The optical properties of vertically aligned ZnO nanowires deposited using a dimethylzinc adduct

The optical properties of zinc oxide nanowires are critically influenced by the growth process. Herein, we describe a metal-organic chemical vapour deposition (MOCVD) process for the growth of ZnO nanowires with improved optical properties. A tetrahydrofuran adduct is used to control the reactivity of dimethylzinc to enable this. Vertically aligned zinc oxide nanowires have been grown on Si(111) substrates by liquid injection MOCVD, using a solution of [Me(2)Zn(tetrahydrofuran)] in the presence of oxygen. The ZnO morphology becomes nanowire-like in a narrow temperature range centred about 500 degrees C. Above and below this temperature range, the ZnO is deposited in the form of polycrystalline films. The ZnO nanowires grow from a polycrystalline nucleation layer, with the (0002) c-axis parallel to the Si[111] substrate orientation. High-resolution electron microscopy reveals a highly crystalline nanowire microstructure. Resonance enhanced ultraviolet Raman spectroscopy shows that the ratio of first- and second-order longitudinal optic modes is commensurate with electron-phonon coupling effects observed previously in ZnO nanostructures. Photoluminescence exhibits intense near band-edge emission with a full width at half-maximum of 110 meV at room temperature and shows negligible defect-related visible emission.

Structure of carbon onions and nanotubes formed by arc in liquids

Since carbon nanotubes and onions were discovered, many methods have been proposed for their production. For applications the main requirements are low capital cost, high purity of the produced material, simplicity of technique, and its potential for scale up. Recently a cathodic arc between two graphitic electrodes immersed in liquids has been demonstrated to be a simple method to produce carbon nanoparticles such as nanotubes and onions. In this paper high-resolution transmission electron microscopy is employed to examine the shape of the nanoparticles and the purity of the final material produced under various conditions. In this study we have used an arc discharge in two different liquids--liquid nitrogen and distilled water--and we have changed the grade of the carbon electrodes. The variety in structure, shape, and size of the produced particles is discussed in line with a model proposed to describe the physical process.

Annular pancreas in two consecutive siblings: an extremely rare case

Annular pancreas is the rare congenital anomaly where the pancreas forms a full or incomplete ring around the second segment of the duodenum, causing various degrees of stenosis or atresia. It is estimated that it appears in 1 out of 12 000-15 000 births of living neonates and until now, in the literature, only 6 cases have been reported among individuals of the same family. We present the case of two siblings, a boy and a girl, with annular pancreas from consecutive pregnancies of the same couple. Both neonates had a prenatal diagnosis of duodenal obstruction and they underwent duodenoduodenal, proximal transverse to distal longitudinal anastomosis. Furthermore, the girl had a mobile ascending colon. Their postoperative condition was perfect. The case we are reporting is an addition to the other 6 cases of familial presentation of annular pancreas and is similar to one of them. In these families, a total of 16 persons present this congenital anomaly while 14 are seemingly healthy. Twelve of the affected persons are female and 4 male. In conclusion, it can be stated that female individuals seem to have a greater propensity to transmit the disease to their descendants, compared to males, suggesting the possible action of an autosomal recessive sex-influenced gene. The recording of such rare family cases should be encouraged, in order to fully recognize a possible type of inherited transmission.

Synthesis of carbon 'onions' in water

The fabrication of carbon nanomaterials usually calls for expensive vacuum systems to generate plasmas and yields are disappointingly low. Here we describe a simple method for producing high-quality spherical carbon nano-'onions' in large quantities without the use of vacuum equipment. The nanoparticles, which have C60 cores surrounded by onion-like nested particles, are generated by an arc discharge between two graphite electrodes submerged in water. This technique is economical and environmentally benign, and produces uncontaminated nanoparticles which may be useful in many applications.