Fabrication of cone-shaped boron doped diamond and gold nanoelectrodes for AFM–SECM

Abstract

We demonstrate a reliable microfabrication process for a combined atomic force microscopy (AFM) and scanning electrochemical microscopy (SECM) measurement tool. Integrated cone-shaped sensors with boron doped diamond (BDD) or gold (Au) electrodes were fabricated from commercially available AFM probes. The sensor formation process is based on mature semiconductor processing techniques, including focused ion beam (FIB) machining, and highly selective reactive ion etching (RIE). The fabrication approach preserves the geometry of the original AFM tips resulting in well reproducible nanoscaled sensors. The feasibility and functionality of the fully featured tips are demonstrated by cyclic voltammetry, showing good agreement between the measured and calculated currents of the cone-shaped AFM-SECM electrodes.

Miniaturized Wide-Range Field-Emission Vacuum Gauge

“…In the subsequent RIE etching step, only SF 6 is used to etch Si 3 N 4 selectively, exposing the conductive tip, whereby the Cr layer protects the rest of the sample as shown in Figure 1c. The removal of the insulation layers Overall, we fabricated more than 30 devices for field emission as well as electrochemical investigations [10], demonstrating the versatility of this approach. With respect to the miniaturized vacuum gauges, we fabricated four devices with a cathode-anode spacing of about h=500 nm, and two devices with a spacing of about 1 µm.…”

Electrochemical current-sensing atomic force microscopy in conductive solutions

“…The difference between I d,calc and I d,exp could be related to unavoidable errors upon estimation of the geometric parameters, as well as to deviations of the tip shapes from an ideal one [33]. For comparison, I d,calc ≈ 4 × I d,exp was previously obtained for another Au-coated tip [32]. We believe that the removal of titanium oxide from the gold tip, as implemented in our new experiments, comprises the critical step to obtain a better agreement between calculated and experimental currents.…”

“…Based on cyclic voltammetry, we demonstrated that these probes have well-defined conductive tips [32]. Later we carried out a detailed investigation of the insulation (leakage and stability) of the entire chip by a step-wise immersion of the probe into the solution ( figure 3).…”

“…In a second double-coating procedure, we combined the Si 3 N 4 insulation of the probes [32] with an electrochemical post-coating step. After wiring of a Si 3 N 4 -coated probe, EP was deposited on the whole probe surface (except of the tip) and on the electric contact of the probe (see paragraph 2.4).…”

Scanning Electrochemical Microscopy-Atomic Force Microscopy Probes from Pyrolyzed Parylene C

“…A potential is applied between the working and reference electrode that is sufficient to oxidize or reduce a species of interest in solution as the probe operates in contact-AFM mode. A number of SECM-AFM probes, which contain gold [2], platinum [1], carbon nanotubes [3], and borondoped diamond [4,5] as electrode material, have been demonstrated previously. An area that SECM-AFM has yet to be applied is for the detection of neurological species in situ.…”