PHARAO
PDI's in situ x-ray diffraction / MBE beamline at BESSY
The PHARAO facility consists of the beamline, the diffractometer and three plug-in MBE machines that can be swapped in and out of the diffractometer.
Our beamline U125/2-KMC at BESSY is located at the direct line ofsight of a permanent magnet insertion device. It consists of a collimating mirror, a double-crystal monochromator (DCM), a double multilayer monochromator (DMM) and a refocusing mirror. The DCM offers an energy range from about 5 to 15 keV with an energy resolution of around 2 eV at 10 keV. The DMM has been added in 2008. It works at a fixed wavelength of 10 keV with an energy resolution around 1%, thereby offering an about 50 times higher primary beam intensity.
The diffractometer is of the six circle type, optimized for surface x-ray diffraction. It is big and stable enough to support growth equipment with a weight of up to one ton and a volume of up to two cubic meters. Except for the incidence angle circle which rotates the entire payload, all rotations have an angular resolution of 1/1000°.
Computer control allows the direct navigation in reciprocal space and the automated acquisition of multidimensional data sets.
The MBE machines of the facility are optimized for the specific requirements of in situ and in vivo x-ray diffraction. The sample is located inside a cylindrical chamber with large Be windows for the incident and exiting beams. The sample normal is horizontal to allow an adjustment of the incidence angle by rotating the machine around the vertical axis. The sample heater is rigidly connected with the diffractometer head. Alignment movements are possible by a flexible bellow, azimuthal sample rotation is made possible through a differentially pumped rotation feedthrough. The growth chambers are cooled by two liquid nitrogen shrouds each and have seven effusion cell ports for standard size effusion sources up to 65 mm in diameter. Each MBE system is equipped with a high performance RHEED system for advanced measurement modes like azimuthal scans, energy-resolved detection and fluorescence analysis.
