1,529 research outputs found

    Incremental Distance Transforms (IDT)

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    A new generic scheme for incremental implementations of distance transforms (DT) is presented: Incremental Distance Transforms (IDT). This scheme is applied on the cityblock, Chamfer, and three recent exact Euclidean DT (E2DT). A benchmark shows that for all five DT, the incremental implementation results in a significant speedup: 3.4×−10×. However, significant differences (i.e., up to 12.5×) among the DT remain present. The FEED transform, one of the recent E2DT, even showed to be faster than both city-block and Chamfer DT. So, through a very efficient incremental processing scheme for DT, a relief is found for E2DT’s computational burden

    Crystallographic influences on the nanomanipulation of gold nanoclusters on molybdenum disulfide

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    This work investigates the manipulation behavior of thermally deposited gold nanoclusters with tens of nanometers in size on monocrystalline Molybdenum Disulfide (MoS2) surfaces. Using scan raster patterns in the order of several m, dozens of Au islands can be displaced with a single scan, revealing a directional locking effect caused by the epitaxial nature of the nanoparticle growth on the MoS2 surface. Statistical analysis of tapping mode manipulation scans using pyramidal and conical AFM tips along with MD simulations lead to the conclusion that frictional anitrosopy governs the direction of displacement, with the preference to move along the zigzag- or armchair direction of the hexagonally structured surface. It further investigates the manipulation behavior on CVD grown mono- and bilayer MoS2 with the goal of formation of gold nanowires. For this several nanomanipulation and nanoscratching techniques are deployed to exploit the unique movement behavior of gold islands on a crystalline surface

    MEMS devices for the control of trapped atomic particles

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    This thesis presents the design and characterisation of novel MEMS scanners, for use in systems involving trapped atomic particles. The scanners are manufactured using multiuser silicon-on-insulator MEMS fabrication processes and use resonant piezoelectric actuation based on aluminium nitride thin films to produce one dimensional scanning at high frequencies, with resonance tuning capabilities of up to 5 kHz. Frequencies of ~100kHz and higher are required to enable for example resonant addressing of trapped atomic particles. This work demonstrates how the 200 Όm and 400 Όm diameter scanners can produce optical deflection angles upwards of 2° at frequencies from 80 kHz to 400 kHz. It proposes an addressing scheme based on Lissajous scanning to steer laser pulses onto 2D grids at a scale compatible with experiments involving single trapped atoms. It also examines frequency tuning capabilities of the scanners using localized on-chip Joule heating and active cooling ; frequency tuning and synchronization are shown to be critical to the implementation of 2-dimensional scanning with multiple scanners. These features are then demonstrated in a prototype implementation using fluorescing samples as a mock target to evaluate the optical performance of the scanning system. Finally, the thesis describes a proof-of-concept for integration of the scanners in a trapped atoms experiment, in which rubidium atoms trapped inside a magneto-optical trap are selectively pumped into a fluorescing state using a beam steered by the MEMS scanners.This thesis presents the design and characterisation of novel MEMS scanners, for use in systems involving trapped atomic particles. The scanners are manufactured using multiuser silicon-on-insulator MEMS fabrication processes and use resonant piezoelectric actuation based on aluminium nitride thin films to produce one dimensional scanning at high frequencies, with resonance tuning capabilities of up to 5 kHz. Frequencies of ~100kHz and higher are required to enable for example resonant addressing of trapped atomic particles. This work demonstrates how the 200 Όm and 400 Όm diameter scanners can produce optical deflection angles upwards of 2° at frequencies from 80 kHz to 400 kHz. It proposes an addressing scheme based on Lissajous scanning to steer laser pulses onto 2D grids at a scale compatible with experiments involving single trapped atoms. It also examines frequency tuning capabilities of the scanners using localized on-chip Joule heating and active cooling ; frequency tuning and synchronization are shown to be critical to the implementation of 2-dimensional scanning with multiple scanners. These features are then demonstrated in a prototype implementation using fluorescing samples as a mock target to evaluate the optical performance of the scanning system. Finally, the thesis describes a proof-of-concept for integration of the scanners in a trapped atoms experiment, in which rubidium atoms trapped inside a magneto-optical trap are selectively pumped into a fluorescing state using a beam steered by the MEMS scanners

