“…Various noninvasive techniques, including Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, nuclear magnetic resonance (NMR), time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and electron energy loss spectroscopy (EELS) are widely employed to characterize the structure of complex organic materials via point analysis and imaging. These techniques are used to probe the speciation and relative quantity of carbon, nitrogen, oxygen, and sulfur. − The advantage of these noninvasive techniques is that unaltered, solid samples can be analyzed, without their decomposition and destruction. Yet, each technique has limitations, and carbon speciation remains challenging due to a multitude of experimental constraints including sample preparation complexity, sample environment, probed depth and sensitivity, and spatial resolution.…”