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The dielectric properties of polymeric thin films (100-200 nm) are hard to measure with the standard approaches as the samples aren't free standing necessitating a supporting substrate. Consequently, a planar interdigitated sample holder has been designed to hold the thin film where the polymeric capacitance was derived from the passing fringing fields. The electrodes were fabricated by creating 120 nm trenches in a SiO2/Si wafer; 20 nm Cr was deposited as an adhesion layer prior to the deposition of Cu by thermal evaporation. The electrical measurements were implemented using HP 4294A and a probe station. Devices of 20 to 70 fingers were measured and the results were compared to the analytical and finite element simulation. At 10 KHz, the total measured capacitance of a 20-finger device was about 8 pF with 3 % represented the polymeric contribution. The measurements differed from the calculations or finite modeling results by about 12%.

Previous studies of serum adenosine deaminase have neglected consideration of the two molecular forms of this enzyme that exist in human tissues. The purpose of this study was to survey the distribution of these forms in normal and pathological human sera. Both molecular forms were present in normal serum, though the small form predominated. This form also predominates in lymphocytes, erythrocytes, and in tissues with high specific activity of this enzyme. The ratio of the two forms is different for plasma and serum and can change with sample storage. The activity of the small form varied over a wider range than the activity of the large form in normal serum. Many pathological samples showed an altered distribution of the two forms. This study demonstrates the potential usefulness of serum forms of adenosine deaminase for distinguishing some pathological conditions.

The integration of hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) with plastic substrates enables emerging technologies such as flexible organic light emitting diode (OLED) displays. Current a-Si fabrication processes, however, create residual thin film stress that affects the underlying flexible substrate due to its high mismatch in the coefficient of thermal expansion resulting in a dimensional instability for fabricating TFTs on large area flexible substrates. The motivation of this thesis is to reduce this non-uniformity and improve fabrication throughput of bottom-gated inverted-staggered a-Si:H TFTs on flexible substrates. This thesis therefore encompasses the study of overlay misalignment on TFTs over 3 inch flexible substrates and investigates the electrical characteristics of the TFTs fabricated on plastic platforms. To reduce overlay misalignment of TFTs fabricated on flexible substrates, a plastic-on-carrier lamination process has been developed. The technique comprises of a polyimide tape to attach a 125 um-thick poly-ethylene-napthalate (PEN) flexible substrate to a rigid carrier. This process has been used to minimize stress induced strain of the PEN substrate during the fabrication process; strain, which has been observed after processing a-Si:H TFTs on free-standing substrates. This technique would in turn assist in fabricating uniform stacked-layers as required for a-Si:H TFT fabrication on the PEN substrates. Overlay misalignment is measured after each of the 5 consecutive lithographic steps at 4 corner-most edges of the PEN substrates using a standard optical microscope. Results have shown an overlay misalignment reduction from 21 um to 2 um on average based on the TFTs fabricated on free-standing flexible substrates while ensuring a centre alignment accuracy of +/- 0.5 um. Post fabrication adhesive removal to separate the PEN substrate from the rigid carrier has been accomplished by sample immersion in acetone. The results present a significant increase in fabrication throughput by reducing lithographic overlay misalignment such that the resolution of large-area flexible electronics would be enhanced. Electrical characteristics show the average performance of a-Si:H TFTs with an ON/OFF current ratio of 10^8, field effect mobility of ~0.8 cm^2/Vs, and gate leakage current of 10^-13 A.

