The oxidation kinetics of thin nickel films between 250 and 500 °C

Abstract

The oxidation kinetics of thin polycrystalline Ni films is of fundamental interest as well as being relevant for potential applications. It was investigated between 250 and 500 °C for 10-150 nm thick films. Even for the thinnest films, oxidation was found to be diffusion controlled. The high density of grain boundaries in the formed NiO layer leads to a tracer diffusion coefficient that is higher than reported in the literature, indicating accelerated Ni diffusion along the grain boundaries. Cr segregation to the bottom interface in doped-NiO films hindered the acceleration of the oxidation of thin films.

Research Update: Ionotronics for long-term data storage devices

“…On the other hand, doping can increase the defect concentration of the oxide film and therefore the oxidation rate constant, as will be investigated in a forthcoming study. 16 Furthermore, below 1000 • C, Ni oxidation is determined by the fast grain boundary diffusion of Ni in NiO. 24,25 We therefore expect that the optimization of the film microstructure by decreasing the oxide grain size will enhance the relevant diffusivity.…”

“…Details can be found in a further study. 16 Note that for surface-reaction-controlled oxidation, a strong change with pO 2 was expected. Furthermore, a thickness of 50 nm exceeds the validity range of the Cabrera-Mott model because electron tunneling is only up to a few nm relevant (cf.…”

“…Doping experiments for NiO will be discussed in a forthcoming publication. 16 (iii) Oxides used as electrolyte materials typically have high D* values (e.g., Y-doped ZrO 2 close to the orange line in Fig. 6).…”

“…Therefore Cr, Al, Ti, V, Zn, Ni, and Co were selected. Films with thicknesses of 50 nm were grown on polycrystalline Al 2 O 3 substrates, and their oxidation kinetics was measured (the resulting oxides were polycrystalline, as found by scanning and transmission electron microscopy studies 16,17 ). The results of these measurements are presented in Fig.…”

Enhanced Oxidation of Nickel at Room Temperature by Low-energy Oxygen Implantation

“…It has been shown (both theoretically and experimentally) that the concentration of cation vacancies scales with the oxygen partial pressure, pO2, as (pO2) n , where the exponent n equals 1/2, 1/4 or 1/6 for the neutral or singly and doubly charged Ni vacancies, respectively. [1,31,32] Consequently, any quantity, x, directly related to the diffusion of charged particles by cation vacancies within the oxide film, such as the oxide thickness or the change in weight as a result of oxidation, should be related to the oxidation time, t, as x= K t n , i.e. log(x)=log(K) +n log(t), where K is the rate constant [1] .…”