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

Adsorption of toluene into commercial organoclay in liquid phase: Kinetics, equilibrium and thermodynamics

Organoclays are usually used as sorbents to reduce the spread of organic compounds and to remove them at contaminated sites. This study investigated the liquid‐phase adsorption of toluene on organoclay (Spectrogel® Type C) of Brazilian company SpectroChem. In spite of not having a large amount of pores, this organoclay is a low‐cost, effective adsorbent. Regarding the pH investigations, considerable effects of pH on the adsorption process were not observed. In the kinetics studies, it was observed that the process comes into equilibrium after 1 h with rates of about 90 % toluene removal. The experimental kinetic data were best fitted by a mass transfer in external film model. For the equilibrium study, the best fit was by the MSAM model at 288.15 K, the Dubinin‐Radushkevitch model at 298.15 K, and the Sips model at 308.15 K. Further, the thermodynamic parameters showed that toluene adsorption on organoclay Spectrogel‐C is an endothermic process. For tests of regeneration, ethanol was the eluent, which proved more promising9369981008CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESsem informaçã

A Noble‐Transition Alloy Excels at Hot‐Carrier Generation in the Near Infrared

Above-equilibrium “hot”-carrier generation in metals is a promising route to convert photons into electrical charge for efficient near-infrared optoelectronics. However, metals that offer both hot-carrier generation in the near-infrared and sufficient carrier lifetimes remain elusive. Alloys can offer emergent properties and new design strategies compared to pure metals. 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. 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 threefold increase in the carrier lifetime, compared to Pd. The discovery that noble-transition alloys can excel at hot-carrier generation reveals a new material platform for near-infrared optoelectronic devices