bluuebunny/crossref_metadata_2025 huggingface dataset:
Bandgap-Engineering of HgCdTe for Two-Color Ir Detector Arrays BY Movpe
Authors: Mitra P. , Case F. C. , Barnes S. L. , Reine M. B. , O'Dette P. , Tobin S. P.
Published: April 2011

Recent results on MOVPE growth of multilayer two-color HgCdTe detectors, for simultaneous and independent detection of medium wavelength (MW, 3–5 μm) and long wavelength (LW, 8–12 μm) bands, are reported. The structures are grown in situ on lattice matched (100) CdZnTe in the double-heterojunction p-n-N-P configuration. A barrier layer is placed between the LW and MW absorber layers to prevent diffusion of MW photocarriers into the LW junction and thereby eliminate spectral crosstalk. X-ray double crystal rocking curve widths are ∼ 45 arc-secs, indicating good epitaxial quality. SIMS depth profile measurements of these 28 μm thick structures show well-defined alloy compositions, and arsenic and iodine doping. SIMS data on a series of thirteen films show that good run-to-run repeatability is obtained on thicknesses, compositions, and dopant levels with values close to the device design targets. Depth profile of etch pits through the thickness of the films show etch pit densities in the range of 8×105-5×106 cm−2.
In Situ Spectroscopic Ellipsometry for Real Time Composition Control of Hg1−xCdxTe Grown by Molecular Beam Epitaxy
Authors: Dat R. , Aqariden F. , Duncan W. M. , Chandra D. , Shih H. D.
Published: April 2011

Spectral ellipsometry (SE) was applied to in situ composition control of Hg1−xCdxTe grown by molecular beam epitaxy (MBE), and the impact of surface topography of the Hg1−xCdxTe layers on the accuracy of SE was investigated. Of particular importance is the presence of surface defects, such as voids in MBE- Hg1−xCdxTe layers. While dislocations do not have any significant impact on the dielectric functions, the experimental data in this work show that MBE- Hg1−xCdxTe samples having the same composition, but different void densities, have different effective dielectric functions.
On the Moss-Burstein Shift In Quantum Confined Optoelectronic Ternary and Quaternary Materials
Authors: Ghatak Vamakhya P. , Bose P. K. , Majumder Gautam
Published: April 2011

In this paper we have studied the Burstein-Moss shift in quantum wires and dots of ternary and quaternary materials on the basis of a newly formulated electron dispersion law which occurs as a consequence of heavy doping. It is found taking Hg1−xCdxTe and In1−xGaxAsyP1−y lattice matched to InP as examples that the Burstein-Moss shift exhibits oscillatory dependences for quantum wires and dots of the said materials with respect to doping and film thickness respectively. Besides, the numerical values of the same shift is greatest in quantum dots and least in quantum wires. In addition, the theroretical analysis is in agreement with the experimental datas as given elsewhere.
Modified Vapor Phase Growth of Cadmium Zinc Telluride: A Progress Report
Authors: Trower W. P.
Published: April 2011

We have completed a series of experiments where we realized Cd(1−x)ZnxTe by modified Vapor Phase Growth in which the CdTe and ZnTe components were separated in the growth ampoule, with their vapors passing through channels and openings designed to mix them stoichiometrically at the growth surface. We have obtained polycrystalline CZT boules 50 mm in diameter and 10 mm high whose structure is strikingly different from that obtained by standard High Pressure Bridgman methods. Our mVPG properties relevant for detector applications include resistivity of∼40 GΩ-cm when voltage is first applied, rising to ∼66 GΩ-cm after ∼20 min when the traps are filled, and electron mobility-lifetimes of∼2 × 10−3 cm2/ν. Here we present some structural and operational characterizations of our mVPG CZT.
Analyses of Compensation Related Defects in II-VI Compounds
Authors: Castaldini A. , Cavallini A. , Fernandez P. , Fraboni B. , Piqueras J.
Published: April 2011

The deep levels present in semiconducting CdTe and semi-insulating (SI) CdTe:Cl and Cd0.8Zn0.2 Te have been investigated by means of cathodoluminescence (CL), deep level transient spectroscopy (DLTS), photo-DLTS (PDLTS) and photo induced current transient spectroscopy (PICTS). PICTS and PDLTS can be applied to SI materials and allow to determine whether the observed deep levels are hole or electron traps.Among the observed deep centers, we have focused our attention on those involved in the compensation process such as the so called center A and the deep traps located near midgap. We have identified a deep acceptor, labelled H, and a deep donor, labelled E, the latter is peculiar to CdTe:Cl and can be a good candidate for the deep donor level needed to explain the compensation process in SI CdTe:Cl.
Control of Defects and Impurities in Production of CdZnTe Crystals by the Bridgman Method
Authors: Glass H. L. , Socha A. J. , Bakken D. W. , Speziale V. M. , Flint J. P.
Published: April 2011

Cadmium zinc telluride crystals were grown by vertical Bridgman processes using in situ compounding from high purity elements into pyrolytic boron nitride crucibles within sealed fused quartz ampoules containing cadmium vapor at a pressure of roughly one atmosphere. These conditions produce material having the low etch pit density, low precipitate density, high infrared transmission and high purity required for use as substrates for infrared focal plane detector arrays fabricated in epitaxial mercury cadmium telluride. Similar processes should be satisfactory for producing cadmium zinc telluride for gamma ray detectors.
Radiation Damage of Amorphous and Microcrystalline Silicon Image Sensor Structure
Authors: Kolodziej A. , Krewniak P.
Published: April 2011

The paper reports radiation damage experiments which influence properties of image sensors using pin photodiodes and thin film transistors. The effect of 60Co radiation at about 1.2MeV on the noise and drain-source current characteristics of hydrogenated amorphous and nanocrystalline silicon film transistor was examined as a function of the γ dose and hydrogen content of the films.

