The effect of air stable n-doping through mild plasma on the mechanical property of WSe2 layers.

Two-dimensional transition metal dichalcogenides have been widely applied to electronic and optoelectronic device owing to their remarkable material properties. Many studies present the platform for regulating the contact resistance via various doping schemes. Here, we report the alteration of mechanical properties of few top layers of the WSe2 flake which are processed by air stable n-doping of N2O with a constant gas flow through mild plasma and present better manufacturability and friability. The single-line nanoscratching experiments on the WSe2 flakes with different doping time reveal that the manufacturable depths are positively correlated with the exposure time at a certain range and tend to be stable afterwards. Meanwhile, material characterization by x-ray photoelectron spectroscopy confirms that the alteration of mechanical properties is owing to the creation of Se vacancies and substitution of O atoms, which breaks the primary molecular structure of the WSe2 flakes. The synchronous Kelvin probe force microscopy and topography results of ROI nanoscratching of a stepped WSe2 sample confirmed that the depth of the degenerate doping is five layers, which was consistent with the single-line scratching experiments. Our results reveal the interrelationship of the mechanical property, chemical bonds and work function changes of the doped WSe2 flakes.

Wet Chemical Method for Black Phosphorus Thinning and Passivation.

Layered black phosphorus (BP) has been expected to be a promising material for future electronic and optoelectronic applications since its discovery. However, the difficulty in mass fabricating layered air-stable BP severely obstructs its potential industry applications. Here, we report a new BP chemical modification method to implement all-solution-based mass production of layered air-stable BP. This method uses the combination of two electron-deficient reagents 2,2,6,6-tetramethylpiperidinyl- N-oxyl (TEMPO) and triphenylcarbenium tetrafluorobor ([Ph3C]BF4) to accomplish thinning and/or passivation of BP in organic solvent. The field-effect transistor and photodetection devices constructed from the chemically modified BP flakes exhibit enhanced performances with environmental stability up to 4 months. A proof-of-concept BP thin-film transistor fabricated through the all-solution-based exfoliation and modification displays an air-stable and a typical p-type transistor behavior. This all-solution-based method improves the prospects of BP for industry applications.

Solution-Based Property Tuning of Black Phosphorus.

The air instability of black phosphorus (BP) severely hinders the development of its electronic and optoelectronic applications. Although a lot of effort has been made to passivate it against degradation in ambient conditions, approaches to further manipulate the properties of passivated BP are still very limited. Herein, we report a simple and low-cost chemical method that can achieve BP passivation and property tailoring simultaneously. The method is conducted by immersing a BP sample in the solution containing both 2,2,6,6-tetramethylpiperidinyl- N-oxyl (TEMPO) and triphenylcarbenium tetrafluorobor in a mixture of water and acetone (v/v = 1:1). After the treatment, the BP sample is functionalized with TEMPO, which not only efficiently passivates BP but also p-dopes BP to a degenerated density level of 1013 cm-2. The performance of the BP field effect transistor is improved after functionalization with a high Ion/ Ioff ratio of 106 and carrier mobility of 881.5 cm2/(V·s). The functionalization-induced doping also significantly reduces the contact resistance between BP and the Cr/Au electrode to 0.97 kΩ·µm. Additionally, we observe a great reduction of BP electrical and optical anisotropies after functionalization. This chemical functionalization method provides a viable route to simultaneously passivate and tune the properties of BP.