Detection of CO2 in N2 and H2O using photoacoustics

Photoacoustic spectroscopy is a technique where absorbed modulated light is released as heat, causing thermal expansion which can be detected using an acoustic transducer. It can be used to determine the absorption spectra or the concentration of a material. In this project, photoacoustic spectroscopy is performed on CO2 in N2 gas and on CO2 dissolved in water in the 2003 - 2006 nm range. Studies on CO2 concentrations can be used in environmental research and fish industries, to mention some applications. Linearity in the signal is demonstrated for concentrations over several orders of magnitude for the gas mixture. The effect of water vapour in the sample is investigated, and the optimal modulation frequency and other relevant factors are determined. For the water sample, different measurement cell configurations are investigated before achieving a photoacoustic signal. With the final configuration used, high concentrations of CO2 in water can be detected indirectly through a small layer of inert gas above the water. Smaller concentrations can not be detected due to a high noise level. Together with instruments for generating and modulating laser light and for detecting the acoustic signal, a gas sample measurement cell and a water sample measurement cell form the experimental setup. LabVIEW from National Instruments is used to develop a software for instrument control, data acquisition and data analysis.Master i FysikkMAMN-PHYSPHYS39

Temperature induced color change in gold nanoparticle arrays: Investigating the annealing effect on the localized surface plasmon resonance

The localized surface plasmon resonance (LSPR) effect in metal nanoparticles is important for a range of applications, including photovoltaics and sensors. The actual LSPR effect is difficult to predict, because it can vary strongly with the size, shape, surface structure, and surrounding media of the nanoparticles. In order to understand this better, more experimental data are needed. Here, the authors present a study of the LSPR effect in macroscopic two-dimensional square arrays of gold nanoparticles, 50–80 nm in diameter with a pitch of approximately 160 nm, fabricated on borosilicate substrates. The arrays were exposed to different annealing temperatures in steps of 50 up to 600 °C. The authors observe an irreversible blue-shift of the LSPR extinction peak, from around 580 to around 520 nm at annealing temperatures of only 450 °C, an effect clearly visible to the naked eye. The authors also present measurements of the shape of the nanoparticles at the different annealing steps. These measurements were obtained using a combination of scanning electron microscopy (SEM) and atomic force microscopy (AFM). A carefully indexed pattern allowed us to measure the exact same nanoparticles with separate AFM and SEM instruments. The only clear effect that can be observed is that the nanoparticles appear to get smoother with annealing. Our results demonstrate that seemingly minor changes in the metal nanoparticle appearance can lead to a strong change in the LSPR effect. Our results also open up for potential applications in temperature sensing. The fact that the effect of temperature exposure can be observed with the naked eye without any need of electronic readout or power supply is particularly advantageous.publishedVersio

Nanostructured Materials for Solar Energy Applications

The work presented in this thesis focuses on nanostructures, and what effect parameters like size, material, and surroundings have on their physical properties, with special emphasis on optical properties. The motivation for this thesis has been to provide foundational work, both experimentally and theoretically, for the exploration of metal nanoparticles for solar energy applications. The devices were fabricated using electron beam lithography and electron beam evaporation. Characterization and imaging were done with scanning electron microscopy and atomic force microscopy. Optical performance was measured using thin film analyzer, dark field microscopy and integrating spheres. Numerical analysis of optical behavior was done using the software Lumerical. The experimental work was done at the University of Bergen NanoStructures laboratory and at Rice University Halas Nanophotonics laboratory. The thesis consists of six articles, which can be divided into three categories. The first, main category focuses on the optical and electrical properties of metal nanoparticles and metal nanostructures, and contains four articles. The first three articles cover theoretical investigations of the absorption properties of a nanofluid, experimental investigations of the effect of annealing on the optical properties, and the influence of fabrication methods on optical properties of metal nanoparticles. The fourth article presents a novel bimetallic metal-insulator-metal (MIM) device, where two metals with different work functions have been used to create a bias for hot-electron extraction. To the best of the authors knowledge this is the first MIM-device that does not require an external bias. The second category concerns non-optical effects of nanosized features. It contains one article, which describes how wetting can be affected by surface treatment. The third category has a more conceptual theme, and contains one article. It describes how to build an affordable nanoscience laboratory, which might help motivate people and local industry to develop nanotechnology in Norway and elsewhere

Detection of CO2 in N2 and H2O using photoacoustics

Photoacoustic spectroscopy is a technique where absorbed modulated light is released as heat, causing thermal expansion which can be detected using an acoustic transducer. It can be used to determine the absorption spectra or the concentration of a material. In this project, photoacoustic spectroscopy is performed on CO2 in N2 gas and on CO2 dissolved in water in the 2003 - 2006 nm range. Studies on CO2 concentrations can be used in environmental research and fish industries, to mention some applications. Linearity in the signal is demonstrated for concentrations over several orders of magnitude for the gas mixture. The effect of water vapour in the sample is investigated, and the optimal modulation frequency and other relevant factors are determined. For the water sample, different measurement cell configurations are investigated before achieving a photoacoustic signal. With the final configuration used, high concentrations of CO2 in water can be detected indirectly through a small layer of inert gas above the water. Smaller concentrations can not be detected due to a high noise level. Together with instruments for generating and modulating laser light and for detecting the acoustic signal, a gas sample measurement cell and a water sample measurement cell form the experimental setup. LabVIEW from National Instruments is used to develop a software for instrument control, data acquisition and data analysis

Light absorption and scattering of 40–170 nm gold nanoparticles on glass substrates

The localized surface plasmon resonance (LSPR) effect in metal nanoparticles is important for many applications ranging from detectors and sensors to photovoltaic devices. The LSPR wavelength is sensitive to the shape, size, surface condition, and surrounding environment. Therefore, it is important to compare the optical properties of metal nanoparticles of nominally similar dimensions and external conditions, but fabricated with different techniques. Here, a systematic study of the optical properties of large, periodic arrays (3 × 3 mm) of cylindrical, gold nanoparticles with diameters ranging from 39 ± 4 nm to 167 ± 5 nm and a height of 25 ± 1 nm is presented. The large arrays allow us to investigate the optical properties using an integrating sphere setup collecting the light scattered and absorbed by the nanoparticles. To the best of our knowledge, such a setup has not been used previously for electron beam lithography (EBL) fabricated samples mainly due the large sample area required. The authors compare our results with relevant literature and find a good agreement, which confirms the expected reproducibility of EBL. Further, the authors compare our absorption and scattering measurements with previous absorption and scattering measurements on large arrays of gold nanoparticles prepared on glass using hole-mask colloidal lithography. Finally, a comparison with simulations using a finite difference time domain software package (Lumerical, Inc.) is presented. The simulation results matches well with experimental results and are also supporting and detailing our comparison with published literature. The authors find a good agreement between the two fabrication methods. The small deviations found can be contributed to differences in the particle size and density distributions