Guided and deterministic self organization of quantum dots

This thesis presents the fabrication and characterization of InGaAs and InAs QDs formed by self-organized anisotropic strain engineering of InGaAs/GaAs SL templates on planar GaAs (311) B substrates, and guided and directed self organization of the SL template formation through artificial patterning of the substrates for creation of complex QD architectures and lateral positioning by MBE. Detailed studies of SL template evolution as a function of growth and annealing temperatures for growth of ordered InGaAs QD arrays and InAs QD molecules, and transition of the QD molecules into single QDs through optimization of growth temperature, InAs amount, and annealing, analyzed in-situ by RHEED, were demonstrated on planar substrates. The QD arrays, molecules and single QDs have been grown on patterned substrates, following the optimization of the growth conditions for well-ordered, mesoscopic InGaAs QD arrays, and isolated InAs QD molecules and single QDs, in order to create complex architectures of QDs and accurate position control of QDs depending on the pattern design. These QDs exhibit excellent optical quality revealed by temperature dependent macro-PL spectra with strong emission up to room temperature and ultra-sharp peaks in micro-PL at low temperature from individual QDs, which is required for future quantum functional devices. Semiconductor QDs have been intensively investigated in recent decades since they possess full size quantization bearing the opportunity for development of novel device applications and/or increase of device performance for applications such as QD-lasers and/or single photon source/detectors for quantum communication. The properties such as electron-hole interactions, spins of electron/holes, light particles (photons), and lattice vibrations (phonons) can be manipulated in single QDs with sizes comparable or smaller than the de Broglie wavelength of charge carriers in bulk material. For producing such QDs with high opto-electronic quality, needed for device fabrication, different growth approaches have been suggested. Molecular beam epitaxy of In(Ga)As on GaAs substrates grown in the SK mode is the most extensively studied technique for self organization of QDs and QWRs. Based on the lattice mismatch between the substrate and QD material, the ordering, density, and structural properties of QDs have been improved by vertical stacking of strained layers providing lower mismatch regions where the QDs nucleate. Moreover, 1-D QD arrays have been formed by self-organized anisotropic strain engineering of InGaAs/GaAs SL templates on planar and patterned GaAs (100) substrates, which has been extended to laterally ordered and well-isolated 2-D QD molecules on planar GaAs (311)B substrates providing the basis for our study. The stacking and annealing in each InGaAs/GaAs SL template period produces a strain modulated surface with 2-D nodes due to lateral and vertical strain field coupling which serves as a template for QD positioning when the number of SL template periods is increased to ten. The InGaAs QD arrays and InAs QD molecules locate preferentially on top of the nodes due to strain-field recognition. The study of the growth- and annealingtemperature dependent SL template evolution provides a systematic understanding of the SL template development as well as QD ordering on top. The size and the density of the QD molecules are controlled by changing the InAs growth temperature followed by annealing. The QD molecules are transformed into single QDs at high InAs and SL template growth temperatures, whose structural quality is enhanced by annealing and reducing the QD layer thickness, analyzed in situ by RHEED during growth. The study of guided self-organized anisotropic strain engineering for formation of complex laterally ordered InGaAs QD arrays and InAs QD groups is demonstrated on shallow-patterned GaAs (311) B substrates. On stripe-patterned substrates the well-ordered, spot-like arrangement of ordered QD molecules on planar, unpatterned substrates is transformed into a zigzag arrangement of periodic stripes which become straight, well ordered, and connected over macroscopic distances on zigzag mesapatterned substrates. In addition, laterally ordered complex InGaAs and InAs QD architectures are created on deep etched artificial patterns where the ordering is based on self-organized strain engineering of InGaAs/GaAs SL templates on stripe, zigzag, and round hole patterns with faceted mesa sidewalls guiding the self organization. The formation of slow-growing facets on deep-patterned substrates produces QD-free mesa sidewalls, while InGaAs QD arrays and InAs QD molecules and single QDs form on the GaAs (311) B top and bottom planes with arrangements modified only close to the sidewalls. Moreover, the QD array and single QD ordering as well as anisotropic self organization due to the slow and fast growing sidewalls is clearly shown for deep etched round holes. As a result, highly ordered complex QD architectures with QD –free and –rich areas along the pattern sidewalls and mesa- top and bottom regions are created on macro- and microscopic scales on shallow- and deep-patterned GaAs (311) B substrates, respectively. The patterns of round holes, zigzags, and stripes with medium depth of 100 nm direct the self-organized anisotropic strain engineering of InGaAs/GaAs superlattice templates on GaAs (311) B substrates for absolute InAs QD position control. Beyond the complex, lateral QD ordering over large and local areas demonstrated precedingly, deterministic self organization is introduced due to stepped and faceted sidewall formation, where rows of densely packed QD molecules and single QDs develop along the pattern sidewalls and corners. The QD molecules and single QDs in the neighborhood are spatially locked to the QD rows, hence, pattern sidewalls and corners, directing the natural lateral ordering with unchanged periodicities. Moreover, the rotation of the pattern orientation counter clockwise by 90º shows that these arrangements strongly depend on the orientation of the sidewalls, which reveals also that the Ga and In diffusion is anisotropic in the [-233] direction. This extends the concept of guided self organization to deterministic self organization with absolute position control of the QDs without one-to-one pattern definition. Finally, photoluminescence studies of capped and uncapped, ordered QD molecules, and single QDs on patterned GaAs (311)B substrates have shown excellent optical quality. Temperature dependent macro-PL analysis of InAs QD molecules on shallow- and deep- etched substrates revealed clear influences of the pattern designs on the PL intensities and emission energies. The micro-PL spectra at low temperature of capped and uncapped single QDs exhibit distinct emission lines which are broadened for uncapped QDs revealing strong interaction with surface states. Ultra-sharp peaks from capped single QDs on patterned GaAs (311) B substrates are observed at low temperature by high resolution micro-PL. These findings highlight the potential of guided and deterministic self-organized anisotropic strain engineering for the realization of future quantum functional devices requiring ordered and position controlled QD arrays with high structural and optical quality

