AVS 72 Session SE-ThP: Advanced Surface Engineering Poster Session

This review evaluates pulsed–laser deposition (PLD) and magnetron sputtering (MS) through a practical, application–oriented lens to help researchers and engineers select the most appropriate route for functional thin films (oxides, nitrides, chalcogenides, carbon-based). Drawing on head–to–head studies that deposit identical materials with both techniques, the paper traces how differences in deposition physics translate into film composition, microstructure, defect populations, mechanical properties and device performance.

PLD is highlighted for its reliable stoichiometric transfer from complex targets, its ability to produce high bonding density and elevated sp³ fractions in carbon films, and its suitability for epitaxial growth and high–hardness coatings; its principal drawback is the tendency to generate particulates from the energetic plume unless droplet–mitigation strategies are employed. Magnetron sputtering (DC/RF) is shown to excel at large–area uniformity, conformal coverage and low macroscopic droplet density; pulsed modes and HiPIMS further boost ionization and substrate bombardment, yielding dense films that can rival PLD in many functional metrics while offering established industrial throughput.

The review also surveys hybrid PLD+MS approaches that leverage PLD’s compositional fidelity together with sputtering’s smoother deposition to reduce defects and increase density. Advances in ultra–high vacuum (UHV) platforms enhance both methods: UHV PLD improves cleanliness and epitaxial control, and UHV MS reduces impurity uptake and tightens reproducibility. Manufacturers of scientific research equipment such as PREVAC exemplify systems that enable in–situ diagnostics and clean sample transfer. Finally, the paper places cost and scalability in context: bench–scale sputter tools are typically less costly to acquire and run than PLD benches, whereas at production scale capital expenditures for high–end HiPIMS sputter systems and wafer–scale PLD platforms converge.

The review closes with a concise decision matrix and actionable guidelines to match deposition choice to stoichiometry, surface quality, throughput and budget constraints.

Magnesium hydride (MgH₂) is solid-state hydrogen storage material, with a theoretical hydrogen storage capacity of 7.6 wt%, making it an attractive candidate due to its high hydrogen affinity, low cost and abundance. But high enthalpy of formation and high decomposition energy of MgH₂ requiring about 76 kJ/mol of heat for each mole of H₂ released lead to increase of hydrogenation temperature, slow hydrogenation and dehydrogenation kinetics. Ni is often used as a catalyst to improve the kinetics of MgH₂ formation in H₂-contained atmosphere due to reduced enthalpy of formation of Mg-Ni alloys (<65 kJ/mol) and also has a reduced activation energy of dissociation of molecular hydrogen in comparison to Mg, suggesting that Ni mainly catalyzes the dissociation/recombination reaction barrier for H₂ solid-state hydrogen storage material reducing the hydrogenation/dehydrogenation temperatures. MgNi thin film coatings were prepared via vacuum cathodic arc deposition on sapphire wafer, aluminum foil, and aluminized polyamide tape. The cathodic arc process conditions for deposition of MgNi coatings were chosen to keep the substrate temperature low for which the arc current was selected from 50 to 70 A, and substrates (both sapphire and metal foil) were installed in a free-standing position at floating potential. The coating architecture consisted of the bottom supporting NiTiCu sublayer having large open columnar microstructure promotes the formation of the columnar microstructure with open voids in the MgNi layer. The Pd top layer deposited by e-beam evaporation improves hydrogen absorbance capability. The films were hydrogenated in Ar/5%H₂ atmosphere at 300°C in atmospheric pressure. The hydrogenation changed the color of the coating surface from silver metal to dark color accompanied by reduced electrical conductivity and increased transparency of the film indicating shift from metallic to insulative ceramic The dehydrogenation of the magnesium hydride containing films was made via laser irradiation at room temperature using 808 nm wavelength CW laser. The hydrogen flow, consisting of both molecular and atomic hydrogen, generated by laser irradiation of one hydrogenated coating spot 1mm x 10mm during 1s ranging from 0.5 to 1 SCCM. It was demonstrated that almost 90% of hydrogen contained in hydrogenated NiTiCu/MgNi/Pd coating can be released by CW laser irradiation from the 1" x 1.25" sample. The partial light transparency and increased light absorbance of MgH₂ improved by columnar microstructure with open voids provide a basis for using amplified light beam to release hydrogen from the thin film, contributing to safe and efficient hydrogen storage.

High-contrast optical systems for space applications require effective dust mitigation strategies to maintain low-scatter surfaces and edges. A novel approach would be to use photodegradable thin films that can remove any dust particles after launch, thereby reducing the likelihood of further particulate accumulation.

In this work, we investigate the photodegradation behavior of polymers such as poly(olefin sulfone) (PMPS) and poly(1-hexene sulfone) (PHS) under space-like conditions, specifically in vacuum under UVC irradiation (254 nm and 172 nm). We demonstrate that these materials undergo efficient dissociative degradation, enabling the removal of dust from coated optical surfaces. Our results show a significant reduction in particle coverage following irradiation of dust-coated films.

Additionally, we report the use of more energetic thin-film materials, including ammonium nitrate, which exhibit similar photodegradation behavior. These materials may provide enhanced dust removal efficiency due to the higher energy stored in their chemical bonds.

Overall, this study highlights the potential of photodegradable thin films as an effective strategy for in situ dust mitigation in space-based optical systems.

Self-assembled monolayers (SAMs) refer to spontaneously formed single-layer molecular sheets on surfaces, which have found applications in corrosion protection, catalysis, drug delivery, molecular sensing, etc. The assembling behaviors of a given molecule on the surface depend on both the molecule-surface interactions and the intermolecular interactions which include covalent bonding, van der Waals interaction, hydrogen bonding or a combination of these forces. Consequently, there are various tuning knobs towards controllable molecular self-assemblies by modifying either the surfaces or the molecules. Here, we report the unconventional self-assembled patterns of a rationally designed m-terphenyl isocyanide ligand, CNAr^Mes2, on Ag surfaces. This molecular ligand binds to metal atoms via its isocyanide group and experiences rich intermolecular interactions upon surface adsorption because of its m-terphenyl skeleton. We anticipated it to form a dimerized linear molecular chain on metal surfaces based on its profile, as confirmed on Cu(100) and Cu(111) surface. Surprisingly, CNAr^Mes2 self-assembles into a few unexpected structures on Ag(111) surface including ribbons, rings and hexagons at low surface coverage and forms closely packed monolayers at high molecule density. A detailed study on these unconventional patterns suggests that CNAr^Mes2 trimer other than the dimer is the building block and that the surface chemistry of Ag plays a vital role in this assembling mechanism change. These observations inspire us to engineer the metal-binding isocyanide group and/or the steric bulks of CNAr^Mes2 to achieve programmed SAMs with on-demand shapes, lattice constants and functionalities on metal surfaces.