An unmeasurable effect upon the noise characteristics of the TFT was observed. The predominant drain-source current with increasing dose was in the form of various shifts of the transfer characteristics toward negative gate voltage and decrease of the transfer characteristic subthreshold slope from 5at% to 26at% of hydrogen content in the films. These, in turn, resulted in a large increase in leakage current for gate voltages at the periods the TFTs were not conducting. The radiation damage of the pin diode has much less influence on operation of array than the damage of the TFT.

Annealing for 3h at 180°C restored TFT threshold voltage properties, particularly in the case of amorphous films with greater contents of hydrogen.
Applicability of Shallow-Impurity Doped Silicon to Proton Flux Sensors Using Stable Particle-Induced Conductivity
Authors: Kishimoto N. , Amekura H. , Kono K. , Lee C. G.
Published: April 2011

High-energy particles incident to a semiconductor sensitively produce electron-hole pairs and the excited current has been used for radiation detectors. Although semiconductors have advantages such as high sensitivity and fast response, a drawback is weakness in radiation damage. To improve the radiation resistance, effects of shallow-impurity doping was explored for Si. Specimens of CZ-Si doped with P or B were bombarded with 17 MeV protons. The radiation-induced current of doped Si has been evaluated, as a function of proton fluence. The signal of particle-induced conductivity showed a fairly constant response to a proton flux, up to 1015 ions/cm2. The fluence range applicable as Si sensors was extended 103-104 times as much as that of non-doped Si, instead of a lower signal-to-noise ratio. Shallow impurities passivate the deep centers of radiation-induced defects, and the radiation tolerance continues until the pre-existent carriers are exhausted. The tolerant fluence is also usable to detect the integrated fluence, by controlling the initial impurity concentration.
High Collection Efficiency Thin Film Diamond Particle Detectors
Authors: Bergonzo P. , Foulon F. , Marshall R. D. , Jany C. , Brambilla A. , Mckeag R. D. , Jackman R. B.
Published: April 2011

Diamond is a resilient material with rather extreme electronic properties. As such it is an interesting candidate for the fabrication of high performance solid state particle detectors. However, the commercially accessible form of diamond, grown by chemical vapour deposition (CVD) methods, is polycrystalline in nature and often displays rather poor electrical characteristics. This paper considers ways in which this material may be used to form alpha particle detectors with useful performance levels. One approach adopted has been to reduce the impurity levels within the feed-stock gases that are used to grow the diamond films. This has enabled significant improvements to be achieved in the mean carrier drift distance within the films leading to alpha detectors with up to 40% collection efficiencies. An alternative approach explored is the use of planar device geometries whereby charge collection is limited to the top surface of the diamond which comprises higher quality material than the bulk of the film. This has lead to collection efficiencies of 70%, the highest yet reported for polycrystalline CVD diamond based detectors. Techniques for improving the characteristics of these devices further are discussed.
Deep Levels Induced by High Fluence Proton Irradiation in Undoped GaAs Diodes
Authors: Castaldini A , Cavallini A , Polenta L , Canali C , Nava F , Ferrini R , Galli M
Published: April 2011

Semi-insulating liquid encapsulated Czochralski grown GaAs has been investigated after irradiation at high fluences of high-energy protons. Electron beam induced current observations of scanning electron microscopy evidenced a radiation stimulated ordering. An analysis has been carried out of the deep levels associated with defects as a function of the irradiation fluence, using complementary current transient spectroscopies. By increasing the irradiation fluence, the concentration of the native traps at 0.37 eV together with that of the EL2 defect significantly increases and, at the same time, two new electron traps at 0.15 eV and 0.18 eV arise and quickly increase in density.
In Situ Spectroscopic Ellipsometry for Real Time Composition Control of Hg1−xcdx Te Grown by Molecular Beam Epitaxy
Authors: Dat R. , Aqariden F. , Duncan W. M. , Chandra D. , Shih H. D.
Published: April 2011

Spectral ellipsometry (SE) was applied to in situ composition control of Hg1−xCdxTe grown by molecular beam epitaxy (MBE), and the impact of surface topography of the Hg1−xCdxTe layers on the accuracy of SE was investigated. Of particular importance is the presence of surface defects, such as voids in MBE- Hg1−xCdx.Te layers. While dislocations do not have any significant impact on the dielectric functions, the experimental data in this work show that MBE- Hg1−xCdxTe samples having the same composition, but different void densities, have different effective dielectric functions.
Recent Improvements in Dry Etching of Hg1−xCdxTe By Ch4 Based Electron Cyclotron Resonance Plasmas
Authors: Seelmann-Eggebert M. , Rar A. , Zimmermann H. , Meisen P.
Published: April 2011

Significant improvements of a previously reported etching process [1] for Hg1−xCdxTe have been achieved with respect to etch rate, surface morphology and surface stoichiometry by optimization of the process parameters. The gas phase and surface reactions driving the etching process have been analyzed by combined optical and electrical characterization of the plasma and surface analyses of the samples. A reaction scheme is suggested which allows to model and upscale the process in a consistent manner.
Use Of A Capillary X-Ray Focused Beam To Investigate The Chemical Composition Of CdZnTe Wafers With High Resolution CdZnTe Detectors
Authors: Fougères P. , Burggraf Ch. , Burggraf Chr. , Koebel J. M. , Koenig C. , Regal R. , Hage-Ali M. , Krauth A. , Siffert P.
Published: April 2011

The control of the concentration of Zn and its fluctuation in the high pressure Bridgman grown CdZnTe crystals is part of our characterization work on the ternary grown ingots grown in house. In order to reach both high sensitivity and high position resolution, we have developed a new system consisting of a X-ray generator, coupled to a focusing X-ray capillary, delivering intense beams in the micron scale, since the intensity gain is around a factor of 100 compared to conventional methods.

