bluuebunny/crossref_metadata_2025 huggingface dataset:
Amber from 1000-Year Old Prehispanic Tombs in Northern Peru
Authors: Shimada Izumi , Anderson Ken B. , Haas Herbert , Langenheim Jean H.
Published: April 2011

Hundreds of large, shaped and perforated amber beads excavated from two Middle Sicán elite shafttombs at Huaca Loro on the northern coast of Peru represent the first scientifically documented case of amber use in prehispanic South America. Amber was highly valued and formed a key component of Sicán sumptuary good production. This paper describes the analytical procedures and archaeological and botanical background for source identification and cultural understanding of amber beads found on pectorals, necklaces and gold alloy objects. Samples were initially identified by XRD and FT-IR microscopy, followed by a more detailed and conclusive analysis using pyrolysis GC-MS. Radiocarbon dating points to a minimum age of 50,000 years. Results were compared with amber from known sources in the New World. Various lines of evidence suggest that the amber was derived from a heretofore unknown source, probably an ancient species ofHymenaea, possibly related toH. oblongifolia(family Leguminosae) occurring today in upper Amazonia.
La Virgincita: Technical Study of an Indo-Christian Statue
Authors: Susan Barger M. , Gong Weiliang
Published: April 2011

A small stone statue of the Virgin Mary was recently found that is one of two free-standing Indo Christian sculptures known to be in the United States. The Indo-Christian style of art marks the transition from pre-Columbian art to Christian art and most examples of this style are found on buildings in Mexico. The statue,”la Virgincita,”is patterned after an European engraving, however the decorative details in the stone carving are Aztecan. This paper is a description of the materials characterization of the statue and a study of its technical details using scanning electron microscopy, transmission electron microscopy, and electron microprobe analysis.
Metallography and Corrosion Product Studies on Archaeological Bronze Fragments from the Qu Cun Site
Authors: Chase W. T. , Wang Quanyu
Published: April 2011

The authors studied a suite of fragments of corroded bronzes from the Tienma-Qu Cun site, a Western Zhou city and cemetery complex dating from ca. 1000 to ca. 650 B.C‥ Conventional metallographic techniques were used along with scanning electron microscope, electron microprobe and x-ray diffraction. The bronzes are very varied in structure and composition. Most are cast, moderate-tin bronzes, but some are high or low in tin or lead. A few show a worked and annealed structure, and some of the cast bronzes were also heat treated (possibly by use as cooking pots). corrosion patterns also vary greatly, from almost uncorroded to total mineralization. Periodic and esquential corrosion phenomena were detected, as well as patination applied when the bronzes were made. We had hoped to be able to ascertain the causes of the different penetration of corrosion in these samples, but that must remain for future work.
Determination of the Three-Dimensional Atomic Structure at Internal Interfaces by Electron Energy Loss Spectroscopy
Authors: Browning N. D. , Wallis D. J. , Pennycook S. J.
Published: April 2011

The fine structure of a core-loss edge contains detailed information on the local atomic environment. It can be used as an extremely sensitive probe of the fluctuations in structure and bonding that can occur at internal interfaces. Interpretation of such fluctuations requires only a knowledge of the location of the electron probe when the spectrum is acquired and a means of interpreting the spectrum. The location of the probe can be controlled with atomic precision in the STEM by the use of the Z-contrast image, while the real space cluster methodology of multiple scattering analysis is ideally suited to the task of interpretation. This approach is used here to derive 3-dimensional models for tilt grain boundaries in TiO2 and SrTiO3.
Stress Induced Structural Changes of Interphase Boundaries and Mechanical Twins in two-Phase γ-Titanium Aluminides
Authors: Appel F. , Wagner R.
Published: April 2011

Conventional and high-resolution electron microscopy has been used to examine the interfacial structures in (α2+ γ) titanium aluminide alloys. Accommodation of misfit which arises because of differences in lattice parameters and crystal structure leads to dense structures of interfacial dislocations and coherency stresses. During deformation stress induced structural changes of misfitting interfaces occur. These are closely related to the generation of perfect and twinning partial dislocations. At elevated temperatures diffusion controlled structural changes take place at an atomic level and seem to limit the structural stability of the material.
Equilibrium Configuration of Bi-Doped ZnO Grain Boundaries: Intergranular Amorphous Films
Authors: Wang Haifeng , Chiang Yet-Ming
Published: April 2011

It is shown that the solid state equilibrium configuration of ZnO grain boundaries saturated with Bi-doping is a nanometer-thick amorphous film. Polycrystalline ZnO samples doped with Bi2O3 were studied using high resolution transmission electron microscopy (HRTEM) and dedicated scanning transmission electron microscopy (STEM). Samples were equilibrated below the eutectic temperature (Teutectic = 740°C) and at 1 atmosphere pressure, starting from three different initial states: one was cooled from above the eutectic temperature; a second was processed entirely below the eutectic temperature; and the third was de-segregated by applying high pressure (1 GPa) followed by annealing at 1 atmospheric pressure. In all instances, ZnO grain boundaries contain an amorphous film 1.0–1.3 ran in thickness, corresponding to a Bi excess equivalent to approximately one monolayer.
Point Defects Migration and Agglomeration in Si at Room Temperature: The Role of Surface and Impurity Content
Authors: Privitera V. , Coffa S. , Kyllesbech Larsen K. , Libertino S. , Mannino G. , Priolo F.
Published: April 2011

