The back recombination processes of electrons from the semiconductor to the oxidized dye and the oxidized redox species can dramatically reduce the efficiency of conventional dyesensitized solar cells (DSSCs). In this work, we have used the electrostatic layer-by-layer (ELBL) assembly technique to specifically manipulate and control the interface between the semiconductor and adsorbed dye layers in DSSCs to potentially minimize this recombination behavior. The interfacial modification has been achieved by applying different combinations and thicknesses of polyelectrolytes using the ELBL method and the performance of the cells has been monitored by measuring the I-V characteristics and the efficiency of the solar cells. The results indicate that an ultrathin polyelectrolyte film, on the order of a few Angstroms, between the semiconductor and the dye layer plays a crucial role on the performance of the solar cell. More specifically, the efficiencies of the DSSCs do not show any improvement after the interfacial treatment when compared to untreated samples. Surprisingly, the efficiency of the cells decreases to some degree, depending on the thickness of the polyelectrolyte films. This suggests that incorporation of a thin (several Angstroms) passive layer between the semiconductor and dye layer in these devices results in an increased resistance of the device and do not significantly reduce the back electron recombination as was originally anticipated. These results show interesting mechanistic information regarding the interfacial interactions of semiconductor/dye interfaces in DSSCs.

The electrical properties of thin polymer films are key parameters in the design of both smaller and faster circuit devices in the microelectronics industry. In this study, we made a three-layer film structure, ABA', to investigate the dielectric interaction between two high-K dielectric polymer thin films, A and A', as a function of the thickness of the middle B layer. The Cole-Cole plot showed clear changes with the thickness of the middle B layer. The total capacitances were evaluated with a simple serial three capacitances model. This ABA' structure is thought to be very useful for studying mechanical and thermal properties of thin polymer film system.

The electrochemical impedance spectroscopy (EIS) has been used for the modelling of the alkyd organic film/carbon steel interface in 3% NaCl solution. Both the dielectric properties of the organic film and the corrosion processes of the metallic substrate were investigated with this method. Analysis of the impedance spectra (Nyquist and Bode plots) and the interpretation with the fitting software developed by Boukamp, established the presence of two time constants in the first 250 immersion hours. One time constant concerning the organic layer describes the electrical and barrier properties of film. The second time constant concerning the substrate represents the corrosion reactions at the film/metal interface. For long immersion periods, after the formation of the conductive pathways in the film and the development of the diffusion processes, are necessary another two time constants concerning these phenomenons. The error magnitude between the measured and calculated data with these electric equivalent circuits is satisfactory. The physical properties obtained from the principal elements of the equivalent electric circuits are in concordance with those obtained from others testing methods.

We have measured the fracture toughness of PMMA slabs with carbon black and colloidal silica fillers placed at the interface. The results show that the fracture toughness decreases linearly with carbon black concentration. The fracture toughness scales as annealing time, t1/2 indicating that it is diffusion limited. Addition of Colloidal Silica drastically reduces the fracture toughness regardless of concentration and annealing time. These results indicate that carbon black introduces physical cross links which decrease dynamics whereas colloidal silica produces permanent chemical cross links which prevent diffusion across the interface.

Emission light through the prism has been investigated from the Kretschmann configuration of the prism/ Ag thin film/ rhodamine-B (RB) LB film in the resonant excitation of the attenuated total reflection (ATR) measurement. The emission light and the spectra strongly depended upon the emission angles where the light was observed. The emission properties corresponded to the dispersion relation of the resonant excitations of surface plasmons (SPs) in the ATR configuration. It was concluded that the emission light was caused by multiple excitations of SPs in the ATR configuration. It is thought that the phenomenon will be used as a new sensing device.

Striking differences have been observed in the deformation modes associated with 2mN constant load nanoscratch events on ultrathin Cr layers deposited on SiOx with and without a dendrimer interlayer. In the absence of the dendrimer distinct ridge formation along the wear track indicative of plowing and wedge formation are observed. By contrast, dendrimer monolayer-mediated films exhibit ridgeless scratches apparently formed in a nearly pure cutting mode. In addition, the width of the scratch trench in the sample without dendrimer is larger than the one with dendrimer.

The surface coating properties of enzymatically polymerized decyl esters of d-tyrosine from aqueous solutions onto gold surfaces have been investigated utilizing the complementary techniques of Potentiometeric Titration, UV-VIS Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS). The aqueous-based coatings are of interest as environmentally friendly and cost-effective replacements for epoxy-based coatings currently employed in the microelectronics industry for both chemical protection and electrical insulation of gold-covered metallic conductors. Experimental results with respect to polymerization pH, immersion pH, and immersion time are presented and compared to the ionization behavior of the monomers in solution. Optimum processing conditions have been established, which yield uniform aqueous-based polymeric coatings on gold conductor surfaces.

