Functional two/three-dimensional assembly of monolayer WS₂ and nickel oxide

Functional assemblies of materials can be realized by tuning the work function and band gap of existing materials. Here we demonstrate the structural assembly of two- and threedimensional (2-D) and (3-D) nanomaterials and investigate the optical and electronic properties of an assembly of monolayer WS₂ on a rough polycrystalline NiO surface. Monolayer WS₂ (2-D material) was transferred onto the NiO surface using a polymer-assisted transfer technique and resulted in a surface roughness about 30 greater than that of WS₂ on SiO₂. Raman maps of WS₂ transferred onto NiO display a spatial nonuniformity of the E1 2g (∼352 cm^?1) and A1g (∼418 cm^?1) peak intensities, indicating that regions of the WS₂ exist in a strained condition on the 3-D NiO surface. Kelvin probe force microscopy measurements show that the WS₂-SiO₂ assembly has a surface potential 62 ± 5 mVlower than that of SiO₂, whereas that of WS₂-NiO is 11 ± 5 mV higher than NiO, indicating that a monolayer of WS₂ is sufficient to modify the surface potential by acting as either an electron donor or acceptor with the underlying surface. Thus, 2-D and 3-D materials can be organized into functional assemblies with electron flow controlled by the WS₂ either as the electron donor or acceptor.