Our recent work on the room temperature migration and trapping phenomena of self-interstitials and vacancies in crystalline Si is reviewed. Spreading resistance profiling and deep level transient spectroscopy measurements were used to monitor the interaction of ion beam generated defects with dopant atoms, intrinsic impurities (i.e. O and C), pre-existing defect marker layers and sample surface. We have found that both interstitials and vacancies undergo fast long range migration which is interrupted by trapping at impurities and by recombination at defects or at the surface. Effective defect migration lengths as large as 5 μm at room temperature have been observed in highly pure, defect free epitaxial Si samples. A lower limit of 1×10−10 cm2/sec for the room temperature diffusivity of self-interstitials has been determined. Furthermore, by monitoring the migration and interaction processes of point defects injected through a mask, we have established that surface acts as an effective sink for the migrating Si self interstitials.
Lattice Monte Carlo Simulations of Vacancy-Mediated Diffusion and Aggregation using Ab-Initio Parameters
Authors: Bunea Marius M. , Dunham Scott T.
Published: April 2011

The lattice Monte Carlo method with parameters from recent first-principle calculations1,2 are used to investigate dopant diffusion in silicon. In the simulations, vacancy hopping on a silicon lattice is biased by changes in system energy, including interactions up to the sixth-nearest neighbor. We find that vacancy-mediated diffusivity increases dramatically above 1020 cm−3, in agreement with experimental observations3 and previous calculations.4 However, for very long simulation times, arsenic diffusivity is reduced due to formation of AsxV complexes, with clustering more pronounced at high doping levels. As suggested by Ramamoorthy and Pantelides,5 we find that As2V complexes are mobile, and although they diffuse much more slowly than AsV pairs, they appear likely to have a significant role in high concentration diffusion due to their much higher numbers. We also investigated dopant fluxes in a vacancy gradient. For dopants like As for which pair diffusion is limited by the dissociation to third-nearest neighbor distances, the dopant flux is less than that predicted by pair diffusion models, with greater difference at higher temperatures. In contrast, for phosphorus/vacancy pairs, whose diffusion is limited by dopant/vacancy exchange, the dopant flux is close to the predictions of pair diffusion.
Thermal Evolution of Rectifier Speed and Deep Levels in Irradiated Silicon
Authors: Ntsoenzok E. , Desgardin P. , Blondiaux G. , Schmidt D. C. , Barbot J. F. , Blanchard C. , Renault P. O.
Published: April 2011

P+NN+ silicon rectifiers have been irradiated by protons and alpha particles. DLTS and reverse recovery time (the so called TRR) measurements were performed in both as-irradiated and annealed (400°C) samples. The evolution of implantation induced-centers with the annealing is not the same when using the two particles. For example, the concentration of the well known A center increases (decreases) with the annealing when protons (alpha particles) are used. On the other hand, the measurements of the TRR show that the rectifier speed decreases with the annealing in all cases studied.
Electrical Defects of Shallow (P+/N) Junctions Formed by Boron Implantation into Ge-Preamorphized Si-Substrates
Authors: Alquier D. , Benzohra M. , Boussaid F. , Olivie F. , Martinez A.
Published: April 2011

In this paper, we report Current-Voltage (I-V), Capacitance-Voltage (C-V) and Deep Level Transient Spectroscopy (DLTS) measurements on ultra-shallow (p+/n) junctions obtained by boron implantation into crystalline and Ge preamorphized Si-substrates. Germanium implantations were carried out at the energies of 30, 60 and 150 keV at a dose of 1015 cm−2. Boron was then implanted at an energy of 3 keV at a dose of 1015 cm−2. Dopant activation was obtained by Rapid Thermal Annealing (RTA) performed at 950°C for 15s in a nitrogen ambient. The aim of this work is to study the relation that exists between a population of End-Of-Range (EOR) defects, measured by TEM, and electrical properties of the Ge preamorphized diodes. The electrical measurements allow us to give the conduction mechanism which dominates in the diodes. Moreover, DLTS measurements showed the presence of two majority-carrier traps in direct relation with the EOR defects, measured at Ec-0,22eV and Ec-0,47eV. The presence of energy-distributed G-R centers independent upon the preamorphization stage is also discussed. Nevertheless, high quality (p+/n) junctions can be obtained by this technology with a judicious choice of Ge implantation energy.
An Equilibrium Based Mean-Field Model for Diffusion in Solids With a Distributed Density of States
Authors: Franz A. J. , Gland J. L.
Published: April 2011

Determination of transport mechanisms and energetics in amorphous silicon presents an interesting modeling challenge. Transport in amorphous silicon films is likely to involve energetically distributed traps and mobile species, as in the case of hydrogen and electron diffusion. Detailed kinetic models using discrete energy levels have been developed, however, the density of states of the diffusing species in amorphous silicon is likely to be continuous and distributed, due to the amorphous nature of the films. We have developed a mean-field, equilibrium based model which utilizes a continuous density of states for the diffusing species. The transport in amorphous silicon is modeled as a function of a gradient in the quasi-chemical potential, rather than concentration, of the diffusing species. The model is applicable when the local equilibration processes are fast relative to the transport process. This approach is extremely numerically efficient, as well as flexible, allowing for modeling of tracer experiments, such as deuterium diffusion in a-Si:H films, and possible changes in density of states with time, temperature, and diffusing species concentration. We demonstrate the utility of the model by simulating hydrogen evolution from a-Si:H films.
Ferroelectric films as a Fashion Object for Polycrystalline Film Investigation
Authors: Petrovsky V. , Anderson H.U. , Shumsky M.
Published: April 2011

