Reproducible electrochemical etching of silver probes with a radius of curvature of 20 nm for tip-enhanced Raman applications

Abstract

The performance of tip-enhanced Raman spectroscopy (TERS) largely depends on probe optimisation. An electrochemical etch using nitric acid and ethanol produces sharp silver probes with radius of curvature between 20 and 60 nm. Optimisation also identified controllable tapers; rough or smooth. Boundary element method simulations comparing the response to 532 nm excitation of silver and gold probes reveal no discernable field enhancement at the gold apex, but strong localised enhancement is observed at the silver apex. The motivation for employing this method of etching silver probes can also be seen in the signal enhancement observed in preliminary TERS data presented.

Development of a candidate reference sample for the characterization of tip-enhanced Raman spectroscopy spatial resolution

“…a circular Au cathode. [23][24][25] This mechanism was electronically controlled by a homemade feedback circuit that automatically cut the voltage aer the wire drop-off and the tips were formed, standardising the procedure to make it operator-independent in order to obtain apices whose curvature radii were centred around 40 nm, with a dispersion of 10 nm. AFM measurements were performed using the Ntegra SPM, in semi-contact mode in order not to modify the structure of the PMMA, using uncoated NT-MDT VIT-P top visual Si probes (resonant frequency $300 kHz).…”

Tip-enhanced Raman spectroscopy: principles and applications

“…4d) can be prepared by this method with high reproducibility. An electrochemical etching method using nitric acid and ethanol to produce sharp, smooth and reproducible silver TERS probes with a tipapex radius of 20 nm was reported by Lloyd et al [40]. …”

“…Electrochemical etching methods have been implemented by different research groups to obtain sharp and smooth metal tips [38][39][40]. For example, in the electrochemical etching of gold tips, a gold wire acts as the anode and a second electrode (gold or platinum) acts as the cathode (as shown schematically in Fig.…”

Electrochemical fabrication of silver tips for tip‐enhanced Raman spectroscopy assisted by a machine vision system

“…[26] Up to now, the main concern of one step method is how to quickly cut off the circuit once the tip is formed. There were some attempts to improve this method to achieve very sharp tips, [25,[27][28][29][30] but it is still difficult to fabricate high quality (considering the sharpness, roughness and tip profile) silver tips with a high reproducibility. It is very complicated to handle all the factors influencing the EC etching, including the cutoff time, composition of etchant, etching voltage, arrangement of electrodes, temperature and so on.…”