六角星形MoSe_2双层纳米片的制备及其光致发光性能

采用化学气相沉积法,以三氧化钼作为钼源,硒粉作为硒源,在H_2/Ar气氛下生长出硒化钼纳米片.扫描电镜、X射线衍射表征结果表明,MoSe_2产物呈六角星状,横向尺寸约10μm,具有很好的晶体质量和结构.拉曼光谱表征其结构,确定其为双层纳米片.研究表明,高温反应时间对双层纳米片的生长具有重要的影响.通过对双层纳米片的生长机理的探究,推测其经历了3个生长过程:在高温下,Mo源和Se源被气化成气态分子并发生硒化反应形成晶核;晶核呈三角形外延生长;当反应时间持续增加,在空间位阻效应的影响下,晶体以中心原子岛为核,外延耦合生长出第二层三角形,最终形成六角星状双层纳米片.光致发光光谱结果表明,六角星状MoSe_2双层纳米片在1.53 eV处具有直接带隙和1.78 eV处具有间接带隙,其较宽范围的激发光谱响应预测其在光电探测器件领域具有潜在的应用前景.

Synthesis and photoluminescence property of hexangular star MoSe2 bilayer

Transition metal dichalcogenides (TMDs) have received widespread attention because of their excellent performances in the field of optoelectronic, nanoelectronic device and photocatalytic exploration. The structures of TMDs can be expressed by the MX₂, M=Mo, W; X=S, Se, Te, etc. As a typical TMD, MoSe₂ has a graphene-like two-dimensional periodic structure with perfect physical, photoelcrtonic and catalytic properties. Currently, there are various methods to prepare the nanolevel MoSe₂, such as the mechanical exfoliation, physical vapor deposition (PVD), hydrothermal method, chemical vapor deposition (CVD), etc, and most studies focused on regular triangular morphologies of the surfaces of different substrates. The new morphology, such as the hexangular star bilayer, has not been systematically investigated. In this study, the hexangular star MoSe₂ nanosheets are successfully synthesized by using a simple CVD method in an atmosphere of mixed H₂/Ar with a flow rate ratio of 1:4. Molybdenum trioxide(MoO₃) and selenium (Se) powders are chosen to be the Mo and Se source, respectively. Moreover, the structure of the obtained MoSe₂ nanosheet is characterized by Raman, SEM, EDS, XRD and TEM. The results of Raman spectrum and SEM indicate that the hexangular star MoSe₂ possesses a bilayer structure. The TEM characterization reveals that the MoSe₂ is a single crystal with a hexagonal lattice structure and good quality. The heating time at high temperature has a remarkable influence on the MoSe₂ bilayer growth process. The growth process of the hexangular star MoSe₂ bilayer is inferred to experience a three-step process. First, Mo and Se sources are gasified into gaseous molecules and then the Mo molecules are selenized into the MoSe₂ crystal nucleus under high temperature. Next, these crystal nucleus are in a triangular epitaxial growth under the action of carrier gas. As heating time increases, the space steric effect leads to different interlayer separations between the two MoSe₂ layers in various stacking configurations, eventually forming a hexangular star bilayer. The PL result shows that the spectra split into two main emission peaks, i.e., the direct and indirect bandgaps of the hexangular star structure appearing at 1.53 eV (810.2 nm) and 1.78 eV (696.9 nm), respectively. It might be due to the spin-orbit coupling interaction between the double MoSe₂ molecules. The wide spectral range of the MoSe₂ bilayer indicates that it has a potencial application in the photoelectric detectors.