Bias-Voltage Dependence of Tunneling Decay Coefficient and Barrier Height in Arylalkane Molecular Junctions with Graphene Contacts as a Protecting Interlayer

Abstract

We studied a molecular junction with arylalkane self-assembled monolayers sandwiched between two graphene contacts. The arrangement of graphene-based molecular junctions provides a stable device structure with a high yield and allows for extensive transport measurements at 78 K. We observed a temperature-independent current density–voltage (J–V) characteristic and the exponential dependency of the current density on the molecular length, proving that the charge transport occurs by non-resonant tunneling through the molecular barrier. Based on the Simmons model, the bias-voltage dependence of the decay coefficient and barrier height was extracted from variable-length transport characterizations. The J–V data measured were simulated by the Simmons model, which was modified with the barrier lowering induced by the bias voltage. Indeed, there isno need for adjustable fitting parameters. The resulting simulation was in remarkable consistency with experimental measurements over a full bias range up to |V| ≤ 1.5 V for the case of graphene/arylalkane/graphene heterojunctions. Our findings clearly showed the demonstration of stable and reliable molecular junctions with graphene contacts and their intrinsic charge transport characteristics, as well as justifying the application of the voltage-induced barrier lowering approximation to the graphene-based molecular junction.

Gaining insight into molecular tunnel junctions with a pocket calculator without I–V data fitting. Five-thirds protocol

“…14,15 Fig. 6 Application of the five-thirds protocol to large area molecular junctions fabricated with a peptide (G6W) 66 (panels a, b, and c; experimental data: courtesy of Cunlan Guo), aryl octane (ArC8) 49 The values of R 2 depicted in blue were computed from eqn (12). Panel c illustrates that the present five-thirds protocol can be also be applied in situations where the bias range sampled in experiment is too narrow for applying TVS.…”

“…14,15,50 Because the transport measurements for large area junctions report current densities (J) rather than current intensities (I), values of the conductivity s rather that conductance G are presented in this figure. In analyzing the ArC8 49 and TCPP 67 data, the bias range considered has been restricted to the bias range for which the orSLM applies. [10][11][12]…”

“…1 below), the orSLM allows to estimate microscopic parameters characterizing real molecular tunnel junctions obviating I-V data fitting. For this reason, a comparison with other data fitting approaches from the literature [43][44][45][46][47][48][49] would be misplaced and will not be attempted.…”

“…Fig.6Application of the five-thirds protocol to large area molecular junctions fabricated with a peptide (G6W)66 (panels a, b, and c; experimental data: courtesy of Cunlan Guo), aryl octane (ArC8)49 (panel d and e; experimental data from digitized Fig. 4a of ref.…”