199 Matching Results

Search Results

Advanced search parameters have been applied.

Recrystallization behavior of ion beam modified. cap alpha. -Al/sub 2/O/sub 3/

Description: Transmission electron microscopy was used to study amorphized implanted ..cap alpha..-Al/sub 2/O/sub 3/. The response of the as-implanted amorphous layer to thermal aging varied with annealing tmperature and time. The recrystallization is total and epitaxial at 1190/sup 0/C. (DLC)
Date: January 1, 1986
Creator: Sklad, P.S.
Partner: UNT Libraries Government Documents Department

Amorphization and recrystallization processes in monocrystalline beta silicon carbide thin films

Description: Individual, as well as multiple doses of /sup 27/Al/sup +/, /sup 31/P/sup +/, /sup 28/Si/sup +/, and /sup 28/Si/sup +/ and /sup 12/C/sup +/, were implanted into (100) oriented monocrystalline ..beta..-SiC films. The critical energy of approx. =16 eV/atom required for the amorphization of ..beta..-SiC via implantation of /sup 27/Al/sup +/ and /sup 31/P/sup +/ was determined using the TRIM84 computer program for calculation of the damage-energy profiles coupled with the results of RBS/ion channeling analyses. In order to recrystallize amorphized layers created by the individual implantation of all four ion species, thermal annealing at 1600, 1700, or 1800/sup 0/C was employed. Characterization of the recrystallized layers was performed using XTEM. Examples of SPE regrown layers containing precipitates and dislocation loops, highly faulted-microtwinned regions, and random crystallites were observed.
Date: January 1, 1985
Creator: Edmond, J.A.; Withrow, S.P.; Kong, H.S. & Davis, R.F.
Partner: UNT Libraries Government Documents Department

Latch-up elimination in bulk CMOS LSI circuits

Description: Recent data on latch-up prevention in CMOS LSI circuits by the use of epitaxial starting material are presented, a modification of the lumped transistor SCR model is discussed, and a useful graphical solution to the latch-up problem is described.
Date: January 1, 1980
Creator: Schroeder, J. E.
Partner: UNT Libraries Government Documents Department

Deuterium and helium-ion irradiation effects on TiB/sub 2/ coatings

Description: The surface damage and erosion of chemically vapor deposited TiB/sub 2/ coatings and commercial grade Ti, caused by 40-, 60- and 120-keV D/sup +/ and /sup 4/He/sup +/ irradiation, has been studied for the as deposited coatings and for the coating surfaces that were mechanically polished prior to irradiation. SEM analysis of polished TiB/sub 2/ samples irradiated with D/sup +/ and /sup 4/He/sup +/ to a dose of 3.1 x 10/sup 18/ ions/cm/sup 2/ reveal significant surface damage due to blistering and flaking whereas for identical irradiation conditions, the as deposited TiB/sub 2/ coatings show very little damage. For similar irradiation conditions the Ti metal samples showed blistering for the /sup 4/He/sup +/ irradiation case but no significant surface damage for the D/sup +/ case. Estimates of the irosion yields due to blister exfoliation in polished TiB/sub 2/ samples show an increase with increasing projectile energy for the total dose studied.
Date: January 1, 1979
Creator: Das, S.K. & Kaminsky, M.
Partner: UNT Libraries Government Documents Department

Upset and latchup thresholds in CD-4000 series CMOS devices. IRT 4337-007

Description: A test program designed to verify that neutron irradiation and subsequent anneal is an effective method for suppressing ionization-induced latchup yielded as a byproduct a large body of data covering the upset and latchup thresholds of non-neutron-irradiated bulk CMOS devices. Sixty-six part types in the hardened RCA CD-4000 series and four National Semiconductor part types were tested. Upset levels ranged from 2-200 rad(Si). Latchup was observed in forty of the seventy part types tested. Latchup thresholds ranged from 9 to 708 rad(Si). Latchup currents ranged from 15 mA to 1.9 A.
Date: January 1, 1980
Creator: Harrity, J. W. & Gammill, P. E.
Partner: UNT Libraries Government Documents Department

