Digital operating tip-enhanced Raman spectroscopy

Tip-enhanced Raman spectroscopy (TERS) can investigate structural and optical characteristics of a range of materials with high optical sensitivity. However, it is not widely deployable due to the complicated hardware configuration of atomic-force microscopy (AFM) part, which is required for TERS. Here, we present a digital operating TERS by replacing the conventional instruments, such as a function generator, a lock-in amplifier, and a PID controller, with the digital algorithms in computer to simplify the configuration. We verify the comparable performance of the digital AFM and the conventional analog AFM by performing control experiments, e.g., frequency response curves, approach curves, and topography measurements. In addition, we demonstrate the simple digital processes to decrease the AFM noise level by optimizing the time constant and the data sampling rate. Furthermore, we demonstrate the gap-dependent and time-dependent TERS spectra for brilliant cresyl blue molecules, which confirms the robust acquisition of nano-spectroscopic responses in ambient conditions. This work provides a facile way to easily build tip-enhanced nano-spectroscopy with a compact apparatus.