Molybdenum disulfide (MoS2) is an extremely intriguing material because of its unique electrical and optical properties. The preparation of large-area and high-quality MoS2 nanosheets is an important step in a wide range of applications. This study demonstrates that monolayer and few-layer MoS2 nanosheets can be obtained from electrochemical exfoliation of bulk MoS2 crystals. The lateral size of the exfoliated MoS2 nanosheets is in the 5–50 μm range, which is much larger than that of chemically or liquid-phase exfoliated MoS2 nanosheets. The MoS2 nanosheets undergo low levels of oxidation during electrochemical exfoliation. In addition, microscopic and spectroscopic characterizations indicate that the exfoliated MoS2 nanosheets are of high quality and have an intrinsic structure. A back-gate field-effect transistor was fabricated using an exfoliated monolayer MoS2 nanosheet. The on/off current ratio is over 106, and the field-effect mobility is approximately 1.2 cm2 V–1 s–1; these values are comparable to...

Large-area atomically thin MoS2 nanosheets prepared using electrochemical exfoliation.

One feature of two-dimensional (2D) molybdenum disulfide nanosheets is the huge sulfur-rich surface area, which might lead to the strong adsorption of Hg2+ in water, because the sulfur on the surfaces could strongly bind to Hg2+. In this work, the adsorption of Hg2+ on 2D molybdenum disulfide sheets in water has been studied in order to develop a novel and efficient adsorbent for removing Hg2+ from water. The study was performed through the measurements of adsorption isotherm and kinetics, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS). The partially oxidized 2D molybdenum disulfide sheets with less than five S–Mo–S layers were prepared through the exfoliation of natural molybdenite. AFM observations illustrated a fast and multilayer Hg2+ adsorption on the surface of 2D molybdenum disulfide. The results of adsorption tests and SEM-EDS have indicated that 2D molybdenum disulfide was a superb adsorbent. The ads...

Two-Dimensional Molybdenum Disulfide as a Superb Adsorbent for Removing Hg2+ from Water

The development of noble-metal-free hydrogen evolution reaction (HER) materials for electrochemical water splitting is the key to achieving low-cost and efficient electrocatalysis that drives electrochemical hydrogen evolution. However, the electrocatalytic activities of most non-noble metals decrease in acidic electrolytes. Here, we have fabricated non-noble-metal electrodes using a bicontinuous and open porous NiMo alloy covered by nitrogen-doped (N-doped) graphene with nanometer-sized holes. This noble-metal-free HER catalyst exhibits performance almost identical with that of a Pt/C electrode, while its original catalytic activity is preserved even in acidic electrolytes. Density functional theory calculations indicate that the interfacial fringes between the nanoholes and NiMo surface induce charge transfer and promote hydrogen adsorption and desorption. The nanometer-sized holes simultaneously provide minimal surface area for chemical reactions, while delaying NiMo dissolution in excessive amounts of...

Cooperation between holey graphene and NiMo alloy for hydrogen evolution in an acidic electrolyte

Molybdenum trioxide (MoO3) is commonly used as a buffer layer in organic electronic devices to improve hole-injection. However, stoichiometric MoO3 is an insulator, and adds a series resistance. Here it is shown that a MoO3 buffer layer can be reduced to form a metallic oxide buffer that exhibits more favorable energy-level alignment with N,N′-diphenyl-N,N′-bis-(1-naphthyl)-1-1′-biphenyl-4,4′-diamine (α-NPD) than does MoO3. This buffer layer thus provides the conductivity of a metal with the favorable energy alignment of an oxide. Photoemission shows the reduced oxide contains Mo4+ and Mo5+, with a metallic valence band structure similar to MoO2.

A metallic molybdenum suboxide buffer layer for organic electronic devices

Single-layer molybdenum disulfide (MoS2) has attracted significant attention due to its electronic and physical properties, with much effort invested toward obtaining large-area high-quality monolayer MoS2 films. In this work, we demonstrate a reactive-barrier-based approach to achieve growth of highly homogeneous single-layer MoS2 on sapphire by the use of a nickel oxide foam barrier during chemical vapor deposition. Due to the reactivity of the NiO barrier with MoO3, the concentration of precursors reaching the substrate and thus nucleation density is effectively reduced, allowing grain sizes of up to 170 μm and continuous monolayers on the centimeter length scale being obtained. The quality of the monolayer is further revealed by angle-resolved photoemission spectroscopy measurement by observation of a very well resolved electronic band structure and spin–orbit splitting of the bands at room temperature with only two major domain orientations, indicating the successful growth of a highly crystalline an...

Maria G. Cattania

Papers

XPS characterization of Ni and Mo oxides before and after “in situ” treatments