We report graphene/self-assembly monolayer vertical molecular transistors operating in the quantum tunneling regime.
Molecular-scale electronics is a branch of nanotechnology, which utilizes molecules as electronic components. Here, we demonstrate that roomtemperature quantum interference (QI) effects identified in single molecules can be translated into ultra-thin-film materials. This breakthrough opens up avenues for exploiting QI in the design of new materials with enhanced electrical, thermal, and sensing functionality. Field effect control using an ionic liquid gate demonstrates that QI can be used to optimize the on-off ratio of ultra-thin-film transistors. (X.D.) HIGHLIGHTS A vertical tunneling organic transistor on grapheneRoom-temperature intramolecular quantum interference in self-assembled monolayers Field effect tuning of the energy levels of a self-assembled monolayer on graphene Quantum interference optimizes the on-off ratio of ultra-thin-film transistors Famili et al., Chem 5,[474][475][476][477][478][479][480][481][482][483][484] February 14, SUMMARYIf single-molecule, room-temperature, quantum interference (QI) effects could be translated into massively parallel arrays of molecules located between planar electrodes, QI-controlled molecular transistors would become available as building blocks for future electronic devices. Here, we demonstrate unequivocal signatures of room-temperature QI in vertical tunneling transistors, formed from self-assembled monolayers (SAMs), with stable room-temperature switching operations. As a result of constructive QI effects, the conductances of the junctions formed from anthanthrene-based molecules with two different connectivities differ by a factor of 34, which can further increase to 173 by controlling the molecule-electrode interface with different terminal groups. Field-effect control is achieved using an ionic liquid gate, whose strong vertical electric field penetrates through the graphene layer and tunes the energy levels of the SAMs. The resulting room-temperature on-off current ratio of the lowestconductance SAMs can reach up to 306, about one order of magnitude higher than that of the highest-conductance SAMs.
Minimising the phonon thermal conductance of self-assembled molecular films, whilst preserving their electrical properties, is highly desirable, both for thermal management at the nanoscale and for the design of high-efficiency thermoelectric materials. Here we highlight a new strategy for minimising the phonon thermal conductance of Christmas-tree-like molecules composed of a long trunk, along which phonons can propagate, attached to pendant molecular branches. We demonstrate that phonon transport along the trunk is suppressed by Fano resonances associated with internal vibrational modes of the branches and that thermal conductance is suppressed most-effectively in molecules with pendant branches of different lengths. As examples, we use density functional theory to demonstrate the reduction in phonon transport in tree-like molecules formed from alkane or acene trunks with various pendant branches.
We present the implementation of a hybrid continuum-atomistic model for including the effects of surrounding electrolyte in large-scale density functional theory (DFT) calculations within the onetep linear-scaling DFT code, which allows the simulation of large complex systems such as electrochemical interfaces. The model represents the electrolyte ions as a scalar field and the solvent as a polarisable dielectric continuum, both surrounding the quantum solute. The overall energy expression is a grand canonical functional incorporating the electron kinetic and exchange correlation energies, the total electrostatic energy, entropy and chemical potentials of surrounding electrolyte, osmotic pressure, and the effects of cavitation, dispersion and repulsion. The DFT calculation is performed fully self-consistently in the electrolyte model, allowing the quantum mechanical system and the surrounding continuum environment to interact and mutually polarize. A bespoke parallel Poisson-Boltzmann solver library, dl mg, deals with the electrostatic problem, solving a generalized Poisson-Boltzmann equation. Our model supports open boundary conditions, which allows the treatment of molecules, entire biomolecules or larger nanoparticle assemblies in electrolyte. We have also implemented the model for periodic boundary conditions, allowing the treatment of extended systems such as electrode surfaces in contact with electrolyte. A key feature of the model is the use of solute-size and solvation-shell-aware accessibility functions that prevent the unphysical accumulation of electrolyte charge near the quantum solute boundary. The model has a small number of parameters-here we demonstrate their calibration against experimental mean activity coefficients. We also present an exemplar simulation of a 1634-atom model of the interface between a graphite anode and LiPF 6 electrolyte in ethylene carbonate solvent. We compare the cases where Li atoms are intercalated at opposite edges of the graphite slab and in solution, demonstrating a potential application of the model in simulations of fundamental processes in Li-ion batteries.
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