Molecularly-induced effects on the synthesis and properties of thin film inorganic/molecular-nanolayer interfaces and their multilayers

Abstract

May2025School of EngineeringInserting molecular nanolayers (MNLs) at inorganic thin film interfaces has been shown to enhance chemical and mechanical stability, and access unexpected electrical/thermal transport and mechanical responses. Stacking inorganic nanolayers and MNLs offer the potential for crafting new classes of high-interface-fraction multilayered composites with emergent responses arising from the superposition of effects from multiple MNL interfaces. This work demonstrates studies on the synthesis of metal-oxide/MNL multilayers and metal/MNL/metal sandwiches, and their mechanical and acoustic properties. Synthesis techniques used include low-temperature atomic layer deposition (ALD) or sputter deposition combined with MNL formation from vapor-phase molecular flux exposures. Results of experiments combining multiple spectroscopy, microscopy, and diffraction techniques unveil different correlations between MNL structure and chemistry on inorganic nanolayer growth kinetics, chemistry, morphology, phase stability, and oxidation, as well as provide insights into their atomistic mechanisms. Ab initio molecular dynamics simulations were used to reveal MNL-induced strain-hardening and toughening in metal/MNL/metal sandwiches, with atomistic insights on the effects of MNL molecular chain length and terminal chemistry. Pump-probe time-domain Brillouin spectroscopy unveiled unusual enhancements in optoacoustic transmission in titania/MNL multilayers at selected sub-terahertz frequencies. This is attributed to MNL-induced global optical effects and interference of acoustic trains reflected from MNL interfaces, and hence, sensitive to and tunable via MNL structure and chemistry. Such tunable MNL-induced emergent responses in inorganic/MNL multilayers could open new vistas for viscoelastic bandgap engineering and phononic laser development.Ph