Electronic Transport Studies of Low Dimensional van der Waals Materials

Ever since the successful isolation of graphene, plenty of researches have been pursued to study fundamental physics in low-dimensional van der Waals materials, referred to as materials with the existence of out of plane van der Waals force. Not only graphene but also many other novel vdW materials start to emerge and play important roles in quantum physics. Due to the highly preserved crystal quality of the nanostructures achieved by micromechanical exfoliation, a variety of new phenomenon have been discovered in these novel materials. This dissertation focuses on the discovery and electronic properties study of new vdW materials both in 2D and 1D systems.;Semiconducting transition metal dichalcogenides with layered structure have been viewed as the promising channel materials for field-effect transistors (FETs) in modern electronics. To characterize the performance, we have fabricated FETs based on multilayer tungsten disulfide (WS2) thin crystals. By using gold as the contact metal and varying the thickness of the crystal, high-performance FETs with on/off ratio of 108 and mobility up to 234 cm2V-1s-1 at room temperature have been realized. The high performance is associated with the minimized Schottky barrier and a shallow impurity level below the conduction band.;Elementary substance and binary compound crystals have limited members belong to 2D or 1D family. Thus, expanding the research to ternary compound materials is necessary. In this regard, we focused on a novel ternary compound 2D material Nb3SiTe6 and studied its magneto-transport. We have discovered that by using such a high crystalline 2D metal, we could study the inelastic electron-phonon (e-ph) interactions involved with reducing dimensions. From 3D bulk to 2D films with a rigid substrate, the weak antilocalization (WAL) signature is gradually enhanced according to our magnetoresistance (MR) measurements. The correlation between the enhancement of WAL and the change of dephasing process has been confirmed. Furthermore, systematic studies of the temperature dependence of the dephasing rate in the crystal with various thicknesses suggest the suppression of electron-phonon interaction due to quantum confinement of the phonon spectrum. Our work shows great consistency with the long-standing predicted theory.;It is well known that the micromechanical exfoliation is usually applied to produce 2D nanoflakes out from high-quality bulk crystals. Interestingly, there is a large group of 1D vdW materials with vdW interactions between ribbons (the smallest repeating unit in 1D system). We have successfully expanded the mechanical exfoliation method to this special material group. As demonstrated by semiconducting quasi-1D materials, Ta2Pd3Se 8 (TPdS) and Ta2Pt3Se8 (TPtS), the external force can efficiently break the weak vdW interactions between ribbons. In our work, we have produced ultrathin 1D TPdS and TPtS nanowires, and fabricated 1D FETs showing p-type and n-type transistor behavior respectively. Moreover, we have successfully built the functional logic NOT gate using these two different 1D FETs.