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

Abstract

McKinstry, "Thickness distribution of sputtered films on curved substrates for adjustable x-ray optics," J.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 ðZr 0.52 Ti 0.48 Þ 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.

Phase Transformation and Characterization of 3D Reactive Microstructures in Nanoscale Al/Ni Multilayers

“…For the atoms that reach the tip of the silicon needles, θ will be close to 0 • while for the atoms that reach the lateral sides of the needles, θ will be close to 90 • . Previous studies demonstrated the influence of the incidence angle on the microstructure of the films deposited by magnetron sputtering [33,34]. The increase in incidence angle results not only in a higher porosity in surface morphology but also in a rougher surface [33].…”

“…Figure 7d reveals the convex shape of the needle tips. During sputter deposition, a curved surface affects the coating's thickness, generating a lateral gradient with the maximum thickness at the center of the tip and the minimum thickness at the corners [34]. Due to the curvature, atoms will arrive at more grazing incidence for points farther from the center of the tip.…”

Lynx X-Ray Observatory: an overview

“…X-ray mirror technologies that were studied in detail by the Lynx team included silicon meta-shell optics developed by GSFC, 4 fullshell optics developed by Brera (INAF/Brera) and Marshall Spaceflight Center (MSFC), 5,6 and adjustable segmented optics developed by the SAO. 7,8 Similarly, multiple technologies were studied for the large-scale active sensor pixel array, dubbed the high-definition x-ray imager (HDXI) [9][10][11][12] and for the XGS. 13,14 The Lynx x-ray microcalorimeter (LXM) [15][16][17][18][19][20][21] is singular but has elements that have multiple candidate technologies.…”

“…These mirror technologies have been reported on in the previous publications, are highlighted in this special section as well, and are silicon meta-shell optics, 4 full-shell optics, 5,6 and adjustable optics. 7,8 A brief summary of each is provided below.…”

Electrical coupling analysis of 2D time-multiplexing memory actuators exhibiting asymmetric butterfly hysteresis

“…New solutions and technologies are developed for realising high actuator densities in DMs 3,4 as well as novel materials tested and manufactured [5][6][7][8] . A recently presented concept of a hysteretic deformable mirror (HDM) 9 for an exoplanetimaging space mission opens up the possibility of deploying an extremely dense actuator array where 2D memory piezoactuators are realized by placing a newly developed piezoelectric shape memory material between two orthogonal layers of electrodes as illustrated in Figure 1.…”