The characteristic X-rays are measured through a high resolution CdZnTe detector (225 eV at 5.9 keV FWHM) cooled by a Peltier system. The results of our investigations on different kinds of crystals will be discussed.
Optical Limiting Processes in Derivatized Fullerenes and Porphyrins/Phthalocyanines
Authors: Kohlman R. , Klimov V. , Shi X. , Grigorova M. , Mattes B. R. , McBranch D. , Wang H. , Wudl F. , Nogués J.-L. , Moreshead W.
Published: April 2011

We review our results from spectral studies of the ultrafast excited-state absorption in fullerenes and derivatized fullerenes. These results allow determination of both the spectral response of reverse saturable absorption (RSA) nonlinearities such as optical limiting (OL) in fullerenes, and the dynamical response for different morphologies. We have investigated the effects of thin film and various sol-gel glass environments on the nanosecond OL and femtosecond dynamics of derivatized fullerenes. These data provide evidence of decay pathways which compete with the intersystem crossing to a triplet from the initial singlet states. With appropriate processing, however, the OL response of derivatized-fullerene sol-gel glasses can be enhanced to approach that of the same molecule in solution, while significantly enhancing the optical damage threshold. The optical limiting of these derivatized fullerenes is compared with that of various porphyrin and phthalocyanine molecules.
Solvato-Controlled Doping of Conducting Polymers: Enhanced Stabilty in Silver-Triflate Doped Films
Authors: Lauritzen Michael V. , Holdcroft Steven
Published: April 2011

Stable, conductive films of poly(3-alkylthiophenes) (P3ATs) can be obtained from a single chloroform based solution containing polymer, oxidant (silver triflate), and an oxidantcoordinating ligand (pyridine). Casting of this solution, followed by evaporation of the ligand, results in an electronically conductive film which is more stable and, notably, in the case of thick films, is free of the cracking which often results from swelling of the films during the doping process. This technique, coined solvato-controlled oxidative doping, results in films possessing enhanced stability compared to those oxidized by conventional dopants such as ferric chloride. Also, these silver-containing films are much more stable than those electrochemically doped with the triflate anion. Thus, the presence of metallic silver in the doped film has a profound effect on the stability of the conducting form.
Melt Processed Electrically Conductive Binary and Ternary Immiscible Polymer / Polyaniline Blends
Authors: Zilberman M. , Siegmann A. , Narkis M.
Published: April 2011

In the present study, conductive binary and ternary blends of PANI with thermoplastic polymers were prepared by melt processing.

The binary blends' investigation focused on the morphology and on the resulting electrical conductivity. Generally, the level of interaction between the doped PANI and the matrix polymer determines the blend morphology, and thus, its electrical conductivity. The morphology of a conductive network is described by a primary structure of small dispersed polyaniline particles, interconnected by secondary short range fine fibrillar structure. In blends containing a semicrystalline matrix the doped PANI network locates within the amorphous regions, leading to a reduction of the percolation concentration.

The ternary blends' investigation focused on a system containing two co-continuous immiscible thermoplastic polymers and PANI. The PANI is preferably located in one of the matrix polymers. This concentration effect enables high electrical conductivities at low PANI contents.
Determination of the Internal Electric Field in the Electrooptic Active Layer of Multilayer Polymer Stacks
Authors: Grossmann S. , Weyrauch T. , Haase W.
Published: April 2011

We report on a method to investigate the inhomogeneous distribution of an electric dc field in multilayer polymer stacks. In situ electroabsorption (EA) measurements are applied in order to estimate the local electric fields in double layer polymer films. The observed time dependent behaviour is compared with a model equivalent circuit. The results indicate that besides the relation of ohmic resistivities and capacities of the different polymer layers in the investigated systems also the influence of the electric properties of polymer/electrode and polymer/polymer interfaces must be considered.
Magnetic Properties of Organic Ferromagnetic TDAE-C60 Single Crystals and Thin Films
Authors: Tokumoto M. , Tsubaki Y. , Pokhodnya K. , sakakibara Y. , Omerzu A. , Mihailovic D. , Uchida T.
Published: April 2011

Recent progress in the study on magnetic properties of molecular soft ferromagnet TDAE-C60 (where TDAE is tetrakis(dimethylamino) ethylene) is reported. Both crystalline and thin film samples are prepared by the diffusion method and the temperature and field dependence of magnetization are studied by SQUID magnetometer. The magnetic behaviors of single crystals were found to vary from sample to sample. In best single crystals, the saturation magnetization as high as 1.0 μB/C60 has been observed. Spontaneous magnetization and its temperature dependence was evaluated from the Arrott plot. The ferromagnetic phase transition was also observed in TDAE-C60 thin films.
Effect of Impurity Ions and Permanent Dipoles for Device Performance of Thin-Film Electroluminescent Diodes
Authors: Tsutsui Tetsuo , Yahiro Masayuki , Zou Dechun
Published: April 2011

