Fig. 6.

Probing surface chemistry in situ. (A) Schematic of monolayer formation on Al₂O₃ in PA solution. (B) Individual spectra of ¹⁹F showing the time evolution for a 1-µM solution. The peak around 1.35 MHz can be assigned to protons (¹H) which are known to be ubiquitous on or within the diamond and are not characteristic of the surface chemistry. (C) Real-time monitoring of the ¹⁹F NMR signal amplitude growth in solution for three different PA concentrations shows a decrease in formation rate for lower concentrations. Small markers are measured data points of repeated experiments connected with a vertical line, averaged data are shown with the large points. Data points are fitted with a single exponential. Background signal of a clean, non-Al₂O₃–coated diamond in a 10-µM PA solution shows no ¹⁹F signal. Note that due to the absolute value of the Fourier transformation, the noise floor is always positive.