Recent advances in exciton based quantum information processing in quantum dot nanostructures

Recent experimental developments in the field of semiconductor quantum dot spectroscopy will be discussed. First we report about single quantum dot exciton two-level systems and their coherent properties in terms of single qubit manipulations. In the second part we report on coherent quantum coupling in a prototype "two-qubit" system consisting of a vertically stacked pair of quantum dots. The interaction can be tuned in such quantum dot molecule devices using an applied voltage as external parameter.Comment: 37 pages, 15 figures, submitted to New Journal of Physics, focus issue on Solid State Quantum Information, added reference

A review of advances in pixel detectors for experiments with high rate and radiation

The Large Hadron Collider (LHC) experiments ATLAS and CMS have established hybrid pixel detectors as the instrument of choice for particle tracking and vertexing in high rate and radiation environments, as they operate close to the LHC interaction points. With the High Luminosity-LHC upgrade now in sight, for which the tracking detectors will be completely replaced, new generations of pixel detectors are being devised. They have to address enormous challenges in terms of data throughput and radiation levels, ionizing and non-ionizing, that harm the sensing and readout parts of pixel detectors alike. Advances in microelectronics and microprocessing technologies now enable large scale detector designs with unprecedented performance in measurement precision (space and time), radiation hard sensors and readout chips, hybridization techniques, lightweight supports, and fully monolithic approaches to meet these challenges. This paper reviews the world-wide effort on these developments.Comment: 84 pages with 46 figures. Review article.For submission to Rep. Prog. Phy

Cavity quantum electrodynamics with three-dimensional photonic bandgap crystals

This paper gives an overview of recent work on three-dimensional (3D) photonic crystals with a "full and complete" 3D photonic band gap. We review five main aspects: 1) spontaneous emission inhibition, 2) spatial localization of light within a tiny nanoscale volume (aka "a nanobox for light"), 3) the introduction of a gain medium leading to thresholdless lasers, 4) breaking of the weak-coupling approximation of cavity QED, both in the frequency and in the time-domain, 5) decoherence, in particular the shielding of vacuum fluctuations by a 3D photonic bandgap. In addition, we list and evaluate all known photonic crystal structures with a demonstrated 3D band gap.Comment: 21 pages, 6 figures, 2 tables, Chapter 8 in "Light Localisation and Lasing: Random and Pseudorandom Photonic Structures", Eds. M. Ghulinyan and L. Pavesi (Cambridge University Press, Cambridge, 2015, ISBN 978-1-107-03877-6

Ultrafast High-pressure AC Electro-osmotic Pumps for Portable Biomedical Microfluidics

This paper details the development of an integrated AC electro-osmotic (ACEO) microfluidic pump for dilute electrolytes consisting of a long serpentine microchannel lined with three dimensional (3D) stepped electrode arrays. Using low AC voltage (1 Volt rms, 1 kHz), power (5 mW) and current (3.5 mA) in water, the pump is capable of generating a 1.4 kPa head pressure, a 100-fold increase over prior ACEO pumps, and a 1.37 mm/sec effective slip velocity over the electrodes without flow reversal. The integrated ACEO pump can utilize low ionic strength solutions such as distilled water as the working solution to pump physiological strength (100 mM) biological solutions in separate microfluidic devices, with potential applications in portable or implantable biomedical microfluidic devices. As a proof-of-concept experiment, the use of the ACEO pumps for DNA hybridization in a microfluidic microarray is demonstrated

Bead-Droplet Reactor for High-Fidelity Solid-Phase Enzymatic DNA Synthesis

Solid-phase synthesis techniques underpin the synthesis of DNA, oligopeptides, oligosaccharides, and combinatorial libraries for drug discovery. State-of-the-art solid-phase synthesizers can produce oligonucleotides up to 200-300 nucleotides while using excess reagents. Accumulated errors over multiple reaction cycles prevent the synthesis of longer oligonucleotides for the genome scale engineering of synthetic biological systems. The sources of these errors in synthesis columns remains poorly understood. Here we show that bead-bead stacking significantly contributes to reaction errors in columns by analyzing enzymatic coupling of fluorescently labelled nucleotides onto the initiated beads along with porosity, particle tracking and diffusion calculations. To circumvent stacking, we introduce dielectrophoretic bead-droplet reactor (DBDR); a novel approach to synthesize on individual microbeads within microdroplets. Dielectrophoretic force overcomes the droplet-medium interfacial tension to encapsulate and eject individual beads from microdroplets in a droplet microfluidic device. Faster reagent diffusion in droplets, and non-uniform electric field induced enhancement in reagent concentration at its surface can improve reaction fidelities in DBDR. Fluorescence comparisons suggest around 3-fold enhancement of reaction fidelity compared to columns. DBDR can potentially enable the high-purity synthesis of arbitrarily long strands of DNA to meet the emerging demands in healthcare, environment, agriculture, materials, and computing

