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 t he introduction of a funnel-shaped microextraction electrode to a conv entional atom probe. The electrode scans over an unsmoothed specimen s urface at a negative bias voltage and stands still right above an apex of a microcusp. Then the high electric field required for field evapo ration of the apex atoms is confined in an extremely small space betwe en the small open hole of the funnel-shaped electrode and the apex of the microcusp. The Pt and Si extraction electrodes are fabricated by m echanical and lithographic processes, respectively, and the diameter o f 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 u nique capability of the SAP, diamond grown by chemical vapor depositio n (CVD) and fabricated by high-pressure high-temperature (HPHT) proces ses was mass analyzed atom-by-atom. The study has revealed that the di amond contains an unexpectedly large amount of hydrogen and that the c lusters of 5, 8, and 16 carbon atoms in the diamond structure are weak ly bound by hydrogen bonds.