bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth and Properties of III-V Nitride Films, Quantum Well Structures and Integrated Heterostructure Devices
Authors: Schetzina J.F.
Published: April 2011

Growth of lll-V nitrides by molecular beam epitaxy (MBE) is being studied at NCSU using an rf nitrogen plasma source. GaN/SiC substrates consisting of ∼3 μm thick GaN buffer layers grown on 6H-SiC wafers by MOVPE at Cree Research, Inc. are being used as substrates in the MBE film growth experiments. The MBE-grown GaN films exhibit excellent structural and optical properties — comparable to the best GaN films grown by MOVPE—as determined from photoluminescence, x-ray diffraction, and vertical-cross-section TEM micrographs. Mg and Si have been used as dopants for p-type and n-type layers, respectively. AlxGa1−xN films (x∼0.06-0.08) and AlxGa1−xN/GaN multi-quantum-well structures have been grown which display good optical properties. Light-emitting diodes (LEDs) based on double-heterostructures of AlxGa1−xN/GaN which emit violet light at ∼400 nm have also been demonstrated. Key issues that must be addressed before lll-V nitride laser diodes can be demonstrated and commercialized are discussed. New integrated heterostructures are proposed for the development of a variety of vertical-transport devices such as light-emitting diodes, laser diodes, photocathodes, electron emitters based on the negative-electron-affinity of AIN, and certain transistor structures.
AlGaInN Quaternary Alloys by MOCVD
Authors: Mcintosh F.G. , Piner E. , Boutros K. , Roberts J.C. , He Y. , Moussa M. , El-Masry N. , Bedair S.M.
Published: April 2011

AlGaInN quaternary alloy based devices can cover the emission wavelength from deep UV to red. This Quaternary alloy also offers lattice matched heterostructures for both optical and microwave devices. We will report on the MOCVD growth of AlxGa1−x-yInyN (0<x<0.12), (0<y<0.15) at 750 °C on sapphire substrates, using TMG, EDMIn, TMAl and NH3 precursors. Chemical composition, lattice constants and bandgaps of the grown films were determined by EDS, X-ray diffraction and room temperature PL. Data indicates that the lattice constants can also be deduced using Vegard's law, indicating a solid solution of this alloy. PL showed band edge emission, however emission from deep levels was also observed. Optimized growth conditions and heterostructures using this quaternary alloy will be presented.
Strain Effects in GaN on Sapphire: Towards a Quantitative Comprehension
Authors: Briot O. , Alexis J.P. , Gil B. , Aulombard R.L.
Published: April 2011

We present here a detailed investigation of the optical properties of GaN epilayers grown by low pressure MOVPE on sapphire substrates, using 2K photoluminescence as well as 2K reflectance spectroscopy. A large series of samples has been grown under eclectic conditions (V/III ratio, growth temperature, nitridation steps,...) which allows us to propose the first semi-quantitative investigation of the sample-dependent band gap energies. This dependence of the bandgap is analyzed in terms of i) residual stress, ii) exciton parameters and iii) deformation potential characteristics of the A, B, C excitons. the residual stress cannot be simply explained in terms of the differences between the thermal expansion coefficients of the various compounds, but are strongly correlated to the V/III growth ratio imposed during the growth, and subsequently to the influence of this parameter at the scale of electronic and structural characteristics of the deposited layers.
Monte Carlo Calculation of Hole Transport in Bulk Zincblende Phase of GaN including a Pseudopotential Calculated Band Structure
Authors: Oguzman I. H. , Kolnik J. , Brennan K.F. , Wang R. , Ruden P. P.
Published: April 2011

In this paper, we present ensemble Monte Carlo based calculations of the steady state hole transport properties, i.e. average energy, drift velocity, and band occupancy of zincblende GaN. The Monte Carlo calculation includes the full details of the valence bands and a numerically determined scattering rate derived from an empirical pseudopotential calculation. Calculations are made for electric field strengths up to 1000 kV/cm. It is found that the average hole energies are much lower than the corresponding electron energies at comparable electric field strengths, and that some anisotropy in the drift velocity and average energy appears at the higher fields examined here.
Excitonic Recombination Processes in Undoped and Doped Wurtzite GaN Films Deposited on Sapphire Substrates
Authors: Freitas J.A. , Doverspike K. , Wickenden A.E.
Published: April 2011

Excitonic recombination processes in GaN films grown by low pressure metalorganic chemical vapor deposition technique have been studied in the temperature range between 6K to 320K by photoluminescence spectroscopy. Low temperature photoluminescence spectra of high resistivity films show well-resolved spectral features associated with the excitonic interband transitions. A detailed spectral analysis allowed us to estimate the exciton binding energy and the energy gap. Spectral studies of Si-doped GaN films demonstrate that the high energy recombination processes in these films are dominated by excitons bound to neutral Si donors. Comparison between the recombination channels in high resistivity and in Si-doped films indicated that Si has a larger exciton binding energy than the unknown pervasive donor in undoped materials. These results confirm the excellent electronic properties of the undoped and doped films.
Magnesium Doping of GaN by Metalorganic Chemical Vapor Deposition
Authors: Lu Hongqiang , Bhat Ishwara
Published: April 2011