Double-layer EL diodes composed of a spin-coated Polyvinylcarbazole (PVCz) layer and a vacuum-sublimed tris-(8-hydroxyquinoline)aluminum (Alq) layer were prepared. The diodes with the same device structure but with PVCz layer with added ionic impurities were also prepared. The diodes were driven at constant voltage and allowed to stand under short-circuit or reverse bias conditions. Observations of luminance-current density-voltage relations at constant voltage driving were repeated. The decrease of both luminance and current density during constant voltage driving were observed. Both spontaneous and reverse-bias assisted recovery of device performances were observed and these degradation and recovery phenomena were discussed in terms of the movement of ionic impurities in organic layers.
Corrosion Protection of Metals by Conductive Polymers III. Improved Performance and Inhibition in NaCl
Authors: Lu Wei-Kang , Elsenbaumer Ronald L. , Chen T. , Kulkarni V. G.
Published: April 2011

The use of conducting polymers for corrosion prevention is an area which has gained increasing attention during the last decade [1]. This study explores the use of polyaniline based polymer coatings for corrosion prevention on mild steel. Data on coating degradation and passivation on electrochemically polarized painted metal specimens exposed to acid chloride solutions and artificial seawater at an ambient temperature are presented. A Systematic comparison between controls and designated coated sample sets has been made to demonstrate good corrosion protection efficiency with synergistic effects between conductive polymers and metals by classical DC monitoring techniques. Brief comparisons are made with data from simulated marine exposure. Meanwhile, in separate experiments, electrochemical data were obtained for conductive polymer primer coatings with epoxy top-coat under fully immersed conditions by using electrochemical noise (ECN) monitoring and scanning electrochemical microscopy (SECM) techniques to discover the initial localized corrosion phenomena in order to achieve further understanding of the protection mechanism. Additionally, electrochemical impedance (EIS) spectra were utilized for the assessment of anti-corrosion performance provided by conducting polymers to mild steel.
Magnetic Field Effect in Highly Pure, Highly Fluorescent Conjugated Polymers
Authors: Graupner W. , Sacher M. , Graupner M. , Zenz C. , Grampp G. , Hermetter A. , Leising G.
Published: April 2011

We report on the magnetic field effect (MFE) on the photoluminescence in films of a highly fluorescent conjugated laddertype poly(paraphenylene) (LPPP). We observe no MFE for the pure material, however, the introduction of a very small content of chemical defects via photo-oxidation leads to a MFE proportional to the amount of defects. The chemically induced increase in MFE is correlated with a change in other properties of the LPPP films, such as photoluminescence emission and excitation spectra, transient photoluminescence and infrared spectra.
Design, Methodology and Preparation of Novel Polymers for Nonlinear Optics
Authors: Chittibabu K. G. , Li L. , Balasubramanian S. , Wang X. , Sukwattanasinitt M. , Yang K. , Kumar J. , Sandman D. J. , Tripathy S. K.
Published: April 2011

One-pot post-polymerization modification reactions such as azo-coupling and tricyanovinylation reactions were employed to synthesize a series of polymers containing different nonlinear optical (NLO) chromophoric as well as ionic functionalities. We have extended and established the versatility of our earlier reported post-modification strategy to incorporate various heteroaromatic chromophores as well as ionic functionalities in the polymers, at the final stage of synthesis. The correlation between different heteroaromatic chromophore structures and the NLO properties of the polymers was extensively studied. Polymers containing heteroaromatic chromophores exhibit improved temporal stability and enhanced NLO activity. Polymers with ionic chromophores were employed to fabricate NLO active ultra-thin films using electrostatic selfassembling (ESA) technique. Attempts were also made to synthesize second order NLO active polydiacetylene derivatives using post azo-coupling reaction.
Synthesis of High-Tg Azo Polymer and the Optimization of its Poling Condition for Stable EO System
Authors: Fukuda Takashi , Matsuda Hiro , Shiraga Takao , Kato Masao , Nakanishi Hachiro
Published: April 2011

A new material for second-order nonlinear optics was synthesized, which was a copolymer of N-phenylmaleimide, 4-isopropenylphenol and 4'-[N-ethyl-N-(4-isopropenylphenoxyethyl) amino]-4”-nitroazobenzene (PMPD). PMPD films were poled by corona-poling technique. The optical nonlinearity of poled PMPD was measured by second harmonic generation (SHG) and electro-optic (EO) effect, and it was demonstrated that this polymer had large optical nonlinearity and a very long-time stability, as was expected. These properties were thought to be sufficient enough for practical EO devices. On the other hand, from the viewpoint of the sample preparation technique, poling conditions were investigated in order to achieve the highest possible dipolar orientation. As a result, it was found that the relationship between the electric resistance of polymer film and substrate was a critical factor for corona-poling efficiency. From a simple model, it was suggested that the poled PMPD film prepared onto the glass substrate with a resistance of ˜0.8 GΩ (at 160 °C) exhibits large SHG and EO coefficients, more than ˜500 × 10−9 e.s.u (d33 at λ = 1.064 μm) and ˜70 pm/V(r33 at λ = 632.8 nm), respectively. It should be noted that this expected values are approximately twice as much as obtained under conventional corona-poling conditions.
Pressure Dependence of Photoluminescence of Oligothiophenes
Authors: Rossi L. , Graupner W. , Resel R. , Meghdadi F. , Leising G. , Sannicolo' F. , Benincori T. , Lanzani G. , Tubino R.
Published: April 2011

