A synchrotron light source is a source of
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 ...
(EM) usually produced by a
storage ring
A storage ring is a type of circular particle accelerator in which a continuous or pulsed particle beam may be kept circulating typically for many hours. Storage of a particular particle depends upon the mass, momentum and usually the charge of t ...
, for scientific and technical purposes. First observed in
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 ...
s, synchrotron light is now produced by storage rings and other specialized
particle accelerator
A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams.
Large accelerators are used for fundamental research in particle ...
s, typically accelerating
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no kn ...
s. Once the high-energy electron beam has been generated, it is directed into auxiliary components such as
bending magnet
A dipole magnet is the simplest type of magnet. It has two poles, one north and one south. Its magnetic field lines form simple closed loops which emerge from the north pole, re-enter at the south pole, then pass through the body of the magnet. T ...
s and
insertion device
An insertion device (ID) is a component in modern synchrotron light sources, so called because they are "inserted" into accelerator tracks. They are periodic magnetic structures that stimulate highly brilliant, forward-directed synchrotron radiati ...
s (
undulator
An undulator is an insertion device from high-energy physics and usually part of a larger
installation, a synchrotron storage ring, or it may be a component of a free electron laser. It consists of a periodic structure of dipole magnets. These c ...
s or
wigglers) in
storage ring
A storage ring is a type of circular particle accelerator in which a continuous or pulsed particle beam may be kept circulating typically for many hours. Storage of a particular particle depends upon the mass, momentum and usually the charge of t ...
s and
free electron laser
A free-electron laser (FEL) is a (fourth generation) light source producing extremely brilliant and short pulses of radiation. An FEL functions and behaves in many ways like a laser, but instead of using stimulated emission from atomic or molecula ...
s.
These supply the strong magnetic fields perpendicular to the beam which are needed to convert high energy electrons into
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...
s.
The major applications of synchrotron light are in
condensed matter physics
Condensed matter physics is the field of physics that deals with the macroscopic and microscopic physical properties of matter, especially the solid and liquid phases which arise from electromagnetic forces between atoms. More generally, the sub ...
,
materials science,
biology
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...
and
medicine
Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pract ...
. A large fraction of experiments using synchrotron light involve probing the structure of matter from the sub-
nanometer
330px, Different lengths as in respect to the molecular scale.
The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re ...
level of
electronic structure
In quantum chemistry, electronic structure is the state of motion of electrons in an electrostatic field created by stationary nuclei. The term encompasses both the wave functions of the electrons and the energies associated with them. Electr ...
to the
micrometer Micrometer can mean:
* Micrometer (device), used for accurate measurements by means of a calibrated screw
* American spelling of micrometre
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; ...
and millimeter level important in
medical imaging
Medical imaging is the technique and process of imaging the interior of a body for clinical analysis and medical intervention, as well as visual representation of the function of some organs or tissues (physiology). Medical imaging seeks to rev ...
. An example of a practical industrial application is the manufacturing of microstructures by the
LIGA
Liga or LIGA may refer to:
People
* Līga (name), a Latvian female given name
* Luciano Ligabue, more commonly known as Ligabue or ''Liga'', Italian rock singer-songwriter
Sports
* Liga ACB, men's professional basketball league in Spain
* Liga ...
process.
Spectral brightness
The primary figure of merit used to compare different sources of synchrotron radiation has been referred to as the "brightness", the "brilliance", and the "spectral brightness," with the latter term being recommended as the best choice by the Working Group on Synchrotron Nomenclature.
Regardless of the name chosen, the term is a measure of the total
flux
Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...
of photons in a given six-dimensional
phase space
In dynamical system theory, a phase space is a space in which all possible states of a system are represented, with each possible state corresponding to one unique point in the phase space. For mechanical systems, the phase space usually ...
per unit
bandwidth (BW).
[
]
The spectral brightness is given by:
:
where
is the photons per second of the beam,
and
are the
root mean square
In mathematics and its applications, the root mean square of a set of numbers x_i (abbreviated as RMS, or rms and denoted in formulas as either x_\mathrm or \mathrm_x) is defined as the square root of the mean square (the arithmetic mean of the ...
values for the size of the beam in the axes perpendicular to the beam direction,
and
are the RMS values for the beam solid angle in the x and y dimensions, and
is the bandwidth, or spread in beam frequency around the central frequency. The customary value for bandwidth is 0.1%.
