bluuebunny/crossref_metadata_2025 huggingface dataset:
Relative Stability of Silicon Self-Interstitial Defects
Authors: Subramanian G. , Jones K.S. , Law M.E. , Caturla M.J. , Theiss S. , Rubia T. Diaz de la
Published: April 2011

{311) defects and dislocation loops are formed after ion-implantation and annealing of a silicon wafer. Recent Transmission Electron Microscopy studies by Li and Jones have shown that sub-threshold dislocation loops nucleate from {311} defects. In our study, the conjugate gradient method with the Stillinger Weber potential is used to relax different configurations such as {311} defects with a maximum of five chains and perfect dislocation loops. From the formation energies thus obtained we find that there is an optimal width for each length of the {311} defects. Moreover the relative stability of {311}s and loops is studied as a function of defect size. We observe that at very small sizes the perfect loops are more stable than the {311}s. This may provide an explanation for the experimental observation by Robertson et al that, in an annealing study of end of range damage of amorphized samples, 45% of the loops had nucleated in the first 10 minutes of anneal. Out of these 25% of the loops could not have nucleated by unfaulting of {311}s. We propose that homogeneous nucleation, as against unfaulting of the {311}s, could be the source of these sub-microscopic loops.
Activation of Implanted Poly Gates by Short Cycle Time Annealing
Authors: Fiory A. T. , Bourdelle K. K.
Published: April 2011

Amorphous silicon films with B, P, and As implants were activated with thermal anneals that include spiking to the maximum temperature. Films were grown over thermal oxide by chemical vapor deposition as two separately implanted 50-nm layers for manipulating dopant placement and diffusion. Electrical activation was determined by Hall van der Pauw and MOS C-V, and dopant diffusion was profiled by secondary ion mass spectroscopy (SIMS). Flat-band voltage was used to benchmark relative thermal budgets for p-type poly. Temperature-time relationships are used to deduce effective activation energies.
Remote Plasma Nitridation of In-Situ Steam Generated (ISSG) Oxide
Authors: Al-Shareef H.N. , Karamcheti A. , Luo T.Y. , Brown G.A. , Watt V.H.C. , Jackson M.D. , Huff H.R. , Jallepally R. , Noble D. , Tam N. , Miner G.
Published: April 2011

Electrical performance of in-situ steam generated (ISSG) oxide nitrided using remote plasma nitridation (RPN) has been evaluated. An equivalent oxide thickness (EOT) of 1.6 nm with gate leakage current around 5×10−3 A/cm2 (at −1.5V) has been achieved. The leakage current of remote plasma nitrided ISSG oxide is lower than that of ISSG only, where more than one order of magnitude leakage current reduction (at the same EOT) has been achieved for some RPN conditions. Moreover, it is observed that the extent to which the RPN process conditions modify device parameters such as EOT, flatband voltage (VFB), and time-to-breakdown (tbd) increases with decreasing ISSG thickness. The thinner ISSG oxides appear to be more susceptible to plasma damage and accumulation of positively charged nitrogen atoms at the oxide/Si interface. Therefore, RPN processes that use lower temperature and shorter time are preferred for very thin oxides. The nitrogen content and profile in the samples evaluated using SIMS analysis, indicate that RPN offers higher nitrogen content and better nitrogen profile compared to conventional nitrogen incorporation methods such as NO annealing [1].
The characteristics of the Electrolyzed D.I.water with chemicals and the outline of the supply system
Authors: Shirakashi Mitsuhiko , Itoh Kenya , Katakabe Ichiro , Tsujimura Mamabu , Saitoh Takayuki , Yamada Kaoru , Miyashita Naoto , Kodera Masako , Matsui Yoshitaka
Published: April 2011

In semiconductor device production, wafers are treated through many cleaning processes. Usually, several chemicals are used so as to match for several purposes like RCA cleaning method. As wafer size becomes larger, large amount of cleaning chemicals usage and waste are necessary, which becomes now a big problem. Considering the above, we developed the Electrolyzed D.I.water with chemicals supply system in order to minimize running cost of chemicals and waste treatment. It is feature that; 1) this system can generate the anode water of the acidity/high ORP (Oxidation-Reduction Potential) and the cathode water of the alkalinity/low ORP by electrolyzing D.I.water adding with a small quantity of chemicals; 2) this system can generate anode water and cathode water at the same time; 3) if necessary, the anode water can be diluted with D.I.water at the optional density, and it is possible with the cathode water that hydrogen peroxide is added. The anode water which shows acidity/high ORP has the effect of removing metal and organic contamination, and the cathode water which shows alkalinity/low ORP has the effect of particle removal. In this report, we explain the outline of this system and the basic characteristic of the Acid and Alkaline water made with this system and its performances.
Spin-dependent electron transport in ferromagnet/semiconductor Schottky barrier structures
Authors: Hirohata Atsufumi , Xu Yong-Bing , Guertler Christian M. , Anthony J. , Bland C. , Holmes Stuart N.
Published: April 2011

Clear evidence for high efficiency spin-polarized electron transport across ferromagnet/semiconductor Schottky barrier interfaces was observed in Ni80Fe20/GaAs structures. Circularly polarized light was used to excite electrons with a spin polarization perpendicular to the film plane. At negative bias, an almost constant difference between the helicity-dependent photocurrent obtained for the magnetization parallel and perpendicular to the photon helicity was detected. An effective asymmetry, A, was also estimated from the helicity-dependent photocurrent difference, attributed to spin-polarized electron tunneling from GaAs to NiFe (spin filtering). A decreases with increasing photon energy, which is consistent with the energy-dependence of the asymmetry of photoexcited electrons in GaAs. Weak spin injection from NiFe to GaAs was seen at a bias corresponding to the Schottky barrier height, which is likely to occur via a ballistic process.
Influence of Growth Temperature and Phosphine Flow on CuPt Type Ordering in InGaP Grown by Chemical Beam Epitaxy
Authors: Bettini J. , de Carvalho M.M.G. , Hayashi M. A. , Cardoso L. P. , Ugarte D.
Published: April 2011

