A5079692037- Molecular Junctions and Nanostructures
- Quantum and electron transport phenomena
- Graphene research and applications
- Force Microscopy Techniques and Applications
- Surface and Thin Film Phenomena
- Carbon Nanotubes in Composites
- Semiconductor materials and devices
- Thermal properties of materials
- Advanced Thermoelectric Materials and Devices
- X-ray Diffraction in Crystallography
- Advanced Chemical Physics Studies
- Magnetism in coordination complexes
- Electrochemical Analysis and Applications
- ZnO doping and properties
- Nanopore and Nanochannel Transport Studies
- Organic Electronics and Photovoltaics
- Electronic and Structural Properties of Oxides
- Crystallization and Solubility Studies
- Machine Learning in Materials Science
- Gas Sensing Nanomaterials and Sensors
- 2D Materials and Applications
- Advanced Thermodynamics and Statistical Mechanics
- Magnetic properties of thin films
- Surface Chemistry and Catalysis
- Nanowire Synthesis and Applications
Universidad de Oviedo
2015-2024
Nanomaterials and Nanotechnology Research Center
2012-2023
Lancaster University
2005-2014
Quaid-i-Azam University
2013
Durham University
2009
University of Liverpool
2009
Ab initio computational methods for electronic transport in nanoscaled systems are an invaluable tool the design of quantum devices. We have developed a flexible and efficient algorithm evaluating $I\text{\ensuremath{-}}V$ characteristics atomic junctions, which integrates nonequilibrium Green's function method with density functional theory. This is currently implemented package SMEAGOL. The heart SMEAGOL our scheme constructing surface functions describing current-voltage probes. It...
A review of the present status, recent enhancements, and applicability SIESTA program is presented. Since its debut in mid-nineties, SIESTA's flexibility, efficiency free distribution has given advanced materials simulation capabilities to many groups worldwide. The core methodological scheme combines finite-support pseudo-atomic orbitals as basis sets, norm-conserving pseudopotentials, a real-space grid for representation charge density potentials computation their associated matrix...
We have developed an efficient simulation tool 'GOLLUM' for the computation of electrical, spin and thermal transport characteristics complex nanostructures. The new multi-scale, multi-terminal addresses a number challenges functionalities that emerged in nanoscale-scale over past few years. To illustrate flexibility functionality GOLLUM, we present range demonstrator calculations encompassing charge, transport, corrections to density functional theory such as LDA+U spectral adjustments,...
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 combined approach using an STM break junction (STM-BJ) and mechanically controlled (MCBJ) setup. We designed characterized structurally distinct OPE-type with varied length HOMO/LUMO energy. Increase the molecular and/or HOMO-LUMO gap leads decrease single-junction conductance linearly conjugate...
We present a study of the thermopower $S$ and dimensionless figure merit $ZT$ in molecules sandwiched between gold electrodes. show that for with side groups, shape transmission coefficient can be dramatically modified by Fano resonances near Fermi energy, which tuned to produce huge increases $ZT$. This shows exhibiting have high efficiency thermoelectric cooling is not conventional ungated only delocalized states along their backbone.
We report the electrical conductance at single molecule level of oligoyne molecular wires Py-(C[triple bond]C)(n)-Py (n = 1, 2 and 4; Py 4-pyridyl) using STM-molecular break junction techniques in Au|molecule|Au configurations. The histograms reveal multiple series peaks attributed to differing contact geometries between pyridyl head groups gold electrodes. Both experimental theoretical evidence point higher conduction being related adsorption group more highly coordinated sites such as step...
We study the magnetic and electronic properties of defects in ${\text{SnO}}_{2}$ using pseudopotential all electron methods. Our calculations show that bulk is nonmagnetic, but it shows magnetism with a moment around $4.00{\ensuremath{\mu}}_{B}$ due to Sn vacancy $({V}_{\text{Sn}})$. The comes mainly from O atoms surrounding ${V}_{\text{Sn}}$ atoms, which couple antiferromagnetically presence ${V}_{\text{Sn}}$. coupling between different vacancies also studied we found these not only...
In realizing practical non-trivial topological electronic phases stable structures need to be determined first. Tin and lead do stabilize an optimal two-dimensional high-buckled phase --a hexagonal-close packed bilayer structure with nine-fold atomic coordination-- they not fullerenes, as demonstrated by energetics, phonon dispersion curves, the structural optimization of finite-size samples. The are metallic due their high coordination. fluorinated tin lacks three-fold symmetry it...
Conductance across a metal|molecule|metal junction is strongly influenced by the molecule–substrate contacts, and for given molecular structure, multiple conductance values are frequently observed ascribed to distinct binding modes of contact at each termini. Conjugated molecules containing trimethylsilylethynyl terminus, –CCSiMe3 give exclusively single value in I(s) measurements on gold substrates, which similar that same backbone with thiol amine based contacting groups when bound...