BaxSr1-xTiO3 (BST), PbZrxTi1-xO3 (PZT) and two layer PZT-BST films were prepared on Pt, Si(100) and Si(111) substrates by a sol-gel method. XRD analysis shows that the PZT films on the Si(111) substrates tended to be preferentially oriented in the (110) direction. The nondestructive readout of the state of ferroelectric polarization was investigated by three methods: the pyroelectric effect, the non-linearity of the capacitance and the field effect in MOS structures. It is shown that all three methods provide nondestructive readout, and the choice between them depends on the intended use.
Accurate Depth Profiling of Ultra-Thin Oxide Films by Secondary
Ion Mass Spectrometry
Authors: Smith Stephen P. , Yang Ming Hong , Chia Victor K. F.
Published: April 2011

SurfaceSIMS depth profile measurements of dopants in silicon wafers with
thin thermal oxide layers are presented. Complete and accurate calibration
of these profiles requires layered data reduction to adjust for residual
matrix effects of a factor of two in the sputter rate and SIMS relative
sensitivity factor in SiO2 compared with bulk silicon. Properly
calibrated profiles show good agreement with expected ion implant profile
shapes, and can reveal dopant pile-up at SiO2/Si interfaces
(phosphorus, for example). Measured SurfaceSIMS profiles of B doping within
the first 10 nm of the substrate Si of experimental large area MOS
capacitors show good agreement with dopant profiles independently obtained
from experimental C-V data.
Thermoelectric Properties of P-Type (Bi1−xSbx)2Te3 Fabricated by Mechanical Alloying Process
Authors: Jung Boo Yang , Choi Jae Shik , Oh Tae Sung , Hyun Dow-Bin
Published: April 2011

Thermoelectric properties of polycrystalline (Bi1−xSbx)2Te3 (0.75 ≤ x ≤ 0.85), fabricated by mechanical alloying and hot pressing methods, have been investigated. Formation of (Bi0.25Sb0.75)2Te3 alloy powder was completed by mechanical alloying for 5 hours at ball- to-material ratio of 5: 1, and processing time for (Bi1−xSbx)2Te3 formation increased with Sb2Te3 content x. When (Bi0.25Sb0.75)2Te3 was hot pressed at temperatures ranging from 300°C to 550°C for 30 minutes, figure-of-merit increased with hot pressing temperature and maximum value of 2.8 × 10−3/K could be obtained by hot pressing at 550°C. When hot pressed at 550°C, (Bi0.2Sb0.8)2Te3 exhibited figure-of-merit of 2.92 × 10−3/K, which could be improved to 2.97 × 10−3/K with addition of 1 wt% Sb as acceptor dopant.
Microstructural and Thermoelectric Properties of P-Type Te–Doped Bi0.5Sb1.5Te3 And N-Type SbI3-Doped Bi2Te2.85Se0.15 Compounds
Authors: Seo J. , Park K. , Lee C. , Kim J.
Published: April 2011

The p-type Te-doped Bi0.5Sb1.5Te3 and n-type SbI3-doped Bi2Te2.85Se0.15 thermoelectric compounds were fabricated by hot pressing in the temperature range of 380 to 440 °C under 200 MPa in Ar. Both the compounds were highly dense and showed high crystalline quality. The grains of the compounds were preferentially oriented and contained many dislocations through the hot pressing. The fracture path followed the transgranular cleavage planes, which are perpendicular to the c-axis. In addition, with increasing the pressing temperature, the figure of merit was increased. The highest values of figure of merit for the p- and n-type compounds, which were obtained at 420 °C, were 2.69 × 10−3/K and 2.35×10−3/K, respectively.
Searching for New Thermoelectrics in Chemically and Structurally Complex Bismuth Chalcogenides
Authors: Chung Duck Young , Hogan Tim , Schindler Jon , Iordanidis Lykourgos , Brazis Paul , Kannewurf Carl R. , Chen Baoxing , Uher Ctirad , Kanatzidis Mercouri G.
Published: April 2011

A solid state chemistry synthetic approach towards identifying new materials with potentially superior thermoelectric properties is presented. Materials with complex compositions and structures also have complex electronic structures which may give rise to high thermoelectric powers and at the same time possess low thermal conductivities. The structures and thermoelectric properties of several new promising compounds with K-Bi-Se, K-Bi-S, Ba-Bi- Te, Cs-Bi-Te, and Rb-Bi-Te are reported.
The Growth of Type-II Infrared Laser Structures
Authors: Yang M. J. , Moore W. J. , Bennett B. R. , Shanabrook B. V. , Cross J. O.
Published: April 2011

The MBE growth temperature for InAs/InGaSb/InAs/AlSb mid-infrared lasers has been studied. It is found that the best growth temperature is between 370°C and 420°C. A growth temperature above this range will result in excessive interlayer mixing, which degrades the radiative efficiency.
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.
Improved CdZnTe detectors grown by vertical Bridgman process
Authors: Lynn K. G. , Weber M. , Glass H. L. , Flint J. P. , Szeles Cs.
Published: April 2011

The γ ray (57Co) and a particle (241Am) detector response of Cd1−xZnxTe crystals grown by vertical Bridgman technique was studied under both positive and negative bias conditions. Postgrowth processing was utilized to produce a high-resistivity material with improved chargecollection properties. Samples of various Zn concentrations were investigated by I–V measurements and thermally stimulated spectroscopies to determine the ionization energies of deep levels in the band gap. When the post-processing conditions were optimized the lowenergy tailing of the γ-ray photopeaks was significantly reduced and an energy resolution of under 5% was achieved for the 122 keV γ-photon line in crystals with x=0.2 Zn content at room temperature. A peak to background ratio of 14:1 for the 122 keV photopeak from 57Co was observed on the best sample, using a standard planar detection geometry. The low-energy 14.4 keV X-ray line could also be observed and distinguished from the noise.
Study on Deep Level Traps in p-HgCdTe With Dltfs
Authors: Kawata S. , Sugiyama I. , Kajihara N. , Miyamoto Y.
Published: April 2011

