Effects of Edge Oxidation on the Structural, Electronic, and Magnetic Properties of Zigzag Boron Nitride Nanoribbons

The effects of edge chemistry on the relative stability and electronic properties of zigzag boron nitride nanoribbons (ZBNNRs) are investigated. Among all functional groups considered, fully hydroxylated ZBNNRs are found to be the most energetically stable. When an in-plane external electric field is applied perpendicular to the axis of both hydrogenated and hydroxylated ZBNNRs, a spin-polarized half-metallic state is induced, whose character is different than that predicted for zigzag graphene nanoribbons. The onset field for achieving the half-metallic state is found to mainly depend on the width of the ribbon. Our results indicate that edge functionalization of ZBNNRs may open the way for the design of new nanoelectronic and nanospintronic devices

Selectivity of a Graphene Nanoribbon-Based Trinitrotoluene Detector: A Computational Assessment

A computational study investigating the suitability of zigzag graphene nanoribbons to serve as selective chemical detectors for trinitrotoluene is presented. Using lithium adatoms as surface anchoring sites, we find that chemisorption of different chemical precursors serving in the trinitrotoluene synthesis process induces unique and distinguishable fingerprints on the electronic structure of the underlying nanoribbon. Furthermore, mixed adsorption of trinitrotoluene and its various chemical precursors may allow the determination of the specific synthesis route used to produce this commonly used explosive material. The understanding of the contaminant adsorption process gained in this study suggests that lithium-decorated graphene nanoribbons may serve as selective chemical detectors

Edge Chemistry Effects on the Structural, Electronic, and Electric Response Properties of Boron Nitride Quantum Dots

The effects of edge hydrogenation and hydroxylation on the relative stability and electronic properties of hexagonal boron nitride quantum dots (<i>h</i>-BNQDs) are investigated. Zigzag edge hydroxylation is found to result in considerable energetic stabilization of <i>h</i>-BNQDs as well as a reduction of their electronic gap with respect to their hydrogenated counterparts. The application of an external in-plane electric field leads to a monotonous decrease of the gap. When compared to their edge-hydrogenated counterparts, significantly lower field intensities are required to achieve full gap closure of the zigzag edge hydroxylated <i>h</i>-BNQDs. These results indicate that edge chemistry may provide a viable route for the design of stable and robust electronic devices based on nanoscale hexagonal boron-nitride systems

Mechanism of Facilitated Diffusion during a DNA Search in Crowded Environments

The key feature explaining the rapid recognition of a DNA target site by its protein lies in the combination of one- and three-dimensional (1D and 3D) diffusion, which allows efficient scanning of the many alternative sites. This facilitated diffusion mechanism is expected to be affected by cellular conditions, particularly crowding, given that up to 40% of the total cellular volume may by occupied by macromolecules. Using coarse-grained molecular dynamics and Monte Carlo simulations, we show that the crowding particles can enhance facilitated diffusion and accelerate search kinetics. This effect originates from a trade-off between 3D and 1D diffusion. The 3D diffusion coefficient is lower under crowded conditions, but it has little influence because the excluded volume effect of molecular crowding restricts its use. Largely prevented from using 3D diffusion, the searching protein dramatically increases its use of the hopping search mode, which results in a higher linear diffusion coefficient. The coefficient of linear diffusion also increases under crowded conditions as a result of increased collisions between the crowding particles and the searching protein. Overall, less 3D diffusion coupled with an increase in the use of the hopping and speed of 1D diffusion results in faster search kinetics under crowded conditions. Our study shows that the search kinetics and mechanism are modulated not only by the crowding occupancy but also by the properties of the crowding particles and the salt concentration

Robust Superlubricity in Graphene/<i>h</i>‑BN Heterojunctions

The sliding energy landscape of the heterogeneous graphene/<i>h</i>-BN interface is studied by means of the registry index. For a graphene flake sliding on top of <i>h</i>-BN, the anisotropy of the sliding energy corrugation with respect to the misfit angle between the two naturally mismatched lattices is found to reduce with the flake size. For sufficiently large flakes, the sliding energy corrugation is expected to be at least an order of magnitude lower than that obtained for matching lattices regardless of the relative interlayer orientation. Therefore, in contrast to the case of the homogeneous graphene interface where flake reorientations are known to eliminate superlubricty, here, a stable low-friction state is expected to occur. Our results mark heterogeneous layered interfaces as promising candidates for dry lubrication purposes

Mechanism of Facilitated Diffusion during a DNA Search in Crowded Environments

The key feature explaining the rapid recognition of a DNA target site by its protein lies in the combination of one- and three-dimensional (1D and 3D) diffusion, which allows efficient scanning of the many alternative sites. This facilitated diffusion mechanism is expected to be affected by cellular conditions, particularly crowding, given that up to 40% of the total cellular volume may by occupied by macromolecules. Using coarse-grained molecular dynamics and Monte Carlo simulations, we show that the crowding particles can enhance facilitated diffusion and accelerate search kinetics. This effect originates from a trade-off between 3D and 1D diffusion. The 3D diffusion coefficient is lower under crowded conditions, but it has little influence because the excluded volume effect of molecular crowding restricts its use. Largely prevented from using 3D diffusion, the searching protein dramatically increases its use of the hopping search mode, which results in a higher linear diffusion coefficient. The coefficient of linear diffusion also increases under crowded conditions as a result of increased collisions between the crowding particles and the searching protein. Overall, less 3D diffusion coupled with an increase in the use of the hopping and speed of 1D diffusion results in faster search kinetics under crowded conditions. Our study shows that the search kinetics and mechanism are modulated not only by the crowding occupancy but also by the properties of the crowding particles and the salt concentration

Graphene Nanoribbons-Based Ultrasensitive Chemical Detectors

A computational study demonstrating the potential application of armchair graphene nanoribbons as ultrasensitive chemical detectors is presented. To this end, we propose the use of lithium adatoms, serving as surface anchoring sites, to allow for aromatic contaminant chemisorption that alters the all-carbon substrate electronic properties. The corresponding variations in the electronic transport characteristics, which are evaluated using a divide and conquer approach based on density functional theory, suggest device sensitivities as low as 10^–5–10^–9 ppbv. The microscopic understanding of the contaminant adsorption process and its influence on the electronic and transport properties of graphene nanoribbons gained in this study may assist in the rational design of ultrasensitive chemical detectors based on low-dimensional graphene derivatives

Role of Backbone Charge Rearrangement in the Bond-Dipole and Work Function of Molecular Monolayers

Self-assembled organic monolayers serve for modifying the work function of inorganic substrates. We examine the role of the molecular backbone in determining monolayer-adsorbed work function, by considering the adsorption of dithiols with either a partially conjugated or a saturated backbone on the GaAs(001) surface. Using a combination of chemically resolved electrical measurements based on X-ray photoelectron spectroscopy and contact potential difference, together with first principles electronic structure calculations, we are able to distinguish quantitatively between the contributions of the band bending and surface dipole components. We find that the substrates coated by partially conjugated layers possess a larger band-bending, relative to that of the substrates coated by saturated layers. This is associated with an increased density of surface states, likely related to the presence of oxygen. At the same time, the samples coated by partially conjugated layers also possess a larger bond-dipole, with the difference found to result primarily from an extended charge rearrangement on the molecular backbone. The two effects are, in this case, of opposite sign, but a significant net change in work function is still found. Thus, design of the molecular backbone emerges as an additional and important degree of freedom in the design of potential profiles and charge injection barriers in monolayer-based structures and devices