bluuebunny/crossref_metadata_2025 huggingface dataset:
Low Temperature Deposition of Transparent Ultra Water-Repellent Thin Films by Microwave Plasma Enhanced Chemical Vapor Deposition
Authors: Wu Yunying , Inoue Yasushi , Sugimura Hiroyuki , Takai Osamu
Published: April 2011

One of the most common methods for obtaining water repellent surfaces is spreading fluoropolymer or fluoroalkylsilane onto substrates. However, this method is not applicable to low heat-resistant substrates such as plastics, since after spreading, the method requires a heating process which is generally conducted at a temperature of about 600K. The objective of this study is the preparation of ultra water-repellent and optically transparent thin films at low temperatures below 373K. The films were deposited by means of microwave plasma enhanced plasma chemical vapor deposition (MPECVD) using organosilane, that is, trimethylmethoxysilane (TMMOS) as a source with adding Ar, CO2, N2, O2 or air as an excitation gas. Under optimized preparation conditions, films with water contact angles more than 150 degrees and optical transparencies more than 90% were successfully fabricated.
New Approaches to the Characterization of Obsidian from the Mediterranean Island Sources: Interpreting Chronological Change in Neolithic Sardinia and Corsica
Authors: Tykot Robert H.
Published: April 2011

Geochemical fingerprinting of obsidian sources was first applied in the Mediterranean region nearly four decades ago. Since then, a number of analytical methods (e.g. INAA, XRF, SEM/Microprobe, ICP-MS) have proven successful in distinguishing the Mediterranean island sources of Giali, Lipari, Melos, Palmarola, Pantelleria, and Sardinia. Moreover, recent geoarchaeological surveys of the central Mediterranean sources have resulted in the more precise location and documentation of each obsidian flow or outcrop, and multiple chemical groups have been identified on at least three of the islands. The ability to specifically attribute artifacts to one of at least five obsidian flows in the Monte Arci region of Sardinia, for example, has enabled the study of specific patterns of source exploitation and the trade mechanisms which resulted in the distribution of obsidian hundreds of kilometers away during the Neolithic period (ca. 6000-3000 BC).

Results are presented here from the chemical analysis of 186 artifacts from several sites in Sardinia and Corsica as part of the largest and most comprehensive study of obsidian sources and trade in the Mediterranean. Analyses of large numbers of artifacts demonstrate the differential use of island subsources, which may be attributed to factors such as access (e.g. topography, distance from coast), size and frequency of nodules, and mechanical and visual properties. The patterns of source exploitation revealed by this study specifically support a down-the-line model of obsidian trade during the neolithic period. In addition, the spatial and chronological patterns of obsidian distribution may be used to address such issues as the colonization of the islands; the introduction of neolithic economies; and the increasing social complexity of neolithic and bronze age societies in the central Mediterranean.
Ancient Raw Copper from Primary Smelting Sites in Cyprus
Authors: Fasnacht W. , Northover J.P.
Published: April 2011

Finds of metallic copper from various primary smelting sites in the Sia valley in Cyprus have been analysed by ICP-OES for their composition and by optical and electron microscopy for metallography. Results show a characteristic pattern of impurities for each of the sites examined which allow an assignment to specific types of ore body and geological matrix. Different zones of the Cyprus Ophiolite Complex were exploited in different periods in antiquity, but these results show different types could be exploited contemporaneously within a specific period, especially during the first millennium BC. One location in this area, Agia Varvara-Almyras, an Iron Age copper smelting site with the only complete chain of operation recorded in ancient Cypriote metallurgy, is used to show how analytical work can guide future field surveys to find ancient furnaces, slag heaps and mines. The ultimate goal of the project is to extend it to reconstruct the complete history of copper production in a well-defined mining district over the last 4000 years.
Examination of Gilded Bronze Artifacts Using Nondestructive Eddy Current Techniques
Authors: Bernstein Johanna R. , McCarthy Blythe
Published: April 2011

In the examination of gilded bronze objects, the analysis of the thickness of the gilding layer, the condition of the substrate and the gilding method is often difficult to manage without taking samples. Yet, the resulting information is vital to research on ancient metalworking and can answer questions of authenticity. The use of nondestructive eddy current techniques can overcome these sampling limitations. Eddy current methods are typically used in the automotive, power and aerospace industries for flaw inspection and alloy selection. In this method, the interaction of an electromagnetic field induced by a coil probe with the metal surface shifts the probe impedance which is measured and correlated to properties of the metal. Results are presented which show that eddy current testing can be used to characterize a gilding layer on a bronze substrate by variations in thickness or composition.
Organization of Flint Sickle Blade Production at an Early Bronze Age Workshop in Anatolia
Authors: Hartenberger Britt E.
Published: April 2011

