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Deposition and Characterization of Pentacene Film.

Description: Many organic materials have been studied to be used as semiconductors, few of them being pentacene and polythiophene. Organic semiconductors have been investigated to make organic thin film transistors. Pentacene has been used in the active region of the transistors. Transistors fabricated with pentacene do not have very high mobility. But in some applications, high mobility is not needed. In such application other properties of organic transistors are used, such as, ease of production and flexibility. Organic thin film transistors (OTFT) can find use as low density storage devices, such as smart cards or I.D. tags, and displays. OTFT are compatible with polymeric substrates and hence can find use as flexible computer screens. This project aims at making 'smart clothes', the cheap way, with pentacene based OTFT. This problem in lieu of thesis describes a way to deposit pentacene films and characterize it. Pentacene films were deposited on substrates and characterized using x-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The substrate used was ~1500Å platinum on silicon wafer or bare silicon wafer. was used. A deposition system for vacuum deposition of pentacene was assembled. The XRD data for deposited pentacene films shows the presence of two phases, single crystal phase (SCP) and thin film phase (TFP), and the increase in percentage of SCP with increase in substrate temperature during deposition or by annealing the deposited film, in vacuum, at 80°C.
Date: December 2003
Creator: Singh, Nidhi
Partner: UNT Libraries

Edmonds et al. Reply

Description: This article is a response to an article by M. Adell et al. [Phy. Rev. Lett. 94, 139701 (2005)] about semiconductor-based spintronics research.
Date: April 8, 2005
Creator: Edmonds, Kevin; Boguslawski, Piotr; Wang, K. Y.; Campion, Richard Paul; Novikov, Sergei; Farley, N. R. S. et al.
Partner: UNT College of Arts and Sciences

FRACTURE TOUGHNESS OF 6.4 MM (0.25 INCH) ARC-CAST MOLOBDENUM AND MOLYBDENUM-TZM PLATE AT ROOM TEMPERATURE AND 300 DEGREES C

Description: THE FRACTURE TOUGHNESS OF 6.4 mm (0.25 INCH) LOW CARBON ARC-CAST (LCAC) MOLYBDENUM AND ARC-CAST MOLYBDENUM-TZM ALLOY PLATE WERE MEASURED AT ROOM TEMPERATURE AND 300 DEGREES C USING COMPACT TNESION SPECIMENTS. THE EFFECT OF CRACK PLANE ORIENTATION (LONGITUDINAL VS. TRANSVERSE) AND ANNEALING PRACTICE (STRESS-RELIEVED VS. RECRYSTALLIZED) WERE EVALUATED. DEPENDING UPON THE TEST TEMPERATURE EITHER A STANDARD K[SUB]IC OR A J-INTEGRAL ANALYSIS WAS USED TO OBTAIN THE TOUGHNESS VALUE. AT ROOM TEMPERATURE, REGARDLESS OF ALLOY, ORIENTATION, OR MICROSTURECTURE, FRACTURE TOUGHNESS VALUES BETWEEN 15 AND 22 MPa m{sup 1/2} (14 AND 20 KSI IN{sup 1/2}) WERE MEASURED. THESE K[SUB]IC VALUES WERE CONSISTENT WITH MEASUREMENTS BY THE AUTHORS. INCREASING TEMPERATURE IMPROVES THE TOUGHNESS, DUE TO THE FACT THAT ONE TAKES ADVANTAGE OF THE DUCTIVE-BRITTLE TRANSITION BEHAVIOR OF MOLYBDENUM. AT 300 DEGREES C, THE FRACTURE TOUGHNESS OF RECRYSTALLIZED LCAC AND ARC-CAST TZM MOLYBDENUM WERE ALSO SIMILAR AT APPROXI MATELY 64 MPa m{sup 1/2} (58 KSI IN{sup 1/2}). IN THE STRESS-RELIEVED CONDITION, HOWEVER, THE TOUGHNESS OF ARC-CAST TZM (91 MPa m{sup 1/2}/83 KSI IN{sup 1/2}) WAS HIGHER THAN THAT OF THE LCAC MOLYBDENUM (74 MPa m{sup 1/2}/67 KSI IN{sup 1/2}).
Date: April 11, 2001
Creator: J. A. SHIELDS, JR.; LIPETZKY, P. & MUELLER, A. J.
Partner: UNT Libraries Government Documents Department

Defect Doping of InN

Description: InN films grown by molecular beam epitaxy have been subjected to 2 MeV He{sup +} irradiation followed by thermal annealing. Theoretical analysis of the electron mobilities shows that thermal annealing removes triply charged donor defects, creating films with electron mobilities approaching those predicted for uncompensated, singly charged donors. Optimum thermal annealing of irradiated InN can be used to produce samples with electron mobilities higher than those of as grown films.
Date: July 22, 2007
Creator: Jones, R.E.; van Genuchten, H.C.M.; Yu, K.M.; Walukiewicz, W.; Li, S.X.; A ger III, J.W. et al.
Partner: UNT Libraries Government Documents Department

