Schroth, Philipp: Growth of self-catalyzed GaAs nanowires using molecular-beam-epitaxy and structural characterization by in-situ X-ray diffractionWachstum selbst-katalysierter GaAs Nanodrähte mittels Molekularstrahlepitaxie und deren strukturelle Charakterisierung durch in-situ Röntgenbeugung. 2016
Inhalt
- Zusammenfassung
- Abstract
- Contents
- Introduction
- 1 Introduction to GaAs nanowires
- 1.1 Synthesis of GaAs nanowires
- 1.2 Polytypism and crystal structure of GaAs nanowires
- 1.3 X-ray scattering from nanowires
- 1.4 Modeling the vertical stacking of polytypic nanowires
- 1.5 Capabilities of the portable MBE system for X-ray analysis
- 2 Growth of self-catalyzed GaAs nanowires on Si(111)
- 2.1 Sample preparation and growth protocol
- 2.2 Epitaxial alignment, polytypism and faceting of self-catalyzed GaAs nanowires observed by in-situ RHEED
- 2.3 The silicon oxide layer: the role of substrate preparation
- 2.3.1 Growth of nanowires on oxide-layers with varying thickness
- 2.3.2 The effect of Ga pre-deposition on the growth of self-catalyzedGaAs nanowires grown on substrates with varying oxide-layerthickness
- 2.4 The parameter window for the growth of self-catalyzed GaAs nanowires grown on Si(111) covered with native oxide
- 2.4.1 Nanowire length and diameter as a function of growth-time
- 2.4.2 Nanowire length and diameter as a function of the Ga-flux
- 2.4.3 Nanowire length and diameter as a function of the As-flux
- 2.4.4 The wetting angle of Ga-droplets after growth
- 2.4.5 Influence of the substrate temperature
- 2.5 Summary: growth of self-catalyzed GaAs nanowires on Si(111)
- 3 X-ray studies of self-catalyzed GaAs nanowires
- 3.1 Characterization of an ensemble of GaAs nanowires by ex-situ X-ray diffraction in symmetric scattering geometry
- 3.2 Scattering from individual self-catalyzed GaAs nanowires and parasitic GaAs crystallites investigated by ex-situ X-ray diffraction using a nano-focus setup
- 3.3 Evolution of polytypism during the growth of self-catalyzed GaAs nanowires
- 3.3.1 Experiment setup and data evaluation
- 3.3.2 Interpretation of time-resolved scattering data in the frame of a Markov model for the stacking sequences
- 3.3.3 Implications on the growth dynamics
- 3.4 Distinguishing the contribution of parasitic growth and epitaxial nanowires by asymmetric ex-situ X-ray diffraction
- 3.5 Comparison of phase fractions of polytypic nanowires determined by symmetric and asymmetric X-ray diffraction
- 3.6 Evolution of the crystal-structure of self-catalyzed GaAs nanowires during growth monitored by time-resolved X-ray diffraction in asymmetric geometry
- 3.7 Time-resolved monitoring of radial growth of self-catalyzed GaAs nanowires: tapering and facet growth
- 3.7.1 Distinguishing non-catalytic facet-growth and catalytic growth processes by scattering features obtained by time-resolved in-situ X-ray diffraction
- 3.7.2 Simulation of time-resolved intensity profiles I(~q, t) and comparisonto the experimental in-situ data
- 3.7.3 Models for catalytic radial nanowire growth
- 3.7.4 Comparison of model and experiment: the evolution of droplet shape (t) during growth of self-catalyzed GaAs nanowires, and the Ga-diffusion length Ga
- 3.8 Summary: X-ray studies of self-catalyzed GaAs nanowires
- 4 Conclusion & Outlook
- Bibliography