30 Matching Results

Search Results

Advanced search parameters have been applied.

Ion-beam mixing in silicon and germanium at low temperatures

Description: Ion-beam mixing of thin marker layers in amorphous silicon and germanium was studied using irradiations with Xe ions at temperatures of 34k and 77k. The marker species, ion energies and doses were: in silicon, markers of Ge and Pt irradiated with 200-keV Xe up to 2.7x10/sup 16/ ions cm/sup -2/; and in germanium, markers of Al and Si bombarded with 295-keV Xe up to 1.63x10/sup 16/ ions cm/sup -2/. In silicon, Pt markers were found to broaden at about the same rate at 34k and 77k; and the rate of broadening was similar to that found by other workers when expressed as an efficiency of mixing, i.e., when dependence on ion dose and deposited energy was factored out. However, a Ge marker irradiated at 34k did not broaden from its original thickness. In germanium, markers of both Al and Si were mixed by irradiation at 34k, but at 77k only the Al marker broadened; the Si marker did not. The broadening of the markers is ascribed to ballistic mixing, while the cases where no broadening occurred are explicable if diffusion by a defect mechanism transported displaced marker atoms back to traps near their original sites.
Date: January 1, 1982
Creator: Clark, G.J.; Marwick, A.D. & Poker, D.B.
Partner: UNT Libraries Government Documents Department

A timeshared foreline and roughing vacuum system

Description: A system to perform turbomolecular drag foreline pumping and scattering chamber roughing was installed in the Surface Modification and Characterization Research Center at Oak Ridge National Laboratory. The system consists of an oil-free mechanical scroll pump that can be connected to either a roughing manifold serving four scattering chambers or to a foreline ballast tank and manifold serving five turbomolecular drag pumps. A controller mediates the demands of the two manifolds, giving priority to the foreline. Due to the low leakage from the accelerator beamlines, the duty cycle in the foreline pumping mode consists of a few minutes of operating time every few days, greatly reducing wear on the scroll pump. Significant savings are realized due to reduced consumption of liquid nitrogen for sorption pumping, elimination of oil changes and repairs to individual mechanical foreline pumps, and lower electrical power consumption.
Date: November 1, 1997
Creator: Hensley, D.K.; Thomas, D.K. & Poker, D.B.
Partner: UNT Libraries Government Documents Department

Application of NRA/channeling to study He{sup +} implanted waveguides

Description: Four different techniques (RBS/channeling, NRA/channeling, prism coupling, and TRIM) for estimating the depth and width of a damaged layer created by ion implantation in LiNbO{sub 3} are compared. Waveguides can be created in LiNbO{sub 3} by lattice disruption damage with light ions (protons, alphas) or by implantation with Ti. End of range damage results in a decrease in refractive index that acts as a low index barrier to create a waveguide. In the electronic stopping region the ordinary index of LiNbO{sub 3} is decreased while the extraordinary index is increased. The damage in the electronic stopping regime is removed by annealing to a temperature lower than that needed to remove the nuclear damage. RBS/channeling is used to examine displacement of Nb atoms and NRA/channeling is used to study displacement of Li atoms using Li(p,{alpha}) and Li(p,{gamma}) reactions. The authors have analyzed waveguides produced by implantation of 1.7 Mev He{sup +}. Comparison of the NRA/Channeling results of as implanted and 175 C and 400 C annealed crystals suggest that electronic stopping induced lattice distortion is responsible for the increase in the extraordinary index in the electronic stopping region.
Date: June 1, 1995
Creator: Williams, E.K.; Ila, D.; Sarkisov, S.; Venkateswarlu, P. & Poker, D.B.
Partner: UNT Libraries Government Documents Department

