bluuebunny/crossref_metadata_2025 huggingface dataset:
The Development and Characterization of Crystallographic Texture in thin films for Magnetic Recording
Authors: Laughlin David E. , Tang Li , Lee Li-Lien , Hsu Yu-Nu , Lambeth David
Published: April 2011

The development of crystallographic texture in thin film longitudinal recording media is discussed. Polycrystalline thin films may obtain their crystallographic texture by means of a nucleation process such as epitaxial nucleation on a polycrystalline underlayer or by means of a process involving a preferred growth direction. In this paper we will discuss various epitaxial nucleation textures that are obtained in media produced for magnetic recording. We will discuss the way that the underlayer controls the crystallographic texture of the magnetic layer, as well as methods used to control the texture of the underlayer itself. We give a brief overview of some of our recent findings in the growth of NiAl and FeAl films used for underlayers. Finally we will briefly discuss what we have called the tilted electron beam technique. In this technique selected area electron diffraction patterns are obtained at different angles of tilt and the development of arcs in the patterns is analyzed so as to determine the type and amount of crystallographic texture which is present in the films.
Magnetic Anisotropy and Growth Texture in Co35Pd65 Films
Authors: Jen S. U. , Huang J. Y. , Huang K. B.
Published: April 2011

Pd-rich Co-Pd alloy films are well known to exhibit perpendicular anisotropy. In this study, Co35Pd65 films were made by the vapor deposition method. The thickness of the films ranged from 80 to 2000 Å. Following measurements were carried out on each film sample: the impurities and alloy compositions were checked by Auger depth profile analysis (AES), the surface topology was mapped out by an atomic force microscope (AFM), the structural analysis was done by using the X-ray diffractometer (XRD), and the magnetic properties, such as magnetic anisotropy and saturation magnetization, were measured by a SQUID magnetometer and/or a MOKE (using the longitudinal or polar effect) apparatus. Magnetic quantities, such as the out-of-plane (either hard or easy axis) squareness ratio Mr/Ms, saturation magnetization Ms, and anisotropy energy Ku, are closely related to the structural properties, such as the degree of (111) texture, grain size D, mode of growth (nucleation texture or growth texture), and impurities in films. The emphasis is placed on the thickness dependence of these quantities, and the interrelationship among them.
Magneto-Optical Effects of Ultrathin Ferro-, Antiferro- and Non-Magnetic Films
Authors: Suzuki Y. , Katayama T. , Geerts W. , .Grünberg P , Takanashi K. , Schreiber R. , Bruno P. , Yuasa S.
Published: April 2011

Thickness dependence of the magneto-optical Kerr effects (MOKE) in ultrathin ferromagnetic films, antiferromagnetic films and nonmagnetic films were measured carefully employing wedge shaped samples at room temperature. The oscillations of the polar Kerr ellipticiry with respect to the film thickness and its energy dependence were observed for the Fe and Au ultrathin films, and revealed a formation of spin-polarized quantum well states both in the bcc-Fe (100) layers and the fcc-Au(001) layers.

On the other hand, bcc-Cr (100) ultrathin layers grown on 3ML of Fe(100) layer showed about 2ML period oscillation of the polar MOKE for the photon energy in between 2.25 and 3.75eV, indicating an existence of a long range antiferromagnetic order. The Cr film also showed energy dependent oscillation peaks for the very thin region (d<10ML). The longitudinal MOKE were measured also for Cr samples, and revealed 2ML period oscillation. The mechanism of the MOKE oscillations is discussed from the view points of quantum size effects and the antiferromagnetic order.
Morphology and Curie Temperature Changes upon Annealing of Co/W(110)
Authors: Bauer A. , Mühlig A. , Günther T. , Farle M. , Baberschke K. , Kaindl G.
Published: April 2011

Annealing of CoAV(110) ultrathin films causes rather strong changes of film morphology and magnetic properties, which has been studied by scanning tunneling microscopy (STM) and alternating-current magneto-optical Kerr effect (ac-MOKE). Annealing above 500 K of room-temperature grown 2 monolayers (ML) thick Co/W(110) films leads to the formation of islands and a decrease of the Curie temperature 7C. At 4 ML, on the other hand, a network of interconnected islands is formed upon annealing, resulting in an enhanced TC. While the increase of TC at 4 ML is explained by an increase of the local film thickness, the anomalous TC behavior at 2 ML is assigned to the occurrence of superparamagnetism.
Magnetic X-Ray Resonant Scattering from a Dysprosium Epitaxial Film
Authors: Dumesnil K. , Stunault A. , Mangin Ph. , Vettier C. , Wermeille D. , Bernhoeft N. , Langridge S. , Dufour C. , Archal G. M.
Published: April 2011

Magnetic X-Ray resonant scattering performed at the Dysprosium Lni absorption edge permits to study the magnetic behaviour of a 3000 Å thick Dy film. The development of an helical magnetic order gives rise to intense magnetic resonant harmonics. The energy dependence of the resonant intensity has been investigated and presents a double resonance at the second harmonic measured in the σ-π geometry. The accurate thermal variation of the turn angle and of the c-parameter is given. These evolutions reveal the stabilisation of the helical phase in the Dysprosium film compared to the bulk case.
Microstructural Studies of Sputtered Co90Fe10/Ag GMR Multilayers
Authors: Jarratt J.D. , Klemmer T.J. , Barnard J.A.
Published: April 2011

