DMS materials (ZnO

Abstract:
ZnO nanoparticles for different thermal treatment temperatures were prepared by using sol–gel method under supercritical drying of ethyl alcohol. The structural properties showed that the ZnO nanoparticles exhibit hexagonal wurtzite structure. Thus, in the case of thermal treatment at 500 °C in air, the powder with an average particle size of 40 nm shows a strong luminescence band around 384 nm in the UV range. However, the optical band gap of our samples varied between 3.34 and 3.21 eV with increasing annealing temperature. The imaginary and real parts of the sample impedance versus frequency, were studied in the range of 40 Hz–2 MHz. The Nyquist diagrams were used to identify an equivalent circuit and the fundamental parameters of the circuit. The characteristics of crystallinity, morphology, photoluminescence and electrical conductivity of ZnO nanoparticles were investigated.

An aqueous solution-based doping strategy was developed for controlled doping impurity atoms into a ZnO nanowire (NW) lattice. Through this approach, antimony-doped ZnO NWs were successfully synthesized in an aqueous solution containing zinc nitrate and hexamethylenetetramine with antimony acetate as the dopant source. By introducing glycolate ions into the solution, a soluble antimony precursor (antimony glycolate) was formed and a good NW morphology with a controlled antimony doping concentration was successfully achieved. A doping concentration study suggested an antimony glycolate absorption doping mechanism. By fabricating and characterizing NW-based field effect transistors (FETs), stable p-type conductivity was observed. A field effect mobility of 1.2?cm2?V ? 1?s ? 1 and a carrier concentration of 6 × 1017?cm ? 3 were achieved. Electrostatic force microscopy (EFM) characterization on doped and undoped ZnO NWs further illustrated the shift of the metal?semiconductor barrier due to Sb doping. This work provided an effective large-scale synthesis strategy for doping ZnO NWs in aqueous solution.

A full characterization of phase separation and the competition between phases is necessary for a comprehensive understanding of strongly-correlated electron materials (SCEM), such as under-doped high temperature superconductors 1,2 , complex oxide heterojunctions 3 , antiferromagnetic 4 and ferromagnetic 5 spinels, multiferroics 6,7 , rareearth ferroelectric manganites 8 , and mixed-valence manganites where phase competition is the dominant underlying mechanism governing the insulator-metal (IM) transition and the associated colossal magnetoresistance (CMR) effect 9-11 . Thin films of SCEMs are often grown epitaxially on planar substrates and typically have anisotropic properties that are usually not captured by edge-mounted four-terminal electrical measurements, which are primarily sensitive to in-plane conduction paths. Accordingly, the correlated interactions in the out-of-plane (perpendicular) direction cannot be measured but only inferred. We address this shortcoming and show here an experimental technique in which the SCEM under study, in our case a 600 Å-thick (La 1-y Pr y ) 0.67 Ca 0.33 MnO 3 (LPCMO) film, serves as the base electrode in a metal-insulator-metal (MIM) trilayer capacitor structure. This unconventional arrangement allows for simultaneous determination of colossal magnetoresistance (CMR) associated with dc transport parallel to the film substrate and colossal magnetocapacitance (CMC) associated with ac transport in the Page 2 of 32 perpendicular direction. We distinguish two distinct strain-related direction-dependent insulator-metal (IM) transitions and use Cole-Cole plots to establish a heretofore unobserved collapse of the dielectric response onto a universal scale-invariant power-law dependence over a large range of frequency, temperature and magnetic field. The resulting phase diagram defines an extended region where the competing interaction of the coexisting ferromagnetic metal (FMM) and charge-ordered insulator (COI) phases 10-15 has the same behavior over a wide range of temporal and spatial scales. At low frequency, corresponding to long length scales, the volume of the phase diagram collapses to a point defining the zero-field IM percolation transition in the perpendicular direction.

A full characterization of phase separation and the competition between phases is necessary for a comprehensive understanding of strongly correlated electron materials, such as under-doped high-temperature superconductors 1,2 , complex oxide heterojunctions 3 , spinels 4,5 , multiferroics 6,7 , rare-earth ferroelectric manganites 8 and mixed-valence manganites in which phase competition is the dominant mechanism governing the insulator-metal (IM) transition and the associated colossal magnetoresistance effect 9-11 . Thin films of strongly correlated electron materials are often grown epitaxially on planar substrates and typically have anisotropic properties that are usually not captured by edge-mounted four-terminal electrical measurements, which are primarily sensitive to inplane conduction paths. We present an experimental study of anisotropic transport in phase-separated manganite thin films by using an unconventional arrangement of contact electrodes that enables the simultaneous determination of colossal magnetoresistance associated with d.c. transport parallel to the film substrate and colossal magnetocapacitance associated with a.c. transport in the perpendicular direction. We distinguish two distinct direction-dependent IM transitions and find a dielectric response that collapses onto a scale-invariant dependence over a large range of frequency, temperature and magnetic field.

A dual layer Benzocyclobutene (BCB) polymer with tailored refractive index values is successfully fabricated using different curing processes, forming a platform for integrated optical devices. The dual layer BCB polymer could potentially solve the high index contrast issue associated with existing glass-polymer structure, which require sub-micron precision when producing single-mode waveguides. Although the two BCB layers display similar physical properties, they have significantly different optical and chemical characteristics. The different curing processes for the undercladding and core layers led to these differences. Single mode waveguides fabricated via photolithography were also demonstrated with an average propagation loss of 2 dB/cm.