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By NASA
5 min read
Atomic Layer Processing Coating Techniques Enable Missions to See Further into the Ultraviolet
Astrophysics observations at ultraviolet (UV) wavelengths often probe the most dynamic aspects of the universe. However, the high energy of ultraviolet photons means that their interaction with the materials that make up an observing instrument are less efficient, resulting in low overall throughput. New approaches in the development of thin film coatings are addressing this shortcoming by engineering the coatings of instrument structures at the atomic scale.
Researchers at the NASA Jet Propulsion Laboratory (JPL) are employing atomic layer deposition (ALD) and atomic layer etching (ALE) to enable new coating technologies for instruments measuring ultraviolet light. Conventional optical coatings largely rely on physical vapor deposition (PVD) methods like evaporation, where the coating layer is formed by vaporizing the source material and then condensing it onto the intended substrate. In contrast, ALD and ALE rely on a cyclic series of self-limiting chemical reactions that result in the deposition (or removal) of material one atomic layer at a time. This self-limiting characteristic results in a coating or etchings that are conformal over arbitrary shapes with precisely controlled layer thickness determined by the number of ALD or ALE cycles performed.
The ALD and ALE techniques are common in the semiconductor industry where they are used to fabricate high-performance transistors. Their use as an optical coating method is less common, particularly at ultraviolet wavelengths where the choice of optical coating material is largely restricted to metal fluorides instead of more common metal oxides, due to the larger optical band energy of fluoride materials, which minimizes absorption losses in the coatings. Using an approach based on co-reaction with hydrogen fluoride, the team at JPL has developed a variety of fluoride-based ALD and ALE processes.
(left) The Supernova remnants and Proxies for ReIonization Testbed Experiment (SPRITE) CubeSat primary mirror inside the ALD coating facility at JPL, the mirror is 18 cm on the long and is the largest optic coated in this chamber to-date. (right) Flight optic coating inside JPL ALD chamber for Pioneers Aspera Mission. Like SPRITE, the Aspera coating combines a lithium fluoride process developed at NASA GSFC with thin ALD encapsulation of magnesium fluoride at JPL. Image Credit: NASA-JPL In addition to these metal-fluoride materials, layers of aluminum are often used to construct structures like reflective mirrors and bandpass filters for instruments operating in the UV. Although aluminum has high intrinsic UV reflectance, it also readily forms a surface oxide that strongly absorbs UV light. The role of the metal fluoride coating is then to protect the aluminum surface from oxidation while maintaining enough transparency to create a mirror with high reflectance.
The use of ALD in this context has initially been pursued in the development of telescope optics for two SmallSat astrophysics missions that will operate in the UV: the Supernova remnants and Proxies for ReIonization Testbed Experiment (SPRITE) CubeSat mission led by Brian Fleming at the University of Colorado Boulder, and the Aspera mission led by Carlos Vargas at the University of Arizona. The mirrors for SPRITE and Aspera have reflective coatings that utilize aluminum protected by lithium fluoride using a novel PVD processes developed at NASA Goddard Space Flight Center, and an additional very thin top coating of magnesium fluoride deposited via ALD.
Team member John Hennessy prepares to load a sample wafer in the ALD coating chamber at JPL. Image Credit: NASA JPL The use of lithium fluoride enables SPRITE and Aspera to “see” further into the UV than other missions like NASA’s Hubble Space Telescope, which uses only magnesium fluoride to protect its aluminum mirror surfaces. However, a drawback of lithium fluoride is its sensitivity to moisture, which in some cases can cause the performance of these mirror coatings to degrade on the ground prior to launch. To circumvent this issue, very thin layers (~1.5 nanometers) of magnesium fluoride were deposited by ALD on top of the lithium fluoride on the SPRITE and Aspera mirrors. The magnesium fluoride layers are thin enough to not strongly impact the performance of the mirror at the shortest wavelengths, but thick enough to enhance the stability against humidity during ground phases of the missions. Similar approaches are being considered for the mirror coatings of the future NASA flagship Habitable Worlds Observatory (HWO).
