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Pyramidal Defects in GaN:Mg Grown with Ga Polarity

Description: Transmission electron microscopy (TEM) studies show formation of different types of Mg-rich defects in GaN. Types of defects strongly depend on crystal growth polarity. For bulk crystals grown with N-polarity, the planar defects are distributed at equal distances (20 unit cells of GaN). For growth with Ga-polarity (for both bulk and MOCVD grown crystals) a different type of defects have been found. These defects are three-dimensional Mg-rich hexagonal pyramids (or trapezoids) with their base on… more
Date: February 15, 2005
Creator: Liliental-Weber, Zuzanna; Tomaszewicz, Tomasz; Zakharov, Dmitri & O'Keefe, Michael A.
Partner: UNT Libraries Government Documents Department
open access

Atomistic Simulation of Defect Properties in BCC Tantalum

Description: The fundamental atomic-level properties of point and line defects in bcc Ta have been simulated by means of quantum-based multi-ion interatomic potentials derived from the model generalized pseudopotential theory (MGPT). The potentials have been applied to the calculations of point defect formation and migration energies. The results are then compared with the ab-initio electronic-structure results and experimental data, which in turn provide rigorous validation tests of the MGPT potentials. Ro… more
Date: April 19, 2002
Creator: Yang, L H; Soderlind, P & Moriarty, J A
Partner: UNT Libraries Government Documents Department
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Final report. Defects and transport in mixed oxides

Description: New results on the point defect chemistry of (Ni{sub x}Fe{sub 1-x}){sub 3-delta}O{sub 4} and on the cation tracer diffusion in this spinel solid solution are presented and discussed. The equation system for the defect chemistry of perovskites of the type A{sub 1-x}B{sub 1+x}O{sub 3-delta} have been worked out and used to derive Kr{umlt o}ger-Vink diagrams. The deviation from stoichiometry, delta, in LA{sub 1-x}Mn{sub 1+x}O{sub 3-delta} has been measured at 1100, 1200, and 1300 degrees Celsius a… more
Date: December 13, 2001
Creator: Dieckmann, R {umlt u}diger
Partner: UNT Libraries Government Documents Department
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Atomistic models of point defects in plutonium metal.

Description: The aging properties of plutonium (Pu) metal and alloys are. driven by a combination of materials composit ion, p rocessing history, and self-irradiat ion effects . Understanding these driving forces requires a knowledge of both t h ermodynamic and defect properties of the material . The multiplicity of phases and the small changes in tempe rat u re, pressure, and/or stress that can induce phase changes lie at the heart of these properties . In terms of radiation damage, Pu metal represents a u… more
Date: January 1, 2003
Creator: Valone, S. M. (Steven M.); Baskes, M. I. (Michael I.); Uberuaga, B. P. (Blas Pedro) & Voter, A. F.
Partner: UNT Libraries Government Documents Department
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Defects at the carbon terminated SiC (001) surface

Description: We present first principle molecular dynamics simulations for selected point defects on the (001) stoichiometric carbon terminated surface of cubic Silicon Carbide. In particular we investigated missing units and coordination defects. The results of our calculations are compared with recent experiments, in particular we discuss simulated STM images, which are in good agreement with measured ones.
Date: July 24, 2000
Creator: Catellani, A & Galli, G
Partner: UNT Libraries Government Documents Department
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Determining the Critcial Size of EUV Mask Substrate Defects

Description: Determining the printability of substrate defects beneath the extreme ultraviolet (EUV) reflecting multilayer stack is an important issue in EUVL lithography. Several simulation studies have been performed in the past to determine the tolerable defect size on EUV mask blank substrates but the industry still has no exact specification based on real printability tests. Therefore, it is imperative to experimentally determine the printability of small defects on a mask blanks that are caused by sub… more
Date: February 28, 2008
Creator: Mccall, Monnikue M.; Han, Hakseung; Cho, Wonil; Goldberg, Kenneth; Gullikson, Eric; Jeon, Chan-Uk et al.
Partner: UNT Libraries Government Documents Department
open access

