Femtosecond spectroscopy on MoS<sub>2</sub>flakes from liquid exfoliation: surfactant independent exciton dynamics

Vella, Daniele; Vega‐Mayoral, Victor; Gadermaier, Christoph; Vujičić, Nataša; Borzda, Tetiana; Topolovsek, Peter; Prijatelj, Matej; Tempra, Iacopo; Pogna, Eva A. A.; Cerullo, Giulio

doi:10.1117/1.jnp.10.012508

Cited by 6 publications

(12 citation statements)

References 34 publications

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“…At higher energies, there is a broad contribution due to the C exciton at 2.87 eV. ,, The large (hundreds meV) broadening of the C peak originates from multiple e–h optical transitions in the region of the Brillouin zone (BZ) where VB and CB have the same dispersion. , The asymmetry of the peak is due to an additional contribution of the D excitonic peak centered ∼3.1 eV, with a lower oscillator strength than the C exciton. This peak was assigned to Van Hove singularities or to impurities. , The absorption in Figure a is well fitted by a sum of four Lorentz oscillators (one for each exciton peak).…”

Section: Results and Discussionmentioning

confidence: 94%

“…This peak was assigned to Van Hove singularities 35 or to impurities. 48,49 The absorption in Figure 2a is well fitted by a sum of four Lorentz oscillators (one for each exciton peak).…”

Section: Resultsmentioning

confidence: 99%

“…The asymmetry of the peak is due to an additional contribution of the D excitonic peak centered at 3.1eV [45], with a lower oscillator strength than the C exciton. This peak was assigned to Van Hove singularities [35] or to impurities [46,47]. The absorption in Fig.…”

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confidence: 97%

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Strongly Coupled Coherent Phonons in Single-Layer MoS₂

et al. 2020

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We present a transient absorption setup combining broadband detection over the visible-UV range with high temporal resolution (∼20fs) which is ideally suited to trigger and detect vibrational coherences in different classes of materials. We generate and detect coherent phonons (CPs) in single layer (1L) MoS2, as a representative semiconducting 1L-transition metal dichalcogenide (TMD), where the confined dynamical interaction between excitons and phonons is unexplored. The coherent oscillatory motion of the out-of-plane A ′ 1 phonons, triggered by the ultrashort laser pulses, dynamically modulates the excitonic resonances on a timescale of few tens fs. We observe an enhancement by almost two orders of magnitude of the CP amplitude when detected in resonance with the C exciton peak, combined with a resonant enhancement of CP generation efficiency. Ab initio calculations of the change in 1L-MoS2 band structure induced by the A ′ 1 phonon displacement confirm a strong coupling with the C exciton. The resonant behavior of the CP amplitude follows the same spectral profile of the calculated Raman susceptibility tensor. This demonstrates that CP excitation in 1L-MoS2 can be described as a Raman-like scattering process. These results explain the CP generation process in 1L-TMDs, paving the way for coherent all-optical control of excitons in layered materials in the THz frequency range.Coherent modulation of the optical properties of a material, following impulsive photo-excitation of the lattice, is fundamentally interesting and technologically relevant because it can be used for applications in sensors[1], actuators and transducers [2][3][4], that can be operated at extremely high frequencies (up to several THz[5]). In order to exploit this effect, it is necessary to understand the mechanism underlying the coherent phonon (CP) generation process and to identify the physical parameters (such as the pump pulse photon energy) that allow their efficient excitation. In view of possible device applications, it is of paramount importance to detect the spectral dependence of the CP amplitude, in order to identify in which photon energy window the optical response of the material can be efficiently modulated.We present a novel transient absorption (TA) setup, combining broadband detection from 1.8 to 3eV, with extremely high temporal resolution (∼20fs). This is ideally suited to trigger and detect vibrational coherences in different classes of materials. We use it to generate and detect CPs in 1L-MoS 2 , as a representative semiconducting 1L-transition metal dichalcogenide (TMD). We focus on TMDs because they support strongly bound excitons with unique physical properties, enabling novel applica-tions in optoelectronics and photonics [6][7][8]. However, in TMDs, the dynamical interaction between excitons and phonons, when constrained to 1L, is unexplored.When TMDs are exfoliated down to 1L, they undergo a transition from indirect to direct band gap[9], accompanied by a strong enhancement of the photoluminescence (PL) quantum yie...

