Design and Construction of a Grazing Incidence X-Ray Reflection System for Liquid-Vapor Interfaces

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We have developed a grazing incidence x-ray reflection apparatus for liquid-vapor interfaces using a conventional x-ray tube (Cu K_<alpha>,2.2kW). A special geometry has been necessitated by the restriction that the liquid surface is horizontal. The main features of our apparatus are as follows. Highly collimated and monochromated x-ray beams are generated using an asymmetrically cut Ge (111) crystal monochromater. An imaging plate, which has a high detective quantum efficiency, a low quantization noise and a wide dynamic range is used as a 2-dimensional area detector. The sample position is slowly elevated to compensate for evaporation during measurements. A device for surface tension measurement by the ring method has been combined with the reflection apparatus so that in situ measurements may be possible.This system was tested by measuring X-ray reflectivity profiles from the free surface of water. We obtained a good agreement with the result reported by Braslau et al. (1985) who used synchrotron radiation. Several liquid alkanes and alcohols have been investigated and the reflectivity profiles have been interpreted in terms of a surface roughness characteristic of the size and shape of the molecules.In spite of using a conventional x-ray tube, the resolution in the momentum transfer of our reflection system is higher than that of synchrotron radiation system by Braslau et al..