bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanobumps in InxAl1-xN/AlN/Sapphire System:A New Kind of Quantum Dots?
Authors: Danylyuk Yuri , Romanov Dmitri , Auner Gregory
Published: April 2011

We have investigated InxAl1-xN layers grown by plasma source molecular beam epitaxy (PSMBE) on c-plane sapphire (0001) substrates with thin (about 100 Å) buffer layers of AlN. The value of x varied from 0 to 1. For all these layers, high resolution X-ray diffraction scans (XRD) show no indication of face segregation, while the atomic force microscope (AFM) images of the structures demonstrate a large number of nanobumps. Our spectroscopic measurements (UV/VIS optical absorption and reflection spectroscopy) of these bumpy structures indicate additional peaks that can be only associated with additional energy levels. We ascribe these levels to electrons, which are confined and quantized near the nanobump tips by strong piezoelectric field caused mainly by biaxial strain of the AlN layer. The calculated energies of these quantized states are in a good agreement with the spectroscopic data.
Optical Absorption of Nitrogen Vacancy in Proton Irradiated AlxGa1-xN thin Films
Authors: Zhou Qiaoying , Manasreh M. O. , Pophristic M. , Ferguson Ian T. , Weaver B. D.
Published: April 2011

Optical absorption measurements were used to investigate deep defects in proton irradiated doped and undoped AlGaN thin films grown on sapphire substrates. Several samples were proton irradiated with energies ranging between 10 keV and 1 MeV. In certain samples, multiple-energy ion implantation was found necessary to produce a defect, which is responsible for the absorption band observed at 4.61 eV with a shoulder at around 4.10 eV in Al0.6Ga0.4N. Furnace thermal annealing of the irradiated samples show that this absorption band starts to anneal out at temperature as low as 200 oC. A combined isochronal and isothermal annealing in the temperature range of 200- 350°C shows that the activation energy (enthalpy associated with the migration process) of this defect is approximately 0.41 eV. This leads us to conclude that this absorption band is due to a N-vacancy related defect. It is observed that the peak position energy of the absorption band due to this defect is shifted depending on the Al mole fraction in good agreement with the theoretical predictions.
Interface roughness, Localization and Radiative Efficiency in InGaN/GaN light emitters
Authors: Singh Madhusudan , Singh Jasprit
Published: April 2011

Quantum wells based in InGaN and GaN have been actively studied over the past serveral years for light emission. It has been seen that in spite of substrate mismatch related dislocation densities of ~107–108 cm-2, one can have reasoable quantum efficiencies in these quantum w ells. In this paper, w ewill explore ho wearrier localization influences radiative efficiency in InGaN/GaN quantum wells. Analysis is done about the relative effects of in terface roughness and effectof potential modification owing to alloy fluctuation in InGaN. This is necessary as InGaN has a large miscibility gap.
Application of Amorphous GaN for Electroluminescence Device
Authors: Honda Tohru , Kawanishi Hideo
Published: April 2011

The vacuum evaporation of GaN thin films using GaN powder (5N) for GaN-based electroluminescence devices (ELDs) is reported. The crystal structures of the evaporated GaN layers were amorphous, which was confirmed from reflection high-energy electron diffraction (RHEED) patterns. Auger electron spectra revealed that the layers have excess Ga metal. Bluish-white light emission was observed from the GaN-based ELD under AC operation at RT. Although the emission intensity was weak, the electroluminescence spectra started from the band edge of h-GaN.
High Mobility Nitrides
Authors: Scott K. , Butcher A. , Wintrebert-Fouquet Marie , Chen Patrick P.–T. , Tansley Trevor L. , Srikeaw Surapon
Published: April 2011

The highest mobility nitrides ever grown were indium nitride polycrystalline thin films. The original reactive ion sputtering unit used to produce those films is still in existence and has been substantially upgraded. In this paper we describe some of the parameters that are important for high purity indium nitride growth, while providing the most recent results for films grown with the upgraded system. A long lag time (greater than 100 hours of growth time) has been observed before obtaining stable material properties for a given set of growth conditions.
Electron and Hole Confinement in GaInN/GaN and AlGaN/GaN Quantum Wells
Authors: Hangleiter A. , Lahmann S. , Netzel C. , Rossow U. , Kent P. R. C. , Zunger A.
Published: April 2011

We show that the strong bowing of the bandgap of GaInN, which is primarily due to bowing of the valence band edge, translates into a strongly composition dependent ratio of the conduction band offset to the valence band offset with respect to GaN. For common In mole fractions of 0-20 % this leads to a reversal of the band offset ratio and to very weak electron con nement. This theoretical picture is veri ed by comparing results of time-resolved spectroscopy on asymmetric AlGaN/GaInN/GaN and AlGaN/GaN/AlGaN quantum wells. Since electron con nement is much stronger for GaN/AlGaN wells than for GaInN/GaN wells, the effect of asymmetry is very weak for the former and fairly strong for the latter.
Measurements of the Band Offset of SiO2 on Clean GaN
Authors: Hurt E.H. , Cook Ted E. , Tracy K.M. , Davis R.F. , Lucovsky G. , Nemanich R.J.
Published: April 2011

