Microstructure evolution and photoluminescence in nanocrystalline Mg(x)Zn(1 - x)O thin films

The effects of Mg concentration and annealing temperature on the characteristics of nanocrystalline Mg(x)Zn(1 - x)O thin films (where x = 0-0.4) were studied using electron microscopy and photoluminescence. The films were prepared by a sol-gel method. The solid solubility limit of MgO in ZnO for the sol-gel-derived Mg(x)Zn(1 - x)O films in the present study was determined to be ∼ 20 at.%. Microstructural characterization of the films showed that the wurtzite crystallites decrease in size with increase in Mg concentration up to the solubility limit. Increasing Mg concentration beyond the solubility limit resulted in a decrease in crystallinity of the films. The bandgap energy was found to increase with Mg concentration whereas the linewidth first increased and then decreased when the Mg concentration was increased beyond the solubility limit. Photoluminescence properties have been correlated to the microstructure of the films. A growth mechanism for Mg(x)Zn(1 - x)O nanocrystalline films under the present processing conditions has also been proposed.

Transport properties of hybrid nanoparticle-nanowire systems and their application to gas sensing

Experimental data and theoretical modelling of the I-V characteristics of a gas sensor constructed from a mat of Au nanoparticle-coated GaN nanowires are presented. The principal mechanism for the response of the gas sensor to methane is explained in terms of the formation of a depletion layer within the nanowires due to the presence of the gold nanoparticles. The depth of the depletion layer is modulated by the potential induced by the physisorption of gas molecules onto the Au nanoparticles. A statistical model of the temperature-dependent I-V characteristics of bare and Au nanoparticle-decorated mats of GaN nanowires based on Poisson's equation has been used to determine the depth of the depletion layers of the nanowires. The room-temperature carrier concentration for the GaN nanowires was determined to be approximately 2.2 × 10(17) cm(-3). The induced potential due to methane physisorption onto the Au nanoparticles that decorate the GaN nanowires was determined to be approximately -37 mV.

Identification and characterization of a gene that controls colony morphology and auto-aggregation in Escherichia coli K12

Many Escherichia coli K12 strains undergo switching between two forms which differ in a number of surface properties including colony morphology and the ability to auto-aggregate. This paper describes the identification of a gene which appears to play a part in controlling this switching phenomenon. This gene has been designated mor and is located at 89 minutes on the E. coli chromosome map between the argECBH operon and the trmA gene. By manipulation of this gene it is possible to overcome the switching of surface properties and fix a strain in one form or the other. The mor gene has been cloned and its DNA sequence determined. The putative protein sequence shows a high level of homology with four regulatory genes, the ilvY, cysB and lysR genes from E. coli and the metR gene from Salmonella typhimurium. It has also been shown that the mor gene is autoregulated at the transcriptional level.

Normal Coordinate Calculations of the Vibrations of Methylene Cyclopropane-h6 and -d6

Normal coordinate calculations for methylene cyclopropane-h6 and -d6 have been carried out using two models. In the first model 31 internal coordinates were used, and in the second model 25 internal coordinates were used. The force constants were, in each case, refined to the 40 frequencies observed for the two molecules. Using the first model 26 force constants, of which four were constrained, fitted the frequencies with an average error of 1.2% for C4H6 and 2.8% for C4D6. Using the second model 24 force constants, of which two were constrained, fitted the frequencies with an average error of 1.4% for C4H6 and 2.8% for C4D6.The very low isotopic shift of the C=C stretching mode can be explained by an interaction with the ethylenic CH2 deformation, which is best assigned at 1047 m−1, rather than at 1139 cm−1, in C4D6. The calculations indicate that the experimental assignment for the A1 ring breathing mode and the A1 methylenic wag in C4H6 should probably be reversed. For the A1and the B1 modes with frequencies between 500 and 1300 cm−1, the normal coordinates change considerably on deuteration. The symmetry coordinates are mixed in the normal modes of C4D6 to a much greater extent than in those of C4H6.

Infrared and Raman spectra and vibrational assignment of methylene cyclopropane-h6 and -d6

Infrared spectra have been recorded in the range 4000 to 20 cm−1 for methylene cyclopropane-h6 and -d6 in the gas phase, and from 4000 to 200 cm−1 for methylene cyclopropane-h6 in the liquid phase. Raman spectra have been recorded for the liquid phases of both species. The fundamental modes of vibration have been assigned using i.r. band contours and Raman depolarization ratios, with the exception of the i.r. inactive A2 modes which were not observed. An interesting feature is the occurrence of remarkably small isotope shifts for certain modes.