We investigated the surface potential (V surf ) of exfoliated MoS 2 flakes on bare and Au-coated SiO 2 /Si substrates using Kelvin probe force microscopy. The V surf of MoS 2 single layers was larger on the Au-coated substrates than on the bare substrates; our theoretical calculations indicate that this may be caused by the formation of a larger electric dipole at the MoS 2 / Au interface leading to a modified band alignment. V surf decreased as the thickness of the flakes increased until reaching the bulk value at a thickness of ∼20 nm (∼30 layers) on the bare and ∼80 nm (∼120 layers) on the Au-coated substrates, respectively. This thickness dependence of V surf was attributed to electrostatic screening in the MoS 2 layers. Thus, a difference in the thickness at which the bulk V surf appeared suggests that the underlying substrate has an effect on the electric-field screening length of the MoS 2 flakes. This work provides important insights to help understand and control the electrical properties of metal/MoS 2 contacts.
In 1987, M. K. Wu and Paul Chu discovered Y 1.2 Ba 0.8 CuO 4 (YBCO) with critical temperature (T c ) of 93 K. It has significantly lowered the cost of cooling of a material up to the point where superconductivity set in. Utilizing the cost reduction of attaining superconductivity and the vast amount of research to understand characteristics of high temperature oxide superconducting materials, there has been effort to use a high temperature superconductor as a coated conductor. It is important to characterize the materials precisely for stable performance before commercializing. We used polarized Raman scattering spectroscopy to study structural and stoichiometric information regarding YBa 2 Cu 3 O 7-x , GdYBa 2 Cu 3 O 7-x , and GdBa 2 Cu 3 O 7-x produced by three leading groups of producing commercial grade high temperature superconductor coated conductors American Superconductor Corporation, Superpower, and SuNAM.
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