Dissertations / Theses on the topic 'Oxidization'

The experiments described in this thesis involve the expression and characterisation of recombinant truncated thioredoxin (tTrx) and the potential involvement that thioredoxin (Trx) has in the cellular responses to oxidative stress. Truncated Trx (80 amino acids) was expressed from a plasmid containing the ORF for tTrx that had been introduced into E.coli BL-21(DE3) cells. The protein was initially extracted using a combination of high concentrations of urea, high pH levels, and multiple sonification steps to remove the tTrx from inclusion bodies formed during expression. This procedure produced a stable solution of tTrx. Purification of tTrx from this protein solution required anion exchange chromatography followed by gel permeation in a HPLC system to obtain fully purified, recombinant tTrx which allowed further characterisation studies to be undertaken. An initial investigation into tTrx was performed to determine some basic physical, biochemical and functional aspects of this hitherto relatively undefined protein. Analysis by sedimentation equilibrium indicated that freshly prepared tTrx forms a single species with a molecular weight of 18.8kDa. This value indicates that recombinant tTrx naturally forms a dimer in solution that was shown to be non-covalent in nature and stable in solution. The capacity of tTrx to reduce protein disulphide bonds was determined using the insulin reduction assay. Results show that tTrx lacks this particular redox ability. The rate of oxidisation at 4 degrees C was analysed using free thiol determination, sedimentation equilibrium and SDS-PAGE patterning. Results indicated a steady rise in the degree of oxidation of tTrx over an eight day period. After six days the oxidated protein consistently displayed the presence of intramolecular disulphide bonds. Covalently-linked disulphide dimers and higher molecular weight oligomers were detectable after eight days oxidation. An investigation of the reducing capacity of the basic Trx system determined that fully oxidised tTrx was unable to act alone as a substrate for thioredoxin reductase (TR). However, when reduced Trx was added to the system, it appeared capable of acting as an electron donor to the oxidised tTrx in order to reduce disulphide groups. Recombinant tTrx was successfully radiolabelled with Trans 35S-methionine/cysteine for use in cell association studies. No evidence was found to indicate the presence of a receptor for tTrx on either MCF-7 or U-937 cells. Findings suggest that a low level of non-specific binding of tTrx to these cell lines rather than a classical ligand-binding mechanism occurs thus suggesting the absence of a cell surface receptor for tTrx. The role that Trx may play in the cellular responses to oxidative stress was also investigated. The chemical oxidants hydrogen peroxide (H2O2) and diamide were used to establish an in vitro model of oxidative stress for the choriocarcinoma cytotrophoblast cell line JEG-3. Cellular function was assessed in terms of membrane integrity, metabolic activity and the ability to synthesis new DNA following exposure to these oxidants. Results indicated that both agents were capable of causing cells to undergo oxidative stress without inducing immediate apoptosis or necrosis. Initially, JEG-3 cells exposed to 38μM or 75μM H2O2 or 100μM diamide were shown to display altered cell metabolism and DNA synthesis without loss to cell viability or membrane integrity. Cells were also shown to be capable of some short-term recovery but later lapsed into a more stressed state. Expression levels of Trx were studied to determine whether this type of chemical stress caused a change in intercellular protein levels. Both cELISA and western blotting results indicated that only cells exposed to 100μM diamide displayed any significant increase in Trx protein levels after 6 or 8hrs exposure to the oxidant. Further studies over a longer time-frame were also performed. These found that when JEG-3 cells were exposed to 18μM H2O2 or 200μM diamide over 12-48hrs, a positive correlation between increasing endogenous Trx protein levels and a decline in cell proliferation was observed. Cytotrophoblast cells, which are responsible for implantation and placentation, are susceptible to oxidative stress in vivo and their anti-oxidant capacity is fundamental to the establishment of pregnancy. The findings obtained during these studies suggest that Trx plays a role in this process.

