Structural characterization of diamond-like carbon films for ultracold neutron applications |
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| Affiliation: | 1. Paul Scherrer Institut, Villigen, Switzerland;2. Fraunhofer Institut für Werkstoff-und Strahltechnik, Dresden, Germany;3. Physik-Institut der Universität Zürich, Switzerland;4. Institut für Technische Chemie, ETH Zürich, Switzerland;5. Stefan Meyer Institut für subatomare Physik, Austrian Academy of Sciences, Vienna, Austria;6. Jagellonian University, Cracow, Poland |
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| Abstract: | We have produced hydrogen-free diamond-like carbon (DLC) films by vacuum arc deposition for use as wall coating material in ultracold neutron (UCN) applications. The sp3 fraction, the main quality factor for DLC used in UCN applications, was varied from 0.4 to 0.9, the coating thickness between 10 nm and 120 nm. The samples were characterized by using X-ray Absorption Near-Edge Spectroscopy (XANES), X-ray induced Photoelectron Spectroscopy (XPS), Laser induced surface Acoustic Waves (LAwave), cold neutron reflectometry and Raman spectroscopy at visible excitation wavelength. We observe reasonable agreement between the different results for film thicknesses below 20 nm. For larger thickness, we find that the surface-sensitive methods XPS and XANES yield smaller sp3 fractions (by up to 20%) than the bulk-sensitive LAwave, being consistent with the assumption of a lower-density surface layer on a nominal-density bulk layer. |
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