P-type GaN films were grown on sapphire substrates in a horizontal metalorganic chemical vapor deposition system using (C5H5)2Mg (Cp2Mg) as the p-dopant source. It is found that the acceptor concentration in the post-growth annealed GaN samples increases with the Mg flow rate and reaches a peak value of 1×1019 cm−3 at Mg flow rate of 0.84 ĉmol/min. The films remain semi-insulating even after annealing when the Mg flow rate is higher than 1.08 ĉmol/min. The effects of annealing temperature and duration on the electrical properties of GaN are also investigated. The results confirm that a 800 °C, 30 minutes post-growth annealing in N2 ambient is sufficient to activate most of the Mg atoms. In addition, study of rapid thermal annealing of Mg-doped GaN was carried out and the results show that the p-type acceptor concentration obtained is comparable to the results obtained using furnace annealing process. Finally, GaN light emitting diodes (LEDs) are demonstrated using undoped layer as the n-type base layer in a p-on-n structure. The light emission spectra are dominated by the 430 nm peak, accompanied with two relatively weak peaks located at 380nm and 550nm.
Growth of GaN without Yellow Luminescence
Authors: Zhang X. , Kung P. , Walker D. , Saxler A. , Razeghi M.
Published: April 2011

We report the growth and photoluminescence characterization of GaN grown on different substrates and under different growth conditions using metalorganic chemical vapor deposition. The deep-level yellow luminescence centered at around 2.2eV is attributed to native defect, most possibly the gallium vacancy. The yellow luminescence can be substantially reduced By growing GaN under Ga-rich condition or doping GaN with Ge or Mg.
Reactive Ion Etching of AlN, AlGaN, and GaN Using BCl3
Authors: Hughes W. C. , Rowland W. H. , Johnson M. A. L. , Cook J. W. , Schetzina J. F.
Published: April 2011

The III-V nitrides are promising materials for use in UV-blue-green optoelectronics, high-temperature electronics, and negative-electron-affinity (NEA) electron emitter applications. In order to realize this potential, it is important to develop an etching technology for device fabrication. The stability of the III-V nitrides to harsh chemical environments makes most wet etching extremely difficult, so that dry etching alternatives are desirable. Recent experiments have shown that BCI3-based chemistries are effective for reactive ion etching of GaN and that KOH-based solutions may preferentially etch AIN from GaN. This paper reports on the use of BCI3 for etching AIN and AlGaN in addition to GaN and the creation of structures such as mesas and lines. It also examines the potential use of potassium Hydroxide (KOH) as a wet etchant of the nitrides. AIN, AlGaN, and GaN films grown by either metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) were patterned with Ni in 250 μm × 250 μm squares and 5 μm wide lines to create mesas and lines for typical light emitting diode (LED) or laser diode applications. Reactive ion etching was performed in a commercial reactor using BCI3 pressures ranging from 5 to 30 mTorr. Gas flow rates of 5 to 50 seem and RF powers of 50 to 150 W were employed. High nitride etch rates of up to 730 Å/min. were observed but lower etch rates were needed to avoid etching of the Ni mask. Smooth mesa surfaces and sidewalls were observed in scanning electron micrographs of the etched nitride structures. Mesas as small as 5 μm × 5 μm were patterned and made in this way. Lines were also made in a similar manner as narrow as 5 μm on GaN/AIN epilayers. Subsequent wet etching of these lines showed that KOH-based solutions such as AZ400K developer attack not only AIN but also GaN depending upon the quality of the film. Possibilities for using this wet etch as a defect etchant or selective etch of nitrides on SiC are discussed.
Calculations of the Specific Resistance of Contacts to III-V Nitride Compounds
Authors: Barnes P.A. , Zhang X-J , Lovejoy M.L. , Drummond T.J. , Hjalmarson H.P. , Crawford M. , Shul R.J. , Zolper J.C
Published: April 2011

We present calculations of the specific contact resistance for metals to GaN. Our calculations include a correct determination of the Fermi level taking into account the effect of the degenerate doping levels, required in creating tunneling ohmic contacts. Using a recently reported improved WKB approximation suitable in representing the depletion width at the metal-semiconductor interface, and a two band k-p model for the effective masses, specific contact resistance was determined as a function of doping concentration. The specific contact resistance was calculated using the best data available for barrier heights, effective masses and dielectric coefficients for GaN. Because the barrier height at the metal-semiconductor interface has a very large effect on the contact resistance and the available data is sketchy or uncertain, the effect of varying the barrier height on the calculated specific contact resistance was investigated. Further, since the III-V nitrides are being considered for high temperature device applications, the specific contact resistance was also determined as a function of temperature.
C-Axis Oriented Ferroelectric thin Films of PbtiO3 on Silicon Substrate by Pulsed Laser Ablation
Authors: Palkar V. R. , Purandare S. C. , Pai S. P. , Chattopadhyay S. , Apte P. R. , Pinto R. , Multani M. S.
Published: April 2011

We are reporting the successful deposition of single phase c-axis oriented ferroelectric thin films of PbTiO3 on Si (100) by pulsed laser deposition. It is shown that the formation of non ferroelectric Pb2Ti2O6 phase at the interface could be avoided by raising the substrate temperature sufficiently high. The film deposition conditions are optimized so as to achieve better ferroelectric properties.
Modeling of Film Growth in Pulsed Laser Deposition
Authors: Tyunin M.
Published: April 2011

Film growth in pulsed laser deposition (PLD) is described as a process of sorption of ablated species on the substrate surface. Film growth rate and composition are qualitatively analyzed as a function of laser fluence and ambient gas pressure. As an example, analysis of the film composition is carried out for BiSrCaCuO and PbZrTiO pulsed laser deposited films.
Tantalum Oxide and Niobium Oxide thin Films Grown by Pulsed Laser Deposition
Authors: FernÁndez FÉlix E. , Marrero Pablo J.
Published: April 2011

