Papers by Author: Masayoshi Umeno

Abstract: Magnetite (Fe₃O₄) nanoparticles were successfully synthesized by ascorbic acid mediated reduction of Fe (acac)₃, without using any intentionally added capping agent. Fine tuning of synthesis parameters such as dropping rate of ascorbic acid solution, addition temperature, reflux temperature and time, and concentration of reactants have yielded nanoparticles of size 15±4 nm. Synthesis is observed to be highly reproducible. Possible mechanism for growth of Fe₃O₄ nanoparticles is suggested. Nanoparticles are characterized for their size, crystallinity and crystal structure, elemental analysis for impurities (if any), and presence of any additional oxide phases – by SEM and TEM, XRD, EDAX and XPS spectroscopy, respectively.

Abstract: Optical emission spectra from plasma during deposition of diamond film were investigated by an optic multi-channel spectrometer using a CCD array sensor. The diamond film was deposited by DC plasma enhanced (PE) chemical vapor deposition (CVD) using hydrogen and methane gas mixture, where substrate was located at near the plasma and the discharge was performed by intermittent discharge. When Pg during the deposition was increased from 50 to 250 Torr, the optical emissions of hydrogen (Hα and Hβ) and C2 were increased, and corresponding to these increases, deposition rate of the diamond film was increased and crystalline quality became superior. When Cm was changed from 1 to 3 %, the emission from C2 was increased, and whereas, the emission from hydrogen was decreased. Corresponding to these changes of the emission, the deposition rate of the film was increased and amorphous component in the deposited film was also increased. These results show that the increase of C2 results in the increase of the deposition rate, and increase of hydrogen is effective to eliminate amorphous component, and therefore, monitoring of the optical emission from hydrogen and C2 is useful for the deposition process of the diamond film.