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arXiv 0807.3430cond-mat.mtrl-sci
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从第一性原理模拟金属表面氧化物形成的开始

Modelling the onset of oxide formation on metal surfaces from first principles

Lucio Colombi Ciacchi

摘要:

在金属表面上形成氧化物层是一个非热激活过程,在非常低的温度下在纳秒内自发发生。本文报道了裸金属表面,特别是Al(111)和TiN(001)的初始氧化的机理细节,通过密度泛函理论内的第一性原理分子动力学模拟获得。它示出,裸露的金属表面与O2分子的反应发生根据“热原子”的解离机制,这是触发由填充的σ星反键分子轨道,其特征在于由突然释放大量的动能。这种释放的能量提供了一个驱动力的金属/氧的位置交换过程,这是负责在几乎0 K和氧覆盖率远低于1单层(ML)的氧化物形成的开始。对氧化反应的进一步模拟表明,在Al(111)上形成了无序的TiO 2氧化物,而在TiN(001)上形成了有序的结构,在氧化物层下面的TiN晶格中留下了Ti空位簇。

英文摘要:

The formation of ultrathin oxide layers on metal surfaces is a non-thermally-activated process which takes place spontaneously at very low temperatures within nanoseconds. This paper reports mechanistic details of the initial oxidation of bare metal surfaces, in particular Al(111) and TiN(001), as obtained by means of first-principles molecular dynamics modelling within the Density-Functional Theory. It is shown that the reactions of bare metal surfaces with O2 molecules take place according to a 'hot-atom' dissociative mechanism which is triggered by the filling of the sigma-star antibonding molecular orbital and is characterised by a sudden release of a large amount of kinetic energy. This released energy provides a driving force for metal/oxygen place-exchange processes which are responsible for the onset of oxide formation at virtually 0 K and at oxygen coverages well below 1 monolayer (ML). Further simulations of the oxidation reactions reveal that a disordered ultrathin oxide forms on Al(111), whereas a rather ordered structure develops on TiN(001) following a selective oxidation process which leaves clusters of Ti vacancies in the TiN lattice underneath the oxide layer.

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