Bismuth vanadate (BVO) is a promising metal oxide semiconductor for photoelectrochemical water oxidation. In this study, BVO was deposited using atomic layer deposition (ALD) of alternating films of bismuth and vanadium oxides. A novel Bi-alkoxide precursor was used to enable precise control of stoichiometry along the spectrum of Bi-rich to V-rich compositions, and phase-pure monoclinic BVO films were obtained after postannealing. A planar photoanode composed of an undoped 41.8 nm BVO thin-film electrode with an ALD SnO2 buffer layer produced a photocurrent density of 2.24 mA/cm2 at 1.23 V vs RHE. ALD was used to conformally coat BVO and SnO2 on a ZnO nanowire template to produce core–shell photoanodes exhibiting a 30% increase in photocurrent density (2.9 mA/cm2 at 1.23 V) relative to planar control electrodes. This is the highest photocurrent reported to date for an ALD-deposited photoanode, and provides a pathway toward rational design of 3-D nanostructured photoelectrode architectures.

Atomic layer deposition (ALD) modification of ultra-high-aspect-ratio structures (>10000:1) is a powerful platform with applications in catalysis, filtration, and energy conversion. However, the deposition of conformal and tunable ALD coatings at these aspect ratios remains challenging, resulting in empirical trade-offs between the precursor utilization and reaction time. Here, we demonstrate tunable control of the ALD infiltration depth into an aerogel monolith (AM) and develop a reaction-diffusion model to accurately describe the coating process. Specifically, we investigate the ALD exposure time and precursor dose needed to conformally coat a silica AM with pore sizes of ∼20 nm, a monolith thickness of ∼2.5 mm, and aspect ratios exceeding 60000:1. We demonstrate complete infiltration into the AM, which is quantified by elemental mapping. A reaction-diffusion model is developed, which accounts for multiple doses and the precursor depletion in the ALD chamber during an exposure step. The experimentally validated model enables the prediction and tuning of infiltration depth into a tortuous, high-aspect-ratio structure such as an AM, allowing for the synthesis of rationally designed material architectures. Additionally, the model allows for co-optimization of the total deposition time and percentage of unreacted precursor, which are important for the manufacturability and sustainability of ALD processing. Lastly, we demonstrate that ultrathin ALD Al2O3 coatings can be used to stabilize silica AMs against structural degradation under high-temperature annealing conditions (700–800 °C) by limiting changes in the surface area and monolith volume. This improved high-temperature stability has implications for numerous aerogel applications, including catalysis and thermal insulation.

Interfacial fracture and delamination of polymer interfaces can play a critical role in a wide range of applications, including fiber-reinforced composites, flexible electronics, and encapsulation layers for photovoltaics. However, owing to the low surface energy of many thermoplastics, adhesion to dissimilar material surfaces remains a critical challenge. In this work, we demonstrate that surface treatments using atomic layer deposition (ALD) on poly­(methyl methacrylate) (PMMA) and fluorinated ethylene propylene (FEP) lead to significant increases in surface energy, without affecting the bulk mechanical response of the thermoplastic. After ALD film growth, the interfacial toughness of the PMMA–epoxy and FEP–epoxy interfaces increased by factors of up to 7 and 60, respectively. These results demonstrate the ability of ALD to engineer the adhesive properties of chemically inert surfaces. However, in the present case, the interfacial toughness was observed to decrease significantly with an increase in humidity. This was attributed to the phenomenon of stress-corrosion cracking associated with the reaction between Al2O3 and water and might have a significant implication for the design of these tailored interfaces.

An instrumented indentation method is developed for generating maps of time-dependent viscoelastic and time-independent plastic properties of polymeric materials. The method is based on a pyramidal indentation model consisting of two quadratic viscoelastic Kelvin-like elements and a quadratic plastic element in series. Closed-form solutions for indentation displacement under constant load and constant loading-rate are developed and used to determine and validate material properties. Model parameters are determined by point measurements on common monolithic polymers. Mapping is demonstrated on an epoxy-ceramic interface and on two composite materials consisting of epoxy matrices containing multi-wall carbon nanotubes. A fast viscoelastic deformation process in the epoxy was unaffected by the inclusion of the nanotubes, whereas a slow viscoelastic process was significantly impeded, as was the plastic deformation. Mapping revealed considerable spatial heterogeneity in the slow viscoelastic and plastic responses in the composites, particularly in the material with a greater fraction of nanotubes.