Microscopical Quantification of Ion‐Induced Nanodefects in Monolayer MoS₂ Based on Differential Reflectance

Abstract

microscope [17,18] (EM), inherent disadvantages of EM method have limited its application due to the expensive and timeconsuming characteristics, and the incapability of large-area test. Another kind of characterizing method is to analyze defects reversely from the measured changes of material properties. For example, the defect density in graphene is evaluated by the Raman intensity ratio of I D /I G , [19,20] and defects in WSe 2 are monitored by the photoluminescence (PL) intensity ratio of I Xb /I X0 . [21] However, the indirect characterizing method still requires an acquisition time of seconds per pixel. Thus, it is necessary to explore a new defect quantification method which is cheap, practical, and of high-speed imaging for large-area online inspection tasks. Here, we develop a practical defect quantification method based on differential reflectance spectroscopy (DRS) mapping. DRS is widely used in thin film characterization, [22][23][24][25][26] and it is well known for the ability to characterize large-area inhomogeneity of stacked thin films at sublayer precision. [27] For example, DRS was used for real-time monitoring of 2D semiconductor film growth. [22,24] As for high-speed imaging, the hyperspectral imaging [28,29] (HSI) technique could be combined as DRS measures the strong first-order optical signal. By taking a series of photos in response to different spectral ranges, HSI performs rapid spectral imaging beyond point-scanning methods. In this paper, a typical 2D semiconductor MoS 2 is selected as the model material due to easy calibration of its defect density by the defect activated Raman characteristic peak at ≈227 cm -1 . [30][31][32] Defects with different densities are induced into monolayer MoS 2 (ML-MoS 2 ) by focused ion beam (FIB) irradiation. The large-area defect mapping of ML-MoS 2 is performed by monochromatic photos after the DRS study. The feasibility of DRS mapping is demonstrated which is expected to achieve high-throughput online detect inspection for 2D materials. Results and Discussion Raman Characterization of ML-MoS 2 Defect SamplesAs a nondestructive vibrational spectroscopy technique, Raman spectroscopy can provide detailed information about chemical structure, phase, crystallinity, and molecular interactions. The layer-number identification of mechanically exfoliated MoS 2 samples was performed by Raman microscopyThe defect engineering is widely used in 2D heterostructure devices as nanodefects (like atomic vacancies) significantly alter the electronic, mechanical, and optical properties of 2D nanomaterials. Defect inspection on large-area samples at video rates is requisite for semiconductor manufacturing industry. Take molybdenum disulfide (MoS 2 ) as the study case, the differential reflectance spectroscopy (DRS) is first introduced into nanodefect quantification of 2D materials. Different densities of defects are induced by ion bombardment and the average interdefect distance L D is calibrated using Raman spectra analysis. The evolutions of several defect-induced DR...

Phonon Scattering in Monolayer Molybdenum Disulfide under Different Defect Concentrations Based on Temperature-Dependent Raman Spectra

“…In order to formulate the effect of defect concentrations, we develop an empirical model based on an allometric function, normalΓ normalp − normald normale = 0.25 σ 0.57 where σ is the defect concentration. The fitting curve is shown in Figure , demonstrating a high level of accuracy.…”

Inspection of Line Defects in Transition Metal Dichalcogenides Using a Microscopic Hyperspectral Imaging Technique

“…The DR spectra consisted of an interference peak P inf and two exciton absorption valleys (assigned to the A and B excitons). 31 The DR of the crack was smaller than the DR of the perfect monolayer MoS 2 , while the DR of the fold was larger. The enhanced or suppressed intensity can be explained by the equivalent layer thickness decrease (increase) of a crack (fold).…”

“…The representative DR curves from defective areas were measured and compared with that from the perfect area (Figure c). The DR spectra consisted of an interference peak P inf and two exciton absorption valleys (assigned to the A and B excitons) . The DR of the crack was smaller than the DR of the perfect monolayer MoS 2 , while the DR of the fold was larger.…”