bluuebunny/crossref_metadata_2025 huggingface dataset:
Test of A Diamond-Tungsten Sampling Calorimeter
Authors: Stone R. , Franklin M. , Fujino D. , Gan K. K. , Gilman R. , Han S. , Kagan H. , Kanda S. , Kania D. R. , Kass R. , Kim S. K. , Kumbartski G. , Lee M. H. , Malchow R. , Morozov B. , Palmer W. , Pan L. S. , Rutf P. , Sannes F. , Schnetzer S. , Somalwar S. V. , Sugimoto Y. , Tesarek R. J. , Thomson G. B. , White C. , Zhao S.
Published: April 2011

Diamond is suitable for use as an ionizing particle detector for high rate, high radiation, and/or chemically harsh environments. A sampling calorimeter, a detector measuring the total energy of an incident particle, consisting of 20 alternating layers of diamond and tungsten has been constructed and tested. The diamond for the detector layers was grown by chemical vapor deposition with an averaged thickness of 500 μm. The active area of each layer was 3×3 cm2 with ohmic contacts on opposite faces forming a metal-insulator-metal structure. The calorimeter was tested with electrons of energies up to 5.0 GeV. The response of the diamond/tungsten calorimeter was found to be linear as a function of incident energy. A direct comparison of diamond/tungsten and silicon/tungsten calorimeters was made.
Properties of MOS Structure Fabricated on 3C-SiC Grown by Reactive Magnetron Sputtering.
Authors: Turan R. , Wahab Q. , Hultman L. , Willander M. , Sundgren J. -E.
Published: April 2011

We report the fabrication and the characterization of Metal Oxide Semiconductor (MOS) structure fabricated on thermally oxidized 3C-SiC grown by reactive magnetron sputtering. The structure and the composition of the SiO2 layer was studied by cross-sectional transmission electron microscopy (XTEM) Auger electron spectroscopy (AES). Homogeneous stoichiometric SiO2 layers formed with a well-defined interface to the faceted SiC(lll) top surface. Electrical properties of the MOS capacitor have been analyzed by employing the capacitance and conductance techniques. C-V curves shows the accumulation, depletion and deep depletion phases. The capacitance in the inversion regime is not saturated, as usually observed for wide-bandgap materials. The unintentional doping concentration determined from the 1/C2 curve was found to be as low as 2.8 × 1015 cm-3. The density of positive charges in the grown oxide and the interface states have been extracted by using high-frequency C-V and conductance techniques. The interface state density has been found to be in the order of 1011cm2-eV-1.
Ion Milling and Reactive Ion Etching of III-V Nitrides
Authors: Pearton S. J. , Abernathy C. R. , Ren F. , Lothian J. R.
Published: April 2011

Dry patterning of GaN, InN, AlN and InGaN grown by MOMBE on GaP, Al2 O3 or GaAs substrates was performed with 100–500 eV Ar+ ions at beam angles of incidence ranging from 0–75° from the normal, or with ECR discharges of BCl3/Ar, CH4/H2 or Cl2/H2. The mill rates normalized to the Ar+ beam current were typically a factor of 2 lower than for GaAs and InP (i.e. maximum values of 300–500 Å·min-1·mA-1·cm-2 at 400eV Ar+ beam energy and 60° angle with respect to the beam normal). The surface morphology of the ion milled nitrides was smooth even at 500 eV Ar+ energy, with no evidence for preferential sputtering of N as determined by AES. The ECR dry etch rates were fastest with elevated temperature Cl2/H2discharges, although both of the other chemistries investigated provide smooth, anisotropie pattern transfer. Since the ion mill rates are slow for single-crystal nitrides and less than the mill rates of common masking materials (SiO2, SiNx, photoresist) it appears this technique is useful only for shallow-mesa applications, and that dry etching methods involving an additional chemical component or ion implantation isolation are more practical alternatives for device patterning.
Characterization of CVD Diamond Films Used for Radiation Detection.
Authors: Foulon F. , Pochet T. , Gheeraert E. , Deneuville A.
Published: April 2011

Diamond films produced by microwave plasma enhanced chemical vapor deposition (CVD) technique and used to fabricate radiation detectors have been characterized. The polycrystalline diamond films have a measured resistivity of 1012 Ω.cm and a carrier lifetime of about 530 ps. The carrier mobility - lifetime product depends on the density of photogenerated carriers. The carrier mobility decreases from 160 to 13 cm2/V.s for a carrier density increase from 2 × 1011 cm-3 to 3.7 × 1013 cm-3. The detector response to laser pulses (λ= 355, 532 and 1064 nm), X-ray flux (2.5 – 16 keV) and alpha particles (241Am, 5.49 MeV) has been investigated. The response speed of the detector is in the 100 ps range. X-ray photon flux measurements and alpha particle counting capabilities of the CVD diamond detectors are demonstrated.
Cobalt Silicide OHMIC Contacts to 6H-SiC
Authors: Lundberg Nils , Östling M.
Published: April 2011

Materials and electrical evaluation were performed to determine the characteristics of ohmic contacts to 6H-SiC. Both elemental metal (Co) and suicides (CoSi and CoSi2) were studied following heat treatments at 500 °C and 900 °C for 5 hours and 2 hours, respectively. Materials analysis by Rutherford Backscattering Spectrometry (RBS) and X-ray Diffraction (XRD) monitored the temperature stability of the contacts after the annealings. Current density-voltage measurements at elevated temperatures established the specific contact resistance pc.
Chemical Reaction Mechanisms of Diamond Growth
Authors: Frenklach Michael
Published: April 2011

