Progress in the burgeoning field of organic electronics is enabling the development of novel technologies such as low-cost, printable solar cells and flexible, high-resolution displays. One exciting avenue of research in this field is nanostructured hybrid organics such as quantum dot (QD)-polymer devices. The incorporation of QDs can greatly improve a device’s efficiency and gives one the ability to tune its electrical and optical characteristics. In order for such technologies to be commercially viable, it is important to classify their mechanical integrity and reliability. Surprisingly little is known about the mechanical properties of QD-polymer thin films (<100 nm). This is in part due to challenges of: (1) isolating the mechanical response of a thin film from the underlying substrate, (2) obtaining a homogeneous dispersion of QDs in the film, and (3) the sensitivity of mechanical properties to the inherent rate dependence of polymer deformation (i.e., viscoelasticity). All of these challenges can introduce significant errors in the measurement of mechanical properties. Furthermore, the deformation mechanisms in nanocomposites are not well understood, so it is difficult to predict the effect of adding QDs on the mechanical behavior of films. In this thesis, these challenges are addressed for characterizing the mechanical properties of thin films of CdSe QD-poly[2-methoxy-5-2(2΄-ethylhexyloxy-p-phenylenevinylene)] (MEH-PPV) nanocomposites using quasi-static nanoindentation testing. Elastic modulus, hardness, and creep are measured as a function of QD concentration and loading and unloading rates. The QDs' ligands are removed by pyridine treatment prior to mixing with MEH-PPV to improve dispersion. The films are prepared via spin-coating onto glass substrates and subsequent annealing in air. Efforts are taken in the mechanical testing to minimize errors due to viscoelastic creep and interference from the substrate. Transmission electron microscopy reveals that the QDs are relatively well-dispersed in the polymer matrix. It is observed that adding QDs increases the elastic modulus (E) and hardness (H) of the films, while reducing the viscoelastic creep. Both E and H increase linearly with the volume percent of QDs. E ranges from 14.5 GPa to 52.7 GPa for pure MEH-PPV (0% QDs) and 100% QD films, respectively, while H ranges from 220 MPa to 1430 MPa for the same films, respectively. The films behave viscoelastically at lower QD loading, but assume a more granular character as the loading approaches 100%.

The hybrid organic-inorganic perovskites (HOIPs), e.g. methylammonium and formamidinium lead halide (MA/FAPbX3, X = I, Br or Cl), are a class of materials that has recently achieved remarkable performances in photovoltaic applications. This thesis describes the synthesis, structure and properties of this class of perovskites, with particular focus on their crystal chemistry, mechanical responses and structural diversity. Understanding the unique crystal chemistry of HOIPs is crucial for device design. While MA-based perovskites have been widely studied, there are still many open questions on the crystal chemistry of FA-based perovskites. In this work, FAPbX3 (X= Br or I) was shown to undergo a cubic (Pm3 ̅m) to tetragonal (P4/mbm) transition on cooling. Studies on the high-pressure crystallography of FAPbI3 exhibited a similar trend and further illustrated band gap tuning via external stimuli. In addition, the cubic lattice of FAPbBr3 was found to be more strained than its MA counterpart. The observed intrinsic strain was modelled with anisotropic line broadening and < 100 > was found to be the least strained direction. To explore potential applications in flexible devices, crystals of single (Pb-based) and double (Bi-based) perovskites were probed by nanoindentation and their mechanical properties, such as Young’s moduli (E) (10 – 20 GPa) and hardnesses (H) (0.2 -0.5 GPa), were determined. The mechanical responses of MA- and FA-based hybrid perovskites correlated well with the chemical and structural variations in these analogues, showing a general trend of ECl > EBr > EI and EPb > EBi. By analogy with classical inorganic perovskites, the hybrid phases can crystallise in both three-dimensional (3D) and low dimensional perovskite-like forms. To improve the stability and remove the toxicity in the current prototypical hybrid perovskites, compositional engineering was applied, focusing on non-toxic bismuth (Bi) as a viable alternative to lead (Pb) in future photovoltaic materials. We report a new layered perovskite, (NH4)3Bi2I9, which exhibits a band gap of 2.0 eV, comparable to MAPbBr3 and FAPbBr3. This work contributes to the materials design goal of more stable and eco-friendly perovskite devices.

