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Mahanama, G. D. K. "Low temperature processing of crystalline silicon solar cells." Thesis, London South Bank University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435235.
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Briseno, Murguia Silvia. "Processing of NiTi Shape Memory Alloys through Low Pressure and Low Temperature Hydrogen Charging." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1157656/.
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Many industries including the medical, aerospace, and automobile industries have increasingly adopted the use of shape memory alloys (SMAs) for a plethora of applications due to their unique thermomechanical properties. From the commercially available SMAs in the market, binary NiTi SMAs have shown the most desirable properties. However, SMA properties can be significantly affected by the fabrication process. One of the most familiar applications of NiTi SMAs is in the design of actuating devices where the shape memory effect properties are highly advantageous. Spring NiTi SMA actuators are among the most commonly used and are generally made by torsion loading a straight wire. Consequently, stress concentrations are formed causing a reduction in recovery force. Other methods for producing springs and other NiTi SMA components is the fast emerging manufacturing method of additive manufacturing (AM). AM often uses metal powders to produce the near-net shape components. A major challenge for SMAs, in particular, is their well-known composition sensitivity. Therefore, it is critical to control composition in NiTi SMAs. In this thesis, a novel method for processing NiTi SMAs for pre-alloyed NiTi SMA powders and springs is presented. A low pressure and low temperature hydriding-pulverization-dehydriding method is used for preparing the pre-alloyed NiTi SMA powders with well-controlled compositions, size, and size distributions from wires. By hydrogen charging as-drawn martensitic NiTi SMA wires in a heated H3PO4 solution, pulverizing, and dehydriding, pre-alloyed NiTi powders of various well-controlled sizes are produced. In addition, a low pressure and low temperature hydriding-dehydriding method is used for producing NiTi SMA helixes from wires. The helix pattern in the pre-alloyed NiTi SMA wires was obtained by hydrogen charging NiTi SMA 500 μm diameter wires at different time intervals, followed by dehydriding to remove the hydrogen. The wires, powders, and resulting helixes were characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and x-ray diffraction (XRD). The relationship between the wire diameter, powder particle size, and helix geometry as a function of hydrogen charging time is investigated. Lastly, the recovery behavior due to the shape memory effect is also investigated after dehydriding.
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Juodawlkis, Paul W. "Low-temperature-grown InGaAs quantum wells for optical device applications." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/13752.
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González-León, Juan A. (Juan Antonio). "Low temperature processing of baroplastic core-shell nanoparticles and block copolymers." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/36202.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, February 2006.Includes bibliographical references (p. 131-144).
Baroplastics are nanophase polymeric materials comprised of two components that can miscibilize under pressure thereby facilitating flow. The possibility of processing these materials at low temperatures was the main focus of this work. Block copolymer baroplastics comprised of a low Tg and a high Tg component that microphase separate, such as polystyrene-block-poly(butyl acrylate) (PS-b-PBA) and polystyrene-b-poly(2-ethyl hexylacrylate) (PS-b-PEHA), were synthesized by ATRP and processed at reduced temperatures by compression molding. The resulting processed specimens were clear and well-defined solid objects. Structural characterization studies on the processed baroplastics showed that the mixing between components during processing is incomplete and distinct hard and soft domains are present even after multiple processing cycles. This suggests that the processing is of a semi-solid nature, where the rigid PS domains are mobilized by the low Tg component. Processing of a control sample exhibiting pressure-induced demixing, polystyrene-block-poly(lauryl methacrylate) (PS-b-PLMA), yielded incompletely processed objects under the same processing conditions and inferior mechanical properties to its acrylate counterparts.
(cont.) Low temperature processing of baroplastics and the proposed semi-solid processing mechanism were further demonstrated with the study of core-shell nanoparticles, where the soft homopolymer (PBA or PEHA) formed the core surrounded by a rigid PS shell. These materials could also be processed at reduced temperatures, displaying a wide range of mechanical properties as a function of their composition, going from tough and rigid materials to soft and rubbery ones comparable to commercial thermoplastic elastomers. Low temperature processing of baroplastics opens a new route to polymer processing, where energy for heating and cooling could be saved, processing times could be reduced and materials with high sensitivity to temperature could be processed.
by Juan A González-León.
Ph.D.
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Young, Avery W. "A Study on NiTiSn Low-Temperature Shape Memory Alloys and the Processing of NiTiHf High-Temperature Shape Memory Alloys." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1157642/.
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Shape memory alloys (SMAs) operating as solid-state actuators pose economic and environmental benefits to the aerospace industry due to their lightweight, compact design, which provides potential for reducing fuel emissions and overall operating cost in aeronautical equipment. Despite wide applicability, the implementation of SMA technology into aerospace-related actuator applications is hindered by harsh environmental conditions, which necessitate extremely high or low transformation temperatures. The versatility of the NiTi-based SMA system shows potential for meeting these demanding material constraints, since transformation temperatures in NiTi can be significantly raised or lowered with ternary alloying elements and/or Ni:Ti ratio adjustments. In this thesis, the expansive transformation capabilities of the NiTi-based SMA system are demonstrated with a low and high-temperature NiTi-based SMA; each encompassing different stages of the SMA development process. First, exploratory work on the NiTiSn SMA system is presented. The viability of NiTiSn alloys as low-temperature SMAs (LTSMAs) was investigated over the course of five alloy heats. The site preference of Sn in near-equiatomic NiTi was examined along with the effects of solution annealing, Ni:Ti ratio adjustments, and precipitation strengthening on the thermomechanical properties of NiTiSn LTSMAs. Second, the thermomechanical processability of NiTiHf high-temperature SMA (HTSMA) wires is presented. The evolution of various microstructural features (grain size reduction, oxide growth, and nano-precipitation) were observed at incremental stages of the hot rolling process and linked to the thermal and mechanical responses of respective HTSMA rods/wires. This work was carried out in an effort to optimize the rolling/drawing process for NiTiHf HTSMAs.
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Garlapati, Suresh [Verfasser], Horst [Akademischer Betreuer] Hahn, and Heinz von [Akademischer Betreuer] Seggern. "Low Temperature Processing of Printed Oxide Transistors / Suresh Garlapati ; Horst Hahn, Heinz von Seggern." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://d-nb.info/1126115932/34.
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Terry, Mason L. Photovoltaic & Renewable Energy Engineering UNSW. "Post???deposition processing of polycrystalline silicon thin???film solar cells on low???temperature glass superstrates." Awarded by:University of New South Wales. Photovoltaic and Renewable Energy Engineering, 2007. http://handle.unsw.edu.au/1959.4/30498.
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In polycrystalline silicon (pc-Si) thin-film solar cells, defect passivation is critical to device performance. Isoelectronic or covalently bonded impurities, hydrogenic, extended defects and defects with localized levels in the bandgap (deep level defects) are typically introduced during the fabrication of, and/or are inherent to, pc-Si thin-film solar cells. These defects dramatically affect minority carrier lifetimes. Removing and/or passivating these defects is required to maximize minority carrier lifetimes and is typically done through thermal annealing and passivation techniques. For pc-Si thin-film solar cells on low temperature glass superstrates, rapid thermal annealing (RTA) and hydrogen plasma passivation (hydrogenation) are powerful techniques to achieve effective removal and passivation of these defects. In this thesis, three silicon thin-film solar cells structures on low-temperature glass are subjected to variations in RTA high-temperature plateaus, RTA plateau times, and hydrogen plasma passivation parameters. These solar cells are referred to as ALICIA, EVA and PLASMA. By varying the RTA plateau temperature and time at plateau, the trade-off between extensive dopant diffusion and maximum defect removal is optimized. To reduce the density of point defects and to electrically activate the majority of dopants, an RTA process is shown to be essential. For all three of the thin-film solar cell structures investigated in this thesis, a shorter, higher-temperature RTA process provides the best open-circuit voltage (Voc). Extensive RTA plateau times cause excessive dopant smearing, increasing n = 2 recombination and shunt resistance losses. Hydrogenation is shown to be an essential step to achieve maximum device performance by `healing' the defects inherent to pc-Si thin-film solar cells. If the hydrogen concentration is about 1-2 times the density of oxygen in the cells as measured by secondary ion mass spectroscopy (SIMS), the cells seem to respond best to hydrogenation, with good resultant Voc and short-circuit for all cells investigated in this thesis. The effect of hydrogen passivation on the Voc is spectacular, typically increasing it by a factor of 2 to 3.5. Hydrogen de-bonding from repeated thermal treatments at increasing temperature provides a deeper understanding of what defects exist and the nature of the defects that limit the cell voltage. The variation in RTA and hydrogenation process parameters produces significant empirical insight into the effectiveness of RTA processes for point defect removal, dopant activation, point defect and grain boundary passivation, and impurity passivation. SIMS measurements are used to determine the impurities present in the cells' bulk and the amount of hydrogen available to passivate defects. From the results presented it appears that pc-Si thin-film solar cells on low-temperature glass are a promising, and potentially lower-cost, alternative to Si wafer based cells.
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Mandal, L. "High performance photo-detectors and field effect transistors based on low temperature solution processing routes." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2013. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2200.
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Zhang, Xinge. "Influence of architecture, materials, and processing on low temperature solid oxide fuel cell (LT-SOFC) performance." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/11262.