The experiments described in this thesis involve the expression and characterisation of recombinant truncated thioredoxin (tTrx) and the potential involvement that thioredoxin (Trx) has in the cellular responses to oxidative stress. Truncated Trx (80 amino acids) was expressed from a plasmid containing the ORF for tTrx that had been introduced into E.coli BL-21(DE3) cells. The protein was initially extracted using a combination of high concentrations of urea, high pH levels, and multiple sonification steps to remove the tTrx from inclusion bodies formed during expression. This procedure produced a stable solution of tTrx. Purification of tTrx from this protein solution required anion exchange chromatography followed by gel permeation in a HPLC system to obtain fully purified, recombinant tTrx which allowed further characterisation studies to be undertaken. An initial investigation into tTrx was performed to determine some basic physical, biochemical and functional aspects of this hitherto relatively undefined protein. Analysis by sedimentation equilibrium indicated that freshly prepared tTrx forms a single species with a molecular weight of 18.8kDa. This value indicates that recombinant tTrx naturally forms a dimer in solution that was shown to be non-covalent in nature and stable in solution. The capacity of tTrx to reduce protein disulphide bonds was determined using the insulin reduction assay. Results show that tTrx lacks this particular redox ability. The rate of oxidisation at 4 degrees C was analysed using free thiol determination, sedimentation equilibrium and SDS-PAGE patterning. Results indicated a steady rise in the degree of oxidation of tTrx over an eight day period. After six days the oxidated protein consistently displayed the presence of intramolecular disulphide bonds. Covalently-linked disulphide dimers and higher molecular weight oligomers were detectable after eight days oxidation. An investigation of the reducing capacity of the basic Trx system determined that fully oxidised tTrx was unable to act alone as a substrate for thioredoxin reductase (TR). However, when reduced Trx was added to the system, it appeared capable of acting as an electron donor to the oxidised tTrx in order to reduce disulphide groups. Recombinant tTrx was successfully radiolabelled with Trans 35S-methionine/cysteine for use in cell association studies. No evidence was found to indicate the presence of a receptor for tTrx on either MCF-7 or U-937 cells. Findings suggest that a low level of non-specific binding of tTrx to these cell lines rather than a classical ligand-binding mechanism occurs thus suggesting the absence of a cell surface receptor for tTrx. The role that Trx may play in the cellular responses to oxidative stress was also investigated. The chemical oxidants hydrogen peroxide (H2O2) and diamide were used to establish an in vitro model of oxidative stress for the choriocarcinoma cytotrophoblast cell line JEG-3. Cellular function was assessed in terms of membrane integrity, metabolic activity and the ability to synthesis new DNA following exposure to these oxidants. Results indicated that both agents were capable of causing cells to undergo oxidative stress without inducing immediate apoptosis or necrosis. Initially, JEG-3 cells exposed to 38μM or 75μM H2O2 or 100μM diamide were shown to display altered cell metabolism and DNA synthesis without loss to cell viability or membrane integrity. Cells were also shown to be capable of some short-term recovery but later lapsed into a more stressed state. Expression levels of Trx were studied to determine whether this type of chemical stress caused a change in intercellular protein levels. Both cELISA and western blotting results indicated that only cells exposed to 100μM diamide displayed any significant increase in Trx protein levels after 6 or 8hrs exposure to the oxidant. Further studies over a longer time-frame were also performed. These found that when JEG-3 cells were exposed to 18μM H2O2 or 200μM diamide over 12-48hrs, a positive correlation between increasing endogenous Trx protein levels and a decline in cell proliferation was observed. Cytotrophoblast cells, which are responsible for implantation and placentation, are susceptible to oxidative stress in vivo and their anti-oxidant capacity is fundamental to the establishment of pregnancy. The findings obtained during these studies suggest that Trx plays a role in this process.
Thesis (Masters)
Master of Philosophy (MPhil)
School of Health Sciences
Full Text

