Low Frequency EPR and EMR Point Spectroscopy and Imaging of a Surface

Low frequency electron paramagnetic resonance (LFEPR) spectrometers operating between 100 and 500 MHz typically have large-volume magnets that accommodate large samples. LFEPR spectroscopy with a 2.9 mm diameter surface coil was used to record point spectra and image the spatial distribution of the spin probe 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and electrophotographic toner in printed letters on a flat surface. The location of the surface coil was fixed on the desired location when a spectrum was recorded. The magnetic field of the spectrometer was fixed on the location of the signal and the sample was scanned under the surface coil in parallel trajectories to produce an image of the signal in the letters "LFEPR". We speculate on the utility of this technique to study flat objects such as paintings and illuminated manuscripts with cultural heritage significance.