bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulsed DC Sputtered Aluminum Nitride: A Novel Approach To Control Stress And C-axis Orientation
Authors: Soussan Philippe , O'Donnell Kathy , D'Haen Jan , Vanhoyland Geert , Beyne Eric , Tilmans Harrie A. C.
Published: April 2011

This paper reports on a novel low temperature sputter deposition of AlN on an Al substrate, yielding films with stresses and crystalline orientation comparable to those of films deposited on Pt. The study focuses on the importance of the initial film growth step on both the stress and crystalline orientation of the film. The AlN layer is deposited using Pulsed DC (250 kHz, 90% duty cycle) magnetron reactive sputtering (93% N2, 7% Ar) using an Al target. The substrates are 150mm Si wafers with an aluminum seed layer (100 nm). The thickness of the AlN films is ≈2.5μm with uniformity across the wafer of 0.4%. The films were deposited in 4 passes of 0.625μm each to avoid overheating of the substrate. The influence of the substrate bias (0 V, 80 V and 120V) and argon pre-sputtering of the aluminum substrate been investigated. The film stress, and to a smaller extent the crystalline orientation, were mainly driven by the properties of the film deposited during the first pass. The bias is useful at the beginning of the film growth for stress control. This study suggests that it is beneficial not to use bias during the entire film deposition. With this approach, it was possible to deposit c-axis oriented AlN layers on Al with a FWHM of the rocking curve of 1.63° and low stress (<300MPa).
Integrated On-chip Planar Solenoid Inductors with Patterned Permalloy Cores for High Frequency Applications
Authors: Kim Jinsook , Ni Weiping , Kan Edwin C.
Published: April 2011

The on-chip magnetic inductors with patterned permalloy (Ni80Fe20) cores are fabricated on Si-substrates with different resistivities and thicknesses as well as on thin membranes. With the patterned permalloy cores, the on-chip magnetic inductors achieve high self-resonant frequencies over 25GHz in thin membranes. To distinguish the influence from the permalloy core patterns and substrate losses on the inductance and quality factor, multiple solenoids in series and parallel are designed to investigate the resistive, capacitive, and magnetic coupling losses.
Prevention of InP/InGaAs/InP Double Heterojunction Bipolar Transistors from Current Gain Reduction during Passivation
Authors: Min Byoung-Gue , Lee Jong-Min , Kim Seong-Il , Ju Chul-Won , Lee Kyung-Ho
Published: April 2011

A significant degradation of current gain of InP/InGaAs/InP double heterojunction bipolar transistors was observed after passivation. The amount of degradation depended on the degree of surface exposure of the p-type InGaAs base layer according to the epi-structure and device structure. The deposition conditions such as deposition temperature, kinds of materials (silicon oxide, silicon nitride and aluminum oxide) and film thickness were not major variables to affect the device performance. The gain reduction was prevented by the BOE treatment before the passivation. A possible explanation of this behavior is that unstable non-stoichiometric surface states produced by excess In, Ga, or As after mesa etching are eliminated by BOE treatment and reduce the surface recombination sites.
Stroboscopic X-Ray Diffraction Measurements of sub-ns Domain Dynamics in Ferroelectric Films
Authors: Zolotoyabko E. , Quintana J. P. , Towner D. J. , Wessels B. W.
Published: April 2011

We used the Advanced Photon Source (APS) at Argonne National Laboratory to perform fast (ps range) time-resolved diffraction measurements of the dynamic characteristics in BaTiO3 films subjected to strong high-frequency electric fields. The time-dependent lattice response measured at frequencies between 6.5 MHz and 1.3 GHz revealed damped domain movements with attenuation time rapidly increasing with electric field frequency, v. We found that at frequencies higher than ν ∼ 600 MHz the domain motions in BaTiO3 films become heavily damped, information that may be important to future device operation. A minimum attenuation time, τ ∼ 330 ps, measured at ν = 1.3 GHz was limited by the time constant of the electrical circuit.
Temperature Dependent Dielectric Properties of Polycrystalline 96%Al2O3
Authors: Chen Liang-Yu , Hunter Gary W.
Published: April 2011

Polycrystalline Al2O3 substrates have been proposed and tested for high temperature micro devices packaging intended for operation at temperatures up to 500°C. The dielectric properties of this material, including dielectric constant and effective volume conductivity, at elevated temperatures are of interest, especially for RF packaging applications. This article reports temperature dependent dielectric properties of polycrystalline 96% Al2O3 substrates from room temperature to 550°C measured by the AC impedance method at 120 Hz, 1 kHz, 10 kHz, 100 kHz, and 1 MHz. We observed negative temperature coefficients of volume electrical conductivity of 96% Al2O3 at 1 k, 10 k, and 100 kHz between room temperature and 50°C. The dielectric constant of the material increases significantly with temperature at frequencies below 10 kHz. The physical mechanisms of these dielectric behaviors of 96% Al2O3 at elevated temperatures are discussed.
Solvable Model of Two-Dimensional Magnetophotonic Crystal
Authors: Khanikaev A. B. , Inoue M. , Granovsky A. B. , Vinogradov A.P.
Published: April 2011

We present theoretical investigation of two-dimensional (2D) magnetophotonic crystal (MPC) with square lattice constructed from two infinite arrays of magnetoactive dielectric sheets at right angle, in the limit of very small sheet thickness and very high dielectric constant, such that their product is constant. Alteration of band structure by external magnetic field is studied. We show that optical activity reduces symmetry of the system and removes degeneracy in the photonic band structure. Also, despite of natural weakness of the magnetooptic activity, dispersion near band edges is found to be strongly sensitive to external magnetic influence.
Optical and Transport Effects in LaGa1-xMnxO3: Experiment and Modeling
Authors: Noginova N. , Chen F. , Chelule G. , Gavrilenko V. I.
Published: April 2011

