Study of the chemistry of NH3 on aluminum nitride and oxynitride under steady-state conditions using external-reflection infrared spectroscopy

Polarization-modulated Fourier-transform infrared reflection absorption spe ctroscopy has been applied to the characterization of thin films of AlN and Al oxynitride ('AION') on NiAL(111) and to the observation of surface chem ical processes under steady-state conditions in a static NH3 ambient of up to 200 Torr. AN films, grown by dosing NiAl(111) with NH3 at similar to 123 0 K, are found to be structurally inhomogeneous and largely disordered, wit h no evidence of chemisorption at 300 K in a background of 200 Torr of NH3. AlON films, grown by dosing NiAl(111) with NO near 300 K and annealing to 1000 K, appear more homogeneous and show distinct surface and bulk vibratio nal modes. The former responds reversibly to chemisorbed NH3 which can be d etected under steady-state conditions by the appearance of the delta(s) sym metric deformation mode. In comparison to similar results for Al2O3, the de lta(s) frequency indicates a lesser degree of Lewis acidity for the AlON su rface. (C) 1999 Elsevier Science S.A. All rights reserved.