Magnetic interlayer coupling is one of the central phenomena in spintronics. It has been predicted that the sign of interlayer coupling can be manipulated by electric fields, instead of electric currents, thereby offering a promising low energy magnetization switching mechanism. Here we present the experimental demonstration of voltage-controlled interlayer coupling in a new perpendicular magnetic tunnel junction system with a GdOx tunnel barrier, where a large perpendicular magnetic anisotropy and a sizable tunnelling magnetoresistance have been achieved at room temperature. Owing to the interfacial nature of the magnetism, the ability to move oxygen vacancies within the barrier, and a large proximity-induced magnetization of GdOx, both the magnitude and the sign of the interlayer coupling in these junctions can be directly controlled by voltage. These results pave a new path towards achieving energy-efficient magnetization switching by controlling interlayer coupling.

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.

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.

<p dir="ltr">Adhesives surround us on a daily basis without us even being aware. They are the unsung heroes of most commercial products we use. Whether it be the car you drive, the shoes you wear, or the furniture you sit on, glue is keeping everything together. Adhesives have been used since the cavemen utilizing tar for keeping stone tools together. Over time, adhesives have exploded in the scientific landscape through a multitude of chemical pathways. Current products are comprised of epoxies, cyanoacrylates, polyurethanes, and many others. The need for adhesives in the manufacturing of products is consistently increasing over the years in the goal of light weighting without compromising on performance of the final material. However, this comes at the cost of glues being both toxic and nonrecyclable. With this in mind an improvement was needed to address both augmenting the glue strength and improving the sustainability of the adhesive.</p><p dir="ltr">Hierarchical structures can be observed on the micro scale in natural materials. Tree limbs are able to withstand a tremendous amount of force applied from winds, human machinery, and animal life. Why they are so resistant lies in the fact there is an ordered structure of multiple length scales working in tandem upholding the integrity of the limb. The question to ask then relating this to adhesives is if there is a way to create a glue that can disperse the forces amongst the overall material without catastrophic failure. The use of fillers such as calcium carbonate and different adhesive strain rates can be used to mimic this interaction.</p><p dir="ltr">Addressing the sustainability factor of current glues, the need was set to create a more bio-based alternative using widely available materials that are cost effective and do not compromise on overall performance. Competing with or outperforming the current market adhesives was a goal in mind. Two generations of bio-based adhesives were generated through multiple formulations using epoxidized soybean oil as the common factor. Soybean oil is one of the most widely produced vegetable oils in the country. Utilizing the oil in a functionalized way through epoxide rings, the replacement of current epoxy technology was achieved.</p>

