Molecular Bridge Engineering for Tuning Quantum Electronic Transport and Anisotropy in Nanoporous Graphene

Abstract

Recent advances on surface-assisted synthesis have demonstrated that arrays of nanometer wide graphene nanoribbons can be laterally coupled with atomic precision to give rise to a highly anisotropic nanoporous graphene structure. Electronically, this graphene nanoarchitecture can be conceived as a set of weakly coupled semiconducting 1D nanochannels with electron propagation characterized by substantial interchannel quantum interferences. Here, we report the synthesis of a new nanoporous graphene structure where the interribbon electronic coupling can be controlled by the different degrees of freedom provided by phenylene bridges that couple the conducting channels. This versatility arises from the multiplicity of phenylene cross-coupling configurations, which provides a robust chemical knob, and from the interphenyl twist angle that acts as a fine-tunable knob. The twist angle is significantly altered by the interaction with the substrate, as confirmed by a combined bond-resolved scanning tunneling microscopy (STM) and ab initio analysis, and should accordingly be addressable by other external stimuli. Electron propagation simulations demonstrate the capability of either switching on/off or modulating the interribbon coupling by the corresponding use of the chemical or the conformational knob. Molecular bridges therefore emerge as efficient tools to engineer quantum transport and anisotropy in carbon-based 2D nanoarchitectures.

Tailoring giant quantum transport anisotropy in nanoporous graphenes under electrostatic disorder

“…1b) and are fundamentally the same for states deeper within the conduction band (see Table S1 for E − E F = 0.7 eV, ESI†). These anisotropy values are also in line with previous predictions for other phenylated NPGs which were recently experimentally fabricated, 32 and are of the same order of magnitude as other low-symmetry 2D materials proposed for in-plane anisotropic electronics, 40 including black phosphorous. 41 However, it is worth highlighting the special case of meta -NPG (see Table 2 and Table S1, ESI†) where the anisotropy is at least one order of magnitude larger than the other NPGs and most low-symmetry 2D materials.…”

“…31 Consequently, the para configuration leads to transversal spreading in the so-called para -NPG material (as in the original NPG 27 ), whereas the meta configuration cuts inter-ribbon coupling due to QI, leading to almost complete 1D transport in the resulting meta -NPG. 29 Importantly, NPGs including para - and meta -connections between GNRs have recently been synthesized, 32 highlighting the experimental feasibility of such QI-engineering of NPGs.…”

“…In particular, electrostatic disorder, which may arise from interactions with underlying substrates or via chemical/atomic adsorbates, 34 could strongly influence the effectiveness of QI-engineering. 29,32 More generally, a priori it is difficult to predict the effect of local impurity scattering on the transport along each in-plane direction in NPGs. Therefore, evaluating the impact of disorder on electrical transport in NPGs is of primary importance to discern their future applicability in various emerging fields such as nanoelectronics, nanosensing, spintronics and quantum technologies.…”

“…We focus our study on the mono-phenylated NPGs, 29 which allows us to isolate the role of QI from other physico-chemical phenomena reported for bi-phenylated NPGs such as the out-of-plane rotation of molecular bridges. 32 Our quantum simulations are based on an efficient wave packet propagation method and the use of the Kubo formalism that gives access to the length- and energy-dependent-conductivity of disordered systems containing many millions atoms. 35 Electrostatic disorder is modelled as local electron–hole puddles randomly distributed throughout each sample.…”

On-Surface Synthesis of Graphene Nanoribbons with Atomically Precise Structural Heterogeneities and On-Site Characterizations

“…The other way to introduce porous structures into GNRs was by fusing GNRs with special edge shapes via inter-ribbon coupling. , For instance, the fusion of the 7–13-AGNRs with multibay regions at edges gave 1D porous GNRs at a low precursor coverage or 2D porous graphene at a high precursor coverage (Figure d) . The porous graphene possessed 2D electronic bands with high anisotropy, contributed by the confined pore states in different directions, making it a highly versatile semiconductor for molecular sieving and sensing and for electrical transport with the interference Talbot effect. , In addition, localized electronic states at pore-ribbon interfaces, forming flat bands, had been observed in porous GNRs with different pore densities and morphologies (Figure e,f), , which are desired platforms for detecting correlative physics in GNR-based nanodevices.…”