Probing photo-induced lattice distortion

We have investigated the photo-induced dynamics of a 2H-MoTe2 crystal by means of time-resolved X-ray photoemission spectroscopy. We detect two distinct phenomena: (1) structural deformations in the out-of-plane direction with lifetime in the sub-nanosecond regime and (2) a surface photovoltage shift that persists for microseconds. These results show that high-resolution time-resolved photoemission, combined with theoretical simulations, can provide valuable information not only on electronic and chemical modifications of photoexcited systems, but also on lattice distortions and phase transitions.

R. Costantini et al. DOI:10.1039/D1FD00105A
       lattice distortion in 2H-MoTe2 transition metal dichalcogenides (TMD)

Transition metal dichalcogenides (TMDs) have been widely explored for the development of innovative nanoscale devices. Molybdenum ditelluride (MoTe2) is a prototypical TMD. It presents two crystal structures at room temperature: the semiconducting hexagonal phase (2H or α-phase) and the semimetallic monoclinic phase (1T′ or β-phase). In its 2H phase, MoTe2 has attracted significant interest from a technological point of view due to its bandgap in the near infrared region (0.9 eV in the bulk and 1.1 eV in the monolayer), which makes it a potential alternative to silicon for optoelectronic applications. Very recently, carrier multiplication has been demonstrated in 2H-MoTe2, making it a promising material for the development of light harvesting devices.
The technological interest in MoTe2 as a phase engineered material is related to the possibility of triggering the 2H–1T′ phase transition by optical excitation, potentially allowing for an accurate patterning of metallic areas into a semiconducting canvas via laser irradiation. In this paper, we investigate the photo-induced modifications of a bulk 2H-MoTe2 crystal by means of time-resolved X-ray photoemission spectroscopy.
We observe that in the microsecond timescale, the core levels shift to higher kinetic energies due to surface photovoltage fields, while in the sub-nanosecond range, the photoemission peaks shift in the opposite direction. With the support of DFT calculations, we ascribe the latter effect to the deformation of the lattice in the out-of-plane direction, which is along the pathway for the 2H–1T′ phase transition.

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Photo-induced lattice distortion in 2H-MoTe2 probed by time-resolved core level photoemission,  R. Costantini, F. Cilento, F. Salvador, A. Morgante, G. Giorgi, M. Palummo and  M. Dell’Angela, Faraday Discussions 236, 429-441 (2022) DOI:10.1039/D1FD00105A
Last Updated on Wednesday, 09 November 2022 14:28