Interface Reactions and Electrical Characteristics of Au/GaSb Contacts

Description: The reaction of Au with GaSb occurs at a relatively low temperature (100 C). Upon annealing, a AuSb{sub 2} compound and several Au-Ga phases are produced. Phase transitions occur toward higher Ga concentration with increasing annealing temperatures. Furthermore, the depth of the contact also increases with increased annealing temperature. They found that the AuSb{sub 2} compound forms on the GaSb surface, with the compound crystal partially ordered with respect to the substrate. The transition of Schottky- to ohmic-contact behavior in Au/n-type GaSb occurs simultaneously with the formation of the AuGa compound at about a 250 C annealing temperature. This ohmic contact forms without the segregation of dopants at the metallic compound/GaSb interface. Therefore it is postulated that transition from Schottky- to ohmic-contact behavior is obtained through a series of tunneling transitions of electrons through defects in the depletion region in the Au/n-type GaSb contacts. Contact resistivities of 6-7 x 10{sup -6} {Omega}-cm{sup 2} were obtained with the annealing temperature between 300 and 350 C for 30 seconds. In Au/p-type GaSb contacts, the resistivity was independent of the annealing temperature. This suggested that the carrier transport in p-type contact dominated by thermionic emission.
Date: July 7, 2000
Creator: Ehsani, H.; Gutmann, R.J. & Charache, G.W.
Partner: UNT Libraries Government Documents Department

High-temperature annealing of natural UO{sub 2+x}

Description: Four powdered samples of natural UO{sub 2+x} (uraninite) were annealed in a reducing atmosphere up to 1200 C. Initial unit cell parameters ranged from a{sub o}=0.5463 to 0.5385 nm. Small amounts of UO{sub 2.25} occur in all samples after annealing. Annealing curves show effects of recovery of point defects in the oxygen sublattice, ordering of U{sup 4+} and U{sup 6+}, vacancy migration in the cation sublattice, and second order phase transformations. Difference in annealing behavior of UO{sub 2+x} with x<0.15 as compared to x=0.25 between 400 and 700 C is due to ordering of U{sup 4+} and U{sup 6+}. Density increased after annealing except for one sample in which a large number of cavities (1-2{mu}m) formed. Oxidation and chemical composition have a more dramatic effect on the structural state of natural UO{sub 2+x} than self-irradiation caused by {alpha}-decay damage.
Date: December 31, 1990
Creator: Janeczek, J. & Ewing, R.C.
Partner: UNT Libraries Government Documents Department

Annealing studies of visible light emission from silicon nanocrystals produced by implantation

Description: The annealing behavior of silicon implanted SiO{sub 2} layers is studied using continuous and time-gated photoluminescence (PL). Two PL emission bands are observed. A band centered at 560 nm is present in as implanted samples and it is still observed after 1000 {degrees}C annealing. The emission time is fast (0.2 -2 ns). A second band centered at 780 nm further increases when hydrogen annealing was performed. The emission time is long (1 {mu}s - 0.3 ms).
Date: December 31, 1996
Creator: Ghislotti, G.; Nielsen, B. & Di Mauro, L.F.
Partner: UNT Libraries Government Documents Department

Mn Interstitial Diffusion in (Ga, Mn)As

Description: This article describes a combined theoretical and experimental study of the ferromagnetic semiconductor (Ga, Mn)As which explains the remarkably lard changes observed on low-temperature annealing.
Date: January 23, 2004
Creator: Edmonds, Kevin; Boguslawski, Piotr; Wang, K. Y.; Campion, Richard Paul; Novikov, Sergei; Farley, N. R. S. et al.
Partner: UNT College of Arts and Sciences

Correlation between Crystallographic and Magnetic Domains at Co/NiO(001) Interfaces

Description: Using soft x-ray spectromicroscopy we show that NiO(001) exhibits a crystallographic and magnetic domain structure near the surface identical to that of the bulk. Upon Co deposition a perpendicular coupling between the Ni and Co moments is observed that persists even after formation of uncompensated Ni spins at the interface through annealing. The chemical composition at the interface alters its crystallographic structure and leads to a reorientation of the Ni moments from the &lt;112&gt; to the &lt;110&gt; direction. We show that this reorientation is driven by changes in the magnetocrystalline anisotropy rather than exchange coupling mediated by residual uncompensated spins.
Date: December 18, 2008
Creator: Ohldag, H.; van der Laan, G. & Arenholz, E.
Partner: UNT Libraries Government Documents Department

