Scanning electrochemical microscopy imaging with laser-pulled probes

Abstract

The fabrication of Pt nanoelectrodes (NEs) and ultramicroelectrodes (UMEs) were explored through the use of a precision laser electrode puller. As a result of the heated pull, the Pt tips of the NEs were exposed immediately during the fabrication process. Newly fabricated NEs were immediately used to observe the topographical and electrochemical characteristics of a TEM grid by scanning electrochemical microscopy (SECM) horizontal line scans. While higher spatial resolution would be offered by NEs, their use in imaging can be restricted due to sample size and instrumental limitations. To accurately characterize an independently addressable microband electrode (IAME) by SECM, a Pt UME of a known size and geometry was used. SECM depth scan and constant height images were obtained of an unbiased IAME. By utilizing a SECM probe that is similar in size to the Pt and glass microbands of the IAME (4.4 vs. 5μm, respectively), redox cycling phenomenon was detected. From these electrochemical images, the Pt microbands appeared to be larger than their physical dimensions, while the glass microbands appeared much smaller. Since redox cycling can be affected by sample tilt, the tilt angle of the IAME was quantified through 3 different methods. The first approach was to use the traditional PAC comparison method over different locations on the sample, while the second and third approaches relied heavily on 3D finite elemental analysis simulations representative of the SECM experiments. The first of these two methods required the fitting of a tilted experimental horizontal sweep against a fixed IAME, while the second approach relied on the direct fitting of the experimental data onto tilted depth scan simulations. Each methodology delivered approximately the same tilt angle, confirming the viability of all the methodologies.