Luminescent molecules and polymers are active component in light-emitting diodes; however, the aggregation and excimer formation in concentrated solution or in the solid film states had limited their applications. Therefore, this study used poly(methyl methacrylate) (PMMA) as separator to prevent the formations of aggregate and excimer and to enhance quantum efficiency. Basically, two systems are involved: (1) Inorganic phosphorescent irdium complex PMMA was doped with inorganic iridium complex IrQB by using THF as solvent. IrQB/PMMA films prepared from dilute solutions exhibit two emissions centered at 560 and 640 nm, respectively; in contrast, only 640-nm emission was observed for films from concentrated solutions. Experimentally, these two bands showed variations on the emission intensity with increasing temperature. Aggregation of IrQB is suggested to be responsible for the 560-nm emission. Chain conformation of PMMA in the solution state strongly affects the incorporated IrQBs and their emission properties. (2) Polybenzoxazines Polybenzoxazines with the built-in fluorenscent fluorine moiety are linear in nature; however, the inherent hydrogen-bond (H-bond) interactions in polybenzoxazines decrease the inter-chain distance and cause the chain aggregation. With the added PMMAs, new H-bonding from the carbonyl groups in PMMA and the hydroxyl groups in polybenzoxazine enhances the mutual miscibility between these two components and decreases the possibility of aggregate formation in polybenzoxazines. Quantum efficiency is therefore promoted by this approach.

In this thesis, we will investigate the degradation of the low temperature polycrystalline silicon TFTs (LTPS TFTS) under the electrical stress. The electrical stress is divided into two parts of ac stress and dc stress. We used ac stress and dc stress conditions to stress different TFTs respectively and investigate the influence of grain boundary in n-type TFT and p-type TFT by use of electrical analysis. On the other hand, degradation mechanism was confirmed by measured capacitance. In n-type TFT, the SLS poly-Si TFT which contains GB perpendicular to the channel direction owns the higher ability against dc stress and poorer ability against ac stress than the poly-Si TFT which does not contain GB. The physical mechanism for these results has been reasonably deduced by use of TFT device simulation tool (ISE_TCAD). In p-type TFT, the enhancement phenomenon is always observed after dc or ac stress. There are both existed a power-law between the variation of the drain current with stress time. The slope of power-law is related to the shortening speed of effective channel length. In either dc stress or ac stress, there are two effective factors. The one factors of them is the degradation of poly-Si film, and another one is the effective channel length shortening. In the competition of these two effective factors, the GB-TFT has more obvious enhancement than GB-TFT during dc stress. Nevertheless, during the ac stress the GB-TFT is without larger enhancement than NGB-TFT because of serious poly-Si film damage.

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Differential scanning calorimeter (DSC) and temperature modulated differential scanning calorimeter (TMDSC) were used to study the isothermal crystallization kinetics and the melting behaviors at heating rates of 2, 10, 50, and 80

In this thesis, the poly-Si TFTs with different channel width and channel length are successfully fabricated and characterized. In particular, by using the T-gate structure and body contact, we can measure the substrate current and body voltage. Therefore, short channel effects in polycrystalline silicon thin-film transistors are investigated clearly. In order to study impact ionization effect and floating body effect more carefully, we measure and compare the electrical behaviors of device with different grain boundary trap density, grain size, and channel dimension. The influences of these factors on the short channel effects are also discussed and explained. In this experiment, it is found that the devices with short channel length, exhibit improved normalized turn on current and smaller threshold voltage. But on the other hand the sever kink effect which generated by the impact ionization also observed. Moreover, the floating body under the channel region serve as a parasitic BJT as in silicon-on-insulator devices. The related single transistor latch-up is observed and discussed for short-channel devices with various channel width. The severe impact ionization effects in polycrystalline silicon thin-film transistors are investigated and characterized. By directly measuring the substrate current from conventional TFTs with body contact, the impact-ionization effects can be characterized and analyzed very clearly. An anomalous substrate current under high gate voltage is observed. The parasitic tunneling effect between inversion region and body region is proposed to explain this phenomenon. Finally, a physically-based model is established and compared with the measured substrate current. Good agreements are found when the vertical field scattering effect is included into the maximum electric field impact ionization model.

Polycyclic aromatic hydrocarbons (PAHs) are environmentally significant compounds due to the toxicity of some members. They are ubiquitous and are persistent bioaccumulative toxins(PBTs). The toxicity of PAHs represents a risk to human health, and there are varied risk assessment approaches to quantifying the risk posed by PAHs based on exposure routes and scenarios. PAHs are not carcinogenic until they are metabolically activated as the body attempts to break them down and forms reactive metabolites that bind to the DNA causing subsequent replication in the cells. Fundamental to assessing the risk posed by PAHs is understanding the metabolism of PAHs. Since exposure to PAHs is never to single PAHs, understanding what differences may occur in mixtures of PAHs gives accurate assessment of the dangers of PAHs. Understanding the dynamics of complex metabolism vis-a-vis single metabolism of PAHs and possible effects on the toxicity expression of PAHs is a necessary advancement to accurately impact and guide remediation strategies. Studies were carried out comparing the metabolism of the PAHs Phenanthrene (PHE), Flouranthene (FLA) and Benzo[a]pyrene (BAP) in single, binary and ternary mixtures by monitoring the disappearance of the parent compound. It was observed that PAH metabolism in the single PAH experiment differed from metabolism in both binary and ternary mixtures. Enzyme competition was evident in the metabolism of mixtures, changing significantly the metabolism patterns of individual PAHs. PAH structure was also seen to affect metabolism in mixtures and the possible creation of toxicity effects during mixture metabolism. PAH concentration changed over time with faster change during single PAH metabolism followed by ternary mixture metabolism and finally binary metabolism. These results affirm that substrate interactions must be considered in the risk assessment approaches to the dangers posed by exposure to PAHs.

