Diffraction studies on ordering of quasi-one-dimensional structures and nanowires on silicon surfaces induced by metals

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Title: Diffraction studies on ordering of quasi-one-dimensional structures and nanowires on silicon surfaces induced by metals
Authors: Timmer, Frederic Yaw
Thesis advisor: Prof. Dr. Joachim Wollschläger
Thesis referee: Prof. Dr. Simone Sanna
Abstract: In this thesis the morphology and the atomic structure of quasi-one-dimensional structures grown on Si were determined by means of diffraction experiments in combination with kinematic diffraction theory calculations. In the first and the second study a formerly unknown superstructure of Dy/Tb on Si(111) was characterized by means of STM, DFT, SPA-LEED experiments and kinematic diffraction calculations. Here, a structure model could be proposed which contains half as many subsurface Si vacancies as compared to the well-known superstructure of Dy/Tb on Si(111) it was derived from. Due to the decreased number of subsurface Si vacancies the reconstruction is subject to an uni-axial strain which is mitigated by the formation of domains separated by anti-phase domain boundaries. It could be shown that two different types of domains alternate across the surface forming quasi-one-dimensional domains. Additionally, the distribution of the domains could be derived by comparison with kinematic diffraction calculations. In the third study a deeper insight into the complex system of bundled rare-earth silicide nanowires on Si(001) was given. Here, the distributions of the NW width, the bundle width and the bundle distance were deduced from the diffraction patterns collected by SPA-LEED and the subsequent comparison to kinematic diffraction theory calculations. Additionally, it was shown that the (2 x 1) reconstruction sometimes observed on top of the NWs by STM cannot exist over larger parts of the sample and instead a (1 x 1) reconstruction needs to be assumed to explain the experimentally observed diffraction data. In the fourth study the atomic structure of the gold induced atomic wires of the Si(111)-(5 x 2)-Au system was analyzed. The Patterson function of the in-plane SXRD data was compared to the Patterson functions derived from the atomic structure models proposed in literature (AN, EBH, KK) ruling out the AN-model. By comparison of the experimental out-of-plane SXRD data to the corresponding (calculated) SXRD data for the EBH- and the KK-model the KK-model could be identified as the most probable model. Additionally, a refined atomic structure model was derived for the KK-model. In conclusion, the results presented in this thesis clearly display the power of diffraction experiments especially in conjunction with the comparison to kinematic diffraction theory calculations and prove that they are applicable even to low dimensional (e.g., quasi-one-dimensional) structures. Furthermore, it was shown that diffraction experiments can deliver complementary information (e.g., information on deeper atomic layers) as compared to local probing methods (e.g. STM or Atomic Force Microscopy) and especially the combination of local probing methods, DFT calculations and diffraction experiments allows for the explanation of even very complicated material systems.
URL: https://osnadocs.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-2017112016336
Subject Keywords: SPA-LEED; SXRD; Quasi-one-dimensional structures; Silicon surfaces
Issue Date: 20-Nov-2017
License name: Namensnennung - Nicht-kommerziell - Weitergabe unter gleichen Bedingungen 3.0 Unported
License url: http://creativecommons.org/licenses/by-nc-sa/3.0/
Type of publication: Dissertation oder Habilitation [doctoralThesis]
Appears in Collections:FB06 - E-Dissertationen

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