linking molecules to expand and stabilize the mechanical property ranges of these gels. Several diamino PEG molecules of varying molecular weight (200, 400, 1000, 3400) were synthesized utilizing carbodiimide chemistry. Sodium alginate was covalently cross-linked with these cross-linking molecules, and mechanical properties of the resulting hydrogels were determined. The elastic modulus of the cross-linked alginates depended on the molecular weight of the cross-linking molecules, and ranged from 10-110 kPa. The theoretical cross-link density in the hydrogels was also varied from 3 to 47% (relative to the carboxylic groups in the alginate) and the mechanical properties were measured. The elastic modulus increased gradually and reached a maximum at a cross-link density of 15%. In summary, covalently coupled hydrogels can be synthesized which exhibit a wide range of mechanical properties, and these materials may be useful in a number of tissue engineering applications.
Biomolecular Surface Engineering of Materials for Controlling Bone Cell Adhesion and Spreading
Authors: Rezania A. , Healy K. E.
Published: April 2011

Model biomaterial surfaces were modified with a peptide that contained a -RGD- (Arg-GlyAsp) sequence, unique to bone sialoprotein, to determine its effect on strength of adhesion, spreading, and focal contact formation of primary bone-derived cells. Peptide surfaces were fabricated by using a heterobifunctional crosslinker to graft the peptide to surfaces (quartz and silicon). Contact angle measurements, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy were used to confirm the chemistry and thickness of the overlayers. Furthermore, spectroscopic ellipsometry was used to estimate the density of immobilized peptide on metal oxide surfaces. A radial flow apparatus was used to measure the strength of adhesion on peptide grafted surfaces. Following 20 min of cell incubation, the strength of cell adhesion was significantly (p<0.05) higher on the -RGD- compared to -RGE- (control) surfaces. The mean area of cells contacting the -RGD- surface was significantly (p<0.05) higher than -RGE- surfaces. Vinculin staining revealed formation of focal contact patches on the periphery of bone cells incubated for 4 hr on the -RGD- surfaces; however, cells seeded on the -RGE- grafted surfaces formed little or no focal contacts. The methods of peptide immobilization utilized in this study can be applied to medical devices, biosensors, and diagnostic assays that require specificity in cell adhesion.
Effect of the End of Range Loop Layer Depth on the Evolution of {311} Defects.
Authors: Raman R. , Law M. E. , Krishnamoorthy V. , Jones K. S.
Published: April 2011

The interactions between end of range dislocation loops and {311} defects as a function of their proximity was studied. The dislocation loops were introduced at 2600 Å by a dual 1 × 1015 cm−2, 30 keV and a 1 × 1015 cm−2 , 120 keV Si+ implantation into Silicon followed by a anneal at 850 °C for 30 minutes. The depth of the loop layer from the surface was varied from 2600 Å to 1800 Å and 1000 Å by polishing off the Si surface using a chemical-mechanical polishing (CMP) technique. A post-CMP 1 × 1014 cm−2, 40 keV Si+ implantation was used to create point defects at the projected range of 580 Å. The wafers were annealed at 700, 800 and 900 °C and plan-view transmission electron microscopy (TEM) study was performed. It was found that the number of interstitials in {311} defects decreased as the projected range damage was brought closer to the loop layer, while the number of rectangular elongated defects (REDs) increased. Experimental investigation showed that REDs are formed at the end-of-range. It is concluded that the interstitials introduced at the projected range are trapped at the end-of-range dislocations. The REDs are formed due to the interactions between the interstitials and the pre-existing loops.
Stacked Layers of C-Induced Ge Quantum Dots
Authors: Schmidt O. G. , Eberl K. , Schieker S. , Jin-Phillipp N. Y. , Phillipp F. , Auerswald J. , Lamperter P.
Published: April 2011

Fifty layers of carbon-induced germanium dots, separated by 9.6 nm Si, are stacked by solid source molecular beam epitaxy. Each dot layer consists of 0.2 monolayers of pre-deposited carbon and 2.4 monolayers of post-grown Ge. These carbon-induced germanium dots are only 10 to 15 nm in diameter and 1 to 2 nm in height. Vertical alignment due to penetrating strain fields of underlying dot layers is not observed. Unlike to an identical structure without the pre-growth of carbon, a variety of advantageous aspects such as strain compensation, strongly enhanced no-phonon photoluminescence at a wavelength of around 1.3 μm and the possibility of effective waveguiding make this stack of C-induced Ge islands an attractive structure for Si based optoelectronic devices.
Magnetron Sputter Heteroepitaxy of Si1-x.Gex/Si(001): The Evolution of the Cross-Hatched Surface
Authors: Vögeli B. , Kummer M. , Känel H. Von
Published: April 2011