Spectral brightness has units of time
−1⋅distance
−2⋅angle
−2⋅bandwidth
−1.
Properties of sources
Especially when artificially produced, synchrotron radiation is notable for its:
* High brilliance, many orders of magnitude more than with X-rays produced in conventional X-ray tubes: 3rd generation sources typically have a brilliance larger than 10
18 photons·s
−1·mm
−2·mrad
−2/0.1%BW, where 0.1%BW denotes a bandwidth 10
−3''w'' centered around the frequency ''w''.
* High level of polarization (linear, elliptical or circular)
* High collimation, i.e. small angular divergence of the beam
* Low emittance, i.e. the product of source cross section and solid angle of emission is small
* Wide tunability in energy/wavelength by
monochromatization Monochromatization in the context of accelerator physics is a theoretical principle used to increase center-of-mass energy resolution in high-luminosity particle collisions. The decrease of the collision energy spread can be accomplished without r ...
(sub-electronvolt up to
the megaelectronvolt range)
* Pulsed
light emission
This is a list of sources of light, the visible part of the electromagnetic spectrum. Light sources produce photons from another energy source, such as heat, chemical reactions, or conversion of mass or a different frequency of electromagnetic ener ...
(pulse durations at or below one
nanosecond
A nanosecond (ns) is a unit of time in the International System of Units (SI) equal to one billionth of a second, that is, of a second, or 10 seconds.
The term combines the SI prefix ''nano-'' indicating a 1 billionth submultiple of an SI unit ( ...
, or a billionth of a second).
Synchrotron radiation from accelerators
Synchrotron radiation may occur in accelerators either as a nuisance, causing undesired energy loss in
particle physics
Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) an ...
contexts, or as a deliberately produced radiation source for numerous laboratory applications. Electrons are accelerated to high speeds in several stages to achieve a final energy that is typically in the gigaelectronvolt range. The electrons are forced to travel in a closed path by strong magnetic fields. This is similar to a radio antenna, but with the difference that the relativistic speed changes the observed frequency due to the Doppler effect by a factor
. Relativistic
Lorentz contraction
Lorentz is a name derived from the Roman surname, Laurentius, which means "from Laurentum". It is the German form of Laurence. Notable people with the name include:
Given name
* Lorentz Aspen (born 1978), Norwegian heavy metal pianist and keyboa ...
bumps the frequency by another factor of
, thus multiplying the gigahertz frequency of the resonant cavity that accelerates the electrons into the X-ray range. Another dramatic effect of
relativity is that the radiation pattern is distorted from the isotropic dipole pattern expected from non-relativistic theory into an extremely forward-pointing cone of radiation. This makes synchrotron radiation sources the most brilliant known sources of X-rays. The planar acceleration geometry makes the radiation linearly polarized when observed in the orbital plane, and circularly polarized when observed at a small angle to that plane.
The advantages of using synchrotron radiation for spectroscopy and diffraction have been realized by an ever-growing scientific community, beginning in the 1960s and 1970s. In the beginning, accelerators were built for particle physics, and synchrotron radiation was used in "parasitic mode" when bending magnet radiation had to be extracted by drilling extra holes in the beam pipes. The first
storage ring
A storage ring is a type of circular particle accelerator in which a continuous or pulsed particle beam may be kept circulating typically for many hours. Storage of a particular particle depends upon the mass, momentum and usually the charge of t ...
commissioned as a synchrotron light source was Tantalus, at the
Synchrotron Radiation Center, first operational in 1968. As accelerator synchrotron radiation became more intense and its applications more promising, devices that enhanced the intensity of synchrotron radiation were built into existing rings. Third-generation synchrotron radiation sources were conceived and optimized from the outset to produce brilliant X-rays. Fourth-generation sources that will include different concepts for producing ultrabrilliant, pulsed time-structured X-rays for extremely demanding and also probably yet-to-be-conceived experiments are under consideration.
