Uniaxial strain on graphene: Raman spectroscopy study and bandgap opening

Abstract: Graphene was deposited on a transparent and flexible substrate and tensile strain up to ~0.8% was loaded by stretching the substrate in one direction. Raman spectra of strained graphene show significant redshifts of 2D and G band (-27.8 cm^-1 and -14.2 cm^-1per 1% strain, respectively), because of the elongation of the carbon-carbon bonds. This indicates that uniaxial strain has been successfully applied on graphene. We also proposed that by applying uniaxial strain on graphene, tunable bandgap at K point can be realized. First principle calculations predicted a bandgap opening of ~300 meV for graphene under 1% uniaxial tensile strain. The strained graphene provides an alternative way to experimentally tune the bandgap of graphene, which would be more efficient and more controllable than other methods that are used to open bandgap in graphene. Moreover, our results suggest that the flexible substrate is ready for such strain process and Raman spectroscopy can be used as an ultra-sensitive method to determine the strain.

• The paper demonstrates that applying uniaxial strain to graphene induces a tunable bandgap with significant Raman shifts of -27.8 cm⁻¹/% (2D band) and -14.2 cm⁻¹/% (G band).
• The study employs a flexible PET substrate and Raman spectroscopy to quantitatively monitor strain effects in both single- and three-layer graphene samples.
• First-principle calculations predict an approximate 300 meV bandgap opening at 1% strain, underscoring graphene's potential for electronic and sensor applications.

Uniaxial Strain on Graphene: Effect on Raman Spectroscopy and Bandgap

Graphene, a single layer of carbon atoms arranged in a honeycomb structure, exhibits intriguing electronic properties that have garnered significant attention in both fundamental research and potential technological applications. One central challenge in leveraging graphene for electronics is engineering a controllable bandgap. This paper investigates a promising approach to accomplish this by applying uniaxial strain to graphene, a method that contrasts with previous techniques such as graphene nanoribbons or graphene on hexagonal boron nitride.

The study involved depositing graphene on a flexible, transparent polyethylene terephthalate (PET) substrate, which was stretched to exert uniaxial tensile strain up to approximately 0.8% on the graphene. Raman spectroscopy was used to monitor the strain-induced changes in the vibrational frequencies of carbon-carbon bonds, specifically analyzing the shifts in the 2D and G bands, which redshifted significantly under strain. For single-layer graphene, these shifts were quantified as -27.8 cm⁻¹/% for the 2D band and -14.2 cm⁻¹/% for the G band. The study also compared these shifts in three-layer graphene, establishing that the strain is more effectively transferred in thinner samples.

From a theoretical perspective, first-principle calculations were performed to assess the electronic structure modifications induced by uniaxial strain. These calculations predicted a bandgap opening of approximately 300 meV for a 1% strain. Such a modification arises from the strain-induced breaking of sublattice symmetry within graphene, a phenomenon that has been previously reported in graphene subjected to different substrates but is here explored in the context of mechanical strain.

The practical implications of this study are significant. By introducing a tunable bandgap, uniaxially strained graphene holds potential for application in electronic and optoelectronic devices where semiconducting properties are desirable. Additionally, the methodology of using a flexible substrate allows for reversible application and removal of strain, showcasing graphene's elasticity and robustness for repeated mechanical manipulation.

Furthermore, the Raman spectroscopy findings underscore graphene's potential as an ultrasensitive strain gauge, a field where carbon nanotubes have already found substantial application. The linear relationship between the Raman peak shifts and strain enables precise measurements and could lead to the development of high-performance sensors.

Going forward, this research sets the stage for further exploration into the strain-dependent transport properties of graphene, as well as the integration of strained graphene into devices. The utilization of piezocrystals as substrates could allow for more precise strain control, fostering advancements in wearable electronics where flexible, conductive materials are paramount.

In conclusion, the application of uniaxial strain to graphene presents an efficient and controllable method to tune its bandgap, making a substantial contribution to the efforts of rendering graphene a viable material for future semiconductor technologies. Further studies into the electronic and mechanical interaction complexities will continue to enhance our understanding and application of strained graphene systems.