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In-situhigh resolution transmission electron microscopy (HRTEM) with a hot-stage holder was used to observe the initial reaction process between molten Ag-Cu-Ti and SiC at the atomic level. In the region in contact with the molten alloy, SiC tended to dissolve along the (0001) plane. The reaction product adjacent to SiC was TiC at the nominal temperature of 1123 K and TiC formed epitaxially on the basal planes of SiC in the liquid phase. The TiC growth process is the rate-determining step, and when the SiC dissolution rate increases, the TiC nanoparticles remain in the liquid phase. It was observed that TiC nanoparticles grew and joined together to form coarser particles.

In-situ high resolution transmission electron microscopy (HRTEM) with a hot-stage holder was used to observe the initial reaction process between molten Ag-Cu-Ti and SiC at the atomic level. In the region in contact with the molten alloy, SiC tended to dissolve along the (0001) plane. The reaction product adjacent to SiC was TiC at the nominal temperature of 1123 K and TiC formed epitaxially on the basal planes of SiC in the liquid phase. The TiC growth process is the rate-determining step, and when the SiC dissolution rate increases, the TiC nanoparticles remain in the liquid phase. It was observed that TiC nanoparticles grew and joined together to form coarser particles.

Electron-ion coincidence (EICO) spectroscopy [K. Mase, M. Nagasono, S. Tanaka, M. Kamada, T.Urisu and Y. Murata: Rev. Sci. Inst. 68 (1997) 1703] has recently been developed to investigate the process of ion desorption induced by the core level excitation. In the present study, we apply EICO spectroscopy to determine the O1s level of condensed H2O (ice) at 100 K. The kinetic energy of O1s photoelectrons which gives the highest coincidence yield of H+desorption is shifted by about -0.7 eV compared to the O1s peak observed in the conventional core-level photoelectron spectroscopy. It is ascribed to a core-level shift in the O1s level from which hydrogen ions desorb. The results indicate the advantages and the possibilities of the EICO spectroscopy for surface analysis.

Scanning tunneling microscopy (STM) has been used to investigate nucleation and initial growth in the heteroepitaxies of calcium fluoride ( CaF2) and barium fluoride ( BaF2) on Si(111) surfaces in situ. The fluoride depositions and the STM measurements are performed at a substrate temperature of about 400° C. STM images clearly show that a BaF2-deposited surface has a different morphology from that of CaF2-deposited surface. Preferential nucleation and island growth of BaF2only occur at steps and domain boundaries on a Si(111)-7×7 reconstructed surface. On the other hand, CaF2islands nucleate not only at steps and domain boundaries but also in domain-boundary-free regions of a Si(111) surface. We attribute the difference in the morphologies to the much higher mobility and diffusion length of a BaF2molecule in comparison to those of a CaF2molecule on a Si(111) surface at 400° C. We also report the first STM measurement of a (CaF2+BaF2)-coexisting surface at 480° C.

GaAs (001) vicinal surfaces which were tilted 2 degrees toward the [010] direction were observed with a scanning tunneling microscope equipped with a molecular beam epitaxy facility. The surface of 30 monolayers of GaAs grown on a substrate consisted of both large flat and narrow terraces. On the other hand, the surface of a 1.5-µm-thick GaAs layer grown on a substrate consisted of relatively uniform-width terraces which reflected the off-angle. However, their terrace edges showed a large atomic-scale fluctuation.

Lattice strains near the Si/NiSi2interface and their effects on electron energy-levels of Si were investigated via experimental and theoretical approaches. For highly spatially resolved analysis, electron nanoprobe techniques were employed: convergent beam electron diffraction (CBED) for lattice strain and electron energy-loss spectroscopy (EELS) for the electron energy-levels. Additionally, a theoretical analysis based on the density-functional theory (DFT) was performed to explain the experimental results. The actual distribution of the lattice strains was complicated; both tensile and compressive strains were found to coexist near the interface. Shifts in the Si L23-edge of the EEL spectra were found to be induced by the lattice strain. Finally, we described the "distribution of the electron energy-levels" as the strain distribution around the interface in a submicron region.

Lattice strain distribution was measured in Si substrates near NiSi2islands. Using the convergent beam electron diffraction (CBED) technique, quantitative and highly spatially resolved evaluations were carried out. Variations in the CBED patterns were found to be due to a combination of stress components with different orientations and magnitude. As a result, it was revealed that, in addition to normal stress components, singular stress with characteristic orientation or extremely high strain concentration was observed, especially near the NiSi2island corner. This actual strain distribution was considered to be highly influenced by the shape, size and orientation of the NiSi2island on Si substrates.

