Positron annihilation analysis of nanopores and growth mechanism of oblique angle evaporated TiO₂ and SiO₂ thin films and multilayers


Positron annihilation analysis of nanopores and growth mechanism of oblique angle evaporated TiO₂ and SiO₂ thin films and multilayers

García-Valenzuela, A.; Butterling, M.; Liedke, M. O.; Hirschmann, E.; Trinh, T. T.; Elsherif, A. G. A.; Wagner, A.; Alvarez, R.; Gil-Rostra, J.; Rico, V.; Palmero, A.; González-Elipe, A. R.

The nano-porosity embedded into the tilted and separated nanocolumns characteristic of the microstructure of evaporated thin films at oblique angles has been critically assessed by various variants of the positron annihilation spectroscopy. This technique represents a powerful tool for the analysis of porosity, defects and internal interfaces of materials, and has been applied to different as-deposited SiO₂ and TiO₂ thin films as well as SiO₂/TiO₂ multilayers prepared by electron beam evaporation at 70° and 85° zenithal angles. It is shown that, under same deposition conditions, the concentration of internal nano-pores in SiO₂ is higher than in TiO₂ nanocolumns, while the situation is closer to this latter in TiO₂/SiO₂ multilayers. These features have been compared with the predictions of a Monte Carlo simulation of the film growth and explained by considering the influence of the chemical composition on the growth mechanism and, ultimately, on the structure of the films.

Keywords: Positron annihilation; Nanopores; OAD thin films; TiO₂; SiO₂; Growing mechanism

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Publ.-Id: 30787