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类型 基础研究 预答辩日期 2017-11-23
开始(开题)日期 2016-03-30 论文结束日期 2017-09-06
地点 田家炳南楼205 论文选题来源 国家自然科学基金项目     论文字数 4.4 (万字)
题目 二维层状材料中缺陷的光谱学研究及性能调控
主题词 二维材料,缺陷,光谱,迁移率,热导率
摘要 二维材料(如石墨烯、过渡金属硫属化合物等)具有优异的电学和光学性能,有望应用于未来纳米电子和光电子器件中。然而,二维材料中存在的不同类型的缺陷对其性能有很大的影响。拉曼和光致发光光谱等光谱学表征方法因其无损和高灵敏度等特点,已经广泛地应用于二维材料中的缺陷表征中。本论文利用拉曼和光致发光光谱分别研究了电子束和氩等离子体辐照单层二硒化钨引入的缺陷,以及化学刻蚀溶剂对铜表面生长石墨烯性能的影响。通过低温光致发光光谱和拉曼光谱表征探测缺陷的浓度和类型,并进一步实现对二维材料的电学、光电和热学等性能的调控。本论文的主要研究内容包括: 1. 研究电子束辐照对二硒化钨的光学和电学性能的影响。(1)实验结果表明电子束辐照能够在单层二硒化钨中引入缺陷。通过测试低温光致发光光谱,发现由于激子被束缚于缺陷态,使得光致发光光谱中出现束缚态激子峰,随着温度的升高束缚激子发光逐渐消失。(2)通过光谱学方法得到了电学性能与缺陷浓度的直接关联。实验发现增加二硒化钨上的电子辐照剂量,束缚态激子发光越来越强,并且近视成线性关系。电学性能测试结果表明,随着缺陷密度的增加,迁移率逐步降低,主要是由于电子束辐照在二硒化钨中引入的缺陷作为载流子散射源所导致。(3)利用转移电极的方法制备微型二硒化钨电学器件,避免电子束曝光制备器件过程中对二维材料样品的辐照损伤,实现了高迁移率的二硒化钨器件。 2. 研究氩等离子体辐照对二硒化钨光学性质的影响。(1)实验研究发现氩等离子体处理单层二硒化钨后,其低温光致发光光谱会出现两个新的由缺陷激活的光致发光峰。功率和温度的依赖性表明这些光致发光峰是激子被束缚到不同类型的缺陷态所发射的。浅能级的缺陷态发光源于激子被束缚在硒空位缺陷处的辐射复合,而深能级的发光可能源于其他类型的缺陷,如钨空位,空位团簇,旋转缺陷或者反位缺陷等。(2)将此缺陷发光与电子束辐照处理的样品进行对比,发现电子束辐照初期只出现浅能级缺陷发光峰,对应于硒空位缺陷的形成;而随着辐射量的增大,也会逐渐出现深能级的缺陷发光峰。通过此实验,我们可以可控的在二硒化钨中引入不同类型的缺陷,有望实现对其光学和电学性能的调控。 3. 研究在化学气相沉积法生长石墨烯的转移过程中,不同化学刻蚀溶剂(例如过硫酸铵、氯化铁和硝酸铁等)对铜表面生长石墨烯性能的影响。(1)拉曼光谱研究表明,由于在转移过程中含铁化合物残留在石墨烯上,导致石墨烯的空穴掺杂和声子寿命的减短。(2)利用拉曼测试了不同化学溶剂转移的石墨烯样品的热导率,发现三氯化铁和硝酸铁转移的样品的热导率明显低于过硫酸铵转移的样品的热导率,证明石墨烯表面缺陷对其热传导性能有巨大影响
英文题目 SPECTROSCOPIC INVESTIGATION OF DEFECTS AND DEFECT ENGINEERING IN TWO-DIMENSIONAL MATERIALS
英文主题词 two-dimensional materials; defect; photoluminescence spectroscopy; Raman spectroscopy; mobility; thermal conductivity
英文摘要 Two-dimensional (2D) materials (e.g. graphene and transition metal chalcogenides) with unique optical and electronic properties, hold great potential for applications of future nanoelectronics and optoelectronic devices. However, different types of structural defects could present in 2D materials and have strong influence on their properties. Optical spectroscopic techniques, e.g. Raman and photoluminescence (PL) spectroscopy, have been widely used for defect characterization in 2D materials due to their time efficient and sensitive characteristics. In this thesis, Raman and PL spectroscopy are employed to investigate the defects in WSe2 introduced by electron beam and Ar+ plasma irradiation and surface modification of graphene introduced by adsorbed chemical solvents. Based on characterization and analysis of PL at low temperature and Raman spectra, we realize the control of the quantification and type of defects, so as to further achieve the modulation of the electrical, optical and thermal performance of 2D materials. The main achievements are summarized as follows: 1. The influence of electron beam irradiation on optical and electrical performance of WSe2 monolayer has been studied. (1) Defects are introduced by electron beam irradiation in WSe2 monolayer. Low temperature PL spectra of WSe2 presents a clear defect-induced PL emission due to excitons bound to defects. The PL intensity of bound exciton is vanished with increasing temperature, which is understandable since excitons are not tightly bound to defects. (2) We provide an optical spectroscopic characterization approach to correlate the number of structural defects and the electrical performance of WSe2 devices. It is found that the PL intensity of bound exciton increases monotonically with increasing electron dosage. Electrical performance test shows that mobility decays dramatically with the increase of electron irradiation density, which is attributed to carriers scattered by defects introduced by electron beam irradiation. (3) By adopting an e-beam-free transfer-electrode technique, we are able to prepare backgated WSe2 device with high mobility because of avoiding damage to 2D materials during electron beam lithography. 