A specialized workshop for the manufacture of flint sickle blades has recently been excavated at the site of Titris Hoyuk in southeastern Anatolia [1]. This paper will examine the sequence of production for the blades as well as the social context of this craft within the site. The workshop is the first example found containing evidence of the complete sequence of production for the ‘Canaanean blade,’ a type commonly used across the Near East in this period [2]. Since bronze was still new and relatively expensive, high-quality flint was used to manufacture sickle blades. Tabular flint was imported in the form of large slabs from several sources in the nearby hills. Specialists then prepared the blade cores, removed the blades, and then traded the final products to local farmers. A range of manufacturing debris has been found to illustrate the production sequence, including chunks of raw flint, core-shaping pieces, debitage pits, and stacks of exhausted and used cores. The large sample of over 1000 blade cores collected ensures a sizable data set for statistical analyses. Several types of raw flint were utilized for making the blades and production appears to vary slightly by these material types. The workshop is located within a household setting and is the only area within the excavated site containing debris from this craft. Spatial analyses of the types of flint used within the household workshop reveal its division into largely distinct areas for domestic versus specialist craft activities. The placement of the workshop in the suburbs far from the site's administrative center may indicate that its activities were independent of any elite. An estimate of the volume of blades produced combined with the location of the workshop at a major regional center suggest that it also supplied blades to other sites in the region.
The Technological Tradition of Korean Black Ware and The Indigenous Development of Glaze Technology In Korea During The First Millennium A.D.
Authors: Hooper Jennifer J. , Vandiver Pamela B.
Published: April 2011

A collection of 70 black ware shards excavated from 16 kiln sites in South Korea and dating from the 3rd-13th centuries were studied using optical microscopy, scanning electron microscopy, and electron beam microprobe analysis to determine the range of technological variability in composition, microstructure and firing temperature. Materials analysis provided a means of deconstructing and reconstructing the development of (1) consistent high temperature firing, (2) unintentional ash glazing on black ware, (3) intentionally applied black glazes, (4) the relationship of grey and black glazes to green and white ones. This paper addresses issues of the influence of high-firing technology on glaze development and the development and continuity of the black glaze tradition. In addition, the black glazed Onggi ware of the late 19th century was compared to the earlier black-glaze tradition, once stabilized in composition in the Koryo dynasty, and results suggest a technological connection with the earlier tradition.
Textile-Clay Laminates: a new-found craft technology from ancient Mesoamerica
Authors: Beaubien Harriet F. , Kaplan Emily , Shah Monica
Published: April 2011

Two Maya-period sites, Las Pacayas and Aguateca, have recently yielded fragments composed of a previously unknown material -- a laminate formed from multiple layers of woven cloth and clay slip. On-site and laboratory conservation efforts enabled the Aguateca finds to be identified as ceremonial headdress elements. Materials analysis and replication experimentation have elucidated technological aspects of this medium, and demonstrate its suitability for fabricating elaborate, lightweight items such as these.
Thin-Film Aerogel Porosity and Stiffness Characterized by Surface Acoustic Wave Spectroscopy
Authors: Flannery C.M. , Murray C. , Baklanov M.R. , Streiter I. , Schulz S.E.
Published: April 2011

Density/porosity and stiffness are the most critical parameters determining properties of porous films, however they are difficult to measure. Here we report characterization of density/porosity and Young's modulus values of a range of nanoporous silica aerogel films via dispersion of laser-generated wideband surface acoustic waves. Results are compared to dielectric constant, Rutherford Backscattering Spectrometry (RBS), Ellipsometric Porosimetry (EP) and Nanoindentation (NI). RBS density correlates well to SAW. EP and NI also show a correlation, however the absolute values do not match. Low Young's modulus values show that the film stiffness is drastically reduced with increasing porosity. The technique is rapid, nondestructive and relatively inexpensive, and yields absolute values of nanoporous aerogel elastic properties which are useful for process control and are difficult to access with other techniques.
Molecular Structure of Interphases Formed by Plasma Polymerized Acetylene Films and Steel Substrates
Authors: Rosales P. I. , Krusling E. J. , Boerio F. J. , Dillingham R. G.
Published: April 2011

The goal of this research was to determine the molecular structure of interfaces between plasma polymerized acetylene films and steel substrates and to elucidate the mechanisms by which the films adhere to the substrates. Inductively-coupled, RF-powered plasma reactors interfaced to an FTIR spectrometer and to an XPS spectrometer were used to deposit films ranging in thickness from a few tens of nanometers to approximately one nanometer onto polished steel substrates. As the thickness of the films was decreased, features in the XPS and FTIR spectra that were characteristic of the bulk of the films decreased in intensity and features characteristic of the interface increased in intensity. A band was observed near 1706 cm−1 in FTIR spectra of the thickest films and attributed to carbonyl groups. Bands were observed near 1600 and 1045 cm−1 in spectra of the thinnest films and attributed to iron carboxylate and iron alkoxide groups that were responsible for adhesion of the films to the substrates. Oxygen required to form these groups was available from water or oxygen molecules adsorbed onto the walls of the reactor.
Influence of Metal Electrodes on the Ferroelectric Responses of Poly(vinylidene fluoride-trifluoroethylene) Copolymer Thin Films
Authors: Xia Feng , Zhang Q. M.
Published: April 2011

Ferroelectric polymer thin films have been investigated for applications such as sensors, MEMS, and memory devices, just name a few. In these thin film devices, it is anticipated that the interface effect will play an important role in determining the device performance. In this paper, we present the results of a recent study on the influence of metal electrodes on ferroelectric switching behavior of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) polymer thin films. The results show that the influence of metal electrodes on the polarization response can be divided into two effects, the bulk effect and interface effect. The bulk effect manifests itself as the built-in bias field when metal electrodes with different work functions were used on the two surfaces of the P(VDF-TrFE) film. The interface effect is more complicated but is directly related to the metal work function. For a metal I/insulator (ferroelectric film)/metal II (MIM) sandwich structure in which the metal I and metal II possess different work functions, the low frequency polarization hysteresis loop shows asymmetric response (different switching fields). The polarization switching time also depends on whether the applied voltage is in parallel or anti-parallel to the built-in bias field. In the fast polarization switching process, it was observed that the interface effect plays a dominating role and the switching time is mainly limited by the charge injection from metal electrodes to the polymer film. For metal electrodes with higher work function, higher injection currents and hence faster polarization switching were observed. The results from I-V studies also show that the charge injection process is a Schottky type and the barrier height estimated from the temperature dependence of the I-V curves is consistent with the metal work functions used.
Organic / Inorganic Hybrid Material for Coating on Metals
Authors: Tang Zhexiong , Alvarez Neil , Yang Sze
Published: April 2011

