Gap opening in graphene by shear strain (1006.1999v1)

Abstract: We exploit the concept of strain-induced band structure engineering in graphene through the calculation of its electronic properties under uniaxial, shear, and combined uniaxial-shear deformations. We show that by combining shear deformations to uniaxial strains it is possible modulate the graphene energy gap value from zero up to $0.9$ eV. Interestingly enough, the use of a shear component allows for a gap opening at moderate absolute deformation, safely smaller than the graphene failure strain.

• The paper demonstrates that applying shear strain to graphene opens a semiconductor band gap up to 0.72 eV at ~16% strain using a tight-binding model.
• The study reveals that Dirac point merging under strain modulates graphene's electronic structure from a gapless to a semiconducting state.
• The research indicates that combining shear and uniaxial strain further increases the band gap to about 0.95 eV, enhancing prospects for graphene-based electronics.

Shear Strain-Induced Band Gap Modulation in Graphene

The paper "Gap opening in graphene by shear strain" explores strain engineering as a method to manipulate the electronic properties of graphene, specifically focusing on the capability of shear strain to induce an energy band gap. Graphene, known for its exceptional electronic properties such as high electron mobility and unique quantum Hall effects, typically lacks an electronic band gap due to its Dirac point structure, hindering its application in electronic devices where a semiconducting behavior is required.

Electronic Band Structure Modification

The paper elucidates the effect of different strain configurations on the electronic band structure of graphene. Utilizing a semi-empirical $sp^3$ tight-binding model, the paper characterizes how uniaxial, shear, and combined uniaxial-shear strains alter graphene's band structure. Notably, the research demonstrates that implementing a shear strain—a deformation type substantially different from pure uniaxial tension or compression—can achieve a band gap of up to 0.72 eV significantly efficiently. This gap emerges at a lower strain threshold ($\sim 16\%$) compared to uniaxial methods, offering a more feasible subsequence far from reaching the mechanical failure strain limit of $\sim 25\%$ in graphene.

Mechanisms of Dirac Point Manipulation

Central to their findings is the observation of Dirac point merging under applied strain, leading to the band-gap opening. This phenomenon arises as the Dirac points move due to lattice symmetry alterations induced by strain, eventually coalescing and shifting the band structure from a gapless state to a semiconductor-like gap. The implications extend further when combining shear with uniaxial strain, evidencing that the gap can be maximized to about 0.95 eV at 17% strain using this method.

Practical and Theoretical Implications

The practical implication of inducing a band gap through strain is significant for graphene electronics, offering a method to render graphene suitable for semiconductor device integration without the detrimental effects of edge roughness, unlike chemical patterning methods. From a theoretical perspective, this approach extends understanding of lattice dynamics and electronic band alteration under mechanical deformation, enriching the principles of strain engineering in two-dimensional materials.

Future Prospects

While the paper provides profound insights into strain-dependent band gap modulation, future research could explore the reversibility of such deformations, long-term stability of strain-induced gaps, and integration methods in conjunction with flexible substrates. Furthermore, expanding this strain engineering approach to other emerging two-dimensional materials like transition metal dichalcogenides could broaden the repertoire of electronic properties accessible through mechanical deformation strategies.

In conclusion, the research outlines a viable pathway for band gap engineering in graphene via shear strain and combined strain modalities, establishing a foundation for future advancements in nanoelectronic applications leveraging the unique properties of graphene.