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The demand for highly sensitive and selective gas sensors has been steadily increasing, driven by applications in various fields such as environmental monitoring, healthcare, and industrial safety. In this context, ternary alloy indium aluminum nitride (InAlN) semiconductors have emerged as a promising material for gas sensing due to their unique properties and tunable material characteristics. This work focuses on the fabrication and characterization of InAlN nanorods grown on sapphire substrates using an ultra-high vacuum magnetron sputter epitaxy with precise control over indium composition and explores their potential for acetone-gas-sensing applications. Various characterization techniques, including XRD, SEM, and TEM, demonstrate the structural and morphological insights of InAlN nanorods, making them suitable for gas-sensing applications. To evaluate the gas-sensing performance of the InAlN nanorods, acetone was chosen as a target analyte due to its relevance in medical diagnostics and industrial processes. The results reveal that the InAlN nanorods exhibit a remarkable sensor response of 2.33% at 600 ppm acetone gas concentration at an operating temperature of 350 degrees C, with a rapid response time of 18 s. Their high sensor response and rapid response make InAlN a viable candidate for use in medical diagnostics, industrial safety, and environmental monitoring., Funding Agencies|National Science and Technology Council of Taiwan

NiO thin films with varied oxygen contents are grown on Si(100) and c-Al2O3 at a substrate temperature of 300 degrees C using pulsed dc reactive magnetron sputtering. We characterize the structure and optical properties of NiO changes as functions of the oxygen content. NiO with the cubic structure, single phase, and predominant orientation along (111) is found on both substrates. X-ray diffraction and pole figure analysis further show that NiO on the Si(100) substrate exhibits fiber-textured growth, while twin domain epitaxy was achieved on c-Al2O3, with NiO(111) k Al2O3(0001) and NiO[1 (1) over bar0]k Al2O3[10 (1) over bar0] or NiO[(1) over bar 10]k Al2O3[2 (1) over bar(1) over bar0] epitaxial relationship. The oxygen content in NiO films did not have a significant effect on the refractive index, extinction coefficient, and absorption coefficient. This suggests that the optical properties of NiO films remained unaffected by changes in the oxygen content.

NiO thin films with varied oxygen contents are grown on Si(100) and c-Al2O3 at a substrate temperature of 300 degrees C using pulsed dc reactive magnetron sputtering. We characterize the structure and optical properties of NiO changes as functions of the oxygen content. NiO with the cubic structure, single phase, and predominant orientation along (111) is found on both substrates. X-ray diffraction and pole figure analysis further show that NiO on the Si(100) substrate exhibits fiber-textured growth, while twin domain epitaxy was achieved on c-Al2O3, with NiO(111) k Al2O3(0001) and NiO[1 (1) over bar0]k Al2O3[10 (1) over bar0] or NiO[(1) over bar 10]k Al2O3[2 (1) over bar(1) over bar0] epitaxial relationship. The oxygen content in NiO films did not have a significant effect on the refractive index, extinction coefficient, and absorption coefficient. This suggests that the optical properties of NiO films remained unaffected by changes in the oxygen content., Funding Agencies|This work was supported financially by the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkping University (Faculty Grant SFO-Mat-LiU No. 2009 00971), the Knut and Alice Wallenberg Foundation through the [2009 00971]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoeping University; Knut and Alice Wallenberg Foundation [2009 00971]; Swedish Research Council (VR) [KAW-2020.0196]; Swedish Energy Agency [2021-03826]; VR-RFI [46519-1]; Swedish Foundation for Strategic Research (SSF) [2019-00191]; [RIF14-0053]