Charge transport and optical properties have been studied experimentally and theoretically in a series of LaGa1-xMnxO3 crystals in the dependence on the material composition. Electron energy structure and optical functions of LaGa1-xMnxO3 are calculated by ab initio pseudopotential method within density functional theory using generalized gradient approximation. Theoretical results are discussed in comparison with the experimental data for different alloy compositions.
Room Temperature Ferromagnetic Properties of Epitaxially Grown Zn1-xCoxO Thin Films
Authors: Yun F. , Rengarajan Varatharajan , Nause J. , Morkoç H.
Published: April 2011

We have conducted a systematic magnetic characterization of a series of Zn1-xCoxO samples with different cobalt composition. The Zn1-xCoxO thin films were epitaxially grown by metal organic chemical vapor deposition (MOCVD) on quartz and ZnO substrates. The Co composition was adjusted by controlling the bubbler temperature and carrier gas flow. The magnetization measurements were performed using a Quantum Design MPMS system, which utilizes a superconducting quantum interference device (SQUID) magnetometer. Magnetic hysteresis curves were observed at 5K which persisted up to 300K, possibly characteristic of ferromagnetic behavior. Temperature dependent magnetization was recorded under both zero-field cooled (ZFC) and field cooled (FC) conditions. Changes of magnetization were observed under ZFC and FC conditions in some samples from 5K up to 300K. Composition-dependent changes in magnetization were also observed among samples with different cobalt doping, indicative of ferromagnetism related directly to cobalt incorporation. Magnetic field dependent magnetization at various temperatures with field up to 5 Tesla suggests the Zn1-xCoxO layers were not paramagnetic.
Structure, proton incorporation and transport properties of ceramic proton conductor Ba(Ce0.7Zr0.2Yb0.1)O3-δ
Authors: Li Yaping , Kolesnikov Alexander I. , Richardson James W. , Zuo Chendong , Lee Tae H. , Balachandran U.
Published: April 2011

Dense ceramics with composition Ba(Ce0.7Zr0.2Yb0.1)O3-β (BCZY) were synthesized by solid state reactions, and their structures were characterized by Rietveld refinements of time-of-flight (TOF) neutron diffraction data collected for the samples at high-temperature and controlled atmospheres. The structure phase transition from orthorhombic Imma to cubic Pm3m was observed at the temperature between 500 and 700°C and in flowing 100ppm H2/Ar gases. At 900°C, the sample was subsequently exposed to different oxygen partial pressures (pO2, ranging from ∼10−17 to ∼10−23 atm) and water vapor pressures (pH2O) up to ∼0.18 atm. The expansion of lattice parameters of BCZY, instead of following the normally expected relationship with pO2, was actually correlated with the increase of pH2O, implying proton incorporation into the structures. The presence of H-containing species in the structure was confirmed by comparing both inelastic neutron scattering spectra and neutron diffraction data collected for dry and “wet” samples at 10K. The observed vibrational peaks at 104 and 150 meV and absence of a peak around 420 meV indicate the hydrogen occupation in the structure but the absence of any hydroxyl groups (hydrogen covalently bonded to oxygen). Electrical conductivities of BCZY were investigated at different temperatures in both dry and wet conditions.
Preparation and Hydrogen Pumping Characteristics of BaCe0.8Y0.2O3-δ Thin Film
Authors: Lee T. H. , Harder B. J. , Zuo C. , Dorris S. E. , Balachandran U.
Published: April 2011

Thin films of BaCe0.8Y0.2O3-δ (BCY) were prepared by colloidal spray deposition. Dense, crack-free BCY films having a grain size of 2–7 μm were successfully deposited on NiO/BCY substrates. Electrochemical hydrogen pumping with the BCY films showed that the maximum current density increased with temperature. The maximum current density was sensitive to the moisture in the cathode gas; the value obtained with a dry cathode gas was only half that with a wet cathode gas. A very high hydrogen-pumping current density of 3.4 A/cm2 was measured at 700°C with an applied voltage of 1.5 V.
Oxygen Permeable Properties of Ce0.8Gd0.2O1.9 - MFe2O4 Composite Thin Films Prepared by a Chemical Solution Deposition Method
Authors: Kagomiya Isao , Iijima Takashi , Takamura Hitoshi
Published: April 2011

Ce0.8Gd0.2O1.9 (CGO) - MFe2O4 (M=divalent cation) is a composite-type oxygen-ionic and electronic mixed conductor. Dense nanocrysalline CGO-CoFe2O4 thin films with a thickness of approximately 1 μm were prepared on CGO porous substrates by a chemical solution spin-coating method. The oxygen permeable flux of the thin film was investigated in temperature range of 700°C - 800°C without physical leak of N2 gas. The permeable flux depends on the measuring time, when the measuring temperature was kept at 750°C before increasing to 800°C. This fact suggests that the O2 permeable properties were affected by a slight change of the film morphology and the crystallinity.
Electrical and Hydrogen Transport Properties of SrCe0.8Yb0.2O3−δ/Ni Cermet Membranes
Authors: Song S.-J. , Lee T. H. , Chen L. , Zuo C. , Dorris S. E. , Balachandran U.
Published: April 2011

