Diamond tips in low temperature scanning tunneling microscopy

Scanning tunneling microscopy and ballistic electron emission microscopy measurements are presented using boron-doped diamond as tip material. The experiments were carried out at 77 K on CoSi2/Si(1 1 1), a system previously investigated by conventional tungsten tips. Compared to tungsten tips, the measurement stability is improved, while atomic resolution is still easy to obtain in topography scans. A threshold shift in ballistic electron emission spectra is found to depend on the magnitude of the tunneling current. We explain this shift in terms of an ohmic series resistance in the tunneling circuit due to poor tip contacting or too low a carrier concentration in the tip material at low temperatures.