bluuebunny/crossref_metadata_2025 huggingface dataset:
Scanning Auger Microscopy and X Ray Photoemission Spectroscopy Studies of Metallic Archaeomaterials
Authors: Paparazzo E. , Moretto L.
Published: April 2011

We report on the surface microchemistry of a Roman iron object and of a Roman lead pipe ‘fistula’. The original patina of the iron sample consists mainly of oxidic phases whose lateral distribution is imaged with a submicron spatial resolution. Metallic iron in the bare surface is covered with a Fe(lll)-Fe(ll) oxidic layer which is several times thicker than in a modern ferritic steel. We find that the presence of a flux minimizes lead oxidation in the joint of the fistula as well as in comparison, ‘modern’ lead soldered samples. In one of these comparison samples the lateral distribution of the chemical species present is imaged with a spatial resolution of about 1000 Å.
Provenance Determination from ICP-MS Elemental and Isotopic Compositions of El Paso Area Ceramics
Authors: Pingitore Nicholas E. , Leach Jeff D. , Villalobos Joshua , Peterson John A. , Hill David
Published: April 2011

To evaluate the performance of inductively coupled plasma mass spectrometry (ICP-MS) in determining ceramic provenance, we analyzed 60 elements in 30 ceramic artifacts from six a priori groups from west Texas-southwestern New Mexico. Discriminant function analysis of the ICP-MS elemental data classified all members of the six a priori groups without error. In repeated analyses using 80% of the data as a training set, overall 75% of the withheld specimens were properly classified. Lead isotope ratios, also measured on the ICP-MS, provided an independent partial discrimination between the groups. The results of this study demonstrate that ICP-MS provides multi-element and lead isotopie characterization of archaeological ceramics suitable for provenance determination. ICP-MS is a rapid, in-house, and relatively inexpensive technology and thus is a reasonable alternative to neutron activation analysis (NAA) for compositional studies of archaeological ceramics.
The Archaeometallurgical Implications of New Findings of Traditional Crafts of Making High Tin ‘Delta’ Bronze Mirrors and ‘Beta’ Bronze Vessels in Kerala State of South India
Authors: Srinivasan Sharada
Published: April 2011

New metallurgical and ethnographic observations of the traditional manufacture of specular high-tin bronze mirrors in Kerala state of southern India are discussed, which is an exceptional example of a surviving craft practice of metal mirror-making in the world. The manufacturing process has been reconstructed from analytical investigations made by Srinivasan following a visit late in 1991 to a mirror making workshop and from her technical studies of equipment acquired by Glover in March 1992 from another group of mirror makers from Pathanamthita at an exhibition held at Crafts Museum, Delhi. Finished and unfinished mirror from two workshops were of a binary, copper-tin alloy of 33% tin which is close to the composition of pure delta phase, so that these mirrors are referred to here as ‘delta’ bronzes. For the first time, metallurgical and field observations were made by Srinivasan in 1991 of the manufacture of high-tin ‘beta’ bonze vessels from Palghat district, Kerala, i‥e of wrought and quenched 23% tin bronze. This has provided the first metallurgical record for a surviving craft of high-tin bronze bowl making which can be directly related to archaeological finds of high-tin bronze vessels from the Indian subcontinent and Southeast Asia. New analytical investigations are presented of high-tin beta bronzes from the Indian subcontinent which are some of the earliest reported worldwide. These coupled with the archaeometallurgical evidence suggests that these high-tin bronze techniques are part of a long, continuing, and probably indigenous tradition of the use of high-tin bronzes in the Indian subcontinent with finds reported even from Indus Valley sites. While the source of tin has been problematic, new evidence on bronze smelting slags and literary evidence suggests there may have been some sources of tin in South India.
Quantitative High Resolution Transmission Electron Microscopy - The Role of Space Charge in Blurring Images
Authors: Schwartz A. M. , Gibson J. M. , Zheng T.
Published: April 2011

We investigate space-charge by analytic methods and Monte Carlo simulations as a possible source of blur in high-resolution TEM images. In doing so we believe to have identified a novel type of space charge effect, namely quantum space charge(QSC) effect. We predict the blur for typical HRTEM images and for electron holograms. Inclusion of this hitherto unrecognized effect in image simulations (and experimental design for HRTEM and related techniques, such as holography) should permit further progress in the critical field of quantitative HRTEM image matching as a means for atomic structure determination.
Quantitative High Resolution Electron Microscopy of Grain Boundaries
Authors: Campbell Geoffrey H. , King Wayne E. , Cohen Dov , Carter Barry
Published: April 2011

The Σ11 (113)/[110] symmetric tilt grain boundary has been characterized by high resolution transmission electron microscopy. The method by which the images are prepared for analysis is described. The statistics of the image data have been found to follow a normal distribution. The electron-optical imaging parameters used to acquire the image have been determined by non-linear least-square image simulation optimization within the perfect crystal region of the micrograph. A similar image simulation optimization procedure is used to determine the atom positions which provide the best match between the experimental image and the image simulation.
Evolution of Morphology During Etching of Si
Authors: Williams Ellen D. , Fu Elain S. , Li Bin
Published: April 2011

