Unraveling the Atomic Structure of Fe Intercalated under Graphene on Ir(111): A Multitechnique Approach

Abstract

The interaction of Fe deposited on graphene grown on Ir(111) was studied in detail to better understand the growth, intercalation, and oxidation of Fe ultrathin films on and under graphene. The study has combined a multiple technique approach that allows extracting at once the chemical, topographic, and precise atomic structure of the system submitted to different conditions of growth and atmospheric environment. For instance, scanning tunneling microscopy (STM) measurements allowed us to follow the formation of Fe nanostructures during Fe deposition and intercalation. Synchrotron-based high-resolution X-ray photoelectron spectroscopy (HR-XPS) untangled the different chemical environments for C–Fe bonds. We have also used photoelectron diffraction experiments to site-specifically unravel the atomic structure of the intercalated Fe under graphene. Oxidation experiments were also performed for samples prepared under different conditions which revealed that indeed one can set the sample temperature to selectively protect or oxidize the intercalated/supported materials, which open interesting possibilities to engineer complex metal-oxide graphene-based devices.

Intercalation of O2 and N2 in the Graphene/Ni Interfaces of Different Morphologies

“…For the first case of the gr/1.6 ML-Ni/Ir(111) system, the exposure to O 2 at room temperature does not lead to any changes of the C 1s and Ni 2p emission lines ( Fig. 3(a,c)) as was also previously observed for other graphene-based intercalation systems [19,32,33]. The similar treatment of the gr/Ni(111) interface leads to the partial intercalation of oxygen already at room temperature as can be visible from the appearance of the shoulder on the low binding energy side of the C 1s peak (third spectrum from the bottom in Fig.…”

Selecting "Convenient Observers" to Probe the Atomic Structure of Epitaxial Graphene Grown on Ir(111) via Photoelectron Diffraction

“…For the clean Ir(111) surface, the Ir 4f 7/2 XPS spectrum exhibits two components: the lower binding energy peak is a surface state (SS) associated with the topmost iridium atomic layer, and the other component is related to the underlying atoms 28,49,50 . Figure 1c shows a high-resolution XPS of Gr/Ir where it is possible to observe the iridium SS, which is not affected by the presence of the carbon layer 9,28,51 .…”

“…For the clean Ir(111) surface, the Ir 4f 7/2 XPS spectrum exhibits two components: the lower binding energy peak is a surface state (SS) associated with the topmost iridium atomic layer, and the other component is related to the underlying atoms 28,49,50 . Figure 1c shows a high-resolution XPS of Gr/Ir where it is possible to observe the iridium SS, which is not affected by the presence of the carbon layer 9,28,51 . Therefore, for the structural analysis, we use the diffraction signal originated from the SS peak to narrow down the number of emitters and concentrate on the first iridium atomic layer, represented by red and blue in figures 1d-e.…”

“…The graphene-iridium distance (d C−Ir ) variation through the unit cell leads to a large number of structural parameters to be determined. Since it is possible to observe a smooth graphene topography via scanning probe techniques such as AFM and STM 10,26,28 , we assume that the graphene topography can be described by continuous functions, particularly Gaussian functions 54,55 . Similarly, in some structural studies, d (C−Ir) is expressed by a truncated Fourier series 26,29,30 .…”

“…Therefore, determining the surface topography is crucial to understand the behavior of the different adsorption sites. The modulated surface can be directly observed by imaging techniques such as Atomic Force Microscopy (AFM) 26 and Scanning Tunnelling Microscopy (STM) 27,28 . Furthermore, the modulation can also be identified via Low Energy Electron Diffraction (LEED), where satellites surround the main reflection spots of the substrate 6 .…”