Fabrication and applications of pillar bowtie nanoantenna arrays

This thesis reports the fabrication technique and applications of a pillar bowtie nanoantenna (p-BNA). We use different tools to fabricate our nanostructure, namely, electron lithographic tools, evaporator and plasma chambers. The theory of operation of the machines, especially electron beam lithography for higher resolution, electron beam evaporation for thin film deposition, reactive ion etching (RIE) for high aspect ratio pillar nanostructure and scanning electron microscopy (SEM) for imaging, has been presented. We carefully explain the reasons for choosing each parameter of each tool. For electron beam lithography, we look into the accelerating voltage and dosage parameters to get a high resolution nanostructure. Then we look into electron beam evaporation to come up with the thicknesses for metal deposition. Finally, we come up with the gas flow, pressure, power and etch time parameters for reactive ion etching (RIE) to complete the fabrication of the p-BNA structure. We demonstrate different experiments to show its usefulness in various areas of nanotechnology. We explain the theory to reduce the gap between pillar bowtie nanoantennas using SEM and experimentally show gap size controllability using a combination of accelerating voltage, current and magnification of SEM. Recording near field optical intensity in our nanostructure has been explained via simulation, fabrication and experimental results as well. Moreover, its use in the near infrared wavelength regime as a plasmonic sensor has been theoretically and experimentally demonstrated by increasing the size of the bowtie nanoantennas. Finally, we propose some exciting future work for our p-BNA structure to show its versatile applications in the field of nanotechnology

Plasmon-Assisted Audio Recording

We present the first demonstration of the recording of optically encoded audio onto a plasmonic nanostructure. Analogous to the ‘‘optical sound’’ approach used in the early twentieth century to store sound on photographic film, we show that arrays of gold, pillar-supported bowtie nanoantennas could be used in a similar fashion to store sound information that is transferred via an amplitude modulated optical signal to the near field of an optical microscope. Retrieval of the audio information is achieved using standard imaging optics. We demonstrate that the sound information can be stored either as time-varying waveforms or in the frequency domain as the corresponding amplitude and phase spectra. A ‘‘plasmonic musical keyboard’’ comprising of 8 basic musical notes is constructed and used to play a short song. For comparison, we employ the correlation coefficient, which reveals that original and retrieved sound files are similar with maximum and minimum values of 0.995 and 0.342, respectively. We also show that the pBNAs could be used for basic signal processing by ablating unwanted frequency components on the nanostructure thereby enabling physical notch filtering of these components. Our work introduces a new application domain for plasmonic nanoantennas and experimentally verifies their potential for information processing.University of Illinois at Urbana-Champaig

Amorphous, self-healed, geopolymers (ASH-G and ceramics (ASH-C) made by the geopolymer processing route

This work describes the cross fertilization of conventional whiteware production by a low energy, geopolymer processing method. Bone china is conventionally made using natural cow bone ash (calcined) of hydroxyapatite (HA). In this study HA and dicalcium phosphate (DCP) particulate reinforcements were investigated in potassium-based geopolymer composites (KGP). Particulate reinforcements of 5, 10 and 15 wt % each of hydroxyapatite and dicalcium phosphate particulate were added to potassium geopolymer to compare with composites made from BASF® Metamax metakaolin (KGP MT), Mymensingh clay metakaolin, KGP(MW) and synthetic Mymensingh clay metakaolin, KGP(MW-SYN). Microstructural properties using SEM, XRD and mechanical properties using Instron were investigated for the geopolymer samples at both room and high temperature. The XRD of pure and reinforced geopolymer samples at RT confirmed the formation of geopolymer analogues with the characteristic X-ray amorphous hump at 280 in 2θ, along with the crystalline peaks observed in KGP (MW), as well as in potassium geopolymer reinforced with hydroxyapatite and dicalcium phosphate. Thermally treated geopolymer composites at 11500C/1h exhibited crystalline peaks of leucite, kalsilite, monetite and quartz confirming the signature of geopolymer ceramics at elevated temperature. SEM revealed fully reacted and homogenous aluminosilicate matrix in all the geopolymer samples cured at room temperature for 7 days. Geopolymer composites KGP (MT)-15 DCP, KGP(MW)-15DCP and KGP(MW-SYN)-15DCP after thermal exposure at 11500C revealed microstructural integrity with the formation of phosphate glass, while a self-glazed surface was developed in KGP (MW) after being heated at 1125 0C/1h. Their high temperature properties are superior to RT properties due to amorphous self-healed glass formation (ASH) from the DCP phosphate glass. Their high temperature properties were superior to RT properties due to amorphous self-healed glass formation (ASH) from the DCP phosphate glass. The optimum DCP content was 10 wt % which gave flexure strengths of ~32 MPa after heat treatment at 1150 °C/1h

