Oligo(ethylene glycol) groups have been used as substituents in poly(p-phenyleneethynylene)s (PPEs) to provide solubility, and to boost quantum yield. Properties such as water-solubility and increased quantum yield in aqueous solution make these conjugated systems promising for biosensory applications. In this thesis, a PPE containing a branched ethylene glycol side chain is synthesized as part of a polymer array for glycan biosensing. I also report that the same side chain can be put to use in a red-emissive polymer to lend water solubility. Another monomeric unit, containing ethylene glycol chains, is incorporated into a PPE to create an ampiphilic polymer. The versatility of these polymers allows them to be used for a variety of purposes, some of which will be described herein.

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Please read the abstract in the section front of this document. / Dissertation (MSc (Physics))--University of Pretoria, 2006. / Physics / unrestricted

After the pioneering investigations into graphene-based electronics at Georgia Tech, great strides have been made developing epitaxial graphene on silicon carbide (EG) as a new electronic material. EG has not only demonstrated its potential for large scale applications, it also has become an important material for fundamental two-dimensional electron gas physics. Graphene is generally considered to be a strong candidate to succeed silicon as an electronic material. However, to date, it actually has not yet demonstrated capabilities that exceed standard semiconducting materials. One disadvantage of conventionally fabricated graphene devices is that nanoscopically patterned graphene tends to have disordered edges that severely reduce mobilities thereby obviating its advantage over other materials. The other disadvantage is that pristine graphene does not contain a band gap, which is critical for standard field effect transistor to operate. This thesis will show that graphene grown on structured silicon carbide surfaces overcomes the edge roughness and promises to provide an inroad into nanoscale patterning of graphene. High-quality ribbons and rings can be made using this technique.

The focus of the following research was to (1) understand the chemistry involved in nitriding an organosilicate glass substrate prior to tantalum deposition, as well as the effect nitrogen incorporation plays on subsequent tantalum deposition and (2) the reduction of a native oxide, the removal of surface contaminants, and the etching of a HgCdTe surface utilizing atomic hydrogen. These studies were investigated utilizing XPS, TEM and AFM. XPS data show that bombardment of an OSG substrate with NH3 and Ar ions results in the removal of carbon species and the incorporation of nitrogen into the surface. Tantalum deposition onto a nitrided OSG surface results in the initial formation of tantalum nitride with continued deposition resulting in the formation of tantalum. This process is a direct method for forming a thin TaN/Ta bilayer for use in micro- and nanoelectronic devices. Exposure to atomic hydrogen is shown to increase the surface roughness of both air exposed and etched samples. XPS results indicate that atomic hydrogen reduces tellurium oxide observed on air exposed samples via first-order kinetics. The removal of surface contaminants is an important step prior to continued device fabrication for optimum device performance. It is shown here that atomic hydrogen effectively removes adsorbed chlorine from the HgCdTe surface.

Groundbreaking progress in molecule-based optoelectronic devices for lighting, display and energy-harvesting technologies demands highly efficient and easily processable functional materials with tunable properties governed by their molecular/supramolecular structure variations. To date, functional coordination compounds whose function is governed by non-covalent weak forces (e.g., metallophilic, dπ-acid/dπ-base stacking, halogen/halogen and/or d/π interactions) remain limited. This is unlike the situation for metal-free organic semiconductors, as most metal complexes incorporated in optoelectronic devices have their function determined by the properties of the monomeric molecular unit (e.g., Ir(III)-phenylpyridine complexes in organic light-emitting diodes (OLEDs) and Ru(II)-polypyridyl complexes in dye-sensitized solar cells (DSSCs)). This dissertation represents comprehensive results of both experimental and theoretical studies, descriptions of synthetic methods and possible application allied to monovalent coinage metal-based functional materials. The main emphasis is given to the design and synthesis of functional materials with preset material properties such as light-emitting materials, light-harvesting materials and conducting materials. In terms of advances in fundamental scientific phenomena, the major highlight of the work in this dissertation is the discovery of closed-shell polar-covalent metal-metal bonds manifested by ligand-unassisted d10-d10 covalent bonds between Cu(I) and Au(I) coinage metals in the ground electronic state (~2.87 Å; ~45 kcal/mol). Moreover, this dissertation also reports pairwise intermolecular aurophilic interactions of 3.066 Å for an Au(I) complex, representing the shortest ever reported pairwise intermolecular aurophilic distances among all coinage metal(I) cyclic trimetallic complexes to date; crystals of this complex also exhibit gigantic luminescence thermochromism of 10,200 cm-1 (violet to red). From applications prospective, the work herein presents monovalent coinage metal-based functional optoelectronic materials such as heterobimetallic complexes with near-unity photoluminescence quantum yield, metallic or semiconducting integrated donor-acceptor stacks and a new class of Au(III)-based black absorbers with cooperative intermolecular iodophilic (I…I) interactions that sensitize the harvesting of all UV, all visible, and a broad spectrum of near-IR regions of the solar spectrum. These novel functional materials of cyclic trimetallic coinage metal complexes have been characterized by a broad suit of spectroscopic and structural analysis methods in the solid state and solution.

