In order to investigate isolated nano-crystals electronically it is necessary to make good electrical contact with both source and drain leads. The typical size of, for example, isolated semiconductor quantum dots, along with their outer capping ligands makes this a difficult task. But this has been achieved as early as the mid-late 90’s; most successfully using molecular self-assembly [1]. Since then a range of electronic functions based on single electron transfer have been demonstrated such as transistors, switches and rectifiers; all fabricated with a bottom up approach [2]. However, almost all of these devices can only be built on an individual basis or in low numbers. This is generally thought to be the largest inhibitor to the uptake of such technologies into the semiconductor industry. Graphene with its unique mechanical and electrical properties may facilitate the parallel fabrication of such devices [3].
In this talk progress on a novel, scalable, single electron device is reported. A monolayer of nano-crystals is sandwiched between a gold bottom electrode and a CVD-grown graphene layer placed on top. Being a strong, continuous conducting sheet, the graphene is capable of electrically contacting the nano-crystals without shorting through the potential pin-holes in the monolayer. Previous work performed in the group last year, that found no evidence of coulomb blockade but observed a negative differential resistance, is assessed for its successes and pitfalls. This leads to an understanding of the latest iterations of the device and their designs. Here a reactive ion plasma etch process allows for the minimisation of coincident graphene/Au boundaries and hence lowers the number of electrically contacted nano-crystals. Current experimental processes are discussed and the long term goals for the project are outlined.
[1] “An approach to electrical studies of single nanocrystals” – Applied Physics Letters 68, 2574 (1996)
David L. Klein and Paul L. McEuen, Janet E. Bowen Katari, Richard Roth, and A. Paul Alivisatos
[2] “Nanogap electrodes” – Advanced materials Vol 22 pp. 286-300 2010
Ti Li, W Hu, D Zhu
[3] “Graphene Veils and Sandwiches” - Nano Lett., 2011, 11 (8), pp 3290–3294
jong Min Yuk , Kwanpyo Kim , Benjamín Alemán , William Regan , A. Paul Alivisatos