Masaaki Matsushima

Experimental evidence for orientation property of Pb(Zr0.35Ti0.65)O3 by manipulating polar axis angle using CaF2 substrate

Perfectly oriented (001), (101), and (111) Pb(Zr0.35Ti0.65)O3 (PZT) films were grown on identical (111)CaF2 substrates by metal-organic chemical vapor deposition. These films exclude domains parallel to the surface; therefore, all domains are actively switchable under the electric field between top and bottom electrodes. Saturation polarization values, Psat(001), Psat(101), and Psat(111), for these PZT films were 75, 50, and 43 μC/cm2, respectively. This orientation dependency was in a good agreement with the theoretical relationship for a tetragonal PZT single crystal, where Psat(001)=Psat(101)/2=Psat(111)/3.

Domain structure of (100)/(001)-oriented epitaxial PbTiO3 thick films with various volume fraction of (001) orientation grown by metal organic chemical vapor deposition

(100)/(001)-oriented epitaxial PbTiO3 films thicker than 1 μm were grown on various types of substrates by chemical vapor deposition. The domain structures of these films with different volume fractions of (001) were investigated. Domain structures, consisting of (100)/(001)-oriented domains, were observed regardless of the type of substrate. However, the tilting angles of the a- and c-domains from the surface normal linearly changed with the volume fraction of the (001) orientation. These results suggest that the volume fraction of the (001) orientation is crucial in identifying the domain structure of PbTiO3 thick films.

Blue Electroluminescence of Thin-Film Diamond Made by the Hot-Filament Method

Blue electroluminescence has been observed in thin-film diamond deposited on a substrate when a mixture of methane and hydrogen gases react under heat treatment by tungsten filament. The diamond active layer is sandwiched between metal oxide insulating layers (HfO2 and Al2O3) which are formed by evaporation of metal oxides in oxygen plasma. Indium tin oxide film is used as a transparent electrode. The electroluminescence spectrum shows the peak at 435 nm and luminance is 3.6 cd/m2 at an applied voltage of 400 V.

Electrical Properties of (110)-Oriented Nondoped Mg 2 Si Films with p -Type Conduction Prepared by RF Magnetron Sputtering Method

Magnesium silicide (Mg2Si) thick films with (110) orientation were fabricated on (001) sapphire substrate using radiofrequency magnetron sputtering. Stoichiometric Mg2Si films with composition Si/(Mg + Si) = 0.33 were achieved over a range of vacuum from 10 mTorr to 140 mTorr and 300°C. On postannealing the film at 500°C, the out-of-plane lattice parameter shifted to lower values and the electrical conductivity increased by two orders of magnitude. A room-temperature Seebeck coefficient of 517 μV K−1 was observed and found to decrease with increasing temperature; the Seebeck coefficient remained at a constant positive value of 212 μV K−1 at 500°C. This can be related to the possibility of p-type conduction in this temperature range.

Impact of thermal expansion of substrates on phase transition temperature of VO2 films

Non-epitaxial, (010)M1-oriented VO2 thin films were grown on various substrates [amorphous SiO2, Si (001), Al2O3 (0001), and CaF2 (001)] with Pt (111)/SiO2 buffer layers. Phase transition from MoO2-type monoclinic to rutile-type tetragonal structures of these VO2 layers was investigated with temperature-controlled micro-Raman spectroscopy. It was confirmed that substrates with larger thermal expansion coefficient cause larger out-of-plane lattice spacings of both Pt and VO2, and thus lower transition temperatures of VO2 films, as a result of higher in-plane shrinkage during cooling from the deposition temperature. The transition temperatures and aM1/2 lengths, estimated from bM1 lengths, of present samples were compared with previous reports in a strain—temperature phase diagram. The present results fit with previous reports better by assuming that in-plane lattice aspect ratio of VO2 films is not clamped by the substrates but is flexible during the temperature change. Thermal expansion of substrates is a...

