Automated control of plasma ion-assisted electron beam-deposited TiO2 optical thin films

Bing Hui, Fu Xiuhua, Desmond Gibson, David Child, Shigeng Song, Lewis Fleming, Guntis Rutins, Hin On Chu, Caspar Clark, Stuart Reid

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Abstract

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.
Original languageEnglish
Article number272
Number of pages11
JournalCoatings
Volume2018
Issue number8
DOIs
Publication statusPublished - 5 Aug 2018

Keywords

  • plasma ion source
  • Titania
  • refractive index
  • accelerator current
  • accelerator voltage

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