The tunable electrical properties of reduced graphene oxide (RGO) make it an ideal candidate for many applications including energy storage.¹ However, in order to utilize the material in industrially applied systems it is essential to understand the behavior of the material on the nanoscale, especially how naturally occurring phenomenon like wrinkling effects the electronic transport. While there have been many theoretical investigations on the transport behavior, there are much fewer experimental measurements.^{2, 3, 4} Here we used a transmission electron microscope (TEM) with scanning tunneling microscope (STM) probe in-situ holder is used to perform localized electrical measurements on wrinkled, supported RGO flakes. The RGO flakes are deposited onto pre-patterned Au electrodes on SiN membranes. The flakes are 1-3 layers thick and have lateral dimensions on the order of single micrometers. They are deposited through an ammonium laurate (AL) aqueous surfactant. The TEM allows for observation of the local wrinkling structure of the RGO and simultaneously a Nanofactory STM-TEM holder is used to perform localized resistance measurements. The holder allows for manipulation with and positioning of Au STM probes, with diameters less than 100 nm, with sub-nanometer precision. The results show that the overall resistance is low, on the order of single kΩ, if the contact between the probe and the RGO is optimized.  Wrinkles reduce the contact resistance between RGO and the probe. The overall trend for more than 70 measurements is that the total resistance decreases with increasing amount of wrinkles and that the contact resistance dominates the resistance when the probe makes contact with wrinkle free RGO. The sheet resistance and maximal contact resistance for our measurements range from 5-20 kΩ/☐ and 6-20E-7Ω cm², respectively, which falls in line with other scanning probe measurements for graphene and metal contacts.^{5, 6}  Here we use a bottom metal contact for the gold electrodes which eliminates the risk of resist contamination and metal doping of the graphene.⁷ These measurements give evidence that RGO with large amounts of wrinkling on a substrate can transport electrons well and that it is thus not necessary to produce suspended, pristine graphene in order to benefit from its electrical transport properties.

(1) Novoselov, K. S.; Fal’ko, V. I.; Colombo, L.; Gellert, P. R.; Schwab, M. G.; Kim, K. A roadmap for graphene. Nature 2012, 490, 192-200.

(2) Guinea, F.; Horovitz, B.; Le Doussal, P. Gauge fields, ripples and wrinkles in graphene layers. Solid State Communications 2009, 149, 1140-1143.

(3) Guo, Y.; Guo, W. Electronic and Field Emission Properties of Wrinkled Graphene. Journal of Physical Chemistry C 2013, 117, 692-696.

(4) Ladak, S.; Ball, J. M.; Moseley, D.; Eda, G.; Branford, W. R.; Chhowalla, M.; Anthopoulos, T. D.; Cohen, L. F. Observation of wrinkle induced potential drops in biased chemically derived graphene thin film networks. Carbon 2013, 64, 35-44.

(5) Yan, L.; Punckt, C.; Aksay, I. A.; Mertin, W.; Bacher, G. Local Voltage Drop in a Single Functionalized Graphene Sheet Characterized by Kelvin Probe Force Microscopy. Nano Letters 2011, 11, 3543-3549.

(6) Robinson, J. A.; LaBella, M.; Zhu, M.; Hollander, M.; Kasarda, R.; Hughes, Z.; Trumbull, K.; Cavalero, R.; Snyder, D. Contacting graphene. Applied Physics Letters 2011, 98.

(7) Babichev, A. V.; Gasumyants, V. E.; Egorov, A. Y.; Vitusevich, S.; Tchernycheva, M. Contact properties to CVD-graphene on GaAs substrates for optoelectronic applications. Nanotechnology 2014, 25.

Figures:

TEM image of RGO flakes resting on a silicon nitride membrane and a gold electrode, shown on the left side of the image. An STM probe can be seen in the lower right side of the image. It is used to perform localized electrical resistance measurements and mechanical manipulation of the RGO.

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EMC Abstracts - https://emc-proceedings.com/abstract/localized-electrical-resistance-measurements-of-supported-reduced-graphene-oxide-using-in-situ-stm-tem/