This thesis describes the research I have done, and partly will do, during my time as a PhD student in the laboratory of Applied Optics at Linköping University. Due to circumstances beyond the scope of this book, this incorporates three quite different projects. The first two, involving gas sensing and measuring on paper with ellipsometry, have been discontinued, whereas the third one, measuring fluorescence with a computer screen and web camera, is in full progress and will be until I complete my studies. Thus the purpose of this work also has several aspects. Partly, it describes performed research and its results, as well as theoretical background. On the other hand, it provides practical and theoretical background necessary for future work. While the three projects are truly quite different, each of them has certain things in common with each of the other. This is certainly also true for the necessary theory. Two of them involve spectroscopic ellipsometry, for example, while another pair needs knowledge of color theory, etc. This makes it impossible to separate the projects, despite of their differences. Hopefully, these links between the different projects, connecting the different chapters, will make this work whole and consistent in its own way. / <p>Report code: LiU-TEK-LIC-200 4-19. On the day of the public defence the status of article I was: In press and the status of article III was: Manuscript and has a new title. The old title was Computer screen photo-assisted spectroscopic fluorimetry.</p>

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Nitride-based semiconductor materials make it possible to fabricate optoelectronic devices that operate in the whole electromagnetic range, since the band gaps of these compounds can be modified by doping. Among these materials, the sp2-hybridized boron nitride has properties that make it a potential candidate for integration in devices operating in the short-wavelength limit, under harsh environment conditions, due to the strength of the B-N bond.  Nevertheless, this binary compound has been the less studied material among the nitrides, due to the lack of complete control on the growth process. This thesis is focused on the study of the optical properties of sp2-hybridized boron nitride grown by hot-wall chemical vapor deposition (CVD) method, at the Department of Physics, Chemistry and Biology, at Linköping University, Sweden. The samples received for this study were grown on c-plane aluminum nitride as the buffer layer, which in turn was grown by nitridation on c- plane oriented sapphire, as the substrate material. The first objective of the research presented in this thesis was the development of a suitable ellipsometry model in a spectral region ranging from the infrared to the ultraviolet zones of the electromagnetic spectrum, with the aim of obtaining in the process optical properties such as the index of refraction, the energy of the fundamental electronic interband transition, the frequencies for the optical vibrational modes of the crystal lattice, as well as their broadenings, and the numerical values of the dielectric constants; and on the other hand, structural parameters such as the layers thicknesses, and examine the possibility of the presence of roughness or porosity on the boron nitride layer, which may affect the optical properties, by incorporating their effects into the model. The determination of these parameters, and their relation with the growth process, is important for the future adequate design of heterostructure-based devices that incorporate this material. In particular, emphasis has been put on the modeling of the polar lattice resonance contributions, with the TO- LO model, by using infrared spectroscopic ellipsometry as the characterization technique to study the phonon behavior, in the aforementioned spectral region, of the boron nitride. On the other hand, spectroscopic ellipsometry in the visible-ultraviolet spectral range was used to study the behavior of the material, by combining a Cauchy model, including an Urbach tail for the absorption edge, and a Lorentz oscillator in order to account for the absorption in the material in the UV zone. This first step on the research project was carried out at Linköping University.  The second objective in the research project was to carry out additional studies on the samples received, in order to complement the information provided by the ellipsometry model and to improve the model itself, provided that it was possible. The characterization techniques used were X-ray diffraction, which made it possible to confirm that in fact boron nitride was present in the samples studied, and made it possible to verify the crystalline quality of the aforementioned samples, and in turn relate it to the quality of the ellipsometry spectra previously obtained; the Raman spectroscopy made it possible to further verify and compare the crystalline qualities of the samples received, as well as to obtain the frequency for the Raman active B-N stretching vibration in the basal plane, and to compare this value with that corresponding to the bulk sp2-boron nitride; scanning electron microscopy made it possible to observe the rough surface morphologies of the samples and thus relate them to some of the conclusions derived from the ellipsometry model; and finally cathodoluminescence measurements carried out at low temperature (4 K) allowed to obtain a broad band emission, on all the samples studied, which could be related to native defects inside the boron nitride layers, i.e., boron vacancies. Nevertheless, no trace of a free carrier recombination was observed. Considering that the hexagonal-boron nitride is nowadays considered to be a direct band gap semiconductor, it may be indirectly concluded, in principle, that the dominant phase present in the samples studied was the rhombohedral polytype. Moreover, it can be tentatively concluded that the lack of an observable interband recombination may be due to the indirect band gap nature of the rhombohedral phase of the boron nitride. Spectroscopic ellipsometry does not give a definite answer regarding this issue either, because the samples analyzed were crystalline by nature, thus not being possible to use mathematical expressions for the dielectric function models that incorporate the band gap value as a fitting parameter. Therefore, the nature of the band gap emission in the rhombohedral phase of the boron nitride is still an open research question. On the other hand, luminescent emissions originating from radiative excitonic recombinations were not observed in the cathodoluminescence spectra. This second step of the project was carried out at the Leroy Eyring Center for Solid State Science at Arizona State University.

