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Determination of the spontaneous polarization of wurtzite (Mg,Zn)OStölzel, Marko, Müller, Alexander, Benndorf, Gabriele, Lorenz, Michael, Patzig, Christian, Höche, Thomas, Grundmann, Marius 07 August 2018 (has links)
We report on the experimental determination of the spontaneous polarization of wurtzite-
(Mg,Zn)O by examination of the recombination dynamics of polar ZnO/(Mg,Zn)O quantum wells
(QWs). The thickness-dependent decay time of the unscreened single-exciton states inside the
QWs was modeled by a self-consistent solution of Schrödinger- and Poisson-equation to deduce
the total polarization across the QW for different Mg-contents inside the barriers. By the separation
of the piezoelectric components of the polarization, a linear increase in spontaneous polarization
with increasing Mg-content x of P/x = (0.151 ± 0.015) C/m2 was determined for Mgx Zn1−x O.
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Impact of strain on electronic defects in (Mg,Zn)O thin filmsSchmidt, Florian, Müller, Stefan, von Wenckstern, Holger, Benndorf, Gabriele, Pickenhain, Rainer, Grundmann, Marius 09 August 2018 (has links)
We have investigated the impact of strain on the incorporation and the properties of extended and
point defects in (Mg,Zn)O thin films by means of photoluminescence, X-ray diffraction, deep-level
transient spectroscopy (DLTS), and deep-level optical spectroscopy. The recombination line Y2,
previously detected in ZnO thin films grown on an Al-doped ZnO buffer layer and attributed to tensile
strain, was exclusively found in (Mg,Zn)O samples being under tensile strain and is absent in
relaxed or compressively strained thin films. Furthermore a structural defect E3′ can be detected
via DLTS measurements and is only incorporated in tensile strained samples. Finally it is shown
that the omnipresent deep-level E3 in ZnO can only be optically recharged in relaxed ZnO samples.
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Phonon-assisted lasing in ZnO microwires at room temperatureMichalsky, Tom, Wille, Marcel, Dietrich, Christof P., Röder, Robert, Ronning, Carsten, Schmidt-Grund, Rüdiger, Grundmann, Marius 11 August 2018 (has links)
We report on room temperature phonon-assisted whispering gallery mode (WGM) lasing in ZnO
microwires. For WGM laser action on the basis of the low gain phonon scattering process high
quality resonators with sharp corners and smooth facets are prerequisite. Above the excitation
threshold power PTh of typically 100 kW/cm2, the recombination of free excitons under emission of
two longitudinal optical phonons provides sufficient gain to overcome all losses in the microresonator
and to result in laser oscillation. This threshold behavior is accompanied by a distinct change of the
far and near field emission patterns, revealing the WGM related nature of the lasing modes. The
spectral evolution as well as the characteristic behavior of the integrated photoluminescence
intensity versus the excitation power unambiguously proves laser operation. Polarization-resolved
measurements show that the laser emission is linear polarized perpendicular to the microwire axis
(TE).
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Experimental Demonstration of Agrivoltaic Systems via Multi-Scale Design and CharacterizationElizabeth Kathleen Grubbs (12232037) 20 April 2022 (has links)
As the global population approaches 11 billion people, demands for sustainable food, energy, and water (FEW) are approaching unprecedented levels. Current technology places sustainable FEW production methods in direct competition with one another for global surface area, such as land area for agriculture versus photovoltaic farms. This is because current installation methods for solar modules create deep shading that suppresses plant growth. The field of agrivoltaics (AgPV) addresses this issue directly by optimizing coproduction strategies for FEW and developing systems where competition is reduced; however, previous work has seen reductions in agricultural output. AgPV, where module architecture is also modified and agricultural output is minimally impacted, requires novel multi-level experimental design and characterization. In my proposed thesis, I will address the following two aspects of the project: (1) a farm-level experimental analysis of existing PV and (2) a device-level analysis of new and emerging PV material candidates. To establish the plausibility of this work, I designed and implemented an agrivoltaic system with two treatments that was successfully farmed this year. In my thesis, I will demonstrate a fully characterized utility scale AgPV array through several steps. First, I will validate the prior simulation work on the constructed AgPV array. Then I will experimentally correlate crop growth underneath the AgPV experiment. Next, the effects of the shadowing from the array on crop growth will be quantified. I will optimize the tracking algorithm for the array to maximize crop growth during the summer and power production during other seasons. Finally, I will investigate a platform for evaluation of novel PV materials and devices tailored for AgPV systems using Photoluminescence Excitation Spectroscopy (PLE) where I redesigned, constructed, and validated a new experimental design.