In this paper, we present the syntheses of nano particles of organic / inorganic hybrid for coating on metal or glass surfaces. The organic component is a π-conjugated polymer, polyaniline. The inorganic component is a metal oxide, e.g., cerium oxide. Since the organic component is a water-dispersible polymeric complex of polyaniline and poly(acrylic acid), the hybrid particles are also dispersed in water. The synthesis of the organic / inorganic composite is described. The water dispersible hybrid material was coated on aluminum and glass substrates using a molecular layer-by-layer coating process.
Atomic and Electronic Structures of Nano-Interface In Au/TiO2 Catalyst - Electron Microscopic Approach -
Authors: Ichikawa S. , Okazaki K. , Akita T. , Okumura M. , Tanaka K. , Kohyama M.
Published: April 2011

The size dependence of the catalytic property of the gold catalysts has been reported. It is especially interesting that the catalytic property of gold suddenly changes to show a platinum-like behavior when the mean size of gold is below 2nm. This phenomenon should be owing to the change of the electronic structure of the gold, however its detail has not been cleared yet. We investigated the size dependence of the mean inner potential of gold catalysts supported on TiO2, which is affected by the outer valence electron, using electron holography and high-resolution electron microscopy. We found the following tendency. When the size of the gold particle is over 5nm, the values of the mean inner potential are the same level as the reported experimental values of the bulk gold (21–23V) and the calculated values of the bulk gold (25–30V). When the size is below 5nm, the mean inner potential begins to increase over 30V, and it begins to increase suddenly over 40V at the size below about 2nm. It indicates that the electronic structure of the gold particles varies from that of the bulk state as the size of the gold particles reduces. Due to the size reduction, the volume fraction of the surface atoms and the interface atoms increases, e.g., almost half of the atoms locate on the surfaces or at the interface in case of the top half of the octahedron particle with the size 1.6nm. The surface dipole and the interface dipole should be formed owing to the electron out of the surface to the vacuum and the local charge transfer from the gold particles to the TiO2 surface. These dipole effects might be effective and one of the reasons for the increase of the mean inner potential of gold particles.
Substrate Dependence of Surface Plasmon Resonance Frequency of Silver Island Films
Authors: Xu Gang , Tazawa Masato , Jin Ping
Published: April 2011

A simple method was demonstrated to tune surface plasmon resonance wavelength of silver island films by introducing an underlayer. The tunability can be much enhanced by varying the underlayer medium. In combination with the size effects of metallic islands the plasmon wavelength can be readily adjusted throughout the visible spectral regions. The experimental results were interpreted based on a generalized Maxwell-Garnett theory.
Dual-probe scanning tunneling microscope and a carbon nanotube ring transistor
Authors: Shigematsu Taishi , Watanabe Hiroyuki , Manabe Chikara , Shimotani Kei , Shimizu Masaaki
Published: April 2011

For measuring molecular device, we developed a dual-probe scanning tunneling microscope (D-STM) composed of two STM systems in which a carbon nanotube (NT) was used for STM tip. Using D-STM, we fabricated a NT ring device. The NT ring device showed a switching behavior with applying gate bias. Furthermore, in STM imaging for various gate biases, we could observe directly hole injection into the NT ring.
STM-REBIC study of nanocrystalline and crystalline silicon.
Authors: Nogales E. , Méndez B. , Piqueras J. , Plugaru R.
Published: April 2011

Electrically active regions of nanocrystalline silicon (nc-Si) films as well as of a p-type crystalline silicon (c-Si) wafer have been investigated by using a scanning electron microscope/scanning tunneling microscope (SEM/STM) combined instrument. The nc-Si films were obtained by boron implantation of amorphous silicon layers with an average nanocrystal size of about 10 nm. STM current constant images reveal a cell structure in the nc-Si films which was also revealed in the STM remote electron beam induced current (REBIC) images with a resolution of up to 20 nm. The contrast in the STM-REBIC images indicate the existence of space charge regions at the boundaries. The influence of the thermal treatment on the cell structure was studied. For comparison, SEM-REBIC and STM-REBIC images from c-Si wafer were obtained.
Modeling Self-Assembly of Nanoparticle Structures: Simulation of Nanoparticle Chemical Potentials in Polymer-Nanoparticle Mixtures
Authors: Marla Krishna T. , Meredith James C.
Published: April 2011

The expanded ensemble Monte Carlo (EEMC) simulation method has been applied to calculation of the chemical potential of nanocolloidal particles in the presence of polymeric surface modifiers. Two general classes of surface modifiers have been studied – nonadsorbing and freely-adsorbing. For both systems, the infinite dilution colloid chemical potential was calculated as a function of the colloid diameter and the modifier chain length. The colloid chemical potential was found to decrease with increasing modifier chain length for both types of modifiers, albeit for different reasons. Empirical power-law scaling relationships were found to represent the simulation results well. A physical interpretation was proposed for the power law exponents obtained in the case of adsorbing modifiers.
Dynamic Tuning of Optical Waveguides with Electrowetting Pumps
Authors: Cattaneo Francesco , Mach Peter , Hsieh Jennifer , Krupenkin Tom , Yang Shu , Rogers John A.
Published: April 2011

