No description available.

A variety of factors make semiconducting polymers a fascinating alternative for both device development and new areas of fundamental research. Among these are solution processability, low cost, flexibility, and the strong dependence of conduction on the presence of charge compensating ions. With the lack of a complete fundamental understanding of the materials, and the growing demand for novel solutions to semiconductor device design, research in the field can take many, often multifaceted, routes. Due to ion-mediated conduction and versatility of fabrication, conducting polymers can provide a route to the study of neural signaling. In the first of three research topics presented, junctions of polypyrrole electropolymerized on microelectrode arrays are demonstrated. Individual junctions, when synthesized in a three-electrode configuration, exhibit current switching behavior analogous to neural weighting. Junctions copolymerized with thiophene exhibit current rectification and the nonlinear current-voltage behavior requisite for complex neural systems. Applications to larger networks, and eventual use in analysis of signaling, are discussed. In the second research topic, nonvolatile resistive memory consisting of gold nanoparticles embedded in a polymer film is examined using admittance spectroscopy. The frequency dependence of the devices indicates space-charge-limited transport in the high-conductivity "on" state, and similar transport in the lower-conductivity "off" state. Furthermore, a larger dc capacitance of the on state indicates that a greater amount of filling of midgap trap levels introduced by the nanoparticles increases conductivity, leading to the memory effect. Implications on the question as to whether or not the on state is the result of percolation pathways is discussed. The third and final research topic is a presentation of enhanced efficiency of polymer light-emitting electrochemical cells (LECs) by means of forming a doping self-assembled monolayer (SAM) at the cathode-polymer interface. The addition of the SAM causes a twofold increase in quantum efficiency. Photovoltaic analysis indicates that the SAM increases both open-circuit voltage and short-circuit current. Current versus voltage data are presented which indicate that the SAM does not simply introduce an interfacial dipole layer, but rather provides a fixed doping region, and thus a more stable p-i-n structure.

No description available.

<p>Silicon oxide films (oxygen-rich or silicon-rich) doped with various rare-earth (RE) [cerium (Ce), terbium (Tb), europium (Eu) and erbium (Er)] elements have been by deposited by electron cyclotron resonance plasma-enhanced chemical vapour deposition (ECR-PECVD). The successful in-situ incorporation of high concentrations of RE elements has been confirmed by Rutherford backscattering spectrometry (RBS), and the optical properties of the films were analyzed by Photoluminescence (PL) spectroscopy.</p><p> Ce, Tb, Eu and Er related emission was observed from the films with corresponding doping and was found to be sensitive to RE concentration, the presence of Si nanoclusters (Si-ncs) and annealing induced structural evolution. The significant enhancement of Ce^3 + emission in Ce-doped oxygen-rich films under annealing in flowing N2 at 1200 °C was found to be related to the formation of cerium silicate whose presence was confirmed by Fourier transform infra-red (FTIR) spectra and high-resolution transmission electron microscopy (HR-TEM) images. The observation of intense Tb^3+ emission from Tb-doped oxygen-rich films under nonresonant excitation revealed the presence of indirect excitation processes. The organic ligands introduced from the Tb(tmhd)3 precursor during deposition was considered as the possible sensitizer. The presence of Si-ncs in Ce or Eu-doped silicon-rich films resulted in the quenching of both RE and Si-ncs PL, while in Tb or Er-doped silicon-rich films the coupling between Si-nes and RE ions can excite RE-related emission efficiently. The formation of Si-ncs with sizes of 2-3 nm in Tb-doped silicon-rich films under annealing in flowing N2 at 1100 and 1200 °C was revealed by HR-TEM images.</p> / Thesis / Master of Applied Science (MASc)

