Preparation and characterization of conductive diamond for a scanning tunneling microscope tip

Owing to its extreme hardness, chemical stability and robustness, conductive diamond is an attractive material for scanning tunneling microscopy (STM). The selection of a suitable diamond and preparation of the STM tip is a challenge because electrically conductive diamonds can be grown using various methods and have anisotropic properties. A new method for the selection of conductive diamonds that is based on the registration and analysis of the tunneling I-V (TIV) characteristics of the tunnel junction between the diamond tip and graphite (0 0 0 1) surface at a constant tunneling gap is proposed. TIV should be monotonous while the tunneling currents vary from 0.1 to 6 nA with increasing bias voltages from 0.05 to 1 V. We found that HPHT diamonds grown in the Fe-Al-C-B growth system are more suitable for STM probs compared to grown in the Fe-Co-C-B system.