Lei Wang

Tsinghua University, Peping, Beijing, China

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Publications (67)133.28 Total impact

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    ABSTRACT: The effects of cation distribution on optical properties of MnxCo2.52−xNi0.48O4 serial thin films are investigated by spectroscopic ellipsometry and Raman technique. The optical constants present a distinctive difference with the change of the cation distribution in the serial films. Three absorption structures are found in the dielectric constant spectra while their intensities strongly depend on the distribution of cations. Complementary Raman scattering measurements corroborate the varying absorptions are mainly contributed by Mn ions in high photon energy range but Co ions in low.
    Materials Letters 08/2015; 153. DOI:10.1016/j.matlet.2015.04.046 · 2.27 Impact Factor
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    ABSTRACT: doi: 10.1021/acs.jpclett.5b01017
    Journal of Physical Chemistry Letters 06/2015; DOI:10.1021/acs.jpclett.5b01017 · 6.69 Impact Factor
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    ABSTRACT: In the present work, a series of Cu/SAPO-34 catalysts with varying number of Brønsted acid sites has been prepared by ion exchanging with potassium to investigate the role of Brønsted acidity in the NH3-SCR reaction. The impact of potassium on the structural and acidic properties of Cu/SAPO-34 catalysts has been studied. No significant changes in both the SAPO-34 structure and the copper species were observed in the presence of potassium. With increasing potassium loading, the NH3-SCR activity of the Cu-K/SAPO-34 catalysts decreased in accordance with the decreasing Brønsted acidity. The quantification method of Brønsted acid sites in the Cu-(K)/SAPO-34 was developed by using IR spectroscopy, which was confirmed by acid site generation mechanism and NH3-TPD results. A linear relationship was found between the amounts of Brønsted OH groups determined by DRIFTS and the NH3 desorbed at high temperatures from NH3-TPD.
    Journal of Catalysis 04/2015; 324. DOI:10.1016/j.jcat.2015.01.011 · 6.07 Impact Factor
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    ABSTRACT: The electrical and microstructural properties of SnO2-based varistor ceramic sample were improved by addition of Pr6O11. It was found that the introduction of Pr6O11 can lead to a great improvement in the threshold voltage and the non-linear electrical properties of SnO2-based varistors. As the amount of Pr6O11 increased from 0.00 to 0.5 mol%, the mean grain size decreases from 16.64 to 7.58 μm, the relative dielectric constant (at 1 kHz) increases from 1243.2 to 4534.6, the non-linear coefficient increases from 15.44 to 18.25 and the break down electrical field increases from 275.3 to 880.5 V/mm. The structure-property relationship is discussed systematically.
    Ceramics International 04/2015; 41(8). DOI:10.1016/j.ceramint.2015.03.315 · 2.09 Impact Factor
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    ABSTRACT: Fifteen novel homocamptothecin derivatives with α-OMe substituted E-rings were designed and synthesized. All of the derivatives exhibited similar or superior cytotoxicities compared with that of SN-38, and they inhibited Topo I activity in a cell-free assay in a manner similar to that of SN-38, confirming that they represent a new class of Topo I inhibitors. Notably, the water soluble compound 36o (1.2mg/mL) exhibited increased lactone stability, and at 0.5mg/kg and 3.0mg/kg, it demonstrated significant antitumor activity in mice bearing a xenograft model using human colon cancer cell line HT-29. On the basis of these positive results, further development of 36o-related compounds as potential anticancer clinical trial candidates is definitely warranted. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Bioorganic & medicinal chemistry 03/2015; 23(9). DOI:10.1016/j.bmc.2015.03.031 · 2.95 Impact Factor
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    ABSTRACT: Spontaneous polarization behaviors of hybrid perovskite CH3NH3PbI3 film were confirmed by in situ PFM and spectroscopic ellipsometry. The film exhibits uniform spontaneous polarization and ferroelectric domain inversion performance. The fitted dielectric constants spectra agree well with the calculated ones. We attribute the spontaneous polarization behaviors of hybrid perovskite to lone pair electrons, and its outstanding photovoltaic performance partially originates from spontaneous polarization and plasma resonance. This report will facilitate understanding of the instinct physical essence of hybrid perovskite solar cells.