Nitrification, a key step in biological nitrogen removal processes, is the oxidation of ammonia into nitrate performed by ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) under aerobic condition. Researchers have focused on factors affecting the performance of nitrification for decades, but the inorganic carbon limitation on nitrification had been neglected. However, the increase in nitrogen in wastewater has increased the need to evaluate and improve our understanding of this limitation. In a previous research, the hypothesis that different inorganic carbon concentrations would enrich different AOB populations has been examined. In this study, the focus was on the effect of inorganic carbon concentration on NOB, which has a close relationship with AOB. Two 5L lab–scale continuous–flow stirred tank reactors (CSTR) were operated to evaluate the nitrification performance and microbial ecology of nitrifier populations acclimated under inorganic carbon sufficient (high–IC) and limited (low–IC) conditions for approximately 700 days. During the operation period, both bioreactors were able to maintain satisfactory nitrification efficiency higher than 95% at an influent ammonium concentration of 250 mg–N/L. Nitrate was the major end product and no significant nitrite accumulation was observed. To evaluate the effects of inorganic carbon on NOB community structures, cloning/sequencing and real–time PCR were applied to target and quantify the two common NOB genera, Nitrospira and Nitrobacter, as no molecular probe targeting all known NOB is available presently. The results showed that these two genera were both found in the two reactors. Nitrospira was the dominant NOB population in the high–IC bioreactor, while Nitrobacter was dominant in the low–IC one after one year acclimation. Kinetic analysis revealed that NOB enriched in the two reactors have different kinetic performances. However, IC concentration did not show a significant impact on the nitrite oxidizing kinetics of NOB in the batch tests.

碩士
大葉大學
電機工程學系碩士班
94
Oxide of semiconductor could be a part of device structure, like MOS structure, or a layer to provide the surface passivation. With the great progress of the applications of GaN on optoelectronic devices and high temperature/high power electronics, GaN is more attractive than ever. Dry or wet thermal oxidation process is a mature technology for the oxidation of silicon. However, it has only limited success on GaN. High temperature process will deteriorate the crystal quality of GaN and further degrade the performance of devices. In this thesis we studied the growth of Ga2O3 oxide film on n-type GaN by photoelectrochemical oxidization (PECO) technique. The first, in order to enhance the oxidation rate, we tried to conduct the wet oxidation of GaN in various concentrations of phosphorus acid (H3PO4) solutions with 0, 1, or 2V bias. The tested samples were examined with α-step profiler、scanning electron microscopy (SEM) and energy dispersive spectrometer (EDX) to evaluate the oxide thickness、the surface morphology and the composition of oxide, respectively. We obtained that the growth rates of oxide with 0.0032M phosphorus acid solution were 224nm/h, 2.8μm/h, and 5μm/h for 0, 1, or 2V bias, respectively. Also, the oxygen atom ratio in the oxide increased with bias from EDX analysis. Hence, an external bias could be used to enhance the oxidation rate of GaN and the growth rate of oxide. In order to evaluate the properties of oxides, the PECO grown oxides were applied to the fabrication of MOS on GaN. Both I-V and C-V measurements were used to characterize the MOS devices. During process, we found the as-grown oxide must be annealed under high temperature to prevent the attack of chemicals during process.

碩士
大同大學
化學工程研究所
89
The main purpose of this research is to study the properties of the films obtained by pulsed current anodizing on aluminum in sulfuric acid electrolyte with ammonium molybdate. The operating conditions are constant voltage 5~20V, pulsed current of 1~5A/dm2 with frequency of 100 Hz and duty cycle of 80 % at bath temperature of 10~50℃ for 30 minutes anodizing duration time. Finally, the specimens were sealed in the solution of 20g/L nickel fluoride for 20 minutes at room temperature. The film thickness is linearly proportional to the anodizing temperature and current density, and is almost not affected by the addition of ammonium molybdate, but the film microhardness increases greatly. Meanwhile, a film of better thickness and microhardness can be obtained under the condition of constant current density than constant voltage. From SEM photos, it can be deduced that the lower temperature below 20℃ will make the pores of the anodic oxide film become smaller and distributed closely. It’s good for film hardness. Besides, the EDS analytic chart reveals that the molybdenum atom is found in the anodic film, this is one of the reasons to increase the microhardness of the anodic film. From experimental results, it can be shown that the microhardness of the anodic film can be greatly improved by adding molybdenum into the sulfuric acid solution. Under the conditions of 20℃ anodizing temperature, 0.025mol/L ammonium molybdate and current density of 8A/dm2 for 30 minutes anodizing duration, the maximum anodic film microhardness of 623Hv can be obtained.

