Investigating the phonon line shapes of TMDs: An analytical approach

Abstract

Several phenomena can affect the phonon bands of low-dimensional systems, and their proper assignment and interpretation are essential in elucidating their effect on electronic, optical, and optoelectronic properties. Using an analytical approach, we investigate the similarities and differences of the layered effect, the phonon confinement effect, the Breit-Wigner-Fano effect, the inhomogeneous heating effect, and disorder-induced effects in the phonon line shapes of WS 2 and MoS 2. The subtle differences and similarities are critical in making proper assignments and interpretations of the phonon line shapes and are useful as guidance in the behavior of phonon bands, particularly in TMDs, and more generally in low-dimensional systems.

Broadband infrared study of pressure-tunable Fano resonance and metallization transition in 2H-$$\hbox {MoTe}_2$$

“… 40 . It is worth noticing that a negative asymmetric parameter , as obtained from the experimental data fit, is perfectly consistent with the presence of n-type doping that is known to cause an asymmetric broadening of the peak on the lower energy side, as previously observed for few-layer graphene 41 – 43 . Conversely, p-type doping would have produced hole states in the proximity of the valence band maximum and an asymmetric broadening of the peak on the higher energy side.…”

Broadband Infrared Study of Pressure-Tunable Fano Resonance and Metallization Transition in 2H-MoTe2

“…However, since the measured samples are n-type semiconductors, as declared by the manufacturer HQ-Graphene and like most of the TMDs grown by Chemical Vapor Transport [13,35], charges in excess giving rise to extra electronic levels, just below the conduction band minimum, could be responsible for electronic excitations with energies comparable with E ph , as also reported in [36]. It is worth noticing that a negative asymmetry parameter θ, as obtained from the experimental data fit, is perfectly consistent with the presence of n-type doping that is known to cause an asymmetric broadening of the peak on the lower energy side, as previously observed for fewlayer graphene [37][38][39]. Conversely, p-type doping would have produced hole states in the proximity of the valence band maximum and an asymmetric broadening of the peak on the higher energy side.…”

MOCVD Growth of Hierarchical Nanostructured MoS2: Implications for Reactive States as the Large-Area Film

“…The slope from 100 to 40 μm is due to the relatively increased intensity of the A 1g mode. However, the slope from 40 μm to the edge is attributed to the relatively rapid increased intensity of the E 2g 1 mode because of the phonon confinement effect that occurred by the correlation between the phonon mean free path and the crystal size . The confinement of phonons in crystallites has been reported to be generated at the nanoscale size of 50 nm or less, That is, layered MoS 2 nanocrystals of less than 50 nm were dominantly overlapped and grown vertically in the 0–40 μm region.…”