Surface morphology of clean and adsorbate covered Au(111) investigated by scanning tunneling microscopy under ambient conditions

Huang, L.

Book/Report

FZJ-2019-01494

Surface morphology of clean and adsorbate covered Au(111) investigated by scanning tunneling microscopy under ambient conditions

Huang, L. (Corresponding author)FZJ*

1996
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Jülich : Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag, Berichte des Forschungszentrums Jülich 3251, 83 p. (1996)

Please use a persistent id in citations: http://hdl.handle.net/2128/21687

Report No.: Juel-3251

Abstract: The surface morphology of clean and adsorbate covered Au(111) has been systematically studied using scanning tunneling microscopy (STM) under ambient conditions.The results demonstrate that using STM and X-ray diffraction (XRD) some particular surface science topics can be investigated also in the ambient environment. The investigations of surface properties under ambient conditions will advance our understanding of many important processes involved in the manufacturing environment.Firstly, the clean Au(111) surface has been studied. Because of its inertness, the Au(111) surface is a well suited substrate for adsorption studies in ambient environment. Furthermore, the clean Au(111) surface undergoes a (22 x $\sqrt{3}$) reconstruction which can be used as an ideal model system to evaluate the performance of our STM operated in air. In most cases, the appearance on both large and atomic scales and behavior of the reconstruction of Au(111) in air show similarities with those in ultrahigh vacuum (DRV). Due to the presence of adsorbates, mobility of the reconstruction patterns in air is higher, particularly at structural imperfections. In rare cases, the decay of the reconstruction and a phase transition between the (22 x $\sqrt{3}$) and (1x1) structure are also observed on the freshly prepared samples. Secondly, iodine adlayer structures on Au(111) have been studied. Since the adlayer forms different phases as a function of coverage, 11 Au(111) serves as a model system to study two dimensional (2D) phenomena such as commensurate-incommensurate (C-1) phase transitions of the surface structures. Three distinct adlayer structures have been obtained using ex-situ coverage control: (i) at low iodine coverage, a commensurate ($\sqrt{3}$ x $\sqrt{3}$)R30° structure is formed. (ii) in the coverage range from 0.33 to 0.4, a uniaxially compressed (p x $\sqrt{3}$) structure is observed. (iii) at the iodine monolayer saturation coverage, a hexagonally compressed moire-type incommensurate structure is found. From the observation of parallel domain walls it follows that the phase transition from (i) to (ii) is of $\textit{second}$ order. The coexistence of phases (ii) and (iii) on the same surface area indicates that the corresponding phase transition in this case is of first order. By changing the tunneling parameters either iodine adlayer or the gold substrate can be "selectively" imaged. In this way the properties of the adlayer structures could be determined with high precision. This unique feature of STM may find wider applications in the study of other adsorption systems. Thirdly, the surface morphology of Au(111) after annealing in high pressure oxygen at high temperatures have been investigated. Two types of oxygen-induced structures on the Au(111) surface have been observed: (i) a hexagonal long-range reconstruction with a periodicity of 60-80 $\mathring{A}$ and a corrugation of $\sim$ 0.5 $\mathring{A}$. At the atomic scale this surface exhibits a ($\sqrt{3}$ x $\sqrt{3}$)R30° structure, which we attribute to atomic oxygen strongly chemisorbed at the Au(111) surface. The superstructure can be satisfactorily described as the result of a moire pattern induced by an in plane lattice mismatch and a slight rotation between the topmost gold layer and its underlying substrate due to the presence of the adsorbate. (ii) a "modified" herringbone structure related to the original herringbone reconstruction of the clean Au(111) surface, but with additional [...]

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