碩士
中原大學
土木工程研究所
93
Ammonia oxidization bacterium are not easy to grow, according to their shapes, it’s hard to distinguish the differences from each species. Autotrophic AOB (ammonia oxidization bacterium) not only grow slowly, but also difficultly culture. To realize the diversity of ammonia oxidization bacterium cultured in sequencing batch membrane bioreactor (SBMBR bioreactor) in laboratory. This research uses amoA gene which is ammonia oxidization bacterium’s special function to combine molecular biological technology and to realize the diversity of AOB, Aim directly at analysis of 16S rDNA gene in activated sludge, to know bacterium’s spreading. According to the research , amoA gene only has two copy numbers, therefore, PCR is not easy to amplify, it will obtain strength single in second time of PCR. Using amoA primer to obtain PCR products with autotrophic culture, then compare the sequence, it shows that the family relation is closed to amoA gene of Nitrosmonas oligotropha. Next, compare the sequence of 16S rDNA gene of ammonia oxidization bacteria, discovered genius of Bacillus has nitrification and denitrification at the same time. Activated sludge and biological membrane are cloned and classify amoA gene into two groups by DGGE and RELP. One of the two groups is closed to Nitrosmonas europaea and the other is closed to Nitrosmonas oligotropha. Therefore, the amoA gene of ammonia oxidization bacterium gathers around Nitrosomonas genius in SBMBR bioreactor. The result of comparison of 16S rDNA gene by SBMBR bioreactor, it shows part of genes have denitrifying. On the contrast, 16S rDNA gene by gene cloning , it shows that part of genes have denitrifying and phosphorus release. This experiment matches the result of SBMBR bioreactor. In addition, the percentage of AOB is pretty lower from cultured numbers. The reason perhaps the AOB are not easy to cultivate and they have lower percentage in SBMBR bioreactor. Consequenly, the result that mentions above leads to get lower ammonia oxidization bacterium in tradition cultivated way.

碩士
國立成功大學
微電子工程研究所碩博士班
97
In this work, we preset an effective method of shrinking gate length by oxidization gate metal. The oxidization method’s advantages are fast, low cost, simple and effective increase devices performance. The gate metal process to be use metal different coefficient of oxidization by oxidization treatment, and the GaN has excellent chemical and physics stability, so it is difficult to be oxidized by the H2O2. We can oxidize the gate metal by using general H2O2 after we finish the gate metal’s process. Because the different coefficient of oxidization of Ni/Au gate meal, it is effective to shrink gate length of metal below the gate.Experiment results indicate that the oxidization process can improve devices DC and microwave characteristics: the saturation drain current density IDSS0 (305mA/mm -> 322 mA/mm), the maximum extrinsic transconductance gm,max (99 mS/mm -> 114mS/mm), the pinch-off voltage Vpinch-off (–3.2 V -> –3 V), the unity current gain cut-off frequency fT (11.1 GHz -> 14.4 GHz), the maximum oscillation frequency fmax (14.6 GHz -> 17.4 GHz), the minimum noise figure NFmin (1.902 dB -> 1.384 dB) and the power-added-efficiency (P.A.E.) (24.5 % -> 31.1 %).

