Soft X-ray microscopy
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An X-ray microscope uses electromagnetic radiation in the soft X-ray band to produce images of very small objects.
Unlike visible light, X-rays do not reflect or refract easily, and they are invisible to the human eye. Therefore, the basic process of an X-ray microscope is to expose film or use a charge-coupled device (CCD) detector to detect X-rays that pass through the specimen. It is a contrast imaging technology using the difference in absorption of soft X-ray in the water window region (wavelength region: 2.34–4.4 nm, photon energy region: 280 – 530 eV) by the carbon atom (main element composing the living cell) and the oxygen atom (main element for water).
Development
Early X-ray microscopes by
In the 1950s Newberry produced a shadow X-ray microscope which placed the specimen between the source and a target plate, this became the basis for the first commercial X-ray microscopes from the General Electric Company.
Notable soft X-ray microscopes
The Advanced Light Source (ALS) in Berkeley, California, is home to XM-1 (http://www.cxro.lbl.gov/BL612/), a full field soft X-ray microscope operated by the Center for X-ray Optics and dedicated to various applications in modern nanoscience, such as nanomagnetic materials, environmental and materials sciences and biology. XM-1 uses an X-ray lens to focus X-rays on a CCD, in a manner similar to an optical microscope. XM-1 held the world record in spatial resolution with Fresnel zone plates down to 15 nm and is able to combine high spatial resolution with a sub-100ps time resolution to study e.g. ultrafast spin dynamics. In July 2012, a group at
The ALS is also home to the world's first soft X-ray microscope designed for biological and biomedical research. This new instrument, XM-2 was designed and built by scientists from the National Center for X-ray Tomography. XM-2 is capable of producing 3-Dimensional tomograms of cells.
Table-top soft X-ray tomography
In contrast to synchrotron-based soft X-ray tomography, lab-based soft X-ray tomography developed by SiriusXT setups offer a compact and easily integratable solution for researchers within laboratory settings. These systems typically utilize laser-driven X-ray sources, with the brightness of the source dependent on the type of target and the power of the laser. Notably, the SXT-100 table-top soft X-ray microscopes represent the only commercially available options in this domain. These microscopes enable the acquisition of soft X-ray tomograms from cryogenically vitrified as well as room temperature samples, employing flat specimen holders such as standard transmission electron microscopy (TEM) grids or glass capillaries.
The SXT-100 system stands out for its versatility, accommodating a variety of specimen formats. For instance, researchers can acquire tomograms on TEM grids, allowing for ±60 degrees range tilt series collected in 1-degree steps within a time frame ranging from under one hour to two hours. In the case of specimens imaged in glass capillaries, the full-tilt tomography may take slightly longer. Resolutions in biological specimens, determined by Fourier Ring Correlations (1/2 Signal-to-Noise ratio), can achieve 55 nm for two-hour tomograms, with the ability to resolve Siemens star lines and spaces as small as 25 nm.
These table-top soft X-ray microscopes enhance the accessibility of high-resolution soft X-ray tomography beyond large-scale facilities. Their integration into currently established correlative light and electron microscopy workflows bridges the resolution gap and significantly improves imaging throughput.
Characteristics and uses
Sources of soft X-rays suitable for microscopy, such as synchrotron radiation sources, have fairly low brightness of the required wavelengths, so an alternative method of image formation is scanning transmission soft X-ray microscopy. Here the X-rays are focused to a point and the sample is mechanically scanned through the produced focal spot. At each point the transmitted X-rays are recorded with a detector such as a proportional counter or an avalanche photodiode. This type of Scanning Transmission X-ray Microscope (STXM) was first developed by researchers at Stony Brook University and was employed at the National Synchrotron Light Source at Brookhaven National Laboratory.
The resolution of X-ray microscopy lies between that of the optical microscope and the
Additionally, X-rays cause fluorescence in most materials, and these emissions can be analyzed to determine the chemical elements of an imaged object. Another use is to generate diffraction patterns, a process used in X-ray crystallography. By analyzing the internal reflections of a diffraction pattern (usually with a computer program), the three-dimensional structure of a crystal can be determined down to the placement of individual atoms within its molecules. X-ray microscopes are sometimes used for these analyses because the samples are too small to be analyzed in any other way.
See also
- Synchrotron X-ray tomographic microscopy
- X-ray microscope
- Electron microscope
References
External links
- Yamamoto Y, Shinohara K (October 2002). "Application of X-ray microscopy in analysis of living hydrated cells". Anat. Rec. 269 (5): 217–23. S2CID 43009840.
- Kamijo N, Suzuki Y, Awaji M, et al. (May 2002). "Hard X-ray microbeam experiments with a sputtered-sliced Fresnel zone plate and its applications". J Synchrotron Radiat. 9 (Pt 3): 182–6. PMID 11972376.
- Scientific applications of soft X-ray microscopy
- National Center for X-ray Tomography
- Arndt Last. "X-ray microscopy". Retrieved 17 October 2012.