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Opacity measurements: extending the range and filling in the gaps

Description: A series of experiments to explore Ge opacity at temperatures where the M-shell is almost filled will be discussed. Data are obtained at lower temperatures than previously explored and allow us to investigate the role of atomic structure calculations and their impact on opacity scalings. The experiment uses the Nova laser to irradiate a gold hohlraum within which a CH-tamped Ge sample is radiatively heated. A Nd backlight probes the sample 2 ns later to produce Ge spectral absorption features in the 1.2-1.5 keV energy range. Temperature is monitored by the use of an Al dopant and density is monitored by measuring the edge-on expansion of the sample. Temporal resolution of about 200 ps is obtained by using a short pulse backlight. Calculations in this photon energy region show significant changes in the spectral features.
Date: March 17, 1997
Creator: Back, C.A.; Perry, T.S.; Bach, D.R.; Wilson, G.; Iglesias, G.A.; Laden, O.L. et al.
Partner: UNT Libraries Government Documents Department

Magnetic properties of epitaxial and polycrystalline Fe/Si multilayers

Description: Fe/Si multilayers with antiferromagnetic interlayer coupling have been grown via ion-beam sputtering on both glass and single-crystal substrates. X-ray diffraction measurements show that both sets of films have crystalline iron silicide spacer layers and a periodic composition modulation. Films grown on glass have smaller crystallite sizes than those grown on single-crystal substrates and have a significant remanent magnetization. Films grown on single-crystal substrates have a smaller remanence. The observation of magnetocrystalline anisotropy in hysteresis loops and (hkl) peaks in x-ray diffraction demonstrates that the films grown on MgO and Ge are epitaxial. The smaller remanent magnetization in Fe/Si multilayers with better crystallinity suggests that the remanence is not intrinsic.
Date: August 1, 1995
Creator: Chaiken, A.; Michel, R.P. & Wang, C.T.
Partner: UNT Libraries Government Documents Department

Measurement of the in-flight pusher density of an indirect drive capsule implosion core using x-ray backlighting

Description: Both the efficiency of an implosion and the growth rate of hydrodynamic instability increase with the aspect ratio of an implosion. In order to study the physics of implosions with high Rayleigh-Taylor growth factors, we use doped ablators which should minimize x-ray preheat and shell decompression, and hence increase in- flight aspect ratio. We use x-ray backlighting techniques to image the indirectly-driven capsules. We record backlit 4.7 KeV images of the full capsule throughout the implosion phase with 55 ps and 15{mu}m resolution. We use these images to measure the in-flight aspect ratios for doped ablators, and we infer the radial density profile as a function of time by Abel inverting the transmission profiles.
Date: May 30, 1996
Creator: Kalantar, D.H.; Haan, S.W.; Hammel, B.A.; Keane, C.J.; Landen, O.L. & Munro, D.H.
Partner: UNT Libraries Government Documents Department

Modification to the Klein-Nishina cross section for Ge electrons at high statistics limit

Description: Modification factors for the Klein-Nishina cross-sections for gamma-ray with energies between 50 keV and 250 keV incident on Ge electrons have been obtained at the high statistics limit. In this limit, the Ge electrons can then be treated as they are obtained from the self-consistent augmented plane wave calculations, without considering the orientation of crystal lattice with respect to incident photons. The kinematics corrections (i.e. outgoing momenta), on the other hand, have to be taken into account on an event by event basis. Even so, the computing time has been reduced dramatically since the relativistic calculation of the modifications to the Klein-Nishina cross sections is the most tedious one. The modification factors are almost linear with respect to incident photon energy in the interesting energy range with respect to a given photon outgoing angle.
Date: November 3, 1995
Creator: Wang, T.F.
Partner: UNT Libraries Government Documents Department

Efficient production of 2--10 keV x-rays by laser heated ``underdense radiators``