The band alignment of SiO2 and GaN is important for passivation of high voltage devices and for gate insulator applications. In this study XPS and UPS techniques are employed to determine the electronic states as SiO2 is deposited onto a clean GaN surface. The substrate was epitaxially grown n-type GaN on 6H-SiC (0001) substrates with an AlN (0001) buffer layer. The GaN surface was atomically cleaned via a 860°C anneal in an NH3 atmosphere. For the clean GaN surface, upward band bending of ~0.3 ±0.1 eV was measured, and the electron affinity was measured to be ~2.9 eV. Layers of Si were deposited on the GaN surface via Molecular Beam Epitaxy (MBE), and the Si was oxidized by a remote O2 plasma. The oxidation of the Si occurred without oxidizing the GaN. Densification of the created SiO2 film was achieved by annealing the substrate at 650°C. Surface analysis techniques were performed after each process, and yielded a valence band offset of ~2.0 eV, and a conduction band offset of ~3.6 eV for the GaN-SiO2 interface.
Electromagnetic Waves Through Disordered Systems: Comparison of Intensity, Transmission and Conductance
Authors: Zypman Fredy R , Cwilich Gabriel
Published: April 2011

We obtain the statistics of the intensity, transmission and conductance for scalar electromagnetic waves propagating through a disordered collection of scatterers. Our results show that the probability distribution for these quantities x, follow a universal form, YU(x) = xne−xμ. This family of functions includes the Rayleigh distribution (when α=0, μ=1) and the Dirac delta function (α →+ ∞), which are the expressions for intensity and transmission in the diffusive regime neglecting correlations. Finally, we find simple analytical expressions for the nth moment of the distributions and for to the ratio of the moments of the intensity and transmission, which generalizes the n! result valid in the previous case.
Photonic Crystals at Near-Infrared and Optical Wavelengths
Authors: Moroz Alexander
Published: April 2011

As demonstrated for the example of a diamond and zinc blende structure of dielectric spheres, small inclusions of a low absorbing metal with the volume fraction fm can have a dramatic effect on a complete photonic band gap (CPBG) between the 2nd-3rd bands. For example, in the case of silica coated silver spheres, the CPBG opens for fm ≍ 1.1% and exceeds 5% for fm ≍ 2.5%. Consequently, any dielectric material can be used to fabricate a photonic crystal with a sizeable and robust CPBG in three dimensions. Absorption in the CPBG of 5% remains very small (≤ 2.6% for λ ≥ 750 nm). The structure enjoys almost perfect scaling, enabling one to scale the CPBG from microwaves down to ultraviolet wavelengths.
Photonic Crystal Narrow Pass-band Filtersa
Authors: Ouyang Zhengbiao , Liu Haishan , Li Jingzhen
Published: April 2011

We present a photonic crystal narrow pass-band optical filter, which is made of two pieces of photonic crystals with different photonic band gaps. Our numerical investigations show that this kind of structure is feasible for narrow pass-band optical filtering. The pass-band may be less than 0.1nm in the infrared communication frequency band. In ideal cases, the optical transmission in the pass band is very close to 1. This means a very low insert energy loss.
The Correlation of Indentation Size Effect Experiments with Pyramidal and Spherical Indenters
Authors: Swadener J. G. , George E. P. , Pharr G. M.
Published: April 2011

Experiments were conducted in annealed iridium using pyramidal and spherical indenters over a wide range of load. For a Berkovich pyramidal indenter, the hardness increased with decreasing depth of penetration. However, for spherical indenters, hardness increased with decreasing sphere radius. Based on the number of geometrically necessary dislocations generated during indentation, a theory that takes into account the work hardening differences between pyramidal and spherical indenters is developed to correlate the indentation size effects measured with the two indenters. The experimental results verify the theoretical correlation.
Pressure Assisted Crystallization of MnAl Thin Films
Authors: Fischer Gregory A. , Rudee M. Lea , Nesterenko Vitali F. , Indrakanti Sastry
Published: April 2011

The effect of hot isostatic pressure processing (HIP) on MnAl films has been compared to vacuum annealing for the purpose of obtaining substantial amounts of tau phase MnAl in films under 200 nm. Films were deposited by dc sputtering from both MnAlNiC an MnAl targets. As-deposited films were nearly amorphous. Post deposition annealing in vacuum produced only small amounts of the ferromagnetic tau-phase in films thinner than 200 nm.

In all instances, regardless of substrate and sputtering target, the use of HIP in place of vacuum annealing increased the degree of crystallinity of the samples when compared to those annealed in vacuum. For the 100 nm samples deposited from the MnAlNiC target, these changes in crystallinity were accompanied by changes in the M-H loops of the samples. MnAlNiC HIP samples had improved magnetic properties compared to those of equal thickness annealed in vacuum. The 100 nm HIP sample sputtered from the MnAl target also showed an increase in moment, though the changes were not as dramatic as those seen in the samples sputtered from the MnAlNiC target.

The 50 nm films from both targets also showed a change in crystallinity when compared to vacuum annealed samples. These films, unlike the 100 nm films, had ferromagnetic properties that were no better than those of the vacuum annealed samples. This suggests that while the 2 kbar of pressure used in this study assists in the formation of tau-phase in 100 nm films, the appropriate pressure for forming tau-phase in 50 nm films is yet to be determined.
MOCVD ZnS:Mn Films: Crystal Structure and Defect Microstructure as a Function of the Growth Parameters
Authors: Dunn Kathleen A. , Dovidenko Katharine , Topol Anna W. , Shekhawat Gajendra S. , Geer Robert E. , Kaloyeros Alain E.
Published: April 2011