The microstructure of Co90Feio/Ag giant magnetoresistive multilayer films has been investigated using x-ray diffraction (XRD) and cross-sectional transmission electron microscopy. Columnar grains with a (111) fiber growth texture is observed. A comparison is made between the observed layering structure and earlier multilayer schematics based on the literature and magnetic and magnetoresistive measurements as a function of layer thickness. A direct correlation is made between superlattice satellite peak signals from selected area electron diffraction patterns and XRD scans.
Magnetic ordering in submonolayer Mn films on fee Co(001) and the effects of oxidation
Authors: O'Brien W.L. , Tonner B.P.
Published: April 2011

Submonolayer films of Mn grown on fcc Co(001) are ferromagnetically ordered with the magnetization direction oriented parallel to the Co substrate magnetization. After exposure to oxygen the Mn atoms remain ferromagnetically ordered but their magnetization direction rotates 180 degrees and is now aligned antiparallel to the Co magnetization. This behavior in magnetic coupling between the Mn and Co films is not consistent with recent theoretical predictions.
Perpendicular Giant Magnetoresistance of Co/Cu Multilayers with Fluctuating Co Layer Thicknesses
Authors: Chiang Wen-C. , Loloee R. , Pratt W.P. , Bass J.
Published: April 2011

J. Mathon has predicted that introducing pseudorandom fluctuations (PRF) in the Co layer thickness could greatly enhance the Current Perpendicular to the Plane (CPP) magnetoresistance (MR) of a Co/Cu superlattice with dimensions comparable to the electron mean-free-path. We have searched for CPP-MR enhancement in sputtered Co/Cu multilayers with Cu layer thicknesses near both the first and second antiferromagnetically coupled peaks in the oscillatory region of the CPP-MR. In both cases, inserting PRF only decreased the CPP-MR.
Theoretical Study of the Magnetic Anisotropy of Ni Films on Cu(001)
Authors: Freyss M. , Lorenz R. , Dreysse H. , Hafner J.
Published: April 2011

The anisotropy properties of Ni films on Cu(001) are quite unusual compared to other systems: The magnetization direction of Ni is in-plane for a coverage smaller than a critical thickness of 7 monolayers and out-of-plane for a coverage larger than 7 monolayers. As a first step in the study of this unusual behaviour, we report results of ab-initio calculations of the magnetic order of Ni films on a Cu(001) substrate. The magnetic moments are computed by means of the real-space Tight-Binding LMTO method allowing non-collinear magnetic moments and including spin-orbit coupling to account for magnetic anisotropy effects. As the number of Ni layers is increased, we discuss the stability of the system with a magnetization in-plane or out-of-plane.
Lattice Effects in Perovskite and Pyrochlore CMR Materials
Authors: Kwei G.H. , Argyriou D.N. , Billinge S.J.L. , Lawson A.C. , Neumeier J.J. , Ramirez A.P. , Subramanian M.A. , Thompson J.D.
Published: April 2011

Colossal magnetoresistance (CMR) in doped lanthanum manganite thin films (Lai.xMx, where M is a divalent ion) has been shown to result in a factor of 106 suppression of the resistance. The driving force for the CMR transition is thought to be the double-exchange (DE) interaction. Many studies of both the crystal structure and the local structure of the Lai.xMxMnO3 (with M = Ca, Sr and Ba, as well as Pb) system have now been carried out. As expected, these systems all show a strong coupling of the lattice to the CMR transition. On the other hand, neutron diffraction data and x-ray absorption studies for the Ti2mn2O7 pyrochlore, which also exhibits CMR, shows no deviations from ideal stoichiometry, mixed valency, or Jahn-Teller distortions of the MnO6 octahedron. We present results of crystallographic and local structural studies of these two important classes of CMR materials. compare the differences in structural response, and discuss the implications of these findings to our understanding of these materials.
Tight-binding calculation of giant magnetoresistance in Co/Cu/Co spin valves with layer-dependent scattering
Authors: Tsymbal E.Yu. , Pettifor D.G.
Published: April 2011

We have modelled the effects of bulk, outer-boundary, and interfacial disorder on conductivity and giant magnetoresistance (GMR) in Co101010/ trilayer taking into account its realistic electronic band structure. Calculations were performed using our model [E. Yu. Tsymbal and D.G. Pettifor, Phys. Rev. B 54 (1996) 15314] extended to the systems with two-dimensional periodicity and layer-dependent disorder. The model is based on the Kubo-Greenwood formula and spin-independent disorder in the on-site atomic energy levels, reflecting the scattering by defects, within an spd tight-binding approximation. Exploring the contributions to conductivity from different layers, we find that the influence on GMR of the boundary and interfacial scattering is similar to the bulk scattering, because the conductivity is non-local and the thicknesses of films are comparable to the electronic mean free path. Increasing the spin-independent disorder causes a decrease of GMR in the spin-valve for both interfacial, outer-boundary and bulk mechanisms of scattering. We have also investigated the effect of outer-boundary and interfacial paramagnetic Co layers on GMR in the trilayer. We find that the GMR, in this case, is strongly reduced due to the strong spin-independent scattering at the paramagnetic layers and hybridization of d states of the paramagnetic layers with the sp bands.
Magnetic Properties of Transition Metal Interfaces
Authors: Mirbt S.
Published: April 2011

The results of first-principles calculations for the interlayer coupling in Fe/Cr/Fe trilayers are presented. We find that a spin-density wave in Cr gives rise to an additional contribution to the interlayer coupling. We investigate the relationship between the spacer magnetic moment and the interlayer coupling. Moreover we calculated the effect of interface adlayers of Cu on the interlayer coupling of a Fe/Cr/Fe trilayer.
Temperature Dependence of Strong Exchange Coupling in Ferrite Heterostructures
Authors: Suzuki Y. , Van Dover R.B. , Felder R.J.
Published: April 2011