Role of Ionizztion in Radiatin Annealing

Description: The role of ionization in the phenomenon of" radiation annealing" of graphite has been studied by using a I-MeV electron beam. Changes in the C-axis of a sample with a Hanford irradiation of 460 Mwd/ct were studied. Two thermal anneals of 4 hours each at 350{degree}C proved sufficient to complete the thermal annealing at this temperature. The samples were then irradiated for 7 {1I2} hrs at a temperature of 340 {degree}c. The samples received an irradiation of 47 microampere-hours, equivalent in ionization to an exposure of 200 Mwd/ct in a Hanford reactor. No changes were noted as a result of the electron bombardment. It is concluded that the ionization is not of major importance in radiation annealing.
Date: October 1, 1954
Creator: McClelland, J.D.; Smith, A.W. & Senkovits, E.J.
Partner: UNT Libraries Government Documents Department

Atomistic Simulations of Grain Boundary Pinning in CuFe Alloys

Description: The authors apply a hybrid Monte Carlo-molecular dynamics code to the study of grain boundary motion upon annealing of pure Cu and Cu with low concentrations of Fe. The hybrid simulations account for segregation and precipitation of the low solubility Fe, together with curvature driven grain boundary motion. Grain boundaries in two different systems, a {Sigma}7+U-shaped half-loop grain and a nanocrystalline sample, were found to be pinned in the presence of Fe concentrations exceeding 3%.
Date: May 22, 2005
Creator: Zepeda-Ruiz, L A; Gilmer, G H; Sadigh, B; Caro, J A & Oppelstrup, T
Partner: UNT Libraries Government Documents Department

Stable, free-standing Ge nanocrystals

Description: Free-standing Ge nanocrystals that are stable under ambient conditions have been synthesized in a two-step process. First, nanocrystals with a mean diameter of 5 nm are grown in amorphous SiO{sub 2} by ion implantation followed by thermal annealing. The oxide matrix is then removed by selective etching in diluted HF to obtain free-standing nanocrystals on a Si wafer. After etching, nanocrystals are retained on the surface and the size distribution is not significantly altered. Free-standing nanocrystals are stable under ambient atmospheric conditions, suggesting formation of a self-limiting native oxide layer. For free-standing as opposed to embedded Ge nanocrystals, an additional amorphous-like contribution to the Raman spectrum is observed and is assigned to surface reconstruction-induced disordering of near-surface atoms.
Date: January 28, 2005
Creator: Sharp, I.D.; Xu, Q.; Liao, C.Y.; Yi, D.O.; Beeman, J.W.; Liliental-Weber, Z. et al.
Partner: UNT Libraries Government Documents Department

EXTENSION OF OPERATING LIFE OF KAPL-30 THIMBLE

Description: Due to extended low-temperature operation of the KAPL30 carbon steel thimble in the Materials Testing Reactor, a radiation damage evaluation was undertaken. Radiation damage in carbon steel may not be annealed under lowtemperature operating conditions. The data used in the evaluation are presented, and an extension of thimble life to 16 reactor cycles is recommended, subject to review if further low-temperature operation occurs. (D.E.B.)
Date: July 22, 1957
Creator: Lewis, D.M.
Partner: UNT Libraries Government Documents Department

Evaluation of Annealing Treatments for Producing Si-Rich Fuel/Matrix Interaction Layers in Low-Enriched U-Mo Dispersion Fuel Plates Rolled at a Low Temperature

Description: During fabrication of U-7Mo dispersion fuels, exposure to relatively high temperatures affects the final microstructure of a fuel plate before it is inserted into a reactor. One impact of this high temperature exposure is a chemical interaction that can occur between dissimilar materials. For U-7Mo dispersion fuels, the U-7Mo particles will interact to some extent with the Al or Al alloy matrix to produce interaction products. It has been observed that the final irradiation behavior of a fuel plate can depend on the amount of interaction that occurs at the U-7Mo/matrix interface during fabrication, along with the type of phases that develop at this interface. For the case where a U-7Mo dispersion fuel has a Si-containing Al alloy matrix and is rolled at around 500°C, a Si-rich interaction product has been observed to form that can potentially have a positive impact on fuel performance during irradiation. This interaction product can exhibit stable irradiation behavior and it can act as a diffusion barrier to additional U-Mo/matrix interaction during irradiation. However, for U-7Mo dispersion fuels with softer claddings that are rolled at lower temperatures (e.g., near 425°C), a significant interaction layer has not been observed to form. As a result, the bulk of any interaction layer that develops in these fuels happens during irradiation, and the layer that forms may not exhibit as stable a behavior as one that is formed during fabrication. Therefore, it may be beneficial to add a heat treatment step during the fabrication of dispersion fuel plates with softer cladding alloys that will result in the formation of a uniform, Si-rich interaction layer that is a few microns thick around the U-Mo fuel particles. This type of layer would have characteristics like the one that has been observed in dispersion fuel plates with AA6061 cladding that are fabricated ...
Date: June 1, 2010
Creator: Dennis D. Keiser, Jr.; Jue, Jan-Fong & Woolstenhulme, Nicolas E.
Partner: UNT Libraries Government Documents Department

