Advances in Scanning Transmission X‐Ray Microscopy for Elucidating Soil Biogeochemical Processes at the Submicron Scale

Abstract

Organic matter, minerals, and microorganisms are spatially associated in complex organo-mineral assemblages within soils. A mechanistic understanding of processes occurring within organo-mineral assemblages requires noninvasive techniques that minimize any disturbance to the physical and chemical integrity of the sample. Synchrotron-based soft (50-2200 eV) X-ray spectromicroscopic techniques, including scanning transmission X-ray microscopy (STXM), transmission X-ray microscopy (TXM), X-ray photoemission electron microscopy (X-PEEM), and scanning photoelectron microscopy (SPEM), coupled with microspectroscopy (e.g., near-edge X-ray absorption fine structure; NEXAFS) allow for determining the spatial association and speciation of most elements found in soils while maintaining sample integrity. This review highlights application of the four spectromicroscopic techniques mentioned above to soil biogeochemical research, with particular emphasis on STXM-NEXAFS, which has contributed to the greatest set of advancements in the understanding of soil organo-mineral interactions, including mineral control on organic carbon cycling and the mechanisms of biomineral formation.

Application of Synchrotron Radiation‐based Methods for Environmental Biogeochemistry: Introduction to the Special Section

“…Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are widely used to obtain information on the arrangement of organo‐mineral associations. Although both of those two approaches are not species sensitive, when coupled to electron‐dispersive X‐ray microscopy or electron energy loss spectroscopy (EELS), these techniques can be used to identify mineral species and/or metal valance ratios, as discussed by Stuckey et al (2017) in this issue. Scanning transmission X‐ray microscopy is a powerful SR‐based technique that uses soft, high‐flux X‐ray photons to map micrometer‐sized environmental samples with nanometer spatial resolution (Jacobsen et al, 2000).…”

“…When STXM is coupled with NEXAFS (STXM‐NEXAFS spectromicroscopy), it can be used for spectral fingerprinting of fine structures. This approach has contributed to the greatest set of advancements in the understanding of soil organo‐mineral interactions in recent years (Stuckey et al, 2017). …”

Additive Nano-Lithography with Focused Soft X-rays: Basics, Challenges, and Opportunities

“…Since synchrotron-based X-ray microscopes offer continuously tunable excitation photon energy, it has been shown that within a multilayer of several photoresists consecutively stacked at the same spot, each layer can be addressed separately by the resonant photon energy of the respective Following the development of suitable focusing optics for soft X-rays [49][50][51], the first soft X-ray microscopes were installed in the mid-1980s [52,53]. Since then, STXM has developed into a versatile method for characterization of suitably thin specimens from various scientific disciplines, such as biology, medicine, catalysis, material science, magnetism, geology, cosmology, and cultural heritage [54][55][56][57][58][59][60][61][62][63][64]. Figure 1 depicts a scheme of a modern STXM with all basic elements and their respective degrees of freedom [59,65,66].…”

Small‐scale distribution of copper in a Technosol horizon studied by nano‐scale secondary ion mass spectrometry

“…Frequently, methods operating at the micrometer scale such as electron‐microprobe analysis (EMPA) or scanning‐electron microscopy (SEM) with energy‐dispersive X‐ray spectroscopy (EDX) have been applied, although individual particles may be present, which are tens to hundreds of nanometers in size. Identifying these particles requires methods operating at the appropriate spatial scale, e.g., transmission‐electron microscopy on samples prepared with a focused ion beam or synchrotron radiation‐based X‐ray spectromicroscopy . Spatially resolved data (maps) obtained by X‐ray spectromicroscopy have been evaluated by image difference, correlation analysis, and principal component analysis‐cluster analysis .…”

“…[3][4][5] Spatially resolved data (maps) obtained by X-ray spectromicroscopy have been evaluated by image difference, correlation analysis, and principal component analysis-cluster analysis. 5,6 Also nano-scale secondary ion mass spectrometry (NanoSIMS) might be an alternative, because its lateral resolution ranges from 50 to 150 nm, and it provides the spatial distribution of ion signals. 7 Thus, like X-ray spectromicroscopic data, NanoSIMS measurements may be similarly evaluated by image analysis to infer the distribution and speciation of elements and species.…”