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Direct observation and measurements of neutron induced deep levels responsible for N{sub eff} changes in high resistivity silicon detectors using TCT

Direct observation and measurements of neutron induced deep levels responsible for N{sub eff} changes in high resistivity silicon detectors using TCT

Date: March 1, 1996
Creator: Li, Z.; Li, C.J.; Eremin, V. & Verbitskaya, E.
Description: Neutron induced deep levels responsible for changes of space charge concentration {ital N{sub eff}} in high resistivity silicon detectors have been observed directly using the transient current technique (TCT). It has been observed by TCT that the absolute value and sign of {ital N{sub eff}} experience changes due to the trapping of non- equilibrium free carriers generated near the surface (about 5 micrometers depth into the silicon) by short wavelength laser pulses in fully depleted detectors. Electron trapping causes {ital N{sub eff}} to change toward negative direction (or more acceptor-like space charges) and hole trapping causes {ital N{sub eff}} to change toward positive direction (or more donor-like space charges). The specific temperature associated with these {ital N{sub eff}} changes are those of the frozen-up temperatures for carrier emission of the corresponding deep levels. The carrier capture cross sections of various deep levels have been measured directly using different free carrier injection schemes. 10 refs., 12 figs., 3 tabs.
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DIRECT OBSERVATION DETONATOR OPERATION

DIRECT OBSERVATION DETONATOR OPERATION

Date: June 1, 2001
Creator: HALL, C. R.
Description: No abstract prepared.
Contributing Partner: UNT Libraries Government Documents Department
Direct Observation of Hydrides Formation in Cavity-Grade Niobium

Direct Observation of Hydrides Formation in Cavity-Grade Niobium

Date: August 1, 2012
Creator: Barkov, F.; Romanenko, A. & /Fermilab
Description: No abstract prepared.
Contributing Partner: UNT Libraries Government Documents Department
Direct Observation of IBW Induced Poloidal Flow in TFTR

Direct Observation of IBW Induced Poloidal Flow in TFTR

Date: November 1, 1998
Creator: Bell, R.E.; Bernabei, S.; Hosca, J.C.; LeBlanc, B.P.; Majeski, R. & al., et
Description: Shearing of the plasma poloidal rotation velocity was observed during application of ion Bernstein wave IBW) power in the Tokamak Fusion Test Reactor (TFTR) tokamak. The first evidence of corroboration between measured poloidal velocity shearing and actively induced Reynolds stress effects is presented. A model reproduces salient experimental features: The observed sheared flow occurs near the tritium fifth harmonic cyclotron resonance layer and depends strongly on the tritium density, in agreement with the model. Furthermore, the model reproduces the observed insensitivity of the induced rotation to the tritium density in the region between the third deuterium harmonic layer and the fifth tritium harmonic layer.
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Direct observation of imprinted antiferromagnetic vortex state in CoO/Fe/Ag(001) disks

Direct observation of imprinted antiferromagnetic vortex state in CoO/Fe/Ag(001) disks

Date: December 21, 2010
Creator: Wu, J.; Carlton, D.; Park, J. S.; Meng, Y.; Arenholz, E.; Doran, A. et al.
Description: In magnetic thin films, a magnetic vortex is a state in which the magnetization vector curls around the center of a confined structure. A vortex state in a thin film disk, for example, is a topological object characterized by the vortex polarity and the winding number. In ferromagnetic (FM) disks, these parameters govern many fundamental properties of the vortex such as its gyroscopic rotation, polarity reversal, core motion, and vortex pair excitation. However, in antiferromagnetic (AFM) disks, though there has been indirect evidence of the vortex state through observations of the induced FM-ordered spins in the AFM disk, they have never been observed directly in experiment. By fabricating single crystalline NiO/Fe/Ag(001) and CoO/Fe/Ag(001) disks and using X-ray Magnetic Linear Dichroism (XMLD), we show direct observation of the vortex state in an AFM disk of AFM/FM bilayer system. We observe that there are two types of AFM vortices, one of which has no analog in FM structures. Finally, we show that a frozen AFM vortex can bias a FM vortex at low temperature.
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Direct observation of mobile protons in SiO{sub 2} thin films: Potential application in a novel memory device

Direct observation of mobile protons in SiO{sub 2} thin films: Potential application in a novel memory device

