Edge and confinement effects allow in situ measurement of size and thickness of liquid-exfoliated nanosheets

Abstract

Two-dimensional nanomaterials such as MoS 2 are of great interest both because of their novel physical properties and their applications potential. Liquid exfoliation, an important production method, is limited by our inability to quickly and easily measure nanosheet size, thickness or concentration. Here we demonstrate a method to simultaneously determine mean values of these properties from an optical extinction spectrum measured on a liquid dispersion of MoS 2 nanosheets. The concentration measurement is based on the size-independence of the low-wavelength extinction coefficient, while the size and thickness measurements rely on the effect of edges and quantum confinement on the optical spectra. The resultant controllability of concentration, size and thickness facilitates the preparation of dispersions with pre-determined properties such as high monolayer-content, leading to first measurement of A-exciton MoS 2 luminescence in liquid suspensions. These techniques are general and can be applied to a range of two-dimensional materials including WS 2 , MoSe 2 and WSe 2 .

Electrical, Mechanical, and Capacity Percolation Leads to High-Performance MoS2/Nanotube Composite Lithium Ion Battery Electrodes

“…Statistical analysis of the TEM images showed the lateral nanosheet size to vary from ~100 to ~800 nm with a mean of 332 nm. Measurements of the optical absorbance spectrum (not shown) of the dispersion allowed us to use published metrics 44 to estimate the mean nanosheet length to be ~350 nm, in good agreement with TEM, and a mean nanosheet thickness of ~18 monolayers.…”

Turbulence-assisted shear exfoliation of graphene using household detergent and a kitchen blender

“…Previously, it has been demonstrated that for sonication-exfoliated nanosheets, the thickness appears to scale with nanosheet area. 29,32 This is unfortunate as it makes it difficult to produce large, yet thin, nanosheets. Shown in Fig.…”

“…To address this, we used the method rst described by Paton et al which calibrates the monolayer height using step height analysis. 26,29 Raman spectra were acquired on a Horiba Scientic LabRam HR aer drop casting 60 ml of the dispersion in total in 10 ml aliquots on preheated (150 C) Si/SiO 2 wafers (300 nm oxide). Areas showing thick deposits from the optical micrographs were chosen.…”

Electrochemical Applications of Two-Dimensional Nanosheets: The Effect of Nanosheet Length and Thickness

“…Without the ability to achieve both these tasks, quantifying the geometrical effects is very difficult. However, recently, advances 31,48 in the processing and characterising of nanosheets produced by liquid phase exfoliation (LPE) has made both these tasks more straightforward.…”

“…27,28 However, one basic factor that has not been comprehensively or quantitatively explored is how the performance of nanosheet-containing electrodes depends on the geometry of the nanosheets within. Nanosheet size is known to strongly affect properties such as amphiphilicity 29 and optical behaviour 30,31 simply because of the relationships between sheet dimensions and parameters such as the fraction of edge atoms. As such, we expect nanosheet geometry to be a critical factor in all the applications described above.…”