Fractional Boundaries for Fluid Spheres

A single Israel layer can be created when two metrics adjoin with no continuous metric derivative across the boundary. The properties of the layer depend only on the two metrics it separates. By using a fractional derivative match, a family of Israel layers can be created between the same two metrics. The family is indexed by the order of the fractional derivative. The method is applied to Tolman IV and V interiors and a Schwarzschild vacuum exterior. The method creates new ranges of modeling parameters for fluid spheres. A thin shell analysis clarifies pressure/tension in the family of boundary layers.Comment: to appear in J. Math. Phy

Micro‐photoluminescence of capped and uncapped ordered single InAs quantum dots on GaAs (311)B

Micro-photoluminescence (PL) of capped and uncapped ordered single InAs quantum dots (QDs) on patterned GaAs (311)B substrates exhibits distinct emission lines which are broadened for uncapped QDs. This indicates strong interaction with surface states paving the way towards high-sensitivity sensor applications

Storage Ring Probes of Dark Matter and Dark Energy

We show that proton storage ring experiments designed to search for proton electric dipole moments can also be used to look for the nearly dc spin precession induced by dark energy and ultra-light dark matter. These experiments are sensitive to both axion-like and vector fields. Current technology permits probes of these phenomena up to three orders of magnitude beyond astrophysical limits. The relativistic boost of the protons in these rings allows this scheme to have sensitivities comparable to atomic co-magnetometer experiments that can also probe similar phenomena. These complementary approaches can be used to extract the micro-physics of a signal, allowing us to distinguish between pseudo-scalar, magnetic and electric dipole moment interactions.Comment: 19 pages, 7 figure

Complex laterally ordered InGaAs and InAs quantum dots by guided self-organized anisotropic strain engineering on shallow- and deep-patterned GaAs (311)B substrates