One of the main challenges in the electronics manufacturing and packaging development is how to integrate more functions inside the same or even smaller size. To meet the demand for higher integration, the interest toward passive and active component embedding has been increasing during the past few years. One of the main reasons for the growing interest toward embedded active components, in addition to demand for higher packaging density, is the need for better electrical performance of the component assemblies. However, it is little known how embedded IC and passives affect the reliability of IC packaging. Solder joints have been used in the electronic industry as both structural and electrical interconnections between electronic packages and printed circuit boards (PCB). When solder joints are under thermal cyclic loading, mismatch in coefficients of thermal expansion (CTE) between the printed circuit boards and the solder balls creates thermal strains and stresses on the joints, which may finally result in cracking. Consequently, the mechanical interconnection is lost, leading to electrical failures (such as hard/intermittent open, parametric failure), which in turn causes malfunction of the circuit or whole system. When a die is embedded into a substrate, Young's modulus of the die is larger than one of the core of the substrate and the CTEs of the die is smaller than those of the substrate. As a result, mismatch in coefficients of thermal expansions (CTE) between the substrate with the embedded device and the solder balls may increase. In the present study, the stress of chip scale packages (CSP) with an embedded die under thermal cycling conditions is evaluated using the finite element method. The viscoplastic model for solders including matrix dislocation mechanism and grain boundary sliding model developed by Yi et al. (2002) is employed.

A process has been developed to make the dielectric layer for organic thin-film transistors (OTFTs) in a roll-to-roll vacuum web coater environment. This dielectric layer combined with an organic semiconductor layer and metal layer deposited in vacuum allows a solvent-free process to make organic/inorganic multilayer structures for thin-film electronic devices on a flexible substrate at, potentially, high speed. The polymeric gate dielectric layers were fabricated by flash evaporation of acrylic monomers onto a polymer film with pre-patterned metal gates followed by radiation curing by electron beam, ultra-violent light (UV) or plasma. With a non-polar dielectric surface, charge carrier mobility (μ) of 1 cm²-V^-1s^-1; on/off curren ratio of 10⁸, sub-threshold swing (SS) of 0.3 V/decade and saturated output curve were routinely achieved in dinaphtho-[2,3-b:2'3'-f]thieno[3,2-b]thiophene (DNTT) transistors with dielectric layer of tripropylene glycol diacrylate (TPGDA) of ~400 nm. Apart from the TPGDA, monomer formulas including 1,6-Hexanediol diacrylate (HDDA) as well as several commercial acrylic resins have been used to make the dielectric layer. The highest areal capacitance of 41nF-cm^-2 was achieved with a pin-hole free film of less than 100 nm made of an acrylate mixture resin. A non-polar dielectric surface treatment layer has been developed based on flash evaporation of lauryl acrylate and HDDA mixture. The transistors with the buffer layer showed constant performance and a mobility fivefold greater than those of untreated samples. The effect of humidity, oxygen, and light during switching cycles of both pentacene and DNTT transistors were studied. Water and oxygen/illumination had a distinct effect on both pentacene and DNTT transistors. Oxygen leads to acceptor-like charge traps under illumination, which shifted the turn-on voltage (V_to) to more positive values. In contrast, water in transistors gave rise to donor-like charge traps, which shifted the V_to and the threshold voltage (V_T) more negatively. The DNTT devices showed good stability in dry air without encapsulation, while pentacene transistors degraded with either repeating measurement or long term storage. A DNTT transistor with a PS-coated TPGDA dielectric layer showed stable drain current (I_d) of ~105A under bias stress of the gate voltage (em>V_g) of -20V and the drain voltage (em>V_d) of -20V for at least 144 hours. The V_to shift after the stress was less than 5 V and was recoverable when the device was kept in dry air for a few days. Possible reasons for the V_to shift have been discussed.

The electronics industry is shifting its emphasis from reducing transistor size and operational frequency to increasing device integration, reducing form factor and increasing the interface of electronics with their surroundings. This new emphasis has created increased demands on the electronic package. To accomplish the goals to increase device integration and interfaces will undoubtedly require new materials with increased functionality both electrically and mechanically. This thesis focuses on developing new interconnect and printable conductive materials capable of providing power, ground and signal transmission with enhanced electrical performance and mechanical flexibility and robustness. More specifically, we develop: 1.) A new understanding of the conduction mechanism in electrically conductive composites (ECC). 2.) Develop highly conductive stretchable silicone ECC (S-ECC) via in-situ nanoparticle formation and sintering. 3.) Fabricate and test stretchable radio frequency devices based on S-ECC. 4.) Develop techniques and processes necessary to fabricate a stretchable package for stretchable electronic and radio frequency devices. In this thesis we provide convincing evidence that conduction in ECC occurs predominantly through secondary charge transport mechanism (tunneling, hopping). Furthermore, we develop a stretchable silicone-based ECC which, through the incorporation of a special additive, can form and sinter nanoparticles on the surface of the metallic conductive fillers. This sintering process decreases the contact resistance and enhances conductivity of the composite. The conductive composite developed has the best reported conductivity, stretchability and reliability. Using this S-ECC we fabricate a stretchable microstrip line with good performance up to 6 GHz and a stretchable antenna with good return loss and bandwidth. The work presented provides a foundation to create high performance stretchable electronic packages and radio frequency devices for curvilinear spaces. Future development of these technologies will enable the fabrication of ultra-low stress large area interconnects, reconfigurable antennas and other electronic and RF devices where the ability to flex and stretch provides additional functionality impossible using conventional rigid electronics.