碩士
南台科技大學
化學工程與材枓工程系
97
In this study, the macroporous polymeric supports were synthesized by the suspension polymerization and that were applied on the oxidation of cyclohexane. The macroporous polymers were composed by glycidyl-methacrylate and styrene with divinylbeneze as cross-linking agents. Iooctane, N, N-dimethylacetamide, cyclohexanol, cyclohexanone were chosen as a porogen to study the porosity formation of polymer particle. Furthermore, the macroporous polymers were modified by iminodiacetic acid via ring-opening reaction with the epoxy function on the support to obtain the chelating copolymer support. Among those porous polymer supports, the maximum specific surface area, pore volume and pore diameter could reach to 402.65 m2/g, 0.88 cm3/g and 10.2 nm, respectively. In addition, the cobalt(II) chelated capacity of porous polymer could reach to 60.22 mg Co2+/g polymer . On the other hands, the high surface area catalysts in the oxidization reaction could get the high conversion of cyclohexance oxidation with short induction time. In addition, the selectivity of cyclohexanone and cyclohexanol could arrive 91 % on 4.9 % conversion. The increased the reaction pressure could increase the oxidation conversion, but do not promote the selectivity of the product. Raised the reaction temperature could effectively increase the oxidation conversion of cyclohxane, however, higher reaction temperature would make the cyclohexanol and cyclohexanone oxidation to adipic acid. As the air purge rate increased, the conversion of oxidaiton reaction would increase. Notable, added the benzaldehyde as the co-catalyst could enhance the oxidation conversion about 5%.

碩士
義守大學
材料科學與工程學系
91
The Gasification and Oxidization of Organic Wastes in Near and Supercritical Water ABSTRACT Oil- and sewage-sludges from Chinese Petroleum Company and toluene were thermally gasified in near and supercritical water. The gasification was an isochoric process in a batch reactor. The investigated temperatures ranged from 360 to 420 ℃, and the final pressures achieved were between 26 and 33 MPa. The gas product is mainly composed of C1 ~ C4 , hydrogen and carbon dioxide. In the gasification of oil- and sewage-sludges, methane is the most abundant product, ~50%, and hydrocarbons of C2, C3 and C4 take up ~18%, ~ 11%, and ~7%, respectively. Hydrogen gas contributes less than 10%. Carbon dioxide content is close to 6%. When toluene were gasified, methane is the most abundant product, ~51%, and hydrocarbons of C1, C2, C3 and C4 take up ~15%, ~ 5%, ~ 2%, and ~1%, respectively. Carbon dioxide contributes almost 26%. Without the addition of nickel to the sewage sludge, the temperature dependence of the product distribution were found to be mild over the entire range of temperatures. However, the nickel effect on the oil sludge is quite complicated. Toluene and Di-Methyl Formamide (DMF) were also oxidized in supercritical water. Hydrogen peroxide , oxygen gas or air is employed as the oxidant to destruct toluene and DMF. The experiments of toluene were carried out with a batch reactor and that of DMF was with a continuous system. Liquid effluent is analyzed for the concentration of toluene or DMF to investigate the Destruction and Removal Efficiency (DRE). The effects of temperature, reaction time, density in the reactor, the weight fraction of toluene or DMF, and the weight ratio of oxidant to toluene or DMF on the DRE are investigated. It is found that the DRE increases with temperature, reaction time, density in the reactor, and the weight ratio of oxygen to toluene or DMF. Increasing the amount of loading and the weight fraction of toluene or DMF in the feed will significantly decrease DRE. In the case of oxidation with air, 99.9% DRE was achieved when the weight ratio of air to DMF is larger than 6.77. This work provides useful information for recycling wastes from industrial sites, and the role of water in pyrolyzing them.

碩士
逢甲大學
土木及水利工程所
93
ABSTRACT There are three major river water pollution sources in Taiwan, respectively, domestic sewage, industrial waste water and livestock breeding, According to the Environment protection Statistic Manual published by Environmental Protection Administration, Executive Yuan in 2003, the discharging amount of domestic sewage had exceed 55%, industrial waste water 28% and livestock breeding 17%. Furthermore, with the prosperous of industrial and commercial developments and the highly concentrated population in city, large amount of waste water (sewage) has discharged to rivers and usually exceed the capacity of rivers largely; consequently, the rivers of various sizes in Taiwan have been polluted in different degrees. As for the dredging of river pollution, the Environmental Protection Administration has applied eco-technology to improve the river water quality since 2002 in order to comply with the tendency of sustainable development, and expecting to reduce pollution and carry out the purpose of environment conservation. Currently, in addition to control pollution sources actively, the Environmental Protection Administration also promotes the eco-technology based water purification project to improve pollution caused by domestic sewage effectively by water cutting. Eco-technology is to adopt ecology based and safety oriented construction method based on the cognition of eco-system and carry out diversified conservation of creatures and continuous development. The technologies include vegetation engineering (wetland, chinampa, phytoplankton, swales, grass strip, and planting filter); soil treatment (irrigation treatment and underground leachate), and contact oxidization (gravel contact, filling filter, deep pool and torrent). The purpose of the thesis is focused on the discussion of contact oxidization in river, and use gravel filling filter to process experimental research and assess the effective of water quality purification treatment. Keywords: Eco-technology, Contact oxidization, Gravel contact, Filling filter

