Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX)
The SEM-EDX is one of the most important methods for the evaluation of topographies, fracture surfaces as well as element composition of a solid.
SEM: In the scanning electron microscope the surface of a sample is depicted with high depth of field. The resolution is in the two-digit nm-area (50,000-times). An electron beam screens the surface of a sample in high vacuum. The hereby emerging interaction is detected and delivers image information about the surface condition via secondary or back scatter electron contrast. By this e.g. evaluations of fracture surfaces are possible.
EDX: Connected with the SEM is a modern X-ray spectroscope, with which element analyses of every just so small sample can be performed. Even isolated particles suffice to receive information about the material composition. Atoms in the sample are stimulated by the electron beam and emit element specific X-rays. These are detected by the silicon drift detector and displayed as qualitative spectrum or element distribution pattern. Every element from boron on can be detected. Elements from sodium can be evaluated quantitatively with a detection limit of 0.1 weight-%.
Normen: AV 272-Mat
One of the most srface sensitive methods for element determination is the Auger-electron-spectroscopy. Hereby you "interrogate" the surface with an electron beam, the atoms are stimulated and the elements of the 10 uppermost atomic layers "respond" by emitting Auger-electrons: electrons with a characteristic, and different kinetic energy depending on the element. In the spectrum - so intensity vs. energy - you assign peak to the elements and concentrations. This non-destructive method is particularly suitable for semiconductor surfaces and metals to e.g. identify and quantify carbon contaminations on bonding surfaces or electrical contacts (detection limits are below 0.1 at%).
Secondary ion mass spectrometry ( ToF-SIMS )
The secondary ion mass spectrometry (ToF-SIMS) analyses the atomic and molecular composition of the upper 1-3 mono layers of a solid. Therefore the surface is fired at with heavy ions (“consulted”), the elements and molecules are “jolted” and the secondary ions “burst out” hereby from the surface are analyzed regarding their mass – extremely sensitive (detection limits up to fmol) and extremely surface sensitive. The method is imaging from ca. 1 µm and can generate depth profiles by sputtering.
Application examples are adhesion failure, rest pollutant analysis, metal purification, plastic additivation, softener migration, optical layers, corrosion, …
X-ray photoelectron spectroscopy (XPS, ESCA)
With help of the X-ray photoelectron spectroscopy the composition of solids and surfaces can be determined qualitatively and quantitatively. The penetration depth hereby only adds up to a few nanometers; by abrasion even depth profiles of the composition can be generated. Besides H and He every element can be detected, in particular for heavier elements the XPS possesses a very high sensitivity (ca. 0.1 at-%). In many cases can be told, in what chemical state the element resides.
The X- ray diffraction (XRD) as for example crystal grid is based on the declension of X-rays in spatially regular structures. The atoms in the crystal work like a three-dimensional declension grid. Depending on the distance and the arrangement of the atoms to each other it comes to the interference between the stooped waves which lead to the effacement in most space directions. Only under certain measuring angles signals can be detected. From the measured diffraction charts conclusions on the crystal structure, and the lattice parameters can be drawn and concomitantly on the chemical composition In addition, crystalline and amorphous shares or different crystalline phases are identified and are quantified.
Glow discharge optical emission spectroscopy (GDOS/GDOES) delivers element compositions of metals, ceramics, plastics, aso.. GDOES delivers in comparison to the spark spectrometry also element depth profiles: coming from the surface the sample is carried off bit by bit in layers by cathode sputtering with argon-ions. The removed atoms emit characteristic wave lengths, which are registrated and quantificated in a spectrometer. Typical applications for the GDOES are as replacement for RFA and spark spectrometries, for anodic coatings, hardening depths, high temperature oxidations, varnishes, impurities, catalysts, ...