Soft x-ray emission spectroscopy
Encyclopedia
Soft X-ray emission spectroscopy is an experimental technique for determining the electronic structure of materials. It is a form of X-ray spectroscopy
.
, and the measurement of the fluorescence
that occurs as the electron relaxes into a lower-energy state. The differences between resonant and non-resonant excitation arise from the state of the atom before fluorescence occurs.
In resonant excitation, the core electron is promoted to a bound state
in the conduction band
. Non-resonant excitation occurs when the incoming radiation promotes a core electron to the continuum. When a core hole
is created in this way, it is possible for it to be refilled through one of several different decay paths. Because the core hole is refilled from the sample’s high-energy free states, the decay and emission processes must be treated as separate dipole transitions. This is in contrast with RIXS, where the events are coupled, and must be treated as a single scattering process.
, where the photon beam is manipulated using special mirrors and diffraction grating
s.
Gratings diffract each energy or wavelength
present in the incoming radiation in a different direction. Grating monochromator
s allow the user the select the specific photon energy they wish to use to excite the sample. Diffraction gratings are also used in the spectrometer
to analyze the photon energy of the radiation emitted by the sample.
X-ray spectroscopy
X-ray spectroscopy is a gathering name for several spectroscopic techniques for characterization of materials by using x-ray excitation.-Characteristic X-ray Spectroscopy:...
.
Uses
X-ray emission spectroscopy (XES) provides a means of probing the partial occupied density of electronic states of a material. XES is element-specific and site-specific, making it a powerful tool for determining detailed electronic properties of materials.Forms
Emission spectroscopy can take the form of either resonant inelastic X-ray emission spectroscopy (RIXS) or non-resonant X-ray emission spectroscopy (NXES). Both spectroscopies involve the photonic promotion of a core level electronElectron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
, and the measurement of the fluorescence
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
that occurs as the electron relaxes into a lower-energy state. The differences between resonant and non-resonant excitation arise from the state of the atom before fluorescence occurs.
In resonant excitation, the core electron is promoted to a bound state
Bound state
In physics, a bound state describes a system where a particle is subject to a potential such that the particle has a tendency to remain localised in one or more regions of space...
in the conduction band
Conduction band
In the solid-state physics field of semiconductors and insulators, the conduction band is the range of electron energies, higher than that of the valence band, sufficient to free an electron from binding with its individual atom and allow it to move freely within the atomic lattice of the material...
. Non-resonant excitation occurs when the incoming radiation promotes a core electron to the continuum. When a core hole
Electron hole
An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice...
is created in this way, it is possible for it to be refilled through one of several different decay paths. Because the core hole is refilled from the sample’s high-energy free states, the decay and emission processes must be treated as separate dipole transitions. This is in contrast with RIXS, where the events are coupled, and must be treated as a single scattering process.
Properties
Soft X-rays have different optical properties than visible light and therefore experiments must take place in ultra high vacuumUltra high vacuum
Ultra-high vacuum is the vacuum regime characterised by pressures lower than about 10−7 pascal or 100 nanopascals . UHV requires the use of unusual materials in construction and by heating the entire system to 180°C for several hours to remove water and other trace gases which adsorb on the...
, where the photon beam is manipulated using special mirrors and diffraction grating
Diffraction grating
In optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as...
s.
Gratings diffract each energy or wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
present in the incoming radiation in a different direction. Grating monochromator
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...
s allow the user the select the specific photon energy they wish to use to excite the sample. Diffraction gratings are also used in the spectrometer
Spectrometer
A spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity but could also, for instance, be the polarization...
to analyze the photon energy of the radiation emitted by the sample.
External links
- Soft X-ray Emission Spectroscopy - Description at beamteam.usask.ca