Apex-Confined Plasmonic Tip for High Resolution Tip-Enhanced Raman Spectroscopic Imaging of Carbon Nanotubes

This paper reports a handy technical scheme to decorate atomic force microscopy (AFM) tips toward tip-enhanced Raman spectros-copy (TERS) applications. The major attraction of these homemade tips lies in that silver decoration can be confined at the apex of commercial tips by the means of an AFM-controlled electrochemical reaction. The reduction of Ag+ occurs in a highly sealed environment to secure the metal coating efficiency. Key factors include silver nitrate solution to provide Ag+, ambient relative humidity and temperature in a humidity cell, electric potential bias, and tip- surface distance. Subsequently, these silver-coated tips are evaluated for TERS measurement of carbon nanotubes (CNTs) so that both morphological and chemical characteristics of CNTs are concurrently obtained. The Raman spectra reveal that our plasmonic tip competently possesses an similar to 30-fold local field signal increase and the corresponding TERS image laterally resolves at the single-pixel level.

Automated summary

This paper presents a convenient technical scheme for enhancing the performance of atomic force microscopy (AFM) tips in tip-enhanced Raman spectroscopy (TERS) applications. The silver decoration on homemade tips is confined to the apex of commercial tips through an AFM-controlled electrochemical reaction. The efficiency of the metal coating is ensured by the reduction of Ag+ in a highly sealed environment. Key factors affecting the process include the use of silver nitrate solution, ambient relative humidity and temperature, electric potential bias, and tip-surface distance. The silver-coated tips are then tested for TERS measurement of carbon nanotubes (CNTs), resulting in simultaneous characterization of the CNTs' morphology and chemical properties. The Raman spectra show that our plasmonic tip exhibits a local field signal increase of approximately 30-fold, and the corresponding TERS image can resolve at the single-pixel level laterally.