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The combined effects of an asymmetric (square or V-shaped) notch and uniaxial strain are studied in a zigzag graphene nanoribbon (ZGNR) device using a generalized tight-binding model. The spin-polarization and conductance-gap properties, calculated within the Landauer–Büttiker formalism, were found to be tunable for uniaxial strain along the ribbon-length and ribbon-width for an ideal ZGNR and square (V-shaped) notched ZGNR systems. Uniaxial strain along the ribbon-width for strains ≥10% initiated significant notch-dependent reductions to the conduction-gap. For the V-shaped notch, such strains also induced spin-dependent changes that result, at 20% strain, in a semi-conductive state and metallic state for each respective spin-type, thus demonstrating possible quantum mechanisms for spin-filtration.

The structure and chemical functionalization of the edges of graphene nanoribbons (GNRs) have a pronounced effect on their properties, such as the band gap and electronic transport [

In addition to patterning, uniaxial strain has also been used to control the properties of GNR and bulk graphene devices [

In this work, the combined effects of an asymmetric notch and uniaxial strain on the magnetism and coherent transport properties of ZGNR devices (

An unstrained ZGNR device (ribbon dimensions ∼40.6 nm × 13.5 nm) with an asymmetric (

A generalized tight-binding (TB) model with a Hubbard-_{iσ }_{i−σ}_{ij}_{iσ}_{i}

The coherent transport properties of the ZGNRs have been calculated using the generalized TB model (Equations (1) and (2)) applied within the Landauer-Bü ttiker formalism [_{σ }_{σ }_{L/Rσ }_{L/R}

The parameters for the generalized TB model (Equation (1)) have been obtained by fitting to local spin-density approximation (LSDA), density functional theory (DFT) results for hydrogen-passivated GNRs, such that _{ij}_{1} = 2.7, _{2} = 0.20, and _{3} = 0.18, for first, second and third nearest-neighbor hopping, respectively (in units of eV) [

Uniaxial strain has been added to the device and the leads by perturbing the generalized TB model via Harrison scaling [_{ij}_{0} and _{x}_{y}

The calculated local spin-polarization (Equation 3) for an ideal ZGNR (

(Color on-line). Pictorial representation of the local spin-polarization for an ideal ZGNR device (unstrained). Yellow (black) corresponds to a net spin-up (down). The magnitude of the spin-polarization (Equation 3) is indicated by the circle radius.

For the notched ZGNRs, a maximum strain of 20% in the

(Color on-line). Local spin-polarization for a zero-strained ZGNR device with a (

The average spin-polarization per edge-atom (including the notch region) in the ideal and notched systems for increasing uniaxial strain is shown in

(Color on-line). The effects of uniaxial strain m the (

The dependence of the device properties on strain can also be seen in the conductance-gap trends for these systems. We define the conductance-gap as the zero-conductance region around the Fermi energy, such that for a metallic (semi-conductive) system, the conductance-gap will be zero (non-zero). As the uniaxial strain in the

(Color on-line). The effects of uniaxial strain in the (

Increasing the uniaxial strain in the

The spin-polarization and conduction-gaps in ideal and asymmetric-notched ZGNRs show the potential for tunability as a function of increasing uniaxial strain. For uniaxial strain along the

Uniaxial strain in the

The authors gratefully acknowledge the support of the EPSRC (UK Engineering and Physical Sciences Research Council).