This thesis explores the diverse optical properties manifested when light interacts with various materials, with an emphasis on circular polarization- and bandgaprelated phenomena. The studies in this work are centered around Mueller matrix spectroscopic ellipsometry, with the objective of synthesizing and characterizing nanostructured and high-quality thin films to expand our understanding of the optical properties arising from their underlying structure and electronic transitions, respectively. Papers I, II, and III of the research address the optical properties associated with circular polarization, emphasizing the importance of the morphology and structure of the sculptured thin films used. To clarify this, AlN-based chiral sculptured thin films are synthesized using glancing angle deposition and magnetron sputtering. The discussion explores the impact of different growth parameters on the morphology and crystal structure of the films. By examining these thin film samples, it is shown how their structure and crystallographic orientation can be designed to reflect narrow spectral bands of circularly polarized light at specific wavelengths. The research also tackles how thin films preferentially reflect one handedness of circularly polarized light over the other with a high degree of circular polarization. A combination of theoretical and experimental studies offers insights into the nuances of growth and light-material interactions, particularly in complex photonic structures. Papers IV and V investigate the optical properties that arise from electronic transitions in thin films, focusing on the complex dielectric function and optical bandgap phenomena. These properties are explored using high-quality single crystalline homogenous thin films of ZnGaO, grown using metal-organic chemical vapor deposition. Various formalisms to calculate bandgap values are evaluated for their precision and applicability. The modified Cody formalism stands out as the preferred choice, Detta arbete utforskar optiska egenskaper som manifesteras när ljus interagerar med olika material. Avhandlingens tonvikt ligger på generation av cirkulärpolariserat ljus samt bandgapsrelaterade egenskaper. Studierna är centrerade kring spektroskopisk Mueller-matrisellipsometri, med målet att syntetisera och karakterisera nanostrukturerade och högkvalitativa tunna filmer. Detta för att utöka förståelsen av de optiska fenomen som uppstår från deras underliggande struktur respektive elektroniska övergångar. Artikel I, II och III i avhandlingen är relaterade till optiska polarisationsstudier och belyser betydelsen av morfologi och struktur hos optiska och fotoniska material. För att studera detta syntetiserar vi AlN baserade kirala skulpterade tunna filmer med hjälp av magnetronsputtring vid små infallsvinklar (glancing angle deposition) och diskuterar inverkan av olika tillväxtparametrar på filmernas morfologi och kristallstruktur. Genom att studera detta visar vi hur struktur och kristallografiska orientering kan skräddarsys för att reflektera smala spektrala band av där ljuset har hög grad av cirkulär polarisation. Vi visar även hur de tunna filmerna selektivt reflekterar den ena polarisationsriktningen (vänster/höger) beroende på det inkommande ljusets infallsvinkel och våglängd. Genom en serie teoretiska och experimentella studier ger vi detaljerad insikt i hur de studerade nanostrukturerna samverkar med ljus. Artikel IV och V undersöker de optiska egenskaperna som härrör från elektroniska övergångar i tunna filmer, med fokus specifikt på dielektricitetsfunktionen och optiska bandgapsfenomen. Dessa egenskaper studeras med för högkvalitativa enkristallina och homogena tunna filmer av ZnGaO, syntetiserade med metallorganisk CVD-teknik (Chemical Vapour Deposition). Vi utvärderar olika formalismer för att beräkna bandgapsvärden och bedömer deras noggrannhet och tillämpbarhet. Den modifierade Cody formalismen framhålls som bästa val på grund av dess egenskap att tillha, Funding agencies: This work was funded by Nanyang Technological University and Linköping University joint Ph.D. programme on Materials and Nanoscience Engineering (DnrLiU-2015-01061), Vetenskapsrådet (2018-04198), Stiftelsen för Strategisk Forskning (2009-00971), Energimyndigheten (grant number 46658-1), Stiftelsen Olle Engkvist Byggmästare (grant number 197-0210), and Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU 2009-00971).

Electronic grade ZnGa2O4 epitaxial thin films were grown on c-plane sapphire substrates by metal-organic chemical vapor deposition and investigated using spectroscopic ellipsometry. Their thickness, roughness and optical properties were determined using a Multiple Sample Analysis based approach by the regression analysis of optical model and measured data. These samples were then compared to samples which had undergone ion etching, and it was observed that etching time up to four minutes had no discernible impact on its optical properties. Line shape analysis of resulting absorption coefficient dispersion revealed that ZnGa(2)O(4 )exhibited both direct and indirect interband transitions. The modified Cody formalism was employed to determine their optical bandgaps. These values were found to be in good agreement with values obtained using other popular bandgap extrapolation procedures. Published by Optica Publishing Group under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published articles title, journal citation, and DOI., Funding Agencies|Vetenskapsradet [2018-04198]; Stiftelsen foer Strategisk Forskning [2009-00971]; STINT foundation [MG2019-8485]; Wafer Works Corporation; Ministry of Science and Technology [109-2221-E-009-143-MY3, 109-2622-E-009-033, 109-2634-F-009-028, 109-2224-E-009-002, 110-2218-E-A49-020-MBK, 110-2622-8-009-018-SB, 110-2224-E-A49-003, 111-2923-E-A49-003-MY3]; MAtek [2021-T-006]