UHV-Cluster
The unique ultra-high vacuum system, which was established as part of the ELSA cluster at TU Wien, is intended to bridge the gap between basic and application-orientated research in the field of surface and interface analysis. The concept of sample transfer between different instruments in the absence of air plays a key role in enabling quasi in-situ experiments (e.g. electrochemical experiments). This was achieved with the help of various components.
Concept
The two main instruments for surface and interface analysis in the ELSA cluster are a scanning X-ray photoelectron spectrometer (XPS) and a high-resolution Auger-Meitner electron spectrometer (AES). A transfer vessel enables sample transfer under exclusion of air between these devices and a glovebox in which samples can be prepared. A radial distribution chamber is also connected to the XPS. This allows a variety of other applications under vacuum. A Kelvin probe and a chamber for electrochemical experiments are currently installed on the distribution chamber, whereby a free flange can be used for special experiments. Another component that can be connected to the distribution chamber is a removable vacuum suitcase. This is actively pumped, can be flanged to other UHV systems (e.g. LEIS, opens an external URL in a new window) and thus complements the possibility of sample transfer under vacuum.
© Jakob Hemetsberger
Concept of the UHV cluster: (AES) Auger-Meitner electron spectrometer; (XPS) X-ray photoelectron spectrometer; (RDC) radial distribution chamber; (P) parking space for samples; (LL) Load-Lock; (KP) Kelvin-probe; (EC) chamber for electrochemical experiments; (TV) transfer vessel; (VS) vacuum suitcase
Components
Auger electron spectroscopy (AES) is a method of surface analysis that utilises the Auger effect. The electrons emitted by the sample, which undergo a series of internal relaxations after the initial excitation, are analysed.
The 710 Auger Nanoprobe used here combines a high-resolution SEM (< 5 nm) with a high-resolution Auger electron spectrometer (< 10 nm). The combination of these techniques enables the creation of element distributions on the surface of materials in the nanometre range, which can be compared with SEM images. This allows the smallest structures, for example in the form of defects, to be detected and chemically analysed.
© Frieda Kapsamer
Ultrahigh vacuum System of the PHI 710 Augerelectron spectrometer
UHV System: (A) FEG electron source/Cylindrical mirror analyser, (B) Secondary electron detector, (C) Ar-Ion source, (D) Focused ion beam (FIB), (E) EDS detector, (F) Ion pumps
X-ray photoelectron spectroscopy (XPS) is a method for determining the chemical composition of the surfaces of vacuum-resistant materials. XPS is based on the external photoelectric effect, in which photoelectrons are released from a solid by electromagnetic radiation. The binding energy, which can be determined from the kinetic energy of the photoelectrons, is characteristic of the atom and allows conclusions to be drawn about the chemical environment of the atoms. The depth of information is a few nanometres (<10 nm).
The Versaprobe III has a scanning, monochromatic X-ray source (Al Kα), which allows the X-ray beam to be focussed to diameters of < 10 μm. By recording X-ray-induced secondary electron images (SXI), "SEM-like" operation is possible, which indicates a local identification of possible inhomogeneities of the sample surfaces, which can subsequently be chemically analysed.
© Daniela Miano
Ultra-high vacuum system of the Versaprobe III
UHV System: (A) Gas Cluster Ion Gun, (B) Twin X-ray source, (C) Monochromatic X-ray source and hemispherical analyser, (D) "Reflection Electron Energy Loss Spectroscopy" electron source, (E) Monochromatic Ar source, (F) Intro chamber, (G) Additional (pre)vacuum pumps, (H) Magnetic field compensation
The radial distribution chamber has greatly increased the flexibility and application range of our instruments. The six usable connection flanges open up a wide range of possibilities. In our case, the XPS, the Kelvin probe and a chamber for electrochemical experiments, an intermediate sample storage unit with a capacity of six samples and a Load Lock are already permanently connected to the distribution chamber. The vacuum suitcase and chambers for special experiments can be connected to the two remaining flanges.
© Jakob Hemetsberger
Radial distribution chamber with (P) parking space for samples; (LL) Load-Lock; (KP) Kelvin-probe; (EC) chamber for electrochemical experiments; (FF) free flange; (VS) vacuum suitcaser; (XPS) X-ray photoelectron spectrometer
A Kelvin-probe is used to determine the work function of polymer, oxide and metal interfaces non-destructively. The underlying principle is based on the flow of electrons between different metals and the resulting electric field. For the measurement, a conductive probe is set in oscillation and an external voltage is set so that the current induced during oscillation is zero. The external voltage then corresponds to the work function difference between the sample and the probe.
Kelvin-probe
The vacuum suitcase is the most important component when transferring samples under vacuum between different UHV systems and can be installed on any CF 40 flange (e.g. radial manifold chamber, LEIS, opens an external URL in a new window, glovebox,...). It is actively pumped with an ion getter pump and can hold up to 12 samples.