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The aim of this work was the study of sputtered zinc oxide (ZnO) film deposition, the optimisation and characterisation of film properties and applications as a sensing material. In recent years there has been increased interest in ZnO in terms of its potential applications as piezoelectric films (or coatings) for surface acoustic wave devices (SAW), for IR and visible light emitting devices and UV sensing. The electrical, optoelectronic and photochemical properties of undoped ZnO have resulted in its use for solar cells, transparent electrodes and blue/UV light emitting devices. ZnO is a unique material that exhibits both semiconducting and piezoelectric properties. In the past decade, numerous studies have been made on both production and application of one-dimensional ZnO. Compared with other semiconductor materials, ZnO has a higher exciton binding energy of 60 meV, which gives it a high potential for room temperature light emission, is more resistant to radiation, and is multifunctional as it has piezoelectric, ferroelectric, and ferromagnetic properties. ZnO-based semiconductor and nanowire devices are also promising for the integration on a single chip. So far, the various applications of ZnO nanomaterials such as biosensors, UV detectors and field emission displays are being developed. In this work, ZnO was sputtered using both DC and RF magnetron sputtering. Reactive DC sputtering was performed with a Zn target and oxygen plasma, while RF sputtering was performed with a ZnO target. Comparisons between films deposited under different conditions on different substrates were employed to assess film properties. Several experiments were performed on as-grown films as a control for subsequence treatments, other samples were post-annealed in N2 at temperatures up to 1200 ºC, the highest reported annealing temperature and the quality of the deposited films was determined using PL, RBS, XRD, SEM and AFM. The piezoelectric properties (d33) of selected films were determined using single beam interferometry, double beam interferometry, and for the first time, using piezoelectric force microscopy (PFM). It was found that DC sputtered films yielded better quality films as evident by PL and XRD analysis and higher piezoelectric response than RF sputtered films. Films deposited using DC sputtering on Si substrates and followed by post-annealing in N2 atmosphere at 1100 ºC showed the highest recorded PL response, while films deposited on sapphire showed good PL response without any need for post-annealing. The d33 of selected films were determined first using single beam interferometry and inflated results were reported, caused by sample bending/buckling. Double beam interferometry results confirmed d33 values in the range of 3.3 to 4.3 pm/V. Piezoelectric force microscopy (PFM) which is based on AFM, was employed to investigate the local electromechanical (piezoelectric) properties of the ZnO films. UV sensing was demonstrated using Schottky contacts and SAW devices on ZnO deposited on Si and post-annealed. In the first instance, Schottky contacts were fabricated on the films and the I V characteristics determined under exposure of various light sources. The current increased up to one order of magnitude during exposure with a halogen light bulb, which is known to emit energy in the UV band. Another experiment was performed using surface acoustic wave (SAW) devices which were fabricated on the films and interrogated using a network analyser. These SAW devices contain an interdigitated transducer and two reflectors each. The signals sent back from the two reflectors were analysed under various light conditions and gave lower readings during exposure to UV light. In order to enable device fabrication of UV sensors a novel “super coating”, achieving both optimised PL and d33 properties, was designed, fabricated and tested. The structure is based on optically transparent Quartz substrate. During this experiment the first DC sputtered coat was optimised to have high PL response by post-annealing at 900 ºC. Afterwards, the second coat was left as-sputtered in order to have highly piezoelectric properties. Preliminary analysis using XRD showed two peaks corresponding to the annealed and not annealed coat, which suggest the super coating combines the properties of the two individual films. This configuration has the potential to be used as UV sensing material and as piezoelectric substrate for SAW devices.

A metal-insulator-semiconductor (MIS) device with a trilayer insulator structure consisting of sputtered SiO₂ (~50nm)/evaporated pure germanium (Ge) layer (2.4nm)/rapid thermal oxide (~5nm) was fabricated on a p-type Si substrate. The MIS device was rapid thermal annealed at 1000°C. Capacitance-voltage (C-V) measurements showed that, after rapid thermal annealing at 1000°C for 300s in Ar, the trilayer device exhibited charge storage property. The charge storage effect was not observed in a device with a bilayer structure without the Ge middle layer. With increasing rapid thermal annealing time from 0 to 400s, the width of the C-V hysteresis of the trilayer device increased significantly from 1.5V to ~11V, indicating that the charge storage capability was enhanced with increasing annealing time. High-resolution transmission electron microscopy results confirmed that with increasing annealing time, the 2.4nm amorphous middle Ge layer crystallized gradually. More Ge nanocrystals were formed and the crystallinity of the Ge layer improved as the annealing time was increased. When the measurement temperature was increased from –50°C to 150°C, the width of the hysteresis of the MIS device reduced from ~10V to ~6V. This means that the charge storage capability of the trilayer structure decreases with increasing measurement temperature. This is due to the fact that the leakage current in the trilayer structure increases with increasing measurement temperature. / Singapore-MIT Alliance (SMA)

