Motoyuki Tanaka

Formation of cubic-A1N in TiN/A1N superlattice

Abstract Ceramic superlattice is one of approaches for new ceramic film development. We deposited TiN/A1N superlattice films by arc ion-plating process, and evaluated the crystal structure of these films by transmission electron diffraction and X-ray diffraction. It was revealed that the crystal structure of A1N changes from Wurtzite type to NaCl type for superlattice periods ≤ 3 nm. The film hardness increased to about twice that of the TiN single layer film at a period = 2.5 nm. NaCl phase of A1N is one of the phases that exists under high pressure and it is expected that there will be a high bulk modulus.

Morphology and X-Ray Diffraction Peak Widths of Aluminum Nitride Single Crystals Prepared by the Sublimation Method

AlN single crystal is one of the promising materials for substrates of GaN-based laser diodes. We prepared aluminum nitride single crystals by the sublimation method and characterized them. The crystals are transparent and slightly yellow. Some crystals are needle-shaped with a hexagonal cross section, diameter of 0.5 mm and length of 3 mm, grown parallel to |001|. Other crystals are plate-shaped with a maximum width of 3 mm, 5 mm length and 0.5 mm thickness, grown with a large (001) face. Also, other crystals are needle-shaped with a rectangular cross section, width of 1 mm, 7 mm length and 0.3 mm thickness, grown with a large (101) face. Their widths of X-ray rocking curves is about 39 arcsec, with a full width at half-maximum, 203 arcsec and 12 arcsec, respectively. The orientation of AlN single crystal axis is sufficient for use in substrates for GaN-based diodes.

An Allene-Doped Liquid Argon Ionization Chamber for O and Ne Ions at 100 MeV/n

An allene-doped liquid argon ionization chamber with a sensitive volume of 48 mm×48 mm×40 mm has been constructed and investigated for precise measurement of the heavy ion energies at around 100 MeV/n. An energy resolution of 1% (full width at half maximum [FWHM]) was achieved for the 99 MeV/n 16O and 125 MeV/n 20Ne ion beams. However, the energy resolution was found to deteriorate as the beam intensity increased. To understand this phenomenon, a simple model is proposed, in which a space-charge electric field due to the positive ions left along the track of an incident ion is taken into consideration. The estimated electric field is strong enough to worsen the energy resolution when the incident beam intensity is only 100 particles/s.