Liquid Crystal on Silicon Devices: Modeling and Advanced Spatial Light Modulation Applications

Liquid Crystal on Silicon (LCoS) has become one of the most widespread technologies for spatial light modulation in optics and photonics applications. These reflective microdisplays are composed of a high-performance silicon complementary metal oxide semiconductor (CMOS) backplane, which controls the light-modulating properties of the liquid crystal layer. State-of-the-art LCoS microdisplays may exhibit a very small pixel pitch (below 4 ?m), a very large number of pixels (resolutions larger than 4K), and high fill factors (larger than 90%). They modulate illumination sources covering the UV, visible, and far IR. LCoS are used not only as displays but also as polarization, amplitude, and phase-only spatial light modulators, where they achieve full phase modulation. Due to their excellent modulating properties and high degree of flexibility, they are found in all sorts of spatial light modulation applications, such as in LCOS-based display systems for augmented and virtual reality, true holographic displays, digital holography, diffractive optical elements, superresolution optical systems, beam-steering devices, holographic optical traps, and quantum optical computing. In order to fulfil the requirements in this extensive range of applications, specific models and characterization techniques are proposed. These devices may exhibit a number of degradation effects such as interpixel cross-talk and fringing field, and time flicker, which may also depend on the analog or digital backplane of the corresponding LCoS device. The use of appropriate characterization and compensation techniques is then necessary

Eurodisplay 2019

The collection includes abstracts of reports selected by the program by the conference committee

Chemical Symmetry Breaking

This book entitled “Chemical Symmetry Breaking” is a collective volume of state-of-the-art reports on unique nonlinear chemical and physical symmetry-breaking phenomena that were experimentally observed upon a thermally or photochemically induced phase transition in various organic condensed phases, such as metastable liquid crystals, crystals, amorphous solids, and colloidal polymer materials, only under nonequilibrium conditions. Each author summarizes the introductory section in simple terms but in detail for beginners in this field. We wish that many readers familiarize themselves with the general concepts and features of nonlinear and nonequilibrium (or out of equilibrium) complexity theory, which govern a variety of unique dynamic behaviors observed in chemistry, physics, life science and other fields, so that they may discover novel symmetry-breaking phenomena in their own research areas

A prototype for 3D electrohydrodynamic printing

Electrohydrodynamic direct writing is a flexible cost effective alternative technique that is capable of producing a very fine jet of liquid in the presence of an external electric field. This jet can then be used to pattern surfaces in an ordered and controlled fashion and offers a robust route to low cost large area micro and nano-manufacturing. Unlike other types of direct writing techniques, the liquid in electrohydrodynamic printing is subjected to both pushing and pulling forces. The pushing force is brought about by the constant flow rate that is maintained via high precision mechanical pumps while a pulling force is applied through a potential difference that is applied between the nozzle and the ground electrode and as a result a fine jet can be generated to pattern surfaces. The impracticality of use and the cost of building micrometre and sub-micrometre sized nozzles to print narrow line widths warrant an investigation into alternative means of dispensing printing inks using nozzles that are cheap to produce, easy to handle and consistent in delivery. The enormous capillary pressures that would have to be overcome in order to print highly viscous materials with micrometre and sub-micrometre sized nozzles may also limit the types of feed that could be used in printing narrow line widths. Thus, the initial work described is focused on improving print head design in an attempt to electrohydrodynamic print pattern narrow line widths using silk fibroin. This is followed by work where we attempt to design and construct of a new electrohydrodynamic printing machine with the sole purpose of expediting research in electrohydrodynamic printing in a flexible, feasible and user friendly manner. To achieve this, replicating rapid prototype technology is merged with conventional electrohydrodynamic printing phenomena to produce a EHD printing machine capable of print depositing narrow line widths. In order to validate the device the work also describes an attempt to print a fully formed human ear out of polycaprolactone. Finally, we investigate an approach to the electohydrodynamic printing of nasal septal scaffolds using the microfabrication system that was developed and optimized in our laboratory. In these initial stages we were successful in showing the degree of control and flexibility we possess when manufacturing constructs out of a biodegradable polymer ( polycaprolactone) from the micro to macro scale through manipulation of just one process parameter (concentration). This work also features characterization of scaffold mechanical properties using a recently invented Atomic force microscopy technique called PeakForce QNM (Quantitative Nanomechanical Property Mapping)

