金覆盖拓扑绝缘体上强表面态促进的CO氧化
CO Oxidation Facilitated by Robust Surface States on Au-Covered Topological Insulators
摘要：
表面态是指在固体材料终止于表面时出现的电子态，并且可以存在于许多系统中。尽管它们在空间上接近材料表面，但表面状态在表面催化和潜在的现实世界应用的基本理解中在很大程度上被忽视，因为它们容易受到局部杂质或缺陷的影响。相比之下，最近发现的三维拓扑绝缘体（3DTI）具有非常强大的金属表面状态，拓扑保护表面污染和缺陷。强拓扑表面态（TSS）为在不太严格的环境中开发新的物理现象和潜在的表面态应用提供了一个完美的平台。在这里，我们采用第一性原理密度泛函理论证明，TSS可以发挥重要的作用，作为一个有效的电子浴，促进表面反应优雅。我们使用CO氧化金覆盖的Bi 2Se 3作为一个原型的例子，并首先表明，TSS被保存时，一个稳定的金膜沉积到Bi-终止的Bi 2Se 3基板。此外，TSS可以显着提高CO和O2分子的吸附能，通过促进不同方向的电子转移。对于CO，TSS接受来自CO-Au系统的电子，从而减少CO反键态的不期望的占据。对于O2，TSS提供所需的电子以促进分子解离吸附。本研究增加了一个新的舞台，技术潜力的3DTI，和TSS作为一个电子浴的中心概念，这里揭示可能会导致新的设计原则，超越传统的d-带理论的多相催化。
英文摘要：
Surface states refer to electronic states emerging as a solid material terminates at a surface, and can be present in many systems. Despite their spatial proximity to material surfaces, surface states have been largely overlooked in fundamental understanding of surface catalysis and potential real-world applications, because of their vulnerability to local impurities or defects. In contrast, the recently discovered three-dimensional topological insulators (3DTI) have exceptionally robust metallic surface states that are topologically protected against surface contamination and imperfection. The robust topological surface state(s) (TSS) provides a perfect platform for exploiting novel physical phenomena and potential applications of surface states in less stringent environments. Here we employ first-principles density functional theory to demonstrate that the TSS can play a vital and elegant role in facilitating surface reactions by serving as an effective electron bath. We use CO oxidation on gold-covered Bi2Se3 as a prototype example, and first show that the TSS is preserved when a stable ultrathin Au film is deposited onto a Bi-terminated Bi2Se3 substrate. Furthermore, the TSS can significantly enhance the adsorption energy of both CO and O2 molecules, by promoting different directions of electron transfer. For CO, the TSS accepts electrons from the CO-Au system, thereby decreasing the undesirable occupation of the CO antibonding states. For O2, the TSS donates the needed electrons to promote the molecule towards dissociative adsorption. The present study adds a new arena to the technological potentials of 3DTI, and the central concept of TSS as an electron bath as revealed here may lead to new design principles beyond the conventional d-band theory of heterogeneous catalysis.
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