We have determined the schematic phase diagram in detail with high reliability for Fe silicides grown by solid phase epitaxy ͑SPE͒ on a Si͑111͒7 ϫ 7 surface at wide Fe coverage ͑0.2-56 monolayers͒ and subsequent annealing temperatures from 300 to 800°C. In the SPE growth, ␦-7 ϫ 7, 1 ϫ 1, bcc-Fe͑111͒1 ϫ 1, 2 ϫ 2, c͑8 ϫ 4͒, 3D-2 ϫ 2 ͑␣-FeSi 2 ͒, ͱ 3 ϫ ͱ 3-R30°, ␤-FeSi 2 , and fine polycrystalline phases are formed on the Si͑111͒ surface depending on Fe coverage and annealing temperature. We have characterized the surface periodic structures and morphologies of all the above Fe silicide phases using low-energy electron diffraction and scanning tunneling microscopy. Reflection high-energy electron diffraction also has been used to determine three-dimensional structures. Based on the overall view regarding the formations and changes of Fe silicide phases on a Si͑111͒ surface, we discuss the growth mechanisms.

The authors have developed an ultrahigh vacuum (UHV) variable-temperature four-tip scanning tunneling microscope (STM), operating from room temperature down to 7 K, combined with a scanning electron microscope (SEM). Four STM tips are mechanically and electrically independent and capable of positioning in arbitrary configurations in nanometer precision. An integrated controller system for both of the multitip STM and SEM with a single computer has also been developed, which enables the four tips to operate either for STM imaging independently and for four-point probe (4PP) conductivity measurements cooperatively. Atomic-resolution STM images of graphite were obtained simultaneously by the four tips. Conductivity measurements by 4PP method were also performed at various temperatures with the four tips in square arrangement with direct contact to the sample surface.

We have constructed an ultrahigh vacuum system in which surface conductivity is measured in situ by microfour-point probe method down to 0.8 K, combined with conventional surface preparation/analysis capability. In order to reduce the data scattering due to changes of the probe spacing, we have employed a dual configuration method in which the combinations with current/voltage probes are switched. The surface-state superconductivity of Si(111)-√ 7 × √ 3-In surface superstructure was confirmed with the critical temperature of 2.8 K. The critical magnetic field was 0.3-0.4 T in the surface-normal direction.

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Ultrathin films of Bi2Se3 grown on Si(111) substrate were etched into submicron-width wires by using a focused ion beam (FIB), and their electrical resistance was measured using the four-probe method with a four-tip scanning tunneling microscope. All of the procedures were performed in situ in ultrahigh vacuum without exposing the sample to air. One-dimensional conduction of the films was confirmed from the dependence of the resistance on the length of wire under measurement, meaning that successful lossless current path control laterally as well as vertically can be obtained with FIB etching. Protecting the sample surface from unintentional gallium ion beam irradiation in the FIB process was also found to be important for maintaining the intrinsic electrical properties of the Bi2Se3 films.