bluuebunny/crossref_metadata_2025 huggingface dataset:
Cracking and Delamination of Heteroepitaxial Barium Hexaferrite Films
Authors: Oliver S.A. , Kozulin I. , Mcgruer N.E. , Yoon S.D. , Vittoria C.
Published: April 2011

Experimental results are shown for the structural and stress behaviors of c-axis oriented barium hexaferrite films on c-plane sapphire (Al2O3) substrates as a function of oxygen growth pressure and film thickness. It is shown that films deposited at 20 mTorr crack and delaminate at thicknesses above 15 µm, but that evidence for these large stresses is not apparent in either substrate curvature measurements or distortion of the c-axis lattice constant for thinner films (< 2 µm). In contrast, films (< 4 µm) deposited at 300 mTorr show large substrate curvatures that relax with increasing film thickness, in tandem with the formation of first large outgrowths, and then polycrystalline grains as the original c-axis film texture is randomized. Correlations between these observations are made to explain the complex evolution of properties in these films.
Solution Synthesis of Epitaxial Rare-Earth Oxide Thin Films on Roll-Textured Nickel
Authors: Morrell Jonathan S. , Xue Ziling B. , Paranthaman Mariappan , Chirayil Thomas G. , Vallet Catherine E. , Beach David B. , Specht Eliot D.
Published: April 2011

Using solution chemistry, epitaxial films of rare-earth oxides of the general formula RE2O3 (where RE = Sm to Lu) were prepared on cubic-textured nickel tapes. Solutions of metal methoxyethoxides or metal acetate/methoxyethoxides in 2-methoxyethanol were used to coat rolltextured nickel tapes using either spin-coating or dip-coating. Coated tapes were subsequently heated in a reducing atmosphere at temperatures between 950 °C and 1160 °C for varying lengths of time. Film quality was determined using X-ray diffraction and electron and surface probe microscopy. Films were found to be oriented both in and out-of-plane of the substrate, free of pinholes and gross defects, and of sufficient quality for use as substrates for high Tc, superconductors.
Modeling of Metal(100) Homoepitaxial Film Growth at Very Low Temperatures
Authors: Caspersen K.J. , Stoldt C.R. , Thiel P.A. , Evans J.W.
Published: April 2011

We model the growth of Ag films deposited on Ag(100) below 140K. Our recent Variable-Temperature Scanning Tunneling Microscopy (VTSTM) studies reveal “smooth growth” from 120-140K, consistent with earlier diffraction studies. However, we also find rougher growth for lower temperatures. This unexpected behavior is modeled by describing the deposition dynamics using a “restricted downward funneling” model, wherein deposited atoms get caught on the sides of steep nanoprotrusions (which are prevalent below 120K), rather than always funneling down to lower four-fold hollow adsorption sites. At OK, where no thermal diffusion processes are operative, this leads to the formation of overhangs and internal defects (or voids). Above 40K, low barrier interlayer diffusion processes become operative, producing the observed smooth growth by 120K. We also discuss how the apparent film morphology mapped out by the STM tip “smears” features of the actual film morphology (which are small at low temperature), and also can lead to underestimation of the roughness.
Heteroepitaxy: The Missing Link Between Surface Chemistry and Dry Corrosion
Authors: Yang Judith C. , Bharadwaj Mridula Dixit , Tropia Lori
Published: April 2011

We have investigated the initial stages of Cu (001) oxidation in dry and moist oxidizing conditions using in situ ultra-high vacuum (UIHV) transmission electron microscopy (TEM). To investigate the role of moisture in the solid state reactions in Cu oxidation, we have examined the oxidation of Cu (001) with water vapor. Our observation indicate that water vapor causes reduction of Cu2O and retards the oxidation rate if both oxygen gas and water vapor are used simultaneously which contradicts the thermochemical data. We are also modeling the nucleation to coalescence of the oxide scale using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation and have noted a qualitative agreement.
Potential of GaN Gunn Devices for High Power Generation Above 200 GHz
Authors: Kamoua Ridha , Zhu Yiming , Corcoran Yunji
Published: April 2011

This paper investigates the potential of Gallium Nitride (GaN) Gunn diodes for generating high power radiation at millimeter and sub-millimeter wave frequencies. Simulations were carried out based on an ensemble Monte Carlo computer model. This model accounts for thermal effects, series resistance, and device circuit interaction through the harmonic balance technique. The accuracy of the model has been validated in the case of InP Gunn devices at frequencies above 100 GHz[1]. Initially uniform and linearly graded doping profiles in the active region were considered. It is found that, similar to devices based on InP, the graded profile resulted in a much improved performance in terms of power, efficiency, and operating temperature. In particular, a GaN Gunn structure consisting of a 1 μm thick active region with a graded doping profile increasing from 6 × 1015 cm−3 at the cathode terminal to 4.6×1016cm−3 at the anode terminal yielded promising results. The DC bias voltage was estimated from the calculated velocity-electric field data to be about 25 V. With this bias, it was found that oscillations in the fundamental mode could be obtained over the frequency range from 220 GHz to 330 GHz subject to a load resistance of 1 Ohm and a maximum operating temperature of 800 K. The maximum output power was 30 mW at 290 GHz with a corresponding conversion efficiency of 0.25 %. Considerable improvement was obtained from a device with a heterojunction at the cathode. For a 1 μm device, an optimum power level close to 150 mW was predicted at 215 GHz with an efficiency of 2 %. This estimated power level is about an order of magnitude higher than what can be achieved from InP Gunn oscillators at the same frequency.
GaN pnp Bipolar Junction Transistors Operated to 250°C
Authors: Zhang A.P. , Dang G. , Ren F. , Han J. , Monier C. , Baca A.G. , Cao X.A. , Cho H. , Abernathy C.R. , Pearton S.J.
Published: April 2011

