Thickness distribution of sputtered films on curved substrates for adjustable x-ray optics

Nathan Bishop, Julian Walker, Casey T. Deroo, Tianning Liu, Mohit Tendulkar, Vincenzo Cotroneo, Edward N. Hertz, Vladimir Kradinov, Eric D. Schwartz, Paul B. Reid, Thomas Nelson Jackson, Susan E. Trolier-McKinstry

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Piezoelectric adjustable x-ray optics use magnetron sputtered thin film coatings on both sides of a thin curved glass substrate. To produce an optic suitable for a mission requiring high-angular resolution like "Lynx," the integrated stresses (stress × thickness) of films on both sides of the optic must be approximately equal. Thus, understanding how sputtered film thickness distributions change for convex and concave curved substrates is necessary. To address this, thickness distributions of piezoelectric Pb 0.995 (Zr 0.52 Ti 0.48) 0.99 Nb 0.01 O 3 films are studied on flat, convex, and concave cylindrical substrates with a 220-mm radius of curvature. A mathematical model of the film thickness distribution is derived based on the geometric properties of the sputter tool and the substrate, and film thicknesses deposited with a commercially available sputtering tool are measured with spectroscopic ellipsometry. Experiment and modeled results for flat and convex curved substrates demonstrate good agreement, with average relative thickness distribution difference of 0.19% and -0.10% respectively, and a higher average difference of 1.4% for concave substrates. The calculated relative thickness distributions are applied to the convex and concave sides of a finite-element analysis (FEA) model of an adjustable x-ray optic prototype. The FEA model shows that, left uncorrected, the relative film thickness variation will yield an optic with an optical performance of 2.6 arc sec half power diameter (HPD) at 1 keV. However, the mirror figure can be corrected to diffraction-limited performance (0.3 arc sec HPD) using the piezoelectric adjusters, suggesting that the tolerances for applying a balanced integrated stress on both sides of a mirror are alleviated for adjustable x-ray optics as compared to traditional static x-ray mirrors. Furthermore, the piezoelectric adjusters will also allow changes in mirror figure over the telescope lifetime due to drift in the stress states of the x-ray surfaces to be corrected on orbit.

Original languageEnglish (US)
Article number021005
JournalJournal of Astronomical Telescopes, Instruments, and Systems
Volume5
Issue number2
DOIs
StatePublished - Apr 1 2019

Fingerprint

x ray optics
Optics
substrate
X rays
Film thickness
film thickness
Substrates
mirrors
Mirrors
optics
arcs
Finite element method
Spectroscopic ellipsometry
Optical resolving power
angular resolution
Telescopes
ellipsometry
Sputtering
distribution
mathematical models

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Control and Systems Engineering
  • Instrumentation
  • Astronomy and Astrophysics
  • Mechanical Engineering
  • Space and Planetary Science

Cite this

Bishop, Nathan ; Walker, Julian ; Deroo, Casey T. ; Liu, Tianning ; Tendulkar, Mohit ; Cotroneo, Vincenzo ; Hertz, Edward N. ; Kradinov, Vladimir ; Schwartz, Eric D. ; Reid, Paul B. ; Jackson, Thomas Nelson ; Trolier-McKinstry, Susan E. / Thickness distribution of sputtered films on curved substrates for adjustable x-ray optics. In: Journal of Astronomical Telescopes, Instruments, and Systems. 2019 ; Vol. 5, No. 2.
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Thickness distribution of sputtered films on curved substrates for adjustable x-ray optics. / Bishop, Nathan; Walker, Julian; Deroo, Casey T.; Liu, Tianning; Tendulkar, Mohit; Cotroneo, Vincenzo; Hertz, Edward N.; Kradinov, Vladimir; Schwartz, Eric D.; Reid, Paul B.; Jackson, Thomas Nelson; Trolier-McKinstry, Susan E.

In: Journal of Astronomical Telescopes, Instruments, and Systems, Vol. 5, No. 2, 021005, 01.04.2019.

Research output: Contribution to journalArticle

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T1 - Thickness distribution of sputtered films on curved substrates for adjustable x-ray optics

AU - Bishop, Nathan

AU - Walker, Julian

AU - Deroo, Casey T.

AU - Liu, Tianning

AU - Tendulkar, Mohit

AU - Cotroneo, Vincenzo

AU - Hertz, Edward N.

AU - Kradinov, Vladimir

AU - Schwartz, Eric D.

AU - Reid, Paul B.

AU - Jackson, Thomas Nelson

AU - Trolier-McKinstry, Susan E.

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