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978-3-8439-2379-8, Reihe Physikalische Chemie

Stefanie Kietzmann
Rolled-Up AlInP-Based Optical Microtube Resonators Coupled to Colloidal and Molecular Emitters for Optofluidic and Sensing Applications

156 Seiten, Dissertation Universität Hamburg (2015), Softcover, A5

Zusammenfassung / Abstract

The optofluidic and sensing capabilities of rolled-up AlInP-based optical microtube resonators, evanescent-field coupled to different colloidal and molecular emitters, are demonstrated and a flow-channel system for on-chip integration of these devices isintroduced.

Semiconductor microtubes are fabricated from strained multilayer systems by wet-chemical undercutting. The strain relaxation induces a self-rolling mechanism that leads to the formation of microtubes. The microtubes investigated in this work consist of AlInP, which advantageously has a large refractive index of 3 and is transparent in the visible spectral range. The semiconductor microtubes with typical radii of 2 to 3 microns exhibit a two-dimensional light confinement via waveguiding within the tube walls, which are typically as thin as 50 to 150 nm. By a tailoring of the microtube geometry in axial direction, also a complete three-dimensional light confinement can be achieved. The confinement mechanisms and the resulting mode spectra can be described by a simple planar waveguide model, which is in good agreement with FDTD simulations and measurements of similar structures.

Different external emitters can be coupled to the microtube resonators via long-ranging evanescent fields. Wet-chemically synthesized emitters like nanocrystals, dot-rods and nanowires are investigated with respect to quantum yield, thermal, chemical and long-term stability and their influence on the mode spectra of AlInP microtubes. Furthermore, a novel hybrid structure is fabricated from an AlInP microtube with a fluorescent NaT2 molecule film. Here, the molecule film acts as emitter and waveguiding element at the same time. Different microtube structures are investigated in measurements and FDTD simulations, evaluating the structure with the largest quality factors.

The sensing capabilities of AlInP microtubes are demonstrated by mode shifts in the emission spectra of a microtube due to a change of the material that fills its hollow core. A mode shift is induced by a change of the refractive index of the microtubes filling. Different approaches of embedding an AlInP microtube into a microfluidic channel system are described and fully functional microchannel systems are successfully realized by two different methods. Confocal fluorescence measurements of the emission spectra of microtubes inside microchannel systems that are flushed with different solvents are presented and the observed mode shifts are discussed.