Laser‐ and Ion‐Induced Defect Engineering in WS₂ Monolayers

Abstract

Tungsten disulfide is one of the prominent transition metal dichalcogenide materials, which shows a transition from an indirect to a direct bandgap as the layer thickness is reduced down to a monolayer. To use monolayers in devices, detailed knowledge about the luminescence properties regarding not only the excitonic but also the defect‐induced contributions is needed. Herein, monolayers are irradiated with ions with different fluences to create different defect densities. Apart from the excitonic contributions, two additional emission bands are observed at low temperatures. These bands can be reduced or even suppressed, if the flakes are exposed to laser light with powers up to 1.5 mW. Increasing the temperature up to room temperature leads to recovery of this emission, so that the luminescence properties can be modified using laser excitation and temperature. The defect bands emerging after ion irradiation are attributed to vacancy defects together with physisorbed adsorbates at different defect sites.

γ-Ray-Induced Surface-Charge Redistribution and Change of the Surface Morphology in Monolayer WS2

“…As can be observed in Figure a, the PL peaks become increasingly asymmetric with increased radiation dosage. The width of the low-energy tail in the PL spectra reflects the energy distribution of the localized states in the film created due to defects. , The corresponding peak extracted from the low-energy shoulder is denoted as the defect peak, X D , whose intensity is significantly enhanced with the radiation dosage (Figure d–f).…”

Understanding the impact of heavy ions and tailoring the optical properties of large-area monolayer WS2 using focused ion beam

“…The trions in as-grown TMDCs are attributed to native defects and TMDC-substrate interaction 34,35 . The lowest energy peak, defectbound exciton peak D S , is attributed to S-deficiency induced emission, previously discussed in the S-based TMDCs, such as MoS 2 and WS 2 [13][14][15][16][30][31][32][33]36 . A hole with 2 μm in diameter and 50 nm in depth was milled on the WS 2 /SiO2/Si samples, with various Ga + beam currents in the range of 10-3000 pA (see METHODS).…”

“…Figure 1b shows the PL spectrum measured from a pristine ML WS 2 on SiO 2 -on-Si substrate, using a microPL setup 29 . The main PL peak energy of pristine ML WS 2 is ~2.03 eV, corresponding to the neutral excitonic transition 16,[30][31][32][33] , denoted as A 0 in Fig. 1.…”

“…FIB lithography is often employed as the all-dry nanofabrication method for plasmonic [2][3][4] , photonic 5,6 and microfluidic 7 devices, in applications such as sensors, photodetectors, and light emitters [8][9][10][11][12] . Alongside these applications, recently FIB has shown great potential in surface modification and defect engineering in two-dimensional materials, especially in the transition metal dichalcogenides (TMDCs) family, with the aim to tailor their optical and electrical properties [12][13][14][15][16][17][18][19] . It has been shown that direct ion beam irradiation can controllably create chalcogenide and transition metal vacancies, thus manipulating the material's stoichiometry.…”

Cratering Induced by Slow Highly Charged Ions on Ultrathin PMMA Films

“…This has been previously explored using swift heavy ions as projectiles [9]. Apart from being fundamental aspects, this information is also important for applications of defect engineering of two-dimensional materials such as graphene [17,[22][23][24][25], hBN [26], MoS 2 [21,27], and WS 2 [28] by ion irradiation [29].…”