Research on hydrogen separation membranes is motivated by the increasing demand for an environmentally benign, inexpensive technology for separating hydrogen from gas mixtures. Although most studies of hydrogen separation membranes have focused on proton-conducting oxides by themselves, the addition of metal to these oxides increases their hydrogen permeability and improves their mechanical stability. This study began by determining the electrical and hydrogen permeation properties of SrCe0.8Yb0.2O3−δ (SCYb). The results showed that the hydrogen permeation rate is limited by electron flow at the investigated temperatures (600 – 900°C). To further enhance hydrogen permeability, a cermet (i.e., ceramic-metal composite) membrane was made by adding Ni to the SCYb. The cermet showed no phase change after sintering in a reducing atmosphere. At 900°C, with 20% H2 /balance He as a feed gas (pH2O = 0.03 atm), the hydrogen permeation rate was 0.113 cm3/min-cm2 for Ni/SCYb (0.43-mm thick) and 0.008 cm3/min-cm2 for SCYb (0.7-mm thick). The dependences of hydrogen permeability on temperature, thickness, and hydrogen partial pressure gradients are also determined. The results demonstrate that adding Ni to SCYb considerably increases its hydrogen permeability by increasing its electron conductivity.
Specificity of the Local Structure of Nanocrystalline Doped Ceria Solid Electrolytes
Authors: Sadykov Vladislav A. , Frolova Yulia V. , Kriventsov Vladimir V. , Kochubei Dmitrii I. , Moroz Ella M. , Zyuzin Dmitrii A. , Potapova Yulia V. , Muzykantov Vitalii S. , Zaikovskii Vladimir I. , Burgina Elena B. , Borchert Holger , Trukhan Sergei , Ivanov Vyacheslav P. , Neophytides Stylianos , Kemnitz Erhard , Scheurell Kerstin
Published: April 2011

This work presents results of studies of the structural features of nanocrystalline doped Ce1−xMexO2−y samples (Me = Sm, Bi, Gd; X = 0–0.5) prepared via the polymerised precursor (Pechini) route by using a combination of diffraction (XRD, TEM, WAXS on SR) and spectroscopic (EXAFS, Raman, FTIRS of lattice modes, XPS, SIMS) methods.
Influence of B-site ion valence on ion conduction for perovskite-type Li ion conductor, (La2/3–1/3p Lip)(Mg1/2W1/2)O3 (p =0.05, 0.11 and 0.14)
Authors: Katsumata Tetsuhiro , Takahata Megumi , Mochizuki Nobuko , Inaguma Yoshiyuki
Published: April 2011

We synthesized perovskite-type Li ion conductor, (La2/3–1/3p Lip)(Mg1/2W1/2)O3 (p =0.05, 0.11 and 0.14), and investigated the variation of the Li ion conductivity with p. Furthermore, the variation of the activation energy with the valence of B-site ion was elucidated from the site potential at A-site and a bottleneck position. As results, it is suggested that the Coulomb repulsion between B-site and Li ions at the bottleneck dominates the activation energy for (La2/3–1/3p Lip)(Mg1/2W1/2)O3.
Growth of Ceria-Zirconia Electrolyte Nanostructures with High Interface Density by Using Sol-gel/GLAD Combination
Authors: Saraf Laxmikant , Matson D. W. , Young J. S. , Wang C. M. , Thevuthasan S.
Published: April 2011

We report a process for the successful incorporation of ceria in to yttria-stabilized zirconia (YSZ) columnar nanostructures grown by glancing angle deposition (GLAD) technique, resulting in high interface density columnar nanostructures. The incorporation of ceria into YSZ columns is confirmed by scanning electron microscopy (SEM) in a cross sectional geometry with in-situ analysis of elemental x-ray mapping technique and energy dispersive x-ray analysis (EDX). Controlled engineering of such nanostructures is potentially important in the future development of high efficiency solid oxide fuel cell electrolytes. The challenges and advantages of this process are discussed.
Advance in Nanostructural Electrochemical Reactors for NOX Treatment in the Presence of Oxygen.
Authors: Hamamoto Koichi , Fujishiro Yoshinobu , Awano Masanobu , Katayama Shingo , Bredikhin Sergei
Published: April 2011

Dramatic improvement in the selective separation and purification of NOX in exhaust gases by an electrochemical reactor with a catalytic electrode has been achieved. The novel electrochemical cells for NOX decomposition were developed by nano-scale control of penetrating pores from the catalytic electrode surface to the bottom of the catalytic electrode layer. The penetration pores and nano-size Ni grains are self-assembled at NiO/YSZ interfaces in the catalytic electrode by oxidization-reduction reaction of the NiO during the cell operation. In order to use reduced Ni for NOX decomposition reaction efficiently, we successfully designed a functional multilayer catalytic electrode. By multilayering of the catalytic electrode, adsorption and decomposition of coexisting oxygen in exhaust gases was suppressed and the selectivity of NOX decomposition reaction is improved. Structural change of the catalytic electrode as a result of the electrochemical processes was investigated and correlated with the NO decomposition properties of the cell.
Dendritic CuIn Films Grown by Electroless Deposition
Authors: Lane David W , Painter Jonathan D , Rogers Keith D , Forbes Ian , Miles Robert W , Hynes Kathleen M
Published: April 2011