Date: December 31, 1996
Creator: Vanheusden, K.; Warren, W.L. & Fleetwood, D.M.
Description: In this work we show that annealing of silicon/silicon-dioxide/silicon structures in forming gas (N{sub 2}:H{sub 2}; 95:5) above 500{degrees}C leads to spontaneous incorporation of mobile H{sup +} ions in the buried SiO{sub 2} layer. We demonstrate that, unlike the alkali ions feared as killer contaminants in the early days, the space charge distribution of these mobile protons within the buried oxide layer can be very well controlled and easily rearranged with relatively high speed at room temperature. The hysteresis in the flat band voltage shift provides a unique vehicle to study proton kinetics in silicon dioxide thin films. It is further shown how this effect can be used as the basis for a reliable nonvolatile FET memory device that has potential to be competitive with state-of-the-art Si-based memory technologies. The power of this novel device is its simplicity; it requires few processing steps, all of which are standard in Si integrated-circuit fabrication.
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Direct Observation of Phase Transformations in Austenitic Stainless Steel Welds Using In-situ Spatially Resolved and Time-resolved X-ray Diffraction

Direct Observation of Phase Transformations in Austenitic Stainless Steel Welds Using In-situ Spatially Resolved and Time-resolved X-ray Diffraction

Date: September 23, 1999
Creator: Elmer, J.; Wong, J. & Ressler, T.
Description: Spatially resolved x-ray diffraction (SRXRD) and time resolved x-ray diffraction (TRXRD) were used to investigate real time solid state phase transformations and solidification in AISI type 304 stainless steel gas tungsten arc (GTA) welds. These experiments were conducted at Stanford Synchrotron Radiation Laboratory (SSRL) using a high flux beam line. Spatially resolved observations of {gamma} {leftrightarrow} {delta} solid state phase transformations were performed in the heat affected zone (HAZ) of moving welds and time-resolved observations of the solidification sequence were performed in the fusion zone (FZ) of stationary welds after the arc had been terminated. Results of the moving weld experiments showed that the kinetics of the {gamma}{yields}{delta} phase transformation on heating in the HAZ were sufficiently rapid to transform a narrow region surrounding the liquid weld pool to the {delta} ferrite phase. Results of the stationary weld experiments showed, for the first time, that solidification can occur directly to the {delta} ferrite phase, which persisted as a single phase for 0.5s. Upon solidification to {delta}, the {delta} {yields} {gamma} phase transformation followed and completed in 0.2s as the weld cooled further to room temperature.
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Direct observation of resonance effects in laser cluster interactions

Direct observation of resonance effects in laser cluster interactions

Date: June 1, 1999
Creator: Zweiback, J
Description: Time resolved dynamics of high intensity laser interactions with atomic clusters have been studied with both theoretical analysis and experiment. A short-pulse Ti:sapphire laser system, which could produce 50 mJ of energy in a 50 fs pulse, was built to perform these experiments. The laser used a novel single grating stretcher and was pumped, in part, by a custom Nd:YLF laser system, including 19 mm Nd:YLF amplifiers. It was found that there is an optimal pulse width to maximize absorption for a given cluster size. This optimal pulse width ranged from 400 fs for 85 A radius xenon clusters to 1.2 ps for 205 {angstrom} radius xenon clusters. Using a pump-probe configuration, the absorption of the probe radiation was observed to reach a maximum for a particular time delay between pump and probe, dependent on the cluster size. The delay for peak absorption was 800, 1400, and 2100 fs for 85 {angstrom}, 130 {angstrom}, and 170 {angstrom} radius xenon clusters respectively. Model calculations suggest that these effects are due to resonant heating of the spherical plasma in agreement with the hydrodynamic interpretation of cluster interactions. While this simple hydrodynamic code produces reasonable agreement with data, it does not include bulk ...
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Direct observation of surface ethyl to ethane interconversion uponC2H4 hydrogenation over Pt/Al2O3 catalyst by time-resolved FT-IRspectroscopy

Direct observation of surface ethyl to ethane interconversion uponC2H4 hydrogenation over Pt/Al2O3 catalyst by time-resolved FT-IRspectroscopy

