Dissertations / Theses on the topic 'Material science- optical properties'
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1
Li, Ling Ph D. Massachusetts Institute of Technology. "Biomineralized structural materials with functional optical properties." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/89955.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 129-143).
Many biological structural materials exhibit "mechanical property amplification" through their intricate hierarchical composite designs. In the past several decades, significant progress has been achieved in elucidating the structure/mechanical property relationships of these materials. However, the design strategies of structural biomaterials with additional functional roles are still largely unexplored. This thesis, by selecting three unique mollusk shell model systems, explores the fundamental design strategies of multifunctional biomineralized materials with dual mechanical and optical functions: transparency, photonic coloration, and lens-mediated vision. The model systems are the bivalve Placuna placenta, the limpet Patella pellucida, and the chiton Acanthopleura granulata, respectively. By investigating the relationships between the mechanical and optical properties and the structural characteristics, this thesis uncovers novel design strategies used to integrate optical functions into mechanically-robust material systems. The high transmission property of the P. placenta shells (~99 wt% calcite), for example, is elucidated through experimental and theoretical analysis based on a light scattering model. This armor utilizes deformation twinning and additional mechanisms at the nanoscale to enhance the energy dissipation efficiency by almost an order of magnitude relative to abiotic calcite. 3D quantitative analysis of the damage zone resulting from high load indentations was performed via synchrotron X-ray micro-computed tomography, revealing the formation of a complex network of microcracks. A unique structural motif, screw dislocation-like connection centers, is identified to enable a high density of crack deflection and bridging. This thesis also leads to the discovery of a unique biomineralized photonic structure in the shell of the blue-rayed limpet P. pellucida. The photonic system consists of a calcite multilayer and underlying particles, which provide selective light reflection through constructive interference and contrast enhancement through light absorption, respectively. Lastly, this thesis presents a detailed investigation of the biomineralized lenses embedded in the armor plates of the chiton A. granulata. The image formation capability of these lenses is experimentally demonstrated for the first time. The optical performance of the eyes is studied via comprehensive ray-trace simulations that take into account the experimentally measured geometry and crystallography of the lens. Mechanical studies illustrate that trade-offs between protection and sensation are present in the plates.
by Ling Li.
Ph. D.
2
Russo, Manuela. "Titanium oxide hydrates : optical properties and applications." Thesis, Queen Mary, University of London, 2010. http://qmro.qmul.ac.uk/xmlui/handle/123456789/597.
Abstract:
TiO2 has been extensively studied in the last decades due to its interesting optical and electronic properties, which, combined with low fabrication costs, renders this material very attractive for applications in photovoltaic and photocatalysis. However, the performances of titania in specific device applications were found to be strongly dependent on the synthetic methods selected for its production. The majority of such synthetic procedures rely on the hydrolysis of suitable precursors and often produce an amorphous solid, generally referred as the “amorphous” titanium oxide beside the crystalline titania. In this thesis, we thus set out to investigate amorphous materials produced by the hydrolysis of titanium tetrachlorides and tetraisopropoxide. We show that these amorphous products consists of titanium oxide hydrates, which are relatively stable at room temperature and fully convert into crystalline titania only after extended temperature treatments. We also find that titanium oxide hydrates may display highly desirable characteristic such as a strong photochromic response – especially when placed in a suitable chemical environment. In the following chapter, we then show 3 that hybrid systems can be readily prepared of titanium oxide hydrates with, for instance, macromolecular materials such as poly(vinylalcohol). The amorphous nature of the titanium oxide hydrates allows to introduce more than 90 vol.% of the inorganic species into such systems – compared to 15 vol.% or less when producing hybrids comprising, e.g., crystalline nanoparticles of TiO2. Therefore, materials can be realized that display a refractive index n of at least 2.1, without compromising transparency of the resulting structures. Remarkably, n can not only be adjusted by varying the content of the inorganic species, but also through suitable heat treatments and/or irradiation with UV-light. Potential applications for such new, versatile and tunable optical systems are also discussed in this thesis.
3
Chang, Wai-Kit. "Porous silicon surface passivation and optical properties." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/41426.
Abstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996."June 1996."
Includes bibliographical references (leaves 84-85).
by Wai-Kit Chang.
S.M.
4
Stolfi, Michael Anthony. "Optical properties of nanostructured silicon-rich silicon dioxide." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37583.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.Includes bibliographical references (p. 190-195).
We have conducted a study of the optical properties of sputtered silicon-rich silicon dioxide (SRO) thin films with specific application for the fabrication of erbium-doped waveguide amplifiers and lasers, polarization sensitive devices and devices to modify the polarization state of light. The SRO thin films were prepared through a reactive RF magnetron sputtering from a Si target in an O2/Ar gas mixture. The film stoichiometry was controlled by varying the power applied to the Si target or changing the percentage of 02 in the gas mixture. A deposition model is presented which incorporates the physical and chemical aspects of the sputtering process to predict the film stoichiometry and deposition rate for variable deposition conditions. The as-deposited films are optically anisotropic with a positive birefringence (nTM > nTE) that increases with increasing silicon content for as-deposited films. The dependence of the birefringence on annealing temperature is also influenced by the silicon content. After annealing, samples with high silicon content (>45 at%) showed birefringence enhancement while samples with low silicon content (<45 at%) showed birefringence reduction. A birefringence of more than 3% can be generated in films with high silicon content (50 at% Si) annealed at 11000C.
(cont.) We attribute the birefringence to the columnar film morphology achieved through our sputtering conditions. Er was incorporated through reactive co-sputtering from Er and Si targets in the same O2/Ar atmosphere in order to investigate the energy-transfer process between SRO and Er for low annealing temperatures. By studying the photoluminescence (PL) intensity of Er:SRO samples annealed in a wide range of temperatures, we demonstrated that the Er sensitization efficiency is maximized between 600°C and 700°C. Temperature-resolved PL spectroscopy on SRO and Er:SRO samples has demonstrated the presence of two different emission sensitizers for samples annealed at 6000C and 1 100°C. This comparative study of temperature-resolved PL spectroscopy along with energy Filtered Transmission Electron Microscopy (EFTEM) has confirmed that the more efficient emission sensitization for samples annealed at 6000C occurs through localized centers within the SRO matrix without the nucleation of Si nanocrystals. Er-doped SRO slab waveguides were fabricated to investigate optical gain and loss for samples annealed at low temperatures.
(cont.) Variable stripe length gain measurements show pump dependent waveguide loss saturation due to stimulated emission with a maximum modal gain of 3 ± 1.4 cm-1 without the observation of carrier induced losses. Pump and probe measurements on ridge waveguides also confirms the presence of SRO sensitized signal enhancement for samples annealed at 6000C. Transmission loss measurements demonstrate a significant loss reduction of 1.5 cm-1or samples annealed at 600°C compared to those annealed at 1000°C. These results suggest a possible route for the fabrication of compact, high-gain planar light sources and amplifiers with a low thermal budget for integration with standard Si CMOS processes.
by Michael Anthony Stolfi.
Ph.D.
5
Anant, Vikas 1980. "Engineering the optical properties of subwavelength devices and materials." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42233.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 145-154).
