bluuebunny/crossref_metadata_2025 huggingface dataset:
Applications of Qualitative Trace Element Analyses: An Interdisciplinary Approach to Materials Conservation
Authors: Sickels-Taves L.B. , Sheehan M.S. , White G.D.
Published: April 2011

This interdisciplinary study was designed to learn the chemical constituency of organic residues found in tabby using nondestructive analytical techniques such as X-Ray Fluorescence (XRF) and Particle Induced X-Ray Emission (PIXE). Important information pertaining to events of the past can be preserved in organic materials. The related disciplines of historic preservation and archaeology can benefit from the recovery of that information, especially when conducting collaborative research.

The purpose of this study was to evaluate the effectiveness of these two techniques in their ability to characterize the chemical composition of tabby, a building material that incorporates large quantities of shell. Although useful qualitative data regarding the chemical composition of tabby was obtained using both methods, the best results were obtained using PIXE.

These results suggest that PIXE represents a viable and accurate alternative for compositional analysis of materials with an organic component commonly encountered by historic preservationists and archaeologists.
Atomic-Resolution Electron Microscopy of TiB2 Precipitates in an Industrial TiAl Alloy
Authors: Inkson B. J. , Möbus G. , Rühle M.
Published: April 2011

TiB2 nano-lamellae, grown in-situ within a TiAl intermetallic melt, have been examined by high resolution electron microscopy. The use of the Stuttgart ARM enables Ti and B columns to be distinguished in the HREM images. Examination of the internal structure of the T1B2 platelets reveals extensive prismatic faulting on {1010}TiB2, {0110}TiB2 and {1100}TiB2 planes. Externally, the TiB2 platelets exhibit an orientational relationship {1010}TiB2 // {001}B2 and [0001]TiB2 // <010>B2 with interleaving platelets of B2-phase, with the predominating interface planes being {1010}TiB2 // {001}B2. The minor facets of the TiB2 platelets are [0001]TiB2 // <010>B2. {0110}TiB2 and {1100}TiB2, with the latter two facets showing no relationship with the interleaving B2-phase. No preferred orientation relationship of the TiB2 with the surrounding γ-TiAl and α2-Ti3Al phases is observed.
Determination of Atomic Structure at Surfaces and Interfaces by High-Resolution Stem
Authors: Pennycook S. J. , Nellist P. D. , Chisholm M. F. , Browning N. D. , Wallis D. J. , Dickey E. C.
Published: April 2011

It is just over one hundred years since Lord Rayleigh first showed the differences between coherent and incoherent imaging in the light microscope, pointing out the advantages of the latter for resolution and image interpretation. The annular detector in the high-resolution STEM provides the same advantages for electrons, allowing incoherent imaging at atomic resolution, with image contrast strongly dependent on atomic number (Z). Since incoherent imaging has no phase problem, these Z-contrast images may be directly inverted to give the (projected) atomic positions. A maximum entropy method avoids false detail associated with direct deconvolution, and gives atomic coordinates to an accuracy of ± 0.1 Å. Electron energy loss spectroscopy can provide valuable complementary information on light element bonding and the presence of impurities in specific atomic planes selected from the image. Together, these techniques have revealed some surprisingly complex interfacial structures. For surface studies, the 1.3 A probe of the VG Microscopes HB603U STEM provides sufficient penetration and contrast to image single Pt and Rh atoms on γ-alumina supports. Such images reveal preferred atomic configurations, and allow possible surface adsorption sites to be deduced.
Boron Clustering in Silicon Under an Interstitial Flux: A Study Using Delta Doped Structures
Authors: Simpson T. W. , Mitchell I. V. , Baribeau J.-M.
Published: April 2011

Understanding has advanced significantly in the interpretation of the thermal release of self interstitials into a silicon lattice from a region, e.g. ion implanted, which is rich in point defects. Progress has been accelerated through the use of delta doped layer structures, especially of boron doping type, where the transient enhanced diffusion (TED) of the dopant marks the arrival of the self interstitial species from a physically separate damage region. Frequently observed in such TED experiments is an immobile, electrically inactive, boron peak on top of the spreading diffusion profile. This signature boron peak has been attributed to the Si-interstitial driven clustering of boron. It has been observed that this feature occurs for high boron concentrations and implant fluences; however, a complete understanding of the clustering mechanism has remained elusive.

We present new data from experiments where the self implant fluence has been varied to allow the intensity of the transient flux to be adjusted and where repeat distances in the MBE structure have been adjusted to test for trapping. This has led to some clarifications to the current picture of boron clustering during TED. These results seem to be important in the context of the search for engineering control over dopant redistribution in Si during post-implantation annealing.
Nonhydrostatic Stress Effects on Boron Diffusion in SI
Authors: Aziz Michael J.
Published: April 2011

The thermodynamics of diffusion under hydrostatic pressure and nonhydrostatic stress is developed for single crystals free of extended defects and is applied to the case of boron diffusion in silicon. The thermodynamic relationships obtained permit the direct comparison of hydrostatic and biaxial stress experiments and of atomistic calculations under hydrostatic stress. Assuming various values for the anisotropy in the migration strain, a currently unknown parameter, comparison is made between various measurements under hydrostatic pressure and nonhydrostatic stress, and various atomistic calculations of the volumetrics of B and Si diffusion by an interstitial-based mechanism. An independent determination of the anisotropy of the migration strain would permit a parameter-free determination of the predominant diffusion mechanism and would permit the prediction of the ratio of the diffusivity normal to the free surface to the diffusivity parallel to the surface for biaxially strained films. Procedures for measuring and calculating the anisotropy in the migration strain are described.
Release of Impurities From Structural Defects in Polycrystalline Silicon Solar Cells
Authors: McHugo S. A. , Imaizumi M.
Published: April 2011