In this work, In0.5Ga0.5P layers were grown by Chemical Beam Epitaxy on GaAs (001) substrates. A set of samples was grown with temperatures kept in the range of 500°C to 560°C with V/III ratio 15. Another set was grown at 560°C with V/II ratio varied in the range 15 to 35. The evolution of ordering as function of growth temperature and V/III ratio was evaluated by photoluminescence measurements at 77K, Transmission Electron Diffraction (TED) and images using Transmission Electron Microscopy (TEM)-Dark Field. A 48meV reduction in the band gap energy was measured by photoluminescence measurements at 77 K when growth temperature was increased. This result is associated to the occurrence of CuPtB ordering in the InGaP layers observed by TED. The TEM-Dark field examination shows that the ordered domains are larger for samples grown at higher temperatures

A small reduction in band gap, from 1.915eV to 1.902eV, occurs when the V/III ratio is increased from 15 to 35. The TED patterns present diffuse scattering for all samples. For those grown with higher V/III ratio, spots are also observed. TEM-dark field images show that the ordered regions become larger, elongated and inclined; some of them exhibit long range ordering
In Situ Study of Barrier Layers Using Spectroscopic Ellipsometry and Mass Spectroscopy of Recoiled Ions
Authors: Gao Y. , Mueller A.H. , Irene E.A. , Auciello O. , Krauss A.R. , Schultz J.A.
Published: April 2011

An in situ study of barrier layers using spectroscopic ellipsometry (SE) and Time-of-Flight (ToF) mass spectroscopy of recoiled ions (MSRI) is presented. First the formation of copper silicides has been observed by real-time SE and in situ MSRI in annealed Cu/Si samples. Second TaSiN films as barrier layers for copper interconnects were investigated. Failure of the TaSiN layers in Cu/TaSiN/Si samples was detected by real-time SE during annealing and confirmed by in situ MSRI. The effect of nitrogen concentration on TaSiN film performance as a barrier was also examined. The stability of both TiN and TaSiN films as barriers for electrodes for dynamic random access memory (DRAM) devices has been studied. It is shown that a combination of in situ SE and MSRI can be used to monitor the evolution of barrier layers and detect the failure of barriers in real-time.
Two Step Process for the Growth of a Thin Layer of Silicon Dioxide for Tunneling Effect Applications
Authors: Águas Hugo , Cabrita Ana , Tonello Pedro , Nunes Patricia , Fortunato Elvira , Martins Rodrigo
Published: April 2011

In today's main crystalline silicon (c-Si) applications in MOS (metal-oxide-silicon), MIS (metalinsulator-semiconductor) or SIS (Semiconductor-Insulator-Semiconductor), the growing of the oxide layer plays the main role, dictating the device performances, in particular if it has to be grown by a low temperature process. Of fundamental importance is the SiO2 interface with the c-Si. A very low defect density interface is desirable so that the number of trapping states can be reduced and the devices performance optimised.

A two step low temperature oxidation process is proposed. The process consists of growing first a layer of oxide by a wet process and then treating the grown oxide with an oxygen plasma. The oxygen ions from the plasma bombard the oxide causing compaction of the oxide and a decrease in the interface roughness and defect density.

Infrared spectroscopy and spectroscopic ellipsometry measurements were performed on the samples to determine the oxide thickness, optical and structural properties. SIS structures were built and capacitance measurements were performed under dark and illuminated conditions from which were inferred the interface defect density and correlated with the oxide growth process.
SiC and GaN High-Voltage Power Devices
Authors: Chow T.P.
Published: April 2011

The present status of development of SiC and GaN devices for high-voltage power electronics applications is reviewed. Device structures that are particularly applicable to these two wide bandgap semiconductors are considered and compared to those commonly used in silicon. The simulated and experimental performance of two-terminal rectifiers and three- terminal transistors and thyristors are compared. The effects of material parameters (mobility, ionization coefficients, lifetimes) and defects on device characteristics are pointed out. Similarities and differences between electronic and photonic device development in these semiconductors are discussed.
Polarization induced 2DEG in MBE grown AlGaN/GaN HFETs: On the origin, DC and RF characterization
Authors: Vetury R. , Smorchkova I.P. , Elsass C.R. , Heying B. , Keller S. , Mishra U.K.
Published: April 2011

The contribution of spontaneous and piezoelectric polarization to the formation of a 2DEG in AlGaN/GaN heterostructures was investigated using undoped AlGaN/GaN structures. Hall measurements of 2DEG density on such structures with varying Al percentage (8%-27%) and varying thickness of the AlGaN layer (30-500Å) indicated that donor-like surface states at an energy of 1.42eV below the conduction band were the source of electrons in the 2DEG. Field effect transistors were fabricated on such undoped heterostructures. For an AlGaN/GaN structure with 0.27 Al mole fraction, power density in excess of 3.5 W/mm at 6 GHz with corresponding maximum PAE of 33.5% was obtained. These results exceed the best reported power performance of MBE grown GaN HFETs on sapphire, thus demonstrating the excellent capability of MBE grown GaN heterostructures for microwave power applications.
Plasma-Induced Damage and Passivation of GaN in Electron Cyclotron Resonance Excited N2 Plasma Source
Authors: Hsieh J. T. , Breitschädel O. , Rittner M. , Fu L. W. , Schweizer H.
Published: April 2011