Ceramic decomposition under irradiation, 1987

Description: Our quantitative determinations of the decomposition of thin film and bulk ceramic materials during electron microscopy has shown that the radiation damage effect is a complex one depending dielectric and thermochemical properties. In low melting temperature glasses, for example, much of the activity is due to field enhanced diffusion of low atomic weight species. This is particularly true of bulk specimens and for the case of binary soda-borosilicate glass the sodium depletion in the SEM can be quantitatively described in terms of this effect. Studies with thin specimens of refractory carbides show that in these materials the carbon depletion is due to direct displacement processes and that here the electric fields give rise to recombination effects. The studies of ceramic thin films suitable for reference standards is continuing as a joint effort with the Rockwell Science Center. Work is in progress to describe the in plane crystallization that is observed in terms of the latent heat involved and the configurational entropy of the propagating interface.
Date: January 1, 1987
Creator: Howitt, D.G.
Partner: UNT Libraries Government Documents Department

Fusion reactor materials semiannual progress report for period ending September 30, 1990

Description: This is the ninth in series of semiannual technical progress reports on fusion reactor materials. This report combines research and development activities which were previously reported separately in the following technical progress reports: Alloy Development of Irradiation Performance; Damage Analysis and Fundamental Studies; and Special Purpose Materials. These activities are concerned principally with the effects of the neutronic and chemical environment on the properties and performance of reactor materials; together they form one element of the overall materials program being conducted in support of the Magnetic Fusion Energy Program of the US Department of Energy. The other major element of the program is concerned with the interactions between reactor materials and the plasma and is reported separately. The Fusion Reactor Materials Program is a national effort involving several national laboratories, universities, and industries. The purpose of this series of reports is to provide a working technical record for the use of the program participants, and to provide a means of communicating the efforts of materials scientists to the rest of the fusion community, both nationally and worldwide.
Date: April 1, 1991
Partner: UNT Libraries Government Documents Department

In-pile intragranular densification of oxide fuels (AWBA Development Program)

Description: This report proposes a model to describe in-pile densification of oxide fuels, by both vacancy boil-off due to thermal excitation and vacancy knockout by the passage of fission fragments through the pores. The model includes the migration rates of both vacancies and interstitials to pores and the production of vacancy-rich damage cascades by fission fragments. It has been coupled with a previously reported swelling and gas release model so that it can predict the total dimensional changes of the fuel as well as predicting intragranular densification for both ThO/sub 2/ and UO/sub 2/ fuels for advanced water breeder reactor applications development effort.
Date: October 1, 1977
Creator: Dollins, C.C. & Nichols, F.A.
Partner: UNT Libraries Government Documents Department

Application of silicon carbide to synchrotron-radiation mirrors

Description: Damage to conventional mirror materials exposed to the harsh synchrotron radiation (SR) environment has prompted the SR user community to search for more suitable materials. Next-generation insertion devices, with their attendant flux increases, will make the problem of mirror design even more difficult. A parallel effort in searching for better materials has been underway within the laser community for several years. The technology for dealing with high thermal loads is highly developed among laser manufacturers. Performance requirements for laser heat exchangers are remarkably similar to SR mirror requirements. We report on the application of laser heat exchanger technology to the solution of typical SR mirror design problems. The superior performance of silicon carbide for laser applications is illustrated by various material trades studies, and its superior performance for SR applications is illustrated by means of model calculations.
Date: September 1, 1983
Creator: Takacs, P.Z.; Hursman, T.L. & Williams, J.T.
Partner: UNT Libraries Government Documents Department

Pulsed laser and ion beam surface modification of sintered alpha-SiC. [Using Ni overlayers]

Description: Pulsed laser annealing and ion beam mixing have been used as surface modification techniques to enhance the physical properties of polycrystalline ..cap alpha..-SiC. Thin Ni overlayers (20 nm to 100 nm) were evaporated onto the SiC surface. The specimens were subsequently irradiated with pulses of a ruby or krypton fluoride (KrF) excimer laser or bombarded with high energy Xe/sup +/ or Si/sup +/ ions. Both processes are nonequilibrium methods and each has been shown to induce unique microstructural changes at the SiC surface which are not attainable by conventional thermal treatments. Under particular (and optimum) processing conditions, these changes considerably increased the mechanical properties of the SiC; following laser irradiation, the fracture strength of the SiC was increased by as much as 50%, but after ion beam mixing, no strength increase was observed. High resolution cross-section transmission electron microscopy (X-TEM), scanning electron microscopy (SEM), and Rutherford backscattering techniques were used to characterize the extent of mixing between the Ni and the SiC as a result of the surface modification.
Date: December 2, 1985
Creator: More, K.L.; Davis, R.F.; Appleton, B.R.; Lowndes, D. & Smith, P.
Partner: UNT Libraries Government Documents Department

Neutron irradiation effects on the mechanical properties of thorium and thorium--carbon alloy