Date: December 10, 2004
Creator: Wasylenko, Walter & Frei, Heinz
Description: Time-resolved FT-IR spectra of ethylene hydrogenation over alumina-supported Pt catalyst were recorded at 25 ms resolution in the temperature range 323 to 473 K using various H2 flow rates (1 atm total gas pressure). Surface ethyl species (2870 and 1200 cm-1) were detected at all temperatures along with the gas phase ethane product (2954 and 2893 cm-1). The CH3CH2Pt growth was instantaneous on the time scale of 25ms under all experimental conditions. At 323 K, the decay time of surface ethyl (122 + 10 ms) coincides with the rise time of C2H6 (144 + 14 ms).This establishes direct kinetic evidence for surface ethyl as the kinetically relevant intermediate. Such a direct link between the temporal behavior of an observed intermediate and the final product growth in a heterogeneous catalytic system has not been demonstrated before to our knowledge. A fraction (10 percent) of the asymptotic ethane growth at 323 K is prompt, indicating that there are surface ethyl species that react much faster than the majority of the CH3CH2Pt intermediates. The dispersive kinetics is attributed to the varying strength of interaction of the ethyl species with the Pt surface caused by heterogeneity of the surface environment. At 473 K, the ...
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Direct Observation of the alpha-epsilon Transition in Shock-compressed Iron via Nanosecond X-ray Diffraction

Direct Observation of the alpha-epsilon Transition in Shock-compressed Iron via Nanosecond X-ray Diffraction

Date: March 21, 2005
Creator: Kalantar, D H; Belak, J F; Collins, G W; Colvin, J D; Davies, H M; Eggert, J H et al.
Description: In-situ x-ray diffraction studies of iron under shock conditions confirm unambiguously a phase change from the bcc ({alpha}) to hcp ({var_epsilon}) structure. Previous identification of this transition in shock-loaded iron has been inferred from the correlation between shock wave-profile analyses and static high-pressure x-ray measurements. This correlation is intrinsically limited because dynamic loading can markedly affect the structural modifications of solids. The in-situ measurements are consistent with a uniaxial collapse along the [001] direction and shuffling of alternate (110) planes of atoms, and in good agreement with large-scale non-equilibrium molecular dynamics simulations.
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Direct observation of threading dislocations in GaN by high-resolution Z-contrast imaging

Direct observation of threading dislocations in GaN by high-resolution Z-contrast imaging

Date: February 1, 1998
Creator: Xin, Y.; Browning, N.D.; Sivananthan, S.; Pennycook, S.J.; Nellist, P.D.; FAurie, J.P. et al.
Description: Wide gap nitride semiconductors have attracted significant attention recently due to their promising performance as short-wavelength light emitting diodes (LEDs) and blue lasers. One interesting issue concerning GaN is that the material is relatively insensitive to the presence of a density of dislocations which is six orders of magnitude higher than that for III-V arsenide and phosphide based LEDs. Although it is well known that these dislocations originate at the film-substrate interface during film growth, thread through the whole epilayer with line direction along <0001> and are perfect dislocations with Burgers vectors of a, c, or c+a, the reason why they have such a small effect on the properties of GaN is unclear. To develop a fundamental understanding of the properties of these dislocations, the core structures are studied here by high resolution Z-contrast imaging in a 300kV VG HB603 scanning transmission electron microscope (STEM) with a resolution of 0.13 nm. As the Z-contrast image is a convolution between the probe intensity profile and the specimen object function, it is possible to obtain more detailed information on the specimen object function, i.e. the structure, through maximum entropy analysis (the maximum entropy technique produces the ``most likely`` object function which is ...
Contributing Partner: UNT Libraries Government Documents Department
Direct observation of two-step crystallization in nanoparticle superlattice formation

Direct observation of two-step crystallization in nanoparticle superlattice formation

Date: October 6, 2011
Creator: Park, Jungwon; Zheng, Haimei; Lee, Won Chul; Geissler, Phillip L.; Rabani, Eran & Alivisatos, A. Paul
Description: Direct imaging of nanoparticle solutions by liquid phase transmission electron microscopy has enabled unique in-situ studies of nanoparticle motion and growth. In the present work, we report on real-time formation of two-dimensional nanoparticle arrays in the very low diffusive limit, where nanoparticles are mainly driven by capillary forces and solvent fluctuations. We find that superlattice formation appears to be segregated into multiple regimes. Initially, the solvent front drags the nanoparticles, condensing them into an amorphous agglomerate. Subsequently, the nanoparticle crystallization into an array is driven by local fluctuations. Following the crystallization event, superlattice growth can also occur via the addition of individual nanoparticles drawn from outlying regions by different solvent fronts. The dragging mechanism is consistent with simulations based on a coarse-grained lattice gas model at the same limit.
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Direct observations of atomic structures of defects in GaN by high-resolution Z-contrast STEM

Direct observations of atomic structures of defects in GaN by high-resolution Z-contrast STEM