Amorphous tantalum pentoxide (Ta2O5) and niobium pentoxide (Nb2O5) thin films were grown from both metal and oxide target by reactive pulsed laser deposition. Film structure and composition were studied as a function of substrate temperature and oxygen pressure. Good quality transparent films were obtained for substrate temperatures greater than 140° C, and O2 pressures of 200 mTorr. Lower temperatures and pressures produced opaque films, associated with lower oxides.
Epitaxial Growth of Metal Fluoride Thin Films by Pulsed-Laser Deposition
Authors: Norton D. P. , Budai J. D. , Chakoumakos B. C. , Geohegan D. B. , Puretzky A.
Published: April 2011

We have investigated the growth of GdLiF4 thin films for optical waveguide applications using pulsed-laser deposition (PLD). Epitaxial, c-axis oriented GdLiF4 films have been grown from undoped GdLiF4 targets in an on-axis PLD geometry on (100) CaF2. These films exhibit a high density of particulates on the surface which are ejected from the target in the ablation process. Growth from Nd-doped polycrystalline GdLiF4 ablation targets results in relatively smooth films with lower particulate densities, as Nd doping significantly increases the optical absorption of GdLiF4 at the ablation laser wavelength of 193 nm and permits efficient pulsed-laser deposition. Optical emission spectra of the ablation pume reveals the presence of atomic fluorine, gadolinium, and lithium, indicating the dissociation of the metal-fluorine bonds in the ablation process. In addition, we find that the residual background oxygen pressure must be sufficiently reduced to avoid the formation of Gd4O3F6 as an impurity oxy-fluoride phase in the films.
Pulsed Laser Ablation of Boron Nitride
Authors: Bae Shin Keon , Min Park Seung , Man Kim Young
Published: April 2011

The probe beam deflection and optical time-of-flight method have been applied to study the dynamics of Nd:YAG laser (266 nm) ablation of pyrolytic boron nitride. Shock wave generation was observed and its velocity was derived by analysis of the acoustic transit time of the acoustic wave produced by laser ablation. The most probable velocities of B and B+ were obtained by optical time-of flight technique. The deposition of boron nitride on silicon substrate by laser ablation was attempted in nitrogen atmosphere. Cubic phase of boron nitride was observed as well as the hexagonal phase.
Raman Studies on Potential substrate Materials of Sr(Al1/2Ta1/2)O3 and Sr(Al1/2Nb1/2)O3 For Htsc
Authors: Tao Ruiwu , Guo A.R. , Tu C.-S. , Siny I. , Katiyar R.S. , Guo Ruyan , Bhalla A.S.
Published: April 2011

Complex oxide perovskites, namely strontium aluminum tantalum oxide (SAT) and strontium aluminum niobium oxide (SAN) were recently investigated to be potential substrate materials for HTSC films in microwave applications. Single crystals were prepared by laser heated pedestal growth technique (LHPG). We report Raman vibrational spectrum studies on them for the first time. Order-disorder effects of (Al, Ta) and (Al, Nb) sites were studied with particular interests by comparing Raman spectra of single-crystal samples with ceramic samples. Influences of B sites (Ta and Nb) on O-O modes are discussed in relation to their dielectric properties.
Control of Threshold Voltage on the Excimer Laser Annealed Poly-Si Tfts by Oxygen Plasma Treatment on Poly-Si Surface
Authors: Woo Jae-Ik , Lee Sang-Gul , Moon Dae-Gyu , Hong Chan-Hee , Soh Hoe-Sup
Published: April 2011

Oxygen plasma treatment was performed on the excimer laser annealed poly-Si surface, followed by gate oxide deposition with low pressure chemical vapor deposition (LPCVD) in order to control the threshold voltage of excimer laser annealed poly-Si thin film transistors (TFTs).

Threshold voltages of n-channel TFTs increase from 0.4 to 2.8 V by varying the treatment time from 0 to 7 min. It is shown the effective charge density increased toward negative direction with increase of the treatment time.

In addition to the increase of threshold voltage, the oxygen plasma treatment on the Si surface led to an increase in the deposition rate of LPCVD oxide films with an apparent reduction of carbon around the interface between gate insulator and poly-Si film after oxygen plasma treatment.
Excimer-Laser Crystallization of Si Films Via Bi-Directional Irradiation of Dual-Layer Films on Transparent Substrates
Authors: Yoon Jung H. , Im James S.
Published: April 2011

In this paper, we report on a new excimer-laser crystallization (ELC) method that is highly effective in extending the super-lateral growth (SLG) distance and which does not involve any preheating of the substrate. The technique utilizes bi-directional irradiation of a dual layer Si film stack (separated by an oxide layer) deposited on a quartz wafer. The top layer is irradiated with a projection system which transfers a mask image in order to produce grain-boundary-location-controlled (GLC) regions, and the bottom layer, upon irradiation with a uniform beam, acts as a medium that favorably affects the thermal evolution of the top layer. The technique is effective and attractive in that the heating is spatially and temporally localized in an optimal manner. The thermal environment required for extending the SLG distance, as is induced by the melting and solidification of the bottom layer, is physically regulated by the melting temperature of Si, and the enthalpy difference between liquid and solid can be used to initially store and subsequently release heat. Using the method, we were able to attain GLC regions with widths up to 10 μm in 1000-Å Si films without any substrate heating. We elaborate on the applicability of the method to various artificially controlled super-lateral growth (ACSLG) techniques, and discuss process optimization by means of varying the multilayer configuration.
Excimer Laser Beam Interaction with Sintered Y2O3- Doped Aluminium Nitride Ceramic: Fundamentals and Appplication
Authors: Detournay N. , Kolev K. , Robert T. , Brunel M. , Laude L.D.
Published: April 2011

Sintered aluminium nitride ceramic is most attractive for applications in modern electronic packaging, due to its high thermal conductivity and its high electrical resistivity. Among the sintering additives which are mentioned in the literature, Y2O3 is used most often as sintering accelerator and densificator for AlN commercial ceramics.