Thin film electroluminescent devices employing zinc sulfide doped with manganese are extensively used for applications in which the weight, brightness and mechanical robustness requirements preclude the use of other types of displays such as cathode ray tubes or liquid crystal displays. The physical, optical and electrical properties of phosphors such as ZnS:Mn can often depend strongly on microstructure, which in turn depends on the growth and processing of the film. For this study, ZnS:Mn layers were fabricated by metalorganic chemical vapor deposition (MOCVD) in the 250°-500°C range on an Al2TiO/ In2SnO5 /glass stack. Selected samples were then subjected to a post-deposition anneal in H2S/Ar at 700°C for up to 4 hours. The microstructure of the ZnS:Mn films was examined by Transmission Electron Microscopy (TEM). For all growth and annealing conditions, the films consisted of columnar grains whose column axis was parallel to the growth direction, and which widened laterally through the thickness of the films. For the as-deposited films, the crystal structure was found to be predominantly 2H structure, with the 8H polytype being identified in the low-temperature ZnS:Mn films. The 700°C post-deposition annealing was found to initiate a solid state transformation to the cubic (3C) ZnS crystal structure. All films contained high densities of stacking faults and microtwins, whose role in the 2H-3C transformation is discussed. Also discussed are initial Ultrasonic Force Microscopy (UFM) results which suggest a correlation between the defect microstructure and the elastic response of the material.
Relaxation of Grain Boundaries in Au {110} Mazed Bicrystal Thin Films Observed by HREM
Authors: Radetic Tamara , Dahmen Ulrich
Published: April 2011

Thin films of gold can be grown on {001} Ge single crystal substrates in two equivalent {110} orientation variants, related to each other by a 90° rotation about the surface normal. The morphology of the films is that of a mazed bicrystal, a polycrystalline film with many randomly distributed columnar grains in only two orientations. All grain boundaries are of the type S99 and display pure tilt character. In this work, we report on observations of the structural relaxation of these grain boundaries, with special emphasis on their characteristic behavior at the intersection with free surfaces and their evolution during thermal annealing.
Texture of Sputtered Thin Copper Films on Amorphous SiO2 and Si3N4 substrates.
Authors: Okolo Brando , Welzel Udo , Lamparter Peter , Wagner Thomas , Mittemeijer Eric J.
Published: April 2011

Cu films with thickness of 500nm and 5nm have been sputter deposited on amorphous SiO2 and Si3N4 substrates without and after sputter cleaning. The crystallographic texture has been characterized by x-ray diffraction techniques. Sputter cleaning of the substrates, by which the oxygen contaminants are removed from the Si3N4 substrates, leads to an increase in the {111} texture strength and sharpness of the Cu films on Si3N4. The texture is sharper in the 500nm thick Cu films than in the 5nm thick films. Roughness differences of the substrate surfaces have no obvious effect on the texture state.
Relaxation of a Strained Elastic Film on a Viscous Layer
Authors: Huang R. , Yin H. , Liang J. , Hobart K. D. , Sturm J. C. , Suo Z.
Published: April 2011

Experiments were conducted with SiGe film islands on a layer of borophosphorosilicate glass (BPSG). Initially the SiGe is under compression. Upon annealing, the glass flows and the SiGe islands relax by both inplane expansion and wrinkling. This paper provides a two-dimensional (2D) model for inplane expansion. The results from the model are compared with the experiments with small SiGe islands. The effect of winkling, which is ignored in the present model, is discussed qualitatively.
Near-Edge X-ray Absorption Fine Structure of Hard Carbon Film Formed by Gas Cluster Ion Beam Assisted Deposition
Authors: Kanda Kazuhiro , Shimizugawa Yutaka , Haruyama Yuichi , Yamada Isao , Matsui Shinji , Kitagawa Teruyuki , Terasawa Mititaka , Tsubakino Harushige , Gejo Tatsuo , Kamada Masao
Published: April 2011

The coordination of the carbon atoms in the diamond-like carbon (DLC) films formed by Ar gas cluster ion beam (GCIB) assisted deposition of fullerene was investigated using synchrotron radiation. Near-edge x-ray absorption fine structure (NEXAFS) spectra of the carbon K-edge of the DLC films formed by various methods were measured over the excitation energy range 275-320 eV, using synchrotron radiation. On the basis of the analysis of the peak corresponding the transition of the excitation electron from carbon 1s orbital to Φ orbital, relative sp2 contents of various DLC films were determined. The DLC films formed by Ar GCIB assisted fullerene deposition were found to consist of a high sp3 hybridized carbon.
Thin Film Characterization Using the Point-Deflection Method
Authors: Tang Ning , Engelstad Roxann L. , Lovell Edward G.
Published: April 2011

The Point-Deflection Method is a potentially useful technique for measuring the internal stresses of freestanding thin films. By applying a small concentrated transverse load at the center of a pre-stretched film, and measuring the corresponding out-of-plane displacement at appropriate locations, the average internal stress can be readily determined. The load-deflection relationship has been derived for both circular and rectangular shapes. The method involves no additional micromachining in sample preparation and has low sensitivity to the variations in boundary constraints. Its feasibility has been further substantiated with finite element simulations from a variety of perspectives, as well as experimental correlations from the stress measurements of a photomask pellicle film.
A Method for Extracting Quantitative Data Duringin-situTEM Nanoindentation
Authors: Minor A.M. , Lilleodden E.T. , Stach E.A. , Morris J.W.
Published: April 2011

