Norihito Ikemiya

In situ AFM observations of oxide film formation o n Cu(111) and Cu (100) surfaces under aqueous alkaline solutions

An in situ electrochemical atomic force microscope (ECAFM) has been used to investigate the formation of oxide films on Cu(111) and Cu(100) surfaces under NaOH solutiions. It has been demonstrated that the clean unreconstructed Cu(111)- and Cu(100)-(1 × 1) surfaces could be ex[osed under NaOH solutions at an electrode potential more negative than −0.5 V versus NHE. After the formation of the Cu2O layer, Cu2O(111)- and Cu2O(100)-(1 × 1) surfaces terminated by oxygen atoms have been observed in the potential range between −0.2 and −0.02 V. We have found a tilted epitaxy as well as parallel epitaxial relationships of Cu2O(111)[110]//Cu(111)[110] and Cu2O(100)[001]//Cu(100)[011] on an atomic level.

In situ observations of the initial stage of electrodeposition of Cu on Au(100) from an aqueous sulfuric acid solution using atomic force microscopy

Abstract We have investigated the atomic structures of underpotentially deposited (UPD) Cu adlayers as well as nucleation and growth mechanisms of bulk Cu deposition on Au(100) from an aqueous sulfuric acid solution using in situ electrochemical atomic force microscopy (ECAFM). The pseudomorphic Cu(1 × 1) layer on Au(100) is formed for a first full monolayer in the presence and absence of Cl − . We have found that the completion of the UPD monolayer is followed by an ideal layer-by-layer bulk Cu deposition (Frank-van der Merwe mode) at a low overpotential range.

Initial stage of the electrodeposition of Ag on Au(100) observed by in-situ atomic force microscopy

Abstract We have investigated atomic structures as well as growth morphologies of thin Ag films on Au(100) under acidic solutions by an in-situ AFM. In the UPD region, the pseudomorphic (1 × 1)-Ag layer for a first monolayer is formed through the c (✓2 × 5✓2) R 45°- Ag structure (coverage, θ = 0.6) in both HClO4 and H2SO4 solutions. In the bulk deposition region, the Ag films are formed by an ideal layer-by-layer growth mode (Frank-Van der Merwe mode) even at a high deposition rate ∼ 7.2 ML/min), which suggests that the surface diffusion process of Ag adatoms is extremely rapid. Noteworthy is that the preferential Ag deposition at regions with higher step densities or imperfections resulted in the extremely flat Ag films.

Observations of the Cu(1 × 1) adlayer on Au(111) in a sulfuric acid solution using atomic force microscopy

Abstract Atomic structures of an underpotentially deposited Cu adlayer on a Au(111) surface have been investigated using in situ atomic force microscopy. A Cu(1× 1) structure adlayer is atomically resolved just before starting the bulk deposition. We demonstrated that the first full Cu monolayer on Au(111) is a pseudomorphic (1× 1) layer in an aqueous sulfuric acid solution. We have confirmed that a Cu(5 × 5) phase adlayer has been induced by Cl−1 in the solution.

Surface structures of MgO(100) and SrTiO3(100) as revealed by atomic force microscopy

Abstract We have investigated surface structures of MgO(100) and SrTiO 3 (100) by atomic force microscopy. Atomically flat terraces separated by monatomic height steps could be obtained on the freshly cleaved MgO(100) surfaces. We have observed an atomic structure indicating a bulk terminated (1 × 1) structure on the terraces. We have found that nanocrystals, which might be an indication of the surface roughening, were formed on the MgO(100) surfaces after O 2 annealing. For SrTiO 3 (100), we have clarified that the step-terrace structure was obtained by O 2 annealing at 1100 K. Annealing at 1300 K, however, resulted in morphology changes from flat to rough and non-faceted surfaces.

Atomic structures and growth morphologies of electrodeposited Te film on Au(100) and Au(111) observed by in situ atomic force microscopy

Abstract We have investigated the atomic structures as well as the growth morphologies of electrodeposited Te films on Au(100) and Au(111) with large lattice misfits from sulfuric acid solutions using in situ atomic force microscopy. On both Au(100) and Au(111) substrates, bulk deposited Te films were formed by a Stranski-Krastanov mechanism even at a slow deposition rate of ca. 0.5 ML/min, which suggests that the surface diffusion process of Te adatoms on a monolayer-Te-coated Au surface is extremely slow. We have found that the atomic structures of Te films changed with increasing film thickness. On both the Au(100) and Au(111) substrates, the data suggested that Te(1010) films were grown through several types of relaxation layers.

Potential dependence of the surface self-diffusion coefficient on Au(100) in sulfuric acid solution measured by atomic force microscopy

Abstract We have measured the surface self-diffusion coefficient, D s values on Au(100) in aqueous 50mM H 2 SO 4 by using electrochemical atomic force microscopy (ECAFM). It was found that the D s minimum appears around the potential of zero charge for the Au(100)-(1 × 1) surface ( E PZC(1 × 1) = 270 mV versus NHE). The minimum D s value of 10 −15 cm 2 s −1 around the E PZC(1 × 1) agrees well with the extrapolated D s value under the vapor phase. The results have shown that the potential dependence of the D s values can be explained by considering not only the anion adsorption but also the role of excess charge densities at the Au(100) surface in altering the interatomic Au-Au bonds.

Superstructure observation on a MgO(100) surface

The morphology and atomic arrangement of annealed MgO(100) surfaces have been investigated. The AFM image demonstrates the existence of two different regions, the one is an atomically flat region and the other a cusp-existing one. AES spectra indicate that this cusp comes from the Ca compound segregated to the (100) surface. RHEED observation clarifies the existence of a high-order superstructure on the annealed surface.

Surface morphology for annealed and etched MgO(100)

Surface morphology dependence of MgO(100) on the variation of the annealing temperatures and times with the intermediate chemical etching are investigated by Auger electron spectroscopy (AES), atomic force microscopy (AFM) and reflection high energy electron diffraction (RHEED). AES spectra reveal that Ca segregates on the substrate surface in the higher temperature than 850 °C and this segregation can be completely removed by chemical etching with P2O5 + 2-propanol. The AFM observation clarifies that the different reconstruction of MgO(100) surface remarkably undergoes over 1000 °C.

Atomic structures and growth mechanisms of electrodeposited Ag and Te films as discerned by atomic force microscopy

We have investigated atomic structures as well as growth morphologies of electrodeposited thin Ag and Te films on Au(100) under an aqueous sulfuric acid solution. The extremely flat Ag films were formed by an ideal Frank–van der Merwe mode even at a high deposition rate [∼7.2 monolayer (ML)/min], which suggests that the surface diffusion process of Ag adatoms is extremely rapid. In the underpotentially deposited Te on Au(100), the (√2×√2)R45°‐Te structure (coverage, θ=0.5) for a first monolayer was formed through the (2×2)‐Te structure (θ=0.25) under an aqueous H2SO4 solution. In contrast with the Ag films, the bulk deposited Te films were formed by a Stranski–Krastanov mode even at a low deposition rate (∼0.5 ML/min), which suggests that the surface diffusion process of Te adatoms is extremely slow. The Te(1010) films (≳80 ML) were grown on Au(100) through the c(√2×3√2)R45° (20–30 ML) and (√2×√2)R45°‐Te(<10 ML) structures.