Beamline Description
A thorough description of the beamline and of its performances can be found in the following article:
Performance of SISSI, the infrared beamline of the ELETTRA Storage-Ring
S. Lupi, A, Nucara, A. Perucchi, P. Calvani, M. Ortolani, L. Quaroni, M. Kiskinova
J. Opt. Soc. America B 24, 959 (2007)
doi:10.1364/JOSAB.24.000.959
Layout
The radiation is collected from bending magnet 9.1 over acceptance angles of 70 mrad (H) and 25 mrad (V) and comprises both edge and constant field emission. The extracted radiation enters the first vacuum chamber, which hosts the plane extraction mirror M1 and the ellipsoid mirror M2. M1 is placed at a distance of 3500 mm from the source and collects the radiation 70 mrad in the horizontal and 25 mrad in the vertical plane. M2 is placed at a distance 100 cm from M1 and focuses the radiation beyond the shielding wall of the synchrotron hall in the intermediate focal point F1 at a distance of 1150 cm from the source. The second vacuum chamber, placed at a distance of 1450 cm from the source, hosts the third M3 (plane) and fourth M4 (ellipsoidal) mirrors, in a symmetric optical configuration with respect to M1 and M2. This optical design permits the aberrations by the transfer optics due to the wide emission angle to be minimised. M4 focuses the IRSR on the CVD diamond window (point F2 at 1550 cm from the source), which is the last UHV component of the first branch. With the help of a retractable mirror (M5), light can be deviated along the second branch, at the end of which a CVD diamond window is also found.
Signal to NoiseThe reproducibility and the noise level of the spectromicroscopy set-up in the mid-IR range hasve been determined using a gold coated Si-wafer test sample placed on the microscope stage and measuring the ratio of two subsequent spectra acquired with a MCT detector in reflection mode by summing 128 scans at a resolution of 4 cm-1.  For apertures smaller than about 40x40 micron, InfaRed Synchrotron Radiation (IRSR) becomes advantageous. Indeed, IRSR provides a good root mean square of the noise on the 100% line (RMS) down to 4x4 micron. In particular, in the whole spectral range using this aperture, a noise level with an excellent RMS ~ 0.3% and ~ 0.75%, repectively in the 2450-2550 cm-1 and 1100-1200 cm-1 spectral region, is obtained. At 2x3 micron the RMS ~ 1.5% obtained above 1000 cm-1 is still acceptable for several applications.
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Imaging CapabilitiesThe imaging capabilities of the SISSI beamline have been checked with the help of lithographic test patterns. The measurements were performed in early 2011, to check the beamline performances after the 2010 storage-ring re-allignment. 
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Spatial Resolution
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In order to evaluate the spatial resolution which can be achieved with our synchrotron beam, we have performed a longitudinal scan of photoresist stripes patterned on a CaF2 substrate. The measurements have been performed in transmission mode with 36x objective and condenser, and apertures set at 3 micron squared. We have acquired one spectrum every 1 micron, and integrated the absorbance between 2800 and 3000 cm-1. The curve of the integrated intensity is reported in the left figure, as a function of the displacement. The curves where then smoothly interpolated before calculating the derivative displayed in the right figure. The Full Width at Half Maximum of the peak in the derivative (corresponding to a step on the sample), provides the lateral resolution of our set-up: 3 micron at 3000 cm-1, corresponding to the diffraction limit. |
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