DataSheet1_3He spin-echo scattering indicates hindered diffusion of isolated water molecules on graphene-covered Ir(111).PDF

The dynamics of water diffusion on carbon surfaces are of interest in fields as diverse as furthering the use of graphene as an industrial-coating technology and understanding the catalytic role of carbon-based dust grains in the interstellar medium. The early stages of water–ice growth and the mobility of water adsorbates are inherently dependent on the microscopic mechanisms that facilitate water diffusion. Here, we use 3He spin-echo quasi-inelastic scattering to probe the microscopic mechanisms responsible for the diffusion of isolated water molecules on graphene-covered and bare Ir(111). The scattering of He atoms provides a non-invasive and highly surface-sensitive means to measure the rate at which absorbates move around on a substrate at very low coverage. Our results provide an approximate upper limit on the diffusion coefficient for water molecules on GrIr(111) of <10−12 m2/s, an order of magnitude lower than the coefficient that describes the diffusion of water molecules on the bare Ir(111) surface. We attribute the hindered diffusion of water molecules on the GrIr(111) surface to water trapping at specific areas of the corrugated moiré superstructure. Lower mobility of water molecules on a surface is expected to lead to a lower ice nucleation rate and may enhance the macroscopic anti-icing properties of a surface.碳表面上水扩散的动力学行为，在多个跨学科领域中具有重要研究价值：既可为石墨烯工业涂层技术的实用化进程提供理论支撑，也有助于解析星际介质中碳基尘埃颗粒的催化作用机制。水冰生长的初始阶段以及水吸附质的迁移特性，本质上由促进水扩散的微观机制所决定。本研究采用³He自旋回波准非弹性散射（3He spin-echo quasi-inelastic scattering）技术，探究孤立水分子在石墨烯包覆与纯Ir(111)表面上的扩散微观机制。氦原子散射是一种非侵入式且高表面灵敏度的表征手段，可用于测量极低覆盖度下基底表面吸附质的迁移速率。本研究结果给出了GrIr(111)表面上水分子扩散系数的近似上限：小于10⁻¹² m²/s，该数值比纯Ir(111)表面的水分子扩散系数低一个数量级。我们将GrIr(111)表面上水分子扩散受阻的现象，归因于水分子被捕获在波纹状莫尔超结构（moiré superstructure）的特定区域内。表面上水分子迁移率的降低，通常会导致更低的冰晶成核速率，进而有望提升表面的宏观防冰性能。