碩士
國立交通大學
光電工程系所
93
We successfully employed rapid thermal oxidized porous silicon (PS) to create silicon nanocrystals (nc-Si). In order to observe the size and the characteristics, experiments on different samples were investigated via transmission electron microscope (TEM)、Raman scattering and photoluminescence. After that, we doped Er ions into silicon rich SiO2 (SRSO) structure and successfully observed the infrared photoluminescence at 1.54μm from Er ions. The relations between infrared photoluminescence and average size of nc-Si were discussed in this study. In this work, we controlled different current density to vary the silicon porosity. The different average size of nc-Si were formed by changing the silicon porosity and rapid thermal oxidization. We observe the red-shift of Raman scattering and the blue-shift of visible photoluminescence from the average size of nc-Si. The intensity of infrared photoluminescence at 1.54μm from Er ions would increase as the decreasing of the average size of nc-Si. This fact means that the Er ions are excited by energy transfer process from the excited nc-Si and the conversion efficiency has relations with the average size of nc-Si.

博士
國立臺北科技大學
工程科技研究所
101
A novel technology of photoelectrocatalysis (PEC) combining with cationic exchange membrane (CEM) was proposed for simultaneous reduction of chromium(VI) and oxidization of carboxylic acid. The objectives of this study were focused on: heterogeneous photoreduction of Cr(VI) in the presence of EDTA; effect of carboxyl groups number (EDTA (4), citric acid (3) and salicylic acid (1)) on the photoreduction of Cr(VI); photoreduction of Cr(VI) over different photocatalysts (DP-25 TiO2 and nitrogen-doped TiO2), and comparison photoreduction of Cr(VI)/ nitrate. The application of CEM was used to enhance the efficiency for prevention of the re-oxidation of reduced chromium with the electron-hole pairs. The results showed that the optimum conversion efficiency occurred at 4 mA/cm2 with the presence of CEM. Higher conversion efficiencies were observed at lower pH due to the electrostatic attractions between positive charged Ti-OH2+, and negatively charged Cr(VI) and EDTA. The optimum TiO2 loading of 1 g/L was depended mainly on the acidic pH range, especially at higher HRT and irradiation intensity. In addition, higher EDTA/Cr(VI) molar ratio enhanced the reduction efficiency of Cr(VI). Carboxylic acids (EDTA, citric acid and salicylic acid) generally experienced positive effects, deriving from their adsorption on TiO2 and susceptibility to photogenerated hole attack. The reduction of Cr(VI) was greatly enhanced under acidic pH, higher current density, HRT, light intensity and EDTA/Cr(VI) molar ratio. Furthermore, Cr(VI) reduction with various carboxyl group number in the presence of different carboxylic acids increases in the following order: 1 (SA) < 3 (CA) < 4 (EDTA). Comparison photoreduction of Cr(VI) by using DP-25 TiO2 with UV light and N-TiO2 with visible light in PEC combined CEM was proposed for simultaneous oxidization of naphthalenesulfonate (NS) and reduction of Cr(VI) by electron-hole pairs. The results shows, both VL/N-TiO2 and UV/DP-25 TiO2 system were capable of reducing Cr(VI) and NS simultaneously, the photocatalytic activities of N-TiO2 under VL irradiation were improved than that of DP-25 TiO2 under UV irradiation. Moreover, longer exhaustion time for N-TiO2 (around 62 hours) compared to that of the DP-25 TiO2 under UV irradiation (around 48 hours). Complete Cr(VI) reduction was observed for pH 3 with N-TiO2 of 1 g/L, and initial NS concentration up to 50 mg/L, indicating NS plays the role of hole scavenger in the system. The generation of sulfate (as sulfur) is equivalent to the degradation of NS (as sulfur), representing the yield of sulfate is an excellent indicator for NS removal. Comparison various oxidants (nitrate) in PEC combined CEM systems had been estimated in this study. The optimal process of nitrate reduction is by using DP-25 TiO2 under UV irradiation with aeration by argon. When the addition of formic acid was demonstrated to act as hole scavengers in the TiO2 surface to accelerate nitrate reduction. Under the same reaction condition, the reactivity of nitrate reductions by using PEC can be ranked as follows: formic acid > EDTA > CA > SA. Meanwhile, the reduction of nitrate and the selectivity to nitrogen were greatly enhanced under acidic pH, higher HRT and light intensity.