CuInS2 films are often grown in a two-step process with the deposition of a Cu-In alloy followed by high temperature sulphurisation in either S vapour or H2 S. Numerous techniques exist for the deposition of Cu-In. In this work Cu-In films have been deposited on tin oxide coated glass using the electroless deposition technique, a low cost, low temperature approach. The films were found to consist of a two layered structure. Initially, Cu islands grew forming a layer on the substrate. The deposition process subsequently produced dendritic Cu-In alloys from the tops of the Cu islands. Various CuIn phases were observed, namely Cu9In4 and CuIn, the presence of which was related to the solution pH. None of the films were found to contain metallic In, indicating that this process may be well suited to subsequent high temperature sulphurisation.
Absorber Films of Antimony Chalcogenides via Chemical Deposition for Photovoltaic Application
Authors: Nair M. T. S. , Rodríguez-Lazcano Y. , Peña Y. , Messina S. , Campos J. , Nair P. K.
Published: April 2011

Antimony sulfide thin films (300 nm) have been deposited on glass substrates at 1–10°C from chemical bath. When heated these become crystalline and photoconductive with optical band gap (direct) of 1.7 eV. Thin films formed from chemical baths containing SbCl3 and sodium selenosulfate are of mixed phase Sb2O3/Sb2Se3, which when heated in the presence of Se-vapor converts to single phase Sb2Se3 film with optical band gap of 1.1 eV. Such films possess dark conductivity of 10-8 ohm-1cm-1 and show photosensitivity of two orders. Reaction of Sb2S3-CuS in nitrogen at 400°C produces crystalline, photoconductive p-type CuSbS2 with optical band gap (direct) of 1.5 eV. By controlling the deposition and heating condition, (i)Sb2S3-(p)CuSbS2 layer is formed, which is utilized in a photovoltaic structure, (n)CdS:In-(i)Sb2S3-(p)CuSbS2, with a Voc of 345 mV and Jsc 0.18 mA/cm2 under 1 kW m-2 tungsten halogen illumination. In the case of a structure, CdS:Cl-Sb2S3-Cu2-xSe, Voc of 350 mV and Jsc of 0.5 mA/cm2 are observed.
AgSbSe2 thin films for photovoltaic structures produced through reaction of chemically deposited selenium thin films with Ag and Sb2S3
Authors: Bindu K. , Nair M. T. S. , Nair P. K.
Published: April 2011

Selenium thin films (350 nm) deposited from a 0.01 M solution of Na2SeSO3 of pH 4.5 maintained at 10 °C for 13 h, have been used as a source of selenium vapour for reaction with vacuum deposited Ag thin film on chemically deposited Sb2S3+Ag layers. When a stack of Sb2S3+Ag is heated in contact with Se film, AgSbSe2 is formed through solid state reaction of Sb2S3 and Ag2Se. The latter is formed at 80°C through the reaction of Ag-film in Se-vapour. This thin film is photoconductive and p-type. The optical band gap is nearly 1 eV and dark conductivity, 10-3 Ω-1cm-1. This thin film has been incorporated to form a photovoltaic structure, SnO2:F-(n)CdS:In-(i)Sb2S3-(p)AgSbSe2-silver print. Voc> 400 mV and Jsc>12 mA/cm2 have been observed in this under an illumination intensity of 1 kWm-2.
Current Transport Study of Schottky and P-N Junction Solar Cells Using Metal-Induced Growth Poly-Si Thin Films
Authors: Ji Chunhai , Kim Joon-Dong , Anderson Wayne A.
Published: April 2011

Poly-Si thin films deposited at low temperature by using the metal-induced growth (MIG) method have the advantage of less metal impurity contaminations and relative large grains with preferred crystal orientation of (220). In recent research, the Schottky solar diode made of MIG poly-Si shows Jsc of 12 mA/cm2 and Voc of 0.214V. In this paper, current transport mechanisms were studied by current-voltage-temperature (I-V-T) testing from 100 K to 400K. For the samples deposited by a one-step sputtering process, the large value of ideality factor (n) and abnormal increase of barrier height with the temperature implies that the current transport mechanism does not follow the pure thermionic-emission theory, which was proven to be thermionic-field emission due to the highly doped Si film. By using a two-step sputtering process, the ideality factor and Au-Schottky barrier height at room temperature were about 1.5 and 0.7 eV, which was improved from one-step sputtering. Hydrogenation by electron cyclotron resonance (ECR) plasma can further improve the Schottky diode ideality factor and barrier height. Although a low-level Phosphors-doped Si target was used for poly-Si thin film deposition, a thermionic-field emission mechanism was still found by plotting the activation energy (E0) versus the testing temperature range. Capacitance-voltage (C-V) analysis revealed an unexpected carrier density of 1017 cm−3 level, which is 1000 times higher than the doping density level in the Si film. “Oxygen thermal donor” effect was assumed due to high oxygen level (1020 cm−3) detected by SIMS and processing at ∼ 600 °C. Increasing of the total carrier density due to the oxygen donor may cause the transport mechanism change from pure thermionic emission to thermionic-field emission. Reducing oxygen in the Si film by filtering the sputtering gas to 50 ppb oxygen level was proven to be effective. C-V results gave ∼1016 cm−3 level of carrier density after using oxygen filtering. P-N junction solar cells were made by B-ion implantation into n-type Si film and dopant activation at 700 °C. I-V-T study showed similar curves for P-N junction as for Schottky junction devices. This implies that the current transport was dominated by the Si films instead of the junctions for both Schottky and P-N junction devices.
Metamorphic GaInP-GaInAs Layers for Photovoltaic Applications
Authors: Bett A. W. , Baur C. , Dimroth F. , Schöne J.
Published: April 2011