It is becoming increasingly apparent that future progress in diamond chemical vapor deposition depends on deeper understanding of the underlying mechanism of surface processes. Substantial efforts toward this goal have led to several conclusions on which consensus is beginning to emerge. Among them are the mediating role of hydrogen atoms, generic features of the growth kinetics, thermodynamic stability of reconstructed (100) surfaces, and the insertion reaction of methyl into (100)-(2×l) dimers. Despite these efforts, an overall picture of diamond growth in terms of elementary processes is still lacking. In this paper, the current state of mechanistic understanding is reviewed, emphasizing common themes, and new results are presented. Among the latter are the effect of reaction reversibility on surface morphology, surface migration, and a new mechanism for diamond growth from acetylene.
Dynamics at a Step on the Diamond (111) Surface
Authors: Davidson Brian N. , Pickett Warren E.
Published: April 2011

Using an accurate tight-binding method, we examine the structure and dynamics at a C(lll) step. We find the H vibration frequencies at a step are distinguishable from the flat surface. Removal of H from the surface creates an unstable bulk terminated diamond structure which relaxes to a graphitic layer and pulls away from the bulk. The explanation for these results can be given in terms of the relationship of the band structure to the relaxed geometries. The addition of H stabilizes this surface and reverts it back to sp3 bonding. The addition of CH3 near a step is also discussed. These results are important towards the understanding of possible diamond growth mechanisms that occur at a step.
Diamond Homoepitaxy Kinetics: Growth, Etching, and the Role of Oxygen
Authors: Rawles Robin E. , D'Evelyn Mark P.
Published: April 2011

Growth and etch rates for diamond homoepitaxy have been measured in situ using Fizeau interferometry. Experiments were conducted in a hot-filament reactor using hydrogen, methane, and oxygen feed gases at a reactor pressure of 25 torr. The substrate temperature dependence for growth on diamond(lOO) was studied for 0.5% and 1% CH4 and 0–0.44% O2. Apparent activation energies of 17 and 5 kcal/mol were determined for growth from 0.5% and 1% CH4 in hydrogen, over the ranges of 700 – 1000 °C and 800 – 1050 °C, respectively. When a minimal amount of Oxygen was added to the feedstock, the growth-rate behavior was similar for that with pure methane. With greater amounts of added oxygen, growth rates were higher than those without Oxygen at low temperatures, proceeded through a maximum, and then decreased until etching was observed at high temperatures. Similar behavior was observed for growth from 1% CH4 with and without oxygen. We also measured the temperature dependence for etching of homoepitaxial diamond films in hydrogen with 0–0.1% O2, and observed etch rates of 0.01 – 0.1 microns/hr in the range of 950 – 1150 °C. We propose that oxygen facilitates diamond growth at low temperatures by enhancing the removal of both sp2- and sp3-bonded “errors” and/or by increasing the efficiency of carbon incorporation by roughening the diamond surface, and that these etching processes become dominant at high temperatures.
Diamond Nucleation Studies on Refractory Metals and Nickel
Authors: Wolter S. D. , Stoner B. R. , Yang P. C. , Lui W. , Glass J. T.
Published: April 2011

Diamond nucleation has been investigated on a variety of potential heteroepitaxial substrate materials. Previous work in this laboratory has demonstrated heteroepitaxial nucleation on both Si and SiC substrates via bias-enhanced nucleation (BEN). In this study the effects of BEN of diamond on refractory metal substrates is investigated in detail. Initial data suggest a strong correlation between the carbide forming nature of the substrate material and the rate of nucleation during biasing. Our second avenue of research involves low pressure diamond growth on nickel. This material is a promising material due to its close lattice match and recent evidence of epitaxy reported by other researchers. To form heteroepitaxial diamond on nickel a high temperature pretreatment routine has been established and is the basis for this area of research. The relative importance of hydrogen absorption during this routine is explored and correlated to the formation and degree of diamond epitaxy.
Defects and Growth of Diamond Wafers
Authors: Shechtman D.
Published: April 2011

Crystallographic defects which form during growth of CVD diamond were studied and their effect on the surface structure of the growing wafer evaluated. The most abundant defects are β=3 twins boundaries whose density is very high at the nucleation side and as low as one twin per 10 /μm at the growth surface. The intersection of these twin boundaries with one another results in a formation of higher order twin boundaries. β=9 as well as β=27 and β=81 boundaries have been analyzed. The surface crystallography of optical quality diamond wafers reveals the role of β=3 twins in promoting fast growth.
Deposition of Diamond using an Electron Cyclotron Resonance Plasma System
Authors: Gilbert Donald R. , Singh Rajiv , Brock Alexander W. , Lee Dong Gu , Doering Patrick
Published: April 2011

We have used an electron cyclotron resonance plasma system to perform chemical vapor deposition experiments on single-crystal, (110) oriented diamond substrates. The depositions were carried out at 0.060 Torr using mixtures of methanol in hydrogen. Substrate temperatures were varied from approximately 620 to 800 °C The film morphology was examined using SEM and microstructural phase determination was attempted using micro-Raman spectroscopy. Based on the results of these experiments, we have determined general trends for the characteristics of films deposited on diamond from the ECR plasma at low pressures and temperatures.
Phase Transformation of Smooth Diamond Films Grown by hot Filament Chemical Vapor Deposition on Positively Biased Silicon Substrates.
Authors: Popovici G. , Chao C. H. , Prelas M. A. , Charlson E. J. , Meese J. M.
Published: April 2011