Silicon Photonics has been a major success story in the last decade, with many photonic devices having been successfully demonstrated. The only missing component is the light source, however, as making an efficient light source in silicon is challenging due to the material's indirect bandgap. The development of a silicon light source would enable us to make an all-silicon chip, which would find many practical applications. The most notable among these applications are on-chip communications and sensing applications. In this PhD project, I have worked on enhancing silicon light emission by combining material processing and device engineering methods. Regarding materials processing, the emission level was increased by taking three routes. In all the three cases the emission was further enhanced by coupling it with a photonic crystal (PhC) cavity via Purcell effect. The three different approaches taken in this PhD project are listed below. 1. The first approach involves incorporation of optically active defects into the silicon lattice by hydrogen plasma treatment or ion implantation. This process results in broad luminescence bands centered at 1300 and 1500 nm. By coupling these emission bands with the photonic crystal cavity, I was able to demonstrate a narrowband silicon light emitting diode at room temperature. This silicon nano light emitting diode has a tunable emission line in the 1300-1600 nm range. 2. In the second approach, a narrow emission line at 1.28µm was created by carbon ion implantation, termed “G-line” emission. The possibility of enhancing the emission intensity of this line via the Purcell effect was investigated, but only with limited success. Different proposals for future work are presented in this regard. 3. The third approach is deposition of a thin film of an erbium disilicate on top of a PhC cavity. The erbium emission is enhanced by the PhC cavity. Using this method, an optically pumped light source emitting at 1.54 µm and operating at room temperature is demonstrated. A practical application of silicon light source developed in this project in gas sensing is also demonstrated. As a first step, I show refractive index sensing, which is a simple application for our source and demonstrates its capabilities, especially relating to the lack of fiber coupling schemes. I also discuss several proposals for extending applications into on-chip biological sensing.

Ο σκοπός της παρούσας διατριβής είναι να συμβάλει στην επιλογή του βέλτιστου σπινθηριστή ανάμεσα σε αυτούς που χρησιμοποιούνται στα σύγχρονα απεικονιστικά συστήματα τομογραφίας εκπομπής ποζιτρονίων PET και PET μικρών ζώων, ο οποίος θα μπορούσε να χρησιμοποιηθεί σε ένα ανιχνευτικό σύστημα πολλαπλών εφαρμογών PET/CT, MV CBCT, κλπ.) με έναν κοινό ανιχνευτή. Για το σκοπό αυτό μελετήθηκαν δείγματα από τους ακόλουθους κρυσταλλικούς σπινθηριστές: α) πυριτικού οξειδίου του γαδολινίου (GSO), β) πυριτικού οξειδίου του λουτεσίου (LSO), γ) πυριτικού οξειδίου του λουτεσίου-υτρίου (LΥSO), δ) αλουμινικού οξειδίου του υτρίου (YAP) και ε) αλουμινικού οξειδίου του λουτεσίου-υτρίου (LuYAP). Όλα τα δείγματα των σπινθηριστών ήταν ενεργοποιημένα με τρισθενές δημήτριο (Ce+3). Η μελέτη έγινε σε ευρεία κλίμακα ενεργειών (20kV-18MV). / The aim of this thesis was to select the best scintillator among the ones currently used in PET and animal PET systems, which could be used in a single detector multimodality scanner. To this aim crystal samples of GSO, LSO, LYSO, LuYAP and YAP scintillators, doped with cerium (Ce+3) were examined under a wide energy range (from 20kV-18MV). Measurements concerning determination of absolute efficiency, energy absorption efficiency, intrinsic conversion efficiency, detector optical gain and detector quantum efficiency, giving information on light yield and the intrinsic properties of the scintillators. Information on the compatibility of the light emission spectrum of the scintillators with the currently used optical photon detectors was obtained by calculating the spectral matching factors of each scintillator examined.

Methods were developed to study delayed light emission (luminiscence) and fluorescence changes in intact leaves of plants. Delayed light emission, detected from plants in darkness, was used to produce images of the plant leaves. The procedure was termed "phytoluminography". The use of the method is suggested for dia- nostic purposes at early stages of disturbances of the leaf tissues, not detectable with the naked eye. The delayed light emission is associated with the photochemistry of photosystem II and the light induced conversion and storage of energy in the thylakoid membrane system of chloroplasts. Fluorescence yield changes were induced by lowering temperature between 20 C and -20 C. The temperature induced fluorescence changes in leaves parallel the temperature induced changes in isolated chloroplasts in reaction preparations mediating photosynthetic electron transport from endogenous water splitting to added NADP. At above freezing temperatures, lowering the temperature at a constant rate of 1 C per minute caused supressed electron transport and increased fluorescence yield which were linearely dependent on the temperature change in frost resistent plants. Repeated freeze-thaw cycles between 20 °C and -20 °C induced variable fluorescence yield changes which were gradually depleated to F0 or Fm when the electron transport was injuried on the oxidizing or on the reduzing side of photosystem II, respectively. The temperature induced fluorescence changes were used to characterize plants with different ability to withstand freezing temperatures. The method also discriminates between plants of different frost resistance, and the method was used in screening for frost tolerance. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1981, härtill 5 uppsatser.</p> / digitalisering@umu

