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No description available.

No description available.

No description available.

A new approach to the fabrication of polymeric thin films is presented. This approach, chemical vapor copolymerization (CVcP), has all the advantages of chemical vapor polymerization (CVP), including exceptional purity, highly conformal coatings, continuous films even when very thin, low stress, and low environmental impact. The range of film properties available by CVcP is much greater than by CVP. A specially modified deposition system was constructed to study deposition kinetics. A model was developed which allowed quantification of the order of initiation of paraxylylene (PX), which is the initiation system for all the work reported here. This model suggests a trimer diradical is the smallest stable diradical species formed by PX at room temperature, confirming thermodynamic predictions. This system also allows the calculation of reactivity ratios of PX with vinylic comonomers. A model is developed in which reactivity ratios can be determined if the following quantities are known: a) thickness vs. position of the final film; b) partial pressures of each reactive species entering the deposition chamber and c) composition vs. position in the final film. This model was tested yielded reasonable values for reactivity ratios. A polymeric film extremely low in refractive index (1.38-1.39 in the visible region) is presented. This film is formed by copolymerizing poly(parachloroxylylene), or PX-C, with perfluorooctyl methacrylate (PFOMA). The refractive index of the homopolymers, by contrast, are in the 1.60-1.68 range. Film growth rates are very low for this new material. Finally, a new deposition procedure is introduced in which a comonomer with a low vapor pressure is codeposited with PX. The reactor temperature is above the ceiling temperature of PX deposition, but at a temperature where the comonomer can condense. This makes the deposition environment extremely rich in comonomer, yielding films whose final properties are nearly identical to films composed entirely of the comonomer. The procedure is demonstrated using n-phenyl maleimide (NPMI) as a comonomer; films produced had thermal stabilities nearly matching those of poly(NPMI). This procedure has great promise for broadening the use of polymeric thin films in the microelectronics industry, as well as other fields. / Ph. D.

Metal alkoxides have been known for many years. Recently, a renewed interest in these compounds has arisen as they have been found to be viable precursors for metal oxide film synthesis. Lead zirconium titanate(PZT) films have shown promise for many applications in the electronics industry. Chemical vapor deposition(CVD) of PZT thin films has been hampered by the lack of a suitable zirconium precursor for low temperature chemical vapor deposition. Currently, both zircbnium alkoxides and zirconium β-diketonate complexes are employed in the CVD process of PZT films. The alkoxides, although volatile are moisture sensitive and are not easily handled under normal atmospheric conditions. Tetrakis β-diketonate complexes of zirconium are more stable than the alkoxides, but they have a deposition temperature that is too high for commercial use. A mixed (β-diketonate)zirconium alkoxide compound could provide the necessary stability while maintaining the volatility necessary for low temperature CVD. From the above reasoning, it was decided to prepare a zirconium di-(2,2,6,6 tetramethyl-3,5 heptadione) di-tert-butoxide compound. The compound was characterized and subjected to a variety of volatility studies. Thermogravimetric analysis provided evidence that the compound was volatile enough to be used in thin film synthesis. Initial attempts at film deposition, however, resulted in no film growth. Changing deposition parameters also resulted in no film growth. Visual inspection of the residue left after the deposition trials gave the first indication that the compound had undergone some change. Analysis of the material left in the reactor suggested the formation of a zirconium cluster compound. Further decomposition studies also resulted in the formation of the same zirconium cluster compound. Attempts to make the compound more stable at deposition temperatures centered on changing the alkoxide. Tri-tert-butyl alcohol(tritox) was prepared, however, the synthesis of the tritox - β-diketonate zirconium complex was unsuccessful. Other changes involved using pivalic acid to replace the alkoxide. Reactions with pivalic acid and zirconium di-(2,2,6,6 tetramethyl-3,5 heptadione) di-tert-butoxide resulted in the decomposition of the starting material. Other β-diketonate complexes were also investigated. Compounds synthesized from 2.4 pentadione(Acac), 1-benzoyl acetone(Bzac) and dibenzoyl methane(Dbzm) could not be purified in order to subject them to chemical vapor deposition. A zirconium complex with two different β-diketonate ligands was also synthesized. The complex was not investigated as a precursor for chemical vapor deposition because the isomers of the complex could not be separated. / Master of Science

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No description available.

No description available.

This thesis presents the development of III-nitride materials for deep-ultraviolet (DUV) light emitting devices. The goal of this research is to develop a DUV laser diode (LD) operating at room temperature. Epitaxial structures for these devices are grown by metalorganic chemical vapor deposition (MOCVD) and several material analysis techniques were employed to characterize these structures such as atomic force microscopy, electroluminescence, Hall-effect measurement, photoluminescence, secondary ion mass spectrometry, transmission electron microscopy, transmission line measurement, and X-ray diffraction. Each of these will be discussed in detail. The active regions of III-nitride based UV emitters are composed of AlxGa1-xN alloys, the bandgap of which can be tuned from 3.4 eV to 6.2 eV, which allows us to attain the desired wavelength in the DUV by engineering the molar fraction of aluminum and gallium. In order to emit photons in the DUV wavelength range (> 4.1 eV), high aluminum molar fraction AlxGa1-xN alloys are required. Since aluminum has very low ad-atom mobility on the growth surface, a very low group V to group III precursor ratio (known as V/III ratio), high growth temperature, and low growth pressure is required to form a smooth surface and subsequently abrupt heterointerfaces. The first part of this work focuses on developing high-quality multi-quantum well structures using high aluminum molar fraction ([Al] > 60%) AlxGa1-xN alloys. Optically pumped DUV lasers were demonstrated with threshold power density as low as 250 kW/cm² for the emission wavelength as short as 248.3 nm. Transverse electric (TE) -like emission dominates when the lasers were operating above threshold power density, which suggests the diode design requires the active region to be fully strained to promote better confinement of the optical mode in transverse direction. The second phase of this project is to achieve an electrically driven injection diode laser. Owing to their large bandgap, low intrinsic carrier concentration, and relatively high dopant activation energy, the nature of these high aluminum molar fraction materials are highly insulating; therefore, efficiently transport carriers into active region is one of the main challenges. Highly conducting p-type material is especially difficult to achieve because the activation energy for magnesium, a typical dopant, is relatively large and some of the acceptors are compensated by the hydrogen during the growth. Furthermore, due to the lack of a large work function material to form a p-type ohmic contact, the p-contact layer design is limited to low aluminum molar fraction material or gallium nitride. Besides the fabrication challenges, these low aluminum molar fraction materials are not transparent to the laser wavelength causing relatively high internal loss (αi). In this work, an inverse tapered p-waveguide design is employed to transport holes to active region efficiently while the graded-index separate-confinement heterostructure (GRINSCH) is employed for the active region design. Together, a multi-quantum well (MQW) ultraviolet emitter was demonstrated.