“…Understanding the morphological and chemical properties of soot is critical for improving particle soot emission reduction techniques. Spectroscopy (i.e., Raman spectroscopy [10-12, Fourier-transform infrared spectroscopy [12][13][14], UV-vis spectroscopy [15,16], X-ray photoelectron spectroscopy [12,17,18], and electron energy loss spectroscopy [19,20]) is often used to characterize the chemical features of soot, while the microscopy (i.e., scanning probe microscopy [21][22][23], transmission electron microscopy with high resolution [20,24], transmission electron microscopy with high resolution [25][26][27], SEM [28,29], and helium ion microscopy [30,31]) is used for morphological properties studies. Microscopy creates pictures of the spatial distribution of density, composition, or morphology, whereas spectroscopy determines the chemical composition and physical structures of soot.…”