Acetone-Sensing Properties of WO3-Based Gas Sensors Operated in Dynamic Temperature Modulation Mode —Effects of Loading of Noble Metal and/or NiO onto WO3—

Two-dimensional (2D) materials are highly compatible with microelectromechanical systems (MEMSs), and the latter can be used to mechanically manipulate 2D materials with micrometerlevel precision.To expand the application scope of 2D material/MEMS devices, the assembly of 2D materials into van der Waals heterostructures (vdWHs) is required.As well as enhancing the quality of the 2D materials, innovative physics emerges from the assembly of 2D materials into heterostructures owing to the interactions between different 2D materials.Therefore, the combination of MEMSs and vdWHs will open up new possibilities for nanodevices, enabling the in situ measurement of the intrinsic properties of vdWHs.However, the transfer of vdWHs onto patterned SiO 2 /Si substrates is a nontrivial task, limiting the potential applications of vdWH/ MEMS devices.Therefore, a stable method for transferring vdWHs onto MEMS surfaces must be established.In this article, we review techniques for transferring vdWHs onto SiO 2 /Si substrates with a view to constructing vdWH/MEMS devices.Although wet methods are commonly used, dry methods are preferable for transferring vdWHs onto MEMS surfaces owing to the fragile nature of the suspended 2D membranes and MEMS substrates.In particular, we propose polyvinyl chloride as an ideal transfer medium for vdWHs on MEMSs.