Development of High Voltage Field Ion Microscope for the Studies of Surface, Interface, and Substrate of Materials

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A high voltage field ion microscope (HV-FIM) has been developed for technological advances of observing atomic structures of surface, interface, and substrate of materials. As is well known, the applications of field io <eta> microscopy have been limited to fine refractory metal wires primarily due to the requirement of a high electric field of 10GV/m. One would require the design of a high voltage vacuum feedthrough in order to observe atomic arrangements of tip-specimen with a large radius of curvature. Main components of the present HV-FIM are ultra-high vacuum chamber of <10^(-7)> Pa, liquid <N_2> cooled cold finger, and the high voltage devices with a maximum voltage of 60kV. An equipment of the specimen exchange chamber enabled efficient observations of a specimen without leaking the whole vacuum system to an ordinary atmosphere.HV-FIM observations boron-coated tungsten were carried out. By heating the coated specimen at 1200 K, the formation of <W_2B_5> was identified, and this coincides with the existence of tungsten borides at the core of boron fibers. An observation of the atomic structure of bulk tungsten, instead of fine tungsten wire, was successfully made using the HV-FIM, and He-ion image of W-atoms was obtained with a high resolution of 0.4nm. The above results obtained from the tip having a large radius of curvature may not be possible without a use of HV-FIM.