Since excimer lasers have recently proved to be efficient in ceramic processing for industry, the effects of excimer laser irradiation on sintered Y2O3;rdoped AlN ceramic have been studied in this work. Raman spectroscopy, low-angle X-ray diffraction and scanning electron microscopy equipped with energy-dispersive X-ray analysis are used for characterizing both the initial and processed materials. The results reveal that yttrium-containing phases which are present at the AlN grain boundaries play an essential role in coupling the (λ =248nm) excimer laser beam with sintered material. Moreover, the laser-induced decomposition of these pre-existing complex phases and the subsequent spinel-like formation upon autocatalytic copper (or nickel) deposition are associated with (and explain) the excellent adhesion of the so-formed metal layer onto the ceramic substrate.
Terraced Copper Growth Deposited Onto Teflon AF1600 by The Excimer Laser Irradiation of Cu(hfac)Tmvs
Authors: Popovici D. , Piyakis K. , Sacher E. , Meunier M.
Published: April 2011

The laser chemical vapour deposition (LCVD) of the organometallic precursor Cu(hfac)TMVS (hexafluoroacetylacetonate)(trimethylvinylsilane) is used to grow copper films on a Teflon AF1600 substrate. Exposure to excimer laser radiation at 248 nm results in a terraced copper growth. A simple model, based on interference effects in the Teflon and copper layers, is presented to account for this structure.
Excimer Laser Induced Photolytic Deposition of Aluminum Nitride: Ftlm Growth and Properties
Authors: Radhakrishnan G. , Adams P.M. , Marquez N.
Published: April 2011

Excimer laser photolysis has been used for the growth of smooth and well-adhering thin films of aluminum nitride (AlN) on Si, fused quartz, and KBr substrates at temperatures as low as 350 K. The photolysis was carried out at 193 nm, with the laser beam propagating parallel to the substrate. Trimethylamine alane and ammonia were used as gas-phase precursors. The growth rate of these films was investigated as a function of laser fluence. These measurements, as well as other investigations of film growth with and without the photolysis laser, reveal that no AlN film is produced in the absence of laser-induced photolysis of the precursors. The morphology and physical properties of these laser-grown films have been studied by scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Optical absorption spectra of films grown on fused quartz were measured as a function of substrate temperature. A substrate temperature of 350 K was found to be optimum for obtaining good film quality while precluding any effects due to the thermal decomposition of the precursors. The films have excellent dielectric properties as shown by I-V and C-V measurements. The details of AlN film growth using low-temperature gas-phase photolysis at 193 nm and the characterization of these laser grown films will be discussed.
Electron Irradiation-Induced Mechanical Property Changes in Reactor Pressure Vessel Alloys
Authors: Alexander Dale E. , Odette G.R. , Lucas G.E. , Rehn L.E.
Published: April 2011

High-energy electrons were used to study tensile property changes in simple Fe-Cu and Fe-Cu-Mn alloys irradiated at 288°C. A comparison was made with neutron irradiation data on the same alloys. An apparent effect of alloy chemistry was observed in which the presence of Mn affected embrittlement differently for electron and neutron irradiation. Comparison of previous experimental studies with the present experimental results indicates that electrons may be more efficient than fast neutrons at producing embrittlement.
Electron Beam Induced Crystallisation in Iron (III) Fluoride
Authors: Saifullah M.S.M. , Boothroyd C.B. , Botton G.A. , Humphreys C.J.
Published: April 2011

Metal fluorides are excellent candidates as high resolution inorganic resists in electron beam nanolithography. Hence it is important to study their damage characteristics under the electron beam to understand their behaviour as inorganic resists. In this paper the electron beam induced damage process in amorphous FeF3 films deposited by different techniques is investigated using selected area diffraction patterns and time resolved parallel electron energy loss spectroscopy. It is found that fluorine is lost from amorphous FeF3 during irradiation and that the material crystallises mainly to FeF2 with some crystalline FeF3. Time resolved energy loss spectroscopy studies show that the coordination polyhedra in amorphous FeF3 are randomly arranged FeF6 octahedra which arrange themselves to give a long range order in the electron beam during crystallisation to FeF2 and FeF3.
Solidification Behaviour of Al Particles Embedded in an Ni Aluminide Matrix
Authors: O'Reilly K.A.Q , Kim W.T. , Cantor B.
Published: April 2011