Single crystalline spinel structure ferrite thin film bilayers exhibit nearly ideal exchange coupling at room temperature. In these bilayers, the blocking temperature is only limited by the Curie temperature of the (Mn,Zn)Fe2O4. Up to the Curie temperature of the soft (Mn,Zn)Fe2O4 layer, the magnetization loops indicate that exchange anisotropy dominates the magnetization of the soft layer up to magnetic fields on the order of the coercive field of the hard CoFe2O4layer.
Bilinear and Biquadratic Exchange Coupling in Fe(110)/Cr/Fe Trilayers
Authors: Elmers H.J. , Schwabenhausen J. , Dürkop T.
Published: April 2011

The indirect exchange coupling in W(110)/Fe/Cr/Fe/Cr trilayers was determined by analysis of magnetization curves measured by Kerr magnetometry. We adjusted the uniaxial in-plane anisotropies in the two Fe layers in such a way that the easy axes were orthogonal, [001] in the 1st, [110] in the 2nd layer. This allows an independent determination of both bilinear (i) and biquadratic (J2) coupling constants. We determined tJ and J2 as a function of Cr interlayer thickness (tcT = 0 – 4 nm), preparation temperature of the interlayer Tcr=100 – 500 K, and as a function of temperature (T = 100 – 300 K). Results for the exchange coupling are correlated to the particular lateral thickness fluctuation of the Cr spacer.
Exchange Coupling and Giant Magnetoresistance in Electrodeposited Co/Cu Multilayers
Authors: Dinia A. , Rahmouni K. , Schmerber G. , El Fanity H. , Bouanani M. , Cherkaoui F. , Berrada A.
Published: April 2011

We present the results of the transport and magnetization measurements of electrodeposited Co/Cu multilayers grown in a single electrolyte based on C0SO4, H3BO3 and CuSO4. The samples are deposited on glass substrate covered by a 500 Å thick Cu buffer layer. X-ray diffraction performed on the samples shows fee structure of both Co and Cu layers with preferential (111) orientation. Resistivity measurements show a giant magnetoresistance effect of about 4% at room temperature for multilayers with Co and Cu thickness between 4 nm ≤ tco ≤ 6 nm and 3 nm ≤ tcu ≤4 nm respectively. For Co thickness tCo ≤ 15 nm, the magnetoresistance completely vanishes indicating that there is no more continuous Co layer. The indirect antiferromagnetic exchange coupling between magnetic Co layers is relatively large for 4 nm thick Cu spacer layer and gives rise to a temperature dependence of about 30% between room temperature and 4.2 K.
A New Spin Filter: The Magnetic Schottky Diode
Authors: Filipe A. , Drouhin H.-J. , Lampel G. , Lassailly Y. , Peretti J. , Safarov V.I. , Schuhl A.
Published: April 2011

We observe spin-dependent transmission of hot electrons through the ferromagnetic metallic layer of a Schottky diode. A 25% spin-polarized electron beam is produced in vacuum by a GaAs photocathode under illumination with circularly polarized light. The photoemitted electrons are then injected from the vacuum into the sample: a 3.5 nm-thick Fe layer deposited on a n-doped GaAs substrate. We measure a transmission coefficient of the order of a few 10-4. Using an incident energy above the Fermi level equal to 5 eV, a 5% asymmetry in the transmitted current is observed by changing the spin-polarization of the incident electrons (i.e. the light polarization) and/or reversing the Fe-layer magnetization. This corresponds to a transmission spin-dependence of 20% for a 100% spin-polarized incident beam.
Low Dielectric Constant Fluorinated Polyimides for Interlayer Dielectric Applications
Authors: Pellerin John , Fox Robert , Ho Huei-Min
Published: April 2011

This paper presents the results of development, characterization and integration screening of low dielectric constant (low k) fluorinated polyimides for interlayer dielectric applications. Evolution of these materials has progressed with the intent of improving fundamental thin film properties, such as thermal stress behavior, modulus, CTE, and dielectric constant. Further refinements to fluorinated polyimides have been to improve their process compatibility and integration characteristics, primarily in the area of deep sub-micron gap filling. The avenues taken to attain these objectives will be illustrated.

Subsequent integration of low k fluorinated polyimides has been achieved for a completed single-level metal BEOL test vehicle to highlight the impacts of the film's adhesion, mechanical and thermomechanical properties. In addition, the completed fluorinated polyimide single-level metal structures have been used to characterize electrical performance in contrast to single-level metal structures with TEOS dielectric. Intralevel capacitance and leakage current have been measured with dual comb and serpentine structures. Modeling has been applied to verify dielectric constant in submicron geometries from the capacitance measurements.
Characterization of Parylene-N Thin Films for Low-K Vlsi Applications
Authors: Selbrede Steven C. , Zucker Martin L.
Published: April 2011

Parylene-N thin films were characterized from the viewpoint of advanced VLSI intermetal dielectric applications. All films were deposited in a prototype production system that included a vacuum chamber, electrostatic cold chuck and a parylene vapor delivery system. Chuck temperatures as low as -30 °C were achieved. The deposition rate was found to be strongly dependent on wafer temperature, increasing dramatically as wafer temperature is reduced. Deposition rate was also strongly dependent on the parylene vapor flow rate and process pressure. These strong dependencies require that extreme care be taken to achieve production worthy repeatability.

