Atomic Level Study of Photo-Stimulated Field Emission from Insulating Thin Layers Utilizing the Scanning Atom Probe

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Irradiation of light to insulators and semi-insulators at a negative bias voltage induces photo-stimulated field emission. Photo-stimulated field ionization and field evaporation are also observed. In this study the correlation between the field emission characteristics and the surface composition of low conductive materials such as CVD and HPHT diamonds, 99.8 and 99.99% purity graphites, vitreous carbon, carbon nano-tubes (CNT), silicon micro-tips, silicon pyramid, silicon grains is investigated utilizing the unique capability of the scanning atom probe(SAP). The photo-stimulated field evaporation was observed by applying pulsed voltage and pulsed YAG laser beam to the specimens. The study revealed that the diamonds contain a large amount of hydrogen depending on the growth process. Many carbon clusters are detected from all carbon specimens, especially form the 99.99% pure graphite. Silicon micro-tips are highly corroded by HF acid. Carbon, oxygen and hydrogen diffuse into the tips. In order to study the photo-stimulated field emission a SiOィイD22ィエD2 layer is deposited covering a transparent conductive layer on a glass plate. However, no photo-stimulated field emission could be observed possibly due to defects in the SiOィイD22ィエD2 layer where leak current flows. Slope and intercept of the F-N plot are plotted. The plotted chart indicates that the work function of the CNT is the lowest among the analyzed specimens. While the work function of the CNT increases by hydrogen adsorption, that of silicon decreases. A new SAP with a position sensitive ion detector is under development to exhibit the 3D-distribution of compositions at an atomic resolution.