The step morphology of clean Si surfaces has been studied under conditions of thermal etching in the temperature range 950 – 1250°C. Kinetic-bunching of steps is caused by direct current in the step-down direction around 950°C. By comparing the rate of thermal decay of these structures with and without direct current, the electromigration force causing this step bunching is estimated to be due to an effective charge of less than or approximately 0.01 electron units. Around 1150°C, step-bunching is caused by direct current in the step-up direction. By analysis of the patterns of step structure, the effective charge of the driving force is found to be approximately -0.1 electron units. Oxygen-induced etching of Si(001) and Si(111) has been studied in the temperature range of 700 – 900 °C, and at a pressure of 5 × 10−7 torr, conditions under which the surface is etched by the desorption of SiO. On Si(001), the original narrow distribution of double-layer height steps is preserved during the oxygen-etching process. On Si(111), the original narrow distribution of mixed single- and triple-layer height steps changes dramatically during oxygen-etching, leaving wide terraces of flat (111) surface separated by regions of high step density. At low etching temperatures (700°C), the steps remain straight within the step bunches and retain their distinct character as single- and triple-height steps. However, following higher temperature etching, the steps begin to merge into facets in the vicinity of defect structures. Following etching at the highest temperatures studied (815 and 830°C), the pinning action of the defect structures becomes apparent, and the pinned step-bunches become identifiable as (113) facets.
STM Study of Reconstruction on Si(III)
Authors: Umekawa M. , Ohara S. , Tatsukawa S. , Kuriyama H. , Matsumoto S.
Published: April 2011

The formation of the boron-induced reconstruction on Si(111) 7×7 surface has been studied with scanning tunneling microscope. By evaporating elemental B on Si elevated at high temperatures, reconstructed structures develop from the step edge to the adjacent lower terrace. They emerge at temperatures between 800°C and 900°C. It indicates that phase transition from 7×7 to 1×1 surface structure is necessary for forming the √3-B reconstructed structures. The phase boundary between 7×7 and regions is a straight line with termination of the faulted halves of 7×7 unit cell. It is also found that strip or triangle regions are formed, depending on the direction of the step propagation.
Ferroelectric Domain Boundaries Induced by Interface Mismatch Dislocations in BaTiO3/LaAlO3
Authors: Wang Z. L. , Dai Z. R.
Published: April 2011

Interface microstractures of BaTiO3/LaAlO3 grown by metal-organic chemical vapor deposition (MOCVD) are studied using high-resolution transmission electron microscopy (HRTEM). Interface dislocations in BaTiO3/LaAlO3 have been shown to be directly linked with the 90° domain boundaries in BaTiO3. This association is a result of strain relief due to a phase transformation on cooling from the growth temperature. The {100} surfaces of BaTiO3 are terminated with the Ba-O layer.
Characterization of Heterointerfaces in Thin-Film Transistors by Cross-Sectional Transmission Electron Microscopy
Authors: Kuroda K. , Tsuji S. , Hayashi Y. , Saka H.
Published: April 2011

Hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) are now widely used as elements for active matrix liquid crystal displays. The nanometer-scale multilayered structure of a-Si:H TFTs has been characterized by cross-sectional transmission electron microscopy (TEM). The discrete layer construction of a faulty TFTs and the generation of defects during manufacturing processes have been investigated. A combination of focused ion beam (FIB) etching and cross-sectional TEM leads to a successful failure analysis. A contamination layer with a thickness of 10–30 nm and microvoids inside multilayers are identified in faulty TFTs. An a-Si layer on silicon nitride (SiNx) is crystallized during TEM observation. Electron energy loss spectroscopy analysis indicates that the diffusion of nitrogen into a-Si layer causes the crystallization.
Analysis of Interface Structures by Quantitative High-Resolution Transmission Electron Microscopy
Authors: Kienzle O. , Exner M. , Ernst F.
Published: April 2011

Quantitative evaluation rather than visual inspection of HRTEM images provides objective, reproducible, and very accurate information on the atomistic structure of internal interfaces. This paper explains the method we have developed to analyze the structure of grain boundaries. To demonstrate the power of our approach we present an analysis of the Σ3 (111) grain boundary in SrTiO3. We have determined the coordinates of the atom columns at this interface with a precision of 0.015 nm. Thus, our experimental results provide a sensitive test for physical theories and model structures obtained by computer simulation. First results of computer modeling are presented in this paper. The calculated structure of minimum energy has the same characteristic features as the structure determined by experiment.
Hydrogen Molecule in Silicon Crystal
Authors: Nakamura K. G. , Ishioka K. , Kitajima M. , Murakami K.
Published: April 2011

Ab initio Hartree-Fock calculations have been performed on a hydrogen molecule in silicon crystal using a cluster model of Si10H16. The hydrogen molecule is stable at a tetrahedral site of silicon. A calculated vibrational frequency of the hydrogen molecule is in reasonable agreement with the experimentally determined frequency of H2 in the silicon crystal.
Boron Gettering by Fluorine in Ion Implanted Silicon
Authors: Krasnobaev L.Ya. , Cuomo J. J. , Vyletalina O. I.
Published: April 2011

Si was implanted with fluorine and boron ions. Boron gettering by fluorine was studied. By varying the implantation energy of F+ ions, three types of samples were made in which Rp(F)Rp(B). There are three special regions in which the redistribution of Boron atoms during annealing differ. The first one is the near surface region in which the Boron concentration exceeds the value of Boron solid solubility at the annealing temperature. In this region, B atoms are intensively redistributed and have two peaks of concentration. The positions of these peaks coincide with the position of the peaks on the fluorine concentration profile. In the second specific region, the boron concentration is less than the value of solid solubility in Si and higher than the value of the intrinsic carrier concentration in Si at the annealing temperature. In this region, the B concentration was identical in all samples, and it exponentially decreased to the value of 5×108 cm−3. The slope of the boron concentration in the third region dictates the depth of p-n junction. A possible mechanism of boron gettering by fluorine is discussed.
Interstitial Silicon Sink Efficiency of Dislocations Studied by Gold Diffusion in FZ and Cz Samples
Authors: Mariani G. , Pichaud B. , Yakimov E.
Published: April 2011

