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Energy dispersive X-ray analysis - EDX
Energy dispersive X-ray analysis is used in a scanning electron microscope to determine the elemental composition of a sample. For this purpose, the X-rays emitted from the surface by the electron bombardment are analyzed energy-selectively. The scanning technique used in the SEM allows the elemental composition to be determined with spatial resolution. The lateral resolution is typically between 1 um and several hundred nm. The depth of information is usually 1-3 um. Both the lateral resolution and the achievable depth of information can be varied within certain limits by selecting the appropriate primary energy and using special preparation techniques.
Devices: Helios Nanolab 600
X-ray photoelectron spectroscopy - XPS
X-ray photoelectron spectroscopy (XPS) is a surface-sensitive spectroscopic method that can be used to analyze the composition of elements and chemical bonds. The method is based on the external photoelectric effect: by irradiating the surface to be examined with high-energy X-rays, electrons are released from the atoms or molecules on the surface. From the kinetic energy of the emitted electrons, conclusions can be drawn about the elements present and the bonding conditions. Due to the very short mean free path of electrons in solids, the mean information depth of XPS is only a few nm. This allows both the chemical properties of surfaces and chemical reactions with surfaces to be investigated very precisely.
Equipment: ESCA MKII, UHV spectroscopy
Auger electron spectroscopy - AES
In auger electron spectroscopy (AES), the surface to be examined is bombarded with electrons and the auger electrons emitted by the surface due to the so-called auger effect are measured. Similar to XPS, the kinetic energy of the Auger electrons provides information about the elements present and, within certain limits, about their bonding state. The information depth of AES is also in the range of a few nm. AES is therefore also a very surface-sensitive measurement method, which can be used to detect surface impurities very accurately, for example. Unlike XPS, Auger electron microscopy in combination with an SEM enables spatially resolved spectroscopic investigations. The lateral resolution is only a few nm so that AES can be used to analyze nanostructures on surfaces, for example.
Devices: ESCA MKII, Omicron NanoSAM
Ultraviolet photoelectron spectroscopy - UPS
Ultraviolet photoelectron spectroscopy (UPS) can be used to spectroscope the valence band of a surface. UPS primarily provides information about chemical bonds. In addition, the work function of the sample surface can be determined. The depth of information is only a few atomic layers, resulting in a very high surface sensitivity. Due to the high interaction cross-section of ultraviolet radiation, adsorbates in the sub-monolayer range can also be investigated with high sensitivity.
Devices: UHV spectroscopy
Electron spectroscopy with metastable atoms - MIES
Electron spectroscopy with metastable atoms (MIES) is an extremely surface-sensitive method with which the valence band of thevery first atomic layer can be spectroscoped. In order to achieve the corresponding surface sensitivity, excited helium atoms are used which are in a metastable state. When the metastable helium atoms hit the surface, a few angstroms before the first atomic layer, excitation processes occur which are determined by the work function and the electronic structure of the surface. Using MIES, surface adsorbates can be investigated with extremely high surface sensitivity. In addition, the method is particularly suitable for investigating molecular orientations.
Equipment: UHV spectroscopy
Quadrupole mass spectrometry - QMS
Quadrupole mass spectrometry can be used to analyze the composition of gases. The molecules contained in the gas are ionized and then analysed according to their mass/charge ratio. Masses between 1 -300 amu can usually be detected.
Devices: Hositrad MGT, MGA, ESCA Lab MK II