Dynamic imaging of nanoparticles on femtoseconds to minutes time scale at atomic resolution

STM;pump-probe;carbon dots;quantum dots;glassy dynamics

Nguyen, Huy Anquoc

关键词: STM;    pump-probe;    carbon dots;    quantum dots;    glassy dynamics;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/107864/NGUYEN-DISSERTATION-2020.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Almost 40 years since its conception, the excellent atomic resolution of the scanning tunneling microscope (STM) continues to be excavated to develop single-molecule techniques. In the last 20 years, our group has developed and improved the single-molecule absorption scanning tunneling microscopy (SMA--STM) technique that enabled high-resolution imaging of nanoparticles' electron probability density. This method has set the stage for the STM to investigate the optical and electronic properties of nanoparticles, on a particle-by-particle basis, with sub-nanometer and 0.1-eV resolutions. Most recent applications of the technique are the imaging and manipulating of energy transfer in PbS quantum dots, the imaging of polarization-dependent plasmons on gold nanoislands, and the unraveling of the carbon dot's fluorescence mechanism. Building on this success, a femtosecond time-resolved optical setup has been implemented to integrate the extra time dimension to provide a complete picture of (space, time, energy) for any given nanoparticle. The combination of improvements in electronics, tip-etching condition, and nanoparticle deposition techniques made this instrumentation project possible. As a result, we were able to image the individual ultrafast energy relaxation and transfer processes in carbon dots as well as quantum dots with characteristic kinetics consistent with bulk scale measurements.Furthermore, in our study of the glassy dynamics of ultra-thin silica films, we achieved exceptional vibrational energy resolution that enabled us to resolve the dynamics and energy levels of 1-nm vibrating silica clusters. In addition, we were able to classify the five characteristic configurational sampling behaviors and the frequencies at which they appear. Our measurements also showed consistency in configurational and vibrational entropies with thermodynamic models of the glass transition and that the entropies are comparable.