Cryo scanning transmission x-ray microscope optimized for spectrotomography

Abstract

A cryo scanning transmission X-ray microscope, the cryo-STXM, has been designed and commissioned at the Canadian Light Source synchrotron. The instrument is designed to operate from 100 -4000 eV (λ = 12.4 -0.31 nm). Users can insert a previously frozen sample, through a load lock, and rotate it ±70° in the beam to collect tomographic data sets. The sample can be maintained for extended periods at 92 K primarily to suppress radiation damage, and a pressure on the order of 10 -9 Torr to suppress sample contamination. The achieved spatial resolution (30 nm) and spectral resolution (0.1 eV) are similar to other current soft X-ray STXMs, as demonstrated by measurements on known samples and test patterns. The data acquisition efficiency is significantly more favorable for both imaging and tomography. 2D images, 3D tomograms and 4D chemical maps of automotive hydrogen fuel cell thin sections are presented Introduction:Scanning transmission X-ray microscopy (STXM) is an established imaging technique for investigating the structure and composition of matter at the micro-to nanometer length scale.Briefly, in STXM an X-ray beam is focused down to a small spot onto a sample using optics such as a zone plate (ZP) lens or Kirkpatrick-Baez (KB) mirrors [1-3]. Two dimensional images are compiled from a series of line scans, performed by scanning the sample downstream of the optic(s), or by scanning the optic(s) upstream of the sample. Modern soft X-ray STXMs, such as the ambient-STXM at the Canadian Light Source (CLS, Saskatoon, Canada) spectromicroscopy (SM) beamline 10ID-1 [4], acquire images of sub-micrometer thick specimens with a bright field spatial resolution that is close to diffraction limited [5]: 30 nm half pitch is now considered routine at most facilities. When a STXM is combined with a soft X-ray beamline at a synchrotron, spectromicroscopy is enabled [2]. The focused beam can be held at one spatial location while the photon energy is scanned to perform X-ray absorption near edge spectroscopy (XANES) on a small volume [2]. More often, a series of monochromatic images over a photon energy range of interest is collected, and each pixel in the resulting "image stack" contains a XANES spectrum [6]. Image stacks can be converted into quantitative chemical maps using thickness normalized reference spectra [2]. Soft X-ray STXMs have found applications in diverse fields such as human health [7], agriculture [8], environmental studies [9], nanofabrication [10], and advanced materials [11].The overall form and function of current ZP based STXMs can be traced back to instruments built in the 1980s at the National Synchrotron Light Source (NSLS, Brookhaven National Laboratory, USA) [12,13]. A concise timeline of instrumentation developments from around the

A bidirectional scanning method for scanning transmission X-ray microscopy

“…Unidirectional scanning is a traditional Z-type scanning to avoid backlash error. After scanning one horizontal line, the motor returns to the starting point of the next line and starts again (Huang et al, 2015;Leontowich et al, 2018). In this method, the detected X-ray flux signals are arranged directly in time order to form an image.…”

“…Quick scanning could not only greatly improve the efficiency of experiments, but also reduce sample damage caused by X-ray dose accumulation (Obst et al, 2009). Currently, the fly-scan method greatly reduces the time required for STXM imaging, which enables STXM-based nanotomography and energy-stack imaging (Leontowich et al, 2018). However, with the continuous development of science and technology, the increasing needs of users and emerging complex imaging methods are stimulating the creation of faster scanning technologies for higher-efficiency STXM imaging.…”

“…In STXM, the X-ray beam is typically scanned across the region of interest following a sawtooth path (Schmahl et al, 1995;Kaznatcheev et al, 2007;Takeichi et al, 2016;Leontowich et al, 2018), as Fig. 1(a) shows, and this is called the unidirectional scan pattern.…”

Development of a scanning soft X-ray spectromicroscope to investigate local electronic structures on surfaces and interfaces of advanced materials under conditions ranging from low vacuum to helium atmosphere

“…Synchrotron-radiation-based soft X-ray (SX) microspectroscopy provides a powerful probe for investigating local electronic structures relating to surface phenomena. To date, extensive work on SX microspectroscopic methods has been made for surface analysis (for example, Gü nther et al, 2002;Watts & McNeill, 2010;Leung et al, 2010;Kaulich et al, Ohigashi et al, 2016;Prabu et al, 2018;Leontowich et al, 2018;Lü hl et al, 2019). SX spectromicroscopes can be classified into two types depending on their working principles: full-field microscopes and scanning microscopes.…”

“…On the other hand, with scanning microscopes, e.g. scanning photoelectron microscopes (SPEM) (Gü nther et al, 2002;Abyaneh et al, 2011;Horiba et al, 2011;Bozzini et al, 2015) and scanning transmission X-ray microscopes (STXM) (Watts & McNeill, 2010;Leung et al, 2010;Kaulich et al, 2011;Hitchcock et al, 2012;Ohigashi et al, 2016;Prabu et al, 2018;Leontowich et al, 2018;Lü hl et al, 2019), a focused SX beam is raster-scanned over the sample (actually the sample is two-dimensionally scanned relative to the SX beam) and then each data-point is corrected separately, which results in time-consuming observations, thus an electron analyzer or an integrating X-ray spectral detector can be utilized. Among the scanning microscopes, however, STXM combined with energy-resolved X-ray fluorescence detection (STXM-XRF) (for example, Kaulich et al, 2011;Hitchcock et al, 2012;Bozzini et al, 2015;Lü hl et al, 2019) has high potentiality of simultaneous multi-element mapping for shortening long measurement time effectively.…”