We report on the dc performance of the first GaN pnp bipolar junction transistor. The structure was grown by MOCVD on c-plane sapphire substrates and mesas formed by low damage Inductively Coupled Plasma etching with a Cl2/Ar chemistry. The dc characteristics were measured up to VBC of 65 V in the common base mode and at temperatures up to 250°C. Under all conditions, IC ∼ IE indicated higher emitter injection efficiency. The offset voltage was ≤ 2 V and the devices were operated up to power densities of 13.9 kW·cm−2.
SiC epitaxial growth on porous SiC substrates
Authors: Melnychuck G. , Mynbaeva M. , Rendakova S. , Dmitriev V. , Saddow S. E.
Published: April 2011

We report on the growth and crystal quality of CVD epitaxial layers grown on porous SiC (PSC) substrates. A layer of porous SiC was fabricated by surface anodization of commercial 4H and 6H-SiC (0001)Si face off-axis wafers. The 4H and 6H-SiC epilayers were grown on porous SiC (PSC) substrates using atmospheric pressure CVD at 1580°C and a Si to C ratio of 0.3. Results of X-ray diffraction, RHEED, SEM and AFM characterization demonstrated good surface quality of the films grown on porous material. PL data indicate a greatly improved defect structure in the epi layers grown on PSC as compared to control samples. Preliminary etch pit experiments to estimate the dislocation density indicate a three-fold reduction in defect density in the epi material grown on PSC substrates as compared to epi grown conventional substrates.
Single Crystal Growth of Gallium Nitride Substrates Using an High Pressure High Temperature Process
Authors: Singh Rajiv K. , Gilbert Donald R. , Kelly Francis , Chodelka Robert , Abbaschian Reza , Pearton Stephen , Novikov Alexander , Patrin Nikolay , Budai John
Published: April 2011

The use of standard bulk semiconductor crystal growth processes for the production of GaN is prohibited by both the high melt temperature of GaN and thermal decomposition of the compound into Ga metal and N2 gas. We have employed a novel hydrostatic pressure system to grow GaN crystals. A high temperature, ultra-high pressure process was developed using a solid-phase nitrogen source to form GaN crystals in a Ga metal melt. Using a thermal gradient diffusion process, in which nitrogen dissolves in the high temperature region of the metal melt and diffuses to the lower temperature, lower solubility region, high quality crystals up to ∼1 mm in size were formed, as determined by SEM, X-ray diffraction and micro-Raman analysis.
Measurement of Transit Time and Carrier Velocity Under High Electric Field in III-Nitride P-I-N Diodes
Authors: Wraback M. , Shen H. , Carrano J.C. , Li T. , Campbell J.C.
Published: April 2011

We present an optically-detected time-of-flight technique with femtosecond resolution that monitors the change in the electroabsorption due to charge transport in a p-i-n diode, and show how it may be used to determine the electron transit time and velocity-field characteristic in GaN at room temperature. The transit time drops with increasing electric field E in the intermediate field regime (50-100kV/cm), and the electron velocity possesses a weak, quasi-linear dependence on E attributed to polar optical phonon scattering. In the high field regime the transit time and the electron velocity gradually become independent of E. The peak electron velocity of 1.9×107 cm/sec, corresponding to a transit time of ∼2.5 ps across the 0.53 μm depletion region, is attained at ∼ 225 kV/cm. The experimental results are in qualitative agreement with theoretical steady-state velocity-field characteristics found in the literature.
Real Time Observation and Characterization of Dislocation Motion, Nitrogen Desorption and Nanopipe Formation in GaN
Authors: Stach Eric A. , Kisielowski C.F. , Wong W.S. , Sands T. , Cheung N.W.
Published: April 2011

Despite the considerable attention focused on GaN and related alloys during the past decade, many outstanding questions remain regarding the mechanisms of defect formation in these materials. In this work, we take advantage of a recently developed processing technique known as laser lift-off to examine the behavior of thin, free-standing, nearly stress-free single crystals of GaN subjected to thermal stimulus. GaN layers of 7 νm thickness were removed from their sapphire growth substrate using the laser lift-off method, then ion-milled to electron transparency. The samples were then annealed at temperatures between 850 and 1025 °C within the objective lens of a 200 kV transmission electron microscope. This allowed real time observation of defect formation via diffraction contrast imaging. Above 925 °C nitrogen desorption first becomes visible at the thinnest edges of the TEM sample. Concomitant with this is the preferential desorption of nitrogen along the cores of those dislocations which are pure screw in character, resulting in the formation of nanopipes. In regions with small residual stresses, those dislocations with mixed edge and screw components propagate parallel to the basal plane in the three close-packed {1 1 00} directions, leaving a hollow tube in their wake. At these temperatures, no motion of dislocations with pure edge character is observed. These results indicate that desorption and plasticity may occur simultaneously in these materials. Additionally, it appears that nanopipe formation may be unavoidable during heteroepitaxial growth by chemical vapor deposition and hydride vapor phase epitaxy, as these deposition methods require substrate temperatures of this magnitude.
Transient Photoresponse from Co Schottky Barriers on AlGaN
Authors: Schwarz R. , Niehus M. , Melo L. , Brogueira P. , Koynov S. , Heuken M. , Meister D. , Meyer B.K.
Published: April 2011

