Satoshi Gonda

Heteroepitaxial Growth of CeO2(001) Films on Si(001) Substrates by Pulsed Laser Deposition in Ultrahigh Vacuum

Pulsed laser deposition in ultrahigh vacuum (UHV) was applied to the epitaxial growth of CeO2 film on Si(001). Although the direct deposition of CeO2(001) on Si(001) was unsuccessful, the desired epitaxy was achieved by inserting the growth of a SrTiO3 layer. The formation of a CeO2(001)//SrTiO3(001)//Si(001) layered structure was verified by reflection high-energy electron diffraction analysis of the growing surface at a temperature between 650 and 700°C in UHV. In addition to lattice matching, chemical interaction at the growing surface had a decisive effect on the epitaxy and orientation of growing ceramic lattices.

CERAMIC LAYER EPITAXY BY PULSED LASER DEPOSITION IN AN ULTRAHIGH VACUUM SYSTEM

Ceramic layer epitaxy, defined as the epitaxial growth of ceramic thin films with thicknesses regulated on an atomic scale, was verified by a new method using pulsed laser deposition in ultrahigh vacuum (UHV). The intensity oscillation of reflection high‐energy electron diffraction (RHEED) was observed in an ArF excimer laser deposition of CeO2 and SrTiO3 films on Si(111) and SrTiO3(001) substrates, respectively, at 650–750 °C under 5×10−7 Pa. The oscillation periodicities corresponded well to interplane distances of CeO2(111) and SrTiO3(001). This first observation of RHEED oscillation in laser deposition of ceramic films suggests that UHV laser deposition is a promising method for producing atomically regulated ceramic layers inclusive of possible new high Tc superconductors.

In situ surface analysis of SrCuO2 heteroepitaxy on SrTiO3 substrate using X-ray photoelectron spectroscopy

Abstract An atomic scale analysis was performed for heteroepitaxial SrCuO 2 film deposition on SrTiO 3 substrate by laser molecular beam epitaxy. A convex shape change in Cu photoelectron intensity was observed during the initial few unit cells growth of SrCuO 2 on SrTiO 3 (001) with TiO 2 plane on the top. Angle-resolved X-ray photoelectron spectroscopy indicates that TiO 2 and SrO planes are the topmost surfaces of SrTiO 3 (001) substrate and growing pitaxial SrCuO 2 film thicker than 1.5 nm, respectively. The switching of the topmost atomic plane from CuO z to SrO y is considered to occur in the initial growth stage of a few unit cells thickness.

Mechanical performances of a symmetrical, monolithic three-dimensional fine-motion stage for nanometrology

A centro-symmetrical, monolithic three-dimensional fine-motion stage was investigated in terms of its static and dynamic characteristics. The outer frame with the size of a 100 mm cube includes differently sized, concentric X/Y/Z linear motion stages. The yaw, pitch and roll of each stage are reduced to less than 0.014 arcsec µm-1 by adjusting the position of the axial load. From three-axis laser-interferometer measurements, a uniaxial load led to linear displacement with the deviation along the other axes of less than 0.06% of 10 µm travel. A simple frequency spectrum for the impulse response without any resonance crosstalk other than the expected resonance peak was obtained for each axis.

Growth Mechanism of Epitaxial Oxide Films by Laser MBE

Crystallographic structure and valence state of CeO 2 and Nd 2 -O 3 films deposited by laser MBE on Si substrates were investigated by reflection high energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS). In contrast with epitaxial growth of CeO 2 (111) and Nd 2 O 3 (111) on Si (111), epitaxial films were not obtained on Si(001). Partially reduced mixed valence (4+ and 3+) Ce was indicated to exist by XPS in the cerium oxide film within 2nm from the interface with Si. Beyond this transition layer, two-dimensional growth of CeO 2 film on Si(111) was verified from in situ RHEED and as well as on Si(001) from XPS measurements.

Fabrication of ceramics heterojunctions and layered cuprates by epitaxial layer-by-layer growth

Atomically regulated layers of perovskite oxides and alkaline earth cuprates were fabricated by laser MBE with the aid of RHEED intensity oscillations clearly observed during film growth. A ceramic superlattice composed of lattice-matched SrVO 3− x and SrTiO 3− y perovskites was prepared on an atomic scale by counting the number of RHEED oscillation. In situ RHEED and XPS analyses indicate that the interface between the laterally grown SrCuO 2− z epitaxial film and the SrTiO 3 (0 0 1) substrate has a transition layer of about 1 nm thick, which apparently reflects an inhomogeneous growth manner at the initial stage.

Impacts of probe-tip tilt on scanning probe microscopy

The effects of tip tilt on measurement uncertainty in scanning probe microscopy and tip-shape calibration for inclined tip have been discussed. Uncertainty of the untouchable region is the essential component of measurement uncertainty. Tip tilt is one of the most important parameters to determine the uncertainty of the untouchable region. The presence of tip tilt deteriorates fidelity of images and precision of critical-dimension measurements. It is necessary to use equivalent tip for calibrating the dilation of feature by inclined tip.

Preparation of SrCuOy film in ultra-high vacuum system

Abstract SrCuO 2 crystal contains two-dimensional CuO 2 planes like those constituting supercurrent path in high T c superconducting cuprates. We have investigated on epitaxial SrCuO y film growth on SrTiO 3 (001) substrate by ArF pulsed laser deposition in ultra-high vacuum. In situ RHEED and XPS diagnoses of the film growth process under a very low NO 2 pressure indicated that there were slight fluctuations in surface and electronic states of the initial 1 nm thick film growth. Beyond this initial stage, the film growth gave streaky RHEED pattern with its intensity oscillated at a periodicity corresponding well to the c -axis length of SrCuO 2 , verifying the layer-by-layer growth. The as-grown film was electrically conductive.

Surface and interface characterization of high Tc related epitaxial films by STM/STS and XPS

We have fabricated high quality and chemically stable epitaxial films of YBa2Cu3O7−δ (YBCO) and SrTiO3 by pulsed laser deposition (PLD) technique and investigated their surface morphology, electronic state, and growth mode. The cryoganic STM/STS measurements on small area (4×4nm) c-oriented YBCO films resulted in the simultaneous observations of lattice images and tunneling spectra with 20meV energy gap. A gap spectrum exhibited almost zero conductance, favoring s-wave superconductivity. Wider scans of the film surfaces by AFM and SEM, however, revealed granular structure of the surfaces with a root mean square (rms) roughness of 5nm, which is far larger than the coherence length of YBCO. Much smoother surfaces were obtained for a- and (110) oriented films. Atomic images and conductive layers could be identified by STM for these films. The surface morphology of epitaxial SrTiO3 films prepared under high vacuum (<10−5Torr:MBE) conditions was found to be improved to such an extent as to show atomically flat images in AFM and STM analyses. By in situ XPS analyses, valence states and film growth mode of SrTiO3 epitaxial films were elucidated on an atomic layer level. Discussions are extended to the processes for controlling the growth mode and carrieres of high Tc related oxide films as well s for fabricating SIS tunnel junctions.

Superconducting gap observation by high-resolution photoelectron yield spectroscopy

Abstract We designed and constructed a cryogenic photoelectron yield spectroscopy having high resolution (≈ 10 meV) and wide dynamic range (≈ 107). The yield spectra taken for Bi2Sr2CaCuOy (BSCCO)single crystals at 10 K showed a dip structure in the vicinity of the Fermi level. The measured data could be well fitted with a curve simulated from the BCS function with a gap value of 20 meV.