AVS 72 Session SE-ThA: Advanced Surface Engineering Oral Session

In-situ Raman spectroscopy is a powerful method to investigate adaptive tribological surfaces. The in-situ Raman spectroscopy is shown to capture tribologically induced changes of adaptive coatings inside the lubricated sliding contact in response to applied mechanical and thermal stresses. For solid lubricated adaptive contacts, duplex plasma-electrolytic oxidation (PEO) and chameleon coating produced on Al alloys were investigated. These were composed of a 80-160 mm thick hard load-supporting Al-Si-O coating and a 5–8 μm top layer of a chameleon coating made of graphite or BN, MoS₂ or WS₂, and Sb₂O₃. For liquid contacts, 52100 steel coupons were tested under lubricant starvation regimes using low viscosity hydrocarbons. The counterpart pins were made of 52100 steel and Si₃N₄. The tests were performed at temperatures ranging from room (liquid lubrication) to 600 °C (solid lubrication). In-situ Raman spectroscopy revealed that the lubricating phases, i.e. MoS₂, WS₂, and graphite, were protected from oxidation by the porous PEO structure. It also revealed a gradual evolution of chameleon composition with diminishing orthorhombic Sb₂O₃ phase presence at the surface in favor of hexagonal lubricating phases of chameleon components. The low shear strength of MoS₂, WS₂, and graphite and the integration of the chameleon coating with the PEO sublayer were responsible for the ultra-low friction behavior. In all examples, the in-situ Raman spectroscopy was shown to reliably detect contact chemical change correlated with the observed friction behavior.

Combinatorial sputter deposition techniques provide an ability to fabricate a large variety of thin films in a relatively short time thereby accelerating materials discovery. Indeed, past studies have reported methods that produce 10s or 100s of unique films in a single vacuum deposition. Despite these advances, new, high-throughput characterization techniques are needed to match the pace of combinatorial synthesis. In particular, automated techniques that accurately reveal the structure and the relevant properties of combinatorial films are of great interest.

Toward this end, we describe automated, ex-situ characterization of biaxial film stress wherein >100 individual, combinatorial thin films are probed in concert. Combinatorial, magnetron sputter-deposited Pt-Au and Pt-Ni films are interrogated using a k-Space Co. Thermal Scan instrument wherein samples are affixed inside a vacuum test cell. This instrument precisely moves a laser spot array to each specimen (before and after deposition) to determine wafer curvature changes. The application of Stoney’s equation to determine the stress of combinatorial films from measured curvatures is discussed. Films are much thinner than the substrates (which satisfies one Stoney assumption), but a laterally graded thickness across each specimen moves away from at least one separate assumption used in the derivation of this often-used equation. Accounting for measured thickness gradients, we demonstrate accurate stress measurements over a range of temperatures up to +600C. Combinatorial Pt-Au and Pt-Ni films produced in single depositions exhibit a variety of stress responses that are ultimately correlated to measured film density and composition. Altogether, we determine their thermal expansion coefficients, pinpoint their onset of relaxation, and reveal changes occurring at high temperature tied to secondary phase formation. The gathered information augments an extensive library of process-structure-property relationships that underly their high-temperature performance.

Sandia National Laboratories is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

Zr–Ti–N coatings with varying thicknesses (1.5, 2.0, 2.5, and 3.0 μm) were deposited on 316 stainless steel substrates by cathodic arc evaporation using separate zirconium and titanium targets in a reactive nitrogen atmosphere. The influence of coating thickness on the microstructure and corrosion behavior of the films was systematically investigated. X-ray diffraction (XRD) analysis revealed the formation of crystalline Zr–Ti–N phases along with the presence of substoichiometric Ti₂N.

Surface and cross-sectional morphologies of the coatings were examined using scanning electron microscopy (SEM), which confirmed dense columnar growth of the deposited films. Cathodic arc-induced droplets were observed on the coating surfaces, and their presence was found to influence surface morphology and localized corrosion characteristics. Variations in coating thickness significantly affected coating compactness, defect density, and structural integrity.

The corrosion behavior of the coatings was evaluated in 0.1 N HCl solution using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The acidic HCl medium was selected to simulate aggressive industrial corrosive environments. Electrochemical studies demonstrated that the corrosion resistance of the coatings improved with increasing coating thickness. The corrosion current density (Icorr) decreased from 136 μA/cm² for 1.5 μm Zr–Ti–N coating to 92.14 μA/cm² for 3.0 μm coating, indicating enhanced barrier protection and reduced electrolyte penetration. EIS results further confirmed the improvement in charge transfer resistance and protective efficiency with increasing coating thickness.

