Michio Koinuma

In-situ and real time monitoring of the InSe surface by atomic force microscopy with atomic resolution during electrochemical reactions

Abstract An atomic force microscope (AFM) was employed to observe the surface atomic structure of the van der Waals face of InSe, one of III–VI compound semiconductors with a layered structure, in water and in electrolyte solutions. In electrolyte solutions the surface structure was monitored by AFM in real time and potential was scanned negative to positive and scanned back. The atomic image was clearly resolved at relatively negative potential, but the atomic image was completely lost at potentials more positive than 0 V, because of the formation of an amorphous Se layer. The atomic image was recovered when potential was returned to negative (

In situ observation of anodic dissolution process of n‐GaAs in HCl solution by electrochemical atomic force microscope

Anodic dissolution of a GaAs(100) face was investigated by in situ electrochemical atomic force microscope (AFM). While no surface structure change was observed at −0.6 V (vs Ag/AgCl) where no current flowed, dome structure on surface was removed, and flat surface was obtained after keeping the potential at 0 V (vs Ag/AgCl) where anodic current of ∼150 μAu2009cm−2 flowed. An atomically resolved AFM image was obtained in the flat region and shows the surface is dominated by a (111) face after the anodic dissolution.

AFM tip induced selective electrochemical etching of and metal deposition on p-GaAs(100) surface

Abstract Electrochemical atomic force microscopic (ECAFM) measurement showed that electrochemical dissolution of a p-GaAs(100) electrode in H 2 SO 4 solution was accelerated by the scanning of an AFM tip. When the AFM tip was scanned on the GaAs surface repeatedly, square hollows or wedges with critical dimensions ranging from 100 nm to several μm were fabricated. The depths of the modified structures were dependent not on the scan rate but on the number of scans as well as the electrode potential. The ECAFM study also showed that the electrodeposition of Cu on p-GaAs electrode surface selectively occurred at the modified sites.

An electrochemical AFM study on electrodeposition of copper on p-GaAs(100) surface in HCl solution

Abstract In situ atomic force microscopy (AFM) was used to observe the surface structure change during electrodeposition of Cu on p -GaAs(100) surface in HCl solution. How the electrodeposition of Cu proceeded was strongly dependent on the structure of the substrate. In the portion where the surface was relatively smooth, Cu tended to deposit first, forming randomly distributed Cu clusters followed by the three dimensional growth of the clusters. On the other hand, when the surface already had some structure, Cu deposited along the structure of the substrate.

Atomic imaging of an InSe single-crystal surface with atomic force microscope

The atomic force microscope was employed to observed in air the surface atomic structure of InSe, one of III‐VI compound semiconductors with layered structures. Atomic arrangements were observed in both n‐type and p‐type materials. The observed structures are in good agreement with those expected from bulk crystal structures. The atomic images became less clear by repeating the imaging process. Wide area imaging after the imaging of small area clearly showed that a mound was created at the spot previously imaged.

Application of scanning tunnelling microscopy to semiconductor/electrolyte interfaces

To study the application of in situ electrochemical scanning tunnelling microscopy (STM) measurements at semiconductor electrode surfaces, the tip current has been measured as a function of the semiconductor potential. It was demonstrated that the surface treatment affects very strongly the potential window for STM measurements on n-GaAs. At an ‘etched’ n-GaAs electrode, the tip current was maintained at a preset value when the potential of n-GaAs was more negative than –250mV and more positive than +700 mV. STM images of n-GaAs in the two potential regions are presented to confirm that imaging is really possible in these regions. While no surface change was observed in the negative-potential region, the surface morphology changed with time in the positive-potential region. If the surface was treated with RuCl3 solution, the preset tip current flowed when the potential was more negative than –100 mV and more positive than +100 mV. On the other hand, if the surface was treated with (NH4)2S–S solution, the preset tip current flowed only when the potential was more negative than –1000 mV, which is very close to the flat-band potential. These results are explained using an energy diagram and the importance of the surface-state density for STM characterisation is stressed. The ‘ruthenium treatment’ and the ‘sulphur treatment’ are considered to introduce and remove, respectively, the surface states. Results for CdS are also presented.

Atomic structure of bare p-GaAs(100) and electrodeposited Cu on p-GaAs(100) surfaces in H2SO4 solutions : an AFM study

Abstract An electrochemical atomic force microscope was employed to observe the surface structure of p -GaAs(100) in H 2 SO 4 solution and of electrodeposited Cu on p -GaAs(100) in CuSO 4 + H 2 SO 4 solution with atomic resolution. The atomic arrangement of GaAs(100)-(1 × 1) structure was observed in H 2 SO 4 solution after the electrode was kept in the negative potential region for 5 min to remove the surface oxide layer. The atomic image was clearer in the potential region where a small cathodic current flowed. An atomically ordered structure of closed packed hexagonal arrangement corresponding to the bulk Cu(111) face was observed at the surface of the Cu deposits on p -GaAs(100). The direction of the atom rows of the Cu deposits varied from grain to grain, suggesting that the Cu deposition on the GaAs surface was not influenced by the orientation of the underlying GaAs(100) surface. The deposition and dissolution of Cu on p -GaAs(100) in CuSO 4 + H 2 SO 4 solution were followed by AFM in real time at the atomic scale during potential cycling. The atomic image was resolved at the negative potential region where Cu deposited on the GaAs surface, but was completely lost at potentials more positive than + 0.05 V as the dissolution of the bulk Cu deposits took place. The atomic image was recovered when the potential was returned to negative (− 0.03 V) as Cu deposited on the GaAs surface again.

In situ observations of atomic resolution image and anodic dissolution process of p-GaAs in HCl solution by electrochemical atomic force microscope

Abstract Surfaces of p-GaAs(100) electrodes in HCl solution were studied by using an electrochemical atomic force microscope with atomic resolution. Truncated pyramids of relatively uniform size (50–100 nm square) were formed if p-GaAs(100) was anodically polarized. An atomic arrangement of (100)−(1 × 1) structure was observed on the terrace of the truncated pyramid when the electrode was kept in the potential region where no current flowed.

Structural study of electrochemically deposited copper on p-GaAs(001) by atomic force microscopy and surface X-ray absorption fine structure measurement

Abstract The structure of electrochemically deposited Cu on p-GaAs(001) was investigated by means of atomic force microscopy (AFM) and X-ray absorption fine structure (XAFS) measurement. AFM measurement showed that the Cu deposition proceeded strongly depending on the applied potential and the concentration of Cu2+ ion in solution. Atomic arrangements corresponding to Cu(111)-(1 × 1) and GaAs(001)-(1 × 1) were observed on top of the Cu deposits and at the regions between the Cu deposits, respectively. XAFS data demonstrated that the Cu microclusters were formed on GaAs as initial deposition.

In situ observation of anodic dissolution process of p-GaAs(001) in HCl solution by surface X-ray diffraction

Abstract The grazing incidence X-ray diffraction technique has been applied to monitor the anodic dissolution process of GaAs(001) in 0.1 M HCl solution. The surface diffraction intensity for the 〈11〉 direction of GaAs(001) was clearly observed and it decreased with time when the positive potential was applied to the electrode.