We report on the nature of emitting states in two different quaterthiophenes: the unsubstituted quaterthiophenes (T4) and a bridged T4 (T4B), where the bridging have been realized by introducing a second bond between the two central thiophene rings. The effect of the chemical bridging on the photophysics of these compounds have been studied via photoluminescence measurements under hydrostatic pressure, which permit to clarify the influence of interchain coupling, conformational effects and intrachain structural changes on the optical properties.
Thermally stable iridescent colors of a new low-molecular-weight cholesteric compound in the solid state and the application to fullcolor recording
Authors: Tamaoki Nobuyuki , Parfenov Alexander V. , Masaki Atsushi , Matsuda Hiro
Published: April 2011

We synthesized a series of new di-cholesteryl esters of several diacids. One of the compounds containing both of a diyne unit and long alkylene units, in the form of a thin solid film, showed stable iridescent colours in the visible region after rapid cooling process from the temperature of the cholesteric liquid crystalline phase. Measurement of selective reflectance of visible light, X-ray diffraction, optical rotation dispersion of the solid films proved that the films remained the cholesteric ordering of the molecules. The cholesteric structure in the solid films were completely stable at room temperature. The colour of the solid film was totally, partially or in imagewise manner changed into selected colours by adjusting the temperature of the surface just before the rapid cooling process. The property of this compound can be applicable to memory media with high density using the spectrum of light, or to thermosensitive full-colour recording materials.
Composition and Electrode Effects on the Electrical Properties of SrBi2Ta2O9
Authors: Thomas Darin T. , Fujimura Norifumi , Streiffer S. K. , Kingon Angus I.
Published: April 2011

SrBi2Ta2O9 has attracted great interest for non-volatile memory applications due to its minimal polarization fatigue. This paper describes systematic studies, using pulsed laser deposition, on the effect of deposition conditions on the Bi-Pt reaction and on the potential for low temperature processing. Changing the deposition temperature (Ts) and oxygen gas pressure during deposition can control the Bi content in the films. At a Ts of 600°C, the films have excess Bi and do not fully crystallize to SBT, resulting in poor remnant polarization (Pr). These films consist mostly of the pyrochlore phase, plus a small amount of disordered, c-oriented layered perovskite SBT. By annealing over 750°C, the films show improved Pr, but further Pt - Bi interactions occur. At a Ts of 700°C, the as-deposited films are fully crystallized and show saturated hysteresis loops. However, Bi deficiency through alloying results in reduced remnant polarization (2Pr = 7.0μC/cm2). Films on Ir/Pt show reduced electrode reactions and improved properties.
Domain Structures of Epitaxial SrRuO3 Thin Films
Authors: Jiang J. C. , Pan X. , Chen C. L.
Published: April 2011

The structural characteristics of SrRuO3 thin films deposited on a (001) SrTiO3 substrate by pulsed laser were studied by transmission electron microscopy (TEM) and high-resolution TEM. TEM studies of cross-sectional specimens revealed the epitaxial growth of the films with the SrRuO3-(110) plane parallel to the SrTiO3-(001) plane. Two types of 90° rotational domain structures were observed in both cross-sectional and plan-viewing specimens. The in-plane orientations of these domains with respect to the substrate are either of SrRuO3-[110] // SrTiO3 - [100] and SrRuO3-[001] // SrTiO3-[010], or of SrRuO3-[110] // SrTiO3-[010] and SrRuO3-[001] // SrTiO3-[100].
Ferroelectric Thin Films of Bi-Containing Layered Perovskites
Authors: Du Xiaofeng , Chen I-Wei
Published: April 2011

Ferroelectric thin films of Bi-containing layered perovskites such as Bi4Ti3O12, PbBi2Nb2O9 and SrBi2Nb2O9 have been processed by metal-organic decomposition (MOD) method. Films with random or c-orientation have been obtained via different heat treatment. Nucleation control has been identified as the mechanism for the texture evolution in these films. A strong polarization anisotropy has been observed which corresponds to the layered polarization in the crystal structure. The fatigue test results show that Ti seems to be a common species that exists in fatigue-prone ferroelectrics.
Phase Transition and Pyroelectric Properties of La-Modified PbTiO3 Thin Films
Authors: Iijima Kenji , Niihara Koichi
Published: April 2011

Phase transition and related electric properties of La-modified PbTiO3 (PLT) thin films were investigated. Curie temperature of the films decreased and the diffuseness of the phase transition increased with increasing La content. Simultaneously, it was losing a ferroelectricity and pyroelectric properties degraded in La-rich region. This is considered to be due to the increase of a defect in the film by exchanging Pb2+ ions to La3+ ions. Compensation of the defect by the addition of Mn ion improve the ferroelectricity of the PLT and the films showed an extremely large pyroelectric properties.
Domain Wall Pinning by Grain Boundaries During Electric Field Poling of KNbO3 Thin Films
Authors: Gopalan Venkatraman , Raj Rishi
Published: April 2011

We present evidence for grain-boundary pinning of domain walls as controlling the electric field poling behavior of KNbO3 thin films. Two epitaxial film systems are compared: (I) film on MgO (100) substrate with KNbO3 (110)// 120Å SrTiO3 (100) //MgO(lOO) and (II) film on SrTiO3 (100) substrate with KNbO3 (110)// SrTiO3 (100). Quantitative measurement of the area fractions of four domain variants in each film system was made using in-situ second harmonic generation measurement while applying an external electric field at room temperature. While the film system (I) showed reversible domain wall motion, the film system (II) snowed some permanent poling after the removal of the external field. Transmission Electron Microscopy revealed a network of low angle grain boundaries of ∼ 1.5–2° misorientation along the substrate cubic axes in the growth plane of the film system (I) and also a network of 6° and 120° walls intersecting these grain boundaries at 45° in the film growth plane. These features were found to be absent in the film system (II). We propose that the observed electric field poling phenomena is due to the pinning of 60° and 120° domain walls by low angle grain boundaries.
Ferroelectric Properties and Crystal Structure of YBa2Cu3O7/BaxSr(1−x)TiO3 Heterostructures
Authors: Schwan CH. , Martin F. , Jakob G. , Martinez J. C. , Adrian H.
Published: April 2011