The study demonstrates that coating thickness, microstructural evolution, and cathodic arc droplet formation play a significant role in determining the corrosion performance of cathodic arc deposited Zr–Ti–N coatings for protective applications in aggressive acidic environments.

As the discovery of new materials and functionalities are occurring at an unprecedented rate, new strategies to accelerate the connection between material state or property to a desired application are necessary. Despite the availability of modern tools, the slow, tedious, and Edisonian research practices of the past are still the standard for areas such as thin films and coatings. The development of a new thin film requires either starting from a known, reported recipe, or the use intuition to determine a suitable starting condition. After thin film deposition is complete, there may be post-growth optimization and characterization, with many iterations of this process necessary until the initial growth conditions match some desired end state.
Laser spike annealing (LSA) is a promising technique for rapidly investigating the modification of thin film materials due to thermal annealing. By scanning a focused, continuous-wave laser across a thin film surface, localized heating can be achieved with heating/quenching times as short as microseconds and temperatures exceeding 1000°C. The laser intensity, scan rate, and annealing environment can be varied, allowing thousands of distinct annealing conditions to be studied on a single sample, including dwell times several orders of magnitude shorter than what can be achieved with rapid thermal annealing. This approach can therefore be used for accelerated materials discovery and optimization by modifying existing thin films in a localized, high throughput manner.
In this work, LSA is applied to the oxidation of various thin film materials, including transition metals such as Hf and transition metal dichalcogenides such as MoS2. Tunable oxidation is achieved by varying the laser conditions in a controlled oxygen environment, enabling access to a wide range of effective temperatures and heating times. The resulting structural and compositional modifications are characterized using X-ray diffraction, Raman spectroscopy, ellipsometry, UV-vis absorption spectroscopy, and X-ray photoelectron spectroscopy. Applications in the study of optical and electronic materials are presented, including refractive index optimization and the development of materials for neuromorphic device applications.

X-ray photoelectron spectroscopy (XPS) analyzes of insulators or inhomogeneous samples containing insulating phases are often done with specimens electrically isolated from ground and the surface potential controlled by the flood gun. While such approach offers the possibility of delivering non-distorted spectra, the consequences for the energy level alignment between sample and the spectrometer are often not considered. The present contribution highlights these aspects by discussing several, carefully selected, case studies that visualize fundamental differences between XPS analyses performed on samples with and without electrical contact to ground. Consequences for core level shifts, energy splitting between peaks from different samples, and spectra referencing are discussed in detail. It is shown that the choice of the measurement configuration (samples with vs. without contact to the spectrometer) determines to what extent binding energies of core level peaks from conducting and insulating samples (or conducting and insulating phases of the same sample) depend on the specimens’ work function. Recognizing these aspects is crucial for the correct spectra referencing and interpretation of core level shifts for series of samples with varying work function.

Glass is central to displays, touchscreens, medical interfaces, and public interactive systems. Integrating additional functions such as antimicrobial activity and mechanical durability to optical clarity is of significant commercial interest which, however, remains challenging. Lithographic techniques provide excellent control over nanoscale geometry and are widely used for surface patterning. However, for applications where random subwavelength features are acceptable, lithography-free routes based on self-assembled metal masks can reduce process complexity and improve compatibility with large-area glass processing.

Among candidate antimicrobial materials, Cu offers well-established ion-mediated antibacterial activity; however, exposed Cu nanostructures are susceptible to wear and optical degradation, limiting their practical use on transparent surfaces. Embedding Cu within glass nanostructures is therefore an attractive strategy to simultaneously enable durability and sustained functionality. In our previous work on abrasion-resistant antireflective glass, thermally dewetted Ag nanoparticles were used to form a Ni nanohole mask for dry etching subwavelength nanoholes into glass. While effective for creating durable antireflective textures, this approach was not suitable for embedding Cu because a selective etchant that could remove the Ni mask without attacking or degrading the embedded Cu could not be identified.

We overcome this limitation by replacing the Ni hard mask with a diluted polymer nanohole mask, enabling wet glass etching and subsequent lift-off of Ti/Cu nanodisks embedded below the glass surface. The resulting surfaces show 80–85% visible transmission, haze below 1%, and near-neutral color. Antimicrobial testing against E. coli OP50 shows approximately 99% bacterial reduction after 1 h, while crockmeter abrasion causes no measurable optical change. Future work will optimize geometry and Cu release to improve antimicrobial efficacy toward sanitizer-level benchmarks and validate performance against standard test strains.