2. The influence of Ar+ plasma treatment on optical performance of WSe2 monolayer has been studied. (1) Two defect-activated PL emission peaks are emerging in the low temperature PL spectra of WSe2 monolayer treated with Ar+ plasma. These emissions are attributed to the recombination of excitons bound to different types of structural defects. The shallow level emission originates from the recombination of excitons at chalcogen vacancies, while the deep level emission might arise from other types of defects, such as transition metal vacancies, cluster of vacancies, rotational defects, or antisite defects. (2) We compare PL spectra of sample treated by Ar+ plasma with sample treated by electron beam. The shallow level emission presents after short time electron irradiation, which corresponds to the formation of selenium vacancies. With the increase of electron irradiation dosage, deep level emission also can be detected. Through this work, the optical and electrical performance of WSe2 monolayer can be modulated by controlling the type of introduced defects. 3. We study the influence of commonly used etching solvents during the transfer process, i.e. ammonium persulfate, ferric chloride, and ferric nitrate, on the properties of graphene grown on the copper suface by Raman spectroscopy. (1) The results of Raman spectroscopy show that residue iron compounds are presented on the surface of graphene during the transfer process, resulting in p-doping and reduction of phonon lifetime of graphene (2) The non-contact optothermal Raman technique is employed to measure the thermal conductivity. A great reduction of thermal conductivity of graphene is introduced due to reduction of phonon lifetime for graphene transferred by ferric chloride and ferric nitrate as compared to that transferred by ammonium persulfate, which illustrates that defects on the surface of graphene have great influence on the thermal conductivity.
学术讨论
主办单位时间地点报告人报告主题
物理系 2014年12月25日上午9点 田家炳楼南203 吴章婷 博士研究生 东南大学 Bound exciton
物理系 2016年5月25日上午10点 田家炳楼南203 Boris I. Yakobson,Rice University, USA Predictive modeling in 2D materials: morphology, dislocations, grain boundaries
物理系 2016年6月25日上午9点 田家炳楼南203 吴章婷 博士研究生 东南大学 TMDs的缺陷研究文献综述
物理系 2016年5月24日上午10点 田家炳楼南203 张华 教授 (Prof. Hua Zhang) 南洋理工大学 Synthesis and Applications of Novel Two-Dimensional Nanomaterials
物理系 2015年7月17日上午9点 田家炳楼南203 吴章婷 博士研究生 东南大学 TMDs的缺陷表征
物理系 2016年3月12日上午9点 田家炳楼南203 吴章婷 博士研究生 东南大学 单层WSe2的光电性能研究
物理系 2016年7月4日上午10点 田家炳楼南203 刘杰 教授 (Prof. Jie Liu) 南京大学 Selective Growth of Semiconducting Single-walled Carbon Nanotubes
物理系 2015年12月9日上午10点 田家炳楼南203 Alister J. Page, University of Newcastle Catalysts, Etchants and Magnetic Fields: How can Carbon Nanostructure Growth be Controlled?
     
学术会议
会议名称时间地点本人报告本人报告题目
8th International Conference on Recent Progress in Graphene/2D Research 2016年9月25日-29日 韩国,首尔 Defects as a factor limiting carrier mobility in WSe2: A spectroscopic investigation
第十一届中美华人纳米论坛 2016年9月18日-20日 中国,南京 Spectroscopic investigation of defects in two dimensional materials
     
代表作
论文名称
The influence of chemical solvents on the properties of CVD graphene
Defects as a factor limiting carrier mobility in WSe2: a spectroscopic investigation
Defect Activated Photoluminescence in WSe2 Monolayer
 
答辩委员会组成信息
姓名职称导师类别工作单位是否主席备注
缪峰 正高 教授 博导 南京大学
董晓臣 正高 教授 博导 南京工业大学
马延文 正高 教授 博导 南京邮电大学
王肖沐 正高 教授 博导 南京大学
李孝峰 正高 教授 博导 苏州大学
游雨蒙 正高 教授 博导 东南大学
      
答辩秘书信息
姓名职称工作单位备注
吕俊鹏 正高 教授 东南大学