Epitaxial YBa2Cu3O7/Ba0.5Sr0.5TiO3 (YBCO/BST) and YBCO/BaTiO3 (BTO) heterostructures were prepared by dc and rf sputtering on SrTiO3 and MgO substrates. The YBCO/BTO bilayers exhibit an inductive superconducting transition temperature of 85 K and the ferroelectric phase transition of BST shows a Curie-Weiss temperature of 310 K. Microstructure was investigated by x-ray-diffraction and atomic force microscopy. In this work we also studied the insulator's conductivity and the contribution of domain walls to permittivity.
Preparation of Boron Nitride Thin Films by MOCVD
Authors: Lee Sang-Yeol , Jin Yong-Gi , Nam Young-Woo , Lee Joong Kee , Park Dalkeun
Published: April 2011

Boron nitride thin films were prepared on Si(100) substrate by CVD. Triethylboron and ammonia were employed as precursors and various operating parameters such as reactor pressure, temperature, feed rates of gases were varied to investigate their effects on deposition rate and film characteristics. Total gas pressure in the reactor was varied from atmospheric to I torr. Deposition temperature was in the range 850 – 1,050 °C. Deposition rate increased with partial pressure of TEB but decreased with total pressure in the reactor. Deposited films were examined with SEM, FTIR, XPS, AES, XRD. Prepared films were BN of turbostratic structure.
Chemically Prepared Lead Magnesium Niobate Dielectrics
Authors: Tuttle B. A. , Voigt J. A. , Sipola D. L. , Olson W. R. , Goy D. M.
Published: April 2011

A chemical solution powder synthesis technique has been developed that produces fine, uniform powders of lead magnesium niobate (PMN) with 60 to 80 nm crystallite size. The synthesis technique was based on the dissolution of lead acetate and alkoxide precursors in acetic acid followed by precipitation with oxalic acid/propanol solutions. Lead magnesium niobate ceramics fabricated from these chemically derived powders had smaller, more uniform grain size and higher dielectric constants than ceramics fabricated from mixed oxide powders that were processed under similar thermal conditions. Chem-prep PMN dielectrics with peak dielectric constants greater than 22,000 and polarizations in excess of 29 μC/cm2 were obtained for 1100°C firing treatments. Substantial decreases in dielectric constant and polarization were measured for chemically prepared PMN ceramics fired at lower temperatures, consistent with previous work on mixed oxide materials.
Low-Temperature, Solution-Based Routes to Nanocrystalline InS Powders and Thin Films
Authors: Hollingsworth Jennifer A. , Buhro William E.
Published: April 2011

We have developed several solution-based preparations for nanocrystalline orthorhombic InS, which is a mid band gap semiconductor (2.44 eV) with potential applications in photovoltaics. Various reagents were used as indium (t-Bu3In, t-Bu2InCl) and sulfur (H2S, (TMS)2S) sources. Growth of crystalline powders was dependent upon the addition or in-situ generation of indium metal. These reactions represent the first reported use of a Solution-Liquid-Solid (SLS) mechanism by which semiconductors are grown from a molten metal flux for a system other than the III-V family of semiconductors. The studies on powder preparations were used to develop a new, low-temperature (185 °C) chemical-bath process for depositing a polycrystalline InS thin film. The film was deposited from a solution of t-Bu3In and elemental sulfur onto an indium-coated fused-silica substrate; the indium film acted as the crystallization medium.
Room Temperature Phase-Selective Synthesis of Metastable Lead Chromium Oxides
Authors: Doxsee Kenneth M. , Jang Meehae
Published: April 2011

The salt metathesis reaction between lead(II) salts and potassium chromate in methanolic solution, mediated by the formation of a soluble complex of potassium chromate with a cyclic polyether, affords orthorhombic PbCrO4rather than the monoclinic modification formed in aqueous solution. When the aqueous metathesis reaction is carried out in the presence of tertiary amines, a lead oxide-rich phase, PbO•PbCrO4(Pb2CrO5), is selectively formed.
Metal-Organic Chemical Vapor Deposition Routes to Films of Transparent Conducting Oxides
Authors: Wang A. , Cheng S. C. , Belot J. A. , Mcneely R. J. , Cheng J. , Marcordes B. , Marks T. J. , Dai J. Y. , Chang R.P.H. , Schindler J. L. , Chudzik M.P. , Kannewurf C. R.
Published: April 2011

This contribution reports the in situ growth of transparent, conducting GaxIn2-xO3 and ZnkIn2Ok+3 films by MOCVD (metal-organic chemical vapor deposition) techniques using In(dpm)3, Ga(dpm)3, and Zn(dpm)2 (dpm = dipivaloylmethanate) as volatile precursors. In the former series, film microstructure in the x = 0.4 – 1.0 range is predominantly cubic with 25° C electrical conductivities as high as 1300 S/cm (n-type; carrier density = 1.2 × 1020 cm−3, mobility = 68 cm2/Vs) and optical transparency in the visible region greater than that of ITO. In the latter series, films in the composition range K = 0.16 – 3.60 were studied; the microstructural systematics are rather complex. Electrical conductivities (25° C) as high as 1000 S/cm (n-type; carrier density = 3.7 × 1020 cm−3, mobility = 18.6 cm2/Vs) for K = 0.66 were measured. The optical transparency window is significantly broader than that of ITO.
Room Temperature Magnetoresistance in LaxCaYMnO3 Thin-Films Deposited by Liquid Delivery Chemical Vapor Deposition
Authors: Studebaker D. , Todd M. , Doubinina G. , Seegal C. , Baum T. H.
Published: April 2011