Co on AlGaN is expected to form a large barrier Schottky contact due to its high work function. We have used this material combination with 18 % of Al in AlxGaN for the study of transient photoresponse in the photovoltaic mode and in secondary photocurrent measurements after pulsed laser excitation. In reverse bias and in short- circuit mode a fast decay with a characteristic time of a few microseconds is dominant at room temperature. This mode is appropriate for UV detector operation. At elevated temperature, a much slower tail extending to several milliseconds is also observed. In forward bias operation the slow tail is dominating at any temperature. We discuss this asymmetry with respect to fast minority carrier collection within the space charge region for primary photocurrents and the slower majority carrier transport in forward bias.
The Temperature Dependent Breakdown Voltage For 4H- and 6H-SiC Diodes
Authors: Lee Y. S. , Han M. K. , Choi Y. I.
Published: April 2011

The breakdown voltages of 6H- and 4H-SiC rectifiers as function of temperature were modeled analytically in both non-reachthrough diode and reachthrough diode. The breakdown voltage was derived by the ionization integral employing accurate hole impact ionization coefficient. The breakdown voltage of SiC rectifiers was increased with increasing temperature and the positive temperature coefficient of breakdown voltage indicates that SiC rectifiers are suitable for high temperature applications. The breakdown voltages of both 6H- and 4H-SiC diodes were increased by M(T)-1/4 in NRDs and M(T)-1/8 in RDs.
Improved Sensitivity SiC Hydrogen Sensor
Authors: Muntele C. I. , Ila D. , Williams E. K. , Muntele Iulia C. , Evelyn A. L. , Poker D. B. , Hensley D. K.
Published: April 2011

We have produced silicon carbide sensors by two techniques: palladium coating and low energy palladium implantation. The palladium implantation was done at 550°C into the Si face of 6H, n-type SiC at various energies and at various fluences. The sensitivity of each sensor was measured at temperatures between 20°C to 400°C. The response of the SiC sensors produced by Pd implantation has revealed a completely different behavior than the SiC sensors produced by Pd deposition. In the Pd deposited SiC sensors, as well as in the ones reported in the literature [1, 2], the current rises in the presence of hydrogen at room temperature as well as at elevated temperatures. In the case of Pd implanted SiC sensors, the current decreases in the presence of hydrogen whenever the temperature is raised above 100°C [3].
Heteroepitaxial Barium Hexaferrite Films on (111) Magnesium Oxide Substrates
Authors: Oliver Steven A. , Yoon Soack Dae , Kozulin Izabella , Chen Ming Ling , Zuo Xu , Vittoria Carmine
Published: April 2011

High quality films of barium hexaferrite (BaFe12O19) were deposited by pulsed laser ablation onto MgO (111) substrates. In contrast to previous films deposited onto c-plane sapphire (Al203), these films were expected to have compressive biaxial stress, and indeed showed no indications for either cracking or delamination to a film thickness of 32 νm. All films were found to be highly c-axis textured by both x-ray diffraction measurements and magnetization results. The saturation magnetization (4πMs = 4.2 kG) and uniaxial anisotropy field (HA = 16 kOe) values for these films approach bulk values. Ferrimagnetic resonance measurements on a calcined 3 μm thick film show a narrow linewidth (ΔH ∼ 100 Oe) for the uniform resonance mode. The properties of these films approach those required for self-biased millimeter wavelength devices.
Phase Transformations in Sol-Gel PZT Thin Films
Authors: Eakin D.P. , Norton M.G. , Bahr D.F.
Published: April 2011

Thin films of PZT were deposited onto platinized and bare single crystal NaCl using spin coating and sol-gel precursors. These films were then analyzed using in situ heating in a transmission electron microscope. The results of in situ heating are compared with those of an ex situ heat treatment in a standard furnace, mimicking the heat treatment given to entire wafers of these materials for use in MEMS and ferroelectric applications. Films are shown to transform from amorphous to nanocrystalline over the course of days when held at room temperature. While chemical variations are found between films crystallized in ambient conditions and films crystallized in the vacuum conditions of the microscope, the resulting crystal structures appear to be insensitive to these differences. Significant changes in crystal structure are found at 500°C, primarily the change from largely amorphous to the beginnings of clearly crystalline films. Crystallization does occur over the course of weeks at room temperature in these films. Structural changes are more modest in these films when heated in the TEM then those observed on actual wafers. The presence of Pt significantly influences both the resulting structure and morphology in both in situ and ex situ heated films. Without Pt present, the films appear to form small, 10 nm grains consisting of both cubic and tetragonal phases, whereas in the case of the Pt larger, 100 nm grains of a tetragonal phase are formed.
Electric and Magnetic Properties of Epitaxial Fe2−xTixO3+σ Films
Authors: Fujii T. , Ayama K. , Nakanishi M. , Sohma M. , Kawaguchi K. , Takada J.
Published: April 2011

Solid solution films of the σ-Fe2O3-FeTiO3 series are one of the candidates for noble half-metallic oxides. They were epitaxially formed on σ-Al2O3(001) single crystalline substrates by O2 -reactive evaporation method. The Fe2−x TixO3+σ films prepared at higher Ts=973 K and with larger Ti content x≤0.4 had the ilmenite structure with R3 symmetry. Other films at lower Ts or with smaller x possessed the corundum structure with R3c. Only the films with R3 symmetry had large ferrimagnetic moments, though the observed spontaneous magnetization was less than half of the ideal value expected from the fully ordered structure. Room temperature resistivity of intermediate composites dropped to 10−lΔcm due to the formation of the mixed valence states between Fe2+ and Fe3+. However the Fe2+ content of the films was rather small as compared with stoichiometric Fe2−xTixO3. The Ti-rich films had large oxygen nonstoichio netry of about σ=0.3.
Density-of-States Effective Mass and Scattering Parameter Measurements on Transparent Conducting Oxides Using Second-Order Transport Phenomena
Authors: Young D. L. , Coutts T. J. , Li X. , Keane J. , Kaydanov V. I. , Gilmore A. S.
Published: April 2011