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Characterization of as prepared and exposed Perovskitesolar cells by microscopic and spectroscopic techniquesGorella, Nagaraju January 2021 (has links)
Studying the microstructural features, optical, and electrical properties of the thin-filmperovskite solar cells (PSC) is the main objective of this thesis work. All the PSCs used in thisthesis work were prepared by spin coating assisted with gas quenching process and the samplesreceived from Interuniversity Microelectronics Centre (IMEC), Belgium.Microstructural and architectural details of the stagewise prepared PSCs were investigatedusing a Scanning Electron Microscope (SEM) - Focused Ion Beam (FIB) technique. With thereference to the given specification from IMEC, the SEM-FIB examinations of the as-preparedPSCs confirmed the presence of different layers such as hole transport layer (HTL), perovskitelayer, and electron transport layer (ETL). Further, the thickness of the perovskite layers wasmeasured and found to be 400 and 500 nm which validates the specification of the as-preparedsamples 1 and 2, respectively. The observed average grain size of the perovskite of the asprepared samples 1 and 2 are significantly different and the values are approximately 83 and169 nm, respectively. The average surface roughness values of perovskite layers (as-preparedsamples 1 and 2) and electron transport layer (as-prepared samples 3) were evaluated by atomicforce microscopy (AFM) and the values are 10, 19, and 12 nm, respectively. Furthermore, theconductive-AFM was performed to evaluate the electrical properties of the perovskite layers,and the results confirmed that the as-prepared sample 2 showed a higher mean current value of4.1 nA, than sample 1 resulted in 2.9 nA. The higher electrical performance of the as-preparedsample 2 could be correlated to the larger grain size, higher thickness, and higher surfaceroughness values of the perovskite layer.Moreover, the performance evaluation of a complete perovskite solar device with a similarconfiguration was evaluated between the as-prepared (newly fabricated) and the exposedsamples (tested under sunlight for ten weeks), and their behavior was studied. The optical andelectrical characteristics of the solar cell at the device level were examined with the help ofphotoluminescence (PL), electroluminescence (EL), and solar simulator techniques. The peakand fullwidth half maximum (FWHM) values of the PL emission spectra of the as-prepareddevice are in line with IMEC specification, whereas these values are slightly decreased for theexposed perovskite solar device. Also, during the EL examination, predominantly uniformluminescence was observed for the as-prepared device, whereas discontinuity in the emissionof electrons, and in some parts absence of luminescence-effect was observed for the exposedsolar cell. The current-voltage characteristics obtained from the solar simulator resultsconfirmed that the power conversion efficiency of the as-prepared device is at least 6 timeshigher than the exposed device. Based on the PL, EL, and PCE results it could be confirmedthat the perovskite solar cell exposed to sunlight for 10 weeks has started to degrade.
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Localization dynamics of paraexcitons and their lattice relaxation at oxygen vacancies in cuprous oxide / 亜酸化銅パラ励起子の酸素欠陥への局在化のダイナミクスと格子緩和の研究Sandhaya Koirala 23 July 2014 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18494号 / 理博第4009号 / 新制||理||1578(附属図書館) / 31380 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 中 暢子, 教授 田中 耕一郎, 教授 金光 義彦 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM
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Fabrications and optical properties of plasmonic arrays without noble metals / 貴金属を用いないプラズモニックアレイの作製と光物性Kamakura, Ryosuke 26 March 2018 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21113号 / 工博第4477号 / 新制||工||1696(附属図書館) / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 田中 勝久, 教授 三浦 清貴, 教授 作花 哲夫 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM
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Study on photoluminescence quantum yields of atomically thin-layered two-dimensional semiconductors transition metal dichalcogenides / 二次元原子層半導体遷移金属ダイカルコゲナイドにおける発光量子効率に関する研究Nur, Baizura Binti Mohamed 23 July 2018 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第21315号 / エネ博第371号 / 新制||エネ||73(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー応用科学専攻 / (主査)教授 松田 一成, 教授 佐川 尚, 教授 大垣 英明 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM
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Photon Emission and Lasing in Bare and Hybrid Plasmonic Semiconductor Nanowires and NanorodsMohammadi, Fatemesadat 29 October 2018 (has links)
No description available.
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Crystallization of Two-Dimensional Transition Metal Dichalcogenides for Tailored Optical PropertiesRai, Rachel H. 26 September 2019 (has links)
No description available.
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