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Section: Results and Discussionmentioning

confidence: 94%

“…This peak was assigned to Van Hove singularities 35 or to impurities. 48,49 The absorption in Figure 2a is well fitted by a sum of four Lorentz oscillators (one for each exciton peak).…”

Section: Resultsmentioning

confidence: 99%

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Strongly Coupled Coherent Phonons in Single-Layer MoS₂

et al. 2020

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“…Studies of liquid-phase synthesized TMDs have been presented, but the material was 3–6 monolayers in thickness or greater with a lateral size of ∼100 nm or more and deposited onto a substrate , rather than dispersed in a liquid, where it might interact with surrounding molecules. Liquid dispersions of few-layer black phosphorus and graphene nanosheets have been studied, , as have dispersions of MoS 2 and WS 2 flakes in a solid. , However, to our knowledge, the ultrafast charge properties of MoS 2 flakes in liquid solvents remain unstudied.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast Charge Dynamics in Dispersions of Monolayer MoS₂ Nanosheets

et al. 2017

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Ultrafast charge dynamics in dispersions of MoS2 nanosheets in N-methyl-2-pyrrolidone are reported. Samples were prepared by the ultrasonication-assisted exfoliation of MoS2 powder, resulting in nanosheets that were predominantly monolayer and had an average sheet size of 32.4 ± 0.1 nm. These dispersions were characterized using absorption and photoluminescence spectroscopy, transient photoluminescence measurements, and atomic force microscopy before the ultrafast charge dynamics were studied via transient absorption spectroscopy. The transient absorption spectra exhibited bleach peaks and photoinduced absorption peaks in spectral regions corresponding to both the A and B excitons of MoS2. The growth and decay of the features in the B exciton region were determined largely by the dynamics of the exciton population, while the features in the A exciton region depend on the dynamics of both excitons and trions.

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“…The successful exfoliation in water of MoS 2 was confirmed by the presence of the excitonic peaks characteristic of MoS 2 in its semiconducting 2H phase (Fig. S1D of the Supplementary Material), namely, the A, B, C and D bands locatedat ~670, 610, 450 and 400 nm, respectively, [20,[29][30] in the UV-vis extinction spectra of such dispersions (Figure 1G). It must be noted that nucleotide-stabilized MoS 2 flakes have a notable absorptive capacity in the infrared (wavelength above 800 nm).…”

Section: Characterization Of the Mos 2 Dispersionsmentioning

confidence: 79%

MoS2 flakes stabilized with DNA/RNA nucleotides: In vitro cell response

Cicuéndez

Silva

Santos

et al. 2019

Materials Science and Engineering: C

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Two-dimensional transition metal dichalcogenides (TMDCs), such as MoS 2 and WS 2 , have recently emerged as nanomaterials with potential use in biomedicine. An attractive means to favor their interaction with biological media is the use of proper biomolecules as exfoliating/dispersing agents. Here, MoS 2 flakes were stabilized with different small functional biomolecules such as adenosine monophosphate (AMP), guanosine monophosphate (GMP) and flavin mononucleotide (FMN) through the strong nucleotide−MoS 2 interaction of Lewis acid-base type, rather than just on the weak dispersive and hydrophobic forces commonly associated with the use of many surfactants. The impact of the nucleotide-stabilized MoS 2 flakes on the viability and cell proliferation, on the production of intracellular reactive oxygen species (ROS), and on the preosteoblast differentiation process (early stage) has been also evaluated, as well as the incorporation and intracellular localization of the nanomaterials by MC3T3-E1 and Saos-2 cells. The nucleotide-stabilized MoS 2 flakes were found to exhibit excellent biocompatibility. Furthermore, their incorporation did not affect the integrity of the cell plasma membrane, which makes them ideal candidates for delivering drug/gene directly into cells. The in vitro cell response of tumor cells to these nanomaterials differs from that of undifferentiated cells, which provides the basis for their potential use in cancer therapy.

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Femtosecond spectroscopy on MoS₂flakes from liquid exfoliation: surfactant independent exciton dynamics

Cited by 6 publications

References 34 publications

Strongly Coupled Coherent Phonons in Single-Layer MoS₂

Strongly Coupled Coherent Phonons in Single-Layer MoS₂

Ultrafast Charge Dynamics in Dispersions of Monolayer MoS₂ Nanosheets

MoS2 flakes stabilized with DNA/RNA nucleotides: In vitro cell response

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Femtosecond spectroscopy on MoS2flakes from liquid exfoliation: surfactant independent exciton dynamics

Cited by 6 publications

References 34 publications

Strongly Coupled Coherent Phonons in Single-Layer MoS2

Strongly Coupled Coherent Phonons in Single-Layer MoS2

Ultrafast Charge Dynamics in Dispersions of Monolayer MoS2 Nanosheets

MoS2 flakes stabilized with DNA/RNA nucleotides: In vitro cell response

Contact Info

Product

Resources

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Femtosecond spectroscopy on MoS₂flakes from liquid exfoliation: surfactant independent exciton dynamics

Strongly Coupled Coherent Phonons in Single-Layer MoS₂

Strongly Coupled Coherent Phonons in Single-Layer MoS₂

Ultrafast Charge Dynamics in Dispersions of Monolayer MoS₂ Nanosheets