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The goal of this dissertation is to develop low temperature solid oxide fuel cells (SOFCs) through the understanding of cell material and component fabrication technology. A typical anode supported thin electrolyte cell structure has been adopted, fabricated by wet ceramic processing and co-firing. Sm₀.₂Ce₀.₈O₁.₉ (SDC) electrolyte cells supported by Ni-Y₀.₁₀Zr₀.₈₄O₁₉₂ (YSZ) cermet substrates, with Sm₀.₅Sr₀.₅CoO₃ cathode and Ni-SDC anode, demonstrate a high performance of 0.89 W cm⁻² at 600°C. A designed experiment quantitatively reveals the internal shorting problem due to the mixed ionic and electronic conductivity of the SDC electrolyte. The internal shorting current density of the thin SDC cell reaches 0.85 A cm⁻² at 600°C under open circuit voltage (OCV) conditions, which limits the fuel utilization to less than 65% and electrical efficiency to below 25%. In order to eliminate the internal shorting problem, a unique bi-layered electrolyte structure has been developed by adding a thin zirconia based electrolyte layer as an electronic blocking layer. A YSZ/SDC bi-layered electrolyte cell prepared by wet ceramic processing and co-firing generated 0.34 W cm⁻² peak power density at 650°C, with an open circuit voltage (OCV) of over 1.0V. Further improvement of the cell performance was achieved by using a Sc₀.₂Ce₀.₀₁Zr₀.₇₉O₁.₉ (SSZ)/SDC bi-layered electrolyte. The cell reached 0.50W cm⁻² at 650°C. Electrochemical impedance analysis reveals that the ionic resistance of the bi-layered electrolyte prepared by co-firing is one order of magnitude higher than the theoretical value, indicating that interaction between the two electrolytes during the co-firing is a main limit. In order to eliminate the bi-layered electrolyte interaction, pulsed laser deposition (PLD) technology is applied for the bi-layered electrolyte cell fabrication. The cell fabricated by PLD reaches power densities of 0.95 W cm⁻² at 600°C, and 1.37 W cm⁻² at 650°C with open circuit voltage (OCV) values larger than 1.02 V, the highest performance ever reported in the literature. Nonetheless, the bi-layered electrolyte cells exhibit relatively high degradation rates. A study on the degradation of bi-layered electrolyte cells indicates that the cathode degradation is the main contributor. Therefore, an optimization of cathode compositions and fabrication conditions is important to improve the cell stability.
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Zheng, Hanguang. "Processing and Properties of Die-attachment on Copper Surface by Low-temperature Sintering of Nanosilver Paste." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/42658.
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As the first level interconnection in electronic packages, chip attachment plays a key role in the total packaging process. Sintered nanosilver paste may be used as a lead-free alternative to solder for die-attachment at sintering temperature below 300 °C without applying any pressure. Typically, the substrate, such as direct bond copper (DBC) substrates, has surface metallization such as silver or gold to protect the copper surface from oxidation during the sintering process. This study focused on developing techniques for die-attachment on pure copper surface by low-temperature sintering of nanosilver paste. One of the difficulties lies in the need for oxygen to burn off the organics in the paste during sintering. However, the copper surface would oxidize, preventing the formation of a strong bond between sintered silver and copper substrate.
Two approaches were investigated to develop a feasible technique for attachment. The first approach was to reduce air pressure as a means of varying the oxygen partial pressure and the second approach was to introduce inert gas to control the sintering atmosphere. For the first method, die-shear tests showed that increasing the oxygen partial pressure (PO2) from 0.04 atm to 0.14 atm caused the bonding strength to increase but eventually decline at higher partial pressure. Scanning electron microscopy (SEM) imaging and energy dispersive spectroscopy (EDS) analysis showed that there was insufficient oxygen for complete organics burnout at low PO2 condition, while the copper surface was heavily oxidized at high PO2 levels, thus preventing strong bonding. A maximum bonding strength of about average 8 MPa was attained at about PO2 = 0.08 atm. With the second method, the die-shear strength showed a significant increase to about 24 MPa by adjusting the oxygen exposure temperature and time during sintering.
The processing conditions necessary for bonding large-area chips (6 mm à 6 mm) directly on pure copper surface by sintering nanosilver paste was also investigated. A double-print process with an applied sintering pressure of less than 5 MPa was developed. Die-shear test of the attached chips showed an average bonding strength of over 40 MPa at applied pressure of 3 MPa and over 77 MPa under 12 MPa sintering pressure. SEM imaging of the failure surface showed a much denser microstructure of sintered silver layer when pressure was applied. X-ray imaging showed a bond layer almost free of voids. Because the samples were sintered in air, the DBC surface showed some oxidation. Wirebondability test of the oxidized surface was performed with 250 μm-diameter aluminum wires wedge-bonded at different locations on the oxidized surface. Pull test results of the bonded wires showed a minimum pull-strength of 400 gram-force, exceeding the minimum of 100-gf required by the IPC-TM-650 test standard.Master of Science
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Dargan, Richard Alan. "Properties of Low-fat Yogurt Made From Ultrafiltered and Ultra-high Temperature Treated Milk." DigitalCommons@USU, 1992. https://digitalcommons.usu.edu/etd/5389.
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Yogurts were made from intermediate-high temperature (100, 110, 120, and 130°C for 4 or 16 s), ultra-high temperature (140°C for 4 or 16 s), and vat heat (82°C for 20 min) treatments of skim milk fortified to 5% protein by either ultrafiltration or the addition of nonfat dry milk (NOM). Whey protein denaturation in heated milks increased with temperature and holding time from indirect plate heating and was highest in vat-heated milks. Whey protein denaturation and yogurt water-holding capacity increased with protein levels in the fortified milks compared to skim milk. Penetrometer gel strength and stirred viscosity in 21 day-old yogurt made from heated ultrafiltered skim milk exceeded those of yogurts made from NOM-fortified skim milk, even though the NOM yogurts contained more solids (13.0 vs 11.4%). Maximum gel strength and viscosity, and least syneresis of yogurts from ultrafiltered and NOM fortified yogurts occurred following intermediate-high temperature treatments of 1 00°C for 16 s, 110°C for 4 or 16 s, and 120°C for 4 s. There was significantly lower whey protein denaturation at these intermediate-high temperatures compared to UHT or vat heating. Gel strength and viscosity were lower and syneresis greater in yogurts from ultrafiltered or NOM-fortified skim milk following UHT treatment compared to yogurts made with intermediate-high temperature treatments or vat heating. The water-holding capacity of yogurts from fortified milks treated at intermediate-high temperatures was comparable to that of yogurts from vatheated milks. Fortification by ultrafiltration, to lower total solids (and without use of stabilizers) resulted in yogurt with higher gel strength and viscosity, and reduced syneresis compared to yogurt from NOM fortification. Yogurt prepared by intermediate-high temperature treatment had comparable or better gel strength and viscosity, and reduced syneresis compared to yogurt prepared by traditional vat heating.
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Singh, Madhav [Verfasser]. "Low temperature processing and electrochemical characterization of phosphate based cathode materials and electrolytes for Li-ion batteries / Madhav Singh." Aachen : Shaker, 2012. http://d-nb.info/1066197385/34.
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Shelton, Travis Edward. "Synthesis and Characterization of Crystalline Transition Metal Dichalcogenides onto Stretchable Substrates by Laser Processing." University of Dayton / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1450405970.
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Makhdoom, Atif [Verfasser], Christoph J. [Akademischer Betreuer] Brabec, and Christoph J. [Gutachter] Brabec. "Low Temperature Processing Route of Silicon Nanoparticle Layers for Solar Cell Application / Atif Makhdoom ; Gutachter: Christoph J. Brabec ; Betreuer: Christoph J. Brabec." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2018. http://d-nb.info/1169913245/34.
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Wang, Xiaoxin. "PROCESSING AND CHARACTERIZATION OF TiB 2 -COLLOIDAL ALUMINA COATING ON CARBON CATHODE IN HALL-HEROULT CELL." University of Cincinnati / OhioLINK, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=ucin971978030.
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Bates, Griffin Michael. "Characterizing the Cold Temperature Performance of Guayule (Pathenium argetnatum) Natural Rubber and Improving Processing of Guayule and Agronomic Practices of Taraxacum kok-saghyz." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1448376403.
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Sandberg, Gary. "Thermal processing of low-acid foods with sub-zero initial temperatures." Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/30316.
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Heat penetration tests were carried out for a flaked ham product and a 40% bentonite dispersion with initial temperatures of 0°C, -5°C, -10°C, -15°C, and -20°C. The cans were processed at 124.4°C for 75 minutes in a steam retort. Data was analyzed by the general method, Ball's formula method and Stumbo's method. Thermal diffusivity and differential scanning calorimetry measurements were also made of the model food and the bentonite dispersion. From this data, a finite difference model was generated to yield an adequate thermal process time and temperature for meat products exhibiting sub-freezing initial temperatures. Substantial agreement was found between experimental cold spot temperatures within cans and cold spot temperatures calculated with the model.Land and Food Systems, Faculty of
Graduate
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Somani, Abhishek. "The responses of lager brewing yeast to low temperatures." Thesis, University of Nottingham, 2013. http://eprints.nottingham.ac.uk/28783/.
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The removal of yeast biomass (cropping) at the end of fermentation to inoculate a subsequent fermentation (serial-repitching) is common practice in the brewing industry. Between successive fermentations cropped yeast is stored as a slurry in cooled storage vessels under anaerobic conditions until required for subsequent use. Maintenance of yeast quality during storage is critical for subsequent fermentation performance. An assumption is made in brewing that all strains benefit from storage at 3-4°C. To test this assumption a model working system was initially established to assess cooling times of lager yeast in different suspension media. Preliminary investigations focussing on freshly propagated yeast slurry demonstrated that whilst the deleterious effects of extremely high storage temperatures on lager brewing yeast physiology was in line with expectation, utilization of traditionally recommended storage temperatures does not necessarily benefit yeast physiology when compared to slurry maintenance at slightly higher temperatures. Genome-scale transcriptional analysis in slurries cropped following an initial fermentation suggested that lager yeast might experience cold stress during slurry maintenance at typically recommended storage temperatures. In contrast, maintenance of lager yeast at a slightly higher storage temperature, in this case 10°C, yielded no adverse impact on key indicators of brewing yeast physiological state or on subsequent fermentation profiles following repitching into fermentations. Whilst these observations were not made using full production scale, they do indicate that optimal storage may not be currently being deployed for brewing yeast at full scale.