Electron cyclotron resonance (ECR) excited N2 plasma exposure were performed to explore a possibility of a robust surface passivation on Ar+ ion beam etched GaN. We adopted Taguchi orthogonal design to optimize the ECR operating parameters with respect to reverse breakdown voltage (VB) and then used the results to determine the VB dependence on the parameters close to the optimum operating point. Rather consistent results were obtained by Taguchi and normal experimental methods. It is clearly indicated that the radio frequency (rf) chuck power play the most important role on the plasma passivation. After N2 plasma treatment, the diode reverse breakdown voltage is drastically restored from 15V to 95V. With the aid of N2 plasma exposure, the Schottky characteristics of ion beam etched GaN can be thus effectively improved.
Surface Disordering and Nitrogen Loss in GaN under Ion Bombardment
Authors: Kucheyev S.O. , Williams J.S. , Jagadish C. , Zou J. , Toth M. , Phillips M.R. , Tan H.H. , Li G. , Pearton S.J.
Published: April 2011

The damage build-up and amorphization behavior in wurtzite GaN films under a wide range of implant conditions are studied by Rutherford backscattering / channeling spectrometry, transmission electron microscopy, and cathodoluminescence spectroscopy. A strong surface peak of lattice disorder, in addition to the expected damage peak in the region of the maximum of nuclear energy loss, has been observed for all implant conditions of this study. Capping of GaN with SiOx and SixNy layers prior to implantation does not eliminate surface disordering. This may suggest that nitrogen loss is not the main reason for the observed enhanced surface disorder, but, rather, the GaN surface acts as a strong sink for migrating point defects. However, pronounced loss of N during ion bombardment is observed for high dose implantation when the near-surface region is amorphized. Moreover, after amorphization, annealing at temperatures above about 400°C leads to complete decomposition of the near-surface layer.
Hydrostatic and Biaxial Strain in BaxSr1-xTiO3Films Grown by Pulsed Laser Deposition
Authors: Carlson C. M. , Parilla P. A. , Rivkin T. V. , Perkins J. D. , Ginley D. S.
Published: April 2011

We grew BaxSr1−xTiO3(BST) films on MgO single crystal substrates by pulsed laser deposition (PLD). We report the in-plane (a) and out-of-plane (c) lattice parameters of BST films deposited in a range of O2deposition pressures [P(02)], as measured by asymmetric rocking curve diffraction. As P(O2) increases, the films' biaxial strain changes from compression (ac). Furthermore, bothaandcare larger than the lattice constant for bulk BST of the same composition. This indicates the presence of a hydrostatic strain component in addition to the biaxial component. From the measured lattice parameters, we calculate the total residual strain in terms of biaxial and hydrostatic components. We also examine the effects of a post-deposition anneal. Characterizing residual strain and understanding its origin(s) are important since strain affects the dielectric properties of BST films and thereby the properties of devices which incorporate them.
Room Temperature Growth of Indium Tin Oxide Films by Ultraviolet-Assisted Pulsed Laser Deposition
Authors: Craciun V. , Craciun D. , Chen Z. , Hwang J. , Singh R.K.
Published: April 2011

The characteristics of indium tin oxide (ITO) films grown at room temperature on (100) Si and Corning glass substrates by an in situ ultraviolet-assisted pulsed laser deposition (UVPLD) technique have been investigated. The most important parameter, which influenced the optical and electrical properties of the grown films, was the oxygen pressure. For oxygen pressure below 1 mtorr, films were metallic, with very low optical transmittance and rather high resistivity values. The resistivity value decreased when using higher oxygen pressures while the optical transmittance increased. The optimum oxygen pressure was found to be around 10 mtorr. For higher oxygen pressures, the optical transmittance was better but a rapid degradation of the electrical conductivity was noticed. X-ray photoelectron spectroscopy investigations showed that ITO films grown at 10 mtorr oxygen are fully oxidized. All of the grown films were amorphous regardless of the oxygen pressure used.
Electrical Characteristics of LSMCD-Derived SrBi2.4Ta2O9 Thin Films Using TiO2 Buffer Layer for Metal/Ferroelectric/Insulator/Semiconductor Field Effect Transistor Devices
Authors: Park Joo Dong , Oh Tae Sung
Published: April 2011

Pt/SBT/TiO2/Si structure was proposed for metal/ferroelectric/insulator/semiconductor field effect transistor (MFIS-FET) applications. SrBi2.4 Ta2O9 (SBT) thin films of 400 nm thickness were prepared using liquid source misted chemical deposition (LSMCD) on Si(100) substrates with TiO2 buffer layers deposited by DC reactive sputtering with the thickness ranging from 5 nm to 200 nm and electrical properties of MFIS structures were investigated. Memory window and maximum capacitance of the Pt/SBT/TiO2 /Si structure increased with decreasing the thickness of TiO2 buffer layer. The Pt/SBT(400 nm)/TiO2(10 nm)/Si structure exhibited C-V hysteresis loop with the memory window of 1.6 V at ±5 V, and could be applicable for MFISFET applications.
Commercial Applications and Review for Direct Write Technologies
Authors: Church Kenneth H. , Fore Charlotte , Feeley Terry
Published: April 2011

Direct write in the past has generated the excitement of possibly replacing photoresist for all electronic applications. Removing the mask would substantially reduce the number of steps required to produce electronic circuits. A reduction in steps represented time and dollar savings. The advantage of being able to direct write a manufacturable device would also save time and money in the design process as well. With all of the obvious advantages, it seemed inevitable that research dollars would continue to mount and thus overcome the obstacles preventing this technology from becoming more than a novel technique used in laboratories. As Moore's law began to settle in, so did photoresist and direct write was little more than a novelty.

