Battery-powered Deposition
Brief Description. ZeCoat is developing a new and novel way of depositing a thin film optical coating. This new method uses many small evaporation sources that fire simultaneously in a controlled manner. This application process allows a large mirror to be uniformly coated in a matter of seconds. There are several advantages to this method of coating, including:
· The ability to install the system in different vacuum chambers
· The ability to coat a mirror in outer space
· A better performing coating which enhances reflectance in the FUV down to 90-nm
Funded Research Titles:
1. “Precision Optical Coating for Large Space Telescope Mirrors”, David A. Sheikh, ZeCoat Corporation, NASA APRA (2017)
Abstract:
This proposal “Precision Optical Coatings for Large Space Telescope Mirrors” addresses the need to develop and advance the state-of-the-art in optical coating technology. NASA is considering large monolithic mirrors 1 to 8-meters in diameter for future telescopes such as HabEx and LUVOIR. Improved large area coating processes are needed to meet the future requirements of large astronomical mirrors. In this project, we will demonstrate a broadband reflective coating process for achieving high reflectivity from 90-nm to 2500-nm over a 2.3-meter diameter coating area. The coating process is scalable to larger mirrors, 6+ meters in diameter. We will use a battery-driven coating process to make an aluminum reflector, and a motion-controlled coating technology for depositing protective layers. We will advance the state-of-the-art for coating technology and manufacturing infrastructure, to meet the reflectance and wavefront requirements of both HabEx and LUVOIR. Specifically, we will combine the broadband reflective coating designs and processes developed at GSFC and JPL with large area manufacturing technologies developed at ZeCoat Corporation. Our primary objectives are to: Demonstrate an aluminum coating process to create uniform coatings over large areas with near-theoretical aluminum reflectance Demonstrate a motion-controlled coating process to apply very precise 2-nm to 5- nm thick protective/interference layers to large areas, Demonstrate a broadband coating system (90-nm to 2500-nm) over a 2.3-meter coating area and test it against the current coating specifications for LUVOIR/HabEx. We will perform simulated space-environment testing, and we expect to advance the TRL from 3 to >5 in 3-years.
2. “Battery-powered Deposition (BPD) Process for Broadband Reflective Coatings”, David A. Sheikh, ZeCoat Corporation, NASA SBIR (2016)
Identification and Significance of the Innovation:
A battery-powered deposition (BPD) process is a significant innovation because it will allow FUV-quality aluminum to be applied to very large areas, at high evaporation rates, and with less outgassing. This will allow contamination-free and low-scatter, aluminum coatings for broadband, space-based astronomy.
· BPD units may also be used to drive off moisture before beginning evaporation or to heat a surface for deposition.
· BPD units may also be sued to coat optics in space, to extend broadband reflectance down into the EUB (50-nm to 90-nm)
· BPD units may be retrofitted into existing vacuum chambers for coating very large ground-based telescope mirrors.
SPIE papers:
1. Manuel A. Quijada, Javier G. Del Hoyo, Emrold Gray, J. Grabriel Richardson, Andrew Howe, Luis Rodriguez de Marcos, David A. Sheikh, "Influence of evaporation rate and chamber pressure on the FUV reflectance and physical characteristics of aluminum films," Proc. SPIE 11819, UV/Optical/IR Space Telescopes and Instruments: Innovative Technologies and Concepts X, 118190G (20 August 2021); https://doi.org/10.1117/12.2595392
Abstract:
Space telescopes for studying astrophysical phenomena from the far ultraviolet (FUV) to the near infrared (NIR) require durable mirror coatings with high and uniform reflectance over a very broad spectral region. While coatings for the optical and NIR region are well developed with proven performance, the FUV band presents significant challenges, particularly below 115 nm. Recent developments in physical vapor deposition (PVD) coating processes of aluminum mirrors that are protected with a metal-fluoride overcoat to prevent oxidation (such as LiF, MgF2, or AlF3) have improved reflectance in the FUV. While the emphasis in these studies has been placed on improving the deposition conditions of the metal-fluoride overcoats, less attention has been devoted to how deposition parameters (such as vacuum conditions or deposition rates) may affect the quality of the aluminum mirrors. This paper presents characterization of Al+MgF2 coupons made by ash evaporation of aluminum followed by resistive evaporation of MgF2. Samples were manufactured under a variety of processing conditions and the relationship between processing variables and mirror FUV re ectivity is analyzed. Performance characterization was based on the measured near-normal reflectance in the FUV (90-180 nm), and normal-incidence transmittance in the visible was done to analyze the possible presence of pinholes in the mirror. We demonstrated pinhole-free Al/MgF2 mirrors deposited at room temperature with a reflectivity of 0.91 at 122 nm wavelength. This reflectivity enhancement was achieved solely through parameter optimization.