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Moussa, Sherif Omar Hassan. "Transient processing and characterizatin of advanced materials /." free to MU campus, to others for purchase, 2003. http://wwwlib.umi.com/cr/mo/fullcit?p3115572.
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Wang, Xingang. "Thermal strain of concrete under low temperatures and durability and Processing techniques of concrete with CNTs." Thesis, University of Colorado at Boulder, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1546581.
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This thesis consists of two topics: Thermal strain of concrete under low temperatures, and durability and processing techniques of concrete with CNTs. The low temperature test studies the anti-freezing action of concrete under cooling environment. Concrete mixes using different amounts of air-entraining agent and water/cement ratios were made and cured under different humidity environments. During the cooling process from 10 ºC to -25 ºC, the strain of concrete was measured every 3~5 ºC. The strain-temperature curve of concrete under different mixing proportion was produced from these results. A numerical model was developed based on the theory of the self-consistent model. No knowledge of real pore shapes is needed to apply in the model. The only inputs for the model came from the (Brunauer-Emmett-Teller) BET test, which gave the pore size distribution of concrete sample. The validity of the numerical model was compared to the experimental results, and showed similarity in trend and peak strain. CNT is one of the most popular topics in engineering. CNT has an extremely high strength and Young's modulus. CNT is a nano-scale material, however, and tends to clump together, which makes it difficult to apply. Other research has successfully incorporated CNT into cement paste and polymer materials. This has not yet been done into concrete. This research mainly focuses on the important factors that must be solved to adopt CNT in concrete area. An ultrasonicator was used to aid the dispersion and distribution of CNT in water, while several chemicals were also adopted for this purpose. Both strength and durability were tested for CNT concrete of different mix designs. It is suggested that ultrasonicator can improve the strength of pure CNT concrete (without chemicals) by around 100%. In addition, the sodium polyacrylate treated CNT concrete has showed best durability result and good strength result.
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Hassenforder, Philippe. "Preparation et etude de couches minces cristallines de polydiacetylenes." Paris 6, 1988. http://www.theses.fr/1988PA066289.
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Preparation des couches minces par irradiation par des electrons monocinetiques de facon a limiter la polymerisation a une epaisseur limitee dependant de l'energie des electrons. Etude par spectroscopie des proprietes specifiques (transition de phase, constantes optiques. . . ) et des defauts de surface apparaissant a partir d'un seuil d'energie d'irradiation critique qui est determine par un modele
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Francou, Mireille. "EEtude de la gravure profonde du silicium dans un réacteur haute-densité micro-onde de type propagatif." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10090.
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Dans le domaine des microtechnologies, la realisation de microcapteurs necessite la maitrise de procedes d'usinage en volume du silicium. La gravure humide, couramment utilisee connait aujourd'hui des limitations dues principalement a la difficulte de realisation de geometries particulieres. La gravure par plasma s'avere donc interessante pour outrepasser ces limitations, car elle devrait permettre une plus grande liberte quand aux geometries obtenues. Les recherches entreprises en gravure seche ont porte essentiellement sur l'optimisation de procedes pour des applications micro-electroniques. Pour une application microtechnologique, cela suppose la mise au point de procede de gravure profonde superieure a 10 microns. Le travail presente ici porte sur la mise au point d'un procede de gravure profonde du silicium par plasma, en associant l'action d'une chimie non polymerisante (sf#6, ar, o#2) conduisant a la formation d'une couche bloquante sur les flancs des tranchees, a un refroidissement a basse temperature du substrat. L'etude a ete realisee dans un reacteur surfaguide haute densite permettant de dissocier la fonction de creation de la decharge de la fonction d'acceleration des especes ionisees. Le substrat est maintenu par clampage mecanique avec injection d'helium en face arriere et refroidi par azote liquide. Dans une premiere partie, l'etude parametrique a conduit a la mise au point d'un procede de gravure anisotrope. Elle a mis en evidence que les deux parametres determinants etaient la temperature du substrat et la concentration en oxygene. Une deuxieme partie a ete consacree au choix d'un procede de gravure resultant de l'etude parametrique et de son optimisation a des profondeurs superieures a 20 microns. A travers cette etude, nous nous sommes interesses aux limites du procede telles que la profondeur de saturation, la degradation des motifs et les rugosites de surface
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Esmail, Adam Ashiq. "Charge dynamics in superconducting double dots." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/270018.
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The work presented in this thesis investigates transitions between quantum states in superconducting double dots (SDDs), a nanoscale device consisting of two aluminium superconducting islands coupled together by a Josephson junction, with each dot connected to a normal state lead. The energy landscape consists of a two level manifold of even charge parity Cooper pair states, and continuous bands corresponding to charge states with single quasiparticles in one or both islands. These devices are fabricated using shadow mask evaporation, and are measured at sub Kelvin temperatures using a dilution refrigerator. We use radio frequency reflectometry to measure quantum capacitance, which is dependent on the quantum state of the device. We measure the quantum capacitance as a function of gate voltage, and observe capacitance maxima corresponding to the Josephson coupling between even parity states. We also perform charge sensing and detect odd parity states. These measurements support the theoretical model of the energy landscape of the SDD. By measuring the quantum capacitance in the time domain, we observe random switching of capacitance between two levels. We determine this to be the stochastic breaking and recombination of single Cooper pairs. By carrying out spectroscopy of the bath responsible for the pair breaking we attribute it to black-body radiation in the cryogenic environment. We also drive the breaking process with a continuous microwave signal, and find that the rate is linearly proportional to incident power. This suggests that a single photon process is responsible, and demonstrates the potential of the SDD as a single photon microwave detector. We investigate this mechanism further, and design an experiment in which the breaking rate is enhanced when the SDD is in the antisymmetric state rather than the symmetric state. We also measure the quantum capacitance of a charge isolated double dot. We observe 2e periodicity, indicating the tunnelling of Cooper pairs and the lack of occupation of quasiparticle states. This work is relevant to the range of experiments investigating the effect of non-equilibrium quasiparticles on the operation of superconducting qubits and other superconducting devices.
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Garlapati, Suresh. "Low Temperature Processing of Printed Oxide Transistors." Phd thesis, 2017. https://tuprints.ulb.tu-darmstadt.de/5999/1/Low%20Temperature%20Processing%20of%20Printed%20Oxide%20Transistors.pdf.
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Solution processed/printed electronics have gained a lot of attention in recent years because they are inexpensive, easy to fabricate, can be produced on very large areas and on all kinds of substrates. The choice of suitable functional/active materials that can be printed is of essential for the performance of the electronic devices in printed electronics. In case of printed field-effect transistors (FETs), which are elemental building blocks of most logic circuits, the right choice of solution-processable semiconductors is the key to obtain high performance electronic devices. In this regard, inorganic oxide semiconductors are considered as a suitable material, because of their excellent electronic transport properties, i.e., high intrinsic charge carrier mobility, in combination with the high thermal and environmental stability. In the design of FETs, apart from the semiconductors, gate insulators/dielectrics play a crucial role. In the present thesis, printable composite solid polymer electrolyte (CSPE) is chosen as gate insulator due to its high capacitance (1-10 μF/cm2). Furthermore, CSPEs provide extremely conformal interfaces to the rough oxide semiconductor channel layer, which is the key for high gating efficiency and exceptional device performance.
Two different approaches, i.e., oxide precursors and nanoparticle dispersions, are used to print the semiconductor channels of FETs. The FETs are prepared from appropriate indium oxide precursors, which are annealed at different temperatures (300-500 °C) to be converted to the oxide; however, the devices need to be heated to 400 °C in order to achieve the best electrical performance characterized by a field effect mobility as high as 126 cm2/Vs and a sub-threshold slope of 68 mV/decade, which is close to the theoretical limit. Furthermore, the effect of the annealing rate on the performance of FETs has been studied. In addition to the single components (FET), complementary metal oxide semiconductor (CMOS) inverters and common source amplifiers have been prepared following a similar fabrication route using indium oxide and copper oxide precursors (annealed at 400 °C). The CMOS inverters have demonstrated a very high signal gain of 21 at 1.5 V. As a second approach and avoiding high processing temperatures, a novel chemical curing method for nanoparticles has been adopted, resulting in a field-effect mobility value of 12.5 cm2/Vs, strikingly high for a nanoparticulate channel completely processed at room temperature (RT). CMOS inverters based on chemically cured indium oxide and copper oxide nanoparticle dispersions have been prepared, which show a signal gain of 18 at 1.5 V. Another novel technique, i.e. photonic curing, has also been used to fabricate printed FETs on plastic substrates at low temperatures. Precursor-based FETs cured by UV-laser and UV-visible light demonstrate mobility values of 15 and 50 cm2/Vs, whereas nanoparticulate-based FETs by the same methods show mobilities of 12 and 8 cm2/Vs, respectively. These values in comparison with those of organic semiconductors verify the outstanding performance of FETs processed at low temperatures (in some cases, even at RT). Furthermore, the low operating voltages (≤ 2V) can be very attractive for battery compatible and portable electronic devices.
