Bertrang Kevin, Hinke Tobias, Kaiser Sebastian, Knechtges Matthias, Loi Federico, Lacovig Paolo, Jahangirzadeh Varjovi Mirali, Esch Friedrich, Baraldi Alessandro, Tosoni Sergio, Kartouzian Aras, Heiz Ueli
TUM School of Natural Sciences, Department of Chemistry, Chair of Physical Chemistry, Technical University of Munich, Catalysis Research Center, Technical University of Munich, Garching D-85748, Germany.
Department of Physics, University of Trieste, 34127 Trieste, Italy.
J Phys Chem C Nanomater Interfaces. 2025 Mar 21;129(13):6511-6523. doi: 10.1021/acs.jpcc.5c00699. eCollection 2025 Apr 3.
The interaction of submonolayer quantities of size-selected and soft-landed Ta ( = 4, 5, 6, 8, 13) clusters with Pt(111) is investigated employing high-resolution X-ray photoelectron spectroscopy (HR-XPS), scanning tunneling microscopy (STM), and density functional theory (DFT) simulations. The deposited clusters are monodispersed and stable under ultrahigh vacuum (UHV) conditions at 40 K. They display a size-specific trend in photoemission spectra, which is reasoned in terms of the distinct in plane coordination of Ta atoms in the clusters. Both the Ta coordination number and distance from the Pt surface influence its Bader charge and, accordingly, the oxidation state of the atoms in the Ta cluster. They already fragment in the presence of low amounts of oxygen and form a common oxidation product observed for all cluster sizes. Based on our observations, we propose an oxidation mechanism in the example of Ta clusters, which is closely comparable to the one discussed in gas-phase studies on the oxidation of cationic Ta clusters of similar size. Concomitant to oxidation-induced fragmentation, the agglomeration into Ta-oxide islands with Ta in an oxidation state of +5 is observed. However, the strong interaction with the Pt surface leads to Ta 4f orbital photoemission features that differ from those commonly observed for TaO. Computational insights concerning the structure of the Ta-oxide islands indicate flat agglomerates that agree with STM observations. They suggest distinct Ta 4f photoemission contributions from interfacial and surface-related Ta configurations. The respective HR-XPS spectra display specific core-level shifts as a function of bonding configuration and vicinity to the Pt surface. By annealing at 900 K in UHV, we observe oxygen loss and concomitant intermixing of Ta atoms with the Pt subsurface lattice to which results in the formation of a Ta-Pt alloy. These species, Ta-oxide islands, and Ta-Pt alloy, can reversibly interconvert by oxidative surface segregation and reductive intermixing.
采用高分辨率X射线光电子能谱（HR-XPS）、扫描隧道显微镜（STM）和密度泛函理论（DFT）模拟，研究了尺寸选择且软着陆的Ta（=4、5、6、8、13）亚单层簇与Pt(111)的相互作用。沉积的簇在40K的超高真空（UHV）条件下单分散且稳定。它们在光发射光谱中呈现出尺寸特异性趋势，这可根据簇中Ta原子不同的面内配位来解释。Ta的配位数和与Pt表面的距离都影响其巴德电荷，进而影响Ta簇中原子的氧化态。它们在少量氧气存在下就会分解，并形成所有簇尺寸都能观察到的常见氧化产物。基于我们的观察，我们以Ta簇为例提出了一种氧化机制，该机制与气相中对类似尺寸阳离子Ta簇氧化的研究中所讨论的机制密切可比。伴随氧化诱导的碎片化，观察到Ta簇聚集成氧化态为+5的Ta氧化物岛。然而，与Pt表面的强相互作用导致Ta 4f轨道光发射特征不同于通常在TaO中观察到的特征。关于Ta氧化物岛结构的计算见解表明，扁平团聚体与STM观察结果一致。它们表明界面和表面相关Ta构型对Ta 4f光发射有不同贡献。相应的HR-XPS光谱显示出特定的核心能级位移，这是键合构型和与Pt表面距离的函数。通过在UHV中900K退火，我们观察到氧损失以及Ta原子与Pt次表面晶格的伴随混合，这导致形成Ta-Pt合金。这些物种、Ta氧化物岛和Ta-Pt合金可通过氧化表面偏析和还原混合而可逆地相互转化。