    Scripta Materialia 02/2015; 102. DOI:10.1016/j.scriptamat.2015.01.030 · 2.97 Impact Factor
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    ABSTRACT: The optical properties of spinel Mn1.56Co0.96Ni0.48O4 thin films have been investigated by spectroscopic ellipsometry in the temperature range from 20 to 260 degrees C. By fitting the measured ellipsometric parameter data with a three-layer model by Tauc-Lorentz oscillator dispersion formula, the refractive index and extinction coefficient of the thin films are determined in the spectral range of 280-850 nm. The refractive index decreases in the short-wavelength region but increases in the long-wavelength region with increasing temperature. The extinction coefficient increases with increasing temperature in all visible region.
    Materials Letters 12/2014; 136:225-228. DOI:10.1016/j.matlet.2014.08.025 · 2.27 Impact Factor
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    ABSTRACT: 0.5BaZr0.2Ti0.8O3-0.5Ba0.7Ca0.3TiO3 thin films have been deposited on Pt/Ti/SiO2/Si substrates by a modified sol-gel technique. The samples are well-crystallized perovskite ferroelectrics at room temperature, with good surface topography. Optical properties of these films in the 280-850 nm wavelength range have been investigated by spectroscopic ellipsometry at room temperature. The measured ellipsometry parameters are well fitted by Tauc-Lorentz oscillator dispersion formula. As the wavelength increases, the refractive index and extinction coefficient rise in the beginning and then descend, with a peak at about 300 nm. The calculated absorption coefficient demonstrates that as-grown films have selective absorption, with a broad transparent range, and possess a big energy gap (4.18 eV).
    Journal of Alloys and Compounds 12/2014; 615:526-530. DOI:10.1016/j.jallcom.2014.06.186 · 2.73 Impact Factor
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    ABSTRACT: We have systematically studied the feasibility of CaMnO3 thin film, an n-type perovskite, to be utilized as the buffer layer for hybrid halide perovskite photovoltaic-thermoelectric device. Locations of the conduction band and the valence band, spontaneous polarization performance, and optical properties were investigated. Results indicate the energy band of CaMnO3 can match up well with that of CH3NH3PbI3 on separating electron-hole pairs. In addition, the consistent polarization angle helps enlarge the open circuit voltage of the composite system. Besides, CaMnO3 film shows large absorption coefficient and low extinction coefficient under visible irradiation, demonstrating high carrier concentration, which is beneficial to the current density. More importantly, benign thermoelectric properties enable CaMnO3 film to assimilate phonon vibration from CH3NH3PbI3. All the above features lead to a bright future of CaMnO3 film, which can be a promising candidate as a buffer layer for hybrid halide perovskite photovoltaicthermoelectric systems.
    Journal of Applied Physics 11/2014; 116:194901. DOI:10.1063/1.4901636 · 2.19 Impact Factor
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    Ceramics International 09/2014; DOI:10.1016/j.ceramint.2014.08.094 · 2.09 Impact Factor
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    ABSTRACT: Although lithium ion battery is known to be an excellent renewable energy provider in electronic markets further application of it has been limited by its notoriously poor performance at low temper- ature, especially below ?20 ? C. In this paper, the electrochemical performance of the LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode materials coated by lithium boron oxide (LBO) glass was investigated at a temperature range from 20 to ?40 ? C. The results show that the LBO coating not only helps to improve the discharge ca- pacity of LiNi 1/3 Co 1/3 Mn 1/3 O 2 at room temperature but also increase the discharge capacity retention of the LiNi 1/3 Co 1/3 Mn 1/3 O 2 from 22.5% to 57.8% at ?40 ? C. Electrochemical impedance spectra results reveal that the LBO coating plays an important role in reducing the charge-transfer resistance on the electrolyte eelectrode interfaces and improving lithium ion diffusion coefficients. The mechanism associated with the change of the structure and electrical properties are discussed in detail.
    Journal of Power Sources 08/2014; 277:139-146. DOI:10.1016/j.jpowsour.2014.11.149 · 5.21 Impact Factor
