Two Dimensional Materials Beyond Monolayer Graphene: Electronic, Optoelectronic and Vibrational Properties
Registration Website : https://goo.gl/anFodh
Two-dimensional (2D) crystals are emerging materials for nanoelectronics, optoelectronics, and thermoelectronics. In this talk, I will first disscuss the role of atomic point defects in tailoring various physical properties of MoS2 samples prepared by mechanical exfoliation, physical and chemical vapour deposition.1 Based on a joint scanning-transmission-electron-microscopy and density-functional-theory investigation, we find the correlation among the method of preparation, the dominate type of defects, and the carrier mobility or magnetism.
I will then present a detailed theoretical investigation of the atomic and electronic structure of few-layer Black phosphorus (BP) in order to predict its electrical and optical properties.2 This system is a direct bandgap semiconductor with rather high and anisotropic hole-dominated carrier mobility. We also predict linear dichroism between the two perpendicular in-plane directions. Strain-engineering of few-layer BP is also discussed in terms of electronic structures and optical properties.3
In the last part of this talk, I will focus on the interlayer vibrational properties of twisted multilayer graphene4 and few-layer BP5. An anormlous softness of interlayer shear modes and the nearly unchanged breathing modes at the twist interface of graphene were observed by Raman spectroscopy and well understood with theoretical calculations.4 For few-layer BP, with increasing sample thickness, we find anomalous redshifts of the frequencies for each optical mode, the splitting of the phonon branches, and strong phonon-phonon coupling. By computing uniaxial stress effects, inter-atomic force constants, and electron densities, we provide a compelling demonstration that these exceptional vibrational properties are the consequence of strong and highly directional interlayer interactions arising from electronic hybridization of the lone electron-pairs, rather than from vdW interactions.
References:
1Jinhua Hong et al., Exploring atomic defects in molybdenum disulphide monolayers, Nature Commun. 6, 6293 (2015).
2Jingsi Qiao et al., High-mobility transport anisotropy and linear dichroism in few-layer black phosphorus, Nature Commun. 5, 5475 (2014), DOI:10.1038/ncomms5475, arXiv:1401.5045.
3Qian Jia, Ju Li, Wei Ji, Strain-engineered optical absorption of few-layer Black Phosphorus, in preparation.
4Jiang-Bin Wu et al., Interface coupling in twisted multilayer graphene by resonant Raman spectroscopy of layer breathing modes, ACS Nano, 2015, 9 (7), pp 7440–7449.
5Zhixin Hu et al., Interlayer electronic hybridization leads to exceptional thickness-dependent vibrational properties in few-layer black phosphorus, arXiv:1503.06735.
In the last part of this talk, I will focus on the interlayer vibrational properties of twisted multilayer graphene4 and few-layer BP5. An anormlous softness of interlayer shear modes and the nearly unchanged breathing modes at the twist interface of graphene were observed by Raman spectroscopy and well understood with theoretical calculations.4 For few-layer BP, with increasing sample thickness, we find anomalous redshifts of the frequencies for each optical mode, the splitting of the phonon branches, and strong phonon-phonon coupling. By computing uniaxial stress effects, inter-atomic force constants, and electron densities, we provide a compelling demonstration that these exceptional vibrational properties are the consequence of strong and highly directional interlayer interactions arising from electronic hybridization of the lone electron-pairs, rather than from vdW interactions.
References:
1Jinhua Hong et al., Exploring atomic defects in molybdenum disulphide monolayers, Nature Commun. 6, 6293 (2015).
2Jingsi Qiao et al., High-mobility transport anisotropy and linear dichroism in few-layer black phosphorus, Nature Commun. 5, 5475 (2014), DOI:10.1038/ncomms5475, arXiv:1401.5045.
3Qian Jia, Ju Li, Wei Ji, Strain-engineered optical absorption of few-layer Black Phosphorus, in preparation.
4Jiang-Bin Wu et al., Interface coupling in twisted multilayer graphene by resonant Raman spectroscopy of layer breathing modes, ACS Nano, 2015, 9 (7), pp 7440–7449.
5Zhixin Hu et al., Interlayer electronic hybridization leads to exceptional thickness-dependent vibrational properties in few-layer black phosphorus, arXiv:1503.06735.
