Images of secondary ion distributions of RB-QD04-0037-01 by ToF-SIMS before pre-sputtering. Images of secondary positive (+) and negative (−) ion distributions of RB-QD04-0037-01 by ToF-SIMS (before pre-sputtering) with its backscattered electron image by SEM. The original particle was crushed into two large pieces during mounting onto In plate, shown as two circles in the SEM image. The left particle was analyzed in this study. The brighter color corresponds to higher concentrations of secondary total ion and specific ion (m/z). Scale bars of ToF-SIMS analysis are 10 μm.