Graphene, despite its exceptional electrical properties, is not suitable as a channel material in field-effect transistors due to its zero band gap. Engineered graphene structures, such as graphene nanoribbons, have been proposed to overcome this limitation. However, nanoribbons, while offering an opened band gap and favourable current on/off ratios, suffer from low individual driving currents. Graphene nanomesh provides a potential solution by maintaining the benefits of nanoribbons while offering higher driving currents due to its two-dimensional structure. However, fabricating graphene nanomesh remains challenging.
This study investigates the fabrication of graphene nanomesh using a transfer-free anodization method with nanoporous anodic alumina as a hard mask in a plasma etching process. Unlike previously published methods, which require the transfer of brittle alumina masks, this work develops a process where anodization is performed directly on aluminium deposited on top of graphene. A two-step anodization process was tested and optimized using aluminium on silicon samples, including the development of a partial stripping variation aimed at preserving pore ordering.
Initial tests on Al-on-Si samples demonstrated promising results, with plasma etching yielding uniform patterns when using the partial stripping technique. However, when applied to graphene samples, significant challenges were encountered. Poor adhesion between aluminium and graphene layers resulted in delamination and bubbling during anodization, disrupting the pore formation process and leading to defects. Efforts to improve adhesion through patterning of the substrate showed no substantial improvements. However, it was confirmed that the Mo and the graphene survived the anodization process.
Although plasma etching produced positive results in regions where delamination was minimized, etching on graphene samples remained inconsistent. Despite these challenges, the study provides valuable insights into the fabrication process, particularly regarding mask stability and adhesion issues.