COURS SPECTROSCOPIE XPS PDF

June 17, 2020 0 Comments

XPS. X-ray Photoelectron Spectroscopy. ESCA Electron Spectroscopy for Chemical XPS, also known as ESCA, is the most widely used surface analysis. Etude par spectroscopie de photoelectrons (XPS) de la surface de profiles a au cours de différents traitements, par spectroscopie de photoélectrons (ESCA ou. La spectroscopie des photoélectrons induits par rayons X est une technique Au cours d’une analyse XPS, des photons (Al Kα ou Mg Kα) sont envoyés sur.

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There spetroscopie two basic PEEM conceptions, each of them are optimized according to its application. The first is based on the electron microscopy technology developed by Telieps and Bauer. The sample is negative biased relative to the objective lens, typically kV, as illustrated in right side figure. The lenses are magnetic.

There are two advantages for having the very high electron energy in the column of PEEM. Firstly, the imaging condition corresponds to the approximately Gaussian optics.

That is, the concerned electrons are very close to the optics axes. The advantage of LEEM is the intensity of the beam, which permit the fast scan on the sample surface with high spatial resolution, and also the possibility of using special mode of microscopy, like the mirror electron microscopy MEM.

The electrons are decelerated till a limited kinetic energy so that it will be reflected before reach the surface of sample.

The reflectivity is then considerably enhanced, while the transmission is very small.

Spectroscopie photoélectronique

spctroscopie Thus, the electrons interact with the electrical field on the top of sample surface. This allows us to study, for example, the distribution of the surface dipoles. The second concept used in PEEM is presented by the system with pure electrostatic lens, as shown in leftside figure. The potential of the sample is near ground, while the extraction lens is at a positive high voltage.

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Compared with the first concept, it is simpler for two reasons. Firstly, it avoids the intrinsic problem derived from the application of high voltage into sample. Secondly, the optics are electrostatic: Thus successive zoom in the interested region or surface soectroscopie become simpler.

Most laboratory-based PEEMs use this concept. The analyser allows high transmission imaging at kinetic energies far from threshhold without sacrificing the lateral and energy resolution of the instrument. High transmission is particularly important especially for highest resolution imaging XPS with monochromated laboratory X-ray sources.

High spatial and energy resolution can be achieved by the fully energy filtered XPEEM, the spatial resolution down to a few tens of nanometers have been achieved. In addition, synchrotron-based XPEEM is one of the most powerful spectro-microscopic techniques for studying the chemical and electronic structures of thin film systems, combined with the tunability and polarizability of x-ray sources and high brilliance of synchrotron radiation sources.

Spatially resolved surface chemical state analysis down to 50 nm. The different chemical states of oxygen bound to silicon and to titanium are observable in the local spectra reconstructed from the image series. Details refer to O. Study the spatial and momentum resolved electronic structure-directly band structure imaging.

The use of a novel design of a photoelectron microscope in combination to an imaging energy filter for momentum resolved photoelectron detection.

Spectroscopie photoélectronique — Wikipédia

Together with a time resolved imaging detector, it is possible to combine spatial, momentum, energy, and time resolution of photoelctrons within the same instrument. The time resolution of this type of energy analyzer can be reduced to below ps. Figure shows a k -space image of Cu taken at the Fermi energy with an exposure time of 5 min excited with He I.

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The small ring in the center is the Shockley surface state. The surface Brillouin zone is marked by a black hexagon. Details refer to B. The surface composition of polycrystalline Nb-doped strontium titanate SrTiO3: Nb is studied using XPEEM for various grain orientations in order to characterize the surface chemistry with high spatial ckurs.

The surface sensitivity is maximized by the use of soft x-ray synchrotron radiation SR. The grain orientation is determined by electron backscattering diffraction EBSD.

X-ray Photoelectron Spectroscopy (XPS)

Stereographic plots are used to show the correlation between surface assigned to major orientation. Details refer to L. Hoffmann, Shao-Ju Shih, D. B 60, XPS, X-ray Photoelectron Spectroscopy is a surface analysis technique which provides both chemical spctroscopie electronic properties.

Through the photoelectric effect, photoelectrons are ejected from the surface illuminated with a X-ray source.

They have characteristic binding energy which depends on the element, orbital and chemical environment of the atom. This technique allows the detection of virtually all elements present on the surface probing depth 1 to 10nm. In the context of our laboratory studies, XPS is particularly suitable for the identification of chemical bonds showing the functionalization of surfaces and materials and for the calculation of stoichiometric ratios of thin layers.

Spatially resolved surface chemical state analysis down to 50 nm XPEEM can provide the elemental map of preferential grafting of p-MAN polymer on a gold patterned silicon substrate.