<title>Evaluation by UV optical measurements of the imaging quality of grazing incidence x-ray optics</title>

ABSTRACTWe demonstrate the use of x-ray diffraction to provide accurate compositional information, together with grazing incidence reflectivity to provide information on layer thicknesses and surface and interface roughnesses, on Si/Si1-xGex superlattice structures of less than 200nm total thickness.The quality of SiGe interfaces has been investigated in superlattices where x varies from 0.1 to 0.5. At low Ge compositions the interfaces are shown to be smooth to a few angstroms. However, as the Ge composition in the SiGe layer approaches 50%, severe roughness is observed at the SiGe to Si interfaces, although the Si to SiGe interfaces remain relatively smooth.Upon annealing for one hour at 850°C the Ge diffuses outwards from the SiGe layers and can be closely modelled by inclusion of a (2.4±0.3)nm linearly graded layer either side of the SiGe layer into a simulation program. The long range roughness at the SiGe to Si interface is lost upon annealing leaving only a short range roughness of similar size to the Si to SiGe interface roughness.Reflectivity measurements have been shown to distinguish between interface roughness and interdiffusion for the annealed system.

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Alignment of the aberration-free XUV Raman spectrometer at FLASH

Journal of Synchrotron Radiation ◽

10.1107/s160057751801576x ◽

2019 ◽

Vol 26 (1) ◽

pp. 18-27 ◽

Cited By ~ 1

Author(s):

Mykola Biednov ◽

Günter Brenner ◽

Benjamin Dicke ◽

Holger Weigelt ◽

Barbara Keitel ◽

...

Keyword(s):

Extreme Ultraviolet ◽

Laser Interferometry ◽

Grazing Incidence ◽

Stray Light ◽

Optical Scheme ◽

Optical Elements ◽

X Ray ◽

Raman Spectrometer ◽

Optical Alignment

An extreme-ultraviolet (XUV) double-stage Raman spectrometer is permanently installed as an experimental end-station at the PG1 beamline of the soft X-ray/XUV free-electron laser in Hamburg, FLASH. The monochromator stages are designed according to the Czerny–Turner optical scheme, adapted for the XUV photon energy range, with optical elements installed at grazing-incidence angles. Such an optical scheme along with the usage of off-axis parabolic mirrors for light collimation and focusing allows for aberration-free spectral imaging on the optical axis. Combining the two monochromators in additive dispersion mode allows for reaching high resolution and superior stray light rejection, but puts high demands on the quality of the optical alignment. In order to align the instrument with the highest precision and to quantitatively characterize the instrument performance and thus the quality of the alignment, optical laser interferometry, Hartmann–Shack wavefront-sensing measurements as well as off-line soft X-ray measurements and extensive optical simulations were conducted. In this paper the concept of the alignment scheme and the procedure of the internal optical alignment are presented. Furthermore, results on the imaging quality and resolution of the first monochromator stage are shown.

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