Bending electromagnets in accelerators were first used to generate this radiation, but to generate stronger radiation, other specialized devices – insertion devices – are sometimes employed. Current (third-generation) synchrotron radiation sources are typically reliant upon these insertion devices, where straight sections of the storage ring incorporate periodic magnetic structures (comprising many magnets in a pattern of alternating N and S poles – see diagram above) which force the electrons into a sinusoidal or helical path. Thus, instead of a single bend, many tens or hundreds of "wiggles" at precisely calculated positions add up or multiply the total intensity of the beam.
These devices are called
wigglers or
undulator
An undulator is an insertion device from high-energy physics and usually part of a larger
installation, a synchrotron storage ring, or it may be a component of a free electron laser. It consists of a periodic structure of dipole magnets. These c ...
s. The main difference between an undulator and a wiggler is the intensity of their magnetic field and the amplitude of the deviation from the straight line path of the electrons.
There are openings in the storage ring to let the radiation exit and follow a beam line into the experimenters' vacuum chamber. A great number of such beamlines can emerge from modern third-generation synchrotron radiation sources.
Storage rings
The electrons may be extracted from the accelerator proper and stored in an ultrahigh vacuum auxiliary magnetic storage ring where they may circle a large number of times. The magnets in the ring also need to repeatedly recompress the beam against Coulomb (
space charge
Space charge is an interpretation of a collection of electric charges in which excess electric charge is treated as a continuum of charge distributed over a region of space (either a volume or an area) rather than distinct point-like charges. Thi ...
) forces tending to disrupt the electron bunches. The change of direction is a form of acceleration and thus the electrons emit radiation at GeV energies.
Applications of synchrotron radiation
*Synchrotron radiation of an electron beam circulating at high energy in a magnetic field leads to radiative self-polarization of electrons in the beam (
Sokolov–Ternov effect
The Sokolov–Ternov effect is the effect of self-polarization of relativistic electrons or positrons moving at high energy in a magnetic field. The self-polarization occurs through the emission of spin-flip synchrotron radiation. The effect was ...
). This effect is used for producing highly polarised electron beams for use in various experiments.
*Synchrotron radiation sets the beam sizes (determined by the
beam emittance
In accelerator physics, emittance is a property of a charged particle beam. It refers to the area occupied by the beam in a position-and-momentum phase space.
Each particle in a beam can be described by its position and momentum along each of ...
) in
electron storage rings via the effects of
radiation damping
Radiation damping in accelerator physics is a way of reducing the beam emittance of a high-velocity charged particle beam by synchrotron radiation.
The two main ways of using radiation damping to reduce the emittance of a particle beam are the us ...
and quantum excitation.
Beamlines
At a synchrotron facility, electrons are usually accelerated by a
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 ...
, and then injected into a
storage ring
A storage ring is a type of circular particle accelerator in which a continuous or pulsed particle beam may be kept circulating typically for many hours. Storage of a particular particle depends upon the mass, momentum and usually the charge of t ...
, in which they circulate, producing synchrotron radiation, but without gaining further energy. The radiation is projected at a tangent to the electron storage ring and captured by
beamline
In accelerator physics, a beamline refers to the trajectory of the beam of particles, including the overall construction of the path segment (guide tubes, diagnostic devices) along a specific path of an accelerator facility. This part is either ...
s. These beamlines may originate at bending magnets, which mark the corners of the storage ring; or
insertion device
An insertion device (ID) is a component in modern synchrotron light sources, so called because they are "inserted" into accelerator tracks. They are periodic magnetic structures that stimulate highly brilliant, forward-directed synchrotron radiati ...
s, which are located in the straight sections of the storage ring. The spectrum and energy of X-rays differ between the two types. The beamline includes X-ray optical devices which control the
bandwidth
Bandwidth commonly refers to:
* Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range
* Bandwidth (computing), the rate of data transfer, bit rate or thr ...