    On Demand Nanoscale Phase Manipulation of Vanadium Dioxide by Scanning Probe Lithography

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    This dissertation focuses on nanoscale phase manipulations of Vanadium Dioxide. Nanoscale control of material properties is a current obstacle for the next generation of optoelectronic and photonic devices. Vanadium Dioxide is a strongly correlated material with an insulator-metal phase transition at approximately 345 K that generates dramatic electronic and optical property changes. However, the development of industry device application based on this phenomenon has been limited thus far due to the macroscopic scale and the volatile nature of the phase transition. In this work these limitations are assessed and circumvented. A home-built, variable temperature, scanning near-field optical microscope was engineered for Vanadium Dioxide manipulations and detections. Using this instrument, various scanning probe lithography based methods are implemented to induce new nanoscale phases. Three new phase transitions are discovered; a monoclinic metallic at the nanoscale, a rutile metallic metastable phase, and a van der Waals layered insulator. These new phases are studied and characterized to further understand phase manipulations in strongly correlated materials. One of the new phase transitions, monoclinic metallic, showcases plasmonic excitations. This phenomenon is used to demonstrate various nanoplasmonic devices such as rewritable waveguides, spatially modulated resonators, and reconfigurable planar optics. Finally, Oxygen Vacancy diffusion of the monoclinic structure is monitored to determine the temporal limitation for device applications. The discovery, demonstration, and study of these phases clearly shows the ability to manipulate Vanadium Dioxide on the nanoscale for the first time. Phase control is accomplished under ambient conditions and is stable over long periods of time. This technology opens the door for multifunctional device application using strongly correlated materials

    Amplitude and phase evolution of optical fields inside periodic photonic structures

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    Optical amplitude distributions of light inside periodic photonic structures are visualized with subwavelength resolution. In addition, using a phase-sensitive photon scanning tunneling microscope, we simultaneously map the phase evolution of light. Two different structures, which consist of a ridge wave-guide containing periodic arrays of nanometer scale features, are investigated. We determine the wavelength dependence of the exponential decay rate inside the periodic arrays. Furthermore, various interference patterns are observed, which we interpret as interference between light reflected by the substrate and light inside the waveguide. The phase information obtained reveals scattering phenomena around the periodic array, which gives rise to phase jumps and phase singularities. Locally around the air rods, we observe an unexpected change in effective refractive index, a possible indication for anomalous dispersion resulting from the periodicity of the array

    Rapid prototyping of micro-optics for brightness restoration of diode lasers

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    Abstract unavailable please refer to PD

    Acoustic data optimisation for seabed mapping with visual and computational data mining

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    Oceans cover 70% of Earth’s surface but little is known about their waters. While the echosounders, often used for exploration of our oceans, have developed at a tremendous rate since the WWII, the methods used to analyse and interpret the data still remain the same. These methods are inefficient, time consuming, and often costly in dealing with the large data that modern echosounders produce. This PhD project will examine the complexity of the de facto seabed mapping technique by exploring and analysing acoustic data with a combination of data mining and visual analytic methods. First we test the redundancy issues in multibeam echosounder (MBES) data by using the component plane visualisation of a Self Organising Map (SOM). A total of 16 visual groups were identified among the 132 statistical data descriptors. The optimised MBES dataset had 35 attributes from 16 visual groups and represented a 73% reduction in data dimensionality. A combined Principal Component Analysis (PCA) + k-means was used to cluster both the datasets. The cluster results were visually compared as well as internally validated using four different internal validation methods. Next we tested two novel approaches in singlebeam echosounder (SBES) data processing and clustering – using visual exploration for outlier detection and direct clustering of time series echo returns. Visual exploration identified further outliers the automatic procedure was not able to find. The SBES data were then clustered directly. The internal validation indices suggested the optimal number of clusters to be three. This is consistent with the assumption that the SBES time series represented the subsurface classes of the seabed. Next the SBES data were joined with the corresponding MBES data based on identification of the closest locations between MBES and SBES. Two algorithms, PCA + k-means and fuzzy c-means were tested and results visualised. From visual comparison, the cluster boundary appeared to have better definitions when compared to the clustered MBES data only. The results seem to indicate that adding SBES did in fact improve the boundary definitions. Next the cluster results from the analysis chapters were validated against ground truth data using a confusion matrix and kappa coefficients. For MBES, the classes derived from optimised data yielded better accuracy compared to that of the original data. For SBES, direct clustering was able to provide a relatively reliable overview of the underlying classes in survey area. The combined MBES + SBES data provided by far the best accuracy for mapping with almost a 10% increase in overall accuracy compared to that of the original MBES data. The results proved to be promising in optimising the acoustic data and improving the quality of seabed mapping. Furthermore, these approaches have the potential of significant time and cost saving in the seabed mapping process. Finally some future directions are recommended for the findings of this research project with the consideration that this could contribute to further development of seabed mapping problems at mapping agencies worldwide

