STM observations of hafnium carbide thin films as a field emission material

We examine microscopic behaviors of work function and topography with scanning tunneling microscopy (STM). Hafnium carbide thin films were deposited on an n-type Si flat substrate by inductively coupled plasma (ICP) assisted magnetron sputtering at the argon pressure of 0.1 Pa. The surface of the films was cleaned by in-situ argon ion sputtering before STM observations. The ion current, duration and acceleration voltage were set at 3.0 /spl mu/A, 10 min, and 0.5 keV or 1.0 keV, respectively. The microscopic work function distribution was evaluated from the local tunneling barrier height (LBH) obtained with an STM apparatus. We adopted the tip-modulation method to evaluate LBH where we can obtain topograph and LBH images simultaneously. We also measured the macroscopic work function of these sample surfaces by a Kelvin probe. The work function of the 1.0 keV sputtered surface is 0.4 eV higher than that of the 0.5 keV sputtered surface.