YB66 - a new soft X-ray monochromator for synchrotron radiation. II. Characterization

YB66, a complex boron-rich man-made crystal, has been singled out as a pote ntial monochromator material to disperse synchrotron soft X-rays in the 1-2 keV region. Results of a series of systematic property characterizations p ertinent for this application are presented in this paper. These include La ue diffraction patterns and high-precision lattice-constant determination, etch rate, stoichiometry, thermal expansion, soft X-ray reflectivity and ro cking-curve measurements, thermal load effects on monochromator performance , nature of intrinsic positive glitches and their reduction. The 004 reflec tion of YB66 has a reflectance of similar to 3% in this spectral region. Th e width of the rocking curve varies from 0.25 eV at 1.1 keV to 1.0 eV at 2 keV, which is a factor of two better than that of beryl(1010) in the same e nergy range, and enables measurements of high-resolution XANES spectra at t he Mg, Al and Si K-edges. The thermal bump on the first crystal arising fro m the low thermal conductivity of YB66 causes an energy drift of a few eVs with storage-ring current and necessitates periodic energy calibration with metal foils. The positive glitches in the transmission function just above the Mg K-edge have substantially been reduced using an Si or SiC mirror wh ich suppresses the sharp reflectivity increases associated with anomalous s cattering for the YB66 006 reflection at the Y L-3- and L-2-edges. Continua l operation over the past five years of a YB66 double-crystal monochromator installed on the JUMBO beamline at Stanford Synchrotron Radiation Laborato ry (SSRL) indeed proves the long-term stability of this material in synchro tron radiation under ultrahigh vacuum conditions as indicated by the invari ance in rocking-curve characteristics after being exposed to an accumulativ e power level of similar to 3 x 10(8) J over this period of time.