Description: The next generation of high power lasers offers the prospect of creating multi-kilovolt x-rays with {gt}10% efficiency. Such efficiencies are achieved with ``underdense radiators``, a non- traditional source of laser generated x-rays. Applications of these sources with the proposed National Ignition Facility (NIF) include volume preheating of experiments; bright, multi-keV backlighting; pumps for fluorescent imaging of capsule dopants and Doppler velocimetry; uniform irradiation of large test objects. This paper presents two-dimensional numerical simulations for these high power lasers with unprecedented efficiency.
Date: May 22, 1996
Creator: Suter, L.J.; Kauffman, R.L.; Maxon, M.S. & Davis, J.F.
Partner: UNT Libraries Government Documents Department

Feasibility of organo-beryllium target mandrels using organo-germanium PECVD as a surrogate

Description: Inertial Confinement Fusion capsules incorporating beryllium are becoming attractive for use in implosion experiments designed for modest energy gain. This paper explores the feasibility of chemical vapor deposition of organo-beryllium precursors to form coating materials of interest as ablators and fuel containers. Experiments were performed in a surrogate chemical system utilizing tetramethylgermane as the organometallic precursor. Coatings with up to 60 mole percent germanium were obtained. These coatings compare favorably with those previously reported in the literature and provide increasing confidence that a similar deposition process with an organo-beryllium precursor would be successful.
Date: March 9, 1995
Creator: Brusasco, R.M.; Dittrich, T. & Cook, R.C.
Partner: UNT Libraries Government Documents Department

Development of a gamma ray box (garbo).

Description: Isomer decays, {beta}-{gamma} and electron-{gamma} spectroscopy, {alpha}-{gamma} fine structure studies, and Coulomb excitation are cases of nuclear structure experiments where the ideal detector is a compact, highly segmented, very efficient germanium (Ge) detector box. In order to develop such a structure, we are working on the R&D of large, segmented, High Purity planar Ge strip detectors (HPGeDSSD) which form the walls of such a box. We have developed a 92mm x 92mm x 20mm HPGeDSSD, which has 16 x 16 orthogonal strips of 5mm width. We are in the process of designing a focal plane detector for the Argonne Fragment Mass Analyzer (FMA) which consists of a 5 sided box, each side having a HPGeDSSD backed by a large segmented clover HPGe detector. MCNP simulations indicate this detector would have an efficiency of {approx}60% for 122 keV gamma rays and {approx}15% for 1.33 MeV radiation, which is ideal for studying the decays of nuclei far from stability that are usually produced with very low cross sections.
Date: May 1, 2002
Creator: Moore, E. F.; Lister, Ahmad, I., Amman, I.; Carpenter, M. P., Fischer, S. M.; Janssens, R. V. F.; Khoo, T. L.; Lauritsen, T. et al.
Partner: UNT Libraries Government Documents Department

Epitaxial Electronic Oxides on Semiconductors Using Pulsed-Laser Deposition

Description: We describe the growth and properties of epitaxial (OO1) CeO{sub 2} on a (001) Ge surface using a hydrogen-assisted pulsed-laser deposition method. Hydrogen gas is introduced during film growth to eliminate the presence of the GeOs from the semiconductor surface during the initial nucleation of the metal oxide film. The hydrogen partial pressure and substrate temperature are selected to be sufficiently high such that the germanium native oxides are thermodynamically unstable. The Gibbs free energy of CeO{sub 2} is larger in magnitude than that of the Ge native oxides, making it more favorable for the metal oxide to reside at the interface in comparison to the native Ge oxides. By satisfying these criteria. the metal oxide/semiconductor interface is shown to be atomically abrupt with no native oxide present. Preliminary structural and electrical properties are reported.
Date: December 1, 1999
Creator: Norton, D.P.; Budai, J.D. & Chisholm, M.F.
Partner: UNT Libraries Government Documents Department