Design, fabrication, and testing of a variable focusing micromirror array lens

A reflective type Fresnel lens using an array of micromirrors is designed and fabricated using the MUMPs?? surface micromachining process. The focal length of the lens can be rapidly changed by controlling both the rotation and translation of electrostatically actuated micromirrors. The suspension spring, pedestal and electrodes are located under the mirror to maximize the optical efficiency. The micromirror translation and rotation are plotted versus the applied voltage. Relations are provided for the fill-factor and the numerical aperture as functions of the lens diameter, the mirror size, and the tolerances specified by the MUMPs?? design rules. Linnik interferometry is used to measure the translation, rotation, and flatness of a fabricated micromirror. The reflective type Fresnel lens is controlled by independent DC voltages of 16 channels with a 0 to 50V range, and translational and torsional stiffness are calibrated with measured data. The spot diameter of the point source by the fabricated and electrostatically controlled reflective type Fresnel lens is measured to test focusing quality of the lens

Design of high-performance Triboelectric Nanogenerators (TENGs) for energy harvesting applications

The growing concerns around the long-term viability of the fossil fuel-based energy and its associated environmental cost are necessitating new research paradigms for energy generation and harvesting. An attractive and effective way to respond to the current energy crisis is through the harvesting of ambient mechanical energy from our environment. The conventional mechanical energy harvesting technologies are highly dependent on either the use of rare earth magnetic materials, high precision microfabrication techniques or composed of brittle materials, which are required to be driven at very high resonant frequencies, not frequently encountered beyond an industrial setting. Recently, triboelectric nanogenerators (TENG), based on the triboelectrification and electrostatic induction effects, have been demonstrated as a novel harvesting technique to collect and transform ambient mechanical energy into electric power. Unlike the other mechanical energy harvesters, the low-cost TENGs fabricated using commodity polymers and facile fabrication techniques, operate at low frequencies (1-10 Hz) with a high energy conversion efficiency. One of the key areas in TENG research is the enhancement of their electrical output to make them suitable for either making a self-powered system viable or powering small portable electronics directly. Except for the judicious use of tribo-materials or the tribo-layer architecture optimisation, the rest of the methods for enhancing the TENG output are reliant on expensive equipment and complicated processing, that undermine the advantages of TENGs and may not provide the required stability and reliability. This PhD study aims to establish novel strategies to enhance output performance of TENG by developing new tribo-materials and phenomena such as coupling of tribo-piezoelectric effects to showcase potential applications of the TENG devices. The research work conducted and the achievements are summarized as follows. Firstly, a novel output performance improvement strategy of utilising stress-induced polarization effect of the piezoelectric materials was proposed. An interfacial layer of piezoelectric zinc oxide (ZnO) nanosheets was deposited to generate additional piezoelectric charge induced by the vertical contact-separate generation cycle. This extra piezoelectric charge is injected into the upper polydimethylsiloxane (PDMS) tribo-negative layer for the enhancement of the surface charge density from ~110 μC.m-2 to ~225.7 μC.m-2. The introduction of the ZnO and Zn-Al:Layered Double Hydroxides (LDH), as charge injection layer and anionic clay, enhanced the instantaneous power output from ~11 W.m-2 to 47 W.m-2. Subsequently, based on a similar principle, a novel composite of lead-free perovskite, zinc stannate (ZnSnO3), and a fluoropolymer, poly(vinylidene fluoride), PVDF, was proposed for the stress-polarisation tribo-negative behaviour with a simplified structure. The PVDF-ZnSnO3 composite membranes were realised through a facile phase-inversion technique leading to higher piezoelectric constant (76.3 pm.V-1) and β-phase (72%) for the composites. When applied to the TENG devices, the PVDF-ZnSnO3 membranes allowed spontaneous polarisation effects which led to significant enhancement of the electrical outputs, with maximum peak-to-peak voltage and effective transferred current density of ~600 V and ~206 µC.m-2, respectively. The surface charge enhancement and distribution of the composite membrane were also probed and demonstrated through the electrostatic force (EFM) and piezoelectric force microscopy (PFM). To overcome the difficulty in processing of the currently known most tribo-negative material, polytetrafluoroethylene (PTFE), an emulsion electrospinning technique incorporating polyethene oxide (PEO) was introduced. It was observed that the subsequent thermal removal of PEO led to a significant degradation in the surface charge density of the obtained PTFE nanofibrous membranes, which was overcome using a facile negative ion-injection process. The measured electrical outputs, with a maximum peak-to-peak voltage output of ~900 V and charge density of ∼149 μC.m−2, demonstrated the excellent effect of the enhanced contact area to the improvement of the outputs. The work eliminates the demonstrated need for surface micro structuring using reactive ion etching of PTFE surfaces by introducing a relatively simple, costeffective, and environmentally friendly technique for fabricating fibrous fluoropolymers tribonegative layer for the energy harvesting applications. Finally, a unique mouldable material, aniline formaldehyde resin (AFR) was synthesised and characterised. The synthesised AFR, as a resinous polymer with significant amine (-NH2) groups acquires the most surface positive charge, is applied as a tribo-positive material. The heatpressed AFR thin-film based TENG was subsequently tested to demonstrate its outstanding performance serving as a tribo-positive layer compared to the Polyamide 6 (PA6) and polyethene oxide (PEO), as one of the most common used tribo-positive materials. In addition, a Kelvin Probe Force Microscopy (KPFM) was subsequently employed to study the surface potential of the produced AFR layer and the surface potential change of the contact layers during the energy generation cycles. All of the produced high-performance TENGs (power output ranging from 9 - 47 W.m-2) have the potential to be utilised further in enabling self-powered systems and can serve as a new alternative energy harvesting source of great significance