Liquid delivery, metal-organic chemical vapor deposition (MOCVD) was used to deposit high quality, A-site deficient crystalline films of LaxCayMnO3 where x + y < 1. The properties of the deposited thin-films are strongly dependent upon the film stoichiometry and display magnetoresistance repsonses at or above room temperature. Using Ca doped A-site deficient thin-films, we can shift the metal to insulator transition (Te) in a controlled manner to temperatures that are useful for commercial applications. Further, these films exhibit useful magnetoresistance at room temperature in relatively small applied magnetic fields.
Boron Nitride Materials for Tribological and High Temperature High Power Devices
Authors: Badi N. , Tempez A. , Starkov D. , Medelcr N. , Bensaoula A. , Kulik J. , Klimentov S. M. , Garnov S. V. , Ageev V. P. , Ugarov M. V. , Lee S. , Perry S. S. , Waters K. , Shultz A.
Published: April 2011

Boron nitride thin films on sapphire substrates were investigated for their tribological and optoelectronic applications. A gridless end Hall gun source and an electron cyclotron resonance (ECR) source were used for nitrogen species delivery while pure boron was evaporated at a rate of 0.2 Å/s. The surface stability of these thin films was investigated by high temperature annealing. Atomic force microscopy (AFM), friction force microscopy (FFM), and Knoop microhardness measurements were performed on the materials in order to assess their merits as tribological coatings. Finally, BN thin films were subjected to laser transient photoconductivity (TPC) experiments to determine both their optical laser damage threshold as well as their photoconductivity characteristics. For both single-pulse shot and multiple-pulse irradiation regimes, preliminary tests showed the higher the ion beam current used during growth (70–150 mA), the higher the optical damage threshold. The lower damage threshold was typical of BN films grown using an ECR plasma source and was measured to be in the range of ∼50 MW/cm2. Optical damage of films grown at ion beam currents above 100 mA was not observed at laser intensities up to few hundreds MW/cm2. A multiphoton excitation technique was utilized to obtain PC signals from this wide band gap material and preliminary results show that unusual PC voltage amplitudes as high as 0.5 V were observed.
Four Revolutions in Diamond Synthesis: The Vindication of Edisonian Chemistry
Authors: Roy Rustum
Published: April 2011

Careless claims by scientists are often expanded further by journalists and grossly distort the scientific “truths” passed on to the public and policy maker. Recently, such overclaims have invaded the field of materials synthesis.

The real first principles of materials synthesis, based on the work of V.M. Goldschmidt (and Linus Pauling), have proved to be, and continue to be, very successful. By combining such principles with Edison's methodology of careful observation, precise experimentation and rapid feedback, thousands of new (inorganic) phases have been, and continue to be made (since 1948, several hundred from our own laboratory), producing dozens of useful, widely commercialized materials.

In contrast, in spite of seventy years of trying, the so-called “first principles” calculations (from the quantum mechanics of cores and electrons) have utterly failed to actually predict and synthesize a single new material or add anything to the deep and reliable insights of well known chemical theories. It is clear that what students and researchers in contemporary materials synthesis need most is a thorough grounding in crystal chemistry and phase equilibria (including metastable equilibria).

The history of the “C3N4” failure, as a harder than diamond candidate, is prototypical of the”calculating” approach to synthesis. It is contrasted with short summaries on four recent real advances into completely new processes for diamond synthesis.
Sol-Gel Precursors and the Oxygen Storage Capacity of PrOy-ZrO2 Materials
Authors: Narula C. K. , Taylor K. L. , Haack L. P. , Allard L. F. , Datye A. , Sinev M. Yu. , Shelef M. , McCabe R. W. , Chun W. , Graham G. W.
Published: April 2011

The gels derived from mixtures of Pr(OiC3H7)3 and Zr(OiC3H7)4•iC3H7OH, upon hydrolysis and pyrolysis, furnish single-phase PrOy-ZrO2 materials crystallized in the fluorite structure. These materials can be coated onto high-surface-area γ-alumina powders or deposited onto dense α-alumina coupons in the form of thin films from a solution of parent alkoxides modified with 2,4-pentanedione in THF. The fluorite structure of the PrOy-ZrO2 in the films appears to be thermally stable in air up to 1200°C. Temperature-programmed-reduction (TPR) measurements show that the bulk PrOy-ZrO2 material with a Pr. Zr molar ratio of 1:1 can store and release oxygen while that with a molar ratio of 1:3 cannot.