The substitutional gold concentration introduced by a diffusion step between 850 and 1000°C was measured by Deep Level Transient Spectroscopy (DLTS) both in FZ and Cz silicon containing different dislocation densities introduced by cantilever bending. The comparison, in the same sample, of dislocated and undislocated regions allows first the self interstitial (Sii) effective diffusivity and then the efficiency of dislocations as sinks for self-interstitials γto be measured. In FZ silicon, γ is quite independent of temperature whereas in Cz Si a remarkable temperature dependence was observed, with an effective activation energy of leV, which can be attributed to the release of dislocations by a thermally stimulated climbing mechanism from obstacles (oxygen segregation or precipitation). Increasing the gold diffusion annealing times for a given temperature (850°C) underlines once more the role of the oxygen precipitation in the samples.
Statistical Analysis of Boundaries in NiO Films Grown on Ni Single Crystals
Authors: Zhilyaev A. P. , Li Hualong , Czerwinski F. , Szpunar J.A.
Published: April 2011

An attempt was made to apply the statistical analysis of NiO grain boundaries to explain the dependence of NiO growth kinetics on the crystallographic orientation of Ni substrate. Study was conducted for two crystals faces of Ni, (100) and (111), which exhibits a difference in oxidation rate constants at 1073 K, over one order of magnitude. The orientation distribution functions (ODF), calculated from X-ray measurements for NiO grown on both Ni faces, were analyzed numerically to assess the grain boundary character. The grain boundary misorientation distribution (GBMD) and grain boundary character distribution (GBCD), used to describe oxide structure, were derived using three different assumptions regarding the spatial correlation in orientation of neighbouring grains. Grain boundary network was created to analyze the high temperature diffusion properties through the oxide using diffusion constants available in the literature under assumption of various contribution of bulk and grain boundary diffusion paths to overall transport of ionic species. The growth parameters obtained were finally verified by comparison with experimentally measured oxidation kinetics.
High Resolution X-Ray Reciprocal Space Mapping of Wavy Layers
Authors: Kidd P. , Fewster P. F.
Published: April 2011

We apply the technique of High Resolution X-ray Reciprocal Space Mapping (HRRSM) to the study of wavy layers in InGaAs multilayer thin films on InP substrates. By accurately measuring the positions of the layer Bragg peaks in reciprocal space we obtain measurements of the compositions and residual coherency strains in the layers. We discuss the contributions to the diffuse scatter around the Bragg peaks from factors such as lattice tilts and interface roughness. By modelling the shapes of the diffraction profiles we obtain measurements of mosaic block size both perpendicular and parallel to the multilayer/substrate interface. We conclude that the wavy interface morphology arises predominantly from layer thickness variations rather than lattice tilts.
Orientation Characteristics with Process Parameters of PLZT(X/70/100) Thin Films Prepared by RF-Magnetron Sputtering
Authors: Kang S.K. , Park M.S. , Kim D.B. , No K.S. , Cho S.H.
Published: April 2011

PLZT(X/70/100) thin films on MgO(100), Pt/Ti/MgO(100), and Pt/Ti/Si(100) have been prepared by RF-magnetron sputtering process from sintered target with compositions of PLZT(X/70/100), where X=5, 10, and 15, respectively. The effects of substrate temperature, substrate and gas pressure on deposited thin films were studied. Crystalline and surface characterization was analyzed using XRD, SEM, AES, and AFM. X-ray rocking curves were measured to examine the film orientation. It was observed that the gas pressure was the dominant influence on having (001) preferred orientation. As a result, the degree of c-axis orientation increased as gas pressure decreased.
Low-Temperature (450 °C) Poly-Si Thin Film Deposition on SiO2 and Glass using a Microcrystalline-Si Seed Layer
Authors: Wolfe D. M. , Wang F. , Lucovsky G.
Published: April 2011

A low-temperature (450 °C), remote plasma-assisted CVD process for deposition of poly-Si thin films on SiO2 and Corning 7059 glass in which interface formation is separated from bulk film growth has been developed. This approach is based on first depositing an ultra-thin (<100 Å) microcrystalline-Si seed layer onto the oxide in order to provide nucleation sites at which low-temperature poly-Si film growth can be initiated. Conditions for poly-Si film deposition were optimized by using a low-temperature, remote plasma process that had previously yielded epitaxial growth of Si thin films on crystalline Si substrates. Microstructural characterization was performed on poly-Si films grown with different seed layer thicknesses, and additionally with exposure of this seed layer to a predeposition hydrogen plasma treatment. Results demonstrated that the seed layer thickness and surface morphology played a significant role in promoting crystallinity in the poly-Si overlayer. For example using deposition conditions that yielded epitaxial film growth on Si substrates, films deposited on un-seeded oxide substrates were amorphous, whereas those deposited using a seed layer were polycrystalline. This indicated that interfacial nucleation was the rate limiting step in promoting the low-temperature deposition of poly-Si thin films.
A Low Temperature Polycrystalline Si TFT Technology for Large area AMLCD Drivers
Authors: Saraswat Krishna C. , Subramanian V. , Jurichich S.
Published: April 2011