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Kwon, Do-Kyun. "Ultra-low temperature processing of barium tellurate dielectrics." 2006. http://www.etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-1148/index.html.
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Chen, Liang-Yu, and 陳良友. "Low Temperature Processing of Tellurate-Base Dielectric Ceramics." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/axrzx2.
Full textAbstract:
碩士國立臺北科技大學
材料科學與工程研究所
95
Ceramics, metals and polymers have unique electrical properties that are combined for electronic devices and systems. It necessitates lower processing temperatures for ceramics to be compatible with metal and polymer systems. Pure tellurium dioxide is well known as a networkformer in the glass industry, although pure tellurium dioxide does not form glass, even at high cooling rates. Most tellurium-based oxide materials can be synthesised and sintered at temperatures below 900oC, which makes them potential candidates for use in low-temperature-cofired-ceramics (LTCC) technology. This research divides into two parts of discussions. First part of research was probed into that the influence of dielectric characterisation of ceramics and the change of microstructure from the TiTe3O8 by adding of SiO2. Result reveal that can produce surface volatilize the phenomenon in the process of sintering at 650~750oC. The phenomenon of volatilize can be controlled by adding a few SiO2.The exaggerated grain growth during sintering ofTiTe3O8 with forming additive 1wt%SiO2. The grain size of pure TiTe3O8 is around 5μm. Grain size of the TiTe3O8 by adding of 1wt%SiO2 that grown into 50μm because the liquid phase sintering. The dielectric constant drops as SiO2 adding amount rise in electricity, and the quality factor is improved to 48000 from 25000, measured at ~7GHz. Second part of research is alkaline-earth oxide (Mg、Ca、Sr、Ba)-TeO2 system. the (Mg、Ca、Sr、Ba)-TeO2 system ceramics were prepared by a solid reaction method. In the calcining process, the compounds have an opportunity oxygen to absorb air by long calcined time. Make its compounds(Mg3TeO6/MgTe2O5、CaTeO4、SrTeO4 and BaTeO3/BaTeO4) produce different structure. The compounds were investigated its microstructure and the properties of dielectric. The above-mentioned compounds display the relative permittivity of around 10~20, the quality factor of around 1000~30000 GHz and the temperature coefficient of resonant frequency of around -9~-100ppm /℃.The compounds are sintered in the temperature range of 700 ~ 1100oC.
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Huang, Yu-Ting, and 黃郁庭. "Investigation of the low stress TEOS SiO2 films by low temperature PECVD processing." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/61098062573600876958.
Full textAbstract:
碩士國立中央大學
光電科學與工程學系
103
Tetra-ethyl-ortho-silicate (TEOS) SiO2 thin films were deposited using low temperature Plasma-enhanced chemical vapor deposition (PECVD) to achieve the performances of low stress and high density. Several process parameters including working pressure, O2 flow rate, TEOS flow rate, high and low frequency power rates, and working temperatures were adjusted to analyze the quality of the films. The results show when the deposition rate is high, the density of the film is low. And the lower density of the film will affect the lower stress. We found out the stress of TEOS SiO2 film has strong correlation by the high film density and slow deposit rates. The working pressure, O2 flow and TEOS flow rate can play important roles for the stress and density of the TEOS SiO2 films. Finally, we found out the high film density and low stress conditions keep the deposition pressure at 4torr, TEOS / O2 ratio at 8.1% and working temperature at 200 degrees. The deposition rate was about 41±2.0Å/sec. the etching rate was about 1100±55Å/sec.The stress of the SiO2 film was compressive and the stress value range was at 300±20Mpa.
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Chang, Hsuan, and 掌軒. "Fabrication of TiO2 photocatalyst films using low temperature processing methods." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/49508142029176480463.
Full textAbstract:
碩士元智大學
化學工程學系
92
High efficient TiO2 photocatalyst thin films were fabricated in this study using sol-gel method and low temperature treatments. The films were prepared by the sol-gel solution coated on glass using hot water bath, wet-air, and dry-air thermal treatment. The photocatalytic effects of operating variables, such as the temperature, time, and atmosphere of thermal treatments on the films were discussed. The material properties affecting on the photocatalytic ability of the films were measured by different analytical instruments. Results show that thermal processing methods can greatly affect the photocatalytic ability of the TiO2 films. The best quality of photocatalytic films were fabricated by wet air at 100oC. In addition, the quality of the films can not be improved using higher temperature and longer time in thermal process. The presence of PEG added in the sol-gel process was found the important factor to affect the photocatalytic effect of the films. The effects of the thermal treatments on the photocatalytic influences were discussed.
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Chen, Yu-Ru, and 陳毓儒. "Study on the Processing of Low Temperature Poly-Si Thin Film." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/44zj8t.
Full textAbstract:
碩士國立成功大學
工程科學系碩博士班
92
At present, the Laser annealing method is the most general way to fabricate the poly-Si film of low temperature for LCD industry. In this study, the working pieces primarily include a-Si film and glass substrate. The KrF excimer laser is used to irradiate the amorphous silicon film. The film melts and then solidifies rapidly as a poly-Si one. SEM is used to investigate the resulting poly-Si film. The control parameters of laser energy intensity, pulse number and coverage fraction are considered in this paper. The effects of these control parameters on the average grain size of poly-Si have been studied. The effect of SiO2 layer put between Si film and glass substrate was also investigated. From the experimental results, it can be found that if the molten pool of Si caused by laser energy doesn’t belong to “complete melt”, the more energy obtained from the laser could lead to the larger average grain size. However, if it belongs to “complete melt”, the average grain size would be much smaller than that of the former one (non-complete melt). With the increase of laser energy, the phenomenon becomes more significant.
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Chen, You Shen, and 陳宥伸. "Preparation of Perovskite Solar Cells Using Low-temperature Solution Processing techniques." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/f2tg2d.
Full textAbstract:
碩士長庚大學
光電工程研究所
104
Solar is a renewable energy, Power generation process does not produce greenhouse gases carbon dioxide emissions, for the protection of the environment is very helpful; from 2012 to the rapid progress of perovskite solar cells, compared with silicon solar cells, which have the advantages of low material cost, Preparation of solution method, low cost manufacturing process, and its photoelectric conversion efficiency of silicon solar cells is expected to catch up, many scientists have also invested in this research effort. Perovskite solar cells perovskite layer made way roughly divided into two types, one is to use the one-step production, is to methylamine iodide (MAI) with lead iodide (PbI2) both Moore and other dissolved proportion after DMF was spin-coated on a substrate; and a two-step rule is the first spin-coated on a substrate PbI2, then soaked after film or iodine drops methylamine grow perovskite crystalline; used in this experiment produced a two-step method. We found that the changed PbI2 standing time will affect their different deposition patterns, the extent of the longer standing PbI2 the aggregation of particles leading to greater perovskite crystal patterns will vary from can be observed on the XRD perovskite films of different PbI2 standing time in the (001) peak characteristic changes significantly, standing at the time when the minimum peak 150s, 150s on behalf of the use of standing time making PbI2 film with 30mg/mL of MAI has the best solution crystalline state. Our success to make efficiency of 10.57% perovskite solar cells, JSC of 16.85mA/cm2, VOC is 1.01V, F.F. of 61.9%, also after continuous measurements found in the first four days up to maximum efficiency 12.65 %. Discussion with the addition of lead iodide standing time of lead iodide with methyl iodide amine concentration both outside, in order to improve the stability of the device, we also try to join the mesoporous layer observation element of the performance, first we direct the dense layer on the ZnO production of mesoporous TiO2 layer, then a two-step method to create elements, we change the spin speed to create different mesoporous layer, only the most efficient battery JSC of 8.89mA/cm2, VOC can reach 1.04V, F.F. of 50.4% efficiency of 4.66%, showed that under these conditions we did not have better cell performance. In addition, we also try to use the TTIP and TiO2(P90) to two different solution volume ratio of production to replace the dense layer of dense ZnO layer found in full without adding TTIP conditions, cell efficiency of up to 7.94%, then this condition further change speed control different mesoporous layer film, you can then create the conditions 1500rpm efficiency of 10.39% of the element JSC up 16.82mA/cm2, VOC is 1.008V, F.F. was 61.3%.
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Nahar, Manuj 1985. "Highly conductive, nanoparticulate thick films processed at low processing temperatures." Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-08-5967.
Full textAbstract:
Applications such as device interconnects require thick, patterned films that are currently produced by screen printing pastes consisting of metallic particles and subsequently sintering the films. For Ag films, achieving adequate electrical conductivity requires sintering temperatures in excess of 700˚C. New applications require highly conductive films that can be processed at lower processing temperatures. Although sintering temperatures have been reduced by utilizing finer nanoparticles (NPs) in place of conventional micron-size particles (MPs), realization of theoretically achievable sintering kinetics is yet to be achieved. The major factors that inhibit NP sintering are 1) the presence of organic molecules on the NP surfaces, 2) the dominance of the non-densifying surface diffusion over grain boundary or lattice diffusion 3) agglomeration of NPs, and 4) low initial density of the NPs. Here, we report a film fabrication technique that is capable of eliminating these deleterious factors and produces near fully dense Ag films that exhibit an order of magnitude higher conductivity when compared to other film fabrication techniques at processing temperatures of 150 – 250 °C. The observed results establish the benefits of NP diffusion kinetics to be far more profound when the deleterious factors to sintering are eliminated. The sintering behavior exhibits two distinct temperature regimes – one above 150 ᵒC where grain boundary diffusion-dominated densification is dominant and one below 100 ᵒC where surface diffusion-dominated coarsening is dominant. An analytical model is developed by fitting the experimental data to the existing models of simultaneous densification and grain growth, and combining this model with existing models of the dependence of conductivity on grain boundary scattering and pore scattering. The combined model successfully describes the evolution of density, grain size and conductivity of nanoparticulate films as a function of annealing treatment, with reasonable accuracy. The model was also used to evaluate the effect of initial NP size and initial relative density of films on the final sintered properties and conductivity of films.text
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Yen, Fu-Cheng, and 顏福成. "Processing and Mechanical Properties of Low-Temperature Sintered Fe-P-C Alloy." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/35374116393421386497.
