G3 Beamline

In situ, time resolved surface scattering & thin film deposition

G3 Station Summary
First Monochromator: Two-bounce, synthetic W/B4C multilayers
Energy Range: 8-13.6 keV
Focused full beam size at 10 keV: 2.0 mm HZ by 1.0 mm VT
Flux: 3 x 1013 photons/mm2/second
Bandwidth: 1.5 %
Typical Applications: In situ thin film growth & surface manipulation

G3 is one of five CHESS hutches fed by a single 49-pole wiggler in the Southwest section of the CESR tunnel. G1, G2, and G3 are fed by the positron beam, whereas A1 and A2 are fed by electrons. The front-end G-line optics consist of an interally water-cooled collimating mirror, two pairs of synthetic multilayer monochromators, and two additional, monochromatic mirrors. The wiggler beam is separated by the upstream multilayers of each pair into upper and lower branches. The upper branch is delivered to G1, whereas the lower branch is used by both G2 and G3. The collimating mirror and monochromatic mirrors are both mounted to dynamic benders, providing vertical focusing. Horizontal, sagittal focusing is provided by the cylindrically-shaped second multilayer. At 10 keV, G3 receives approximately 6x1013 photons/second in a 2 mm x 1 mm beam, with a bandwidth ΔE/E of 1.5%. An in-hutch, channel-cut Si(111) monochromator may be inserted on-the-fly for measurements demanding narrower bandwidth. The monochromatic flux at G3 is currently the largest available at CHESS in this energy regime, making G3 a superlative station for flux-limited experiments as well as feasibility studies involving novel optics and detectors. In particular, G3 science has focused on surface-senstive x-ray scattering at time scales relevant to thin film growth.

A key and nearly unique feature of G3 is the presence of in-hutch gas cabinets to allow for the use of hazardous gases often employed for thin film growth and processing. G3 also houses a 348-nm excimer laser for pulsed laser deposition. Examples of prior studies include the use of both specular [ref Fleet] and diffuse scattering [Ferguson] to characterize the interplay of surface time and length scales during pulsed laser deposition. Different process chambers (Figure 1) are exchanged onto a newly upgraded 3-axis optical table (Figure 2, ADC, Lansing, IL) that is used to align the chamber to the beam and provides a vertical axis of rotation for the chamber. The table also mounts a Huber 440 stage mounted with its rotation axis horizontal, approximately 27 cm from the table surface. Use of G3 for thin-film processing generally requires the user group to provide its own process chamber, for which critical specifications can be provided.