It is critical to understand the behavior of metallic impurities in polycrystalline silicon used for solar cells. These impurities significantly increase the minority carrier recombination rate and, in turn, degrade cell performance. Impurity gettering is a commonly used method to remove these impurities from the material, however, past work has suggested that impurity release from structural defects drastically limits the gettering process. Presently, there is only a limited understanding of impurity release from structural defects. In this work, a correlation between structural defects and the location of metal impurities in as-grown material is established and the release of nickel and copper from structural defects in polycrystalline silicon was studied in as-grown material and after sequential thermal treatments which dissolve the impurities into the silicon matrix. Synchrotron-based x-ray fluorescence impurity mapping with spatial resolution of ≈ 1μm, was used to determine impurity distributions after each thermal treatment.
Impurity Removing at Dislocations in Float Zone Silicon by Aluminium-Silicon Alloying
Authors: Perichaud I. , Martinuzzi S.
Published: April 2011

Aluminium-silicon alloying is applied to dislocation-containing FZ silicon samples in order to verify if this external gettering technique is able to remove impurities trapped by these defects. Samples were scratched (front surface), bent and annealed at 750°C for 6h in order to create dislocation arrays. Standard samples and also nickel contaminated samples were investigated by light beam induced current (LBIC) mapping technique before and after alloying at 900°C for 4h with a 1 μm thick aluminium layer deposited on the backside. The LBIC technique detects the features of the dislocation array in agreement with X ray topographs. In the standard samples, the contrast is relatedto an inadvertent contamination of the samples and disappears after gettering. In the contaminated samples, dislocation contrast is higher, the aluminium treatment attenuates strongly the dislocations electrical activity but not so neatly as for the standard samples. This result is explained by the possible microprecipitation of nickel at dislocations.
Ebic Study of Fe Precipitation on Bulk Stacking Fault in Czochralski-Grown Silicon
Authors: Shen B. , Sekiguchi T. , Chen P. , Yang K. , Chen Z. Z. , Zheng Y. D. , Sumino K.
Published: April 2011

Fe precipitation on bulk stacking faults in Czochralski-grown silicon are investigated by means of the electron-beam-induced-current (EBIC) technique and other techniques. It is found that Fe impurities only precipitate on Frank partial dislocations bounding stacking faults when the specimen is cooled slowly; however, they precipitate on both Frank partials and fault planes when the specimen is cooled fast. It is explained that small oxygen precipitates on fault planes, together with Frank partials, serve as the gettering centers for Fe impurities in the fast cooled specimen.
Room-Temperature Migration of Ion-Implanted Boron in Silicon
Authors: Collait E. J. H. , Weemers K. , Gravesteijn D. J. , van Berkum J. G. M. , Cowern N. E. B.
Published: April 2011

Room temperature migration and clustering behaviour of implanted boron into silicon has been investigated by performing ion implantation of the 11B isotope into MBE-grown in-situ 10B-doped epitaxial Si-layers. We, for the first time, show that a fraction of the implanted boron migrates very deep into the bulk of the Si with substitutional 10B acting as trap centers for the migrating 11B.
Wet Oxidation of Poly-Si1-xGex Layer Grown on SiO2/Si
Authors: Han Ping , Wu Mang , Ma Junru , Huang XiaoDong , Chen Hao , Hu Liqun , Zheng Youdou
Published: April 2011

In this paper, we report on the experiment results of wet oxidation of Si1-xGex on SiO2. AES and XPS measurements were performed to study the effect of the oxidation on the Si1-xGex layer. A possible mechanism was proposed.
Photoresist Stripping using Ozone/Deionized Water
Chemistry
Authors: Kashkoush I. , Matthews R. , Novak R. , Brause E. , Carrillo F. , Rajaram B.
Published: April 2011

The use of sulfuric acid to strip photoresist from silicon wafers is a
widely employed technique in the semiconductor manufacturing community. In
most cases, the acid is combined with hydrogen peroxide to oxidize stripped
photoresist material, though the use of sparged ozone in sulfuric solution
is also used to remove resist residues on wafers following the ashing
process. Although they have been used for many years, sulfuric acid
processes also have proven to be costly. This is due to the need for
frequent bath change-outs and the use of high temperature which impose
safety and environmental concerns. As a result of these and other
considerations, the use of mixtures of ozone and de-ionized water for
photoresist stripping has been investigated. Results show that the technique
effectively removes hard-baked resist (ashed and un-ashed) from bare silicon
and patterned wafers and produces cleaner surfaces (i.e. particles and
metals), compared to outcomes from SPM processes.
Mirror-Polishing Residual Damage characterization in the
Subsurface of Si Wafers Using N2 Laser /mm-Wave Photoconductivity
Amplitude Technique
Authors: Ogita Y. , Hosoda Y. , Miyazaki M.
Published: April 2011

The problem is occurring that gate oxide integrity (GOI) might be influenced
on the residual subsurface damages induced by mirror polishing. The
correlations between mirror polishing conditions, micro roughness, and
photoconductivity amplitude (PCA) signals are measured and discussed in a
small roughness region of micro roughness Rrms such as 0.095 nm
to 0.247 nm. The theoretical analysis shows that PCA signal is possible to
reflect a subsurface lifetime.The discussions lead to result that the GOL is
mainly dependent on subsurface damages in such small roughness region, PCA
signals measured with an UV/mm-wave noncontact technique correlate closely
with the GOI yield. It is concluded that the PCA technique makes it possible
to characterize subsurface damages and to estimate GOI yield.
Comparison of Removal Efficiency of Cu Impurity on Si(100)
Depending on the Cleaning Splits of (UV/O3 + HF) and
(H2O2 + HF)
Authors: Jeon Hyeongtag , Choi Baikil
Published: April 2011

