T.J. Tate

Corrosion behaviour of nitrogen implanted titanium in simulated body fluid

Abstract Titanium is one of the most important materials for medical applications, as a result of its uniquely high biocompatibility. The effect of nitrogen implantation on the biocompatibility and the corrosion resistance of cp titanium are reported. Grazing incidence X-ray diffraction studies showed that implantation formed a δ-TiNx phase. Electrochemical tests in HBSS showed an optimal decrease in corrosion current density for specimens implanted with 3 × 1017 ions cm-2 at 25 keV, compared with unimplanted titanium. Following implantation and immersion in a commercial physiological solution, phases are precipitated which are rich in calcium and phosphorus, and these hydroxyapatite precursors indicate that this implantation regime confers optimal properties of corrosion resistance and biocompatibility.

An investigation of doping of SnO2 by ion implantation and application of ion-implanted films as gas sensors

Abstract Thin films of SnO 2 were doped with 90 keV ions of Nb, Sb and Bi at a dose of 3 × 10 16 ions cm −2 . The implanted films were characterized by X-ray and ultraviolet photoemission spectroscopy, Auger depth profiling and sheet resistance measurements. Sb produces the most dramatic reduction in sheet resistance and is unique in introducing a sufficient concentration of electrons into the Sn 5s conduction band to be observable by photoemission. The response of the resistance of Sb-doped films to pulses of Ch 4 , CO and H 2 O in a flow of synthetic air was investigated over a range of concentrations and temperatures. The films display relatively poor selectivity in their sensor response. By contrast, the more highly resistive Bi-doped films show marked selectivity towards CO relative to CH 4 in sensor applications.

Adhesion of bone cells to ion-implanted titanium

The use of ion-implantation to encourage osseointegration has been investigated using an in vitro model cell culture system and surface analysis. Polished titanium discs were implanted with calcium, potassium and argon ions. The adhesion of bone-derived cells was measured using radioactively labeled cells and the morphology examined using scanning electron microscopy. Similar numbers of cells were found to adhere to the potassium and argon-implanted titanium as to control (non-implanted) titanium. However, adhesion to the calcium-implanted titanium discs was significantly reduced. Moreover, although the cells were found to be well spread on the calcium and potassium-implanted titanium, a much greater proportion of cells appeared to remain rounded and poorly attached on the argon-implanted surface. These differences are discussed in relation to the observed surface roughness and chemistry, which were assessed using interferometry and X-ray photoelectron spectroscopy, respectively.

Amorphization and crystalline regrowth of GdBa2Cu3O7 thin films by ion implantation and RTA

Abstract Thin films (about 300 nm) of GdBa2Cu3O7 (GBCO), sputtered onto MgO substrates, have been implanted with 20Ne+ ions, to doses of 5 × 1014 ions cm−2 (200 keV) and 3 × 1014 ions cm−2 (150 keV). Either implant causes amorphization above a damage threshold, the former extending throughout the film thickness, while the latter leaves some crystalline material near to the substrate interface. Rapid thermal annealing (20 s, in oxygen, at a temperature around 840 °C), induces recrystallization, which can lead to a recovery of the superconducting phase. By patterning the film with arrays of dots, it is possible to retain columnar crystalline seeds (masked from the amorphizing radiation by the dots) surrounded by an amorphous field. Subsequent annealing will induce solid-solution grain growth, leading to arrays of c-axis-oriented crystals with centres in defined positions. The ultimate aim is to extend this seeded crystal growth to cover the entire film area. While TEM is the preferred method for following the grain growth, a technique of differentially etching amorphous, micro-polycrystalline and polycrystalline material has been devised to speed up characterization. Results are presented from Tc, XRD, optical microscopy, and TEM investigations.