No abstract

Understanding the atomistic origin of defects in two-dimensional transition metal dichalcogenides, their impact on the electronic properties, and how to control them is critical for future electronics and optoelectronics. Here, we demonstrate the integration of thermochemical scanning probe lithography (tc-SPL) with a flow-through reactive gas cell to achieve nanoscale control of defects in monolayer MoS 2. The tc-SPL produced defects can present either p-or n-type doping on demand, depending on the used gasses, allowing the realization of field effect transistors, and p-n junctions with precise sub-μm spatial control, and a rectification ratio of over 10 4. Doping and defects formation are elucidated by means of X-Ray photoelectron spectroscopy, scanning transmission electron microscopy, and density functional theory. We find that p-type doping in HCl/H 2 O atmosphere is related to the rearrangement of sulfur atoms, and the formation of protruding covalent S-S bonds on the surface. Alternatively, local heating MoS 2 in N 2 produces n-character.

The unprecedented ultrahigh interlayer stiffness of supported two-layer epitaxial graphene on silicon carbide (SiC) has been recently reported by our research group. We found that under localized pressure a two-layer epitaxial graphene behaves as an ultra-hard and ultrastiff coating, showing exceptional mechanical properties that far exceed those of bare SiC. Density functional theory (DFT) calculations indicate that this unique behavior stems from a sp 2-to-sp 3 reversible phase transition of carbon films under compression, leading to a single-layer diamond-like structure that we called diamene. In this paper, force versus indentation depth curves from high-resolution nanoindentation experiments of CVD diamond and sapphire are carried out and compared to those obtained from two-layer epitaxial graphene on SiC. These new measurements confirm that the stiffness of epitaxial graphene is larger than that exhibited by CVD diamond and sapphire substrates. Our measurements show that areas of the film consisting of buffer layer plus one, or at most two, additional graphene layers are the ones most likely to exhibit phasechanging behaviors and larger-than-diamond stiffness.