The van der Waals heterostructures have evolved as novel materials for complementing the Si-based semiconductor technologies. Group-10 noble metal dichalcogenides (e.g., PtS₂, PtSe₂, PdS₂, and PdSe₂) have been listed into two-dimensional (2D) materials toolkit to assemble van der Waals heterostructures. Among them, PdSe₂ demonstrates advantages of high stability in air, high mobility, and wide tunable bandgap. However, the regulation of p-type doping of PdSe₂ remains unsolved problem prior to fabricating p–n junction as a fundamental platform of semiconductor physics. Besides, a quantitative method for the controllable doping of PdSe₂ is yet to be reported. In this study, the doping level of PdSe₂ was correlated with the concentration of Lewis acids, for example, SnCl₄, used for soaking. Considering the transfer characteristics, the threshold voltage (the gate voltage corresponding to the minimum drain current) increased after SnCl₄ soaking treatment. PdSe₂ transistors were soaked in SnCl₄ solutions with five different concentrations. The threshold voltages from the as-obtained transfer curves were extracted for linear fitting to the threshold voltage versus doping concentration correlation equation. This study provides in-depth insights into the controllable p-type doping of PdSe₂. It may also push forward the research of the regulation of conductivity behaviors of 2D materials.

Human beings perceive the world through the senses of sight, hearing, smell, taste, touch, space, and balance. The first five senses are prerequisites for people to live. The sensing organs upload information to the nervous systems, including the brain, for interpreting the surrounding environment. Then, the brain sends commands to muscles reflexively to react to stimuli, including light, gas, chemicals, sound, and pressure. MXene, as an emerging two-dimensional material, has been intensively adopted in the applications of various sensors and actuators. In this review, we update the sensors to mimic five primary senses and actuators for stimulating muscles, which employ MXene-based film, membrane, and composite with other functional materials. First, a brief introduction is delivered for the structure, properties, and synthesis methods of MXenes. Then, we feed the readers the recent reports on the MXene-derived image sensors as artificial retinas, gas sensors, chemical biosensors, acoustic devices, and tactile sensors for electronic skin. Besides, the actuators of MXene-based composite are introduced. Eventually, future opportunities are given to MXene research based on the requirements of artificial intelligence and humanoid robot, which may induce prospects in accompanying healthcare and biomedical engineering applications.