Fig. 3: Crystal quality and non-covalent functionalisation of the 2D sheets.

a Raman spectrum of the as-prepared (grey trace) and annealed at 1100 °C (red trace) graphene 2D sheets. Inset: Intensity ratio \(I_{\rm{D}}/I_{\rm{G}}\) versus \(I_{{\rm{D}}{\prime}}/I_{\rm{G}}\) measured for the annealed graphene obtained from fitting three Lorentzian functions to the spectrum. The data are approximated by a linear dependence with a slope close to three²⁹. b Raman spectra of bulk hBN and annealed hBN 2D sheets (circles) and the Lorentzian approximation used to find the position and width of the E_2g mode³⁰. The micrographs in the insets to a, b show the position of the laser spot. Scale bars: 3 μm. c The comparison of the peak position (squares) and FWHM (circles) as a function of the number of layers for the tape exfoliated (open symbols) and acid-assisted exfoliated 2D sheets (light blue symbols) vs. bulk particles (solid symbols). Error bars represent one standard deviation. d Raman spectra of the tape exfoliated (black trace) and acid-assisted exfoliated 2D sheets (green circles) of MoS₂. Inset: The spectrum at around 820 cm⁻¹ attributed to the molybdenum oxide³¹. e The XPS spectrum of graphene (red circles) and graphite (black trace) highlighting the sulfur 2p, carbon 1s, and oxygen 1s levels. f The XPS spectrum of the exfoliated hBN (black squares) and bulk hBN (black curves) highlighting boron 1s, nitrogen 1s, and oxygen 1s levels. The oxygen 1s peaks in e, f were deconvoluted to extract the relative contribution from sulfur bound oxygen. g Electrophoretic mobility of LPE (open symbols) and acid-assisted exfoliated (solid symbols) for graphene (circles) and exfoliated hBN (squares) in the water at different pH. The vertical grey band highlights the isoelectric region for LPE 2D sheets.