The incorporation of waste tyre rubber into thermoplastics to develop a class of polymer composites with both elastomeric and thermoplastic behaviour has gained a lot of attention and is becoming one of the most straightforward and preferred options to achieve the valorisation of waste tyres. In view of the unique properties rubber possesses and the rapid expansion and versatile application of wood plastic composites (WPC) materials, the inclusion of tyre rubber as raw material into WPC to develop an entirely new generation of WPC, namely rubber-wood-plastic composites (RubWPC), was presumed to be another highly promising solution to turn waste tyres into value-added materials. This research starts with the interfacial optimisation of Rubber-PE composites and WPC by the use of maleated and silane coupling agents, aiming at addressing their poor constituent compatibility and interfacial bonding, thus enabling the optimal design of RubWPC. Chemical, physical and mechanical bonding scenarios of both untreated and treated composites were revealed by conducting ATR-FTIR, NMR, SEM and FM analyses. The contribution of the optimised interface to the bulk mechanical property of the composites were assessed by carrying out DMA and tensile property analysis. The influence of the coupling agent treatments on the in situ mechanical property of WPC was first determined by nanoindentation analysis, which led to a thorough understanding of the interfacial characteristics and the correlation between in situ and bulk mechanical properties. This research focuses on the novel formulation of RubWPC and the understanding of bonding mechanism. Chemical bonding and interface structure studies revealed that interdiffusion, molecular attractions, chemical reactions, and mechanical interlocking were mutually responsible for the enhancement of the interfacial adhesion and bonding of the coupling agent treated RubWPC. The improved interface gave rise to the increase of bulk mechanical properties, while the continuous addition of rubber particle exerted an opposite influence on the property of RubWPC. The composite with optimised interface possessed superior nanomechanical properties due to the resin penetration into cell lumens and vessels and the reaction between cell walls and coupling agents.

