Book/Report

FZJ-2018-03337

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Untersuchung von Defekten auf einer gestuften Silber(111)-Fläche mit einem Tieftemperatur- Rastertunnelmikroskop und hochauflösender Elektronenbeugung

Wolf, J. F. (Corresponding author)FZJ*

1990
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/18806

Report No.: Juel-2391

Abstract: A new ultra-high-vacuum chamber was designed and built to study the defects and structure and growth of surfaces and thin films with a scanning tunneling microscope (STM) and high-angle-resolution low-energy-electron-diffraction (SPALEED). A main feature of the STM is its variable temperature capability, ranging from 10 to 20 K up to 450 K. This enables the influence of the substrate temperature on the defects of the surfaces and the structure and growth of thin films to be studied over a wide range. The experiments focused on the defects of a. vicinal Ag(111) surface, misoriented by 1.6° towards the [2$\overline{1}$$\overline{1}$] direction. Single, assymetrically broadened SPA-LEED-peaks showed the step distribution to be irregular, despite extensive preparation of the crystal surface. The mean terrace width was determined to be 150 $\mathring{A}$. The STM revealed the structure of the surface in more detail: it consisted of large (111) terraces separated by 300-400 $\mathring{A}$ wide strips with high step density, oriented preferentially perpendicular to the [2$\overline{1}$$\overline{1}$] direction. The terrace width in these strips ranged from 10-50 $\mathring{A}$, corresponding to a misorientation angle of roughly 5°. This can be understood in terms of a repulsive step-step interaction limiting the minimum terrace width to 10 $\mathring{A}$ and preventing low free energy (100)-facets from being formed. Screw dislocations were imaged with the STM and their local distortion field was measured. The step associated with the screw dislocation reaches its full monatomic height at a distance of 120-200 $\mathring{A}$ from the dislocation line. The height of the (111) plane in the vicinity of the dislocation line changes linearly with the distance along a circle centered around the dislocation line. The slope is the same for different radii. The course of the step often changed abruptly to a (110) direction in the direct vicinity of the dislocation line. This is obviously due to the cristalline nature of the sample, which is not taken into account in classical continuum theory. It can be understood as a relaxation of tension through a slip along a {111} plane. Defects with step heights of 1/3 and 2/3 of a monatomic step height were found on the surface. They are caused by stacking faults in the ($\overline{1}$11), (1$\overline{1}$1) and (11$\overline{1}$) planes, which are induced by the ion bombardment during sample preparation. The submonatomic steps appeared at dislocation lines of screw dislocations, at normal monatomic steps as well as on (111) terraces. A complete stacking fault tetrahedra was imaged. At room temperature all monatomic steps appeared rough in the STMT images, in contrast to the submonatomic steps caused by stacking faults. The steps have frazzled edges parallel to the scanning direction which are one to two atoms wide. The details of this roughness are time dependent. Adatoms diffusing along the steps are proposed as the cause of the rough appearance. Experiments performed at 27 K showed all steps to be sharp, regardless of their step height. Furthermore single adatoms and small adatom clusters adsorbed on (111) terraces were imaged and proved to be stable for the duration of the experiment.

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Contributing Institute(s):

1. Publikationen vor 2000 (PRE-2000)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

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