Morales Carlos, Urbanos Fernando J, Del Campo Adolfo, Leinen Dietmar, Granados Daniel, Prieto Pilar, Aballe Lucía, Foerster Michael, Soriano Leonardo
Departamento de Física Aplicada and Instituto de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, Francisco Tomás y Valiente 7, E-28049 Madrid, Spain.
IMDEA Nanociencia, Faraday, 9, E-28049 Madrid, Spain.
Nanotechnology. 2021 Mar 23;32(24). doi: 10.1088/1361-6528/abe0e8.
The interaction of graphene with metal oxides is essential for understanding and controlling new devices' fabrication based on these materials. The growth of metal oxides on graphene/substrate systems constitutes a challenging task due to the graphene surface's hydrophobic nature. In general, different pre-treatments should be performed before deposition to ensure a homogenous growth depending on the deposition technique, the metal oxide, and the surface's specific nature. Among these factors, the initial state and interaction of graphene with its substrate is the most important. Therefore, it is imperative to study the initial local state of graphene and relate it to the early stages of metal oxides' growth characteristics. Taking as initial samples graphene grown by chemical vapor deposition on polycrystalline Cu sheets and then exposed to ambient conditions, this article presents a local study of the inhomogeneities of this air-exposed graphene and how they influence on the subsequent ZnO growth. Firstly, by spatially correlating Raman and x-ray photoemission spectroscopies at the micro and nanoscales, it is shown how chemical species present in air intercalate inhomogeneously between Graphene and Cu. The reason for this is precisely the polycrystalline nature of the Cu support. Moreover, these local inhomogeneities also affect the oxidation level of the uppermost layer of Cu and, consequently, the electronic coupling between graphene and the metallic substrate. In second place, through the same characterization techniques, it is shown how the initial state of graphene/Cu sheets influences the local inhomogeneities of the ZnO deposit during the early stages of growth in terms of both, stoichiometry and morphology. Finally, as a proof of concept, it is shown how altering the initial chemical state and interaction of Graphene with Cu can be used to control the properties of the ZnO deposits.
石墨烯与金属氧化物的相互作用对于理解和控制基于这些材料的新器件制造至关重要。由于石墨烯表面的疏水性，在石墨烯/衬底系统上生长金属氧化物是一项具有挑战性的任务。一般来说，根据沉积技术、金属氧化物和表面的特定性质，在沉积之前应进行不同的预处理以确保均匀生长。在这些因素中，石墨烯与其衬底的初始状态和相互作用是最重要的。因此，研究石墨烯的初始局部状态并将其与金属氧化物生长特性的早期阶段联系起来势在必行。本文以通过化学气相沉积在多晶铜片上生长然后暴露于环境条件下的石墨烯作为初始样品，对这种暴露于空气中的石墨烯中的不均匀性及其对后续氧化锌生长的影响进行了局部研究。首先，通过在微米和纳米尺度上对拉曼光谱和X射线光电子能谱进行空间关联，展示了空气中存在的化学物质如何在石墨烯和铜之间不均匀地插入。其原因正是铜载体的多晶性质。此外，这些局部不均匀性还会影响铜最上层的氧化水平，进而影响石墨烯与金属衬底之间的电子耦合。其次，通过相同的表征技术，展示了石墨烯/铜片的初始状态在生长早期如何在化学计量和形态方面影响氧化锌沉积物的局部不均匀性。最后，作为概念验证，展示了如何通过改变石墨烯与铜的初始化学状态和相互作用来控制氧化锌沉积物的性质。
