The integration of various low dimensional materials into large area, scalable, heterostructures is highly desirable. For example, 0D semiconducting nanocrystals (NCs) exhibit attractive optical emission and absorption properties, while single layer 2D graphene is ideally suited to act as a transparent electrode due to its superior electrical and mechanical properties.
The integration of silica encapsulated1, 0D semiconducting NCs with 2D graphene grown by chemical vapor deposition (CVD) is presented in this work. Large area NC films were deposited onto graphene using the Langmuir-Blodgett (LB) method, a technique which allows for the deposition of nanomaterials on a liquid surface. The surface properties of the silica coated NCs necessitated the use of a novel electrospray method (Figure 1a) to successfully spread the NCs2. Large area graphene/NC/graphene (Gr/NC/Gr) heterostructures, seen in Figure 1b, were assembled after film deposition. Topographic, mechanical and electrical properties were investigated using scanning probe techniques and scanning electron microscopy. Photoluminescence (PL) and Raman measurements provided complementary optical and spectroscopic information.
The liquid employed in the LB trough was found to be critical for successful film transfer. By using dimethyl sulfoxide instead of water, continuous, homogenous films were obtained which maintained the optical properties of the NCs (Figure 1c). Raman measurements revealed a significant intensity enhancement of the top graphene sheets, along with additional characteristics attributed to the rippling and straining of the graphene on the NC film.