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: During the course of the CSIR’s research into the characterisation of explosive sources to devise methods of active intervention against threats, the need has arisen to research a particular means of early identification of the threat, which is the intense light flash during the threat detonation. For this purpose, a low cost rugged fast optical sensor was sought, since the application thereof would imply possible destruction, especially if integrated into an active intervention system later on. Given the average time of about 1ms available for intervention, it is clear that the active intervention system needs to operate within that period, hence the interest in the characteristic light emission of detonations in the pre-millisecond time frame. It was thought that by characterising this emitted light in terms of wavelength (temperature) and amplitude (and maybe other unique phenomena), the size of the threat could be determined and logic decisions derived therefrom. Needless to say, the environment in which the detonation light emission sensor is to operate, is extremely hostile in terms of shock, dust, flying debris, fast rise time of the explosive event, and Electro-magnetic Interference ( EMI) caused by the detonation itself. It must be noted that the light sensor research was driven by the outcome of research tests performed in aid of the development of an active intervention system. During this research the possibility of using commercially available low cost optical detectors at room temperature in combination with cost effective narrow band pass op- tical filters for the relative measurement of the light emission at discrete wavelengths during explosive detonation events were investigated. In 2006, not much applicable lit- erature could be found on this subject, hence the educated “shot-in-the-dark” approach then, which, by a systematic approach of explosive tests and continuous evaluation up to 2011, led to a surprisingly simple and robust low cost optical sensor. The research commenced with a range of optical detector elements selected for their responsivity and bandwidth in the optical spectrum of interest; the optical filtering by means of the recording of the emitted light signal during scaled down explosive tests at the Blast Impact Survivability Research Unit (BISRU) at the University of Cape Town. These tests were followed by full-scale tests at DBEL, and confirmed the findings at BISRU that the light emissions at the longer wavelengths (>2 m) manifest themselves too late for use within the intervention time frame. It was therefore decided to concentrate on the ultra-violet (UV) to near infra-red (NIR) spectrum of the emitted light for further full scale tests, since these discrete spectra showed the most promise for characterisa- tion of the emitted light. During this period a robust sensor housing with detector and filter mounts was designed for protection against blast shock and EMI. During the following years, certain types of optical detectors that were used during previous tests were eliminated according to results obtained, and more discrete narrow band pass filters added in the visible to NIR spectrum. A dedicated fast instrumen- tation amplifier (bandwidth > 1MHz and selectable gain up to 40dB) was developed to amplify weak signals (mainly caused by the heavy load in the detector circuit to improve rise times). However, the emission of light per wavelength in this region was measured to be relatively strong, and actually not as fast as was anticipated. This meant that the load resistor value of the detector element could be increased without affecting the signal negatively (bandwidth sufficient), thus adding to the amplitude of the signal to such a point that amplification in a 10m to 30 meter stand-off scenario was no longer needed. This culminated in an unamplified universal detector element being used with various narrow band pass filters up to 1 m, integrated as a very robust analog sensor at a discrete wavelength, and facilitating the direct comparison of light amplitude/relative intensity of the detonation at discrete spectral points. The sensor was employed in the field at various full scale explosive tests at DBEL, which led to the capture of a vast amount of light emitted data for different types of explosives, at various distances from the detonation, and of varying mass. Analysis of this data showed that the broadband light intensity of the emitted light scales to the explosive mass1/3 (as published by FJ Mostert and M Olivier in the Journal for Applied Physics, October 2011). Further analysis also confirmed the