Glass-Like Heat Conduction in Crystalline Semiconductors

Description: The thermal conductivity and structural properties of polycrystalline and single crystal semiconductor type-1 germanium clathrates are reported. Germanium clathrates exhibit thermal conductivities that are typical of amorphous materials. This behavior occurs in spite of their well-defined crystalline structure. The authors employ temperature dependent neutron diffraction data in investigating the displacements of the caged strontium atoms in Sr{sub 8}Ga{sub 16}Ge{sub 30} and their interaction with the polyhedral cages that entrap them. Their aim is to investigate the correlation between the structural properties and the low, glass-like thermal conductivity observed in this compound.
Date: June 13, 1999
Creator: Nolas, G.S.; Cohn, J.L.; Chakoumakos, B.C. & Slack, G.A.
Partner: UNT Libraries Government Documents Department

Nanocrystals and quantum dots formed by high-dose ion implantation

Description: Ion implantation and thermal annealing have been used to produce a wide range of nanocrystals and quantum dots in amorphous (SiO{sub 2}) and crystalline (Al{sub 2}O{sub 3}) matrices. Nanocrystals of metals (Au), elemental semiconductors (Si and Ge), and even compound semiconductors (SiGe, CdSe, CdS) have been produced. In amorphous matrices, the nanocrystals are randomly oriented, but in crystalline matrices they are three dimensionally aligned. Evidence for photoluminescence and quantum confinement effects are presented.
Date: January 1, 1996
Creator: White, C.W.; Budai, J.D.; Zhu, J.G.; Withrow, S.P.; Hembree, D.M.; Henderson, D.O. et al.
Partner: UNT Libraries Government Documents Department

Morphological stability of thin films

Description: The boundary element method for elastostatics is applied to a thin stability problem arising in solid state surface science. An aim of this work is to determine the morphology of Ge deposited on a Si substrate. Nonstandard boundary conditions at the material interface are used to model the epitaxially grown film. In addition to determining the deformed geometry, it is also necessary to compute the surface stress tensor. Although the surface displacement at the junction between the interface and the Si free surface is not differentiable, the hypersingular integral equation for surface stress can still be used. These techniques are described along with results from 2-D calculations.
Date: December 31, 1993
Creator: Gray, L.J.; Chisholm, M.F. & Kaplan, T.
Partner: UNT Libraries Government Documents Department

Alternative Gate Dielectrics on Semiconductors for MOSFET Device Applications

Description: We have investigated the synthesis and properties of deposited oxides on Si and Ge for use as alternative gate dielectrics in MOSFET applications. The capacitance and leakage current behavior of polycrystalline Y{sub 2}O{sub 3} films synthesized by pulsed-laser deposition is reported. In addition, we also discuss the growth of epitaxial oxide structures. In particular, we have investigated the use of silicide termination for oxide growth on (001) Si using laser-molecular beam epitaxy. In addition, we discuss a novel approach involving the use of hydrogen to eliminate native oxide during initial dielectric oxide nucleation on (001) Ge.
Date: December 6, 1999
Creator: Norton, D.P.; Budai, J.D.; Chisholm, M.F.; Pennycook, S.J.; McKee, R.; Walker, F. et al.
Partner: UNT Libraries Government Documents Department

Ion beam synthesis of nanocrystals and quantum dots in optical materials

Description: High-dose ion implantation has been used to synthesize a wide range of nanocrystals and quantum dots, and these structures can be encapsulated in a number of host materials using this technique.
Date: June 1, 1996
Creator: White, C.W.; Budai, J.D.; Withrow, S.P.; Zhu, J.G.; Pennycook, S.J; Magruder, R.H. et al.
Partner: UNT Libraries Government Documents Department

Plasma analysis and diagnostics for high efficiency amorphous solar cell production. Final report

Description: This is a project that sought to improve the amorphous silicon-germanium (SiGe) thin film deposition process in the production of solar cells. To accomplish this, the electron cyclotron resonance (ECR) plasma discharge, employed for the thin film deposition, was modified. Changes in the parameters of the plasma were monitored with diagnostic techniques, similar to those used in fusion plasma studies. That was the primary contribution from ORNL. Only one phase was contained in the statement of work, with the following tasks: (1) Develop a detailed program for plasma characterization. (2) Carry-out plasma modeling and analysis to support deposition systems design. (3) Operate experimental deposition systems for the purpose of plasma characterization. (4) Analyze data. (5) Modify deposition as directed by measurements. (6) This final report, which was deemed to be the only deliverable of this small project. And while the modified ECR discharge did not show measurable improvement of the conditions relevant to the deposition process, much was learned about the plasma parameters in the process. Some ideas on alternative designs are being discuss and funding options for testing such designed are being sought.
Date: December 21, 1994
Creator: Klepper, C.C.
Partner: UNT Libraries Government Documents Department