A number of film properties were measured including; dielectric constant, refractive index, stress, adhesion, conformality, OH-content, metals-content and thermal stability.
Properties of New Low Dielectric Constant Spin-on Silicon Oxide based Polymers
Authors: Hacker Nigel P. , Davis Gary , Figge Lisa , Krajewski Todd , Lefferts Scott , Nedbal Jan , Spear Richard
Published: April 2011

Low dielectric constant materials (k < 3.0) have the advantage that higher performance IC devices may be manufactured with minimal increases in chip size. The reduced capacitance given by these materials permits shrinking spacing between metal lines to below 0.25 μm and the ability to decrease the number of levels of metal in a device. The technologies being considered for low k applications are CVD or spin-on of inorganic or organic polymeric materials. Traditional spin-on silicates or siloxanes have been used as planarizing dielectrics during the last 15 years and usually have k > 3.0.
Microscopic Mechanisms for Reduced Static Dielectric Constants in Si-O-F Alloy Films
Authors: Yang H. , Lucovsky G.
Published: April 2011

There is considerable interest in insulators with static dielectric constants lower than SiO2; an alloy system attracting recent attention is Si-O-F. Alloying of F atoms into plasma-deposited SiO2films leads to major changes in the SiO2bond-stretching and -bending infrared bands accounting for a significant fraction of the reduction in the dielectric constant. These changes are explained by F induced modifications of force constants and effective charges of the neighboring Si-O-Si groups.
Cure of Hydrogen Silsesquioxane for Intermetal Dielectric Applications
Authors: Bremme J.N. , Liu Y. , Gruszynski K.G. , Dall F.C.
Published: April 2011

Cure is a significant process during back end of the line fabrication of integrated circuits with hydrogen silsesquioxane since it affects structure and properties of the spin on dielectric material. Reported herein is the effect of soak temperature, time, and oxygen concentration process parameters on structure and properties of hydrogen silsesquioxane. Results of the study emphasize the importance of an inert environment during the baseline recommended cure conditions of 400 °C for one hour in order to avoid oxidation and formation of polar silanol or water species. A 350 °C cure temperature is more robust to oxidation providing similar or improved properties. Shorter cure times result in similar structure and properties as the baseline cure which suggests that lower temperature and/or shorter cure time may provide value worth investigating by integrated circuit manufacturers.
Direct Patterning of Low-K Material for Damascene Process
Authors: Chu Cheng-Jye , Chu C-T. , Wei Q.
Published: April 2011

There are several activities in the development of low dielectric constant materials, including fluorlnation of SiO2, low-k organic polymers, and porous materials. No one material satisfies all the requirements for multilevel interconnections, which include low dielectric constant, high mechanical strength, good dimensional stability, good high temperature stability, easy processing, and low H2O absorption and outgassing. In this research, a new material system has been studied. This process-controlled low-k material can have dielectric constant as low as 2.0 with good thermal stability. It can provide low viscosity for reflow processing to achieve excellent planarization and gap filling. Low moisture uptake and high mechanical strength can be achieved. Most interesting is, it can be made to be photosensitive at deep-UV range, which provides the possibility of eliminating many chemicals and complicated processes in photolithography. Process cost can be expected to drop significantly. Damascene and dual damascene processes were proposed using this new low-k material, which can be much simpler compared to the traditional process.
Reaction between Low Dielectric Constant Fluorinated Polyimide and Aluminum
Authors: Tong H. Y. , Szalkowski F. J. , Shi F. G. , Zhao B. , Brongo M. , Wang S.-Q. , Vasudev P. K.
Published: April 2011

Interactions between fluorinated polyimide and aluminum under different thermal treatment conditions have been investigated using transmission electron microscopy (TEM) and x-ray diffractometry (XRD) techniques over a wide temperature range. Our results suggest that the oxygen from the dielectric materials may result in the oxidation of the underlying aluminum either on the surface or along the grain boundary. This work implies that processing conditions, such as curing temperature and time, may play critical roles in affecting the performance of polymeric dielectric materials.
Silk Polymer Coating with Low Dielectric Constant and High Thermal Stability for Ulsi Interlayer Dielectric
Authors: Townsend P. H. , Martin S. J. , Godschalx J. , Romer D. R. , Smith D. W. , Castillo D. , DeVries R. , Buske G. , Rondan N. , Froelicher S. , Marshall J. , Shaffer E. O. , Im J-H.
Published: April 2011

A novel polymer has been developed for use as a thin film dielectric in the interconnect structure of high density integrated circuits. The coating is applied to the substrate as an oligomeric solution, SiLK*, using conventional spin coating equipment and produces highly uniform films after curing at 400 °C to 450 °C. The oligomeric solution, with a viscosity of ca. 30 cPs, is readily handled on standard thin film coating equipment. Polymerization does not require a catalyst. There is no water evolved during the polymerization. The resulting polymer network is an aromatic hydrocarbon with an isotropie structure and contains no fluorine.

The properties of the cured films are designed to permit integration with current ILD processes. In particular, the rate of weight-loss during isothermal exposures at 450 °C is ca. 0.7 wt.%/hour. The dielectric constant of cured SiLK has been measured at 2.65. The refractive index in both the in-plane and out-of-plane directions is 1.63. The flow characteristics of SiLK lead to broad topographic planarization and permit the filling of gaps at least as narrow as 0.1 μm. The glass transition temperature for the fully cured film is greater than 490 °C. The coefficient of thermal expansivity is 66 ppm/°C below the glass transition temperature. The stress in fully cured films on Si wafers is ca. 60 MPa at room temperature. The fracture toughness measured on thin films is 0.62 MPa m ½. Thin coatings absorb less than 0.25 wt.% water when exposed to 80% relative humidity at room temperature.
Evaluation of a New Strategy for Transverse Tem Specimen Preparation by Focused-Ion-Beam Thinning
Authors: Shaapur F. , Stark T. , Woodward T. , Graham R. J.
Published: April 2011

