Nanocrystalline diamond AFM tips for chemical force spectroscopy: fabrication and photochemical functionalization†

The chemical modification of nanocrystalline diamond (NCD) atomic force microscope (AFM) tips was investigated and used for chemical force spectroscopy (CFS). In contrast to common chemical modification routes for gold or silicon AFM tips, this method creates stable C–C bonding to attach functional moieties to the NCD tip. There have been no previous studies reporting the chemical functionalization of NCD AFM tips. In this study, hydrogen-terminated NCDs (H-NCDs) were deposited on both silicon wafers and silicon AFM tips and subsequently subjected to a photochemical reaction with undecylenic acid (UA) to create UA attached to NCD surface (UA-NCD). The UA-NCD on wafers were used for surface analyses (water contact angle, attenuated total reflectance-Fourier transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) measurements) to confirm the chemical modification. The UANCD AFM tips were subjected to fluorescent labelling to confirm the existence of carboxylic acid on the tip and AFM adhesion measurements to assess their performance as a probe for the detection of chemical species on surfaces. These results indicate the promising ability of this method to serve as an ideal platform for CFS, which requires robust chemical functionalities on the AFM tip surfaces.