The development of a novel transmission electron microscope holder has made real time observations of nanoindentation possible. Using a piezo-ceramic loading mechanism, a diamond indenter is pushed into the surface of a sample, while the electron beam images the deforming sample in cross section. In this paper, we present the method for calibrating the force-displacement-voltage relation and load-frame compliance associated with this instrument. This allows quantitative force-displacement measurements to be obtained, in the manner of traditional indentation experiments. As an example of the utility of this technique, we present observations of the indentation behavior of an Al thin film on silicon, which have been previously shown [1]. Indentation into a coarse grain shows a displacement excursion corresponding to the nucleation of dislocations, and is compared to force-displacement responses measured with instrumented indentation techniques.
Nano-Creep Test for Anatase Polycrystalline Films
Authors: Sugata Hironori , Ohshio Shigeo , Saitoh Hidetoshi
Published: April 2011

We introduce an analytical technique for time-dependent deformation behavior of the polycrystalline films using a nano-indenter. This technique permits evaluation of structural deformation of the nanometer scale of the thin films. In this paper, good accuracy conditions were determined to measure deformation behavior of the polycrystalline films. The polycrystalline films of anatase were used to investigate the grain boundary structure. We prove that the analysis of time-dependent deformation behavior is effective to investigate the structure of the polycrystalline films.
Mechanistic Understanding of the Stress-Induced Failure of Si3N4 Metal-Insulator-Metal Capacitors
Authors: Suh Dongwoo , Mheen Bongki , Lee Seung-Yun , Shim Kyu-Hwan , Kang Jin-Yeong
Published: April 2011

The failure of Si3N4 metal-insulator-metal (MIM) capacitors fabricated by plasma enhanced chemical vapor deposition (PECVD) was investigated using cross-sectional transmission electron microscopy (XTEM) and residual stress analysis. As a result we noted that the failure of the Si3N4 MIM capacitors originated from the microvoids formed over the Si3N4 dielectric and the TiN interlayer. The microvoid of the MIM capacitor, particularly in case of having a very thin Si3N4 of less than 50 nm-thick, caused it to leak out much of the current to the extent of a few microamperes even at bias of 3 volts. The formation of microvoids was explained by the residual stress of the constituent layers at a mechanistic point of view. The stress analysis showed that the absolute stress normalized by the thickness of the Si3N4 layer should be less than 31 MPa/nm to avoid microvoiding. In this research it was noted in conclusion that the stress state of not only the dielectric but also the interlayer should be taken into account for the successful design of high capacitive Si3N4 MIM capacitors.
Effects of Various Passivation Dielectrics and Via Reservoir Lengths on Stress and Electromigration Reliability of Metal Interconnects
Authors: Park Young-Bae , Cho Young-Ah , Lee Won-Gyu
Published: April 2011

Reservoir length dependencies of electromigration lifetime in multilevel interconnect were compared for two passivation dielectrics, that is, FOX (Flowable Oxide) and HDP FSG (High Density Plasma Fluorinated Silicate Glass). The higher electromigration resistance of interconnects passivated by FOX can be best explained by their lower stress and vacancy concentration levels than the case for FSG. It was also proposed that lower levels of stress and vacancy concentration in the longer reservoir could partially contribute to the better electromigration reliability of interconnect with the longer reservoir.
The Design of Multilayered Polysilicon for MOEMS Applications
Authors: Sherman D. , Kahn H. , Phillips S.M. , Ballarini R. , Heuer A.H.
Published: April 2011

A rigorous analysis of a multilayered polysilicon laminated system, constructed by alternating deposition of low-pressure chemical vapor deposition (LPCVD) polysilicon at two different temperatures is presented. Different residual deformation fields are generated in these polysilicon thin films as a function of fabrication temperatures, due to different crystallization behavior at the two temperatures. The combination of the two layers, however, enables precise control of the radius of curvature of released structures, provided the material properties are well defined. We describe a new method, which combines experimental and numerical procedures, to define the material properties, which are responsible for the residual stresses as a function of layer thickness, as well as a procedure to design the desired curvature of a multilayered Micro-optical-electromechanical system (MOEMS) device. A linear deformation field is assumed. It is shown that precise design of the thicknesses of the individual layer is a prerequisite for controlled curvature. The procedure we have developed predicts the curvature of multilayered polysilicon systems with good precision.
Wear and Adhesion Optimization of Thin TiAlN Films by Structure Design
Authors: E. Lugscheider , Knotek O. , Bobzin K. , Beckers M. , Colmenares C. , Leyendecker A. , Erkens G.
Published: April 2011

The structure of TiAlN and other thin films depends on the coating method, parameter variation and an eventual treatment of the coating after deposition. Concerning the coating process, reactive sputter and evaporation parameters influence structure formation as well as plasma driven chemical reaction on the substrate surface. Besides, crystal formation and agglomeration depends on energetic level and flow rates in the coating system, the kind and number of reactive partners, temperature and specific parameters of the coating plant.

Post-deposition treatments on the other hand may influence the formation of residual stresses but not the crystallization of different phases within the complete coating. Besides, mechanical treatment may change the coating's morphology which may be important depending on the application since sometimes a columnar structure is to be optimized in size, amount and location. Thus a homogeneous coating is not always the optimum solution. In the experiments presented here we investigated the wear properties of thin TiAlN films. They were post-treated by sandblasting and heating in order to reduce frictional forces between the contacting bodies or analyze the effects of elevated temperatures respectively. These wear properties were evaluated by turning of 42CrMo4V at low cutting speed.
Coarse-Grained Molecular Dynamics: Dissipation Due to Internal Modes
Authors: Rudd Robert E.
Published: April 2011