Transparent conducting oxides (TCO) have relatively low mobilities, which limit their performance optically and electrically, and which limit the techniques that may be used to explore their band structure via the effective mass. We have used transport theory to directly measure the density-of-states effective mass and other fundamental electronic properties of TCO films. The Boltzmann transport equation may be solved to give analytic solutions to the resistivity, Hall, Seebeck, and Nernst coefficients. In turn, these may be solved simultaneously to give the density-of-states effective mass, the Fermi energy relative to either the conduction or valence band, and a scattering parameter, s, which characterizes the relaxation time dependence on the carrier energy and can serve as a signature of the dominate scattering mechanism. The little-known Nernst effect is essential for determining the scattering parameter and, thereby, the effective scattering mechanism(s). We constructed equipment to measure these four transport coefficients on the same sample over a temperature range of 30 – 350 K for thin films deposited on insulating substrates. We measured the resistivity, Hall, Seebeck, and Nernst coefficients for rf magnetron-sputtered aluminum-doped zinc oxide. We found that the effective mass for zinc oxide increases from a minimum value of 0.24me, up to a value of 0.47me, at a carrier density of 4.5 × 1020 cm−3, indicating a nonparabolic conduction energy band. In addition, our measured density-of-states effective values are nearly equal to conductivity effective mass values estimated from the plasma frequency, denoting a single energy minimum with a nearly spherical, constant-energy surface. The measured scattering parameter, mobility vs. temperature, along with Seebeck coefficient values, characterize ionized impurity scattering in the ZnO:AI and neutral impurity scattering in the undoped material.
Growth and Chemical Substitution of Transparent p-Type CuAlO2
Authors: Stauber R.E. , Parilla P.A. , Perkins J. D. , Ginley D.S.
Published: April 2011

CuAlO2 is one of several materials currently being investigated for application as a p-type transparent conducting oxide. In this paper we report a method of making c-axis oriented CuAlO2 thin films which eliminates previously reported phase-purity and surface morphology problems. Thin film precursors of CuA1O2 were deposited on YSZ (100) substrates by roomtemperature radio frequency sputtering. Subsequent annealing in 10mT of oxygen at temperatures as low as 800°C resulted in phase-pure, textured CuAlO2. The films were p-type and transparent with a gap of 3.5eV, but typical carrier concentrations were low (on the order of 1016 cm−3). Oxygen anneals at 700°C in 1 atm of O2 raised this to 1018 cm−3 in some samples. In order to increase the carrier concentration further, we are testing chemical substitution on the metal sublattice. Initial experiments were done with Mg as a dopant, either by direct solid-state synthesis for bulk materials or by alternating deposition of MgO and CuAlO2 during the pulsed laser deposition of thin films. At Mg molar concentrations of 1% or less, the bulk material was phase-pure CuAlO2 by x-ray diffraction, but was mixed-phase CuAl2O4 and CuO when the Mg concentration was increased to 2%. Thin films sputtered from the 1% Mg substituted target crystallized to CuA102 after a 940°C anneal at 10T 02, but were more than 30 times more resistive than the undoped films.
Characteristics of Ultra violet-Assisted Pulsed Laser Deposited Thin Oxide Films
Authors: Craciun V. , Singh R.K.
Published: April 2011

The properties of thin oxide films such as Y2O3, ZnO and Ba0.5Sr0.5TiO3 grown using an in situ ultraviolet (UV)-assisted pulsed laser deposition (UVPLD) technique have been studied. With respect to films grown by conventional PLD under similar conditions but without UV illumination, the UVPLD grown films exhibited better structural and optical and electrical properties, especially for lower substrate temperatures. They also exhibited a better stoichiometry and contained less physisorbed oxygen than the conventional PLD grown layers. These improvements can be traced to several factors. Firstly, deep UV photons and ozone ensure a better in situ cleaning of the substrate prior to the deposition. Secondly, the presence of more reactive gaseous species like ozone and atomic oxygen formed by photodissociation of molecular O2 promotes the growth of more oxygenated films. Thirdly, absorption of UV photons by adatoms could result in an increased of their surface mobility. All these factors have a beneficial effect upon crystalline growth, especially for moderate substrate temperatures. For optimised growth conditions, the crystalline quality and properties of ultraviolet-assisted pulsed laser deposited films was similar to that of films grown using conventional PLD at substrate temperatures of at least 200°C higher.
The Seeding Effect of Lanthanum Nickel Oxide Ceramic/Ceramic Nanocomposite Thin Films Prepared by the MOD Method
Authors: Zhang Yu , Zhou Qifa , Chan Helen Lai-wa , Choy Chung-Loong
Published: April 2011

