Infrastructure - Shared Labs

X-ray photoelectron spectroscopy (XPS)

The working principle of the XPS is based on the extraction of electrons from a sample surface irradiated by X-ray photons.
X-rays are produced when an electron beam with enough energy to promote transitions between atomic core levels impacts an anode. The produced X-rays are redirected to a monochromator, where radiation with an energy of 1486.6 eV is selected. These X-ray photons are guided onto a sample. The interaction of the X-ray beam with the sample atoms results in excitation and extraction of electrons. Extracted electrons are collected in a detector, where their kinetic energy is measured. 

By knowing the energy of the incoming X-rays (hν), the required binding energy (BE) of the electron (Ebin) within the atom can be determined.

Each element is characterised by the binding energies of electrons in the di erent atomic core levels. The only elements which are not detectable within the XPS are hydrogen and helium. Chemical bonding between atoms leads to a shift in binding energy position, which allows a chemical analysis of the measured samples. This technique is called ESCA (Electron Spectroscopy for Chemical Analysis). 

X-ray Photoelectron Spectroscopy is performed using a Versaprobe spectrometer from Physical Electronics (PHI 5000 VersaProbe). At an aluminium anode, Al K α radiation with an energy of hν = 1486.6 eV is produced. A resolution of 0.5 eV is achieved for survey spectra using a pass energy of 187.85 eV. A spectral resolution of 0.05 eV for a pass energy of 23.5 eV is usually applied for measurements of single peaks. Best resolution achieved is 0.025 eV. The measurement spot can be applied to diameters of 20 μm, 100 μm or 200 μm. Standard measurements are performed at a tilt angle of 45° between the sample and the detector. For angle resolved measurements, angles between 15° and 85° can be used. An ion gun with an argon surce is adapted so that a sputtering of the samples with energies between
20 V and 4 kV can be used.

Three kinds of sample holders are avaible, the small one is a circular 1 inch holder, the bigger one is a circular 2 inch holder. Finally, there is a angle resolved sample holder on which up to eight samples can be mounted. The circular sample holders have masks which can be installed to measure wafers or any other solid sample.

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The JEOL JSM-6510 is a Scanning Electron Microscope (SEM). It achieves visualization of a sample by irradiating a focused beam of electrons producing secondary electrons at the surface. Collecting the secondary electrons by means of a detector results in an image of the topography. This enables scanning of a sample with a magnification of up to x300.000 with a resolution of 3 nm using a 30 kV electron beam. The accelerating voltage can be varied between 0.5 and 30 kV.





Energy Resolved Mass Spectrometer

The Hiden EQP 300 HE is an energy resolved mass spectrometer which is used to measure time resolved ion energy distribution functions (IEDF) of high power pulsed magnetron sputtering (HiPIMS) discharges.

The mass spectrometer has a quadrupol filter which allows the detection of ion masses up to 300 atomic mass units (amu) with a precision of 0.01 amu. In its standard variation the energy filter, consisting of two parallel plates with a voltage apllied to, is capable of measuring the energy of ions in a range of -100 eV up to 100 eV in steps of 0.01 eV. The addition of the high energy component (HE) allows for measurements of ion energies from -1000 eV up to 1000 eV. An ionisator can be used for the detection of neutral particles.

A secondary electron multiplier is used as a detector to count ion rates. Attached to the analogue output of the detector is a transient recorder which is capable of counting events with a temporal resolution of 100 ns.

The mass spectrometer needs to be pumped separately from the vacuum chamber to which it is attached. The separate pumping reduces the amount of collisions that particles undergo in the mass spectrometer and, thus, increases the transmission of the particles.


Phase resolved optical emission spectroscopy (PROES) is a technique that alows the investigation of the discharge emission according to the time, especially, phase of the applied excitation voltage. In addition, the combination of an ICCD-Chip and optical filter establishes the spatial resolution of the emission of a selected in wavelenghts.

Here, the camera (LaVison PicoStar HR16) works with a time resolution of about 100 ps. The ICCD-Chip has 512x512 pixels and enables a spatial resolution of few µm. The camera can detect emission in range between 350 nm and 750 nm.






Multi Resonance Probe/Plasma Absorption Probe

The head of the Multipole Resonance Probe (MRP) con­sists of two metallic hemispheres working as electrodes of a small an­ten­na and separated by a dielectric layer. The head’s diameter is 6 mm and is en­clo­sed by a dielec­tric tube (thickness of 1 mm) which is im­mer­sed in the plas­ma. This makes the probe insensitive against ceramic coatings which is needed in many applications. A self-developed electronic or, as an alternative, a net­work ana­ly­zer feeds an rf si­gnal sweep to the an­ten­na and dis­plays the fre­quen­cy de­pen­dence of the power ab­sorp­ti­on. This method is known as active plasma resonance spectroscopy (APRS). From the ab­sorp­ti­on spec­trum the value of the elec­tron den­si­ty is cal­cu­la­ted. In comparison to other APRS probes, the MRP shows a geometrical and electrical symmetry which significantly decreases the complexity of the model. The measurement range of the electron density is between 1013 m-3 and >1018 m-3. Time resolution lies in the range of sub ms, depending on the used electronic.

The plas­ma ab­sorp­ti­on probe (PAP) was in­ven­ted as an eco­no­mi­cal and ro­bust dia­gnostic de­vice to de­ter­mi­ne the elec­tron den­si­ty di­stri­bu­ti­on in tech­ni­cal plas­mas. It con­sists of a small an­ten­na en­clo­sed by a dielec­tric tube which is im­mer­sed in the plas­ma. A net­work ana­ly­zer feeds a rf si­gnal to the an­ten­na and dis­plays the fre­quen­cy de­pen­dence of the power ab­sorp­ti­on. From the ab­sorp­ti­on spec­trum the value of the elec­tron den­si­ty is cal­cu­la­ted. The ori­gi­nal eva­lua­ti­on for­mu­la was based on the dis­per­si­on re­la­ti­on of plas­ma sur­face waves pro­pa­ga­ting along an in­fi­ni­te dielec­tric cy­lin­der. In this let­ter the aut­hors pre­sent the ana­ly­sis of a less idea­li­zed con­fi­gu­ra­ti­on. The cal­cu­la­ted spec­tra are in good qua­li­ta­ti­ve agree­ment with their ex­pe­ri­men­tal coun­ter­parts, but dif­fer con­s­i­der­a­b­ly from those pre­dic­ted by the sur­face wave an­satz. An eva­lua­ti­on sche­me which takes our fin­dings into ac­count will im­pro­ve the per­for­mance of the PAP tech­ni­que fur­ther.

The measurement range of the electron density is between 1014 m-3 and 1018 m-3. Time resolution lies in the range of sub ms.