Smooth diamond films have been grown by hot filament chemical vapor deposition under d.c. bias on mirror-polished Si substrates. Films a few micrometers thick were obtained in 30 minutes. Raman spectra showed very broad diamond peaks. X-ray diffraction showed the presence of diamond and also other carbon phase with a line 2.11 Å. With time, the films apparently underwent a phase transformation.
ECR-Assisted Reactive Magnetron Sputtering of InN
Authors: Bryden W. A. , Ecelberger S. A. , Hawley M. E. , Kistenmacher T. J.
Published: April 2011

The growth of high-quality thin films of the Group IIIA nitrides is exceedingly difficult given their propensity for nonstoichiometry and the lack of suitable substrates for either homoepitaxial or heteroepitaxial growth. A novel deposition technique, ultrahigh vacuum electron cyclotron resonance-assisted reactive magnetron sputtering, has been developed for the preparation of Group IIIA nitride thin films. Thus far, thin films of the semiconductor InN have been deposited on AlN-seeded (00.1) sapphire substrates, and the properties (structural, morphology, and electrical transport) of these films studied as a function of growth temperature. Comparison to InN thin films grown by conventional reactive magnetron sputtering shows enhanced Hall mobilities (from about 50 to over 100 cm2/V-sec), a decreased carrier concentration (by about a factor of 2–3), an increased optical bandgap, and an apparent reduction in homogeneous strain that is in part to be due to film relaxation induced by the ECR beam and in part to enhanced nitrogen content and more nearly stoichiometric films.
Deposition And Characterization of CNx Films
Authors: Cui X. T. , Zhang Z. H. , Chen Q. Y. , Romero-Borja F. , Liu J. R. , Zheng Z. S. , Pan D. W. , Wood L. T. , Chu W. K.
Published: April 2011

CNx films with x around 1.0 have been made by inverted cylindrical DC magnetron sputtering. RBS, XPS, IR spectroscopy, ERD and SEM were used to characterize the composition and bonding properties of the films, while X-ray diffraction was used for crystal structure determination. XPS data indicated the existence of the tetrahedral C3N4 phase in the CNx films, which was consistent with the C-N single bond suggested by IR spectra. The annealing effect on CNx films will also be discussed.
NMR Spin Lattice Relaxation in NITROGEN-Doped 6H Silicon Carbide
Authors: Stephen Hartman J. , Narayanan Arjun , Wang Youxiang
Published: April 2011

Nuclear magnetic resonance (NMR) spin lattice relaxation is highly sensitive to the nature, amount, and homogeneity of unpaired-electron-containing impurities in silicon carbide and similar solids, and is a promising tool for the study of dopants and impurities. In nitrogen-doped 6H silicon carbide, 13C and 29Si NMR spin lattice relaxation is highly site-dependent. Not only do carbon sites relax much more rapidly than the corresponding silicon sites, but also there are unprecedented differences in relaxation efficiency among the different carbon (and silicon) sites, consistent with much higher unpaired electron density at the higher-symmetry (Types A and B) sites than at the lowest-symmetry (Type C) site. In contrast, all sites relax at equivalent rates in undoped samples and in commercial abrasive grade material with high levels of impurities, although there are large differences in relaxation efficiency among samples. The change in the nature of the relaxation process, from exponential in high-purity to stretched exponential in lower-purity samples, is apparently related to changes in unpaired-electron mobility.
Electronic Structure of Diamond, Silicon Carbide, and the Group-III Nitrides
Authors: Lambrecht Walter R. L.
Published: April 2011

This paper describes the trends in the electronic structure of diamond, silicon carbide, the group-Ill nitrides and some related materials. The relationships between the electronic band structures in the zincblende and wurtzite structures are adressed. For SiC, the discussion is extended to other poly types. The trends with ionicity and atomic number are explained. The purpose of this discussion is to help identify the similarities and differences between the various classes of wide bandgap semiconductors. The strain effects on the band structure are discussed and calculated elastic constants are given for SiC, GaN and AlN. Spectroscopie probes of the band structure such as pholoemission and UV-refiectivity are discussed for GaN and SiC. Materials with the formula II-IV-2 are proposed to be an interesting complement to the III-N's. In particular, BeCN2 is a direct gap semiconductor with elastic properties close to those of diamond and may also be useful as a bufferlayer for diamond growth.
A Spin Resonance Study of The 2.9 eV Luminescence Centers in Natural and Synthetic Diamond
Authors: Hofmann D. M. , Stadler W. , Meyer B. K. , Pereira L. , Santos L. , Pereira E.
Published: April 2011

Time resolved photoluminescence and optically detected magnetic resonance experiments were performed on the 2.985 eV (N3) luminescence band in natural diamond and the 2.964 eV luminescence center in synthetic diamonds. For the N3 luminescence the resonance occurs in the 2E excited state of the center. On the 2.964 eV luminescence a strongly anisotropie resonance signal is observed. The frequency response of the magnetic resonance signals confirms the time resolved photoluminescence measurements.
Native Defects in Wurtzite GaN And AlN
Authors: Boguslawski P. , Briggs E. , White T. A. , Wensell M. G. , Bernholc J.
Published: April 2011

The results of an extensive theoretical study of native defects in GaN and of vacancies in AlN are presented. We have considered cation and anion vacancies, antisites, and intersti-tials. The computations were carried out using quantum molecular dynamics, in supercells containing 72 atoms. Due to the wide gap of nitrides, the formation energies of defects depend strongly on the position of the Fermi level. The N vacancy in GaN introduces a shallow donor level that may be responsible for the n-type character of as-grown GaN.Other defects introduce deep states in the gap, with strongly localized wave functions.
Surface Cleaning, Topography, and Temperature Measurements of Single Crystal Diamond
Authors: D'Evelyn Mark P. , Struck Lisa M. , Rawles Robin E.
Published: April 2011