Many applications demand materials with seemingly incompatible optical characteristics. For example, immersion photolithography is a resolution enhancing technique used to fabricate the ever-shrinking nanostructures in integrated circuits but requires a material that has-at the same time--a large index of refraction and negligible optical loss. Other applications require devices that have optical properties that seem exorbitant given the constraints posed by the geometry, materials, and desired performance of these devices. The superconducting nanowire single-photon detector (SNSPD) is one such device that, on the one hand, needs to absorb and detect single telecom-wavelength photons (A = 1.55 pm) with near-perfect efficiency, but on the other hand, has an absorber that is subwavelength in its thickness (A/390). For both cases, it is simply not enough to look for alternative materials with the desired optical properties, because the materials may not exist in nature. In fact, it has become necessary to engineer the optical properties of these devices and materials using other means. In this thesis, we have investigated how the optical properties of materials and devices can be engineered for specific applications. In the first half of the thesis, we focused on theoretical schemes that use subwave-length, resonant constituents to realize a material with interesting optical properties. We proposed a scheme that can achieve high index (n > 6) accompanied with optical gain for an implementation involving atomic vapors. We then explored the applicability of this high-index system to immersion lithography and found that optical gain is problematic. We solved the issue of optical gain by proposing a scheme where a mixture of resonant systems is used. We predicted that this system can yield a high refractive index, low refractive index, anomalous dispersion, or normal dispersion, all with optical transparency. In the second half, we studied the optical properties of SNSPDs through theoretical and experimental methods. In the study, we first constructed a numerical model that predicts the absorptance of our devices. We then fabricated SNSPDs with varying geometries and engineered a preprocessing-free proximity-effect correction technique to realize uniform linewidths. We then constructed an optical apparatus to measure the absorptance of our devices and showed that the devices are sensitive to the polarization of single photons.
by Vikas Anant.
Ph.D.
6
Wang, Lei 1972. "Morphology and optical properties of polyolefin blown films." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36728.
Abstract:
Optical properties of polyethylene blown films are of great commercial and scientific interest. An understanding of the relationship between morphology and optical properties will have a significant impact on product and process optimization.In this work, a number of linear low density polyethylene (LLDPE) resins of different molecular and structural characteristics were studied. Intrinsic properties such as refractive index and absorption coefficient were estimated from resin compositions using group contribution models. The refractive indices of sample films were also measured using the method of Transmission Spectrum.
The morphology of polyethylene films was investigated using Atomic Force Microscopy (AFM) and Near-field Scanning Optical Microscopy (NSOM). Both the surface and bulk morphologies were evaluated. The observation shows the dominant spherulitic structure on the surface as well as in the bulk, as the result of nucleation and crystallization during the film blowing process. In addition to qualitative observations and comparisons; quantitative characterization methods were employed to describe the features of the morphology.
Based on the morphology characterization, the surface reflection was described by the Beckmann-Davies theory of reflection of electro-magnetic waves by rough surface. The directional distribution of reflected intensity was computed according to the surface roughness information. The gloss values of sample films were computed accordingly and compared with experimental measurements. Furthermore, the problem of light transmission and scattering was investigated. A scattering geometry was proposed from the observations of the morphology of sample films. The light scattering by the surface of polymer films was analyzed using a model that is based on the Mie theory of scattering. The haze values of sample films were computed and compared with experimental measurements.
7
Supplee, William Wagner. "Structural, magnetic, and optical properties of orthoferrite thin films." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/44813.
Abstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Includes bibliographical references (leaves 41-43).
Pulsed laser deposition was used to create thin films of Ce-Fe-O and Y-Fe-O systems. Deposition temperature and ambient oxygen pressure were varied systematically between samples to determine which deposition conditions were most favorable to the formation of cerium/yttrium orthoferrite. The structure and composition of each film were then determined using X-ray diffraction and wavelength dispersive spectroscopy respectively. In addition, the magnetic and optical properties of the yttrium films were characterized to determine the suitability of these materials as Faraday isolators at A=1550 nm. Results show that orthoferrite crystal structures in these systems are not stable in the temperature and oxygen ranges tested. It was also found that increasing oxygen pressure caused exponential decay in the deposition rate. Most films were amorphous, exhibiting a paramagnetic M-H plot and a Verdet coefficient between 0.37 and 0.89 deg cm-1 Gauss-1
by William Wagner Supplee, Jr.
S.B.
8
Chen, Jimmy Kuo-Wei. "The electrical and optical properties of doped yttrium aluminum garnets." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/32136.
9
Gallivan, Rebecca Anne. "Investigating coordinate network based films through mechanical and optical properties." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111257.
Abstract:
Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (page 31).
Both biological and synthetic materials crosslinked via metal coordinate dynamic chemistry display interesting advanced behavior. In particular, coordinate networks have been shown to form self-healing, self-assembling, and stimuli-responsive behaviors through its tunable optical and mechanical properties as well as its ability to for dynamic networks. However, while the majority of research has focused on characterization of bulk coordinate networks, coordinate complexes have also been shown to be useful in molecular film formation [1 and 2]. This study investigates the mechanical and optical properties of tannic acid and 4 arm catechol polyethylene glycol based coordinate network films. It shows that these films can contribute to energy dissipation and undergo pH-induced optical shifts when used as coatings on soft hydrogels. It also provides evidence that the molecular architecture of the network formers may have considerable effect on the properties and behavior of coordinate network films. Ultimately this work lays the foundation for further investigation of the underlying mechanisms and engineering potential of coordinate network based films.
by Rebecca Anne Gallivan.
S.B.
10
Brewster, Megan Marie. "The interplay of structure and optical properties in individual semiconducting nanostructures." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/69662.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from PDF version of thesis. Vita.
Includes bibliographical references (p. 163-174).
Semiconductor nanostructures exhibit distinct properties by virtue of nano-scale dimensionality, allowing for investigations of fundamental physics and the improvement of optoelectronic devices. Nanoscale morphological variations can drastically affect overall nanostructure properties because the investigation of nanostructure assemblies convolves nanoscale fluctuations to produce an averaged result. The investigation of individual nanostructures is thus paramount to a comprehensive analysis of nanomaterials. This thesis focuses on the study of individual GaAs, AlGaAs, and ZnO nanostructures to understand the influence of morphology on properties at the nanoscale. First, the diameter-dependent exciton-phonon coupling strengths of individual GaAs and AlGaAs nanowires were investigated by resonant micro-Raman spectroscopy near their direct bandgaps. The one-dimensional nanowire architecture was found to affect exciton lifetimes through an increase in surface state population relative to volume, resulting in Fröhlich coupling strengths stronger than any previously observed. Next, ZnO nanowire growth kinetics and mechanisms were found to evolve by altering precursor concentrations. The cathodoluminescence of nanowires grown by reaction-limited kinetics were quenched at the nanowire tips, likely due to point defects associated with the high Zn supersaturation required for reaction-limited growth. Further, cathodoluminescence was quenched in the vicinity of Au nanoparticles, which were found on nanowire sidewalls due to the transition in growth mechanism, caused by excited electron transfer from the ZnO conduction band to the Au Fermi level. Finally, ZnO nanowalls were grown by significantly increasing precursor flux and diffusion lengths over that of the ZnO nanowire growth. Nanowall growth began with the Au-assisted nucleation of nanowires, whose growth kinetics was a combination of Gibbs- Thomson-limited and diffusion-limited, followed by the domination of non-assisted film growth to form nanowalls. Nanoscale morphological variations, such as thickness variations and the presence of dislocations and Au nanoparticles, were directly correlated with nanoscale variations in optical properties. These investigations prove unequivocally that nanoscale morphological variations have profound consequences on optical properties on the nanoscale. Studies of individual nano-objects are therefore prerequisite to fully understanding, and eventually employing, these promising nanostructures.
by Megan Marie Brewster.