The surface step structure of step graded Si1-xGex buffers was investigated by scanning tunneling microscopy (STM). On pseudomorphically grown samples, single atomic steps were found, with the 2×8 reconstruction indicating Ge segregation. Upon strain relaxation, surface slips and the development of the cross-hatched surface takes place. Here, close to the surface slips, the step structure was found to consist of double height DA steps. This feature is not simply kinematically driven step bunching but can be attributed to the anisotropic strain field on the surface and to the Ge segregation. Analysis of STM cross-sections were taken to estimate the relaxation of our samples. The obtained values agree well with x-ray measurements. The relaxation is found to depend exponentially on the temperature, as theoretically expected.
Feasibility Of Novel Si-Based Interminiband Lasers
Authors: Sun Gregory , Friedman Lionel , Soref Richard A.
Published: April 2011

We have designed a parallel interminiband lasing in superlattice structures of coherently strained Si0.5Ge0.5/Si quantum wells (QWs). Population inversion is achieved between the non-parabolic heavy-hole valence minibands locally in-k-space. Lasing transition is at 5.4μm. Our analysis indicates that an optical gain of 134/cm can be obtained when the laser structure is pumped with a current density of 5kA/cm2.
Direct Optical Measurement of the valence band offset of p+ Si1−x−yGexCy/p− Si (100) by Heterojunction Internal Photoemission
Authors: Chang C. L. , Rokhinson L. P. , Sturm J. C.
Published: April 2011

Optical absorption measurements have been performed to study the effect of carbon on the valence band offset of compressively strained p+ Si1−x−yGexCy/(100) p− Si heterojunction internal photoemission structures grown by Rapid Thermal Chemical Vapor Deposition (RTCVD) with substitutional carbon levels up to 2.5%. Results indicated that carbon decreased the valence band offset by 26 ± 1 meV/ %C. Results from optical measurement in this study agreed with previous data from capacitance-voltage measurements. Based on previous reports of carbon effect on the bandgap of compressively strained Si1−x−yGexCy, our work suggests that the effect of carbon incorporation on the band alignment of Si1−x−yGexCy/Si is to reduce the valence band offset, with a negligible effect on the conduction band alignment.
SiGe RF - Electronic: Devices, Circuits, Competitors, Markets
Authors: König U.
Published: April 2011

The outstanding performance of the SiGe/Si heterosystem and its compatibility to the dominating Si-technology, opens perspectives for a new generation of high volume microelectronic components, just for communication markets. This paper reviews device and circuit results from experiments and simulations for SiGe HBTs and for SiGe HFETs, and compares those to device results made from competitive materials. Figures of merit considered are gains, transconductances, frequencies, noise, power, delays and bandwidths.
Low Temperature Epitaxy Of Si/Si1-xGex/Si Multilayers By Low Pressure Rtcvd For Very Thin Soi Applications
Authors: McNeill D.W. , Gay D.L. , Lip X. , Armstrong B.M. , Gamble H.S.
Published: April 2011

The growth by rapid thermal chemical vapour deposition of Si/Si1-xGex/Si multilayer structures, suitable for thin bond and etch-back silicon-on-insulator fabrication has been investigated. Surface topography was studied by scanning probe microscopy, and layer contamination by secondary ion mass spectrometry. Smooth layers are only achieved at high growth temperatures (>700°C), and when surface oxide contamination is reduced by a combination of ex-situ HF vapour treatment and in-situ high temperature H2 bake. A surface peak-to-peak roughness of 15nm for a Si/Si1-xGex/Si multilayer structure has been achieved by reducing the growth time at 700°C or less. Further improvement is possible, especially if carbon contamination can be reduced.
Thermal Stability Of SiGe/Si Quantum Well Structures Grown By APCVD
Authors: Zhao Q. X. , Nur O. , Södervall U. , Patel C. J. , Willandera M. , Holtz P.O. , de Boer W.B.
Published: April 2011

