Nanostructures formations, electrical transitions and implanted impurity migration in α-alumina modified by Ti ion beam assisted W deposition and subsequent thermal annealing

Abstract

Concentration depth profiles of implanted impurities and surface microstructure of modified polycrystalline α-Al 2O 3 were studied in the vicinity of the post-implantation annealing temperature of 1380 °C where a transition to low-resistance state occurs. The modification procedure was Ti ion implantation with simultaneous deposition of W (IBAD) and subsequent isochronal annealing in vacuum at temperatures ranging from 900 to 1500 °C. Direct metal vapor vacuum arc pulsed implantation of Ti ions (50–150 keV, 10 17 ions per cm 2, RT) was used. This treatment of ceramics is of interest for both basic and applied research. On the scientific side, it is intended to elucidate the correlation between the physical properties of ceramics and their nanostructure. From the point of view of the applications, this treatment is promising for production of low-cost, high ohmic thin film resistors and advanced gradient thermally stable metal/ceramic interfaces. Rutherford backscattering spectrometry (RBS) of 4He + ions with initial energy of 1.8 MeV was used to determine the concentration depth profiles of the implanted impurity in the Al 2O 3 matrix. Scanning electron microscopy was applied to surface microstructure studies of the ceramics. RBS spectra were measured from the alumina samples annealed at temperatures corresponding to the maximum of the sheet resistivity–annealing temperature curve. The effective diffusion coefficient of implanted Ti in Al 2O 3 was found to be 2.43×10 −14 cm 2 s −1 for a temperature range of 1150–1230 °C. Nanocrystalline grains with a typical diameter of approximately 40–50 nm were formed at all post-implantation annealing temperatures. These nanocrystallites agglomerate into larger particles, the latter forming a quasi-crystalline surface structure at approximately 1150 °C. The transition to the low resistance electric state in Al 2O 3 at the post-implantation annealing temperature of approximately 1380 °C occurs simultaneously with a redistribution of the implanted Ti ions towards the near-surface layer and with a formation of a 2D honeycomb (average structure unit is 330 nm in length) nanostructure like an infinite cluster. The grain growth depression observed at temperatures near or above 1150 °C is consistent with the assumption that a diffusion barrier of the W and Ti constituents is formed on the nanocrystallite surfaces.