XPS investigation of niobium implanted into sapphire after annealing in reducing atmosphere

X-ray photoelectron spectroscopy (XPS) has been used to determine the depth profile and chemical states of the implanted niobium in (<01(1)over bar2>) sapphire after annealing with a series of steps from 500 degrees C to 1100 degrees C in a reducing atmosphere. It is found that such an annealing procedure for the 380 keV niobium with a dose of 5 x 10(16) ions/cm(2) implanted into (<01(1)over bar2>) sapphire at room temperature causes Nb migration towards the surface and results in a two-peak feature distribution profile with the large peak at the surface. The implanted niobium in sapphire is in different local environments with different charge states after annealing. Higher charge states of Nb+5 and Nb+4 are distributed mainly in the near surface region due to oxidation under environment. The metallic state was caused by annealing in reducing atmosphere and was distributed mainly in the sub-surface region with a profile of two-peak feature. The other charge states such as Nb+2 and Nb+1 may be associated with the defects retained in sapphire and distributed to deeper distance. The concentration of each charge state of niobium with depth is also presented in this paper. (C) 1998 Elsevier Science B.V. All rights reserved.