Nicole Bordes

Alpha-, boron-, silicon- and iron-ion-induced current transients in low-capacitance silicon and GaAs diodes

High-speed current transient measurements were made over a large range of linear energy transfer (LET), using a wideband 70-GHz (6-ps-risetime) sampling oscilloscope on high resistivity GaAs diodes and 1-, 3-, and 10- Omega -cm silicon diodes. For 3- and 5-MeV alpha particles, 12-MeV boron, 18-MeV silicon, and 12- and 100-MeV iron ions incident on these devices, risetimes in the range from about 38 ps to 100 ps were produced depending on LET and device resistivity. Results are compared to the productions of various models. >

A comparison between the irradiation damage response of spinel and zirconia due to Xe ion bombardment

The mechanical properties of Xe-implanted spinel and cubic zirconia surfaces, as determined by nano-indentation measurements, are distinct and the differences can be related to their microstructures. Upon Xe(2+) ion irradiation at cryogenic temperature (120K), the Young`s modulus of irradiated spinel increases slightly (a few percent) then falls dramatically until the modulus is only about 3/4 the unirradiated value. The maximum modulus occurs concurrent with the formation of a metastable crystalline phase of spinel. The subsequent elastic softening at higher Xe(2+) doses is an indication of the onset of amorphization of the spinel. Xe-implanted zirconia surfaces behaves differently, in all cases showing almost no change in elastic modulus with increasing Xe(2+) ion dose. This is consistent with microstructural observations of Xe-implanted zirconia crystals which, unlike spinel, show no change in crystal structure with increasing ion dose. The defected layer in zirconia due to ion damage simply thickens with increasing Xe(2+) dose. This thickening may be a consequence of compressive stresses that form in the ion- implanted surface region. The hardness of both spinel and zirconia increases slightly for low Xe(2+) ion doses. At higher doses, zirconia shows little change in hardness, while the hardness of the implanted spinel falls by more than a factor of two. The initial increase in hardness of both spinel and zirconia is probably due to point defect accumulation and the precipitation of small interstitial clusters, while the drop in hardness of spinel at high Xe(2+) ion doses is due to the formation of an amorphous phase.

Properties of thin-film YBa2Cu3O7−x superconductors grown on ion-irradiated SrTiO3 substrates

Abstract The surfaces of [001] SrTiO 3 substrates were modified by implantation of 400 keV Ne 2+ ions at 77 K at doses of 5 × 10 14 , 10 15 and 5 × 10 15 ions / cm 2 . Superconducting YBa 2 Cu 3 O 7 − x thin films were then deposited on these substrates by the electron beam co-evaporation and post-annealing process. The microstructure and properties of these films were characterized by various techniques and compared to a reference film that was grown on an unirradiated SrTiO 3 substrate. The film on the substrate irradiated at the highest dose (5 × 10 16 ions / cm 2 ) showed a deterioration of its properties as reflected by a loss in epitaxy, decrease in transition temperature and increase in transition width. However, films grown on the substrates irradiated at the lower doses showed improvements in the properties as compared to the reference film. The best film was obtained on the substrate irradiated at 10 15 ions/cm 2 . This film exhibited a significant improvement in epitaxy and an increase in the transition temperature as compared to the reference film.

Dislocation loops in spinel crystals irradiated successively with deep and shallow ion implants

This study examines the influence of microstructural defects on irradiation damage accumulation in the oxide spinel. Single crystals of the compound MgAl{sub 2}O{sub 4} with surface normal [111] were irradiated under cryogenic temperature (100K) either with 50 keV Ne ions (fluence 5.0 {times} 10{sup 12}/cm{sup 2}), 400 keV Ne ions (fluence 6.7 {times} 10{sup 13}/cm{sup 2}) or successively with 400 keV Ne ions followed by 50 keV Ne ions. The projected range of 50 keV Ne ions in spinel is {approximately}50 mn (``shallow``) while the projected range of 400 keV Ne ions is {approximately}500 mn (``deep``). Transmission electron microscopy (TEM) was used to examine dislocation loops/defect clusters formed by the implantation process. Measurements of the dislocation loop size were made using weak-beam imaging technique on cross-sectional TEM ion-implanted specimens. Defect clusters were observed in both deep and shallow implanted specimens, while dislocation loops were observed in the shallow implanted sample that was previously irradiated by 400 keV Ne ions. Cluster size was seen to increase for shallow implants in crystals irradiated with a deep implant (size {approximately}8.5 nm) as compared to crystals treated only to a shallow implant (size {approximately}3.1 nm).

Superconducting YBaCuO thin films by Cu-ion implantation

We have investigated the fabrication of thin‐film superconductors by Cu‐ion implantation into initially Cu‐deficient Y(BaF2)Cu thin films. The precursor films were co‐evaporated on SrTiO3 substrates, and subsequently implanted to various doses with 400 keV 63Cu2+. Implantations were performed at both LN2 temperature, and at 380 °C. The films were post‐annealed in oxygen, and characterized as a function of dose by four‐point probe analysis, x‐ray diffraction, ion‐beam backscattering and channeling, and scanning electron microscopy. It was found that a significant improvement in film quality could be achieved by heating the films to 380 °C during the implantation. The best films made became fully superconducting at 60–70 K, and exhibited good metallic R vs T behavior in the normal state.

The Influence of Tte Substrate Surface on the Nucleation and Growth of Superconducting Thin Films

The quality of epitaxially grown superconducting thin films is dependent on the nature of the substrate surface. In this study, the surface of oriented SrTiO{sub 3} single crystals was modified by mechanical polishing, thermal annealing and chemical etching. A study of the YBa{sub 2}Cu{sub 3}O{sub 7-x} thin films grown on these substrates showed that high quality superconducting films were obtained when the substrate surface was highly oriented in the direction and was also microscopically smooth. 7 refs., 3 figs., 1 tab.