Characterisation of thin films of graphene–surfactant composites produced through a novel semi-automated method

Abstract

SummaryIn this paper we detail a novel semi-automated method for the production of graphene by sonochemical exfoliation of graphite in the presence of ionic surfactants, e.g., sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB). The formation of individual graphene flakes was confirmed by Raman spectroscopy, while the interaction of graphene with surfactants was proven by NMR spectroscopy. The resulting graphene–surfactant composite material formed a stable suspension in water and some organic solvents, such as chloroform. Graphene thin films were then produced using Langmuir–Blodgett (LB) or electrostatic layer-by-layer (LbL) deposition techniques. The composition and morphology of the films produced was studied with SEM/EDX and AFM. The best results in terms of adhesion and surface coverage were achieved using LbL deposition of graphene(−)SDS alternated with polyethyleneimine (PEI). The optical study of graphene thin films deposited on different substrates was carried out using UV–vis absorption spectroscopy and spectroscopic ellipsometry. A particular focus was on studying graphene layers deposited on gold-coated glass using a method of total internal reflection ellipsometry (TIRE) which revealed the enhancement of the surface plasmon resonance in thin gold films by depositing graphene layers.

Graphene-based LbL deposited films: further study of electrical and gas sensing properties

“…This is quite common observation for thin transparent films, where ' represent changes in the film thickness while < reflects changes in the refractive index. Ellipsometry data fitting based on the Lorenz oscillator model for graphene layers [3] yields the thickness increment of 2.5 nm for PEI/graphene-SDS bilayer which is similar to what was observed directly with AFM.…”

“…sodium dodecyl sulphate (SDS) and cetyl-trimethyl-ammonium bromide (CTAB), as described earlier [2,3]. The resulted two graphenesurfactant composite materials, namely graphene-CTAB, and graphene-SDS (see schematic diagrams in figure 1a, b) appeared to be soluble in both water and some organic solvents, such as chloroform, and thus suitable for both layer-by-layer (LbL) electrostatic deposition and LB (Langmuir-Blodgett) deposition.…”

“…All graphene-surfactant composite films studied before [3] and recently show Ohmic behaviour as illustrated in figure 4. The dependence of the current against the number of PEI/graphene-SDS bi-layers deposited is nonlinear since the surface coverage in the first couple of layers is less then 100%.…”

“…The resulting products, i.e. graphenesurfactant composite materials, have the useful properties of solubility in water and some organic solvents, thus enabling deposition by the simple thin film technologies of Langmuir-Blodgett (LB), spin-coating, and electrostatic layer-by-layer deposition [2,3]. The electric properties of such films must be different from those of pristine graphene exhibiting high conductivity in the range of 10 6 S/cm caused by the large conjugated system of S-electrons with a zero band gap [4,5].…”

Toward Large-Scale Production of Oxidized Graphene

“…therefore cannot be solely relied upon [51]. In this context, we used the full width at half maximum (FWHM) to evaluate the 2D peak.…”