That was then, and this is now. Developers have come to terms with the true value direct write can supply to the manufacturers and design engineers. Techniques such as Focused Ion Beam (FIB), Laser Chemical Vapor Deposition (LCVD), ink jetting and ink penning have found real applications that are making a difference in industry. A summary will be presented describing the various direct write techniques, their current applications and the possible or probable applications.
Initial Stages of Sintering of TiO2 Nanoparticles: Variable-Charge Molecular Dynamics Simulations
Authors: Ogata Shuji , Iyetomi Hiroshi , Tsuruta Kenji , Shimojo Fuyuki , Nakano Aiichiro , Vashishta Priya , Kalia Rajiv K. , Loong Chun-K.
Published: April 2011

Variable-charge molecular dynamics simulation of 32 TiO2-nanoparticles with diameter 60Å is performed for 40 ps at 1 GPa and 1,400 K for both rutile and anatase phases, to investigate their phase-dependent sintering mechanisms. In the rutile case, the nanoparticles rotate around their centers during the first 20 ps. Varying degrees of neck formation between neighboring rutile-nanoparticles are found at ∼ 40 ps. In the anatase case, the nanoparticles maintain their original orientations. Similar degrees of neck formation are observed at contacting regions of the anatase nanoparticles.
Intra-Monolayer Hydrogen-Bonding in Monolayer Protected Gold Clusters
Authors: Boal Andrew K. , Rotello Vincent M.
Published: April 2011

Unlike the highly ordered Self-Assembled Monolayers (SAMs) formed on flat gold surfaces, those on gold nanoparticles radiate from a roughly spherical center and are amorphous in structure. One result of this structural motif is that the strength of intra- monolayer non-covalent interactions, such as Φ-stacking and hydrogen bonding, are a function of the distance of the recognition element from the colloidal core. We present here an exploration of these phenomena in amide functionalized thiols in MPCs where the amide functionality position was varied in the alkane chain. [1]
A ‘Building Block’ Approach To Mixed-Colloid Systems Through Electrostatic Self-Organization
Authors: Galow Trent H. , Boal Andrew K. , Rotello Vincent M.
Published: April 2011

We have developed a ‘building block’ approach to electrostatically-mediated construction of modular self-assembled colloid-colloid ensembles. Our strategy involves functionalization of one type of colloidal building block with a primary amine, and a counterpart building block with a carboxylic acid derivative (Scheme 1). By combining the two systems, acid-base chemistry followed by immediate charge-pairing resulted in the spontaneous formation of electrostatically-bound mixed-colloid constructs. The shape and size of these ensembles was controlled via variation of particle size for the two components and their stoichiometries.
Temperature dependences of channel mobility and threshold voltage in 4H- and 6H-SiC MOSFETs
Authors: Harada S. , Kosugi R. , Senzaki J. , Suzuki S. , Cho W. J. , Fukuda K. , Arai K.
Published: April 2011

We have investigated the effect of polytype and oxidation condition on the temperature dependence of channel mobility and threshold voltage in 4H- and 6H-SiC MOSFETs. The behaviors of the channel mobility are apparently different for 4H- and 6H-SiC MOSFETs. In contrast to the polytype effect, dry and wet oxidation samples have almost similar channel mobilities. The variation of the threshold voltage with temperature is proportional to the number of the interface states near the conduction band extracted from n-type MOS capacitors. Therefore, we argue that the distribution of the interface states near the conduction band in p-type SiC MOS structure can be represented by that in n-type SiC MOS structure. Although the oxidation condition varies the distribution of the interface states in the energy range between 0.2 and 0.4 eV from the conduction band, it has little influence on the channel mobility.
Difference in Secondary Defects between High Energy B+ and Al+ implanted 4H-SiC
Authors: Ohno Toshiyuki , Kobayashi Naoto
Published: April 2011

The differences of secondary defects between B+ and Al+ implanted layers in high-energy implantation were investigated. At the same volume concentration of implanted ion, density of secondary defects in Al+ implanted layer is higher than that in B+ implanted layer. On the contrary, mean defect size in B+ implanted layer is larger than that in Al+ implanted layer. The structure of secondary defect is thought to be a dislocation loop formed by an extra Si-C layer or localized lattice strain correlated to agglomerated interstitials. The amount of interstitials used for secondary defect formation is estimated. It almost coincides the same amount of implanted ions, and this correlation doesn't depend on ion species. B+ and Al+ implanted layers have different activation energy for secondary defect formation. This result means that they have different agglomerating mechanism of interstitials, which cause the differences of defect size and density between them.
IRAS Analysis of the Early Stage of Thermal Oxidation on a SiC Surface
Authors: Jikimoto Tamotsu , Tsuchida Hidekazu , Kamata Isaho , Izumi Kunikazu
Published: April 2011