A hypereutectic Al-40wt%Ni alloy has been manufactured by melt spinning, and the resulting microstructure examined by transmission electron microscopy. As-melt spun hypereutectic Al-40wt%Ni consists of an Ni aluminide matrix and an A1-rich phase distributed in the form of particles with sizes ∼ 50-100 nm, and as an irregular layer at the cell and grain boundaries. Diffraction analysis of the Ni aluminide matrix is consistent with the ASTM x-ray diffraction standard 2θ values for the orthorhombic NiAl3 phase, a=6.6114 Å, b=7.3662 Å andc=4.8112 Å. The solidification nucleation kinetics of Al-rich particles have been examined by heating and cooling experiments in a differential scanning calorimeter over a range of heating and cooling rates. Solidification of the Al-rich phase at the cell and grain boundaries nucleates catalytically on the surrounding Ni aluminide matrix at an undercooling of ∼ 3 K. Analysis of the solidification nucleation kinetics of the Al-rich phase in Al-40wt%Ni supports the hypothesis [1-4] that the classical spherical cap model of heterogeneous nucleation breaks down at low undercoolings and small contact angles.
A Study of the Kinetics and Energetics of Solid State Reactions in Pd/Sn Diffusion Couples
Authors: Chromik R.R. , Cotts E. J.
Published: April 2011

Using differential scanning calorimetry, supplemented by measurements from scanning electron microscopy images, we have investigated solid state reactions in Pd/Sn multilayer composites to form PdSn4 and PdSn3. Planar diffusion couples of Pd and Sn were prepared by means of mechanical co-deformation in a rolling mill. A phase formation sequence was determined using differential scanning calorimetry and x-ray diffraction. Growth of the PdSru phase was studied from room temperature to the melting point of Sn. For temperatures between 430 and 460K diffusion limited growth of PdSn4 was observed. From heat flow data over this limited temperature range, the form of the reaction constant was found to be k2 −k0 exp(−Ea / kbT), where k0= 0.16 cm2/s and Εn= 0.8 eV/atom. Also determined was a heat of formation, ΔHf = −27±1 kJ/mol for PdSn4 from Pd and Sn.
Crystallization Kinetics of Rutile Formation from Amorphous Titania Films
Authors: Wiggins M.D. , Nelson M.C. , Atta C.R.
Published: April 2011

Titania films with two types of phase composition were sputter deposited on fused silica substrates: Type (I) amorphous+anatase+rutile and Type (II) amorphous+rutile. These films were subjected to various annealing procedures in air. We studied three relevant transitions: 1) amorphous→crystalline (anatase and rutile) at temperature <800 °C, 2) amorphous→mitile at an temperatures, and 3) anatase→rutile in the 750–800 °C temperature range.

X-ray diffraction was used for phase identification and crystallographic orientation. The films had a preferred orientation, with (101) anatase and/or (110) rutile planes parallel to the substrate. The activation energy for the amorphous-to-rutile transformation was 0.3 eV. The anatase-to-rutile transformation occurring at 750 °C was modelled using the Avrami relation, which yielded an exponent of unity.

From the results of this study, we propose a model for titania crystallization in which site saturation of rutile and/or anatase nuclei already exists in the as-deposited film. Further crystallization upon annealing occurs by one dimensional growth of these nuclei into the amorphous material. If no anatase seeds exist in the as-deposited material, then no anatase will form upon annealing, indicating again that no new nuclei are formed during annealing. In this manner, highly oriented rutile titania films can be produced at temperature below the bulk anatase-to-rutile transformation temperature (750 °C).
Effect of Initial Composition Distribution on the Phase Transformation Behavior in the Fe-Cr-Ni System
Authors: Vitek J. M. , David S. A.
Published: April 2011

A finite-difference implicit numerical model was used to study the diffusion-controlled α-γ solid-state phase transformation in the Fe-Cr-Ni system. The influence of a non-uniform initial composition distribution was examined in order to assess the impact that non-uniform solute profiles resulting from solidification may have on subsequent transformation behavior in weldments and castings. A significant impact on the transformation kinetics and transformation path was found in some cases. The factors that affect the degree of influence are discussed.
Kinetic Model of Thermoelastic Martensite Transformation in Niti and NiMn Based Shape Memory Alloys
Authors: Wu K. H. , Shi J.D. , Yang F. , Pu Z. J.
Published: April 2011

A new, quantitative model was developed to describe the martensite transformation kinetics of thermoelastic shape memory alloys (SMAs). In addition, a series of experiments were conducted to study the Kinetics of thermoelastic martensite transformation in four SMA systems: NiTi, NiTi-15at%Hf, NiTi-20at%Zr and NiMn-7.5at%Ti alloys. Comparisons between data of the kinetic of martensite transformation with the present theoretic models show that the proposed model is in good agreement and concurs with the experimental data. Also, a comparison of data from the proposed model with data from existing kinetic models, such as Liang's and Magee's [1,7], indicates that the proposed model can better describe the experimental data, including the relationship between dξ(T)/dT and ξ, and dξ(T)/dT and T.
Kinetics of Surface Segregation in Metallic Alloys with First-Principles Interaction Parameters
Authors: Wille L. T. , Ouannasser S. , Dreyssé H.
Published: April 2011

We report the results of Monte Carlo simulations of the kinetics of surface segregation at the (001) face of CuNi and MoW alloys. These two systems were selected because they are based on different lattice structures and show contrasting segregation behavior: CuNi exhibits a monotonie profile, while that of MoW is oscillatory. To describe the energetics we have determined a set of effective cluster interactions (ECI) which govern the ordering or clustering tendencies of these alloys. The ECI were obtained by means of tight-binding electronic structure calculations in which no adjustable or experimentally determined parameters were used. Equilibrium segregation profiles are calculated and a series of quenches are performed. The layer concentrations are studied as a function of time and the existence of metastable phases in the surface region is investigated.
Temperature Dependent Raman Scattering in CsTiOAsO4 Single Crystal
Authors: Guo A.R. , Tu C.-S. , Tao Ruiwu , Katiyar R.S. , Guo Ruyan , Bhalla A.S.
Published: April 2011