Orientadores: João Domingos Biagi, Antonio Carlos de Oliveira Ferraz / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola / Made available in DSpace on 2018-08-12T05:33:01Z (GMT). No. of bitstreams: 1 Fraiha_Marcos_D.pdf: 1875565 bytes, checksum: a372a466eacf5e49b82f4cdc2d006270 (MD5) Previous issue date: 2008 / Resumo: O objetivo geral deste trabalho foi determinar os efeitos da taxa de cisalhamento, temperatura e pressão gerados no processo de extrusão de alimentos para animais sobre a viabilidade de esporos bacterianos. Baseado na fundamentação teórica de reologia de materiais, foi possível a construção de um reômetro fundamental utilizando materiais e operações simples de tornearia. Para caracterizar o comportamento reológico de alimentos para animais, uma mistura de grãos de milho e soja na proporção 70:30 (massa:massa) foi submetida ao reômetro capilar sob 3 níveis de temperatura e umidade da massa, e 4 taxas de cisalhamento aparente: 80, 120 e 160°C, 26,5±0,08; 30,4±0,31 e 33,4±0,05%; 30,4; 72,9; 304,3 e 728,6 s-1 respectivamente. Diferentes taxas de deformação e dimensões da matriz foram utilizadas para obtenção das taxas de cisalhamento acima. Os efeitos de umidade e temperatura da massa, e taxa de cisalhamento sobre a mistura de milho e soja foram ajustados para uma expressão única (P<0.001, R2 = 0.93): ?=18.769,7 (?) -0,86 e (-9,34U+935T), onde (?) é a taxa de cisalhamento, U é a teor de água na amostra e T é o inverso da temperatura na massa, em escala Kelvin. Como esperado, a mistura moída de milho e soja apresentou comportamento pseudoplástico. Outro experimento objetivou determinar os parâmetros de destruição térmica de esporos de Bacillus sterothermophilus ATCC 7953 e a estimativa de suas dimensões. Os valores de D121,1°C e z para os esporos suspensos em solução salina foram 8,8 min e 12,8 °C, respectivamente. Para aqueles suspensos em mistura milho e soja, D121,1°C e z foram 14,2 min e 23,7 °C , respectivamente. As micrografias indicaram que os esporos apresentam-se como bastonetes, homogêneos em forma e dimensão, cujos comprimento e diâmetro foram estimados em 2 e 1 µm, respectivamente. Outro experimento visou determinar o efeito da taxa de cisalhamento sobre a viabilidade de esporos de B. stearothermophilus sob escoamento viscométrico em reômetro capilar. Os esporos foram inoculados em mistura de milho e soja para contagem e umidade de 106 UFC/5g, e 30,0±0,30%, respectivamente. As amostras foram submetidas às taxas de cisalhamento aparentes variando de 728,6 a 3.643,0 s-1, sob 80°C. As contagens microbiológicas foram menores quando comparadas ao controle (P < 0,001). Baseados nos parâmetros termobacteriológicos dos esporos, a redução de viabilidade observada não pode ser explicada pelo efeito do calor isoladamente, e confirma a hipótese do efeito do fenômeno mecânico sobre a redução celular. Outro trabalho visou determinar o efeito do calor, pressão e taxa de cisalhamento sobre a viabilidade de esporos termodúricos em ração animal submetida ao processo de extrusão. Os esporos foram semeados em mistura de grãos moídos de milho e soja, para contagem final de 106 UFC/5g e umidade de 30%, e submetidos ao processo em extrusora de rosca simples. A pressão estática não influenciou a viabilidade, porém temperatura e tensão cisalhante reduziram a viabilidade dos microorganismos. O percentual da redução da viabilidade dos microorganismos está diretamente relacionado ao volume de material submetido ao gradiente de velocidade de escoamento. / Abstract: The overall objective of this thesis was to determine the effects of mass temperature, pressure and shear rate on the viability of bacterial spores. The first paper describes the design and construction of a capillary rheometer attached to an universal testing machine used to characterize feed ingredients. To characterize the rheological behavior of animal feed under viscometric flow, a 70:30 (mass:mass) mixture of ground corn and soybean grains was submitted to a capillary rheometer at 3 temperatures and moisture levels, and 4 shear rates: 80, 120 and 160 °C, 26.5±0.08; 30.4±0.31 and 33.4±0.05%; 30.4; 72.9; 304.3 and 728.6 s-1 respectively. Based on experimental data, moisture content, mass temperature and shear rate effects on apparent shear viscosity of corn-soy mix were fitted to a single expression (P<0.001, R2 = 0.93): ?=18.769,7 (?) -0,86 e (-9,34U+935T), where (?) is the shear rate, U is the sample moisture and T is the sample reciprocal temperature in Kelvin scale. In order to determine thermobacteriological parameters for B. stearothermophilus spores, they were suspended in saline solution medium (0,85%, pH 6,7) and in ground corn-soy mix to a final count of 106 CFU/mL and 106 CFU/5g, respectively, distributed to TDT tubes and submitted to heat, from 100 to 126 °C, for a period of time varying from 0 to 40 min. D121,1°C and z values for these spores, as determined in the saline solution, were 8.8 min and 12.8 °C, respectively. D121,1°C and z values determined in the corn-soy mix were 14.2 min and 23.7 °C, respectively. The micrographs indicated that the spores are homogeneous in shape and size, which length and diameters are 2 and 1 µm, respectively. Another experiment aimed to determine shear effects on the viability of bacterial spores under viscometric flow. The spores were inoculated in the feed mixture to a final count of 106 CFU/5g, and 30.0±0.30% moisture. Samples were submitted to apparent shear rates varying from 728.6 to 3,643.0 s-1 at 80 °C in a capillary rheometer. Microbial counts were lower after treatments compared to control (P<0.001). A final work determined the heat, pressure and shear rate effects on the viability of the spores sowed into feed, submitted to extrusion. Bacillus stearothermophilus spores were sowed into corn and soy grain mixture to 106 CFU/5g and moisture of 30%, and then submitted to the extrusion process in a single screw extruder. Static pressure had no effect, but heat and shear stress reduced microbial count. The higher shear rate due to rotational speed increase of screw did not affect cell viability. It was concluded that static pressure level did not affect the viability of Bacillus stearothermophilus spores but heat and shear stress did. These conclusions indicated that the volume of feed under a velocity gradient during mass flow through the screw channel remained unchanged in the last case, what resulted in the same percentage of spores submitted to shear stress. / Doutorado / Tecnologia Pós-Colheita / Doutor em Engenharia Agrícola