We studied the characteristics of deep-level traps in p-type HgCdTe diodes using the Deep Level Transient Fourier Spectroscopy (DLTFS) method. For both holes and electrons, two types of traps were observed. The DLTFS signal intensity of one type of trap increased with the carrier density in the HgCdTe, while the other did not exhibit a monotonic increase. While measuring the stability of these traps during cooling cycles, the DLTFS signal intensity of the first group was almost constant while that of the latter fluctuated with every cooling cycle. Stable traps originated from Hg vacancies, unstable traps are attributed to vacancy-impurity complex defects.
Modeling Interdiffusion in Superlattice Structures
Authors: Gass Richard G. , Jackson Howard E.
Published: April 2011

Compositional interdiffusion in Al0.3 Ga0.7 As/GaAs superlattices induced by Si focused ion beam implantation and subsequent rapid thermal annealing is modeled using a set of diffusion equations which take into account the dynamics of the vacancy spatial profile. The inclusion of a new phenomenological term, which depends on the time derivative of the vacancy concentration spatial profile, provides good agreeement with experiment.
Cation Interdiffusion in GaInP/GaAs Single Quantum Wells
Authors: Micallef Joseph , Brincat Andrea , Shiu Wai-Chee
Published: April 2011

The effects of cation interdiffusion in Ga0.51In0.49P/GaAs single quantum wells are investigated using an error function distribution to model the compositional profile after interdiffusion. Two interdiffusion conditions are considered: cation only interdiffusion. and dominant cation interdiffusion. For both conditions the fundamental absorption edge exhibits a red shift with interdiffusion, with a large strain build up taking place in the early stages of interdiffusion. In the case of cation only interdiffusion, an abrupt carrier confinement profile is maintained even after significant interdiffusion, with a well width equal to that of the as-grown quantum well. When the interdiffusion takes place on two sublattices. but with the cation interdiffusion dominant, the red shift saturates and then decreases. The model results are consistent with reported experimental results. The effects of the interdiffusion-induced strain on the carrier confinement profile can be of interest for device applications in this material system.
Disorder-Delineated AlGaAs/GaAs Quantum-Well Phase Modulator
Authors: Choy Wallace C. H. , Weiss Bernard L.
Published: April 2011

Modeling is used to investigate waveguide phase modulators, with 0.5 μm and 1 μm quantum well active regions which are defined by implantation induced disordering. By controlling the extent of the interdiffusion in the lateral claddings, the refractive index difference between the core and claddings is used to provide single mode operation. The performance of the phase modulator is studied in terms of optical confinement, phase change per unit voltage per unit length, chirping property and absorption loss. Our result shows that the 0.5 μm one is a more efficient structure and its absorption loss can be reduced by increasing the applied field from 50 kV/cm to 100 kV/cm.
ZnGeP2 and its Relation to Other Defect Semiconductors
Authors: Vere A. W. , Taylor L. L. , Smith P. C. , Flynn C. J. , Saker M. K. , Jones J.
Published: April 2011

The paper discusses progress in the development of ZnGeP2 (ZGP) for optical parametric oscillator (OPO) applications and draws parallels with other semiconductors with volatile components, in which the presence of lattice defects gives rise to non-stoichiometry. In particular, attention is drawn to the microprecipitation which accompanies deviation from stoichiometry. In other materials this has been shown to result in spatial non-uniformity in the density of point defects.
Extra-Wide Tuning Range Mid-Ir Optical Parametric Generator Pumped by Er-Laser Pulses
Authors: Vodopyanov K. L.
Published: April 2011

Infrared pulses, continuously tunable in the 3–19 μm range, and with up to 1MW peak power, have been achieved using single-stage frequency conversion in a travelling-wave optical parametric generator (OPG) based on ZnGeP2, CdSe and GaSe crystals. The OPG was pumped by 100ps pulses from an actively mode-locked, Q-switched and cavity dumped 2.8 μm Cr,Er:YSGG laser. The quantum conversion efficiency reached 17%.
Improved CdZnTe detectors grown by vertical Bridgman Process
Authors: Lynn K. G. , Weber M. , Glass H. L. , Flint J. P. , Szeles Cs.
Published: April 2011

The γ ray (57Co) and α particle (241Am) detector response of Cdl-xZnxTe crystals grown by vertical Bridgman technique was studied under both positive and negative bias conditions. Postgrowth processing was utilized to produce a high-resistivity material with improved chargecollection properties. Samples of various Zn concentrations were investigated by I-V measurements and thermally stimulated spectroscopies to determine the ionization energies of deep levels in the band gap. When the post-processing conditions were optimized the lowenergy tailing of the γ-ray photopeaks was significantly reduced and an energy resolution of under 5% was achieved for the 122 keV γ-photon line in crystals with x=0.2 Zn content at room temperature. A peak to background ratio of 14:1 for the 122 keV photopeak from 57Co was observed on the best sample, using a standard planar detection geometry. The low-energy 14.4 keV X-ray line could also be observed and distinguished from the noise.
New CdTe Quantum Sensor, With Improved Spatial Resolution, for Fast X-Ray and γ-Ray Imaging
Authors: Gerstenmayer Jean-Louis , Bonnin Olivier , Gerbe Vincent , Glasser Francis , Peyret Olivier
Published: April 2011