, photon flux, beam dimensions, focus, and collimation of the rays. The optical devices include slits, attenuators, crystal
monochromator
A monochromator is an optical device that transmits a mechanically selectable narrow band of wavelengths of light or other radiation chosen from a wider range of wavelengths available at the input. The name is from the Greek roots ''mono-'', "s ...
s, and mirrors. The mirrors may be bent into curves or
toroid
In mathematics, a toroid is a surface of revolution with a hole in the middle. The axis of revolution passes through the hole and so does not intersect the surface. For example, when a rectangle is rotated around an axis parallel to one of its ...
al shapes to focus the beam. A high photon flux in a small area is the most common requirement of a beamline. The design of the beamline will vary with the application. At the end of the beamline is the experimental end station, where samples are placed in the line of the radiation, and detectors are positioned to measure the resulting
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 ...
, scattering or secondary radiation.
Experimental techniques and usage
Synchrotron light is an ideal tool for many types of research in
materials science,
physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
, and
chemistry
Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...
and is used by researchers from academic, industrial, and government laboratories. Several methods take advantage of the high intensity, tunable wavelength, collimation, and polarization of synchrotron radiation at beamlines which are designed for specific kinds of experiments. The high intensity and penetrating power of synchrotron X-rays enables experiments to be performed inside sample cells designed for specific environments. Samples may be heated, cooled, or exposed to gas, liquid, or high pressure environments. Experiments which use these environments are called ''in situ'' and allow the characterization of atomic- to nano-scale phenomena which are inaccessible to most other characterization tools. ''In operando'' measurements are designed to mimic the real working conditions of a material as closely as possible.
Diffraction and scattering
X-ray diffraction (XRD) and
scattering experiments are performed at synchrotrons for the structural analysis of
crystalline
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, macrosc ...
and
amorphous
In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal.
Etymology
The term comes from the Greek ''a'' ("wi ...
materials. These measurements may be performed on
powders
A powder is a dry, bulk solid composed of many very fine particles that may flow freely when shaken or tilted. Powders are a special sub-class of granular materials, although the terms ''powder'' and ''granular'' are sometimes used to distin ...
,
single crystals
In materials science, a single crystal (or single-crystal solid or monocrystalline solid) is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries.RIWD. "Re ...
, or
thin films
A thin film is a layer of material ranging from fractions of a nanometer ( monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ...
. The high resolution and intensity of the synchrotron beam enables the measurement of scattering from dilute phases or the analysis of
residual stress
In materials science and solid mechanics, residual stresses are Stress (physics), stresses that remain in a solid material after the original cause of the stresses has been removed. Residual stress may be desirable or undesirable. For example, l ...
. Materials can be studied at
high pressure
In science and engineering the study of high pressure examines its effects on materials and the design and construction of devices, such as a diamond anvil cell, which can create high pressure. By ''high pressure'' is usually meant pressures of th ...
using
diamond anvil cell
A diamond anvil cell (DAC) is a high-pressure device used in geology, engineering, and materials science experiments. It enables the compression of a small (sub-millimeter-sized) piece of material to extreme pressures, typically up to around 1 ...
s to simulate extreme geologic environments or to create exotic forms of matter.
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 ...
of
proteins
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
and other macromolecules (PX or MX) are routinely performed. Synchrotron-based crystallography experiments were integral to solving the structure of the
ribosome
Ribosomes ( ) are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA (mRNA) molecules to ...
;
this work earned th
Nobel Prize in Chemistry in 2009
The size and shape of
nanoparticles
A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 1 ...
are characterized using
small angle X-ray scattering
Small-angle X-ray scattering (SAXS) is a small-angle scattering technique by which nanoscale density differences in a sample can be quantified. This means that it can determine nanoparticle size distributions, resolve the size and shape of (monodi ...
(SAXS). Nano-sized features on surfaces are measured with a similar technique,
grazing-incidence small angle X-ray scattering (GISAXS). In this and other methods, surface sensitivity is achieved by placing the crystal surface at a small angle relative to the incident beam, which achieves
total external reflection
Total external reflection is a phenomenon traditionally involving X-rays, but in principle any type of electromagnetic or other wave, closely related to total internal reflection.
Total internal reflection describes the fact that radiation (e.g. ...
and minimizes the X-ray penetration into the material.