Doctor of Philosophy(PhD) / Objectives As the outer cover of teeth structure, enamel is the hardest, stiffest and one of the most durable load-bearing tissues of the human body. Also, enamel is an elegantly designed natural biocomposite. From a material science point of view, scientists are interested in the structure and function of the nature material. How does nature design the material to meet its functional needs? From a dental clinic point of view, dental practitioners are keen to know the properties of enamel and compare it with different dental materials. What kind of dental materials can best simulate enamel as a restoration in the oral cavity? The research presented in this thesis on the mechanical behaviour of enamel in respect of its structural and compositional characteristics will attempt to provide answers or indications to the above questions. Theoretical analysis, as well as experimental investigations of both man-made and natural composites materials, has shown that hierarchical microstructure and organic matrix glues the inorganic particles together and plays an important role in regulating the mechanical properties of the composite. Bearing this finding in mind, in the current investigations, we assume the hierarchical microstructure and trace protein remnants in enamel regulate the mechanical behaviour of the natural biocomposite to meet its functional needs as a load bearing tissue with superb anti-fatigue and wear resistant properties. One of the important reasons that dental hard tissues haven’t been thoroughly investigated is due to the limited sample volume. Fortunately, with the development of nanoindentation technique and equipment, it is now possible to explore the mechanical properties of small volume samples. The application of nanoindentation on dental hard tissues has been documented. However, most investigations have concentrated on only reporting the basic mechanical properties such as elastic modulus and hardness. Very few of them have taken the role of microstructure and composition of these natural biocomposites into their considerations. The main aim of this investigation is to interpret how microstructural and compositional features of enamel regulate its mechanical behaviour. To achieve this goal, the analytical methods considering nanoindentation data need to be expanded so that more information not only elastic modulus and hardness but also stress-strain relationship, energy absorption ability, and creep behaviour may be evaluated with this technique. These new methods will also be of benefit to dental material evaluation and selection. Materials and methods Based on the Oliver-Pharr method1 for the analysis of nanoindentation data, Hertzian contact theory2 and Tabor’s theory3, a spherical nanoindentation method for measuring the stress-strain relationship was developed. Furthermore, nanoindentation energy absorption analysis method and nanoindentation creep test were developed to measure the inelastic property of enamel. With the above methods, sound enamel samples were investigated and compared with various dental materials, including dental ceramics and dental alloys. • Firstly, using a Berkovich indenter and three spherical indenters with 5, 10 and 20 µm nominal radius, the elastic modulus, hardness and stress-strain relationship of different samples were investigated and compared. • Secondly, mechanical properties of enamel in respect to its microstructure were investigated intensively using different indenters by sectioning teeth at different angles. • Thirdly, inelastic behaviour of enamel such as energy absorption and creep deformation were observed and compared with a fully sintered dense hydroxyapatite (HAP) disk to illustrate the roles of protein remnants in regulating the mechanical behaviour of enamel. • Fourthly, to confirm the functions of protein remnants in controlling mechanical behaviour of enamel, enamel samples were treated under different environments such as burning (300°C exposure for 5 min), alcohol dehydration and rehydration to change the properties of proteins before the nanoindentation tests. • Lastly, micro-Raman spectroscopy was employed to measure and compare the indentation residual stresses in enamel and HAP disk to evaluate the role of both hierarchical microstructure and protein remnants in redistributing the stresses and reinforcing the mechanical response of enamel to deformation. Results and significance Nanoindentation is an attractive method for measuring the mechanical behaviour of small specimen volumes. Using this technique, the mechanical properties of enamel were investigated at different orientations and compared with dental restorative materials. From the present study, the following results were found and conclusions were drawn.  Although some newly developed dental ceramics have similar elastic modulus to enamel, the hardness of these ceramic products is still much higher than enamel; in contrast, despite the higher elastic modulus, dental metallic alloys have very similar hardness as enamel. Furthermore, enamel has similar stress-strain relationships and creep behaviour to that of dental metallic alloys. SEM also showed enamel has an inelastic deformation pattern around indentation impressions. All of these responses indicated that enamel behaves more like a metallic material rather than a ceramic.  Elastic modulus of enamel is influenced by highly oriented rod units and HAP crystallites. As a result, it was found to be a function of contact area. This provides a basis to understand the different results reported in the literature from macro-scale and micro-scale tests. Anisotropic properties of enamel, which arise from the rod units, are well reflected in the stress-strain curves. The top surface (perpendicular to the rod axis) is stiffer and has higher stress-strain response than an adjacent cross section surface because of the greater influence of the prism sheaths in the latter behaviour.  Enamel showed much higher energy absorption capacity and considerably more creep deformation behaviour than HAP, a ceramic material with similar mineral composition. This is argued to be due to the existence of minor protein remnants in enamel. Possible mechanisms include fluid flow within the sheath structure, protein “sacrificial bond” theory, and nano-scale friction within sheaths associated with the degustation of enamel rods.  A simple model with respect of hierarchical microstructure of enamel was developed to illustrate the structural related contact deformation mechanisms of human enamel. Within the contact indentation area, thin protein layers between HAP crystallites bear most of the deformation in the form of shear strain, which is approximately 16 times bigger than contact strain in the case of a Vickers indenter. By replotting energy absorption against mean strain value of a protein layer, data from different indenters on enamel superimposed, validating the model. This model partially explained the non-linear indentation stress-strain relationship, inelastic contact response and large energy absorption ability of enamel and indicated the inelastic characteristics of enamel were related to the thin protein layers between crystallites.  Following different treatments, mechanical properties of enamel changed significantly. By denaturing or destroying the protein remnants, mechanical behaviour, especially inelastic abilities of enamel decreased dramatically, which indicates matrix proteins endow enamel better performance as a load bearing calcified tissue.  Comparison of Raman derived residual maps about indentations in enamel and a sintered homogeneous HAP showed the hierarchical structure influenced the residual stress distribution within enamel. Moreover, less residual stresses were found in enamel and were a consequence of the protein remnants. These are evidence as to how the microstructure meets the functional needs of the enamel tissue. In general, evidence from different approaches indicated that the hierarchical microstructure and small protein remnants regulated the mechanical behaviour of enamel significantly at various hierarchical levels utilising different mechanisms. This investigation has provided some basis for understanding natural biocomposites and assisting with dental clinic materials selection and treatment evaluation procedures. References 1. Oliver WC, Pharr GM. An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments. J Mater Res. 1992;7(6):1564-83. 2. Hertz H. Miscellaneous Papers. London: Jones and Schott, Macmillan; 1863. 3. Tabor D. Hardness of Metals. Oxford: Clarendon Press; 1951.