Pagrindinis disertacijos tikslas – optinio ZnMgRE (RE = Y, Ho, Er) kvazikristalų atsako tyrimais atskleisti jų elektroninės posistemės ypatumus. Disertaciją sudaro eksperimentiniai rentgeno-difrakciniai (XRD) ir optiniai spektroskopiniai tyrimai, kvazikristalų elektroninės posistemės modelio konstravimas ir teorinis jų optinio atsako aprašymas. Atliktais eksperimentiniais XRD tyrimais buvo siekiama atskleisti kvazikristalų atvirkštinės gardelės vektorius, apibrėžiančius potencinį kvazikristalinį lauką, veikiantį į elektroninę posistemę. Optiniai spektroskopiniai tyrimai buvo atlikti kombinuotu spektroskopinės elipsometrijos ir atspindžio spektroskopijos metodu, paremtu darbe pasiūlyta inkaro lango duomenų analizės schema. Naudotas spektroskopinių tyrimų metodas įgalino atskleisti patikimus ZnMgRE optinio laidumo spektrus plačioje, 0.01 – 6 eV, spektrinėje srityje. Darbe išplėstas ZnMgRE elektronų posistemės modelis, kuris anksčiau buvo pasiūlytas kvazikristalų fotoemisinio atsako analizei. Nepriklausomų Fermi paviršiaus sankirtų su Bragg’ų plokštumomis schema formuluota išplėstiniame juostiniame atvaizdavime. Teorinė optinio laidumo skaičiavimų schema, anksčiau pasiūlyta kristalinių junginių optinio laidumo skaičiavimams, šiame darbe išplėsta įskaitant įvairias Fermi lygmens padėtis pseudotarpo atžvilgiu. Teoriniai ZnMgRE optinio laidumo skaičiavimai, atlikti darbe pasiūlyto elektroninės posistemės modelio rėmuose, detaliai atkartoja eksperimentinius optinio laidumo spektrus... [toliau žr. visą tekstą] / The main goal of the dissertation was to reveal the electronic structure of ZnMgRE (RE = Y, Ho, Er) quasicrystals by investigations of their optical response. The thesis comprises experimental X-ray diffraction (XRD) and optical spectroscopy studies of the quasicrystals, a construction of their electron subsystem model, and a theoretical description of their optical response. The XRD studies were carried out to determine the reciprocal quasicrystalline lattice vectors, which define the atomic potential field acting on an electron subsystem. The optical spectroscopy studies were carried out by the combined spectroscopic ellipsometry and reflectance spectroscopy technique, based on a suggested anchor-window method. High-accuracy ZnMgRE optical conductivity spectra were recorded in the wide, 0.01 – 6 eV, spectral range. The model of ZnMgRE electron energy spectrum, previously suggested for an interpretation of experimental ZnMgRE photoemission spectra, was developed. The nearly-free-electron gas model of independent intersections was formulated in the extended zone presentation. A scheme of the theoretical optical conductivity calculations was extended to account for various positions of the Fermi level with respect to a pseudogap. The experimental ZnMgRE optical conductivity spectra can be reproduced in detail by theoretical calculations performed within the framework of the suggested electron energy spectrum model. The set of the electron energy spectrum parameters determined... [to full text]