The atomic- to nano-scale details of
surfaces
A surface, as the term is most generally used, is the outermost or uppermost layer of a physical object or space.
Surface or surfaces may also refer to:
Mathematics
*Surface (mathematics), a generalization of a plane which needs not be flat
* Sur ...
, interfaces, and
thin films
A thin film is a layer of material ranging from fractions of a nanometer ( monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ...
can be characterized using techniques such as
X-ray reflectivity X-ray reflectivity (sometimes known as X-ray specular reflectivity, X-ray reflectometry, or XRR) is a surface-sensitive analytical technique used in chemistry, physics, and materials science to characterize surfaces, thin films and multilayers.J. ...
(XRR) and
crystal truncation rod (CTR) analysis.
X-ray standing wave (XSW) measurements can also be used to measure the position of atoms at or near surfaces; these measurements require high-resolution optics capable of resolving
dynamical diffraction phenomena.
Amorphous materials, including liquids and melts, as well as crystalline materials with local disorder, can be examined using X-ray
pair distribution function
The pair distribution function describes the distribution of distances between pairs of particles contained within a given volume. Mathematically, if ''a'' and ''b'' are two particles in a fluid, the pair distribution function of ''b'' with respect ...
analysis, which requires high energy X-ray scattering data.
By tuning the beam energy through the
absorption edge An absorption edge, absorption discontinuity or absorption limit is a sharp discontinuity in the absorption spectrum of a substance. These discontinuities occur at wavelengths where the energy of an absorbed photon corresponds to an electronic tran ...
of a particular element of interest, the scattering from atoms of that element will be modified. These so-called resonant anomalous X-ray scattering methods can help to resolve scattering contributions from specific elements in the sample.
Other scattering techniques include
energy dispersive X-ray diffraction,
resonant inelastic X-ray scattering
Resonant inelastic X-ray scattering (RIXS) is an X-ray spectroscopy technique used to investigate the electronic structure of molecules and materials.
Inelastic X-ray scattering is a fast developing experimental technique in which one scatters hi ...
, and magnetic scattering.
Spectroscopy
X-ray absorption spectroscopy
X-ray absorption spectroscopy (XAS) is a widely used technique for determining the local geometric and/or electronic structure of matter. The experiment is usually performed at synchrotron radiation facilities, which provide intense and tunabl ...
(XAS) is used to study the coordination structure of atoms in materials and molecules. The synchrotron beam energy is tuned through the absorption edge of an element of interest, and modulations in the absorption are measured.
Photoelectron
The photoelectric effect is the emission of electrons when electromagnetic radiation, such as light, hits a material. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physics, and solid sta ...
transitions cause modulations near the absorption edge, and analysis of these modulations (called the
X-ray absorption near-edge structure (XANES) or
near-edge X-ray absorption fine structure (NEXAFS)) reveals information about the
chemical state and local symmetry of that element. At incident beam energies which are much higher than the absorption edge, photoelectron scattering causes "ringing" modulations called the
extended X-ray absorption fine structure
Extended X-ray absorption fine structure (EXAFS), along with X-ray absorption near edge structure (XANES), is a subset of X-ray absorption spectroscopy ( XAS). Like other absorption spectroscopies, XAS techniques follow Beer's law. The X-ray a ...
(EXAFS).
Fourier transformation
A Fourier transform (FT) is a mathematical transform that decomposes functions into frequency components, which are represented by the output of the transform as a function of frequency. Most commonly functions of time or space are transformed ...
of the EXAFS regime yields the bond lengths and number of the surrounding the absorbing atom; it is therefore useful for studying liquids and
amorphous
In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal.
Etymology
The term comes from the Greek ''a'' ("wi ...
materials as well as sparse species such as impurities. A related technique,
X-ray magnetic circular dichroism
X-ray magnetic circular dichroism (XMCD) is a difference spectrum of two X-ray absorption spectra (XAS) taken in a magnetic field, one taken with left circularly polarized light, and one with right circularly polarized light. By closely analyzing ...
(XMCD), uses circularly polarized X-rays to measure the magnetic properties of an element.
