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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Environment Controlled Dewetting of Rh-Pd Bilayers: A Route for Core-Shell Nanostructure Synthesis
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Environment Controlled Dewetting of Rh-Pd Bilayers: A Route for Core-Shell Nanostructure Synthesis

机译：Rh-Pd双层的环境控制去湿：核壳纳米结构合成的途径。

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Chemical environment plays a significant role on the size, shape, or surface composition of nanostructures. Here, the chemical environment effects are studied in the context of core-shell nanoparticle synthesis. The environment driven dynamics and kinetics of Rh/Pd bilayers is investigated by in situ ambient pressure X-ray photoelectron spectroscopy. Thin Rh (～1.5 nm)/Pd (~ 1.5 nm) bilayers were grown on thermally oxidized Si substrates. The films were heated in CO or NO environments or heated in vacuum with a subsequent NO/CO cychng. This study demonstrates that not the initial stacking sequence but the chemical environment plays a crucial role in controlling the surface composition. Heating in CO results in a surface enrichment of Pd at ~200 °C and is followed by film dewetting at ～300 °C. Heating in NO results in progressive oxidation of Rh starting at ～150 °C, which stabilizes the film continuity up to >～375 °C. The film rupture correlates with the thermal destabilization of the surface oxide. Heating in vacuum results in a significant increase in surface Pd concentration, and the following NO/CO cycling induces periodic surface composition changes. The quasi-equilibrium states are ～50% and ～20% of Rh/(Rh + Pd) for NO and CO environments, respectively. Possible surface composition change and dewetting mechanisms are discussed on the basis of the interplay of thermodynamic (surface/oxide energy and surface wetting) and kinetic (surface oxidation and thermally induced and chemically enhanced diffusion) factors. The results open alternative ways to synthesize supported (core-shell) nanostructures with controlled morphology and surface composition.
机译：化学环境对纳米结构的大小，形状或表面组成起着重要作用。在这里，在核壳纳米粒子合成的背景下研究化学环境效应。通过原位环境压力X射线光电子能谱研究了Rh / Pd双层的环境驱动动力学。在热氧化的Si衬底上生长了薄的Rh（〜1.5 nm）/ Pd（〜1.5 nm）双层。将膜在CO或NO环境中加热或在真空中随后进行NO / CO循环。这项研究表明，不是最初的堆叠顺序，而是化学环境在控制表面成分方面起着至关重要的作用。在CO中加热会导致Pd在〜200°C的表面富集，然后在〜300°C进行薄膜脱湿。在NO中加热会导致Rh从〜150°C开始逐渐氧化，从而使膜的连续性稳定到>〜375°C。膜破裂与表面氧化物的热不稳定有关。真空加热导致表面Pd浓度显着增加，随后的NO / CO循环导致周期性的表面组成变化。对于NO和CO环境，准平衡态分别为Rh /（Rh + Pd）的〜50％和〜20％。在热力学（表面/氧化物能量和表面润湿）和动力学（表面氧化，热诱导和化学增强扩散）因素之间相互作用的基础上，讨论了可能的表面组成变化和反润湿机理。结果为合成具有受控形态和表面组成的支撑（核-壳）纳米结构开辟了替代途径。

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