The longitudinal (LO) and transverse (TO) A1 vibrational modes have been measured between 30-1200 cm−1 as a function of temperature (30–1240 K) for CsTiOAsO4 (CTA). The frequencies for all corresponding Raman components shifted to lower frequencies on increasing the temperature, however, there is no typical soft-mode like behavior observed in the measured frequency range. The relative intensities of the low frequency bands increase dramatically with increasing temperature due to high mobility of Cs+ ion. A higher symmetry structure taking place above 940K has been confirmed by changes in the phonon spectra.
Development of Microstructure in Rapidly Solidified Intermetallics
Authors: Assadi H. , Greer A. L.
Published: April 2011

The solid-state transformations following rapid solidification of intermetallics can include ordering of primary disordered phase(s), resulting in anti-phase domain boundaries (APDBs). The present work focuses on the Ni-Al system. A qualitative model for solid-state ordering, originally developed by Chen and Khachaturyan [1] has been modified to simulate the APD formation during solidification of a disordered phase. An interpretation is suggested for the formation of various APD patterns observed in sequentially ordered Ni3Al.
Undercooling Experiments in a High Temperature Differential Scanning Calorimeter
Authors: Baricco M. , Ferrari E. , Battezzati L.
Published: April 2011

Several samples of metals and alloys have been undercooled during scanning in a high temperature DSC. Liquid Ni was undercooled of about 230 K when previously fluxed in molten B2O3. From enthalpy data of melting and solidification as a function of temperature, the excess heat capacity of liquid metals and alloys was evaluated. The specific heat of the liquid is definitely higher than that of the corresponding crystalline phases for glass-forming alloys, whereas it is close to that of the solid for pure metals. The Ni-B system has been studied in detail around the Ni-Ni3B eutectic. On undercooling, a new metastable phase (Ni23B6) was produced. A metastable Ni-B phase diagram has been drawn using data of thermal analysis of several alloys containing the metastable phase.
Analysis of Reflection High Energy Electron Diffraction Pattern of Silicon Carbide Grown on Silicon
Authors: Teichert G. , Pezoldt J. , Cimalla V. , Nennewitz O. , Spiess L.
Published: April 2011

RHEED pattern of SiC layers on both (100) and (111)Si grown by carbonization were studied. Different deviations from the single crystalline structure were found ranging from twinning up to changes in the orientation and textured growth. Special attention was drawn on lattice relaxation and morphology evolution during the growth of the formed SiC. Relationships between the occurrence of typical RHEED pattern and the morphology and process parameters are presented.
Misfit Dislocations and Elastic Relaxation
Authors: Strunk H.P , Christiansen S. , Albrecht M.
Published: April 2011

Prior to relaxation of misfit strain by formation of misfit dislocations, a growing heteroepitaxial layer can relax elastically by forming surface undulations called ripples. With increasing amplitude of the ripples the misfit strain and thus stress fields grow markedly inhomogeneous, and dislocation formation may thus be triggered in areas of maximum shear stress. The surface directly above such a new dislocation then represents a band of preferential growth and develops into a ridge, which in turn redistributes the strain in the growing layer. This interwoven elastic/plastic relaxation mechanism can comparably easily be deduced from transmission electron and atomic force microscopy studies of SiGe layers grown onto silicon by liquid phase epitaxy. This growth technique exerts only very small driving forces and thus operates very near thermodynamical equilibrium. The local strain tensor and strain energy density are calculated for the actual layer geometries by three dimensional finite element method and provide for quantification of the mechanism.
Investigation of Relationships between Dislocations and Crystal Surface Ledges
Authors: Zimmerman Jonathan A. , Gao Huajian
Published: April 2011

Molecular Dynamics (MD) simulations are performed on two-dimensional, triangular lattice models. The program used to perform these simulations was based on codes developed by Farid F. Abraham at the IBM-Almaden Research Center in San Jose, CA and by J.M. Haile, but also contained modifications to increase efficiency. These simulation models contain three constrained sides and a free surface, use a Lennard-Jones 6:12 interatomic potential, and initially exist with various amounts (∼ 5 to 10 %) of compressive strain. Our paper studies the formation of dislocations from atomic ledges during relaxation from a compressive state, as well as the subsequent motion of these dislocations. These simulations are particularly relevant to understanding morphological changes on the surface and nucleation of dislocations in heteroepitaxial thin films.
Effect of the Introduction of a MBE Buffer Layer on the Morphology of InSb Almbe Layers Grown on InP Substrates
Authors: Ferrer J.C. , Cornet A. , Peiró F. , Morante J.R. , Utzmeier T. , Briones F.
Published: April 2011

In this paper we report on the morphology of InSb layers grown by atomic layer molecular beam epitaxy (ALMBE) onto InP substrates at low temperatures (330<T<400°C), comparing the nature and densities of defects with those found in ALMBE InSb films grown over InSb/InP buffer layers grown by molecular beam epitaxy (MBE). The main types of defects for ALMBE direct layers are threading dislocations and stacking faults with similar defect densities along both á110ñ directions. The inclusion of the intermediate InSb/InP MBE grown buffer layers leads to lower threading dislocation densities but higher and anisotropic stacking fault distribution. Moreover, different types of three-dimensional defects appear, which are associated with pyramidal or truncated pyramidal hillocks on the surface. These defects, consisting in twins associations are originated at the InSb/InP MBE interface and they are induced by an anomalous growth of InSb layers. In all the cases, the strain caused by the large lattice mismatch is accommodated by means of a pure edge-type misfit dislocation network placed at the interface.
First-Principles Study of Domain Evolution of IR on IR(111)
Authors: Habar M. , Ouannasser S. , Stauffer L. , Dreyssé H. , Wille L. T.
Published: April 2011

