Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 90-92). Also available on the World Wide Web.

Thesis (Ph. D.)--Oregon Graduate Center, 1988.

The high level of molecular control makes the Langmuir-Blodgett (LB) technique an appealing method of film deposition. The uniform nature of the films produced allows convenient investigation of intermolecular interactions and provides information pertaining to the orientation of molecules within films. LB films of two amphiphilic materials with contrasting molecular structures have been deposited. AmPc5 (a metal-free phthalocyanine (pc)) is a two-dimensional, cyclic molecule, whereas AmAzl (a resorcinol calixarene) possesses a three-dimensional basket-type structure. The amphiphilic nature of both molecules is as a result of functional side-chains. The AmPc5 spreading solution was prepared by dissolving in trichloroethane to a concentration of 0.1 mg/ml. After spreading 500-600 ul, the resulting Langmuir film was found to have a critical pressure of 28 mN/m and an area per molecule of 1.61 nm2 on the water surface. Monolayer deposition onto glass substrates enabled spectroscopic examination of the films and comparison to solution spectra. The solution spectrum shows the split Q-band absorption peaks at 700 nm and 733 nm characteristic of metal-free pc's. The LB film spectrum shows a broadening of both peaks and a red shift of the 733 nm peak, and a blue shift of the 700 nm peak. The 700 nm peak is suppressed as a result of the stack-like packing structure of AmPc5. Absorption spectra of floating AmPc5 monolayers imply that the material does not assume the monomer state at any stage of compression. This is characteristic of rigid molecules that induce order within the floating monolayer. The refractive indices (n) and extinction coefficients (k) were determined across the visible wavelength range. Both the n and k values are shown to increase with monolayer thickness, although the n value tends towards a steady value of 2.1. Deposition onto gold coated glass substrates enabled surface plasmon resonance analysis and determination of n and k at specific film thickness'. The n was found to increase with film thickness, tending towards a steady state value of 2.0. This is in excellent agreement with spectroscopic analysis. Absorption spectra measured using polarised light show AmPc5 exhibits dichroism. The calculations indicate that the pc ring lies almost perpendicular to the substrate. AmAzl was dissolved in chloroform to a concentration of 0.5 mg/ml with 10% ethanol to aid solubility. The optimum solution spreading quantity required to form a floating monolayer was found to be between 50 and 100 ul. The film was shown to have a critical pressure of 30 mN/m and an area per molecule of 1.86 nm2 on the water surface. Both LB film and solution spectra show a single absorbance peak at 454 nm which is due to transitions in the azo functional side chains. Calculation of n and k shows that they tend towards steady values of 1.5 and 2.0, respectively. The n obtained via surface plasmon resonance analysis shows a steady state value of 1.43 on silver coated glass and 1.35 on gold coated glass. This suggests a different type of packing structure on all three substrates. The lack of dichroism exhibited by AmAzl indicates the formation of in-plane amorphous films. AmAzl was deposited in alternating layers with tricosenoic acid. The structure was confirmed by X-ray diffraction studies and investigated using second harmonic generation. The second harmonic signal was shown to be proportional to the square of the number of bilayers.

Rapid thermal annealing was used to produce n⁺-surface layers in tin- and selenium-implanted GaAs. Hall effect and differential Van der Pauw measurements were performed and peak electron carrier concentrations of about 9 x 10¹⁸ cm⁻³ with corresponding sheet resistivities as low as 28 Ω/□, were achieved for high-dose, room-temperature Sn and Se implants. To realise this, development of new encapsulants and improvements to existing annealing methods were made. A novel method of depositing evaporated AIN for protecting the GaAs surface has been developed. This consists of the evaporation of Al in the presence of pure ammonia gas or an aqueous NH3/N5 gas mixture. The evaporated AlN layers were characterised using RBS and RHEED techniques and found to consist mainly of Al, N and 0 (as contaminant). These layers were used to successfully encapsulate GaAs at temperatures of up to 1100°C which is well above 950°C, the characteristic maximum useful temperature achieved using the existing CVD Si₃N₄. A double-layer encapsulant, consisting of ≈ 300 Å CVD Si₃N₄ plus 600 Å evaporated AlN was also developed and found to withstand even higher temperatures (≈1150°C) and to provide more reliable and reproducible results than either AlN or Si₃N₄ when used singly.