Defect Measurements of CdZnTe Detectors Using I-DLTS, TCT, I-V and Gamma-ray Spectroscopy

Description: In this work we measured the crystal defect levels and tested the performance of CdZnTe detectors by diverse methodologies, viz., Current Deep Level Transient Spectroscopy (I-DLTS), Transient Current Technique (TCT), Current and Capacitance versus Voltage measurements (I-V and C-V), and gamma-ray spectroscopy. Two important characteristics of I-DLTS technique for advancing this research are (1) it is applicable for high-resistivity materials (>10{sup 6} {Omega}-cm), and, (2) the minimum temp… more
Date: August 11, 2008
Creator: Gul,R.
Partner: UNT Libraries Government Documents Department
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Point defect production, geometry and stability in silicon: A molecular dynamics simulation study

Description: We present results of molecular dynamics computer simulation studies of the threshold energy for point defect production in silicon. We employ computational cells with 8000 atoms at ambient temperature of 10 K that interact via the Stillinger-Weber potential. Our simulations address the orientation dependence of the defect production threshold as well as the structure and stability of the resulting vacancy-interstitial pairs. Near the <111> directions, a vacancy tetrahedral-interstitial pair is… more
Date: February 1, 1994
Creator: Caturla, M.J.; Rubia, T.D. de la & Gilmer, G.H.
Partner: UNT Libraries Government Documents Department
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Interaction between point defects and edge dislocation in BCC iron

Description: We present results of atomistic simulations of the interaction between self interstitial atoms and vacancies with edge dislocations in BCC iron. The calculations are carried out using molecular dynamics with an energy minimization scheme based on the quasi-Newton approach and use the Finnis-Sinclair interatomic potential for BCC iron developed by Ackland et al. Large anisotropy in the strain field of self interstitials is observed and it causes strong interaction with edge dislocations even whe… more
Date: October 12, 1998
Creator: Diaz de la Rubia, T. & Shastry, V.
Partner: UNT Libraries Government Documents Department
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Fermi level stabilization energy in group III-nitrides

Description: Energetic particle irradiation is used to systematically introduce point defects into In{sub 1-x}Ga{sub x}N alloys over the entire composition range. Three types of energetic particles (electrons, protons, and {sup 4}He{sup +}) are used to produce a displacement damage dose spanning five decades. In InN and In-rich InGaN the free electron concentration increases with increasing irradiation dose but saturates at a sufficiently high dose. The saturation is due to Fermi level pinning at the Fermi … more
Date: January 7, 2005
Creator: Li, S. X.; Yu, K. M.; Wu, J.; Jones, R. E.; Walukiewicz, W.; AgerIII, J. W. et al.
Partner: UNT Libraries Government Documents Department
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Simulation of neutron radiation damage in silicon semiconductor devices.

Description: A code, Charon, is described which simulates the effects that neutron damage has on silicon semiconductor devices. The code uses a stabilized, finite-element discretization of the semiconductor drift-diffusion equations. The mathematical model used to simulate semiconductor devices in both normal and radiation environments will be described. Modeling of defect complexes is accomplished by adding an additional drift-diffusion equation for each of the defect species. Additionally, details are giv… more
Date: October 1, 2007
Creator: Shadid, John Nicolas; Hoekstra, Robert John; Hennigan, Gary Lee; Castro, Joseph Pete Jr. & Fixel, Deborah A.
Partner: UNT Libraries Government Documents Department
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Effects of self-irradiation on local crystal structure and 5flocalization in PuCoGa5

Description: The 18.5 K superconductor PuCoGa{sub 5} has many unusual properties, including those due to damage induced by self-irradiation. The superconducting transition temperature decreases sharply with time, suggesting a radiation-induced Frenkel defect concentration much larger than predicted by current radiation damage theories. Extended x-ray absorption fine-structure measurements demonstrate that while the local crystal structure in fresh material is well ordered, aged material is disordered much m… more
Date: October 20, 2006
Creator: Booth, C. H.; Daniel, M.; Wilson, R. E.; Bauer, E. D.; Mitchell, J. N.; Moreno, N. O. et al.
Partner: UNT Libraries Government Documents Department
open access