    Nanometer-precision electron-beam lithography with applications in integrated optics

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (p. 179-185).Scanning electron-beam lithography (SEBL) provides sub-10-nm resolution and arbitrary-pattern generation; however, SEBL's pattern-placement accuracy remains inadequate for future integrated-circuits and integrated-optical devices. Environmental disturbances, system imperfections, charging, and a variety of other factors contribute to pattern-placement inaccuracy. To overcome these limitations, spatial-phase locked electron-beam lithography (SPLEBL) monitors the beam location with respect to a reference grid on the substrate. Phase detection of the periodic grid signal provides feedback control of the beam position to within a fraction of the period. Using this technique we exposed patterns globally locked to a fiducial grid and reduced local field-stitching errors to a < 1.3 nm. Spatial-phase locking is particularly important for integrated-optical devices that require pattern-placement accuracy within a fraction of the wavelength of light. As an example, Bragg-grating based optical filters were fabricated in silicon-on-insulator waveguides using SPLEBL. The filters were designed to reflect a narrow-range of wavelengths within the communications band near 1550-nm. We patterned the devices in a single lithography step by placing the gratings in the waveguide sidewalls. This design allows apodization of the filter response by lithographically varying the grating depth. Measured transmission spectra show greatly reduced sidelobe levels for apodized devices compared to devices with uniform gratings.by Jeffrey Todd Hastings.Ph.D

    Ga(^+) focused Ion beam irradiated Ni(_81)Fe(_19) thin films and Planar nanostructures investigated by the Magneto-Optical Kerr Effect

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    Patterned magnetic films are of interest for storing and sensing information, and possible logic applications, and find commercial applications in consumer goods such as personal computers. This thesis addresses the fast magnetic patterning of capped ultrathin Ni(_81)Fe(_19) films in Chapter 5, and the patterning and controlled magnetic switching of planar nanowires in Chapter 4. Controlled domain wall switching of complex wire geometries with comer structures, artificial trapping sites, 3-terminal junctions and more complex wire circuits is described in Chapters 6-7.The magnetic switching of planar Ni(_81)Fe(_19) nanowires fabricated by 30 keV, focused ion beam Ga(^+) ions was investigated, in the width range 60-500 nm. Experimentally measured wire easy axis coercivity is inversely proportional to width, similar to Stoner-Wohlfarth switching behaviour. Angular switching data for wires is presented. Significantly, wire coercivity and anisotropy field are shown to be strongly dependent on the ion beam raster direction during wire fabrication. The controlled propagation of head-to-head domain walls in a 27 Hz anticlockwise rotating magnetic field, through smoothly rounded comers is experimentally demonstrated. Domain wall propagation fields, 7 ± 3 Oe, just above the intrinsic domain wall coercivity were found. Using an L-shaped rounded comer geometry, the magnetic fields at which domain walls are introduced into wires and the domain wall propagation field were separated. Reproducible pinning and depinning of single domain walls on artificial domain wall traps with depths from 35-125 nm is demonshated.3-Terminal continuous Ni(_81)Fe(_19) wire junctions, suitable for AND/OR domain wall logic operations are described, in which the magnetic switching field of the device output is strongly dependent on the number of domain walls (0, 1, or 2), at the junction. An operating field phase diagram is presented in the context of junction integration with existing domain wall logic elements. Capped NigiFei9 films were ferromagnetically quenched by radiation induced transport of bilayer interfacial atoms. For Si/ Ni(_81)Fe(_19)/Al or Si/ Ni(_81)Fe(_19)/Au bilayers, the critical Ga(^+) ion dose to quench ferromagnetic ordering (Ί), measured by the magneto-optical Kerr (MOKE) effect, is demonstrated to be linearly proportional to the square of NigiFei9 thickness, (tNiFe)(^2) Therefore ultrathin-capped Ni(_81)Fe(_19) films can be magnetically quenched at ion doses ~ an order of magnitude lower then Ni(_81)Fe(_19)/Si samples, which are typically patterned by radiation sputtering from the vacuum- surface interface. Bilayer coercivity, uniaxial anisotropy field, remanent magnetization, and saturation magnetization as measured by MOKE, were tailored by controlled localized ion doses. Ga(^+) ion doses as low as 8 x 10(^13) ions.cm(^-2) reproducibly quenched measured room temperature ferromagnetism in 2 nm thick buried (_81)Fe(_19) films. Patterning of 200 nm wide in-plane magnetized wires embedded between a non magnetic cap and substrate is demonstrated

