Ultrahigh Spatiotemporal-resolved Investigation On Surface Electrons Of Metal And Two-dimensional Materials

In the past few years,the developments of ultrahigh spatiotemporal-resolved measurement technology and novel two-dimensional materials,have inject new vitality to nanophotonics.Among them,the nanoscale near-field optical properties and carrier dynamics of two-dimensional materials have drawn widely attention.Surface plasmon resonances,as a typical research object of near-field optics,have drawn many interests in their nanofemto evolutions of localized field and angular momentum.In addition,two-dimensional materials,especially graphene-like transition metal dichalcogenides,have been favored due to their excellent photoelectric properties.The two-dimensional properties also provide ideal platform for the investigation of surface physics,and they are suitable for the investigation of light and matter interaction in two-dimensional scale.The ultrahigh spatiotemporal-resolved photoemission electron microscopy has both the characteristics of ultrafast optics and surface electron detection,and is a strong tool for the investigations of surface and interface physics of nanophotonic stuctures.This thesis includes the setup of spatiotemporal-resolved system,the investigation on the correlation of near-field enhancement and dephasing of localized surface plasmon resonances,the investigation of carrier dynamics of two-dimensional transition metal dichalcogenides in multiple dimensions,and the outlook of light and matter interaction in two-dimensional scale.The main results are as follows:1.Setup of ultrahigh spatiotemporal-resolved system based on photoemission electron microscopyTo investigate the ultrafast carrier dynamics of surface plasmon resonances,we set up the interferometric pump-probe optical system based on few-cycle laser source,and the nanofemto evolution of surface plasmons can be realized.To investigate the ultrafast carrier dynamics of two-dimensional materials,we set up the multiple wavelength-tunable pumpprobe system based on 100 fs' laser source,and the carrier dynamics can be probed in multiple dimensions by combining with spatial and energy resolution of photoemission electron microscopy.In addition,we set up the pump-probe system using few-cycle laser pulses and their second harmonic pulses,to realize the two-color pump-probe measurements in 100 fs.2.Investigation of the correlation of near-field enhancement and dephasing time of plasmonic dimersNear-field enhancement and dephasing time are two key parameters of localized surface plasmon resonances.Here,using a coupling system,gold dimers,we obtain near-field enhancement and dephasing time of the same structures through excitation wavelengthdependent photoemission measurements and few-cycle interferometric pump-probe measurements.The correlation between the two parameters depends on the gap sizes of dimers.The polarizations of light can be used to choose modes and change near-field enhancement and dephasing time.This correlation is determined by near-and far-field coupling and plasmon localization.3.Investigation of the ultrafast electron cooling and decay in two-dimensional transition metal dichalcogenidesWe observe the hot carrier dynamics in monolayer WS2 from time,space and energy dimensions,by using two-color pump-probe measurements.We attribute the fast and slow components of dynamics to electron cooling and defect trapping,through the analysis of energy band and the characterization of far-field photoluminescence and Raman spectra.Our research demonstrates the important role of defect trapping in photoemission experiments.These works demonstrate the power of ultrahigh spatiotemporal photoemission electron microscopy in nanophotonics,and can be extended to investigate light and matter interaction in two-dimensional scale.