MoS2 is considered a promising two-dimensional active channel material for future nanoelectronics. However, the development of a facile, reliable, and controllable doping methodology is still critical for extending the applicability of MoS2. Here, we report surface charge transfer doping via thiol-based binding chemistry for modulating the electrical properties of vacancy-containing MoS2 (v-MoS2). Although vacancies present in 2D materials are generally regarded as undesirable components, we show that the electrical properties of MoS2 can be systematically engineered by exploiting the tight binding between the thiol group and sulfur vacancies and by choosing different functional groups. For example, we demonstrate that NH2-containing thiol molecules with lone electron pairs can serve as an n-dopant and achieve a substantial increase of electron density (Δn = 3.7 × 10(12) cm(-2)). On the other hand, fluorine-rich molecules can provide a p-doping effect (Δn = -7.0 × 10(11) cm(-2)) due to its high electronegativity. Moreover, the n- and p-doping effects were systematically evaluated by photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), and electrical measurement results. The excellent binding stability of thiol molecules and recovery properties by thermal annealing will enable broader applicability of ultrathin MoS2 to various devices.

Nanotransfer printing technology offers outstanding simplicity and throughput in the fabrication of transistors, metamaterials, epidermal sensors and other emerging devices. Nevertheless, the development of a large-area sub-50 nm nanotransfer printing process has been hindered by fundamental reliability issues in the replication of high-resolution templates and in the release of generated nanostructures. Here we present a solvent-assisted nanotransfer printing technique based on high-fidelity replication of sub-20 nm patterns using a dual-functional bilayer polymer thin film. For uniform and fast release of nanostructures on diverse receiver surfaces, interface-specific adhesion control is realized by employing a polydimethylsiloxane gel pad as a solvent-emitting transfer medium, providing unusual printing capability even on biological surfaces such as human skin and fruit peels. Based on this principle, we also demonstrate reliable printing of high-density metallic nanostructures for non-destructive and rapid surface-enhanced Raman spectroscopy analyses and for hydrogen detection sensors with excellent responsiveness.

Among the layered transition metal dichalcogenides (TMDs) that can form stable two-dimensional crystal structures, molybdenum disulfide (MoS) has been intensively investigated because of its unique properties in various electronic and optoelectronic applications with different band gap energies from 1.29 to 1.9 eV as the number of layers decreases. To control the MoS layers, atomic layer etching (ALE) (which is a cyclic etching consisting of a radical-adsorption step such as Cl adsorption and a reacted-compound-desorption step via a low-energy Ar-ion exposure) can be a highly effective technique to avoid inducing damage and contamination that occur during the reactive steps. Whereas graphene is composed of one-atom-thick layers, MoS is composed of three-atom-thick S-Mo-S layers; therefore, the ALE mechanisms of the two structures are significantly different. In this study, for MoS ALE, the Cl radical is used as the adsorption species and a low-energy Ar ion is used as the desorption species. A MoS ALE mechanism (by which the S, Mo, and S atoms are sequentially removed from the MoS crystal structure due to the trapped Cl atoms between the S layer and the Mo layer) is reported according to the results of an experiment and a simulation. In addition, the ALE technique shows that a monolayer MoS field effect transistor (FET) fabricated after one cycle of ALE is undamaged and exhibits electrical characteristics similar to those of a pristine monolayer MoS FET. This technique is also applicable to all layered TMD materials, such as tungsten disulfide (WS), molybdenum diselenide (MoSe), and tungsten diselenide (WSe).

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Na/FeS batteries have remarkable potential applicability due to their high theoretical capacity and cost-effectiveness. However, realization of high power-capability and long-term cyclability remains a major challenge. Herein, ultrafine Fe S @C nanocrystals (NCs) as a promising anode material for a Na-ion battery that addresses the above two issues simultaneously is reported. An Fe S core with quantum size (≈10 nm) overcomes the kinetic and thermodynamic constraints of the Na-S conversion reaction. In addition, the high degree of interconnection through carbon shells improves the electronic transport along the structure. As a result, the Fe S @C NCs electrode achieves excellent power capability of 550 mA h g (≈79% retention of its theoretical capacity) at a current rate of 2700 mA g . Furthermore, a conformal carbon shell acts as a buffer layer to prevent severe volume change, which provides outstanding cyclability of ≈447 mA h g after 1000 cycles (≈71% retention of the initial charge capacity).