Photoluminescence from Liquid‐Exfoliated WS₂ Monomers in Poly(Vinyl Alcohol) Polymer Composites

Abstract

While liquid phase exfoliation can be used to produce nanosheets stabilized in polymer solutions, very little is known about the resultant nanosheet size, thickness or monolayer content. Here we use semi-quantitative spectroscopic metrics based on extinction, Raman and photoluminescence (PL) spectroscopy to investigate these parameters for WS2 nanosheets exfoliated in aqueous polyvinylalcohol (PVA) solutions. By measuring Raman and PL simultaneously, we can track the monolayer content via the PL/Raman intensity ratio while varying processing conditions. We find the monolayer population to be maximized for a stabilizing polymer concentration of 2 g/L. In addition, the monolayer content can be controlled via the centrifugation conditions, exceeding 5% by mass in some cases. These techniques have allowed us to track the ratio of PL/Raman in a droplet of polymer-stabilized WS2 nanosheets as the water evaporates during composite formation. We find no evidence of nanosheet aggregation under these conditions although the PL becomes dominated by trion emission as drying proceeds and the balance of doping from PVA/water changes. Finally, we have produced bulk PVA/WS2 composites by freeze drying where >50% of the monolayers remain unaggregated, even at WS2 volume fractions as high as 10%.2

Dual nanoparticles effect on the frictional and vibrational dissipation behaviors of polymer‐based water‐lubricated bearing materials

“…The heights of the WS 2 peaks became more pronounced in parallel with the increment of WS 2 content, as shown in Figure 3b. These phenomena are similar to the results of some previous researches 49–54 . Through these characterizations, it can be verified that both TiO 2 and WS 2 nanoparticles were uniformly dispersed inside the polymer.…”

Large-Area WS2 Film with Big Single Domains Grown by Chemical Vapor Deposition

“…Furthermore, the strong PL peak located at 627 nm is in agreement with the reported direct bandgap of ~ 2 eV [ 26 , 27 ]. The full width at half maximum (FWHM) value of ~ 47 meV is close to those from mechanically exfoliated monolayers in previous reports [ 28 , 29 ]. Figure 8 g shows the PL intensity image of the triangular WS 2 monolayer, which exhibits non-uniform emission intensity across the flakes.…”

Spectroscopic metrics allow in situ measurement of mean size and thickness of liquid-exfoliated few-layer graphene nanosheets

“…From the scatter in the data used to generate this metric we estimate the relative error in the extracted values of 〈L〉 to be ∼20%. In contrast to measurements conducted on graphite nanocrystallites produced by heat treatment of diamond-like amor-phous carbon, 49,63,64 we observe a significant D-band of 0.2 even in the case of the samples with mean nanosheet length as large as 800 nm. In the case of the nanocrystallites, a significant D-band only evolved for nanosheets with crystallite sizes of <100 nm.…”