Lanthanum nickel oxide (LNO) is a conducting ceramic which has potential to be used as electrodes in multilayer ceramic actuators. Thick LNO films have been formed by incorporating nanosized LNO powder (annealed at 700°C, with diameter around 100 nm) into a LNO solution prepared by a metal-organic decomposed ( MOD ) method. Three different weight percents, 2%, 4%, and 10% of LNO powder have been added. The structural variation of the ceramic/ceramic composite film with annealing temperature was studied by X-ray diffraction and differential thermal analysis. The crystallization temperature of the film is found to decrease from ∼590°C to ∼510°C due to the seeding effect introduced by the nano-powder.
Thermal Stability and Semiconducting Properties of Epitaxial La0.7Sr0.3MnO3 Films
Authors: So K. S. , Wong K. H. , Wu W. B.
Published: April 2011

La0.7Src.3MnO3 (LSMO) perovskite oxide films have been grown on (001) LaAlO3 (LAO) by pulsed laser deposition. The films were deposited in an ambient oxygen pressure of 0.1 m Torr to 200 mTorr and under different substrate temperatures. Their structural properties were examined by X-ray diffractometry. Heteroepitaxial growth was confirmed for films deposited at 650°C or above. Electrical measurements suggest that the charge carrier concentraticn of the films varies with their oxygen content and shows high stability against further thermal treatment. Semiconducting LSMO films at room temperature were obtained for deposition at oxygen pressure ≤ 60 m Torr. The epitaxial LSMO films have been used as the semiconducting channel of a ferroelectric field effect transistor. Heteroepitaxial Pb(Zr0.52Ti0.48)O3/LSMO/LAO structures have been fabricated and characterized.
Transport Anisotropy in PLD-Made La0.75Sr0.25MnO3 Films
Authors: Johnsson P. , Khartsev S.I. , Grishin A.M.
Published: April 2011

A sequence of epitaxial La0.75Sr0.25MnO3 (LSMO) films with thickness ranging from 2400 to 50 Å have been prepared by pulsed laser deposition onto (110) SrTiO3 (STO) substrates. Compared with oar previous results on LSMO/STO(100) films [1], films on STO(110) substrates exhibit strong, anisotropy of electrical resistivity p. p measured in [110] direction is comparable with the resistivity of LSMO/STO(100) films while p in [001] direction is 25 times higher than in STO(100) case. The maximum value of anisotropy parameter p[001]/p[110] = 25 is reached for thick films at the low temperature of 90 K. Distinct crossover from 3D to 2D case has been observed. For thick films anisotropy monotonously decreases with the temperature increase. Films thinner than 200 Å exhibit a maximum of anisotropy parameter, which shifts to lower temperatures with the thickness decrease. The maximum temperature coefficient of resistivity (TCR) was found to be around 2% if measured along [001] direction and about 50 % higher in [11O] inplane direction. We explain the observed effects in terms of the crystalline properties of fabricated films.
Junction Properties of Metal/SrTiO3 Systems
Authors: Shimizu Takashi , Okushi Hideyo
Published: April 2011

Electrical properties of Nb-doped SrTiO3 (STO:Nb) Schottky barrier (SB) junctions have been investigated in detail for a comprehensive understanding of metal/oxide interfaces. Using a high-purity ozone surface treatment, rectification ratio over 9th order of magnitude has been successfully obtained, while without the surface treatment, anomalous large reverse bias leak currents were observed in the current-voltage characteristic of the junctions. The X-ray photoelectron spectroscopy (XPS) shows that carbon contamination which adsorbed the STO:Nb surface in air, induces surface states in the band gap of the STO:Nb, which probably originate the large reverse bias leak currents of the metal/STO:Nb junctions. Thus we present importance, of surface treatment for oxides to obtain controllability and reproducibility of the electrical properties of the oxide devices. Photocapacitance spectroscopy has been performed to investigate deep levels due to bulk defects and impurities in the Au/STO:Nb junctions. The photocapacitance spectra clearly indicate existence of the deep levels in the Au/STO:Nb and the concentration of the deep levels were of the order of 1013∼1015 cm−3. These values are too low to affect the Fermi level pinning at the interface if the deep levels exist in the near surface region of the bulk STO:Nb. We have shown some interesting electrical properties, characteristic of the SB junction of the dielectric oxide compared with that of the conventional semiconductor's. The schematic band diagram of the Au/STO:Nb junction with the intrinsic low permittivity layer at the interface has been proposed, which explains all the characteristic electrical properties. Considering the chemical trend of the SB height (SBH) estimated from the J-V results, we have pointed out the importance of the metal reactivity for understanding the formation mechanism of the SBH.
High Resolution Copper Lines by direct Imprinting
Authors: Hong C.M. , Sun X. , Wagner S. , Chou S.Y.
Published: April 2011

One-micrometer wide copper lines are patterned by direct imprinting and thermolysis. First, a layer of plastic copper hexanoate is spun on a substrate and patterned by direct imprint. Then the copper hexanoate line pattern is converted to copper metal lines by thermal and hydrogen anneals. The converted copper film resistivity is ∼8 μωcm. The direct imprinting of a fine metal pattern points the way to the direct patterning of device materials at high resolution
All-Printed Inorganic Logic Elements Fabricated by Liquid Embossing
Authors: Bulthaup Colin , Wilhelm Eric , Hubert Brian , Ridley Brent , Jacobson Joe
Published: April 2011

The liquid embossing process, devices made by this process, and their characteristics are presented. Structures fabricated and discussed here include: conductive lines with cross line resistance greater than 100 Gω and resistivities 4 times that of the bulk material, multilayer structures with etched sacrificial materials, vias that conduct through an embossed insulating layer, photodetectors made with nanocrystal solutions of CdSe, and all printed inorganic field effect transistors
Thermal Stability and Analysis of Laser Deposited Platinum Films
Authors: Berry G.J. , Cairns J.A. , Davidson M.R. , Fan Y.C. , Fitzgerald A.G. , Fzea A.H. , Lobban J. , McGivernt P. , Thomson J. , Shaikh W.
Published: April 2011

