Time-Resolved Research (X-ray Science Division)

Time-resolved x-ray techniques have been recognized worldwide as a critical tool to investigate the temporal development of non-equilibrium processes responsible for the control of complex materials and processes, as well as real-time evolution of structures on second to picosecond time scales.

In the Time-resolved Research Group, we develop a combination of x-ray scattering, spectroscopy and imaging tools in the time domain and in a pump-probe fashion to explore ultrafast processes (microsecond to 100 picosecond), such as phase transitions in magnetic systems, non-equilibrium phonon dynamics, and propagation of acoustic pulses, strain dynamics of nanoscale ferroelectric switches and nanocrystals, photochemistry in solutions, atomic and molecular physics with high fields, and ultrafast fluid dynamics. On slower time scales from second to ms, we also probe dynamics and kinetics in polymers, nanoparticles and their nanocomposites in either thin film or bulk forms to facilitate development of functional materials and energy-related devices.

Taking advantages of the APS hard x-rays with high brilliance, intensity and unique timing structures, we operate dedicated beamlines specializing in pump-probe, x-ray photon correlation spectroscopy, grazing-incidence x-ray scattering, ultrafast imaging techniques at Sectors 7 and 8 (7-ID, 7-BM, and 8-ID). We conduct x-ray science R&D on ultrafast beamline components, detectors and coherence preserving optics to support the general user and staff research programs.

R&D ACTIVITIES

7-ID-B,C,D: Pump-probe experiments for studying ultrafast structural dynamics far from the equilibrium

At 7-ID, we use synchrotron based ultrafast x-ray scattering, spectroscopy to characterize both local and long-range structures and their changes after the stimulus, which are often laser, electric, and other pump pulse. The uniqueness here is that x rays serve as a direct structural probe of dynamical changes in materials with Å spatial resolution.

Most active pump-probe experiments use laser pulses to generate excitation in materials and systems after which x-rays are used to probe the structural changes. Research in areas from atomic and molecular physics to condensed matter physics, and chemistry have demonstrated the large impact of femtosecond-laser-based time-resolved x-ray studies at 7-ID. Through collaboration with general users of the sector, the research at the sector includes but is not limited to

Probing aligned molecules in strong field generated by laser pulses
Spatiotemporal evolution of laser-generated plasmas
Unfolded acoustic phonons in solid-state thin films
Acoustic oscillations in III-V semiconductor nanowires
Thermal transportation in heterostructures
Transient molecular/solvent structures of halogen atoms in solutions
Nanoscale piezoelectric and multiferroic materials under fast and strong stimulus
Develop timing and synchronization capabilities
R&D to prepare Sector 7 as the future home of the APS Short Pulse X-ray

8-ID-E and 8-ID-I: Kinetics and dynamics in colloids and nanocomposite of soft materials

Complex fluids and nanocomposites are believed to be associated with novel electronic, magnetic, and photonic properties of organic and inorganic components. Even in self-assembly, the structural evolution of the nanocomposites can be extremely dynamic, far from commonly believed near-equilibrium conditions.

We take two experimental approaches to understand the structure of those systems and its transformation: 1) grazing incidence x-ray-scattering (GIXS) in both small-angle (GISAXS) and wide-angle (GIWAXS) for understanding the kinetics, and 2) small-angle x-ray scattering (SAXS) geometry via x-ray photon correlation spectroscopy (XPCS) or x-ray intensity fluctuation spectroscopy (XIFS) to probe equilibrium and nonequilibrium fluctuations in the colloids and nanocomposites. We operate two independent beamlines at 8-ID that provide the two dedicated experimental end stations, 8-ID-E and 8-ID-I. Sector 8 hosts many collaborative scientific programs such as

Kinetics of self-assembly of highly ordered nanostructures and two-dimensional crystals
Block-polymer-based lithography
Organic semiconductors and organic photovoltaic materials
Capillary waves at liquid polymer films
Dynamics and rheology in gels bi-entry of glassy materials
Surface freezing
Photonic crystals
Developing high-quality beamline optics to preserve the coherent flux for supporting user experiments involving XPCS, GISAXS, and GIWAXS:
- vertical focusing
- coherent imaging and scattering
- fast detectors for XPCS application (collaboration with Lawrence Berkeley Lab)

Ultrafast x-ray imaging of fuel sprays (supported by EERE/DOE)

High-pressure, high-speed sprays are an essential technology in many industrial and consumer applications, including fuel injection, inkjet printers, liquid-jet cutting and cleaning systems. In particular, liquid fuel sprays and their atomization and combustion processes have numerous technological applications including energy sources for propulsion and transportation systems including internal combustion engines.

In fuel-spray applications, diesel and gasoline direct-injection systems aim to achieve better fuel efficiency and control of emissions. Both objectives motivate in- and near-nozzle characterization of the fuel flow and the spray formation in order to optimize transient injection and spray characteristics to optimize the operation of internal-combustion engines and improve efficiency and reducing emissions.

At the APS, we have developed ultrafast radiographic and tomographic techniques for probing the fuel distribution and dynamics close to the nozzles of direct-injection diesel and gasoline injectors As a result, a dedicated fuel spray beamline was built at 7-BM (partially supported by funding from EERE/DOE) for hosting this application. Recently, near-nozzle high-pressure and high-speed diesel and biodiesel sprays were imaged for the first time with single-shot x-ray pulses and µm spatial resolution.

The knowledge acquired from x-ray measurements will help to understand the fluid dynamics associated with multiphase turbulent liquid jets on micrometer and nanosecond to microsecond scales. The data can immediately be used for combustion simulations and diagnostics to correlate spray quality with combustion efficiency and emission generation from internal combustion engines.