Coherent diffractive imaging (CDI) and scanning transmission x-ray microscopy (STXM) are two popular microscopy techniques that have evolved quite independently. CDI promises to reach resolutions below 10 nanometers, but the reconstruction procedures put stringent requirements on data quality and sample preparation. In contrast, STXM features straightforward data analysis, but its resolution is limited by the spot size on the specimen. We demonstrate a ptychographic imaging method that bridges the gap between CDI and STXM by measuring complete diffraction patterns at each point of a STXM scan. The high penetration power of x-rays in combination with the high spatial resolution will allow investigation of a wide range of complex mesoscopic life and material science specimens, such as embedded semiconductor devices or cellular networks.

https://science.sciencemag.org/content/sci/321/5887/379.full.pdf

High-Resolution Scanning X-ray Diffraction Microscopy

Fluorescence correlation spectroscopy (FCS) is an experimental technique using statistical analysis of the fluctuations of fluorescence in a system in order to decipher dynamic molecular events, such as diffusion or conformational fluctuations of biomolecules. First introduced by Magde et al to measure the diffusion and binding of ethidium bromide onto double-stranded DNA, the technique has been undergoing a renaissance since 1993 with the implementation of confocal microscopy FCS. Since then, a flurry of experiments has implemented FCS to characterize the photochemistry of dyes, the translational and rotational mobilities of fluorescent molecules, as well as to monitor conformational fluctuations of green fluorescent proteins and DNA molecules. In this review, we present the analytical formalism of an FCS measurement, as well as practical considerations for the design of an FCS setup and experiment. We then review the recent applications of FCS in analytical chemistry, biophysics and cell biology, specifically emphasizing the advantages and pitfalls of the technique compared to alternative spectroscopic tools. We also discuss recent extensions of FCS in single-molecule spectroscopy, offering alternative data processing of fluorescence signals to glean more information on the kinetic processes.

/pdf/fluorescence-correlation-spectroscopy-the-technique-and-its-8ujv0hsulo.pdf

Fluorescence correlation spectroscopy: the technique and its applications

This self-contained, comprehensive book describes the fundamental properties of soft x-rays and extreme ultraviolet (EUV) radiation and discusses their applications in a wide variety of fields, including EUV lithography for semiconductor chip manufacture and soft x-ray biomicroscopy. The author begins by presenting the relevant basic principles such as radiation and scattering, wave propagation, diffraction, and coherence. He then goes on to examine a broad range of phenomena and applications. The topics covered include EUV lithography, biomicroscopy, spectromicroscopy, EUV astronomy, synchrotron radiation, and soft x-ray lasers. He also provides a great deal of useful reference material such as electron binding energies, characteristic emission lines and photo-absorption cross-sections. The book will be of great interest to graduate students and researchers in engineering, physics, chemistry, and the life sciences. It will also appeal to practicing engineers involved in semiconductor fabrication and materials science.

X-Rays and Extreme Ultraviolet Radiation: Principles and Applications

The understanding and management of strain is of fundamental importance in the design and implementation of materials. The strain properties of nanocrystalline materials are different from those of the bulk because of the strong influence of their surfaces and interfaces, which can be used to augment their function and introduce desirable characteristics. Here we explain how new X-ray diffraction techniques, which take advantage of the latest synchrotron radiation sources, can be used to obtain quantitative three-dimensional images of strain. These methods will lead, in the near future, to new knowledge of how nanomaterials behave within active devices and on unprecedented timescales.

Coherent X-ray diffraction imaging of strain at the nanoscale.

Ordering in thin films of block copolymers: Fundamentals to potential applications

The rapid development of new sources of coherent X-rays, such as third-generation synchrotrons, high-harmonic-generation lasers1 and X-ray free-electron lasers2, has led to the emergence of the new field of X-ray coherent science. The extension of coherent methods to the X-ray regime makes possible methods such as coherent diffraction, X-ray photon-correlation spectroscopy, speckle interferometry and ultrafast probing at atomic resolution and femtosecond timescales. Despite rapid improvements in the resolution that conventional X-ray optics can achieve, new methods for manipulating X-rays are required to push this to the atomic scale3. Here we demonstrate a coherent imaging technique that enables us to image the complex field at the focus of an X-ray zone plate without the need for conventional X-ray lenses. There are no fundamental limits on the resolution of this lensless imaging technique other than the wavelength of the X-rays themselves. The ability to characterize the beam with one measurement makes the method ideally suited to characterizing the fields generated by pulsed coherent X-ray sources.

/pdf/diffractive-imaging-of-highly-focused-x-ray-fields-39afxc045w.pdf

Diffractive imaging of highly focused X-ray fields

A measurement of the horizontal coherence function of 7.9 keV radiation from an undulator beam line at the Advanced Photon Source is reported. X-ray diffraction from a phase-shifting mask was used, and the coherence function was measured as a function of the width of beam-conditioning slits in the beam line. The coherence distribution is found to be best described by a Lorentzian function.

/pdf/measurement-of-the-spatial-coherence-function-of-undulator-ums0prab7f.pdf

Measurement of the Spatial Coherence Function of Undulator Radiation using a Phase Mask

We have observed x-ray speckle at grazing incidence from gold-coated films of symmetric diblock copolymers of polystyrene (PS) and polymethylmethacrylate (PMMA). The polymer films consisted of micron-sized islands on a uniform surface. Coherent 6-keV photons were selected by monochromatizing and collimating the x-ray beam from a bending magnet synchrotron source. The visibility of the speckle patterns was enhanced with increasing degrees of spatial coherence of the photons. Speckles due to coherent scattering from islands with length scales up to 100 \ensuremath{\mu}m were clearly identified.

Observation of x-ray speckle by coherent scattering at grazing incidence.

We have demonstrated that x-ray fluorescence correlation spectroscopy, in conjunction with microfocused synchrotron x-ray beams, can be used for elucidating particle dynamics. The dynamics of gold and ferromagnetic colloidal particles and aggregates undergoing both diffusion and sedimentation in water has been studied by measuring the time autocorrelation of the x-ray fluorescence intensity from a small illuminated volume. The dynamical parameters obtained are in excellent agreement with theoretical estimates and other measurements. Potential applications of the technique are discussed. [S0031-9007(97)05208-3]

/pdf/x-ray-fluorescence-correlation-spectroscopy-a-method-for-zr6gdz32vb.pdf

X-ray Fluorescence Correlation Spectroscopy: A Method for Studying Particle Dynamics in Condensed Matter

We have demonstrated that x-ray fluorescence correlation spectroscopy, in conjunction with microfocused synchrotron x-ray beams, can be used for elucidating particle dynamics. The dynamics of gold and ferromagnetic colloidal particles and aggregates undergoing both diffusion and sedimentation in water has been studied by measuring the time autocorrelation of the x-ray fluorescence intensity from a small illuminated volume. The dynamical parameters obtained are in excellent agreement with theoretical estimates and other measurements. Potential applications of the technique are discussed. {copyright} {ital 1998} {ital The American Physical Society}

Z. Cai

Papers

Diffractive imaging of highly focused X-ray fields

Measurement of the Spatial Coherence Function of Undulator Radiation using a Phase Mask

Observation of x-ray speckle by coherent scattering at grazing incidence.

X-ray Fluorescence Correlation Spectroscopy: A Method for Studying Particle Dynamics in Condensed Matter

X-Ray Fluorescence Correlation Spectroscopy: A Method for Studying Particle Dynamics in Condensed Matter