Reversible Photoluminescence Tuning by Defect Passivation via Laser Irradiation on Aged Monolayer MoS₂

Abstract

Atomically thin (1L)-MoS 2 emerged as a direct band gap semiconductor with potential optical applications. The photoluminescence (PL) of 1L-MoS 2 degrades due to aging-related defect formation. The passivation of these defects leads to substantial improvement in optical properties. Here, we report the enhancement of PL on aged 1L-MoS 2 by laser treatment. Using photoluminescence and Raman spectroscopy in a gas-controlled environment, we show that the enhancement is associated with efficient adsorption of oxygen on existing sulfur vacancies preceded by removal of adsorbates from the sample's surface. Oxygen adsorption depletes negative charges, resulting in suppression of trions and improved neutral exciton recombination. The result is a 6-to 8-fold increase in PL emission. The laser treatment in this work does not cause any measurable damage to the sample as verified by Raman spectroscopy, which is important for practical applications. Surprisingly, the observed PL enhancement is reversible by both vacuum and ultrafast femtosecond excitation. While the former approach allows switching a designed micropattern on the sample ON and OFF, the latter provides a controllable mean for accurate PL tuning, which is highly desirable for optoelectronic and gas sensing applications.

How defects influence the photoluminescence of TMDCs

“…One widely reported strategy is to deplete excessive electrons through charge transfer. Some gas molecules, such as O2, H2O, and N2 molecules, can be directly adsorbed on chalcogen vacancies and extract electrons from the TMDCs [15][16][17]37]. These molecules, acting as "molecule gating", result in a significant PL enhancement for natively n-doped monolayer TMDCs (Fig.…”

Measurement of Quantum Yields of Monolayer TMDs Using Dye-Dispersed PMMA Thin Films

“…A high density of structural defects in these systems has been proven to be the main cause of the low QYs of 1L-TMDs [9][10][11][12][13]. Methods to improve the QYs of 1L-TMDs through the treatment of these defects using bis(trifluoromethane) sulfonimide (TFSI) [13][14][15][16], hydrohalic acids (HBr) [17], poly(4-styrenesulfonate) [18], and light illumination [19][20][21] have been reported. However, the effectiveness of these methods is not clear without the general assessment of the QYs of 1L-TMDs.…”

Photoluminescence and electronic transition behaviors of single-stranded DNA

“…On the basis of the results obtained from this study we find, from a viewpoint of physics, that the photo-induced light emission from ssDNA is akin to that from, e.g., a direct band-gap semiconductor with radiative impurity states [33][34][35] . The LUMO and…”

“…These functional groups are fluorophores for PL emission in long wavelength regime. The PL peaks in relatively long excitation wavelengths in Fig.1and the PLE peaks in Fig.3are similar to photo-induced light emission from radiative impurity sates in a doped semiconductor.The photo-induced light generation from impurity states in a semiconductor depends normally on the excitation wavelength[33][34][35] .The results obtained from this study indicate that for A-, T-, C-and G-based ssDNA, due to different base structures and functional groups attached to the base, the features of the PL emission look markedly different. Through examining the dependence of the PL and PLE peaks along with the amplitude of the PL peaks upon the excitation wavelength, we are able to identify optically the ssDNA with different bases and the same base but with different base numbers.…”