Development of a short pulse Ne-like x-ray laser

Description: We are developing techniques to shorten the time duration of neon-like x-ray Iners while maintaining their high brightness in order to optimize, their usefulness as a plasma diagnostic. Adjusting the duration of the pump laser pulse is shown to directly influence the duration of neon-like x-ray laser transitions. Using slab targets, multiple 100 ps pulses and traveling wave geometry we have shortened the duration of lasing transitions down to 45 ps for both the neon-like germanium and yttrium x-ray lasers. However for the neon-like yttrium laser the intensity of short duration pulses are down two orders of magnitude from the long duration pulses because of limitations of the driving laser. We are presently looking at curved targets and pulse shaping in order to more efficiently pump the Ne-like x-ray laser system and increase the output intensity of the lasing lines. The relative merits of using the germanium x-ray laser at 196 {Angstrom} compared to the yttrium x-ray laser at 155 {Angstrom} are discussed.
Date: June 1, 1995
Creator: Moreno, J.C.; Cauble, R.C.; Celliers, P.; Da Silva, L.B.; Nilsen, J. & Wan, A.S.
Partner: UNT Libraries Government Documents Department

Germanium Nanocrystals Embedded in Sapphire

Description: {sup 74}Ge nanocrystals are formed in a sapphire matrix by ion implantation followed by damage. Embedded nanocrystals experience large compressive stress relative to bulk, as embedded in sapphire melt very close to the bulk melting point (Tm = 936 C) whereas experience considerably lower stresses. Also, in situ TEM reveals that nanocrystals ion-beam-synthesized nanocrystals embedded in silica are observed to be spherical and measured by Raman spectroscopy of the zone center optical phonon. In contrast, reveals that the nanocrystals are faceted and have a bi-modal size distribution. Notably, the matrix remains crystalline despite the large implantation dose and corresponding thermal annealing. Transmission electron microscopy (TEM) of as-grown samples those embedded in silica exhibit a significant melting point hysteresis around T{sub m}.
Date: April 15, 2005
Creator: Xu, Q.; Sharp, I. D.; Liao, C. Y.; Yi, D. O.; Ager, J. W., III; Beeman, J. W. et al.
Partner: UNT Libraries Government Documents Department

A Scanning Tunneling Microscopy Study of As/Ge(mnn) and P/Ge(mnn) Surfaces

Description: Ge(mnn) surfaces between (100) and (111) were annealed under either arsine or phosphine in a metal-organic chemical vapor deposition chamber, then imaged with a scanning tunneling microscope. In general, arsine-exposed Ge surfaces are facetted, while phosphine-exposed surfaces remain flat. For the arsine-exposed Ge surfaces, four stable facetting directions have been identified: (100), (11,3,3), (955), and (111).
Date: November 14, 2000
Creator: McMahon, W.E. & Olsen, J.M.
Partner: UNT Libraries Government Documents Department

SIMS Characterization of Amorphous Silicon Germanium Alloys Grown by Hot-Wire Deposition

Description: In this paper, we present methods for the quantitative secondary ion mass spectrometry (SIMS) characterization of amorphous SiGe:H alloy materials. A set of samples was grown with germanium content ranging from 5% to 77% and was subsequently analyzed by electron probe X-ray microanalysis (EPMA) and nuclear reaction analysis (NRA). Calibration of the SIMS quantification was performed with respect to EPMA data for germanium and NRA data for hydrogen.
Date: October 16, 1998
Creator: Reedy, R. C.; Mason, A. R.; Nelson, B. P. & Xu, Y.
Partner: UNT Libraries Government Documents Department