The structure of thermal oxide film thinner than 2nm on a SiC surface was investigated using in-situ infrared reflection absorption spectroscopy (IRAS). In the case of oxide films on 6H-SiC(0001), the peak frequencies of the TO mode (≈1050 cm−1) of the Si-O-Si stretch vibration shifts toward lower wave number with decreasing oxide thickness in the range of 0.2nm to 2nm and shift toward a higher frequency as the growth temperature rises. The LO mode (≈1250 cm−1) of the Si-O-Si stretch vibration remains almost constant with the increase in oxide thickness from 0.2 nm to 2 nm. These results indicate that there is a considerable difference in the structure near the interface between a thermally grown oxide layer formed on SiC and one formed on Si.
Characterization of SiC grown on Ge modified silicon substrates
Authors: Pezoldt J. , Stauden Th. , Förster Ch. , Masri P.
Published: April 2011

Silicon carbide layers were grown by solid source molecular beam epitaxy on silicon (111). Prior to the silicon carbide growth different amounts of germanium were predeposited on the silicon surface. Structural and morphological investigations with reflection high energy electron diffraction, x-ray diffraction, atomic force microscopy and spectroscopic ellipsometry revealed an improvement of the surface and interface properties for Ge coverages around and below 1 ML. The improved structural properties of the heterojunction lead to an amendment of the forward and reverse properties of the SiC/Si heterojunction.
Selective Doping of 4H-SiC by Aluminum/Boron Co-diffusion
Authors: Gao Ying , Soloviev S. I. , Wang X. , Tin C. C. , Sudarshan T. S.
Published: April 2011

Based upon graphite mask, selective aluminum/boron doping of SiC by thermal diffusion has been successfully realized in a temperature range of 1800 to 2100°C. Secondary ion mass spectrometry (SIMS) was used to identify the doping profiles, which showed very high aluminum concentration (5×1019 cm−3) near the surface and linearly graded boron profile up to several micrometers in depth. Hall-effect measurement was also employed to obtain the carrier concentration, which showed more than 1019 cm−3 carrier concentration at room temperature. Cathodoluminescence (CL) image clearly illustrated the locally diffused pattern. In addition, planar p-n diodes based upon this technique were fabricated and current-voltage (I-V) characteristics were measured. Excellent rectification property has been obtained. Built-in voltage of 2.9 V in the formed p-n junction was obtained by capacitance-voltage (C-V) measurement.
Deep-level luminescence at 1.0 eV in 6H SiC
Authors: Magnusson B. , Ellison A. , Son N. T. , Janzén E.
Published: April 2011

Results from photoluminescence (PL) and Zeeman effect measurements of a PL center, labeled UD-1, in 6H SiC are presented. The spectrum consists of three no phonon-lines (NPLs) at 0.9952, 1.0015 and 1.0020 eV. The luminescence starts decreasing in intensity above 40 K and is completely quenched at 80 K. The observed Zeeman splitting reveals a spin one half of the ground state of the two highest energy lines. No splitting of the 0.9952 eV line is detected. The g║-value for the 1.0015 eV and 1.0020 e║ lines are g║ = 1:4 and g║ = 1:7, respectively. For both lines, g⊥ = 0. The C3v symmetry indicates that the UD-1 center is either a substitutional defect or a complex with its constituents lying along the c-axis of the lattice.
A Novel Direct Pulse Laser Deposited Nickel Silicide Ohmic Contact to n-SiC
Authors: Cole M. W. , Joshi P. C. , Hubbard C. W. , Ngo E. , Demaree J. D. , Hirvonen J. K. , Wood M. C. , Ervin M. H.
Published: April 2011

Pulsed laser direct deposit Ni2Si Ohmic contacts were successfully fabricated on n-SiC. The electrical, structural, compositional, and surface morphological properties were investigated as a function of heat treatments ranging from 700 °C to 950 °C. The as-deposited and 700 °C annealed samples were non-Ohmic. Annealing at 950 C° yielded excellent Ohmic behavior, an abrupt void free interface, and a smooth surface morphology. No residual carbon was present within the contact film or at the film-SiC interface and the contact showed no appreciable contact expansion as a result of the 950 °C annealing process. Results of this investigation demonstrate that 950 °C annealed pulse laser deposited Ni2Si-SiC contacts possess excellent electrical, interfacial, microstructural, and surface properties, which are required for reliable device operation.
Temperature Dependence of Dislocation Motion and Crack Propagation in a Two-Dimensional Binary Model Quasicrystal
Authors: Krdzalic Galib , Brunelli Marco , Trebin Hans-Rainer
Published: April 2011

A twodimensional binary model quasicrystal (Roth-Mikulla tiling) was subjected to shear of constant rate (Lees-Edwards boundary conditions). Lennard-Jones forces were applied between the atoms and the evolution of the system was followed by isothermal molecular dynamics simulations. Temperature was controlled by a Nosé-Hoover thermostat. Dislocation dipoles were created followed by phason walls, which broadened with increasing shear. Widening happens by transversal shear induced diffusion. It starts with the onset of failure and is saturating after reaching two planes of high interface energy parallel to the glide plane. Thus a structurally damaged layer arises along which viscous glide is developing. The transverse diffusion constant follows an Arrhenius law at low temperature. With increasing temperature it is bending to a flatter slope similar as in the model of phason induced diffusion by Kalugin and Katz. First results of temperature-dependent crack-propagation are reported, too.
Bulk Mg-Cu-Y-Al Alloys in the Amorphous, Supercooled Liquid and Crystalline States
Authors: Linderoth S. , Pryds N. , Eldrup M. , Pedersen A.S. , Ohnuma M. , Zhou T.-J. , Gerward L. , Jiang J.Z. , Lathe C.
Published: April 2011