As the trend towards device miniaturisation continues, surface effects and the thermal stability of metal deposits becomes increasingly important. We present here a study of the morphology and composition of platinum films, produced by the UV-induced decomposition of organometallic materials, under various annealing conditions. The surface composition of the metal deposits was studied by X-ray photoelectron spectroscopy, both as-deposited and following thermal treatment. In addition, the morphology of the surface was studied by atomic force microscopy which enabled the investigation of film restructuring. These studies were performed over a range of temperatures up to 1000°C in air and up to 600°C in reducing environments. Complementary information regarding the film morphology has been obtained from transmission electron microscopy. The data has been used to provide an insight into the effects of elevated temperatures on metal films deposited by a direct write method
Real-World Applications of Laser Direct Writing
Authors: Ehrlich D. J. , Aucoin Richard , Burns M. J. , Nill Kenneth , Silverman Scott
Published: April 2011

Laser microchemical direct write deposition and etching methods have found an essential niche in debug and design for yield of wire-bonded and flip-chip integrated circuits. Future applications should develop in package-level system modification.
µ-Mold Shape Deposition Manufacturing of Ceramic Parts
Authors: Nam S.W. , Stampfl J. , Liu H.C. , Kang S. , Prinz F. B.
Published: April 2011

Rapid Prototyping is a versatile method to build complex-shaped ceramic or metallic parts on a mesoscopic scale. In this work the fabrication of ceramic gas turbine engine parts with Mold Shape Deposition Manufacturing (Mold SDM) is described. Mold SDM exists of two steps: The pattern generation in wax using deposition and machining of wax layers and the pattern transfer process with gel-casting. For parts with feature sizes that are too small for machining, microfabrication methods are used to fabricate the mold. By combining micro- and macro-fabrication, complex parts in a wide variety of sizes can be manufactured.

The surface quality of the mold significantly influences the mechanical properties of the final ceramic part. The contribution of the mold quality to the final mechanical properties is studied in this work.
Freeform Fabrication of Functional Silicon Nitride Components by Direct Photo Shaping
Authors: Ventura S. , Narang S. , Guerit P. , Liu S. , Twait D. , Khandelwal P. , Cohen E. , Fish R.
Published: April 2011

This paper describes a new multilayer solid freeform fabrication process, “Direct Photo Shaping” (DPS), where visible digital light projection is used as a maskless tool to build images on photocurable ceramic dispersions (ceramic powders in photopolymerizable liquid monomers) by flood exposure. For each layer, the projected image is changed according to the CAD data describing the object being built and solidification takes place by photocuring the exposed areas. Multiple layers are dispensed and photocured to fabricate the object of interest. A final rinse with a suitable solvent allows the removal of any uncured ceramic dispersion. The porous free formed “green” ceramic object can then be fired and sintered into a highly dense ceramic part. Digital Light Processing™ technology (developed by Texas Instruments) enables SRI International to project digital, high resolution, high brightness, high contrast visible light to photocure and form components with a good degree of accuracy. This paper describes the Direct Photo Shaping process and its advantages, and how DPS is being applied to the fabrication of ceramic (Honeywell AS800) gas turbine components for military and commercial applications. ASS00 test specimens with flexural strength in excess of 800MPa were fabricated by DPS. A first-stage AS800 turbine vane for the Rolls-Royce Allison Model 501-K industrial gas turbine was fabricated by DPS and tested in a gas-burner test rig at 1204°C. Initial tests show that ceramic samples with optimized surface finish (comparable to that achieved by ceramic bisque machining) can be fabricated by applying a pixel anti-aliasing filter along the boundaries of the sample projected slice images.
TEM Observation of Nanocrystalline Copper During Deformation
Authors: Youngdahl Carl J. , Hugo Richard C. , Kung Harriet , Weertman Julia R.
Published: April 2011

Nanocrystalline samples of copper were prepared using inert gas condensation and an optimized sequence of powder outgassing and compaction. TEM specimens were cut, electropolished, and mounted in a straining stage. In situ TEM observations including real-time video were captured during straining in the microscope. Areas of presumed increased stress concentration were identified near small cracks around the perimeter of the electropolished hole. Such locations were observed in the TEM while the specimen was pulled in tension. Several microstructural changes were captured during deformation including numerous sudden shifts in contrast of grains and parts of grains, occasional dislocation motion, opening and propagation of the crack. Relationships between grain size and deformation are described.
Superplasticity in Nanocrystalline Ni3Al and Ti Alloys
Authors: Mcfadden Sam X. , Sergueeva Alla V. , Kruml Tomas , Martin Jean-Luc , Mukherjee Amiya K.
Published: April 2011

The advent of nanocrystalline materials has provided new opportunities to explore grain size dependent phenomenon. Superplasticity is such a grain size dependent phenomenon defined by the ability to attain tensile elongation of 200% or more. Superplasticity in microcrystalline materials has been well characterized. The constitutive equations that describe microcrystalline superplasticity predict enhanced properties for nanocrystalline materials. Enhanced properties in such nanocrystalline material include lower superplastic temperature at constant strain rate, higher superplastic strain rate at constant temperature, and lower flow stresses. Investigations with nanocrystalline Ni3Al and ultra-fine grained Ti-6Al-4V alloy have shown a reduction in the superplastic temperature. However, the flow stresses in these materials are significantly higher than expected. The high flow stresses are accompanied by strong strain hardening.