In this paper we describe a low thermal budget technology to fabricate high performance CMOS thin-film transistors (TFTs) in polycrystalline silicon and silicon/germanium on low cost glass substrates, for active-matrix liquid crystal display (AMLCD) applications. Based on modeling of delay times of the scan and data lines driven by n-channel TFTs we show that for AMLCDs with integrated drive circuits, mobility in excess of 40 cm2/V. sec will be required. Through proper optimization of amorphous film deposition, crystallization (nucleation and grain growth), fabrication process parameters and device structure we have obtained mobility in excess of 50 cm2/V. sec in Si TFTs, using conventional manufacturing technology compatible with glass substrates. Economic modeling suggests that low-temperature poly-TFT LCDs with integrated drivers will have a competitive manufacturing cost to LCDs of an equivalent size and resolution with α-Si pixel TFTs and single crystal drivers.
Planarization of Gratings using Magnetorheological Finishing
Authors: Yang Fuqian , Golini D. , Raguin D. H. , Jacobs S. D.
Published: April 2011

Surface planarization of BK7 glass gratings with periods of 130, 30, 16, 8 and 5 gm was performed with the magnetorheological finishing (MRF) process at the Center for Optics Manufacturing (COM). Approximately 0.5 μm of material was removed in the experiments. Grating height decreased as a function of grating period, going from ∼0.44 μm to ∼0.044 μm for a 130 μm period, and ∼0.44 μm to ∼30 Å for grating periods of 30, 16, 8 and 5 gm. The microroughness on ridges and in valleys of the grating structures also decreased with material removal from ∼100 Å to ∼10 Å for gratings with 30 and 16 μm periods.
Low pH Chemical Etch Route for Smooth H-Terminated Si(100) And
Study Of Subsequent Chemical Stability
Authors: Hinds B. J. , Aspnes D. E. , Lucovsky G.
Published: April 2011

To form atomically flat H-passivated Si(100) surfaces, wet chemical etching
of sacrificial SiO2 layer has been examined. Roughness and
chemical overlayer thickness, as monitored by ellipsometry shows a minima at
an optimal solution of 1:0.5:30 HF(49wt\%):H2SO4
(98wt\%):H2O. A mechanistic study offers no evidence for a
chemical smoothing from preferential non-Si(100) facet etching. Silicon
planarization can be induced by rapid thermal annealing RTA of chemical
oxides. The H-terminated Si(100) surfaces are found to be moderately
reactive to ambient conditions as monitored by in-situ ellipsometry and
Auger analysis. Atomic force microscopy (AFM) measurements show Si(100)
surfaces to have a rms ∼1.0Å and Rmax values of 1.6–0.9Å. With
measured roughness incorporate into ellipsometric model, a 5Å native oxide
overlayer is rapidly incorporated into the Si(100) surface.
Lifetime Characterization of Poly-Silicon Back Sealed Wafers
with Bi-Surface Photoconductivity Decay Method
Authors: Ogita Y. , Uematsu Y. , Daio H.
Published: April 2011

Bi-surface photoconductivity decay (BSPCD) method has been useful to obtain
the true bulk lifetime and surface recombination velocities in silicon
wafers with variously finished surfaces. Thermally oxidized n-type CZ
silicon wafers with and without a poly-Si back seal (PBS) were characterized
with the BSPCD method using 500 MHz-UHF wave reflection. It has been found
that the surface recombination velocity of the PBS surface is, 4027 cm/s
while that of the no-PBS surface is 16 cm/s, for example. The very fast
surface recombination velocity is attributed to the poly-Si / Si interface
character. Moreover, the bulk lifetime calculated in the PBS wafer is much
higher than that in the no-PBS one, which reveals the PBS gettering
performance for the thermal oxidation induced contamination.
Growth Chemistry of Ultrathin Silicon Nitride and Oxynitride
Passivation Layers on Si(100)
Authors: Kamath A. , Kim B. Y. , Blass P. M. , Sun Y. M. , White J. M. , Kwong D. L.
Published: April 2011

We have studied the thermal growth chemistry and bonding structure of three
promising ultrathin (5–20Å), nitrogen rich passivation layers on Si(100),
namely-Si3N4, NO/Si(100) grown oxynitride and NO
annealed SiO2. These films are intended to serve as substrates
with excellent diffusion barrier/interface properties during deposition of
high- K dielectrics such as Ta2O5, with
tSiO2 equivalent <30Å for ULSI applications. In this paper
we show that it is possible to form films with a tailored composition and
nitrogen profile using techniques that can easily be integrated with
existing silicon processing technology. Alternating growth and surface
analysis by X-Ray Photoelectron Spectroscopy (XPS) is used to non
destructively characterize the growth.
Effect of Cl in Gate Oxidation
Authors: Mertens P. W. , McGeary M. J. , Schaekers M. , Sprey H. , Vermeire B. , Depas M. , Meuris M. , Heyns M. M.
Published: April 2011

The present study reviews the use of Cl in gate oxidation furnaces for growth of high quality gate oxides with a thickness in the range of 2 to 15 1nm. The following, commercially available, “state of the art” Cl-precursors have been tested: 1,1,1- trichloroethane (TCA),trans-1,2-dichloroethylene (DCE) and oxalyl chloride (OC). Different parameters were evaluated including: metal removal efficiency, poly-silicon haze, Fe bulk incorporation, carrier lifetime and Cl-incorporation in the oxide. Cl2was identified as the active component in Cl-oxidation. As a consequence, OC was identified as being the most efficient Cl-source. In particular, OC is the most suited Cl-source for applications requiring reduced oxygen concentration, such as the manufacturing of ultra thin gate oxides.
Thermoelectric Properties of N-Type Bi2(Tel−xSex)3 Fabricated by Mechanical Alloying and Hot Pressing
Authors: Kim Hee-Jeong , Choi Jae-Shik , Oh Tae-Sung , Hyun Dow-Bin
Published: April 2011

