Kazushige Imagawa

SrRuO3 Thin Films Grown under Reduced Oxygen Pressure

SrRuO3 thin films are grown under reduced oxygen pressures between 10-6 Torr and 100 mTorr by pulsed laser deposition. The thin films grown at temperatures above 640° C and at a pressure of 10-6 Torr are characterized in terms of the lattice shrinkage due to oxygen deficiency. The resistivity increases and the temperature dependence changes to semiconductive from metallic as the oxygen pressure during growth is decreased. The Hall coefficient of the film grown at 740° C and at a pressure of 10-6 Torr is thirty times higher at low temperatures than at room temperature. The transport properties of the film are thought to result from the high carrier concentration but the low mobility due to the oxygen deficiency.

Thin Film Growth of YBa2Cu3O7-x by ECR Oxygen Plasma Assisted Reactive Evaporation

A new apparatus equipped with an ECR oxygen plasma source, a co-evaporation system of Y, Ba and Cu and a differential pumping system was developed. YBa2Cu3O7-x superconducting films were obtained at a substrate temperature of 450–500°C. The critical temperatures of films deposited on SrTiO3, MgO and Si substrates were 87 K, 80 K and 63 K, respectively. These properties were closely related to the crystallinity of the film.

Platinum Film Growth by Chemical Vapor Deposition Based on Autocatalytic Oxidative Decomposition

Platinum thin films were prepared by chemical vapor deposition based on the oxidative decomposition of (methylcyclopentadienyl)trimethylplatinum [CH 3 C 5 H 4 Pt(CH 3 ) 3 ] as a precursor. The film growth is characterized by slow growth during the initial stage followed by explosive growth on the initial layer. With increasing oxygen ratio and temperature, the duration of the initial stage is shortened and the growth rate on the initial growth layer is increased, However, an Arrhenius plot gives an activation energy of 0.7 eV regardless of the temperature or the oxygen ratio. Therefore, the rate-determining step of the entire reaction is the oxidative decomposition of the precursor on the growth front. On the other hand, an autocatalysis of platinum enhances the oxygen adsorption, which increases the collision frequency between the oxidizing species adsorbed and the source transferred on the growing surface. That is, the oxygen molecules that adsorbed and eventually saturated on the substrate surface shorten the duration of the initial stage and increase the growth rate, since the oxidative decomposition is enhanced by the autocatalysis of a self-seed platinum layer.

Orientation and Crystal Structure of SrTiO3 Thin Films Prepared by Pulsed Laser Deposition.

SrTiO3 thin films are grown on MgO(001) substrates at growth temperatures between 600-800° C and at oxygen pressures between 10-1-10-6 Torr. The initial stage of growth is controlled by graphoepitaxy with a cube-on-cube orientation. In the growth temperature range from 600° C to 740° C, graphoepitaxy occurs only at 10-6 Torr or 740° C. At 10-6 Torr the internal and kinetic energies of the evaporated particles contribute to the surface mobility necessary for graphoepitaxy, while at 740° C heat energy assures surface migration. However, at 800° C, the orientation changes to (111) with increasing thickness. This is because the dominant factor of film growth changes to the formation of a close-packed surface as the growth front gets farther from the substrate surface.

Hydrogen Reduction Properties of RuO 2 Electrodes

The thermodynamic stability of RuO2 under a reducing atmosphere containing hydrogen gas was investigated. The RuO2 electrode is reduced to Ru metal at 200°C in 0.3% H2 and at 300°C in 0.03% H2, even when the electrode is stacked with a (Ba, Sr)TiO3 dielectric layer. The reduction decreases the electrode volume. Our findings indicate that application of the RuO2 electrode in device integration will be difficult because of the thermodynamic instability as long as the thermal equilibrium state of reduction is attained during hydrogen sintering.

Low-Temperature Annealing Effect on Bi-Sr-Ca-Cu-O Thin Films Prepared by Layer-by-Layer Deposition

Thin films of Bi-Sr-Ca-Cu-O superconductors are prepared by layer-by-layer deposition using automatically controlled shutters. The films are deposited by microwave-discharged plasma assisted reactive evaporation. The thin films of the 2201 phase, 2212 phase, and 2223 phase are obtained in accordance with respective shuttering sequences. As-grown films do not show superconductivity, because of excess oxygen content. Superconducting thin films of the 2212 phase with zero resistance at 40 K are obtained by low-temperature annealing at 550°C in an oxygen partial pressure of 0.1 atm.

Insufficient oxidation in pulsed laser deposition

The influence of the ratio of oxygen atoms to ablated species in the ablation plume on the oxidation state of thin films was examined through the film growth of SrTiO3 by pulsed laser deposition. The amount of the ablated species was adjusted by changing the laser spot size on the target while keeping the oxygen pressure and laser energy density constant. The oxidation state is not defined by the background oxygen pressure during deposition. Instead, it is dominated by the oxidation which occurs when a burst of deposited species interacts with the oxygen atoms in the plume and incorporates oxygen ions into the lattice.

Growth of RuO2 thin films by pulsed-laser deposition

We prepared RuO2 thin films on Si substrates by pulsed-laser deposition using a sintered oxide target, and investigated the crystallographic nature and the thermodynamic stability of the films in terms of the growth conditions: temperature and oxygen pressure. Faceted grains grew in a highly oxidizing atmosphere. The films grown at room temperature included a large quantity of oxygen ions in the Ru metal matrix. An oriented Ru metal film grew under a non-oxidizing atmosphere. The grain morphology was closely related to the oxygen pressure.

Magnetic and Microstructural Properties of Co–Cr Film Fabricated by Continuous Roll Coater

Co–Cr thin films with a Ge layer between the basefilm and Co–Cr film have been fabricated at a high deposition rate using a continuous roll coater. The effects of the Ge layer and deposition conditions on the magnetic properties and microstructures have been investigated. It is concluded that the Ge layer is remarkably effective in improving the preferred c-axis orientation and magnetic properties, even though the Co–Cr films are fabricated at an extremely high deposition rate. In addition, the tilting angle of the c-axis from the normal of the film plane, which is caused by the oblique incident of the vapor, is affected by the deposition temperature and rate as well as the incident direction of the vapor.

The Effect of Microwave-Plasma on Decomposition and Oxidation of Ba(THD)2

The effect of microwave-plasma on the decomposition and the oxidation of Ba(THD)2 is studied for estimating the possibility of low-temperature chemical vapor deposition of oxide superconducting thin film. Pseudo in situ auger electron spectroscopy clarifies that carbon-free film is grown with oxygen-plasma at over 400°C. Pseudo in situ electron diffraction analysis indicated that the film grown at over 400°C is crystalline BaO. These results support the possibility that oxide superconducting film can grow at around 400°C by chemical vapor deposition using THD complexes.