Application of RBS and NRA in the fabrication of carbon based devices

Description: We have used Nuclear Reaction Analysis (NRA) and Rutherford Backscattering Spectrometry (RBS) as well as resonant backscattering as analytical tools in fabricating carbon based drug delivery bio-implants, electrodes for batteries, and devices to entrap or filter specific toxins. Precursor is resol C{sub 7}H{sub 8}O{sub 2} liquid, which converts to fully cured phenolic resin C{sub 7}H{sub 6}O (sp gr 1.25) on heating at 170 C. This resin further transforms with no change in shape to glassy carbon (sp gr 1.45) on heating to 1000 C. Final product consists of long ribbon-like molecules of sp2 carbon atoms aggregated locally to form subcrystalline domains arranged randomly in space. RBS and NRA were used in measuring the porosity before and after activation, in concentration profiling of stored drugs before and after leaching, in detecting low level light element impurities, and in detecting changes in the structure of the device due to fabrication.
Date: June 1, 1995
Creator: Ila, D.; Zimmerman, R.L.; Maleki, H.; Evelyn, A.L. & Poker, D.B.
Partner: UNT Libraries Government Documents Department

Investigation of Mn Implanted LiNbO{sub 3} applying electron paramagnetic resonance technique

Description: The effect of ion implantation on the LiNbO{sub 3} crystal is studied using electron paramagnetic resonance spectroscopy (EPR). EPR measurements on these crystals were performed as a function of ion species Mn and Fe and fluence at room temperature. Also the effect of the laser illumination on the EPR signal was determined by illuminating the crystal in situ and measuring the decay and growth of the EPR signal. LiNbO{sub 3}:Mn{sup 2+} at a depth of approximately 200 nm was formed by implantation of 2.5 {times} 10{sup 14} Mncm{sup 2} and 1 {times} 10{sup 17} Mn/cm{sup 2} at 2 MeV. The implanted samples were compared with bulk doped crystals. It was found that the decay and growth of Mn EPR for the implanted crystal is very small compared with the bulk doped LiNbO{sub 3}:Mn crystal. This was found to be primarily due to the spin concentration on the crystals. On the other, hand the decay time of the high fluence is about 40% slower than the decay of the low fluence implanted crystal.
Date: October 1, 1997
Creator: Darwish, A.; Ila, D.; Poker, D.B. & Hensley, D.K.
Partner: UNT Libraries Government Documents Department

KeV Ion Beam Induced Surface Modification of SiC Hydrogen Sensor

Description: Silicon carbide, a wide-bandgap semiconductor, is currently used to fabricate an efficient high temperature hydrogen sensor. When a palladium coating is applied on the exposed surface of silicon carbide, the chemical reaction between palladium and hydrogen produces a detectable change in the surface chemical potential. Rather than applying a palladium film, we have implanted palladium ions into the silicon face of 6H, n-type Sic samples. The implantation energies and fluences, as well as the results obtained by monitoring the current through the sample in the presence of hydrogen are included in this paper.
Date: November 29, 1999
Creator: Muntele, C.I.; Ila, D.; Williams, E.K.; Poker, D.B. & Hensley, D.K.
Partner: UNT Libraries Government Documents Department

Ion beam modification of PVDC and PE polymers

Description: Electronic and nuclear stopping effects produced by MeV ion bombardment in polyvinylidine chloride and polyethylene are separated by stacking thin films of the polymers. Resulting multi-layer laminates of each polymer were bombarded with 3.5-MeV alpha particles. Energy of the incident ions was selected using the TRIM code so that the first layers experienced most of the effects of the electronic energy deposited and the last layers received most of the effects of the nuclear stopping power. Changes in conductance and chemical structure of each layer were measured by direct resistivity measurements and Raman microprobe analysis.
Date: December 31, 1995
Creator: Evelyn, A.L.; Ila, D.; Fisher, J. & Poker, D.B.
Partner: UNT Libraries Government Documents Department