Low temperature carrier transport properties in isotopically controlled germanium

Description: Investigations of electronic and optical properties of semiconductors often require specimens with extremely homogeneous dopant distributions and precisely controlled net-carrier concentrations and compensation ratios. The previous difficulties in fabricating such samples are overcome as reported in this thesis by growing high-purity Ge single crystals of controlled {sup 75}Ge and {sup 70}Ge isotopic compositions, and doping these crystals by the neutron transmutation doping (NTD) technique. The resulting net-impurity concentrations and the compensation ratios are precisely determined by the thermal neutron fluence and the [{sup 74}Ge]/[{sup 70}Ge] ratios of the starting Ge materials, respectively. This method also guarantees unprecedented doping uniformity. Using such samples the authors have conducted four types of electron (hole) transport studies probing the nature of (1) free carrier scattering by neutral impurities, (2) free carrier scattering by ionized impurities, (3) low temperature hopping conduction, and (4) free carrier transport in samples close to the metal-insulator transition.
Date: December 1994
Creator: Itoh, K.
Partner: UNT Libraries Government Documents Department

Electronic processes in uniaxially stressed p-type germanium

Description: Effect of uniaxial stress on acceptor-related electronic processes in Ge single crystals doped with Ga, Be, and Cu were studied by Hall and photo-Hall effect measurements in conjunction with infrared spectroscopy. Stress dependence of hole lifetime in p-type Ge single crystals is used as a test for competing models of non-radiative capture of holes by acceptors. Photo-Hall effect shows that hole lifetime in Ga- and Be-doped Ge increases by over one order of magnitude with uniaxial stress at liq. He temps. Photo-Hall of Ge:Be shows a stress-induced change in the temperature dependence of hole lifetime. This is consistent with observed increase of responsivity of Ge:Ga detectors with uniaxial stress. Electronic properties of Ge:Cu are shown to change dramatically with uniaxial stress; the results provide a first explanation for the performance of uniaxially stressed, Cu-diffused Ge:Ga detectors which display a high conductivity in absence of photon signal and therefore have poor sensitivity.
Date: February 1, 1996
Creator: Dubon, O.D. Jr.
Partner: UNT Libraries Government Documents Department

LBNL report of the vetting review of the GRETINA project

Description: GRETINA is a gamma-ray detector array capable of reconstructing the energy and spatial positions of gamma-ray interactions within the germanium crystals. It will be used to study the structure and stability of nuclei under various conditions. The new capabilities provided by gamma-ray tracking will give large gains in sensitivity for a large number of experiments, particularly those aimed at nuclei far from beta stability. A proposal for GRETINA was submitted to DOE in June 2003. It presented the scientific case, the readiness of technical development, the design, the suggested management organizations, and a proposed cost and schedule. The GRETINA proposal received its CD0 approval in August 2003. The CD-1 review will be held on December 3 and 4, 2003, and will be handled by the DOE-N. This report presents the charge to the GRETINA vetting review committee, and the findings, comments and recommendations of this committee. The purpose of this project vetting review was to assure that the GRETINA project is on track to provide DOE and the nuclear physics community with the agreed upon deliverables within the agreed upon budget and schedule. The vetting review committee was asked to cover both technical and management aspects of the GRETINA Project. Reviewers offer expert knowledge in relevant areas and provide recommendations and findings to the project's management team. Upon successful completion, the Laboratory's Integrated Project Management Office (IPMO) will recommend signoff of the project to the Laboratory Directorate. The GRETINA vetting review committee was asked to consider all relevant aspects of the project's management, project execution plan (PEP), technical approach and status, cost estimate, resources, schedule and risk and, in doing so, to advise as to whether the GRETINA Project was likely to successfully provide the agreed upon deliverables within the agreed upon budget and schedule. The review committee was asked ...
Date: March 29, 2004
Creator: Robinson, K.E.; Bercovitz, J.H.; Bieser, F.S.; Jared, R.C.; Karpenko, V.P.; Klein, S.R. et al.
Partner: UNT Libraries Government Documents Department