Academic literature on the topic 'Advanced materials fabrication'

Semiconductor photocatalysts have attracted a great amount of multidiscipline research due to their distinctive potential for solar-to-chemical-energy conversion applications, ranging from water and air purification to hydrogen and chemical fuel production. This unique diversity of photoinduced applications has spurred major research efforts on the rational design and development of photocatalytic materials with tailored structural, morphological, and optoelectronic properties in order to promote solar light harvesting and alleviate photogenerated electron-hole recombination and the concomitant low quantum efficiency. This book presents a collection of original research articles on advanced photocatalytic materials synthesized by novel fabrication approaches and/or appropriate modifications that improve their performance for target photocatalytic applications such as water (cyanobacterial toxins, antibiotics, phenols, and dyes) and air (NOx and volatile organic compounds) pollutant degradation, hydrogen evolution, and hydrogen peroxide production by photoelectrochemical cells.

The green materials of alumina (Al2O3) and titania (TiO2) are to be well received in the modern building. Control of fabrication parameters when preparing small-scale samples for academic research is not difficult. In mass production environments, however, maintenance of the stable parameters becomes the critical issues. An advance mold design may overcome the issues. In this article, we design the convenience molds that can maintain a constant current density and to facilitate the occurrence of electrochemical reactions in designated areas. The high quality and functional green building materials can therefore be easily fabricated.

There have been a variety of efforts demonstrating the use of solid freeform fabrication (SFF) for prosthetic socket fabrication though there has been little effort in leveraging the strengths of the technology. SFF encompasses a class of technologies that can create three dimensional objects directly from a geometric database without specific tooling or human intervention. A real strength of SFF is that cost of fabrication is related to the volume of the part, not the part's complexity. For prosthetic socket fabrication this means that a sophisticated socket can be fabricated at essentially the same cost as a simple socket. Adding new features to a socket design becomes a function of software. The work at The University of Texas Health Science Center at San Antonio (UTHSCSA) and University of Texas at Austin (UTA) has concentrated on developing advanced sockets that incorporate structural features to increase comfort as well as built in fixtures to accommodate industry standard hardware. Selective laser sintering (SLS) was chosen as the SFF technology to use for socket fabrication as it was capable of fabricating sockets using materials appropriate for prosthetics. This paper details the development of SLS prosthetic socket fabrication techniques at UTHSCSA/UTA over a six-year period.

The last decade created tremendous advances in new and unique thermoelectric generation materials, devices, fabrication techniques, and technologies via various global research and development. This article seeks to elucidate and highlight some of these advances to lay foundations for future research work and advances. New advanced methods and demonstrations in TE device and material measurement, materials fabrication and composition advances, and device design and fabrication will be discussed. Other articles in this Special Issue present additional new research into materials fabrication and composition advances, including multi-dimensional additive manufacturing and advanced silicon germanium technologies. This article will discuss the most recent results and findings in thermoelectric system economics, including highlighting and quantifying the interrelationships between thermoelectric (TE) material costs, TE manufacturing costs and most importantly, often times dominating, the heat exchanger costs in overall TE system costs. We now have a methodology for quantifying the competing TE system cost-performance effects and impacts. Recent findings show that heat exchanger costs usually dominate overall TE system cost-performance tradeoffs, and it is extremely difficult to escape this condition in TE system design. In regard to material performance, novel or improved enhancement principles are being effectively implemented. Furthermore, in addition to further advancements in properties and module developments of relatively established champion materials such as skutterudites, several high performance ZT ≈≥ 2 new material systems such as GeTe, Mg3(Sb,Bi)2 have also been relatively recently unearthed and module applications also being considered. These recent advancements will also be covered in this review.

Electrostatic assembly is one of the bottom–up approaches used for multiscale composite fabrication. Since its discovery, this method has been actively used in molecular bioscience as well as materials design and fabrication for various applications. Despite the recent advances and controlled assembly reported using electrostatic interaction, the method still possesses vast potentials for various materials design and fabrication. This review article is a timely revisit of the electrostatic assembly method with a brief introduction of the method followed by surveys of recent advances and applications of the composites fabricated. Emphasis is also given to the significant potential of this method for advanced materials and composite fabrication in line with sustainable development goals. Prospective outlook and future developments for micro-/nanocomposite materials fabrication for emerging applications such as energy-related fields and additive manufacturing are also mentioned.