GaxIn1−xAs and GayIn1−yP layers were grown lattice mismatched to GaAs and Ge by low-pressure metal organic vapor phase epitaxy (LP-MOPVE). These materials are very promising for further increasing the efficiency of monolithic triple-junction solar cells. Different buffer layer structures were realized. Transmission electron microscopy and x-ray diffraction analysis were used to characterize the quality of the crystal. Both linear and step-graded buffers in GaxIn1−xAs were successfully used under an active solar cell structure. GayIn1−yP as buffer material showed a worse performance. Excellent solar cell performance was achieved for lattice mismatched single-, dual- and triple-junction solar cells.
Effects of Grain Boundaries in Amorphous/Multicrystalline Silicon Heterojunction Photovoltaic Cells
Authors: Farrokh Baroughi M. , Sivoththaman S.
Published: April 2011

Spectral response and dark current-voltage characteristics of heterojunctions are used to investigate grain boundary degradation in photovoltaic properties of a-Si/mc-Si heterojunction solar cells. Measured spectral response inside the grain and on the grain boundary shows small but consistent QE degradation due to minority carrier recombination at the grain boundaries. No consistent difference is observed in dark current-voltage characteristics because of large diode area and periphery leakage current in the employed heterojunction diodes. Comparing measurement results and results from device modeling using the simulation software Medici, a recombination velocity of 4900 cm/sec is found at the grain boundaries of employed multicrystalline silicon wafer. The modeling and experimental results can also be used to define an effective grain area that serves as a measure of grain boundary recombination and the influence of grain size.
Characterization of the Local Titanium Environment in Doped Sodium Aluminum Hydride using X-ray Absorption Spectroscopy
Authors: Graetz J. , Ignatov A.Yu. , Tyson T.A. , Reilly J.J. , Johnson J.
Published: April 2011

Ti K -edge x-ray absorption spectroscopy was used to explore the local titanium environment and valence in 2–4 mol% Ti-doped sodium alanate. An estimate of the oxidation state of the dopant, based upon known standards, revealed a zero-valent titanium atom. An analysis of the near-edge and extended fine structures indicates that the Ti does not enter substitutional or interstitial sites in the NaAlH4 lattice. Rather, the Ti is located on/near the surface and is coordinated by 10.2±1 aluminum atoms with an interatomic distance of 2.82±0.01 Å, similar to that of TiAl3. The Fourier transformed EXAFS spectra reveal a lack of long-range order around the Ti dopant indicating that the Ti forms nano-clusters of TiAl3. The similarity of the spectra in the hydrided and dehydrided samples suggests that the local Ti environment is nearly invariant during hydrogen cycling.
Noncovalent Functionalization of Single Walled Carbon Nanotubes Using Alternate Layer-By-Layer Polyelectrolyte Adsorption for Nanocomposite Fuel Cell Electrodes
Authors: Dhullipudi R. B. , Dobbins T. A. , Adiddela S.R. , Zheng Z. , Gunasekaran R. A. , Lvov Y. M. , Tittsworth R.
Published: April 2011

Electrodes which are resistant to chemical poisoning by CO, S, and other fuel impurities are needed to replace Pt in proton exchange membrane (PEM) fuel cells. We have designed composite electrodes comprised of single walled carbon nanotubes (CNTs) within a conducting polymer matrix. A method for solubilizing single-walled carbon nanotubes (CNTs) in aqueous media using polyelectrolyte layer-by-layer (LbL) nanoassembly of polystyrene sulfonate (PSS) and polyallylamine (PAH) at the CNT surface is elucidated. Once soluble, the CNTs were assembled onto planar substrates using alternate LbL nanoassembly to form nanocomposite films. These films will later be tested for their potential as alternative anodes in proton exchange membrane fuel cells.
Magnesium-Hydride Slurry Technology for Hydrogen Storage
Authors: Krishnan A. , Lu X. G. , Pal U. B. , McClaine A. W.
Published: April 2011

Magnesium hydride particles are suspended in an oil-based medium with dispersants to create a slurry that has great potential for hydrogen production and storage. Hydrogen is generated whenever needed by mixing the magnesium hydride slurry with water in a mixer. The byproduct is benign magnesium hydroxide (milk of magnesia). The primary purpose of the slurry is to moderate the reaction, allow thermal management and make it pumpable so it can be transported and metered like liquids so that the existing transportation infrastructure can be used. Thus, the magnesium hydride slurry lends itself well for automotive applications in conjunction with fuel cells. For such large-volume automotive applications, the success and economic viability of employing magnesium hydride slurry to transport and store hydrogen will depend on developing an effective recycling system for the magnesium hydroxide by-products. This paper discusses the feasibility of employing the Solid-Oxide-Oxygen-Ion-Conducting-Membrane (SOM) process for converting the by-product magnesium hydroxide to magnesium and regenerating the magnesium hydride slurry. The SOM process, in principle, utilizes a tubular yttria-stabilized-zirconia-based solid-oxide-fuel-cell as an anode in the temperature range 1100 – 1300 °C. The magnesium hydroxide is dissolved in a molten ionic flux and with the application of an electrical potential between an inert cathode in the flux and the anode, the oxygen ions are pumped out of the flux through the zirconia membrane and are oxidized at the anode. Magnesium vapor evolves at the cathode and is condensed in a separate chamber (condenser). By performing in-situ reforming of gaseous hydrocarbons within the tubular zirconia anode one can minimize the electrical power required for the electrolysis and generate the required hydrogen needed to convert the magnesium vapors in the condenser back to magnesium hydride.
Atomically Resolved STM Images of CVD Grown Carbon Nanotubes
Authors: Chiang Daniel , Lei Philip Zifeng , Dong Lifeng , Jiao Jun
Published: April 2011