We have designed and tested a new compact, very sensitive (>1 μRad), X-ray quantum sensor for high energy (0.5 -10 MeV) flash imaging. Monte Carlo simulations have been computed for several interesting detector materials (CdZnTe, HgI2-a, BGO, CsI, LSO...). From these calculations, we obtain general design rules and curves which allow one to optimize the pixel size of a sensor to the dose levels. An experimental CdZnTe detector array and its performance is presented.
Radiation Source Dependence of Degradation in Mosfets on SIMOX Substrate
Authors: Hakata T. , Ohyama H. , Simoen E. , Claeys C. , Takami Y. , Kawamura K. , Miyahara K. , Hososhima M.
Published: April 2011

Results are presented for the first time of a study on the degradation of the electrical performance of MOSFET's processed on SIMOX substrates and subjected to a 220-MeV carbon irradiation. For the n-MOSFETs an unstable increase of the drain current in linear operation is found, while for the p-MOSFETs, a drastic reduction is observed, both in linear operation and in saturation. The radiation damage is also compared to the results for 1-MeV electrons, 1-MeV fast neutrons and 20-MeV alpha rays. The differences in the damage coefficients are explained by the differences in the number of knock-on atoms and the nonionizing energy loss (NIEL). The recovery behavior of the device performance by isochronal annealing is also reported.
High Purity Liquid Phase Epitaxial GaAs For Radiation Detectors
Authors: Wynne D. I. , Tull C. S. Rossington , Haller E. E.
Published: April 2011

We report on the growth of high purity n-GaAs using Liquid Phase Epitaxy (LPE) and the fabrication of room temperature p-i-n radiation detectors. Our epilayers are grown from a Ga solvent in a graphite boat in a pure hydrogen atmosphere. Growth is started at a temperature of approximately 800 °C. Our best epilayers show a net-residual-donor concentration of 2×1013 cm−3, confirmed by Hall effect measurements. The residual donors have been analyzed by far infrared spectroscopy and found to be sulfur and silicon. Epilayers with thicknesses of up to 120 µm have been deposited on 650 µm thick semi-insulating GaAs substrates and on 500 µm thick n+-type GaAs substrates. We report the results obtained with Schottky barrier diodes fabricated from these high purity n-type GaAs epilayers and operated as X-ray detectors. The Schottky barrier contacts consisted of evaporated circular gold contacts on epilayers on n+ substrates. The ohmic contacts were formed by evaporated and alloyed Ni-Ge-Au films on the back of the substrate. Several of our diodes exhibit currents of the order of 1 to 10 nA at reverse biases depleting approximately 50 µm of the epilayer. This very encouraging result, demonstrating the possibility for fabricating GaAs p-i-n diodes with depletion layers in high purity GaAs instead of semi-insulating GaAs, is supported by similar results obtained by several other groups. The consequences of using high purity instead of semi-insulating GaAs will be much reduced charge carrier trapping. Diode electrical characteristics and detector performance results using 55Fe and 241Am radiation will be discussed.
An Approach to Sub-Pixel Spatial Resolution in Room Temperature X-Ray Detector Arrays with Good Energy Resolution
Authors: Warburton W. K.
Published: April 2011

In this paper we examine a recently proposed concept for obtaining sub-pixel spatial resolution in compound semiconductors where hole transport properties are relatively poor. [1] This approach uses weighted sums and differences of local pixel signals to extract both accurate x-ray energy estimates and interpolate location at the sub-pixel level. A simple analysis, including noise estimates, suggests the possibility of obtaining locations at the 50–100 micron level using 1–2 mm wide stripe electrodes while obtaining 1–2% energy resolution for x-rays up to 100 keV. Following this examination, we will present the most recent experimental results from our program to develop electronics to implement this scheme.
Synthesis of New Multifunctional Polymers inCorporating BIS-(Diphenylamino)Diphenylpolyene Moieties
Authors: Spangler C. W. , Faircloth T. , Elandaloussi E. H. , Reeves B.
Published: April 2011

A series of bis-(diphenylamino)diphenylpolyenes containing up to eight double bonds has been synthesized, both as parent model compounds, and functionalized for attachment as pendant chromophores. Oxidative doping of these new materials yields exceptionally stable bipolaronlike dications, even at the triene level. These new materials show promise as bimechanistic optical limiters by reverse saturable absorption and by 2-photon absorption.
Performances of Sexithiophene Based Thin-Film Transistor Using Self-Assembled Monolayers
Authors: Collet J. , Tharaud O. , Legrand C. , Chapoton A. , Vuillaume D.
Published: April 2011

High performance thin-film transistors (TFT) made of conducting oligomers are obtained when the organic films are well ordered at a molecular level. Highly ordered films are obtained provided that oligomers have a sufficient mobility on the substrate surface during film formation. One possible way to fulfill such a condition is to evaporate oligomers on heated substrates [1,2]. In this work, we suggest that a high surface mobility is obtained by a chemical functionalization of the silicon dioxide surface, and the corresponding improvements of the TFT performances are evidenced. A self-assembled monolayer of octadecyltrichlorosilane (OTS) was deposited on the SiO2 by chemisorption from solution before the evaporation of sexithiophene film. Room temperature current-voltage measurements indicate that the presence of the OTS monolayer improves TFT performances : threshold voltage is decreased, subthreshold slope is decreased, a high current ratio Ion/Ioff is obtained for a reduced gate voltage excursion, the fieldeffect mobility is slightly increased. We have also fabricated and characterized a nanometer scale organic FET (gate length = 50 nm) made of 6T films and only with a self-assembled monolayer as the insulating film between the degenerated silicon substrate (gate) and the conducting channel (no thick SiO2, we call it « oxide-free » organic FET). Performances of this nanometer size organic FETs are the following : subthreshold slope of 0.35V/dec, threshold voltage of −1.3V, effective mobility of 2×10−4 cm2/V.s.
Organic/Inorganic Langmuir-Blodgeti Films Based on Metal Phosphonates
Authors: Talham Daniel R. , Fanucci Gail E. , Petruska Melissa A. , Seip Candace T.
Published: April 2011

