Ultrafast Transmission Electron Microscopy Studies On Nanomaterial Dynamics And Surface Plasmons

Base on ultrafast transmission electron microscope(UTEM),the ultrafast structure and electron dynamic,surface plasmons,free electron-near field interaction of carbon nanotubes(CNTs)and silver nanowire had been studied by photon-induced near-field electron microscopy(PINEM),ultrafast electron diffraction and femtosecond resolution electron energy-loss spectroscopy(EELS).More,metallic laser accelerator was proposed and applied in efficiently accelerate electron.It mainly includes the following parts:1.Femtosecond-resolved electron diffraction and EELS measurements were conducted on single-walled CNTs.The experimental results demonstrated that dominant time constants of the dynamic processes were ～1.4 ps for electron-driven lattice expansion,～17.4 ps for thermal phonon-driven lattice expansion associated with electron–phonon coupling.The time-resolved EELS measurements clearly revealed a notable red shift of plasmon peaks by ～100 me V upon femtosecond laser excitation.Different features of charge carrier excitation and relaxation were carefully discussed in correlation with the lattice dynamics of single-walled CNTs.2.The optical polarization dependent dynamic properties of multi-walled CNTs are investigated using UTEM.Lattice contractions in the femtosecond time regime are observed upon excitation of localized azimuthal plasmon by light polarized perpendicular to the tubular axis.The polarization dependence of the plasmon near field was examined using PINEM.The lattice changes resulting from azimuthal plasmon enhance ultrafast alterations in both localized evanescent field and the collective charge excitation,which play critical roles governing the light-mater interaction.These results suggest that ultrafast responses of lattice degrees of freedom in nanomaterials could be essential for understanding the mechanism of surface plasmon enhanced effects.3.Based on PINEM,the surface plasmon near-field distribution of single silver nanowire is directly imaged with nanometer resolution and the near-field structure is analyzed.Single-photon order-selected electron images revealed the wavelike and banded structure of electric equipotential regions for a confined near-field integral associated with typical absorption of photon quanta.Multimodal plasmon oscillations and second-harmonic generation were simultaneously observed,and the polarization dependence of plasmon wavelength and symmetry properties were analyzed.4.Based on silver grating,metallic laser accelerator with high accelerate gradient is proposed.Quantized energy-transfer and strong energy-gain simultaneously observed in the metallic medium interaction.Efficiently and continually accelerate free electrons with low power laser system was achieved.Such strong interaction allowed us to directly imaging the inelastic scattering in real space.The stretched electron spot revealed that both the energy and momentum of incident photon could directly transfer to electron assistance by near field.In bowtie structure metallic laser accelerator,significant nonlinear optical effect is observed,which result to most electrons lies in energy-gain states and greatly enhanced the acceleration performance.