Ph.D.
11
Zhou, Xiang Ph D. Massachusetts Institute of Technology. "IIl-nitride nanowires and heterostructures : growth and optical properties on nanoscale." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/89962.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, June 2014.Cataloged from PDF version of thesis. "June 2014."
Includes bibliographical references (pages 172-194).
Gallium nitride (GaN) and indium gallium nitride (InGaN) nanowires promise potential for further improving the electricity-to-light energy conversion efficiencies in light emitting diodes due to strain relaxation, reduced density of structural defects, and easier light extraction. Material quality and effective band engineering of such III-nitride nanowires are crucial for the design and fabrication of their optoelectronic applications such as LEDs, lasers and photodetectors. In this thesis, we first demonstrate effective control over GaN nanowire size, growth rate and structural quality through careful choice of metal seed particles. The differences in morphology, structural defects and optical properties of GaN nanowires grown by metalorganic chemical vapor deposition were studied systematically by electron microscopy and photoluminescence, and related to supersaturation in different seed particles and nanowire nucleation mechanisms. These results also demonstrate that systematic screening of seed materials is essential for synthesizing nanostructures with defect-free structures and other functional heterostructures. Next, challenges for nanoscale mapping of band engineering were successfully addressed through direct spatial correlation of optical properties to a variety of III-nitride heterostructures grown by molecular beam epitaxy, including GaN p-n junction nanorods, InGaN nanodisks, and GaN quantum disks and quantum wires. We demonstrate that effective doping, alloying and quantum confinement can be readily achieved in nanowire heterostructures, by cathodoluminescence in scanning transmission electron microscopy. P-n junction position and carrier diffusion lengths inside a single GaN nanorod were determined with nanometer spatial resolution. InGaN disk compositional uniformities were quantified from their optical emissions, which revealed substantial compositional inhomogeneity in bottom-up synthesized nanostructures. The studies on optical properties of individual GaN quantum structures demonstrated that small differences in the degree of quantum confinements resulted in substantial changes in the optical band gap. More importantly, reduced light emissions are directly correlated to regions containing grain boundaries, dislocations and stacking faults, which were formed as a result of nanorod coalescence and fluctuations in growth environment during nanostructure synthesis. Our findings demonstrate that controlling compositional and structural homogeneity, understanding defect formation mechanism and their effects on materials properties are key challenges to be addressed for developing large scale functional devices based on bottom-up synthesized nanostructured materials.
by Xiang Zhou.
Ph. D.
12
Yoo, Jee Soo. "Computational study on controlling the optical properties of solar thermal fuels." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/123622.
Abstract:
Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 62-72).
Solar thermal fuels utilize molecules that undergo reversible photo-isomerization to convert solar energy into stored thermal energy.¹ Because solar thermal fuels produce no emissions and can store and convert energy within one material, they are an attractive option for a renewable energy source. However, it has remained a challenge to identify a suitable solar thermal fuel material that exhibits high energy density, high energy conversion efficiency, long energy storage lifetime, and can be produced at low cost. A recent proposal is a nanotemplate-photoisomer hybrid system, e.g. functionalized azobenzene, a well-known photoisomer molecule, attached to carbon nanostructure templates such as carbon nanotubes, graphene, pentacene or alkene chains. Such structures have been suggested and tested as candidate solar thermal fuel materials with high energy density and long storage time²⁻⁴ In this thesis work, we further investigated optical properties of functionalized azobenzene and geometry-modified azobenzene. We found the best structure that yields maximum optical isomerization rate for trans-azobenzene and minimum optical isomerization rate for cis-azobenzene, calculating the reaction rate based on overlap between the solar spectrum and optical spectra calculated using time-dependent density functional theory (TDDFT). We showed that energy-charged-state molecule (cis-isomer) content at the photostationary state can be improved from 73 percent for pure azobenzene to 83 percent and to 97 percent by functionalizing azobenzene and a designing different geometry for azobenzene, respectively. From this, a desired structure for nanotemplates-photoisomer hybrid system can be estimated and same calculation technique may be employed to calculate and optimize photostationary state of the nanotemplates-photoisomer hybrid system.
by Jee Soo Yoo.
S.M.
S.M. Massachusetts Institute of Technology, Department of Materials Science and Engineering
13
Kim, Donghun Ph D. Massachusetts Institute of Technology. "Understanding electronic and optical properties of PbS QDs for improved photovoltaic performance." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101458.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 131-139).
Photovoltaic (PV) solar cells that constitute semiconducting sunlight absorber and metallic electrical contacts convert solar energy to electricity. Even though silicon represents roughly 90% of installed solar PV capacity as the clear current leader among PV technology, another class of solid-state solar cells, referred to as quantum dot (QD) solar cells, have gained much attentions from both academia and industry with the ability to provide further substantial enhancement of PV efficiency, together with the low possible manufacturing/installation cost. The power conversion efficiencies (P.C.E.) of QD-PVs based on lead sulfide (PbS) have been enhanced dramatically in only several years: current leading groups are able to fabricate reliably QD-PVs with 7-10% P.C.E. owing to favorable optical properties of PbS QDs including facile tunability of bandgaps with the variation in dot sizes or shapes, wide spectral responses, and multiple exciton generation. To date, the efficiency advances of QD solar cells have been carried out almost exclusively through tremendous numbers of trial and error experiments. Examples include materials set variations, donor and acceptor layer thickness optimization, and device structure modification. The core of the work described in this thesis deals with the theoretical understanding and design of PbS QDs with the goal of achieving a deeper and more fundamental understanding of the wide range of material's properties at the atomic scale in these devices. To this end, we employ a technique of computational electronic structure calculation methods, namely density functional theory (DFT) calculations. In this thesis, we select and investigate, using DFT calculations, three important electronic or optical properties: 1) band-edge energy (Chapter 2), 2) trap states (Chapter 3), and 3) Stokes shift (Chapter 4), all of which can contribute to PV performance improvements only if appropriately tailored. It is worth emphasizing that ligands which are used during QD synthesis for prevention of QD agglomeration plays a key role in tuning each property of interest in this thesis. Our theoretical work of band-edge energy shifts presented in Chapter 2 identifies ligand-induced surface dipoles as a hitherto-underutilized means of control over the absolute energy levels in PVs, complementary to well known bandgap tuning. This work have guided our experimental collaborators to build up a device architecture with a novel interfacial band alignment where a surplus loss of current collection can be minimized, leading to "certified" efficiency of 8.6% in 2014. Improvements of JSC presented in Chapter 2 led us to pay much attention to another figure of merit, open-circuit voltage (VOC): maximum Voc of 0.5-0.6 (V) has been achieved in single-junction PVs using PbS QDs with the bandgap of 1.1-1.3 (eV). Such large deficit of Voc in QD-PVs is attributed to the following sources: (1) high density of mid-gap trap states, (2) large Stokes shift, each of which is investigated and elaborated on in Chapters 3 and 4. Based on the fundamental understanding on the origin of these properties obtained from DFT calculations, we together with our experimental collaborators are actively working to develop PbS QD films with improved properties and to incorporate them into PV devices for further performance enhancements. This thesis document is organized as follows: Chapter 1 introduces PbS QDs and PVs, Chapters 2,3, and 4 illustrates theoretical investigations of key electronic and optical properties of PbS QDs (i.e. band-edge energy, trap states, and Stokes shift, respectively) supported by relevant experimental results from collaborators for better understanding of the this thesis. Lastly Chapter 5 closes the thesis with brief summary of works and future impacts to PVs and other optoelectronic applications.
by Donghun Kim.