Langmuir-Blodgett (LB) bilayers of organophosphonic acids can be prepared where the phosphonic acid headgroups bind metal ions to form the same layered extended-solid structures present in solid-state metal phosphonates. The inorganic extended-solid network enhances the stability of the LB films, but can also be designed to introduce physical properties, such as magnetism, that are typical of the inorganic solid-state. By preparing films based on functionalized organophosphonic acids, the metal phosphonate approach can be used to produce “dualnetwork” LB films, where both the organic and inorganic networks add function to the thin film assembly. To begin to understand the design constraints associated with dual-network metal phosphonate films, LB bilayers of a phosphonic acidderivatized azobenzene amphiphile are formed with Cd2+ and La3+ and the structures are compared to octadecylphosphonate LB films prepared with the same metals.
Metal Complex Polymers for Electroluminescent Applications
Authors: Tao X. T. , Suzuki H. , Zhang Y. D. , Watanabe T. , Miyata S. , Wada T. , Sasabe H.
Published: April 2011

We report the synthesis and characterization of a soluble metal complex polymer for electroluminescent (EL) applications. The polymer was prepared by the reaction of a zinc Schiff base with 4,4′-diphenylmethane-diisocyanate. The polymer is amorphous and with glass transition temperature of 156 °C and is soluble in common organic solvents such as chloroform, tetrahydrofuran (THF), and N-methylpyrrolidinone (NMP). High optical quality films were obtained by spin-coating the polymer solution of THF. The zinc Schiff base, and the polyurethane (PU) shows strong photoluminescence under a UV-lamp illumination. Single and double layer EL devices consisting ITO/hole transfer layer (HTL)/PU/Al have been fabricated and characterized. The results indicated that the complex polymer could act as both electron transport and emissive layers for EL devices.
A Study on Langmuir Monolayers of Methacrylate Homo- and Copolymers Derivatized with Disperse Red Dyes
Authors: Dhanabalan Anantharaman , Balogh Débora , Constantino Carlos José Leopoldo , Riul Antonio , Oliveira Osvaldo N. , Giacometti José A.
Published: April 2011

We report on the organization of different disperse red dye derivatized methacrylate homo- and copolymers as Langmuir monolayers at the air-water interface. The monolayers were investigated using surface pressure and surface potential isotherms. Methacrylic homopolymers containing disperse red-1 (HPDR1) and disperse red-13 (HPDR13) and methacrylic copolymers with different mole percentages of the dye and hydroxyethyl spacer groups were synthesized and characterized. A comparison of the monolayer characteristics of HPDR1 and HPDR13 revealed the influence of the chlorine substitution in the aromatic ring of the dye. Studies with copolymers indicated a clear transition in the monolayer behavior with the change of mole percentage of the dye incorporated in the polymer. While copolymers with low dye content (up to about 5 mole%) presented an expanded monolayer, the copolymers containing higher dye content (12% and above) formed a condensed monolayer similar to that of the homopolymer. These results indicated the critical role of the dye component in the polymer chain in forming the monolayer at the air-water interface.
Crystallization Mechanism of Ferroelectric SBT Thin Films
Authors: Ikeda Yuji , Hironaka Katsuyuki , Isobe Chiharu
Published: April 2011

ABSTRCT

We characterize, via selected area electron diffraction and high resolution TEM, the multistage crystallization process by which strontium bismuth tantalate(SBT) thin films are transformed from initial amorphous phase to the fully formed layer-structured perovskite. During the annealing process at 800°C, we found that an intermediate fluorite-like stage is formed after 3min as the SBT precursor crystallizing into the final SBT structure. This new information will be very important for formation and crystallization of ferroelectric SBT films.
Effects of Buffer Layer on the Fabrication and Characteristics of Ferroelectric Thin Films
Authors: Song Han Wook , Lee Joon Sung , Kim Dae-Weon , Kim Kwang Ho , Sung Tae-Hyun , No Kwangsoo
Published: April 2011

MgO thin films were deposited on Si(100) substrate with different temperatures from 500 °C to 800 °C and different e-beam powers from 25W to 100W using e-beam evaporation method. Pb(Zr0.53Ti0.47)O3(PZT) thin films were deposited on MgO/Si(100) substrates with different drying temperatures from 190 °C to 310 °C using sol-gel technique. If there were no buffer layer between the PZT thin film and Si substrate, the peaks corresponding to perovskite PZT phase were not observed. However the buffer layer were inserted between the PZT thin film and Si substrate, it was possible to fabricate perovskite PZT phase. The barrier effects of MgO thin film to the interdiffusion of Pb were investigated by AES study. Optimum thickness of MgO at which PZT/MgO/Si structure shows P-E hysteresis was calculated, and the hysteresis was tested for PZT/MgO/Si structures with different MgO thicknesses.
The Effects of Film Thickness and Texture on the high and Low-Field stress Response of Lead Zirconate Titanate Thin Films
Authors: Shepard J. F. , Chu F. , Xu B. , Trolier-McKinstry S.
Published: April 2011