This paper reviews some of our recent work on a new class of photonic component that uses electrowetting pumps and microfluidic channels for dynamic tuning of the characteristics of optical waveguides. These pumps exploit the ability to alter the contact angle of conductive liquids situated on top of a dielectric layer with appropriately patterned underlying electrodes. By applying different voltages to opposite sides of a conductive fluid plug, the contact angle imbalance created between the ends of the liquid drives fluid motion toward the higher field regions [1]. In our design, this electrically controlled, fully reversible motion of fluids contained within recirculating channels is used to alter the effective indices of waveguide modes of three different types of optical fiber structures: fiber Bragg and long period gratings and etched or tapered fiber. Our systems operate non-mechanically and have excellent optical performance, including low insertion and polarization-dependent losses. These characteristics suggest a promising potential for electrowetting-based microfluidic tuning of optical fiber devices and other photonic components.
Microreactors for Thin-Film Calorimetry
Authors: Rodríguez-Viejo J. , Chacón M. , Lopeandía A.F. , Clavaguera-Mora M.T. , Arana Leonel R. , Jensen K.F.
Published: April 2011

We have designed and developed a calorimeter that is capable of measuring the heat released by ultrathin films in the temperature range from 77 to 1050 K. Semiconductor processing techniques are used to fabricate the microreactors. The symmetric design of the Pt heaters in the microreactor channel provide a good temperature profile across the active region of the membrane making it suitable for accurate calorimetric measurements. The low thermal mass of our system allows for a high sensitivity. The effective heat capacity of the microcalorimeters with a 200 nm SixNy membrane is 0.14 μJ/K at room temperature. In high vacuum heating rates of 2×106 K/s have been achieved. Under these conditions the microcalorimeter works as an adiabatic scanning calorimeter and therefore heat capacity is directly obtained from the input power. A thermal characterization of the microcalorimeters in the transient state and calorimetric measurements on indium thin films and films made of CdSe nanocrystals are briefly discussed to show the potentiality of the microreactors.
Growth of Polycrystalline Silicon Carbide on Thin Polysilicon Sacrificial Layers for Surface Micromachining Applications
Authors: Wiser R.F. , Chung J. , Mehregany M. , Zorman C.A.
Published: April 2011

Polycrystalline silicon carbide (poly-SiC) films were deposited by atmospheric pressure chemical vapor deposition (APCVD) at epitaxial growth temperatures on planar, 100 nm-thick polysilicon sacrificial layers using two recipes that included or excluded a pre-growth carbonization step. Poly-SiC films grown using the carbonization-based recipe exhibited a relatively high degree of (111) 3C-SiC texture and had uniform, well-defined, void-free poly-SiC/polysilicon interfaces. In contrast, poly-SiC films grown without carbonization were randomly oriented, had numerous poly-SiC inclusions that sometimes completely penetrated the polysilicon underlayer, and had a higher surface roughness than the films grown with carbonization. Analysis of micromechanical clamped-clamped (C-C) beam resonators fabricated from films grown using the two differing recipes shows that the carbonization step is needed to protect the thin polysilicon sacrificial layer from voids and inclusions and thus maintain the proper spacing between the drive electrodes and the resonant beams.
Fabrication of Micro-Relief Structures in Thick Resist for Anti-Counterfeiting Applications
Authors: Leech Patrick W. , Zeidler Henning
Published: April 2011

Micro-relief surfaces including grating structures, greytone/micrographic features and microramps have been fabricated with depth features of up to 30 μm. Grey scale lithography has been used to produce the microstructures by a single UV exposure into a layer of thick resist. Arrays of the pixelated microstructures have formed the security features on the surface of optically variable devices. Each of the microstructures was designed to provide an intended optical effect in features such as portraits, symbols and lettering which comprised a larger image (typically 2.5 × 3 cm). An essential part of the process has been the determination of the optimum conditions for coating of the thick resist (AZ P4620) as a function of spin speed and exposure.
Fabrication Of Flat RF MEMS Switch Membrane By Minimizing Of Stress Gradients In The Au Membrane Structure
Authors: Kim Jong-Seok , Song Hoon , Cho Jin Woo , Lee Eun Sung , Park Sun Hee , Lee Mun Chul , Shim Dong Hwa , Song In Sang , Kim Jung Woo , Kang Seok Jin , Song Ki Moo
Published: April 2011

RF MEMS(Micro-Electro-Mechanical-System) switch technology is one of powerful solution for future RF systems. This technology provides low insertion loss, High linearity and broad bandwidth. Wide driving membrane used MEMS switch can reduce driving voltage but it is easy to bend because of the stress gradient. In order to solve this problem we fabricated Au cantilever in various sputtering condition and various substrate materials. As a result of this experiment, we fabricated cantilever which was bent within 1 um, with 2 um thickness and 340 um length. We applied this condition to RF MEMS switch and we fabricated switch membrane within 1 um bend, under 10MPa stress gradient.
Modeling of a Rotaxane-based Molecular Device
Authors: Zheng Xiange , Sohlberg Karl
Published: April 2011