Atomically resolved images of single-wall carbon nanotubes (CNT) grown in a chemical vapor deposition (CVD) chamber were obtained with the scanning tunneling microscope (STM) under ambient conditions. We found that the average diametersdof the CVD-grown CNTs appear to fall into a bimodal distribution of 1.0 and 0.6 nm, and the chiral angle Ø was observed to be close to zero degree. The summation of the lattice indices(n+m)was determined to be 14 and 9 ford=1.0nm andd=0.6nm, respectively. The most possible lattice index pairs(n, m)with a chiral angle close to zero degree are(7, 7)and(5, 4), which indicates that the larger nanotubes are metallic and the smaller nanotubes are semi-conductive.
A Scanning Tunneling Microscopy Study: Si/SiO2 Interface Roughness Induced by Chemical Etching
Authors: Yu Jixin , Liu Lequn , Lyding Joseph W.
Published: April 2011

The Si/SiO2 interface roughness has received tremendous interest due to its relation to channel mobility degradation and dielectric reliability. We have used ultra-high vacuum scanning tunneling microscopy to directly examine the Si/SiO2 interface and study the roughening effect caused by chemical etching. The rms-roughness extracted quantitatively from the STM topography was found to be doubled from 0.111nm to 0.232nm by the normal NH4OH/H2O2 treatment, and further increased to 0.285nm for additional etching steps. It was also found that there were no regular single steps on the SiO2/Si(100) interface.
Optical near-field enhancement around lithographic metallic nanostructures using an azo-dye polymer: direct observation and realization of sub-wavelength complex structures
Authors: Hubert Christophe , Rumyantseva Anna , Lérondel Gilles , Grand Johan , Kostcheev Sergeï , Billot Laurent , Vial Alexandre , Bachelot Renaud , Royer Pascal , Chang Gilbert , Gray Stephen K. , Wiederrecht Gary P. , Schatz George C.
Published: April 2011

We report on the direct observation of optical near-field enhancement around metallic nanoparticles. We used an easy to set up approach which consists in irradiating a photosensitive azo-dye polymer film spin-coated on metallic nanostructures. Photoinduced topographical modifications of the polymer film surface are characterized after irradiation by atomic force microscopy (AFM). Comparisons between AFM images and numerical simulations show that these photo-induced topography agrees with the near-field intensity distribution around the nano-structures. The possibility of generating complex structures is demonstrated.
The Features of Investigations and Observations of Nanoamorphous Metals and Nanocrystalline Oxides on Electron Microscope
Authors: Malkhasyan R. , Karakhanyan R. , Nazaryan M. , Khachatryan A. , Markosyan A.
Published: April 2011

The present paper discusses two different active influences of an electron beam on a nanosize sample.

The first observed influence is the formation of nanoparticle agglomerates due to the beam charge. This can be likened to the formation of fine sand and it enables the determination of grain magnitude of the given nanomaterial. This also enables to get a clear picture of the sample, which is latent at first due to the coating of nanoparticles and their agglomerates. For example, removal of nanopowder coatings has enabled for the first time to find self - assembling systems in a shape of double chain spatial helixes from inorganic particles (as DNA).

The second type of influence is related to transformations, which distort the sample. Transformation of amorphous particles of metal into a crystalline state by means of local heating is the one of most importance.

Growth of thread-shaped hollow and solid nanowhiskers from nanoparticles and their further disintegration to a great number of small crystals under influence of electron beam in the chamber of electron microscope was observed. Therefore it can be confirmed that it is necessary to use an electron microscope with special precautionary measures, when working with nanoamorphous metals.
Stress relaxation and medium-range order in diamond-like amorphous carbon films
Authors: Chen Xidong , Sullivan John , Friedmann Tom , Miller Dean
Published: April 2011

In this paper, we have studied the relationship between medium-range order structures in and stress relaxation in amorphous diamond-like carbon films with fluctuation microscopy. Our preliminary results show strong correlation between stress relaxation and medium-range order. Our previous results showed that annealing films that had been through stress relaxation procedures caused great increase of medium-ranger order. In this paper, we have found that the increase of medium-range order in films that have been annealed before going through stress relaxation through removal of substrates is less pronounced than that of films that have been annealed after removal of substrates. We will discuss interpretations and implications of these results.
Structure and Dynamics of Water Adsorbed in Carbon Nanotubes: A Joint Neutron-Scattering and Molecular-Dynamics Study
Authors: de Souza Nicolas R. , Kolesnikov Alexander I. , Loong Chun-Keung , Moravsky Alexander P. , Loutfy Raouf O. , Burnham Christian J.
Published: April 2011

The advent of nanocarbons, from single- and multiple-walled nanotubes to nanohorns, avails model studies of confined molecules on the nanoscale. Water encapsulated inside the quasi-one-dimensional channels of these materials is expected to exhibit anomalous behavior due to the unique geometry of nanotubes and the weak interaction between the water molecules and the carbon atoms. We have employed neutron small-to-wide angle diffraction, quasielastic and inelastic scattering in conjunction with molecular-dynamics simulations to characterize the structures and dynamics of water adsorbed in open-ended single- and double-walled nanotubes over a wide range of spatial and temporal scales. We find that a square-ice sheet wrapped next to the inner nanotube wall and a water chain in the interior are the key structural elements of nanotube-confined water/ice. This configuration results in a hydrogen-bond connectivity that markedly differs from that in bulk water. This significantly softened hydrogen-bond network manifests in strong energy shifts of the observed and simulated inter- and intra-molecular vibrations. The very large mean-square displacement of hydrogen atoms observed experimentally and the strong anharmonicity inferred from simulations explain the fluid-like behavior at temperatures far below the freezing point of normal water.
X-ray scattering: a wonderful tool to probe lattice strains in materials with small dimensions
Authors: Thomas Olivier , Loubens Audrey , Gergaud Patrice
Published: April 2011

