Communication: No guidance needed: Ordered structures and transformations of thin methanol ice on hydrophobic surfaces

Nanoscale Energy Transport Dynamics across Nonbonded Solid-Molecule Interfaces and in Molecular Thin Films

Thermal conductance across a solid-solid interface requires an atomic- or molecular-level understanding, especially when a system is in a non-equilibrium state and/or consists of nanosized materials with prominent differences in structures, properties, and vibrational behaviors. Here, we report the lattice dynamics of graphite-supported molecular thin films of ethanol, whose layers exhibit in-plane hydrogen-bonded chains and out-of-plane van der Waals stacking with clear structural anisotropy. The direct structure-probing method of ultrafast electron diffraction reveals a surprising temperature difference of more than 400 K at pico- to sub-nanosecond times across the graphite-ethanol interface, yet the temporal behavior signifies a reasonably large thermal boundary conductance. This apparent conflict in a non-equilibrium condition can be resolved by considering the coupling of out-of-plane motions, instead of the commonly used temperature-based model, at transient times for energy transport across the interface separated by van der Waals interactions with mismatched unit sizes and no strong bonds. The importance of spatiotemporally resolved structural dynamics at the atomic or molecular level is emphasized.

Order-Determined Structural and Energy Transport Dynamics in Solid-Supported Interfacial Methanol

Energy transport dynamics in different nanostructures are crucial to both a fundamental understanding of and practical applications for heat management at the nanoscale. It has been reported that thermal conductivity may be severely impacted by stacking disorder in layered materials. Here, using ultrafast electron diffraction in the reflection geometry for direct probing of structural dynamics, we report a fundamental behavioral difference due to stacking order in an entirely different system-solid-supported methanol assemblies whose layered structures may resemble those of two-dimensional (2D) and van der Waals (vdW) solids but with much weaker in-plane hydrogen bonds. Thermal diffusion is found to be the transport mechanism across 2D-layered films without a cross-plane stacking order. In stark contrast, much faster ballistic energy transport is observed in 3D-ordered crystalline solids. The major change in such dynamical behavior may be associated with the efficiency of vibrational coupling between vdW-interacted methanol layers, which demonstrates a strong structure-property relation.

Reflection high energy electron diffraction (RHEED) study of ice nucleation and growth on Ni(111): influences of adspecies and electron irradiation

How interfacial molecular interactions influence nucleation and growth processes of water ice is explored using pristine, oxygenated, and CO-adsorbed Ni(111) substrates based on RHEED, together with the effects of high-energy electron irradiation on the crystallization kinetics. A monolayer of amorphous solid water deposited onto the pristine Ni(111) substrate crystallizes into ice Ic at ca. 150 K, whereas ice Ih (Ic) is formed preferentially during water vapor deposition at 135 K (125 K). The ice nucleation tends to be hampered on the oxygenated Ni(111) surface because of the hydrogen bond formation with chemisorbed oxygen, leading to the growth of randomly-oriented ice Ic crystallites via spontaneous nucleation. The amorphization and recrystallization of initially crystalline ices are observed during prolonged RHEED measurements at 20 and 70 K, respectively, signifying that high-energy electron irradiation has both thermal and non-thermal effects on the water phase transition. The epitaxial growth (non-epitaxial growth) of ice occurs during electron irradiation of amorphous solid water formed on the pristine and oxygenated Ni(111) substrates (CO-adsorbed Ni(111) substrate) even at 100 K (120 K) because nucleation and growth are initiated at the substrate interface (in the ASW film interior).

Crystallization kinetics of thin water films on Pt(111): effects of oxygen and carbon-monoxide adspecies

This paper describes nucleation, epitaxial growth, and wettability of water on Pt(111) and how they are influenced by oxygen and carbon-monoxide adspecies, based on reflection high energy electron diffraction (RHEED), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and temperature-programmed desorption (TPD). Amorphous solid water deposited onto the pristine Pt(111) substrate crystallizes into ice Ih together with a 2D layer at 150 K, whereas ice Ic (stacking disordered ice or a mixture of ice Ic and Ih) is formed preferentially onto oxygenated Pt(111) (CO-adsorbed Pt(111)) at 155-160 K (150 K). The ice nucleation and epitaxial growth tend to be hampered on the oxygenated Pt(111) surface via hydrogen bond formation with chemisorbed oxygen. The CO-adsorbed Pt(111) surface is hydrophobic, as evidenced by the fact that water forms a complex with CO during evaporation of crystallites at 160-165 K. A disordered 2D layer remains on pristine Pt(111) up to 175 K, whereas an ordered 2D layer exhibiting the (√3 ×√3)R30° structure formed on oxygenated Pt(111) up to 200 K.

Crystallization kinetics of water on graphite

The nucleation and growth of water crystallites on a graphite substrate are discussed in terms of the initial film thickness, deposition temperature, and effects of adspecies.