attenuation of the emitted light intensity by the square of the distance. Besides the aforesaid, various other key inputs to a possible active intervention algorithm have been identified. These findings are inputs to the determination of i.a. the detonation threat size, a vital component in the active intervention algorithm. The results of these experiments confirmed that the final low cost analog sensor can measure relative light emission at discrete wavelengths from detonation of explosives in the very early stages of development, and that the sensor has many other applications in the detonics research fields as well. / AFRIKAANSE OPSOMMING: Gedurende die WNNR se navorsing om detonerende bronne te karakteriseer ten einde aktiewe teenmaatreëls daar te stel, het die behoefte na vore gekom om die intense ligflits van ’n detonasie te ondersoek en te karakteriseer. Vir hierdie doel is ’n lae koste ligsensor benodig, synde die uiteindelike aanwending van hierdie ligsensor die vernietiging daarvan sou beteken, aldus die lae koste vereiste. Gegewe die kort tydsduur van die detonasie (’n paar millisekondes), is dit duidelik dat die ligflits karakerisering voor 1ms moet geskied, en daarom moet die ligsensor ook baie vinnig reageer om insette te lewer tot ’n aktiewe teenmaatreëlstelsel. Daar moet op gelet word dat die ligsensor se ontwikkeling uitkomsgedrewe was deur die navorsingstoetse om ’n aktiewe teenmaatreëlstelsel daar te stel. Een van die insette tot so ’n aktiewe teenmaatreëlstelsel is die grootte van die bedreiging: deur die ligflits te karakteriseer met die lae koste ligsensors t.o.v. golflengte, ligamplitude en moontlik ander verskynsels, kan bv. die massa inset verkry word wat nodig is vir die teenmaatreël algoritme. Die omgewing waarin die ligsensor moet funksioneer is baie onvriendelik i.t.v. skok, stof, vlieënde partikels en elektromagnetiese steurings, en sou daarteen beskerm moes word. Gedurende die navoring om so ’n ligsensor te ontwikkel (samelopend met die teen- maatreël navorsing), is kommersiële kamertemperatuur detektors oorweeg en aange- wend, in samewerking met nouband optiese filters. Die doel was om die ligopbrengs per golflengte te karakteriseer m.b.t. die plofstof massa, plofstof tipe en geometrie, en die afstand vanaf die detonasie. Bitter min literatuur oor die ligmeting van detonasies is aanvanklik gevind, aldus is ’n basislyn daargestel en deur sistematiese toetsing, ontleding en verbetering voortgegaan met die navorsing. Dit het gelei tot ’n verrassend eenvoudige en verharde lae koste ligsensor, wat deur meting sleutelinsette kon lewer tot die gesogte aktiewe teenmaatreël algoritme. Kommersiële detektors en nouband optiese filters is uitgesoek na aanleiding van hul prys en prestasie, en waar nodig, is versterking van die seine aangebring. Verskeie toetse met plofstof (op klein en groot skaal) is uitgevoer, waartydens ligmeting by spesifieke golflengtes opgeneem is. Analise van hierdie data het getoon dat die langer golflengtes (>2 m) se verskyning te laat is vir insluiting in die teenmaatreël algoritme, en is dus geleidelik (of sistematies) uitgeskakel. Die klem het geskuif na die detonasie liguitsetting in die UV tot naby infrarooi spektrum, wat nuwe detektors en filters tot gevolg gehad het (uitkoms gebasseerde navorsing). In die proses is ’n instrumentasie versterker ontwerp en gebou, vir buffering en versterking van seine hoër as 1 MHz met ’n selekteerbare aanwins van tot 40dB. Toetse met volskaalse ladings het egter getoon dat die liguitset besonder sterk is in die UV tot naby infrarooi spektrum, en ’n onversterkte ligsensor is aldus op die proef gestel. Hierdie proeflopie het getoon dat die onversterkte ligsensor besonder goed funksioneer op afstande tot en met 30m, en daar is op hierdie model voortgebou. Die verharde onversterkte ligsensor is aangewend in verskeie verdere volskaalse plofstof toetse, en het data gelewer t.o.v. detonasie liguitstraling by spesifieke golflengtes vir tipes plofstof, plofstof massas, plofstof geometrie en afstande vanaf die detonasie. Analise van hierdie data het getoon dat breëband liguitsetting se intensiteit skaal met die plofstof massa1=3 (gepubliseer as ’n artikel deur FJ Mostert en M Olivier in die Journal of Applied Physics’ - Oktober 2011). Verdere analise het verskeie sleutelinsette tot ’n aktiewe teenmaatreël algoritme geïdentifiseer. Die uitkoms van hierdie eksperimentele navorsing het getoon dat die lae koste lig- sensor relatiewe liguitsetting van ’n detonasie by gekose golflengtes vinnig kan meet in die baie vroeë stadia van die detonasie. Buiten dit, het die sensor verskeie ander nuttige aanwending in die detonasie navorsingsveld.

