Significant photoelectrical response of epitaxial graphene grown on Si-terminated 6H-SiC

Photoelectrical response characteristics of epitaxial graphene (EG) films on Si- and C-terminated 6H-SiC, and transferred chemical vapor deposition (CVD) graphene films on Si-terminated 6H-SiC have been investigated. The results show that upon illumination by a xenon lamp, the photocurrent of EG grown on Si-terminated SiC significantly increases by 147.6%, while the photocurrents of EG grown on C-terminated SiC, and transferred CVD graphene on Si-terminated SiC slightly decrease by 0.5% and 2.7%, respectively. The interfacial buffer layer between EG and Si-terminated 6H-SiC is responsible for the significant photoelectrical response of EG. Its strong photoelectrical response makes it promising for optoelectronic applications.     

氧化石墨制备温度对石墨烯结构及其锂离子电池性能的影响

采用改进的Hummers 法, 以石墨粉为原料制备氧化石墨, 然后使用微波还原法制备石墨烯, 最后以石墨烯作为负极材料组装锂离子电池. 系统的研究了高温氧化阶段中温度对氧化石墨的氧化程度、石墨烯的还原程度和比表面积以及锂离子电池性能的影响. 利用场发射扫描电镜(FESEM)、 X射线光电子能谱(XPS)、X射线衍射仪(XRD)、BET测量仪对氧化石墨和石墨烯的微观结构及比表面积等进行测试和表征. XRD, XPS及电化学测试的结果显示当高温阶段氧化温度为90 °C时, 氧化石墨的氧化程度最高, 相应的石墨烯也具有最高的还原程度和最大的比表面积423.2 m²/g, 同时石墨烯锂离子电池也具有更好的性能: 首次放电比容量为1555.5 mAh/g, 充电容量为1024.6 mAh/g, 其循环放电比容量达到600 mAh/g.     

Temperature dependence of the thickness and morphology of epitaxial graphene grown on SiC （0001） wafers

Epitaxial graphene is synthesized by silicon sublimation from the Si-terminated 6H–SiC substrate. The effects of graphitization temperature on the thickness and surface morphology of epitaxial graphene are investigated. X-ray photoelectron spectroscopy spectra and atomic force microscopy images reveal that the epitaxial graphene thickness increases and the epitaxial graphene roughness decreases with the increase in graphitization temperature. This means that the thickness and roughness of epitaxial graphene films can be modulated by varying the graphitization temperature. In addition, the electrical properties of epitaxial graphene film are also investigated by Hall effect measurement.     

基于倏逝场耦合的石墨烯波导光传输相位特性仿真与实验研究

石墨烯材料应用到各种光波导器件中正成为新一代光子器件的重要发展方向之一,目前基于石墨烯的光纤和集成光子器件研究越来越受到国内外的重视. 本文建立了一种由微纳光纤耦合光倏逝场,并在石墨烯薄膜中传输的模型. 通过有限元分析法,研究了光在这种石墨烯波导中传输光场的强度分布和相位特性,并通过实验进行了验证. 结果表明,沿着微纳光纤-石墨烯光波导传播的倏逝场的强度分布和相位均受石墨烯材料作用,石墨烯材料能有效聚集和导行波导中传输的高阶模,在单位传输长度上具有更密集的等相位面. 本文提出了一种利用微纳光纤耦合光倏逝场研究石墨烯相位响应特性的新方法,对基于石墨烯波导的新型调制器、滤波器、激光器和传感器等光子器件的设计和应用具有一定的参考意义. 关键词： 石墨烯平面光波导 倏逝波 光场强度 相位     

Low platinum loading PtNPs/graphene composite catalyst with high electrocatalytic activity for dye-sensitized solar cells

Platinum nanoparticles(PtNPs)/graphene composite materials are synthesized by a controlled chemical reduction of H2PtCl6 on graphene sheets.The electrocatalytic activity of a PtNPs/graphene composite counter electrode for a dye-sensitized solar cell(DSSC) is investigated.The results demonstrate that the PtNPs/graphene composite has high electrocatalytic activity for the dye-sensitized solar cell.The cell employing PtNPs(1.6 wt%)/graphene counter electrode reaches an conversion efficiency(η)of 3.89% upon the excitation of 100 mW/cm2 AM 1.5 white light,which is comparable to that of the cell with a Pt-film counter electrode(η=3.76%).It suggests that one can use only 14% Pt content of the conventional Pt-film counter electrode to obtain a comparable conversion efficiency.It may be possible to obtain a high performance DSSC using the PtNPs/graphene composite with a very low Pt content as a counter electrode due to its simplicity,low cost,and large scalability.     

Significant performance enhancement in AlGaN/GaN high electron mobility transistor by high-κ organic dielectric

The electrical properties of AlGaN/GaN high electron mobility transistor (HEMT) with and without high-κ organic dielectrics are investigated. The maximum drain current I_{D max} and the maximum transconductance g_{m max} of the organic dielectric/AlGaN/GaN structure can be enhanced by 74.5%, and 73.7% compared with those of the bare AlGaN/GaN HEMT, respectively. Both the threshold voltage V_T and g_{m max} of the dielectric/AlGaN/GaN HEMT are strongly dielectric-constant-dependent. Our results suggest that it is promising to significantly improve the performance of the AlGaN/GaN HEMT by introducing the high-κ organic dielectric.     

Cu掺杂TiO2及其纳米管的制备、表征与光催化性能

通过溶胶-凝胶法和水热法制备了Cu掺杂TiO₂纳米粉末及其纳米管,并通过XRD、TEM、FE-SEM、EDS、UV-Vis/DRS等手段分析了样品的结构。发现以Cu掺杂TiO₂纳米粉末为水热反应原料制备的纳米管中不含Cu,对其原因进行了分析讨论并通过Zn掺杂TiO₂纳米粉末证实：以金属掺杂TiO₂纳米粉末为原料,通过水热法制备TiO₂纳米管中不含有相应金属离子,这是由于金属离子在强碱水热条件下形成金属配离子,使金属离子溶解于水中而不能形成金属掺杂TiO₂纳米管。对所得样品进行了光催化性能测试,发现：Cu掺杂TiO₂粉末的光催化产氢效率为0.75 μmol·(g·h)^-1,高于由其本身及P25通过水热法制备的TiO₂纳米管(分别为：0.42 μmol·(g·h)^-1,0.25 μmol·(g·h)^-1)的光催化产氢效率。     

A compact graphene Q-switched erbium-doped fiber laser using optical circulator and tunable fiber Bragg grating

We demonstrate a passively Q-switched tunable erbium-doped fiber laser(EDFL)based on graphene as a saturable absorber(SA).A three-port optical circulator(OC)and a strain-induced tunable fiber Bragg grating(TFBG)are used as the two end mirrors in an all-fiber linear cavity.The Q-switched EDFL has a low pump threshold of 23.8 mW.The pulse repetition rate of the fiber laser can be widely changed from 9.3 kHz to 69.7 kHz by increasing the pump power from23.8 mW to 219.9 mW.The minimum pulse duration is 1.7μs and the highest pulse energy is 25.4 nJ.The emission wavelength of the laser can be tuned from 1560.43 nm to 1566.27 nm by changing the central wavelength of the straininduced TFBG.