Development of twin-tip STM and application to surface science

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Twin-tip STM has been manufactured by way of trial to apply it into surface science for example, measurement of electric conductivity of surfaces, observation of wide area of surfaces, study on surface electromigration and fabrication and characterization of nanostructures on surfaces. Atomic resolution images of the Si(111)7x7 reconstructed surface have been obtained using either of scanning tips. The instrument has two retractable electrodes in addition to the two scanning tips so that the rlectric conductivity is measured by using four(six)-probe method. The electrodes can be used for applying the sample bias to a thin film insulated from the substrate for the STM observation of the sulface. It has been found that the sample valtage under the tip can be measured through the voltage of the tip under the STM imaging condition (sample bias of 2V and tunneling current of 1nA). thus, the electric conductivity of the sample can be measured without mechanical contact between the sample and … More the tip, the damage of the sample surface and the tip being avoided. Since probe current can be fed into the sample through the tip, electric property of Schottky contact beyween the tip and the sample can be studied under the well-defined condition.The electric conductivity of the bulk part of semicoductor samples becomes much larger at high temperatures, where many sulface phase transition occurs and good quality adsorbate-induced structures and crystalline films grow. Semiconductor thin films insulated from the substrate are needed to measure the change of the surface electric conductivity due to the surface phase transitions and structure changes. Thus, epitaxial growth method of silicon thin crystal film which is insulated from the Si(111) substrate by calcium fluoride (CaF_2) film has been developed. Metal adsorption induced facetting of vicinal silicon surfaces has been also studied. Anisotropic surfaces formed there will be good subject of the twin-tip STM study, becouse those are expected to show interesting relation between the atomic structures and the electronic properties. Less