Laser-induzierte Selbstorganisation an äußeren und inneren Grenzflächen

Das Leitmotiv der vorliegenden Disseration ist es, das Wissensspektrum über Laser-induzierte Selbstorganisation in Folge der Wechselwirkung zwischen linear polarisierten Nanosekunden-Laserpulsen (~ 5-8 ns) bei einer Wellenlänge von 532 nm mit unterschiedlichen Substraten, z.B. Leitern, Halbleitern u...

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Bibliographic Details
Main Author: Nürnberger, Philipp
Contributors: Hampp, Norbert (Prof. Dr.) (Thesis advisor)
Format: Doctoral Thesis
Published: Philipps-Universität Marburg 2017
Online Access:PDF Full Text
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The aim of the present dissertation is to expand the range of knowledge about laser-induced selforganization resulting from linearly polarized nanosecond-laser pulses (~ 5-8 ns) at a central wavelength of 532 nm, which interact with different substrate materials, e.g. conductors, semi-conductors and dielectrics. The cumulative work is seperated into two parts which deal in detail with the formation of a unique selforganization phenomenon denoted as laser-induced periodic surface structures (LIPSS) on external and internal boundary surfaces. \\ In the first part, the influence of the substrate microcrystallinity on the orientation of LIPSS is demonstrated. On polycrystalline stainless steel EN 1.4301, the expansion of LIPSS is limited to the grain size of EN 1.4301, and furthermore, is affected by the crystal orientation of the individual grains. In contrast to monocrystalline silicon (100), additional orientions of LIPSS are found on EN 1.4301, which are not covered by the state-of-the-art-theories and thus determine the crystallinitiy of a substrate for an unknown factor, which directly influences the formation of LIPSS. \\ In the second part, the effects of LIPSS on internal boundary surfaces of layered systems, and vice versa, are investigated. LIPSS are demonstrated to induce alloying and dealloying processes between gold (Au) and silicon (Si) in submicron spatial confinements and with nanosecond temporal resolution. A thin film of Au can be thermally dewetted into Au-nanoparticles with a size in the range from 5 nm - 50 nm. Subsequent illumination of these Au-nanoparticles with ns-laserpulses leads to the formation of periodically aligned AuSi-ribbons (LIPSS), which were found to be electrically conductive by conductive-atomic fore microscopy (C-AFM). Also, the design of AuSi-LIPSS can be controlled by the incident angle of the laserpulses. In addition, the internal interface between Au and Si is modified by LIPSS, facilitating the development of mesoporous Si, which attracts attention in several sophisticated applications. The laser-induced alloying was repeated with other metals, e.g. platinum, silver and copper. Apart from the alloying effects LIPSS were found to be a versatile tool for the controlled growth and alignment of copper-silicide nanocrystals. Thin copper films were sputter-deposited onto single crystal silicon (100) substrates with a thin oxide layer, and subsequently exposed to linearly polarized nanosecond laser pulses. The irradiation triggers \textit{pulsed laser-induced dewetting} (PliD) of the Cu film and simultaneous formation of periodic Cu-nanowires (LIPSS), which partially penetrate the oxide layer to the Si substrate. These LIPSS act as nucleation centers for the growth of CuSi-nanocrystals during thermal processing at 500°C under forming gas (95% N_2 /5% H_2) atmosphere. As a third aspect, a strong influence of silicondioxide (SiO_2)-layer thicknesses on the formation of LIPSS in SiO_2/Si-layered systems is demonstrated. The SiO_2-layer thickness determines which interface of the system controls the formation, i.e. the orientation, of LIPSS. For thin SiO_2-layers LIPSS formation by ns-laser pulses may be nicely explained assuming a thin layer of molten silicon. Surface plasmon polaritons (SPP) excited at the interface air/molten Si primarily contribute to the formation of LIPSS with a perpendicular orientation towards the incident light polarization. As SiO_2 layers exceed the theoretically determined penetration depth of SPP into SiO_2, the orientation of LIPSS rotates by 90 degrees, showing parallel alignment towards the incident light polarization. The parallel alignment of LIPSS may be interpreted in terms of interference between the incident light field and the electric fields of bulk electron plasma waves. Irradiation of SiO_2-layers in the transition range of 80 nm to 120 nm causes the formation of orthogonally superimposed LIPSS. These crossed LIPSS result from the interaction of both formation mechanisms, visualized by etching off the SiO_2 layer with hydrofluoric acid. \\ In conclusion, the dissertation provides insights into several unknown aspects of LIPSS formation. Moreover the conducted research paves the way for potential applications of LIPSS, e.g. microelectronics and semiconductor devices.