Description: The effects of neutron exposure to 3.0 x 10/sup 18/ neutrons/cm/sup 2/ on the mechanical properties of thorium and thorium-carbon alloy are described. Tensile measurements were done at six different test temperatures from 4/sup 0/K to 503/sup 0/K and at two strain rates. Thorium and thorium-carbon alloy are shown to display typical radiation hardening like other face-centered cubic metals. The yield drop phenomenon of the thorium-carbon alloy is unchanged after irradiation. The variation of shear stress and effective shear stress with test temperature was fitted to Seeger's and Fleischer's equations for irradiated and unirradiated thorium and thorium-carbon alloy. Neutron irradiation apparently contributes an athermal component to the yield strength. However, some thermal component is detected in the low temperature range. Strain-rate parameter is increased and activation volume is decreased slightly for both kinds of metal after irradiation.
Date: April 1, 1978
Creator: Wang, S.C.P.
Partner: UNT Libraries Government Documents Department

Laser deposition and laser modification of high-temperature superconducting thin films

Description: Applications of high-temperature superconductors (HTSC) may require epitaxial films with {Tc}{ge}77 K, and J{sub c}{ge}10{sup 6} A/cm{sup 2}. In situ pulsed laser deposition (PLD) is suitable for fabrication of such films. We report parametric studies on the effect of laser and processing parameters on the crystallinity, epitaxy and electrical properties of laser-deposited HTSC thin films. In addition, several laser-based processes were used to modify the electrical properties ({Tc} and J{sub c}) of PLD thin films. A direct-write laser heating (1.06 {mu}m at {approx}0.5 kW/cm{sup 2} for {approx}5 min) process in an oxygen atmosphere at {approx}590 Torr was shown to selectivity regenerate high-{Tc} material in microscopic domains from films that were partially deoxygenated. In separate work, electrical responses and crystallinity of HTSC films were measured as a function of excimer laser exposure using fluences in the range 20--150 mJ/cm{sup 2}. The critical current and boundary layer could be modified with a high degree of accuracy. 17 refs., 4 figs.
Date: January 1, 1991
Creator: Dye, R.C.; Foltyn, S.R.; Nogar, N.S.; Wu, X.D.; Peterson, E.J. & Muenchausen, R.E.
Partner: UNT Libraries Government Documents Department

Microstructure and properties of TiB/sub 2/ implanted with 1-MeV nickel

Description: Polycrystalline samples of TiB/sub 2/ were implanted at ambient temperatures with 1-MeV Ni/sup +/ ions to a fluence of 1 x 10/sup 17/ ions/cm/sup 2/. This fluence corresponds to a calculated nickel-to-titanium ratio, within the half width of the ion distribution, of approximately 0.12. Analytical electron microscopy was used to study the resultant microstructure. The starting microstructure was modified to a depth of approximately 750 nm, significantly deeper than the calculated peak in the deposited nickel profile of 389 nm. The results also show a change in the character of the microstructure, from one exhibiting a moderate density of tangled dislocations to a high density of small defects, as well as a change in the concentration of nickel as a function of depth from the implanted surface. There was no evidence of nickel precipitation. Surface mechanical properties such as hardness and wear resistance were significantly increased.
Date: January 1, 1983
Creator: McHargue, C.J.; Sklad, P.S. & Angelini, P. Lewis, M.B.
Partner: UNT Libraries Government Documents Department

Effects of plasma-deposited silicon nitride passivation on the radiation hardness of CMOS integrated circuits

Description: The use of plasma-deposited silicon nitride as a final passivation over metal-gate CMOS integrated circuits degrades the radiation hardness of these devices. The hardness degradation is manifested by increased radiation-induced threshold voltage shifts caused principally by the charging of new interface states and, to a lesser extent, by the trapping of holes created upon exposure to ionizing radiation. The threshold voltage shifts are a strong function of the deposition temperature, and show very little dependence on thickness for films deposited at 300/sup 0/C. There is some correlation between the threshold voltage shifts and the hydrogen content of the PECVD silicon nitride films used as the final passivation layer as a function of deposition temperature. The mechanism by which the hydrogen contained in these films may react with the Si/SiO/sub 2/ interface is not clear at this point.
Date: January 1, 1980
Creator: Clement, J. J.
Partner: UNT Libraries Government Documents Department

