Open-faced z-shaped channel-cut x-ray monochromator

Abstract

ABSTRACT Channel-cut monochromators can be easily incorporated in high-resolution image techniques. However, polishing on the inner diffracting surfaces is difficult because of blockage by the opposite face. To address this difficulty, an open-faced monolithic monochromator has been designed, produced and tested using x-rays at the Advanced Photon Source (APS). The open-faced channel cut has a “Z”-shape geometry with a ho le in the mid section to allow passage of the diffracted beam. The open geometry allowed chemical mechanical polis hing so that an optically smooth finish on both surfaces was achieved. The high-resolution x-ray imaging and topography measurements revealed that the new design introduces significantly less distortions in the phase-contrast images compared with conventional channel-cut monochromators produced using etching alone. Keywords: polished channel-cut monochromator, silicon, high-resolution x-ray topography. 1. INTRODUCTION Fabrication of a channel-cut x-ray monochromator with polis hed diffracting surfaces has been requested by APS users. The concept and design of an open-faced Z-shaped channel-cu t x-ray monochromator has been presented previously [1]. The actual monochromator is a modification of a two-bounce classic channel-cut crystal with totally open diffracting surfaces, which makes it easier to polish them. To achieve highly polished [better than 30 nm peak-to-valley (P-V) flatness, and 1-2 A root mean square (rms) roughness] diffracting surfaces with conventional polishing techniques still remains a challenge, but should be explored before applying expansive technologies such as ion-beam figuring (IBF) [2]. In this paper we will present characteristics of polished diffracting surfaces of a Z-monochromator made of silicon single crystal by conventional polishing methods, dependence of background patterns of high-resolution x-ray topography measurements on polishing quality, and will discuss possible ways to enhance the performance of the monochromator.