We have calculated the effective cluster interactions (ECI) which govern the ordering of Ir adatoms on the Ir(111) surface. The computations are based on a tight-binding Hamiltonian in which no adjustable or experimentally determined parameters were introduced. Both atoms adsorbed in ‘bulk’ sites (i.e. continuing the fee lattice) and those in ‘surface’ sites (i.e. producing hep stacking) are considered. We use this formalism to determine the relative stability of various adsorption sites and cluster shapes at zero temperature. The overall trends are in excellent agreement with the experimental results found by Ehrlich and co-workers. Next, we employ these ECI in Monte Carlo simulations of the kinetics of domain growth and evolution. Specifically we analyze the effect of diffusion barriers and the competition between the ordering tendencies of the system and entropic effects. Typical ‘snapshots’ in a range of temperatures and coverages are discussed.
Double Periodicity Formation in EuTe/PbTe Superlattices
Authors: Shima M. , Salamanca-Riba L. , Springholz G. , Bauer G.
Published: April 2011

Molecular beam epitaxy was used to grow EuTe(x)/PbTe(y) short period superlattices with x=1-4 EuTe(111) monolayers alternating with y≈3x PbTe monolayers. The superlattices were characterized by transmission electron microscopy and high resolution x-ray diffraction. Regions with double periodicity were observed coexisting with areas of nominal periodicity. The sample with x=3.5 and y=9, for example, contains regions with double periodicity of x=7 and y=17. X-ray diffraction measurements confirm the formation of the double periodicity in these samples by the appearance of weak satellites in between the satellites of the nominal periodicity. The double periodicity in the superlattice is believed to result from interdiffusion during the growth. A model for this process is presented.
Structural Stability of CdSe Nanocrystallite Dispersions
Authors: Mattoussi H. , Murray C.B. , Bawendi M.G. , Ober R.
Published: April 2011

X-ray scattering at small angles (SAXS) is used to study the structure and the thermodynamic properties of dispersions of CdSe nanocrystallite particles. In particular, this study allowed us to probe the inter particle interactions, and their dependence on several relevant parameters, such as the nature and size of the capping units attached to the crystallite surface and solvent.
Order-Disorder Transition Under Shearing : Application to Ball Milling
Authors: Pochet P. , Bellon P. , Chaffron L. , Martin G.
Published: April 2011

The evolution under sustained shear of an ordered crystal with B2 structure is studied by Monte-Carlo simulation: the effect of shearing is modelled by shifts of atomic planes, while thermally activated atomic diffusion is promoted by the motion of one vacancy. The tricritical point expected in the dynamical phase diagram from mean field theories and from Monte-Carlo simulations in the limit of weak driving (few atoms shifted at once) does not appear in such simulations, much in the same way as for "large cascade size" in alloys under irradiation. However an unexpected bifurcation in microstructures is observed which could be related to the order-disorder transition experimentally observed under ball-milling.
Structure and Properties of Novel Superhard Nanocrystalline/Amorphous Composite Materials
Authors: Vepřek S. , Haussmann M. , Reiprich S.
Published: April 2011

We have developed a theoretical concept for the design of novel superhard materials and verified it experimentally on several systems nc-MenN/a-Si3N4 (nc-MenN is a nanocrystalline transition metal nitride imbedded in a thin amorphous Si3N4 matrix). Hardness in excess of 5000 kg/mm2 (about 50 GPa) and elastic modulus of ≥550 GPa have been achieved [1-3]. Here we address the questions of the universality of the concept for the design of a variety of nc/a systems and the upper limit of the hardness which may be achieved.
The Effects of Elevated Temperature Deformation on Nanocrystalline Titanium-Aluminum
Authors: Kim Lisa S. , Klassen Thomas , Altstetter Carl J. , Averback Robert S.
Published: April 2011

Nanocrystalline titanium aluminum powder, of composition Ti-48Al, was synthesized using a Fritsch planetary ball mill with a grain size of approximately 10nm. The powder was compacted into cylindrical specimens with a relative density of 79% and subjected to uniaxial compressive loading at 600°C in a mechanical testing machine. From these results, the deformation of nanocrystalline titanium aluminum is examined with relation to the applied load and the resulting grain structure. The results suggest a grain refining mechanism occurring during the deformation process.
Magnetic Behavior of Ultrathin Films of Pseudomorphic Binary Alloys
Authors: Wu S.Z. , Schumann F.O. , Mankey G.J. , Willis R.F.
Published: April 2011

In this work we compare the ferromagnetic behavior of ultrathin FexNi(1-x) and CoxNi(1-x) films grown on Cu(100) epitaxially with varying stoichiometry. The thickness regime chosen was 1 to 5 ML over a wide range of alloy composition. Using a finite-size scaling law we proposed for the Curie temperature vs. film thickness measurements, we extrapolate and plot the bulk fee Curie temperature as a function of composition. The results suggest that the growth of these films is pseudomorphic with the films adapting a fee structure and the Cu lattice constant. Besides, the Invar effect is not observed in these ultrathin films of FexNi(1-x) alloys and the magnetic phase of Fe atoms is the low-spin ferromagnetic phase. The CoxNi(1-x) films show the expected monotonic decrease in Tc with increasing Ni content.
Preparation of Fe/SiO2 films by sputtering and their magnetic properties.
Authors: Akai Tomoko , Tabuchi Mitsuharu , Funahashi Ryoji , Yamanaka Hiroshi
Published: April 2011