Single and double Si1-xGexx/Si quantum well (QW) structures, which were grown by atmospheric pressure chemical vapor deposition (APCVD), are characterized by photoluminescence and secondary ion mass spectrometry. Systematic post-growth annealing treatments were carried out at temperatures between 600°C and 1100°C in pure N2 ambient. The interdiffusion between the Si layer and the Si1-xGex, well layers occurs at the annealing temperature around 900°C. The diffusion coefficient is deduced at different temperatures from SIMS measurements for single QW structures. The activation energy is about 3.9 eV in the temperature range between 950°C and 1100°C. The double QW structures show a similar value, but the accurate value is more difficult to obtain because it is more complicated to analyze the SIMS profile of the double QW structures. The intensity of the exciton recombination related to carriers confined in the double QW structures decreases with increasing annealing temperatures and becomes strongly suppressed at 750°C. When the annealing temperature is increased further, the intensity of the QW emission recovers. The results indicate that nonradiative centers were generated at annealing temperature of about 750°C
Low-Temperature Epitaxial Growth of IN-Situ HeavilY B-Doped Si1-xGex, Films Using Ultraclean LPCVD
Authors: Morrya A. , Sakuraba M. , Matsuura T. , Murota J. , Kawashima I. , Yabumoto N.
Published: April 2011

In-situ heavy doping of B into Si1-xGex epitaxial films on the Si(100) substrate have been investigated at 550°C in a SiH4(6.0Pa)-GeH4(0.1−6.0Pa)-B2H6(1.25 ×10−5−3.75 × 10−2Pa)-H2(17–24Pa) gas mixture by using an ultraclean hot-wall low-pressure CVD system. The deposition rate increased with increasing GeH4 partial pressure, and it decreased with increasing B2H6 partial pressure only at the higher GeH4 partial pressure. As the B2H6 partial pressure increased, the Ge fraction scarcely changed although the lattice constant of the film decreased. These characteristics can be explained by the suppression of both the SiH4 and GeH4 adsorption/reactions in a similar degree due to B2H6 adsorption on the Si-Ge and/or Ge-Ge bond sites. The B concentration in the film increased proportionally up to 1022cm3 with increasing B2H6 partial pressure.
The Formation of Abrupt N+ Doping Profiles Using Atomic Hydrogen and Sb During Si MBE
Authors: Thompson P.E. , Silvestre C. , Twigg M. , Jernigan G. , Simons D.S.
Published: April 2011

Previously, atomic hydrogen has been shown to be effective in reducing the segregation of Sb on Si(100) during solid source molecular beam epitaxy growth. In this work we have investigated the electrical activation of the Sb. Using Hall measurements, spreading resistance profilometry, and secondary ion mass spectrometry, we have demonstrated that the co-deposition of atomic hydrogen during Sb doping of Si at 500°C produced well-defined doping spikes. Comparing the sheet carrier concentration obtained by Hall measurements to the Sb atomic concentration obtained by SIMS, the overall activation of the Sb was greater than 50%.
Raman Spectroscopy of Epitaxial Si/Si1-xGe, xHeterostructures
Authors: Liu Ran , Zollner Stefan , Liaw Ming , O'meara David , Cave Nigel
Published: April 2011

Raman scattering studies were carried out on epi Si/Si1-xGex (x = 0.1 to 0.3) heterostructures consisting of a thin Si cap layer (100 - 400 A˚), a grade-down Si1-xGex layer, a constant Si1-xGex, buffer layer and a grade-up graded Si1-xGex layer on (100) oriented Si substrates. Different Ge composition, Si1-xGex layer thicknesses and thermal treatment were used to achieve different relaxation in the Si1-xGex layers. It has been revealed that, to a very good approximation, the absolute strains in the cap Si and constant Si1-xGex layers follow a simple sum-rule that is imposed by the lattice mismatch between unstrained Si and completely relaxed Si1-x Gex. This sum rule can be used to determine the Ge composition and stresses in both cap Si and constant Si1-xGex layers. Excellent agreement was found between the theoretical curve obtained with LO phonon strain coefficient b=−930cm−1 and the experimental total strain for all samples, regardless of the degree of the relaxation of the grade-up Si1-xGex layer.