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Huang R.,Beijing National Center for Electronic Microscopy | Zhu J.,Beijing National Center for Electronic Microscopy
Materials Chemistry and Physics | Year: 2010

Silicon nanowire array films were prepared by metal catalytic etching method and applied as anode materials for rechargeable lithium-ion batteries. The films completely consisted of silicon nanowires that were single crystals. Aluminum films were plated on the backs of the silicon nanowire films and then annealed in an argon atmosphere to improve electronic contact and conduction. In addition to easy preparation and low cost, the silicon nanowire film electrodes exhibited large lithium storage capacity and good cycling performance. The first discharge and charge capacities were 3653 mAh g -1 and 2409 mAh g -1, respectively, at a rate of 150 mA g -1 between 2 and 0.02 V. A stable reversible capacity of about 1000 mAh g -1 was maintained after 30 cycles. The good properties were ascribed to the silicon nanowires which better accommodated the large volume change during lithium-ion intercalation and de-intercalation. © 2010 Elsevier B.V. All rights reserved.


Butt S.,Tsinghua University | Butt S.,Institute of Space Technology | Ren Y.,Tsinghua University | Farooq M.U.,University of Science and Technology Beijing | And 4 more authors.
Energy Conversion and Management | Year: 2014

We present the temperature dependent thermoelectric properties of polycrystalline misfit-layered ceramics; (Ca2- xMxCoO3)0.62 (CoO2) , (M: Ba and Pb, x = 0, 0.1, 0.2), fabricated by sol-gel method followed by spark plasma sintering technique. The X-ray diffraction results confirmed the substitution of Ba and Pb in the lattice of (Ca 2CoO3)0.62 (CoO2) at Ca-site. An improved grain-alignment was observed at small scale with Ba-doping, which helped increasing the electrical conductivity but for the Pb-doped specimens, the electrical conductivity was suppressed by catastrophic grain-alignment. The bivalent metallic-doping induced a spin-entropy enhancement which resulted in an enhanced thermopower. For Ba-doped specimens, the simultaneous increase in the electrical conductivity and the thermopower resulted in an increased power factor exhibiting the highest value of 527 μW/mK2. On the other hand, Pb-doping increased the thermopower but on the expense of electrical conductivity. Although, Pb-doping decreased the electrical conductivity but on the other hand, the enhanced thermopower and the suppressed thermal conductivity were sufficient for achieving ZT value higher than that of pure (Ca 2CoO3)0.62 (CoO2). Among all the pure and doped samples, the highest ZT value of ∼0.33 at 1000 K was achieved by Ba-doping which is about 100% higher than that of the pure (Ca 2CoO3)0.62 (CoO2). © 2014 Elsevier Ltd. All rights reserved.


Wu L.H.,Tsinghua University | Wu L.H.,Beijing National Center for Electronic Microscopy | Wu L.H.,Shanghai Aircraft Design and Research Institute | Zhang X.,Tsinghua University | And 6 more authors.
Applied Physics Letters | Year: 2011

Nonsaturating positive magnetoresistance (MR) of intrinsic bulk silicon (i-Si) was observed at forward bias, exhibiting an almost linear behavior at high magnetic fields (5 T


Ahmad M.,Beijing National Center for Electronic Microscopy | Pan C.,Beijing National Center for Electronic Microscopy | Zhao J.,Beijing National Center for Electronic Microscopy | Zhu J.,Beijing National Center for Electronic Microscopy
Journal of Nanoscience and Nanotechnology | Year: 2011

In this letter, effect of Pb-doping on the electrical and optical properties of the as grown ZnO nanowires (NWs) have been investigated. The microstructural investigations show that the Pb-dopant substituted into wurtzite ZnO nanowires without forming any secondary phase. The amount of contents and valence state of Pb ions has been investigated through energy dispersive spectroscopy and X-ray photospectroscopy The doped nanowires show a remarkable reduction of 15.3 nm (127.4 meV) in the optical band gap, while an increase amount of deep-level defects transition in visible luminescence. Furthermore, the reduction in the band gap and the presence of deep-level defects induces strong effect in the electrical resistivity of doped NWs, which makes their potential for the fabrication of nanodevices. The possible growth mechanism is also briefly discussed. © 2011 American Scientific Publishers.


Ahmad M.,Beijing National Center for Electronic Microscopy | Pan C.,Beijing National Center for Electronic Microscopy | Zhao J.,Beijing National Center for Electronic Microscopy | Iqbal J.,Tsinghua University | Zhu J.,Beijing National Center for Electronic Microscopy
Materials Chemistry and Physics | Year: 2010

The effect of high-energy (200 keV) electron irradiation on ZnO-tetrapod (ZnO-T) nanostructure has been investigated by employing in situ scanning tunneling microscopy (STM) holder inside TEM. The microscopic results have revealed that the product consists of highly single-crystalline ZnO-T structures. The photoluminescence spectra show the increased amount of defects which lead to shift in the emission peak position in ultraviolet (UV) region and enhance the PL performance in visible luminescence (VL) region of ZnO-T nanocrystals. The in situ measurements show asymmetric Schottky contacts at the both ends interfaces under electron irradiation. The current-voltage (I-V) characteristics have revealed that the increase in electron density (range of ∼0-25 pA cm-2) leads to an increase in the current along with the increase in carrier concentration from 1.1 × 1017 cm-3 to 3.2 × 1017 cm-3. In addition, it has been interestingly found that at high bias voltage, Schottky contacts turn to Ohmic contacts at the both ends with the influence of irradiation-matter interaction. The results strongly suggest that the ZnO-T is considered as a promising candidate for applications in irradiation environments. © 2009 Elsevier B.V. All rights reserved.

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