Thermoelectric properties of polycrystalline Bi2(Te1−xSex)3 (0.05 ≤ x ≤ 0.25), fabricated by mechanical alloying and hot pressing, have been investigated. Formation of n-type Bi2(Te0.9 Se0.1)3 alloy powders was completed by mechanical alloying for 3 hours at ball-to-material ratio of 5: 1, and processing time for Bi2(Te1−xSex)3 formation increased with Bi2Se3 content x. Figure-of-merit of Bi2(Te0.9Se0.1) was markedly increased by hot pressing at temperatures above 450°C, and maximum value of 1.9 × 10−3/K was obtained by hot pressing at 550°C. With addition of 0.015 wt% Bi as acceptor dopant, figure-of-merit of Bi2 (Te0.9Se0.1)3, hot pressed at 550°C, could be improved to 2.1 × 10−3/K. When Bi2(Te1−xSex)3 was hot pressed at 550°C, figure-of-merit increased from 1.14 × 103/K to 1.92 × 10−3/K with increasing Bi2Se3 content x from 0.05 to 0.15, and then decreased to 1.30 × 103/K for x = 0.25 composition.
Filled Skutterudite Antimonides: Validation of the Electron-Crystal Phonon-Glass Approach to New Thermoelectric Materials
Authors: Mandrus D. , Sales B. C. , Keppens V. , Chakoumakos B. C. , Dai P. , Boatner L. A. , Williams R. K. , Thompson J. R. , Darling T. W. , Migliori A. , Maple M. B. , Gajewski D. A. , Freeman E. J.
Published: April 2011

After a brief review of the transport and thermoelectric properties of filled skutterudite antimonides, we present resonant ultrasound, specific heat, and inelastic neutron scattering results that establish the existence of two low-energy vibrational modes in the filled skutterudite LaFe3CoSb12. It is likely that at least one of these modes represents the localized, incoherent vibrations of the La ion in an oversized atomic “cage.” These results support the usefulness of weakly bound, “rattling” ions for the improvement of thermoelectric performance.
Properties Of Cosb3 Films Grown by Pulsed Laser Deposition
Authors: Christen Hans-Martin , Mandrus David G. , Norton David P. , Boatner Lynn A. , Sales Brian C.
Published: April 2011

Polycrystalline CoSb3 films were grown on a variety of electrically insulating substrates by pulsed laser ablation from a stoichiometric hot-pressed target. These films are fully crystallized in the skutterudite structure, and the grains exhibit a strongly preferred alignment of the cubic [310]-axis perpendicular to the substrate surface. The film quality is studied for different single-crystal substrates and as a function of growth temperature and background gas.

Hall measurements show that the films are p-type semiconducting with a room-temperature carrier density of 3×1020 holes/cm3. The Hall mobility is found to be 50 to 60 cm2 /Vs, which is high for such a heavily-doped material. The Seebeck coefficient and the resistivity are measured as a function of temperature and are compared to bulk measurements.
Influence of Structural Defects and Zinc Composition Variation on the Device Response of Cd1−xZnxTe Radiation Detectors
Authors: Yoon H. , Scyoc J. M. Van , Gilbert T. S. , Goorsky M. S. , Brunett B. A. , Lundt J. C. , Hermon H. , Schieber M. , James R. B.
Published: April 2011

Zinc composition variation and gross structural defects including grain and tilt boundaries, twins, and mechanical cracks in high pressure Bridgman Cd1−xZnxTe are characterized and correlated to various detector-related responses. Triple axis x-ray diffraction, double crystal x-ray topography, infrared microscopy, and etch pit density measurements are used to reveal and quantify the spatial distribution and the nature of the structural defects. Mechanical cracks in the material are found to act as conductive “shorting paths”, indicated by excessive leakage currents and reduced charge (electron) collection measured along these cracks. Reduced charge collection is also obtained across grain boundaries and in regions with poor crystallinity, indicating that they serve as carrier recombination sites. Finally, the effects of the zinc composition variation on the measured leakage current and the amount of electrons collected are found to be masked by gross structural defects. These characterization techniques provide a wealth of information which can be used not only to study the relationship between the structural and device properties of CdZnTe but also to screen production material for subsequent device fabrication.
Performance of P-I-N CdZnTe Radiation Detectors and Their Unique Advantages
Authors: Sudharsanan R. , Stenstrom C. C. , Bennett P. , Vakerlis G. D.
Published: April 2011

We present the performance characteristics of CdZnTe radiation detectors with a new P-I-N design and their unique advantages over metal-semiconductor-metal (M-S-M) devices. In M-S-M CdZnTe detectors the bulk resistivity of the substrate largely determines the leakage current. High leakage current is a dominant noise factor for CdZnTe detector arrays, coplanar detectors, and detectors used for low X-ray energy applications. P-I-N devices provide low leakage currents. Early CdZnTe detectors exhibited polarization, were limited to small detection volumes, and some required high deposition temperatures. We have developed a new heterojunction design which can be deposited at low temperatures so that even high-pressure Bridgman CdZnTe can be used. Using the P-I-N design, CdZnTe detectors with high detection volumes (>200 mm3) were fabricated and exhibited low leakage current, good energy resolution, and no polarization. These detectors have significant advantages over M-S-M detectors in three specific areas. First, X-ray fluorescence studies require detectors with low leakage currents to provide less spectral broadening due to electronic noise. Second, less expensive vertical Bridgman CdZnTe material can be used for imaging applications since it normally possesses too low of a bulk resistivity to be useful as a M-S-M detector. Third, leakage currents across the anode grid in large volume coplanar detectors can be significantly reduced.
X-ray Characterization of PbTe/SnTe Superlattices
Authors: Ferreira S. O. , Abramof E. , Rappl P. H. O. , Ueta A. Y. , Closs H. , Boschetti C. , Motisuke P. , Bandeira I. N.
Published: April 2011

