Recent years have witnessed two revolutionary developments in x-ray imaging science. First, large- and small-scale coherent x-ray sources, such as advanced synchrotron sources, x-ray free electron lasers (XFELs) and high harmonic generation (HHG) sources, are under rapid development worldwide. XFELs increase the coherent x-ray flux by nine orders of magnitude, while tabletop HHG represents a coherent version of the Röntgen x-ray tube, with unprecedented spectral coverage from 1 to 100nm, and pulse durations of »fs, making it ideal for capturing the fastest processes relevant to function in a 3D nanosystems. Second, a new approach to x-ray crystallography, known as coherent diffractive imaging (CDI), enables structure determination of non-crystalline specimens and nanocrystals with a resolution limited only by the spatial frequency of the diffracted waves. Moreover, CDI enables simultaneous amplitude and phase contrast imaging. STROBE brings together leading national efforts in CDI using both small- and large-scale coherent x-ray sources, and integrates powerful reconstruction algorithms, fast low noise detectors, and big data handling expertise to perform functional nanoscale imaging with temporal resolutions ranging from femtoseconds to minutes.
II.1) Real-time 3D x-ray imaging of materials with elemental/chemical specificity. STROBE will develop two world leading soft x-ray ptychographic microscopes with wavelength limited resolution (1-5 nm) and chemical/magnetic specificity. To realize this goal, we will harness unique coherent x-ray light sources at Berkeley (ALS, ns time resolution) and Boulder (tabletop HHG, fs time resolution), and combine these with advanced 3D reconstruction algorithms, efficient data handling, fast detectors and ultrastable scanning systems, in order to implement real-time functional nanoscale imaging. These advances will remove the resolution limitations of conventional x-ray microscopy and achieve world-class, real-time 3D x-ray imaging with elemental/chemical specificity, and allow STROBE to capture nano and mesoscale energy, charge and spin transport in inhomogeneous, nanostructured, and interface-dominated systems.
II.2) Pushing the spatial and temporal resolutions of dynamic CDI to the limit. By taking advantage of the extremely short HHG and XFEL pulses, CDI is ideally suited to probe functioning systems at the nanoscale - at multiple sites simultaneously. A new form of CDI - hyperspectral imaging based on ptychography - makes it possible to retrieve an image at several different x-ray wavelengths simultaneously, encoding instantaneous charge and spin information. We will also improve dynamic CDI to achieve spatial resolutions <10 nm and temporal resolutions of ~10 fs. Such a powerful imaging technique with high spatial-temporal resolutions is expected to profoundly expand our understanding of a wide range of dynamic phenomena, ranging from phase transitions, charge transfer, transport, nucleation, melting, superheating, crack and shock formation to lattice and grain boundary dynamics.
II.3) Multimodal and multiscale functional imaging by correlating x-ray CDI with electron microscopy and optical nano-probe. We will take advantage of STROBE’s unique expertise to develop multimodal correlative microscopy. We will combine x-ray CDI with electron microscopy to probe energy and quantum materials at multi-length and multi-time scales. We will also correlate CDI with optical nano-probe to image the dynamics of biological materials. Finally, we will develop common sample holders to study the same specimen using different imaging modalities.