Ph. D.
14
Golea, Mostefa. "AB(2)C(4) semiconducting compounds crystal growth, intrinsic defects and optical properties." Thesis, University of Ottawa (Canada), 1988. http://hdl.handle.net/10393/5374.
15
Shakya, Bijayandra. "Magneto-Optical Properties of One-Dimensional Photonic Crystals." Youngstown State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1329155177.
16
Weisenbach, Lori ann. "Processing, characteristics, and optical properties of wet chemically derived planar dielectric waveguides." Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186581.
Abstract:
An experimental study of the processing and attenuation characteristics of solution derived, thin film, planar waveguides was made. In this study, the densification and attenuation characteristics of a variety of compositions were compared. To insure that the effects measured reflected compositional differences and not processing artifacts, guidelines for the reproducible fabrication of optical quality layers, irrespective of composition, were established. A broad range of compositions were prepared and an effort was made to keep the various solution syntheses as simple and similar as possible. The densification and attenuation of binary SiO₂-TiO₂ compositions was measured, then compared to the densification and attenuation of SiO₂-TiO₂-RₓO(y) (where R = Al or Zn) ternary compositions. Film densification was not strongly dependent upon composition, and was successfully modelled using the Lorentz-Lorenz relation, assuming the open volume in the undensified films were filled with adsorbed water. The attenuation measured at 632.8 nm did not vary with composition, except for the Zn ternary samples. Waveguides with losses of < 1dB/cm could be fabricated from all other compositions. Waveguide attenuation was measured for films of different thickness, and compared to modelled predictions. The attenuation increased as layer thickness decreased, suggesting the predominance of the surface scattering contribution. To confirm that absorption losses were negligible, the wavelength dependence of the waveguides was measured. The wavelength dependence varied with composition, suggesting the absorption varied with composition. Possible mechanisms of absorption in the waveguides were discussed; the interaction of the atmosphere with the film structure is proposed as the cause of the deterioration. Film development for the binary SiO₂-TiO₂ films was also studied as a function of increased firing time at 500°C. Multiple firings at 500°C increased the film density and the resistance to deterioration, but also increased the surface roughness of the films. Increased surface roughness, increased the scattering losses measured for the guide. The application of solution derived thin films was demonstrated with the successful fabrication of a novel optical device. The fabrication of the Single Leakage-Channel Grating Coupler illustrated specific design tolerances could be met and the resulting device performance near the theoretical maximum.
17
Nicolas, Ubrig. "Optical properties of carbon based materials in high magnetic fields." Phd thesis, Université Paul Sabatier - Toulouse III, 2011. http://tel.archives-ouvertes.fr/tel-00646148.
Abstract:
La découverte des nanotubes de carbone, il y a maintenant une vingtaine d'années, a été un des moteurs de la recherche des nanotechnologies. Ces particules illustrent l'amalgame entre le monde macroscopique et le monde appelé nano. Cette discipline a également relancée la recherche sur le graphite et le carbone en général, qui atteint un nouveau sommet avec la découverte du graphène, une monocouche de graphite. Rapidement la physique des nanotubes et du graphène ont suscité l'intérêt d'être étudié sous champ magnétique avec la découverte de l'effet Aharonov-Bohm dans les nanotubes ou l'effet hall quantique dans le graphène. Cette thèse a pour but d'approfondir la connaissance des propriétés optiques des nanotubes, du graphène et du graphite sous champ magnétique intense. Pour cela nous nous interesserons dans un premier temps à la problématique des excitons sombres. Nous étudierons ensuite les propriétés magnétiques et dynamiques des tubes. La famille métallique est paramagnétique le long de son axe et diamagnétique perpendiculaire à celui-ci. La famille semiconductrice est diamagnétique par rapport à ces deux orientations mais la valeur perpendiculaire est plus élevée. De ce fait tous les nanotubes vont s'aligner parallèlement à un champ magnétique appliqué. Nous utiliserons des méthodes de spectroscopie optique pour étudier ce phénomène. La deuxième partie de la thèse consistera à examiner les propriétés optiques du graphène et du graphite et plus précisément les transitions entre niveaux de Landau sous champs intenses. La particularité du graphène est que ses porteurs de charge se comportent comme des particules relativistes avec une masse nulle. Les niveaux de Landau se trouvent modifiés avec une dépendance en racine du champ magnétique, par rapport aux systèmes deux dimensionels classiques, où l'on retrouve une dépendance linéaire comme pour l'électron libre par exemple. Ceci nous entrainera également à reéxaminer les propriétés du graphite et d'approfondir les connaissances, notamment à champ très élevé, sur ce matériau à priori bien connu et étudié dans le passé.
18
Kagan, Cherie R. 1969. "The electronic and optical properties of close packed cadmium selenide quantum dot solids." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10603.
19
Panthani, Matthew George. "Colloidal Nanocrystals with Near-infrared Optical Properties| Synthesis, Characterization, and Applications." Thesis, The University of Texas at Austin, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3572875.
Abstract:
Colloidal nanocrystals with optical properties in the near-infrared (NIR) are of interest for many applications such as photovoltaic (PV) energy conversion, bioimaging, and therapeutics. For PVs and other electronic devices, challenges in using colloidal nanomaterials often deal with the surfaces. Because of the high surface-to-volume ratio of small nanocrystals, surfaces and interfaces play an enhanced role in the properties of nanocrystal films and devices.
Organic ligand-capped CuInSe2 (CIS) and Cu(InXGa 1-X)Se2 (CIGS) nanocrystals were synthesized and used as the absorber layer in prototype solar cells. By fabricating devices from spray-coated CuInSe nanocrystals under ambient conditions, solar-to-electric power conversion efficiencies as high as 3.1% were achieved. Many treatments of the nanocrystal films were explored. Although some treatments increased the conductivity of the nanocrystal films, the best devices were from untreated CIS films. By modifying the reaction chemistry, quantum-confined CuInSe XS2-X (CISS) nanocrystals were produced. The potential of the CISS nanocrystals for targeted bioimaging was demonstrated via oral delivery to mice and imaging of nanocrystal fluorescence.
The size-dependent photoluminescence of Si nanocrystals was measured. Si nanocrystals supported on graphene were characterized by conventional transmission electron microscopy and spherical aberration (Cs)-corrected scanning transmission electron microscopy (STEM). Enhanced imaging contrast and resolution was achieved by using Cs-corrected STEM with a graphene support. In addition, clear imaging of defects and the organic-inorganic interface was enabled by utilizing this technique.
20
Premathilaka, Shashini M. "Synthesis and Optical Properties of Colloidal PbS Nanosheets." Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1561463157379607.
21
Stadler, Bethanie J. Hills (Bethany Joyce Hills). "Relationships between optical properties and processing in Al2O3-Y2O3 thin film waveguides and amplifers." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/28082.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994.Includes bibliographical references (leaves 148-151).
by Bethanie J. Hills Stadler.
Ph.D.
22
Kumar, Priyank Vijaya. "Enhanced electrical, optical and chemical properties of graphene oxide through a novel phase transformation." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98736.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 86-98).