Optical and electrical properties of electrochemically lithium ion intercalated thin films of x-ray amorphous tungsten oxide made by magnetron sputtering on glass substrates coated with a thin layer of conductive tin doped indium oxide, have been studied. The composition and the density of the films were characterized by the ion beam analysis methods Rutherford Backscattering Spectroscopy and Elastic Recoil Detection Analysis. The optical properties, transmittance and reflectance were investigated by spectophotometry in the wavelength range 300-2500 nm. The absorption coefficients were calculated at different lithium intercalation levels. It was found that the absorption coefficient in an as-deposited blue film has a similar asymmetric shape as for films intercalated to a Li/W ratio of ~0.03. It was possible to electrochemically bleach this film to transparency. Stoichiometric films show optical irreversibility between the bleached and the colored state in the first cycle. A polaron absorption model has been compared to the absorption coefficient for films of different intercalation levels. An increase in the Fermi level and in the polaron band width, and a nearly constant activation energy was found as the Li/W value increased. The radius of the polaron wavefunction for different lithium intercalation levels and film compositions has been estimated from electrical measurements. The total absorption coefficient has been compared to the site-saturation model. The model is good for films intercalated in the optically reversible region. A modified site-saturation model that could be applied also in the optically irreversible region and involves electron transitions between W6+, W5+ and W4+ sites, has also been compared to experimental values. It was found that the total absorption, optical density and the coloration efficiency is higher for the WO2.63 film than in the less oxygen deficient films and that this film is optically more durable in an electrochemically cyclic lifetime device test.

Tin oxide (SnO2) has been investigated and used as a gas sensing material for numerous applications from the very start of the sensor industry. Most of these sensors use semiconductors (mostly SnO2) as the sensing material. In this work, SnO2 was prepared using 2 techniques: firstly the MOCVD where we dope the sample with fluorine and secondly sputtering technique where samples are undoped in our case. These samples were tested at different conditions of temperature varying from room temperature to 150 degrees C, in ambient gas atmosphere of 200 CC Nitrogen (N2). The typical thickness of the sputtered samples was 1500 A with a sheet resistance of 300; and these sputtered samples were found to be more porous. These samples when tested in room temperature showed a change of -4 [mu]A change for 10% and -9 [mu]A for 90% of H2. While at higher temperatures (150 degrees C) the current change for 10% increased from -4 [mu[A to -2 mA showing that higher ambient temperatures increased the sensitivity of the samples. The repeatability of the samples after a period of 3 days were found to be well within 10%. The samples prepared by MOCVD were fluorine doped, the samples were conductive to 1 order of magnitude more than the sputtered ones. 3 different samples of approximate thicknesses 3000, 6000 and 9000 A were prepared and tested in this work, with typical resistivity of 6 /cm and the grains in this case are typically more compact. The conductive samples showed no response at room temperature, including the 6000 and 9000 A samples. While at higher temperatures (150degreesC) the 3000 A sample showed very sensitive response to H2. Also noticed was that the response was linear compared to the sputtered samples. The samples showed very good repeatability and sensitivity.

In this thesis, we present the investigation of influence of methanol crossover, which significantly decreases the performance of DMFC (Direct Methanol Fuel Cell). Additionally the poisoning effect occurs on the cathode side. The durability of cathode catalyst exposed by methanol vapor is studied. Moreover, the regene- rative behavior after exposition has been found. The comparison of commercial catalyst with our own sputtered Pt and PtCo and PtRu thin layers as cata- lyst is presented. Obtained results have shown that PtCo is reasonable compro- mise between pure Pt, which has high performance, and PtRu, which is tolerant to methanol poisoning. Future research should further evaluate the advantages of PtCo cathode catalyst prepared by standard procedures and its market poten- tial in comparison with PtRu. 1

