The use of channel-cut crystal monochromators has been traditionally limited to applications that can tolerate the rough surface quality from wet etching without polishing. We have previously presented and discussed the motivation for producing channel cut crystals with strain-free polished surfaces . Afterwards, we have undertaken an effort to design and implement an automated machine for polishing channel-cut crystals. The initial effort led to inefficient results. Since then, we conceptualized, designed, and implemented a new version of the channel-cut polishing machine, now called C-CHiRP (Channel-Cut High Resolution Polisher), also known as CCPM V2.0. The new machine design no longer utilizes Figure-8 motion that mimics manual polishing. Instead, the polishing is achieved by a combination of rotary and linear functions of two coordinated motion systems. Here we present the new design of C-CHiRP, its capabilities and features. Multiple channel-cut crystals polished using the C-CHiRP have been deployed into several beamlines at the Advanced Photon Source (APS). We present the measurements of surface finish, flatness, as well as topography results obtained at 1-BM of APS, as compared with results typically achieved when polishing flat-surface monochromator crystals using conventional polishing processes. Limitations of the current machine design, capabilities and considerations for strain-free polishing of highly complex crystals are also discussed, together with an outlook for future developments and improvements.
The use of a channel-cut monochromator is the most straightforward method to ensure that the two reflection surfaces maintain alignment between crystallographic planes without the need for complicated alignment mechanisms. Three basic characteristics that affect monochromator performance are: subsurface damage which contaminates spectral purity; surface roughness which reduces efficiency due to scattering; and surface figure error which imparts intensity structure and coherence distortion in the beam. Standard chemical-mechanical polishing processes and equipment are used when the diffracting surface is easily accessible, such as for single-bounce monochromators. Due to the inaccessibly of the surfaces inside a channel-cut monochromator for polishing, these optics are generally wet-etched for their final processing. This results in minimal subsurface damage, but very poor roughness and figure error. A new CMP channel polishing instrument design is presented which allows the internal diffracting surface quality of channel-cut crystals to approach that of conventional single-bounce monochromators.
The Mesoscopic MEMS (MicroElectroMechanical Systems) technology developed at UIC allows the fabrication of structures not possible with conventional planar thin film patterning methods. These techniques enable the fabrication of an agile micro-mirror that can rapidly tip and tilt by large angles in two independent directions with a small footprint on the substrate. The mirrors can be electrostatically deflected, and rotate around a spherical pivot that is a drop of a conducting liquid. The drop can be forced to spread by applying a small voltage to an electrode surrounding the drop and this provides piston motion for the third degree of freedom. The drop is confined to a lithographically defined wetting area on the mirror and the substrate surfaces. The drop provides a surface tension restoring force to balance the electrostatic torque, as well as electrical and thermal conduction between the mirror and the substrate. The fabrication method uses aligned shadow masks to deposit electrodes on a non-planar substrate. The fabrication requires precision dispensing of approximately 10 pL liquid drops using inkjet printing technology.