Scanning tunneling microscopy (STM) was used to investigate nucleation and growth phenomena in the heteroepitaxy of calcium fluoride ( CaF2) on a Si(111) surface. CaF2was evaporated at room temperature on Si(111), and annealed to about 450° C. Subsequently, characteristically, shaped islands, with steps arranged in the [10] direction, were observed both on a terrace and a step edge of Si(111). After annealing this surface to about 600° C, STM images clearly showed that these islands underwent a structural transformation to well-ordered heteroepitaxial layers which consisted of rows running along the [10] direction and grew from Si step edges. These findings show that at a high temperature the preferential nucleation sites are distributed on the Si step edges and that CaF2molecules have sufficient surface diffusion length to form the heteroepitaxial layers at the step edges.

The island-formation processes of GaAs heteroepitaxial growth on InP (lattice constant (a) is 3.7% larger than that of GaAs) and InAs (ais 7.2% larger than that of GaAs) surfaces were investigated using a scanning tunneling microscope (STM) multichamber system equipped with a molecular beam epitaxy facility. In the case of GaAs/InP heteroepitaxial growth, two-dimensional (2D) growth was observed when less than 2.0 monolayers (MLs) of GaAs were deposited on the InP surfaces. On the other hand, three-dimensional (3D) growth was confirmed for more than 2.0 ML GaAs deposition. In the case of GaAs/InAs heteroepitaxial growth, the same transition from 2D to 3D island growth occurred when more than 0.75 ML of GaAs was deposited.

We have performed ballistic electron emission microscopy (BEEM) measurements on the Au/ CaF2/n-Si(111) system in which calcium fluoride ( CaF2) (about 2 monolayers (ML)) was introduced at the Au/Si interface. A BEEM image clearly shows the coexistence of two types of terrace for each of which the BEEM I-Vspectrum has a different shape. A typical threshold voltage of the BEEM current for one type is about 0.75 V. In contrast, the second type shows a threshold voltage of about 3.5 V, which is much higher than the value of the first type. Furthermore, the BEEM current on the second type is significantly reduced and saturates above about 6 V. We attribute the coexistence of the two types of terrace in the BEEM image to the different degrees of coverage of the CaF2intralayers between them. At the second type of terrace, a Au/2 ML CaF2/1 ML CaF/Si(111) interface exists, although the first type has a Au/1 ML CaF/Si(111) interface without a CaF2intralayer.

Lattice strain distribution was measured in Si (111) substrates near NiSi2islands. Quantitative measurements with high spacial resolution were performed using convergent beam electron diffraction (CBED). Distorted and lower-symmetry CBED patterns were observed up to 2.0 µm from NiSi2islands. We show that these CBED patterns can be accounted for by a combination of stress components with different orientations. Stresses were found to be tensile perpendicular to NiSi2island edges and compressive parallel to them. In addition, another stress component which had a characteristic orientation was detectable within 0.5 µm of NiSi2island edges.

The crystal growth of Si in SiO2/a-Si/SiO2layered structures is examined by high resolution transmission electron microscopy. In a thin a-Si layer (10 nm), crystal growth halts with the crystallite size roughly equal to the layer thickness. In a thick layer (50 nm), crystal growth continues beyond the layer thickness. An expression for this halt in growth is derived from the free energy change. The halt in growth of Si crystallites suggests that the a-Si/SiO2interface and the a-Si/c-Si interface are more stable than the c-Si/SiO2interface.

A multi-chamber ultrahigh vacuum scanning tunneling microscopy (UHV-STM) system has been constructed for investigations of processed GaAs surfaces. This system comprises five UHV chambers connected by UHV tunnels. A specially designed STM unit which can be used with a 23-mm-diameter molybdenum block, is installed in an STM-chamber for surface observations. A molecular beam epitaxy (MBE) chamber for epitaxial growth of GaAs layers and a process-chamber for argon ion-bombardment are included in the five chambers. First, the surface of the MBE-grown layer on a GaAs (001) wafer was observed with STM. The sample was then transferred to the process-chamber and bombarded with argon ions. Many defects, which seemed to be caused by the ion-bombardment, were found in an STM image taken with the ion-bombarded sample.

We have observed GaAs growth processes on an InP (001) surface thermally cleaned in an arsenic flux using a multichamber ultrahigh-vacuum scanning tunneling microscope (UHV-STM) equipped with a molecular beam epitaxy (MBE) facility. When either 1 monolayer (ML) or 1.5 ML GaAs was deposited on an InP (001) surface, two-dimensional growth was observed. On the other hand, island formation was observed for 2.5 ML GaAs deposition.