In the past two decades much effort has been put in the characterization of the mechanical and surface properties at the nano-scale in order to conceive reliable N/MEMS (Nano and Micro ElectroMechanical Systems) applications. Techniques like nanoindentation, nanoscratching, atomic force microscopy have become widely used to measure the mechanical and surface properties of materials at sub-micro or nano scale. Nevertheless, many phenomena such us pile-up and pop-in as well as surface anomalies and roughness play an important role in the accurate determination of the materials properties. The first goal of this report is to study the infulence of these sources of data distortion on the experimental data. The results are discussed in the first experimental chapter. On the other hand, conceptors would like to adapt/tune the mechanical and surface properties as a function of the required application so as to adapt them to the industrial need. Coatings are usually applied to materials to enhance performances and reliability such as better hardness and elastic modulus, chemical resistance and wear resistance. In this work, the magnetron sputtering technique is used to deposit biocompatible thin layers of different compositions (titanium carbide, titanium nitride and amorphous carbon) over a titanium substrate. The goal of this second experimental part is the study of the deposition parameters influence on the resulting mechanical and surface properties. New materials such as nanocrystal superlattices have recently received considerable attention due to their versatile electronic and optical properties. However, this new class of material requires robust mechanical properties to be useful for technological applications. In the third and last experimental chapter, nanoindentation and atomic force microscopy are used to characterize the mechanical behavior of well ordered lead sulfide (PbS) nanocrystal superlattices. The goal of this last chapter is the understanding of the deformation process in order to conceive more reliable nanocrystal superlattices.

Wide band gap semiconductors ZnO/GaN attracted a great deal of interests for decade, due to their wide direct band, high electron binding energy, excellent chemical and thermal stability, good heat conductivity and capability, high electron mobility and transparent properties at room temperature. They have many potential applications such as laser, biosensor, piezoelectric power generator, nano-electromechanical systems and flat panel field emission displays. However, unexpected contact loading during processing or packaging may induce residual stresses and/or an increase in defect concentration in ZnO/GaN wafer or thin film, causing possible degenerated reliability and efficient operation of the piezoelectric and photonic device. To ensure and improve the performance of devices based on ZnO/GaN, a better understanding of the mechanical/optoelectronic response under different processing and loading conditions and even the measuring methods are necessary. In this thesis, our aim is to reveal a comprehensive investigation of the mechanical responses on polar/non-polar GaN/ZnO single crystal under low dimensional stress. We try to provide the fundamental theoretical and experimental studies for further application and researches, such as tension testing, residual stress, low temperature cathodoluminescence and Raman spectroscopy analysis. In this study, the theoretical Young¡¦s modulus and Poisson ratio of ZnO/GaN are extracted from elastic constants for comparison and further estimation. The nano-scaled mechanical properties, such as Young¡¦s modulus, hardness and yield stress, are identified by using the nanoindentation system. The experimental values were fitting by the Hertzian contact theory. The results are in good agreement with the theoretical predictions. No significant strain rate influence is observed over the strain rate from 1x10-2 s-1 to 1x10-4 s-1. The comparisons of mechanical properties between the polar and non-polar planes of ZnO are firstly examined. The results reveal that the non-polar planes are softer than the polar plane. Both a-plane and m-plane ZnO have lower hardness and yield stress than c-plane ZnO. The microstructure and deformation mechanism are analyzed by using X-TEM and SEM. No pop-out or slope changing was found in their load-displacement curves, suggesting no phase transformation, twining or crack domain deformation occurred under microcompression and nanoindentation testing. Taking all considerations for the higher resulting Schmid factor and lower Burgers¡¦ vector, the most possible slip system for c-plane hexagonal structures is the pyramidal plane. The a-plane has shorter burger¡¦s vector on the slip plane which leads the lower yield stress than c-plane. To erase the effect of FIB induced Ga ion implantation, the c-plane ZnO was annealed at 900oC for 1 hour. We found that the yield stress under microcompression decreases and the intensity of the cathodoluminescence spectrum increases after the annealing process. This result indicates that the thermal treatment is a good way to refine the crystal quality and decrease the defects density. The E2 peak of Raman spectrometer exhibits high residual compression stress constrain in the c-plane GaN thin film. Due to the high surface/volume ratio of pillar, nil residual stress remains in the GaN pillar after the FIB milling process. Even after the yield point, nil residual stress remains in the c-GaN pillar. Results indicate that the one dimensional geography is a good way to erase residual stress.