The precursors play an important role in determining phase composition of the resulting PrOy-ZrO2 material. A mixture of monoclinic and cubic or tetragonal phases was found in PrOy-ZrO2 prepared from a new single-source heterometallic alkoxide, Pr2Zr6(μ4-O)2(μ-OAc)6(μ-OiPr)10(OiPr)10, whereas a mixture of cubic and tetragonal phases was present in PrOy-ZrO2 made previously by coprecipitation from aqueous solutions of the metal nitrates.
The Partial Oxidation of Methanol by MoO3(010) Surfaces with Controlled Defect Distributions
Authors: Smith Richard L. , Rohrer Gregory S.
Published: April 2011

Atomic force microscopy has been used to determine how MoO3(010) surfaces with controlled defect populations evolve during reactions with MeOH/N2 mixtures. The structural evolution of the freshly cleaved surface is compared to surfaces reduced in 10%H2/N2 at 400 °C. While the freshly cleaved surfaces are flat and nearly ideal, the reduced surfaces contain voids bounded by step loops where Mo atoms in reduced coordination are found. In both cases, reacting the MoO3(010) surface with MeOH/N2 mixtures between 300 and 400 °C leads to H intercalation and the nucleation of acicular precipitates of HxMoO3. On the freshly cleaved surface, the H-bronze phase precipitates uniformly. On the reduced surface, the precipitates form preferentially at the void edges, where undercoordinated Mo atoms are found.
Structural and Electrical Properties of Phosphorous-Doped Amorphous Diamond
Authors: Camphausen S. M. , Myers A. F. , Bozeman S. P. , Cuomo J. J.
Published: April 2011

Hard carbon films can be prepared by the condensation of energetic carbon species at or below room temperature. These amorphous films are primarily tetrahedrally coordinated and contain high fractions of sp3 bonds leading to the terminology amorphous diamond. These films have been successfully doped with phosphorus up to 1 at.%, by other researchers by using a phosphorus doped graphite target. We have also investigated evaporated phosphorus in conjuction with a filtered cathodic arc to incorporate phosphorus into the films and have successfully incorporated phosphorus up to 40 at.% into our films using this technique. XPS showed that some of the phosphorus was clustered. PEELS revealed that with an incorporation of 40 at.% of phosphorus, the sp3 content was approximately 20%.
Amorphous Diamond-Like Carbon Films Prepared by Dc Saddle-Field Glow-Discharge Method: Doping with Boron and Phosphorus
Authors: Chan W. , Allen T. , Gaspari F. , Szurmak J. , Sagnes E. , Zukotynski S.
Published: April 2011

Our preliminary results show that controllable doping of amorphous hydrogenated DLC films prepared by DC saddle-field glow-discharge technique is possible. We have found deposition conditions when the doping with boron is electrically effective.
Analysis and Modification of Amorphous and Partially-Crystalline Thin Films
Authors: DiNardo N. J. , Mercer T. W. , Martinez-Miranda L. J. , Siegal M. P. , Friedmann T. A. , Sullivan J. P. , Plank R. V. , Vohs J. M.
Published: April 2011

Thin films of light atomic weight elements in amorphous, partially-crystalline, or crystalline forms have applications in a broad range of technologies. For example, amorphous tetrahedral carbon (a-tC) and polymeric thin films impact electronic materials technology as electron- and light-emitting device elements, respectively. A lack of crystallinity introduces complexity in the experimental and theoretical characterization of these materials but is not necessarily a limiting factor in their performance. While the growth process is clearly a major factor governing the physical properties of a film, interactions with the substrate are also important, so surface and interface analysis provides an important complement to bulk measurements. Currently, the fundamental and applied aspects of the atomic, electronic and vibrational structure of these complex materials are being elucidated by novel approaches combining several experimental techniques with theoretical calculations. This paper focuses on several approaches in the characterization and modification of thin films made possible by recent experimental advances. The structural and electronic properties of two model systems are considered as examples: a-tC thin films grown by pulsed laser deposition (PLD) and poly aniline thin films grown by vapor deposition. First, scanning probe microscopies and x-ray scattering are used to investigate the structural aspects of a-tC films as a function of PLD growth conditions. The possible connection of nanoscale surface modification and characterization with electron emission properties will be discussed. Second, the results of inelastic scattering spectroscopy and other surface techniques will be discussed to obtain information on both interfacial aspects of the growth of polyaniline thin films and microscopic and macroscopic aspects of electrical conductivity upon doping. Comparisons will be made with other studies that address properties of analogous crystalline systems as appropriate. A brief assessment of the broader problem of analyzing these systems will be given.
Melt Energetics at High Temperature and Pressure
Authors: Wilding Martin C. , Navrotsky Alexandra
Published: April 2011

The physical behavior of silicate liquids at high pressure is important in modeling the dynamic processes of the deep earth. The density of the silicate liquids determines the transport properties of silicate melts and volumetric properties of silicate melts are therefore of prime importance. However, the partial molar volumes of melt components are difficult to evaluate since it is difficult to observe the molten state at high pressure. A variety of approaches are used to investigate silicate melt properties. Individual melt components can be used and complex mixing terms used to describe mixing behavior. Alternatively the melt species themselves can be investigated, although there is little information as to what these actually are. In both cases the accurate determination of the dP/dT slope of the melting curves is critical.

Speciation reactions can be studied in situ at one atmosphere through high temperature calorimetry. An approach has been developed where the dissolution of melt components which are readily soluble in silicate solvents and which have a large heat effect can be used to determine the dependence of the activities of these components on melt structure. In addition the high temperature calorimetrie data can be used in combination with solution calorimetrie data at lower temperatures to evaluate the temperature-dependent stability of these melt species. These studies are independent of and complementary to spectroscopie determinations and provide a description of the temperature-dependence of melt structure at one atmosphere. Recent studies have focused on the solution of La2O3 and TiO2 in model silicate melts to assess the role of melt structure in the complexing of these components. The next obvious step is to extrapolate to high pressure. One possible approach is to combine one atmosphere data with existing melting relationships to determine the optimized melt compositions for a model natural systems. The next step is to then assess the stability of melt species from the partial molar properties and the partitioning of the elements between coexisting melts and mineral phases at pressures and temperatures of interest.