Highly sensitive and label-free digital detection of whole cell E. coli with interferometric reflectance imaging

Bacterial infectious diseases are a major threat to human health. Timely and sensitive pathogenic bacteria detection is crucial in identifying the bacterial contaminations and preventing the spread of infectious diseases. Due to limitations of conventional bacteria detection techniques there have been concerted research efforts towards development of new biosensors. Biosensors offering label free, whole bacteria detection are highly desirable over those relying on label based or pathogenic molecular components detection. The major advantage is eliminating the additional time and cost required for labeling or extracting the desired bacterial components. Here, we demonstrate rapid, sensitive and label free E. coli detection utilizing interferometric reflectance imaging enhancement allowing for visualizing individual pathogens captured on the surface. Enabled by our ability to count individual bacteria on a large sensor surface, we demonstrate a limit of detection of 2.2 CFU/ml from a buffer solution with no sample preparation. To the best of our knowledge, this high level of sensitivity for whole E. coli detection is unprecedented in label free biosensing. The specificity of our biosensor is validated by comparing the response to target bacteria E. coli and non target bacteria S. aureus, K. pneumonia and P. aeruginosa. The biosensor performance in tap water also proves that its detection capability is unaffected by the sample complexity. Furthermore, our sensor platform provides high optical magnification imaging and thus validation of recorded detection events as the target bacteria based on morphological characterization. Therefore, our sensitive and label free detection method offers new perspectives for direct bacterial detection in real matrices and clinical samples.First author draf

Factors Affecting Fishers’ Attitude and Willingness to use Cage Aquaculture as an Alternative Livelihood for Reducing Fishing Pressure in Haor Areas, Bangladesh

Inland capture fisheries are providing cost of livings of about 1.2 million BDT in Bangladesh. However, overexploitation causing the declination of the abundance of native fish species which adversely affects the livelihoods of haor dwellers. The present study was conducted in two haor villages (Sutarpara and Changnoagaon) of Kishoreganj, Bangladesh to explore the factors (economic and non-economic) affecting fishers’ attitude and willingness about cage aquaculture considered as livelihood alternative for reducing fishing pressure. The methodologies applied to do this study were semi-structured face-to-face interview, key informants and questionnaire survey using Likert scale (LS), focus group discussions (FGD). The result revealed that willingness to switch from traditional way of fishing to cage aquaculture activities was significantly (P<0.05) higher in those fishers’ groups that had more inclination in fishing activities. Simultaneously, non-economic factors like powerful traders and fishers, traditional belief, taking risk, launching period of cage aquaculture venture and investment duration played vital role in decisions on whether to fish or not. The economic factors were fewer in number than non-economic factors. This comparative research is significantly important for future social aquaculture researchers as well as the country policy makers for giving emphasis to gather data based on the prevailing economic and non-economic factors to innovate alternative livelihood activity concurrently

Biofuel production using thermochemical conversion of heavy metal-contaminated biomass (HMCB) harvested from phytoextraction process

Over the past few decades, bioenergy production from heavy metal-contaminated biomasses (HMCBs) has been drawing increasing attention from scientists in diverse disciplines and countries owing to their potential roles in addressing both energy crisis and environmental challenges. In this review, bioenergy recovery from HMCBs, i.e. contaminated plants and energy crops, using thermochemical processes (pyrolysis, gasification, combustion, and liquefaction) has been scrutinized. Furthermore, the necessity of the implementation of practical strategies towards sustainable phytoextraction and metal-free biofuels production has been critically discussed. To meet this aim, the paper firstly delivers the fundamental concepts regarding the remediation of the brownfields using phytoremediation approach, and then, reviews recent literature on sustainable phytoextraction of heavy metals from polluted soils. Thereafter, to find out the possibility of the cost-efficient production of metal-free biofuels from HMCBs using thermochemical methods, the impacts of various influential factors, such as the type of feedstock and metals contents, the reactor type and operating conditions, and the role of probable pre-/post-treatment on the fate of heavy metals and the quality of products, have also been discussed. Finally, based on relevant empirical results and techno-economic assessment (TEA) studies, the present paper sheds light on pyrolysis as the most promising thermochemical technique for large-scale electricity and heat recovery from HMCBs

