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Structure and Chemical State of Cesium on Well-Defined Cu(111) and Cu2O/Cu(111) Surfaces
The Journal of Physical Chemistry C ( IF 3.7 ) Pub Date : 2020-01-22 , DOI: 10.1021/acs.jpcc.9b10608
Rebecca C. E. Hamlyn 1 , Mausumi Mahapatra 2 , Ivan Orozco 1 , Iradwikanari Waluyo 3 , Adrian Hunt 3 , José A. Rodriguez 1, 2 , Michael G. White 1, 2 , Sanjaya D. Senanayake 2
Affiliation  

The deposition of cesium (Cs) onto the metallic and oxidized surfaces of Cu(111) was investigated using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and density functional theory calculations (DFT) to elucidate the properties of alkali metals when supported on metal and oxide surfaces. At low coverages, cesium adopts partially cationic (Csδ+), highly mobile, and likely atomic structures on the metal surface of Cu(111). Such structures are not observable at room temperature using STM due to rapid surface mobility but can be quantified using XPS. This is further verified by DFT calculations which show that Cs adsorption on Cu(111) is site insensitive, where atop, bridge, and hollow sites yield identical adsorption energy. Reaction with O2 (1 × 10–7 Torr) at room temperature of the Cs/Cu(111) surface results in both CsOx and CuxO formation, initially from the Cs sites and Cu step edges and then subsequently encompassing the terraces. The presence of Cs promotes the oxidation process by O2, and we have identified the oxidized Csδ+ and Cu1+ using XPS. In contrast to the metallic substrate, the deposition of Cs onto the preoxidized surface of Cu2O/Cu(111) allows for the anchoring of the oxidized Csδ+ nanostructures (few nm) which appear indiscriminately on the oxide surface with high dispersion and low mobility. While clearly distinguishable using STM, we have revealed a rich geometric heterogeneity of the nanostructures of Cs on Cu2O/Cu(111), likely templated through a strong interaction between the Cs and the Cu2O substrate. In addition, it is also evident that Cs imparts a destabilizing effect on the ordered oxide substrate, as observed through the increase of surface defects. Finally, the thermal stability of the Cs structures was studied, using sequential annealing steps revealing that Cs remained stable up to 550 K with some loss of both cesium and oxygen at higher temperatures of 650 K. DFT calculations show that unlike Cu(111), the adsorption energy of Cs on CuxO/Cu(111) is highly dependent on adsorption site, and electronic effects enabled through the interaction between Cs, O, and Cu.

中文翻译:

定义明确的Cu(111)和Cu 2 O / Cu(111)表面上铯的结构和化学状态

使用扫描隧道显微镜(STM),X射线光电子能谱(XPS)和密度泛函理论计算(DFT)研究了铯(Cs)在Cu(111)的金属和氧化表面上的沉积,以阐明负载在金属和氧化物表面的碱金属。在低覆盖率下,铯在Cu(111)的金属表面上采用部分阳离子(Csδ +),高迁移率且可能是原子结构。由于快速的表面迁移率,这种结构在室温下使用STM无法观察到,但可以使用XPS进行定量。DFT计算进一步证实了这一点,该计算表明Cs在Cu(111)上的吸附是位点不敏感的,在该位点的顶,桥和空心位点产生的吸附能量相同。与O 2(1×10室温下Cs / Cu(111)表面的–7 Torr)既导致CsO x和Cu x O的形成,也首先来自Cs部位和Cu台阶边缘,然后包括台阶。Cs的存在促进了O 2的氧化过程,我们已经使用XPS鉴定了被氧化的Csδ +和Cu 1+。与金属衬底相比,Cs沉积到Cu 2 O / Cu(111)的预氧化表面上可以锚定氧化的Csδ +纳米结构(几纳米)以高分散性和低迁移率无差别地出现在氧化物表面上。虽然可以使用STM进行明显区分,但我们发现了Cu 2 O / Cu(111)上Cs纳米结构的丰富几何异质性,很可能是通过Cs和Cu 2 O底物之间的强相互作用进行模板化的。另外,很明显,如通过表面缺陷的增加所观察到的,Cs对有序氧化物基底赋予去稳定作用。最后,使用顺序退火步骤研究了Cs结构的热稳定性,结果表明,在650 K的较高温度下,Cs保持稳定至550 K,同时铯和氧都有损失。DFT计算表明,与Cu(111)不同, Cs对Cu的吸附能x O / Cu(111)高度依赖于吸附位点,并且通过Cs,O和Cu之间的相互作用实现电子效应。
更新日期:2020-01-23
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