Sculpting molecular structures from bilayer graphene and other materials

We demonstrate a technique for creating unique forms of pure sp(2)-bonded carbon and unprecedented heteromolecules. These new structures, which we refer to as sculpturenes, are formed by sculpting selected shapes from bilayer graphene, heterobilayers, or multilayered materials and allowing the shapes to spontaneously reconstruct. The simplest sculpturene is topologically equivalent to a torus, with dimensions comparable to those of fullerenes. The topology of these new molecular structures is stable against atomic-scale defects. We demonstrate that sculpturenes can form the basic building blocks of hollow, multiconnected structures, with potential applications to nanofluidics and nanoelectronics

Electronic properties of sculpturenes

We investigate the electronic properties of sculpturenes, formed by sculpting selected shapes from bilayer graphene, boron nitride or graphene-boron nitride hetero-bilayers and allowing the shapes to spontaneously reconstruct. The simplest sculpturenes are periodic nanotubes, containing lines of non-hexagonal rings. More complex sculpturenes formed from shapes with non-trivial topologies, connectivities and materials combinations may also be constructed. Results are presented for the reconstructed geometries, electronic densities of states and current-voltage relations of these new structures

Tuning the thermoelectric properties of metallo-porphyrins

We investigated the thermoelectric properties of metalloporphyrins connected by thiol anchor groups to gold electrodes. By varying the transition metal-centre over the family Mn, Co, Ni, Cu, Fe, and Zn we are able to tune the molecular energy levels relative to the Fermi energy of the electrodes. The resulting single-molecule room-temperature thermopowers range from almost zero for Co and Cu centres, to +80 μV K−1 and +230 μV K−1 for Ni and Zn respectively. In contrast, the thermopowers with Mn(II) or Fe(II) metal centres are negative and lie in the range −280 to −260 μV K−1. Complexing these with a counter anion to form Fe(III) and Mn(III) changes both the sign and magnitude of their thermopowers to +218 and +95 respectively. The room-temperature power factors of Mn(II), Mn(III), Fe(III), Zn and Fe(II) porphyrins are predicted to be 5.9 × 10−5 W m−1 K−2, 5.4 × 10−4 W m−1 K−2, 9.5 × 10−4 W m−1 K−2, 1.6 × 10−4 W m−1 K−2 and 2.3 × 10−4 W m−1 K−2 respectively, which makes these attractive materials for molecular-scale thermoelectric devices

Sensing single molecules with carbon-boronnitride nanotubes

We investigate the molecular sensing properties of carbon nanotube-boron nitride-carbon nanotube (CNT-BN-CNT) junctions. We demonstrate that the electrical conductance of such a junction changes in response to the binding of an analyte molecule to the region of BN. The change in conductance depends on the length of the BN spacer and the position of the analyte and therefore we propose a method of statistically analysing conductance data. We demonstrate the ability to discriminate between analytes, by computing the conductance changes due to three analytes (benzene, thiol-capped oligoyne and a pyridyl-capped oligoyne) binding to junctions with five different lengths of BN spacer

Tuning thermoelectric properties of graphene/boron nitride heterostructures

Using density functional theory combined with a Green's function scattering approach, we examine the thermoelectric properties of hetero-nanoribbons formed from alternating lengths of graphene and boron nitride. In such structures, the boron nitride acts as a tunnel barrier, which weakly couples states in the graphene, to form mini-bands. In un-doped nanoribbons, the mini bands are symmetrically positioned relative to the Fermi energy and do not enhance thermoelectric performance significantly. In contrast, when the ribbons are doped by electron donating or electron accepting adsorbates, the thermopower S and electronic figure of merit are enhanced and either positive or negative thermopowers can be obtained. In the most favourable case, doping with the electron donor tetrathiafulvalene increases the room-temperature thermopower to -284 μv K(-1) and doping by the electron acceptor tetracyanoethylene increases S to 210 μv K(-1). After including both electron and phonon contributions to the thermal conductance, figures of merit ZT up to of order 0.9 are obtained

Supporting Information: Defect-induced transport enhancement in carbon-boron nitride-carbon heteronanotube junctions

-Additional analysis and calculations, including a figure with the types of defects and calculations of the local density of states and the Seebeck coefficients. -Transparent Peer Review report available.Peer reviewe

Selective sensing of 2,4,6-trinitrotoluene and triacetone triperoxide using carbon/boron nitride heteronanotubes

The detection of reactive compounds represents a significant challenge. Here we demonstrate that heteronanotubes formed by covalently bonded carbon (CNT) and boron nitride (BN) nanotubes can be used to selectively sense trinitrotoluene (TNT) and triacetone triperoxide (TATP). We show that the energy band gap can be created and tuned in carbon/boron nitride (C/BN) heteronanotubes. Once TNT or TATP is physisorbed on C/BN heteronanotubes, new resonances are formed within the energy gap of heteronanotubes. Crucially, transport resonances associated with TNT are formed above the Fermi level and are due to nitro group whereas TATP resonances happen to be below the Fermi level. Consequently, a negative Seebeck coefficient is expected for C/BN heteronanotubes devices in the presence of TNT in contrast to a positive Seebeck coefficient in the presence of TATP. This can be used for selective sensing of these species

Towards nanotube-based sensors for discrimination of drug molecules

The proper detection of drug molecules is key for applications that have an impact in several fields, ranging from medical treatments to industrial applications. In case of illegal drugs, their correct and fast detection has important implications that affect different parts of society such as security or public health. Here we present a method based on nanoscale sensors made of carbon nanotubes modified with dopants that can detect three types of drug molecules: mephedrone, methamphetamine and heroin. We show that each molecule produces a distinctive feature in the density of states that can be used to detect it and distinguish it from other types of molecules. In particular, we show that for semiconducting nanotubes the inclusion of molecules reduces the gap around the Fermi energy and produces peaks in the density of states below the Fermi energy at positions that are different for each molecule. These results prove that it is possible to design nanoscale sensors based on carbon nanotubes tailored with dopants, in such a way that they might be able to discriminate between different types of compounds and, especially, drug molecules whose proper recognition has important consequences in different fields.Laith A. Algharagholy acknowledges the Iraqi Ministry of Higher Education and Scientific Research and University of Sumer for the support. V. M. García-Suárez acknowledges funding from the project PGC2018-094783 (MCIU/AEI/FEDER, EU). Ohood Abdullah Albeydani and Jehan Alqahtani acknowledge Taibah University and King Khalid University, Saudi Arabia, for the support.Peer reviewe

Nanopore arrangement for DNA sequencing

An electrical sensor arrangement for measuring a property of a chemical species (32) comprises first and second electrodes (72, 74) comprising first and second generally planar molecular layers (76, 78) each consisting of an array of covalently bonded atoms. The first molecular layer (76) is covalently bonded (82) to the second molecular layer (78) to define an aperture (84) through both the first and second molecular layers. The aperture (84) is configured to enable the chemical species (32) to pass through. The sensor arrangement further comprises an electrical power supply (86) connected to the first electrode (76) and the second electrode (78) and configured to apply a voltage across the first electrode (76) and the second electrode (78)