Photoluminescence of freestanding single- and few-layer<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mtext>MoS</mml:mtext><mml:mn>2</mml:mn></mml:msub></mml:math>

Scheuschner, Nils; Ochedowski, Oliver; Kaulitz, Anne-Marie; Gillen, Roland; Schleberger, Marika; Maultzsch, Janina

doi:10.1103/physrevb.89.125406

Cited by 254 publications

(200 citation statements)

References 27 publications

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“…Figure 2i shows the map of PL full width at half maximum (FWHM) over the mapped area. The FWHM of the A⁻ peak was found unaffected by the substrate; 21 and we also find a small variation of 115  5 meV over the mapped area. These results indicate that the MoS2 film has been n-type doped, and the origin of the doping could be the polymer residues left behind the transfer process.…”

Section: Resultsmentioning

confidence: 74%

“…These results indicate that the MoS2 film has been n-type doped, and the origin of the doping could be the polymer residues left behind the transfer process. 14,21 Next, single point Raman measurements were carried out on one fixed location in the film (near the center of the mapped area) over a temperature range from RT to 305 °C with a step of 20 °C. Figure 3a shows temperature dependent Raman spectra, showing red-shifts of both E2g and A1g modes with increasing temperature.…”

Section: Resultsmentioning

confidence: 99%

“…19 It has been proposed that charge transfer between the film and the substrate can significantly modify the doping concentration, and influence the optical properties. 14,20,21 These excessive charged carriers may couple with neutral excitons to form trions: A⁻ (negatively charged) and A + (positively charged). 22 Furthermore, the monolayer MoS2 is often grown by CVD and then transferred to another substrate with polymer-assisted transfer processes, leaving behind residuals on the surface of MoS2 which is challenging to be removed.…”

Section: Introductionmentioning

confidence: 99%

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In Situ Monitoring of the Thermal-Annealing Effect in a Monolayer of MoS2

Cao

et al. 2017

Phys. Rev. Applied

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We perform in-situ two-cycle thermal cycling and annealing studies for a transferred CVDgrown monolayer MoS2 on a SiO2/Si substrate, using spatially resolved micro-Raman and PL spectroscopy. After the thermal cycling and being annealed at 305 °C twice, the film morphology and film-substrate bonding are significantly modified, which together with the removal of polymer residues cause major changes in the strain and doping distribution over the film, and thus the optical properties. Before annealing, the strain associated with ripples in the transferred film dominates the spatial distributions of the PL peak position and intensity over the film; after annealing, the variation in film-substrate bonding, affecting both strain and doping, becomes the leading factor. This work reveals that the film-substrate bonding, and thus the strain and doping, is unstable under thermal stress, which is important for understanding the substrate effects on the optical and transport properties of the 2D material and their impact on device applications.

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Section: Resultsmentioning

confidence: 74%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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In Situ Monitoring of the Thermal-Annealing Effect in a Monolayer of MoS2

Cao

et al. 2017

Phys. Rev. Applied

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“…8,9,26 This can be probed by a variety of spectroscopic tools. 8,9,[26][27][28][29][30][31] For example, as an indirect-gap material, bandgap PL in bulk 2H-MoS 2 is very weak because it is a phonon-assisted process and known to have negligible quantum yield. Appreciable PL is observed in FL-MoS 2 and surprisingly bright PL is detected in 1L-MoS 2 , which is indicative of it being a direct-gap semiconductor.…”

Section: -16mentioning

confidence: 99%

Phonon and Raman scattering of two-dimensional transition metal dichalcogenides from monolayer, multilayer to bulk material

et al. 2015

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Two-dimensional (2D) transition metal dichalcogenide (TMD) nanosheets exhibit remarkable electronic and optical properties. The 2D features, sizable bandgaps, and recent advances in the synthesis, characterization, and device fabrication of the representative MoS2, WS2, WSe2, and MoSe2 TMDs make TMDs very attractive in nanoelectronics and optoelectronics. Similar to graphite and graphene, the atoms within each layer in 2D TMDs are joined together by covalent bonds, while van der Waals interactions keep the layers together. This makes the physical and chemical properties of 2D TMDs layer dependent. In this review, we discuss the basic lattice vibrations of monolayer, multilayer, and bulk TMDs, including high-frequency optical phonons, interlayer shear and layer breathing phonons, the Raman selection rule, layer-number evolution of phonons, multiple phonon replica, and phonons at the edge of the Brillouin zone. The extensive capabilities of Raman spectroscopy in investigating the properties of TMDs are discussed, such as interlayer coupling, spin-orbit splitting, and external perturbations. The interlayer vibrational modes are used in rapid and substrate-free characterization of the layer number of multilayer TMDs and in probing interface coupling in TMD heterostructures. The success of Raman spectroscopy in investigating TMD nanosheets paves the way for experiments on other 2D crystals and related van der Waals heterostructures.

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“…Another approach reduces interaction by placing samples over patterned cavities or trenches etched into a supporting substrate [10,11]. Samples prepared using either of these approaches have shown that suspended MoS 2 samples exhibit altered electronic properties from those of MoS 2 supported directly on the substrate, including a photoluminescence blueshift in the optical gap in freestanding monolayer MoS 2 [12] and a 2-to 10-fold improvement in the carrier mobility in suspended MoS 2 [13].…”

Section: Introductionmentioning

confidence: 99%