Considering the atomic scattering cross sections for neutrons they are an excellent tool to investigate lubrication problems. Two different shear cells have been built to investigate both the dynamics and structural properties of liquids under shear: one cell has been optimised for quasielastic and inelastic neutron scattering while another one has been designed for reflectivity and diffraction work. The dynamical aspects have been studied on the high-resolution backscattering instrument (IN16 at Institut Laue-Langevin (ILL)). Data with a commercial motor oil as a sample have been taken in contact with an aluminium boundary showing directly the developing anisotropy of diffusion under shear. Furthermore within the same set-up it has been possible to monitor the macroscopic velocity distribution including surface slip. In addition, a diffraction experiment has been carried out, demonstrating from a measurement of the position and the profile of the graphite 002 reflection that the ordering of macroscopic graphite particles in a flowing liquid can be studied with neutrons and an ordering with a tilt angle of the particles of 5° to the flow has been determined.

Phase separating binary fluids with the addition of immobile particles, which act as osmotic force centres, were simulated using a Lattice Boltzmann model in two dimensions. In the hydrodynamic over-damped limit, where the flow is entirely driven by capillary effects, the presence of particles that are preferentially wetted by one of the fluid components significantly affects the kinetics of the growth of the fluid domains. The late time dynamics is governed by the wetting interactions and the final size of the domains can be tailored by varying the strength of the particles-fluid interaction as well as the particles concentration. These features are predicted within a simple theoretical model and are amenable of experimental checks.

Scratch resistance of polymers has been the subject of numerous studies, which have lead to specific definitions for plastic characteristic and fracture phenomena during scratch behavior. Viscoelastic and viscoplastic behavior during a scratch process has been related to dynamic mechanical properties that can be measured via dynamic nano-indentation testing. Yet, the understanding of the origin of the fracture process of a polymer during scratch remains approximate. Parameters like tip geometry and size, scratch velocity and loading rate, applied strain and strain rates, have been considered critical parameters for the fracture process, but no correlation has been clearly established.

The goal of this work was to analyze the scratch resistance and indentation properties of PMMA as a function of temperature. Compression and tensile properties from literature have also been compared to the scratch results for more complete understanding of the material's behavior.

The analysis of the evolution of the properties of PMMA at various temperatures, along with the evolution of the fracture toughness during scratch with temperature and scratch velocity has helped in identifying a correlation between the tensile stress-strain behavior and scratch fracture toughness for PMMA. This correlation brings a new understanding of the origin of the fracture mechanisms during a scratch process, and the strain effect on the fracture strength of PMMA.

To avoid delamination which often occurs in microelectronic packaging as a result of widely varying thermal expansion coefficients, epoxy underfill is often loaded with particulate silica filler. This filler typically complicates the fracture behavior of the epoxy and surrounding layers. However, delamination of interfaces within the composite may contribute to toughening if the fracture path is adhesive between the epoxy and surrounding layers or otherwise removed from filler-epoxy delamination regions. In this work, the interface between silica filler and epoxy is altered with the use of silane coupling agents to elucidate the fracture and toughening mechanisms of filled epoxies. Two model epoxies are investigated, and coupling agents were chosen to encourage chemical reaction with each system. For the aliphatic epoxy system, coupling agents were identified which both augment and degrade the interface between filler and epoxy. In composite structures, it was observed that those coupling agents which degrade the filler-epoxy interface act as toughening agents. SEM indicates that most deformation is not at the filler-epoxy interface, but rather through the epoxy, very close to the filler particle surfaces. In contrast, no coupling agents were identified which act as toughening agents in the bisphenol-f system. Further, no variation in fracture toughness of composite structures was observed with the use of coupling agents, indicating that filler-epoxy delamination does not occur in this system. With few exceptions, SEM supports this interpretation.

Adhesion properties of acrylic pressure sensitive adhesives were examined by means of normal (JKR) contact at room temperature. Cylindrically shaped samples were synthesized in capillary tubes in presence of a cross-linking agent in order to obtain an elastic response. The results reveal power law increase of adhesion at higher rates of interfacial separation. Transition from low- to high-power is revealed and explained as a result of bulk shielding of interfacial fracture mechanism. Further results will be available soon. Bulk viscoelastic dissipation and molecular interactions at the interface are thought to jointly govern this behavior.

Poly(itaconic acid) (PIA) was grown from surface-tethered initiator sites via atom transfer radical polymerization (ATRP). The surface-tethered PIA layers were grown from hydroxyl-terminated SAMs capped with initiator molecules of 4-(chloromethyl)-benzoylchloride. This polymerization initiator molecule and a copper-based organometallic catalyst allowed tethered PIA chains to be grown via ATRP at room temperature in aqueous solutions. Ellipsometric studies and external-reflection, Fourier-transform infrared spectroscopy (ER-FTIR) confirm the presence and growth of the surface-tethered PIA layer. We describe here how changing the temperature of polymerization alters the layer growth and kinetics of the process, and demonstrate, via ER-FTIR spectroscopy, that these surface-tethered layers do bind cationic dyes through ion-exchange mechanisms.