We describe progress on the issue of pathological elastic wave reflection in atomistic and multiscale simulation. First we briefly r eview Coarse-Grained Molecular Dynamics (CGMD). Originally CGMD was formulated as a Hamiltonian system in which energy is conserved. This formulation is useful for many applications, but recently CGMD has been extended to include generalized Langevin forces. Here we describe how Langevin dynamics arise naturally in CGMD, and we examine the implication for elastic wave scattering.
Self-assembling and Ordering of Ge/Si Quantum Dots on Flat and Nanostructured Surfaces
Authors: Motta N. , Sgarlata A. , Balzarotti A. , Rosei F.
Published: April 2011

We have studied by Scanning Tunneling Microscopy (STM) the effect of step bunching on Ge/Si(111) epitaxy. We have verified that self-organization of Ge islands is greatly influenced by “step bunching” which arises from the flash-annealing procedure used to reconstruct the Si surface. Two different growth regimes arise: initially islands nucleate and evolve only at steps, up to complete ripening; subsequently the same evolution is observed on flat areas of the sample. The average distance between islands and steps is nearly constant, originating a single row of equally spaced islands, followed by other rows of islands in between. The exploitation of this phenomenon, which is governed by the surface diffusion length of Ge on Si (estimated from our data) and by the terrace width, constitutes one possible path to achieve self-organization of quantum dots.
Optical and structural prorerties of InAs epilayer on graded InGaAs
Authors: Kim Gu Hyun , Choi Jung Bum , Lee Joo In , Kang Se-Kyung , Ban Seung Il , Kim Jin Soo , Kim Jong Su , Lee Sang Heon , Leem Jae-Young
Published: April 2011

We have studied infrared photoluminescence (PL) and x-ray diffraction (XRD) of 400 nm and 1500 nm thick InAs epilayers on GaAs, and 4 nm thick InAs on graded InGaAs layer with total thickness of 300 nm grown by molecular beam epitaxy. The PL peak positions of 400 nm, 1500 nm and 4 nm InAs epilayer measured at 10 K are blue-shifted from that of InAs bulk by 6.5, 4.5, and 6 meV, respectively, which can be largely explained by the residual strain in the epilayer. The residual strain caused by the lattice mismatch between InAs and GaAs or graded InGaAs/GaAs was observed from XRD measurements. While the PL peak position of 400 nm thick InAs layer is linearly shifted toward higher energy with increase in excitation intensity ranging from 10 to 140 mW, those of 4 nm InAs epilayer on InGaAs and 1500 nm InAs layer on GaAs is gradually blue-shifted and then, saturated above a power of 75 mW. These results suggest that adopting a graded InGaAs layer between InAs and GaAs can efficiently reduce the strain due to lattice mismatch in the structure of InAs/GaAs.
In-situ surface x-ray scattering study on the buried interfacial layer of Co/Si(111) interface
Authors: Kang Tae Soo , Je Jung Ho , Kim Hyo Jung , Noh Do Young , Kim Nam Dong , Chung Jin Wook
Published: April 2011

The highly strained interfacial structure and reaction of Co on Si(111) in the initial growth stage was studied by in-situ surface x-ray scattering. Co was deposited on Si(111) – (7×7) reconstruction by electron beam evaporation in ultra high vacuum. Our study reveals that the interfacial layer, formed by the reaction of Co with Si in the initial growth stage at room temperature, is a silicide layer with stoichiometry of Co2Si. The interfacial silicide layer is a commensurate phase of pseudohexagonal Co2Si, which shows a significant local atomic displacements imposed by Si substrate. The intensity oscillations at the anti-Bragg position with Co coverage show that a layer-by-layer consumption of silicon substrate occurs for the first 15 monolayers (ML) of Co deposited.
SiGe Epilayer Stress Relaxation: Quantitative Relationships Between Evolution of Surface Morphology and Misfit Dislocation Arrays
Authors: Gray Jennifer L. , Hull Robert , Floro Jerrold A.
Published: April 2011

Stress relaxation mechanisms have been investigated during growth of SiGe/Si heterostructures in a regime where misfit dislocations and surface morphological evolution strongly interact. Stress evolution was measured in real time using in situ wafer curvature measurements during molecular beam epitaxy of Ge0.3Si0.7 on Si (001). This real-time data has been combined with detailed analysis of the evolving surface morphology and misfit dislocation density using atomic force microscopy and transmission electron microscopy. Several distinct stages of microstructural evolution were observed during epitaxial growth of Ge0.3Si0.7alloys at intermediate temperatures (550°C) and relatively high deposition rate (0.9 Å/s). Initial planar, coherent growth was followed by pyramidal pit formation in the metastable wetting layer for 15nm thick films. Subsequent cooperative nucleation of island ridges occurs along <100> directions surrounding the pits. Dislocations are next introduced into the film abruptly at 50nm film thickness and relieve 40% of the film stress by 100nm of growth. Cross-hatch features aligned along the <110> directions accompany the introduction of misfit dislocations. As the dislocation density increases in the film, the coherent island/pit structures begin to disappear and the film morphology is dominated by the evolving cross-hatch. Implications for competitive and/or correlated relaxation of strain by misfit dislocations and surface morphology based upon this data will be discussed. This work demonstrates that combining real-time stress measurements with microscopy enables mechanistic and quantitative understanding of coupled relaxation modes in strained layer heteroepitaxy.
Computational Investigation of Selective Movpe of AlXGa1-XAs in Presence of Hcl
Authors: Nemirovskaya Maria , Cavallotti Carlo , Jensen Klavs
Published: April 2011