Synthesis and characterization of a metastable (SiC){sub 3}N{sub 4} phase

Description: A metastable C-SI-N compound has been synthesized by high dose N{sup +} implantation into polycrystalline {beta}-SiC (cubic phase). The thin films formed upon 100 keV implantation were characterized with respect to various ion doses and target temperatures. X-ray diffraction with a position-sensitive detector and cross-sectional transmission electron microscopy revealed that the as-implanted surfaces contained {approximately} 0.15 {mu}m thick continuously-buried amorphous layers. Rutherford backscattering spectroscopy showed that the peak concentration of nitrogen saturated up to approximately 54 at. % with increasing doses, suggesting a new phase formation.
Date: December 31, 1994
Creator: Uslu, C.; Park, B. & Poker, D.B.
Partner: UNT Libraries Government Documents Department

Investigation of optical loss mechanisms in oxide thin films

Description: KNbO{sub 3}, K(Ta,Nb)O{sub 3}, KTaO{sub 3}, and Ta{sub 2}O{sub 5} thin films have been grown by ion-beam sputter deposition. KNbO{sub 3} has excellent nonlinear properties for second harmonic generation; however, high optical losses are still characteristic of these films. Several loss mechanisms, such as, high angle grain boundaries, twin domains, interface and surface scattering, and oxygen vacancies can all contribute to the high losses. In order to isolate the various mechanisms, amorphous Ta{sub 2}O{sub 5} films, epitaxial cubic KTaO{sub 3} and tetragonal K(Ta,Nb)O{sub 3} films were grown on MgO and Al{sub 2}O{sub 3} substrates subjected to post-deposition annealing treatments and various oxygen pressure conditions. The optical losses and refractive indices were observed to differ depending on the substrate surface and annealing treatments. Resonant scattering experiments were performed to analyze the oxygen composition. The optical properties of these oxide thin film systems are reported and the breakdown of the loss mechanisms is addressed.
Date: May 1995
Creator: Chow, A. F.; Kingon, A. I.; Auciello, O. & Poker, D. B.
Partner: UNT Libraries Government Documents Department

Synthesis of (SiC){sub 3}N{sub 4} thin films by ion implantation

Description: We have investigated the synthesis of carbon-silicon-nitride compounds by ion implantation. In these experiments, 100 keV nitrogen ions were implanted into polycrystalline {beta}-SiC (cubic phase) at various substrate temperatures and ion doses. These thin films were characterized by x-ray diffraction with a position-sensitive detector, transmission electron microscopy with chemical analysis, and Rutherford backscattering spectroscopy. The as-implanted samples show a buried amorphous layer at a depth of 170 nm. Peak concentration of nitrogen saturates at approximately 45 at. % with doses above {approximately} 9.0 {times} 10{sup 17} N/cm{sup 2} at 860{degree}C. These results suggest formation of a new phase by nitrogen implantation into {beta}-SiC.
Date: December 31, 1993
Creator: Uslu, C.; Lee, D. H.; Berta, Y.; Park, B.; Thadhani, N. N. & Poker, D. B.
Partner: UNT Libraries Government Documents Department

Properties of ion implanted Ti-6Al-4V processed using beamline and PSII techniques

Description: The surface of Ti-6Al-4V (Ti64) alloy has been modified using beamline implantation of boron. In separate experiments, Ti64 has been implanted with nitrogen using a plasma source ion implantation (PSII) technique utilizing either ammonia (NH{sub 3}), nitrogen (N{sub 2}), or their combinations as the source of nitrogen ions. Beamline experiments have shown the hardness of the N-implanted surface saturates at a dose level of {approximately} 4 {times} 10{sup 17} at/cm{sup 2} at {approximately} 10 GPa. The present work makes comparisons of hardness and tribological tests of (1) B implantation using beamline techniques, and (2) N implanted samples using ammonia and/or nitrogen gas in a PSII process. The results show that PSII using N{sub 2} or NH{sub 3} gives similar hardness as N implantation using a beamline process. The presence of H in the Ti alloy surface does not affect the hardness of the implanted surface. Boron implantation increased the surface hardness by as much as 2.5x at the highest dose level. Wear testing by a pin-on-disk method indicated that nitrogen implantation reduced the wear rate by as much as 120x, and boron implantation reduced the wear rate by 6.5x. Increased wear resistance was accompanied by a decreased coefficient of friction.
Date: December 31, 1996
Creator: Walter, K.C.; Woodring, J.S.; Nastasi, M.; Munson, C.M.; Williams, J.M. & Poker, D.B.
Partner: UNT Libraries Government Documents Department