Glow discharge sputtering has been used for many years to produce thin films but its commercial applications are severely limited by low deposit ion rates. The DC planar magnetron, developed a decade ago, allows much higher deposition rates and its commercial use has expanded rapidly. Non-reactive magnetron sputtering of metallic thin films is well understood and utilized. However when a reactive gas is introduced the process becomes harder to control and can switch between two stable modes. Often films are produced simply by using one of these stable modes even though this does not lead to optimum film properties or high deposition rates. This work gives a model of reactive magnetron sputtering and verifies experimentally its predictions. A 0.5 m long magnetron was designed and built specifically to allow reactive sputtering onto A4 rigid substrates. This magnetron has a variable magnetic field distribution which allows plasma bombardment of the substrate during film growth. This was shown to activate reactions at the substrate. The target lifetime was extended in our design by broadening the erosion zone and increasing the target thickness. The reactive sputtering process was shown to be inherently unstable and a control system was designed to maintain the magnetron in an unstable state. Light emission by the plasma at metal line emission wavelengths changes across the instability and so with this control signal a feedback system was built. The accuracy of control was shown experimentally and theoretically to depend on the delay time between measurement, action and effect. In practice this delay was limited by the time constant of the gas distribution manifold. The time constant of such manifolds was measured and calculated. Using our controller high quality films were produced at high rates in normally unstable deposition systems. Conducting indium oxide was produced at 6 nm/s with a resistivity of 6 x 10-6 ohm. metres onto A4 glass sheets. Tin oxide was produced at increased rates onto 2.5 m by 3 m substrates.

The effect of the configuration of the confining magnetic field on the operating characteristics of a planar magnetron has been observed. In particular, the heat load and charged particle bombardment of the substrate were measured. A circular planar magnetron was constructed with a magnetic field which could be controlled by the adjustment of the current flowing through coils placed around the circumference and with a separate supply feeding a coil around the centre pole. This allowed the magnetic field configuration to be unbalanced and caused the negative glow plasma to be incident on the substrate. It was found that the "unbalanced" electrically-controlled model could give six times the heat load to a substrate in comparison with a balanced permanent magnet structure. Such a load resulted from the bombardment of the substrate with the plasma (revealed by the measurement of the I-V characteristics), and gave a 30 volt negative bias as well as saturated electron and ion currents of around 90 and 1 mA respectively (a magnetron operating current: 0.8A). The heat load was lkWm⁻². This compared to a 1 volt positive bias with current of 1.4 and 0.5 mA for the balanced case. This bombardment was used as a neutralised ion beam to enhance film growth during sputtering. The effect of the magnetic field configuration has been observed on the operating characteristics of a planar magnetron. In particular, the deposition rate, the currents to a probe and heat load, as a function of the outer pole solenoid current, were measured. The deposition rate/input power was constant at 19 mÅ/s/W, independent of the outer pole solenoid current. In the region from 20 to 40 A of the outer pole solenoid current, the configuration of the magnetic field seemed to be concentric and the electrons were confined by it. But from 40 to 80 A, the magnetic field became dispersed outwards along the direction to the magnetron and the electrons followed it. Consequently, following bombardment of the surface by electrons and neutralising ions, the currents to a probe and the heat load, gave a behaviour. The effect of the pressure has been observed on probe current, floating potential and heat load. With the pressure increasing, they decreased. It seems that the mean free path of particles becomes shorter and then scattering of them increases. The influence of the magnetic field strength on the plasma, created at the rear of a substrate, has been observed. In particular, the floating potential and the charged particle bombardment of the substrate were measured. Permanent magnets at the rear of the substrate, outside of the chamber, could make the configuration of the magnetic field change and control the floating potential from -3 to -59 V. At the same time, they influenced the current-voltage characteristics of a probe and made it change following the direction of the field. Ti0₂ is a very important thin film material in optics because the refractive index is high and it can also satisfy the requirements of a hard, dense and chemically stable coating. In our study, the effect of the floating potential, and the resulting ion beam bombardment on the properties of Ti0₂ thin films deposited by reactive planar magnetron sputtering, has been observed. In reactive magnetron sputtering of Ti0₂, as the partial pressure of oxygen is increased, reaction products form on the target (it is poisoned) which lead to an unstable situation with the cathode switching from metal to oxide uncontrollably. More sophisticated control techniques are required in order to get a stoichiometric Ti0₂, film. The oxygen flow was controlled by observation of the light emission of the Ti spectral line. This was measured using a band pass filter and a photomultiplier. It maintained the oxygen flow by regulating a piezovalve. The optical emission controller gave a complete range of Ti to oxygen ratios. As a result, we obtained samples with a high refractive index of 2.52 at 633 nm and a high deposition rate of 4 Å/s. The properties measured were the refractive index, the surface composition and morphology, and the crystallinity. The relationship between the refractive index and the proportions of 'anatase' and 'rutile' crystal structures of the Ti0₂ films was especially considered and the dependence on the floating potential was assessed. Also, Al₂0₃, Cuo, ZnO have been sputtered and the effect of pressure instability assessed. Their properties were measured.

