Graphene oxide (GO) is the oxidized form of graphene. It is a single-atomic-layered material that is formed by the oxidation of graphite which is cheap and readily available. Graphene oxide thin films find usage in many different applications such as optoelectronics and biosensors. Due to oxygen groups, graphene oxide is hydrophilic and thus dispersible to water. Dispersibility makes the solution-based deposition of graphene oxide possible.
One of the biggest advantages of graphene oxide is its dispersibility to water and other organic solvents. This makes it possible to use solution-based deposition methods that are typically less time consuming and lower-cost equipment are needed than for gas-phase deposition. Many of the application for graphene oxide require morphologically well-defined, continuous thin monolayer films to be deposited on large areas. Graphene oxide morphology is difficult to control with most typical solution-based deposition methods such as spin coating or drop-casting. Langmuir-Blodgett method, or LB, in short, has been successfully used to deposit well-defined films of nanoparticles and the method also offers better control over GO deposition.
In the LB method, the graphene oxide monolayer is typically formed at air-water where it is trapped due to amphiphilic nature of the GO. The graphene oxide dispersion which is most often methanol: water mixture is spread on a water surface in a Langmuir-Blodgett trough. Moving barriers are used to compress the monolayer formed at the air-water interface to make a closed-packed monolayer of GO. This monolayer can then be transferred to solid substrate with the help of a dipper.
Langmuir-Blodgett method offers also an additional advantage, as the quality of the thin film can be checked prior to deposition on the solid substrate. This is done with the technique called Brewster angle microscopy. In this method, polarized light is introduced to the interface at Brewster angle which for air-water interface is about 53 degrees. When there is no monolayer, there is no reflection and the image is black. When the laser hits the monolayer, the image is reflected on the detector and seen as white. This method allows a visual inspection of the floating monolayer prior to deposition.
To hear more about the Langmuir-Blodgett method as well as Brewster angle microscopy, please watch the webinar below.
Susanna is an Application Scientist at Biolin Scientific. In her PhD thesis, she developed fabrication methods for a new type of inorganic-organic polymers. Microfabricated polymer chips were utilized as tool for biomolecule separation in analytical chemistry.