Date: December 1, 1997
Creator: Xin, Y.; Pennycook, S.J.; Browning, N.D.; Sivananthan, S.; Nellist, P.D.; Faurie, J.P. et al.
Description: GaN/(0001) Sapphire grown by low pressure MOVPE is studied by high resolution Z-contrast imaging using STEM. First direct observation of the threading dislocation with edge character shows the atomic core structure, which appears to have a similar configuration to the {l_brace}10-10{r_brace} surface. The surfaces of the nanopipe walls are on {l_brace}10-10{r_brace} with the terminating layer between the atoms with one bond per pair. In addition, the high resolution Z contrast image of the prismatic stacking fault confirms the results by conventional HRTEM.
Contributing Partner: UNT Libraries Government Documents Department
Direct Observations of Defect Structures in Optoelectronic Materials by Z-Contrast STEM

Direct Observations of Defect Structures in Optoelectronic Materials by Z-Contrast STEM

Date: August 31, 1998
Creator: Beaumont, B.; Browning, N.D.; Chen, Y.P.; Faurie, J.-P.; Gibart, P.; Nellist, P.D. et al.
Description: Optoelectronic semiconductor materials have wide and important technological applications. For example, wide gap nitride semiconductors have attracted significant attention recently due to their promising performance as short-wavelength light emitting diodes (LEDs) and blue lasers, while HgCdTe II-VI semiconductors are the most promising candidates for applications as infrared detectors, or large array x-ray or r-ray detectors. In this paper, two examples are given to show that high-resolution Z-contrast imaging is an effective technique to determine the atomic structures of defects in these complex semiconductor materials.
Contributing Partner: UNT Libraries Government Documents Department
Direct observations of defect structures in optoelectronic materials by Z-contrast STEM

Direct observations of defect structures in optoelectronic materials by Z-contrast STEM

Date: February 1, 1998
Creator: Xin, Y.; Browning, N.D. & Pennycook, S.J.
Description: Optoelectronic semiconductor materials have wide and important technological applications. For example, wide gap nitride semiconductors have attracted significant attention recently due to their promising performance as short-wavelength light emitting diodes (LEDs) and blue lasers, while HgCdTe II-VI semiconductors are the most promising candidates for applications as infrared detectors, or large array x-ray or gamma-ray detectors. In this paper, two examples are given to show that high-resolution Z-contrast imaging is an effective technique to determine the atomic structures of defects in these complex semiconductor materials. One interesting issue concerning GaN is that the material is relatively insensitive to the presence of a density of dislocations which is six orders of magnitude higher than that for III-V arsenide and phosphide based LEDs. To develop a fundamental understanding of the properties of the dislocations in GaN, the core structures are determined here by atomic-resolution Z-contrast imaging in a scanning transmission electron microscope (STEM) with a resolution of 0.13 nm. As the Z-contrast image is a convolution between the probe intensity profile and the specimen object function, it is possible to obtain detailed information on the atomic column positions through maximum entropy analysis. For a sphalerite semiconductor, polarity is an important issue, as the ...
Contributing Partner: UNT Libraries Government Documents Department
Direct Optical Coupling to an Unoccupied Dirac Surface State in the Topological Insulator Bi2Se3

Direct Optical Coupling to an Unoccupied Dirac Surface State in the Topological Insulator Bi2Se3

Date: September 10, 2013
Creator: Sobota, J.A.; Yang, S.-L.; /SIMES, Stanford /SLAC /Stanford U., Geballe Lab /Stanford U., Physics Dept.; Kemper, A.F.; /LBNL, Berkeley; Lee, J.J. et al.
Description: Abstract Not Provided
Contributing Partner: UNT Libraries Government Documents Department
Direct Overt U.S. Aid and Military Reimbursements to Pakistan, FY2002-FY2009

Direct Overt U.S. Aid and Military Reimbursements to Pakistan, FY2002-FY2009

Date: April 20, 2009
Creator: Kronstadt, K. Alan
Description: Aid and military reimbursements made to Pakistan from 2002-2009. The list is divided by agency.
Contributing Partner: UNT Libraries Government Documents Department
Direct Overt U.S. Aid and Military Reimbursements to Pakistan, FY2002-FY2011

Direct Overt U.S. Aid and Military Reimbursements to Pakistan, FY2002-FY2011

Date: February 16, 2010
Creator: Kronstadt, K. Alan
Description: Aid and military reimbursements made to Pakistan from 2002-2011. The list is divided by agency.
Contributing Partner: UNT Libraries Government Documents Department
Direct Overt U.S. Aid Appropriations for and Military Reimbursements to Pakistan, FY2002-FY2014