The purpose of this study is using titanium dioxide (TiO2) as gate oxide on thin film transistor (TFT) and discussed with their physical, chemical and electrical properties. Amorphous silicon (a-Si) and polycrystalline silicon (poly-Si) are used as substrates. The metal-organic chemical vapor deposition (MOCVD) and the liquid phase deposition (LPD) are used as the TiO2 growth methods. About the LPD growth method, ammonium hexafluoro-titanate ((NH4)2TiF6) and hexafluorotitanic acid (H2TiF6) are used as Ti sources. We are interested in two parts: (1) the growth mechanisms, physics properties, chemical properties and electrical properties of MOS structure; (2) the fabrication processes and electrical properties of devices. In the first part, we discuss the thin films characteristics on a-Si and poly-Si substrates. For the MOCVD growth method, the MOCVD-TiO2 film tends to form the poly structure. Poly structure has a higher dielectric constant, however, higher traps and dangling bonds also exist at the grain boundaries. Thus, poly structure of TiO2 film has a higher leakage current. For the LPD growth method, the film tends to form the amorphous structure. Amorphous structure has lower leakage current but also has lower dielectric constant. The film that grown from the (NH)2TiF6 source is called LPD-TiO2 film. The film that grown from the (NH)2TiF6 source is called LPD-TixSi(1-x)Oy film. Both films are incorporated with OH and F ions during the growth, the OH and F ions can be outgassed during the low temperature annealing process. In addition, appropriate F ions in the film can passivate the traps and dangling bonds. The low temperature treatments in N2 or O2 ambient and post-metallization annealing (PMA) are adopted to improve the film characteristics. On the other hand, the substrate is not a prefect structure (not a single structure). Thus the film may be influenced by substrate during the annealing treatment. In the second part, the electrical properties of TFT devices were discussed under the coplanar structure. There are several differences of the operation principle in TFT and MOSFET. A-Si and poly-Si are the un-doped substrates with many traps in the bulk. The channel should be occurred through the full depletion mode. The full depletion region is the substrate that under the gate electrode. Thus, the key point is kept the suitable thickness. Too thick, the channel can not appear. Too thin, the substrate may be over-etched. For ion implantation, due to the thinner active layer, the ion implantation energy should be lowed. In addition, the activation temperature and activation time should be adjusted suitable. We have fabricated the TFT devices with the MOCVD-TiO2 as gate oxide on poly-Si substrate. From the I-V characteristics, the Kink effect can be observed. However, the Ion/Ioff ratio is still low. We must further study how to increase the Ion/Ioff ratio.

Poly(ethylene succinate) (PES), poly(trimethylene succinate) (PTS) and their copolyesters with various compositions were synthesized through a direct polycondensation reaction with titanium tetraisopropoxide used as the catalyst. Results obtained from intrinsic viscosity and gel permeation chromatography (GPC) studies have significantly contributed to the preparation of polyesters with high molecular weight. Compositions and sequence distributions of the synthesized copolyesters were determined by analyzing the spectra of 1H NMR and 13C NMR. According to those results, the sequence distributions of ethylene succinate (ES) units and trimethylene succinate (TS) units were found to be random. Thermal properties were then characterized using differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA). All copolymers exhibited a single glass transition temperature (Tg). These polyesters did not significantly differ in thermal stability. Next, thermal stability was estimated using polarized light microscopy (PLM). Isothermal growth rates for polyesters were observed after pre-melting at various temperatures. The thermal degradation temperature (Td) was estimated, at which the growth rate for polyesters increased abruptly. The Td value of PES and PETSA 95/05 was found to be 213 and 200 ¢XC, respectively, which was 35−45 ¢XC lower than that determined by TGA. Wide-angle X-ray diffractograms (WAXDs) were obtained for polyesters that were crystallized isothermally at a temperature 5−10 ¢XC below their melting temperatures. Only the crystal form of PES was appeared in the diffractograms of PES-rich copolyesters. The TS units in polyesters may be excluded and located in the amorphous part of polyesters. WAXD results indicate that incorporating TS units into PES could significantly inhibit the crystallization behavior of the latter. Additionally, dynamic mechanical properties of moldable polyesters were investigated using a Rheometer operated at 1 Hz. Below Tg, incorporating TS units into PES led to a decline in the storage modulus, while above Tg, the effect of crystallinity on the storage modulus could be found. The sphreulite growth rates for crystallizable polyesters were measured by PLM. The growth rate of polyesters decreased with an increasing moiety of TS units. The regime II¡÷III transition of PES was estimated to occur at ca. 71 ¢XC, which is extremely close to values in the literature. The regime transition of PETSA95/05 and PETSA 80/20 was found to be 65.0 ¢XC and 51.4 ¢XC, respectively. A dynamic crystallization experiment was performed by PLM and compared with time consuming isothermal experiments. Above data closely corresponded to those data points determined in the isothermal experiments. Results of the regime analysis for the continuous data of polyesters closely resembled those of isothermal experiments. The maximum growth rate was formulated in Arrhenius and WLF expressions for the molecular transport term. A master curve of the crystal growth rate for PES was constructed based on the continuous data of PES. Plotting the reduced growth rates after normalization against the reduced temperatures revealed a universal master curve for PES and two PES-rich copolyesters. Finally, the lateral surface free energy, fold surface free energy and work for chain folding of polyesters were evaluated based on kinetic analysis. According to those results, the works for chain folding decreased with an increasing moiety of TS units.

Reproduction de : Thèse doctorat : Chimie des matériaux : Reims : 2007. / Titre provenant de l'écran titre. Bibliogr. p. 174-188.