Van der Waals (vdW) interactions play a central role in the surface-related physics and chemistry. Tuning of the correlated charge fluctuation in a vdW complex is a plausible way of modulating the molecules interaction at the atomic surface. Here, we report the vdW interaction tunability of the graphene–CO₂ complex by combining the first-principles calculations with the vdW density functionals and the time evaluation measurements of CO₂ molecules adsorption/desorption on graphene under an external electric field. The field-dependent charge transfer within the complex unveils the controllable tuning of CO₂ from acceptor to donor. Meanwhile, the configuration of the adsorbed molecule, the equilibrium distance from graphene and O–C–O bonding angle, is modified accordingly. The range of electrical tunability is a unique feature for each type of molecule.

Doping plays a significant role in affecting the physical and chemical properties of two-dimensional (2D) dichalcogenide materials. Controllable doping is one of the major factors in the modification of the electronic and mechanical properties of 2D materials. MoS₂ 2D materials have gained significant attention in gas sensing owing to their high surface-to-volume ratio. However, low response and recovery time hinder their application in practical gas sensors. Herein, we report the enhanced gas response and recovery of Nb-doped MoS₂ gas sensor synthesized through physical vapor deposition (PVD) toward NO₂ at different temperatures. The electronic states of MoS₂ and Nb-doped MOS₂ monolayers grown by PVD were analyzed based on their work functions. Doping with Nb increases the work function of MoS₂ and its electronic properties. The Nb-doped MoS₂ showed an ultrafast response and recovery time of t_rec = 30/85 s toward 5 ppm of NO₂ at their optimal operating temperature (100 °C). The experimental results complement the electron difference density functional theory calculation, showing both physisorption and chemisorption of NO₂ gas molecules on niobium substitution doping in MoS₂.

The graphene nano-electro-mechanical switches are promising components due to their outstanding switching performance. However, most of the reported devices suffered from a large actuation voltages, hindering them from the integration in the conventional complementary metal-oxide-semiconductor (CMOS) circuit. In this work, we demonstrated the graphene nano-electro-mechanical switches with the local actuation electrode via conventional nanofabrication techniques. Both cantilever-type and double-clamped beam switches were fabricated. These devices exhibited the sharp switching, reversible operation cycles, high on/off ratio, and a low actuation voltage of below 5 V, which were compatible with the CMOS circuit requirements.