PbTe/SnTe superlattices have been proposed many years ago for use as base material for infrared detectors. However, many difficulties have prevented its use, mainly the ones related to obtaining low concentration SnTe. Recently we have shown that SnTe layers with relatively low hole concentration can be grown by molecular beam epitaxy at low temperature using stoichiometric charges. In this work we investigate the structural properties of PbTe/SnTe superlattices grown by molecular beam epitaxy on (111) BaF2 substrates. Sample characterization has been done by high resolution x-ray diffraction. Information on strain was obtained from reciprocal space maps of asymmetric Bragg reflections and used as input parameters for dynamical simulation of the diffraction spectra.
Bridgman Growth and Characterization of Bulk Single Crystals of Ga1−xInxSb for Thermophotovoltaic Applications
Authors: Boyer J. R. , Haines W. T.
Published: April 2011

Thermophotovoltaic generation of electricity is attracting renewed attention due to recent advances in low bandgap (0.5–0.7 eV) III-V semiconductors. The use of mixed pseudo-binary compounds allows for the tailoring of the lattice parameter and the bandgap of the material. Conventional deposition techniques (i.e., epitaxy) for producing such ternary or quaternary materials are typically slow and expensive. Production of bulk single crystals of ternary materials, for example Gal-xlnxSb, is expected to dramatically reduce such material costs. Bulk single crystals of Ga1−xInxSb have been prepared using a Bridgman technique in a two-zone furnace. These crystals are 19 mm in diameter by approximately 50 mm long and were produced using seeds of the same diameter. The effects of growth rate and starting materials on the composition and quality of these crystals will be discussed and compared with other attempts to produce single crystals of this material.
Thermal Interdiffusion in InGaAs/GaAs Strained Multiple Quantum Well Infrared Photodetector
Authors: Lee Alex S. W. , Li E. Herbert , Karunasiri Gamani
Published: April 2011

RTA at 850 °C for 5 and 10 s is carried out to study the effect of interdiffusion on the optical and electrical properties of strained InGaAs/GaAs quantum well infrared photodetector. Photoluminescence measurement at 4.5 K shows that no strain relaxation or misfit dislocation formation occurs throughout the annealing process. Absorption and responsivity peak wavelengths are red shifted continuously without appreciable degradation in absorption strength. The normal incident absorption, which is believed to be the result of band-mixing effects induced by the coupling between the conduction and valence and is usually forbidden in conventional polarization selection rule, is preserved after interdiffusion. Responsivity spectra of both 0° and 90° polarization are of compatible amplitude and the shape of the annealed spectra becomes narrower. Dark current of the annealed devices is not very sensitive to temperature variation and is found to be an order of magnitude larger than the as-grown one at 77K.
Phase-matched 2nd harmonic generation in asymmetric doublequantum wells
Authors: Vodopyanov K. L. , Phillips C. C. , Vurgaftman I. , Meyer J. R.
Published: April 2011

Phase-matched SHG, resonantly enhanced near λ=8.6μm, with ∼1% efficiency and up to 30 W peak power has been observed in asymmetric double multi-quantum well structures. Waveguide-mode and 45° wedge multi-bounce geometries were used.
Growth of NLO Chalcopyrite Materials by Omvpe
Authors: Timmons M. L. , Bachmann K. J.
Published: April 2011

This paper describes the application of organometallic vapor phase epitaxy to the growth of II-1V-V2 chalcopyrite materials that have high figures of merit for nonlinear optical (NLO) applications. ZnGeAs2, although not a particularly interesting NLO material, is used as a model for the growth of ZnGeP2, which is. Both compounds, as well as others, have been successfully grown by vapor phase on III-V substrates that provide a close lattice match. Doping studies using Group II and VI elements have been undertaken to control the p-type conductivity found in both compounds. Except for the possible case of indium, the results of these experiments are less than encouraging. Minority-carrier lifetimes of 150 ns have been measured in ZnGeAs2.

The results of this work are used to make projections about the growth of CdGeAs2. CdGeAs2 is promising for the next generation of NLO mid-infrared materials if an absorption band that occurs at about 5 μm can be reduced. The growth projections suggest that this compound will be difficult to grow epitaxially and has no III-V substrate that provides a close lattice match. Mixing CdGeAs2 with other II-IV-V2 materials may offer solutions to the substrate problem. The defect properties of CdGeAs2 have not, to our knowledge, been studied.
Refractive Index Measurements of Barium Titanate From .4 to 5.0 Microns and Implications for Periodically Poled Frequency Conversion Devices
Authors: Zelmon David E. , Small David L. , Schunemann Peter
Published: April 2011

Barium titanate has recently been suggested as a possible candidate for use in periodically poled optical frequency conversion devices. We report refractive index measurements which are critical to periodically poled device designers and present quasi phase matching loci which can be used to design an optical parametric oscillator in periodically poled barium titanate
Photoreflectance Study of MBE Grown Te-doped GaSb at the E0+Δ0 Transition
Authors: Iyer S. , Mulugeta S. , Li J. , Mangalam B. , Venkatraman S. , Bajaj K. K.
Published: April 2011