Si surface cleaning has been studied intensively in these days. One of the
major concerns is about the removal of metallic impurities on Si surface. In
this study we choose contaminant element of Cu which shows high
electronegativity value compared to Si's. The Si substrate was cleaned with
using piranha (H2SO4:H2O2=4:1)
and HF (HF:H2O=1:100) solutions to eliminate the organic
impurities and native oxide. The initial Si substrate was then contaminated
intentionally by dipping into the 1 ppm standard solution of Cu and cleaned
by the cleaning splits of the chemical solution HF combined with
UV/O3 treatment and the chemical mixture of
H2O2 and HF. The initial substrates which were
contaminated with the standard Cu solution exhibited the contamination
levels of 1013–1015 atoms/cm2 and these
substrates were cleaned and showed Cu concentration down to the levels as
lower as 1010 atom/cm2 which were monitored by TXRF
(total reflection X-ray fluorescence). And repeated treatments of these
cleaning splits improved the surface microroughness of these initial
substrate which were measured by AFM (atomic force microscope). The surface
and interface morphologies contaminated with Cu were examined by SEM
(scanning electron microscope) and TEM (transmission electron microscope).
It was observed that Cu impurities were adsorbed on Si surface not in a thin
film but in a particle form as a hemispherical shape. The chemical
composition of Cu impurities and interface between Cu and Si substrate was
investigated by AES (Auger electron spectroscope). The result exhibited that
Cu element adsorbed on Si surface by chemical adsorption and this resulted
in oxidation of Si substrate.
Comparison and Reproducibility of H-Passivation of Si(100) with
HF in Methanol, Ethanol, Isopropanol and Water by IBA, TMAFM, and
FTIR'
Authors: Atluri V. , Herbots N. , Dagel D. , Jacobsson H. , Johnson M. , Carpio R. , Fowler B.
Published: April 2011

Three different HF:alcohol solutions are investigated to etch native
SiO2 and passivate Si(100) surfaces with H which can the be
desorbed at low temperature (T < 600°C). The resulting passivated Si(100)
surfaces are compared using as a reference Si(100) passivated by a standard
aqueous HF: solution (1:98 parts of HF: H2O). After a modified
RCA cleaning, Si(100) etched by HF:Methanol, HF:IPA, or HF:Ethanol, is
characterized by Ion Beam Analysis (IBA), Tapping Mode Atomic Force
Microscope (TMAFM), and Fourier Transform Infrared Spectroscopy (FTIR). The
absolute coverage of O and C is measured by nuclear reaction analysis (NRA)
combined with ion channeling at 3.05 MeV for O and 4.265 MeV for C. Hydrogen
is measured via the elastic recoil detection (ERD) of
4He2+ at 2.8 MeV.

Compared to aqueous HF, HF:alcohol passivates Si(100) leaving a lower O
residue by an average factor of 0.62 and a similar C residue. H coverage is
higher by an average factor of 1.43. Surface coverages are found to be
reproducible in average by 1.4 × 1014 atoms/cm2 for C,
and by 1.25 × 1014 atoms/cm2 for O when measured by
IBA on samples identically processed. H coverage is reproducible within 5.5%
when measured by ERD.

Selective area analysis by TMAFM shows that an increasing number of
particulates is responsible for the apparent increase in root-mean -square
(rms) surface roughness when the rms is measured over a whole image. Taking
this effect into account, all passivated surfaces exhibit similar roughness
when compared to the original Si(100) surface with little difference between
alcohols and with the reference aqueous HF solution.

FTIR in the attenuation total reflection (ATR) mode detected SiHx
species mostly as a dihydride. Both IBA and FTIR detected significant levels
of oxygen on surfaces passivated HF in alcohol and aqueous HF. This
indicates that while Si(100) exhibits more H when passivated with HF in
alcohol and can be desorbed at lower temperature than when treated with
aqueous HF, H is not bonded to Si only but likely bonds into a more complex
surface termination, such as SiOH.
Infrared Spectroscopy of Covalently Bonded Species on Silicon
Surfaces: Deuterium, Chlorine, and Cobalt Tetracarbonyl
Authors: Luo Huihong , Chidsey Christopher E. D. , Chabal Yves
Published: April 2011

We report the formation of deuterium-terminated Si(111) and Si(100) surfaces
in deuterated aqueous KF. The reaction of a deuterated Si(100) surface with
H2O is investigated. We find that H2O etches the
surface to give hydrogen termination and oxidized silicon hydrides.
Hydrogenterminated surfaces react with various reagents under non-UHV
conditions to form other covalent bonded species, including Cl-Si and
Co(CO)4-Si. These species are characterized by polarized ATR
and transmission FTIR. On Cl-Si(111) surfaces, Cl-Si is perpendicular to the
surface. Chlorine-terminated Si(100) reacts with H2O to produce
the hydrogen terminated surface. On Co(CO)4-Si(111) surfaces, one
carbonyl is perpendicular to the surface, and the other three are
approximately parallel to the surface.
The use of Metal additions to Phosphoric Acid to Etch
Polysilicon in Poly Buffered Locos Processes
Authors: Pearce Charles W. , Chung B. C.
Published: April 2011

