Thin films of PbTiO3(PT), 5-360 nm in thickness, were grown on miscut (001)SrTiO3(ST) substrate (miscut angle of 1.7°) at 600°C by rf planar magnetron sputtering. The sputtered PT thin films showed three-dimensional crystal orientation, and the surfaces were extremely smooth over a large area. The crystal form of bulk PT is cubic at 600°C, but the epitaxial PT thin films on ST substrate become deformed from cubic to tetragonal form by compressive force in the a-b plane during film growth since the lattice parameter of ST is smaller than that of PT. The deformed crystal structure was quenched during a cooling cycle in the deposition process. The PT thin films were coherent to the substrate and tightly bonded on the surface of the substrate. The transition from tetragonal to cubic phase could not be observed even when the temperature of the PT thin films was elevated from room temperature to Curie temperature.
We have developed a nanofabrication and measurement system for nano-devices such as single electron transistors. This system can perform all of the required processes in ultrahigh vacuum, such as preparation of substrate surface, fabrication of metallic electrodes on a substrate using a precise mask deposition equipment, nanofabrication of gold dots and lines using a scanning tunneling microscope (STM), and measurement of electric properties of the nano-devices using a low temperature four-contact probe apparatus. Using a novel atom transfer method from the gold tips, highly reproducible fabrication of gold nano-dots and nano-lines have been demonstrated here. Some technical innovations required for this development are briefly introduced.
Several surface potential control methods were evaluated with a focusing monochromatic X-ray photoelectron spectroscopic measurement for a silica glass. Distortion of the O1s signal was easily improved by the combination of a low energy electron flood gun and an electrically grounded Ni mesh screen mounted about 1 mm above the sample surface. It was also found that the potential could be controlled by the combination of Ar gas introduced into vacuum chamber and an ion gun with no accelarating bias.
In order to submit surface analysis database, we have studied how to measure AES and XPS spectra of thermal silicon dioxide (SiO2) films which is one of the most popular materials in silicon ULSI devices. We investigated damages induced by an electron beam probe and by inert gas ion for surface cleaning. It was found that low energy electrons cause heavier damages than high energy electrons in AES measurements. In XPS measurements it was revealed that a peak width (FWHM) is broadened by inert gas ion irradiation, and that SiO2 surfaces are reduced by ion irradiation. Carbon-free surfaces on SiO2 were obtained by the anneal (400°C, 2h) in air. We are certain that the annealing process can be used as a more practical cleaning method than inert gas ion cleaning.
Formate species synthesized on Cu(111) by the hydrogenation of CO2 at atmospheric pressure in a reactor was observed by UHV-STM. The ordered structure of the formate species changed in the order of p(2×4), c(2×8), (7×7), p(2×3), (5×5) and c(2×4) with increasing coverage, indicating that various ordered structures appeared corresponding to a small change in the formate coverage. The coverage of formate species in the c(2×4) structure corresponded to ΘHCOO= 0.25, which was in good agreement with a saturation coverage measured by XPS at the same reaction condition; thus, particles seen in the STM images indicate each formate species. Further, at a low formate coverage (ΘHCOO= 0.02), formate chains were observed.
Focused Ion Beam (FIB) technique is applicable to prepare a sharp tip for Scanning Tunneling Microscope (STM). Our simple calculation shows that radius of the FIB milled tip apex can be reduced to be smaller than the spot size of the FIB. In this study, a GaAs tip, which has a potential ability to resolve information about electron spin polarization in tunneling currents, was formed by means of the FIB. The FIB produces damaged layers on the semiconductor surface, which are thicker than those on metals and thus prevent electrons from tunneling through the layers. After the damaged tip was dipped in HCl solution which can selectively remove the damaged layer, Highly Oriented Pyrolytic Graphite (HOPG) surface atoms were observed and the I-V curves showed characteristics of the semiconductor.
Fe thin films with underlayers of various materials were continuously prepared by the evaporation method with an electron beam heating equipment on glass substrates at room temperature. The film thickness dependence of the saturation magnetization Is and of the coercive force Hc of double-layered Fe/(Ag, Cu, Bi, or Si) films was measured. The largest value of saturation magnetization Is among the double-layered films was 20 kG, for an underlayer material of Ag with a thickness of 50.0 nm, and was larger than that of Fe thin films deposited directly on glass substrates. The compositions and the surface morphologies of an Fe/Ag double-layered film were also investigated by measuring the AES spectra and the AFM images, respectively. These results indicate that the surface morphology of Fe thin film with underlayer is closely related to the magnetic properties.
Hydrogen molecules are formed in the crystalline silicon treated with hydrogen atoms at substrate temperatures between 180 and 500°C. The vibrational Raman line (Q1) of hydrogen molecule in the hydrogenated crystalline silicon is observed at around 4160 cm-1. The line shape changes with hydrogenation temperature, and is composed of at least two components. The two components are ascribed to hydrogen molecule in two different interstitial sites in crystalline silicon. Each component is much broader than that of hydrogen molecules in gas phase. The line broadening can not be explained by collisional or motional broadening, but is attributed due to the configurations of hydrogen molecule with different orientations in the crystalline silicon.
Sb desorption on a single-domain Si(001)2×1 surface has been studied using grazing-incidence reflection high energy electron diffraction and Auger electron spectroscopy (RHEED-AES). From the time evolution of Sb coverage, θSb, during Sb desorption as monitored from Sb MNN Auger spectra, we have found that the Sb desorption kinetics are divided into two coverage regions; (I) 1 ML>θSb>0.3 ML and (II) 0.3 ML>θSb>0 ML. It was also found that the Sb desorption is a first-order reaction in each coverage region with activation energies of (I) 3.61 eV and (II) 3.63 eV and pre-exponential factors of desorption coefficient of (I) 2.9×1015 S-1 and (II) 5.0×1015 S-1. This difference in pre-exponential factor is explained in term of the change in the morphology and structure of Sb layer as monitored by RHEED.
Chemical adsorption of Al and Rh ions on SiO2 in aqueous solutions are examined. It is revealed that complex cations, such as [Al(H2O)6]3+, [Al(OH)(H2O)5]2+ and [Al(OH)2(H2O)4]+, are adsorbed on SiO2 in the pH range 4 to 9 and that the adsorption results in the shifts of values in zeta-potential up to ca. +60 mV. On the other hand, Rh ions, which are inert in the pH range, are not adsorbed on SiO2 and no substantial differences are observed between values of zeta-potentials in Rh solutions and those in metal-free solutions. In the pH range 10 to 12, however, it is observed that both Al and Rh ions are adsorptive on SiO2. In All Rh containing solutions, the values of zeta-potential are between -50 to -60 mV, which are about 10 mV smaller than those in metal-free solutions. Therefore, it is supposed that complex anions, such as [Al(OH)4(H2O)2]- and [Rh(OH)4(H2O)2]-, are adsorbed in the alkaline solutions. As for the mechanism, we propose that the adsorption proceeds through ligand-exchange reactions of hydrated Al/Rh ions.