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

Abstract

A scanning atom probe (SAP) was constructed by modifying an ultrahigh vacuum scanning tunneling mi- croscope. A unique feature of the SAP is the introduction of a funnel-shaped microextraction electrode to a conven- tional 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 con- fined in an extremely small space between the small open hole of the funnel-shaped electrode and the apex of the mi- crocusp. 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 elec- trode is in the range of 2 to 50 mm and its height is 0:1 to 0: 3m m. 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 car- bon atoms in the diamond structure are weakly bound by hydrogen bonds.