Graphene oxide (GO) is a versatile, solution-processable candidate material for next-generation, large-area, ultrathin electronics, optoelectronics, energy conversion and storage technologies. GO is an atom-thick sheet of carbon functionalized with several oxygen-containing groups dominated by the epoxy and hydroxyl functional groups on the basal plane, with carboxyls and lactols at the sheet edges. It is well known that reduction of GO at temperatures > 150°C leads to the removal of oxygen atoms from the carbon plane, leading to the formation of reduced GO (rGO) structures. Although GO has been utilized for multiple applications in the last decade, our understanding of the structure-property relationships at the atomic-level has still been lacking owing to the amorphous nature and chemical inhomogeneity of GO, which has in turn limited our ability to design and tailor GO nanostructures for high-performance applications. In particular, the material's structure and its structural evolution at mild annealing temperatures (< 1000°C) has been largely unexplored. In this thesis, we use a combination of first-principles computations, classical molecular dynamics simulations based on reactive force fields and experiments to model realistic GO structures and develop a detailed understanding of the relationship between the carbon-oxygen framework and the sheet properties, at the atomic level. Based on our understanding, we demonstrate a new phase transformation in GO sheets at mild annealing temperatures (50-80°C), where the oxygen content is preserved and as-synthesized GO structures undergo a phase separation into prominent oxidized and graphitic domains facilitated by oxygen diffusion. Consequently, as-synthesized GO that absorbs mainly in the ultraviolet region becomes strongly absorbing in the visible region, photoluminescence is blue shifted and electronic conductivity increases by up to four orders of magnitude. We then use this novel phase transformation to improve two sets of applications. 1) We demonstrate that cell capture devices making use of phase transformed-GO substrates have higher capture efficiencies compared to devices making use of as-synthesized GO substrates. 2) We show that the reduction of phase transformed-GO leads to better electrical properties of rGO thin films. Our results fill an important gap and establish a complete theory for structural evolution of GO over the entire range of temperatures, i.e. from room temperature to ~1000°C. Taken together, this structural transition in GO enables us to predict and control the sheet properties in new ways, as opposed to reduction, which is till date the only handle to control the structure of GO. This could potentially open the door for completely new applications or for enhancing the performance of existing applications based on GO.
by Priyank Vijaya Kumar.
Ph. D.
23
Joshi, Vinay Joshi. "ELECTRO-OPTICAL AND FLEXOELECTRO-OPTICAL PROPERTIES ENHANCED BY BIMESOGEN-DOPED CHIRAL NEMATIC LIQUID CRYSTALS." Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1543053053654711.
24
Chiao, Shu-Chung 1958. "The influence of stoichiometry on the properties of titanium oxide films for optical coatings." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/290580.
Abstract:
This study investigates various properties of titanium oxide thin films. The samples are prepared by electron-beam evaporation of the Ti₂O₃ material in an oxygen environment. Papers about the vaporization study of the titanium-oxygen system are reviewed; special attention is paid to the congruent vaporization in the titanium-oxygen system. The occurrence of congruent vaporization in our coating system is discussed. The compositions of the films are identified by Rutherford Backscattering Spectrometry. The effect of water vapor and the substrate temperature on the oxygen contents in RBS measurements is discussed. The optical properties of the samples are measured. With the spectrophotometric measurements, the methods for deriving the optical constants of transparent and opaque films are developed. The absorption of the TiO₂ film is investigated, and the corresponding mechanisms are discussed. The envelope method is employed to find the optical band gap of the TiO₂ film. The electrical resistivity of the titanium oxide films are measured with the four-point probe method, and the phenomenon of metal to insulator transition is demonstrated. The tensile stresses in our titanium oxide films are examined with a Nomarski microscope. The grain boundary model is adopted to explain the influence of thickness and oxygen content on the stresses development in thin film. Molecular dynamics simulation is used to study the structure and the thermal expansion of titanium dioxide rutile.
25
Chen, John Tsen-Tao. "Influence of a liquid crystalline block on the microstructure and optical properties of block copolymers." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10425.
Abstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997.Vita.
Includes bibliographical references (leaves 275-286).
by John Tsen-Tao Chen.
Ph.D.
26
Souza, Dantas Nilton. "Electronic structure and optical properties of PbY and SnY (Y=S, Se, and Te)." Licentiate thesis, Stockholm : Materialvetenskap, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4444.
27
Nakos, James Spiros. "Effects of crystal growth process parameters on the microstructural optical and electrical properties of CdTe and CdMnTe." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14574.
28
Rai, Rachel H. "Crystallization of Two-Dimensional Transition Metal Dichalcogenides for Tailored Optical Properties." University of Dayton / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1565191101735252.
29
Buschle, William. "Effect of Polymerization Variables on the Properties of Poly(N-Ethyl aniline)." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1305893685.
30
Huang, Mantao. "Voltage control of electrical, optical and magnetic properties of materials by solid state ionic transport and electrochemical reactions." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/127898.
Abstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, May, 2020Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 139-153).
Reversible post-fabrication control of material properties enables devices that can adapt to different needs or environmental conditions, and brings additional levels of functionality, paving the way towards applications such as reconfigurable electronics, reconfigurable antennas, active optical devices and energy efficient data storage. One promising way of achieving the controllability is through solid-state ionic transport and electrochemical reactions in thin film structures, where the properties of materials can be electrically controlled by a gate voltage in an addressable way. Here we explore using such ionic gating method to control the electrical, optical and magnetic properties of solid-state thin film layers, and show that large modification can be achieved for a wide range of properties. We demonstrate a new type of three terminal resistive switching device where the resistivity of a thin film conductive channel can be controlled by a gate voltage. We demonstrate solid-state ionic gating of the optical properties of metals and oxides and show the versatility of the approach by implementing voltage-controlled transmission, thin film interference, and switchable plasmonic colors. We also show that the approach allows for voltage control of ferrimagnetic order, demonstrating voltage induced 180-degree switching of the Néel vector, as a new way of magnetic bit writing. These findings extend the scope of voltage programmable materials and provide insights into the mechanisms of voltage controlled material properties by solid-state ionic transport and electrochemical reactions.
by Mantao Huang.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Materials Science and Engineering
31
Adhikari, Dipendra. "Optical and Microstructural Properties of Sputtered Thin Films for Photovoltaic Applications." University of Toledo / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1573118517150321.
32
Sedhain, Ashok. "Optical properties of ALN and deep UV photonic structures studied by photoluminescence." Diss., Kansas State University, 2011. http://hdl.handle.net/2097/8522.