Full textAbstract:
碩士國立臺灣大學
材料科學與工程學研究所
94
Alloyed parts with complicated shape, smooth surface toughness and near net shape can be fabricated in metal injection molding (MIM) process. But green parts made by MIM process just have only 50-60% relative density, it is necessary to use lower than 10μm ultra fine powder as starting powder and sinter at 1200-1300℃ high temperature for 2 horses then 94% relative density can be ontained. Higher equipment cost and energy consumption followed by high temperature sintering result in lower competition for MIM process. So design alloy composition for low temperature sintering to make allying parts sinter at belt furnace with lower cost then have sintered density above 90% and good mechanical properties. It is showed that Fe-0.7P-C sintered at 1080℃ for 30mins can get the value of 7.4g/cm3 in sintered density, 800MPa in ultimate tensile strength, HRB98 in hardness, 12% in elongation in this study, that is superior to standard MIM-4605 counterpart which has better mechanical properties in MPIF. The uniform elemental distribution and ductile dimple structure can be observed by EPMA and SEM equipment even sintered at low temperature Additionally, the possibility of P content causing segregation and its mechanism were also studied in this experiment. According to the experimental results, when P content in Fe-C alloy is more than 0.7wt%, the original ductile dimple structure turning into brittle intergranular structure on fracture surface was observed. Fe-0.7-C alloy sintered at low temperature for short time has optimal mechanical properties as compared to other counterparts in this study.
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Lin, Shieh-Chieh, and 林士傑. "Deploying a On-Line Analytical Processing System of Low-Temperature Distribution Center." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/82283250122827073534.
Full textAbstract:
碩士元智大學
企業管理學系
93
This thesis is to build up an OLAP application for low-temperature distribution center. We first conducted a thorough study on the business flow of storage processing in a low-temperature logistics center. We then design the system functions, which are related to inventory flows, and create data cubes for efficient information retrieval for stock management. We finally implement a system prototype, with which users can visualize and monitor inventory flows more clearly and easily so as to help improve inventory management.
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Chae, Minjung. "Low-temperature post-harvest processing for reducing Vibrio parahaemolyticus and Vibrio vulnificus in raw oysters." Thesis, 2007. http://hdl.handle.net/1957/5705.
Full textAbstract:
Oysters are filter-feeding bivalves, which filter water for nutrients and often accumulate contaminants and human pathogens such as Vibrio parahaemolyticus and Vibrio vulnificus naturally occurring in the marine environment. These naturally occurring pathogens have been frequently isolated from raw shellfish, particularly oyster, in the United States and are recognized as the leading causes of human gastroenteritis associated with seafood consumption. Human illness caused by consumption of raw oyster contaminated with V. parahaemolyticus and Vibrio vulnificus typically results in reduced sales of oysters and a consequent significant financial burden for the producers. The United States produces more than 27 million pounds of oysters each year with a large portion of them being produced from the coastal water of the Gulf of Mexico. It is estimated that 20 million Americans eat raw shellfish and consumption of raw oyster
is responsible for about 95% of all deaths associated with seafood consumption in the U.S., making raw oysters one of the most hazardous seafoods. Several post-harvest processes, including low temperature pasteurization, freezing, high pressure processing and irradiation, have been reported capable of reducing Vibrio contamination in raw oysters. However, most of them require either a significant amount of initial investment or operation costs, and oysters are often killed during processing. Cost-effective post-harvest processing for reducing V. parahaemolyticus in raw oysters without significant adverse effects on the oysters remains to be developed. This study was conducted to determine impacts of low-temperature (15, 10 and 5°C) depuration and frozen storage on reducing V. parahaemolyticus and V. vulnificus in raw oysters. Depuration of the Gulf oyster (Crassostrea virginica) with electrolyzed oxidizing (EO) water (chlorine, 30 ppm; pH 2.82; oxidation-reduction potential, 1,131mV) containing 3% NaCl was found ineffective on reducing both V. parahaemolyticus and V. vulnificus in the oysters. Reductions of V. parahaemolyticus and V. vulnificus in oyster after 48 h of EO water depuration at 22°C were limited to 0.7 and 1.4 log MPN/g, respectively. Depuration with EO water at lower temperatures did not enhance reductions of Vibrio in the oysters. Greater reductions of V. parahaemolyticus (1.2 log MPN/g) and V. vulnificus (2.0 log MPN/g) were observed when the oysters were depurated with artificial seawater (ASW) at room temperature (22°C) for 48 h. Decreasing temperature of ASW to 15°C for depuration significantly increased the reductions of V. parahaemolyticus and V. vulnificus to 2.1 and 2.9 log MPN/g, respectively, after 48 h of process. However, depuration of oyster in ASW at 10 and 5°C were found less effective than at 15°C in reducing Vibrio in
the Gulf oysters. An extended depuration with ASW at 15°C for 96 h was capable of achieving 2.6 and 3.3 log MPN/g of reductions of V. parahaemolyticus and V. vulnificus, respectively, in the Gulf oysters. Study of effects of frozen storage at -10, -23 and -30°C on reducing V. parahaemolyticus in raw half-shell Pacific oyster (Crassostrea gigas) found that the population of the bacterium decreased faster in oysters stored at -10 than at -23 or -30°C. Holding half-shell Pacific oyster at -10°C for three months or at -23°C for four months was capable of achieving a greater than 3-log (MPN/g) reduction of V. parahaemolyticus in the Pacific oyster.Graduation date: 2008
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EL-KHAZEN, JOHN. "LOW TEMPERATURE CLEAVAGE FRACTURE OF MICROALLOYED BAINITIC PLATE STEELS." Thesis, 2009. http://hdl.handle.net/1974/2572.
Full textAbstract:
Low temperature cleavage fracture behaviour was investigated using four experimental microalloyed bainitic plate steels. The four plate samples were produced by different thermomechanical processing (TMP) schedules and had yield strengths in the range 540 - 670 MPa.
Microstructures were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD). Quantitative data was obtained for prior austenite grain (PAG) size, volume fractions of two bainite types (conventional bainite and acicular ferrite) and EBSD 15° domain size. Charpy impact tests (using two notch orientations) were carried out over a range of temperatures. Cleavage facet sizes were measured on -196°C Charpy samples.
The range of TMP schedules produced variations in PAG width, type of bainite and 15° domain size. The effects of these three microstructural features on cleavage crack propagation are discussed. Results indicate that the microstructures are controlled by i) deformation below TNR and ii) accelerated cooling rate. Domain structure reflects TMP. There is no clear correlation between domain size and cleavage facet size.Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2009-07-30 19:17:01.25
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Tung-Sheng, Lee, and 李東昇. "Low temperature processing of Metal/Ferroelectrics/Insulator/Si structures and their hysteresis loops of conduct current." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/21412083503633544758.
Full textAbstract:
碩士國立交通大學
電子工程系
90
SrBi2Ta2O9 (SBT) ferroelectric films have been demonstrated to possess the fatigue-free property to apply in the non-destructive MFISFET，but suffer from the issue of the low remanent polarization and high crystallization temperature。In this thesis，the stoichiometric SBT films prepared by using the metal-organic solution deposition (MOD) method was doped with the Bi3TiTaO3 (BTT) and Bi3TiNbO3 (BTN) for promoting the remanent polarization and achieving the goal of decreasing the process temperature below to 600℃。Moreover，the C-V measurement also reveals the broader memory widows of 1.3V as the sweep voltage in the 5V，and the leakage current density is as low as1E-8 A/ 。On the other hand，the hysteresis loop of conducting current in the MFIS structure also reveals the effect of the polarization behavior of ferroelectric film 。Furthermore，the effect of leakage current on the operation of the MFIS structure is discussed。
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Yen, Wen-shiang, and 顏文祥. "Effect of the peroxotitanic acid (PTA) on the Low-temperature paste and High-temperature processing for the performance of Dye-sensitized Solar Cells." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/95691941979759458895.
Full textAbstract:
碩士中原大學
化學研究所
99
In this study, We use titanium isopropoxide (TTIP) and hydrogen peroxide (H2O2) to prepare a gel (peroxy titanate peroxotitanic acid, PTA). The gel was used as a binder between nanoscale titanium dioxide and nano-level between FTO glass substrate titanium dioxide. In the part of low temperature paste, we use a commercially available nano-titanium dioxide (TiO2) powder (PT-501A and P90) developed a low-temperature slurry production process apply to be fexiable of dye sensitized solar cells (dye-sensitized solar cells). Then use the doctor-blade coating method of titanium dioxide film on glass and plastic substrate with conductive features. Finally, made into a solar cells. In the part of high temperature paste, we use the sol-gel process to prepare a high temperature TiO2 slurry. The solution of PTA in ethanol was sprayed between the FTO glass substrate and the nanoscale titanium dioxide as a pretreatment film. Then the slurry was screen printed above the pretreatment film on the FTO glass substrate. Finally, made into a solar cells.
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Chen, Shau-Kang, and 陳孝剛. "The Processing and the Properties of Low temperature High Strain Rate Superplastic Zn-22 wt.% Al Alloys." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/75326344349277768805.
