ULTRAFAST OPTICAL RESPONSE AND TRANSPORT PROPERTIES OF STRONTIUM TITANATE-BASED COMPLEX OXIDE NANOSTRUCTURES

As the silicon-based semiconductor integrated circuits led by Moore's Law approaching their physical limits, the search for a new generation of nanoelectronic and nanophotonic devices is becoming a hot topic in this post-Moore era. The strontium titanate-based complex oxide heterostructure appears to be a promising alternative due to its diverse emergent properties. Being able to control the metal-insulator transition at the polar/nonpolar LaAlO3/SrTiO3 interface using conductive atomic force microscopy (c-AFM) lithography has made LaAlO3/SrTiO3, in particular, an attractive platform. Expanding the class of heterostructures which can be controlled at nanoscale dimensions is important for alternative oxide-based nanodevices. In this dissertation, the writing and erasing of nanostructures at the nonpolar/nonpolar oxide interface of CaZrO3/SrTiO3 using c-AFM lithography is investigated. Conducting nanostructures as narrow as 1.2 nm at room temperature is achieved. Low-temperature transport measurements based on these nanostructures provide insight into the electronic structure of the CaZrO3/SrTiO3 interface. Such extreme nanoscale control, with dimensions comparable to most single-walled carbon nanotubes, holds great promise for oxide-based nanoelectronic devices. Nanophotonic devices operating at terahertz frequencies, on the other hand, offer unique information for many applications. In this dissertation, broadband nanoscale terahertz generators based on c-AFM lithography defined LaAlO3/SrTiO3 nanojunctions are proved to be able to detect the plasmonic response of a single gold nanorod. By femtosecond pulse shaping using a home-built pulse shaper, over 100 THz bandwidth selective difference frequency generation at LaAlO3/SrTiO3 nanojunctions is also demonstrated, which has great potential in both studying fundamental light-matter interaction and realizing selective control of rotational or vibrational resonances in nanoparticles. With this unprecedented control of THz field, the two-dimensional (2D) material graphene and its coupling with the quasi-2D LaAlO3/SrTiO3 interface are also under investigation. The preliminary data shows evidence for graphene response up to 60 THz. These results help to fill the terahertz gap as well as offer new opportunities for oxide-based nanophotonic devices or even hybrid optoelectronic integrated circuits

Terahertz (THz) Waveguiding Architecture Featuring Doubly-Corrugated Spoofed Surface Plasmon Polariton (DC-SSPP): Theory and Applications in Micro-Electronics and Sensing

Terahertz (10^12 Hz) has long been considered a missing link between microwave and optical IR spectra. This frequency range has attracted enormous research attentions in recent years, with ever-growing anticipation for its applications in remote sensing, molecular spectroscopy, signal processing and next-generation high-speed electronics. However, its development has been seriously hindered by the lack of waveguiding and manipulating architectures that could support the propagation of THz radiations without excessive signal distortion and power loss. Facing this challenge, this work exploits the spoofed surface plasmon polariton (SSPP) mode of the THz oscillation and introduces the doubly corrugated SSPP (DC-SSPP) architecture to support sub-wavelength, low-dispersion THz transmission. DC-SSPP displays unique bandgap structure, which can be effectively modulated via structural and material variables. These unequaled properties make DC-SSPP the ideal solution to support not only signal transmission but also THz sensing and THz-electronics applications. In this thesis, theoretical analysis is carried out to thoroughly characterize the THz propagation, field distribution and transmission band structures in the novel architecture. Via numerical approximation and finite element simulations, design variations of the DC-SSPP are further studied and optimized to fulfill application-specific requirements. We demonstrate effective DNA sensing by adopting the Mach-Zehnder interferometer (MZI) or waveguide-cavity-waveguide insertions, which showed detectability with minuscule sample size even in the aqueous environment. We manifest high-speed analog-to-digital conversion via a combination of MZI DC-SSPP with nonlinear, partial-coupling detector arrays. Full characterization of the proposed ADC is carried out where high operation speed, small signal distortion, and great output linearity is shown. Also included in this work is a detailed review of the THz emitters and detectors, which are indispensable constituents of the THz system discussed herein. The future of the DC-SSPP in building THz bio-computing and THz digital circuits, considered as the next step of this research work, is also explored and demonstrated with the novel concept of directed logic network.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/137130/1/xuzhao_1.pd