The use of poly-buffered LOCOS processing is a common feature of many
sub-micron integrated circuit fabrication processes. However, the silicon
layer interposed between the nitride oxidation mask and the pad oxide is
often difficult to remove. Different strategies involve dry and/or wet
etching of the film. We have demonstrated the utility of adding metals such
as Fe or Cu to a conventional phosphoric bath used to etch silicon nitride.
Briefly, the presence of the metals is thought to result in a classic
oxidation-reduction reaction between the metal and the silicon. Additions of
60ppm of Cu+2 resulted in etch rates of 20Å /min. on undoped
polysilicon at a process temperature of 165°C, whereas, the etch rate of
SiO2 was less than 1Å/min. Similar results were obtained for
additions of Fe+3 and other metals.
Electrical Transport Properties of the Pentatelluride Materials Hfte5 and Zrte5
Authors: Tritt T. M. , Wilson M. L. , Littleton R. L. , Feger C. , Kolis J. , Johnson A. , Verebelyi D. T. , Hwu S. J. , Fakhruddin M. , Levy F.
Published: April 2011

We have measured the resistivity and thermopower of single crystals as well as polycrystalline pressed powders of the low-dimensional pentatelluride materials: HfTe5 and ZrTe5. We have performed these measurements as a function of temperature between 5K and 320K. In the single crystals there is a peak in the resistivity for both materials at a peak temperature, Tp where Tp ≈ 80K for HfTe5 and Tp ≈ 145K for ZrTe5. Both materials exhibit a large p-type thermopower around room temperature which undergoes a change to n-type below the peak. This data is similar to behavior observed previously in these materials. We have also synthesized pressed powders of polycrystalline pentatelluride materials, HfTe5 and ZrTe5. We have measured the resistivity and thermopower of these polycrystalline materials as a function of temperature between 5K and 320K. For the polycrystalline material, the room temperature thermopower for each of these materials is relatively high, +95 μV/K and +65 μV/K for HfTe5 and ZrTe5 respectively. These values compare closely to thermopower values for single crystals of these materials. At 77 K, the thermopower is +55 μV/K for HfTe5 and +35 μV/K for ZrTe5. In fact, the thermopower for the polycrystals decreases monotonically with temperature to T ≈ 5K, thus exhibiting p-type behavior over the entire range of temperature. As expected, the resistivity for the polycrystals is higher than the single crystal material, with values of 430 mΩ-cm and 24 mΩ-cm for Hfre5 and ZrTe5 respectively, compared to single crystal values of 0.35 mΩ-cm (HfTe5) and 1.0 mΩ-cm (ZrTe5). We have found that the peak in the resistivity evident in both single crystal materials is absent in these polycrystalline materials. We will discuss these materials in relation to their potential as candidates for thermoelectric applications.
High-Power Low-Threshold Optically Pumped Type-ll Quantum-Well Lasers
Authors: Lin Chih-Hsiang , Murry S. J. , Yang Rui Q. , Pei S. S. , Le H. Q. , Yan Chi , Gianardi D. M. , McDaniel D. L. , Falcon M.
Published: April 2011

Stimulated emission in InAs/InGaSb/InAs/AlSb type-II quantum-well (QW) lasers was observed up to room temperature at 4.5 μm, optically pumped by a pulsed 2-μm Tm:YAG laser. The absorbed threshold peak pump intensity was only 1.1 kW/cm2 at 300 K, with a characteristic temperature T0 of 61.6 K for temperatures up to 300 K. We will also study the effects of internal loss on the efficiency and output power for type-II QW lasers via optical pumping. Using a 0.98-μm InGaAs linear diode array, the devices exhibited an internal quantum efficiency of 67% at temperatures up to 190 K, and was capable of < 1. 1-W peak output power per facet in 6-μs pulses at 85 K. The internal loss of the devices exhibited an increase from 18 cm−1 near 70 K to ∼ 60–100 cm−1 near 180 K, which was possibly due to inter-valence band free carrier absorption.
Band-reject infrared metallic photonic band gap filters on flexible polyimide substrate
Authors: Gupta Sandhya , Tuttle Gary , Sigalas Mihail , Ho Kai-Ming
Published: April 2011

Metallic photonic band gap (MPBG) structures are multi-layer metallic meshes imbedded in a dielectric medium. We report the successful design, fabrication, and characterization of infrared band-reject filters using MPBG structures in a flexible polyimide substrate. The metal layers of the MPBG have square grid patterns with short perpendicular cross-arm defects added halfway between each intersection. The transmission characteristics of these filters show a higher order band-reject region in addition to a lower order band gap that extends from zero to particular cut off frequency. The critical frequencies of the filters depend on the spatial periodicity of the metal grids and length of the cross-arm defects. Optical transmission measurements of the bandreject filters show lower edge cutoff frequency of about 2 THz and the higher order bandgap region centered around 4.5THz with attenuation of more than 35 dB in the bandgap region. This is in good agreement with the theoretical calculations. The filters maintain their optical characteristics after repeated bending, demonstrating mechanical robustness of the MPBG structure and have minimal dependence on angle of incidence.
HgCdTe– an Unexpectedly Good Choice for (Near) Room Temperature Focal Plane Arrays
Authors: Tennant W. E. , Cabelli C.
Published: April 2011

Fueled by a broad range of government needs and funding, HgCdTe materials and device technology has matured significantly over the last two decades. Also in this same time period, we have come to understand better the phenomenology which limits imager performance. As a result of these developments, it appears that HgCdTe arrays may be tailored in wavelength to outperform GaAs-based image intensifier devices in sensitivity and to compete with bolometric and pyroelectric imaging arrays in NEDT at temperatures at or near room temperature (250K–295K). These benefits can be fully realized, however, only if HgCdTe can be brought to a level of maturity where the material and detectors made from it are limited by fundamental mechanisms. We will discuss the state of HgCdTe near room temperature performance and the practical and theoretical limits which constrain it.
Quantum Well Intermixing for Optoelectronic Applications
Authors: Jagadish C. , Tan H. H. , Yuan S. , Gal M.
Published: April 2011