The deposition of AlGaAs in the presence of HCl was investigated at the macroscopic and mesoscopic scales. Fluid dynamics simulations were first performed in order to study the dependence of the deposition rate on the operating conditions. Unknown gas phase and surface kinetic parameters were estimated by quantum chemistry and transition state computations. The fluxes of all species to the surface were thus computed and provided the input to a kinetic Monte Carlo model used to investigate the morphology evolution of the film.
Rapid Prototyping of Ceramic Based Photonic Bandgap Structures
Authors: Synowczynski Jennifer , Hirsch Samuel , Gersten Bonnie
Published: April 2011

A three-dimensional photonic bandgap (PBG) structure was fabricated from CAD models using a method based on lost wax rapid prototyping and ceramic gelcasting. The inverse PBG mold was constructed from a low melting point thermoplastic using a high precision Sanders Rapid Toolmaker. An aqueous stable slurry (200-300 cp) containing 50-75wt% of the ceramic powders (BaSrTiO3, MgO), a 15wt% solution of monomer (Methacylamide) and crosslinker (Poly(ethylene glycol) dimethacrylate), and a free radical initiator (2,2'Azobis(2-amidino-propane) dihydrochloride) was cast into the mold. A polymerization reaction was thermally activated at 50°C to immobilize the ceramic powders. The wax mold was then removed by drying the green body in a high humidity oven at 120°C. Scanning Electron Microscopy (SEM) of the unfired part showed that atmosphere hampered the polymerization reaction at the surface of the part. The green density, sintered density, and permittivity all increased as the solids loading increased. In order to optimize the dielectric properties and minimize cracking and warping in the sintered part, the solids loading had to be greater than 80 wt%. This study investigated several steps in the lost mold / gelcasting procedure including stabilizing the ceramic suspension, the correlation between the solids loading and the green and sintered densities, binder removal, and the effect of shrinkage during sintering on the net shape.
Dielectric Properties of Spray Deposited BaTiO3 and Ba0.68Sr0.32TiO3
Authors: Ahn Kipyung , Wessels Bruce W. , Greenlaw Robert , Sampath Sanjay
Published: April 2011

The microstructure and dielectric properties of BaTiO3 and Ba0.68Sr0.32TiO3 thick films deposited by thermal spray were investigated. The as-deposited films were predominantly crystalline with a small amount of an amorphous second phase. The as-deposited BaTiO3 films had dielectric constants as high as 240 at room temperature. Upon annealing in air at 500°C, the dielectric constant increased to 480. This increase in dielectric constant was attributed, in part, to the crystallization of the amorphous second phase. The stabilized phase depended on the spray process used. The high velocity oxy fuel (HVOF) spray process resulted in the deposition of paraelectric BaTiO3, whereas the plasma spray process resulted in the ferroelectric phase.
Direct-Write Construction of Tissue-Engineered Scaffolds
Authors: Kachurin Anatoly M. , Stewart Robert L. , Church Kenneth H. , Warren William L. , Fisher John P. , Mikos Antonios G. , Kraeft Stine-Katherine , Chen Lan Bo
Published: April 2011

A computer-controlled xyz dispensing system called the Biological Architecture Tool (BAT) has been extensively tested in the creation of multilayered and three-dimensional biological objects: tissue scaffolds and plain and patterned cellular-array slides. The BAT dispensing system has proven its versatility and reliability in tissue engineering and biological experiments. The potential employments of modified versions of the xyz dispensers for in vivo minimally invasive surgery and other in vitro aspects of biological and medical research are discussed.
Sensitivity and Resolution Limits in Scanning Capacitance Microscopy
Authors: Lányi 'Stefan , Hruŝkovic Miloslav
Published: April 2011

The capacitance detection techniques, applicable to Scanning Capacitance Microscopes, have been analyzed from the point of view of signal-to-noise ratio that finally affects the achievable lateral resolution. It was found that comparable sensitivities can be achieved from relatively low frequencies below 1 MHz up to the GHz region. On conducting surfaces, resolution better than 5 nm has been achieved. It is limited by the minimum probe-to-sample distance, below which large tunneling current would occur. Increasing the applied voltage above a few volts increases the sensitivity at the cost of lateral resolution, since, at high voltage and small probe-sample distance, field emission could occur.
Detection of Compositional Fluctuations in High Temperature Exposed Waspaloy
Authors: Zou Xiaodong , Makram Tariq , Gerhardt Rosario A.
Published: April 2011

Waspaloy is a nickel base super-alloy used in aircraft engines. When this alloy is placed in service, it is subjected to long term exposure at high temperatures, which can cause the reinforcing gamma prime precipitate population to fluctuate and thus affect its structural integrity. The population fluctuates as a result of coarsening, dissolution or re-precipitation. Samples exposed to 1200° F for times ranging from 0 to 12626 hours were characterized using impedance spectroscopy, microhardness measurements, x-ray diffraction and quantitative stereology. Two important parameters were derived from the impedance measurements: (1) the imaginary admittance peak magnitude (Ymax) and (2) the associated relaxation frequency (fmax). As the distribution, shape and size of the precipitates change with exposure time, these parameters were also found to vary. In addition to the changes in precipitate geometry, lattice constant changes detected by analyzing x-ray diffraction data suggest that there are compositional shifts in the matrix as well as the gamma prime precipitates. Furthermore, the preferred orientation of the precipitates can also be seen to change with exposure time. These changes in composition, size and shape as a function of thermal exposure time are accompanied by changes in the volume fractions of primary and secondary gamma prime particles present. Using effective medium models, it is possible to predict that the measured properties are related to the gamma prime population. The grain boundary carbides do not appear to play any role at the conditions presented.
Displacement Current Staircase due to Coulomb Blockade
Authors: Nagano Kouhei , Okuda Atsushi , Majima Yutaka
Published: April 2011

