Tip Recycling for Atomic Force Microscopy-Based Tip-Enhanced Raman Spectroscopy

Abstract

Tip-enhanced Raman spectroscopy (TERS) is a powerful tool for the characterization of surfaces and two-dimensional materials, delivering both topographical and chemical information with nanometer-scale spatial resolution. Atomic force microscopy (AFM)–TERS combines AFM with a Raman spectrometer and is a very versatile technique, capable of working in vacuum, air, and liquid, and on a variety of different samples. A metalized AFM tip is necessary in order to take advantage of the plasmonic enhancement. The most commonly used metal is Ag, thanks to its high plasmonic activity in the visible range. Unfortunately, though, the tip metallization process is still challenging and not fully reliable, yielding inconsistent enhancement factors even within the same batch of tips; as a consequence, many tips are usually prepared at once (for a single experiment), to ensure that at least one of them is sufficiently active. As the lifetime of an unprotected, Ag-coated plasmonic probe is only a few hours, the procedure is inefficient and results in a substantial waste of materials and money. In this work, we establish a cleaning routine to effectively re-use Ag-coated AFM–TERS probes, drastically reducing costs without compromising the quality of the experimental results.