碩士
國立成功大學
微電子工程研究所碩博士班
96
Native oxide as gate insulators on InGaP/InGaAs pseudomorphic high electron mobility transistors (PHEMT) were fabricated and characterized in this thesis through a liquid phase oxidation (LPO) method. Compared with others, the LPO is a simple, economic, and effective technique used to form a native oxide layer on GaAs material, at near-room temperature (30-70°C) without any other extra energy. Additionally, transmission electron microscope analysis indicated that an oxide layer with a thickness of 6 nm actually existed on the InGaP surface 30 minutes after the LPO process. As such, we demonstrated the implementation of LPO on InGaP as effective gate insulators that improved InGaP/InGaAs pHEMTs performance. In this work, the gate length and width of the device was 0.7μm×100μm, while the peak extrinsic transconductance and the breakdown voltage for the MOS-pHEMTs (conventional pHEMTs) were 151 (138) mS/mm and -13.8 (-6.6) V, respectively. Furthermore, the cut-off frequencies and maximum oscillation frequencies of the MOS-pHEMTs (conventional pHEMTs) were 15.8 (11.35) GHz and 22.3 (18.46) GHz, respectively. In addition, the proposed MOS-pHEMTs improved the saturated output power from 13.8dBm (119.94mW/mm) to 14.62 dBm (144.87mW/mm). The maximum small-signal increased from 10.41dB to 11.91 dB, and the maximum power-added-efficiency rose from 29.2% to 37.8%. According to the DC and RF results, the LPO method could be considered a promising procedure for applying InGaP/InGaAs pHEMTs to high power and wireless communication applications.

碩士
大同工學院
化學工程研究所
87
The main purpose in this research is to study the difference of film by different processes. At first, the A1100 aluminum sheet was dipping in the solution of 0.025 mole/L ammonium molybdate and 0.1 mole/L ammonium fluoride for 40 minutes. The dipping temperature was controlled at about 60℃ and the pH value was dominated about 3. Then the anodizing conditions are 10wt% or 15wt% sulfuric acid, anodizing temperature of 10~50℃, anodizing duration time of 10~50 minutes, constant voltage of 20V and p.c. frequency of 100Hz (duty cycle from 20% to 80%). Finally, the specimens were sealed by hot water at a temperature greater than 95℃ or were sealed in the solution of 20g/L nickel fluoride for 20 minutes at room temperature. SEM photos show that the pores of the anodic film obtained from 15wt% sulfuric acid are smaller and distributed closely and uniformly than that from 10wt% sulfuric acid. The EDS analytic chart reveals that the amount of some elements of the anodic film obtained from 15wt% sulfuric acid is richer thanthat from 10wt% sulfuric acid. Under the conditions: Aluminum dipping in the solution of 0.025 mole/L ammonium molybdate and 0.1 mole/L ammonium fluoride, then anodized in 15wt% sulfuric acid, 30℃ anodizing temperature, 80% duty cycle, 50 minutes anodizing time and cold sealing, the thickest anodic film of about 52μm can be obtained. Similar conditions except at 20℃ anodizing temperature for 30 minutes anodizing time, the hardest anodic film of about 613±10(Hv50) can be obtained. There is 27% promotion than by the conventional method.