Point Defect Incorporation During Diamond Chemical Vapor Deposition

Description: The incorporation of vacancies, H atoms, and sp{sup 2} bond defects into single-crystal homoepitaxial (100)(2x1)- and(111)-oriented CVD diamond was simulated by atomic-scale kinetic Monte Carlo. Simulations were performed for substrate temperatures from 600 C to 1200 C with 0.4% CH{sub 4} in the feed gas, and for 0.4% to 7% CH{sub 4} feeds with a substrate temperature of 800 C. The concentrations of incorporated H atoms increase with increasing substrate temperature and feed gas composition, an… more
Date: August 2, 1999
Creator: Battaile, C.C.; Srolovitz, D.J. & Butler, J.E.
Partner: UNT Libraries Government Documents Department
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Point Defects in Binary Laves-Phase Alloys

Description: Point defect mechanisms in the binary C15 NbCr{sub 2} and NbCo{sub 2}, and C14 NbFe{sub 2} systems on both sides of stoichiometry was studied and clarified by both bulk density and X-ray lattice parameter measurements. It was found that the vacancy concentrations in these systems after quenching from 1000 C are essentially zero. The constitutional defects on both sides of stoichiometry for these systems were found to be of the anti-site type in comparison with the model predictions. However, th… more
Date: November 30, 1998
Creator: Liaw, P. K.; Liu, C. T.; Pike, L. M. & Zhu, J. H.
Partner: UNT Libraries Government Documents Department
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Electron emission and defect formation in the interaction of slow,highly charged ions with diamond surfaces

Description: We report on electron emission and defect formation in theinteraction between slow (v~;0.3 vBohr) highly charged ions (SHCI) withinsulating (type IIa) and semiconducting (type IIb) diamonds. Electronemission induced by 31Pq+ (q=5 to 13), and 136Xeq+ (q=34 to 44) withkinetic energies of 9 kVxq increase linearly with the ion charge states,reaching over 100 electrons per ion for high xenon charge states withoutsurface passivation of the diamond with hydrogen. Yields from bothdiamond types are up t… more
Date: May 31, 2006
Creator: Sideras-Haddad, E.; Shrivastava, S.; Rebuli, D.B.; Persaud, A.; Schneider, D.H. & Schenkel, T.
Partner: UNT Libraries Government Documents Department
open access

MOLECULAR DYNAMICS SIMULATIONS OF DISPLACEMENT CASCADES IN MOLYBDENUM

Description: Molecular dynamics calculations have been employed to simulate displacement cascades in neutron irradiated Mo. A total of 90 simulations were conducted for PKA energies between 1 and 40 keV and temperatures from 298 to 923K. The results suggest very little effect of temperature on final defect count and configuration, but do display a temperature effect on peak defect generation prior to cascade collapse. Cascade efficiency, relative to the NRT model, is computed to lie between 1/4 and 1/3 in a… more
Date: September 8, 2003
Creator: Smith, Richard Whiting
Partner: UNT Libraries Government Documents Department
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Te Inclusions in CZT Detectors: New Method for Correcting Their Adverse Effects

Description: Both Te inclusions and point defects can trap the charge carriers generated by ionizing particles in CdZnTe (CZT) detectors. The amount of charge trapped by point defects is proportional to the carriers’ drift time and can be corrected electronically. In the case of Te inclusions, the charge loss depends upon their random locations with respect to the electron cloud. Consequently, inclusions introduce fluctuations in the charge signals, which cannot be easily corrected. In this paper, we descri… more
Date: October 25, 2009
Creator: Bolotnikov, A. E.; Babalola, S.; Camarda, G. S.; Cui, Y.; Egarievwe, S. U.; Hawrami, R. et al.
Partner: UNT Libraries Government Documents Department
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