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Fu D.,University of California at Berkeley | Fu D.,Nanjing University | Fu D.,Nanjing National Laboratory of Microstructures | Levander A.X.,University of California at Berkeley | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We report an effect that occurs in semiconductors where internal electrical fields interact with a temperature gradient. Steady current vortices and a magnetic field develop in the system, even without external carrier injection. The effect is electrodynamic, energy dissipative, and fundamentally distinct from any previously described electrothermal effects. In bipolar structures the effective thermopower can be significantly modified by the vortices. Joule heating arising from the vortices reduces the thermal conductivity by an amount comparable to the electronic thermal conductivity. © 2011 American Physical Society.

Fu D.,University of California at Berkeley | Fu D.,Nanjing University | Fu D.,Nanjing National Laboratory of Microstructures | Zou J.,University of California at Berkeley | And 7 more authors.
Nano Letters | Year: 2011

Charge transfer, surface/interface, defect states, and internal fields strongly influence carrier statics and dynamics in semiconductor nanowires. These effects are usually probed using spatially resolved scanning current techniques, where charge carriers are driven to move by diffusion force due to a density gradient, drift force due to internal fields, and thermoelectric force due to a temperature gradient. However, in the analysis of experimental data, analytical formulas are usually used which are based on the assumption that a single component of these forces dominates the carrier dynamics. In this work we show that this simplification is generally not justified even in the simplest configurations, and the scanning microscopy data need to be analyzed with caution. We performed a comprehensive numerical modeling of the electrothermal dynamics of free charge carriers in the scanning photocurrent microscopy configuration. The simulation allows us to reveal and predict important, surprising effects that are previously not recognized, and assess the limitation as well as potential of these scanning current techniques in nanowire characterization. © 2011 American Chemical Society.

Zhang X.,Nanjing National Laboratory of Microstructures | Zhang X.,Gannan Normal University | Xu Z.,Nanjing National Laboratory of Microstructures | Tang S.,Nanjing National Laboratory of Microstructures | And 2 more authors.
Crystal Growth and Design | Year: 2011

Single-crystalline alkaline-earth metal manganites CaMn3O 6, SrMn3O6-x and Ba6Mn 24O48 nanoribbons have been successfully synthesized by a facile ion-exchange approach based on molten-salt reaction between Na 0.44MnO2 nanoribbons and CaCl2, SrCl 2, and BaCl2. All of these as-prepared nanoribbons are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Taking the synthesis of single-crystalline SrMn3O6-x nanoribbons as an example, we researched in detail the conversion process from Na0.44MnO2 nanoribbons to SrMn3O6-x nanoribbons. Our results indicate that Na0.44MnO2 nanoribbons serve as the precursor template and the final products are obtained via ion-exchange reaction. Although there is a complete cation exchange, a change in stoichiometry, and a change in crystal structure, the morphology is nearly perfectly maintained. The synthetic method is thought to be a self-sacrificing templating route. © 2011 American Chemical Society.

Fu D.Y.,Nanjing University | Fu D.Y.,Nanjing National Laboratory of Microstructures | Zhang R.,Nanjing University | Zhang R.,Nanjing National Laboratory of Microstructures | And 13 more authors.
Journal of Applied Physics | Year: 2010

The influences of biaxial and uniaxial strain on the ultraviolet emission efficiencies of both c- and m-plane AlxGa1-xN films with different Al concentrations are investigated under the framework of kp perturbation theory. The optimal high efficiency windows, for ultraviolet light emissions are quantitatively estimated. c-plane AlxGa1-xN modified by uniaxial strain, shows more advantages over biaxial-strained Al xGa1-xN. This is due to the relatively more flexible tuning range and the advantage of obtaining pure linear polarization, which can be utilized to design polarized emission devices. For m-plane Al xGa1-xN, there are always in-plane polarized emissions under both biaxial and uniaxial strain conditions, thus, it is more likely to obtain high surface emission efficiency. © 2010 American Institute of Physics.

Deng Y.,Nanjing University | Deng Y.,Nanjing National Laboratory of Microstructures | Zhou J.,Nanjing University of Aeronautics and Astronautics | Wu D.,Nanjing National Laboratory of Microstructures | And 2 more authors.
Japanese Journal of Applied Physics | Year: 2012

Featherlike (CoFe2O4)0.3-(BaTiO 3)0.7 (CFO-BTO) nanostructures were synthesized by a hydrothermal reaction and polymer-assisted deposition. With CFO nanopillars embedded in the BTO matrix, the nanostructures show an average diameter of 250nm and lengths of up to 5 μm. The microstructure and growth mechanism of the nanostructures were investigated. A large magnetoelectric (ME) coefficient of 51.8mVcm-1 Oe-1 at room temperature and a strong phonon abnormality between 110 and 140 °C are discussed. # 2012 The Japan Society of Applied Physics. © 2012 The Japan Society of Applied Physics.

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