In this paper, different variations of a recently developed focused ion beam (FIB)-based TEM specimen preparation technique are studied conceptually and experimentally, compared, and evaluated. This procedure mainly consists of formation, removal, transport, and mounting of an electron transparent transverse membrane on a support grid for TEM study. Based on the experimental results obtained from this evaluation, some modifications have been conceived and implemented. These details as well as other critical information have been presented and discussed.
Focused Ion Beam Sample Preparation of Non-Semiconductor Materials
Authors: Phaneuf M. W. , Rowlands N. , Carpenter G. J. C. , Sundaram G.
Published: April 2011

Focused Ion Beam (FIB) systems have been steadily gaining acceptance as specimen preparation tools in the semiconductor industry. This is largely due to the fact that such instruments are relatively commonplace as failure analysis tools in semiconductor houses, and are commonly used in the preparation of cross-sections for imaging under the ion beam or using an electron beam in an SEM. Additionally, the ease with which cross-sectional TEM specimens of semiconductor devices can be prepared using FIB systems has been well demonstrated. However, this technology is largely unknown outside the semiconductor industry. Relatively few references exist in the literature on the preparation of cross-sectional TEM specimens of non-semiconductor materials by FIB.
This paper discusses a specific use of FIB technology in the preparation of cross-sectional TEM specimens of non-semiconductor samples that are difficult to prepare by conventional means. One example of such materials is commercial galvannealed steel sheet that is used to form corrosion resistant auto-bodies for the automobile industry. Cross-sectional TEM specimens of this material have proved difficult and time-intensive to prepare by standard polishing and ion milling techniques due to galvanneal's inherent flaking and powdering difficulties, as well as the different sputtering rates of the various Fe-Zn intermetallic phases present in the galvannealed coatings. TEM results from cross-sectional samples of commercial galvannealed steel coatings prepared by conventional ion milling and FIB techniques are compared to assess image quality, the size of the electron-transparent thin regions that can be readily prepared and the quality of samples produced by both techniques. Specimen preparation times for both techniques are reported.
Surface Science Aspects of Contamination in Tem Sample Preparation
Authors: Grant John T. , Walck Scott D. , Scheltens Frank J. , Voevodin Andrey A.
Published: April 2011

With the advent of the modem analytical electron microscope with its ultrahigh vacuum conditions, extremely high current density in a very small probe, and its light element analysis capability, it is imperative that contamination of the TEM sample, particularly by hydrocarbons, is eliminated. The degree of cleanliness required for analysis using surface sensitive techniques is also much greater than for other forms of analysis. Contamination of samples can occur (a) prior to analysis, due to the way samples are prepared or handled, or (b) during analysis. Examples of surface contamination prior to analysis and during analysis will be given, in order to illustrate their effect on an analysis.Polished Si, Ni, and Ti bulk samples and pre-thinned TEM Ni and Ti samples were intentionally contaminated by two methods. One set of samples was put on a liquid nitrogen cooled stage for one hour in a diffusion pumped Gatan Duomill in which the liquid nitrogen cold trap above the diffusion pump was intentionally left warm. The other set was contaminated by dipping them into a 100 ml solution of acetone containing 0.04 g of an acetone-soluble low temperature wax. Two commercially available plasma cleaners, specifically designed for eliminating hydrocarbon contamination, were used to clean the samples. The bulk samples were examined with x-ray photoelectron spectroscopy and the TEM samples were examined in a 200 keV analytical TEM. The results from these experiments will be discussed.
Kinetic Lattice Monte Carlo Simulations of Diffusion and Decomposition Kinetics In Fe-Cu Alloys: Embedded Atom and Nearest Neighbor Potentials
Authors: Wirth B. D. , Odette G. R.
Published: April 2011

In principle, Kinetic Lattice Monte Carlo (KLMC) methods can accurately simulate the precipitation of coherent phases by tracking the motion of a vacancy and the corresponding diffusion and clustering of solutes. The fidelity of the KLMC simulations depends primarily on the validity of the assumed interatomic potentials. These potentials must provide accurate solute-solute-solvent-vacancy energetics over the length scales relevant to the physical decomposition paths. Of course, simulating long range strain energy interactions is the biggest challenge, but the significance of this contribution is less in systems manifesting primarily dilational strains. Simple nearest neighbor (NN) potentials, used in previous KLMC of decomposition kinetics of dilute Fe-Cu alloys are generally not able to reproduce alloy property combinations like vacancy formation energies, dilute heats of solution and the coherent interface energies. Further, solute diffusion in bcc alloys requires jumps between first and second nearest neighbors, and is governed by, at minimum, at least three independent jump frequencies. The jump frequencies are controlled by the binding energies of atoms out to at least second nearest neighbor positions (which are only about 15% further away from the solute than the first nearest neighbor) and are also influenced by solute-modified saddle point activation energies. Thus longer range multiatom embedded-atom-method (EAM) type potentials can, in principle, provide a more realistic simulation of diffusion and solute clustering compared to NN based models. However, this refinement comes at a much higher computational cost. While they cannot be directly compared, this study presents KLMC results for both a simplified EAM versus a NN potential, and describes important new mechanistic insight provided by these atomistic simulations.
Computer Investigations on Phase Decomposition in Real Alloy Systems Based on a Discrete Type Phase Field Method
Authors: Miyazaki Toni , Koyama Toshiyuki , Kozakai Takao
Published: April 2011

