Superemission in vertically-aligned single-wall carbon nanotubes

Presently we used two samples of vertically aligned single-wall carbon nanotubes (VA SWCNTs) with parallelepiped geometry, sized 0.02 cm x 0.2 cm x 1.0 cm and 0.2 cm x 0.2 cm x 1.0 cm. We report absorption and emission properties of the VA SWCNTs, including strong anisotropy in both their absorption and emission spectra. We found that the emission spectra extend from the middle-IR range to the near-1R range, with such extended spectra being reported for the first time. Pumping the VA SWCNTs in the direction normal to their axis, superemission (SE) was observed in the direction along their axis. The SE band maximum is located at 7206 0.4 cm(-1). The energy and the power density of the superemission were estimated, along with the diffraction-limited divergence. At the pumping energy of 3 mJ/pulse, the SE energy measured by the detector was 0.74 mJ/pulse, corresponding to the total SE energy of 1.48 mJ/pulse, with the energy density of 18.5 mJ cm(-2)/pulse and the SE power density of 1.2 x 10(5) W cm(-2)/pulse. We report that a bundle of VA SWCNTs is an emitter with a relatively small divergence, not exceeding 3.9 x 10(-3) rad. We developed a theoretical approach to explain such absorption and emission spectra. The developed theory is based on the earlier proposed SSH theory, which we extended to include the exchange interactions between the closest SWCNT neighbors. The developed theoretical ideas were implemented in a homemade FORTRAN code. This code was successfully used to calculate and reproduce the experimental spectra and to determine the SWCNT species that originate the respective absorption bands, with acceptable agreement between theory and experiment. Published by Elsevier B.V

Application of electrospun thin films for supra-molecule based gas sensing

Methods for preparation of high-quality thin films for fabrication of selective supra-molecular based gas sensors are proposed. Several thin films were developed for sensing of methane, ammonia, volatile organic gas compounds, and humidity. The thin films were deposited using a custom-made electrospraying set-up. Using this system, we employed suitable metal-organic framework materials to fabricate sensors for detection of organic vapours at different concentrations for the first time to the best of our knowledge. Cryptophane A was synthesized and incorporated in thin films that were deposited on the surface of quartz resonators in two different ways of electrospinning using siloxane polymers and spin-coating( followed by exposure) with SU-8 for methane sensing. The detection limit of the fabricated sensors is lower than the best reported values for similar sensors. Thin films of different ratios of poly(vinyl alcohol) and poly(acrylic acid) were electrospun and used for effective detection and sensing of ammonia and humidity. The results of this thesis lay the foundation for the development of low-power multi-gas sensors

Self-consistent Vlasov-Poisson analysis of carrier transport in vacuum-based thermionic/thermoelectronic devices

Thermionic conversion involves the direct conversion of heat, including light-induced heat, from a source such as solar energy, to electricity. The progress of thermionic converters has been limited by issues such as the space charge effect and lack of materials with desirable mechanical, electrical and thermal properties. Nanotechnology could help address some of the main challenges that thermionic converters encounter. However, existing models, which were developed for macroscopic converters, are not adequate for many aspects of nanostructured devices. The work presented in this thesis primarily advances a new model to partially address this void and study emergent thermionic devices. We demonstrate a self-consistent and iterative approach to the Vlasov-Poisson system that overcomes the inherent limitations of the traditional methods. This approach serves as the foundation for more advanced and yet crucial cases of the operation of thermionic converters in the presence of back-emission, grids in the inter-electrode region and low-pressure plasmas. We develop the physics of the device in the presence of grids and demonstrate that momentum gaps could arise in the phase space of the electrons; taking into account these gaps, which had not been noticed in the past, is key to designing efficient thermionic converters and we predict improvements of 3 orders of magnitude in current density using a properly designed grid. We also develop the physics of the device in the presence of low-pressure plasmas, which are prime candidates for reducing space charge. We show that the output power density of a thermionic converter can improve by a factor of ~ 10 using a modest plasma pressure of 500 Pa. On a different front, we have also improved the traditional analytical model and developed an approach to extract the internal device parameters such as emission area and workfunction based on a limited set of experimental output characteristics. These parameters are highly dependent on the operating conditions and ex-situ measurements are not applicable. Therefore, our approach allows for a more systematic study of the device and material properties, which is key to further the development of thermionic converters, in particular based on novel materials and nanostructures.Applied Science, Faculty ofElectrical and Computer Engineering, Department ofGraduat

Protective Effects of Acetylation on the Pathological Reactions of the Lens Crystallins with Homocysteine Thiolactone.

Various post-translational lens crystallins modifications result in structural and functional insults, contributing to the development of lens opacity and cataract disorders. Lens crystallins are potential targets of homocysteinylation, particularly under hyperhomocysteinemia which has been indicated in various eye diseases. Since both homocysteinylation and acetylation primarily occur on protein free amino groups, we applied different spectroscopic methods and gel mobility shift analysis to examine the possible preventive role of acetylation against homocysteinylation. Lens crystallins were extensively acetylated in the presence of acetic anhydride and then subjected to homocysteinylation in the presence of homocysteine thiolactone (HCTL). Extensive acetylation of the lens crystallins results in partial structural alteration and enhancement of their stability, as well as improvement of α-crystallin chaperone-like activity. In addition, acetylation partially prevents HCTL-induced structural alteration and aggregation of lens crystallins. Also, acetylation protects against HCTL-induced loss of α-crystallin chaperone activity. Additionally, subsequent acetylation and homocysteinylation cause significant proteolytic degradation of crystallins. Therefore, further experimentation is required in order to judge effectively the preventative role of acetylation on the structural and functional insults induced by homocysteinylation of lens crystallins