A couple of zinc oxide (ZnO) single crystals with single boundaries (ZnO-ZnO single-contacts) are fabricated by the traditional vapor reaction method and their electrical properties are characterized. The ZnO-ZnO singlecontacts obtained show nonlinear current-voltage (I-V ) characteristics without varistor-forming constituents. Some of the ZnO-ZnO single-contacts show pronounced nonlinear I-V characteristics with negative resistance. The I-V characteristics of the ZnO-ZnO single-contacts are apparently similar to those of ZnO varistors; however, there are marked differences in the electric structure of the boundaries between the ZnO-ZnO single-contacts and ZnO varistors. The capacitance-voltage (C-V ) relations of the ZnOZnO single-contacts are quite different from that of ZnO varistors and no evidence for the formation of doubleSchottky barriers at the boundary region are found. A very slow response to current stress is a feature of ZnO-ZnO single-contacts and it is suggested that any thermal processes including Joule heat would modify the carrier transport efficiency through the boundaries.

SynopsisThe fine structure of cotton cellulosic fibers carbamoylethylated and carboxyethylated at 30 and 2OoC in the presence of 3% and 20% sodium hydroxide was investigated by measuring moisture regain, water imbibition, x-ray photograph, degree of crystallinity, spacing, and crystallite size under dry and wet conditions. As carbamoylethyl and carboxyethyl substituents are introduced in amorphous regions of the samples reacted with acrylamide in 3% sodium hydroxide, the fine structure of the crystalline regions is not affected by the reaction. On the other hand, in the samples reacted in 2W0 sodium hydroxide, the substituents are introduced not only in amorphous regions but also in crystalline regions to make them disordered. Although spacing between ( l O i ) planes does not change, spacing between (101) planes increases by the reaction in 20% sodium hydroxide. Comparing crystallite sizes normal to (hkl) planes under dry conditions with those under wet conditions, it is supposed that cohesive forces between (101) planes are different from those between (107) planes, and the former is hydrogen bonds and the latter resemble Van Der Waals forces. As a result, carbamoylethyl and carboxyethyl groups are introduced selectively between (101) planes.

Cotton cellulosic fibers were treated with aqueous solutions containing 7% acrylamide and 3% sodium hydroxide at 30°C, and 7% acrylamide and 20% sodium hydroxide at 20°C. The fibers were easily carbamoyl ethylated and carboxyethylated in the presence of 20% sodium hydroxide as compared with the case of 3% sodium hydroxide. In both reaction systems, the total degree of substitution was increased as reaction time proceeded. _iowever, in the reaction system containing 20% sodium hydroxide, number of carbamoylethyl groups was increased at the initial period of reaction, and decreased at the latter stage of reaction. On the contrary, number of carboxyethyl groups increased rapidly as that of carbamoylethyl groups was decreased. These phenomena are elucidated by hydrolysis of carbamoylethyl groups to carboxyethyl groups under alkaline conditions. Degree of crystallinity of the treated cellulose was measured with X-ray diffractometer under dry and wet conditions. The degree of crystallinity of cotton fibers treated in the presence of 3% sodium hydroxide was almost unchanged under dry and wet conditions as same as untreated fibers. However, the degree of crystallinity of cellulose treated in the reaction system containing 20% sodium hydroxide measured under wet conditions was less than that under dry conditions. It is thought to be caused from the fact that carbamoyl ethylation and carboxyethylation occurred not only in the amorphous regions, but also in crystalline regions in the reaction system containing 20% sodium hydroxide, and in the case of 3% sodium hydroxide solution the substitution reaction did not occur in crystalline regions. Moisture regain of the treated fibers was not changed mostly by carbamoylethylation and carboxyethylation. However, water imbibition increased remark ably by treatment in the reaction system containing 20% sodium hydroxide. Grafting reaction of ethylacrylate to the fibers treated in the reaction system containing 20% sodium hydroxide for 10 hr was also carried out. The X-ray diffractgram of the grafted sample was flat even measured under dry conditions. It was found that stable decrystallization of cotton fibers was achieved by graft copolymerization onto the fibers carbamoyl ethylated and carboxyethylated in the presence of 20% sodium hydroxide. Such results are considered to be due to carbamoylethylation and carboxyethylation, and subsequent graft copolymerization occurred in the crystal regions of fibers. From the results mentioned above, it is assumed that crystalline region of fibers treated with acrylamide in the presence of 20% sodium hydroxide is stiff and stable under dry conditions, but very unstable under wet conditions, and stable decrystallization was achieved by graft copolymerization in the treated fibers in 20% sodium hydroxide solution.