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    ABSTRACT: LaMnO3 thick films doped with Al were fabricated on Al2O3 substrates by screen printing technique. Significantly composition-dependent structural phase transformation and grain size were observed in Al-doped LMO thick films by X-ray diffraction and scanning electron microscopy. The resistivity of all the thick films decreased with the increase of temperature, indicating a negative temperature coefficient effect. Al doping resulted in a sharp rise in room resistivity (rho(0)) and thermal constant (B) as compared with non-doped films. Among the films investigated, the film with composition x=0.4 showed a unique electrical property and was further examined in detail using the complex impedance analysis, in order to unveil the structure property relationship.
    Ceramics International 08/2014; 40(7-7):10505-10510. DOI:10.1016/j.ceramint.2014.03.022 · 2.09 Impact Factor
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    ABSTRACT: Inorganic-organolead halide perovskite CH3NH3PbI3 modified BiFeO3 polycrystalline film has been established. The composite photoelectrode presents much larger open voltage and several magnitudes superior photoelectric conversion performance in comparison to the ordinary BiFeO3 polycrystalline film. The I-V curve shows that the short-circuit current (Jsc) is 1.74 mA·cm−2 and open-circuit voltage (Voc) is 1.62 V, the device's photon to current efficiency is over 1%. The large open voltage and high photovoltaic efficiency is believed to attributed to the spontaneous polarization of composite perovskite induced by BiFeO3 lattice and modified reduced work function of the modified BiFeO3 surface. Our results clearly show that the present BiFeO3-CH3NH3PbI3 planar device is capable to generate a large voltage in macro scale under visible light, leading an approach to further applications on photodetectors and optoelectronic switch.
    Applied Physics Letters 07/2014; 105(1):013901-013901-5. DOI:10.1063/1.4888912 · 3.52 Impact Factor
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    ABSTRACT: A new way to prepare BiFeO3 nano-powders by low-heating temperature solid state precursor method is presented in this paper. Room-temperature solid state reaction was adopted to prepare the precursors, which were further calcined in low-heating temperature at 500°C to synthesize nano-BiFeO3. The particle size of BiFeO3, ranging from 18 to 80 nanometers, can be effectively controlled by different alkali in raw materials. Owing to the quantum size effect, the optical band gaps and magnetic characteristics of BiFeO3 increased with the decreasing particle size.
    Integrated Ferroelectrics 06/2014; 156(1). DOI:10.1080/10584587.2014.906888 · 0.37 Impact Factor
  • Integrated Ferroelectrics 05/2014; 153(1):33-41. DOI:10.1080/10584587.2014.902668 · 0.37 Impact Factor
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    ABSTRACT: Effect of BiFeO3 (BFO) content on the microstructure and electrical properties of BaTi0.9Zr0.1O3 (BTZ) ceramics prepared by the solid-state reaction technique was investigated. X-ray diffraction analyses show that BFO diffused into the lattice of BTZ to form a solid solution with perovskite structure. The relative density of the BTZ ceramics is increased by the introduction of BFO. The dielectric study reveals that the dielectric constant and the average dielectric loss of the solid solution decreased simultaneously with an increase in BFO content. The materials undergo a diffuse type ferroelectric phase transition. The diffusivity increases with increase in BFO contents in the studied composition range. On the other hand, the piezoelectric coefficient and electromechanical coupling coefficient decrease simultaneously with increasing the BFO content, whereas the mechanical quality factor increases gradually. The structure–property relationship and the mechanism associated with the change of the electrical properties are discussed intensively.
    Ceramics International 05/2014; 40(4):5173–5179. DOI:10.1016/j.ceramint.2013.10.075 · 2.09 Impact Factor
