Abstract
An X-ray reflectometer using a laboratory X-ray source for quick measurements of the specular X-ray reflectivity curve is presented. It uses a bent-twisted crystal to monochromatize and focus the diverging X-rays (Cu Kα1) from a laboratory point source onto the sample. The reflected X-rays are recorded with a two-dimensional detector. Reflectivity curves can be measured without rotating the sample, detector or X-ray source during measurements. The instrument can separate the specularly reflected X-rays from the diffuse scattering background, so low reflectivities can be measured accurately. For a gold thin film on silicon, the reflectivity down to the order of 10-6 was obtained with a measurement time of 100 s and that down to 10-5 with a measurement time of 10 s. Reflectivity curves of a silicon wafer and a liquid ethylene glycol surface are shown as well. Time-resolved measurements of a TiO2 surface during UV irradiation are also reported.
Highlights
Specular X-ray reflectivity is an established tool for structural characterization of surfaces and interfaces of materials (AlsNielsen et al, 1994; Daillant & Gibaud, 1999)
For time-resolved observation of irreversible structural changes, where the pump–probe method (Nuske et al, 2011) cannot be used, the time resolution of the angle-scan method is of the order of minutes, even using synchrotron radiation (Gonzalez-Silveira et al, 2007; Yano et al, 2010)
The energy-dispersive method using a solid state detector and Bremsstrahlung from a laboratory X-ray source can be used for obtaining the reflectivity curve over a wide vertical momentum transfer range simultaneously, and time-resolved studies using this approach have been carried out (Paci et al, 2005, 2006; Rossi Albertini et al, 2003)
Summary
Specular X-ray reflectivity is an established tool for structural characterization of surfaces and interfaces of materials (AlsNielsen et al, 1994; Daillant & Gibaud, 1999). Naudon et al (1989) reported a method in which the reflectivity curve over a wide vertical momentum transfer range is simultaneously measured using characteristic X-rays from a line-focus laboratory X-ray source, a knife edge close to the sample surface and a one-dimensional detector. With their method diffuse scattering from the incident X-ray beam cannot be separated from the signal intensity. Results of time-resolved measurements with a time resolution of 10 s are reported
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