Nanocrystal formation via yttrium ion implantation into sapphire

Description: Ion implantation has been used to form nanocrystals in the near surface of single crystal {alpha}-Al{sub 2}O{sub 3}. The ion fluence was 5 x 10{sup 16} Y{sup +}/cm{sup 2}, and the implant energies investigated were 100, 150, and 170 keV. The morphology of the implanted region was investigated using transmission electron microscopy, x-ray energy dispersive spectroscopy, Rutherford backscattering spectroscopy and ion channeling. The implantation causes the formation of an amorphous surface layer which contains spherical nanosized crystals with a diameter of {approximately}13 nm. The nanocrystals are randomly oriented and exhibit a face-centered cubic structure with a lattice parameter of {approximately}4.1 A {+-} .02 A. Preliminary chemical analysis shows that these nanocrystals are rich in aluminum and yttrium and poor in oxygen relative to the amorphous matrix.
Date: December 31, 1995
Creator: Hunt, E.M.; Hampikian, J.M. & Poker, D.B.
Partner: UNT Libraries Government Documents Department

Effects of MeV Ions on PE and PVDC

Description: We studied the effects of 3.5 and 5.0 MeV alpha bombardment on polyethylene and polyvinylidene chloride both of which have simple chemical structures. Using a thin polymer film stacking technique, we were able to map the effects of the MeV alpha particles in their track. The first layer of the thin polymer film stack experienced most of the effects of the electronic energy deposited and the last layer received most of the effects of the nuclear stopping. Using Raman microprobe analysis and measuring the ratio of the formation of graphene structures (G-line) to the disordered (amorphous) carbon line (D-line), we were able to separate the severed bond effects in the end of the alpha particles` track in the last polymer film layers from the effects of the electronic energy deposited in the first polymer film layers. The results are in agreement with our other measurements of each polymer film using FTIR, RBS and resistance measurements.
Date: December 1997
Creator: Evelyn, A. L.; Ila, D.; Zimmerman, R. L.; Bhat, K.; Poker, D.B. & Hensley, D. K.
Partner: UNT Libraries Government Documents Department

Mechanisms of formation of nonlinear optical light guide structures in metal cluster composites produced by ion beam implantation

Description: Ion implantation has been shown to produce a high density of metal colloids in glasses and crystalline materials. The high-precipitate volume fraction and small size of metal nanoclusters formed leads to values for the third-order susceptibility much greater than those for metal doped solids. This has stimulated interest in use of ion implantation to make nonlinear optical materials. On the other side, LiNbO{sub 3} has proved to be a good material for optical waveguides produced by MeV ion implantation. Light confinement in these waveguides is produced by refractive index step difference between the implanted region and the bulk material. Implantation of LiNbO{sub 3} with MeV metal ions can therefore result into nonlinear optical waveguide structures with great potential in a variety of device applications. The authors describe linear and nonlinear optical properties of a waveguide structure in LiNbO{sub 3}-based composite material produced by silver ion implantation in connection with mechanisms of its formation.
Date: November 1, 1997
Creator: Sarkisov, S.S.; Williams, E.K.; Curley, M.; Smith, C.C.; Ila, D.; Venkateswarlu, P. et al.
Partner: UNT Libraries Government Documents Department

Fabrication of optical channel waveguides in the GaAs/AlGaAs system by MeV ion beam bombardment

