This thesis mainly focuses on the fabrication and transport measurement of three different materials: two-dimensional (2D) MoS₂ and germanane, and one-dimensional (1D) carbon nanotube.

In MoS₂ electrical double layer transistor, artificial hetero states are induced at the top and bottom surface of a single few-layer flake, forming a homojunction with atomically sharp and clean interface. The doping level of the top and bottom surface are controlled by ionic gating and back gating, where superconductivity and Shubnikov-de Haas quantum oscillation is observed, respectively. The interaction between these two states can be electrically tuned between weak and strong coupling. Phenomenologically, an insulating bottom surface serves as an additional dielectric layer for the carrier tu...[ Read more ]

This thesis mainly focuses on the fabrication and transport measurement of three different materials: two-dimensional (2D) MoS₂ and germanane, and one-dimensional (1D) carbon nanotube.

In MoS₂ electrical double layer transistor, artificial hetero states are induced at the top and bottom surface of a single few-layer flake, forming a homojunction with atomically sharp and clean interface. The doping level of the top and bottom surface are controlled by ionic gating and back gating, where superconductivity and Shubnikov-de Haas quantum oscillation is observed, respectively. The interaction between these two states can be electrically tuned between weak and strong coupling. Phenomenologically, an insulating bottom surface serves as an additional dielectric layer for the carrier tuning of top superconducting channel by back gating, while a conducting bottom channel causes anti-proximity effect between top and bottom surface which suppress the superconductivity in top channel. Furthermore, a lateral superconductor-normal-superconductor junction is realized at the surface of MoS₂ by partially isolating the surface from ionic liquid. An anomalous magnetoresistance is observed, which is attributed to the non-monotonic behavior probability of Andreev reflection with the increase of magnetic field.

Germanane (GeH) transistor is fabricated for studying its electronic properties. Due to its large band gap nature, the as-made GeH transistor shows little conductivity. After thermal annealing, however, the conductivity is greatly improved, and the conductivity increases with increasing annealing temperature. Eventually a metallic state is established, showing very high conductivity which is comparable to metal and higher than any allotrope of germanium. Combined with the Raman spectra, we argue that the enhancement of conductivity is dominated by the dehydrogenation. During annealing, hydrogen atoms escape from the framework of GeH, leaving behind the multi-layer germanene. Weak antilocalization is observed at low temperature, suggesting that the spin-orbit interaction is strong in multi-layer gemanene.

Ultra-small (0.4 nm) single-walled carbon nanotubes (SWCNTs) are synthesized in the linear channels of AFI zeolite crystal. An efficient CVD process of growing uniform 0.4 nm-SWCNTs using ethylene and CO is developed. From the Raman spectra, both the RBM and G band are clearer and stronger than the old process which use the template molecules as the carbon source for growing SWCNTs. The two clear RBM peaks at 535 and 551 cm^-1 indicate that the 0.4 nm-SWCNT@AFI are mainly composed of (5,0) and (3,3) nanotubes. This conclusion is supported by theoretical simulation of the RBM. By using ethylene as the carbon feedstock, the optimal conditions are found to be heating under high pressure with a temperature of 700°C, both the quantity and quality of 0.4 nm-SWCNTs in the AFI channels are significantly improved.