Fig. 5: Mapping Molecular Information of Nanothin Materials on Silicon.
a Height map of a 4 nm thick PMMA film on Silicon. b Closed-loop (CL) baseline corrected infrared maps of 1732 and 1850 cm−1 of the 4 nm film collected off resonance at 500 kHz. c Same measurement as (b) collected at 460 kHz near the cantilever’s 3rd resonance mode. d Magnitude of the PMMA film signal extracted from CL hyperspectral images compared to FTIR. CL image contrast recorded near cantilever resonance had increased sensitivity (i.e., lower substrate noise) but also additional signal uncorrelated with the local PMMA absorption which was attributed to photo-induced sample acoustics. e Comparison of CL and OL maps at 1732 cm−1. Line profiles reveal improved signal to noise ratio (SNR) for CL operation. The color scale for the OL measurement was scaled by a factor of 2 due to the increase noise. f Same maps as (e) using previous state-of-the-art Resonance Enhanced (RE) and Photo Thermal Induced Resonance (PTIR) methods. For RE measurements, the 3rd resonance mode was tracked using the commercial Nano-IR2 software. Overall this slowed acquisition time down by a factor of 2.5 in addition to worse performance when compare to CL. For PTIR measurements, coaveraging was set to produce a pixel rate equivalent to the CL and OL measurements.