Bulk Mg-Cu-Y-Al alloys, prepared by casting into a wedge-shaped copper mold, have been studied in the as-prepared, the supercooled liquid, and the crystalline states. In the as-prepared state x-ray diffraction of sub-millimeter sized regions were performed using a focused x-ray beam. The phase composition of the cross section as well as of the surface of the wedge-shaped specimen was investigated as a function of position. The cooling history of the alloy was experimentally determined and compared to results of a control-volume finite-difference modelling study. The experimentally determined and the calculated cooling rates were correlated with the observed amorphous/crystalline structure. The transition from an amorphous to a crystalline state was followed by x-ray diffraction studies as a function of time at specific temperatures in the region between the glass transition and the crystallization temperature. Based on these results a temperature-time-phase diagram was constructed. The dependence of external pressure on the crystallisation temperature was investigated by in situ high-temperature and high- pressure x-ray powder diffraction by using synchrotron radiation. The investigations form the basis for a selection of the optimum temperature in the supercooled liquid region for performing deformation/shaping of the Mg-based alloys.
Glass Forming Ability and Crystallization Behaviors of the Ti-Cu-Ni-(Sn) Alloys with Large Supercooled Liquid Region
Authors: Kim Y.C. , Yi S. , Kim W.T. , Kim D.H.
Published: April 2011

The thermal stability and crystallization behavior of melt spun amorphous Ti50Cu35Ni15-xSnx (x=0, 3, 5, 7) alloys has been studied in by thermal analysis (DSC and DTA) and X-ray diffractometry. Partial replacement of Ni by Sn up to 5 at % in Ti50Cu35Ni15 alloy improved thermal stability and glass forming ability. The onset temperature of the first exotherm increased from 739 to 756 K with increasing Sn content x from 0 to 5, and then decreased to 745 K for the alloy with x=7 due to change in crystallization sequence. Melt spun amorphous Ti50Cu35Ni12Sn3 and Ti50Cu35Ni10Sn5 alloys exhibit ΔTx exceeding 78 and 76 K, respectively, which is significantly larger than ΔTx of 46 K in Ti50Cu35Ni15 alloy. Amorphous Ti50Cu35Ni15 alloy crystallized by precipitation of supersaturated cubic Ti(Ni,Cu) phase followed by decomposition into a mixture of TiCu and TiNi at higher temperature. Amorphous Ti50Cu35Ni15-xSnx (x=3, 5) phase crystallized by precipitation of cubic Ti(Ni,Cu) phase, followed by transformation into a mixture of TiNi, TiCu, Ti3Sn phases. Amorphous Ti50Cu32Ni8Sn7 phase crystallized by co- precipitation of cubic Ti(Ni,Cu) phase and unidentified phase, followed by transformation into a mixture of TiNi, TiCu, Ti3Sn phases.
Critical Behaviour of the Fe3Nd Cluster Glass Phase in Bulk Glassy Nd60Fe30Al10 Hard Magnets
Authors: Ortega-Hertogs R. J. , Inoue A. , Rao K.V.
Published: April 2011

The magnetic properties of novel bulk glassy Nd60Fe30Al10 magnets around the transition to the paramagnetic state have been studied in order to understand the magnetic microstructure in these materials. Analyses of the critical behavior of the magnetic isotherms suggest a transition from a low field magnetic state to a ferromagnetic-like state upon the application of high enough magnetic fields. The ferromagnetic-like state is evidenced by a scaling of the magnetization curves with critical exponents λ=1.5(1), β=0.65(5), and TC=465 K. These results are consistent with the predictions for weak random magnetic anisotropy systems.
An Investigation of The Effects of Temperature on Fatigue Crack Growth Behavior of a Cast Nearly Lamellar Ti-47A1–2Cr-2Mn + 0.8 Vol. %TiB2 Gamma Titanium Alloy
Authors: Lou J. , Mercer C. , Soboyejo W.O.
Published: April 2011

This paper presents the results of a study of the effects of temperature on fatigue crack growth in Ti-47A1–2Cr-2Mn + 0.8 Vol. %TiB2 gamma titanium aluminide intermetallics. Fatigue crack growth rate data are presented for the cast lamellar microstructure at 25,450 and 750°C. The trends in the fatigue crack growth rate data are explained by considering the combined effects of crack-tip deformation mechanisms and oxide-induced crack closure. Faster fatigue crack growth rates at 450°C are attributed to the high incidence of irreversible deformation-induced twinning, while slower crack growth rates at 700°C are due to increased deformation by slip and the effects of crack-tip shielding provided by oxide-induced wedging, which is analyzed using a modified Dugdale-Barenblatt model.
Experimental and Theoretical Investigations of the Phase Transformation in Al-rich TiAl Intermetallic Compounds
Authors: Koyama T. , Doi M. , Naito S.
Published: April 2011

The phase decomposition of the Al-rich γ TiAl intermetallic compound in the TiAl(L10) and Ti3Al5(P4/mbm) two phases region is investigated experimentally. On the phase decomposition of the Ti-56at%Al alloy, the single precipitate(Ti3Al5) shape is an oblate spheroid at the early stage of precipitation and each particle is aligned along certain direction of the orientation about 20 degrees from [100]. During coarsening, the precipitates encounter each other, then, the shape of the particle becomes the slanted or bended plate. In the case of phase decomposition of the Ti-58at%Al alloy, the tweed-like structure is observed at the beginning of the aging. The precipitates are connected each other during coarsening, finally the microstructure becomes the large layered structure with a zigzag-shaped interface. These microstructure changes are simulated based on the phase field model. The morphology and the time development of the simulated microstructure are in good agreement with the experimental results.
Synthesis and Characterization of Mechanically Alloyed and HIP-Consolidated Fe-25Al-10Ti Intermetallic Alloy
Authors: Zhu Su-Ming , Tamura Makoto , Sakamoto Kazushi , Iwasaki Kunihiko
Published: April 2011