Ion implantation induced intermixing of GaAs-AlGaAs quantum well structures with H, O and As ions is investigated by low temperature photoluminescence. Large energy shifts are observed in all the cases, though recovery of photoluminescence intensities in proton case is more significant than others. Energy shifts are linear with proton dose and no saturation was observed even up to a dose of ∼ 5 × 1016 cm−2. Saturation in energy shifts are seen for both As and 0 ions at high doses. Energy shifts are also found to be dependent on Al composition of the barriers. Wavelength shifted quantum well lasers are fabricated with energy shifts of about 5 nm with no changes in threshold current using proton implantation. Anodic oxide induced intermixing of GaAs-AlGaAs quantum wells is demonstrated.
Effect of Geometric Factors on Polarization Properties of Vertical-Cavity Surface-Emitting Lasers With Tilted Pillar Structures
Authors: Park Min Soo , Ahn Byung Tae , Chu Hye Yong , Yoo Byueng-Su , Park Hyo-Hoon
Published: April 2011

We have studied the effect of geometric factors on the polarization properties of verticalcavity surface-emitting lasers with tilted pillar structures. Laser pillars with circular, square, diamond, and rectangular shapes were formed using reactive ion beam etching, by tilting the substrate with an angle of 15° ∼ 30° toward the [110] or [110] direction. We measured the polarization characteristics for the devices of 10 ∼ 20 atm size. We observed that an effective geometric factor on the polarization selectivity in tilted pillar structures is an asymmetric shape of vertical-cavity rather than an anisotropic shape of device area in planar direction.
Comparison Between Cadmium Zinc Telluride Crystals Grown in Russia and in the Ukraine
Authors: Hermon H. , Schieber M. , James R. B. , Yang N. , Antolak A. J. , Morse D. H. , Kolesnikov N. N. P. , Ivanov Yu. N. , Komar V. , Goorsky M. S. , Yoon H. , Toney J. , Schlesinger T. E.
Published: April 2011

A comparative analysis of different Cd1−xZnxTe (CZT) crystals grown by a vertical high pressure Bridgman (VHPB) method is reported. The results of several analytical techniques, such as triple axis x-ray diffraction (TAD), rocking curves, low temperature photoluminescence (PL), scanning electron microscopy (SEM), and proton induced x-ray emission (PIXE) are discussed. Segregated carbon inclusions were identified by SEM and energy dispersive x-ray fluorescence (EDXRF), and the results are interpreted in terms of constitutional supercooling of the solidifying CZT melt. The carbon inclusions significantly decrease the resistivity, and in some cases, the noise is too large for the fabrication of radiation detectors. Combining these results with other measurements reported by our research team [1], we identify correlations between the growth and the defects identified in these CZT crystals.
Optical, Electrical and Surface Characterization of Mercuric Iodide Platelets Grown in the HgI 2-HI-H2O System
Authors: Fornaro L. , Chen H. , Chattopadhyay K. , Chen K.-T , Burger A.
Published: April 2011

The optical, electrical and surface properties of mercuric iodide platelets grown from solution in a HgI2-HI-H2O system were investigated by comparing them with Physical Vapor Transport (PVT) grown crystals. The absence of bulk imperfections and the uniformity of the as-grown surfaces and the KI solution etched surfaces were confirmed by optical microscopy. The as-grown surface uniformity is higher for solution grown crystals than that of PVT crystals, since the platelets do not have to be cleaved or polished. AFM studies show that the roughness for the cleaved, aged and etched surfaces were 0.06 nm, 0.48 nm and 0.3 nm respectively. Low temperature photoluminescence properties were measured for the two kind of crystals and will be discussed. However, I-V curves give higher current density and lower apparent resistivity values for the solution grown than for PVT grown crystals. Correlations between optical and surface quality as well as the electrical properties of the crystals grown from both solution and PVT methods are also discussed.
Enhancement of Mercuric Iodide Detector Performance Through Crystal Growth in Microgravity: the Roles of Lattice Order
Authors: Steiner Bruce , Berg Lodewijk Van Den , Laor Uri
Published: April 2011

The hole-mobility•carrier-lifetime product of α mercuric iodide high energy radiation detectors has been enhanced through vapor crystal growth in microgravity. This improvement is closely correlated with specific characteristics of the crystal lattice, which have been identified by high resolution synchrotron x-ray diffraction imaging. These structural features and the associated performance are now being approached in terrestrial growth of α mercuric iodide.

Gravity may affect the uniformity of this crystal lattice in two distinct ways: 1) directly through deformation that it imposes on the lattice during growth and 2) indirectly through convection, which mixes any extraneous material. Inclusions associated with these processes harden the lattice and facilitate lattice folding. These changes affect the electronic parameters of detectors made from the crystals. As purification procedures are optimized, the incorporation of extraneous material is curtailed, enhancing electronic properties in spite of lattice flexing through loss of precipitation hardening.