The oxidation of dopamine in aqueous solutions deposits thin conformal films on a wide variety of material surfaces. These films consist of a material known as polydopamine (PDA), and they exhibit chemical and structural similarities to melanin pigments and adhesive proteins secreted by mussels. The facile synthesis and versatile adhesion of PDA enable the functional modification of numerous material surfaces for applications in biomedical devices, energy storage, and water purification. This thesis details fundamental investigations into the deposition, oxidation, and adhesive mechanisms of PDA films. Depositing PDA films on substrates with different controlled chemistries revealed the importance of solution pH and initial deposition rates on the morphology of the films. The deposition of PDA molecules with increasing pH depends on two competing factors: increased generation rate of PDA molecules versus increased solubility due to catechol ionization. The areal density and coverage of three-dimensional PDA islands is influenced by the surface charge and hydrophobicity of the substrate in aqueous solutions. Spectroscopic and electrochemical characterization of PDA films revealed that redox-inactive metal cations can accelerate the oxidation of PDA. The generation of radicals of 5,6-dihydroxyindole were monitored in situ via ultraviolet-visible spectroscopy as a function of cation concentration and pH. The extent of oxidation was quantified by cyclic voltammetry. The resulting oxidation modifies the metal sorption properties of PDA by generating more carboxylic acid groups and enhancing the iron chelation of the films. The adhesive stability of PDA films was characterized by delamination kinetics of films on SiO2 and indium tin oxide (ITO). PDA film adhesion is a substrate, salt, and oxidation-dependent phenomenon. Long-term adhesive stability of PDA films can be promoted by use of higher dopamine concentrations during synthesis, incorporation of multivalent cations, and avoiding alkaline conditions and strongly oxidizing electrical bias. Elastic moduli of PDA films were quantified by compressive thin film wrinkling, and the measured value of 2.0 ± 0.9 GPA agrees with simulations of PDA based on an oligomeric aggregate model. This thesis helps develop a framework for understanding the synthesis, composition, microstructure, and stability of PDA films.

This work focuses on the impact of defects, intrinsic or artificially introduced, on the functional properties of thin, epitaxial oxide films. In the first part, the origin of the ferromagnetic properties of Mn-doped and undoped zinc oxide is studied. The deposition conditions are found to have a significant impact on the structural, transport and magnetic properties of the thin films. Combining x-ray magnetic circular dichroism and magnetometry experiments, it is established that the transition metal dopants (i.e. Mn) have no influence on the ferromagnetic nature of the zinc oxide, but that localised magnetic moments on intrinsic defects are in fact responsible for the ferromagnetic behaviour. A relation between strain (related to defect concentration) and magnetisation is established. In the second part of this dissertation, artificially introduced defects are employed in order to discover the fundamental conduction mechanism behind the two-dimensionally conductive LaAlO3/SrTiO3 interface. All experiments, from varying deposition temperature, to oxygen pressure, to laser fluence or to the insertion of (doped) perovskite layers, point towards a structurally governed conduction mechanism, although the exact details are still unclear. Distinct transitions in the resistance versus temperature curves are observed at different values than the bulk phase transformation temperature. These transitions form the boundaries of different conduction modes, with tendencies towards non-Fermi-liquid behaviour observed in certain two-dimensionally conducting samples in limited temperature regimes. By optimising the (defect) structure at the interface, i.e. by introducing a single unit cell of (La0.5,Sr0.5)TiO3 or SnTiO3, it is shown that the sheet carrier density can be dramatically enhanced, up to an order of magnitude higher than unmodified LaAlO3/SrTiO3 interfaces with a value of 1e14 cm−2 at 200 K. Finally, attempts at functionalising the conductive heterointerface by doping and inserting (anti)ferromagnetic layers are made.