The present study is concerned with the processing, microstructural characterization, mechanical and tribological properties of fine-grained Fe-25Al-10Ti intermetallic alloy. The alloy was synthesized from elemental powders by mechanical alloying in an attritor-type ball milling system for 100 h, followed by hot isostatic pressing (HIP). After HIP treatment at 1073 K under an ultra-high pressure of 980 MPa, fully dense compacts with a grain size of about 200 nm were produced. Mechanical properties were evaluated by compression tests from room temperature to 1073 K. At room temperature, the alloy exhibits yield strength as high as 2.4 GPa, together with considerable rupture strain of 0.16. The yield strength decreases monotonically with increasing test temperature with no positive temperature dependence observed. The grain growth after high temperature deformation is not severe, indicating that the alloy has a relatively high thermal stability. Finally, tribological properties of the alloy were evaluated by using a ball-on-disk type wear tester and compared with those for gray cast iron, a currently used material for automotive brake rotors.
Effects of ternary additions on the deformation behavior of single crystals of MoSi2
Authors: Inui Haruyuki , Ishikawa Koji , Yamaguchi Masaharu
Published: April 2011

Effects of ternary additions on the deformation behavior of single crystals of MoSi2 with the hard [001] and soft [0 15 1] orientations have been investigated in compression and compression creep. The alloying elements studied include V, Cr, Nb and Al that form a C40 disilicide with Si and W and Re that form a C11b disilicide with Si. The addition of Al is found to decrease the yield strength of MoSi2 at all temperatures while the additions of V, Cr and Nb are found to decrease the yield strength at low temperatures and to increase the yield strength at high temperatures. In contrast, the additions of W and Re are found to increase the yield strength at all temperatures. The creep strain rate for the [001] orientation is significantly lower than that for the [0 15 1] orientation. The creep strain rate for both orientations is significantly improved by alloying with ternary elements such as Re and Nb.
Processing and Properties of Gamma+Laves Phase in-situ Composite Coatings Deposited via Magnetron Sputtering
Authors: Huang Feng , Epling William S. , Barnard John A. , Weaver Mark L.
Published: April 2011

Recent research efforts have established that Laves phase reinforced gamma titanium aluminides (i.e. γ + Laves) offer significant potential as oxidation resistant coating in high-temperature structural applications and as wear-resistant coatings for cutting tools. In this study, TiAlCr coatings were magnetron sputtered from a Ti-51Al-Cr alloy target onto various substrates. The microstructure, hardness, and stress behavior of the as-deposited and annealed coatings have been investigated.
Tensile Properties of B2-Type CoTi Intermetallic Compound
Authors: Kaneno Y. , Takasugi T.
Published: April 2011

B2-type CoTi intermetallic compound that was hot-rolled and recrystallized was tensile-tested as functions of temperature and testing atmosphere. The tensile strength showed a peak at intermediate temperature (∼800K). The brittle-ductile transition (BDT) defined by tensile elongation took place at about 800K, above which large tensile elongation was observed. Corresponding to this transition, SEM fractography showed a change from cleavage-like pattern mixed with intergranular fracture pattern to large cross-sectional reduction, i.e. necking of the tensile specimen. Also, the observed mechanical properties were independent of heat-treatment procedures, indicating that retained vacancies did not affect the mechanical properties of CoTi intermetallic compound. However, the tensile elongation and UTS at room temperature were dependent on testing atmosphere, indicating that moisture-induced embrittlement occurred in CoTi intermetallic compound.
Incommensurate Structure in Al-rich TiAl Alloys
Authors: Wang S. , Fort D. , Jones I. P. , Abell J. S.
Published: April 2011

The microstructures of Ti-Al alloys in the range 56–62 at.% Al have been studied. These compounds consist of a basic L10 structure on which is superimposed an irrational modulation (Ti3Al5 related). This is incommensurate by occupation. It has two-dimensional modulations in which the wave vectors are q1 = α(a* + b*) and q2 = α(-a* + b*) where a* and b* are the L10 reciprocal basis and α is an irrational fraction. α decreases from 0.282 to 0.26 as the Al concentration increases to 60 at.% Al, i.e., the positions of the satellites change continuously with varying Al concentration. A third phase, TiAl2, appears at a composition of 62 at.% Al which means that no Ti3Al5 (62.5 at.% Al) of stoichiometric composition can ever exist.
Improving the Understanding of Ion-Beam-Induced Defect Formation and Evolution by Atomistic Computer Simulations
Authors: Posselt Matthias
Published: April 2011

The morphology of the as-implanted damage in silicon is investigated using a recently developed combination of time-ordered computer simulations based on the binary collision approximation (BCA) with classical molecular dynamics (MD) calculations. The method is applied to determine the type and the amount of defects formed within the first nanosecond after ion impact. The depth profile and the total number of different defect species (vacancies, interstitials, disordered atoms, etc.) produced on average per incident ion are calculated for B+ (15 keV), P+ (5, 10, 20, 30 keV), and As+ (15 keV) implantations. It is shown that the as- implanted defect structure depends not only on the nuclear energy deposition per ion but also explicitly on the ion mass. Therefore for each ion species the damage morphology exhibits characteristic features. For heavy ions the percentage of extended defects is higher than for light ions. In all cases investigated the number of free or isolated interstitials exceeds the amount of free vacancies. The results obtained allow a microscopic interpretation of the phenomenological model for the as-implanted damage employed in conventional BCA simulations in order to describe the dose dependence of the shape of ion range profiles. They can be also applied to get more realistic initial conditions for the simulation of the defect kinetics during post-implantation annealing.
Film Fracture Phenomena During Indentation
Authors: Bahr D.F. , Pang M. , Rodriguez-Marek D.
Published: April 2011