Transmission electron microscopy in situ straining of nanocrystalline Ni3Al has shown that grain boundary sliding and grain rotation occurred during straining. The sliding and rotation decreased with strain. Dislocation activity was observed but was not extensive. There was no observable dislocation storage. The parameters of the generalized constitutive equation for superplasticity for nanocrystalline Ni3Al and Ti-6Al-4V are in reasonable agreement with the parameters for microcrystalline material. The rate parameters suggest that nanocrystalline superplasticity shares common features with microcrystalline superplasticity. In contrast, the observed flow stresses and strong strain hardening indicate that nanocrystalline superplasticity is not a simple extension of microcrystalline behavior scaled to finer grain size.
The Role Played By Two Parallel Free Surfaces In The Deformation Mechanism Of Nano-crystalline Metals: A Molecular Dynamics Simulation
Authors: Derlet P. M. , Swygenhoven H. Van
Published: April 2011

Former molecular dynamics computer simulations of polycrystalline Ni and Cu metals with mean grain sizes ranging between 3 and 12 nm demonstrated a change in deformation mechanism as a function of grain size: at the smallest grain sizes all deformation is accommodated in the grain boundaries. In this paper we report on the influence of the presence of two free surfaces on the deformation behaviour. The purpose of this simulation is to study which phenomena observed in in-situ tensile experiments performed in the electron microscope can be expected to be intrinsic properties of the deformation process and which phenomena are due to the presence of two free surfaces separated by a very small distance.
Molecular Dynamics Simulation of Nano-Sized Crystallization During Plastic Deformation in an Amorphous Metal
Authors: Tarumi R. , Ogura A. , Shimojo M. , Takashima K. , Higo Y.
Published: April 2011

An NTP ensemble molecular dynamics simulation was carried out to investigate the mechanism of nano-sized crystallization during plastic deformation in an amorphous metal. The atomic system used in this study was Ni single component. The total number of Ni atoms was 1372. The Morse type inter-atomic potential was employed. An amorphous model was prepared by a quenching process from the liquid state. Pure shear stresses were applied to the amorphous model at a temperature of 50 K. At applied stresses of less than 2.4GPa, a linear relation between shear stress and shear strain was observed. However, at an applied shear stress of 2.8 GPa, the amorphous model started to deform significantly until shear strain reached to 0.78. During this deformation process, phase transformation from amorphous into crystalline structure (fcc) was observed. Furthermore, an orientation relationship between shear directions and crystalline phase was obtained, that is, two shear directions are parallel to a (111) of the fcc structure. This crystallographic orientation relationship agreed well with our experimental result of Ni-P amorphous alloy. Mechanisms of phase transformation from amorphous into crystalline structure were discussed.
Computer Simulation of Misfit Dislocation Mobility in Cu/Ni and Cu/Ag Interfaces
Authors: Kurtz Richard J , Hoagland Richard G. , Heinisch Howard L.
Published: April 2011

The mobility of misfit dislocations in semicoherent Cu/Ni and Cu/Ag interfaces is determined by molecular dynamics and elastic band simulation methods. Cube-on-cube oriented Cu/Ni and Cu/Ag systems were studied with the interfaces parallel to (010). Core structures of misfit dislocations in semicoherent interfaces are found to be quite different in these systems. In Cu/Ni the misfits have very narrow cores in the plane of the interface. Consequently, the shear stress to move these dislocations is large, ∼1.1 GPa. The core width and hence the misfit mobility can be changed by placing the misfit away from the chemical interface. Placement of the misfit oneatom layer into the Cu increased the core width a factor of 1.6 and lowered the threshold shear stress to 0.4 GPa. The misfit dislocations in Cu/Ag interfaces, on the other hand, are wide and therefore are much more mobile. The threshold shear stress for misfit movement in Cu/Ag is very low, ∼0.03 GPa.
Biased Deposition of Nanocrystalline Be1−xCux Coatings
Authors: Jankowski A.
Published: April 2011

Coatings of Be1−xCux are prepared by magnetron sputter deposition onto spherical polymer mandrels. The application of an applied bias during deposition refines the columnar morphology of the coating and surface finish to the nanoscale. A mechanical testing technique is developed to load the thin-walled spherical capsules under uniaxial tension at constant strain to fracture. The bias-deposited material exhibits an increase in strength by a factor of three or more following a Hall-Petch type relationship with surface roughness.
Dislocation Models for Strengthening in Nanostructured Metallic Multilayers
Authors: Misra A. , Hirth J. P. , Kung H. , Hoagland R. G. , Embury J. D.
Published: April 2011

Ultra-high strength metallic multilayers are ideal for investigating the effects of length scales in plastic deformation of metallic materials. Experiments on model systems show that the strengths of these materials increase with decreasing bilayer period following the Hall-Petch model. However, as the layer thickness is reduced to the nm-scale, the number of dislocations in the pile-up approaches one and the pile-up based Hall-Petch model ceases to apply. For nm-scale semi-coherent multilayers, we hypothesize that plastic flow occurs by the motion of single dislocation loops, initially in the softer layer, that deposit misfit type dislocation arrays at the interface and transfer load to the harder phase. The stress concentration eventually leads to slip in the harder phase, overcoming the resistance from the misfit arrays at the interface. A model is developed within the framework of classical dislocation theory to estimate the strengthening from this mechanism. The model predictions are compared with experimentally measured strengths.
Atomistic Simulations of Steps in Bimetallic Interfaces as Barriers to Interface Slip Transmission
Authors: Henager Charles H. , Heinisch Howard L. , Kurtz Richard J. , Hoagland Richard G.
Published: April 2011