Temperature and electric field stabilities of dielectric and insulating properties for c-axis-oriented CaBi4Ti4O15 films

Temperature and electric field dependencies of the dielectric and insulating properties of (001)-oriented epitaxial CaBi4Ti4O15 films grown on (100)cSrRuO3//(100)SrTiO3 substrates were investigated and compared with those of conventional (100)-oriented epitaxial (Ba0.3Sr0.7)TiO3 and SrTiO3 films. All films showed negative temperature dependency of the capacitance from 25 to 500 °C, and their changes were −18%, −83%, and −58% for CaBi4Ti4O15, (Ba0.3Sr0.7)TiO3, and SrTiO3 films, respectively. Smaller change of the capacitance against dc electric field was also observed for CaBi4Ti4O15 films. Moreover, the maximum leakage current density of CaBi4Ti4O15 films measured at ±100 kV/cm was below 10−3 A/cm2 up to 500 °C, which was smaller than those of (Ba0.3Sr0.7)TiO3 and SrTiO3 films. These results indicate that (001)-oriented CaBi4Ti4O15 films are a useful candidate as the capacitor material applicable for the high temperature use because of its high stability against temperature and an electric field as well a...

Unusual 90° domain structure in (2/3)Bi(Zn1/2Ti1/2)O3-(1/3)BiFeO3 epitaxial films with giant 22% tetragonal distortion

Epitaxial films of tetragonal (001)/(100)-oriented (2/3)Bi(Zn1/2Ti1/2)O3-(1/3)BiFeO3 were grown on (100)cSrRuO3//(100)SrTiO3 substrates by metalorganic chemical vapor deposition. 93% of the film is occupied by c-domain [(001) orientation], and the out-of-plane (c-axis) and in-plane (a-axis) lattice parameters are 0.465 nm and 0.381 nm, respectively. The tetragonal distortion, (c/a)-1, is 22% which is 3.5 times larger than that of PbTiO3 (6.3%). High-angle annular dark-field-scanning transmission electron microscopy images show clear c-/a-domain structures with unusual boundary angles of 51°/39° due to the large c/a ratio of tetragonal phase. High temperature X-ray diffraction measurements reveal that the Curie temperature of this film is above 800 °C.

Thermally stable dielectric responses in uniaxially (001)-oriented CaBi4Ti4O15 nanofilms grown on a Ca2Nb3O10-nanosheet seed layer

To realize a high-temperature capacitor, uniaxially (001)-oriented CaBi4Ti4O15 films with various film thicknesses were prepared on (100)cSrRuO3/Ca2Nb3O10− nanosheet/glass substrates. As the film thickness decreases to 50 nm, the out-of-plane lattice parameters decrease while the in-plane lattice ones increase due to the in-plane tensile strain. However, the relative dielectric constant (εr) at room temperature exhibits a negligible degradation as the film thickness decreases to 50 nm, suggesting that εr of (001)-oriented CaBi4Ti4O15 is less sensitive to the residual strain. The capacitance density increases monotonously with decreasing film thickness, reaching a value of 4.5 μF/cm2 for a 50-nm-thick nanofilm, and is stable against temperature changes from room temperature to 400 °C irrespective of film thickness. This behaviour differs from that of the widely investigated perovskite-structured dielectrics. These results show that (001)-oriented CaBi4Ti4O15 films derived using Ca2Nb3O10− nanosheets as seed layers can be made candidates for high-temperature capacitor applications by a small change in the dielectric properties against film thickness and temperature variations.

Structural characterization of epitaxial Mg2Si films grown on MgO and MgO-buffered Al2O3 substrates

(110)-oriented epitaxial Mg2Si films were grown on (100), (110), and (111) MgO single crystals by RF magnetron sputtering. Two, one, and three types of in-plane variants were observed for (100), (110), and (111) MgO single crystals, respectively. In addition, it was also demonstrated that epitaxial Mg2Si films can be grown on (001) Al2O3 substrates using an epitaxially grown (111) MgO buffer layer. Transmission electron microscopy studies revealed a clear interface between Mg2Si and the MgO buffer layer with an epitaxial relationship. This result indicates that Mg2Si films can be epitaxially grown on other substrates by using an epitaxial buffer layer of MgO.

Preparation of preferentially (111)-oriented Mg2Si thin films on (001)Al2O3 and (100)CaF2 substrates and their thermoelectric properties

Mg2Si thin films were deposited at 320 °C on (001)Al2O3 and (100)CaF2 substrates by radio-frequency magnetron sputtering. Both films showed a preferential (111) out-of-plane orientation with an in-plane random orientation irrespective of post-heat treatment. Mg2Si films on (001)Al2O3 substrates were under in-plane tensile strain, while those on (100)CaF2 substrates were under in-plane compressive strain both before and after heat treatment. Heat-treated films showed p-type conduction up to 500 °C. Their electrical conductivity and Seebeck coefficient were almost independent of the kind of substrate within the limit of the present study, from 0.22% compressive strain to 0.34% tensile strain at room temperature.