過渡性金屬硫族化合物二硫化錸為二維層狀材料，其晶體結構為具有結構異向性的三斜晶系(triclinic structure, 1T)。在過去的研究中，發現平行b晶軸方向之電導率高於垂直b軸，因此在電子元件、光電元件和能源材料之應用具有潛在優勢。本研究以化學氣相傳輸法成長晶體，藉由X光繞射和拉曼量測，證實為高品質的二硫化錸單晶。由文獻可知，過渡性金屬硫族化合物在奈米結構中，存在表面主導電傳輸的特性，因此若能了解其材料本質的特性，就能進一步控制其電傳輸。為了解二硫化錸表面電子結構，利用機械剝離法將晶體原有表面移除，量測內部的新鮮表面(fresh surface)，再透過掃描穿隧顯微鏡和角度解析光電子能譜來分析，結果發現其費米能階接近導帶邊緣，表示fresh surface具有很高的電子濃度。而在角度解析光電子能譜分析中也顯示fresh surface隨者環境變化，其費米能階偏移不大，說明此表面特性是很穩定的。除此之外，藉由變溫場效應電晶體的量測證實了表面具有很強散射和金屬性行為。最後，綜合以上量測結果，說明了二硫化錸具有表面主導電傳輸的特性是由於表面有大量的電子聚集，使表面存在很高的電子濃度。

Rhenium disulfide (ReS2), one of transition metal dichalcogenides (TMDCs) and two-dimensional or layered materials, is known to exhibit anisotropic properties due to the reduced symmetry from distorted 1T structural phase. The electronic transport properties from its anisotropy show that the conductivity parallel to the b-axis is higher than that normal to the b-axis. This inherent structural fundamental from ReS2 has become its potential benefits for electronic device application. In addition, many articles have also reported its application for optoelectronic device, energy storage, and solar cell. The high-quality ReS2 crystals grown by chemical vapor transport (CVT) using chlorine (Cl2) as the transport agent has been achieved and characterized by X-ray diffraction (XRD) and Raman spectroscopy. Because the nanostructure in TMDCs can emerge the hidden characteristics from the surface, observing its intrinsic properties should consider the control to the apparent properties. In this study, the surface of ReS2 was analyzed by two surface electronic measurement: scanning tunneling spectroscopy (STS) and angle resolved photoemission spectroscopy (ARPES). The fresh surface achieved by mechanical exfoliation introduced the occurrence of high electron density from the electronic band structure pinning the conduction band edge near the fermi level position. The other clarification with ARPES shown the small change of electronic band energy after exposing the freshly exfoliated surface in ambient environment. The stability from this ambient influence suggested the presence of high electron concentration in the fresh surface of ReS2. In addition to this study, the field effect transistor (FET) device and temperature dependence measurement were performed to explain the scattering and metallic behavior in ReS2. The FET configuration of ReS2 nanoflake results the high concentration of ReS2 nanostructure, explained on its two-dimensional transport behavior. The high calculated electron concentration from both electrical measurement and electronic structure characterizations indicated the presence of surface electron accumulation in ReS2.

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