A computational procedure is presented for investigating photo-induced switchable rotaxanes and demonstrated for a known system. This procedure starts with the generation of more than 104 chemically reasonable rotaxane conformations based on an empirical intramolecular potential energy function. Single-point energy calculations at the semi-empirical (AM1) level are carried out for each structure in the singlet (ground), triplet, and anionic doublet states. The structural features are assigned and then correlated with energy for each state. What emerges is a profile of the structure-energy relationship that captures the salient features of the system that endow it with device-like character. Full geometry optimization of a subset of co-conformations (∼1%) demonstrates that the procedure based on single-point calculations is sufficient to obtain a profile of the relationship of structural features to energy that is consistent with experiments, at greatly reduced computational cost.
Semi-Empirical Study of a pH-Switchable [2] Rotaxane
Authors: Frankfort Laura , Sohlberg Karl
Published: April 2011

Semi-empirical (AM1) electronic structure calculations are reported on a pH-switchable [2] rotaxane whose synthesis was reported in [Angew. Chem. Int. Ed., 36 (1997) 1904]. The [2] rotaxane possesses two cationic binding sites, with different affinities toward dibenzo [24] crown-8 (the ring component of the [2] rotaxane) depending upon the pH of the system. The computational results capture this pH-sensitive bistability, the key device-like characteristic of the rotaxane.
Epitaxial Growth and Characterization of 4H-SiC(11–20) and (03–38)
Authors: Kimoto T. , Hashimoto K. , Fujihira K. , Danno K. , Nakamura S. , Negoro Y. , Matsunami H.
Published: April 2011

Homoepitaxial growth, impurity doping, and diode fabrication on 4H-SiC(11–20) and (03–38) have been investigated. Although the efficiency of nitrogen incorporation is higher on the non-standard faces than on (0001), a low background doping concentration of 2∼3×1014 cm-3 can be achieved. On these faces, boron and aluminum are less effectively incorporated, compared to the growth on off-axis (0001). 4H-SiC(11–20) epilayers are micropipe-free, as expected. More interestingly, almost perfect micropipe closing has been realized in 4H-SiC (03–38) epitaxial growth. Ni/4H-SiC(11–20) and (03–38) Schottky barrier diodes showed promising characteritics of 3.36 kV-24 mΩcm2 and 3.28 kV–22 mΩcm2, respectively. The breakdown voltage of 4H-SiC(03–38) Schottky barrier diodes was significantly improved from 1 kV to above 2.5 kV by micropipe closing.
Effect of Pressure on the energy band gaps of InxGa1-xN and InxAl1-xN
Authors: Dridi Z. , Bouhafs B. , Ruterana P.
Published: April 2011

Using a first-principles method, we study the effect of pressure on the band gap energies of wurtzite InxGa1-xN, and InxAl1-xN. The fundamental band gap energies are direct and increase rapidly with pressure. The pressure coefficients vary in the range of 19.8–24.8 meV/GPa for InxGa1-xN, and 16.7–20.7 meV/GPa for InxAl1-xN; they depend on alloy composition with a strong deviation from linearity. The band gap bowing of the InGaN increases continuously with pressure while those of InAlN strongly decreases at p=14 GPa.
Searching for the Influence of the Sapphire Nitridation Conditions on GaN Films Grown by Cyclic PLD
Authors: Sanguino P. , Niehus M. , Koynov S. , Melo L. , Schwarz R. , Soares M. J. , Boemare C. , Monteiro T.
Published: April 2011

We have deposited highly c-axis oriented GaN films on sapphire by the Cyclic Pulsed Laser Deposition Technique. Nitridation of the sapphire substrates for these samples was performed at 200 °C, 400 °C and 600 °C. For that purposed, we used a radio frequency nitrogen plasma during four hours. The films were compared in terms of crystal structure, surface morphology and optical quality. Although small, the biggest differences were detected in the surface morphology of the films. Additionally, a typical GaN sample nitridated at 200 °C was analysed by photoluminescence and showed the typical donor bound excitonic luminescence (D0X ) transition at 3.47 eV and a line near 3.42 eV. These lines show a FWHM of 20 meV and 30 meV at 13K, respectively.
Effect of Thickness Variation in High-Efficiency Ingan/Gan Light Emitting Diodes
Authors: Narayan J. , Wang H. , Ye Jinlin , Hon Schang-Jing , Fox Kenneth , Chen Jyh Chia , Choi H. K. , Fan John C.C.
Published: April 2011

We have found that InxGa(1-x)N/GaN multi-quantum-well (MQW) light emitting diodes (LEDs) having periodic thickness variation (TV) in InxGa(1-x)N active layers exhibit substantially higher optical efficiency than LEDs with uniform InxGa(1-x)N layers. In these nano-structured LEDs, the thickness variation of the active layers is shown to be more important than In composition fluctuation in quantum confinement of excitons (carriers). Detailed STEM-Z contrast analysis, where image contrast is proportional to Z2(atomic number)2, was carried out to investigate the thickness variation as well as the spatial distribution of In. In the nanostructured LEDs, there are short-range (SR-TV, 3 to 4 nm) and long-range thickness variations (LR-TV, 50 to 100 nm) in InxGa(1-x)N layers. It is envisaged that LR-TV is the key to quantum confinement of the carriers and enhancing the optical efficiency. We propose that the LR-TV thickness variation is caused by two-dimensional strain in the InxGa(1-x)N layer below its critical thickness. The SR-TV may be caused by In composition fluctuation. The observations on thickness variation are in good agreement with model calculations based upon strain effects.
Evolution of Subgrain Boundaries in Heteroepitaxial GaN/AlN/6H-SiC Grown by Metalorganic Chemical Vapor Deposition
Authors: Liu H. X. , Ali G. N. , Palle K. C. , Mikhov M. K. , Skromme B. J. , Reitmeyer Z. J. , Davis R. F.
Published: April 2011

