W0441

Small-Angle X-Ray Scattering Measurements of Hydrogen Evolution from an Epitaxial Nb Film. Monica M.C. Allain,¹ Brent J. Heuser, ¹ and W.C. Chen², ¹Univ. of Illinois, Dept. of Nuclear, Plasma, and Radiological Engineering, Urbana, IL 61801, ²NIST Center for Neutron Research, NIST, Gaithersburg, MD 20899.

Small-angle x-ray scattering (SAXS) measurements have been performed to investigate particle morphology during in situ hydrogen evolution from a 1000 Å epitaxial Nb film on (11-20) sapphire initially loaded to saturation with hydrogen. The SAXS intensity follows the plate or disk single particle form factor (Q^-2, where Q is the wavevector transfer) during hydrogen evolution. A fit to this power-law behavior yields a plate thickness of approximately 7 Å. A second power-law behavior (Q^-3) was observed after complete hydrogen evolution. This power law corresponds to the small-angle scattering response from edge dislocations and is consistent with the broadening of the lattice mosaic induced by hydride decomposition. Film coherence lengths before and after hydrogen exposure determined from x-ray diffraction indicate severe lattice distortion has taken place, consistent with dislocation formation during an incoherent phase transformation.