Atomic Layer Deposition to Enable the Production, Optimization and Protection of Spaceflight Hardware Project (ALD)

Atomic Layer Deposition (ALD) a cost effective nano-manufacturing technique allows for the conformal coating of substrates with atomic control in a benign temperature and pressure environment. Through the introduction of paired precursor gases thin films can be deposited on a myriad of substrates ranging from glass, polymers, aerogels, and metals to high aspect ratio geometries thus allowing NASA/GSFC to facilitate the production, optimization and protection of valuable space centric hardware. Novel deposition methods and materials justified the design and installation of a custom reactor where dynamic in situ measurements reduced the formulation of the materials system to prototype at a fraction of the cost.  Two specific examples of the reactors benefit include the formation of nanolaminated films and additive material protection. Nanolaminate films constitute diverse materials of periodic layers with distinct film thickness that measure on the order of nanometers.  The multilayered structure often imparts unique characteristics to the nanolaminate film where the periodic morphology may have physical properties that are far superior to single or pure material films. Polymers and polymer composite materials used for lightweight spacecraft structural components are susceptible to surface damage by high-energy collisions with atomic oxygen found in low-Earth orbit and by the high fluxes of vacuum ultraviolet radiation. Because these materials are insulators, they also can accumulate significant levels of surface charge. Plasma-enhanced chemical vapor deposition (PECVD) of SiO2 films is effective at protecting polymer materials, but relatively thick PECVD must be used to eliminate pinholes and to assure sufficient film thicknesses over surfaces with significant topography.  An investigation of TiO2 and TiN coupled films is underway.  While each of these materials alone can provide a protective layer for the polymer, the TiO2 is particularly well suited to VUV protection and the TiN, being conductive, will help dissipate static charge.  A tertiary product of metal oxide ALD is its ability to protect polymeric films such as Kapton from AO erosion in low earth orbiting missions.   NASA Glen confirmed this property where samples of Kapton film coated with an ALD of a metal oxide were exposed to AO fluxes equivalent to 10 years resulted in mass conservation of 98%.        
 

Atomic Layer Deposition (ALD) is a cost effective nano-manufacturing technique that allows for the conformal coating of substrates with atomic control in a benign temperature and pressure environment.  By utilizing the effectiveness of this technique an ALD production method for depositing laminated films of Iridium and metal nitride source material for multilayer x-ray optics, a lamination of TiO2 and TiN for VUV protection and static charge dissipation and the formation of tuned nanopillars for sensors and filters is in the process of being developed.  The film deposition will be done utilizing a custom built in-house ALD reactor and the proposed work is in collaboration with the University of Maryland at College Park. Success of the this work has been demonstrated through the development of a Passive Variable Emittance Film prototype for thermal control, Iridium Coated X-Ray Optics and nanolaminated film for the three-dimensional growth of carbon nanotubes for stray light suppression. Novel deposition methods and materials justified the design and installation of a custom reactor where dynamic in situ measurements reduced the formulation of the materials system to prototype at a fraction of the cost.  Three specific examples of the reactors benefit include the formation of nanolaminated films, additive material protection and tunable nanopillars. Nanolaminate films constitute diverse materials of periodic layers with distinct film thickness that measure on the order of nanometers.  The multilayered structure often imparts unique characteristics to the nanolaminate film where the periodic morphology may have physical properties that are far superior to single or pure material films. Polymers and polymer composite materials used for lightweight spacecraft structural components are susceptible to surface damage by high-energy collisions with atomic oxygen found in low-Earth orbit and by the high fluxes of vacuum ultraviolet radiation. Because these materials are insulators, they also can accumulate significant levels of surface charge. Plasma-enhanced chemical vapor deposition (PECVD) of SiO2 films is effective at protecting polymer materials, but relatively thick PECVD must be used to eliminate pinholes and to assure sufficient film thicknesses over surfaces with significant topography.  An investigation of TiO2 and TiN coupled films is underway.  While each of these materials alone can provide a protective layer for the polymer, the TiO2 is particularly well suited to VUV protection and the TiN, being conductive, will help dissipate static charge.  A tertiary product of metal oxide ALD is its ability to protect polymeric films such as Kapton from AO erosion in low earth orbiting missions.   NASA Glen confirmed this property where samples of Kapton film coated with an ALD of a metal oxide were exposed to AO fluxes equivalent to 10 years resulted in mass conservation of 98%. The formation of the tuned nanopillars is accomplished by utilizing nanomolds of sputtered aluminum on the substrate of choice.  The sputtered aluminum can be transformed into spatially arrayed pores of predefined length and diameter utilizing acidic baths and an applied voltage.  After pore/hole formation, material can be deposited within these structures utilizing ALD to produce standing nanotubes or pillars.  These initial developments in scaffold assisted nanogeometric formations have potential applications in rectifying nanoantennas, sensors (chemical, biological, medical), and novel p-type semiconductors for solar cells, natural gas filtration, catalysis and nanocapacitors.  This application has a potential follow on funding from technology that requires filtration or catalytic capabilities for non-hydrazine based “green” fuels.