Two-Tip stm conductance characteristics of individual planar graphene nanoribbon
I will explore intrinsic charge conductance characterization of electrically decoupled individual graphene nanoribbon (GNR) in the lateral planar configuration by using two-tip scanning tunneling microscopy (STM) approach. For this purpose, on-surface synthesized GNRs of width ~1-2 nm and length <20-100 nm on metallic Au (111) surface will be considered. A unique two-tip STM microscope, which has been standardized at the host’s lab (in CEMES-CNRS), will be used for its excellent vertical (z) stability (Δz <2 pm) of piezo scanners to control the tip-to-GNR contacts. With ultimate precision, the proposed approach reserves atomic cleanliness under ultrahigh vacuum (UHV) starting from on-surface GNR synthesis on metallic Au(111) surface till the end of two-tip STM conductance characterization. We will use intermediate atomic thin layers of insulating gap sodium chloride (NaCl) to electrically decouple GNR from the Au(111) surface during charge conductance measurements with electrically disconnected substrate (floating substrate potential). We focus on the fundamental challenges associated with the two-tip charge conductance measurements of GNR, notably, establishment of stable STM tip point contacts to the GNR. Indeed, different types of contact configurations are expected depending on the tip-to-GNR distance, such as tunneling, van der Waals, chemical and mechanical, which can be monitored by recording the jump-to-contact characteristics (tunneling current vs tip height (I-z) spectra). Conductance characteristics of GNR are investigated in tip-to-tip configuration through planar GNR, which include current-voltage (I-V), voltage dependent resistance R(V), conductance G = I/V, differential conductance (dI/dV), current decay with tip-to-GNR distance (dI/dz), etc. Overall, we are determined to provide an atomic clean approach to explore the conductance characteristics of molecular GNR (width ~1-2 nm and length <20-100 nm).