Thermal modification of microstructures and grain boundaries in silicon carbide

Description: Polycrystalline SiC samples hot-pressed with aluminum, boron, and carbon sintering additions (ABC-SiC) were characterized using transmission electron microscopy. The study focused on the effects of high temperature treatment on microstructure.
Date: May 23, 2003
Creator: Zhang, Xiao Feng & De Jonghe, Lutgard C.
Partner: UNT Libraries Government Documents Department

Transmission electron microscopy study in-situ of radiation-induced defects in copper at elevated temperatures

Description: Neutrons and high-energy ions incident upon a solid can initiate a displacement collision cascade of lattice atoms resulting in localized regions within the solid containing a high concentration of interstitial and vacancy point defects. These point defects can collapse into various types of dislocation loops and stacking fault tetrahedra (SFT) large enough that their lattice strain fields are visible under diffraction-contrast imaging using a Transmission Electron Microscope (TEM). The basic mechanisms driving the collapse of point defects produced in collision cascades is investigated in situ with TEM for fcc-Cu irradiated with heavy (100 keV Kr) ions at elevated temperature. The isothermal stability of these clusters is also examined in situ. Areal defect yields were observed to decrease abruptly for temperatures greater than 300 C. This decrease in defect yield is attributed to a proportional decrease in the probability of collapse of point defects into clusters. The evolution of the defect density under isothermal conditions appears to be influenced by three different rate processes active in the decline of the total defect density. These rate constants can be attributed to differences in the stability of various types of defect clusters and to different loss mechanisms. Based upon observed stabilities, estimations for the average binding enthalpies of vacancies to SFT are calculated for copper.
Date: December 1, 1996
Creator: Daulton, T.L.; Kirk, M.A. & Rehn, L.E.
Partner: UNT Libraries Government Documents Department

Atomic scale modeling of boron transient diffusion in silicon

Description: We presents results from a predictive atomic level simulation of Boron diffusion in Silicon under a wide variety of implant and annealing conditions. The parameters for this simulation have been extracted from first principle approximation models and molecular dynamics simulations. The results are compared with experiments showing good agreement in all cases. The parameters and reactions used have been implemented into a continuum-level model simulator.
Date: June 17, 1998
Creator: Caturla, M. J.; Diaz de la Rubia, T.; Foad, M.; Giles, M.; Johnson, M. D.; Law, M. et al.
Partner: UNT Libraries Government Documents Department

Effect of ramp rate and annealing temperature on boron transient diffusion in implanted silicon: kinetic Monte Carlo simulations

Description: We present results of recent kinetic Monte Carlo simulations of the effect of annealing time and ramp rate on boron transient enhanced diffusion (BTED) in low energy ion implanted silicon. The simulations use a database of defect and dopant energetics derived from first principle calculations. We discuss the complete atomistic details of defect and dopant clustering during the anneals, and the dependence of boron TED on ramp rate. The simulations provide a complete time history of the evolution of the active boron fraction during the anneal for a wide variety of conditions. We also studied the lateral spreading of the boron during the annealing for two different conditions, furnace anneal and ramp anneal.
Date: June 17, 1998
Creator: Caturla, M. J.; Diaz de la Rubia, T. & Foad, M.
Partner: UNT Libraries Government Documents Department

Atom Probe Tomography Characterization of the Solute Distributions in a Neutron-Irradiated and Annealed Pressure Vessel Steel Weld

Description: A combined atom probe tomography and atom probe field ion microscopy study has been performed on a submerged arc weld irradiated to high fluence in the Heavy-Section Steel irradiation (HSSI) fifth irradiation series (Weld 73W). The composition of this weld is Fe - 0.27 at. % Cu, 1.58% Mn, 0.57% Ni, 0.34% MO, 0.27% Cr, 0.58% Si, 0.003% V, 0.45% C, 0.009% P, and 0.009% S. The material was examined after five conditions: after a typical stress relief treatment of 40 h at 607 C, after neutron irradiation to a fluence of 2 x 10{sup 23} n m{sup {minus}2} (E &gt; 1 MeV), and after irradiation and isothermal anneals of 0.5, 1, and 168 h at 454 C. This report describes the matrix composition and the size, composition, and number density of the ultrafine copper-enriched precipitates that formed under neutron irradiation and the change in these parameters with post-irradiation annealing treatments.
Date: January 30, 2001
Creator: Miller, M.K.
Partner: UNT Libraries Government Documents Department