Np-Dimer Lab Report

Second, we further studied the continuous rotation dynamics of NP-dimers with increasing asymmetries, and observed a full transition picture from the conventional diffusive to superdiffusive rotation, and further to ballistic rotation. Because a better statistic is needed for revealing this transition picture, we performed the following experiments in the continuous e-beam imaging mode where each experiment could contain hundreds to thousands of data points. Presented in Fig. 4A are the typical snapshots of a NP-dimer (D1), with two NPs in similar diameters of 60 and 67 nm (with ratio 1:1.1), respectively, at different fs-laser illumination times (repetition rate 1kHz; fluence 2.4 mJ/cm2) (see the trajectory in Fig. S6 and Movie S2). Notably, at this low fluence, the continuous motion is induced by the accumulation of the repeated pulse heating, as the heating from one single pulse is insufficient. Before illumination, the NP-dimer is stabilized in the liquid cell by the weak substrate attraction (first image of Fig. 4A). Evidently, upon excitation, the NP-dimer shows distinct …show more content…
S8 and also Movie S3 and S4), typical anomalous rotation dynamics begin to emerge (Fig. 4B and C). The diameters of the two NPs for D2 and D3 dimers are 60 and 80 nm (with ratio 1:1.3), and 60 and 90 nm (with ratio 1:1.5), respectively, as shown by the inset images in Fig. 4C. It is interesting to find that the angular displacement distribution of D2 dimer strongly biases to the negative side (second column of Fig. 4B), indicating a much higher probability of clockwise rotation than that of counter-clockwise rotation. In sharp contrast, the angular displacement of D3 dimer totally distributes at the positive side (third column of Fig. 4B), representing a unidirectional counter-clockwise rotation with random step length, where the photoinduced impulsive torques are unidirectional but random in