This thesis reports the light emission in ion gel gated, thin film organic semiconductor transistors and investigates the light emission mechanism behind these devices. We report that ion gel gated organic polymer semiconductor transistors emit light when the drain source voltage is swept slightly beyond the energy gap of the polymer divided by the elementary charge (Vds > Eg/e). In particular, the light emission in poly(9,9'-dioctylfluorene-co-benzothiadiazole)(F8BT) polymer semiconductor, with 1-ethyl-3-methylimidazoliumbis (trifluoromethylsulfonyl)imide/ poly(styrene-block-ethylene oxide-block-styrene) (EMIM TFSI/ SOS) ion gel as dielectric material is reported. The current-voltage characteristics corresponding to the light emission, where the systematic increase of the drain current, correlated with light emission is reported. In low voltage regime, (Vds < Eg/e), well saturated transistor characteristics are observed. By charge modulation spectroscopy (CMS) study we show that there is a prominent electrochemical doping occurring with gate voltages. Further, owing to the movement of ions with voltages,irrespective of the location of electrodes, we show that the ion gel, bilayer planar devices emit light in Vds > Eg/e regime (without any gate voltages), at room temperature. Based on thelocation of the recombination zone in the proximity of electron injecting electrode and CMS results showing prominent di ffusion of negative ions into the polymer layer, we conclude that the light emitting mechanism is akin to light emitting electrochemical cells (LECs). Even in the the transistor regime, where Vds << Eg/e, with the signatures of increasing drain current for fixed Vg and Vds values, we show that the transistor can not be of purely electrostatic operation alone. We study the fluorescence quenching of an operating bilayer device under a constant bias over a period of time and compare the results with the electroluminescence of the device and show that the formation of the p-n junction within the polymer layer due to the penetrated ions from the gel dielectric into the polymer semiconductor layer on the application of the voltage is the cause behind the light emission. We show that diffusivity of the cation (EMIM) is very low compared to the anion (TFSI). This is consistent with the fact that the recombination zone is near theelectron injecting electrode in these devices. We have developed a theoretical model for the ions movement within the semiconductor polymer matrix governed by both diffusion and drift independently, for the bilayer, polymer ion gel planar, light emitting electrochemical cells. We have further developed a 2- dimensional numerical modelbased on the theoretical model and have compared the results of the numerical model with theresults of a fluorescence probing of the bilayer device with time, at constant potential across the bilayer LEC and report that the drift coefficient of 1x10⁻¹³ cm²/V.s and a diffusion coefficient of 1 x 10⁻¹⁵cm²/V.s for TFSI ions in F8BT matrix.

Interactions of Asthma Drugs with Artificial Saliva and Mucus. Modeling pulmonary particulate transport requires related biofluid physicochemical properties. Aims included measuring the effects of common aerosol drugs on artificial saliva and diffusivities of asthma medications in mucus. Artificial saliva solutions doped with asthma medications were characterized by pH, interfacial tension, and rheology. To measure diffusion, drug concentration was monitored by time-dependent FTIR spectra, and diffusivity obtained using Fick¡¦s second law. Measured theophylline and albuterol diffusivities were ca. 10-6 cm2/s. Surface Modification of Polymer Films with Light-Emitting Chemicals. To develop a polymer film system that changed color in response to radiation, acid groups of poly(ethylene-co-acrylic acid) were used to attach two light-emitting polymers: 4„S-(octyloxy)-4-biphenylcarboxylic acid and 2,7-bis(bromomethyl)-9,9-dihexyl-9Hluorene. Each reaction step was confirmed using static contact angle goniometry, FTIR spectroscopy, and X-ray photoelectron spectroscopy. UV-Vis and fluorescence spectroscopy measured the absorption spectra. Modified films were irradiated (ƒÜ=254 nm) and produced blue emissions.