Hybrid graphene-nanocrystal materials have been proposed as promising candidates for a variety of applications, such as energy harvesting and light-emitting devices, due to the electrical properties of graphene and the superb optical properties of semiconducting nanocrystals. In this work, we use hybrid structures of graphene and silica-capped semiconducting nanocrystals as resonant tunnelling devices for unique electrical identification.
It has been demonstrated that atomic scale defects in resonant tunnelling diodes lead to measurable shifts in the negative differential resistance peaks in the I-V characteristics. These defects cannot be controlled nor characterised during fabrication and thus act as unique signatures of each individual device.
We propose the use of resonant tunnelling, through arrays of quantum dots, to further increase the quantum confinement and uniqueness of such devices. In order to achieve this goal, we prepared silica-capped CdSe/ZnS colloidal nanocrystal thin films via Langmuir-Blodgett deposition on top of a CVD-grown graphene sheet. A second graphene membrane was then transferred on top of the structure to act as the top contact. The silica shell acts as a double tunnelling barrier sandwiching the nanocrystal, the electrons being able to tunnel through the whole structure only when the resonant tunnelling condition is met.
To characterise the devices, we performed Raman and photoluminescence spectroscopy in the different stages of the fabrication process, as well as different scanning probe techniques to characterise the topography and the electrical properties of the hybrid structures.