2. Manuel A. Quijada, David A. Sheikh, Javier G. Del Hoyo, J. Gabriel Richardson, "ZERODUR(R) substrates for application of high-temperature protected-aluminum far-ultraviolet coatings," Proc. SPIE 11116, Astronomical Optics: Design, Manufacture, and Test of Space and Ground Systems II, 111160T (12 September 2019); https://doi.org/10.1117/12.2530585
Abstract:
Recent development in coating deposition processes for aluminum (Al) mirrors that are protected with a metal-fluoride overcoat (such as LiF, MgF2, or AlF3) have improved reflectance performance particularly in the far- ultraviolet (FUV) part of the optical spectrum. The active research in this area is motivated by the fact that these gains in reflectance are expected to significantly increase the throughput of any future FUV sensitive NASA missions into the Lyman Ultraviolet. These reflectance improvements are attributed, in part, by performing the metal-fluoride overcoat depositions with the substrates at an elevated temperature as high as 250 °C. ZERODUR® is a widely used material as a mirror substrate because, among other things, it exhibits a low coefficient of thermal expansion (CTE) over a wide range of temperatures. Moreover, ZERODUR® has recently been proposed for several future NASA concept missions where this improved FUV mirror coating may be used. Given the elevated temperature at which these improved FUV coatings are produced, it is imperative to make sure that heating of the substrate will not significantly impact the final figure of the coated mirror. In this paper, we will study and report the effects of heating ZERODUR® up to the highest temperature mentioned above (250 °C) during a simulated coating process. These studies are relevant since it has been reported the CTE will change if ZERODUR® is cooled down from application temperatures between 130°C and 320°C with rates that differ from the initial production annealing rate of 3°C/hr.
3. David A. Sheikh, "Battery-powered thin film deposition process for coating telescope mirrors in space," Proc. SPIE 9904, Space Telescopes and Instrumentation 2016: Optical, Infrared, and Millimeter Wave, 99046J (29 July 2016); https://doi.org/10.1117/12.2234335
Abstract:
Aluminum films manufactured in the vacuum of space may increase the broadband reflectance response of a space telescope operating in the EUV (50-nm to 115-nm) by eliminating absorbing metal-fluorides and metal-oxides, which significantly reduce aluminum’s reflectance below 115-nm. Recent developments in battery technology allow small lithium batteries to rapidly discharge large amounts of energy. It is therefore conceivable to power an array of resistive evaporation filaments in a space environment, using a reasonable mass of batteries and other hardware. This paper presents modeling results for coating thickness as a function of position, for aluminum films made with a hexagonal array of battery powered evaporation sources. The model is based on measured data from a single battery-powered evaporation source.
4. D. A. Sheikh, Manuel A. Quijada, Javier Del Hoya, Joseph G. Richardson, "Mathematical analysis of hexagonal source arrangement for making uniform reflective aluminum coatings," Proc. SPIE 11116, Astronomical Optics: Design, Manufacture, and Test of Space and Ground Systems II, 111160Q (9 September 2019); https://doi.org/10.1117/12.2529530
Abstract:
This paper presents modeling results for coating thickness as a function of position, for aluminum films made with a hexagonal array of evaporation sources. The computer simulation is based on measured plume data from a single evaporation source. The model is used to determine optimum source spacing for a given plume shape. The analysis revealed that arrangement of multiple sources in a hexagonal array can produce uniform coatings while utilizing a reasonable number of evaporation sources per square meter of coating area. Monte Carlo simulations followed by gradient descent optimization methods were used to determine optimal flatness solutions for groups of deposition sources with varied deposition times. Thin aluminum films with exceptional coating flatness are needed to meet the wavefront error requirements of future space-based telescope concepts such as HabEx, LUVOIR, CETUS and others.
For more information on this technology, contact us by email at info@zecoat.com