Organic semiconductors are envisioned to have widespread applications in flexible displays, radio-frequency identification (RFID) tags, bio- and chem-sensors, as well as organic solar cells. Polymer semiconductors are particularly suitable for the low-cost manufacture of organic electronics using printing techniques due to their excellent solution processability and mechanical properties. This work focuses on the development of two novel building blocks, IBDF and DTA, which can be used for the construction of high performance organic thin film transistors (OTFTs) and organic photovoltaics (OPVs). Two copolymers, P6-IBDF-T and P5-IBDF-T, and a homopolymer P6-IBDF were prepared using the IBDF building block. Copolymer P6-IBDF-T has been prepared via the Stille-coupling polymerization. This polymer exhibits a small band gap of 1.36 eV with HOMO/LUMO energy level of -5.69 eV/-4.43 eV. P6-IBDF-T showed stable electron transport performance in encapsulated thin film transistors and ambipolar transport performance in non-encapsulated TFTs. Balanced hole/electron mobilities of up to 8.2 ??10-3/1.0 ??10-2 cm2V-1s-1 was achieved in bottom-contact, bottom-gate organic thin film transistors. In addition, the broad absorption of the polymer over the UV-Vis range suggested that this polymer is suitable for applications in solar cells. The effect of conjugation on mobility and UV-vis spectra of the polymer was studied by comparing P5-IBDF-T with P6-IBDF-T. The ideal of indirect electron transition was proposed to explain the difference between UV-Vis light absorption spectra for these two polymers. DTA building block was used to construct four D-A copolymers, namely PDTA-T, PDTA-BT, PDAT-BTV, and PDTA-TT. These polymers were characterized by UV-Vis, CV, DSC, TGA, AFM and XRD. Device performance was also investigated on OTFTs. The device performance of DTA based polymer increased as the area of electron donor increase from T in PDTA-T to BTV in PDTA-BTV. PDTA-BTV exhibits hole mobility of 1.3??10-3 cm2 V-1 s-1 with Ion/Ioff value of ~103-4 in bottom-contact, bottom-gate organic thin film transistors. All DTA based copolymers exhibited small optical bandgaps (1.18 ??? 1.27 eV) and required none or moderate thermal treatment during fabrication process. These make them promising candidates for cost-effective OPV applications.

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RF-sputtered CoCr films have been characterized for a variety of deposition conditions, and the most effective parameters which bring about perpendicular anisotropy have been evaluated. In particular bias sputtering has been noted for its role in improving the crystallographic orientation and magnetic properties when applied to the substrate at certain values, hence the root mechanism of the observed improvement has been, as far as possible , investigated . These investigations have, in particular, focused on the extent to which impurity gases are likely to effect the magnetic properties of sputtered films, as well as quantifying the gas contents of the films using as yet unexploited (in this area) method of thermal desorption experiments. In a further attempt to quantify tolerable level of impurity species in the sputtering environment , impurity gases of nitrogen, oxygen and hydrogen, which are commonly present even in high vacuum systems, were intentionally introduced in the sputtering chamber and their effects on both magnetic and crystallographic properties of CoCr were noted . To measure the perpendicular and in-plane magnetic properties of CoCr , a combined polar-transverse Kerr magneto- optic system was costructed , through which direct magnetic measurement of CoCr/NiFe becomes feasible . This method was further exploited to compare volume and surface magnetic properties of CoCr , as measured using a V.S.M and this M-O system. Finally , a CoCr/NiFe W1nchester disc was fabricated on which a recording experiment was successfully performed.

As a contribution to increasing the areal density of digital data stored on a magnetic recording medium, this thesis provides mathematical analyses of various magnetic recording heads. Each of the heads considered here is for use in a perpendicular recording system, writing to or reading from a multi-layer medium which includes a high magnetic permeability layer between the data storage layer and the substrate. The exact two-dimensional analysis is performed in each case by one of two methods: either Fourier analysis or conformal mapping. The types of heads analysed include conventional styles but particular emphasis is placed on the effects of the novel idea of potential grading across the pole pieces. Exact head fields are derived for thin film heads with both constant and linearly varying pole potentials, single pole heads with linearly and arbitrarily varying pole potentials and shielded magnetoresistive heads, all in the presence of a magnetic underlayer. These and other published solutions are used to derive output characteristics for perpendicular replay heads, which are compared with published theoretical and experimental results where possible. The Fourier solutions obtained are in the form of infinite series dependent on at least one set of coefficients which are determined by infinite systems of linear equations. Approximations to the potentials in the head face planes, independent of these coefficients, are derived from the exact Fourier solutions. The accuracy of these approximations is demonstrated when they are used to estimate the vertical field components and the spectral response functions. Heads with graded pole potentials are found to have more localised vertical field components than the corresponding constant potential heads. They are also better suited for use with thin media for 'in contact' recording.

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No description available.