Highlights

Fabrication of Scanning Electrochemical – Atomic Force Microscopy Probes by Atomic Layer Deposition of Aluminum Oxide

Scientific Achievement

This work focused on the development of scanning electrochemical–atomic force microscopy (SECM-AFM) probe fabrication procedures.  SECM-AFM probes consist of an exposed nanoelectrode integrated into the apex of a conventional AFM probe, allowing for simultaneous imaging of surface topography and electrochemical or biological activity.  The primary fabrication obstacle is the localized removal of an insulating film at the probe apex to expose the nanoelecrode.  Dual-beam focused ion beam (FIB) milling is used for this process, as it provides for high resolution removal of the insulating film.

Initial attempts focused on conductive AFM probes coated with 50 nm of Al₂O₃.  FIB milling is used to remove the Al₂O₃ film at the apex and expose the underlying conductive film as the nanoelectrode.  However, successful probe fabrication by this procedure is limited by imprecise milling.  For example, if insufficient Al₂O₃ is removed, the conductive film is not exposed.  Conversely, if excessive material is removed, the probe becomes unnecessarily blunt and exhibits limited spatial resolution.

To address this issue, a nanopillar probe geometry was pursued.  Utilizing the electron-beam induced deposition (EBID) capabilities of the dual-beam FIB, a 60 nm diameter nanopillar is reproducibly deposited onto the apex.  The nanopillar is then coated with a conductive film and an insulating film and then milled in cross-section to expose the conductive film as a nanoelectrode.  This approach provides for reproducible probe and electrode dimensions due to templating by the nanopillar.  Additionally, this approach eliminates the need for precise FIB milling, as the nanopillar can be milled anywhere along its length to expose the nanoelectrode.

Significance

This work has demonstrated an approach for the simple and reproducible fabrication of SECM-AFM probes with dimensions approaching 100 nm, which represents a significant improvement over commonly reported SECM-AFM probes with dimensions of the order of 1 mm.  Such probes provide a route for high resolution imaging of surface topography and electrochemical or biological activity.  Such high resolution imaging has potential applications in areas including corrosion initiation and biological membrane transport.

Future work will focus on further decreasing the dimensions of the fabricated probes.  This will focus on developing a better understanding of the EBID process to minimize the nanopillar dimensions and also minimizing the thickness of the insulating Al₂O₃ film.

Performers