Application of surface science methods to single crystal diamond surfaces requires the preparation of clean, well-ordered surfaces and accurate measurement of substrate temperature. Cleaning of diamond (100) in H2SO4/HNO3/HClO4 produced several infrared absorption features between 1025 and 1275 cm-1, as observed by infrared multiple-internal-reflection spectroscopy. These modes are assigned to surface hydroxyl and bridge-bonded oxygen. Heating an oxidized surface to ca. 1130 °C caused disappearance of a surface hydroxyl mode centered at 1080 cm-1. We show by atomic force microscopy that an as-polished diamond (100) sample is covered by grooves and ridges several nm in height, implying a modest density of atomic steps. The surface of a diamond that underwent etching via numerous adsorption/desorption experiments in ultrahigh vacuum and was acid cleaned several times was essentially unchanged, indicating a minimal perturbation of the surface topography. The capability of Fizeau interferometry for accurate measurement of single-crystal diamond temperatures is demonstrated.
Materials Aspects of Diamond-Based Electronic Devices
Authors: Zeidler J. R. , Hewett C. A. , Nguyen R.
Published: April 2011

An overview of enabling materials technologies required for fabrication of electronic devices on diamond is presented. Emphasis is placed on electronic doping of diamond by boron ion implantation. Van der Pauw resistivity and Hall Effect measurements were used to determine the net carrier concentration, carrier mobility and resistivity of natural and synthetic diamonds implanted under various conditions. The measured results for a range of implantation conditions and post-annealing temperatures are discussed in the context cf a model developed by J.F. Prins1. The requirements placed on ohmic contacts to diamond, and a process for fabricating ohmic contacts, is discussed briefly. Finally, current-voltage characteristics of a simple MISFET fabricated on ion implanted natural diamond are presented and analyzed. 1J.F. Prins, Physical Review B, 38 (1988) 5576.
Mechanical, Thermal and Flow Dynamics Issues in Compound Semiconductor MOCVD Reactor Design
Authors: Gurary A.I. , Tompa G.S. , Moy K. , Zawadzki P.
Published: April 2011

In recent years Metalorganic Chemical Vapor Deposition (MOCVD) becomes a key epitaxial process for a variety of compound semiconductor devices such as: GaAs/AlGaAs lasers, HEMTs, LEDs, photocathodes, solar cells, and MESFETs; InP/InGaAsP long wavelength lasers and detectors; InP/InGaAs quantum wells and detectors, etc. Development of reliable, high throughput equipment is a major task in the implementation of MOCVD into cost-effective manufacturings. We have used Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) software to model thermal, structural, and flow processes for the scaling of EMCORE vertical, high speed rotating disk reactor (RDR) to large dimensions (four 4″ wafers located on 12″ wafer carrier). Flow modeling was used to determine basic reactor geometry and the relation between process parameters such as total reactant flow, temperature, pressure, and rotation speed. Thermal and structural analysis was used to produce a uniform substrate temperature, avoid reactor overheating and decrease thermal stress. Flow and temperature distribution predicted by the modeling were found to be well correlated with experimental results.
Novel Group V Sources for Use in Mombe
Authors: Abernathy C. R. , Bohling D. A. , Muhr G. T. , Wisk P. W.
Published: April 2011

Due to the extreme toxicity, and in the case of Sb stability, of the Group V hydrides, alternative gaseous Group V sources for III-V epitaxy are highly desirable. Trisdimethylaminoarsenic (DMAAs) has proven to be a useful replacement for AsH 3 for growth of GaAs and AlGaAs by MOMBE. This paper will discuss the P and Sb analogs to this compound, namely trisdimethylaminophosphorus (DMAP) and trisdimethylaminoantimony (DMASb). Both sources decompose readily on the growth surface. InP surfaces, for example, can be maintained with either source over a wide range, 375° - 525°C, as can GaAs, 375° - 600°C. Using DMAP, GaP can be grown at rates up to 200Å/min with slightly less carbon contamination than obtained with similar flows of PH3. When trimethylindium (TMI) is introduced, however, the DMAP does not readily decompose thus leaving In droplets on the surface. InP was successfully grown by thermally cracking the DMAP prior to injection to the chamber. The dependence of cracking efficiency and impurity uptake on cracker temperature will also be presented. DMASb was found to produce just the opposite effect, apparently preventing the adsorption of TEG, TIBG, or TMAA on the surface for sufficient time to allow growth to occur.
Dry ETCH Induced Defects and H Passivation of GaAs Surfaces Produced by CH4/H2/Ar Plasmas
Authors: McLane G. F. , Buchwald W.R.
Published: April 2011

An investigation was performed of surface region etch-induced damage of GaAs magnetron reactive ion etched in CH4/H2/Ar gas mixtures for 10% and 20% Ar concentrations. Schottky barrier I-V measurements showed that changes in surface potential (ϕb) upon etching and subsequent annealing can be explained by a combination of H passivation effects and As removal from the surface region. Changes in Schottky barrier ideality factor (n) can be explained by the presence of etch-induced surface region defects such as donor-like As vacancies and deep level recombination centers, both of which are passivated by H. Schottky barrier C-V measurements indicated that H passivation extends about 0.3 μm below the surface. Rapid thermal annealing at 400°C for 30 s was effective in removing most of the H passivation effects.
Temperature Dependence of Carbon Incorporation in AlxGa1-xAs Grown by Metalorganic Chemical Vapor Deposition (MOCVD)
Authors: Forbes D.V. , Coleman J.J.
Published: April 2011