Spoof Surface Plasmon Polariton Based THz Circuitry

Terahertz, abbreviated as THz, is defined as the frequency band spanning from 300 GHz to 10 THz, which is located between the microwave from the electronic side of the electromagnetic (EM) spectrum to mid-Infra-Red on the photonic side of the EM spectrum. As accelerated research and innovations over the past seven decades have resulted in widespread commercialization of both electronic and photonic components, THz band has remained underdeveloped, underexploited, and mostly unallocated by the Federal Communications Commission (FCC). Though certain definitive merits of EM waves at THz have evoked interests of physicists, chemists, biologists and material scientists to deploy THz in Time-Domain Spectroscopy (TDS), bio-sensing, and classical imaging applications, the field of THz circuits (also known as THz electronics) has continued to remain in embryonic stage due to the speed limitations of conventional Silicon and compound semiconductor devices like Field Effect Transistors (FETs), Hetero-junction Bipolar Transistors (HBTs), and Hot Electron Mobility Transistors (HEMTs). On the other hand, conventional photonic devices cannot be readily adopted to design new THz circuits and systems. Our research vision in THz circuits and systems is to study the meta-material properties of THz in various forms of sub-wavelength structures and exploit those unique properties to invent the designs of large THz systems like the THz switch, Analog-to-Digital Converter (ADC), etc. The potential large bandwidth and high propagation speed helps photonic circuitry to be proposed against the above-mentioned challenges faced by its electronic counterpart. Optical-assisted as well as all-optical systems in various forms have been reported to realize different data-processing functionalities. For example, analog-to-digital converters (ADC) with the potential of high speed operation have been demonstrated by optical-assisted or all-optical approaches. Photonic logic has also been reported in numerous works by coding the Boolean information in the amplitude, phase or wavelength of the optical signals. Despite these efforts, however, the key element to address the fundamental deficiencies of CMOS circuit remained missing. The use of optical frequencies in these works brought about common shortcomings including dimension mismatch, lack of coherent detection, inflexibility, susceptibility to mechanical and environmental variations, and the presence of bulky optical elements (i.e., mirrors, beam splitters, lenses, etc.). More seriously, these works inherited sequential circuit designs directly from CMOS. It indicates that the cumulative delay still dominated the speed performance, which prevented further decrease of the circuit latency. In light of these problems, we foresee the implementation of THz circuitry as the next reasonable step to take in designing high-speed analog as well as digital circuits. Spoofed Surface Plasmon Polariton (SSPP) is known as a pseudo-surface mode in THz frequencies that mimics the slow wave nature and localized E-M field distribution of the plasmon mode typically observed in optical domain. By introducing periodic corrugations on the surfaces of a metal-dielectric-metal structure, SSPP mode is realized for propagating THz signal, and its mode dispersion is strongly dependent on the geometric dimensions as well as the material properties of the architecture. Recently propagation of THz wave utilizing Spoof surface plasmon polariton (SSPP) earned a great deal of attention due to the ability of SSPP modes to guide THz waves at very low dispersion. In this research, we exploit and investigate the SSPP modes in different periodic structure and utilizing them in different structure to introduce new THz devices, such as, polarization rotator, THz switch, ADC, etc.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/144105/1/mahdia_1.pd

Photodetectors

In this book some recent advances in development of photodetectors and photodetection systems for specific applications are included. In the first section of the book nine different types of photodetectors and their characteristics are presented. Next, some theoretical aspects and simulations are discussed. The last eight chapters are devoted to the development of photodetection systems for imaging, particle size analysis, transfers of time, measurement of vibrations, magnetic field, polarization of light, and particle energy. The book is addressed to students, engineers, and researchers working in the field of photonics and advanced technologies

Design, fabrication and characterisation of graphene electromechanical resonators