High prevalence of caesarian sections at a referral hospital in Bangladesh

The rate of Caesarean delivery in Bangladesh is not known but thought to have increased markedly in recent years. This observational study addressed the prevalence of various types of deliveries conducted on 2714 subjects attending the postnatal ward of a referral hospital in Dhaka from August 1994 to March 1995. During this period data were collected retrospectively from their registries and clinical history sheets. Of these participants 1509 (55.6%) had a history of normal delivery and 1150 (42.4%) underwent Caesarean sections. Very few (1.7%) had other means of delivery and only 0.7% were reported to have forceps delivery. The Caesarian delivery for the first baby was 14.1%, which gradually decreased in subsequent deliveries. Most of the deliveries, be it normal or Caesarean, were conducted by the trainee doctors (43.6%) and Medical Officers (25.7%). Professors and Assistant Professors performed less than 1%. The normal or Caesarean deliveries were assisted mostly by trainee doctors (54.4%), interns (19.0%) and nurses (15.8%); and very few were conducted by Medical Officers (8.3%) and Assistant Registrars (2.1%). The study observes that the rate of Caesarean delivery is much higher than that observed in western countries. Most of the deliveries in this hospital, whether normal or Caesarean, were found to be conducted by the trainee or junior doctors. Ibrahim Med. Coll. J. 2009; 3(1): 21-2

Temperature-induced phenomena in systems of magnetic nanoparticles

Magnetic nanoparticle ensembles have received a lot of attention, stemming in part from their current and potential applications in biomedicine and in the development of high-density magnetic storage media. Key to the functionality of these systems are microscopic structures and mechanisms that make them exhibit unique properties and behave differently from their bulk counterparts. We studied microscopic structures and processes that dictate macroscopic properties, behavior and functionality of magnetic nanoparticle ensembles. As the temperature T strongly influences the magnetic behavior of these systems, we studied temperature dependent magnetic properties using AC-susceptibility and DC-magnetization measurements carried out over a broad range of temperatures, between 3 and 300 K. We extracted structural information from X-ray diffraction (XRD) and direct imaging techniques and correlate it with magnetic properties, in an attempt at better understanding the microscopic structures and magnetic mechanisms responsible for the macroscopic magnetic behavior. We studied ensembles of magnetic nanoparticles: nickel ferrite immobilized in a solid matrix and cobalt ferrite immersed in carrier fluid respectively, in order to explore their potential use in biomedical applications and magnetic recording. For both NiFe2O4(NFO) and Co0.2Fe2.8O4 (CFO) relaxation mechanisms were determined. Structural properties and average particle sizes were derived from XRD, including synchrotron XRD, and direct imaging techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Temperature dependent magnetic measurements, FC-ZFC DC magnetometry, as well as AC complex susceptibility measurements at frequencies between 10 and 10,000 Hz were carried out within the temperature range 3

Broadband Light Absorption Using Ultrathin Plasmonic Super Absorbers

Nanophotonics is an emerging technology that involves the interaction of light with small structures. One of the significant fields of nanophotonics is Plasmonics and metamaterials. The field of plasmonics has emerged as an interesting area for the fundamental studies, with important application possibilities in miniaturized photonics components. Plasmonic structures allow for the control of fundamental optical processes such as absorption, emission and refraction at the nanoscale due to the large field enhancement of localized or propagating surface plasmon resonances on the surface of the substrate. This thesis is focused on fabricating such a device which yields broadband light absorption over the visible spectrum (400-700 nm) as well as in the infrared spectrum (750 nm -1000 nm). The design is based on an ultrathin plasmonic super absorber consisting of a metal-insulator-metal stack with a nanostructured top silver film composed of circular holes of fishnet type structure for the visible spectrum and periodic elliptical holes of fishnet type structure for the infrared spectrum. Proposed broadband absorbers will open new device possibilities in thermal sensors, photovoltaic, optoelectronic devices, and also to conceal photo detectorsunpublishednot peer reviewedU of I OnlyUndergraduate senior thesis not recommended for open acces