Masafumi Chiba

Fabrication of Micro-Pyramidal Probe Array with Aperture for Near-Field Optical Memory Applications

A new optical memory system is urgently required to realize high memory capacity and fast data transfer rates in the coming multimedia era. To overcome the current capacity barrier of far-field techniques, a novel near-field optical memory of evanescent wave has been proposed using a vertical cavity surface emitting laser (VCSEL) probe array, consisting of the VCSEL array as a light source and the micro-pyramidal probe array as an evanescent wave exit. The design and fabrication for the aperture probe array were developed in this research. An array of up to 10,000 pieces was prepared successfully using microfabrication processes, including photolithography, silicon wet etching, thermal oxidation and thin film deposition. The pyramidal probes in the array show little variation in size and are sufficiently sharp to apply to the near-field recording head. The probe tip has a small size of 100 nm and the aperture has a diameter of around 150 nm. A smaller aperture can be fabricated with more careful control of the experimental procedures, including the etching process and thermal wet oxidation.

Microstructure and magnetic properties of iron oxide thin films by solid reaction

The ferrite (FeO-Fe 2 O 3 ) thin films have been prepared by solid reaction at low temperature including an oxidation process based on Fe-layer/α-Fe 2 O 3 films. The formation of the iron oxide Fe 3 O 4 requires the choice of a suitable heating rate, when the metallic iron is led to oxidize and produce a change in the magnetite. The optimum heating condition for the reaction of ferrite formation is around 30 C/min from 10 C/min.

Magnetic properties and microstructure of Ni–Fe nitride films by reactive sputtering

Abstract The nickel iron nitride Ni3Fe-N seems to have the face-centered cubic structure of A4B type. It can be considered that the magnetic structure is decided by the relationship of the electronic orbits N-2p and Ni-3d. The thin films of Ni3Fe-N were prepared by a reactive RF-sputtering method. It was found that the amount of the N2 flow rate greatly affects the crystal growth.

Study on Microstructure and Magnetic Properties of TM-Mg (TM: Fe, Co) Alloys Synthesized by Mechanical Alloying

Magnesium alloys are extremely attractive candidates for hydrogen storage applications since they can potentially absorb hydrogen between 3 and 8 wt.%. The purpose of this work is to understand the microstructural and the magnetic properties for 3d-transition metal and magnesium alloys with the difficult to alloy by the conventional method due to the positive value of mixing enthalpy. We successfully formed alloys of iron or cobalt, and magnesium powders with a wide range of compositions by mechanical alloying and characterized synthesized alloys with an X-ray diffractometer, a TEM, an SEM-EPMA and a vibration sample magnetometer. The obtained Fe-Mg alloys containing less than 25 at.% Mg were single phase bcc with expanded lattice parameter. The average powder particle size changes with Mg composition. The magnetization of the samples showed a linear dilution with content of Mg. The opposite variations in lattice parameter and the coercive force with Mg content were observed. On the other hand, we observed markedly broadened XRD lines from Co-Mg alloy compounds. The microstructure of these powders implies that the alloy could be partially amorphized or changed into a nanostructure as expected from microscopy and an XRD results.

Liquid Phase Deposition of Carbon Nitride Films for Application as Low-k Insulating Materials

CNx films are fabricated using liquid phase deposition by applying a DC bias voltage to Si substrates immersed in acrylonitrile. X-ray photoelectron spectra reveal that C, N, and O are major components of the deposited films. From analysis of C 1s and N 1s spectra, the major bonding state in the CNx film is attributed to a mixture of C≡N and partially hydrogenated C=N bonds. Metal–insulator–semiconductor capacitors incorporating the CNx insulating layers are fabricated to evaluate the electrical properties of the deposited films. The lowest dielectric constant k of the CNx film is determined to be 2.6 from the accumulation capacitance and the thickness of the film, suggesting that the CNx film formed by liquid phase deposition is a promising low-k material for use in ultralarge-scale integration multilevel interconnections.

Microscopic Structure and Magnetic Properties of Bi Added FeMn Alloy

Magnetic thin films of Mn-ferrite (MnFe<inf>2</inf>O<inf>4</inf>) have shown a large perpendicular magnetic anisotropy by the evaporation method. The evaporation substances are the (A¿Bß)<inf>100¿x</inf>C<inf>x</inf> system, where A, B, and C represent the matrix elements of combination for Mn, Fe, and Bi, respectively. For (Mn<inf>25</inf>Fe<inf>75</inf>)<inf>97</inf>Bi<inf>3</inf>, column-shaped MnFe<inf>2</inf>O<inf>4</inf> grains deposited on a substrate have an anisotropy constant of 4.4 × 10⁵ erg/cm³, 4¿M<inf>s</inf> of 1.6 × 10³ G, and H<inf>c</inf> of 540 Oe. The structure and magnetic properties of such evaporated films are closely related. It was recognized that in order to obtain magnetic thin films with perpendicular anisotropy, it is important to form a first Bi-phase layer with ≪102≫ orientation on the substrate.

Microscopic Structure and Magnetic Properties in State of FeMn Alloy Added Bi

Fe-Mn-Bi films were formed by electron beam vacuum evaporation, and then oxidized by annealing in an oxygen atmosphere to obtain ferromagnetic oxide films. The film composition profiles and magnetic properties were then investigated. Depth profiles as determined by AES indicated a uniform film composition, but X-ray diffraction indicated the formation of FeMnBiO4 upon annealing. From the annealing temperature dependences of the saturated magnetization and coercive force, a magnetic transformation point exists near 300°C, a result confirmed by separate resistivity measurements.