Characterization of nanoscale atomic motion of Si in polycrystalline Cu layer.

Atomic migration of silicon through grain boundaries of a thin polycrystalline Cu film and island formation on the Cu surface were studied in the temperature range of 403-520 K. Samples used in these experiments was prepared on Si(111) wafers by room temperature magnetron sputtering and they consisted of amorphous Si layer (80 nm) and polycrystalline Cu layer (40 nm). The silicon layer served as the source layer of diffusion, while the copper surface was the accumulation surface. Detection of Si atoms on the accumulation surface after penetration through the Cu layer was made by low energy ion scattering spectroscopy and the grain boundary diffusion coefficient DGB was determined from the appearance time. The depth distribution of Si in the Cu film was analysed by secondary neutral mass spectroscopy. From this depth distribution, DGB was also determined. By scanning probe microscope and electron microscope measurements, it was experimentally detected that Si atoms on the Cu surface did not form a continuous layer. Instead, amorphous Si islands were formed at the accumulation surface with surface protrusions in their centres.

Calcium silicate layer on titanium fabricated by electrospray deposition.

Titanium and its alloys have been used as implant materials. Non-ideal osseointegration of the implant materials has facilitated the development of the bioactive coatings on the implant surfaces. In this work, the bioactive calcium silicate (CaSi) powder prepared in a green synthesis route was used to cover the surface of Ti implants by a facile electrospray deposition method. Post annealing in air was also applied to form the oxidation layer on the Ti surface with the aim of increasing the bond strength between the CaSi coating layer and Ti substrate. For the characterization of the coatings several analytical methods such as X-ray diffraction, scanning electron microscopy, secondary neutral mass spectrometry, and Raman-spectroscopy were used, in addition to the measurement of bond strength and corrosion resistance. The results indicated a uniform CaSi layer with a thickness of about 1 µm deposited on the Ti substrate. Annealing in the range of 700-900 °C in air resulted in the formation of rutile phase of TiO2; more importantly, annealing at 800 °C did not significantly affect the composition of the CaSi layer consisting of ß-Ca2SiO4. The bond strength between the coating layer and Ti substrate can be remarkably enhanced at an annealing temperature of 700 or 800 °C compared with the as-prepared coating without annealing. The annealed coatings had a better corrosion resistance than the as-prepared coating. It is concluded that the electrospray method associated with the post-annealing can be successfully used for the deposition of a CaSi layer with a defined structure and composition on titanium implants.