    Active Plasmonic and Dielectric Nanoantennas

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    This thesis presents results on the fabrication, investigation and characterization of active optical nanoantennas. The three partial results in order of their occurrence are: (i) The demonstration of the operational capability and versatility of a quantum dot deposition technique by fabricating active plasmonic and dielectric nanoantennas. (ii) The optical detection of dark modes of plasmonic nanoantennas. (iii) The optical characterization of the novel dielectric nanoantennas. A versatile method to deposit quantum dots on nanostructured samples to produce an active optical nanoantennas was developed during the course of this thesis. The deposition technique is based on electron-beam lithography, where a template is written in a resist. The developed holes in the polymer define sites to deposit the quantum dots. To ensure an enduring attachment, a zero-length linking is used. The versatility of the method was shown in this thesis by producing structured quantum dot films of various sizes and placing quantum dots on top of nanostructures of divers materials. Precise placed quantum dots were used to built active gold and hafnium dioxide nanoantennas. The experiments on the well known gold rod nanoantennas focused on the investigation of dark modes. Modes are called dark, when they are non-dipolar and thus do not or only weakly interact with far fields under normal incident. Using the quantum dots as feed elements in the hot spot of the antennas, resonances in the nanoantennas were excited with a near-field method, i.e., the quantum dot emitted fluorescence moderated by the antenna into the far field. As expected, the first-order resonance, as measured with the dark-field spectroscope, produced an enhanced, polarized fluorescence signal. Additionally, a fluorescence enhancement for longer antennas was measured. Since it does not coincidence in strength or spectrally with the third-order mode, it can be attributed to the second-order, non-dipolar mode. Thus, this measurement is a proof of principle of a direct detection of dark modes in nanostructures. This additional insight in the operating principles of nanostructures could benefit the design of more complex plasmonic applications. The second nanostructure investigated is a novel type of optical antenna. The nanoantenna design based on the operating principle of leaky-wave antennas was fabricated and equipped with quantum dots. It consists of only two simple dielectric building blocks and has a total length of approximately three times the free-space operation wavelength. The fluorescence of the quantum dots excites a leaky mode in the director by end-fire coupling. Light propagating along the director is continuously coupled to radiating modes in the substrate and emitted into the glass. With Fourier imaging, the far-field pattern of individual antennas was measured and shown to be highly directional. The directivity of the antenna was measured to be D=12.5 dB.Together with numerical calculations, polarization dependent measurements gave insight in the different coupling strength in regards of the quantum dots' dipole orientation relative to the antenna. Experiments with different antenna sizes indicate the broadband operation of the nanoantenna design. It can be easily adapted to various low-loss dielectric materials. Moreover, its non-resonant nature makes the antenna design inherently robust against fabrication imperfections and guarantees broad-band operation
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