X-ray photoelectron spectroscopy
X-ray photoelectron spectroscopy (XPS) is a surface-sensitive quantitative spectroscopic technique based on the photoelectric effect that can identify the elements that exist within a material (elemental composition) or are covering its surface, ...
(XPS) can be performed at beamlines equipped with a
photoelectron analyzer. Traditional XPS is typically limited to probing the top few nanometers of a material under vacuum. However, the high intensity of synchrotron light enables XPS measurements of surfaces at near-ambient pressures of gas. Ambient pressure XPS (AP-XPS) can be used to measure chemical phenomena under simulated catalytic or liquid conditions. Using high-energy photons yields high kinetic energy photoelectrons which have a much longer
inelastic mean free path The inelastic mean free path (IMFP) is an index of how far an electron on average travels through a solid before losing energy.
If a monochromatic primary beam of electrons is incident on a solid surface, the majority of incident electrons lose t ...
than those generated on a laboratory XPS instrument. The probing depth of synchrotron XPS can therefore be lengthened to several nanometers, allowing the study of buried interfaces. This method is referred to as high-energy X-ray photoemission spectroscopy (HAXPES). Furthermore, the tunable nature of the synchrotron X-ray photon energies presents a wide range of depth sensitivity in the order of 2-50 nm. This allows for probing of samples at greater depths and for non destructive depth-profiling experiments.
Material composition can be quantitatively analyzed using
X-ray fluorescence
X-ray fluorescence (XRF) is the emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by being bombarded with high-energy X-rays or gamma rays. The phenomenon is widely used for elemental analysis ...
(XRF). XRF detection is also used in several other techniques, such as XAS and XSW, in which it is necessary to measure the change in absorption of a particular element.
Other spectroscopy techniques include
angle resolved photoemission spectroscopy
Angle-resolved photoemission spectroscopy (ARPES) is an experimental technique used in condensed matter physics to probe the allowed energies and momenta of the electrons in a material, usually a crystalline solid. It is based on the photoelec ...
(ARPES),
soft X-ray emission spectroscopy X-ray emission spectroscopy (XES) is a form of X-ray spectroscopy in which the X-ray line Spectrum, spectra are measured with a spectral resolution sufficient to analyze the impact of the chemical environment on the X-ray line energy and on branchin ...
, and
nuclear resonance vibrational spectroscopy
Nuclear resonance vibrational spectroscopy is a synchrotron-based technique that probes vibrational energy levels. The technique, often called NRVS, is specific for samples that contain nuclei that respond to Mössbauer spectroscopy, most commonl ...
, which is related to
Mössbauer spectroscopy
Mössbauer spectroscopy is a spectroscopic technique based on the Mössbauer effect. This effect, discovered by Rudolf Mössbauer (sometimes written "Moessbauer", German: "Mößbauer") in 1958, consists of the nearly recoil-free emission and abso ...
.
Imaging
![APS - Nanoprobe](https://upload.wikimedia.org/wikipedia/commons/1/15/APS_-_Nanoprobe.jpg)
Synchrotron X-rays can be used for traditional
X-ray imaging
Radiography is an imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical radiography ("diagnostic" and "therapeut ...
,
phase-contrast X-ray imaging
Phase-contrast X-ray imaging or phase-sensitive X-ray imaging is a general term for different technical methods that use information concerning changes in the phase of an X-ray beam that passes through an object in order to create its images. St ...
, and
tomography
Tomography is imaging by sections or sectioning that uses any kind of penetrating wave. The method is used in radiology, archaeology, biology, atmospheric science, geophysics, oceanography, plasma physics, materials science, astrophysics, quantu ...
. The Ångström-scale wavelength of X-rays enables imaging well below the
diffraction limit
The resolution of an optical imaging system a microscope, telescope, or camera can be limited by factors such as imperfections in the lenses or misalignment. However, there is a principal limit to the resolution of any optical system, due to t ...
of visible light, but practically the smallest resolution so far achieved is about 30 nm. Such
nanoprobe sources are used for
scanning transmission X-ray microscopy
Scanning transmission X-ray microscopy (STXM) is a type of X-ray microscopy in which a zone plate focuses an X-ray beam onto a small spot, a sample is scanned in the focal plane of the zone plate and the transmitted X-ray intensity is recorded as a ...
