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)o ver bar2>) sapphire after annealing with a series of steps from 500 de grees C to 1100 degrees C in a reducing atmosphere. It is found that s uch 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 t emperature causes Nb migration towards the surface and results in a tw o-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 t o oxidation under environment. The metallic state was caused by anneal ing in reducing atmosphere and was distributed mainly in the sub-surfa ce 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 s apphire 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.