Fabrication and chemical modification of carbon nanodots/monolayer hexagonal boron nitride/substrate heterostructures and their terahertz optoelectronic properties

Carbon nanodots (CNDs) can be potentially applied in optoelectronic devices such as full-color display and LED. In this study we fabricate, for the first time, CNDs/monolayer hexagonal boron nitride (ML-hBN)/sapphire heterostructures, where i) ML-hBN is compatible with both CNDs and sapphire due to the presence of the van der Waals (vdW) forces between ML-hBN and these materials and ii) the CNDs can be chemically modified by attaching chemical bonds and/or functional groups on the surface/edges of the carbon-cores of CNDs. The basic physical and chemical properties of CNDs and the heterostructures are characterized. We further apply terahertz time-domain spectroscopy to measure the optical conductivity of CNDs/ML-hBN vdW heterostructures and to determine optically the key physical parameters of these heterostructures. The temperature dependence of these parameters is examined. We find that the agglomeration of dried CNDs on sapphire substrate can be largely suppressed by the presence of ML-hBN and the electronic and optoelectronic properties of the heterostructure can be controlled and modulated by chemical modification on CNDs. The results obtained from this study can be helpful for the fabrication, integration and modulation of CND based vdW heterostructures for practical device applications.