Graphene is a 2-dimensional allotrope of carbon in sheet form one atom thick. Extraordinary mechanical, thermal, electrical and optical properties of graphene stimulate ever growing body of research with this material. Most experiments with and applications of graphene require a stable and controllable substrate on which graphene is synthesized or transferred.
Anodic Aluminum Oxide (AAO) has been used in synthesis or modification of graphene in a number of ways:
- As a substrate to either directly grow or to transfer graphene from one substrate to another.
- As a shadow mask to create holes in graphene sheets (‘holey graphene’) or deposit materials onto graphene sheets, generally with a goal of modifying zero bandgap electronic structure of graphene.
- As a filter to extract exfoliated graphene from solutions
AAO as a support for graphene / graphene oxide
AAO as a Mask
- A Graphene Nano Mesh (GNM) was created using AAO as mask. A thin film of AAO grown on Al foil was spin coated with a PMMA layer, the underlying Al was etched away, and the AAO was placed over a reduced graphene oxide (rGO) layer on a Si/ SiO2 After removing the PMMA layer, an O2 plasma etch was used to create holes in the rGO layer. Holes in the rGO correspond to the AAO pores, while the rGO covered by the non-porous portion of the AAO mask the rGO. The defects or holes in the rGO result in a raised bandgap.
- A highly uniform Nano Patterned Graphene (NPG) was created via O2 plasma etch without the PMMA layer by using a ‘floating in water’ technique. Here, a thin film of AAO was separated, kept in solution, and a Si/SiO2 graphene substrate was raised up underneath the AAO, then annealed and the graphene was etched through the AAO pores.
- AAO was used as a mask to create nanoporous graphene, which was then in turn used to chemically etch an Si wafer. The researchers dub this technique ‘GaCE’ (Graphene assisted Chemical Etch) and present it as an alternative to the traditional MaCE (Metal assisted Chemical Etch).
AAO as a Filter
In most of the published research, however, relatively little attention is given to the alumina membranes, in particular to the potential of improving yields and engineering graphene / graphene oxide properties by varying nanoporous alumina geometry and crystal structure.
InRedox anisotropic AAO membranes offer very tight pore size distribution in a broad range of pore sizes (from 2-4 to 100 nm) that are not available with filters from other vendors. Additionally, InRedox membranes can be annealed to change the crystal structure from amorphous alumina to polycrystalline alumina, dramatically extending the pH range.
Contact us for more information about anisotropic AAO membranes.