This thesis presents the research results of a correlation and model based on nano and macroindentation hardness measurements. The materials used to develop and test the correlation include bulk tantalum and O1 tool steel. Following the literature review and a detailed description of the experimental techniques, the results of the nanoindentation hardness measurements are presented. After applying the methods and correlation recommended here, the results should give an accurate value of hardness in the Vickers scale for microstructural features that are too small to be precisely and exclusively measured using the traditional macroindentation hardness technique. The phenomena and influential factors in nanoindentation hardness testing are also discussed. These phenomena and theories are consistent with the microstructural behavior predicted in the Nix and Gao model for mechanism-based strain gradients. Implementing the correlation factors and/or correlation curve, accurate results can be found for metals over a broad hardness range. Initially, this research may impact the pipeline division of the petroleum industry by providing a correlation to the Vickers scale for nanoindentation testing of microstructural features. This thesis may also provide a research methodology to develop hardness correlations for materials other than metals. This thesis consists of eight chapters. Following an introduction in Chapter I, the research motivations and objectives are highlighted in Chapter II. Chapter III explains the multi-scale indentation techniques used in this thesis and Chapter IV presents the materials preparation techniques used. Then, the results are presented in Chapter V, followed by the factors affecting nanoindentation hardness in Chapter VI. Finally, Chapters VII and VIII reveal the indentation contact analysis, correlation, and conclusions of this research, respectively.

This study presents thin film transistor (TFT) electrode structures in flat panel displays by imprint and electroless silver plating techniques. Imprint technique is not limited to the physical properties of optical lithography. In the imprinting process, the glass mold designed for imprinting process is fabricated by semiconductor manufacturing technology to imprint photoresist (AZ-650). The material is evaluated for imprint process. In addition, at present, electrode materials used in TFT process are aluminum (Al), chromium (Cr) and so on. In other research, the thin film plating technique adopts sputtering process to manufacture TFT electrode structures. This study uses electroless silver plating process to fabricate TFT electrode structures. The experimental result shows that the silver film can be deposited on the glass wafer by electroless plating, The mechanical properties of the silver films such as hardness, coefficient of elasticity and Young¡¦s module are measured by nanoindentation system,compared with the bulk materials.

The microstructure and residual stress of Ni thin film coating on Si influence the properties significantly, which play an important role in advanced applications of the electric and magnetic properties. The properties of Ni thin film deposited on Si at various temperatures and for different thickness have been studied in this work. Samples were characterized by nanoindentation, Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), electrical measurement, grazing angle X-ray diffraction (XRD) and photo reflection spectroscopy of white light. The nanoindentation measurements reveal similar loading curves and young¡¦s modulus for Ni thin films on Si at different deposition temperatures. However, the higher the deposition temperature, the lower is the hardness of the Ni thin film on Si. A maximum stress occurs at deposition temperature of 88-122 ¢XC. From FTIR spectra an unusual IR oscillating absorption of the Ni/Si film was observed from the samples which was deposited at 230 ¢XC for 15 min (23 nm) and for 30 min (52 nm) compared to other deposition duration and deposition temperatures at room temperature, 88 ¢XC, and 122 ¢XC. Furthermore, annealing experiments of the samples were performed after deposited at room temperature, and then annealed at respective temperatures of 88, 122, 230 ¢XC for the durations of 15 min and 30 min for comparison. However, the unmoral IR oscillation doesn¡¦t occur else where. The phase change of Ni/Si was analyzed by grazing angle XRD. A single phase of NiSi (103) structure was observed only in the samples deposited at 230 ¢XC. Further study of the oscillation in the FTIR spectra shows its origin should be related to surface plasmon resonance (SPR) mode. The SPR absorption peaks at 471 nm and 616 nm are analyzed by a photo reflection experiment. The SPR absorption is due to the nano structure of nickel silicide on Ni/Si surface formed during deposition at 230 ¢XC.

¡@¡@The purpose of thesis is to study the responses of nanoindentation in fused silica. By experiments the mechanical properties of intrinsic fused silica were obtained. From the finite element simulation the response of material was estimated. Our main work is on simulation. This part includes the effects of different coefficient of friction, different indentation depth, tip rounding, and substrates of thin films. ¡@¡@First, the experimental load¡Vdisplacement curves were obtained through the nanoindentation sensing system. Then, a three-dimensional finite element was successfully modeled through the comparison of the load¡Vdisplacement curves of the experiment and the simulation. The yield stress and the strain-hardness trend of intrinsic fused silica were obtained. ¡@¡@For different coefficient of friction and different tip radii, no significant differences were found through the load¡Vdisplacement curves and von Mises stress distributions. For different indentation depths, varied trends were found through the load¡Vdisplacement curves and von Mises stress distributions. For substrate effect, no significant differences could be found through the normalized hardness. The intrinsic film hardness could be obtained for indentation depth less 20% of the total indentation depth.