Yasunori Hayashi

PROPERTIES OF VARIOUS SPUTTER-DEPOSITED CU-N THIN FILMS

Compositions and structures of sputter-deposited Cu–N films are strongly dependent on the total sputtering pressure and on the content of nitrogen gas. The Cu–N films obtained can be classified into four categories: metallic Cu-rich Cu3N films with a positive temperature coefficient of resistivity (TCR), semiconducting Cu-rich Cu3N films, semiconducting stoichiometric Cu3N films, and semiconducting N-rich Cu3N films with a negative TCR. The current–voltage curves of various Cu–N films are presented. The metallic conduction and semiconductor conduction are two main electrical conduction mechanisms for various Cu–N films. The decomposition temperature of various Cu–N films has been determined to be around 604–614 K using both thermogravimetry and dynamical measurement of electrical resistance during heating in a vacuum furnace. The great scattering of data over the electrical resistivity of Cu3N reported up to now is mainly due to the nonstoichiometry of the Cu3N. The optical band gap of stoichiometric Cu3N...

Preparation of Giant Magnetoresistance Co/Cu Multilayers by Electrodeposition

Reflection electron microscopy of electrodeposited Co, Cu/(111) Pt ultrathin layers and bilayers has revealed a heteroepitaxial and simultaneous multinuclear multilayer growth. Giant magnetoresistance and oscillatory antiferromagnetic interlayer coupling have been observed in a (111) textured Co/Cu multilayered nanostructure, which is compositionally modulated over nanometer length scales with distinct ferromagnetic Co-Cu alloy and nonmagnetic Cu layers, prepared by electrodeposition under potential control in the presence of a very slight amount of CrO{sub 3}. Such a multilayered structure containing a nominal Cu spacer layer thickness of 3.2 nm exhibits a large saturation magnetoresistance of more than 18% at room temperature. Currently the development of new magnetic multilayered nanostructures has attracted considerable attention for potential applicability to magnetoresistive sensor devices.

Effect of nonstoichiometry upon optical properties of radio frequency sputtered Al–N thin films formed at various sputtering pressures

Colored Al–N films can be easily made through changing the content of nitrogen gas at various sputtering pressures. For films deposited at 5×10−2 Torr, with only slight change in the proportion of nitrogen gas from 0% to 2.5%, 5%, 7.5%, and 10%, the respective visual appearance changed from silver–gray to gray, gray, green–yellow to transparent. With the further increase in the content of nitrogen gas up to 100%, the obtained films were all transparent. For films formed at 5×10−1 Torr, with the content of nitrogen gas being 0%, 2.5%, 5%, 7.5%, 10%, and 20%, the corresponding visual appearance of the films were silver–gray, black, dark‐green–yellow, green–yellow, light‐yellow and transparent. When the content of nitrogen gas changed from 20% to 100%, there was almost no difference in the visual appearance. For films formed at 1 Torr, when the content of nitrogen gas was only over 2.5%, the film became clear. Measurements of transmittance, reflectance, and thickness, calculations of the absorption coefficie...

Synthesis and electrical properties of phosphorus-doped homoepitaxial diamond (111) by microwave plasma-assisted chemical vapor deposition using triethylphosphine as a dopant source

A phosphorus-doped (111) diamond film was formed homoepitaxially on a nondoped diamond film, which was also formed homoepitaxially on a type Ib (111) diamond substrate, by microwave plasma-assisted chemical vapor deposition using CH4 as the carbon source and triethylphosphine (TEP, P(C2H5)3) as the dopant source. The P-doped film, which was approximately 800 nm in thickness, exhibited an n-type conduction in the temperature range of 100–500 K. This represents the first such observation, for a film prepared using TEP as the dopant. The activation energy for carrier concentration was 0.09 eV in the range of 145–500 K. The Hall mobility reached a maximum of approximately 3.5 cm2/(Vs) at 145 K and decreased to 0.15 cm2/(Vs) at 500 K. Phosphorus was uniformly incorporated into the diamond film, as evidenced by secondary ion mass spectrometry.

