In this dissertation, we study the optical property of 2D graded photonic super-crystals (GPSCs) for photon management. We focused primarily on manipulation and control of light by using the newly discovered GPSCs which present great opportunity for electromagnetic wave control in photonic devices. The GPSC has been used to explore the superior capability of improving the light extraction efficiency of OLEDs. The enhancement of extraction efficiency has been explained in term of destructive interference of surface plasmon resonance and out-coupling of surface plasmon through phase matching provided by GPSC and verified by e-field intensity distributions. A large light extraction efficiency up to 75% into glass substrate has been predicted through simulation. We also study the light trapping enhancement in GPSCs. Broadband, wide incident angle, and polarization independent light trapping enhancement is achieved in silicon solar cells patterned with the GPSCs. In addition, novel 2D GPSCs were fabricated using holographic lithography through the interference lithography by two sets of multiple beams arranged in a cone geometry using a spatial light modulator (SLM). Finally, we also report a fabrication of GPSCs with a super-cell size of 12a×12a by using e-beam lithography. Diffraction pattern from GPSCs reveals unique diffraction properties. In an application aspect, light emitting diode arrays can be replaced by a single light emitting diode shinning onto the diffraction pattern for a uniform fluorescence.

The diploma thesis deals with the experimental study of surface plasmon polaritons (SPPs) on nano-structures with the Au/Co/Au multilayer. Plasmonic structures were prepared by the electron beam lithography and by the focused ion beam. A Scanning optical near-field microscope was used for detection of surface plasmon polaritons. SPPs were confirmed by the experiment with different polarizations of the illuminating light. Furthermore, differences in plasmon interference wavelengths was measured for different surface dielectric functions. Finally, the decantation of the SPPs interference image was measured in dependence on the external magnetic field.

This diploma thesis is focused on the applications and fabrication of graphene membrane from graphene prepared by the chemical vapor deposition. Theoretical part deals with transport properties of the graphene and multiple scattering processes limiting the charge carrier mobility in this material. Included is short review of graphene membrane applications. Experimental part provides fabrication process for achieving suspended graphene device by utilizing electron beam lithography, focused ion beam, chemical etching and patterning of graphene. Graphene membrane is characterized by transport properties measurement and compared to non-suspended graphene.

The aim of this master's thesis is to explore and study dynamic aberration correction options in electron-beam lithography systems. For the calculations, the thesis uses the optical column of the BS600 electron-beam writer. The thesis focuses on corrections of the third order field curvature, astigmatism, and distortion aberrations of the currently used magnetic deflection system and a newly designed electrostatic deflection system. The parameters of the two deflection and correction systems were compared.

This thesis deals with deposition of gallium nitride thin films on silicon substrates covered by negative HSQ rezist. Rezist was patterned via electron beam lithography to create masks, where the selective growth of crystals was achieved. Growth of GaN layers was carried out by MBE method. For achievement of desired selective growth, the various deposition conditions were studied.

The thesis deals with preparation of graphene nanostructures and their applications in the measurement of transport properties of graphene. The contacts for measurement of resistance are fabricated by electron beam lithography on graphene exfoliated flakes, CVD graphene layers and grains. Graphene is also shaped using the same method. Resistivity of the layer, concentration and mobility of charge carriers are determined by different approaches. Hysteresis appearing in dependence of resistivity on the gate voltage is discussed as well. A significant part of the work is dedicated to monitoring the response of graphene resistance to relative humidity changes and potential use of graphene as a sensor of relative humidity.

No description available.