The dependence of carbon concentration on growth temperature and V/HII ratio for high composition AlxGal-xAs (x>0.40) grown by metalorganic chemical vapor deposition using trimethyl sources has been investigated. The carbon concentration exhibits at least two temperature regimes having different trends with temperature. In the region of 600-675°C, the carbon concentration decreases with temperature, while in the range of 700-800°C, the carbon concentration increases with temperature. This dependence was observed in samples grown in two separate reactors. High values of V/III ratio have been found to suppress the low temperature carbon incorporation in AlAs. The results are qualitatively explained in terms of the chemical reactions and surface kinetics that may occur during the growth of GaAs or AlxGal-xAs.
Nitrogen Location on ZnSe Surface During MBE Growth
Authors: Kubo Minoru , Sasai Yoichi , Narusawa Tadasi
Published: April 2011

We first present the nitrogen location on radical nitrogen doped ZnSe-MBE surface studied by ISARS(Ion Scattering And Recoiling Spectrometry). In the recoiling nitrogen measurements of heavy doped ZnSe:N surface, a two-peak structure is observed corresponding to two recoil processes, i.e., direct recoil (DR) and surface recoil(SR). DR events occur due to the singlecollision recoiling from Se site nitrogen. On the other hand, SR events occur due to the nitrogen recoiling scattered by second layers and is highly sensitive to the nitrogen location on ZnSe:N surface during MBE growth. The experimental results and calculation suggest that the optimum doped nitrogen atoms locate in the substitutional Se sites but excess nitrogen atoms locate in the interstitial sites.
Hrxrd Study of the Strain Properties of MBE-Grown ZnSe and ZnSTe on GaAs
Authors: Sou I.K. , Mou S.M. , Chan Y.W. , Xu G.C. , Wong G.K.L.
Published: April 2011

We have studied the structural properties of MBE-grown ZnSe/GaAs and ZnSTe/GaAs heterostructures using high resolution X-ray diffraction (HRXRD). The transition from pseudomorphic to partially and then fully relaxed strained layers is observed as a function of ZnSe layer thickness. The critical thickness for the on-set of strained relaxation for ZnSe on GaAs(001) is determined to be between 1600 and 1850 Å. Using a simulation program based on the dynamical theory, the poisson's ratio of ZnSe is accurately determined to be v=0.380±0.002. A set of ZnSl-xTex epilayers with 0 ≤ × ≤ 1 was grown on GaAs by MBE for the first time. A linear dependence of the lattice constant upon Te composition is found, which agrees well with the Vegard's Law. The characteristic behaviors of inclination between the layer and substrate planes as a function of layer thickness has been studied on both ZnSe/GaAs and ZnSTe/GaAs systems. The atomic planes of both ZnSe and ZnSTe layers are observed to tilt from those of the GaAs substrate.
The influence of tellurium interdiffusion on the optical properties of MOVPE-grown ZnSe-ZnTe superlattices
Authors: Aulombard R.L. , Briot O. , Briot N. , Cloitre T. , Gwl B. , Sallese J.M. , Gailhanou M. , Bonard J.M.
Published: April 2011

We have used low pressure MOVPE to grow a series of short-period ZnSe-ZnTe strained-layer superlattices onto either ZnSe or ZnTe buffer layers. Typical superlattice periods range from 2 to 6.5 nm with constant ZnSe thickness of 2 monolayers. X-Ray diffraction analyses have shown that the superlattices are free-standing if grown on a ZnSe buffer but lattice matched to ZnTe if grown on ZnTe buffer layers. The luminescence emitted by the free standing samples has been studied using both the photoluminescence technique at low temperature and cathodoluminescence at higher temperature, for improved pumping. Our samples exhibit a complicated temperature dependence similar to the behaviour of ZnSeTe alloys where exciton self-trapping to tellurium gives strong photoluminescence bands labelled SI and S2. A high temperature, high energy feature is observed and is associated with the fundamental superlattice transition. The energy position of this structure suggest a high value of the ZnSe/ZnTe valence band offset, in the range 1200-1400 meV.
Influence of Substrate Preparation on the Two-Stage MOCVD of CdTe on (001)GaAs
Authors: Cheng T.T. , Aindow M. , Jones I.P. , Hails J.E. , Graham A. , Giess J. , Williams D.J. , Astles M.G.
Published: April 2011

A TEM study of the initial nucleation layers for the two-step growth of CdTe on 2°-off (001) GaAs substrates by MOCVD is presented. When the substrates are degreased and etched in the usual manner, the initial deposits are oriented with their axes parallel to those of the substrates. When the substrates are, instead, prepared by thermal etching at 545-585°C, the initial deposits contain both (001) and (111)-oriented grains. When these polycrystalline initial deposits are heated to the “bulk” growth temperature, epitaxial regrowth occurs giving a single crystal film with a very distinctive anisotropic defect microstructure. Possible reasons for these effects are discussed.
Modelling of the Texture Formation in Electro-Deposited Metal Films
Authors: Li D. Y. , Szpunar J. A.
Published: April 2011