In this thesis, the design, fabrication and characterisation of graphene electromechanical resonators have been presented. Graphene features ultrahigh Young’s modulus and large surface to volume ratio that make it ideal for radio frequency (RF) components, sensors and other micro/nano-electromechanical systems (MEMS/NEMS). A novel batch fabrication process for graphene electromechanical resonators has been developed by using poly-Si film as sacrificial layer. Previously reported fabrication processes of graphene resonators use SiO2 as sacrificial layer only because graphene is visible on 300nm SiO2/Si substrate. However, the wet etching of SiO2 involves HF, which is not compatible with metal connections or SiO2 serving as dielectric or passivation layer in graphene NEMS devices. Moreover, the liquid surface tension during drying after wet etching could damage graphene bridges even critical point drying is used. Therefore, in this work, poly-Si is adopted as the sacrificial material. To facilitate the fabrication of graphene resonators, a poly-Si/SiO2/Si substrate has been designed and optimised to make graphene visible under optical microscope for the first time to the author’s knowledge. Chemical vapour deposition (CVD)-grown monolayer graphene sheet has been transferred onto the optimised poly-Si/SiO2/Si substrate and patterned into strips. Metal electrodes have been deposited by lift-off process to make electrical connections, which is prerequisite for integrating graphene resonator into practical devices. The graphene bridges have been released by etching the poly-Si layer with XeF2 in vapour phase, which completely avoids the capillary force induced damage to the graphene bridges. De-fluorination process has been performed by hydrazine reduction to recover graphene’s conductivity. This fabrication process is scalable for massive production of graphene electromechanical resonators, thus furthering their practical application. One-source current mixing characterisation setup has been constructed to test the graphene resonators. Besides the fundamental peak, the activation and enhancement of the second mode of doubly clamped resonator by electrostatic actuation have been observed for the first time. The second mode amplitude reaches 95% of the fundamental mode, whereas only odd higher modes of small intensity have been reported before in other MEMS/NEMS resonators actuated by electrostatic force or magnetomotive force. The findings in this thesis could lead to substantial increase of the sensitivity of sensors based on the graphene resonators. Modal analysis based on Euler-Bernoulli equation has been performed to understand the mechanism behind the activation and enhancement of the second mode. Finite element analysis agrees very well with experimental results and complies with the theoretical model. Finally, a set of novel alignment marks has been designed, which can be incorporated to process mechanically exfoliated 2D material flakes of micron size and irregular shape with conventional photolithography tools, as have been demonstrated by the successful fabrication of a graphene transistor. This optical alignment technique provides an alternative for prototype device development besides electron beam lithography to prevent electron-induced damage to fragile 2D materials

Laser Systems for Applications

This book addresses topics related to various laser systems intended for the applications in science and various industries. Some of them are very recent achievements in laser physics (e.g. laser pulse cleaning), while others face their renaissance in industrial applications (e.g. CO2 lasers). This book has been divided into four different sections: (1) Laser and terahertz sources, (2) Laser beam manipulation, (3) Intense pulse propagation phenomena, and (4) Metrology. The book addresses such topics like: Q-switching, mode-locking, various laser systems, terahertz source driven by lasers, micro-lasers, fiber lasers, pulse and beam shaping techniques, pulse contrast metrology, and improvement techniques. This book is a great starting point for newcomers to laser physics

Design and characterisation of millimetre wave planar Gunn diodes and integrated circuits

Heterojunction planar Gunn devices were first demonstrated by Khalid et al in 2007. This new design of Gunn device, or transferred electron device, was based on the well-established material system of GaAs as the oscillation media. The design did not only breakthrough the frequency record of GaAs for conventional Gunn devices, but also has several advantages over conventional Gunn devices, such as the possibility of making multiple oscillators on a single chip and compatibility with monolithic integrated circuits. However, these devices faced the challenge of producing high enough RF power for practical applications and circuit technology for integration. This thesis describes systematic work on the design and characterisations of planar Gunn diodes and the associated millimetre-wave circuits for RF signal power enhancement. Focus has been put on improving the design of planar Gunn diodes and developing high performance integrated millimetre-wave circuits for combining multiple Gunn diodes. Improvement of device design has been proved to be one of the key methods to increase the signal power. By introducing additional δ-doping layers, electron concentration in the channel increases and better Gunn domain formation is achieved, therefore higher RF power and frequency are produced. Combining multiple channels in the vertical direction within devices is another effective way to increase the output signal power as well as DC-to-RF conversion efficiency. In addition, an alternative material system, i.e. In0.23Ga0.77As, has also been studied for this purpose. Planar passive components, such as resonators, couplers, low pass filters (LPFs), and power combiners with high performance over 100 GHz have been developed. These components can be smoothly integrated with planar Gunn diodes for compact planar Gunn oscillators, and therefore contribute to RF power enhancement. In addition, several new measurement techniques for characterising oscillators and passive devices have also been developed during this work and will be included in this thesis

Photonic based Radar: Characterization of 1x4 Mach-Zehnder Demultiplexer

This work is based on a research activity which aims to implement an optical transceiver for a photonic-assisted fully–digital radar system based on optic miniaturized optical devices both for the optical generation of the radiofrequency (RF) signal and for the optical sampling of the received RF signal. The work is more focused on one very critical block of receiver which is used to parallelize optical samples. Parallelization will result in samples which will be lower in repetition rate so that we can use commercial available ADCs for further processing. This block needs a custom design to meet all the system specifications. In order to parallelize the samples a 1x4 switching matrix (demux) based on Mach Zehnder (MZ) interferometer has been proposed. The demux technique is Optical Time Division Demultiplexing. In order to operate this demux according to the requirements the characterization of device is needed. We need to find different stable control points (coupler bias and MZ bias) of demux to get output samples with high extinction ratio. A series of experiments have been performed to evaluate the matrix performance, issues and sensitivity. The evaluated results along with the whole scheme has been discussed in this document