Metal contacts are a key limiter to the electronic performance of two-dimensional (2D) semiconductor devices. Here we present a comprehensive study of contact interfaces between seven metals (Y, Sc, Ag, Al, Ti, Au, Ni, with work functions from 3.1 to 5.2 eV) and monolayer MoS 2 grown by chemical vapor deposition. We evaporate thin metal films onto MoS 2 and study the interfaces by Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and electrical characterization. We uncover that, 1) ultrathin oxidized Al dopes MoS 2 ntype (>2×10 12 cm -2 ) without degrading its mobility, 2) Ag, Au, and Ni deposition causes varying levels of damage to MoS 2 (broadening Raman E' peak from <3 cm -1 to >6 cm -1 ), and 3) Ti, Sc, and Y react with MoS 2 . Reactive metals must be avoided in contacts to monolayer MoS 2 , but control studies reveal the reaction is mostly limited to the top layer of multilayer films. Finally, we find that 4) thin metals do not significantly strain MoS 2 , as confirmed by X-ray diffraction. These are important findings for metal contacts to MoS 2 , and broadly applicable to many other 2D semiconductors.

Transmission electron microscopy, in particular selected area electron diffraction, was used to investigate the orientational relationship of Al, Ag, Cu, Mn, Mo, Ni, Pd, Ru, Re, and Zn deposited via physical vapor deposition on MoS 2 at room temperature. Past work has shown that a few facecentered cubic (FCC) metals (Ag, Au, Pb, Pd, and Pt) could be deposited epitaxially on MoS 2 . However, we found that additional FCC metals (Al and Cu) could be deposited epitaxially at room temperature on MoS 2 with the orientational relationship M(111)∥MoS 2 (0001) and M[22̅ 0]∥MoS 2 [112̅ 0], while a hexagonally close-packed (HCP) metal Zn was epitaxial on MoS 2 with a M(0001)∥MoS 2 (0001) and M[112̅ 0]∥MoS 2 [112̅ 0] relationship. However, the FCC metal Ni, body-centered cubic metal Mo, and HCP metals Re and Ru were not epitaxial on deposition or even after annealing at 673 K for 4 h. By comparing the results with both physical constants and modeling of the metal/MoS 2 systems, we observed that metals with a close-packed plane with six-fold symmetry, a high homologous temperature, and a low barrier to surface diffusion on MoS 2 are more likely to grow epitaxially at room temperature on MoS 2 .

Chemical warfare agents (CWA) can be absorbed by variety of materials including polymeric coatings like paints through bulk liquid contact, thus presenting touch and vapor hazards to interacting personnel. In order for accurate hazard assessments and subsequent decontamination approaches to be designed, it is necessary to characterize the absorption and distribution of highly toxic species, as well as their chemical simulant analogs, in the subsurface of engineered, heterogeneous materials. Using a combination of judicious sample preparation in concert with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), it should be possible to directly measure the uptake and distribution of CWA simulants in the subsurface of complex multilayer coatings. Polyurethane and alkyd coatings were applied to aluminum and silicon substrates and contaminated with 2-chloroethyl ethyl sulfide (CEES) and dimethyl methylphosphonate (DMMP). The surfaces and cross-sectional interfaces of the contaminated coatings were probed with SEM-EDS to provide imaging, spectral, and elemental mapping data of the contaminant-material systems. This work demonstrated SEM-EDS capability to detect and spatially resolve unique elemental signatures of CWA simulants within military coatings. The visual and quantitative results provided by these direct measurements illustrate contaminant spatial distributions, provide order-of-magnitude approximations for diffusion coefficients, and reveal material characteristics that may impact contaminant transport into complex coating materials. It was found that contaminant uptake was significantly different between the topcoat and primer layers.

Physical vapour deposition of Mn metal followed by annealing in air is a promising route to prepare MnOx-anodes for water-oxidation.