The main goal of the dissertation was to reveal the electronic structure of ZnMgRE (RE = Y, Ho, Er) quasicrystals by investigations of their optical response. The thesis comprises experimental X-ray diffraction (XRD) and optical spectroscopy studies of the quasicrystals, a construction of their electron subsystem model, and a theoretical description of their optical response. The XRD studies were carried out to determine the reciprocal quasicrystalline lattice vectors, which define the atomic potential field acting on an electron subsystem. The optical spectroscopy studies were carried out by the combined spectroscopic ellipsometry and reflectance spectroscopy technique, based on a suggested anchor-window method. High-accuracy ZnMgRE optical conductivity spectra were recorded in the wide, 0.01 – 6 eV, spectral range. The model of ZnMgRE electron energy spectrum, previously suggested for an interpretation of experimental ZnMgRE photoemission spectra, was developed. The nearly-free-electron gas model of independent intersections was formulated in the extended zone presentation. A scheme of the theoretical optical conductivity calculations was extended to account for various positions of the Fermi level with respect to a pseudogap. The experimental ZnMgRE optical conductivity spectra can be reproduced in detail by theoretical calculations performed within the framework of the suggested electron energy spectrum model. The set of the electron energy spectrum parameters determined... [to full text] / Pagrindinis disertacijos tikslas – optinio ZnMgRE (RE = Y, Ho, Er) kvazikristalų atsako tyrimais atskleisti jų elektroninės posistemės ypatumus. Disertaciją sudaro eksperimentiniai rentgeno-difrakciniai (XRD) ir optiniai spektroskopiniai tyrimai, kvazikristalų elektroninės posistemės modelio konstravimas ir teorinis jų optinio atsako aprašymas. Atliktais eksperimentiniais XRD tyrimais buvo siekiama atskleisti kvazikristalų atvirkštinės gardelės vektorius, apibrėžiančius potencinį kvazikristalinį lauką, veikiantį į elektroninę posistemę. Optiniai spektroskopiniai tyrimai buvo atlikti kombinuotu spektroskopinės elipsometrijos ir atspindžio spektroskopijos metodu, paremtu darbe pasiūlyta inkaro lango duomenų analizės schema. Naudotas spektroskopinių tyrimų metodas įgalino atskleisti patikimus ZnMgRE optinio laidumo spektrus plačioje, 0.01 – 6 eV, spektrinėje srityje. Darbe išplėstas ZnMgRE elektronų posistemės modelis, kuris anksčiau buvo pasiūlytas kvazikristalų fotoemisinio atsako analizei. Nepriklausomų Fermi paviršiaus sankirtų su Bragg’ų plokštumomis schema formuluota išplėstiniame juostiniame atvaizdavime. Teorinė optinio laidumo skaičiavimų schema, anksčiau pasiūlyta kristalinių junginių optinio laidumo skaičiavimams, šiame darbe išplėsta įskaitant įvairias Fermi lygmens padėtis pseudotarpo atžvilgiu. Teoriniai ZnMgRE optinio laidumo skaičiavimai, atlikti darbe pasiūlyto elektroninės posistemės modelio rėmuose, detaliai atkartoja eksperimentinius optinio laidumo spektrus... [toliau žr. visą tekstą]

This diploma thesis is focused on preparation of perovskite methylammonium lead bromide thin film layers and also thin film layers of its precursors, namely methylammonium bromide and lead(II) bromide, by spin-coating from the solution; and optical characterisation of the prepared thin film layers by UV-VIS spectroscopy and spectroscopical ellipsometry. Methylammonium bromide does not absorb in visible nor ultraviolet region, the maximum absorption of lead(II) bromide occurred in ultraviolet region, methylammonium lead bromide absorbs in visible region. Optical band gaps were determined by Tauc method to (3,5 ± 0,1) eV for lead(II) bromide and 2,15 eV, respectively 2,25 eV for perovskite. Refractive indices and extinction coefficients were determined by ellipsometry in range of wavelengths from 290 nm to 830 nm and their dependence with layer thickness was discussed. Ellipsometry model used in this thesis consist on Tauc-Lorentz oscillators for methylammonium bromide, methylammonium lead bromide and partially for lead(II) bromide, which another part is formed by New Amorphous oscillator.

Thesis in theoretical part is focused on the principle of spectroscopic ellipsometry and formation of thin films by plasma-enhanced chemical vapor deposition (PECVD). In the experimental part we describe the deposition system, ellipsometer and mathematical evaluation of ellipsometric data, materials used for film formation and processing of the samples. Single-layer and multilayer structures of polymeric materials were prepared. We revealed that the optical properties of thin films are independent of film thickness. We also described the effect of the effective power and deposition gas mixture on optical properties of thin films.

