Papers by Author: Kenichi Tanaka

Abstract: Hydrogen storage by calcium nitride or magnesium nitride has been undertaken by the use of ammonia, in which the possibility of ammonia as a vector for hydrogen carriers has been studied. When the calcium imide ornitride obtained by thermal decomposition of calcium amide dispersed on active carbon (AC) was brought into contact with ammonia gas (300 Torr) at room temperature, NH3 uptake readily occurred. When the sample after NH3 uptake was heated, the absorbed ammonia was released in the form of hydrogen and nitrogen. The ammonia is possibly absorbed in the form of the decomposed state in the imide ornitride. This type of hydrogen storage has been extensively studied and characterized.For magnesium nitride, ammonia was absorbed and desorbed without the decomposition.

Abstract: Scanning tunneling microscopy (STM) proved the existence of quasi-compounds on solid surfaces. A typical example is (-Ag-O-) or (-Cu-O-) chains grown on Ag(110) or Cu(110) surface by exposing to O2. The (-Ag-O-) chains on a Ag(110) reacts with Cu atoms to form a new quasi-compound of (-Cu-O-) chains on the Ag(110) surface. The (-Cu-O-) on the Ag(110) readily decomposes at ca. 570ºK to form Cu6 dots, and a reversible reaction of (Cu2)3 + O2. ↔ (-Cu-O-) takes place by exposing to O2. Deposited Zn, Sn and Ag atoms on a Si(111)-7x7 surface stabilize by forming Zn3, Sn2 and Sn, and Ag in a half unit cell. Layer-by-layer growth of Zn3 clusters occurs in a half unit cell, which results in the growth of a semi-conductive honeycomb layer of Zn3 clusters on the Si(111)-7x7 surface. By prohibiting hopping migration of Ag atoms on the Si(111)-7x7 surface by the adsorption of C2H5OH, nano-size Ag dots grow layer-by-layer in a limited mold spacing. The band gap of Ag-dots becomes narrower and narrower and becomes metallic at higher than 6 layers.