Multilayer structures of aluminum and metal fluorides can also function as bandpass filters (filters that allow only signals within a selected range of wavelengths to pass through to be recorded) in the UV. Here, ALD is an attractive option due to the inherent repeatability and precise thickness control of the process. There is currently no suitable ALD process to deposit aluminum, and so additional work by the JPL team has explored the development of a custom vacuum coating chamber that combines the PVD aluminum and ALD fluoride processes described above. This system has been used to develop UV bandpass filters that can be deposited directly onto imaging sensors like silicon (Si) CCDs. These coatings can enable such sensors to operate with high UV efficiency, but low sensitivity to longer wavelength visible photons that would otherwise add background noise to the UV observations.
Structures composed of multilayer aluminum and metal fluoride coatings have recently been delivered as part of a UV camera to the Star-Planet Activity Research CubeSat (SPARCS) mission led by Evgenya Shkolnik at Arizona State University. The JPL-developed camera incorporates a delta-doped Si CCD with the ALD/PVD filter coating on the far ultraviolet channel, yielding a sensor with high efficiency in a band centered near 160 nm with low response to out-of-band light.
A prototype of a back-illuminated CCD incorporating a multi-layer metal-dielectric bandpass filter coating deposited by a combination of thermal evaporation and ALD. This coating combined with JPL back surface passivation approaches enable the Si CCD to operate with high UV efficiency while rejecting longer wavelength light. Image credit: NASA JPL Next, the JPL team that developed these coating processes plans to focus on implementing a similar bandpass filter on an array of larger-format Si Complementary Metal-Oxide-Semiconductor (CMOS) sensors for the recently selected NASA Medium-Class Explorer (MIDEX) UltraViolet EXplorer (UVEX) mission led by Fiona Harrison at the California Institute of Technology, which is targeted to launch in the early 2030s.
For additional details, see the entry for this project on NASA TechPort
Project Lead: Dr. John Hennessy, Jet Propulsion Laboratory (JPL)
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Last Updated Mar 18, 2025 Related Terms
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By NASA
Students, mentors, and team supporters donning team colors watch robots clash on the playing field at the FIRST Robotics Los Angeles regional competition in El Segundo on March 16. NASA/JPL-Caltech Robots built by high schoolers vied for points in a fast-moving game inspired by complex ocean ecosystems at the FIRST Robotics Los Angeles regional competition.
High school students who spent weeks designing, assembling, and testing 125-pound rolling robots put their fast-moving creations into the ring over the weekend, facing off at the annual Los Angeles regional FIRST Robotics Competition, an event supported by NASA’s Jet Propulsion Laboratory in Southern California.
Four of the 43 participating teams earned a chance to compete in April at the FIRST international championship tournament in Houston, which draws winning teams from across the country.
Held March 14 to 16 at the Da Vinci Schools campus in El Segundo, the event is one of many supported by the nonprofit FIRST (For Inspiration and Recognition of Science and Technology), which pairs students with STEM professionals. Teams receive the game rules, which change every year, in January and sprint toward competition, assembling their robot based on FIRST’s specifications. The global competition not only gives students engineering experience but also helps them develop business skills with a range of activities, from fundraising for their team to marketing.
For this year’s game, called “Reefscape,” two alliances of three teams competed for points during each 2½-minute match. That meant six robots at a time sped across the floor, knocking into each other and angling to seed “coral” (pieces of PVC pipe) on “reefs” and harvesting “algae” (rubber balls). In the final seconds of each round, teams could earn extra points if their robots were able to hoist themselves into the air and dangle from hanging cages, as though they were ascending to the ocean surface.
The action was set to a bouncy soundtrack that reverberated through the gym, while in the bleachers there were choreographed dancing, loud cheers, pom-poms, and even some tears.