(STXM). Imaging can be combined with spectroscopy such as
X-ray fluorescence
X-ray fluorescence (XRF) is the emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by being bombarded with high-energy X-rays or gamma rays. The phenomenon is widely used for elemental analysis ...
or
X-ray absorption spectroscopy
X-ray absorption spectroscopy (XAS) is a widely used technique for determining the local geometric and/or electronic structure of matter. The experiment is usually performed at synchrotron radiation facilities, which provide intense and tunabl ...
in order to map a sample's chemical composition or oxidation state with sub-micron resolution.
Other imaging techniques include
coherent diffraction imaging
Coherent diffractive imaging (CDI) is a "lensless" technique for 2D or 3D reconstruction of the image of nanoscale structures such as nanotubes, nanocrystals, porous nanocrystalline layers, defects, potentially proteins, and more. In CDI, a highl ...
.
Similar optics can be employed for
photolithography
In integrated circuit manufacturing, photolithography or optical lithography is a general term used for techniques that use light to produce minutely patterned thin films of suitable materials over a substrate, such as a silicon wafer, to protect ...
for
MEMS
Microelectromechanical systems (MEMS), also written as micro-electro-mechanical systems (or microelectronic and microelectromechanical systems) and the related micromechatronics and microsystems constitute the technology of microscopic devices, ...
structures can use a synchrotron beam as part of the
LIGA
Liga or LIGA may refer to:
People
* Līga (name), a Latvian female given name
* Luciano Ligabue, more commonly known as Ligabue or ''Liga'', Italian rock singer-songwriter
Sports
* Liga ACB, men's professional basketball league in Spain
* Liga ...
process.
Compact synchrotron light sources
Because of the usefulness of tuneable
collimated
A collimated beam of light or other electromagnetic radiation has parallel rays, and therefore will spread minimally as it propagates. A perfectly collimated light beam, with no divergence, would not disperse with distance. However, diffraction p ...
coherent
Coherence, coherency, or coherent may refer to the following:
Physics
* Coherence (physics), an ideal property of waves that enables stationary (i.e. temporally and spatially constant) interference
* Coherence (units of measurement), a deri ...
X-ray radiation, efforts have been made to make smaller more economical sources of the light produced by synchrotrons. The aim is to make such sources available within a research laboratory for cost and convenience reasons; at present, researchers have to travel to a facility to perform experiments. One method of making a compact light source is to use the energy shift from
Compton scattering
Compton scattering, discovered by Arthur Holly Compton, is the scattering of a high frequency photon after an interaction with a charged particle, usually an electron. If it results in a decrease in energy (increase in wavelength) of the photon ...
near-visible laser photons from electrons stored at relatively low energies of tens of megaelectronvolts (see for example the Compact Light Source (CLS)
). However, a relatively low cross-section of collision can be obtained in this manner, and the repetition rate of the lasers is limited to a few hertz rather than the megahertz repetition rates naturally arising in normal storage ring emission. Another method is to use plasma acceleration to reduce the distance required to accelerate electrons from rest to the energies required for UV or X-ray emission within magnetic devices.
See also
*
List of synchrotron radiation facilities
This is a table of synchrotrons and storage rings used as synchrotron radiation sources, and free electron laser
A free-electron laser (FEL) is a (fourth generation) light source producing extremely brilliant and short pulses of radiation. An F ...
*
List of light sources
This is a list of sources of light, the visible part of the electromagnetic spectrum. Light sources produce photons from another energy source, such as heat, chemical reactions, or conversion of mass or a different frequency of electromagnetic ener ...
References
External links
Elettra Sincrotrone Trieste - Elettra and FERMI lightsourcesImaging ancient insects with synchrotron light source -- BBC
{{DEFAULTSORT:Synchrotron Light Source
Synchrotron radiation
Synchrotron-related techniques
Particle physics
Light
Light sources
Materials testing
Particle accelerators