Abstract:
Doctor of PhilosophyDepartment of Physics
Jingyu Lin
Time-resolved deep ultraviolet (DUV) Photoluminescence (PL) spectroscopy system has been employed to systematically monitor crystalline quality, identify the defects and impurities, and investigate the light emission mechanism in III-nitride semiconducting materials and photonic structures. A time correlated single photon counting system and streak camera with corresponding time resolutions of 20 and 2 ps, respectively, were utilized to study the carrier excitation and recombination dynamics. A closed cycle He-flow cryogenic system was employed for temperature dependent measurements. This system is able to handle sample temperatures in a wide range (from 10 to 900 K). Structural, electrical, and morphological properties of the material were monitored by x-ray diffraction (XRD), Hall-effect measurement, and atomic force microscopy (AFM), respectively. Most of the samples studied here were synthesized in our laboratory by metal organic chemical vapor deposition (MOCVD). Some samples were bulk AlN synthesized by our collaborators, which were also employed as substrates for homoepilayer growth. High quality AlN epilayers with (0002) XRD linewidth as narrow as 50 arcsec and screw type dislocation density as low as 5x10[superscript]6 cm[superscript]-2 were grown on sapphire substrates. Free exciton transitions related to all valence bands (A, B, and C) were observed in AlN directly by PL, which allowed the evaluation of crystal field (Δ[subscript]CF) and spin-orbit (Δ[subscript]SO) splitting parameters exerimentally. Large negative Δ[subscript]CF and, consequently, the difficulties of light extraction from AlN and Al-rich AlGaN based emitters due to their unique optical polarization properties have been further confirmed with these new experimental data. Due to the ionic nature of III-nitrides, exciton-LO phonon Frohlich interaction is strong in these materials, which is manifested by the appearance of phonon replicas accompanying the excitonic emission lines in their PL spectra. The strength of the exciton-phonon interactions in AlN has been investigated by measuring the Huang-Rhys factor. It compares the intensity of the zero phonon (exciton emission) line relative to its phonon replica. AlN bulk single crystals, being promising native substrate for growing nitride based high quality device structures with much lower dislocation densities (<10[superscript]4 cm[superscript]-2), are also expected to be transparent in visible to UV region. However, available bulk AlN crystals always appear with an undesirable yellow or dark color. The mechanism of such undesired coloration has been investigated. MOCVD was utilized to deposit ~0.5 μm thick AlN layer on top of bulk crystal. The band gap of strain free AlN homoepilayers was 6.100 eV, which is ~30 meV lower compared to hetero-epitaxial layers on sapphire possessing compressive strain. Impurity incorporation was much lower in non-polar m-plane growth mode and the detected PL signal at 10 K was about an order of magnitude higher from a-plane homo-epilayers compared to that from polar c-plane epilayers. The feasibility of using Be as an alternate p-type dopant in AlN has been studied. Preliminary studies indicate that the Be acceptor level in AlN is ~330 meV, which is about 200 meV shallower than the Mg level in AlN. Understanding the optical and electronic properties of native point defects is the key to achieving good quality material and improving overall device performance. A more complete picture of optical transitions in AlN and GaN has been reported, which supplements the understanding of impurity transitions in AlGaN alloys described in previous reports.
33
Sheng, Yuewen. "Formation and optical properties of mixed multi-layered heterostructures based on all two-dimensional materials." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:d5fcf1b1-f379-43e3-afbb-619569d72c3f.
Abstract:
The production of large area, high quality two-dimensional (2D) materials using chemical vapour deposition (CVD) has been an important and difficult topic in contemporary materials science research, after the discovery of the diverse and extraordinary properties exhibited by these materials. This thesis mainly focuses on the CVD synthesis of two 2D materials; bilayer graphene and monolayer tungsten disulphide (WS2). Various factors influencing the growth of each material were studied in order to understand how they affect the quality, uniformity, and size of the 2D films produced. Following this, these materials were combined to fabricate 2D vertical heterostructures, which were then spectroscopically examined and characterised. By conducting ambient pressure CVD growth with a flat support, it was found that high uniform bilayer graphene could be grown on the centimetre scale. The flat support provides for the consistent delivery of precursor to the copper catalyst for graphene growth. These results provide important insights not only into the upscaling of CVD methods for growing large area, high quality graphene and but also in how to transfer the product onto flexible substrates for potential applications as a transparent conducting electrode. Monolayer WS2 is of interest for use in optoelectronic devices due to its direct bandgap and high photoluminescence (PL) intensity. This thesis shows how the controlled addition of hydrogen into the CVD growth of WS2 can lead to separately distributed domains or centimetre scale continuous monolayer films at ambient pressure without the need for seed molecules, specially prepared substrates or low pressure vacuum systems. This CVD reaction is simple and efficient, ideal for mass-production of large area monolayer WS2. Subsequent studies showed that hexagonal domains of monolayer WS2 can have discrete segmentation in their PL emission intensity, forming symmetric patterns with alternating bright and dark regions. Analysis of the PL spectra shows differences in the exciton to trion ratio, indicating variations in the exciton recombination dynamics. These results provide important insights into the spatially varying properties of these CVD-grown TMDs materials, which may be important for their effective implementation in fast photo sensors and optical switches. Finally, by introducing a novel non-aqueous transfer method, it was possible to create vertical stacks of mixed 2D layers containing a strained monolayer of WS2, boron nitride, and graphene. Stronger interactions between WS2 on graphene was found when swapping water for IPA, likely resulting from reduced contamination between the layers associated with aqueous impurities. This transfer method is suitable for layer by layer control of 2D material vertical stacks and is shown to be possible for all CVD grown samples, a result which opens up pathways for the rapid large scale fabrication of vertical heterostructure systems with large area coverage and controllable thickness on the atomic level.
34
Lombardo, David. "Accurate Determination of Nonlinear Optical Properties of Cadmium Magnesium Telluride." University of Dayton / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1429272337.
35
Kennemore, Charles Milton III. "The effects of ion-assisted deposition on the mechanical, physical, chemical and optical properties of magnesium fluoride thin films." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185917.
Abstract:
This dissertation investigates the results of ion assisted deposition (IAD) on various properties of magnesium fluoride thin films deposited on room temperature substrates. MgF₂ films deposited in this manner have increased abrasion resistance and increased adhesion comparable to that found in films deposited at the usual substrate temperature of approximately 300°C. IAD tends to drive the normal high tensile stress of non-IAD films to a more compressive state thereby reducing the overall stress. The IAD MgF₂ films have a higher index of refraction than non-IAD films, as high as 1.41, and the ultraviolet absorption edge in shifted to longer wavelengths beginning about 350 nm but no detectable absorption at visible wavelengths is seen in the films deposited with less than 250 eV bombardment energies. However, at higher IAD energies beginning at approximately 600 eV an absorption band is present in the red end of the visible spectrum making low energy bombardment the parameter of choice. Transmission electron microscopy and X-ray diffraction studies show that the IAD films have a more amorphous-like structure with fewer and smaller crystallites than non-IAD films deposited on either heated or unheated substrates. Rutherford backscattering spectroscopy (RBS) shows the bombarded films have fluorine depletion that roughly scales with the energy of bombardment with F:Mg ratios as low as 1.69 being found. Bombardment by fluorinated compounds, specifically C₂F₆ and SF₆, limit this depletion and in some instances super fluorinate the resulting compound. Additionally, RBS shows that IAD introduces a significant amount of oxygen throughout the film that is unaccountable as water take-up. X-ray photoelectron spectroscopy (XPS) indicates the presence of two compounds of oxygen that are attributed to MgO and Mg(OH)₂ or some oxy-fluoride complex similar to them and it is the introduction of these compounds which provide for the changes in the properties of IAD MgF₂ as compared to non-IAD films of MgF₂.
36
Mikhail, Sarah Shawky. "Optical Properties of Two Brands of Composite Restorative Materials and Confirmation of Theoretical Predictions for Layering." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1316436113.
37
Kidd, Ian V. "Object Dependent Properties of Multicomponent Acrylic Systems." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1404912862.
38
Montgomery, Patrick D. "MAGNETO-OPTICAL PROPERTIES OF THIN PERMALLOY FILMS: A STUDY OF THE MAGNETO-OPTICAL GENERATION OF LIGHT CARRYING ANGULAR MOMENTUM." UKnowledge, 2018. https://uknowledge.uky.edu/ece_etds/126.