Direct Overt U.S. Aid Appropriations for and Military Reimbursements to Pakistan, FY2002-FY2014

Date: April 11, 2013
Creator: Kronstadt, K. Alan
Description: This report provides data regarding the direct overt U.S. aid appropriations and military reimbursements to Pakistan.
Contributing Partner: UNT Libraries Government Documents Department
Direct Overt U.S. Aid Appropriations for and Military Reimbursements to Pakistan, FY2002-FY2015

Direct Overt U.S. Aid Appropriations for and Military Reimbursements to Pakistan, FY2002-FY2015

Date: March 6, 2014
Creator: Kronstadt, K. A. & Epstein, Susan
Description: This report provides data regarding the direct overt U.S. aid appropriations and military reimbursements to Pakistan.
Contributing Partner: UNT Libraries Government Documents Department
Direct Overt U.S. Aid Appropriations for and Military Reimbursements to Pakistan, FY2002-FY2015

Direct Overt U.S. Aid Appropriations for and Military Reimbursements to Pakistan, FY2002-FY2015

Date: March 26, 2014
Creator: Kronstadt, K. Alan & Epstein, Susan
Description: This report provides data regarding the direct overt U.S. aid appropriations and military reimbursements to Pakistan.
Contributing Partner: UNT Libraries Government Documents Department
Direct Overt U.S. Aid Appropriations for and Military Reimbursements to Pakistan, FY2002-FY2017

Direct Overt U.S. Aid Appropriations for and Military Reimbursements to Pakistan, FY2002-FY2017

Date: February 24, 2016
Creator: Kronstadt, K. Alan & Epstein, Susan
Description: This report provides data regarding the direct overt U.S. aid appropriations and military reimbursements to Pakistan.
Contributing Partner: UNT Libraries Government Documents Department
Direct participation of electrical loads in the California independent system operator markets during the Summer of 2000

Direct participation of electrical loads in the California independent system operator markets during the Summer of 2000

Date: April 1, 2001
Creator: Marnay, Chris; Hamachi, Kristina S.; Khavkin, Mark & Siddiqui, Afzal S.
Description: California's restructured electricity markets opened on 1 April 1998. The former investor-owned utilities were functionally divided into generation, transmission, and distribution activities, all of their gas-fired generating capacity was divested, and the retail market was opened to competition. To ensure that small customers shared in the expected benefit of lower prices, the enabling legislation mandated a 10% rate cut for all customers, which was implemented in a simplistic way that fossilized 1996 tariff structures. Rising fuel and environmental compliance costs, together with a reduced ability to import electricity, numerous plant outages, and exercise of market power by generators drove up wholesale electricity prices steeply in 2000, while retail tariffs remained unchanged. One of the distribution/supply companies entered bankruptcy in April 2001, and another was insolvent. During this period, two sets of interruptible load programs were in place, longstanding ones organized as special tariffs by the distribution/supply companies and hastily established ones run directly by the California Independent System Operator (CAISO). The distribution/supply company programs were effective at reducing load during the summer of 2000, but because of the high frequency of outages required by a system on the brink of failure, customer response declined and many left the tariff. The ...
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Direct Penetrating Radiation Monitoring Systems: Technical Evaluation for Use at Area G, Los Alamos National Laboratory

Direct Penetrating Radiation Monitoring Systems: Technical Evaluation for Use at Area G, Los Alamos National Laboratory

Date: October 1, 1999
Creator: Kraig, D.; Treadaway, W. A. & Wechsler, R. J.
Description: Recent advances and commercialization of electret-ion-chamber (EIC) technology for photon measurements prompted us to consider EKs as a replacement for our TLD system. After laboratory tests indicated that both systems gave adequate results for controlled exposures, throughout 1998 we conducted field tests with paired TLDs and EICS, in LANL technical areas and in public areas. We had approximately 30 paired sampling sites at Area G. At each sampling site, we deployed three TLDs and three EICS. The EICS were contained in air-tight jars, each of which was placed in a Tyvek envelope and hung about 1 m above the ground. The dosimeters were read (and, if necessary, replaced) every three months. At the sites outside Area G, the TLD readings for the first two quarters were statistically significantly higher than those of the EICS: group average exposures were 38 and 36, compared with 33 mR (both quarters) for the EICS; during quarter 3, the EIC average (40 mR) was higher than the TLD average (34 mR); and during quarter 4, the two systems were statistically the same: EIC = 42, TLD = 41 with a p-value of 0.61. We are still evaluating these differences and performing additional laboratory studies to ...
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