These studies provide insight into the contribution of various aspects of crystalline order in α-mercuric iodide crystals to property improvement. This knowledge has led to modification of requirements for starting materials, adjustment of physical vapor growth procedures, and change in crystal handling procedures. As a result, the electronic performance of terrestrially grown radiation detectors has been improved, and we provide evidence that further enhancement is still possible.
Modeling of the Signal Induced by an Incident Radiation in Semi-Insulating GaAs Detectors
Authors: Cola Adriano , Vasanelli Lorenzo , Reggiani Lino
Published: April 2011

We develop a Monte Carlo simulator of the charge signal induced by an external radiation on a semi-insulating GaAs detector. The role played by trapping and detrapping processes and the dynamics of generated carriers are investigated. The relative contribution to the charge signal of fast and slow time components as well as the time constant of the slow component are studied as a function of the applied voltage. Present findings provide a physical interpretation of available experimental results.
Possible Extensions of XIA'S Digital Spectrometer Technology to Portable and Remote Monitoring Instrumentation
Authors: Warburton W. K. , Darknell D. A. , Hubbard-Nelson B.
Published: April 2011

The XIA DXP-4C is a 4 channel, CAMAC based, x-ray spectrometer which digitally processes directly digitized preamplifier signals. The DXP-4C was designed for instrumenting multi-detector arrays for synchrotron radiation applications, and optimized for very high count rates at a low cost per detector channel. This produced a very compact and low power (3.4 W/channel) instrument for its count rate and MCA capabilities, which thus provides a strong basis for portable applications. Because all functions are digitally controlled, it can be readily adapted to various user interfaces, including remote access interfaces. Here we describe the design and examine approaches to lowering its power to 50 mW/channel. We then consider the issues in applying it to three typical portable or remote spectrometry applications.
Monolithically Integrated X-Ray Detector Arrays for Computed Tomography
Authors: Sudharsanan R. , Yoganathan M. , Vakerlis G. , Ferekides C. S. , McCandless B. , Birkmire R. , Deych R. , Luhta R.
Published: April 2011

The design and performance of a high sensitivity monolithic X-ray detector array fabricated by depositing CdTe photodiodes on CdWO4 scintillators for computed tomography (CT) are presented. CdTe photodiodes offer improved sensitivity due to the better match to the CdWO4 scintillator emission spectrum than the Si photodiodes used in current CT scanners. A CdTe photodiode fabricated on glass mechanically stacked to a CdWO4 scintillator showed 30% improvement in signal strength over Si photodiodes stacked to CdWO4-. Monolithic X-ray detector arrays were fabricated by depositing a CdTe photodiode structure on CdWO4 using close-spaced sublimation technique. Preliminary results on the detector's X-ray response, signalto- noise ratio and the X-ray temporal response show that monolithic CdTe X-ray detectors are suitable for practical CT scanner applications.
Material Requirements for a Boron Phosphide Thermal Neutron Counter
Authors: Viles T. P. , Brunett B. A. , Yoon H. , Lund J. C. , Hermon H. , Buchenauer D. , McCarty K. , Clifft M. , Dibble D. , James R. B.
Published: April 2011

Electrical characterization (current versus voltage and capacitance versus voltage) of nonstoichiometric amorphous boron phosphide Schottky diodes for neutron detection is presented. These results are incorporated in a Monte Carlo model of detector response to determine material requirements for a boron phosphide neutron counter.
Self-Assembled Multilayers and Photoluminescence Properties of a New Water-Soluble Poly(Para-Phenylene)
Authors: Shi Xiaobo , Li DeQuan , Lütt M. , Fitzsimmons M. R. , Van Patten G. P.
Published: April 2011

This paper reports the synthesis and characterizations of a new water-soluble poly(paraphenylene) (PPP) and its applications in preparing self-assembled multi-layer films. This new water-soluble conducting polymer was prepared through the sulfonation reaction of poly(pquarterphenylene- 2,2'-dicarboxylic acid). The incorporation of sulfonate groups has dramatically improved PPP's solubility in water at a wide pH range, whereas previous PPP is only slightly soluble in basic solutions. Dilute aqueous solutions of this polymer with acidic, neutral or basic pH emit brilliant blue light while irradiated with UV light. The sulfonated PPP emits from 350 nm to 455 nm with a maximum intensity at 380 nm. Self-assembled multilayers of this sulfonated PPP were constructed with a positively charged polymer poly(diallyl dimethyl ammonium chloride) and characterized with various surface analyses. Conductive (RuO2 and ITO), semiconductive (Si wafer), and non-conductive (SiO2) substrates were used in the preparation of self-assembled multilayers. Electrical, optical and structural properties of these novel self-assembled thin films will be discussed.
High E-O Coefficient Polymers Based on a Chromophore Containing Isophorone Moiety for Second-Order Nonlinear Optics
Authors: Chen Jinghong , Zhu Jingsong , Todorova Galina , He Mingqian , Dalton Larry R. , Garner Sean M. , Chen Antao , Lee Sang-Shin , Chuyanov Vadim , Steier William H.
Published: April 2011

A high -μβ chromophore APII utilizing isophorone as π-conjugation bridge was processed into both PMMA guest host and crosslinked (XL) polyurethane network with various loading densities. High electro -optic coefficients, r33 = 30 pm/V (in PMMA) and r33 = 32 pm/V (in polyurethane) at 1.06 μm were obtained. Alignment temporal stability ranged from 90 to 120°C for XL polymer network. There is virtually no intrinsic absorption loss at 1.3 μm (solution measurement). Also noteworthy is that high optimum loading densities of this chromophore are attainable in both cases without detectable chromophore aggregation due to intermolecular electrostatic interactions.
Synthesis and Nonlinearity of Triene Chromophores Containing the Cyclohexene Ring Structure
Authors: Ermer Susan , Lovejoy Steven M. , Leung Doris S. , Warren Hope , Moylan Christopher R. , Twieg Robert J.
Published: April 2011

