Mechanical exfoliation and layer number identification of MoS
                    <sub>2</sub>
                    revisited

Ottaviano, L.; Palleschi, Stefano; Perrozzi, Francesco; D’Olimpio, Gianluca; Priante, F.; Donarelli, M.; Benassi, P.; Nardone, M.; Gonchigsuren, Munkhsaikhan; Gombosuren, M.; Lucia, Arianna; Moccia, G.; Cacioppo, Onofrio Antonino

doi:10.1088/2053-1583/aa8764

Cited by 113 publications

(102 citation statements)

References 53 publications

(127 reference statements)

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“…Recently, the band gap of semiconductor TMDCs has been exploited to fabricate optoelectronic devices, such as photodetectors [8][9][10][11][12][13][14] and solar cells [15][16][17][18][19]. Photoluminescence studies also demonstrated that a reduction in thickness has a strong effect on the band structure of MoS2 and other semiconductor TMDCs, including a change in the band gap and a thickness mediated direct-toindirect band gap crossover [20][21][22][23][24]. The thickness dependent band gap can have a strong influence on other electrical [25] and optical properties, such as the absorption [25][26][27], and it has been also exploited to fabricate photodetectors where their spectral bandwidth is determined by the number of layers of the semiconductor channel [9,11].…”

Section: Introductionmentioning

confidence: 99%

Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2

et al. 2018

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The research field of two dimensional (2D) materials strongly relies on optical microscopy characterization tools to identify atomically thin materials and to determine their number of layers. Moreover, optical microscopy-based techniques opened the door to study the optical properties of these nanomaterials. We presented a comprehensive study of the differential reflectance spectra of 2D semiconducting transition metal dichalcogenides (TMDCs), MoS2, MoSe2, WS2, and WSe2, with thickness ranging from one layer up to six layers. We analyzed the thickness-dependent energy of the different excitonic features, indicating the change in the band structure of the different TMDC materials with the number of layers. Our work provided a route to employ differential reflectance spectroscopy for determining the number of layers of MoS2, MoSe2, WS2, and WSe2.

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Section: Introductionmentioning

confidence: 99%

Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2

et al. 2018

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“…However, using only optical contrast to distinguish the thickness is not accurate, as the reflectance contrast is not a monotonic function of the layer numbers, and it is easily influenced by non-uniform illumination, contaminations, sample-to-sample variations, etc. [17]. Each sample area has to be verified with AFM before layer identification can proceed [23].…”

Section: Resultsmentioning

confidence: 99%

“…The weak, van der Waals interactions between the layers of the corresponding bulk materials enable atomically thin layers of TMDCs to be isolated easily by mechanical exfoliation. In fact, every new layered 2D material research starts with mechanically exfoliated flakes [17,18]. However, due to the physical nature of the method, the exfoliation results in randomly distributed flakes of various thicknesses in small sizes.…”

Section: Introductionmentioning

confidence: 99%

Facile and Reliable Thickness Identification of Atomically Thin Dichalcogenide Semiconductors Using Hyperspectral Microscopy

et al. 2020

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Although large-scale synthesis of layered two-dimensional (2D) transition metal dichalcogenides (TMDCs) has been made possible, mechanical exfoliation of layered van der Waals crystal is still indispensable as every new material research starts with exfoliated flakes. However, it is often a tedious task to find the flakes with desired thickness and sizes. We propose a method to determine the thickness of few-layer flakes and facilitate the fast searching of flakes with a specific thickness. By using hyperspectral wild field microscopy to acquire differential reflectance and transmittance spectra, we demonstrate unambiguous recognition of typical TMDCs and their thicknesses based on their excitonic resonance features in a single step. Distinct from Raman spectroscopy or atomic force microscopy, our method is non-destructive to the sample. By knowing the contrast between different layers, we developed an algorithm to automatically search for flakes of desired thickness in situ. We extended this method to measure tin dichalcogenides, such as SnS2 and SnSe2, which are indirect bandgap semiconductors regardless of the thickness. We observed distinct spectroscopic behaviors as compared with typical TMDCs. Layer-dependent excitonic features were manifested. Our method is ideal for automatic non-destructive optical inspection in mass production in the semiconductor industry.

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“…This procedure allows one to obtain few microns squared multi and monolayer MoS 2 flakes. MoS 2 exfoliation was carried out as explained in [9]. The number of exfoliations was kept at a minimum in order to avoid a too significant decrease in the lateral size of the layers.…”

Section: Methodsmentioning

confidence: 99%

“…Two-dimensional transition metal dichalcogenides (TMDCs), such as MoS 2 , WSe 2 , and WS 2 , are planar crystals made of one or a limited number of TMDC unit cells, possessing plentiful electronic, optical, mechanical, and chemical properties [7]. As for graphene [8], one can quickly obtain TMDC via the universally known 'scotch tape' mechanical exfoliation method [9,10]. Single-layered TMDCs are described by the formula MX 2 , where M is the transition metal from the fourth and tenth groups of the periodic table and X is a chalcogen (S, Se, or Te).…”

Section: Introductionmentioning

confidence: 99%

Vertically Coupling ZnO Nanorods onto MoS2 Flakes for Optical Gas Sensing

Faglia

Ferroni

et al. 2020

Chemosensors

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Hybrid structures composed of layered one-dimensional (1D) and two-dimensional (2D) materials opened new perspectives and opportunities through the build-up of hetero-junctions with versatile layered structures and led to fascinating fundamental phenomena and advanced devices. We succeeded in depositing by magnetron sputtering vertically aligned 1D ZnO nanorods on 2D MoS2 flakes obtained by exfoliation, preserving the structure of the 2D materials. The photoluminescence (PL) optical properties of the hybrid structure were assessed towards developing a contactless optical chemical sensor.

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Mechanical exfoliation and layer number identification of MoS ₂ revisited

Cited by 113 publications

References 53 publications

Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2

Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2

Facile and Reliable Thickness Identification of Atomically Thin Dichalcogenide Semiconductors Using Hyperspectral Microscopy

Vertically Coupling ZnO Nanorods onto MoS2 Flakes for Optical Gas Sensing

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Mechanical exfoliation and layer number identification of MoS 2 revisited

Cited by 113 publications

References 53 publications

Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2

Thickness-Dependent Differential Reflectance Spectra of Monolayer and Few-Layer MoS2, MoSe2, WS2 and WSe2

Facile and Reliable Thickness Identification of Atomically Thin Dichalcogenide Semiconductors Using Hyperspectral Microscopy

Vertically Coupling ZnO Nanorods onto MoS2 Flakes for Optical Gas Sensing

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Mechanical exfoliation and layer number identification of MoS ₂ revisited