On the basis of the discrete phase field method where the difference expression of non-linear kinetic equation, the composition dependencies of the atomic interchange energy and the inhomogeneous elasticity are taken into consideration so as to be applicable for the real alloy system. The phase decomposition and the microstructure formation are computer simulated for the Fe-Al- Co ternary ordering alloy by utilizing the thermodynamic data.
Mobility of Ag Atoms in the Binary System Ag2Se-Ag2S: A Molecular Dynamics Study
Authors: Smith A. , Ravelo R. , Pingitore N.
Published: April 2011

The compounds in the binary system Ag2Se-Ag2S are known to undergo a phase transition to a superionic phase at a temperature which varies with concentration. The diffusion mechanism of Ag ions have been studied in a Molecular Dynamics formalism. We have calculated the diffusion coefficient as function of temperature and concentration and have calculated the activation energy for diffusion from the Arrhenius plot of DAg vs temperature. Results obtained for the end points Ag2Se and Ag2S agree with experimental measurements.
Orientational Order Phase Transition in Solid C60
Authors: Soto J. R. , Valladares R. M. , Calles A.
Published: April 2011

The phonon spectrum and thermal parameters such as specific heat, effective temperature and amplitude of vibration of solid C60 are studied from ab-initio calculations. The relative orientations between the C60 balls are taken into account in a sc phase below 261.4K. The same properties are studied above the transition temperature (261.4K) where the balls are randomly oriented in a fcc structure. A difference is found in some of the thermal parameters due to the relative inter-molecular orientation. In particular, the low energy vibrational spectrum (which is separated by a ∼20meV gap from the intra-molecular spectrum) is changed.
Surface Energy Driven Crystallization of Amorphous Pd81si19
Authors: Schumacher Gerhard , Wahi Rajeshwar P.
Published: April 2011

In-situ TEM investigations during thermal treatment of amorphous Pd81Si19 have been performed. It was found that crystalline nuclei are formed near the perforation edge of the hole produced by electrochemical polishing. After impinging with neighboring crystals, a crystallization front formed which was aligned parallel to the perforation edge. The crystallization front moved in the direction perpendicular to the perforation edge. Crystal growth was found to proceed faster in thinner parts of the specimen than in thicker parts. The results are described qualitatively within a thermodynamic model taking into account volume-, surface- and interfacial free energies and an appropriate specimen geometry.
Magnetic Softening and Hardening in Metglas® 2605SC at the Onset of Nanocrystallization
Authors: Aburto S. , Jiménez M. , Marquina V. , Gómez R. , Marquina M. L. , Ridaura R. , Valenzuela R.
Published: April 2011

Mössbauer spectroscopy, coercive field and permeability were used to study the transformations produced by annealing at 375°C as-quenched amorphous ribbons of Metglas® 2605 SC of nominal composition Fe81B13.5Si3.5C2. The coercive field showed a decrease (softening) in the 0-30 min range, followed by an increase (hardening) for annealing times above 30 min. Permeability exhibited the opposite behavior, with a maximum for about 30 min. The Mössbauer magnetic hyperfine spectra showed variations in the intensities ratios, which were related with macroscopic measurements in good agreement with the softening-hardening processes.
Structural Stability Diagrams for Thin-Film Multilayers
Authors: Dregia S. A. , Banerjee R. , Fraser H. L.
Published: April 2011

Structural stability in thin-film multilayers is described in terms of classical thermodynamics, involving the competition between bulk and interfacial energies. A new type of phase diagram is introduced, thebiphase diagram,in which concurrent phase stabilities are mapped as a function of two degrees of freedom, corresponding to two independent layer thicknesses in a periodic multilayer. The model is used to explain our observations of phase stabilities in Al/Ti multilayers, as a function of varying layer thicknesses. The model is also applied to explain the experimental observations made by other investigators on phase stability in Co/Cr thin-film multilayers.
The Selective Synthesis of Molybdenum Silicides from Modulated Elemental Reactants
Authors: Johnson Christopher D. , Johnson David C.
Published: April 2011

Elementally modulated reactants with repeat layer thicknesses of less than 30Å were found to crystallize various molybdenum silicides depending on their composition. Reactants with compositions near 1:2 Mo:Si were found to nucleate h-MoSi2, at 400°C with an activation energy of 1.9eV, even though h-MoSi2 is metastable with respect to t-MoSi2 below 1900°C. Reactants with compositions near 5:3 Mo:Si were found to nucleate Mo3Si3 at 650°C with an activation energy of 3.0eV. Reactants with compositions near 3:1 Mo:Si were found to nucleate Mo3Si at 720°C with an activation energy of 2.2eV. The ability to control the crystalline product via the initial composition is distinctly different from the behavior reported for multilayers with larger repeat spacings, which were observed to form h-MoSi2 regardless of overall composition. The measured nucleation energy as a function of composition suggests that the phase selectivity is nucleation controlled. The selectivity depends on the elimination of large composition gradients at the reacting interfaces before nucleation of the crystalline product.
Formation of Metallic Systems Far From Equilibrium By Pulsed Laser Deposition
Authors: Krebs Hans-Ulrich , Hamp Marco , Fähler Sebastian , Störmer Michael , Sturm Kai , Weisheit Martin
Published: April 2011