Self-organized anisotropic strain engineering guided on shallow- and deep-patterned GaAs (311)B substrates is exploited for formation of complex laterally ordered architectures of connected InGaAs quantum dot (QD) arrays and isolated InAs QD groups by molecular beam epitaxy. The combination of strain and step engineerings on shallow stripe-patterned substrates transforms the periodic spotlike arrangement of the InGaAs QD arrays and InAs QD groups (on planar substrates) into a zigzag arrangement of periodic stripes which are well ordered over macroscopic areas on zigzag mesa-patterned substrates. In contrast, the formation of slow-growing facets on deep-patterned substrates produces QD-free mesa sidewalls, while InGaAs QD arrays and InAs QD groups form on the GaAs (311)B top and bottom planes with arrangements modified only close to the sidewalls depending on the sidewall orientation. The QDs on the shallow- and deep-patterned substrates exhibit excellent optical properties up to room temperature. Therefore, the concept of guided self-organization demonstrated on shallow-patterned (due to steps) and deep-patterned (due to facets) substrates is highlighted for creation of complex architectures of laterally ordered QDs for future quantum functional devices. © 2007 American Institute of Physic

Hybrid Modeling and Experimental Cooperative Control of Multiple Unmanned Aerial Vehicles

Recent years have seen rapidly growing interest in the development of networks of multiple unmanned aerial vehicles (U.A.V.s), as aerial sensor networks for the purpose of coordinated monitoring, surveillance, and rapid emergency response. This has triggered a great deal of research in higher levels of planning and control, including collaborative sensing and exploration, synchronized motion planning, and formation or cooperative control. In this paper, we describe our recently developed experimental testbed at the University of Pennsylvania, which consists of multiple, fixed-wing UAVs. We describe the system architecture, software and hardware components, and overall system integration. We then derive high-fidelity models that are validated with hardware-in-the-loop simulations and actual experiments. Our models are hybrid, capturing not only the physical dynamics of the aircraft, but also the mode switching logic that supervises lower level controllers. We conclude with a description of cooperative control experiments involving two fixed-wing UAVs

DIVERSITY OF MICROFUNGI ON FAGACEAE IN ULUDAG FORESTS

WOS: 000363091600042Forests ecosystems are sources of oxygen and wood products, also they prevent soil erosion, improve water and air quality, serve as homes for wildlife; and therefore, they preserve and increase biodiversity. Forests can host a diverse community of fungal species with various effects on their host trees. In this research, trees of Fagaceae family of Uludag forests of Bursa province were investigated between the years of 2002 and 2008. By microscopic examination we identified 38 microfungi species in 27 genera belongs to Ascomycota and 1 microfungus species in 1 genus belongs to Basidiomycota. The taxa belong to 15 families: Botryosphaeriaceae, Diaporthaceae, Diatrypaceae, Dothioraceae, Erysiphaceae, Gnomoniaceae, Incertae sedis, Melanconidaceae, Microstromataceae, Nectriaceae, Pseudovalsaceae, Rhytismataceae, Trichosphaeriaceae, Valsaceae and Xylariaceae. The distribution of species by trophic groups revealed a dominance of xylotrophic species. With this study, fungal diversity of Fagaceae family in Uludag forests was identified and included in the mycobiota of Turkey

The Mooring Pattern Study for Q-Flex Type LNG Carriers Scheduled for Berthing at Ege Gaz Aliaga LNG Terminal

Ever growing energy industry requires larger quantities of LNG to be transported by bigger ships between terminals. Every day, new kind of large vessels created by new technologies, and these are used to trade around the globe. This is the dynamic change in shipping industry. But on the other hand these new vessels need to safely berth to existing terminals which we may accept as more static part of the trade. Thus this study born by the request of Ege Gaz Aliaga LNG Terminal management to determine if it is safe to berth to the terminal by a new breed of large LNG carrier type named as Q-Flex and Q-Max. Transas Bridge Simulator NTPRO 5000 series was used in this study for extensive experiments which had been simulated by the use of hook function. During the study, every force applied to mooring hooks and dolphins by the ship lines were divided into 3 dimensions and then measured by simulation experiments. With analysis of the data, required hook and dolphins strengths were determined for the safe mooring arrangements. Upon the completion of the study Ege Gaz Aliaga LNG Terminal became the first safe berth for Q-Flex type vessels in the Mediterranean and the Black Sea. And finally all experiments were confirmed with real life experience when the first Q-Flex type LNG carrier berthed to the Ege Gaz Aliaga LNG Terminal