X-ray diffraction was recognized from the early days as highly sensitive to atomic displacements. Indeed structural crystallography has been very successful in locating with great precision the position of atoms within an individual unit cell. In disordered systems it is the average structure and fluctuations about it that may be determined. In the field of mechanics diffraction may thus be used to evaluate elastic displacement fields. In this short overview we give examples from recent work where x-ray diffraction has been used to investigate average strains in lines, films or multilayers. In small objects the proximity of surfaces or interfaces may create very inhomogeneous displacement fields. X-ray scattering is again one of the best methods to determine such distributions. The need to characterize displacement fields in nanostructures together with the advent of third generation synchrotron radiation sources has generated new and powerful methods (anomalous diffraction, coherent diffraction, microdiffraction, …). We review some of the recent and promising results in the field of strain measurements in small dimensions via X-ray diffraction.
Single-state electronic structure measurements using time-resolved x-ray laser induced photoelectron spectroscopy
Authors: Nelson A. J. , Dunn J. , van Buuren T. , Hunter J.
Published: April 2011

We demonstrate single-shot x-ray laser induced time-of-flight photoelectron spectroscopy on semiconductor and metal surfaces with picosecond time resolution. The LLNL COMET compact tabletop x-ray laser source provides the necessary high photon flux (>1012/pulse), monochromaticity, picosecond pulse duration, and coherence for probing ultrafast changes in the chemical and electronic structure of these materials. Static valence band and shallow core-level photoemission spectra are presented for ambient temperature Ge(100) and polycrystalline Cu foils. Surface contamination was removed by UV ozone cleaning prior to analysis. In addition, the ultrafast nature of this technique lends itself to true single-state measurements of shocked and heated materials. Time-resolved electron time-of-flight photoemission results for ultra-thin Cu will be presented.
In situX-ray Reflectivity Study of Oxidation Kinetics in Iron and Stainless steel
Authors: Kim D. H. , Kim S. S. , Lee H. H. , Jang H. W. , Kim J. W. , Tang M. , Liang K. S. , Sinha S. K. , Noh D. Y.
Published: April 2011

In situspecular x-ray reflectivity was applied to study the growth kinetics of passive oxide films on iron and stainless steel substrates in pH 8.4 borate buffer solution. Under electrical potential from 0 to 800 mV, the growth rate of oxide films decreases exponentially in thickness following the direct logarithmic growth law predicted in the point defect model. The electric field in the oxide on iron is independent of the applied potentials consistent with the point defect model. In stainless steel, however, the electric field depends strongly on the applied potential indicating that the oxide properties change as the applied potential varies.
Fluctuation X-ray Microscopy for Measuring Medium-Range Order
Authors: Fan Lixin , McNulty Ian , Paterson David , Treacy Michael M.J. , Murray Gibson J.
Published: April 2011

Many x-ray techniques exist to probe long- and short-range order in matter, in real space by imaging and in reciprocal space by diffraction and scattering. However, measuring mediumrange order (MRO) in disordered materials is a long-standing problem. Based on fluctuation electron microscopy, which was applied successfully to the understanding of MRO in amorphous materials, we have developed fluctuation x-ray microscopy (FXM). This novel approach offers quantitative insight into medium-range correlations in materials at nanometer and larger length scales. It examines spatially resolved fluctuations in the intensity of a series of x-ray speckle patterns. The speckle variance depends on higher order correlations that are more sensitive to MRO. Systematically measuring the speckle variance as function of the momentum transfer and x-ray illumination size produces a fluctuation map that contains information about the degree of MRO and the correlation length. This approach can be used for the exploration of MRO and subtle spatial structural changes in a wide range of disordered materials from soft condensed matter to nanowire arrays, semiconductor quantum dot arrays and magnetic materials. It will also help us to understand the mechanisms of order-disorder transitions and may lead to control of ordering, which is important in developing ordered structures tailored for particular applications. A theory for FXM and preliminary experimental results from polystyrene latex spheres are discussed in this paper.
2D and 3D X-Ray Structural Microscopy Using Submicron-Resolution Laue Microdiffraction
Authors: Budai John D. , Yang Wenge , Larson Bennett C. , Tischler Jonathan Z. , Liu Wenjun , Ice Gene E.
Published: April 2011

We have developed a scanning, polychromatic x-ray microscopy technique with submicron spatial resolution at the Advanced Photon Source. In this technique, white undulator radiation is focused to submicron diameter using elliptical mirrors. Laue diffraction patterns scattered from the sample are collected with an area detector and then analyzed to obtain the local crystal structure, lattice orientation, and strain tensor. These new microdiffraction capabilities have enabled both 2D and 3D structural studies of materials on mesoscopic length-scales of tenths-to-hundreds of microns. For thin samples such as deposited films, 2D structural maps are obtained by step-scanning the area of interest. For example, 2D x-ray microscopy has been applied in studies of the epitaxial growth of oxide films. For bulk samples, a 3D differential-aperture x-ray microscopy technique has been developed that yields the full diffraction information from each submicron volume element. The capabilities of 3D x-ray microscopy are demonstrated here with measurements of grain orientations and grain boundary motion in polycrystalline aluminum during 3D thermal grain growth. X-ray microscopy provides the needed, direct link between the experimentally measured 3D microstructural evolution and the results of theory and modeling of materials processes on mesoscopic length scales.
Microscopic View on Grain Nucleation and Growth Kinetics During Solidification of Aluminum Alloys
Authors: Iqbal N. , van Dijk N. H. , Offerman S. E. , Moret M. , Katgerman L. , Kearley G. J.
Published: April 2011