The properties of metallic thin films prepared by pulsed laser deposition (PLD) strongly differ from samples grown by conventional thin film techniques like sputtering and evaporation. In many systems (Fe-Nb, Fe-Zr, Cu-Co, Fe-Ag and Ni-Ag), strongly supersaturated solid solutions are formed, a broader formation range occurring for amorphous samples, and nanocrystalline phases are produced. Additionally, metastable phases of larger thickness at the interfaces of multilayers occur. Reasons for these behaviors are discussed with respect to atomic mixing and implantation effects induced by the high instantaneous deposition rate during PLD and the high kinetic energy (>100 eV) of the deposited ions.
Phase Stability in the Nanocrystalline Tio2 System
Authors: Zhang Hengzhong , Banfield Jillian F.
Published: April 2011

Initial thermodynamic analysis predicts surface tension of fine solid particles decreases with decrease in particle size. Free energy of fine solid particles increases with decrease in particle size. In the nanocrystalline TiO2 system, the surface tensions and the surface energies of both anatase and rutile were estimated by modeling available thermochemical data and kinetic data. The particle size versus temperature phase diagram of the nanocrystalline TiO2 system was calculated, which reveals 1–8 nm anatase is more stable than rutile of the same size at certain temperatures.
Low-Temperature Mechanical Alloying Of Cu-Fe and Cu-Ta Powders
Authors: He J.-H. , Ma E.
Published: April 2011

A model analysis is presented which explains ball-milling induced alloying in positive-heatof- mixing systems in terms of a dynamic balance between externally forced mixing and thermal phase decomposition mediated by deformation-enhanced population of defects. The possibility of eliminating the thermal decomposition to force single phase formation is examined by milling Cu- Fe and Cu-Ta powder mixtures at the liquid nitrogen temperature (LN2T). Over a range of compositions for Cu-Fe and almost the entire composition range for Cu-Ta, the two-phase region observed for room-temperature (RT) milling persisted after cryomilling. The moderate temperature dependence of milling-induced alloying is interpreted by analyzing the dynamics of the generation and annihilation of the nonequilibrium vacancies during deformation and impacts in a SPEX mill.
Phase Evolution During Ball Milling of Al In NH3 and Subsequent Annealing
Authors: Nikolov J. I , Williams J. S. , Llewellyn D. J. , Calka A.
Published: April 2011

Phase evolution during ball milling of Al in both N2 and NH3 gas has been compared and the annealing behaviour studied in some detail. X-ray diffraction, differential thermal analysis, combustion analysis and scanning and transmission electron microscopy have been used as analytical techniques. Results have shown that a nitride is not formed in N2 but that Al forms into many small, hollow spheres during milling. In contrast, milling in NH3 results in an amorphous AlxNy(O) phase which transforms into crystalline AIN and A12O3 on annealing to 1000°C.
The Effect of Hydrogen Carrier Gas on the Morphological Evolution and Material Properties of GaN on Sapphire
Authors: Ng T. B. , Han J. , Biefeld R. M. , Zolper J. C. , Crawford M. H. , Follstaedt D. M.
Published: April 2011

In-situ optical reflectance is used to monitor the morphological evolution of the two-step GaN growth on sapphire. The amount of H2 carrier gas used in the growth is observed to strongly influence the morphological evolution of the low temperature buffer layer and the subsequent high temperature nucleation behavior, which in turn affects the structural and electrical properties of the GaN epitaxial films. The optical reflectance transients correlate with the sizes and distributions of nuclei as observed by AFM.
Diluent Gas Effects on Properties of Ain and GaN Thin Films Grown by Metalorganic Vapor Phase Epitaxy on α(6H)-SiC Substrates
Authors: Hanser Andrew , Wolden Colin , Perry William , Zheleva Tsvetanka , Carlson Eric , Hartlieb Philip , Davis Robert F.
Published: April 2011

Thin films of AIN and GaN were deposited on α(6H)-SiC(0001) wafers using metalorganic vapor phase epitaxy (MOVPE) and H2 and N2 diluents. A computational fluid dynamic model of the deposition process was used to analyze the film growth conditions for both diluents. Low temperature (12 K) photoluminescence of the GaN films grown in N2 had peak intensities and full widths at half maximum of ∼7 meV which were equal to or better than those films grown in H2. Cross-sectional and plan-view transmission electron microscopy of films grown in both diluents showed similar microstructures with a typical dislocation density of 109/cm2. Hall measurements of n-type (Si doped) GaN grown in N2 revealed Hall mobilities equivalent to those films grown in H2. Acceptor-type behavior of Mg-doped GaN grown in N2 was repeatably obtained without post-growth annealing. Secondary ion mass spectrometry revealed equivalent levels of H in Mg-doped GaN films grown in both diluents.
AIN/GaN and AIGaN/GaN Heterostructures Grown by HVPE on SiC Substrates
Authors: Melnik Yu. V. , Nikolaev A. E. , Stepanov S. I. , Zubrilov A. S. , Nikitina I. P. , Vassilevski K. V. , Tsvetkov D. V. , Babanin A. I. , Musikhin Yu. G. , Tretyakov V. V. , Dmitriev V. A.
Published: April 2011

GaN, AIN and AIGaN layers were grown by hydride vapor phase epitaxy. 6H-SiC wafers were used as substrates. Properties of AIN/GaN and AIGaN/GaN structures were investigated. AIGaN growth rate was about 1 μm/min. The thickness of the AIGaN layers ranged from 0.5 to 5 μm. The AIN concentration in AIGaN layers was varied from 9 to 67 mol. %. Samples were characterised by electron beam micro analysis, Auger electron spectroscopy, X-ray diffraction and cathodoluminescence.

