Study on functional two-dimensional transition metal dichalcogenide processing technology and its applications

Abstract

Two–dimensional transition metal dichalcogenides (TMDs) have been of particular interest in various research fields based on their fascinating optical, electrical, and mechanical properties combined with atomically thin nature. TMD can be exfoliated into single or few layer from its bulk state due to existence of weak van der Waals bonds between those individual layers. Among various exfoliation methods, liquid-phase chemical exfoliation of TMDs has huge advantages of solution-processability that enables mass production with low cost, as well as its high exfoliation yield and thickness controllability. Strikingly, 1T-phase TMDs can be obtained through liquid-phase chemical intercalation method exhibiting metallic properties with remarkable electrical and catalytic properties, thus the 1T-phase TMD materials have been regarded as a new class of materials for a broad range of applications such as catalysts, optoelectronics, and biosensor. Although previous research groups have reported the TMD-based energy devices including hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and lithium-ion battery, however, an effective role of 1T-phase TMDs and their processing technologies for a broad range of applications are underexplored. In this thesis, we prepare various kinds of 1T-phase TMDs ($MoS_2, WS_2, and MoSe_2$) and systematically investigate their electrical, chemical, and optical properties, which are closely related to oxidation capacity and charge transfer characteristics, and we fabricate transparent TMD-based antibacterial film for biomedical display devices. Also, we develop edge engineering of TMD nanosheets and propose a novel synthetic approach for achieving nanometer scale copper nanowire using edge-engineered TMD nanosheets in order to demonstrate high performance transparent conductor as an alternative of conventional indium-tin-oxide for next-generation wearable display applications. The high quality copper nanowires with an average diameter of 11.3 nm are successfully synthesized, and size-tunable copper nanowires are demonstrated by controlling the dimension of TMD nanosheets. Furthermore, we develop surface engineering of chemically exfoliated TMD nanosheets via thiol chemistry, in which the thiol conjugation of ligand on the TMD surface is achieved and greatly enhance electrical performance of TMD based triboelectric nanogenerator. Therefore, our studies provide new insights into the immense potential of chemically exfoliated TMDs as an innovative material toward next-generation biomedical, optoelectronic, and energy applications.