The effect of network changes on the surface and interface properties of amine-cured epoxy has been investigated. Samples of different crosslinked epoxies are prepared by mixing stoichiometrically pure diglycidyl ether of bisphenol A (n=0.03) with different ratios of 1,3-bis(aminomethyl)cyclohexane (terafunctional amine) and cyclohexylmethylamine (difunctional amine). All samples are cured in CO2-free air. Both the film surface in contact with air and that in contact with the silicon substrate (the interface) are analyzed using atomic force microscopy (AFM) and nanoindentation. Small angle neutron scattering (SANS), attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, and contact angle measurements, are used to assist in the interpretation of AFM results. Substantial morphological and mechanical differences are observed between the surface and the interface for different crosslinked epoxies. The findings have strong implications on the wettablity, adhesion, and durability of amine-cured epoxies.

C60-Perdeuterated Styrene Copolymer (C60-DPS) was synthesized by the free radical polymerization. Thin films of C60-DPS were prepared by the Langmuir-Boldgett (LB) technique. The surface morphology and friction performance were characterized by atomic force microscopy (AFM). Results exhibit the presence of spherical granules in the compact LB films, which result from self-polymerization of C60 and showed friction of the LB films increased basically as C60 content of C60-DPS decreased.

A novel technique called Cross-Sectional Scratch (CSS) has been established. The technique employs a sliding contact of an indenter tip across a polymer stack cross-section. The main advantage of the technique is that it allows to measure/quantify interfacial adhesion in multilayer polymer films that are only a few microns thick. CSS has successfully tested both glassy/glassy and glassy/soft polymer interfaces. Thus, PS/PE, PET/PE, PS/PMMA and PVdF/PMMA co-extruded films were chosen as sample systems and tested at room temperature. It was found that indenter speed has a strong effect on the magnitude of the adhesion energy measured. The dependence has a power law form with indices ∼ 0.1-0.2. More viscoelastic systems have higher power law index, a measure of rate sensitivity.

The beneficial mechanical properties of segmented polyurethanes derive from microphase separation of immiscible hard and soft segment-rich domains at room temperature. We are interested in the structure of the domains, how these are affected by hydrolytic aging, and how the structure is modified by low molecular weight plasticizers. To assessed the distribution of the plasticizer in polyurethane, we did small-angle neutron scattering measurements on mixtures of 23% hard segment poly(esterurethane) with different amounts of either non-deuterated or deuterated plasticizer. We analyzed the results using a simple model in which the contrast, Δρ = ρH Š ρ, between the hard and soft segment-rich domains is varied by the amount of deuterated or hydrogenated plasticizer, using the fact that I(Q) ∼ Δρ2. The result demonstrated that the plasticizer is largely associated with the soft segment rich domains. The structure of PESU with the chain extender of the hard segment was assessed after aging under hydrolytic conditions. The results show that the microphase structure coarsens and segregates and that the hard and soft segments segregated as a result of the loss of constraints from hydrolytic soft segment chain scission. The results on plasticizer distribution and the effects of hydrolytic aging give insight on the loss of mechanical properties that occur in each case.

Secondary ion mass spectroscopy is used to examine the dark, non-emissive defects on the organic light-emitting device. Boundary movements are originated from electrode imperfection. Due to flexibility and movability of polymer layer, distribution variations and a more severe Indium and Calcium overlapping are detected in dark spot defect area. Boundary movements are not in good agreement between different layers. Interfaces became undulate. The closeness and proximity between the In sharp spikes and cathode metal protrusion leads to the initial point of dark spot. We demonstrate that the presence of cathode imperfection and interface roughness of different layers correlated to the device dark spot formation.

Characterising the morphology of thin films for use in device applications requires the ability to study both the structure within the plane of the film, and also through its thickness. Environmental scanning electron microscopy has proved to be a fruitful technique for the study of such films both because contrast can be seen within the film without the need for staining (as is conventionally done for electron microscopy), and because cross-sectional images can be obtained without charging artefacts. The application of ESEM to a particular blend of relevance to photovoltaics is described.

The manner in which the dynamics of a polymer are affected by thin film confinement is of technological significance, impacting thin film applications such as lubricants, adhesives, and chemically amplified photoresists. In this manuscript we use specular X-ray reflectivity (SXR), beam positron annihilation lifetime spectroscopy (PALS), and incoherent neutron scattering (INS) to study the influence of thin film confinement on the apparent glass transition temperature Tg and the thermal expansion coefficients of thin polycarbonate (PC) films. Both the SXR and PALS indicate a significant suppression of Tg when the film thickness becomes less than 200 Å. However, the INS measurements suggest an increase in the apparent Tg below this same length scale. These disparate estimates of the thin film Tg seem to indicate that each technique is sensitive to slightly different aspects of the glass formation process. However, all three agree that thin film confinement results in reduced thermal motion, regardless of the precise temperature that is ‘designated' as the thin film Tg.