Full textAbstract:
碩士大同工學院
材料工程研究所
87
In this study thermal and thermomechanical processings were applied to a monotectoid Zn-22 wt.% Al and a Zn-22 wt.% Al-0.1 wt.% Zr alloys to produce fine grain microstructures for low strain temperature as well as high strain rate superplasticity studies. It was observed in one-step thermal processing that aging at room temperature for a sufficient time period would produce an ultra-fine equiaxed grain mixture of α and β phases by a general precipitation reaction, having proper superplastic behaviors, and that aging at 240℃ would quickly develop a lamellar structure by a discontinuous precipitation reaction, with poor superplastic properties. Two-step aging and for-step thermomechanical processing schedules were designed in this study to produce ultrafine equiaxed grain structures for superplasticity examinations. The results showed that, among many processing routes, a specific 2-step aging process, consisted of natural aging for 2 weeks and artificial aging at 240℃ for 60 minutes, produces a proper grain structure with satisfactory low strain temperature and high strain rate superplasticity properties. Surprisingly, the superplastic properties obtained in the 4-step thermomechanical processed Zn-Al and Zn-Al-Zr alloys were found to be inferior to those in the 2-step aged alloys. A specific 2-step aging process, consisted of natural aging for 2 weeks and artificial aging at 240℃ for 60 minutes, produces a proper grain structure with satisfactory low strain temperature and high strain rate superplasticity properties. The maximum elongations obtained at 250℃ in the 2-step aged Zn-Al alloy is 1240% under an initial strain rate of 1×10-1 s-1, while the maximum elongation obtained in the 2-step aged Zn-Al-Zr alloy is 1120% under an initial strain rate of 5×10-2 s-1.
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Shye, Der-Chi, and 史德智. "Low-Temperature Processing Techniques Applied on Barium Strontium Titanate Films for the Applications of DRAM Storage Capacitors." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/85373278879314570415.
Full textAbstract:
博士國立交通大學
電子工程系所
93
The characteristics of (Ba, Sr)TiO3 thin films, prepared by novel techniques of low temperature treatments, were systematically studied in this thesis. Pt/TiN/Ti/Si substrates were applied on each sample to simulate the real capacitor over bit-line (COB) structure of dynamic random access memory (DRAM). (Ba, Sr)TiO3 (BST) films were sputtered by radio frequency (RF) magnetron system with dual targets at low substrate temperature, lower than 450oC (340oC at sample surface), and the effects of the process parameters were also investigated. The work pressure, the sputtering gun power and the gas-mixing ratio are the important parameters in the BST film deposition. Material analyses and electrical testing show that the low temperature BST films are significantly affected by those process parameters. The O2/(Ar+O2) mixing ratio (OMR) is a most critical parameter during BST film sputtering. Plasma emission spectra indicate that the deposition rate declines at a higher OMR due to oxide formation on the target surface. The dielectric constant of the BST films can reach a maximum of 364 at 5% OMR. The ten-year lifetime of the time-dependent dielectric breakdown (TDDB) implies that the reliability of the capacitor can be enhanced at a higher OMR due to the compensation of oxygen vacancies and smaller grain sizes. Current-voltage analysis indicates that the leakage current of the Pt/BST/Pt capacitor is limited by Schottky emission (SE)/Poole-Frenkel emission (PF) at a lower/higher applied field, accordingly. The applied field boundary between SE and PF shifts toward higher field as OMR increases. Moreover, an energy-band model was proposed and this leakage mechanism was also discussed. Post low-temperature treatments were applied on the BST films to further improve their crystallinities and electrical properties. A novel process, KrF excimer laser annealing (ELA) at the wavelength of 248 nm, had been undertaken to implement BST films at a process temperature of 300o C to avoid the steep thermal gradient in thin films. The dielectric constant of the amorphous (α) BST film was remarkably enhanced from 80 to over 250 after ELA treatment. The optical testing and the heat conduction analyses indicate that the underlayer films and devices cannot be damaged during ELA treatment due to a very shallow light absorption depth (20 nm) of the BST film at the wavelength of 248-nm. Besides, the laser energy fluence and film thickness greatly influence the thermal conduction and the temperature distribution within the BST films. In the meanwhile, the as-deposited films revealed (mm0) preferred orientation, and, intriguingly, the preferred orientations changed into (m00) and (mmm) after ELA treatments. The optical and the high frequency properties may be affected by this preferred-orientation change. However, although the ELA can perform “shallow-depth annealing” for BST thin film, the degradation of upper surface is strongly influenced by the laser energy fluence. Hence, the leakage current will be significantly affected by the energy fluence of the laser. The leakage current of the ferroelectric film increases after sputtering process and post ELA treatment, but post oxygen plasma treatment can effectively improve the BST film surface to suppress the leakage at low processing temperature of 250oC. According to the analysis results in this thesis, the oxygen plasma treatment can effectively passivate the oxygen vacancies of BST films, decreasing the leakage currents. The leakage current can be reduced as many as two orders of magnitude under proper control of plasma conditions. The characteristics of the dielectric reliability, TDDB, can be also improved by this treatment due to the compensation of the surface oxygen vacancies. In addition, a nano-scaled chromium (Cr) layer is applied onto (Ba, Sr)TiO3 (BST) thin film capacitor as an inter-layer to enhance thermal stability of capacitance and suppress leakage current. Temperature coefficient of capacitance (TCC) using this BST/Cr/BST (200nm/2nm/200nm) multifilm can achieve 30% lower than that using BST mono-layer (400nm) film. Besides, the leakage current can be also greatly suppressed by applying this nano-scaled Cr layer onto BST thin film capacitor. TCC and leakage current behave as functions of Cr thickness, so the optimal properties can be obtained with the Cr thickness of 2nm. Microstructure analysis suggests that the interfacial continuity strongly influences the TCC and leakage property due to scattering centers and series capacitance formed at imperfect interface. The correlated mechanisms between electric and material properties are systematically investigated in this work. BST thin film can be the most promising candidate for Giga-bit generation cell capacitor, because the low temperature processes can be compatible to the IC’s integration. In this thesis, the optimal properties of the BST films can be obtained by adjusting process parameter, applying post treatments and using thermal stabilization structures to achieve thorough low-temperature processes.
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Wang, Mu-Shiun, and 王睦勛. "Reduction of low-temperature induced defects in yellow-green AlGaInP light emitting diodes by post-growth processing." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/65118460336893216977.
Full textAbstract:
碩士義守大學
電子工程學系碩士班
96
The improved lifetime in AlGaInP yellow-green light-emitting diodes (YG-LEDs) for low temperature operation by different chip process technologies are reported. For conventional YG-LEDs, light intensity decayed 23% under 20-mA injection current after 20-h testing at ambient temperature of -40℃. By employ different chip process technologies, the light intensity of YG-LEDs decayed within 15% after 160-h testing. The improvement of lifetime characteristic can be attributed to reduced quantity of defects in YG-LEDs. The detail process technologies for improve lifetime in YG-LEDs will be described in this thesis.
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Chan, Cheng Tsung, and 鄭宗展. "The Studies of Low Temperature Ploy-Silicon Processing Issue and Thin-Film Grating for Solar Cell Performance Improvement." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/17418528235411953331.
Full textAbstract:
博士南台科技大學
電子工程系
95
This paper is mainly discussing two topics: to improve the method of Low Temperature Ploy-Silicon and enhance the amount of power transforming to efficiency in solar cell. In the part of Low Temperature Ploy-Silicon.The feasibility to transform LPCVD a-Si into Poly-Si by using excimer laser annealing has been approved. More discussion and study on how to make optimization on Poly-Si are also proceeding. Excimer laser annealing (ELA) amorphous silicon (a-Si) to poly-silicon (poly-Si) in different gas environment is studied, i.e. N2 or N2 mixed O2:2%, Influence of laser power on the surface morphology, grain size and height of gibbous grain is investigated. The variation of threshold laser power for the generation of surface ablation in N2 and N2:98% mixed O2:2% environment is also discussed. From experiment, it is found that the combination of O2:2% enhance the threshold laser power for the generation of surface ablation from 320mJ/cm2 to 390mJ/cm2. In the condition of average grain over 0.25um, the process window is 30mJ/cm2 for N2, but is 50mJ/cm2 for N2 mixed O2:2% environment. In the part of improve the power conversion efficiency of solar energy by using the reflection character of grating. Under normal sunlight, light albedo of silicon surface falls between 30% ~ 35%, we can improve the battery power for solar energy by using 30%~35% reflection light. Therefore, the study of this thesis is to use high polymer diffraction grating mold on solar plates by coating with a layer of 212.24 nm depth , 0.52μm circle and grating of 5.9% albedo used for improve the light receiving of solar battery and further enhance the power conversion efficiency.
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Urrutia, Benet Gabriel [Verfasser]. "High-pressure low-temperature processing of foods: impact of metastable phases on process and quality parameters / Gabriel Urrutia Benet." 2005. http://d-nb.info/978127013/34.
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"Novel Low Temperature Processing for Enhanced Properties of Ion Implanted Thin Films and Amorphous Mixed Oxide Thin Film Transistors." Doctoral diss., 2013. http://hdl.handle.net/2286/R.I.17989.
