Field Effect and Local Gating in Nitrogen‐Terminated Nanopores (NtNP) and Nanogaps (NtNG) in Graphene

Abstract

Functionalization of electrodes is a wide‐used strategy in various applications ranging from single‐molecule sensing and protein sequencing, to ion trapping, to desalination. We demonstrate, employing non‐equilibrium Green′s function formalism combined with density functional theory, that single‐species (N, H, S, Cl, F) termination of graphene nanogap electrodes results in a strong in‐gap electrostatic field, induced by species‐dependent dipoles formed at the electrode ends. Consequently, the field increases or decreases electronic transport through a molecule (benzene) placed in the nanogap by shifting molecular levels by almost 2 eV in respect to the electrode Fermi level via a field effect akin to the one used for field‐effect transistors. We also observed the local gating in graphene nanopores terminated with different single‐species atoms. Nitrogen‐terminated nanogaps (NtNGs) and nanopores (NtNPs) show the strongest effect. The in‐gap potential can be transformed from a plateau‐like to a saddle‐like shape by tailoring NtNG and NtNP size and termination type. In particular, the saddle‐like potential is applicable in single‐ion trapping and desalination devices.

Tunnel junction sensing of TATP explosive at the single-molecule level

“…As recently reported, 30,37 the tunneling current through a molecule placed in the nanogap between carbon-based electrodes depends on the polar-bond termination type: C–N polar-bond termination enhances the tunneling current. The C–N polar bonds generate an in-gap strong electrostatic potential (more than 1 eV per electron) that shifts the molecular HOMO (highest occupied molecular orbital) energy closer to the Fermi energy of electrodes, promoting the hybridization of the probed molecule with electrodes.…”

Predicting Finite-Bias Tunneling Current Properties from Zero-Bias Features: The Frontier Orbital Bias Dependence at an Exemplar Case of DNA Nucleotides in a Nanogap

“…The first two rules recommend using asymmetrical anchoring groups [30,48,49] for promoting HOMO and LUMO energy alignment with E F , which would produce the strong pinning of both levels to electrochemical potentials of corresponding electrodes. For DNA and protein sequencing devices, the alignment of frontier orbital energies and pinning could be achieved using asymmetric electrodes [20] or proper electrode functionalization [40], as the use of anchoring groups to align HOMO and LUMO to Fermi energy seems too challenging. We chose a simple system with symmetric electrodes to emphasize the studied properties.…”

“…We chose a simple system with symmetric electrodes to emphasize the studied properties. The hydrogen termination of CNTs promotes LUMO alignment [40]. Thus, for all nucleotides, the orbital with a principal contribution to transport is LUMO.…”

“…Similarly, for both dCMP and dTMP, the LUMO orbital primarily occupies the nucleobase part (Figure 1b,d). At zerobias, the E P along the midline in the z-direction in an empty gap between H-terminated CNTs is given in Figure 2a, whose shape (magenta line) originates from the dipoles at CNT terminations [39,40]. Figure 2b shows the empty-gap electrostatic potential energy E P (bias) − E P (0) along the same line at different bias values and average z coordinates of HOMO and LUMO (<z HOMO > and <z LUMO >, orange and purple vertical lines, respectively, and also Figure 1) of nucleotides.…”

“…At those voltages, 0.2 V for dTMP and 1 V for dCMP, both HOMO and LUMO energies of both nucleotides deviate from the WP lines. Simultaneously, the charge Q (Figure 3), obtained from the Hirshfeld population analysis, begins to accumulate on the molecule, causing the strong pinning of the orbitals to the electrochemical potential μL of the left electrode (light blue line in Figure 3) [39,40]. 2b).…”