Self-assembly of helical ribbons from chiral amphiphiles

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2001.Includes bibliographical references (p. 209-220).The study of the self-assembly of helical structures has been motivated by their newly found biological and technological importance. In many systems, helical ribbons are precursors to the formation of tubules, which may be used in the controlled release of drugs or as templates for micron scale electronic components. Used as springs, helical ribbons open up an entirely new avenue for the measurement of forces on the biological scale. Given the importance of these structures, a series of experiments to probe the kinetics and energetics of helix formation has been performed. Theoretical interpretation and experimental measurements of helix elastic properties have also been performed. It was shown that the formation of helical ribbons of pitch angles of 11 and 54ʻ, previously thought to be a property unique to model bile systems, is a general phenomenon of quaternary sterol systems composed of a bile salt or nonionic detergent, a phosphatidylcholine or a (mixture of) fatty acid(s), and a steroid analog of cholesterol in water. The majority of helical ribbons were right-handed; but some left-handed helices have been found. Additionally, a small number of helices with pitch angles between 30 and 47ʻ were found in some systems. The elastic properties of the low pitch helical ribbons in Chemically Defined Lipid Concentrate were studied via relaxation experiments and measurements of force versus extension curves using silicon cantilevers as force probe. The helices exhibited linear behavior over a large range of extensions (up to 200% of helix original axial length). The forces involved in the deformation of low pitch helices have been found to be in the 0.25-1.0 nN range making them ideal for use as biological force probes.(cont.) Additionally, a novel tension-induced reversible straightening transition of the helical ribbons has been observed: when a helix is extended beyond a critical value, part of it unwinds leaving separate straight and helical sections in equilibrium with each other. Probing these fascinating elastic properties is currently the best hope for more fully illuminating the microscopic nature of helical ribbons and the driving force behind their formation.Yevgeniya Vladimirovna Zastavker.Ph.D