The conductance and the decay of as a function molecular length within homologous series oligoynes, Me3Si—(C≡C)n—SiMe3 (n = 2, 3, 4, or 5), is shown to depend strongly on solvent medium. Single molecule junction measurements have been made with I(s) method for each member 5) in mesitylene (MES), 1,2,4-trichlorobenzene (TCB), propylene carbonate (PC). In mesitylene, lower obtained across whole higher (β ≈ 1 nm–1). contrast, give values 0.1 0.5 nm–1 respectively). This behavior rationalized...
Pseudopotential-based Density-Functional Theory (DFT) permits the calculation of material properties with a modest computational effort, besides an acknowledged tradeoff generating and testing pseudopotentials that reproduce established benchmark structural electronic properties. To facilitate needed benchmarking process, here we present pragmatic method to optimize for arbitrary materials directly from eigenvalue sets consistent all-electron results. This thus represents much route creation...
Using first principles simulations we perform a detailed study of the structural, electronic, and transport properties monatomic platinum chains, sandwiched between electrodes. First, demonstrate that most stable atomic configuration corresponds to zigzag arrangement gradually straightens as chains are stretched. Second, find averaged conductance shows slight parity oscillations with number atoms in chain. Additionally, fixed oscillates end pulled apart, due gradual closing opening channels...
We examine electron transport through a single-molecule magnet ${\mathrm{Mn}}_{12}$ bridged between Au electrodes using the first-principles method. find crucial features which were inaccessible in model Hamiltonian studies: spin filtering and strong dependence of charge distribution on local environments. The remains robust with different molecular geometries interfaces, correlations, while over strongly depends them. point out qualitative difference locally charged free-electron-charged...
We study the electronic and transport properties of two novel molecular wires made atomic chains carbon atoms (polyynes) capped with either benzene-thiols or pyridines. While both molecules are structurally similar, electrical conductance benzene-thiol-capped attached to gold electrodes is found be much higher than that pyridine-capped chains. predict almost independent length, which suggests these could ideal for sub-10 nm circuitry. Both systems exhibit negative differential resistance...
To demonstrate the potential of nanopores in bilayer graphene for DNA sequencing, we computed current-voltage characteristics a junction containing nanopore and found that they change significantly when nucleobases are transported through pore. sensitivity selectivity example devices, probability distribution PX(β) quantity β representing logarithmic current pore due to presence nucleobase X (X = adenine, thymine, guanine, or cytosine). We quantified bilayer-graphene by showing exhibits...
Transmissions (in a wide and narrow energy window around the Fermi level) of nanopore Tor with TATP molecule inside rotated 0° (a), 90° (b) 180° (c) 270° (d).
We analyze a new family of carbon nanotube-based molecular wires, formed by encapsulating metallocene molecules inside the nanotubes. Our simulations, which are based on combination nonequilibrium Green function techniques and density functional theory, indicate that these wires can be engineered to exhibit desirable magnetotransport effects for use in spintronics devices. The proposed structures should also resilient room-temperature fluctuations, expected have high yield.
The magnetism and electronic structure of Li-doped SnO${}_{2}$ are investigated using first-principles LDA/LDA$+U$ calculations. We find that Li induces in when doped at the Sn site but becomes nonmagnetic O interstitial sites. calculated formation energies show prefers as compared with site, agreement previous experimental works. interaction native defects (Sn V${}_{\mathrm{Sn}}$ V${}_{\mathrm{O}}$ vacancies) is also studied, we not only behaves a spin polarizer, vacancy stabilizer, i.e.,...
First-principles electronic structure calculations are very widely used thanks to the many successful software packages available. Their traditional coding paradigm is monolithic, i.e., regardless of how modular its internal may be, code built independently from others, compiler up, with exception linear-algebra and message-passing libraries. This model has been quite for decades. The rapid progress in methodology, however, resulted an ever increasing complexity those programs, which implies...
Abstract We demonstrate the bottom-up in-situ formation of organometallic oligomer chains at single-molecule level. The are formed using mechanically controllable break junction technique operated in a liquid environment, and consist alternating isocyano-terminated benzene monomers coordinated to gold atoms. show that chaining process is critically determined by surface density molecules. In particular, we reducing local supply molecules within junction, either lowering molecular...
We present in this feature article a broad overview of the fields molecular electronics and spintronics. This is supplemented by pedagogical introduction that presents basic concepts electronic transport, whose purpose to show most pressing issues faced microelectronics industry.
The magnetism of C-doped SnO2 (001) surfaces is studied using first-principles calculations. It found that carbon does not induce in bulk when located at the oxygen site but shows a large magnetic moment surface. mainly contributed by atoms due to empty minority spins p orbitals and localized surface subsurface atoms. No observed atom sites. origin discussed context bonding.