Description: We have fabricated optical channel waveguides in planar GaAs/AlGaAs waveguides using 10 MeV oxygen ions at a fluence of 3 {times} l0{sup 13} and 3 {times} l0{sup 14} ions/cm{sup 2}. Although disordering o GaAs/AlGaAs quantum well structures has previously been reported, to the best of the authors` knowledge the fabrication of channel waveguides using high energy oxygen bombardment has not been demonstrated in this material system. This technique may provide a totally new concept of localized material modifications in GaAs/AlGaAs waveguides by creating compositional disordered regions that act as optical confinement channels. The masking technique used to provide selective disordering of the planar waveguide structures will be presented. Optical measurements were performed on the channel waveguides at a wavelength of 1.3 {mu}m.
Date: December 31, 1994
Creator: Taylor, T.; Ila, D.; Zimmerman, R.L.; Ashley, P.R. & Poker, D.B.
Partner: UNT Libraries Government Documents Department

Study of the effects of MeV Ag and Au implantation on the optical properties of LiNbO{sub 3}

Description: The authors present the results of characterization of linear absorption and nonlinear refractive index of Au and Ag nanoclusters made by MeV ion implantation into LiNbO{sub 3}. Ag was implanted at 1.5 MeV to fluences of 2 to 17 {times} 10{sup 16}/cm{sup 2} at room temperature. Au was implanted to fluences of 5 to 20 {times} 10{sup 16}/c{sup 2}m at an energy of 2.0 MeV. Optical absorption spectrometry indicated an absorption peak at 560 nm for the Au implanted samples after a 30 minute heat treatment at 500 C in air. The peak shifted to {approximately} 620 nm after heat treatment at 1,000 C. The Ag implanted samples had absorption peaks at 445 to 485 nm before heat treatment. After 500 C heat treatment for 1 h the peaks decreased in height and shifted to 545--560 nm. Heat treatment at 800 C was sufficient to return the Ag implanted crystals to a clear state. The size of the clusters was determined from the absorption peaks. The Ag clusters did not change appreciably in size with heat treatment. The Au clusters increased from 1 to 3 nm upon heat treatment at 1,000 C. Measurements of the nonlinear refractive indices were carried out using the Z-scan method with a tunable dye laser pumped by a frequency doubled mode locked Nd:YAG laser. The dye laser had a 4.5 ps pulse duration time and 76 MHz pulse repetition rate (575 nm).
Date: October 1, 1997
Creator: Williams, E.K.; Ila, D.; Sarkisov, S.; Curley, M.; Cochrane, J.C.; Poker, D.B. et al.
Partner: UNT Libraries Government Documents Department

Fabrication of copper and gold nanoclusters in MgO (100) by MeV ion implantation

Description: MeV ions of Au and Cu were implanted into single crystals of MgO (100) and the formation of metallic nanoclusters was observed by an indirect method of optical absorption spectrophotometry. Using Mei`s theory the authors related the observed optical absorption band to the formation of nanoclusters and using Doyle`s theory, as well as Rutherford Backscattering Spectrometry (RB S), the authors correlated the fill width half maximum (FWHM) of the absorption bands to the estimated size of the metallic nanoclusters between 1--10 nm. These clusters were formed by implantation above the threshold fluence for cluster formation and by a combination of threshold fluence of the implanted species and thermal annealing. The changes in the estimated size of the nanoclusters, after annealing at temperatures ranging from 5,000 C to 10,000 C, were observed using optical absorption spectrophotometry and calculated using Doyle`s theory.
Date: October 1, 1997
Creator: Zimmerman, R.L.; Ila, D.; Williams, E.K.; Sarkisov, S.S.; Poker, D.B. & Hensley, D.K.
Partner: UNT Libraries Government Documents Department

