Figure - available from: Journal of Nanoparticle Research
This content is subject to copyright. Terms and conditions apply.
Benzene molecule between two H-terminated (3, 3) CNTs with a 6, b 8, c 10, and d 12 Å gap. e Nicotine molecule in the 12-Å gap. The gap size is the distance between H atoms of the left and the right electrode, as indicated by the blue arrow in b. The central region is fully relaxed in SIESTA, for which the red dashed rectangle indication is given for a 6-Å gap only
Source publication
The requirement for controllable frontier orbital energy shift in single-molecule devices based on electronic (tunneling) transport yielded several rules for device design that lean on molecular level pinning to the electrochemical potential of nano-electrodes. We previously found that the pinning (designated as the strong pinning) was the conseque...
Citations
... We have previously shown, using density functional theory (DFT) and non-equilibrium Green's functions (NEGF), the existence of two different regimes of bias dependence of the frontier orbitals in molecular junctions: the strong and the weak pinning [18,29]. The former refers to the classical meaning of pinning: bias variations of the molecular orbital energy and the electrochemical potential of anelectrode are the same. ...
... In the weak pinning (WP) regime, the bias dependence of (frontier) orbital energies is driven mainly by the empty gap electrostatic potential energy E P and their spatial positions in the gap [29]. Figure 1 presents the spatial distribution of frontier orbitals of four DNA nucleotides. ...
... In the weak pinning (WP) regime, the bias dependence of (frontier) orbital energies is driven mainly by the empty gap electrostatic potential energy EP and their spatial positions in the gap [29]. Figure 1 presents the spatial distribution of frontier orbitals of four DNA nucleotides. ...
The electrical current properties of single-molecule sensing devices based on electronic (tunneling) transport strongly depend on molecule frontier orbital energy, spatial distribution, and position with respect to the electrodes. Here, we present an analysis of the bias dependence of molecule frontier orbital properties at an exemplar case of DNA nucleotides in the gap between H-terminated (3, 3) carbon nanotube (CNT) electrodes and its relation to transversal current rectification. The electronic transport properties of this simple single-molecule device, whose characteristic is the absence of covalent bonding between electrodes and a molecule between them, were obtained using density functional theory and non-equilibrium Green’s functions. As in our previous studies, we could observe two distinct bias dependences of frontier orbital energies: the so-called strong and the weak pinning regimes. We established a procedure, from zero-bias and empty-gap characteristics, to estimate finite-bias electronic tunneling transport properties, i.e., whether the molecular junction would operate in the weak or strong pinning regime. We also discuss the use of the zero-bias approximation to calculate electric current properties at finite bias. The results from this work could have an impact on the design of new single-molecule applications that use tunneling current or rectification applicable in high-sensitivity sensors, protein, or DNA sequencing.
Triacetone triperoxide (TATP) is a highly potent homemade explosive commonly used in terrorist attacks. Its detection poses a significant challenge due to its volatility, and the lack of portability of current sensing techniques. To address this issue, we propose a novel approach based on single-molecule TATP detection in the air using a device where tunneling current in N-terminated carbon-nanotubes nanogaps is measured. By employing the density functional theory combined with the non-equilibrium Green's function method, we show that current of tens of nanoamperes passes through TATP trapped in the nanogap, with a discrimination ratio of several orders of magnitude even against prevalent indoor volatile organic compounds (VOCs). This high tunneling current through TATP's highest occupied molecular orbital (HOMO) is facilitated by the strong electric field generated by N-C polar bonds at the electrode ends and by the hybridization between TATP and the electrodes, driven by oxygen atoms within the probed molecule. The application of the same principle is discussed for graphene nanogaps and break-junctions.