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    ABSTRACT: Three-dimensional hierarchical structure coral-like BaTiO3 nanoparticles have been self-assembled by a facile one step hydrothermal method. Cetyltrimethyl ammonium bromide (CTAB), Ba(OH)2·8H2O and tetrabutyl titanate have been used as precursors. The prepared BaTiO3 exhibits cubic perovskite phase at room temperature, and the coral-like architecture is a micro-nano hiberarchy consisted of dendrimer-like structure and trunk-like structure. By adjusting the hydrothermal duration and the precursor substances, a surfactant induced mechanism is proposed to understand the self-assembly process. UV-vis measurement demonstrates that the as-prepared BaTiO3 nanoparticles exhibit dozens of times overwhelming absorptive character compared to the ordinary nanospheres at ultraviolet band, which is benefited from the coral-like porous framework. Moreover, halogen anions( F−, Cl−, Br−, and I−) have been chosen to adjust the coral-like BaTiO3 physical properties. Results show the halogen doping produces distinct modulation effect on the grain size, UV-vis absorbance and photoluminescence properties of the materials. The coral-like BaTiO3 nanoparticle and its halogen modified ramifications offer significant opportunities to develop nano-laser devices, photon detectors, photocatalyst based on BaTiO3 perovskite materials.
    Journal of Materials Science and Technology -Shenyang- 04/2014; 31(2). DOI:10.1016/j.jmst.2014.04.002 · 1.61 Impact Factor
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    ABSTRACT: The increasing number of spectral survey telescopes that are soon commissioned for exploring the universe will confront us with many new challenges on the use of optical fibers. A fiber-switching problem for telescope's terminal instrument is as important as a well-known problem of positioning fibers on telescope's focal plane. For a modern survey telescope, it generally feeds several terminal instruments with different functions. According to the observation, these instruments are seriously in need of switching fiber-link with telescope as soon as possible. A kind of multi-fiber coupling plugs introduced in this paper will work for switching fiber-link between Multi-object Exoplanet Search Spectral Interferometer (MESSI) and low resolution spectrograph at Guoshoujing telescope (LAMOST). It includes an inserter, a receptor and a socket in general. The number of simultaneously coupling fibers is up to 25 per group, and any broken fiber in a single plug can be replaced by a new standard one soon without wasting entire fiber bundle. In addition, Most of mechanical part can also be individually replaced when a normal loss happens after a long working time. The related test result is given in detail, including the machining precision and coupling efficiency.
    Proceedings of the International Astronomical Union 03/2014; 8(S293). DOI:10.1017/S1743921313013240
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    ABSTRACT: Camptothecin (CPT) is a natural topoisomerase I inhibitor with powerful antineoplastic activity against colorectal, breast, lung and ovarian cancers. To discover more potent antitumor agents, a series of new CPT derivatives were synthesized utilizing click chemistry. All compounds were assessed for cytotoxicity against A549, HCT-116, HT-29, LoVo, MDA-MB-231 cell lines, and some compounds exhibited good in vitro potency. Furthermore, all compounds kept or enhanced Topo I inhibition.
    Chinese Journal of Chemistry 02/2014; 32(2). DOI:10.1002/cjoc.201300703 · 1.04 Impact Factor
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    ABSTRACT: In an effort to discover potent antitumor agents, a series of novel C-7-heteroaryl-substituted camptothecin derivatives were designed and synthesized via microwave-promoted Suzuki coupling reaction. These analogs were then assessed for cytotoxicity against three human tumor cell lines, A549, HCT116, HT-29, and inhibitory effects on topoisomerase I. All of the new compounds showed potent inhibition of human tumor cell growth, among which compound 10a showed higher cytotoxic activity than that of SN-38. Furthermore, this series of compounds retained or enhanced Topo I inhibition.
    Bioorganic & medicinal chemistry letters 01/2014; 24(6). DOI:10.1016/j.bmcl.2014.01.049 · 2.33 Impact Factor

Publication Stats

262 Citations
133.28 Total Impact Points

Institutions

  • 2010–2015
    • Tsinghua University
      • School of Materials Science and Engineering
      Peping, Beijing, China
  • 2007–2015
    • Chinese Academy of Sciences
      Peping, Beijing, China
  • 2014
    • Zhejiang University
      • Department of Chemistry
      Hang-hsien, Zhejiang Sheng, China
  • 2013–2014
    • East China Normal University
      • Department of Chemistry
      Shanghai, Shanghai Shi, China
    • China Academy of Chinese Medical Sciences
      Peping, Beijing, China
  • 2011
    • Shandong University of Science and Technology
      Tsingtao, Shandong Sheng, China