Víctor M. García-Suárez

Long-range electron tunnelling in oligo-porphyrin molecular wires

Short chains of porphyrin molecules can mediate electron transport over distances as long as 5–10 nm with low attenuation. This means that porphyrin-based molecular wires could be useful in nanoelectronic and photovoltaic devices, but the mechanisms responsible for charge transport in single oligo-porphyrin wires have not yet been established. Here, based on electrical measurements of single-molecule junctions, we show that the conductance of the oligo-porphyrin wires has a strong dependence on temperature, and a weak dependence on the length of the wire. Although it is widely accepted that such behaviour is a signature of a thermally assisted incoherent (hopping) mechanism, density functional theory calculations and an accompanying analytical model strongly suggest that the observed temperature and length dependence is consistent with phase-coherent tunnelling through the whole molecular junction. A combination of calculations and electrical measurements on oligo-porphyrin wires in single-molecule junctions strongly suggest that the mechanism of long-range charge transport is phase-coherent electron tunnelling.

Correlations between Molecular Structure and Single-Junction Conductance: A Case Study with Oligo(phenylene-ethynylene)-Type Wires

The charge transport characteristics of 11 tailor-made dithiol-terminated oligo(phenylene-ethynylene) (OPE)-type molecules attached to two gold electrodes were studied at a solid/liquid interface in a combined approach using an STM break junction (STM-BJ) and a mechanically controlled break junction (MCBJ) setup. We designed and characterized 11 structurally distinct dithiol-terminated OPE-type molecules with varied length and HOMO/LUMO energy. Increase of the molecular length and/or of the HOMO-LUMO gap leads to a decrease of the single-junction conductance of the linearly conjugate acenes. The experimental data and simulations suggest a nonresonant tunneling mechanism involving hole transport through the molecular HOMO, with a decay constant β = 3.4 ± 0.1 nm(-1) and a contact resistance R(c) = 40 kΩ per Au-S bond. The introduction of a cross-conjugated anthraquinone or a dihydroanthracene central unit results in lower conductance values, which are attributed to a destructive quantum interference phenomenon for the former and a broken π-conjugation for the latter. The statistical analysis of conductance-distance and current-voltage traces revealed details of evolution and breaking of molecular junctions. In particular, we explored the effect of stretching rate and junction stability. We compare our experimental results with DFT calculations using the ab initio code SMEAGOL and discuss how the structure of the molecular wires affects the conductance values.

Vacancy-induced magnetism in SnO 2 : A density functional study

We study the magnetic and electronic properties of defects in

Giant thermopower and figure of merit in single-molecule devices

{\text{SnO}}_{2}

Tuning the electrical conductivity of nanotube-encapsulated metallocene wires

using pseudopotential and all electron methods. Our calculations show that bulk

Simplifying the conductance profiles of molecular junctions: the use of the trimethylsilylethynyl moiety as a molecule–gold contact

{\text{SnO}}_{2}

Surface-induced magnetism in C-doped SnO2

is nonmagnetic, but it shows magnetism with a magnetic moment around

First-principles study of electron transport through the single-molecule magnet Mn12.

4.00{\ensuremath{\mu}}_{B}

Stabilizing intrinsic defects in SnO2

due to Sn vacancy

Graphene sculpturene nanopores for DNA nucleobase sensing

({V}_{\text{Sn}})