H. Kawanowa

Evaluation of Misfit Relaxation in α-Ga2O3 Epitaxial Growth on α-Al2O3 Substrate

Corundum-structured α-Ga2O3 epitaxial thin films were grown on c-plane α-Al2O3 (sapphire) substrates by a mist chemical vapor deposition method. To reveal the defect structures, the α-Ga2O3 film was observed by high-resolution transmission electron microscopy (TEM). We found that the α-Ga2O3 thin film was in-plane compressive stressed from the α-Al2O3 substrate. Although misfit dislocations were periodically generated at the α-Ga2O3/α-Al2O3 interface owing to the large lattice mismatches between α-Ga2O3 and α-Al2O3, 3.54% (c-axis) and 4.81% (a-axis), most of the misfit dislocations did not thread through the layer. An extra-half plane was {110} consisting only of Ga. Screw dislocations were not confirmed, i.e., the density was under 107 cm-2. The threading dislocation density was 7 ×1010 cm-2.

Structure Analysis of Monolayer Graphite on Ni(111) Surface by Li+-Impact Collision Ion Scattering Spectroscopy

The surface structure of monolayer graphite (MG) on a Ni(111) surface has been investigated using Li+-impact collision ion scattering spectroscopy (ICISS) and reflection high-energy electron diffraction (RHEED). The RHEED pattern showed a 1 ×1 structure for MG formed on the Ni(111) surface, and the ICISS measurement clearly showed the difference between a clean Ni(111) surface and that with MG. The surface structure was determined via comparison of computer simulations and ICISS measurements. The C atoms locate on top and hollow sites of the Ni(111) surface, to form monolayer graphite, which is consistent with the model proposed by a tensor Low energy electron diffraction study.

STM study of oxygen-adsorbed TiC(111) surface

Abstract The surfaces of TiC(111) and TiC(111)-( 3 × 3 )R30-O were investigated using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED) and DV-Xα calculation. Atomically resolved STM images of an oxygen-adsorbed surface were observed to have bright spots with a ( 3 × 3 )R30 periodicity. The STM image contrast was invariant with respect to the polarity of the sample bias voltage. The STM images and the calculation results are discussed in terms of surface geometry and local electronic state.

Characterization of Bar-Shaped Stacking Faults in 4H-SiC Epitaxial Layers by High-Resolution Transmission Electron Microscopy

Stacking faults in 4H-SiC epitaxial layers were investigated by micro-photoluminescence (PL) mapping at room temperature and by transmission electron microscopy (TEM) observation. Stacking faults with a peak emission wavelength of 420 nm were identified by the PL measurements with a He–Cd laser of 325 nm excitation wavelength. The shape of the stacking faults was revealed to be bar-shape by the micro-PL intensity mapping at emission wavelength of 420 nm. The stacking sequences of the bar-shaped stacking faults were determined as (...2, 3, 2...), (...2, 3, 3, 3, 2...), and (...2, 3, 3, 3, 3, 3, 2...) in the Zhdanovs notation by high-resolution TEM.

Morphology of Si(100)-2×1 surface with submonolayers of LiF studied by UHV-STM

Abstract The surface morphology of Si(100)-2×1 with submonolayers of LiF adsorbate and its annealing behavior are studied using scanning tunneling microscopy. LiF adsorbs randomly on the Si(100)-2×1 surface at room temperature (RT), and the 2×1 structure disappears when the coverage of LiF is close to 1 monolayer. Interaction of the Si surface and the LiF adsorbate is enhanced by specimen annealing, which causes dissociation of the LiF and fluorination of the Si surface. Desorption of SiFx (x=1, 2, 3, 4) results in surface etching. After annealing at 700°C for 5 min, fluorine on the surface decreased below the limit of the detection by X-ray photoelectron spectroscopy, and the Si surface is reconstructed to 2×1 at about 800°C.

Scanning tunneling microscopy of the Si(111) surface interacting with LiF adsorbates

Abstract Submonolayers of LiF were thermally deposited on the Si(111)-7×7 surface. Scanning tunneling microscopy studies showed that there are no preferential sites in the 7×7 unit cell for adsorption of LiF. At coverages higher than 0.4 monolayer (ML), the 7×7 structure disappeared. After annealing the LiF-covered surface, most of the corner Si adatoms reappear at a temperature of 325°C, which essentially exhibits a 7×7 geometry, and the surface returned to 7×7 structure with a few atomic-level defects at 800°C. The adsorption of LiF on silicon can be understood via the interaction between the directional dangling bonds and the active dipole of the adsorbed LiF molecule or F pieces formed by dissociation of LiF. The annealing behavior of the covered surface can be understood by desorption of silicon fluorides and silicides formed following dissociation of LiF on the surface, as well as diffusion of silicon clusters.

Size effects of incident ions on electron transition between LaB6(001) surface and metastable atoms

Abstract Auger-type electron emission from LaB6(001) surface by incident rare-gas ions show two intense peaks in energy spectra. These strong electron emissions in the high and the low energy regions are due to the autodetachment (AU) and Auger de-excitation (AD), respectively. From the energy of AU peaks and AD peaks, the transition distances of the electrons from the surface to the excited atoms are estimated by means of an image potential effect for the emitted electrons. The results show the size effect of incident ions on the electron transition between the surface and the metastable atoms.

Structural Analysis of LiTaO3(0001) Surfaces Using Low-Energy Neutral Scattering Spectroscopy

The atomic structure of the LiTaO3(0001) surface was investigated by low-energy neutral scattering spectroscopy (LENS). LENS was developed for surface-structure and -composition analyses, particularly of highly insulating materials, and was successfully applied to the structural analysis of the LiTaO3(0001) surface. The polar angle dependences of scattered He0 intensities indicate that O atoms cover the surfaces. The surface structure is almost the same as the bulk structure truncated at the (0001) plane, and the layer spacings between the first Li, the Ta and the outermost O layer are 0.01±0.01 nm and 0.09±0.01 nm, respectively.

Resonant ion stimulated desorption of protons from cerium oxide

Abstract The emission of protons from the polycrystalline CeO x surface was investigated during noble-gas ion bombardment ( E 0 E 0 =100 eV). At the reduced CeO x surface, the proton survives neutralization with a higher probability when scattered from oxygen than from cerium. The surface hydrogens are sputtered as protons by ion irradiation via the non-collisional electronic transition. The probability for H + desorption decreases in order of He + , Ne + and Ar + . This is because hydrogen desorbs from the antibonding OH group with an O 2s core hole which is created via the quasi-resonant charge exchange with the primary ions. The ionization of hydrogen occurs during the O–H bond breakage via the interatomic Auger decay of the O 2s hole. The resulting H + ion survives neutralization preferentially from O of CeO 2 as confirmed from the H + scattering experiment. On the basis of these findings, we propose resonant ion stimulated desorption (RISD) as a tool for quite sensitive detection of surface hydroxyl group and apply it to in situ observations of hydrogen segregation to the surface.