The texture formation during the electrodeposition process was simulated using a Monte Carlo technique. The simulation uses a two dimensional hexagonal lattice to map the microstructure of the deposit. The criteria for the texture formation was based on the minimization of the system’s free energy. The anisotropy of surface-energy was taken into account. Since a metal’s surface energy is influenced by hydrogen adsorption, the texture of metal deposits may vary with hydrogen co-deposition.
A Microstructural Comparison of Cu(In,Ga)Se2 Thin Films Grown from CuxSe and (In,Ga)2Se3 Precursors
Authors: Gabor Andrew M , Tuttle J. R. , Albin D. S. , Matson R. , Franz A. , Niles D. W. , Contreras M. A. , Hermann A. M. , Noufi R.
Published: April 2011

We fabricated CulnSe2 and Cu(In,Ga)Se2 thin films by two different pathways using physical vapor deposition. In the first we formed a Cu-Se precursor and then reacted it with a flux of (In,Ga) + Se. These films had large grains but were too rough for optimal device performance. In the other pathway, we first formed a smooth precursor of (In,Ga)2Se3 and then exposed it to a flux of Cu+Se. We overshot the optimal film composition to allow recrystallization of the film by a secondary CuxSe phase. We then consumed the excess CuxSe in a third stage deposition of (In,Ga) + Se. The recrystallization step increased the grain sizes, and the resulting films remained smooth. Photovoltaic solar cells made from these films have produced the highest total-area efficiencies of any non-single-crystal, thin-film solar cell.
A Unified Approach to Grain Boundary Diffusion and Nucleation in Thin Film Reactions
Authors: Coffey K. R. , Barmak K.
Published: April 2011

An alternative model is proposed to extend the conventional view of diffusion under a concentration gradient in a grain boundary phase of width δ. The conventional model is well developed and readily applied to the thickening kinetics of polycrystalline product phases in binary diffusion couples, however it is not readily extended to other phenomena of interest in thin films, i.e., the nucleation and growth of the product phase crystallites prior to formation of a product phase layer. In the alternative model presented here, non-equilibrium thermodynamics is used to define the chemical potentials, μi, for each atomic specie in the grain and interphase boundaries of a polycrystalline diffusion couple. The chemical potential difference for each specie between the bulk phases of the diffusion couple is partitioned between the driving force for grain boundary diffusion and that for interfacial reaction. This partition leads to a characteristic decay length that describes the spatial variation of μi. Numerical calculations of μi are used to show that boundary diffusion favors heterogeneous nucleation. Product nucleation in thin film reactions is seen to be similar to precipitation from a bulk solid solution.
Orientation Imaging of the Microstructure of Polycrystalline Materials
Authors: Adams Brent L.
Published: April 2011

Recent developments, coupling the scanning electron microscope with image processing and crystallographic analysis, now make it possible to automatically index many thousands of lattice orientations exposed on section planes in polycrystalline materials. Backscattered Kikuchi diffraction patterns obtained from high-gain SIT and CCD cameras are analyzed using the Hough transformation (Cartesian coordinates - polar coordinates) in order to identify diffraction band widths and interplanar angles. From this basic information local lattice orientation can be determined. Information from raw data sets (in excess of 100,000 single orientations in some examples) can be used to construct orientation imaging micrographs which emphasize certain aspects of the exposed field of lattice orientations. Thus, features of the spatial placement of lattice orientation (including grain boundary misorientation, microtexture, and connectivity of the microstructure) are readily studied. In this paper these techniques are reviewed, and recent explorations of the connectivity of grain boundary misorientation structure are presented for an interesting nickel-chromium-iron alloy.
The Thermal Stability of Ti-Al-C Pvd Coatings
Authors: Knotek O. , Löffler F. , Wolkers L.
Published: April 2011

While (Ti,Al)N coatings are well known and established in wear applications like drilling and milling, the corresponding TiC based metastable system Ti-Al-C is not well examined. This paper investigates the phase stability and the phase transition behaviour of post-deposition heat-treated Ti-Al-C coatings. The samples were annealed in a temperature range from 600–1400 °C in a high vacuum furnace. The influence of deposition parameters like coating compositions via the Ti/Al ratio and the metal/metalloid ratio on the properties were investigated. Another very important parameter in this investigation is the carbon carrier gas. Examined gases were methane, ethane, ethylene and ethine. The changes in microhardness, lattice parameters and particle sizes were analysed with respect to their temperature dependence.

The phase formation depends on the target composition and on the reactive gas. A formation of a metastable (Ti,Al)C phase can be observed. A higher C:H ratio of the reactive gas leads to better incorporation of carbon into the coating. An Al-loss independent of the coating composition begins 1000 °C. The microhardness increases with higher annealing temperature and decreases with higher Al-content.
The Effects of Cross Hatch Angle (CHA) on Magnetic Properties and Read/Write Characteristics of CoCrPtTaB Thin Film Media
Authors: Chen Ga-Lane , Do H. , Yeh T.-A. , Sivertsen J. M. , Judy J. H.
Published: April 2011

Cross-hatch type texturing has been widely used to replace circumferential texturing in the thin film media industry for optimizing tribology performance. However, higher “cross hatch angle” (CHA) may degrade magnetic performance. The relationship between texturing cross hatch angle (CHA) and magnetic properties and their effects on the read/write characteristics of sputtered thin film media are discussed in this paper. As the CHA increases, both the orientation ratio (OR) and the squareness ratio “S(c)/S(r)” decrease. The film with the highest OR is located at CHA=90, which has the lowest media noise. The medium has highest signal/noise ratio when CHA is equal to 90. PW50 can decrease as much as 4 nanoseconds as CHA increases to 730. By calculating a ratio of the intensity of Cr (110) + CoCrPtTaB (0002) to the intensity of Cr (200), we are able to correlate the intensity ratio to magnetic properties and read/write characteristics.
The Microstructure of Sputtered Co-Cr Magnetic Recording Media
Authors: Pundt Astrid , Busch Ralf , Michaelsen Carsten
Published: April 2011

