Deciphering the alignment of vertically aligned multi-walled carbon nanotubes in wet state using surface enhanced Raman spectroscopy

Vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) display a structural transformation when transitioning from dry to wet states, often collapsing into angled conical structures. This study probes whether such a transition arises inherently from liquid immersion or because of the drying process. Utilizing Surface Enhanced Raman Spectroscopy (SERS) with gold caps on VA-MWCNTs tips, deposited through a modified Glancing Angle Deposition (GLAD) technique, and Rhodamine 6 G as a molecular probe, we analyze the alignment dynamics of VA-MWCNTs between their wet and dry states. Comparative SERS data from freshly immersed and previously wetted-dried VA-MWCNTs revealed superior Raman enhancement in the angled conical structures. Hence, we conclude that the nanotubes largely retain their vertical stance in liquid environments but undergo an irreversible deformation during the drying process due to (partial) MWCNT severance from the substrate base. This insight is pivotal for applications sensitive to VA-MWCNTs' wet-dry transitions.