Thin films of PbTiO3 (PT) and (Pb, La)TiO3 (PLT) were grown at 600oC on (100)MgO substrates by rf-magnetron sputtering. The crystal orientation of the PT thin films was investigated with various cooling rates (8oC/min to 33oC/min). It is found that the degree of c-axis orientation of the PT thin films increases with increasing cooling rates and the degree of a-axis orientation increases with decreasing cooling rates. While, c-axis orientation of the PLT thin films is grown independent of the cooling rates. The cooling rates are essential for the control of the orientation of the PT thin films on (100)MgO substrates.
Geometric and electronic structures of both neutral and anionic clusters, (Vn and Crn, n = 2∼8) have been studied using a density-functional method. The most stable structures of these clusters up to octamers were newly determined or reexamined. The calculated electron affinity (EA) of V3∼V7 clusters was in good agreement with their experimental values. The average spin magnetic moment for the Cr cluster showed odd-even alternation behavior, which is consistent with antiferromagnetic character of the bulk.
The aggregating states of octadecyltrimethylammonium bromide, C18TAB on mica surfaces were investigated by using AFM. The C18TAB physisorbed and/or chemisorbed on mica surface from aqueous solutions by dipping aggregates to various forms depending on the concentration of the solutions. The aggregates formed discontinuously on the surface from dilute solutions, while from concentrated solutions just below cmc, the aggregates covered the surface continuously. Most of the aggregates were easily desorbed with rinsing water and only remained ion-exchanged C18TA+ ions on the mica surface. On the mica surface immersed in high concentration solution, ion-exchanged by C18TA+ ions occurred almost on the whole surface. Thus the aggregates formed regularly in array.
Thin film growth of CaF2 on Si(111)7×7 depending on the substrate temperature has been studied by Reflection High-Energy Electron Diffraction (RHEED). In this study, three aspects such as solid-phase epitaxy, vapor-phase epitaxy and electron stimulated desorption (ESD) effect were investigated. In the solid-phase epitaxy, a 7×1 surface structure has been newly found at a very narrow temperature range of 840-850oC. In the vapor-phase epitaxy, RHEED intensity oscillations were observed at the substrate temperature range of 100-450oC, which suggests a layer by layer growth due to 2-dimensional nuclei. In the range of 500-700oC, the oscillation disappears but the reflection intensity is kept at a high level, which suggests a step-flow growth mode. It was judged from the change of Kikuchi pattern that CaF2 thin films grown at the substrate temperature range of 200-700oC were all of type-B; however, that grown at 100oC was of type-A. Since the ESD effect on the CaF2 surface is generally serious, the effect is also examined.
X-ray photoelectron (XPS) and X-ray Auger electron spectroscopy (XAES) were used for investigating the chemical and structural states of various aluminates. A clear chemical shift in Al modified Auger parameter (AP) for coordination state of Al atom was observed. For similar chemical composition, the AP of tetrahedral Al was higher than that of octahedral Al. In the same coordination state, the AP became larger by the following order; Al oxide ≈ Al double oxide < Al phosphate ≈ Al hydroxide < Al silicate. This order correlated with an electron affinity of secondary coordinated cations. On the other hand, the effective electrostatic force of Al-O calculated by bond strength showed a correlation with the AP of the samples except for several aluminosilicates. Since these aluminosilicates have solid acidity, the deviation from the correlation may be used as an index of solid acidity in Al sites.
Cobalt and Cobalt-Nickel alloy thin films were electrodeposited on polycrystalline copper substrates. Electrochemical investigation was focused on the initial stage of electrodeposition by pulsed current in terms of electrode potential. Changes in the immersion potential, Eimm, and the deposition potential, Edep, were obtained for each rum of pulsed current. This electrochemical behavior of electrode surface proves to be related to alloy elements, surface topograph, and magnetic properties of deposit of several atomic layers.
Monolayers or submonolayers of zincphthalocyanine (ZnPc) deposited on highly oriented pyrolytic graphite (HOPG) substrates have been investigated by scanning tunneling microscopy (STM). Structures of ZnPc layers show characteristic low dimensional structures. When the ZnPc coverage is under 1 ML, twined stripestructures with three-fold symmetry were observed. This structure can be explained in terms of a commensurate superstructure of unit cell β form crystalline on the HOPG. When the ZnPc coverage is over 1 ML, one-dimensional structures like a wire were observed. The width and length of the wire are 6 nm and longer than 1 μm, respectively. These structures would also originate from the π-staking of ZnPc molecules.
We have improved the field electron emission from amorphous carbon films using platinum-silicide (PtSi) formed between silicon substrate and amorphous carbon (a-C). Pt films were sputter-deposited onto n-Si(100) substrates at room temperature. In order to form PtSi at the interface annealing was made at 400∼600oC in a vacuum chamber. a-C films were then deposited onto Pt/Si substrates using by laser ablation at room temperature. The field electron emission property of a-C/Pt/Si is found to be better than that of a-C/Si, and it is shown that the property was improved with increasing annealing temperature. The reasons why the field electron emission from a-C film was improved can be considered as follows, (1) the resistance of a-C films decreased due to graphitization, (2) effective electric field concentration occurred because of the rough surface morphology of the a-C films deposited on Pt/Si substrates, (3) annealing induced reaction between Pt film and Si substrate decreased the interfacial resistance between Pt film and Si substrate.
We have investigated In reevaporation during MBE growth of InGaAs on GaAs substrates at various substrate temperatures (540oC∼680oC) and In/(Ga+In) flux ratios (0.1∼0.3). For comparison, we have performed similar experiments on lattice matched InGaAs on InP substrates. The growth rates RInGaAs for InGaAs and RGaAs for GaAs were determined by RHEED intensity oscillation. A proposed rate-equation model for surface processes has proved that the In surface segregation effects due to the In-Ga replacement on the activation energy for In desorption are negligibly small. The activation energy for In reevaporation decreases with an increase in strain in InGaAs/GaAs. The In incorporation fraction decreases with strain in InGaAs. The In incorporation fractions of unstrained InGaAs/InP systems are larger than those of strained InGaAs/GaAs systems. The compressive stress in InGaAs exerts stronger influence on decreasing In incorporation than tensile stress.
Secondary ion mass spectrometry (SIMS) provides very sensitive chemical and elemental information. Nano dimensional SIMS analysis is, however, very difficult to carry out by conventional methods mainly because of the primary beam diameter and vibrations. Using the latest technology for fine beam formation, we intended to develop a nano-scale FIB (Focused Ion Beam) SIMS. For the purpose of achieving nano-scale spatial resolution, we observed the influence of vibrations that deteriorate spatial resolution. In order to minimize the influence, sample was mounted on the end cap of FIB column directly. Under the condition, the ion induced secondary electron image of a vacuum-evaporated Au film on a carbon plate was obtained with nano-scale image resolution. By eliminating the influence of vibrations, measurements with nano-scale dimensions became possible. Use of the FIB column, which produces over 10 A/cm2 beam density, will realize a new local analytical method.