Lead zirconate titanate (PZT) thin films are currently employed in non-volatile ferroelectric memories (FRAM's) and are intended to be used as the active material in a number of microelectromechanical systems (MEMS). Several groups have reported that both the piezoelectric and dielectric characteristics of ferroelectric thin films improve with an increase of film thickness, though the reasons for those improvements are unclear. Previous investigations on the effects of biaxial mechanical stress indicate that non-180° domain wall motion is limited in PZT 52/48 films less than 0.5 μm thick. It is possible that some of the improvements of the dielectric and piezoelectric characteristics reported for thicker films (i.e. films thicker than 0.5 μm) are associated with an increase of extrinsic contributions to the properties. To evaluate domain wall mobility in thicker films, the high and low-field stress response of sol-gel PZT fabricated with either rapid thermal processing or conventional furnace annealing were investigated. Films with thicknesses ranging from 0.6 to 5.0 μm thick were measured as a function of applied biaxial stress (±110 MPa). It was found that for all films tested the changes of capacitance were on the order of 2–3%. High-field measurements showed: (1) the coercive field to be insensitive to applied stress, (2) remanent polarizations to decrease about 20% at the maximum applied tension, (3) remanent polarizations to increase less than 10% with applied compression, and (4) all changes to be reversible over the stress range investigated. These results suggest that extrinsic contributions are limited for the films tested.
Surface and size effects on the Ferroelectric Phase Transition and Surface Polarization of Thin Films: Monte Carlo Simulations
Authors: Romero J. , Fonseca L. F.
Published: April 2011

The macroscopic polarization of ferroelectric thin films was studied by Monte Carlo simulations using a Transverse Ising Model Hamiltonian with four-spins interactions. The dependence of the ferroelectric phase transition temperature, Tc, on the thickness of the film was obtained resulting in a shifting of Tc towards lower temperatures and a change from first-order to second-order phase transition as the thickness of the film is reduced. Comparison between the surface and internal order was carried out by the calculation of layer-averaged polarizations as a function of the sample temperature and the surface interaction parameters. These comparisons show that increasing disorder at the surface can be reverted by increasing the four-spins surface interactions.
Control of Growth Dynamics by Molecular Design in the MOCVD of Electronic Ceramics
Authors: Jones A. C. , Leedham T. J. , Wright P. J. , Crosbie M. J. , Williams D. J. , Lane P. A. , O'brien P.
Published: April 2011

The MOCVD technique is being used increasingly for the deposition of electronic ceramics such as Pb(Zr,Ti)O3, Ta2O5and TiO2. For the mil potential of MOCVD to be realised, it is sometimes necessary to modify existing precursors so that process parameters in the MOCVD process are optimised. In this paper we describe our approach to “molecular design” and discuss how the substitution of simple alkoxide groups by β-diketonates or donor-functionalised ligands can result in precursors with improved physical properties and optimum MOCVD characteristics.
A Surface Raman and Scanning Tunneling Microscopy Study of The Spatial Distribution of Corner-Sharing and Edge-Sharing Octahedra on thermally Oxidized Tungsten
Authors: Côté Matthew J. , Radloff Corey , Osman Joseph M. , Bussjager Rebecca , Martin Villarica R. , Nash Fazio , Chaiken J.
Published: April 2011

We have measured the dependence of the strength of Raman activity of polycrystalline m-WO3 on spot size at constant laser power density. These data are compared to surface area scaling measurements obtained using scanning tunneling microscopy. We argue that the spatial distribution of scattering centers is the complement of the spatial distribution of crystallographic shear (CS) structures on or near the oxide surface. Our results are consistent with there being an essentially uniform spatial distribution of scattering sites which implies the spatial distribution of defect sites is also uniform. At the laser power density involved and at the defect densities studied, we found no evidence suggesting a large amount of cooperativity in the formation of CS structures. These results suggest a qualitative description of the structure of common oxide surfaces in agreement with a basic assumption of the JMAK theory of first order phase transformations.
Thick Films of Pb(Mg,Nb)TiO by Aerosol Combustion
Authors: Greenwald A. C. , Kussmaul A. , Morse T. F. , Wei C. H.
Published: April 2011

Thick films of solid solutions of lead-magnesium-niobium-oxide (PMN) and lead-titanate (PTO) were deposited by aerosol combustion. Films consisted of submicron ceramic particles synthesized by combustion of a metalorganic solution in a methane-oxygen flame. The particulate material was deposited on heated substrates (200°C) and subsequently sintered at elevated temperatures. Results varied with starting chemistry and sintering conditions. As-deposited materials were mixed perovskite-pyrochlore phase. Sintering at low temperatures produced pure perovskite material that was not completely dense. Sintering at high temperatures produced dense ceramics of pyrochlore material. This technique requires further optimization for direct deposition of continuous films, but is immediately suitable for producing fine powders for tape casting of capacitors, etc.
Catalytic Properties of Fullerene Materials
Authors: Malhotra R. , Hirschon A. S. , McMillen D. F. , Bell W. L.
Published: April 2011