Photoreflectance (PR) measurements have been performed on MBE grown GaSb samples at the E0+Δ0 transition. The transition energy has been measured from 4 to 300 K in the 1.35 to 1.8 eV energy region. Transition energy of 1.614 eV and broadening of 53 meV have been obtained at 4 K from a representative Te-doped sample while no PR signals were obtained from undoped samples. The logarithmic dependence of the PR amplitude and invariance of the line shape on the modulating pump intensity, and absence of Franz-Keldysh oscillations are typical of the PR spectra in the low-field regime. Good fits were obtained using line shape analysis of the PR spectra and the temperature dependence of the transition energy and broadening have been determined.
Oxygen-Related Defects in In0.5(AlxGa1−x)0.5P Grown by MOVPE
Authors: Cederberg J. G. , Bieg B. , Huang J.-W. , Stockman S. A. , Peanasky M. J. , Kuech T. F.
Published: April 2011

Oxygen related defects in Al-containing semiconductors have been determined to degrade luminescence efficiency and reduce free carrier lifetime, affecting the performance of light emitting diodes and laser diodes. We have used the oxygen doping source, diethylaluminum ethoxide, (C2H5)2A1OC2H5, to intentionally incorporate oxygen-related defects during growth of In0.5(AlxGa1−x)0.5P by Metalorganic Vapor Phase Epitaxy (MOVPE). Our investigations have identified several defects which are ‘intrinsic’ or present in non-intentionally oxygen-doped n-type In0.5(AlxGa1−x)0.5P as well as those due to oxygen, which introduces defect states near the middle of the conduction band. Deep level transient spectroscopy and photoluminescence data obtained for these defects over a range of composition, are presented illustrating the trends in defect structure with alloy composition. The impact of oxygen contamination on the visible emission spectrum is presented and discussed in terms of the defect structure.
MID-IR Vertical Cavity Surface-Emitting Lasers
Authors: Vurgaftman I. , Bewley W. W. , Felix C. L. , Aifer E. H. , Meyer J. R. , Goldberg L. , Chow D. H. , Selvig E.
Published: April 2011

An optically pumped mid-infrared vertical-cavity surface-emitting laser based on an active region with a “W” configuration of type-II antimonide quantum wells is reported. The emission wavelength of 2.9 ym has a weak temperature variation (dλ/dT ≈ 0.07 – 0.09 nm/K), and the multimode linewidth is quite narrow (2.5–4 nm). Lasing is observed up to T = 280 K in pulsed mode and up to 160 K cw. Under cw excitation at T = 78 K, the threshold pump power is as low as 4 mW for a 6 am spot, and the differential power conversion efficiency is 4.5%.
Fano Factor Determination For CZT
Authors: Redus R. H. , Pantazis J. A. , Huber A. C. , Jordanov V. T. , Butler J. F. , Apotovsky B.
Published: April 2011

Continued improvements in the manufacturing of Cd1−xZnxTe (CZT) material have resulted in a practical thermoelectrically cooled X-ray and gamma-ray detector of very high energy resolution. A high resolution spectroscopy system was used to measure the Fano factor in CZT at temperatures down to -40°C. The best resolution of the 5.9 keV 55Fe peak was measured to be 188 eV FWHM, while the best resolution of the 59.5 keV 241Am peak was measured to be 482 eV FWHM. The minimum measured Fano factor was 0.082, with several measurements yielding a value of 0.089±0.005. With a resolution of 4.2 keV FWHM for the 662 keV peak of 137Cs, these detectors demonstrate excellent performance in detecting X-rays and gamma rays.
On the Active Volume of Cadmium Zinc Telluride Gamma-Ray Spectrometers
Authors: Lund J. C. , Brunett B. A. , Viles T. P. , Hilton N. R. , James R. B.
Published: April 2011

In this paper we develop quantitative models to predict the active volume of cadmium zinc telluride (CZT) detectors operated as gamma-ray pulse height spectrometers. Three cases are considered: a conventional planar detector, a unipolar device, and a detector in which electronic signal processing has been applied to correct for charge trapping effects. We find that existing detectors are very limited in their maximum attainable active volume, but unipolar devices with charge correction show promise for producing large active volume devices.
Study of The Homogeneity Of Cadmium Zinc Telluride Detectors
Authors: Hermon H. , Schieber M. , Yang N. , James R. B. , Kolesnikov N. N. P. , Ivanov Yu. N. , Komar V , Goorsky M. S. , Yoon H. , Toney J. , Schlesinger T. E.
Published: April 2011

Several analytical techniques have been used in the study of the homogeneity of Cadmium Zinc Telluride (CZT) single crystals grown by the vertical high pressure Bridgman (VHPB) method. The presence of black inclusions and tubular hollow pipes has been observed by a few methods, such as photoluminescence (PL), infrared (IR) transmission microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The crystals investigated were grown commercially in the USA, at the Institute of Single Crystals in Kharkov, Ukraine, and at the Institute of Solid State Physics, Moscow, Russia. We discuss the homogeneity of the various CZT crystals based on the results from these measurement techniques.
Modular 64×64 CdZnTe Arrays With Multiplexer Readout for High-Resolution Nuclear Medicine Imaging
Authors: Woolfenden J. M. , Barber H. B. , Barrett H. H. , Dereniak E. L. , Eskin J. D. , Marks D. G. , Matherson K. J. , Young E. T. , Augustine F. L.
Published: April 2011

We are developing modular arrays of CdZnTe radiation detectors for high-resolution nuclear medicine imaging. Each detector is delineated into a 64×64 array of pixels; the pixel pitch is 380 jim. Each pixel is connected to a corresponding pad on a multiplexer readout circuit. The imaging system is controlled by a personal computer. We obtained images of standard nuclear medicine phantoms in which the spatial resolution of approximately 1.5 mm was limited by the collimator that was used. Significant improvements in spatial resolution should be possible with different collimator designs. These results are promising for high-resolution nuclear medicine imaging.
Fabrication of CdZnTe Strip Detectors for Large Area Arrays
Authors: Stahle C. M. , Shi Z. Q. , Hu K. , Barthelmy S. D. , Snodgrass S. J. , Lehtonen S. J. , Mach K. J. , Barbier L. , Gehrels N. , Krizmanic J. F. , Palmer D. , Parsons A. M. , Shu P.
Published: April 2011