With the increase of magnetic storage capacity in view, sub grain decomposition in Co-Cr magnetic recording material is examined with the field ion microscope / atom probe (FIM/AP) on a nanometer scale. Concentration variations in sputtered 50 nm Co-20at% Cr and 3 μm Co-22at% Cr films are analysed. Layers with up to 50 nm thickness are sputtered directly onto tungsten FIM tips. FTM-tips of layers with up to 3 μm thickness are prepared by a lithography and etching technique. The measurements show decomposition on the scale of a few nanometers. The concentration amplitudes vary between 11 at% Cr and 42 at% Cr within 50 nm films. Within 3 μm films the concentration varies from about 10 at% Cr to 30 at% Cr. Furthermore, at grain boundaries 3–4 nm precipitates of about 40 at% Cr are observed. The observed concentrations depend on substrate temperature. The compositional inhomogeneity can be explained by a miscibihty gap in the hep phase solid solution which is induced by magnetism at low temperatures.
Stress, Microstructure and Magnetic Properties of Thin Sputtered Co Alloy Films
Authors: Ross C. A. , Ranjan R. , Chang J.
Published: April 2011

The internal stress and magnetic properties have been measured for cobalt alloy films deposited using a range of sputter conditions. The sputter conditions affect the internal stress and the microstructure, both of which contribute to the magnetic properties of the films. Stress influences the magnetic properties via magnetostriction, while the microstructural effect on coercivity comes primarily from the degree of separation and size of the grains in the film. The effect of stress on coercivity was investigated separately by applying external stresses to the films, and magnetostriction coefficients were derived for different alloys. The change in coercivity with sputter parameters indicates that in alloys such as Co77Ni7Cr4Pt12, the microstructure has the dominant effect on coercivity.
Effects of Substrate Temperature on Magnetic and Crystallographic Properties of Co-Cr-Pt/Cr Films Deposited by Laser Ablation
Authors: Ishikawa Akira , Shiroishi Yoshihiro , Sinclair Robert
Published: April 2011

The effects of the substrate temperature on the magnetic properties and crystal structure of Co89Cr7Pt4/Cr films deposited by laser ablation were studied. A pulsed KrF excimer laser with a wavelength of 248 nm was focused on ablation targets in a vacuum chamber. The laser irradiation energy was estimated to 10 J/cm2. Cr underlayer and Co89Cr7Pt4 films were successively deposited on the Si substrate at a rate of 0.012 nm/pulse. At a substrate temperature lower than 350 °C, an in-plane coercivity of 30 nm thick CoCtjPu film deposited on 50 nm thick Cr underlayer was 50∼150 Oe showing no significant influence by the substrate heating. The coercivity at 450 °C, however, increased to 800 Oe showing a maximum at this temperature. X-ray diffraction analyses showed that the magnetic films formed at lower than 350 °C have fcc-Co phase, while the films deposited at 450 °C had hep-Co phase with the c-axis oriented parallel to the substrate. At temperatures higher than 450 °C, the coercivity decreased concomitant with a disappearance of the oriented hep-Co phase. The grain size of the films increased from 10 nm to 20∼30 nm by increasing the substrate temperature. The increase of coercivity is probably due to annealing effects resulting in the grain growth of Cr underlayer and the phase transformation of the magnetic films to form the hep-Co phase.
Effect of Interlayers Upon Texture and Magnetic Properties in Co Alloy Multilayer Films for Longitudinal Magnetic Recording
Authors: Visokay M. R. , Kuwabara M. , Saffari H. , Hayashi H. , Sinclair R , Onishi Y.
Published: April 2011

CoCrNi bilayer films with Cr, Ti and Zr interlayers were deposited by DC magnetron sputtering onto ultra densified amorphous carbon substrates and characterized using cross-section transmission electron microscopy and vibrating sample magnetometry. The films are polycrystalline with a columnar microstructure. In the Cr interlayer case there is layer-to-layer epitaxy throughout a given column. Magnetic measurements snowed a simple in-plane easy axis magnetic hysteresis loop. In the Zr and Ti interlayer cases epitaxy within a column was lost beginning with the first CoCrNi/(Zr/Ti) interface, resulting in a magnetic layer consisting of two crystallographically unrelated CoCrNi films. Magnetic measurements revealed a complex step-structure hysteresis loop for this case. Annealing the Zr interlayer film led to a significant growth of the amorphous layer due to a solid state amorphization reaction between the Zr and CoCrNi, which was accompanied by a decrease in the saturation magnetization.
Giant Magnetoresistance Studies of NiFe-Based Spin-Valve Multilayers
Authors: Lin Chien-Li , Sivertsen John M. , Judy Jack H.
Published: April 2011

The giant magnetoresistance in FeMn exchange-biased NiFe-based multilayer spin-valve structures prepared by rf-diode sputtering technique were studied. Experiments were performed on samples with different thicknesses of each layer in these multilayers. The magnetic properties were measured using a vibrating sample magnetometer and the giant magnetoresistance was measured using an in-line four-point magnetoresistance probe. A magnetoresistance of 6.5% in a magnetic field of less than 15 Oe was obtained in a Cu(30Å)/FeMn(150Å)/NiFe(50Å)/Co(15Å)/ Cu(20Å)/Co(15Å)/NiFe(60Å) multilayer structure at room temperature. Annealing experiments of these multilayers were performed to study the thermal stability during the recording head fabrication processes. No degradation in the magnetoresistance has been found for annealing these films at 230°C up to four hours.
The Geometry of Grain Disappearance in Thin Polycrystalline Films
Authors: Townsend S. J. , Nichols C. S.
Published: April 2011