Abstract:
Magneto-optical materials such as permalloy can be used to create artificial spin- ice (ASI) lattices with antiferromagnetic ordering. Magneto-optical materials used to create diffraction lattices are known to exhibit magnetic scattering at the half- order Bragg peak while in the ground state. The significant drawbacks of studying the magneto-optical generation of OAM using x-rays are cost, time, and access to proper equipment. In this work, it is shown that the possibility of studying OAM and magneto-optical materials in the spectrum of visible light at or around 2 eV is viable. Using spectroscopic ellipsometry it is possible to detect a change in the magnetization of thin permalloy films with thicknesses between 5 and 20 nm. Patterns consistent with OAM were found at 1.95 eV using a square lattice with a 4𝜋 radial phase shift in the antiferromagnetic ground state. Evidence of magnetic scattering at the half-order Bragg peak using 1.95 eV was also found.
39
Ma, Yingfang. "Electronic Structure, Optical Properties and Long-Range-Interaction Driven Mesoscale Assembly." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1497049273517057.
40
Ugolini, Cristofer Russell. "Optical and structural properties of Er-doped GaN/InGaN materials and devices synthesized by metal organic chemical vapor deposition." Diss., Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/1021.
41
Wagner, Michael Christopher. "An Investigation of the Optical and Physical Properties of Lead Magnesium Niobate-Lead Titanate Ceramic." University of Dayton / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1608306745644145.
42
Alam, Mohammad. "High performance magneto-optic garnet materials for integrated optics and photonics." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2012. https://ro.ecu.edu.au/theses/528.
Abstract:
This work explores the preparation, characteristics and properties of highly bismuth (Bi) substituted, metal doped, iron garnet compounds and investigates their potential for various emerging applications in the visible and near infrared spectral regions.
Bi-substituted iron garnet and garnet-oxide nanocomposite films of generic composition type (Bi, Dy/Lu)3(Fe, Ga/Al)5O12 are prepared by using a radio frequency (RF) magnetron sputtering technique. The physical properties (crystallinity, film morphology, optical absorption spectra across the visible spectral range and the elemental composition of layers), and magneto-optic behaviour (Faraday rotation, hysteresis loops of Faraday rotation, and magnetic switching behaviour) of these sputtered garnet films are investigated in this work. These garnet materials possess high quality nanocrystalline thin-film microstructures and demonstrate excellent combination of optical and magneto-optical (MO) properties which makes them very attractive for use in magneto-optical applications. Record-high MO performance, in terms of the material’s MO figures of merit achieved (which exceeded most or all of the values reported previously for any semi-transparent MO materials across most of the visible spectrum), is achieved simultaneously with high Faraday rotation, making them suitable for a wide range of applications in integrated optics and photonics. The effects of annealing on the garnets of type (Bi,Dy)3(Fe,Ga)5O12, when performed in air atmosphere, are investigated and a systematic study is conducted to figure out the annealing behaviour and the crystallization kinetics of garnet formation within the garnet-bismuth oxide nanocomposites. Also, several nano-engineered magnetooptically active heterostructures (all-garnet multilayer-type thin film structures) based on magnetic layers with dissimilar uniaxial (Ku > 0) and in-plane (Ku < 0) magnetic anisotropies are prepared with the purpose of achieving the customised magnetic behaviour and properties (not attainable in single garnet layers) which are very attractive for the development of MO sensing devices and ultra-fast switches.
43
Li, Donghui. "Lifetime and Degradation Studies of Poly (Methyl Methacrylate) (PMMA) via Data-driven Methods." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1586535156011492.
44
Tang, Yiteng. "Exciton Physics of Colloidal Nanostructures and Metal Oxides." Bowling Green State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1617121207654824.
45
Lambert, Henry A. R. "Electronic excitations in semiconductors and insulators using the Sternheimer-GW method." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:eb6210c9-e0cc-45e8-93eb-719bdcc83857.
Abstract:
In this thesis we describe the extension and implementation of the Sternheimer- GW method to a first-principles pseudopotential framework based on a planewaves basis. The Sternheimer-GW method consists of calculating the GW self-energy operator without resorting to the standard expansion over unoccupied Kohn- Sham electronic states. The Green's function is calculated by solving linear systems for frequencies along the real axis. The screened Coulomb interaction is calculated for frequencies along the imaginary axis using the Sternheimer equa- tion, and analytically continued to the real axis. We exploit novel techniques for generating the frequency dependence of these operators, and discuss the imple- mentation and efficiency of the methodology. We benchmark our implementation by performing quasiparticle calculations on common insulators and semiconductors, including Si, diamond, LiCl, and SiC. Our calculated quasiparticle energies are in good agreement with the results of fully-converged calculations based on the standard sum-over-states approach and experimental data. We exploit the methodology to calculate the spectral func- tions for silicon and diamond and discuss quasiparticle lifetimes and plasmaronic features in these materials. We also exploit the methodology to perform quasiparticle calculations on the 2-dimensional transition metal dichalcogenide system molybdenum disulfide (MoS2). We compare the quasiparticle properties for bulk and monolayer MoS2 , and identify significant corrections at the GW level to the LDA bandstructure of these materials. We also discuss changes in the frequency dependence of the electronic screening in the bulk and monolayer systems and relate these changes to the quasiparticle lifetimes and spectral functions in the two limits.
46
Larsson, Arvid. "Optical spectroscopy of InGaAs quantum dots." Doctoral thesis, Linköpings universitet, Halvledarmaterial, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-64707.
Abstract:
The work presented in this thesis deals with optical studies of semiconductor quantum dots (QDs) in the InGaAs material system. It is shown that for self-assembled InAs QDs, the interaction with the surrounding GaAs barrier and the InAs wetting layer (WL) in particular, has a very large impact on their optical properties. The ability to control the charge state of individual QDs is demonstrated and attributed to a modulation in the carrier transport dynamics in the WL. After photo-excitation of carriers (electrons and holes) in the barrier, they will migrate in the sample and with a certain probability become captured into a QD. During this migration, the carriers can be affected by exerting them to an external magnetic field or by altering the temperature. An external magnetic field applied perpendicular to the carrier transport direction will lead to a decrease in the carrier drift velocity since their trajectories are bent, and at sufficiently high field strength become circular. In turn, this decreases the probability for the carriers to reach the QD since the probability for the carriers to get trapped in WL localizing potentials increases. An elevated temperature leads to an increased escape rate out of these potentials and again increases the flow of carriers towards the QD. These effects have significantly different strengths for electrons and holes due to the large difference in their respective masses and therefore it constitutes a way to control the supply of charges to the QD. Another effect of the different capture probabilities for electrons and holes into a QD that is explored is the ability to achieve spin polarization of the neutral exciton (X0). It has been concluded frequently in the literature that X0 cannot maintain its spin without application of an external magnetic field, due to the anisotropic electron – hole exchange interaction (AEI). In our studies, we show that at certain excitation conditions, the AEI can be by-passed since an electron is captured faster than a hole into a QD. The result is that the electron will populate the QD solely for a certain time window, before the hole is captured. During this time window and at polarized excitation, which creates spin polarized carriers, the electron can polarize the QD nuclei. In this way, a nuclear magnetic field is built up with a magnitude as high as ~ 1.5 T. This field will stabilize the X0 spin in a similar manner as an external magnetic field would. The build-up time