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 μA, 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.