Atomistic models of coherent interfaces in the CuNi system with and without (111)-steps were used to study slip transmission across interfaces in CuNi metallic bilayers. The lattice mismatch of the CuNi system results in large coherency stresses at the interface. The (111)-steps afford a larger barrier to slip than the flat, coherent interface. The coherent flat interface dislocation barrier is largely due to the large compressive stresses in the Cu layer that must be overcome by applied tensile stresses. Additional Koehler forces are present as the dislocation in the elastically softer Cu approaches the stiffer Ni layer. The step, however, possesses a small residual edge dislocation with a Burgers vector equal to the difference of bCu and bNi times the height of the (111)-step in (111)-layers. We find that these steps are potent slip barriers, which suggests that homogeneous slip is preferred in such systems.
Sol-gel synthesis and characterization of mesoporous organosilicas by using block copolymer templates
Authors: Cho Eun-Bum , Kwon Kwan-Wook , Char Kookheon
Published: April 2011

Mesoporous organosilicas based on a bridged organosilicate have been synthesized using a triblock PEO-PLGA-PEO copolymer containing more hydrophobic poly(DL-lactic acid-coglycolic acid) block and the structural difference between mesoporous organosilicas prepared from PEO-PLGA-PEO and PEO-PPO-PEO block templates is discussed.
Millimeter-Wave Driven Polyol Processing of Nanocrystalline Metals
Authors: Kurihara L. K. , Lewis D. , Jung A. M. , Fliflet A. W. , Bruce R. W.
Published: April 2011

Nanocrystalline metallic powders and coatings have been synthesized using a millimeter wave driven polyol process. We have been able to prepare powders of single elements, alloys, metastable alloys, composites and coatings. Examples of a few of the metals processed in this study include Fe, Co, Ni, Cu, Ru, Rh, Pt, Au, FePt, FexCo100−x, NiAg and Cu-Ni. The polyol experiment was set up in the millimeter wave processing chamber, the beam was directed into the center of the solution and it was brought to reflux, using the millimeter wave beam as a heat source. Varying the power input easily controlled the rate of reflux.
Atomic Scale Characterization of Supported and Assembled Nanoparticles
Authors: Pauwels B. , Yandouzi M. , Schryvers D. , Tendeloo G. Van , Verschoren G. , Lievens P. , Hou M. , Swygenhoven H. Van
Published: April 2011

Different structural configurations of nanoparticles have been investigated by advanced transmission electron microscopy (TEM) techniques. The cluster-surface interaction of Au clusters, produced in a laser vaporization source and deposited with low energy on MgO cubes, is investigated by high-resolution transmission electron microscopy (HRTEM). A dilation of the Au lattice that perfectly accommodates the misfit with the MgO lattice is measured and modeled with Molecular Dynamics (MD). To study the chemical ordering in bimetallic clusters, Au-Cu alloy clusters with different stoichiometries are produced and deposited in the same way as the Au clusters. Electron diffraction (ED) ring patterns obtained from these alloy clusters lying on amorphous carbon, are indexed as face-centered cubic, which is confirmed by HRTEM. This indicates that clusters of Au-Cu alloys are solid solutions, i.e. no ordering takes place in these clusters. Assembled nanoclusters of Ni3Al, produced by the inert gas condensation (IGC) technique and pressed under high pressure (2 GPa), are investigated by HRTEM. These studies indicate that nanocrystalline Ni3Al consists of small crystallites of random crystallographic orientations separated by grain boundaries, with the presence of several nanoscaled voids. From the selected area electron diffraction (SAED) ring pattern, an incomplete L12 ordering is concluded.
Nanoparticles and Polymers. Bricks and Mortar Self-Assembly of Nanostructures
Authors: Boal Andrew , Ilhan Faysal , Rotello Vincent , Russell Thomas
Published: April 2011

Polymers provide a useful tool for the controlled assembly of colloidal nanoparticles. We have developed a bricks and mortar strategy in which colloidal gold particles functionalized with recognition elements serve as the bricks and polymers bearing complementary functionality serve as mortar to hold together the nanoparticles. In this methodology, the conformational flexibility of the polymer compensates for irregularities in the size and shape of the aggregate structure. We have used this method to create discrete micrometer-scale spherical assemblies based on 2 nm gold nanoparticles. Both the size and shape of these assemblies can be controlled, providing spherical assemblies ranging from 50 nm to 1500 nm, as well as network structures.
Nanoparticles and Nanocomposites in RF Plasma
Authors: Cao Jin , Matsoukas Themis
Published: April 2011

The use of low pressure radio-frequency (rf) plasma for nanoparticle formation and the deposition of thin film on particulate substrates are reported. Plasma polymer particles are synthesized in a capacitively-coupled Ar/monomer discharge at rf power of 15-30 W. A variety of particle structures are observed, including monodispersed nanospheres and liquid-like viscous nano-droplets. Styrene in particular is observed to produce hollow nanospheres. By manipulating the process parameters, films of plasma polymers can be deposited onto suspended submicron particles. We take advantage of the electrostatic trapping of “dusty plasma” to suspend small particles in plasma for extended periods of time until the desired coating thickness is achieved. Sub-micron silica particles introduced into a low pressure rf Ar/monomer plasma are coated with film of thickness ranging from 2 to 70 nm.