Low-temperature galvanomagnetic effects in the presence of shallow attractive traps

Investigations are carried out on the low-temperature galvanomagnetic effects of non-equilibrium carriers in covalent semiconductors in the presence of shallow attractive traps. Expressions for the galvanomagnetic coefficients are obtained both under fixed field and under fixed current conditions. The calculations are made with the approximation of a parabolic law of dispersion. Numerical results are obtained for n-Ge at 4·2 K. It is shown that the results are useful for the determination of some capture parameters and also for the estimation of degree of compensation in high purity samples.     

Magnetic and electric properties of antimony selenide (Sb2Se3) crystals

The magnetic susceptibility in the three principal crystallographic directions, and the electrical conductivity and thermoelectric power parallel and perpendicular to the basal plane of Sb₂Se₃ single crystals, have been measured over the temperature range 100–550 K. The different results obtained from the magnetic and electric studies have been accounted for on the basis of non-stoichiometry of the compound and localized lone electrons. A hopping mechanism in the higher temperature region simultaneously with impurity excitation is suggested.     

Some new butylthiobenzoatotin(IV) compounds: spectral studies and analysis of ligand's bonding

Five new monorganotin(IV) compounds with thiobenzoate ligand, [BuSn(SOCPh)2]2O (1), [BuSn(O)(SOCPh)]2 (2), BuSn(Cl)(SOCPh)2 (3), BuSn(Cl)2(SOCPh) (4) and [BuSn(OH)(Cl)(SOCPh)]2 (5) were synthesized and characterized by elemental analyses, IR, 1H and 13C NMR spectroscopy. 119Sn NMR spectroscopy was used to determine the coordination geometry around Sn(IV) in the cases of 2 and 4. 1, 2 and 5 are dimeric while 3 and 4 are monomeric. In all these molecules the thiobenzoate ion is coordinated only through its sulfur atom. Molecular structures of the compounds have been optimized by MM2 calculations. Semi-empirical quantum mechanical calculations (PM3 method) were performed to explain the monodentate-bonding pattern of thiobenzoate ligand.     

Ambipolar gate effect and low temperature magnetoresistance of ultrathin La0.8Ca0.2MnO3 films

Ultrathin La(0.8)Ca(0.2)MnO(3) films have been measured in a field-effect geometry. The gate electric field produces a significant ambipolar decrease in resistance at low temperatures. This is attributed to the development of a pseudogap in the density of states and the coupling of localized charge to strain. Within a mixed phase scenario, the gate effect and magnetoresistance are interpreted in the framework of a "general susceptibility," which describes how phase boundaries move through a hierarchical pinning landscape.     

Thermal conductivity of nanoscale colloidal solutions (nanofluids)

Researchers have been perplexed for the past five years with the unusually high thermal conductivity (k) of nanoparticle-laden colloidal solutions (nanofluids). Although various mechanisms and models have been proposed in the literature to explain the high k of these nanofluids, no concrete conclusions have been reached. Through an order-of-magnitude analysis of various possible mechanisms, we show that convection caused by the Brownian movement of these nanoparticles is primarily responsible for the enhancement in k of these colloidal nanofluids.     

Depletion layers and domain walls in semiconducting ferroelectric thin films

Commonly used ferroelectric perovskites are also wide-band-gap semiconductors. In such materials, the polarization and the space-charge distribution are intimately coupled, and this Letter studies them simultaneously with no a priori ansatz on either. In particular, we study the structure of domain walls and the depletion layers that form at the metal-ferroelectric interfaces. We find the coupling between polarization and space charges leads to the formation of charge double layers at the 90 degrees domain walls, which, like the depletion layers, are also decorated by defects like oxygen vacancies. In contrast, the 180 degrees domain walls do not interact with the defects or space charges. Implications of these results to domain switching and fatigue in ferroelectric devices are discussed.     

Growth of nanostructures of Zn/ZnO by thermal evaporation and their application for room-temperature sensing of H<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>S gas

ZnO micro- and nanostructures were prepared by thermal evaporation of Zn and a mixture of ZnO with graphite. On heating Zn powder in a quartz tube at temperatures between 600 °C to 800 °C, radial growth of nanowires was observed on the source. On increasing the temperature to 900 °C, various interesting micro- and nanostructures of Zn and ZnO were observed to have deposited all over the quartz tube. On the other hand, when ZnO was heated in the presence of graphite, predominant growth of ZnO nanotetrapods was observed. Nanowires and tetrapods of ZnO were characterized by photoluminescence measurements and were found to show significantly improved response for detection of H₂S gas at room temperature when compared with earlier studies. The response was seen to improve with increase in oxygen vacancies in the material. PACS 78.55.Et; 07.07.Df     

First triaxial superdeformed band in 170Hf

First evidence is presented for triaxial superdeformation in ¹⁷⁰Hf. High-spin states in this nucleus have been investigated in a γ-ray coincidence measurement using the EUROBALL spectrometer array. A new band was discovered which has moments of inertia that are very similar to the ones of triaxial superdeformed bands in neighbouring Hf and Lu nuclei. The intensities with which these bands are populated are different from what may be expected from calculated potential-energy minima. Received: 11 September 2002 / Accepted: 15 October 2002 / Published online: 10 December 2002 RID="a" ID="a"e-mail: neusser@iskp.uni-bonn.de Communicated by D. Schwalm