Bismuth layer-structured ferroelectrics have been recognised as promising film materials for ferroelectric random access memory application due to their excellent fatigue resistance and other electrical properties. This work deals with the deposition and characterisation of epitaxial and polycrystalline W-doped SrBi2Ta2O9 (SBT) and lanthanide-doped bismuth titanate (BiT) films. SBT and W-doped SBT films were fabricated by pulsed laser deposition (PLD) on platinised silicon substrates. The effects of fabrication temperature and W-doping level on film properties were studied. The crystallinity of SBTW films improved with increasing fabrication temperatures, resulting in enhanced ferroelectric properties and dielectric properties above the fabrication temperature of 750 °C. Dense ceramic samples of Nd- and Sm-doped BiT (BNdT and BSmT) were successfully fabricated for PLD targets by solid state processing. Highly epitaxially (001)-, (118)-, and(104)-oriented Nd-doped bismuth titanate (BNdT) films were grown by PLD on (001)-, (011)-,and (111)-oriented SrTiO3 (STO) single crystal substrates, respectively. A three-dimensional orientation relationship between films and substrates was derived as: BNdT(001)//STO(001),BNdT[ 110 ]//STO[100]. Films showed strong dependence of structural and ferroelectric properties on the crystal orientation. PLD-grown BSmT films on platinised silicon substrates were studied as a function of fabrication temperature, effects of Pt bottom layer orientation, Sm doping level, and LaNiO3 buffer layer. An alkoxide-salt chemical solution deposition (CSD) method was adopted to prepare the precursors for BSmT (BNdT) film fabrication. Precursors of Bi-Sm(Nd)-Ti which were stable for at least eight months in air ambient were successfully developed. In-situ FT-IR studies suggest that acetic acid serves as chelating agent to improve the homogeneity of the precursor solution by generating a dense and homogeneous Ti-O-Ti polymeric network. The electrical properties of the films fabricated in this study (dielectric and ferroelectric properties, leakage current characteristics and electrical fatigue properties), are comparable or superior to these previously reported for similar films developed by other techniques or with other doping elements. Low temperature electrical properties of BSmT films suggest that the films are very promising for extremely low temperature nonvolatile memory applications. The results of BNdT films annealed at different oxygen partial pressure (O2, air, N2) showed that oxygen ambience affected structural properties of the films by enhancing the growth of perovskite phase (phase formation), increasing grain size (grain growth), and assisting the growth of (117)-oriented grains (crystallographic orientations). Piezoresponse force microscopy (PFM) was adopted to characterise BSmT films. Domain structures were clearly observed in a PLD-grown BSmT film, which were closely related to the grain structures. Domain manipulation was carried out in a CSD-derived BSmT film, showing that the film can be nearly uniformly polarised, which can be used in nanoscale device fabrication. Clear hysteresis loops were measured by PFM, which was an important proof of ferroelectricity. Large spatial variations of piezoelectric hysteresis loops of a CSD-derived BSmT film were observed across the film surface. Effective electrostriction coefficient (Qeff) of a PLD-grown BSmT film was measured, showing that BSmT films had better piezoelectric properties (higher Qeff, higher dzz) than SBT films, un-doped BiT ceramics and films. It suggests that BSmT films are promising piezoelectric materials for MEMS use.

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