In the two-junction system of the scanning vibrating probe/ Au dot / vacuum / Si structure, theoretical equations of both the displacement current waveform iD(t) and the mean displacement current ID(VP) due to Coulomb blockade are analyzed by using the orthodox theory. By usingtheoretical iD(t), the single electron motion on a Coulomb island in a period of probe vibration isexplained. Experimental ID(VP) curves due to Coulomb blockade under a constant probe voltage VP clearly show the displacement current staircase and are in good agreement with the theoretical ID(VP) curve. By using this method, the average number of quantized electrons on Au dots is directly measured through the displacement current staircase.
Investigation of Pt/Si/CeO2/Pt MOS Device Structure by Impedance Spectroscopy
Authors: Lappalainen Jyrki , Kek Darja , Tuller Harry L.
Published: April 2011

Epitaxial growth of dielectric layers on silicon substrates has attracted a great deal of recent interest given their potential applicability in the fabrication of high quality silicon-on-insulator (SOI) structures, high density capacitor devices, and stable buffer layers between silicon and other materials. Cerium dioxide (CeO2) appears to be a particularly attractive candidate, given its high dielectric constant and its compatibility with Si. To date, measurements of the electrical properties of CeO2 films on Si have been largely limited to room temperature. In this study, thin films of CeO2 were prepared by in situ pulsed laser deposition (PLD) on n-type (100) silicon substrates, with varied deposition conditions. Capacitance-voltage measurements (C-V) were used to characterize the response of the Pt/Si/CeO2/Pt MOS capacitor structure. Impedance measurements were performed from room temperature to 350°C. This enabled the independent characterization of the electrical signature of the Pt/Si interface which was found to contribute insignificantly above approximately 150°C. The CeO2 film conductivity was found to be thermally activated with activation energy of ∼0.45 eV, with its magnitude strongly dependent on film microstructure.
FT-IR spectra of Li(AlxCo1-x)O2 (x=0.1-0.5)
Authors: Hao W. , Li C. , Meng X. , Chen G. , Xu W.
Published: April 2011

FT-IR spectra from Li(AlxCo1-x)O2 (x=0.1-0.5) are reported. It was found out that there are four peaks located at 556cm−1, 601cm−1, 1438cm−1, 1498cm−1. First two peaks at 556cm−1 and 601cm−1 can be assigned to A2u and Eu vibration modes, respectively. The other two new peaks at 1438cm−1 and 1498cm−1 can not be explained clearly. With the increasing of Al concentration, all peaks position remain unchanged. However a relative change in the intensity of A2u and Eu peaks was observed.
Relation Between Heat-Treatment Temperature and Characteristics of Polyparaphenylene(PPP)-Based Carbon Materials for Lithium Ion Secondary Batteries
Authors: Osawa Kozo , Nakazawa Tatsuo , Oshida Kyoich , Endo Morinobu , Dresselhaus Mildred S.
Published: April 2011

Polyparaphenylene (PPP)-based carbon powder is expected for materials of the negative electrode of the lithium ion secondary batteries. In this study, effects of heat treatment temperature on the PPP materials are investigated by means of electrical and structural measurement. The layer structure of the powder is analyzed in detail by the transmission electron microscope observation combined with digital image processing. Charge-discharge current characteristics, electrical resistivity under pressure and layer structure of the PPP-based carbon powder are measured and discussed.
Electrical Characterization of Inhomogeneous and Heterogeneous Systems with Microstuctural Periodicity
Authors: Maier Joachim
Published: April 2011

This paper discusses how inhomogeneities and heterogeneities enter impedance and conductivity analyses in the case of microstructural periodicity. The specific considerations of various examples of ionically and ionically/electronically conductiong materials systems (bicrystals, microcrystalline and nanocrystalline samples) show how a reliable and thorough characterization is possible.
Percolation properties of cellular composite systems
Authors: Chiteme C. , McLachlan D.S.
Published: April 2011

Percolation phenomena were studied in a series of six composites with a cellular structure. Measurements made on the composites include dc and ac electrical conductivity, dielectric constant, 1/for flicker noise and magnetoresistance. Results arising from these extensive measurements were fitted to the percolation power laws and a phenomenological equation to give various exponents, which are presented, discussed and compared.
Combinatorial Synthesis and Characterization of CoMnGe Alloys
Authors: Tsui Frank , He Liang , Ma Lei
Published: April 2011

Ternary alloys of CoMnGe have been synthesized and characterized using combinatorial molecular beam epitaxy techniques. Structural evolution was studied using real-time scanning reflection high-energy electron diffraction, and magnetic properties were probed using magnetooptic Kerr effect imaging and SQUID magnetometry. Growth and properties on several substrate orientations were explored. These alloys exhibit a rich variety of magnetic and magnetooptic behavior, including a robust phase near Co2MnGe with high spin polarization, Tc, and magnetooptic response. The observed magnetic responses show strong correlation with structural transformations, such that structural ordering leads to enhanced magnetism. The observed magnetic behavior and the alloys’ compatibility with Ge and Si substrates make them potential candidates for spin electronic transport studies and applications.
High Throughput Optimization of Y-Type Magnetoplumbite Epitaxial thin Film Growth by Combinatorial Pulsed Laser Deposition Technique
Authors: Ohkubo I. , Matsumoto Y. , Ohtani M. , Hasegawa T. , Ueno K. , Itaka K. , Parhat A. , Chikyow T. , Kawasaki M. , Koinuma H.
Published: April 2011