A series of conjugated donor-acceptor trienes in which the central double bond is incorporated into an unsaturated isophorone, verbenone or chromone ring has been synthesized. In each case, the donor group consists of an amine and an aromatic or heterocyclic ring system, and the acceptor is the dicyanomethylidene group. The nonlinear optical properties of each of the compounds has been measured and correlated with its structure. The dipole moments and molecular hyperpolarizabilities of these compounds, like those of other conjugated polyenes, are large enough to be used as the active components of electro-optic polymers. Unlike other donor-acceptor polyenes, however, these compounds exhibit the thermal stability required for such applications.
Synthesis of Conjugated Polymers by Vapor Deposition Polymerization
Authors: Hsu Chain-Shu , Lin Ting-Li
Published: April 2011

The synthesis of poly(2,5-thienylene vinylene) and poly(4,7-thianaphthene) by vapor deposition polymerization is presented. 2,5-Di(bromomethyl)thiophene was subjected to vapor phase pyrolysis at 550°C to form a reactive intermediate. Upon condensation, the reactive intermediate polymerized spontaneously at a temperature higher than -25°C to produce poly(2,5-thienylene vinylene). The obtained poly(2,5-thienylene vinylene)s were fractionated into THF soluble and insoluble fractions. The number average molecular weights of the THF soluble fractions range from 1500 to 4000 as determined by GPC measurements. The obtained polymer shows no glass transition and melting point on the DSC scans. Doping of a poly(2,5-thienylene vinylene) film with I2 vapor led to a conductivity of 1 × 10−4 S c−1. In the second part of this study, 2,3-diethynylthiophene was subjected to vapor phase pyrolysis at 300°C to yield a reactive intermediate, 4,7- dehydrothianaphthene. Upon condensation, the obtained 4,7-dehydrothianaphthenene was polymerized spontaneously at a temperature higher than -25°C to produce poly(4,7-thianaphthene). The obtained poly(4,7-thianaphthene) was insoluble in common laboratory solvents and shows also no melting point and glass transition on the DSC scans.
Design of Flat Panel Displays Based on Organic Light Emitting Devices
Authors: Gu G. , Burrows P. E. , Forrest S. R.
Published: April 2011

We provide a systematic and quantitative analysis of the design of flat panel displays (FPDs) based on organic light emitting devices (OLEDs). Key performance parameters are estimated for OLED-based displays; system issues, including addressing schemes and strategies required to achieve full color displays, are treated quantitatively. Furthermore, addressing schemes for recently demonstrated, full color, high resolution stacked OLEDs are discussed. Our analysis shows that OLED technology is suitable for many FPD applications, and can provide performance superior to that achieved using alternative display technologies.
Synthesis and Incorporation of Thienylene Vinylene Oligomers in Main-Chain Copolymers
Authors: Madrigal L. G. , Elandaloussi E. H. , Spangler C. W.
Published: April 2011

Poly [2,5-thienylene vinylene] (PTV) has been studied extensively over the past decade for both its metallic conductivity behavior upon chemical doping, as well as its interesting third order nonlinear optical properties. PTV oligomers have been synthesized by our group 1, as well as others 2, and the formation of polaron-like radical-cations or bipolaron-like dications by oxidative doping has been demonstrated. In this paper we describe a general synthetic approach to PTV oligomers functionalized for copolymer formation by step-growth reaction.
Femtosecond Pump and Probe Spectroscopy on Poly(Para-Phenylenes)
Authors: Graupner W. , Cerullo G. , Kranzelbinder G. , Lanzani G. , Stagira S. , Nisoli M. , Silvestri S. De , Leising G.
Published: April 2011

We studied the sub-picosecond dynamics of photoexcitations in methyl-substituted poly(para--phenylene)-type ladder polymer (m-LPPP) films in a wide excitation density range up to values typical for the regime of narrow band emission by pump-probe spectroscopy. The singlet excitons relaxation dynamics, monitored at the stimulated emission (SE) peak at 2.53 eV, showed an intensity dependent ultrafast decay component, which occurs on a sub-picosecond time scale, ascribed to the onset of amplified spontaneous emission (ASE). In addition we identified photoinduced absorption (PA) bands of singlet excitons at 1.48 eV and polarons at 1.9 eV respectively. At high excitation density an additional absorption band becomes evident at 2.63 eV.
Optical Characterization of C60 Organic Semiconductor and Bilayers
Authors: Rainho J. P. , Santos L. , Kharlamov A. A.
Published: April 2011

Preparation and characterization either by optical absorption, photoluminescence and micro-Raman spectroscopy of individual components as well as bilayers consisting of organic dye semiconductor Zinc Phthalocyanine (ZnPc) and fullerene, C60, thin films are reported. The layers and structures were deposited in vacuum and some fullerene films were also prepared by casting the C60 solution in benzene. The optical absorption and photoluminescence dependencies on film thickness in bilayers C60/ZnPc were observed and may be discussed in a context of interface induced simmetry reduction of C60 molecules.
Hillock Growth at the Surface of Pt/TiN Electrodes for Ferroelectric Capacitors During Annealing in N2/O2 Ambient
Authors: Miura H. , Kumagai Y. , Fujisaki Y.
Published: April 2011

The hillock growth mechanism at the surface of Pt/TiN electrodes is investigated. TEM and SEM observations confirm that local delamination occurs at the Pt/TiN interface first, and then, plastic deformation of the Pt films under compressive stress forms hollow domes, which result in hillocks. Hillocks always start to grow when the internal stress in the Pt films reaches about −1000 MPa during annealing in N2/O2 ambient. Since the initial internal stress of Pt thin films varies from −500 to 500 MPa, depending on their deposition temperature, the hillock growth temperature strongly depends on the deposition temperature of the Pt films. It is very important, therefore, to control the initial internal stress in Pt films in order to eliminate hillock growth at the surface of Pt/TiN electrodes.
Crystallization and Electrical Properties of Bi4TiO12 Films Derived from Bismuth Acetate and Bismuth Nitrate Precursor Solutions
Authors: Kim Chang Jung , Chung C. W. , Lee Kyu Sang
Published: April 2011