The winning alliance was composed of Warbots from Downey’s Warren High School, TorBots from Torrance’s South High School, and West Torrance Robotics from Torrance’s West High School. The Robo-Nerds of Benjamin Franklin High in Los Angeles’ Highland Park and Robo’Lyon from Notre Dame de Bellegarde outside Lyon, France, won awards that mean they’ll also get to compete in Houston, alongside the Warbots and the TorBots.
NASA and its Robotics Alliance Project provide grants for high school teams across the country and support FIRST Robotics competitions to encourage students to pursue STEM careers in aerospace. For the L.A. regional competition, JPL has coordinated volunteers — and provided coaching and mentoring to teams, judges, and other competition support — for 25 years.
For more information about the FIRST Los Angeles regional, visit:
https://cafirst.org/frc/losangeles/
News Media Contact
Melissa Pamer
Jet Propulsion Laboratory, Pasadena, Calif.
626-314-4928
melissa.pamer@jpl.nasa.gov
2025-037
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Last Updated Mar 17, 2025 Related Terms
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By European Space Agency
Video: 01:08:00 Watch the replay of our Hera mission Mars flyby event. On 12 March 2025, ESA’s Hera mission came to within 5000 km of the surface of the red planet and 300 km of Mars’s more distant and enigmatic moon Deimos. During this flyby, Hera performed observations of both Mars and the city-sized Deimos. Hera then needed to swing its High Gain Antenna back to Earth to transmit its data home. On Thursday, 13 March, these images were premiered by Hera’s science team from ESA’s ESOC mission control centre in Darmstadt, Germany, explaining what they reveal, during our public webcast starting at 11:50 CET. The team was joined by ESA astronaut Alexander Gerst and renowned science fiction writer Andy Weir, author of The Martian and Project Hail Mary, as well as a surprise special guest!
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By European Space Agency
While performing yesterday’s flyby of Mars, ESA’s Hera mission for planetary defence made the first use of its payload for scientific purposes beyond Earth and the Moon. Activating a trio of instruments, Hera imaged the surface of the red planet as well as the face of Deimos, the smaller and more mysterious of Mars’s two moons.
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By European Space Agency
Video: 00:02:43 On 12 March 2025 ESA’s Hera spacecraft for planetary defence performs a flyby of Mars. The gravity of the red planet shifts the spacecraft’s trajectory towards the Didymos binary asteroid system, shortening its trip by months and saving substantial fuel.
This is a simulation of that flyby, sped up 500 times, with closest approach to Martian moon Deimos taking place at 12:07 GMT and Mars occurring at 12:51 GMT. It was made using SPICE (Spacecraft, Planet, Instrument, C-matrix, Events) software. Produced by a team at ESA’s ESAC European Space Astronomy Centre, this SPICE visualisation is used to plan instrument acquisitions during Hera’s flyby.
Hera comes to around 5000 km from the surface of Mars during its flyby. It will also image Deimos, the smaller of Mars’s two moons, from a minimum 1000 km away (while venturing as close as 300 km). Hera will also image Mars’s larger moon Phobos as it begins to move away from Mars. In this sped-up simulation, Deimos is seen 30 seconds in, at 12:07 GMT, while the more distant star-like Phobos becomes visible at two minutes in, at 12:49 GMT.
The spacecraft employs three of its instruments over the course of these close encounters, all located together on the ‘Asteroid Deck’ on top of Hera:
Hera’s Asteroid Framing Camera is formed of two redundant 1020x1020 pixel monochromatic visible light cameras, used for both navigation and science.
The Thermal Infrared Imager, supplied by the Japanese Aerospace Exploration Agency, JAXA, images at mid-infrared wavelengths to determine surface temperatures.
Hera’s Hyperscout H is a hyperspectral imager, observing in 25 visible and near-infrared spectral bands to prospect surface minerals.
Did you know this mission has its own AI? You can pose questions to our Hera Space Companion!
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