Identifying the Origin of Defect-Induced Raman Mode in WS₂ Monolayers via Density Functional Perturbation Theory

Abstract

Transition metal dichalcogenides (TMDs) are being actively studied in nextgeneration semiconductor applications owing to their excellent optoelectronic properties. Therefore, numerous defect-related studies have been conducted to improve TMD quality. In the study of defects, Raman spectroscopy is widely used to obtain information regarding the defects on a surface. A single sulfur-vacancy-induced Raman peak was recently reported. However, the origin of this vibrational mode has not yet been identified. Therefore, quantum mechanical calculations were performed on the sulfur-vacancy-containing supercell structure to elucidate the origin. By calculating the band structure and phonon dispersion, the phonon momentum was obtained, considering the possible scattering of electrons. After comparing the phonon momentum and phonon dispersion, it was identified that the phonon vibrational origin of a single sulfurvacancy-induced Raman peak is A′ 1 (k).

Theoretical Analysis of the Nanoscale Composition, Tip-Enhanced Raman Spectroscopy, and Electronic Properties of Alloys in 2D MoS2–WS2 Heterostructures

“…Furthermore, Lee et al reported the appearance of higher-frequency defect-related modes in WS 2 monolayers and a red-shift of the A′ 1 mode due to S vacancies . Recently, Yoo et al reported that the defect mode in single S-vacant 1L-WS 2 originates from A′ 1 phonon vibrations . Following the lead of these prior studies, and noting that the presence of S vacancies was speculated in the original work, we hypothesize that the current discrepancies between the calculated and measured Raman responses occur in part due to the mismatch in S vacancies between the two systems.…”

“…49 Recently, Yoo et al reported that the defect mode in single S-vacant 1L-WS 2 originates from A′ 1 phonon vibrations. 60 Following the lead of these prior studies, and noting that the presence of S vacancies was speculated in the original work, 21 we hypothesize that the current discrepancies between the calculated and measured Raman responses occur in part due to the mismatch in S vacancies between the two systems. The discrepancies above are largely resolved by incorporating S vacancies into the model.…”

Study of Punctual Defects in Monolayer WS2: Evidence of Correlations Between Raman and Photoluminescence Spectroscopy

“…These two last modes are better observed in resonance conditions. 48 Several other second (or more)-order Raman peaks situated between 240 and 290 cm −1 are also enhanced due to the exciton−phonon resonance effect, as discussed by Berkdemir et al 51 Following the same idea, the band around 298 cm −1 might be assigned as a double resonance process involving two ZA(M) phonons, 52,53 although several works attribute this feature to a fourth-order process. 51,54 Figure 2b shows a typical room-temperature photoluminescence spectrum of a WS 2 monolayer.…”

Structure modulation of two-dimensional transition metal chalcogenides: recent advances in methodology, mechanism and applications

“…Modulated point structures, for example, single atomic vacancies, often induce folded Brillouin zones in prime structures, and then result in attached phonon states. 368 With the comprehension of the centroid transformation of modulated structures, phonons present changes in frequencies, serving as quasi-particles describing the lattice vibration. Thus, the isotopic doping condition indicates a shift in the Raman characteristic peaks, which has been utilized to reveal the growth mechanism of graphene.…”