We have characterized the surface morphology and luminescence properties of GaN/AlN/ SiC layers of various thicknesses using secondary electron imaging (SEI), panchromatic room temperature cathodoluminescence (CL), atomic force microscopy (AFM), optical Nomarski microscopy, and room and low temperature photoluminescence (PL). The nominally undoped GaN layers were grown by MOCVD on 0.1 m thick AlN buffer layers on commercial 6H-SiC(0001) substrates. The GaN layer thicknesses are 0.5, 1.0, 1.6, and 2.6 m. A second 1.0 m thick layer was grown by identical procedures on a 6H-SiC substrate that was first etched in H2 to remove scratches and damage due to mechanical polishing. Biaxial compressive lattice mismatch stress is present in all layers and decreases with increasing layer thickness, while PL linewidths decrease. The 1 m layer on the H-etched substrate is as relaxed as the 2.6 m layer on a non H-etched substrate, however. Pronounced surface structures, apparently corresponding to columnar subgrain boundaries, are observed on the samples on non H-etched SiC. Their typical sizes increase from about 3 to 10 m with increasing layer thickness. They are absent in the H-etched sample. These structures are generally nonradiative in CL images, although mottled contrast is also observed inside them. Similar layers doped with 3×1018 cm−3 Si do not show these features, suggesting a different microstructure.
Wavelength-Invariant Resist Composed of Bimetallic Layers
Authors: Tu Y. , Karimi M. , Morawej N. , Lennard W. N. , Simpson T. W. , Peng J. , Kavanagh K. L. , Chapman G. H.
Published: April 2011

Two layer co-sputtered Bi over In thin films (40 nm/layer) act as a microfabrication resist with many potential applications. Their physical, chemical and optical characteristics change after laser exposures that produce a rapid thermal anneal in selected areas. Unlike organic photoresists, Bi/In is a bimetallic thermal resist whose sensitivity shows a near wavelength invariance for wavelengths from Near IR to UV. The laser-induced patterns are developed by an etch that selectively removes unexposed areas and retains converted ones. The optical density (OD) of 40 nm thick Bi/In films on quartz substrates, for example, changes from 3.3 OD to 0.37 OD in the annealed area. This has enabled the creation of direct-write photomasks for standard photoresist exposures. In this paper, the composition, morphology, and nanostructure of the resist before and after laser processing were studied in order to determine the mechanism of the laser-induced material conversion. AFM, XRD, and TEM show that the as-deposited films are polycrystalline, continuous, but with a rough, island morphology. Furnace anneals in air above the eutectic temperature (150–250°C, 3 hours) result in the formation of the tetragonal phase BiIn with a small degree of oxidation. The island morphology is maintained but there is evidence of melting and recrystallization. Transparency is much lower than after laser annealing. RBS and NRA depth profile analysis show that Bi/In films exposed to laser annealing in air contain a large fraction of oxygen and suggest that the converted film may be a BiIn0.6O6 /Bi0.3InO6 bilayer.
Ultrashallow SIMS Study of Implanted Dopants in NiSi/Si(100)
Authors: Yakovlev Nikolai L. , Wong Andrew S.W. , Lai Doreen M.Y. , Chi Dongzhi
Published: April 2011

Ultrashallow doping of silicon wafers with boron was done by implantation of B+ or BF2+. Nickel silicide on them was formed by annealing of thin Ni layer. As it was revealed by secondary ion mass spectrometry, after the growth of NiSi, boron remains in Si just under the silicide layer, but fluorine accumulates in the NiSi layer. This accumulation suppresses agglomeration of the silicide.
First Principles Modeling Of High-K Dielectric Materials
Authors: Jun Gyuchang , Cho Kyeongjae
Published: April 2011

First-principles calculations are performed for high-K gate dielectric materials using model bulk and interface systems. Detailed electronic structures and atomic configurations are investigated for transition metal (Hf and Zr) oxide, metal doped silicate bulk system and a model Si-silicate interface system. Pseudo polymorphs of metal oxides are investigated to elucidate the underlying driving mechanisms in microscopic configurations of metal oxides and silicates in amorphous structures. We studied energetics and electronic structure of metal oxide pseudo morph with varying oxygen coordination. Dielectric constants of metal oxide and silicate materials are also investigated using the density functional perturbation theory method implemented in the ABINIT code. Electronic and dielectric properties of silica interface layers between high-κ dielectric and Si substrate are investigated leading to a confirmation that 1 nm is the physical limit of gate oxide thickness. Furthermore silica interface layer is found to have small dielectric constant of 3.4∼3.9.
Sol-Gel Derived PZT Thick Films with Nano-Sized Microstructure
Authors: Zhao C. L. , Wang Z. H. , Zhu W. , Tan O. K. , Hng H. H.
Published: April 2011

