High-accuracy physical optics calculation methods used in the “Synchrotron Radiation Workshop” (SRW) allow for multiple applications of this code in different areas, covering development, commissioning, diagnostics and operation of X-ray instruments at light source facilities. This presentation focuses on the application of the SRW code for the simulation of experiments at these facilities. The most complete and most detailed simulation of experiments with SRW is possible in the area of elastic coherent scattering, where the interaction of radiation with samples can be described with the same transmission-type “propagators” that are used for the simulation of fully- and partially-coherent radiation propagation through X-ray optical elements of beamlines. A complete “source-to-detector” simulation of such an experiment for a lithographic sample is described here together with comparisons of the simulated coherent scattering data with actual measurements results, obtained at the Coherent Hard X-ray (CHX) beamline of the National Synchrotron Light Source II (NSLS-II). Particular attention is paid to the analysis of visibility of speckles and intensity levels in the scattered radiation patterns at different degrees of coherence of the radiation entering the sample.
The paper presents an overview of the main functions and new application examples of the “Synchrotron Radiation Workshop” (SRW) code. SRW supports high-accuracy calculations of different types of synchrotron radiation, and simulations of propagation of fully-coherent radiation wavefronts, partially-coherent radiation from a finite-emittance electron beam of a storage ring source, and time-/frequency-dependent radiation pulses of a free-electron laser, through X-ray optical elements of a beamline. An extended library of physical-optics “propagators” for different types of reflective, refractive and diffractive X-ray optics with its typical imperfections, implemented in SRW, enable simulation of practically any X-ray beamline in a modern light source facility. The high accuracy of calculation methods used in SRW allows for multiple applications of this code, not only in the area of development of instruments and beamlines for new light source facilities, but also in areas such as electron beam diagnostics, commissioning and performance benchmarking of insertion devices and individual X-ray optical elements of beamlines. Applications of SRW in these areas, facilitating development and advanced commissioning of beamlines at the National Synchrotron Light Source II (NSLS-II), are described.
X-ray Absorption Near Edge Structure (XANES) imaging, an advanced absorption spectroscopy technique, at the Transmission X-ray Microscopy (TXM) Beamline X8C of NSLS enables high-resolution chemical mapping (a.k.a. chemical composition identification or chemical spectra fitting). Two-Dimensional (2D) chemical mapping has been successfully applied to study many functional materials to decide the percentages of chemical components at each pixel position of the material images. In chemical mapping, the attenuation coefficient spectrum of the material (sample) can be fitted with the weighted sum of standard spectra of individual chemical compositions, where the weights are the percentages to be calculated. In this paper, we first implemented and compared two fitting approaches: (i) a brute force enumeration method, and (ii) a constrained least square minimization algorithm proposed by us. Next, as 2D spectra fitting can be conducted pixel by pixel, so theoretically, both methods can be implemented in parallel. In order to demonstrate the feasibility of parallel computing in the chemical mapping problem and investigate how much efficiency improvement can be achieved, we used the second approach as an example and implemented a parallel version for a multi-core computer cluster. Finally we used a novel way to visualize the calculated chemical compositions, by which domain scientists could grasp the percentage difference easily without looking into the real data.
This paper presents the advance in spectroscopic imaging technique and analysis method from the newly developed
transmission x-ray microscopy (TXM) at the beamline X8C of National Synchrotron Light Source. Through leastsquares
linear combination fitting we developed on the in situ spectroscopic images, a time-dependent and spatially
resolved chemical composition mapping can be obtained and quantitatively analyzed undergone
chemical/electrochemical reactions. A correlation of morphological evolution, chemical state distribution changes and
reaction conditions can be revealed. We successfully applied this method to study the electrochemical evolution of CuO,
an anode material of Li-ion battery, during the lithiation-delitiation cycling.
Full field transmission x-ray microscopy (TXM) is a newly developed x-ray imaging technique to provide quantitative
and non-destructive 3D characterization of the complex microstructure of materials at nanometer resolution. A key
missing component is an in situ apparatus enabling the imaging of the complex structural evolution of the materials and
to correlate the structural change with a material’s functionality under real operating conditions. This work describes the
design of an environmental cell which satisfies the requirements for in situ TXM studies. The limited space within the
TXM presents a spatial constraint which prohibits the use of conventional heaters, as well as requiring consideration in
designing for safe and controlled operation of the system and alignment of the cell with the beam. A gravity drip-fed
water cooling jacket was installed in place around the heating module to maintain critical components of the microscope
at safe operating temperatures. A motion control system consisting of pulse width modulated DC motor driven XYZ
translation stages was developed to facilitate fine alignment of the cell. Temperature of the sample can be controlled
remotely and accurately through a controller to temperatures as high as 1200 K. Heating zone measurement was carried
out and shows a 500 x 500 x 500 μm3 homogeneous zone volume for sample area, which is a critical parameter to ensure
accurate observation of structural evolution at nanometer scale with a sample in size of tens of microns. Application on
Ni particles for in situ oxidation experiment and dehydrogenation of aluminum hydride is also discussed.