Surface Intensive Materials Processing for Multi-Functional Purposes

Description: We have chosen silicon carbide (SiC) as a multi-functional material to demonstrate the application of surface intensive processing for device fabrication. We will highlight two devices which are produced in house at the Center for Irradiation of materials of Alabama A and M university: (A) High temperature electronic gas sensor, (B) High temperature optical properties/sensor.
Date: March 6, 2000
Creator: Ila, D.; Williams, E.K.; Muntele, C.I.; George, M.A.; Poker, D.B.; Hensley, D.K. et al.
Partner: UNT Libraries Government Documents Department

Growth of highly doped p-type ZnTe films by pulsed laser ablation in molecular nitrogen

Description: Highly p-doped ZnTe films have been grown on semi-insulating GaAs (001) substrates by pulsed-laser ablation (PLA) of a stoichiometric ZnTe target in a high-purity N{sub 2} ambient without the use of any assisting (DC or AC) plasma source. Free hole concentrations in the mid-10{sup 19} cm{sup {minus}3} to > 10{sup 20} cm{sup {minus}3} range were obtained for a range of nitrogen pressures The maximum hole concentration equals the highest hole doping reported to date for any wide band gap II-VI compound. The highest hole mobilities were attained for nitrogen pressures of 50--100 mTorr ({approximately}6.5-13 Pa). Unlike recent experiments in which atomic nitrogen beams, extracted from RF and DC plasma sources, were used to produce p-type doping during molecular beam epitaxy deposition, spectroscopic measurements carried out during PLA of ZnTe in N{sub 2} do not reveal the presence of atomic nitrogen. This suggests that the high hole concentrations in laser ablated ZnTe are produced by a new and different mechanism, possibly energetic beam-induced reactions with excited molecular nitrogen adsorbed on the growing film surface, or transient formation of Zn-N complexes in the energetic ablation plume. This appears to be the first time that any wide band gap (Eg > 2 eV) II-VI compound (or other) semiconductor has been impurity-doped from the gas phase by laser ablation. In combination with the recent discovery that epitaxial ZnSe{sub l-x}S{sub x} films and heterostructures with continuously variable composition can be grown by ablation from a single target of fixed composition, these results appear to open the way to explore PLA growth and doping of compound semiconductors as a possible alternative to molecular beam epitaxy.
Date: April 1, 1995
Creator: Lowndes, D.H.; Rouleau, C.M.; Budai, J.D.; Poker, D.B.; Geohegan, D.B.; Zhu, Shen et al.
Partner: UNT Libraries Government Documents Department

Loss measurements of stoichiometric Ti and O implanted LiNbO{sub 3} waveguides

Description: Lithium niobate is a commercially important electro-optical material, part of the advanced technology effort in optical communication and computing. Electro-optical devices are now used to substitute traditional electronic devices in communications and in information processing. Planar waveguides created by the implementation at 500 C of 2.5 {times} 10{sup 17} Ti ions/cm{sup 2} and 7.5 {times} 10{sup 17} O ions/cm{sup 2} have been characterized for loss by the scattered light technique. Preliminary results indicate losses of less than 2.5 dB/cm.
Date: December 31, 1995
Creator: Williams, E.K.; Ila, D.; Sarkisov, S.; Venkateswarlu, P. & Poker, D.B.
Partner: UNT Libraries Government Documents Department

Loss measurements and stoichiometric dependence of Ti and O implanted LiNbO{sub 3} waveguides

Description: Planar waveguides created by the implantation at 500 C of 2.5 x 10{sup 17} Ti ions/cm{sup 2} and 2.5, 5.0 and 7.5 x 10{sup 17} O ions/cm{sup 2} have been characterized for loss by the scattered light and cutback techniques. Results indicate losses of less than 2.5 dB/cm to 3 dB/cm for waveguides with a Ti:O ratio of 1:3 and losses of over 7 dB/cm{sup 2} for waveguides with Ti:O ratios of 1:1 and 1:2.
Date: October 1, 1996
Creator: Williams, E.K.; Ila, D.; Sarkisov, S.; Venkateswarlu, P.; Poker, D.B. & Hensley, D.K.
Partner: UNT Libraries Government Documents Department