An X-ray microscope uses

electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic field, electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, inf ...

in the soft

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

band to produce images of very small objects. Unlike visible

light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 tera ...

, 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 A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor. CCD sensors are a ...

(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 Paul Kirkpatrick and Albert Baez used

grazing incidence The angle of incidence, in geometric optics, is the angle between a ray incident on a surface and the line perpendicular (at 90 degree angle) to the surface at the point of incidence, called the normal. The ray can be formed by any waves, such as o ...

reflective optics to focus the X-rays, which grazed X-rays off parabolic curved mirrors at a very high angle of incidence. An alternative method of focusing X-rays is to use a tiny

fresnel Augustin-Jean Fresnel (10 May 1788 – 14 July 1827) was a French civil engineer and physicist whose research in optics led to the almost unanimous acceptance of the wave theory of light, excluding any remnant of Newton's corpuscular theo ...

zone plate A zone plate is a device used to focus light or other things exhibiting wave character.G. W. Webb, I. V. Minin and O. V. Minin, “Variable Reference Phase in Diffractive Antennas”, ''IEEE Antennas and Propagation Magazine'', vol. 53, no. 2, ...

of concentric gold or nickel rings on a

silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

substrate. Sir

Lawrence Bragg Sir William Lawrence Bragg, (31 March 1890 – 1 July 1971) was an Australian-born British physicist and X-ray crystallography, X-ray crystallographer, discoverer (1912) of Bragg's law, Bragg's law of X-ray diffraction, which is basic for t ...

produced some of the first usable X-ray images with his apparatus in the late 1940s. In the 1950s

Newberry Newberry is a surname, a variant of Newbury. Notable people with the surname include: * Booker Newberry III (born 1956), American singer and keyboardist * Brennan Newberry (born, 1990), American professional stock car racing driver * Brian Newb ...

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 The General Electric Company (GEC) was a major British industrial conglomerate involved in consumer and defence electronics, communications, and engineering. The company was founded in 1886, was Britain's largest private employer with over 250 ...

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

DESY The Deutsches Elektronen-Synchrotron (English ''German Electron Synchrotron''), commonly referred to by the abbreviation DESY, is a national research center in Germany. It operates particle accelerators used to investigate the structure of matt ...

claimed a record spatial resolution of 10 nm, by using the hard X-ray scanning microscope at PETRA III. 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.

Characteristics and uses

Sources of soft X-rays suitable for microscopy, such as

synchrotron A synchrotron is a particular type of cyclic particle accelerator, descended from the cyclotron, in which the accelerating particle beam travels around a fixed closed-loop path. The magnetic field which bends the particle beam into its closed p ...

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 The proportional counter is a type of gaseous ionization detector device used to measure particles of ionizing radiation. The key feature is its ability to measure the energy of incident radiation, by producing a detector output pulse that is ''prop ...

or an

avalanche photodiode An avalanche photodiode (APD) is a highly sensitive semiconductor photodiode detector that exploits the photoelectric effect to convert light into electricity. From a functional standpoint, they can be regarded as the semiconductor analog of pho ...

. 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 The National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory (BNL) in Upton, New York was a national user research facility funded by the U.S. Department of Energy (DOE). Built from 1978 through 1984, and officially shut down o ...

Brookhaven National Laboratory Brookhaven National Laboratory (BNL) is a United States Department of Energy national laboratory located in Upton, Long Island, and was formally established in 1947 at the site of Camp Upton, a former U.S. Army base and Japanese internment c ...

. The resolution of X-ray microscopy lies between that of the optical microscope and the

electron microscope An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...

. It has an advantage over conventional

electron microscopy An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...

in that it can view biological samples in their natural state. Electron microscopy is widely used to obtain images with nanometer level resolution but the relatively thick living cell cannot be observed as the sample has to be chemically fixed, dehydrated, embedded in resin, then sliced ultra thin. However, it should be mentioned that

cryo-electron microscopy Cryogenic electron microscopy (cryo-EM) is a cryomicroscopy technique applied on samples cooled to cryogenic temperatures. For biological specimens, the structure is preserved by embedding in an environment of vitreous ice. An aqueous sample sol ...

allows the observation of biological specimens in their hydrated natural state, albeit embedded in water ice. Until now, resolutions of 30 nanometer are possible using the Fresnel zone plate lens which forms the image using the soft X-rays emitted from a synchrotron. Recently, the use of soft X-rays emitted from laser-produced plasmas rather than synchrotron radiation is becoming more popular. Additionally, X-rays cause

fluorescence Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...

in most materials, and these emissions can be analyzed to determine the

chemical element A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...

s of an imaged object. Another use is to generate

diffraction Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a s ...

patterns, a process used in

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

. By analyzing the internal reflections of a diffraction pattern (usually with a computer program), the three-dimensional structure of a

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

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.

References

External links

* *
Scientific applications of soft X-ray microscopyNational Center for X-ray Tomography
* {{X-ray science

Microscope A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisibl ...

Microscopy

Development

Notable soft X-ray microscopes

Characteristics and uses

See also

References

External links