Automated Control of Plasma Ion-Assisted Electron Beam-Deposited TiO2 Optical Thin Films
by
Bing Hui 1,2, Xiuhua Fu 1,*, Des Gibson 2,*
, David Child 2, Shigeng Song 2, Lewis Fleming 2, Guntis Rutins 2, Hin On Chu 2, Caspar Clark 3 and Stuart Reid 4
Bing Hui 1,2, Xiuhua Fu 1,*, Des Gibson 2,*, David Child 2, Shigeng Song 2, Lewis Fleming 2, Guntis Rutins 2, Hin On Chu 2, Caspar Clark 3 and Stuart Reid 4
1
School of OptoElectronic Engineering, Changchun University of Science and Technology, Changchun 130012, China
2
Scottish Universities Physics Alliance (SUPA), The Institute for Thin Films, Sensors & Imaging, University of the West of Scotland, Paisley PA1 2BE, UK
3
CJS Instrumentation Ltd., Easter Inch Industrial Estate, Bathgate EH48 2FJ, UK
4
Scottish Universities Physics Alliance (SUPA), Department of Biomedical Engineering, University of Strathclyde, Glasgow G1 1QE, UK
*
Authors to whom correspondence should be addressed.
Coatings 2018, 8(8), 272; https://doi.org/10.3390/coatings8080272
Received: 4 July 2018 / Revised: 20 July 2018 / Accepted: 3 August 2018 / Published: 5 August 2018
(This article belongs to the Special Issue Applications of Optical Thin Film Coatings)
A hollow cathode plasma source has been operated automatically, demonstrating independent control of plasma ion energy and ion current density for plasma ion-assisted electron beam-deposited titania (TiO2). The lanthanum hexaboride hollow cathode design described in this work utilizes both the interior and exterior cathode surfaces, with the additional electrons generated removing the need for a separate neutralizing source. Automatic feedback control of plasma source cathode-to-anode accelerator voltage (AV—via argon gas flow to the anode and/or cathode plasma source areas) and accelerator current (AC—via an external high-current power supply) provides independent control of the ion energy distribution function and ion current density, respectively. Automated run-to-run reproducibility (over six separate deposition runs) in TiO2 refractive index (550 nm) was demonstrated as 2.416 ± 0.008 (spread quoted as one standard deviation), which is well within the required refractive index control for optical coating applications. Variation in refractive index is achievable through control of AV (ion energy) and/or AC (ion current density), directly influencing deposited TiO2 structural phase. Measured dependencies of TiO2 refractive index and extinction coefficient on AV and AC are described. Optimum plasma source parameters for assisted electron beam deposition of TiO2 optical thin-film applications are highlighted.
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MDPI and ACS Style
Hui, B.; Fu, X.; Gibson, D.; Child, D.; Song, S.; Fleming, L.; Rutins, G.; Chu, H.O.; Clark, C.; Reid, S. Automated Control of Plasma Ion-Assisted Electron Beam-Deposited TiO2 Optical Thin Films. Coatings 2018, 8, 272.
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