Doctor of Philosophy

dissertationMicrofluidics is an emerging field that deals with the technology and science of manipulation of fluid in microchannels. Since its birth in the 1990s, it has now gradually matured into an enabling technology, like microelectronics and software engineering. A majority of current applications of microfluidics are in life sciences. Polydimethylsiloxane (PDMS) is a soft elastomer and a popular material for fabricating microfluidic devices. This is due to PDMS's unique set of material properties and low cost. Furthermore, the unique mechanical properties of thin PDMS layers/membranes (< 200 µm) can be used to increase the functionality of PDMS-based microfluidic systems. In this presentation, three unique neuroscience applications of PDMS-based microfluidic devices are presented. The working principle behind each of these devices depends on the unique properties of thin PDMS layers. In the first project a fabrication protocol was developed to stack 30 patterned 10-um thick PDMS layers on top of each other without any trapped air bubbles or wrinkles. Each PDMS layer was patterned by spin-coating uncured PDMS on a photolithographic micromold at very high spin speeds and thermally curing the layer later. The layer stacking procedure was done manually using no specialized tools and did not cause any layer deformation to inhibit functionality. This fabrication protocol was used to develop the first ever microfluidic Magnetic Resonance Imaging Phantom to stimulate brain white matter. In the second project, laser ablation was used to rapidly prototype micromolds and by using these micromolds a unique fabrication protocol was developed and characterized to build microvalve arrays (consisting of 100s of microvalves) without access to any cleanroom facility. This was achieved by manipulating the stiffness of thin PDMS layers that are inherent part of pneumatic microvalves. These microvalve arrays were used to build a microfluidic platform for manipulation of C. elegans (a type of a small round worm), which are used extensively for neuronal behavioral analysis. In the last project using similar fabrication techniques (as described in the second project) microfluidic genotyping devices are developed for zebrafish embryos that are less than 2 days old. The unique advantage of the microfluidic zebrafish genotyping devices is that they enable researchers to collect genetic material (for genotyping) from a zebrafish embryo (1 to 2 days old) without causing any harm to its health. This capability is not possible with any other model multicellular organism to date. The working principle behind one of the presented genotyping devices depends on the controlled actuation of PDMS membranes

FABRICATION OF MAGNETIC TWO-DIMENSIONAL AND THREE-DIMENSIONAL MICROSTRUCTURES FOR MICROFLUIDICS AND MICROROBOTICS APPLICATIONS

Micro-electro-mechanical systems (MEMS) technology has had an increasing impact on industry and our society. A wide range of MEMS devices are used in every aspects of our life, from microaccelerators and microgyroscopes to microscale drug-delivery systems. The increasing complexity of microsystems demands diverse microfabrication methods and actuation strategies to realize. Currently, it is challenging for existing microfabrication methods—particularly 3D microfabrication methods—to integrate multiple materials into the same component. This is a particular challenge for some applications, such as microrobotics and microfluidics, where integration of magnetically-responsive materials would be beneficial, because it enables contact-free actuation. In addition, most existing microfabrication methods can only fabricate flat, layered geometries; the few that can fabricate real 3D microstructures are not cost efficient and cannot realize mass production. This dissertation explores two solutions to these microfabrication problems: first, a method for integrating magnetically responsive regions into microstructures using photolithography, and second, a method for creating three-dimensional freestanding microstructures using a modified micromolding technique. The first method is a facile method of producing inexpensive freestanding photopatternable polymer micromagnets composed NdFeB microparticles dispersed in SU-8 photoresist. The microfabrication process is capable of fabricating polymer micromagnets with 3 µm feature resolution and greater than 10:1 aspect ratio. This method was used to demonstrate the creation of freestanding microrobots with an encapsulated magnetic core. A magnetic control system was developed and the magnetic microrobots were moved along a desired path at an average speed of 1.7 mm/s in a fluid environment under the presence of external magnetic field. A microfabrication process using aligned mask micromolding and soft lithography was also developed for creating freestanding microstructures with true 3D geometry. Characterization of this method and resolution limits were demonstrated. The combination of these two microfabrication methods has great potential for integrating several material types into one microstructure for a variety of applications

