Unlike 2D graphene which is a semi-metal, 1D graphene nanoribbons can have an electronic bandgap, thereby enabling electronic/optoelectronic applications. We demonstrate both bottom-up and top-down methods for fabricating graphene nanoribbons. First, we present surface-assisted bottom-up fabrication of atomically precise armchair graphene nanoribbons (AGNRs) with predefined widths, namely 7-, 14- and 21-AGNRs, on Ag(111) as well as their spatially resolved width-dependent electronic structures [1]. Second, we demonstrate an intramolecular junction produced by the controllable unzipping of single-walled carbon nanotubes, combining a graphene nanoribbon and single-walled carbon nanotube in a 1D nanostructure [2]. This junction shows a strong gate-dependent rectifying behaviour. We demonstrate the use of the junction in prototype directionally dependent field-effect transistors, logic gates and high performance photodetectors.In contrast to 2D graphene, 2D transition metal dichalcogenides (TMDs), especially MX2 (M = Mo, W; X = S, Se, Te), have a direct bandgap, facilitating electronic and optical applications. We use high resolution scanning tunneling microscopy (STM) and spectroscopy (STS) to study the atomic structure and intrinsic electronic properties of MoS2 layers (mono-, bi-, tri-) directly deposited on HOPG substrates by chemical vapor deposition (CVD) [3]. We have also investigated highly crystalline and large-area tungsten diselenide (WSe2) monolayers on sapphire grown by CVD [4]. The monolayer films display strong photoluminescence, opening up potential applications in optoelectronics. We fabricate monolayer WSe2 transistors with ON/OFF current ratio of up to 109, and mobility larger than 7.3cm2/Vs. Using low work function contacts, WSe2 photodetectors display fast response times of <23ms, and better photocurrent linearity as a function of incident optical power. References [1] H. Huang, D.C. Wei, J.T. Sun, S.L. Wong, Y.P. Feng, A.H. Castro Neto, A.T.S. Wee, Scientific Reports  2 , 983 (2012).[2] D.C. Wei, L.F. Xie, K.K. Lee, Z.B. Hu, S.H. Tan, W. Chen, C.H. Sow, K.Q. Chen, Y.Q. Liu, A.T.S. Wee, Nature Communications  4 , 1374 (2013).[3] Y.L. Huang, submitted.[4] W.J. Zhang, submitted.

Graphene nanoribbons and 2D materials for novel device applications

248th National Meeting (2014)

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