Fig. 1. (a) Schematic showing the controllable shaping of a spherical Si nanoparticle placed on an ITO/SiO2 or an Au/SiO2 substrate into an ellipsoidal one by using femtosecond laser pulses. (b) Schematic showing the controllable transformation of a spherical Ge nanoparticle placed on an Au/SiO2 substrate into an ellipsoidal one by using femtosecond laser pulses. A spherical Ge nanoparticle placed on an ITO/SiO2 substrate cannot be shaped by femtosecond laser pulses because of melting of the Ge nanoparticle.

Fig. 2. (a) Evolution of the luminescence spectrum with increasing laser power measured for a Si nanoparticle (particle A). (b) Scattering spectra measured for a Si nanoparticle (particle A) before and after the laser irradiation above the threshold. The SEM images before and after the laser irradiation are shown as insets. The polarization of the laser light is indicated by arrows. The length of the scale bar is 100 nm. (c) Evolution of the luminescence spectrum with increasing laser power measured for another Si nanoparticle (particle B). (d) Scattering spectra measured for another Si nanoparticle (particle B) before and after the laser irradiation above the threshold. The SEM images before and after the laser irradiation are shown as insets. The polarization of the laser light is indicated by arrows. The length of the scale bar is 100 nm. (e) Two-dimensional scattering spectra calculated for ellipsoidal Si nanoparticles with fixed dimensions in the XY plane (dx=220  nm, dy=222  nm) and variant dimension in the z direction (dz=190–230  nm). Measured results before and after laser irradiation are indicated with yellow dashed lines. (f) Two-dimensional scattering spectra calculated for ellipsoidal Si nanoparticles with fixed dimensions in the XY plane (dx=214  nm, dy=216  nm) and variant dimension in the z direction (dz=190–230  nm). Measured results before and after laser irradiation are indicated with yellow dashed lines.

Fig. 3. (a) Evolution of the luminescence spectrum with increasing laser power measured for a Ge nanoparticle placed on an ITO/SiO2 substrate. The luminescence images recorded by using a CCD at different laser powers are also provided. (b) Scattering spectra measured for a Ge nanoparticle placed on an ITO/SiO2 substrate before and after the laser irradiation above the threshold. The SEM images before and after the laser irradiation are shown as insets. The length of the scale bar is 100 nm. (c) Evolution of the luminescence spectrum with increasing laser power measured for a Ge nanoparticle placed on an Au/SiO2 substrate. The luminescence images recorded by using a CCD at different laser powers are also provided. (d) Dependence of the luminescence intensity on the polarization angle of the analyzer. The dependence of the laser light intensity on the polarization angle is also provided for reference. (e) Scattering spectra measured for a Ge nanoparticle (particle C) placed on the Au/SiO2 substrate before and after the laser irradiation above the threshold. The SEM images before and after the laser irradiation are shown as insets. The polarization of the laser light is indicated by arrows. The length of the scale bar is 100 nm. (f) Scattering spectra measured for another Ge nanoparticle (particle D) placed on the Au/SiO2 substrate before and after the laser irradiation above the threshold. The SEM images before and after the laser irradiation are shown as insets. The polarization of the laser light is indicated by arrows. The length of the scale bar is 100 nm.

Fig. 4. (a) Optical force induced on a Ge nanoparticle by femtosecond laser pulses. (b) Evolution of the temperature calculated inside the Ge nanoparticles (d=134  nm and 184 nm) placed on an ITO/SiO2 substrate and an Au/SiO2 substrate within one laser pulse period. Transient temperature distributions in the XZ plane (corresponding to one laser pulse excitation) calculated for a Ge nanoparticle (d=134 nm and 184 nm) placed on an ITO/SiO2 substrate and an Au/SiO2 substrate, as shown in the insets (i) and (ii), respectively. (c) Scattering spectra measured for four different Ge nanoparticles irradiated by laser light above the threshold. The corresponding SEM images of the Ge nanoparticles are provided. The length of the scale bar is 100 nm. (d) Scattering spectra measured for a Ge nanoparticle irradiated by laser light above the threshold for different rounds. The corresponding SEM images of the Ge nanoparticle are provided.

Fig. 5. (a) Schematic showing the measurements of the forward scattering spectra of a Ge nanoparticle placed on an Au/SiO2 substrate by using polarized white light. (b) Simulated and measured scattering spectrum of an ellipsoidal Ge nanoparticle under unpolarized white light. The dimensions of the Ge nanoparticle extracted from SEM image in the x, y, and z directions are assumed to be dx=293  nm, dy=220  nm, and dz=121  nm, respectively. The simulated and measured forward scattering spectra under polarized white light with different polarization angles are shown in (c) and (d), respectively. The length of the scale bar is 100 nm.