My dissertation primarily focuses on the fabrication of materials for solid phase microextraction (SPME) and separation devices. In my first project, I used direct current magnetron sputtering (DCMS) to prepare sputtered silicon coatings on fused silica fibers. These fibers were then subjected to the chemical vapor deposition of 6-phenyhexylsilane (6-PH) as a stationary phase. Six different types of fibers were made using two different throw distances (4 cm and 20 cm) and three different silicon thicknesses (0.5, 1.8, and 2.8 µm). These coatings were characterized by time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), spectroscopic ellipsometry (SE), and contact angle goniometry. These SPME fibers were evaluated using gas chromatography (GC). The extraction efficiencies of sputtered, 6-PH-coated fibers were compared to that of a commercial fiber (7 µm PDMS) for polycyclic aromatic hydrocarbons (PAHs). Our 2.8 µm thick sputtered silicon coatings showed competitive extraction of low molecular weight PAHs and ca. 3 times the extraction efficiency for higher molecular weight PAHs. In addition, it outperformed the commercial fiber by showing better linearity, repeatability, and detection limits. A method for analyzing polyaromatic hydrocarbons in baby formula was developed, which showed very good linearity (0.5-125 ppb), repeatability (2-26%), detection limits (0.12-0.81 ppb), and recoveries (103-135%). In my second project, I focused on preparing sputtered carbon SPME fibers using DCMS sputtering. These fibers were tested with and without PDMS coatings on top by SPME-GC-MS. In addition, a new SPME evaluation mix was developed for testing the newly developed SPME fibers. The evaluation mix included analytes with diverse functionalities and properties. Our best carbon fiber showed very competitive extraction capabilities on a per volume basis when compared with a commercial 95 µm carbon-based fiber. In a third project, I built an ALD system to deposit thin films inside GC capillary columns. This system has a unique design that also allows for ALD on witness silicon samples before and after the capillary column. This system yields very promising results with ALD of alumina inside 5 and 12 m long capillary columns. The ALD coatings deposited inside the columns were characterized by transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). The thicknesses of the coatings on witness shards were almost identical to the thicknesses of the coatings in the capillaries. My fourth project focused on characterizing a liquid polymer (diphenyl siloxane dimethyl siloxane (DPS-DMS)) via SE. This material was a potential stationary phase for our SPME fibers. Transmission measurements were obtained via a dual cuvette approach that eliminated the effects of the cuvettes and their interfaces. The optical function of this material was modeled with a Sellmeier function in its transparent region.

Electrochemical anodization is a facile technique to synthesize ordered oxide nanostructures. Though the number of materials exhibiting anodized nanostructures has increased considerably in the recent years, only nanoporous alumina and nanotubular titania have been investigated extensively for various applications. Anodized nanostructures, nanotubes and nanopores, of zirconia are also of considerable interest for applications such as templates, sensors and solid-oxide fuel cells. In spite of the potential applications of zirconia, these nanostructures have been barely studied. As most of these applications require elevated temperatures in excess of 400C, thermal stability becomes an important attribute. Even though zirconia (Tm=2715C) has as higher melting point than alumina(Tm = 2072C), literature reports and initial research showed that the thermal stability of anodized zirconia was limited to 500C-1 h compared to 1000C-4 h for alumina. The work carried out as a part of this research showed that halide ions used in the synthesis are the possible cause for the lower thermal stability. Chemical treatment of the zirconia membranes to neutralize the halide ions helped enhance the stability to 1000C-1 h, thus, improving their usability for most of the applications mentioned above. Most of the current reported work on aluminum, zirconium, and titanium is predominantly limited to anodization of foils which can only yield free-standing nanostructures. As synthesis of these nanostructures on a substrate would further facilitate their usage, supported anodized zirconia nanostructures were synthesized by anodizing sputtered zirconium films. This study showed that the anodized morphology depends strongly on the sputtered film microstructure, which changes in accordance with the Thornton’s zone diagrams. A general approach thus developed is expected to be applicable to anodization of all metallic films. Most applications involving zirconia also require stabilization against a tetragonal-monoclinic phase transformation by suitable alloying such as with yttria. Towards this end, routes to develop anodized yttria-stabilized zirconia nanostructures, which are nonexistent, were explored. The synthesis of yttria stabilized zirconia nanostructures with no detectable monoclinic phase was achieved. Yttrium alloying using a solution treatment was found to enhance stability of the supported nanostructures to 900C-16 h, which makes it possible to now evaluate these nanostructures, especially for micro-SOFC applications.