Gaussian deformations in graphene ribbons: Flowers and confinement

Scientific Reports

A theoretical investigation on electron transport properties of rectangular graphene quantum dots (GQDs) with non-centro-symmetric out-of-plane Gaussian deformation of elliptic type is presented. Different levels of deformation are explored to estimate system geometry optimal for potential electronic applications. Electronic properties of deformed GQDs are studied in terms of local density of states (LDOS), band-gap opening and equilibrium ballistic conductance. In particular, it was observed that the symmetry of spatial LDOS structure is directly linked with the symmetry of properly defined local strain field (LSF) map, for a wide energy range. The relationship confirms qualitatively predictions obtained on the basis of the concept of a pseudomagnetic field, used in continuum models of graphene, including strain induced effects. The conductance spectra of deformed GQD as a device connected to semi-infinite graphene armchair nanoribbons as reservoirs are studied in a frame of tight-...

Physical Review B, 2010

Density functional study of strain effects on the electronic band structure and transport properties of the graphene nanoribbons (GNR) is presented. We apply a uniaxial strain (ε) in the x (nearest-neighbor) and y (second nearest-neighbor) directions, related to the deformation of zigzag and armchair edge GNRs (AGNR and ZGNR), respectively. We calculate the quantum conductance and band structures of the GNR using the Wannier function in a strain range from −8% to +8% (minus and plus signs show compression and tensile strain). As strain increases, depending on the AGNR family type, the electrical conductivity changes from an insulator to a conductor. This is accompanied by a variation in the electron and hole effective masses. The compression ε x in ZGNR shifts some bands to below the Fermi level (E f) and the quantum conductance does not change, but the tensile ε x causes an increase in the quantum conductance to 10e 2 /h near the E f. For transverse direction, it is very sensitive to strain and the tensile ε y causes an increase in the conductance while the compressive ε y decreases the conductance at first but increases later.

The Journal of Chemical Physics, 2008

We report a first-principles study on the electronic structures of deformed graphene nanoribbons ͑GNRs͒. Our theoretical results show that the electronic properties of zigzag GNRs are not sensitive to uniaxial strain, while the energy gap modification of armchair GNRs ͑AGNRs͒ as a function of uniaxial strain displays a nonmonotonic relationship with a zigzag pattern. The subband spacings and spatial distributions of the AGNRs can be tuned by applying an external strain. Scanning tunneling microscopy dI / dV maps can be used to characterize the nature of the strain states, compressive or tensile, of AGNRs. In addition, we find that the nearest neighbor hopping integrals between -orbitals of carbon atoms are responsible for energy gap modification under uniaxial strain based on our tight binding approximation simulations.

Solid-State Electronics, 2013

Transport properties of sub-5 nm-wide graphene nanoribbons (GNRs) are investigated by using atomistic non-equilibrium Green's function (NEGF) simulations and semiclassical mobility simulations of large ensembles of randomly generated nanoribbons. Realistic GNRs with dimensions targeting the 12 nm CMOS node are investigated by accounting for edge defects, vacancies and potential fluctuations.

Deformations in graphene systems are central elements in the novel field of straintronics. Various strain geometries have been proposed to produce specific properties but their experimental realization has been limited. Because strained folds can be engineered on graphene samples on appropriate substrates, we study their effects on graphene transport properties. We show the existence of an enhanced local density of states (LDOS) along the direction of the strained fold that originates from localization of higher energy states, and provides extra conductance channels at lower energies. In addition to exhibit sublattice symmetry breaking, these states are valley polarized, with quasi-ballistic properties in smooth disorder potentials. We confirmed that these results persist in the presence of strong edge disorder, making these geometries viable electronic waveguides. These findings could be tested in properly engineered experimental settings.

Physical Review B, 2018

Straintronic devices made of carbon-based materials have been pushed up due to the graphene high mechanical flexibility and the possibility of interesting changes in transport properties. Properly designed strained systems have been proposed to allow optimized transport responses that can be explored in experimental realizations. In multi-terminal systems, comparisons between schemes with different geometries are important to characterize the modifications introduced by mechanical deformations, specially if the deformations are localized at a central part of the system or extended in a large region. Then, in the present analysis, we study the strain effects on the transport properties of triangular and hexagonal graphene flakes, with zigzag and armchair edges, connected to three electronic terminals, formed by semi-infinite graphene nanoribbons. Using the Green's function formalism with circular renormalization schemes, and a single band tight-binding approximation, we find that resonant tunneling transport becomes relevant and is more affected by localized deformations in the hexagonal graphene flakes. Moreover, triangular systems with deformation extended to the leads, like longitudinal three-folded type, are shown as an interesting scenario for building nanoscale waveguides for electronic current.

arXiv: Mesoscale and Nanoscale Physics, 2019

The interplay between uniaxial strain and charging effects in zigzag graphene nanoribbons (ZGNR) is investigated by using non-equilibrium Green's function formalism. The I-V characteristic curves and especially negative differential resistance (NDR) induced by some quantum selection rules are affected by the type, strength and also direction of the applied strain. For the oblique strain, the parity conservation fails while it conserves at the longitudinal and transverse strains. Therefore, in the oblique strain, on-off current ratio drastically decreases in compared to the un-strained case. For the tensile strain along the ribbon axis, $ I_{on}/I_{off} $ ratio increases while for the compressive strain, NDR will be gradually disappeared. This property can be useful for nano-electromechanical switch in which by changing the tensile to compressive strain, current switches between its on and off-current state. Furthermore, under influence of the oblique uniaxial strain, the geometr...

Frontiers in Electronics, 2013

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Physica E: Low-dimensional Systems and Nanostructures, 2015

We studied the effect of uniaxial strain on the transport properties of Z-shaped GNR. The energy gap of armchair GNR is sensitive to the uniaxial strain. The uniaxial strain could induce a metal-to-semiconductor transition. The threshold voltage is sensitive to the uniaxial strain parameter strength.

Nanotechnology, 2011

Electronic transport properties of monolayer graphene with extreme physical bending up to 90 o angle are studied using ab Initio first-principle calculations. The importance of key structural parameters including step height, curvature radius and bending angle are discussed how they modify the transport properties of the deformed graphene sheet comparing to the corresponding flat ones. The local density of state reveals that energy state modification caused by the physical bending is highly localized. It is observed that the transport properties of bent graphene with a wide range of geometrical configurations are insensitive to the structural deformation in the low-energy transmission spectra, even in the extreme case of bending. The results support that graphene, with its superb electromechanical robustness, could serve as a viable material platform in a spectrum of applications such as photovoltaics, flexible electronics, OLED, and 3D electronic chips.