Akio Hiraki

Synthesis and structural study of nano/micro diamond overlayer films

Abstract The nano/micro diamond overlayer films have been successfully fabricated by means of bias growth technique using microwave plasma-enhanced chemical vapor deposition method. During the diamond growth, as a negative bias (−100xa0V) is applied midway on the substrate side, the nanocrystalline diamond layer can be controllably deposited on the as-grown microcrystalline diamond to form a nano/micro overlayer structure. Transmission electron microscopy images reveal that the nanocrystalline layer consists of ultra-fine diamond crystallites, of which the average grain size is only about 4–5xa0nm. The formation mechanism of diamond nanocrystals on diamond micrograins under the bias conditions is discussed. Moreover, by the repeat-biasing way, three or more layered diamond films can be produced as well.

Reducing the grain size for fabrication of nanocrystalline diamond films

Abstract Microwave plasma-enhanced chemical-vapor-deposited (MPECVD) diamond films grown under various bias conditions applied to the substrates have been examined by electron microscopy. It is noticed that in a certain range, increasing the bias voltage can effectively reduce the diamond grain size. Transmission electron microscopy (TEM) images distinctly reveal that the diamond films consisting of ultrafine crystallites of about 7–10xa0nm can be successfully fabricated by applying an appropriate bias voltage. Comparing the conventional diamond films deposited without bias and the nanocrystalline diamond films grown with a bias, one can see that the latter have better field emission properties.

Growth and structural analysis of nano-diamond films deposited on Si substrates pretreated by various methods

Nanocrystalline diamond lms have been deposited on Si substrates by microwave plasma-enhanced chemical-vapordeposition (MPECVD) method. The microstructure and morphology of the as-deposited carbon lms are found to be strongly in#uenced by substrate pretreatment methods. Under higher methane concentration conditions, nanocrystalline diamond lms could be grown on Si substrates which were ultrasonically scratched both by diamond and SiC powders, but their surface topographies were rather di!erent. On the substrates which were mechanically abraded by the Al 2 O 3 grits, nano-diamond particles are formed in the amorphous matrix, that is considered to be the diamond-like carbon (DLC). The pretreatment e!ects on the formation of nano-diamonds are discussed related to the nucleation processes. The study also indicates that by a two-step (high methane concentration followed by a low methane concentration) growth process, even on the substrates scratched by the low-cost nondiamond abrasives, fabrication of polycrystalline diamond lms with high grain density is possible. ( 2000 Elsevier Science B.V. All rights reserved.

Carbon nanofibers synthesized by decomposition of alcohol at atmospheric pressure

In the present study, we fabricated the carbon nanofibers (CNFs) by decomposition of methyl alcohol at atmospheric pressure. The CNFs were grown on Ni/Si substrates using simplified hot-filament chemical vapor deposition equipment. The deposits mainly consist of the semicrystalline CNFs, in which a few of carbon nanotubes are included. On the 30-nm-thick Ni/Si substrates, the mean length of the CNFs is 2–3 μm, and their average diameter is less than 100 nm. The as-deposited CNFs were evaluated by both scanning and transmission electron microscopes. The field-electron-emission properties of CNFs were characterized as well.

Low-temperature (200°C) growth of diamond on nano-seeded substrates

Abstract Fabrication of diamond (including diamond-like carbon: DLC) films as electronic materials requires several conditions. They are: (1) low-temperature fabrication (or deposition on several substrates) below 300°C, (2) wide-area film deposition onto wide substrates of several square inches, like Si wafer, (3) reproducible deposition of well-defined film quality, and (4) others. In these respects, we have initiated, in the authors laboratories at Osaka University and Kochi University of Technology, a quite new approach to satisfy the above requirements by using microwave plasma CVD under a magnetic field to be called as “magneto-active plasma CVD.” The films thus fabricated, combined with our special nano-seeding method, have been used as electron emitter with high efficiency for a 3-year Japanese national project “Development of Ultra Thin Flat Panel Display” that started in 1997 with the author being appointed as the project leader.

In-situ monitoring of PE-CVD growth of TiO2 films with laser Raman spectroscopy

Abstract A new plasma-enhanced chemical vapor deposition (CVD) system with an in-situ monitoring system by laser Raman spectroscopy was developed by which it is possible to obtain Raman spectra even when the thickness of a TiO2 film is only about 27.5 A. A peak corresponding to titanium silicide was observed at the early growth stage of TiO2. It was made clear that titanium silicide decomposes with the process of growth and plays a role in the conversion of amorphous titanium dioxide to a crystalline one and enhances the growth of crystal.

Field electron emission of diamond films grown on the ultrasonically scratched and nano-seeded Si substrates

In the present study, we compare the field emission properties of diamond films grown on ultrasonically scratched and nano-seeded Si substrates. The diamond films were fabricated in a microwave plasma chemical vapor deposition system. It is confirmed that these two kinds of pretreatment methods, scratched or nano-seeded, result in rather different field emission properties. The diamond films grown on the ultrasonically scratched Si substrates present much higher emission current and lower threshold field than those of the films grown on the nano-seeded substrates. Cross-sectional transmission electron microscopy has been employed to evaluate the diamond films, and the field electron emission behaviors are analyzed in relation to the interface structures.

Electron emission from nitrogen-doped chemical vapour deposited diamond

Abstract We have used urea ((NH 2 ) 2 CO) as a dopant and grown N-doped polycrystalline diamond using hot filament chemical vapor deposition (HFCVD) technique, and in addition, the mold-based technique is used in order to obtain the pyramidal-shape array structure. Both polycrystalline films and pyramidal-shape array are identified as diamond from the results of Auger electron spectroscopy (AES) and Raman spectroscopy. The nitrogen concentrations of the film are evaluated using Rutherford backscattering (RBS) technique and it is found to be about 10 20 xa0cm −3 . A turn-on field as low as 0.5xa0V/μm in the emission properties has been confirmed and the emission current fluctuations are discussed.

Electron-emitter fabricated at low temperature by diamond-nano-seeding technique

Abstract Fabrication of diamond (including diamond like carbon: DLC) films as electronic materials, for example, to be used as electron-emitter, requires several following conditions. They are: (1) low-temperature fabrication (or deposition on several substrates and sometimes ones with low melting point, like glasses) below 400°C; (2) wide area film deposition onto wide substrates of several square inches, like Si wafer and glass substrate; (3) reproducible deposition of well-defined film quality and (4) others. In these respects, we have initiated, in the author’s laboratories at Osaka University and Kochi University of Technology, a quite new approach to satisfy the above requirements by using microwave plasma CVD under a magnetic field to be called as “magnetoactive plasma CVD”. The films fabricated by the magnets-active plasma CVD and also recently by cathodic arc methods combined with our special nano-seeding method, have been utilized for electron-emitter to exhibit very high efficiency.

Electron field emission from diamond-like carbon films after dielectric breakdown and from diamond films after the activation process

Abstract The effects of the activation process on the electron field emission characteristics of diamond-like carbon (DLC) films and polycrystalline diamond films have been studied. Electron emission of the insulating DLC films was enabled by dielectric breakdown in a high field. Emission sites of some complex structures were initiated in the films by the dielectric breakdown. The diamond films, of poor quality and low conductivity, sometimes started electron emission on applying an extracting field for the first time. For subsequent measurements, the emission properties were stable and reproducible. On applying the extracting field the first time, the diamond film was heated locally by the emission current and a small hole was burned out in the film.