S. Hyodo

Field ion‐scanning tunneling microscopy of alkali metal adsorption on the Si(100) surface

We have constructed a scanning tunneling microscope (STM) equipped with a field ion microscope (FIM), by which one can monitor and shape the STM probe tip on an atomic scale in situ in the STM chamber. Taking advantage of a well‐defined tip prepared by a FIM, we have greatly improved the stability and reproducibility of the performance of the STM. Li and K adsorption on the Si(001) 2×1 surface has been investigated by field ion‐scanning tunneling microscopy (FI‐STM). The STM images have shown that at the initial stage of adsorption, Li (K) atoms (1) adsorb on top of one of the dimer‐forming Si surface atoms and (2) stabilize the asymmetric (buckled) dimerization, and (3) form linear chains, perpendicular to the substrate 2×1 dimer rows. Our observations suggest that alkali metal adsorption on the Si(001) 2×1 surface may be significantly different from the conclusions of earlier reports.

Atomic hydrogen chemisorption on the Si(111) 7×7 surface

Chemisorption of atomic hydrogen on the Si(111) 7×7 surface was investigated using scanning tunneling microscopy. Contrary to the recent report by Golovchenko’s group that the monohydride phase is not stable even at room temperature, resulting in the formation of the trihydride phase, our scanning tunneling microscopy (STM) experiment has shown that the monohydride phase is indeed the stable phase on the clean Si(111) 7×7 surface.

New versatile room‐temperature field ion scanning tunneling microscopy

We have designed and developed a series of room‐temperature field ion scanning tunneling microscopes (RT FI‐STMs). The great advantages of the RT FI‐STM are (1) almost simultaneous use of both the STM mode and FIM mode is possible without wasting machine time and thermal drift; (2) inspection and manipulation of a STM tip in situ in the STM system can be performed and, thus, each tip can be used over several months, maintaining a desired atomic resolution; and (3) a well‐characterized tip ensures a very high (∼100%) success rate in STM imaging with a known resolution. Several examples are given.

Scanning tunneling microscope equipped with a field ion microscope

A combined field ion (FIM) and scanning tunneling microscope (STM), which is called ‘‘FI–STM,’’ was designed, constructed with multiple surface analytical functions. The instrument has been operated successfully by observing the detailed structures of the graphite (0001) and the Si(111)7×7 surfaces. The FI–STM is equipped with a low‐energy electron diffraction/Auger electron spectroscopy system and a sputtering gun and/or heating devices for preparing and characterizing specimen surfaces. The field ion microscope is operated at room temperature to observe the geometry of the STM scanning tip in situ in the course of STM investigations.

Anomalous Permeation of Low Energy Neon Atoms in Tungsten at Low Temperatures

Atomic depth profiles of tungsten tips irradiated with neon atoms of low thermal energy [i) 77 K ii) 300 K] were measured with the aid of an atom-probe field ion microscope. The tip temperature was maintained usually at 25 ± K during the course of atom-probe measurements to practically eliminate thermal diffusion. In the case of i), neon atoms were detected at locations as deep as 300 layers from the surface, a depth much greater than that predicted assuming the usual diffusion mechanism. In the case of ii), however, no neon atoms were detected in the matrix. At present no theory seems to have been established to explain such anomalous penetration of low energy neon atoms.

Field ion scanning tunneling microscopy and its application to oxygen adsorption on the Ag(110) 1×1 surface

A field ion-scanning tunneling microscope (FI-STM), a combination of a scanning tunneling microscope (STM) and a field ion microscope (FIM), was constructed with successful performance. It was applied to the investigation of the oxygen adsorption on the Ag(110) surface. The FI-STM results show that atomic oxygen is mobile on the Ag surface at room temperature until it finds two free mobile Ag atoms to form an Ag-O-Ag linear chain along the direction. Our FI-STM data suggest that, in addition to this type of atomic oxygen adsorption, there is another type of oxygen adsorption over the Ag-O-Ag linear chains with much weaker bonding to the Ag substrate

Intermittent Automodulation Observed in Fe-3%Si Reeds

Automodulation was observed to occur in Fe-3%Si polycrystalline reed specimens intermittently and rather irregularly. This forms a striking contrast to the continuous automodulation usually observed in such materials as Zn or Mg. This unfamiliar automodulation, which seems to have three different modes, was explained in terms of phase transformation and stochastic processes.

Resonance Curves Obtained in the Vibration of Fe-3%Si Reeds

A series of amplitude-vs-driving-frequency measurements were performed for the forced vibration of Fe-3%Si reeds. With an increase in the magnitude of the driving force, the resonance frequency tended to shift to the lower side, similarly to soft-spring-type resonance. For sufficiently large driving force, however, it was found that the resonance curve became skewed and the resonance frequency began to shift to the higher side, similarly to hard-spring-type resonance.