Noble-Transition Alloy Absorbers for Near-Infrared Hot-Carrier Optoelectronics

Optoelectronics is the field of technology concerned with the study and application of electronic devices that source, detect and control light. Here we focus on the optical communications field which relies on optical fiber systems to carry signals to their destinations operating in the near-infrared range. To improve the performance of current optical fiber systems, one of the paths is to develop better near-infrared photodetectors. The current group of materials used for near-infrared photodetection relies in the III-V semiconductor family. Although their spectral photosensitivity correlates well with the near-infrared, response time performance and electronic circuit integration remain limited for this class of material. Complementary metal-oxide-semiconductor-Si photonics technology can be coupled with metal interface to form a Schottky barrier extending the silicon detection range to near-infrared. Above-equilibrium “hot” carrier generation in metals is a promising route to convert photons into electrical charge for optoelectronics. However, metals which offer both hot-carrier generation in the near-infrared and sufficient carrier lifetimes remain elusive. The aim of this thesis is to contribute to the development of a novel class of materials for near-infrared optoelectronic applications. Early progress in hot-carrier generation showed that one can tune optical and electronic properties of noble metals by alloying. The performance of these noble-metals alloys relied however on visible light application. Transition metals have a band structure much more favorable for hot-carrier generation in the near-infrared. However, due to the electron-electron scattering rates, oxidation states, and broad, weak or absence plasmon resonance, they have not gained attention in this field. Prior to this thesis, no noble-transition alloy for hot-carrier generation had been reported. Here, it is shown that a noble-transition alloy, AuxPd1-x, outperforms its constituent metals concerning generation and lifetime of hot carriers when excited in the near infrared. We show that at optical fiber wavelengths (e.g., 1550 nm) Au50Pd50 provides a 20-fold increase in the number of ~0.8 eV hot holes, compared to Au, and a 3-fold increase in the carrier lifetime, compared to Pd. In addition, we show that to keep their properties, these alloys should not be exposed to high temperatures (450 oC) during fabrication steps or application

Adsorption Of Benzene, Toluene, And Xylene (btx) From Binary Aqueous Solutions Using Commercial Organoclay

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Organoclays are promising alternative adsorbents for the removal of organic pollutants. The aromatic hydrocarbons benzene, toluene, and xylene (BTX) are typical petroleum contaminants found simultaneously in natural leaking. Therefore, investigations on multi-component adsorption become essential to study this issue. Based on that, in the present study, a commercial organoclay from Brazil has been tested for its adsorption potential for binary aqueous mixtures of BTX. Kinetic and equilibrium batch adsorption experiments were performed to elucidate the differences in the affinities between the BTX contaminants and the organoclay. The kinetic study indicated that for benzene-toluene, benzene-xylene, and toluene-xylene systems the contaminants preferentially adsorbed were toluene, p-xylene, and p-xylene (in the beginning of the assays), respectively. The affinity for the organoclay might be related to physicochemical properties of BTX. In the adsorption equilibrium studies, the obtained BTX isotherms were all linear, characterized by constant adsorption affinities. The observed differences between BTX adsorption capacities at equilibrium for mono and bi-component systems confirmed the competition for adsorption sites of the organoclay.95610341044CNPq [300986/2013-0]CAPESConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Printed Electrode for Measuring Phosphate in Environmental Water

Phosphate is a major nonpoint source pollutant in both the Louisiana local streams as well as in the Gulf of Mexico coastal waters. Phosphates from agricultural run-off have contributed to the eutrophication of global surface waters. Phosphate environmental dissemination and eutrophication problems are not yet well understood. Thus, this study aimed to monitor phosphate in the local watershed to help identify potential hot spots in the local community (Mississippi River, Louisiana) that may contribute to nutrient loading downstream (in the Gulf of Mexico). An electrochemical method using a physical vapor deposited cobalt microelectrode was utilized for phosphate detection using cyclic voltammetry and amperometry. The testing results were utilized to evaluate the phosphate distribution in river water and characterize the performance of the microsensor. Various characterizations, including the limit of detection, sensitivity, and reliability, were conducted by measuring the effect of interferences, including dissolved oxygen, pH, and common ions. The electrochemical sensor performance was validated by comparing the results with the standard colorimetry phosphate detection method. X-ray photoelectron spectroscopy (XPS) measurements were performed to understand the phosphate sensing mechanism on the cobalt electrode. This proof-of-concept sensor chip could be utilized for on-field monitoring using a portable, hand-held potentiostat