During grain growth, shrinking columnar grains in thin-film polycrystalline microstructures eventually reach sizes comparable to the film thickness. Due to surface drag, the sides of such grains may bow inward rather than remaining fiat through the bulk of the film. The grain boundaries delimiting such small shrinking grains may become unstable long before the surface of the shrinking grain reaches zero area. We report simulation results demonstrating such an instability in the limit of infinite surface drag. This may lead to extremely rapid disappearance of 4- or 5- sided grains, such as have been recently observed in in situ hot-stage TEM experiments on aluminum thin film polycrystals.
Interfaces in Ferroelectric Metal Oxide Heterostructures
Authors: Ramesh R. , Lee J. , Keramidas V. G. , Fork D. K. , Ghonge S. , Goo E. , Auciello O.
Published: April 2011

Realization of a viable nonvolatile ferroelectric thin film memory technology hinges on the successful solution of the reliability problems associated with the ferroelectric capacitor concurrent with the integration of these materials with the appropriate Si-CMOS based drive electronics. This integration process introduces a variety of structural, chemical, ionic and electronic interfaces in the memory elements. In this paper, the influence of some of the interfaces on the ferroelectric properties and on the process integration is discussed.
The Effect of Layer Thickness on Polycrystalline Zirconia Growth in Zirconia-Alumina Multilayer Nanolaminates
Authors: Scanlan C. M. , Wiggins M. D. , Gajdardziska-Josifovska M. , Aita C. R.
Published: April 2011

The mechanical properties of zirconia are known to be a function of phase composition. We show here that a nanolaminate geometry can be used to control the phase composition of zirconia films. The experiment consisted of growth of nanoscale multilayer films (nanolaminates) of polycrystalline zirconia and amorphous alumina by reactive sputter deposition on Si (111) and fused silica substrates. The films were characterized using x-ray diffraction and high resolution electron microscopy. The results show that both monoclinic (m) and tetragonal (t) zirconia polymorphs were formed in the zirconia layers. Most crystallites are oriented with either close-packed {111}-t or {111}-m planes parallel to the substrate. The volume fraction of tetragonal zirconia, the desired phase for transformation-toughening behavior, increases with decreasing zirconia layer thickness. Nanolaminates with a volume fraction of tetragonal zirconia exceeding 0.8 were produced without the addition of a stabilizing dopant, and independent of the kinetic factors that limit tetragonal zirconia growth in pure zirconia films.
Texture and Phases in Oxide Films on Zr-Nb Alloys
Authors: Lin Y. P. , Woo O. T. , Lockwood D. J.
Published: April 2011

Oxide films, 0.2-2.0 μm in thickness on Zr-2.5Nb and 11 μm thick on Zr-20Nb alloys, formed in steam at 673 K, have been examined using TEM, XRD and Raman spectroscopy. Columnar grains of mostly monoclinic Zr02 in oxide films on Zr-2.5Nb exhibit a dual texture: a fibre mode with an axis close to the 102m pole and a [001]m growth mode with an orientation relationship [100]m // [4510]α and (010)m // (0001)α with the α-Zr metal. In both modes, “tetragonal” (and/or cubic) ZrO2 was present. Raman spectroscopy differentiated two non-cubic “tetragonal” forms of ZrOz within the [001]m growth texture. In thin oxides (0.5 μm or less), this corresponds to the tetragonal ZrO2 observed in ceramic zirconia and is characterised by a Raman band near 260 cm−1. The 278 and related 438 cm−1 Raman bands observed here in some oxide films (and in other Zr corrosion oxides) are attributed to a separate, non-cubic phase structurally related to the tetragonal ZrO2. The intensities of the 278 and 438 cm−1 bands are dependent not only on the amount of this modified-tetragonal phase but also on the oxide texture (related to the metal texture) and the beam orientation. The lack of Raman response from the “tetragonal” ZrO2 within the fibre mode of texture indicates either a low volume fraction or a cubic-like structure. For oxide on Zr-20Nb, XRD and Raman spectroscopy show a mixture of monoclinic and “tetragonal” ZrO2; the Raman results indicate the “tetragonal” ZrO2 has a high crystal symmetry or nearly cubic structure.
Computer Simulation of Strain Energy and Surface- and Interface-Energy on Grain Growth in Thin Films
Authors: Carel R. , Thompson C. V. , Frost H. J.
Published: April 2011

We have simulated strain energy effects and surface- and interface-energy effects on grain growth in thin films, using properties of polycrystalline Ag (p-Ag) on single crystal (001) Ni on (001) MgO for comparison with experiments. Surface- and interface-energy and strain energy reduction drive the growth of grains of specific crystallographic orientations. The texture that will result when grain growth has occurred minimizes the sum of these driving forces. In the elastic regime, strain energy density differences result from the orientation dependence of the elastic constants of the biaxially strained films. In the plastic regime, strain energy also depends on grain diameter and film thickness. In p-Ag/(001) Ni, surface- and interface-energy minimization favors Ag grains with (11) texture. In the absence of a grain growth stagnation, the texture at later times is always (111). However, for high enough strains and large enough thicknesses, the strain energy driving force can favor a (001) texture at early times, which reverts to a (111) texture at later times, once the grains have yielded.