Lead zirconate titanate (PZT) films are promising for acoustic micro-devices applications because of their extremely high electromechanical coupling coefficients and excellent piezoelectric response. Thicker PZT films are crucial for these acoustic applications. A hybrid sol-gel technology has been developed as a new approach to realize simple and cost-effective fabrication of high quality PZT thick films. In this paper, PZT53/47 thick films with a thickness of 5–50 μm are successfully deposited on Pt-coated silicon wafer by using the hybrid sol-gel technology. The obtained PZT thick films are dense, crack-free, and have a nano-sized microstructure. The processing parameters of this technology have been evaluated. The microstructure of the film has been observed using field-emission scanning electron microscopy and the crystallization process has been monitored by the X-ray diffraction. The thick films thus made are good candidates for fabrication of piezoelectric diaphragm which will be an essential element of microspeaker and microphone arrays.
Improved Dielectric Properties of Heterostructured Ba0.5Sr0.5TiO3 Thin Film Composites for Microwave Dielectric Devices
Authors: Jain M. , Majumder S. B. , Katiyar R. S. , Bhalla A. S. , Agrawal D. C. , Van Keuls F. W. , Miranda F. A. , Romanofsky R. R. , Mueller C. H.
Published: April 2011

In the present work we have deposited MgO and Ba0.5Sr0.5TiO3 (BST50) thin layers in different sequences to make MgO:BST50 hetero-structured thin films. These films were characterized by X-ray diffraction and found to be highly (100) textured. The figure of merit {(C0-Cv)/(C0.tand)} of the hetero-structured films was found to be higher as compared to pure BST50 films measured at 1 MHz frequency with electric field of 25.3 kV/cm. These films were used to make eight element coupled micro-strip phase shifter and characterized in a frequency range of 13–15 GHz. The high frequency figure of merit (k factor, defined as the ratio of degree of phase shift per dB loss) measured at around 14 GHz with electric field of 333 kV/cm has been markedly improved (around 64.28 °/dB for hetero-structured film as compared to 24.65 °/dB for pure film). Improvement in dielectric properties in a wide frequency range in the MgO:BST are believed to be due to the higher densification of the hetero-structured films.
Growth of Epitaxial Site-Engineered Bi4Ti3O12-Basded Thin Films by Mocvdand Their Characterization
Authors: Funakubo Hiroshi , Sakai Tomohiro , Watanabe Takayuki , Osada Minoru , Kakihana Masato , Saito Keisuke , Noguchi Yuji , Miyayama Masaru
Published: April 2011

Thin films of BIT, La-substituted BIT (BLT) and La- and V-cosubstituted BIT(BLTV) were epitaxially grown on SrRuO3//SrTiO3 substrates at 850°C by metalorganic chemical vapor deposition (MOCVD), and their electrical properties were systematically compared. All films on (100), (110) and (111)-oriented substrates were epitaxially grown with (001)-, (104)-/(014)-and (118) –preferred orientations, respectively. The leakage current density of the BLTV film was almost the same with that of the BLT film, but was smaller than that of BIT film, suggesting that the La substitution contributed to the decrease of the leakage current density especially in pseudoperovskite layer. Spontaneous polarization of the BLTV film was estimated to be almost the same with the BLT film but was smaller that that of the BIT film. This is explained by the decrease of Tc with the La substitution, while V did not contribute to the change of the Curie temperature (Tc ). On the other hand, the coercive field (Ec) value of the BLTV was smaller than that of the BIT and the BLT films. As a result, La substitution contributed to the decrease of the leakage current density together with the decrease of the spontaneous polarization due to the decrease of the Tc. On the other hand, V substitution contributes to the decrease of the defects that suppress the domain motion and increases the Ec value. Therefore, each substitution of La and V plays different roles and this contribution is remarkable for the films deposited at lower temperature.
Investigation of Domain Wall Velocity and Nucleation Rate in Polarization Switching of Epitaxial Pb(Zr,Ti)O3 Thin Films Using Piezoresponse Scanning Force Microscopy
Authors: Fujisawa H. , Yagi T. , Shimizu M. , Niu H.
Published: April 2011

Domain wall velocity and nucleation rate in 250nm-thick epitaxial Pb(Zr,Ti)O3 thin films were studied by piezoresponse scanning force microscopy (PFM). Domain growth observed after applying switching pulses shorter than the switching time can be described using the Ishibashi theory. At a pulse voltage of +5V, experimental results indicated that new nucleation occurred during the switching period, which corresponded to the Category I in the Ishibashi theory. Switching time, domain wall velocity and nucleation rate at +5V can be obtained as 70ns, 8.3m/s and 43μs-1 μm-2, respectively. As compared with experimental results reported in BaTiO3 single crystals, domain wall velocity was much smaller but nucleation rate was much larger than those in single crystals.
Mechanisms of Stress Corrosion Cracking in Si: A Hybrid Quantum-Mechanical/Molecular-Dynamics Simulation
Authors: Belkada Rachid , Ogata Shuji , Shimojo Fuyuki , Nakano Aiichiro , Vashishta Priya , Kalia Rajiv K.
Published: April 2011

We investigate mechanisms of stress corrosion cracking in Si using a hybrid quantum-mechanical/molecular-dynamics simulation code developed recently for parallel computers. We perform the simulation for a cracked Si-model under tension (mode-I opening) with three H2O molecules around the crack front to investigate possible effects of both saturation of dangling bonds of Si with hydrogen atoms and environment molecules on the fracture initiation. Our results demonstrate existence of a path for an H2O molecule to react with Si-Si bonds at the crack front in contrast to a previous theoretical study based on the molecular orbital theory [W. Wong-Ng et al., Comp. Mater. Sci. 6, 63 (1996)].
NIST's Advanced Technology Program: New Developments in Membrane Technology R&D
Authors: Beyerlein Robert A. , Ceasar Gerald P.
Published: April 2011

