چكيده به لاتين
New technological approaches are needed to exploit the full potential offered by the emergent novel properties of 2D materials. A promising technological approach is the application of the high sensitivity of these materials to external mechanical forces and strains due to their low dimensionality. However, the knowledge of the strain-induced effects on diverse 2D materials is crucial for the utilization of the opportunity offered by this approach. In particular, strain is suitable to overcome the limited on-off ratio driven by lack of backscattering and bandgap in graphene. Whilst, for another group of 2D materials, transition metal dichalcogenides (TMDs), strain is best suitable for tailoring the optical properties due to their efficient light-matter interaction.
In this dissertation, we investigate the impacts of in-plane strain on optical and electronic properties of graphene-based hetero- and twisted bilayers along with TMDs. We show that these properties enormously change with regard to the distortion of the lattice structures and provide access toward the technological application of these materials in the development of strain-based electronic devices and sensors.
Based on our DFT computations on the strain-induced modifications of the electronic properties of commensurate twisted bilayer graphene (TBG) and graphene/hexagonal boron nitride (G/hBN) superlattices, we found that for both lattices the interplay of few percents in-plane strains and moire pattern leads to considerable valley drifts, band gap modulation and enhancement of the substrate-induced Fermi velocity renormalization. Interestingly, when applying in-plane non-equibiaxial strains to G/hBN superlattices, regardless of the strain alignment, the graphene zigzag direction becomes more efficient for electronic transport. Moreover, our calculations show that for large mixed strains TBG superstructures demonstrate direct-indirect bandgap transition.
Our calculations show that for TMDs the strain-induced changes of the linewidth of the absorption spectra are due to the changes in the relative spectral position of excitonic states. Our theoretical results explain well the observed partially opposite changes in the excitonic linewidth of different TMDs at room temperature. Furthermore, we predict the linewidth behavior of excitonic resonances when applying compressive strain and at low temperatures.
Keywords: 2D materials, Moire patterns, Strain, Electronic and optical properties