SiO2 thin films containing fine Fe particles were prepared by a co-sputtering method. α-Fe particles were then formed by heat-treating the film at 650°C to 700°C. The average size of the particles was controlled by changing heat-treatment time and temperature. The magnetic properties of these samples were investigated and discussed in terms of the size of the particles. It was found that the coercivity of the sample containing α-Fe particles (average particle size = 24nm) is as large as 36 Oe which is much higher than that of the bulk Fe.
Synthesis and Characterization of Nanostructured M50 Steel
Authors: Gonsalves K. E. , Rangarajan S. P. , Garcia-ruiz A. , Law C. C.
Published: April 2011

The synthesis of nanostructured multicomponent (Fe-Mo-Cr-V-C) M50 type steel has been carried out by two chemical routes: the sonochemical decomposition of organometallic precursors and the co-reduction of the respective metal halides. Both methods produce amorphous nanopowders, but the co-reduction method requires an additional heat treatment in vacuum at 700 °C to remove the by-product LiCl. In this paper we describe the synthetic methods and the characterization of the powders by XRD and SEM-EDAX. The powders exhibit a composition very close to that of M50 steel with an average grain size in the nanometer regime. In both cases the powders have been compacted in a vacuum hot press after they were heat treated in hydrogen. The characterization of the compacted specimens by XRD and SEM-EDAX is also discussed. The TEM characterization is presented for the sonochemically produced powders and compacts. A similar characterization of the co-reduced powders and the compacts is in progress. The consolidated specimens are homogeneous and dense, with an average grain size of ∼30 nm. Their hardness is higher as compared with that of the conventional M50 alloy.
Ti-Interlayer Mediated Epitaxy of CoSi2 with Ti Capping
Authors: Tung R. T. , Schrey F.
Published: April 2011

The growth of CoSi2 layers on Si(100) by Ti-interlayer mediated epitaxy (TIME) was studied. The use of a thin (1–3nm) Ti cap, the choice of an appropriate interlayer, and the removal of a metastable reaction by-product were found important for the fabrication of uniform CoSi2 layers. High quality, pinhole-free, single crystal [100]-oriented CoSi2 layers were fabricated. Multiply-oriented formation on heavily arsenic doped Si, void formation near oxide edges, and other salicide-related issues are also discussed.
Manufacturability Issues for Application of Silicides In 0.25 μm CMOS Process and Beyond
Authors: Wang Q. F. , Lauwers A. , Jonckx F. , de Potter M. , Chen Chun-Cho , Maex K.
Published: April 2011

Key issues associated with the self-aligned silicide technology, such as formation of silicides on narrow poly gate, shallow silicided junction formation, gate to source/drain bridging, and interface contact resistance, are discussed. The comparison of important technological aspects for TiSi2 and CoSi2 is presented. The emphasis of this work is focused on the CoSi2 salicide technology with different variations, namely conventional process, Co/Ti capping process, and Ti/Co process. Based on the experimental results, CoSi2 should be considered as an attractive alternative to TiSi2 for the applications in sub-0.25 μm ULSI integrated circuits.
Kinetics of the C49 TO C54 Phase Transformation in TiSi2 thin Films on Deep-Sub-Micron Lines
Authors: Kittl J. A. , Prinslow D. A. , Apte P. P , Pas M. F.
Published: April 2011

The kinetics of the TiSi2 C49 to C54 phase transformation in thin films on patterned deepsub- micron lines, were studied to obtain the full time, temperature and linewidth dependence of the fraction transformed during rapid thermal annealing. A Johnson-Mehl-Avrami kinetic analysis was performed, obtaining Avrami exponents of 0.8±0.2 for all sub-micron lines and 1. 9±0.2 for a 40 μm side square structure, indicating heterogeneous nucleation followed by one dimensional growth for the narrow lines, and two dimensional growth for the square structure. The activation energy, of 3.9 eV, was independent of linewidth in the sub-micron range. Transformation times increased dramatically for decreasing linewidth, as the linewidth approached the grain size of the starting C49 phase. A kinetic model based on the density of nucleation sites as a function of linewidth and C49 grain size is proposed and shown to fit the data, for samples with two different C49 grain sizes.
Study on Ti-SiO2 Reaction - Thermodynamic Approach
Authors: Fontes M. B. A. , Capocchi J. D. T. , Acquadro J. C.
Published: April 2011

Interactions between Ti and SiO2 thin films have been studied in self-aligned transistor process in the MOS Integrated Circuits Technology. A thermodynamic study of this interaction was conducted on the titanium and silicon dioxide chemistry. The Gibbs free energy was analyzed in the 25 to 1000°C range and it was concluded that the 11/3 Ti + SiO2 --> 1/3 Ti5 Si3 + 2 Ti reaction has the lowest free energy. Ti thin films were deposited by sputtering over dry silicon oxide and then sintered in atmospheric pressure furnace - RTP at argon ambient. The samples were analyzed by X-RAY Diffraction (XRD), Rutherford Backscatering Spectroscopy (RBS) and fourpoint- probe resistivity measurements. It was showed that experimental results can be modeled by theoretical analysis.