Monolayers of transition metal dichalcogenides (TMDCs) have attracted a great interest for post‐silicon electronics and photonics due to their high carrier mobility, tunable bandgap, and atom‐thick 2D structure. With the analogy to conventional silicon electronics, establishing a method to convert TMDC to p‐ and n‐type semiconductors is essential for various device applications, such as complementary metal‐oxide‐semiconductor (CMOS) circuits and photovoltaics. Here, a successful control of the electrical polarity of monolayer WSe2 is demonstrated by chemical doping. Two different molecules, 4‐nitrobenzenediazonium tetrafluoroborate and diethylenetriamine, are utilized to convert ambipolar WSe2 field‐effect transistors (FETs) to p‐ and n‐type, respectively. Moreover, the chemically doped WSe2 show increased effective carrier mobilities of 82 and 25 cm2 V−1s−1 for holes and electrons, respectively, which are much higher than those of the pristine WSe2. The doping effects are studied by photoluminescence, Raman, X‐ray photoelectron spectroscopy, and density functional theory. Chemically tuned WSe2 FETs are integrated into CMOS inverters, exhibiting extremely low power consumption (≈0.17 nW). Furthermore, a p‐n junction within single WSe2 grain is realized via spatially controlled chemical doping. The chemical doping method for controlling the transport properties of WSe2 will contribute to the development of TMDC‐based advanced electronics.

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The growth of single-layer graphene on Cu metal by chemical vapor deposition (CVD) is a versatile method to synthesize high-quality, large-area graphene. It is known that high CVD temperatures, close to the Cu melting temperature (1083 ºC), are effective for the growth of large graphene domains, but the growth dynamics of graphene over the high-temperature Cu surface is not clearly understood. Here, we investigated the surface dynamics of the single-layer graphene growth by using heteroepitaxial Cu(111) and Cu(100) films. At relatively lower temperatures, 900~1030 ºC, the as-grown graphene showed the identical orientation with the underlying Cu(111) lattice. However, when the graphene was grown above 1040 ºC a new stable configuration of graphene with 3.4º-rotation became dominant. This slight rotation is interpreted by the enhanced graphene-Cu interaction due to the formation of long-range ordered structure. Further increase of the CVD temperature gave the graphene which is rotated with a wide angle distributions, suggesting the enhanced thermal fluctuation of the Cu lattice. The band structures of CVD graphene grown at different temperatures are well correlated with the observed structural change of the graphene. The strong impact of high CVD temperature on a Cu catalyst was further confirmed by the structural conversion of a Cu(100) film to Cu(111) which occurred during the high temperature CVD process. Our work presents important insight on the growth dynamics of CVD graphene, which can be developed to high quality graphene for future high-performance electronic and photonic devices.

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