Hardening in AlN induced by point defects

Description: Pressureless-sintered AIN was neutron irradiated and the hardness change was examined by Vickers indentation. The hardness was increased by irradiation. When the samples were annealed at high temperature, the hardness gradually decreased. Length was also found to increase and to change in the same way as the hardness. A considerable density of dislocation loops still remained, even after the hardness completely recovered to the value of the unirradiated sample. Thus, it is concluded that the hardening in AIN is caused by isolated point defects and small clusters of point defects, rather than by dislocation loops. Hardness was found to increase in proportion to the length change. If the length change is assumed to be proportional to the point defect density, then the curve could be fitted qualitatively to that predicted by models of solution hardening in metals. Furthermore, the curves for three samples irradiated at different temperatures and fluences are identical. There should be different kinds of defect clusters in samples irradiated at different conditions, e.g., the fraction of single point defects is the highest in the sample irradiated at the lowest temperature. Thus, hardening is insensitive to the kind of defects remaining in the sample and is influenced only by those which contribute to length change.
Date: January 1, 1991
Creator: Suematsu, H.; Mitchell, T.E. (Los Alamos National Lab., NM (United States)); Iseki, T. & Yano, T. (Tokyo Inst. of Tech. (Japan))
Partner: UNT Libraries Government Documents Department

Irradiation behavior of pyrolytic silicon carbide. [HTGR]

Description: Fuel particles for the High-Temperature Gas-Cooled Reactor (HTGR) contain a layer of pyrolytic silicon carbide to act as a miniature pressure vessel and primary fission-product barrier. Optimization of the SiC with respect to fuel performance involves four areas of study: characterization of as-deposited SiC coatings; thermodynamics and kinetics of chemical reactions between SiC and fission products; irradiation behavior of SiC in the absence of fission products; and combined effects of irradiation and fission products. This paper reports the behavior of SiC deposited on inert microspheres and irradiated to fast-neutron fluences typical of HTGR fuel at end-of-life.
Date: January 1, 1983
Creator: Lauf, R.J.
Partner: UNT Libraries Government Documents Department

Environmental test program for superconducting materials and devices: Preliminary results of testing program at Savannah River Site

Description: The properties of YBa{sub 2}Cu{sub 3}O{sub 7-x} superconducting tapes designed and fabricated into SAFIRE-type, encapsulated, grounding links by the Ceramic Engineering Department at Clemson University are under investigation. Testing at the Savannah River Site will include gamma irradiation, vibration, and long-term evaluation. The gamma irradiation portion of testing has been completed. The long-term testing began in January and will continue. The vibration test has yet to be started.
Date: May 30, 1991
Creator: Randolph, H. (Westinghouse Savannah River Co., Aiken, SC (United States)) & Verebelyi, D. (Westinghouse Savannah River Co., Aiken, SC (United States) Clemson Univ., SC (United States))
Partner: UNT Libraries Government Documents Department

Damage energy functions for compounds and alloys

Description: The concept of the damage energy of an energetic primary knock-on atom in a material is a central component in the procedure used to calculate dpa for metals exposed to neutron and charged particle radiation. Coefficients for analytic fits to the calculated damage energy functions are given for Al/sub 2/O/sub 3/, Si/sub 3/N/sub 4/, Y/sub 2/O/sub 3/, and NbTi. Damage efficiencies are given for Al/sub 2/O/sub 3/. (MHR)
Date: January 1, 1977
Creator: Parkin, D.M. & Coulter, C.A.
Partner: UNT Libraries Government Documents Department

Database of average-power damage thresholds at 1064 nm

Description: We have completed a database of average-power, laser-induced, damage thresholds at 1064 nm on a variety of materials. Measurements were made with a newly constructed laser to provide design input for moderate and high average-power laser projects. The measurements were conducted with 16-ns pulses at pulse-repetition frequencies ranging from 6 to 120 Hz. Samples were typically irradiated for time ranging from a fraction of a second up to 5 minutes (36,000 shots). We tested seven categories of samples which included antireflective coatings, high reflectors, polarizers, single and multiple layers of the same material, bare and overcoated metal surfaces, bare polished surfaces, and bulk materials. The measured damage threshold ranged from < 1 J/cm/sup 2/ for some metals to > 46 J/cm/sup 2/ for a bare polished glass substrate. 4 refs., 7 figs., 1 tab.
Date: December 14, 1987
Creator: Rainer, F.; Hildum, E.A. & Milam, D.
Partner: UNT Libraries Government Documents Department