Discontinuities during both load and depth controlled continuous indentation tests have been ascribed to dislocation nucleation or multiplication and film fracture. In materials which exhibit permanent deformation prior to a discontinuity in loading, it is more likely that the phenomena is indeed controlled by film fracture, and not the rapid generation of dislocations. The current study has been undertaken to examine the properties of passivating films on engineering alloys. An electrochemical cell coupled with a scanning probe microscope and nanoindentation system allows growth and mechanical testing of passive films on an austenitic stainless steel as well as a titanium alloy. A complementary set of ex situ experiments shows the presence of deformation prior to film fracture with both load – depth sensing techniques as well as imaging the surface topography. The occurrence of excursions is shown in these materials to be linked directly with film fracture, rather than dislocation multiplication.
Molecular Dynamics simulations of displacement cascades: role of the interatomic potentials and of the potential hardening
Authors: Becquart C.S. , Domain C. , Legris A. , Duysen J.C. van
Published: April 2011

The role of the interatomic potentials on the primary damage has been investigated by Molecular Dynamics (MD) simulations of displacement cascades with three different interatomic potentials dedicated to α-Fe. The primary damage, caused by the neutron interaction with the matter, has been found to be potential sensitive. We have investigated the equilibrium parts of the potential as well as the “short distance interactions” which appear to have a strong influence on the cascade morphology and defects distribution at the end of the cascade. The static properties as well as dynamical (thermal) characteristics of the potentials have been considered; the kinetic and potential energy transfers during the collisions have also been studied.
Crystallization of Isolated Amorphous Zones in Semiconductor Materials
Authors: Hollar Eric P. , Robertson Ian M. , Jenčič Igor
Published: April 2011

Crystallization of spatially isolated amorphous zones in Si, Ge, GaP, InP and GaAs was stimulated thermally and by irradiation with electrons and photons. The amorphous zones were created by a 50 keV Xe+ implantation. Significant thermal crystallization occurred at temperatures greater than 425 K, 375 K and 200 K in Si, Ge and GaAs, respectively. Electrons with energies between 25 and 300 keV stimulated crystallization in all materials at temperatures between 90 K and room temperature. For electron energies above the displacement threshold, the crystallization rate decreased as the electron energy decreased. As the electron energy was decreased below approximately 100 keV, the crystallization rate unexpectedly increased. The crystallization rate was independent of temperature for all electron irradiations. Irradiation with a 532 nm green laser (hv= 2.33 eV) caused crystallization in Si (Eg = 1.11 eV) and Ge (Eg = 0.67 eV) at a rate comparable to a thermal anneal at 425 K and 375 K, respectively, and caused minimal crystallization in GaP (Eg = 2.26 eV). The electron and photon irradiation results are consistent with the model that crystallization is controlled by defects (dangling bonds and kinks) created by electronic excitation at the amorphous-crystalline interface.
Inverse Ostwald Ripening and Self-Organization of Nanoclusters due to Ion Irradiation
Authors: Heinig K.-H. , Schmidt B. , Strobel M. , Bernas H.
Published: April 2011

Under ion irradiation collisional mixing competes with phase separation if the irradiated solid consists of immiscible components. If a component is a chemical compound, there is another competition between the collisional forced chemical dissociation of the compound and its thermally activated re-formation. Especially at interfaces between immiscible components, irradiation processes far from thermodynamical equilibrium may lead to new phenomena. If the formation of nanoclusters (NCs) occurs during ion implantation, the phase separation caused by ion implantation induced supersaturation can be superimposed by phenomena caused by collisional mixing. In this contribution it will be studied how collisional mixing during high-fluence ion implantation affects NC synthesis and how ion irradiation through a layer of NCs modifies their size and size distribution. Inverse Ostwald ripening of NCs will be predicted theoretically and by kinetic lattice Monte-Carlo simulations. The mathematical treatment of the competition between irradiation-induced detachment of atoms from clusters and their thermally activated diffusion leads to a Gibbs-Thomson relation with modified parameters. The predictions have been confirmed by experimental studies of the evolution of Au NCs in SiO2 irradiated by MeV ions. The unusual behavior results from an effective negative capillary length, which will be shown to be the reason for inverse Ostwald ripening. Another new phenomenon to be addressed is self-organization of NCs in a δ-layer parallel to the Si/SiO2 interface. Such δ-layers were found when the damage level at the interface was of the order of 1-3 dpa. It will be discussed that the origin of the δ-layer of NCs can be assigned to two different mechanisms: (i) The negative interface energy due to collisional mixing gives rise to the formation of tiny clusters of substrate material in front of the interface, which promotes heteronucleation of the implanted impurities. (ii) Collisional mixing in the SiO2produces diffusing oxygen, which may be consumed by the Si/SiO2 interface. A thin layer parallel to the interface becomes denuded of diffusing oxygen, which results in a strong pile up of Si excess. This Si excess promotes heteronucleation too. Independent of the dominating mechanism of self-organization of a d-layer of NCs, its location in SiO2 close to the SiO2/Si interface makes it interesting for non-volatile memory application.