Measurement of Aromatic-hydrocarbons With the DOAS Technique

Long-path DOAS (differential optical absorption spectroscopy) in the ultraviolet spectral region has been shown to be applicable for low-concentration measurements of light aromatic hydrocarbons. However, because of spectral interferences among different aromatics as well as with oxygen, ozone, and sulfur dioxide, the application of the DOAS technique for this group of components is not without problems. This project includes a study of the differential absorption characteristics, between 250 and 280 nm, of twelve light aromatic hydrocarbons representing major constituents in technical solvents used in the automobile industry. Spectral overlapping between the different species, including oxygen, ozone, and sulfur dioxide, has been investigated and related to the chemical structure of the different aromatics. Interference effects in the DOAS application due to spectral overlapping have been investigated both in quantitative and in qualitative terms, with data from a field campaign at a major automobile manufacturing plant

Spectroscopy on the Dot : Photoelectron Spectroscopy and Time-Resolved Studies of Lead Sulfide Quantum Dots for Solar Cells

Renewable energy is an important topic as global energy consumption continues to rise. Because the sun emits an enormous amount of energy, solar energy is a promising source. However, most of the commercial solar cell technology is manufactured in an energy demanding process and there is a need for new, easily processed materials. This thesis concerns quantum dots, which are nanoparticles that can absorb light of different energies depending on their size. They can be synthesised by solution-based chemistry and turned into solid thin films to harvest sunlight. The fundamental properties of quantum dots need to be better understood before production on large scales may commence. The aim of this thesis was to investigate the fundamental properties of lead sulfide quantum dots. The methods used in this thesis are based on photoelectron spectroscopy. They allowed investigation of materials as-is, but also changes upon excitation by laser or X-rays. Using a laser, dynamics on pico- to microsecond timescales were studied by time-resolved photoelectron spectroscopy. Using a range of X-rays, the probability of charge transfer in the attosecond range was investigated.  Steady-state investigation showed that different surface treatment of the quantum dots caused different resistance towards surface oxidation and X-ray damage. Different layers in the structure of solar cells can influence the photovoltage, an important parameter in achieving high power conversion efficiencies. Time-resolved photoelectron spectroscopy was developed and used to investigate the contributions of the layers to photovoltage generation. We observed photovoltage dynamics on a timescale covering six orders of magnitude. The mechanism of charge transfer in quantum dots of different sizes was studied by core-hole clock spectroscopy in the attosecond regime. Our results show that quantum confinement affects the charge transfer only at low excitation energies. Förnybar energi är viktig då den globala energikonsumtionen fortsätter öka. Solenergi är en lovande energikälla eftersom solen strålar ut otroligt mycket energi. Då kommersiell solcellsteknologi använder mycket energikrävande tillverkningsprocesser finns det behov av nya material som är enkla att tillverka. Denna avhandling handlar om kvantpunkter som är nanopartiklar vilka kan absorbera ljus av olika energi, beroende på partiklarnas storlek. Lösningsbaserad syntes är en teknik för att tillverka tunna filmer av kvantpunkter. Grundläggande egenskaper hos kvantpunkter behöver kartläggas ytterligare innan storskalig produktion av sådana kan påbörjas. Målet med denna avhandling var att undersöka grundläggande egenskaper hos kvantpunkter bestående av blysulfid.   Analysmetoderna i denna avhandling baseras på fotoelektron-spektroskopi. Dessa möjliggör studier av material utan ytterligare bearbetning samt hur de förändras när de påverkas av laserljus eller röntgenstrålning. Med laserpåverkan har dynamik på pico- till mikrosekundsskala kunnat studeras med tidsupplöst fotoelektron-spektroskopi och genom att använda röntgenstrålning med olika energi har sannolikheten för laddningsöverföring studerats på attosekundtidsskalan.Tidsoberoende studier visade att olika ytbehandlingar på kvantpunkterna gav upphov till olika motstånd mot oxidation och strålskador. Olika lager i solcellers struktur kan påverka fotospänningen, vilken är en viktig parameter för att uppnå hög energiomvandlingseffektivitet. Tidsupplöst fotoelektronspektroskopi utvecklades och användes för att undersöka olika lagers bidrag till fotospänningen. Vi observerade tidsberoendet hos fotospänningen på en tidskala som spände över sex storleksordningar.Laddningsöverföringsmekanismen hos kvantpunkter med olika storlek studerades på attosekundstidsskalan med kärnhålsklocks-spektroskopi. Våra resultat visar att kvanteffekter orsakade av instängning påverkar laddningsöverföringen enbart vid låga excitationsenergier. </p

New metal-rich mixed chalcogenides with intergrowth structures: Ni8.21Ge2S2 and Ni8.45Ge2Se2

New metal-rich mixed nickel germanium chalcogenides, Ni8.21(1)Ge2S2 and Ni8.45(1)Ge2Se2, were synthesized by a high-temperature ceramic technique. Ni8.21Ge2S2 decomposes incongruently at 798(5) degrees C, while Ni8.45Ge2Se2 is stable only between approximately 600(5) degrees C and 813(5) degrees C. Single crystals were grown from a molten flux and by a recrystallization of presynthesized charge. The X-ray diffraction study revealed that Ni8.21Ge2S2 and Ni8.45Ge2S2 are isostructural and crystallize in the tetragonal system (space group 14/mmm, Z = 2) with a = 3.578(1) angstrom, c = 24.687(5) angstrom, and a = 3.601 (1) angstrom, c = 25.427(6) angstrom, respectively. Their crystal structures comprise heterometallic (2)(infinity) [Ni6Ge2] slabs and are closely related to the Ni8.54Ga2Se2 and Ni8.93Sn2S2 structure types. The geometrical changes of structural units upon p-element substitution in all known Ni(10-delta)E(2)Q(2) (E = element of group 13 or 14; Q = chalcogen) compounds are discussed. The relation to the intergrowth structure of Ni5.46GeSe2 is analyzed.</p

The structure and bonding of Ni3Sn

The electronic structure of Ni3Sn was calculated at ab initio levels for the crystal structure of the low-temperature modification of Ni3Sn refined upon data of single-crystal X-ray diffractometry (P6(3)/mmc, a=5.2950(7), c=4.247(1) Angstrom R=0.0288). The calculations were made with the use of fixed Gaussian (CRYSTAL98 software) and energy-dependent (Stuttgart TB-LMTO-ASA software) basis sets. Difference electron charge density maps were analysed and compared with that of a hypothetical hcp Ni in order to understand bonding in Ni3Sn. It was found that bonding in Ni3Sn has multicentre character with Ni-Sn interaction stronger than Ni-Ni one.</p

Dye-Sensitized Photoelectrochemical Cells

Production cost per peak watt of solar electricity produced is critical to various PV technologies and second-generation thin-film solar cells. The dye-sensitized solar cell (DSC), a molecular solar cell technology, has the potential to significantly lower production costs below previous PV technologies. DSC research groups have been established around the world. Integration into different products opens up new commercial opportunities for niche applications with large flexibilities in product shape, color, and transparency. © 2018 Elsevier Ltd All rights reserved.</p