In this investigation, the cation distribution in ferrites of spinel-type structure is spectroscopically investigated with respect to the observed magnetic behavior. The ferrite thin films were fabricated by pulsed laser deposition and consequently annealed at different temperatures as well as atmospheres. Structural properties were determined with various methods and the crystalline quality was examined. The dielectric function line-shape was parametrized based on empirical evidence and was found to be dominated by electronic transitions between d orbitals of Fe2+ cations as well as transitions from O 2p to 3d and 4s orbitals of iron and zinc cations. The strongest magneto-optical response was observed for transitions involving cations, which correspond to lattice disorder and inversion within the normal spinel structure. With the decrease in the substrate temperature during fabrication, a decrease in the magnetic response was observed. The diminishing ferrimagnetic order was directly correlated to the decrease in strength of the transitions, involving Fe3+ on tetrahedral lattice sites. After thermal treatment in argon atmosphere and at a temperature below the deposition temperature, the increase in the magnetic response was explained through the facilitation of oxygen vacancies. With the increase in treatment temperature, a decrease in ferrimagnetic order was related to the recrystallization of the disordered spinel structure toward a more stable normal configuration, evident in the dielectric function spectra. The cationic configuration distribution in the surface as well as the bulk region, as a function of Zn concentration, was determined from approximation of the XPS and the dielectric function spectra, respectively. The difference in the cation configuration distribution, in films of predominantly inverse configuration, was related to the weak magnetic response, as opposed to films of predominantly normal spinel configuration. Our results demonstrate that a defect-rich surface region could serve as a possible explanation for the ferrimagnetic order in a nominally non-magnetic normal spinel ZnFe2O4. In combination with structural property determination, the net magnetic behavior is explained through the local cationic disorder, determined from the parametrization of the dielectric function spectra in a wide spectral range.:1 Introduction 2 Theoretical background and fundamental considerations 2.1 Spinel ferrite crystal structure 2.2 Crystal field stabilization energy 2.3 Band structure description 2.4 Verwey transition 2.5 Magnetic exchange interactions 3 Sample preparation and modification 3.1 Macroscopic spinel film formation 3.2 Pulsed laser deposition 3.3 Thermal treatment 3.4 Sample overview 4 Methods and general properties 4.1 Structure characterization techniques 4.1.1 X-ray diffraction 4.1.2 X-ray reflectivity 4.1.3 Energy dispersive X-ray spectroscopy 4.1.4 Focused ion beam and scanning electron microscopy 4.1.5 Raman spectroscopy 4.2 Surface properties 4.2.1 Atomic force microscopy 4.2.2 X-ray photoelectron spectroscopy 4.3 Dielectric tensor properties 4.4 Spectroscopic ellipsometry 4.5 Magneto-optical Kerr effect 4.6 Magneto-static properties 5 Results and discussion 5.1 Magnetic and optical properties of Fe3O4 thin film and single crystal 5.2 Magneto-optical properties of ZnxFe3−xO4 thin films 5.3 Fabrication temperature dependent ferrimagnetic order 5.4 Thermally induced structural stabilization 5.5 Cation configuration in dependence on the Zn concentration 5.5.1 Structural property determination 5.5.2 Composition characterization 5.5.3 Magneto-static behavior 5.5.4 Section summary and discussion 6 Summary and outlook Bibliography List of article contributions Selbstständigkeitserklärung Acknowledgments

The major part of my dissertation consists of thin films deposited using atomic layer deposition on flat and powder substrates. It details the various optimization experiments for process parameters like dose time, purge time, temperature, and pressure on silicon shards and powder substrates. Spectroscopic ellipsometry (SE) was used to characterize these films over a wide wavelength range (191-1688 nm). An optical model with a BEMA (Bruggeman effective medium approximation) layer was used to fit the ellipsometric data to investigate the optical properties of the alumina surface. The optimized process parameters on the flat surfaces were used for coating powder substrates. I propose a set of experiments to optimize the conditions for coating of powders and high aspect ratio structures by atomic layer deposition (ALD). The coated powders were analyzed by surface analytical techniques like X-ray photoelectron spectroscopy, spectroscopic ellipsometry, transmission electron microscopy, energy X-ray dispersive spectroscopy (EDAX), and BET. The first chapter introduces the technique of atomic layer deposition, and details its advantages and limitations over conventional thin film deposition techniques like chemical vapor deposition and physical vapor deposition. The second chapter details the initial deposition experiments performed on flat surfaces and characterization of thin films using surface analytical tools. I conducted multi-sample analysis on eleven different thin films for calculation of optical constants of alumina. The third chapter introduces thin film deposition experiments performed on powder substrates, several challenges associated with achieving conformal thin films and characterization. The fourth chapter details the experiments to achieve unilateral ALD achieved on one side of the substrates. The fifth chapter details various unconventional materials including liquid water, Coca-Cola, a coffee bean, nitrogen gas, human tooth, and printed office paper, which were analyzed by near ambient pressure XPS (NAP-XPS). This dissertation contains appendices of other tutorial articles I wrote on obtaining optical constants liquid samples using spectroscopic ellipsometry, and good experimental techniques for maintenance of vacuum equipment.