Microsphere probe: combining microsphere-assisted microscopy with AFM.

In recent years, microsphere-assisted microscopy (MAM) and atomic force microscope (AFM) have been rapidly developed to meet the measurement needs of microstructures. However, the positioning of microspheres, the inability of AFM to touch the underlying sample through the transparent insulating layer, and the challenge of AFM fast positioning limit their use in practical measurements. In this paper, we propose a method that combines MAM with AFM by adhering the microsphere to the cantilever. This method allows MAM and AFM to work in parallel, and their imaging positions can correspond with each other. We use this method to measure memory devices, and the results show that MAM and AFM yield complementary advantages. This approach provides a new tool for analyzing complex structures in devices and has potential for wide application.

Engineering of Oxidized Line Defects on CVD-Grown MoS2 Flakes.

Defect engineering is a promising means to create patterns on two-dimensional (2D) materials to enable unconventional properties. However, defects usually exist abundantly and randomly on 2D materials, which makes it difficult to tune the properties in a controllable manner. Therefore, it is highly desirable to find out the formation mechanism and controllable fabrication method of defects on 2D materials. In this report, we systematically investigated the line defects on monolayer MoS2 formed by introducing oxygen during the CVD growth. The line defects were formed due to the overoxidation of the MoS2 flake along crystal boundaries, which bulged out of the surface and had the same surface potential as the basal plane. Therefore, the MoS2 flake with line defects maintained the optical and electrical integrity but exhibited distinct properties as compared to the pristine one. By controlling the oxygen concentration during CVD growth, the density of the line defects can be precisely controlled to implement controllable property tuning. Moreover, during the transfer process, the MoS2 flake was easily broken along the line defects, which increased the active sites to achieve enhanced hydrogen evolution reaction performance. This work is expected to inspire the development of patterned functional 2D materials by defect engineering.

Dielectric engineering enable to lateral anti-ambipolar MoTe2heterojunction.

Atomically two-dimensional (2D) materials have generated widespread interest for novel electronics and optoelectronics. Specially, owing to atomically thin 2D structure, the electronic bandgap of 2D semiconductors can be engineered by manipulating the surrounding dielectric environment. In this work, we develop an effective and controllable approach to manipulate dielectric properties of h-BN through gallium ions (Ga+) implantation for the first time. And the maximum surface potential difference between the intrinsic h-BN (h-BN) and the Ga+implanted h-BN (Ga+-h-BN) is up to 1.3 V, which is characterized by Kelvin probe force microscopy. More importantly, the MoTe2transistor stacked on Ga+-h-BN exhibits p-type dominated transfer characteristic, while the MoTe2transistor stacked on the intrinsic h-BN behaves as n-type, which enable to construct MoTe2heterojunction through dielectric engineering of h-BN. The dielectric engineering also provides good spatial selectivity and allows to build MoTe2heterojunction based on a single MoTe2flake. The developed MoTe2heterojunction shows stable anti-ambipolar behaviour. Furthermore, we preliminarily implemented a ternary inverter based on anti-ambipolar MoTe2heterojunction. Ga+implantation assisted dielectric engineering provides an effective and generic approach to modulate electric bandgap for a wide variety of 2D materials. And the implementation of ternary inverter based on anti-ambipolar transistor could lead to new energy-efficient logical circuit and system designs in semiconductors.

Modulation of MoTe2/MoS2 van der Waals heterojunctions for multifunctional devices using N2O plasma with an opposite doping effect.

van der Waals layered heterojunctions have a variety of band offsets that open up possibilities for a wide range of novel and multifunctional devices. However, due to their poor pristine carrier concentrations and limited band modulation methods, multifunctional p-n heterojunctions are very difficult to achieve. In this report, we developed a highly effective N2O plasma process to treat MoTe2/MoS2 heterojunctions. This allowed us to adjust the hole and electron concentrations in the two materials independently and simultaneously. More importantly, for the first time, we were able to create opposite doping on the two sides of the junction through a single-step treatment. With a very wide doping range from pristine to degenerate levels, a MoTe2/MoS2 heterojunction can be modulated to behave as a forward rectifying diode with enhanced rectifying ratio and as a tunneling transistor with negative differential resistance at room temperature. The new approach provides an effective and generic doping scheme for heterojunctions to construct versatile and multifunctional electronic devices.