Crystal structure determinations of xenon nanoparticles and X-ray induced transient lattice contraction in the solid-to-plasma transition [electronic resource]
- Kenneth Ramon Ferguson.
- Physical description
- 1 online resource.
- Ferguson, Kenneth Ramon.
- Bucksbaum, Philip H., primary advisor.
- Hastings, Jerome, 1948- advisor.
- Reis, David A., 1970- advisor.
- Stanford University. Department of Applied Physics.
- With the advent of free-electron lasers, the electronic and mechanical properties of single nanoparticles can be studied with intense, femtosecond x-ray bursts. X-ray coherent diffractive imaging techniques on single, non-periodic structures under the `diffraction-before-destruction' principle proves atomic resolution is within reach, but before the full potential of free-electron lasers is realized, a complete understanding of x-ray--matter interaction is of utmost importance. Xenon nanoclusters in the gas phase are ideal model systems for investigating light--matter interactions and x-ray induced electronic and structural effects. The experiments presented in this work were performed on such systems at the Coherent X-ray Imaging (CXI) Instrument of the Linac Coherent Light Source (LCLS). So far, serial femtosecond crystallography (SFX) experiments at the LCLS have been limited to particles larger than 100 nm, but in this study these techniques are extended to investigate nanoparticles 10--30 nm in diameter. In a first experiment, xenon nanoparticles were illuminated with hard x-ray flashes. When properly oriented in the ~100 nm FEL focus, Bragg scattering from the xenon crystals was recorded on a high resolution x-ray pixel array detector. Crystallite size, determined from Bragg peak shape, conform well to known scaling parameters. Structural determinations highlight the `crystal structure problem' for rare gas clusters, and suggest complex growth dynamics. Namely, the xenon cluster crystal structure is highly dependent on particle size, with more observed crystal faults as the particle size is increased. The data suggests a hexagonal close-packed (hcp) structure emerges from stacking faults in the face-centered cubic (fcc) structure of large clusters. All matter irradiated by intense FEL pulses is ionized within femtoseconds. The nanoplasma formation process is crucial for understanding x-ray--matter interactions. In a second experiment, the novel twin bunch operating mode for producing two hard x-ray pulses at the LCLS is utilized to investigate nanoplasma dynamics in 70 nm Xe clusters. An initial hard x-ray pump pulse (~15 fs, 1/3 mJ) isochorically heats the nanocluster and a second hard x-ray probe pulse (~15 fs, 2/3 mJ), delayed by up to 80 fs, probes the state of the nanoplasma. In addition to electronic and structural damage, time-resolved signals show an unexpected lattice contraction as the nanoplasma evolves. This contraction is attributed to the strongly enhanced electron mobility, resulting in a drastic change in bond character.
- Publication date
- Submitted to the Department of Applied Physics.
- Thesis (Ph.D.)--Stanford University, 2016.