<p>In the realm of tunable optical devices, 3D nanostructures with metals and dielectrics have been utilized in a wide variety of practical applications ranging from optical switching to beam-steering devices. 2D materials, on the other hand, have enabled the exploration of truly new physics unattainable with 3D systems due to quantum confinement leading to unique optical properties and enhanced light-matter interactions. Transdimensional materials (TDMs) – atomically thin films of metals – can couple the robustness of 3D nanostructures with the new physics enabled by 2D features. However, the evolution of the optical properties in the transdimensional regime between 3D and 2D is still underexplored. The optical properties of metallic TDMs are expected to show unprecedented tailorability, including strong dependences on the film thickness, composition, strain, and surface termination. They also have an increased sensitivity to external optical and electrical perturbations, owing to their extraordinary light-confinement. Additionally, the small atomic thicknesses may lead to strongly confined surface plasmons and quantum and nonlocal phenomena. The strong tunability and light-confinement offered by TDMs have resulted in a search for atomically thin plasmonic material platforms that facilitate active metasurfaces with novel functionalities in the visible and near infrared (NIR) range. In this research, we explore the plasmonic properties and tailorability of atomically thin titanium nitride (TiN). We experimentally and theoretically study the thickness-dependent optical properties of epitaxial TiN films with thicknesses down to 1 nm to demonstrate confinement induced optical properties. Overall, this research demonstrates the potential of TDMs for unlocking novel optical phenomena at visible and NIR wavelengths and realizing a new generation of atomically thin tunable nanophotonic devices. </p>

Spin-polarized two-dimensional electron states (2DESs) at surfaces and interfaces of magnetically active materials attract immense interest because of the idea of exploiting fermion spins rather than charge in next generation electronics. Applying angle-resolved photoelectron spectroscopy, we show that the silicon surface of GdRh2Si2 bears two distinct 2DESs, one being a Shockley surface state, and the other a Dirac surface resonance. Both are subject to strong exchange interaction with the ordered 4f-moments lying underneath the Si-Rh-Si trilayer. The spin degeneracy of the Shockley state breaks down below ~90 K, and the splitting of the resulting subbands saturates upon cooling at values as high as ~185 meV. The spin splitting of the Dirac state becomes clearly visible around ~60 K, reaching a maximum of ~70 meV. An abrupt increase of surface magnetization at around the same temperature suggests that the Dirac state contributes significantly to the magnetic properties at the Si surface. We also show the possibility to tune the properties of 2DESs by depositing alkali metal atoms. The unique temperature-dependent ferromagnetic properties of the Si-terminated surface in GdRh2Si2 could be exploited when combined with functional adlayers deposited on top for which novel phenomena related to magnetism can be anticipated.

<p dir="ltr">Conducting polymers have garnered enormous attention due to their unique properties, including tunable chemical structure, high flexibility, solution processability, and biocompatibility. They hold promising applications in flexible electronics, renewable energies, sensing, and healthcare. Despite notable progress in conducting polymers over the past few decades, most of them still suffer from complicated synthesis routes, limited processability, low electrical conductivity, and poor ambient stability compared to their inorganic counterparts. Additionally, the susceptibility of conducting polymers to high temperatures makes them not applicable in real-life electronics. To address the challenges of developing high-performance and stable conducting polymers, we present two key approaches: dopant innovation for polymer-dopant interaction engineering and the discovery of new conjugated polymer hosts. From the perspective of dopant design, we first utilize cross-linkable chlorosilanes (C-Si) to design thermally and chemically stable conductive polymer composites. C-Si can form robust siloxane networks and simultaneously<i> </i>dope the host conjugated polymers. Besides, we have introduced a new class of dopants, namely aromatic ionic dopants (AIDs). The use of AIDs allows for the separation of doping and charge compensation, two processes involved in molecular doping, and therefore leads to highly efficient doping and thermally stable doped systems. We then provide insights into the design of novel conjugated polymer hosts. Remarkably, we have developed the first thermodynamically stable n-type conducting polymer, n-doped Poly (3,7-dihydrobenzo[1,2-b:4,5-b′]difuran-2,6-dione) (n-PBDF). n-PBDF is synthesized from a simple and scalable route, involving oxidative polymerization and reductive doping in one pot in the air. The n-PBDF ink is solution processable with excellent ink stability and the n-PBDF thin film is highly conductive, transparent, patternable, and robust. In addition, precise control over the doping levels of n-PBDF has been achieved through chemical doping and dedoping. By tuning the n-PBDF thin films between highly doped and dedoped states, the system shows controllable conductivity, optical properties, and energetics, thereby offering potential applications in a variety of organic electronics. Overall, this research advances the fundamental understanding of molecular doping and offers insights for the development of high-conductivity, stable conducting polymers with tunable properties for next-generation electronics.</p>

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No description available.