Characterization of electrodeposited Co/Cu ultrathin films and multilayers

Abstract Reflection electron microscopy (REM-RHEED) studies of electrodeposited Co,Cu/Pt(111) ultrathin layers have revealed a heteroepitaxial and simultaneous multinuclear mutilayer growth in a range from submonolayer up to some ten monolayer coverages. ‘Giant’ magnetoresistance and oscillatory antiferromagnetic interlayer coupling have been observed in a (111) textured Co/Cu multilayered nanostructure, which is compositionally modulated over nanometer length scales with distinct ferromagnetic Co Cu alloys and nonmagnetic Cu layers, prepared by electrodeposition under potential control. Such a multilayered structure containing a nominal Cu spacer layer thickness of 3.2 nm exhibits a large saturation magnetoresistance of more than 18% at room temperature. This value is nearly comparable to those previously reported in vapor-deposited multilayers.

Preparation and characterization of electrodeposited Pt/Co multilayers

Abstract Reflection electron microscopy (REM) of electrodeposited Co/Pt(111) ultrathin layers and sandwiches has revealed a heteroepitaxial and simultaneous multinuclear multilayer growth up to coverages of some ten monolayers and an interfacial alloy formation. Cross-sectional transmission electron microscopy (TEM) has provided direct evidence for composition modulation across successive layers in a Pt/Co nanometer-multilayered structure prepared by electrodeposition under potential control.

Preparation of Giant Magnetoresistance Co‐Cu Heterogeneous Alloys by Electrodeposition

Reflection electron microscopy of electrodeposited Co, Cu/(111) Pt ultrathin layers has revealed a heteroepitaxial and simultaneous multinuclear multilayer growth or a three-dimensional island growth, which depends on the deposition overpotential. Giant magnetoresistance has been observed in heterogeneous Co-Cu alloy films, which consist of ultrafine fcc Co-rich clusters in a nonmagnetic polycrystalline Cu matrix, prepared by electrodeposition under potential control. Such a heterogeneous Co 0.2 Cu 0.8 alloy exhibits a large saturation magnetoresistance of more than 20% at room temperature.

Study on corrosion properties of sputter coating of oxides on stainless steels

To improve the corrosion resistivity of steels, the effect of oxide coating has been studied. Various oxides were coated on stainless steels by r.f. sputtering and corrosion properties of the steels were examined in acidic solutions. Structural defects, pinholes, were inevitable in the sputter-coated oxides. The defect probability was determined by electrochemical measurements and direct observations using a liquid crystal. The anodic current was analyzed assuming current flow through the defects. The corrosion properties were discussed, taking the electrical charge on the surface of oxides in solutions into account.

Preparation and characterization of electrodeposited metallic multilayers

Abstract Multilayered films of Co/Pt were prepared by alternating electrodeposition of Co and Pt using two electrolytic baths. The structure of the electrodeposited multilayers was analyzed by reflection electron microscopy (REM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The magnetic anisotropy of the films was examined by changing the thickness of Co layers. Though the perpendicular magnetization characteristics are not good enough, electrodeposition may be feasible for multilayer deposition.

Characterization of electrodeposited magnetic multilayers

Electrodeposition will prove to be a promising candidate for the preparation of magnetic nanostructures. Multilayered Co/Pt nanostructures grown on a Cu(111) single-crystal substrate by electrodeposition under potential control exhibit a remanent perpendicular magnetization and a large coercivity, which depend on the deposition overpotential and hence the multilayer growth mechanism. Giant magnetoresistance and oscillatory antiferromagnetic interlayer coupling have been observed in a face-centered cubic (fcc) (111) textured Co/Cu multilayered nanostructure. Moreover, a large saturation magnetoresistance of more than 20% has been achieved at room temperature for a heterogeneous Co-Cu alloy, which consists of ultrafine fcc Co-rich clusters in a nonmagnetic Cu matrix.