Fullerenes were found to catalyze coupling and transalkylation reactions of mesitylene, engage in transfer hydrogenations with dihydroaromatics, and cleave strong bonds such as those in diarylmethanes. In all of these reactions, fullerenes show a marked ability to accept and to transfer hydrogen atoms. The key structural feature that endows fullerenes with many of its characteristics is the presence of a pentagon surrounded by hexagons. We suspected that fullerene soot, unlike graphitic carbon, contained pentagons in a hexagonal lattice, and that these sites imparted the soot with the desired chemical attributes of strong electrophilic nature and an ability to stabilize radicals. In subsequent studies, we have shown fullerene soot to be very effective in catalyzing various H-transfer reactions, including the conversion of methane into higher hydrocarbons. When compared with other carbons, such as activated carbons and acetylene black, the fullerene soot is much more reactive for oligomerization and hydrodealkylation of alkylbenzenes. Because this activity remains, even in chemically extracted and partially oxidized soot, the observed catalysis is not a result of residual soluble fullerenes.
Esr of Purified Carbon Nanotubes Produced Under Different Helium Pressures
Authors: Wong S. P. , Zhang Haiyan , Ke Ning , Peng Shaoqi
Published: April 2011

Carbon nanotubes were prepared by the dc arc-discharge method under a controlled helium pressure ranging from 10 to 80 kPa and subsequently purified by oxidation in air. The purified carbon nanotubes were observed by transmission electron microscopy. The room temperature electron spin resonance (ESR) spectra of the purified nanotubes were measured. The variations in the ESR line shape, g-value, linewidth and relative spin density of the purified nanotubes on helium pressure were studied and discussed.
Dense Oxide Membranes for Oxygen Separation and Methane Conversion
Authors: Jacobson A. J. , Kim S. , Medina A. , Yang Y. L. , Abeles B.
Published: April 2011

Methane conversion to synthesis gas in membrane reactors that use dense mixed electronic-ionic conducting membranes for oxygen separation has received much recent attention. The oxygen flux achievable in these reactors depends on a combination of the bulk diffusion rate for oxygen transport and the surface reaction rate for oxygen activation and either recombination or reaction with methane. Here we compare recent oxygen permeation data for tubular membranes of La0.5Sr0.5Fe0.8Ga0.2O3-δ with our previous results for SrCO0.8Fe0.2O3-δ, SrFeCO0.5O3.25-δ. The pressure dependence of the oxygen permeation flux has been measured at different temperatures and used to determine the relative importance of bulk and surface kinetics for these oxides.
Comparison of Nanocrystalline and Polycrystalline Oxide Supports for Catalytic Oxidation of Methane
Authors: Hahn Horst H. , Hesemann Heiko , Epling William S. , Hoflund Gar B.
Published: April 2011

Nanocrystalline and polycrystalline ZrO2, CeO2 and Mn3O4 without and with 5 wt% Pd have been tested for methane oxidation. The nanocrystalline catalysts perform better than the polycrystalline catalysts on a weight basis. Nanocrystalline (n)-CeO2 performs much better than n-ZrO2, and both perform much better than polycrystalline (P)-CeO2 and P-ZrO2. 5 wt% Pd/n-ZrO2 is the best catalyst tested, but 5 wt% Pd/n-CeO2 performs nearly as well. A 20 wt% Ag/p-ZrO2 and a 20 wt% Ag/n-ZrO2 catalyst were also tested. The Ag yields a significant improvement over the bare supports, but not as much so as Pd.
Cathodic Arc Deposition of Tetrahedral Amorphous Carbon: Influence of Process Parameters on Microstructure and Hardness
Authors: Camphausen S. M. , Myers A. F. , Bozeman S. P. , Baldwin D. A. , Cuomo J. J.
Published: April 2011

The cathodic arc provides a method for depositing extremely hard thin carbon films. These films are potentially useful in a variety of tribological applications including protection of magnetic media and recording heads. Effective application of this technology requires an improved understanding of the influence of process parameters on the microstructure and hardness of the deposited films. In this work, we use a commercially available filtered cathodic arc to deposit tetrahedral amorphous carbon at several deposition angles.
Deposition of Diamondlike Carbon Films and Structural, Optical, and Electron Emission Characteristics
Authors: Choi S. W. , Paek M. C. , Lee J. H. , Hong S. U. , Nam K. S.
Published: April 2011

We have deposited thin films of diamond-like-carbon by plasma enhanced chemical vapor deposition, and examined the electron emission characteristics of the optimized DLC-coated field emitters. The bonding spectra and microstractures are controlled by energetic ions depending on deposition parameters which affect the structural, optical, and electrical characteristics. Raman spectra and IR analysis identify that as-deposited DLC contains mixtures of sp2- and sp3-bonding with a wide range of hydrogen, but annealing causes its conversion to graphite structure due to a depletion of hydrogen. From the measurement of field emission characteristics, turn-on gate voltage is lowered to 50 V and anode current is increased for DLC-coated Si field emitter tip arrays.
Supercritical Fluid Phase Separations Induced by Chemical Reactions
Authors: Ree Francis H. , Viecelli James A.
Published: April 2011

Statistical mechanical studies predict that a chemically reactive system containing species composed of C, H, N, O atoms can exhibit a phase separation into a N2-rich and a N2-poor phase. The present work is concerned with the effect of the fluid phase separation upon addition of F atoms to the system. Our study shows that F atoms mainly appear as a constituent of HF in a N2-poor fluid phase up to a certain pressure beyond which they occur as CF4 in a N2-rich phase and that the phase separation may be abrupt in a thermodynamic sense. The pressure at the phase boundary can occur at about 30 GPa at 3000 K and about 10 GPa to 20 GPa at 1000 K. Some of these ranges may be accessible by present-day experimental high-pressure techniques. We discuss implications of this study to detonation physics.