Recently techniques have been developed which enable the conductance of individual molecules sandwiched between metal electrodes to be measured. This has revealed important fundamental science and has the potential to deliver unparalleled miniaturisation of electronic devices. The use of ferromagnetic metal electrodes is expected to lead to devices with interesting spin transport behaviour, however experiments are typically performed under ambient conditions so that Au or another non-reactive metal must be used to prevent sample contamination. Here a scanning tunnelling microscope break junction technique was developed to measure the conductance of single-molecule junctions with clean ferromagnetic electrodes under electrochemical conditions. The use of electrochemical control protects the metal contacts from oxidation and enables electrochemical gating behaviour to be explored. An electromagnet was constructed to provide an in-situ magnetising field during the experiments and a procedure for the automatic selection of data exhibiting features consistent with the formation of molecular junctions was also developed. Initial measurements were performed using Au contacts. The conductance was found to depend strongly on the chemical structure of the molecules and was in good agreement with previously reported values. 4,4'-Bipyridine and closely related molecules measured using Ni contacts exhibited larger conductance and stronger gating behaviour compared to Au-based junctions, whilst Co contacted molecules produced even larger conductance values. Ni 14,4' vinylenedipyridine 1 Ni junctions were also influenced by changes in pH. The differences between Ni and Au contacts were explained in terms of the strong interaction between the molecule and the Ni d-band, which unlike Au has a large density of states at the Fermi level. Magnetoresistance measurements were carried out for Ni 14,4'-bipyridine 1 Ni single-molecule junctions by comparing the conductance obtained with a variety of different magnetic fields applied. A giant magnetoresistance of 48±6% was measured, however this result was not reproducible due to inadequate control of the magnetic configuration. Anisotropic magnetoresistance experiments did not reveal any magnetoresistance effect.

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The stop-band tuning of elastomeric distributed Bragg reflectors (DBRs) by deformation, and the underlying mechanical phenomena were studied. The main findings can be summarized as the follows. 1. Repeatable full-colour tuning of the DBR is possible by inflating the DBR into an axisymmetric balloon. 2. The heterogeneous distribution of strain originating from the inflated shape has an impact on the optical and mechanical response of the DBR. 3. Thin elastomer films are under strong influence of surface tension which influences their stress and strain during the fabrication process. The thesis will be organized as follows. After an introduction to the thesis in Chapter 1, Chapter 2 will discuss the theoretical background. The materials and methods used in the experiments will be covered in Chapters 3. The optics and the mechanics of elastomeric DBRs will be discussed in Chapter 4 and 5. Throughout these chapters, the elastomeric DBRs were studied in axisymmetrically inflated states. The inhomogeneous strain distribution arising from the geometry of the inflated state and the mechanical property of the material, gave rise to a novel colour mixing effect. Chapter 6 discusses the strain induced by the fabrication method of the elastomeric DBR. Soft materials are highly susceptible to buckling and related instabilities; therefore studying the stress and strain in a systematic fashion would open the door for improving the quality, scalability and reproducibility of the fabrication of elastomeric DBRs and related optical devices.

This thesis explores an alternative route to induce and control the structure formation process in thin films by the use of strong electric fields. The objective of this thesis is to investigate, establish and apply the use of the electrohydrodynamic (EHD) lithography as a versatile patterning tool on the sub-micrometre and nanometre length scales for functional materials in thin films. Thin films are ubiquitous, they are found in nature and used in almost every aspect of daily life. While film instabilities are often undesirable in nature and technology, they can be utilized to produce structures by precisely controlling the destabilization of the film. EHD lithography utilizes instabilities induced by means of an electric field to fabricate periodic structures. While still in the developing phase, EHD patterning is set to become a competitive candidate for low-cost lithographic technology for a number of applications. Herein, the applied potential of this lithographic process is explored by expanding its applicability to a broad range of materials and material combinations and by a simultaneous patterning of multilayer systems or functional polymers yielding hierarchical architectures with novel functionalities. An intrinsic problem of the EHD patterning process is the rather long pattern generation times, which has to be overcome. A number of low-viscosity materials are exploited as high-speed resists to significantly reduce the patterning time of EHD to a few seconds. These results demonstrate the versatility of the EHD method and render it technologically appealing. Further work presents a route towards controlled reproducible alignment of carbon nanotubes (CNTs) during an EHD patterning process of nanocomposite. The degree of nanotube alignment is tuned by adjusting the EHD parameters and the degree of alignment is mirrored by the conductivity across the film. Patterned surfaces decorated by CNT brushes are also generated in this study. A method to create controlled self-organized hierarchical nanostructures using EHD instabilities is an additional topic of this thesis. Herein, pattern formation harnesses a sequential instability in multilayer thin films induced by an electric field to guide the layer material into design structures, allowing different materials to be patterned in a one-step procedure. This pattern formation enables the fabrication of multi-scale structured arrays as surface enhanced Raman scattering (SERS)-active platforms. Each of the formed structures is effectively tailored to provide high SERS enhancement. Furthermore, crystalline and conductive polymers are patterned using the EHD approach and the underlying structure formation mechanisms are discussed. This extension towards functional material systems offers interesting prospects for potential applications. Finally, the EHD formation of hierarchical structures spanning several length scales is demonstrated. Confining conductive block copolymers in presence of an electric field into fabricated microstructures gives rise to an internal vertical alignment of the copolymers nanometric domains with an additional molecular orientation. Inside the superstructure films ordered arrays of nanocrystals of the constituting block are aligned in a smectic phase giving rise to birefringence. The alignment of the nanodomians improves the charge conduction toward the electrodes. These findings are very promising for use in optoelectronic devices.

The thesis investigates the effects of sand and dust storms on the propagation of microwave radiation. To investigate this the dielectric properties of the basic constituents of these storms, at microwave frequencies, for concentrations varying between 1.3 to 10-6 gm. cm-3 in air, have been determined. The microwave bridge and a phase shifter technique have been used for high (or bulk) concentration studies of sand and dust (1.3 <P <1.9 gm. cm3). A special technique using an open cavity resonator (having high Q-factor) has been used for studies at very low (or powder) concentrations (10 6< P< 10-2 gm.cm3) typically found in storms. The. values of the refractive indices and loss tangents obtained from the open cavity resonator measurements were then compared with those extrapolated from the simpler bulk measurements results and the various well-documented equations (relating permittivities of dispersed particles). The Bottcher and the Bruggeman equations are examples of these extrapolation formulae. In conclusion the open cavity resonator results were preferred. Using the actual experimental results the possible effects of these storms (e. g. attenuation and refraction) on the performance of-communication systems are also discussed.

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