The Advanced Technology Program (ATP) is a unique partnership between government and private industry designed to accelerate the development of innovative, high-risk technologies for broad national benefit. Topics for ATP projects are proposed by industry, and awards are made on the basis of announced competitions that consider both the technical and business merits of the proposed work. Companies of any size may apply, and universities or governmental research institutions may partner with industry in ATP projects. Between 1990 and September, 2002, ATP provided a total of $2.0 billion in funding across all technology areas for 642 high-risk, industrial R&D projects. Approximately equivalent matching funds have been provided by the industry partners for a total investment of $3.9 billion. Small businesses are thriving; more than 60% of all projects are led by small businesses. On average, more than half of all ATP projects include university participation, with more than 160 universities participating. Over 25 national laboratories participate.
Controlling nanoparticle template morphology: effect of solvent chemistry
Authors: Cortalezzi Maria M. , Colvin Vicki , Wiesner Mark R.
Published: April 2011

Porous solids were obtained from self-assembled deposits of silica nanoparticles used as templates to form 3-D porous membranes. The effect of the solvent chemistry on the morphology of the deposits was investigated. The parameters of interest are surface tension and ionic strength of the solvent, due to electrostatic and capillary interactions. Deposits of nanoparticles of different sizes were obtained for a variety of conditions. The deposits were imaged using SEM and showed distinctive structures for each of the solvent chemistries. The phenomenon is consistent with the DVLO theory and calculations of capillary interaction energy.
Mechanical and Structural Stability of Perovskites Membranes in Reducing Environments
Authors: Nagabhushana Nagendra , Haslebacher William F. , Venkataraman Venkat K. , Bandopadhyay Sukumar
Published: April 2011

Mixed ionic electronic conducting perovskite type oxides are promising materials for potential use in various applications such as in fuel cells and membranes for air separation. An important issue in the development of the perovskites is the structural, chemical and mechanical stability of these materials at high temperatures and reducing environments (oxygen partial pressure from 0.21 to 10−17 atm) encountered in membrane reactors. SrFeO3 oxides doped with La on the A-site and Cr on the B-site showed high strength at room temperature in air. The strength degrades rapidly with an increase in temperature in air as compared to in N2 and CO2/CO environment. Fracture in the material is characterized by non-equilibrium segregation of elements within the grains. The observations provide valuable structure-property correlation as applicable to the long-term behavior of the material in advanced catalytic membrane reactors.
Mechanical and thermal properties of single crystals of ZrB2
Authors: Oka moto N. L. , Kusakari M. , Tanaka K. , Inui H. , Yamaguchi M. , Otani S.
Published: April 2011

Coefficients of thermal expansion (CTE), elastic constants and plastic deformation behaviors of single crystals of ZrB2, which possesses a hexagonal layered structure where pure Zr and pure B atomic planes stack alternatively along the c-axis, have been investigated in wide temperature ranges. While the observed elastic constants indicate highly anisotropic nature of atomic bonding being consistent with the layered structure, the observed CTE values are rather isotropic. Two operative slip systems, (0001)<1120> and on {1100}<1123>, are identified in compression tests. The observed plastic behaviors are discussed in the light of the deduced anisotropy in atomic bonding.
Calculation of thermal expansion of iron-aluminides with transition metal additives
Authors: Seletskaia Tatiana , Muratov Leonid , Cooper Bernard R.
Published: April 2011

The addition of transition metal elements can significantly modify physical properties of intermetalic compounds. We studied the influence of Molybdenum and Vanadium additives on thermal expansion coefficient (CTE) of Fe3Al and FeAl over the wide range of temperatures. The site preference of both transition metals was determined by full-potential LMTO method within the grandcanonical formalism. At low temperatures CTEs were found directly from the FP-LMTO calculations by incorporating them into the Debye model of a solid. The obtained thermal expansion for pure Fe3Al and FeAl is within 10% of its experimentally measured values. At high temperatures we performed Molecular Dynamics (MD) simulations based on our many-body atomistic potentials. The parameters were fitted to reproduce the total energy of a crystal under various types of deformations obtained by FP-LMTO method and were tested with respect to different structures and vacancy formation energies. Our calculations show that addition of V decreases the CTEs of both iron-aluminides, while the addition of Mo makes Fe3Al DO3 structure unstable.
Bending Ductility of Heavily Cold-Rolled Ni3Al Thin Foils
Authors: Kobayashi Satoru , Demura Masahiko , Kishida Kyosuke , Hirano Toshiyuki
Published: April 2011

Our recent studies revealed that heavily cold-rolled Ni3Al foils have a good bending ductility in spite of almost no elongation in tensile test. In this paper, bending characteristics of 95% cold-rolled foils around transverse and rolling directions (TD and RD, respectively) were examined to understand the bending mechanism. Fracture elongation on the tension surface shows a large bending anisotropy: 5 % for the TD bending, while less than 1% for the RD bending. The bending ductility is due to {111}<110> slip deformation. In the TD bending, slip occurs on the slip systems operated during cold rolling, and cracks initiate along the shear bands. In the RD bending, slip occurs on the other {111} planes besides the slip planes operated during cold rolling, and fracture occurs as a result of the dislocation interaction in the both planes.