I. Kamiya

Field ion-scanning tunneling microscopy

Abstract A scanning tunneling microscope combined with a field ion microscope, which we call “FI-STM” has been constructed and tested successfully. The details of the principles and performance of the FI-STM are described. Several examples of its applications for Si (111) and Si (100) surfaces are presented as illustrations of the power of the instrument.

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.

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.

A role of a tip geometry on STM images

Scanning tunnelling microscopes operable in both ultrahigh vacuum (UHV) and aqueous conditions are described with emphasis on a tip geometry. An atomically resolved STM image was obtained for the Si(111)‐Mo√3 surface in UHV condition and changes of a diffraction grating surface in aqueous condition due to an electrochemical reaction were monitored.

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.

Atom-probe study of the initial stage of selective oxidation of Ni from the Cu-Ni alloy system

Abstract The initial oxidation stages of Ni and Ni-Cu alloys have been studied using the atom-probe field ion microscope (AP-FIM). Oxide layers were formed in situ in the FIM chamber on the clean metal surfaces at 1 × 10 −4 Torr (10 −2 Pa) O 2 at 870, 970 or 1070 K for less than l min. The atom-probe analysis on the {111} and {100} surfaces of these oxidized alloys showed that only NiO formed on all of the alloys for this relatively low oxygen partial pressure, although incipient Cu 2 O formation could not be ruled out in a few samples of the Cu-rich alloys. The concentration of oxygen in the NiO fluctuated layer-by-layer in the 〈111〉 direction as expected for its NaCl-type structure. Ne field ion images and atom-probe analyses of the oxidized samples revealed a sharp NiO/metal interface for pure Ni and for the Cu-rich alloys, and a diffuse interface extending over a few atomic layers for the Ni-rich alloys. The NiO and Ni were cube/cube oriented.

Scanning Tunneling Microscope with a Field Ion Microscope

A combined field ion (FIM) and scanning tunneling microscope (STM), which we call “FI-STM,” was designed and constructed with multiple surface analytical functions. The system is equipped with a LEED/AES system and a sputtering gun and/or heating devices for preparing and characterizing specimen surfaces. The field ion microscope (FIM) is operated at room temperature to observe the geometry of the STM scanning tip in-situ in the course of STM investigations. The instrument has been operated successfully by observing the structures of the graphite (0001), the Si (111) 7×7 and the Si (100) 2×1 surfaces.