Ultra thin ultrafine-pitch chip-package interconnections for embedded chip last approach

Ever growing demands for portability and functionality have always governed the electronic technology innovations. IC downscaling with Moore s law and system miniaturization with System-On-Package (SOP) paradigm has resulted and will continue to result in ultraminiaturized systems with unprecedented functionality at reduced cost. The trend towards 3D silicon system integration is expected to downscale IC I/O pad pitches from 40µm to 1- 5 µm in future. Device- to- system board interconnections are typically accomplished today with either wire bonding or solders. Both of these are incremental and run into either electrical or mechanical barriers as they are extended to higher density of interconnections. Alternate interconnection approaches such as compliant interconnects typically require lengthy connections and are therefore limited in terms of electrical properties, although expected to meet the mechanical requirements. As supply currents will increase upto 220 A by 2012, the current density will exceed the maximum allowable current density of solders. The intrinsic delay and electromigration in solders are other daunting issues that become critical at nanometer size technology nodes. In addition, formation of intermetallics is also a bottleneck that poses significant mechanical issues. Recently, many research groups have investigated various techniques for copper-copper direct bonding. Typically, bonding is carried out at 400oC for 30 min followed by annealing for 30 min. High thermal budget in such process makes it less attractive for integrated systems because of the associated process incompatibilities. In the present study, copper-copper bonding at ultra fine-pitch using advanced nano-conductive and non-conductive adhesives is evaluated. The proposed copper-copper based interconnects using advanced conductive and non-conductive adhesives will be a new fundamental and comprehensive paradigm to solve all the four barriers: 1) I/O pitch 2) Electrical performance 3) Reliability and 4) Cost. This thesis investigates the mechanical integrity and reliability of copper-copper bonding using advanced adhesives through test vehicle fabrication and reliability testing. Test vehicles were fabricated using low cost electro-deposition techniques and assembled onto glass carrier. Experimental results show that proposed copper-copper bonding using advanced adhesives could potentially meet all the system performance requirements for the emerging micro/nano-systems.M.S.Committee Chair: Prof. Rao R Tummala; Committee Member: Dr. Jack Moon; Committee Member: Dr. P M Ra

Hierarchical self-assembly of di-, tri- and tetraphenylalanine peptides capped with two fluorenyl functionalities: from polymorphs to dendrites

Homopeptides with 2, 3 and 4 phenylalanine (Phe) residues and capped with fluorenylmethoxycarbonyl and fluorenylmethyl esters at the N-terminus and C-terminus, respectively, have been synthesized to examine their self-assembly capabilities. Depending on the conditions, the di-and triphenylalanine derivatives self-organize into a wide variety of stable polymorphic structures, which have been characterized: stacked braids, doughnut-like shapes, bundled arrays of nanotubes, corkscrew-like shapes and spherulitic microstructures. These highly aromatic Phe-based peptides also form incipient branched dendritic microstructures, even though they are highly unstable, making their manipulation very difficult. Conversely, the tetraphenylalanine derivative spontaneously self-assembles into stable dendritic microarchitectures made of branches growing from nucleated primary frameworks. The fractal dimension of these microstructures is similar to 1.70, which provides evidence for self-similarity and two-dimensional diffusion controlled growth. DFT calculations at the M06L/6-31G(d) level have been carried out on model beta-sheets since this is the most elementary building block of Phe-based peptide polymorphs. The results indicate that the antiparallel beta-sheet is more stable than the parallel one, with the difference between them growing with the number of Phe residues. Thus, the cooperative effects associated with the antiparallel disposition become more favorable when the number of Phe residues increases from 2 to 4, while those of the parallel disposition remained practically constant.Peer ReviewedPostprint (author's final draft