| The main focus of this dissertation is centered around the study of structural dynamics and phase transition in charge-density waves (CDW) materials. Due to their quasi-reduced dimensionality, a CDW presents a unique system to study the interplay between electron and lattice, effect of symmetry breaking, and electronic condensates. Femtosecond time-resolved pump-probe technique with electron crystallography offers the perfect tool to disentangle the two main players in CDW: electrons and ions. By illumination with intense femtosecond optical pulses to increase the electron energy, we monitor how the energy flows to other subsystems, and explore regions of the energy landscape that are not accessible through conventional methods.;Taking advantages of the uniaxial CDW formation of CeTe3 allows us to differentiate non-CDW-related contributions to the lattice response and isolate the CDW-related structural response from the thermal effects on lattice. From the two-component structural dynamics, we examine how strongly the electron and lattice couple to each other, and further distinguish the internal energy transfer between each charge and lattice subsystems. From this CeTe3 experiment, we provide an explanation to a signature phenomena belonging to "classical Peierls" CDW systems.;Compared to the classical CDW in CeTe3, 1T-TaS2 is at the other end of spectrum with its well decorated phase diagram including almost all flavors of CDW, Mott insulating, and superconducting states. Utilizing femtosecond photo-doping, we explore the energy landscape for states or phases that are not accessible by other conventional means, like chemical doping and pressure induced modification.;The remaining part of this dissertation presents the journey we embarked on when trying to unveil the mystery of water, the ubiquitous molecule that sustains life on earth. Utilizing water delivery system designed specifically for our ultra-high-vacuum chamber, we explore the structural change near the water phase boundary and carrier redistribution or diffusion at the water/nanoparticle/silicon interface. |