for this nuclear field was determined to be ~ 10 ms and the polarization degree achieved for X0 is ~ 60 %. In contrast to the case of X0, the AEI is naturally cancelled for the negatively charged exciton (X-) and the positively charged exciton (X+) complexes. This is due to the fact that the electron (hole) spin is paired off in case of X- (X+). Accordingly, an even higher polarization degree (~ 73 %) is measured for the positively charged exciton. In a different study, pyramidal QD structures were employed. In contrast to fabrication of self-assembled QDs, the position of QDs can be controlled in these samples as they are grown in inverted pyramids that are etched into a substrate. After sample processing, the result is free-standing AlGaAs pyramids with InGaAs QDs inside. Due to the pyramidal shape of these structures, the light extraction is considerably enhanced which opens up possibilities to study processes un-resolvable in self-assembled QDs. This has allowed studies of Auger-like shake-up processes of holes in single QDs. Normally, after radiative recombination of X+, the QD is populated with a ground state hole. However, at recombination, a fraction of the energy can be transferred to the hole so that it afterwards occupies an excited state instead. This process is detected experimentally as a red-shifted luminescence satellite peak with an intensity on the order of ~ 1/1000 of the main X+ peak intensity. The identification of the satellite peak is based on its intensity correlation with the X+ peak, photoluminescence excitation measurements and on magnetic field measurements.Arbetet som presenteras i denna avhandling rör studier av kvantprickars optiska egenskaper. En kvantprick är en halvledarkristall som endast är några tiotals nanometer stor. Den ligger oftast inbäddad inuti en större kristall av ett annat halvledarmaterial och pga. den begränsade storleken får en kvantprick mycket speciella egenskaper. Bland annat så kommer elektronerna i en kvantprick endast att kunna anta vissa diskreta energinivåer liknande situationen för elektronerna i en atom. Följaktligen kallas kvantprickar ofta för artificiella atomer. För halvledarmaterial gäller det generellt att det inte endast är fria elektroner i ledningsbandet, som kan leda ström utan även tomma elektrontillstånd i valensbandet, vilka uppträder som positivt laddade partiklar, kan leda ström. Dessa kallas kort och gott för hål. I en kvantprick har hålen såsom elektronerna helt diskreta energinivåer. Precis som är fallet i en atom, så kommer elektroniska övergångar mellan olika energinivåer i en kvantprick att resultera i att ljus emitteras. Energin (dvs. våglängden alt. färgen) för detta ljus bestäms av hur energinivåerna i kvantpricken ligger, för elektronerna och hålen, och genom att analysera ljuset kan man således studera kvantprickens egenskaper. Studierna i den här avhandlingen visar att växelverkan mellan en kvantprick och den omgivande kristallen, som den ligger inbäddad i, har stor inverkan på kvantprickens optiska egenskaper. T.ex. visas att man kan kontrollera antalet elektroner, som kommer att finnas i kvantpricken genom att modifiera hur elektronerna kan röra sig i omgivningen. Dessa rörelser modifieras här genom att variera temperaturen och genom att lägga på ett magnetiskt fält. Ett magnetiskt fält, vinkelrätt mot en elektrons rörelse, kommer att böja av dess bana och dess chans att nå fram till kvantpricken kan således minskas. Elektronen kan då istället fastna i andra potentialgropar i kvantprickens närhet. Genom att öka temperaturen, vilket ger elektronerna större energi, kan deras chans att nå fram till kvantpricken å andra sidan öka. En annan effekt, som studerats, är möjligheten att kontrollera spinnet hos elektronerna i en kvantprick. Även i dessa studier visar det sig att växelverkan med omgivningen spelar stor roll och kan användas till att kontrollera elektronens spin. Mekanismen som föreslås är att om elektronerna hinner före hålen till kvantpricken, så hinner de överföra sitt spin till atomkärnorna i kvantpricken. På detta sätt kan man få atomkärnornas spin polariserat, vilket resulterar i ett inbyggt magnetfält, i storleksordningen 1.5 Tesla, som i sin tur hjälper till att upprätthålla en hög grad av spinpolarisering även hos elektronerna. För att få elektronerna att hinna först, måste deras rörelser i omgivningen kontrolleras. I en ytterligare studie undersöktes den process där en elektronisk övergång i kvantpricken inte enbart resulterar i emission av ljus, utan även i att en annan partikel tar över en del av energin och blir exciterad. Dessa processer avspeglas i att en del av det ljus som emitteras har lägre energi. Detta ljus är också mycket svagt, ca 1000 ggr lägre intensitet, och möjligheten att kunna mäta detta är helt beroende på hur ljusstarka kvantprickarna är. De prover som använts i denna studie består av pyramidstrukturer, ca 7.5 mikrometer stora, med kvantprickar inuti. Denna geometri ger ca 1000 ggr bättre ljusutbyte jämfört med traditionella strukturer, vilket möjliggjort studien.
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Dryden, Daniel M. "Long-Range Interactions in Biomolecular-Inorganic Assemblies." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1405078771.
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Rybka, Marcin. "Optical properties of MAX-phase materials." Thesis, Linköping University, Applied Optics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-60008.
Abstract:
MAX-phase materials are a new type of material class. These materials are potentiallyt echnologically important as they show unique physical properties due to the combination of metals and ceramics. In this project, spectroscopic ellipsometry in the spectral range of 0.06 eV –6.0 eV was used to probe the linear optical response of MAX-phases in terms of the complexd dielectric function ε(ω) = ε1(ω) + iε2(ω). Measured data were fit to theoretical models using the Lorentz and generalized oscillator models. Data from seven different samples of MAX-phase materials were obtained using two ellipsometers. Each sample dielectric function was determined, including their infrared spectrum.
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Zhang, Qinglin. "IMPROVING THE CAPACITY, DURABILITY AND STABILITY OF LITHIUM-ION BATTERIES BY INTERPHASE ENGINEERING." UKnowledge, 2016. http://uknowledge.uky.edu/cme_etds/60.
Abstract:
This dissertation is focus on the study of solid-electrolyte interphases (SEIs) on advanced lithium ion battery (LIB) anodes. The purposes of this dissertation are to a) develop a methodology to study the properties of SEIs; and b) provide guidelines for designing engineered SEIs. The general knowledge gained through this research will be beneficial for the entire battery research community.
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Arthington, Matthew Reginald. "Photogrammetric techniques for characterisation of anisotropic mechanical properties of Ti-6Al-4V." Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:51e4f4d9-75e2-4784-9fbf-103d07496e23.
Abstract:
The principal aims of this research have been the development of photogrammetric techniques for the measurement of anisotropic deformation in uniaxially loaded cylindrical specimens. This has been achieved through the use of calibrated cameras and the application of edge detection and multiple view geometry. The techniques have been demonstrated at quasi-static strain rates, 10^-3 s^-1, using a screw-driven loading device and high strain rates, 10^3 s^-1, using Split Hopkinson Bars. The materials that have been measured using the technique are nearlyisotropic steel, anisotropic cross-rolled Ti-6Al-4V and anisotropic clock-rolled commercially pure Zr. These techniques allow the surface shapes of specimens that deform elliptically to be completely tracked and measured in situ during loading. This has allowed the measurement of properties that could not have been recorded before, including true direct stress and the ratio of transverse strains in principal material directions, at quasi-static and elevated strain rates, in tension and compression. The techniques have been validated by measuring elliptical prisms of various aspect ratios and independently measuring interrupted specimens using a coordinate measurement machine. A secondary aim of this research has been to improve the characterisation of the anisotropic mechanical properties of cross-rolled Ti-6Al-4V using the techniques developed. In particular, the uniaxial yield stresses, hardening properties and the associated anisotropic deformation behaviour along the principal material directions, have all been recorded in detail not seen before. Significant findings include: higher yield stresses in-plane than in the through-thickness direction in both tension and compression, and the near transverse-isotropy of the through-thickness direction for loading conditions other than quasi-static tension, where significant anisotropy was observed.