Electrical measurements performed on AIGaN/GaN/SiC samples indicated that undoped AIGaN layers are conducting at least up to 50 mol. % of AIN.
Sublimation Sandwich Growth of Free Standing GaN Crystals
Authors: Vodakov Yu. A. , Mokhov E. N. , Ramm M. G. , Ramm M. S. , Roenkov A. D. , Ostroumov A. G. , Wolfson A. A. , Karpov S. Yu. , Makarov Yu. N. , Jürgensen H.
Published: April 2011

Thick epitaxial layers of GaN on SiC and sapphire are grown by using the sublimation sandwich method. It is shown that growth of good quality GaN crystals with the growth rates up to 0.5 mm/hour is possible using this technique. The grown layers have been separated from the seed and free standing GaN crystals up to 15 mm size were obtained.
MBE Growth of GaN on NdGaO3(101)
Authors: Fechtmann C. , Kirchner V. , Einfeldt S. , Heinke H. , Hommel D. , Lukasiewicz T. , Luczynski Z. , Baranowski J.
Published: April 2011

We report on the growth of GaN on NdGaO3(101) by plasma assisted molecular beam epitaxy (MBE). NdGaO3(101) is an interesting alternative substrate compared to A12O3due to its smaller lattice mismatch of +1.2 % to hexagonal (0001) GaN. Using photoluminescence (PL), X-ray diffraction (XRD), reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM) the optical and structural properties of the GaN thin films grown on NdGaO3are investigated and compared to those grown on c-plane sapphire. The intended epitaxial relationship of [0001] GaN ║ [101] GaN is hard to realise as confirmed by several tilted or even polycrystalline films. However, the layer quality was found to improve considerably, when the NdGaO3surface showed a (l × 1) instead of other reconstructions.
Single Crystal Gallium Nitride on Silicon Using SiC as an Intermediate Layer
Authors: Ustin S. A. , Ho W.
Published: April 2011

GaN films have been grown atop SiC intermediate layers on Si(001) and Si(111) substrates using supersonic jet epitaxy (SJE). GaN growth temperatures ranged between 600 °C and 775 °C. Methylsilane (H3SiCH3) was used as the single source precursor for SiC growth and triethylgallium (TEG) and ammonia (NH 3) were the sources for GaN epitaxy. The GaN growth rate was found to depend strongly on substrate orientation, growth temperature, and flux. Structural characterization of the films was done by transmission electron diffraction (TED) and x-ray diffraction (XRD). Growth of GaN on SiC(002) produces a cubic or mixed phase of cubic and wurtzite depending on growth conditions. Growth on SiC(111) produces predominantly wurtzite GaN(0002). Minimum rocking curve widths for GaN(0002) on SiC/Si(111) and GaN(002) on SiC/Si(001) are 0.6° and 1.5°, respectively. Cross Sectional Transmission Electron Microscopy (XTEM) was also performed.
Structural and Optical Properties of Group III-Nitride Quantum Wells Studied by (S)Tem and CL
Authors: Lakner H. , Liu Q. , Brockt G. , Radefeld A. , Schulze-Kraasch F. , Scholz F.
Published: April 2011

Wurtzite InGaN/GaN and AlGaN/GaN heterostructures grown on sapphire by metal organic vapor phase epitaxy were studied using scanning transmission electron microscopy (STEM), cathodoluminescence (CL) combined with secondary electron (SE) imaging, high resolution x-ray diffractometry (HRXRD), and atomic force microscopy (AFM).

SE imaging and AFM were used to study the surface morphology. The results indicate the presence of the following structural defects on the surface of InGaN/GaN heterostructures: hexagonal mesa-like structures, hexagonal pyramids and micropipes, while the surface of the AlGaN/GaN heterostructures are mirror-like smooth. The local optical properties of defects and defect free regions were studied using spatially resolved CL at low temperature. In addition, the dependence of the optical properties of both sorts of heterostructures on the quantum well width or chemical composition of ternary materials was investigated. The structural properties of the heterostructures were studied by STEM and HRXRD. Convergent beam electron diffraction (CBED) and corresponding simulations, convergent beam imaging (CBIM), and high resolution x-ray diffraction (HRXRD) were used to study the strained layers. Dislocations and interface properties were characterized using bright-field imaging, while the chemical compositions fluctuations were analyzed by Z-contrast imaging and energy dispersive x-ray microanalysis (EDX).
Organometallic Chemical Vapor Deposition of Group-III Nitride Thin Films using Single Source Precursors
Authors: Fischer Roland A. , Rogge Wolfram
Published: April 2011

The OMCVD of AlN, GaN and InN thin films using the novel single source precursors (N3)2Ga[(CH2)3NMe2] (1), (N3)In[(CH2)3NMe2]2 (2) and (N3)Al(CH2)3NMe2]2 (3) is reported. The compounds are non-pyrophoric. Compound 2 is air stable. No additional N-sources were used for the growth of the nitrides. We achieved epitaxial (AlN, GaN) or polycrystalline (InN) growth at least 200°C below the decomposition temperature of the respective nitride. Some aspects of the reactivity of the precursors with ammonia and the resulting influence on the deposition process were investigated.
In-Situ Rheed-Traxs Monitoring Alloy Composition of the Surface During RF-MBE Growth of GaInN and AIGaN
Authors: Ito A. , Sakai H. , Inagaki M. , Nomura G. , Nakamura Y , Yasuda T. , Amano H. , Akasaki I.
Published: April 2011

In-situ reflection high energy electron diffraction total reflection angle X-ray spectroscopy (RHEED-TRAXS) was performed to monitor alloy composition at the surface during growth of nitrides by RF-MBE for the first time. TRAXS signal of the GaLα line is found to be more sensitive to the composition at the surface than the GaKαline. A difference in the composition of layer adsorbed on the surface and the solid alloy layer has been identified.