Non-resonant light scattering in dispersions of 2D nanosheets

Abstract

Extinction spectra of nanomaterial suspensions can be dominated by light scattering, hampering quantitative spectral analysis. No simple models exist for the wavelength-dependence of the scattering coefficients in suspensions of arbitrary-sized, high-aspect-ratio nanoparticles. Here, suspensions of BN, talc, GaS, Ni(OH)2, Mg(OH)2 and Cu(OH)2 nanosheets are used to explore non-resonant scattering in wide-bandgap 2D nanomaterials. Using an integrating sphere, scattering coefficient (σ) spectra were measured for a number of size-selected fractions for each nanosheet type. Generally, σ scales as a power-law with wavelength in the non-resonant regime: σ(λ)∝[λ/〈L〉]−m, where 〈L〉 is the mean nanosheet length. For all materials, the scattering exponent, m, forms a master-curve, transitioning from m = 4 to m = 2, as the characteristic nanosheet area increases, indicating a transition from Rayleigh to van der Hulst scattering. In addition, once material density and refractive index are factored out, the proportionality constant relating σ to [λ/〈L〉]−m, also forms a master-curve when plotted versus 〈L〉.

Equipartition of Energy Defines the Size–Thickness Relationship in Liquid-Exfoliated Nanosheets

“…In most cases, liquid phase exfoliation by sonication has previously been demonstrated and yields dispersions of nanosheets with unaltered chemical composition. 13,19,[22][23][24][25][26][27][28] Here, in all cases but GaS, the crystals were exfoliated in aqueous sodium cholate by tip sonication according to established procedures (see methods). Since GaS is prone to oxidation, it was exfoliated in the solvent NMP using bath sonication.…”

Negative Gauge Factor Piezoresistive Composites Based on Polymers Filled with MoS2 Nanosheets

“…The long tail at high wavelength is indicative of scattering as expected for large nanosheets. 40 Using an integrating sphere to remove the scattering spectrum 41 (red line in figure 1A) yields the true absorbance spectrum (blue) which has the shape expected from MoS2, typified by the A-exciton peak around 670 nm. 41 Using published metrics, 41 we can use this excitonic position as well as the spectral shape to estimate the mean nanosheet thickness and length to be ~5-6 nm and ~240 nm respectively.…”

Liquid Exfoliation of Ni2P2S6: Structural Characterization, Size-Dependent Properties, and Degradation

“…As demonstrated for a range of 2D materials, 19,24,26,36,37 . 37,54,55 The spectra in figure 4A show the extinction coefficients as a function of wavelength, calculated from gravimetric mass determination (see methods) for the different size-selected fractions of the first cascade (for the 2 nd cascade data see SI Figures S9-10). The optical spectra clearly change with the increasing size of the material as indicated by the arrow.…”