Full textAbstract:
abstract: This research emphasizes the use of low energy and low temperature post processing to improve the performance and lifetime of thin films and thin film transistors, by applying the fundamentals of interaction of materials with conductive heating and electromagnetic radiation. Single frequency microwave anneal is used to rapidly recrystallize the damage induced during ion implantation in Si substrates. Volumetric heating of the sample in the presence of the microwave field facilitates quick absorption of radiation to promote recrystallization at the amorphous-crystalline interface, apart from electrical activation of the dopants due to relocation to the substitutional sites. Structural and electrical characterization confirm recrystallization of heavily implanted Si within 40 seconds anneal time with minimum dopant diffusion compared to rapid thermal annealed samples. The use of microwave anneal to improve performance of multilayer thin film devices, e.g. thin film transistors (TFTs) requires extensive study of interaction of individual layers with electromagnetic radiation. This issue has been addressed by developing detail understanding of thin films and interfaces in TFTs by studying reliability and failure mechanisms upon extensive stress test. Electrical and ambient stresses such as illumination, thermal, and mechanical stresses are inflicted on the mixed oxide based thin film transistors, which are explored due to high mobilities of the mixed oxide (indium zinc oxide, indium gallium zinc oxide) channel layer material. Semiconductor parameter analyzer is employed to extract transfer characteristics, useful to derive mobility, subthreshold, and threshold voltage parameters of the transistors. Low temperature post processing anneals compatible with polymer substrates are performed in several ambients (oxygen, forming gas and vacuum) at 150 °C as a preliminary step. The analysis of the results pre and post low temperature anneals using device physics fundamentals assists in categorizing defects leading to failure/degradation as: oxygen vacancies, thermally activated defects within the bandgap, channel-dielectric interface defects, and acceptor-like or donor-like trap states. Microwave anneal has been confirmed to enhance the quality of thin films, however future work entails extending the use of electromagnetic radiation in controlled ambient to facilitate quick post fabrication anneal to improve the functionality and lifetime of these low temperature fabricated TFTs.Dissertation/Thesis
Ph.D. Materials Science and Engineering 2013
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Liau, Jing-Ti, and 廖景義. "Kinetic Analysis of Thermal degradation of Poly(vinyl butyral)/Glass Ceramic/Ag in Low Temperature Co-fired Ceramic processing." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/15164140677399520374.
Full textAbstract:
碩士元智大學
化學工程學系
91
Kinetic analysis of thermal degradation of poly(vinyl butyral) (PVB), PVB/glass ceramic, PVB/Ag and PVB/glass ceramic/Ag was investigated in different environment. Dynamic data of the PVB thermal degradation were detected and utilized for the kinetic analysis by thermogravimetry (TG) and Fourier-Transform Infrared (FT-IR) measurements. Results of the kinetic analysis revealed that PVB thermal degradation was little affected by the presence of these inorganic materials in nitrogen. However, the reaction rates and pathways of thermal degradation of PVB with glass ceramic and Ag were obviously altered in air. The results also indicated that the degradation rates were accelerated in lower temperature and the composition of the volatile gas ( reaction pathway) was changed for these cases of PVB with different composition of the inorganic materials. The catalytic effect of glass ceramic and Ag on PVB thermal degradation was verified in air environment.
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Wang, Chien-Yu, and 王健宇. "Image Processing and Temperature Correction of Pressure-Sensitive Paint for Airofoil Surface Pressure Measurement in Low Speed Wind Tunnel." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/9n7ca7.
Full text
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Divya, Mitta. "Printed and Low Temperature Processed Oxide Electronics with Superior Electrical Performance and Mechanical Reliability." Thesis, 2021. https://etd.iisc.ac.in/handle/2005/5758.
Full textAbstract:
In line with the forthcoming industrial revolution, printed and flexible electronics is a rapidly developing research area that involves wearable and consumer electronics to be produced in large quantities and be connected via Internet of Things (IoT). In relation to solution processed/printed electronics, oxide semiconductors have developed into a serious contender alongside the organic alternatives, which lead to the plastic electronics excitements in early days, a couple of decades ago. Oxides are increasingly chosen for printed electronics technologies because they are abundant, inexpensive, nontoxic, demonstrate way superior environmental/thermal reliability, and most importantly, possess excellent electronic transport properties. However, on the downside, there are also major challenges, such as high process temperatures, thereby making them not suitable for low-cost, flexible polymer substrates. In addition, their limited mechanical strain tolerance (typically <1%) lower their selection possibilities in typical flexible electronic applications. On the other hand, printed electronics do suffer from a major roadblock, irrespective of the chosen semiconductor technology, which stems from the limited printing resolution that dictates the minimum channel lengths and therefore the maximum operation frequency that can be achieved.
In the present thesis, efforts have been made to look for solutions of some of the above-stated bottlenecks in the printed oxide electronics domain. First, an inorganic-organic composite semiconductor precursor ink has been developed; the printed and thermally cured semiconductor film of the composite material can maintain the excellent carrier mobility of the oxide semiconductors, even when they are in near-equal amounts. On the other hand, the presence of large quantity of organics ensures its superior strain tolerance and unaltered transistor properties for bending fatigue tests
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performed down to 1.5 mm bending radius. Next, devices made out of oxide nanoparticles have also been investigated, here the curing temperature can be as low as 100 °C, and therefore, such devices may very well be fabricated on paper or polyethylene terephthalate (PET) substrates. Here, our proposed approach offers a general recipe for low temperature curable nanodispersions/nanoinks; in this case, aromatic surfactants have been used to stabilize the nanoparticles that sublimates near room temperature. In this regard, stable nanoinks from In2O3 nanoparticles are developed using an aromatic compound thymol as the stabilizer; a quick heating at 100 °C ensures its complete removal from the semiconductor film/particle surfaces. High performance field-effect transistors (FETs) have been fabricated and characterized. Next, printable conducting inks are also the essential elements to print passive components in every electronic device; they also have a widespread use in various other application domains, such as transparent touch sensors, heaters, antistatic coating, antenna etc. Here, a precisely controlled synthesis of a mixed-phase of Ag-Ag2O nanoparticles and further a nanoink has been carried out that demonstrated low curing temperature of 80 °C to 120 °C, alongside excellent strain tolerance of layers printed on standard photo-paper substrates.
Next, attempts have been made to circumvent the printing resolution limits that at present hover around tens of micrometers range and are three orders of magnitude larger than the dimensions typically used in Si-technology. In this regard, an innovative device architecture that allows easy printing of edge-FETs with near vertical electronic transport through the printed semiconductor layer has been proposed; this can lower the effective channel lengths down to few tens of nanometers, as in this case the thickness of the printed layer becomes the dimension of interest. The FETs fabricated on PET substrate demonstrate high current saturation, On-Off ratio etc.,
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however, more interestingly, the depletion-mode inverters have demonstrated a signal gain >200 and switching frequency >300 kHz. In addition, taking advantage of the vertical device geometry a tensile strain tolerance up to 5% has been demonstrated.
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Serrazina, Ricardo Nazaré. "Flash sintering of lead free perovskite oxides towards sustainable processing of materials for energy and related applications." Doctoral thesis, 2021. http://hdl.handle.net/10773/32637.
Full textAbstract:
Piezoelectrics as K0.5Na0.5NbO3 (KNN) have currently an emerging importance
due to their lead-free nature and high transition temperature, which permits a
wide range of high-tech applications as sensors, actuators, energy harvesters,
biosensors, etc. However, monophasic dense KNN products are yet difficult to
obtain, due to the high temperature and long time of conventional sintering
processes.
This PhD proposes a new method to densify materials abruptly above a threshold
condition using FLASH sintering, where the densification occurs by a
combination of furnace environment (temperature and/or atmosphere) and
electrical field directly applied to the specimen. There are several proposed
mechanisms for FLASH. Joule heating is the most reported one, but also defectrelated
theories have been proposed. The phenomena are not yet completely
understood, but most probably, FLASH sintering is a combination of both effects,
with particle surfaces energy and conductivity performing a significant role.
The present work aims to exploit FLASH for sintering of KNN ceramics but also
to depict the fundamental phenomena behind FLASH sintering, and specifically,
FLASH sintering of KNN. The ultimate goal is to develop sintering of ceramics
towards room temperature, contributing to the energy economy low thermal
budget of ceramic industry.
The use of Finite Element Modelling (FEM) tools allowed to study the particle
orientation effect on the Joule heating during FLASH, while the simulated
temperature gradients were used to explain the presence of FLASH sinteringinduced
stresses in dense ceramics. The production of different size and purity
KNN powders permitted to establish the link between FLASH temperature (TF)
and particle size/purity. Following, the establishment of an engineered thermal
cycle before the application of the electric field for the FLASH was responsible
for increasing the final densification of KNN ceramics to 95%. The link between
FLASH parameters, as current density and holding time, was determined and
the relationship with final density and grain size of ceramics studied. TEM and
FEM studies allowed to propose a FLASH sintering mechanism for KNN,
in which the current flow through particles’ surfaces promotes the partial melting of
contacts and the particle sliding towards pore removal and compact
densification.
To allow a significant decrease on the TF of KNN, atmosphere-assisted FLASH
sintering (AAFS) was presented, and the temperatures were decreased to TF ≈ 265 ºC, however, the final densification was limited to 79%.
The ferroelectric and dielectric performance of FLASH sintered KNN was studied
and compared with that of conventionally sintered ceramics. Similar performance
was attained after a heat treatment for electrode cure; however, a detailed
analysis revealed FLASH sintering-fingerprints in both as-sintered and heattreated
ceramics.