A CdZnTe strip detector large area array (∼ 60 cm2 with 36 detectors) with capabilities for high resolution imaging and spectroscopy has been built as a prototype for a space flight gamma ray burst instrument. The detector array also has applications in nuclear medical imaging. Two dimensional orthogonal strip detectors with 100 μm pitch have been fabricated and tested. Details for the array design, fabrication and evaluation of the detectors will be presented.
Lead Iodide X-Ray and Gamma-Ray Spectrometers for Room and High Temperature Operation
Authors: Hermon H. , James R. B. , Lund J. , Cross E. , Antolak A. , Morse D. H. , Medlin D. L. , Soria E. , Scyoc J. Van , Brunett B. , Schieber M. , Schlesinger T. E. , Toney J. , Goorsky M. , Yoon Hojun , Burger A. , Salary L. , Chen K.-T. , Chang Y.-C. , Shah K.
Published: April 2011

In this study we report on the results of the investigation of lead iodide material properties. The effectiveness of a zone refining purification method on the material purity is determined by ICP-MS and ICP-OES and correlated to the electrical and physical material properties. We show that this zone refining method is very efficient in removing impurities from lead iodide, and we also determine the segregation coefficient for some of these impurities. Triple axis x-ray diffraction (TAD) analysis has been used to determine the crystalline perfection of the lead iodide after applying various cutting, etching and fabrication methods. The soft lead iodide crystal was found to be damaged when cleaved by a razor blade, but by using a diamond wheel saw, followed by etching, the crystallinity of the material was much improved, as observed by TAD. Low temperature photoluminescence also indicates an improvement in the material properties of the purified lead iodide. Electrical properties of lead iodide such as carrier mobility, were calculated based on carrier - phonon scattering. The results for the electrical properties were in good agreement with the experimental data.
Dopants in Hgcdte
Authors: Berding M. A. , Sher A.
Published: April 2011

In this paper we discuss our ab initio calculations of native point defect and impurity densities in HgCdTe. Our calculations have explained the experimental finding in general, and in particular have explained the in-active incorporation of the group VII elements under mercury-deficient conditions; have shown that the group I elements have a large fraction of interstitial incorporation, thereby explaining their fast diffusion; and have described a microscopic mechanism for the amphoteric behavior of the group V elements. We discuss the trends found among the compounds in terms of the underlying bond strengths to understand why the various elements behave the way they do.
Metal Contact Formation On Zinc Cadmium Telluride Detector Material
Authors: Burger Arnold , Chen Henry , Chen Kuo-Tong , Shi Detang , Collins W. Eugene , James R. B.
Published: April 2011

The understanding of the electric contact formation process is critical in exploiting the full potential of Cd1−xZnxTe(CZT) material for room temperature detection applications. The metalsemiconductor electrical characteristics were shown in this study to be strongly affected by the surface preparation steps prior to metallization (polishing, and chemical etching), the choice of the metal and contact deposition technique, and by the subsequent surface passivation of CdZnTe. In this paper, we also present the implementation new detector fabrication processing stepsresulting in a significant lowering of the dark leakage current and an improvement in the detector performance.
Characterizing and Circumventing Intermolecular Electrostatic Interactions in Highly Electro-Optic Polymers
Authors: Harper Aaron W. , Zhu Jingsong , He Mingqian , Dalton Larry R. , Garner Sean M. , Steier William H.
Published: April 2011

In general, polymers possessing non-resonant electro-optic activities exceeding 20 pm/V require chromophores with strong electron withdrawing groups (cyanovinyls, carbon acid moieties, etc.) as well as highly polarizable bridges. Although much progress has been made on designing and preparing materials with molecular “electrooptic” activities, their incorporation into polymers to show comparably large bulk electro-optic activities has been met with little success. We report here the mature of the difficulty of the translation of microscopic to macroscopic electro-optic activity. The optimization of molecular activity increases intermolecular electrostatic interactions between chromophores, and these interactions impede induction of polar acentric order in the polymers. Theoretical analysis of the problem is presented, as well as one example of a material that is designed to circumvent these interactions. The resulting material possesses electro-optic coefficients as high as 29 pm/V and optical losses as low as 1.5 dB/cm.
Light-Emitting and Hole-Transporting Polymers for LEDs
Authors: Ohnishi Toshihiro , Doi Shuji , Ueda Masato , Yamaguchi Fumi , Noguchi Takanobu
Published: April 2011

Various copolymers of arylene vinylenes, having strong fluorescence, showed predominantly the emission in the multi-layer device using an electron-transporting material(ETM) such as tris(8-quinolinolato)aluminum(Alq3). The emission from Alq3 was suppressed due to the high hole-injection barrier from the copolymers to ETM in spite of low or no barriers of electron injection from ETM to the copolymers. We have successfully prepared highly hole-transporting polysilane having a triphenylamine group as a side chain(TPA-PS). The hole mobility as high as 10 cm3cm2/Vs is attributable to the intermolecular hopping process facilitated by the interaction between the polysilane backbone and the triphenylamine group. The polysilane is effectively used as a hole transporting material. The bilayer LED device consisting of TPA-PS and Akb3 showed high luminance (2000cd/m2) and high efficiency (4cd/A).