In present dissertation, field-driven quantum well (QW) device is proposed to obtain high-speed and high-efficiency all-optical wavelength converter (AOWC). A new type QW material, InGaAsP/InGaAlAs, is employed to improve not only quantum confined Stark effect, but also carrier life time during high electric field excitation. The bandwidth as well as efficiency can be enhanced. Thus, the slow gain recovery mechanism (~100ps) from conventional semiconductor optical amplifier (SOA)-based AOWC can be overcome. The dispersion- and efficient- limited fiber-based AOWC (~10ps) can also be avoided. -3dB frequency bandwidth exceeding 40GHz for both electrical-to-optical and photocurrent response has been observed from InGaAsP/InGaAlAs waveguide of AOWC, leading to above 40GHz bandwidth in optical-to-optical response. A 40 Gb/s measurement setup is finally used for testing eye-diagram and bit-error-ratio in order to verify the data transmission of AOWC. Low power penalty with 0.5 dB comparing with back-to-back system performance is measured, suggesting InGaAsP /InGaAlAs waveguide is applicable to all-optical processing. By exciting short optical pump pulse in such waveguide, as short as 6.4ps probe pulse is observed, breaking through 10ps order in conventional type of QW and thus indicating the plausibility of performing 100Gb/s all optical processing.

Just as conventional mechatronic systems rely on switches and relays, machines that are soft and elastically deformable will require compliant materials that can support field-controlled reconfiguration. In this dissertation, I present several novel approaches to shape programmability that primarily rely on condensed soft matter and are stimulated by electric or magnetic fields. I begin with electric-field-driven methods for achieving shape programmability of elastomer-based systems. These include dielectric elastomer actuators and electrostatic beams that undergo extreme stretch. Classical theories in elasticity and electrostatics are used to examine the mechanical responses and instabilities of these soft, hyperelastic systems. Such modeling techniques are also used to examine another switching mode based on the snap through behavior of a buckled ferromagnetic beam under magnetic load. I will then discuss a unique approach to shape programmability that is based on electrochemistry and exploits the coalescence and separation of anchored liquid metal drops. In this case, electrical signals under 10V are utilized to manipulate surface energies and transition between bi-stable states. Experiments and Surface Evolver simulations show that oxidation and reduction on opposing poles of the coalesced drops create an interfacial tension gradient that eventually leads to limit-point instability. Theory derived from bipolar electrochemistry and vertical electrical sounding predicts droplet motion and separation based on geometry and bath conductivity, facilitating the optimization of reconfigurable devices using this phenomenon. I conclude with the application of the bi-stable droplets to a simple toggle switch capable of changing circuit conductivity by over three orders of magnitude.

abstract: Novel electric field-assisted microfluidic platforms were developed to exploit unique migration phenomena, particle manipulation, and enhanced droplet control. The platforms can facilitate various analytical challenges such as size-based separations, and delivery of protein crystals for structural discovery with both high selectivity and sensitivity. The vast complexity of biological analytes requires efficient transport and fractionation approaches to understand variations of biomolecular processes and signatures. Size heterogeneity is one characteristic that is especially important to understand for sub-micron organelles such as mitochondria and lipid droplets. It is crucial to resolve populations of sub-cellular or diagnostically relevant bioparticles when these often cannot be resolved with traditional methods. Herein, novel microfluidic tools were developed for the unique migration mechanism capable of separating sub-micron sized bioparticles by size. This based on a deterministic ratchet effect in a symmetrical post array with dielectrophoresis (DEP) for the fast migration allowing separation of polystyrene beads, mitochondria, and liposomes in tens of seconds. This mechanism was further demonstrated using high throughput DEP-based ratchet devices for versatile, continuous sub-micron size particle separation with large sample volumes. Serial femtosecond crystallography (SFX) with X-ray free-electron lasers (XFELs) revolutionized protein structure determination. In SFX experiments, a majority of the continuously injected liquid crystal suspension is wasted due to the unique X-ray pulse structure of XFELs, requiring a large amount (up to grams) of crystal sample to determine a protein structure. To reduce the sample consumption in such experiments, 3D printed droplet-based microfluidic platforms were developed for the generation of aqueous droplets in an oil phase. The implemented droplet-based sample delivery method showed 60% less sample volume consumption compared to the continuous injection at the European XFEL. For the enhanced control of aqueous droplet generation, the device allowed dynamic triggering of droplets for further improvement in synchronization between droplets and the X-ray pulses. This innovative technique of triggering droplets can play a crucial role in saving protein crystals in future SFX experiments. The electric field-assisted unique migration and separation phenomena in microfluidic platforms will be the key solution for revolutionizing the field of organelle separation and structural analysis of proteins. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2020

High performance natural materials typically employ highly tuned structures spanning the nanoscopic to macroscopic length scales. Synthetically recapitulating this degree of complexity has become a unifying goal connecting the fields of chemistry, nanoscience, biology, and materials science. One common strategy is to direct the bottom up assembly of nanoparticle building blocks into hierarchical structures using stimuli such as electric fields. Despite the promise and great versatility of electric fields, there are many knowledge gaps surrounding their use to assemble highly complex structures. In this thesis, we explore the assembly of nanoparticles into hierarchical structures through dielectrophoresis (DEP), or the motion of polarizable objects in non-uniform electric fields. Critically, through a systematic approach, we study the fundamental polarizability of individual particles, the assembly of particle dimers, and finally the emergence of macroscopic structure from nanoscopic particles. Interweaving these explorations are instrumentation advances that broaden our ability to measure fundamental particle properties and explore hierarchical structures. Initially, we measure the polarizability of nanoparticles in solution using fluorescence microscopy. Specifically, we quantify the polarizability of solution-phase semiconductor quantum dots (QDs) for the first time. Through analyzing the thermodynamic distribution of particles in a microfluidic device with a non-uniform electric field profile, we identify a striking 30-fold increase in polarizability in the presence of low salt conditions due to the Debye screening length being commensurate with the particle size. This increase in polarizability indicates that nanoparticles assemble far more rapidly and easily than previously predicted. Next, we study the assembly of nanoparticles in the vicinity of anisotropic template particles as a path to realizing hierarchical structures. Specifically, we explore eight particle geometries using finite element analysis and find a >10-fold local field enhancement near some shapes, potentially promoting hierarchical assembly. We subsequently introduce a framework for predicting the assembly outcome of particles with multiple distinct sizes and shapes that includes thermodynamic and kinetic considerations. Then, we perform experiments demonstrating the hierarchical assembly of QDs into macroscopic structures. Despite theory predicting the formation of chains, we observe a macroscopic foam-like cellular phase when the QDs experience a combination of alternating current (AC) and direct current (DC) voltages. The resulting materials are both highly hierarchical in that they are 200 µm thick materials comprised of 20 nm particles, but they also represent extremely low-density materials. Finally, we report the invention of a novel instrument for imaging hierarchical materials. Specifically, we describe a massively parallel atomic force microscope with >1000 probes that is made possible through the combination of a new cantilever-free probe architecture and a scalable optical method for detecting probe-sample contact that provides sub-10 nm vertical precision. / 2022-09-28T00:00:00Z