Toshiaki Osaka

Influences of substrate surface structures and water vapor on the nucleation, epitaxy and graphoepitaxy of tin thin films grown on potassium chloride substrates

Abstract This film of tin were prepared by vapor deposition on vacuum-cleaved potassium chloride substrates with and without exposure to water vapor, and on air-cleaved substrates. Examination by optical and electron microscopy revealed that the cleavage surface of the substrate had structured composed of six characteristic features. On clean substrates, {100} epitaxial films and graphoepitaxial films were produced, depending upon the surface structures of the substrate. For the case of air-cleaved and water-vapor-exposed substrates, a decrease of the {100} epitaxy and modifications of the substrate surface were observed. Possible mechanisms for these findings are discussed.

Role of chemical bonding in the epitaxial growth of noble metals on ionic crystal substrates

Thin films of Au were deposited onto MgO substrates cleaved in ultrahigh vacuum. The films, which were examined by transmission electron microscopy and electron diffraction, did not grow with a (111) orientation observed in a Au/NaCl system but with a (100) orientation which had been observed in a Pd/MgO system. In order to obtain some insight into the differences in the epitaxial orientations, we studied interfacial chemical bonding states in Au/MgO(100), Pd/MgO(100), and Au/NaCl(100) systems using total pair‐potential calculations and discrete variational Xα calculations. The results show that interfacial interaction in both the Au/MgO and the Pd/MgO system is stronger than that in the Au/NaCl system. The relation between the strength of the interfacial chemical bond and the epitaxial orientation in the above systems is discussed.

Lattice location study on H in Ta by the channeling method

By the channeling method using the nuclear reaction 1 H( 11 B, α)αα, the lattice location of H in TaH 0.07 (α-phase) was determined at room temperature, and the effect of strain on the hydrogen location was investigated by introducing internal strains by thermal cycling that gives rise to precipitation and redissolution of the β-phase. It is concluded that hydrogen atoms are located at tetrahedral sites in the α-phase of a Ta-H system, and the location does not change by such thermal cycling. Compared with the previous results on H in V and Nb, the present result indicates that the hydrogen location in Ta is less sensitive to the strain than in V as in the case of Nb.

Surface Phonon Dispersion Curves of NiAl(111)

The surface phonon dispersion curves of the NiAl(111) surface have heen measured along \overlineΓK of the two dimensional Brillouin zone by means of high-resolution energy loss spectroscopy. The observed dispersion curves were compared with lattice dynamical calculations of a slab shaped crystal on the basis of a force constant model including up to the third nearest-neighbor interaction. Good agreement between the experimental and calculated curves was obtained for two different combinations of the surface force constants, which suggests the existence of two different models concerning the surface atomic relaxation.

Nucleation and growth of vacuum-deposited tin on amorphous substrates having microscopic steps

Abstract SiO was deposited onto UHV-cleaved KCl crystals in order to produce amorphous substrates having a step whose radii of curvature at the corner are smaller than 1 nm. Sn was then deposited from the vapor phase onto these substrates at 150°C. The resulting Sn particles were examined by high resolution TEM and electron diffraction. Particles in contact with the step walls grew over the steps and aligned graphoepitaxially in the following three orientations: (100), (101), or (001) planes which were parallel to the step terrace and the [010] direction which was perpendicular to the step wall. The radii of curvature of the stepped amorphous substrates were measured from TEM images. The results indicated that the vapor-deposited Sn nucleated in the liquid state at the corner of the steps of the SiO substrate and then aligned graphoepitaxially with the step walls and terraces, through the processes of solidification.

Non-epitaxial and graphoepitaxial growth of tin thin films on an UHV-cleaved sodium chloride substrate

Abstract Thin films of tin were prepared by vacuum deposition on an UHV-cleaved sodium chloride substrate at room temperature in order to study the growth features. The small particles of tin, which were examined by high resolution TEM and electron diffraction, grew graphoepitaxially on steps, whereas those on flat areas were located and oriented almost randomly. The results, therefore, indicate that several works concerning teh epitaxial growth of tin that has been reported so far have been performed on surfaces with a high density of steps parallel to the 〈100〉 direction of the substrate.

Profile imaging of the InSb{111}A,B-(2 × 2) surfaces

Abstract The InSb{111}A,B-(2 × 2) surfaces have been investigated using ultrahigh vacuum high-resolution transmission electron microscopy in the profile-imaging geometry. The multi-slice image simulation for these two surfaces shows that a through-focal series of experimental images strongly supports the In-vacancy buckling model for the InSb(111)A-(2 × 2) surface and the T 4 -site Sb trimer model for the InSb(111)B-(2 × 2) surface.

Direct observation of Au deposition processes on InSb{111}A,B -(2 × 2) surfaces

We have studied in situ direct observations of depositing Au onto InSb{111}A,B -(2 ? 2) surfaces up to monolayer (ML) thickness and their reaction processes by using high-resolution transmission electron microscopy in the profile-imaging geometry. During Au deposition up to ?ML coverage, the In-vacancy and Sb-trimer outermost layers of the surfaces change their (2 ? 2) structures to (1 ? 1) periods, and the deposited Au atoms form the regions which agglutinate in the vicinity of their surfaces. Further, Au deposition (e.g.??ML) leads to a partial disruption of the substrate and to an infiltration of the substrates inside. The difference between the (111)A and the (111)B substrates is that the infiltration in the latter slowly progresses in comparison with the former. The difference in growth of gold in these systems is probably due to the polarity and the surface structures of their substrates.

Structure and Electronic States of the α-Sn(111)-( 2×2) Surface

Scanning tunneling microscopy (STM) has been used to study the surface structure and electronic states of α-Sn(111) films grown heteroepitaxially on InSb(111)A-(2×2). The wide area STM image shows a large number of domains existing on the terrace, each having an average size of about 100 A and a period of (2×2). The magnified image shows evidence of a T 4 -adatom and rest-atom pair reconstructed structure for the α-Sn(111)-(2×2) surface, as expected from the ab initio calculations. Furthermore, the result that the adatom and the rest-atom appear simultaneously in the occupied state image can be explained by the existence of back bond states in the adatom configuration.

Direct imaging of the evolving Au/InSb(111) B interface

In situ high-resolution transmission electron microscopy in the profile geometry has been used to observe the evolving features of the Au/InSb(111) B-(2×2) interface. During Au deposition in the range between 0 monolayer (ML) and ∼1 ML coverage, the outermost Sb-trimer layer of the InSb(111) B-(2×2) substrate changes in contrast, presumably revealing that deposited Au atoms are partially captured into it. At ∼2 ML coverage, an unknown phase emerges on the outermost layer, beyond which it continues to grow epitaxially in an island state, causing partial disruption of the substrate. The phase is identified as Au9In4 alloy with a γ-brass structure determined from a digital Fourier transform diffractogram and a transmission electron diffraction pattern. The epitaxial relationship of Au9In4 with the substrate is given by (111) InSb∥(111) Au9In4 and [110] InSb∥[110] Au9In4. The high resolution-profile transmission electron microscopy images of this alloy agree well wITH the results calculated by the multislic...