Thin films of Y-type magnetoplumbite (Ba2Co2Fe12O22: Co2Y) with such a huge unit cell length as 43.5 Å has been successfully fabricated for the first time with the aid of combinatorial optimization of pulsed laser deposition process. Planning a thickness gradient CoO buffer layer on MgAl2O4(111) substrate was very effective for prevent the phase separation of Co deficient impurity (BaFe2O4) to reside in the formation of desired Co2Y phase.From the TEM analysis, the CoO buffer layer of optimum thickness was incorporated into the Co2Y film to make theinterface with the make an atomically sharp.
Array Based Carbon Black-Polymer Composite Vapor Detectors for Detection of DNT in Environments Containing Complex Analyte Mixtures
Authors: Briglin Shawn M. , Freund Michael S. , Sisk Brian C. , Lewis Nathan S.
Published: April 2011

Thin films of carbon black-organic polymer composites have been deposited across two metallic leads, with sorption of vapors producing swelling-induced resistance changes of the detector films. To identify and classify vapors, arrays of such vapor sensing elements have been constructed in which each element of the array contains a different polymer as the insulating phase and a common conductor, carbon black, as the conducting phase. The differing gas-solid partition coefficients for the various polymers of the detector array produce a pattern of differential resistance changes that is used to classify vapors and vapor mixtures. The performance of this detector array system towards 2,4-dinitrotoluene, the predominant signature in the vapor phase above land mines, in the presence high concentrations of water or of acetone (as a selected volatile organic carbon vapor), has been evaluated.
Development of Robot System and X-ray Powder Diffraction for Combinatorial Materials Research
Authors: Yanase Ikuo , Fujimoto Kenjiro , Takada Kazunori , Ohtaki Takugo , Watanabe Mamoru
Published: April 2011

We developed a combinatorial robot system as the first step of combinatorial approach to wet and dry synthesis of ceramics. In this study, nanoparticles mixtures having maghemite and a small amount of Y2O3 were prepared successively by using the combinatorial robot system. maghemite and Y2O3 slurries were volumetrically and automatically measured and mixed by repetition of sucking and injecting with a micro-pipette attached to the robot arm. The structural phase transition temperature of maghemite to hematite, which was investigated from the exothermic peak in the DTA curve, increased from ca.813K to ca.1093K by 2atom%Y2O3 addition. It was considered that Y2O3 dissolution into the crystal structure of maghemite had an important role on increasing the temperature of the structural phase transition for stabilizing maghemite phase. (Combinatorial, Slurries, Maghemite, Nanoparticles, Phase transition)
Photochemical Nucleation of Copper on Polyimide Surface with 10ns Laser Irradiation - Growth of Copper Metal on Copper Nuclei and Deposition of SiO2 film on Copper Metal
Authors: Tokunaga H. , Ogawa Y. , Murahara M.
Published: April 2011

Copper atoms were substituted on the polyimide surface in the presence of CuSO4 solution with only 10ns single shot of ArF laser. Then, we have succeeded in substituting copper atoms with dangling bonds of carbon cross- linking with oxygen atoms. In this study, we placed fused silica glass on the polyimide surface firstly, and poured the sulfate solution into the gap between the silica glass and the film, forming a thin liquid layer. Then, one shot of circuit patterned ArF laser light having 42mJ/cm2 was irradiated vertically onto the sample. The photon is dissociating and exciting the copper sulfate solution and the polyimide surface. The dissociated copper atoms form the C-O-Cu bond with active oxygen on the polyimide surface. However, we were able to grow a copper thin film of about 24μm after immersing the sample into the electro less plating solution for 15 minutes at 60.

On the other hand, we have laminated transparent and low dielectric constant SiO2 film at room temperature on polyimide surface by using Xe2 excimer lamp. Then, the copper film deposited on polyimide film and the piece of silicon were placed in the reaction chamber with mixing NF3 and O2 gasses in the ratio of 10:1; total pressure 330 Torr. Then, Xe2 excimer lamp was irradiated for 20 minutes. By the photochemical reaction, SiF4 and NO2 were produced. The adsorbed SiF4 on copper and polyimide surface of one molecule layer and NO2 up react with NO2, and growth SiO2 film on the sample surface. A chain reaction of film formation is brought about by these two chemical reactions of adsorption and oxidization. By this film formation film thickness was not more than 600 after 20 minutes with the Xe2 excimer lamp irradiation in order to lose in SiF4. Then, the silicon was supplied, and insufficient SiF4 was filled by ablating the silicon wafer by focused ArF excimer laser beam.
The Rational Discovery FrameworkTM: A Novel Tool for Computationally Guided High-Throughput Discovery
Authors: Landrum Gregory A. , Genin Hugh
Published: April 2011

The Rational Discovery Framework(TM) is a novel approach for providing computational guidance in the high-throughput discovery process. The Framework uses a proprietary machine-learning algorithm to construct predictive models from existing experimental data. These predictive models are used to computationally screen the contents of large virtual libraries. A variety of experimental design techniques can be brought to bear on the results of a virtual library screen in order to suggest an optimal set of synthesis candidates for the next round of experimentation. We have demonstrated the power and generality of the Rational Discovery Framework in a series of proofs of concept. Here we present an overview of the Framework as well as the results of studies aimed at developing predictive models for materials properties: ferromagnetism in ordered and disordered transition-metal alloys; and prediction of Tc values for superconductors.