Ferroelectric Bi4Ti3O12 thin films were prepared by the sol-gel method to examine the effect of precursors on the variation of ferroelectric properties. Two kinds of Bi4Ti3O12 sol-gel precursor solutions were synthesized by dissolving bismuth acetate and bismuth nitrate in glacial acetic acid and then adding titanium acetate. The films were deposited on Pt coated Si substrates by the spin-coating method and crystallized by double heat-treatment. The Ps, the Pr, and the Ec values of the film derived from the Bi-acetate were 34.8 μC/cm2, 16.2 μC/cm2, and 128 kV/cm, respectively. The Ps, the Pr, and the Ec of the films from the Bi-nitrate were 14.2 μC/cm2, 5.7 μC/cm2, and 105 kV/cm, respectively. The Bi4T3O12 films prepared from the Bi-acetate revealed better ferroelectricity and resistivity compared to those obtained from the Bi-nitrate.
Large Area PbZr1−xTixO3 (PZT) Thin Films Deposited by MOCVD Processes
Authors: Li Tingkai , Hartford Elliot , Zawadzki Pete , Stall Richard A.
Published: April 2011

An advanced oxide MOCVD tool and processes have been developed to deposit large area PbZr1−xTixO3 (PZT) thin films on 6” Si and Pt/Ti/SiO2/Si substrates. The experimental results show the advanced oxide MOCVD tool can achieve the growth of PZT thin films with thickness uniformity of 2% and composition uniformity better that 3% on both 6” Si and Pt/Ti/SiO,/Si wafers at high deposition rates. X-ray patterns showed a single PZT perovskite phase, and AFM showed homogeneous microstructure and low surface roughness. Typically, 300 nm thick PZT films with a grain size about 0.3 μm have Pr greater than 20 - 30 μC/cm2 at 5V, a dielectric constant around 1000, low coercive field (Ec 50 - 70 kV/cm), and fatigue rate (the normalized polarization is about 0.6 after 1010 cycles at 5 V), and leakage current of 2 - 6×lO−7 A/cm2 at 150 kV/cm and room temperature on Pt electrodes. In addition, the effects of reactor design and process conditions on the thickness and composition uniformity, as well as the m i ero structure and properties were also investigated.
A Study on the Improvement of Characteristics of BST Thin Films Fabricated on Iridium Electrode
Authors: Kil Deok-Sin , Lee Byung-Il , Joo Seung-Ki
Published: April 2011

BST thin films have been fabricated by RF magnetron sputtering onto Ir layer as a bottom electrode. When the substrate temperature was maintained at 600 °C during deposition, BST films deposited at that temperature showed very small oxide equivalent thickness of 0.36nm as well as very low leakage current density of about 10−8A/cm2at 1.5V. But as substrate temperature was increased to 700 °C in order to obtain high dielectric constant, oxide equivalent thickness exhibited very low value of about 0.3nm, however, leakage current density drastically increased to 10−4/cm2. BST thin films were fabricated by two step process, which consists of bottom layer deposited at high substrate temperature of 700 °C and top layer deposited at low substrate temperature. In the case of BST thin films which are composed of 20nm thick bottom layer deposited at 700 °C and 30nm thick top layer deposited at 500 °C, we obtained very small oxide equivalent thickness of 0.31nm and low leakage current density of 4 × 10−8A/cm2. at 1.5V.
Sol-Gel Synthesis of Epitaxial Films of (Sr,Ba)Bi2(Nb,Ta)2O9 and Bi4Ti3O12 on [100] SrTiO3
Authors: Morrell Jonathan S. , Xue Ziling B. , Specht Eliot D. , Beach David B.
Published: April 2011

An all-alkoxide sol-gel process utilizing methoxyethoxide complexes in 2-methoxyethanol was used to prepare epitaxial films of SrBi2Nb2O9, SrBi2Ta2O9, BaBi2Nb2O9, BaBi2Ta2O9, and Bi4Ti3O12 on [100] oriented SrTiO3 single crystals. Films were prepared by spin coating strontium titanate substrates with partially hydrolyzed alkoxide solutions and firing in air at 850 °C for 20 minutes. Out-of-plane orientation was confirmed by θ-2θ scans which showed only [002ℓ] reflections. In-plane orientation was determined by pole figures and phi-scans about the [105] plane in the case of the (Sr,Ba)Bi2(Nb,Ta)2O9 complexes and the [117] plane in the case of Bi4Ti3O12. Lattice constants and full-width at half-maximum (fwhm) values for both in-plane and out-of-plane reflections are reported.
New Type of Advanced Catalytic Material Based Upon Alumina Epitaxially Grown onto Thin Alumina Foil
Authors: Tikhov S. F. , Chernykh G. V. , Sadykov V. A. , Salanov A. N. , Tsybulya S. V. , Alikina G. M. , Lysov V. F.
Published: April 2011

Formation of planar layered Al2O3/Al composites via aluminum foil anodic-spark oxidation was studied by using SEM and XRD. A lateral growth of the primary non-porous alumina islands was shown to proceed to an extent where the entire surface was covered, and this layer is responsible for determining the high thermal stability of composite. A washcoating by an alumina suspension substantially increases pore volume and water absorption capacity. Catalysts based on the platinum group metals and transition metal oxides exhibit high activity for the reactions of CO and hydrocarbon oxidations and the selective reduction of nitrogen oxides by hydrocarbons.