Molybdenum disulfide (MoS2) has recently received much attention for nanoscale electronic and photonic applications. To explore the intrinsic properties and enhance the performance of MoS2-based field-effect transistors, thorough understanding of extrinsic effects such as environmental gas and contact resistance of the electrodes is required. Here, we report the effects of environmental gases on the transport properties of back-gated multilayered MoS2 field-effect transistors. Comparisons between different gases (oxygen, nitrogen, and air and nitrogen with varying relative humidities) revealed that water molecules acting as charge-trapping centers are the main cause of hysteresis in the transfer characteristics. While the hysteresis persisted even after pumping out the environmental gas for longer than 10 h at room temperature, it disappeared when the device was cooled to 240 K, suggesting a considerable increase in the time constant of the charge trapping/detrapping at these modestly low temperatures. The suppression of the hysteresis or instability in the easily attainable temperature range without surface passivation is highly advantageous for the device application of this system. The humidity dependence of the threshold voltages in the transfer curves indicates that the water molecules dominantly act as hole-trapping centers. A strong dependence of the on-state current on oxygen pressure was also observed.

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A local oxidation technique using atomic force microscopy (AFM) was performed in order to modify magnetic domain structures in ferromagnetic nanostructures. Co-based nanostructures with a rectangular shape were fabricated by using electron beam lithography followed by AFM nano-oxidation. After fabricating a Co-oxide nanowire across a Co nanodot by AFM nano-oxidation, a domain structure of the dot observed before the nano-oxidation was divided into two parts of the domain. AFM nano-oxidation for a higher aspect ratio of height/width of the fabricated nanostructures was also investigated. By applying a dc bias between an Al2O3/Ni double layer film and the AFM tip, the Ni layer was locally oxidized through the capped Al2O3 insulating layer. The nanowires of oxide obtained on the Al2O3/Ni double layer film were thicker and had a higher aspect ratio of height/width than those obtained on a Ni single layer film.

The interface between two-dimensional semiconductors and metal contacts is an important topic of research of nanoelectronic devices based on two-dimensional semiconducting materials such as molybdenum disulfide (MoS2). We report transport properties of thin MoS2 flakes in a field-effect transistor geometry with Ti/Au and Al contacts. In contrast to widely used Ti/Au contacts, the conductance of flakes with Al contacts exhibits a smaller gate-voltage dependence, which is consistent with a substantial electron doping effect of the Al contacts. The temperature dependence of two-terminal conductance for the Al contacts is also considerably smaller than for the Ti/Au contacts, in which thermionic emission and thermally assisted tunneling play a dominant role. This result is explained in terms of the assumption that the carrier injection mechanism at an Al contact is dominated by tunneling that is not thermally activated.Comment: 17 pages, 9 figure

Single crystals of ZrS2 of the Group IVB transition metal dichalcogenide are synthesized by a chemical vapor transport method. The crystals are characterized by Raman spectroscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, and energy dispersive X‐ray spectroscopy. Field‐effect transistors are fabricated on Si substrates using exfoliated multilayer ZrS2 flakes as a channel material. N‐channel characteristics with an on/off ratio of approximately 200 are observed, and the field‐effect mobility is estimated. The large hysteresis in the transfer curves and the time‐dependent drain‐to‐source current can be attributed to the charge‐trapping centers at the ZrS2/SiO2 interface. These results imply the significance of the interface and the potential applicability of ZrS2 as a novel 2D material for nanoelectronic devices.