Paper EM-WeA9
A Novel Route Towards Electrical Connection and Probing of Nano-scaled Devices on Semiconductor Surfaces

Wednesday, November 11, 2009, 4:40 pm, Room B1

A major challenge in Nanotechnology is the incorporation of single nano-devices into larger integrated circuits. Although work on individual (and non-integrated) nano-structures such as molecules is intense, the question of their electrical connection with more than two probes (such as conventional SPM experiments) remains an open question. Established nano-lithography techniques such as EBL and FIB seem to not satisfy requirements for ultra clean and defined contact structures at the atomic scale. Traditional instrumentation for analysis is fundamentally limited: How to cover the dimensional range of an integrated circuit (mm) down to the atomic scale of a single molecule device and at the same time to have an adequate integrated navigation system? To meet these requirements, we have established and being advancing a new approach integrating SPM technology with high resolution electron microscopy: (1) Bridging dimensions by combined SEM (down to below 3nm resolution) and STM operation at the atomic scale; (2) Rapid SEM navigation of four local STM probes; (3) Individual probe fine positioning by high resolution STM imaging; (4) STM based probe approach for "soft-landing" of sharp and f-ragile probes and controlled electrical contact for transport measurements. To open a route for fundamental evaluation of the potential of single molecule devices, this instrumental technology is employed to establish electrical connection for local transport measurements. As a model system, we have chosen Au nano-islands on MoS₂. These islands represent contact pads, each electrically connected by an individual STM probe. As good band gap (approx. 1.3eV transverse gap) semiconductor, MoS₂ has the potential to sufficiently decouple those nano-structures electrically at low voltage. Those Au triangular nano-islands have a lateral size of typically 10-30nm and form an "atomically" ultra clean and defined metal-semiconductor interface. We present measurements that prove (1) SEM based navigation and STM based electrical contacting with a tip radius in the 10nm range: (2) reproducible Schottky like IV properties for the individual STM tip/Au nano-island/substrate contact; (3) surface conductance measurements with variable inter-island distance down to 17nm; (4) comparison with surface conductance measurements of the bare MoS2 substrate. We also show that the individual STM probe can be employed under SEM to manipulate those Au nano-islands [1] with high precision in order to generate arbitrary multi probe planar contact configurations.

[1]: J.S. Yang, D. Jie, N. Chandrasekar and C. Joachim J. Vac. Sci. Tech. B, 25, 1694 (2007).