The HE-SGM beamline is a dipole beamline optimized for NEXAFS spectroscopy in the VUV range. It is designed to cover the light element (C, N, O and F) K-edges which contain important spectroscopic information about soft matter samples, carbon (nano) materials and molecules adsorbed on catalytically relevant surfaces. The beamline monochromator allows for fast scanning over the energy ranges of interest (100 eV - 800 eV). There are a number of similar beamlines at other synchrotron facilities worldwide. With regard to the spectroscopic parameters, the HE-SGM beamline is considered to be in the top three of comparable dipole beamlines. The optical elements of the beamline (mirror, monochromator) were addittionally cleaned with oxygen plasma to remove carbon contamination from their surfaces resulting in crucial decrease of parasitic contributions to the experimental data (Fig. 3). Such uniqueness allows to acquire proper experimental data for organic moleculas thin films with a thickness down to 0.1 monolayer. During reinstallation of the beamline, the adjustment of the entrance slit was improved resulting in a better polarization factor - which increased to 91%.
Fig.1 HE-SGM Beamline
Fig.2 Optical lay-out and measured performance data
Fig.3 Dependence of the direct beam intensity on the photon energy (transmission function) around C K-edge
Properties of the beamline
The NEXAFS/XPS experimental station is a multi-chamber UHV system produced by PREVAC (Poland) and consists of the following chambers:
1. Two load-locks: the first one is used for fast sample exchange with a storage facility of up to six samples; the second one is used for sample exchange with a storage facility for two sample holders and with an opportunity to install a special vacuum transfer box allowing to transport samples under UHV conditions. Moreover, the park station connected to the distribution chamber allows the storage of six additional sample holders under UHV conditions.
2. The unique sample transfer system including the distribution chamber of the carrousel-type (a base pressure better than 10-10 mbar) and manipulators allow fast (less than 1 minute) transfer of samples from one chamber to another. It was established that during the sample transfer in the cold state (~100 K) the temperature doesn't increase by more than 20 K.
3. A versatile preparation chamber operated at a base pressure of better tha 5x10-10 mbar accepting up to 5 evaporators for metals or organics and/or other sources (for example, atomic H source, etc.), two sputter guns, gas dosing systems, as well as an LEED system for control of sample quality. One of the evaporators is permanently installed and available to all HE-SGM users. A special receiving station of the manipulator allows for cooling with liquid nitrogen to 100 K and for heating up to 2000 K.
4. A main chamber with base pressuer of better than 10-10 mbar is equipped with a hemispheric electron energy analyser (Scienta R3000), a sputter gun, and a home-built double channel plane detector enabling NEXAFS spectroscopy in partial electron yield (PEY) or total electron yield (TEY) mode. The energy analyser and the MCP-NEXAFS detector can be read out at the same time thus allowing simultaneous recording of integrated secondary electrons (PEY or TEY) and energy-resolved Auger electrons. For the measurements the sample is transferred to a 5-axes manipulator with three translational and two rotational (polar and azimuthal) degrees of freedom. A continuous-flow liquid He cryostat installed in the chamer allows sample cooling down to 30 K, while samples can be heated up to 2000 K (depending on the sample holder).
Fig.1 HE-SGM experimental station
Properties of the experimental station