Fusion neutron irradiation of NiSi alloys at 4. 2K

Description: Two Ni alloys with 4 at.% Si and 12.7 at.% Si in solution have been irradiated at 4.2K with 14 MeV fusion neutrons. The resistivity damage rate of well annealed Ni-4%Si alloy showed an initial transient in the plot of d..delta..rho/d..delta..phit versus ..delta..rho. A high dislocation density appeared to reduce this transient. The resistivity damage rate of Ni-12.7%Si alloy showed an unusual behavior; d..delta..rho/d..delta..phit increases with ..delta..rho after the initial transient period. This behavior is attributed to precipitation and growth of Ni/sub 3/Si during irradiation. Post-irradiation isochronal annealing results showed significant effects of cold work and composition on recovery. Ni-4%Si recovered slower than pure nickel and a high dislocation density enhanced its recovery. For the Ni-12.7% Si alloy, recovery ended after being annealed to 38K, after which the resistivity increased with annealing temperature. This is attributed to further precipitation and growth of Ni/sub 3/Si.
Date: March 18, 1986
Creator: Guinan, M.W.; Huang, J.S. & Hahn, P.A.
Partner: UNT Libraries Government Documents Department

High threshold HR (highly reflective) coatings at 1064 nm

Description: We have conducted as extensive series of laser damage measurements on highly reflective (HR) dielectric coatings which have yielded 1064-nm thresholds as high as 40 J/cm{sup 2} for 8- to 10-ns pulses at pulse-repetition frequencies (PRF) of 10 Hz. Moreover, by laser conditioning these coatings with subthreshold pulses, the thresholds of some coatings were raised to levels exceeding 70 J/cm{sup 2}. These are the highest threshold dielectric HR coatings that we have tested in this regime. The coatings were originally developed to produce HR-overcoated metal mirrors for free-electron-laser (FEL) applications at high PRF. Our tests included coatings deposited on both dielectric substrates and molybdenum (Mo) substrates. In each category we also examined coatings with a pre-coat of Mo between the substrate and the HR stack. The improved dielectric HR stacks effectively shielded the Mo from the laser irradiation so that the thresholds of virtually all Mo samples exceeded levels of the best dielectric-enhanced and dielectric-HR-coated metal mirrors we have tested to date. In addition to the low PRF measurements, we also conducted 1064-nm damage tests at 6-kHz PRF using 65-ns pulses from the Kilroy damage test facility. The coatings survived thermal loading of fluences ranging from 2 to 10 J/cm{sup 2} with respective small spot sizes on the order of 1.2 to 0.3 mm (1/e{sup 2} diameter). 6 refs., 3 figs.
Date: December 17, 1990
Creator: Rainer, F.; DeMarco, F.P.; Hunt, J.T.; Morgan, A.J. (Lawrence Livermore National Lab., CA (USA)); Mott, L.P.; Marcelja, F. et al.
Partner: UNT Libraries Government Documents Department

Review of 1064-nm damage tests of electron-beam deposited Ta/sub 2/O/sub 5//SiO/sub 2/ antireflection coatings

Description: Damage tests of Ta/sub 2/O/sub 5//SiO/sub 2/ antireflection films deposited under a variety of conditions showed that thresholds of films deposited at 175/sup 0/C were greater than thresholds of films deposited at either 250/sup 0/C or 325/sup 0/C. Deposition at high rate and low oxygen pressure produced highly absorptive films with low thresholds. Thresholds did not correlate with film reflectivity or net stress in the films, and correlated with film absorption only when the film absorption was greater than 10/sup 4/ ppM. Baking the films for four hours at 400/sup 0/C reduced film absorption, altered net film stress, and produced an increase in the average damage threshold.
Date: December 18, 1981
Creator: Milam, D.; Rainer, F.; Lowdermilk, W.H.; Swain, J.E.; Carniglia, C.K. & Hart, T.T.
Partner: UNT Libraries Government Documents Department

Experimental determination of radiation damage function for graphite

Description: Highly oriented pyrolytic-graphite samples were irradiated in three different neutron sources with average energies of 1.5, 5.5, and 14.8 MeV, respectively. The resulting changes in the basal-plane elastic shear moduli of these samples show that the relative damage rate is substantially higher at the higher neutron energies than is predicted by existing models. The results of these experiments have been used to generate a new relative damage function which will allow better projections of graphite radiation behavior in fusion reactors based on data obtained by irradiations in fission reactors.
Date: July 1, 1979
Creator: Gray, W.J. & Morgan, W.C.
Partner: UNT Libraries Government Documents Department