fig3

Figure 3. UV-Vis absorption spectra and color changes of a 30 mg/L MO solution during magnetic stirring in an Si-coated beaker: (A) without suspended particles; (B) with suspended Al₂O₃ I particles; (C) Schematic illustration of friction-induced excitation of electron-hole pairs in a silicon single crystal by Al₂O₃ particles; (D) Optical micrograph of the silicon single-crystal surface after 10 h of magnetic stirring with Al₂O₃ I particles. (A-D) are adapted with permission from^[36]. Adhering to the CC BY 4.0 agreement. PTFE: Polytetrafluoroethylene; UV-Vis: ultraviolet-visible.