This work presents a clear contribution for the development of FLASH sintering
in ceramics, namely in piezoelectric KNN.Piezoelétricos como o K0.5Na0.5NbO3 (KNN) têm uma importância emergente devido à sua natureza livre de chumbo e variada aplicabilidade em componentes como sensores, atuadores, dispositivos de recolha de energia, biossensores, etc. No entanto, o KNN monofásico continua a ser difícil de produzir devido à elevada temperatura e tempo associados ao processo de sinterização convencional. Este doutoramento propõe a utilização de um método alternativo de densificação, a sinterização FLASH, que acima de uma condição limite promove a densificação repentina de cerâmicos por uma combinação de ambiente do forno (atmosfera e/ou temperatura) com a aplicação de campo elétrico diretamente no material. Existem vários mecanismos reportados para explicar a sinterização FLASH. O aquecimento por efeito de Joule é um dos mais reportados e aceites, mas também têm sido sugeridos mecanismos envolvendo a criação e movimento de defeitos por efeito do campo elétrico. Uma compreensão clara do fenómeno continua por ser apresentada, mas muito provavelmente a sinterização por FLASH resulta duma combinação destes dois efeitos, sendo que a energia e condutividade das superfícies das partículas desempenham um papel fundamental. Este trabalho pretende explorar a sinterização por FLASH de cerâmicos, mas também estudar os seus fenómenos fundamentais, mais especificamente, na sinterização FLASH de KNN. O objetivo último deste trabalho é o desenvolvimento de processos de sinterização de cerâmicos que operem à temperatura ambiente, contribuindo para a economia energética e sustentabilidade da indústria cerâmica. A utilização de ferramentas de Modelação por Elementos Finitos (MEF, ou FEM) permitiu estudar o efeito da orientação das partículas na geração de calor por efeito de Joule durante o FLASH, enquanto a modelação da distribuição temperatura local e respetivos gradientes térmicos foram usados para explicar tensões induzidas em cerâmicos densos. A produção de pós de KNN com diferentes tamanhos e pureza permitiu estabelecer a sua relação com a temperatura de FLASH (TF). Em consequência, o estabelecimento de um ciclo térmico apropriado, antes da aplicação do campo elétrico, permitiu obter cerâmicos de KNN com densidade relativa de 95%. A ligação entre os parâmetros de FLASH, como densidade de corrente e tempo, foi determinada, e a relação com a densidade final e tamanho de grão dos cerâmicos foi estudada. Estudos em TEM e FEM permitiram propor um mecanismo para a sinterização por FLASH de KNN, em que o fluxo de corrente pelas superfícies das partículas promove uma fusão parcial nos seus contactos e o rearranjo para a remoção de poros e densificação do compacto. De forma a permitir um decréscimo acentuado na TF do KNN, a sinterização FLASH assistida por atmosfera foi apresentada, e a temperatura foi diminuída para TF ≈ 265 ºC. No entanto, a densificação final foi limitada aos 79%. As propriedades ferroelétricas e dielétricas do KNN sinterizado por FLASH foram estudadas e comparadas com as de cerâmicos sinterizados convencionalmente. Um desempenho semelhante entre ambos foi obtido após um tratamento térmico para cura de elétrodos. No entanto, uma análise detalhada mostrou que as propriedades são afetadas pelo processo de FLASH em cerâmicos tratados ou não termicamente. Este trabalho apresenta uma contribuição clara no desenvolvimento da sinterização FLASH de cerâmicos, especificamente, no piezoelétrico KNN.
Programa Doutoral em Materiais e Processamento Avançados
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Kelly, Adrian L., Elaine C. Brown, and Philip D. Coates. "The effect of screw geometry on melt temperature profile in single screw extrusion." 2006. http://hdl.handle.net/10454/3917.
Full textAbstract:
NoExperimental observations of melt temperature profiles and melting performance of extruder screws are reported. A novel temperature sensor consisting of a grid of thermocouple junctions was used to take multiple temperature readings in real time across melt flow in a single screw extruder. Melt pressure in the die and power consumption were also monitored. Three extruder screws at a range of screw speeds were examined for a commercial grade of low density polyethylene. Results showed melt temperature fields at low throughputs to be relatively independent of screw geometry with a flat-shaped temperature profile dominated by conduction. At high throughputs, melting performance and measured temperature fields were highly dependent upon screw geometry. A barrier-flighted screw with Maddock mixer achieved significantly better melting than single flighted screws. Low temperature "shoulder" regions were observed in the temperature profiles of single-flighted screws at high throughput, due to late melting of the solid bed. Stability of the melt flow was also dependent upon screw geometry and the barrier-flighted screw achieving flow with lower variation in melt pressure and temperature. Dimensionless numbers were used to analyze the relative importance of conduction, convection, and viscous shear to the state of the melt at a range of extrusion conditions.
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Yang, Hsiu-Ting, and 楊琇婷. "Study on the Photovoltaic Performances of the Hydrothermally- grown ZnO Nanowires Based Perovskite Solar Cells at Low Processing Temperatures." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/16987262067184419177.
Full textAbstract:
碩士國立交通大學
電子研究所
105
In recent years, the burning of the fossil fuel causes the aggravating of the global warming due to the increasing energy demand. Development of the renewable energy has attracted worldwide extensive attention, especially solar cells. Perovskite is an emerging material as the active layer of the solar cells, and it has been widely studied by scientists all around the world. The PCEs of perovskite solar cells has surpassed those for the other kinds of solar cells in a relatively short period. Due to the advantages like high absorption coefficient, high carrier mobility, low photo-carriers recombination rate, easy fabrication, capable of large-area preparation, and low-temperature fabrication for the application on flexible substrates and so on, the perovskite solar cells has gradually been paid attention to. In this thesis, the vertically-aligned ZnO nanowires grown via low-temperature hydrothermal growth process are used as the electron transfer layer (ETL) of the perovskite solar cells. Sequentially, the solution-processed perovskite using two-step method is collocated with the hydrothermally-grown ZnO nanowires to form the perovskite solar cells. The main idea of this thesis is utilizing the 3D structures of the hydrothermally-grown ZnO nanowires to increase the junction area to improve the photovoltaic performance of the perovskite solar cells. In the beginning of this thesis, the length effect of the hydrothermally-grown ZnO nanowires on the power conversion efficiencies (PCEs) of the perovskite solar cells is discussed. The infiltration and the surface coverage of the perovskite precursor solution changed as tuning the length of the ZnO nanowires. It is revealed that the devices with ZnO NW of 150 nm demonstrated the best PCE of 8.46 % under the AM 1.5G illumination (100 mW/cm2). However, the surface roughness of the perovskite film on the ZnO nanowires of 150 nm was still room for improvement. For the purpose to improve the surface roughness of the perovskite layer, the substrate preheating method which is heating the substrate to a temperature before dipping the PbI2 solution was carried out to solve the problem. The substrate preheating method prevents PbI2 crystallize too fast and lower the viscosity of the PbI2 solution so that the surface of the PbI2 solution can flow smoothly before the crystallization of the PbI2. From the result of the experiment, it is proved that the surface of the PbI2 spin-coated at a higher temperature might form a smoother surface, fewer pinholes, and higher PbI2 crystallinity. However, there is a trade-off between the crystallinity of PbI2 and the conversion to perovskite. This thesis demonstrated that the surface of PbI2 with the substrate preheating temperature at 200 oC is the smoothest, but the resulting high crystallinity inhibited the conversion of perovskite. Therefore, the best PCE of 10.34% was achieved for the substrate preheating at 150 oC. In this work, perovskite solar cells with hydrothermally-grown ZnO nanowires fabricated at low processing temperature demonstrated the excellent photovoltaic performance, easy fabrication, low-temperature process, and low cost, making it promising for the future developments in the solar cells on flexible substrates.
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Wang, Tsai-Hui, and 王彩惠. "Emission Behaviors of CF3-Substituted Triphenyl(triphenylethynyl)benzenes in Different States, Fluoro-Substituted Hexabenzocoronene Derivatives with Low Processing Temperatures, and Biaxial Nematics from Polar Cross-like Liquid Crystals." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/susnqf.
Full textAbstract:
博士淡江大學
化學學系博士班
106
Luminescent behaviors of CF3-substituted triphenyl(triphenylethynyl)benzenes (TPTPEB) in different states and two types of liquid crystalline materials, hexabenzocoronene derivatives and cross-like 1,2,4,5-tetrabiphenylethynylbenzenes, are investigated in this thesis. In the first part, TPTPEB derivatives are designed as a new aggregation-induced emission (AIE) luminogen skeletons. The influence of electronic effect and steric effect, by incorporating CF3 group into ortho-, meta-, para- sites of peripheral phenyls in TPTPEB, are found to influence significantly the materials’ emission in different states. In the second part, fluoro-substituted hexabenzocoronene (HBC) dervatives are designed to be synthesized with eight possible regioisomers as an eutectic composition in one pot to lead to low eutectic transition temperatures. Various oxidation conditions to cyclize peripheral phenyls of fluoro-substituted hexaphenylbenzenes are examined to result in only incomplete cyclization products. Nevertheless, the major cyclization product with two un-cyclized sites are separated to achieve HBC derivatives showing significantly low clearing temperatures (ca. 176 oC) for potential practical applications. In the third part, biaxial nematic cross-like molecules with polar side arms are designed and synthesized. The incorporation of polar groups is expected to lead the molecular packing with parallel molecular long and short axes respectively to enhance biaxiality. Cross-like compound 3-11d shows a very wide nematic liquid crystalline temperature range. Biaxialities of the single crystal and the nematic phase of cross-like 3-11d were investigated by single-crystal X-ray and powder X-ray diffraction on the magnetic-field-aligned sample respectively. Compound 3-14a is a non-polar molecule but with two polar fluoro groups in trans relationship of the central benzene ring to lead to a wide nematic liquid crystalline temperature range (ca. 60 oC) for future biaxial investigations. In summary, a new research direction on biaxial nematics by polar interaction in cross-like liquid crystalline materials is developed.