Integrating logic functions inside a single molecule

Abstract

In Stadler et al (2003 Nanotechnology 14 138), a scheme for a molecular memory was presented. It was based on the influence of the positions of chemical side-groups attached to aromatic molecules on the paths for electrons propagating through these molecules in the ballistic and tunnelling transport regimes. Here we extend this concept in the following ways. (i) A graphical method is derived from an electron scattering formalism based on a topological Hückel description, which allows us to estimate whether the electron transport between two electrodes attached to specific atomic sites in an arbitrary molecule is finite or zero at the Fermi level. (ii) The same scheme that was used for the implementation of the molecular memory is extended to logic functions, in particular a half-adder. (iii) A more realistic description of the chemical nature of the proposed intra-molecular circuits is achieved by using the elastic scattering quantum chemistry (ESQC) technique in an extended Hückel implementation and by specifying the side-groups as nitro-groups, which are rotated in order to feed the signal inputs into the computational circuit.

Destructive quantum interference in electron transport: A reconciliation of the molecular orbital and the atomic orbital perspective

“…In praxis this is not really a limitation, since potential functional molecules of interest are usually conjugated systems, where π-transmission is dominant. In order to allow for a simple analytical treatment, the derivation of the scheme also originally assumed sites with identical onsite energies and couplings to each other 30,31 . This assumption was later lifted in an attempt to generalize the method now also allowing for hetero atoms in the molecular structure but this came at the price of increased mathematical complexity 32,49 .…”

“…27 . Such DQI effects when occurring in the transmission close to the Fermi energy E F can be used for data storage 28 , inducing thermoelectricity 29 or the design of logic circuits 30 . Simple models have been proposed for their analysis, which were derived from tight-binding (TB) or topological Hückel theory and validated by DFT calculations: One of them which we refer to as "the graphical AO scheme" in the following has been derived specifically for the prediction of DQI and is based on a graphical analysis of the connectivity matrix of atomic orbitals (AOs) 30−34 , while the other interprets the efficiency of transmission in a broader sense in terms of the signs and amplitudes of molecular orbitals on the atomic sites directly connected to the electrodes 35−40 , and the analysis is sometimes limited to a "frontier orbital approximation" where only the highest occupied (HOMO) and the lowest unoccupied MO (LUMO) are taken into account.…”

“…2d 65 . This claim has later been refuted 33 , where it was shown that the predictions of the graphical AO scheme were also correct for azulene with 1,3-contacts when closed loops of AOs and not only pairs of them are considered which always has been a central aspect of the scheme 30,31 . NEGF-DFT calculations for azulene containing compounds with different electrode contact sites including the 1,3-and 5,7-cases can be e.g.…”

Inelastic electron tunneling spectroscopy in molecular junctions showing quantum interference

“…Quantum interference (QI) between different molecular orbital pathways has recently emerged as a new route for controlling electronic transport in molecular devices [1][2][3][4][5][6][7]. This quantum mechanical effect arises from simultaneous and opposite contributions to coherent charge transport of at least two molecular orbitals and induces a strong antiresonance in the energy dependent transmission function at the single molecule scale.…”

Quantum interference in thermoelectric molecular junctions: A toy model perspective

“…[23][24][25] Recently, the effect of QI on electron transport in molecular junctions has been getting an increasing amount of attention due to its unique physics and its possible applications in various fields. [50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67] The QI effect emerges as additional peaks or dips in transmission spectra. These features can improve a performance of molecular switches/sensors, 28,56 and thermoelectric devices.…”