X-ray diffraction with hard X-rays (E = 70 keV) was used to investigate the grain nucleation and grain growth during solidification of a grain refined Al-0.3Ti-0.02B (wt.%) alloy. The investigations showed for the first time the nucleation profile during solidification and how nucleation rate increases with cooling rate. The results indicate that the nucleation process is complete for solid fraction below 30 %, irrespective of the cooling rate. This is explained in terms of the release of latent heat during solidification. The growth of individual aluminium grains during solidification is experimentally observed and compared to model predictions for the diffusion limited grain growth. The experimental results are only in agreement with the theory in the first stage of the transformation. The difference between the experiment and the theory is discussed qualitatively.
In-Situ Neutron Diffraction Study of Strain-Induced Martensite Formation in 304L Stainless Steel at a Cryogenic Temperature
Authors: Tao Kaixiang , Wall James J. , Brown Donald W. , Li Hongqi , Vogel Sven C. , Bourke Mark A. M. , Choo Hahn
Published: April 2011

In-situ, time-of-flight neutron diffraction was performed to investigate the martensitic phase transformation during quasi-static uniaxial compression testing of 304L stainless steel at 300K (room temperature) and 203K. In-situ neutron diffraction study enabled the bulk measurement of intensity evolution for each hkl atomic plane during the austenite (fcc) to martensite (hcp and bcc) phase transformation. The neutron diffraction patterns show that the martensite phases started to develop at about 2.5% applied strain (600 MPa applied stress) at 203K. However, at 300K, the martensite formation was not observed throughout the test. Furthermore, from changes in the relative intensities of individual hkl atomic planes, the selective phase transformation can be well understood and the grain orientation relationship between the austenite and newly-forming martensite phases can be determined. The results show that the fcc grain families with {111} and {200} plane normals parallel to the loading axis are favored for the “fcc to hcp” and “fcc to bcc” transformations, respectively.
Probing Mesoscopic Strain Evolution during Creep Deformation: An In-Situ Neutron Diffraction Study
Authors: Choo Hahn , Brown Donald W. , Bourke Mark A. M. , Swindeman Robert W.
Published: April 2011

The development of lattice strain was studied using in-situ time-of-flight neutron diffraction during constant-load tensile creep deformation of an austenitic 316FR stainless steel at 180, 240, and 300MPa at 873K (a power-law creep regime) with time resolution of 900 seconds. The macroscopic (global) and mesoscopic (lattice) strains were measured simultaneously during creep using an extensometer and neutron diffraction, respectively. The hkl-specific lattice strains were measured to gain insights into the plastic anisotropy at various stages of creep deformation (i.e., primary, secondary, and tertiary regimes). Furthermore, the creep-induced lattice strain behavior was compared to the result obtained from a quasistatic tension test at 873K. The lattice strain evolution in the axial direction (direction parallel to the tensile loading axis) during the primary and secondary creep (dislocation creep) is quite similar to the quasistatic case (slip). However, in the tertiary creep regime, the creep-induced lattice strain accumulation is smaller than the quasistatic case at a given total strain, except the (111) reflection.
Micro-Raman Mapping and Analysis of Indentation-Induced Phase Transformations in Germanium
Authors: Jang Jae-il , Lance M. J. , Wen Songqing , Huening J. J. , Nemanich R. J. , Pharr G. M.
Published: April 2011

Although it has been confirmed by diamond anvil cell experiments that germanium transforms under hydrostatic pressure from the normal diamond cubic phase (Ge-I) to the metallic β-tin phase (Ge-II) and re-transforms to Ge-III (ST12 structure) or Ge-IV (BC8 structure) during release of the pressure, there are still controversies about whether the same transformations occur during nanoindentation. Here, we present new evidence of indentation-induced phase transformations in germanium. Nanoindentation experiments were performed on a (100) Ge single crystal using two triangular pyramidal indenters with different tip angles - the common Berkovich and the sharper cube-corner. Although the indentation load-displacement curves do not show any of the characteristics of phase transformation that are well-known for silicon, micro-Raman spectroscopy in conjunction with scanning electron microscopy reveals that phase transformations to amorphous and metastable crystalline phases do indeed occur. However, the transformations are observed reproducibly only for the cube-corner indenter.
Modeling indentation in linear viscoelastic solids
Authors: Cheng Yang-Tse , Cheng Che-Min
Published: April 2011

Using analytical and finite element modeling, we study conical indentation in linear viscoelastic solids and examine the relationship between initial unloading slope, contact depth, and viscoelastic properties. We will then discuss whether the Oliver-Pharr method for determining contact depth, originally proposed for indentation in elastic and elastic-plastic solids, is applicable to indentation in viscoelastic solids.
Correlated Single Molecule Fluorescence and Scanning Probe Microscopies: Applications to the Study of Soft Materials
Authors: Slade Andrea L. , Shaw James E. , Yang Guocheng , Chhabra Neetu , Yip Christopher M.
Published: April 2011

We recently developed an integrated imaging platform that combines single molecule evanescent wave fluorescence imaging (and spectroscopy) with in situ scanning probe microscopy. The advantages, challenges, and potential represented by this coupled tool will be described in the context of the structure-function characteristics of nanostructured biomaterials and thin lipid films.