<p>   The arrival of Si transistors and integrated circuit technology more than half a century ago made vacuum electronic technology almost extinct. Today, there are only a few niche applications for vacuum electronics. The main issues with this technology are its high voltage requirement and high-power consumption, difficult and costly fabrication technology, lack of integration capability, and poor reliability characteristics. Some of these issues may be addressed by going to nm scale fabrication that did not exist 60 years ago. Other problems such as reliability and lack of integration capability require alternative solutions to what has been proposed so far. Vacuum is the ultimate conduction media allowing electrons to reach the speed of light without any scattering. Consequently, a vacuum transistor, if designed correctly, can achieve THz frequency performance, while delivering Watt-level powers. No semiconductor technology can compete with vacuum technology to deliver such performance. </p> <p>In this work, novel methods for implementing nanoscale field emitter arrays used in vacuum electronics are proposed. Gated and ungated field emitters are fabricated with self-assembly technology and electron beam lithography. Different anisotropic dry etching recipes are developed to achieve emitters with different sharpness and aspect ratios. Our methods lead to field emitter array operation under low voltages (less than 20 V) and high current densities (around 50 A/cm2) using self-assembly and soft film anode-cathode isolator, and field emitter devices with ~4.5 A/cm2 current density with a turn-on voltage less than 50 V using electron beam lithography and oxide anode-cathode isolator. </p> <p>Making reliable field emitter devices is challenging. Due to Joule heating, ion bombardment, and geometrical variations for each tip in the field emitter arrays, emission current becomes nonuniform across the array. Sharper tips emit at a higher rate and eventually, the heat generated at the tip deforms the tips leading to electron emission at a lower rate. With ultra-low doped emitters, the current of each tip is limited to a few nano-amperes leading to a negligible current fluctuation at the tips. </p> <p>Our fabricated ultra-low doped devices with both self-assembly and electron beam lithography techniques presented constant emission current with almost no change over 24 hours of continuous operation. Such excellent reliability characteristics in vacuum field emitter devices have not been demonstrated to date.</p> <p>The screening effect in close-packed field emitter arrays which occurs by nearby conductive or semiconductive objects is thoroughly investigated and different solutions are proposed to reduce this effect between the emitters. Simulation studies using Sentaurus TCAD, MATLAB, and COMSOL Multiphysics simulators facilitated the design and optimization of gated and ungated field emitter arrays. These studies included the effect of sharpness, the distance between neighboring emitters, enclosing the emitters by a Si block around the emitters as well as anode-cathode separation on the electrical characterization of field emitter arrays. </p> <p>The optimum location and operating voltages which lead to a maximum gate control and emitter current density are also studied for gated field emitter arrays. Instead of individually gating each field emitter, it was found that controlling the emission of a sub-array with a metallic all-around gate is more efficient and it leads to higher current densities. Guided by simulations, gated field emitter arrays with 5×5 and 2×2 sub-arrays are developed. In terms of strength of the grid control (transconductance), turn-on voltage, maximum emission current, and field intensification factor, the device with the 2×2 sub-array was superior to the one with the 5×5 sub-array. The VFET with 5×5 sub-arrays achieved a higher current density due to a larger number of field emitters packed per active emission area. Finally, plans to further improve the technology and transitioning into the fabrication of vacuum integrated circuits are discussed.</p> <p>  </p>

No description available.

The aim of this project was to produce an integrate-able free space optical transceiver for Specks. Specks are tiny computing units that together can form a powerful network called a SpeckNet. The SpeckNet platform is developed by the SpeckNet consortium, which consists of five Scottish Universities and combines computer science, electrical engineering and digital signal processing groups. The principal goal of creating an optical transceiver was achieved by integrating in-house fabricated VCSELs (with lasing thresholds below 400 uA) and custom designed detectors on the SpeckNet platform. The transceiver has a very low power consumption (approximately 100 uW), which removes the need for synchronous communication through the SpeckNet thus making the network more efficient. I describe both static and dynamic beam control techniques. For static control, I used micro-lenses. I fabricated the lenses by greyscale electron beam lithography and integrated them directly on VCSEL arrays. I achieved a steering angle of 10 degrees with this design. I also looked at integrated gratings etched straight into a VCSEL and observed beam steering with an efficiency of 60% For dynamic control, I implemented a liquid crystal (LC) design. I built a LC cell with 30 individually controlled pixels, but I only achieved a steering angle of 1 degree. Furthermore, I investigated two different techniques for achieving beam steering by interference, using coupled VCSELs (a phased array approach). Firstly, using photonic crystals etched into the surface of the VCSEL, I built coupled laser cavities. Secondly, I designed and built bow-tie type VCSELs that were optically coupled but electrically isolated. These designs work by differential current injection causing an interference effect in the VCSELs far field. This technique is the first stepping stone towards realising a phased optical array. Finally, I considered signal detection. Using the same VCSEL material, I built a resonant-cavity detector. This detector had a better background rejection ratio than commercially available silicon devices.