Development of a scanning atom probe and atom-by-atom mass analysis of diamonds

A scanning atom probe (SAP) was constructed by modifying an ultrahigh vacuum scanning tunneling microscope. A unique feature of the SAP is the introduction of a funnel-shaped microextraction electrode to a conventional atom probe. The electrode scans over an unsmoothed specimen surface at a negative bias voltage and stands still right above an apex of a microcusp. Then the high electric field required for field evaporation of the apex atoms is confined in an extremely small space between the small open hole of the funnel-shaped electrode and the apex of the microcusp. The Pt and Si extraction electrodes are fabricated by mechanical and lithographic processes, respectively, and the diameter of the open hole at the sharp end of the electrode is in the range of 2 to 50 mu m and its height is 0.1 to 0.3 mm. In order to examine the unique capability of the SAP, diamond grown by chemical vapor deposition (CVD) and fabricated by high-pressure high-temperature (HPHT) processes was mass analyzed atom-by-atom. The study has revealed that the diamond contains an unexpectedly large amount of hydrogen and that the clusters of 5, 8, and 16 carbon atoms in the diamond structure are weakly bound by hydrogen bonds.