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Two-dimensional (2D) transition metal dichalcogenides (TMDs) possess a variety of polymorphs that exhibit distinctive atomic and electronic structures and the consequent material properties. Hence, exploiting the dynamics of phase transition between different polymorphs will lay a foundation toward controlled phase engineering based applications. In this Letter, we reported a solid-state approach to realize the H to T′ transition in monolayer molybdenum disulfide in situ inside a transmission electron microscope. The release of lithium ions and the subsequent lithiation were driven by energetic electron beam irradiation, both of which in turn triggered the H to T′ phase transition of the object monolayer MoS2. The as-formed T′ phase domains showed a random nucleation behavior. Interestingly, the reverse process, i.e., T′ back to H phase transition, caused by prolonged e-beam illumination, was also captured in situ. During both phase transformation processes, i.e., H → T′ and T′ → H, we did not observe any large area T phase existing in monolayer MoS2. Our results will be instructive to elucidate the microscopic mechanisms of the phase transition and should also be extendable to other 2D TMD materials.

This experimental work studies the translocation of bovine serum albumin (BSA) proteins through MoS2 nanopores. A simple method of device fabrication is developed based on dry-transfer of exfoliated MoS2 membranes and subsequent TEM drilling, yielding MoS2 nanopores of a few monolayers thick and diameters as small as ∼11 nm. The current-voltage relation and low-frequency current noise of the devices are characterized. Typical BSA translocation signals that possibly correspond to various orientations are observed in the MoS2 devices, exhibiting enhanced amplitude and similar characteristics when compared to those from a silicon nitride (SiNx) control. Furthermore, the statistical data of the signal amplitude and dwell time at various biases are analyzed. These results show opportunities of single-molecular protein analysis using MoS2 nanopores.

With sulfur partially substituted by 3d transition metals, magnetism in a molybdenum disulphide monolayer is investigated comprehensively by the calculation of a spin-polarized density functional theory. The magnetic moment induced by a single defect is found to be equal to the absolute value of the magnetic moment of this defect atom subtracted by two Bohr magnetons. A detailed analysis on the locally projected density of states demonstrates that the underlying mechanism can be qualitatively interpreted in a simple ionic scenario. Subsequently, quasi one-dimensional superlattices of defects are built for the exploration of long range magnetic orders. Among four candidates of chromium and copper superlattices for high temperature dilute magnetic semiconductors (DMSs), a particular chromium superlattice holds the promise of a room temperature DMS against the change of the on-site Coulomb interaction.

Well characterized in situ electron field-emission measurements have been made on individual ZnO nanowires (NWs) inside a transmission electron microscope. It is found that the electron field-emission current from a semiconductor NW is determined not only by the NW/vacuum interface, but also by the Schottky barrier formed at the electrode/NW interface. It is demonstrated that the electron injection efficiency through the Schottky barrier and therefore the final electron emission current can be modulated by electronic excitations in the metal electrode, and it is proposed that this phenomenon could be used to design Schottky barrier switches for nanoelectronics.

Electrical transport measurements were conducted on semiconducting nanowires and three distinct current-voltage (I-V) characteristics were observed, i.e., almost symmetric, almost rectifying, and almost linear. These I-V characteristics were modeled by treating the transport in the nanowire as in a metal-semiconductor-metal structure involving two Schottky barriers and a resistor in between these barriers, and the transport is shown to be dominated by the reverse-biased Schottky barrier under low bias and by the semiconducting nanowire at large bias. In contrast to the conventional Schottky diode, the reverse current in the nano-Schottky barrier structure is not negligible and the current is largely tunneling rather than thermionic. Experimental I-V curves are reproduced very well using our model, and a method for extracting nanowire resistance, electron density, and mobility is proposed and applied to ZnO, CdS, and Bi2S3 nanowires.