Doutoramento em Ciência e Engenharia de Materiais
This work is about the combination of functional ferroelectric oxides with Multiwall Carbon Nanotubes for microelectronic applications, as for example potential 3 Dimensional (3D) Non Volatile Ferroelectric Random Access Memories (NVFeRAM). Miniaturized electronics are ubiquitous now. The drive to downsize electronics has been spurred by needs of more performance into smaller packages at lower costs. But the trend of electronics miniaturization challenges board assembly materials, processes, and reliability. Semiconductor device and integrated circuit technology, coupled with its associated electronic packaging, forms the backbone of high-performance miniaturized electronic systems. However, as size decreases and functionalization increases in the modern electronics further size reduction is getting difficult; below a size limit the signal reliability and device performance deteriorate. Hence miniaturization of siliconbased electronics has limitations. On this background the Road Map for Semiconductor Industry (ITRS) suggests since 2011 alternative technologies, designated as More than Moore; being one of them based on carbon (carbon nanotubes (CNTs) and graphene) [1]. CNTs with their unique performance and three dimensionality at the nano-scale have been regarded as promising elements for miniaturized electronics [2]. CNTs are tubular in geometry and possess a unique set of properties, including ballistic electron transportation and a huge current caring capacity, which make them of great interest for future microelectronics [2]. Indeed CNTs might have a key role in the miniaturization of Non Volatile Ferroelectric Random Access Memories (NVFeRAM). Moving from a traditional two dimensional (2D) design (as is the case of thin films) to a 3D structure (based on a tridimensional arrangement of unidimensional structures) will result in the high reliability and sensing of the signals due to the large contribution from the bottom electrode. One way to achieve this 3D design is by using CNTs. Ferroelectrics (FE) are spontaneously polarized and can have high dielectric constants and interesting pyroelectric, piezoelectric, and electrooptic properties, being a key application of FE electronic memories. However, combining CNTs with FE functional oxides is challenging. It starts with materials compatibility, since crystallization temperature of FE and oxidation temperature of CNTs may overlap. In this case low temperature processing of FE is fundamental. Within this context in this work a systematic study on the fabrication of CNTs - FE structures using low cost low temperature methods was carried out. The FE under study are comprised of lead zirconate titanate (Pb1-xZrxTiO3, PZT), barium titanate (BaTiO3, BT) and bismuth ferrite (BiFeO3, BFO). The various aspects related to the fabrication, such as effect on thermal stability of MWCNTs, FE phase formation in presence of MWCNTs and interfaces between the CNTs/FE are addressed in this work. The ferroelectric response locally measured by Piezoresponse Force Microscopy (PFM) clearly evidenced that even at low processing temperatures FE on CNTs retain its ferroelectric nature. The work started by verifying the thermal decomposition behavior under different conditions of the multiwall CNTs (MWCNTs) used in this work. It was verified that purified MWCNTs are stable up to 420 ºC in air, as no weight loss occurs under non isothermal conditions, but morphology changes were observed for isothermal conditions at 400 ºC by Raman spectroscopy and Transmission Electron Microscopy (TEM). In oxygen-rich atmosphere MWCNTs started to oxidized at 200 ºC. However in argon-rich one and under a high heating rate MWCNTs remain stable up to 1300 ºC with a minimum sublimation. The activation energy for the decomposition of MWCNTs in air was calculated to lie between 80 and 108 kJ/mol. These results are relevant for the fabrication of MWCNTs – FE structures. Indeed we demonstrate that PZT can be deposited by sol gel at low temperatures on MWCNTs. And particularly interesting we prove that MWCNTs decrease the temperature and time for formation of PZT by ~100 ºC commensurate with a decrease in activation energy from 68±15 kJ/mol to 27±2 kJ/mol. As a consequence, monophasic PZT was obtained at 575 ºC for MWCNTs - PZT whereas for pure PZT traces of pyrochlore were still present at 650 ºC, where PZT phase formed due to homogeneous nucleation. The piezoelectric nature of MWCNTs - PZT synthesised at 500 ºC for 1 h was proved by PFM. In the continuation of this work we developed a low cost methodology of coating MWCNTs using a hybrid sol-gel / hydrothermal method. In this case the FE used as a proof of concept was BT. BT is a well-known lead free perovskite used in many microelectronic applications. However, synthesis by solid state reaction is typically performed around 1100 to 1300 ºC what jeopardizes the combination with MWCNTs. We also illustrate the ineffectiveness of conventional hydrothermal synthesis in this process due the formation of carbonates, namely BaCO3. The grown MWCNTs - BT structures are ferroelectric and exhibit an electromechanical response (15 pm/V). These results have broad implications since this strategy can also be extended to other compounds of materials with high crystallization temperatures. In addition the coverage of MWCNTs with FE can be optimized, in this case with non covalent functionalization of the tubes, namely with sodium dodecyl sulfate (SDS). MWCNTs were used as templates to grow, in this case single phase multiferroic BFO nanorods. This work shows that the use of nitric solvent results in severe damages of the MWCNTs layers that results in the early oxidation of the tubes during the annealing treatment. It was also observed that the use of nitric solvent results in the partial filling of MWCNTs with BFO due to the low surface tension (<119 mN/m) of the nitric solution. The opening of the caps and filling of the tubes occurs simultaneously during the refluxing step. Furthermore we verified that MWCNTs have a critical role in the fabrication of monophasic BFO; i.e. the oxidation of CNTs during the annealing process causes an oxygen deficient atmosphere that restrains the formation of Bi2O3 and monophasic BFO can be obtained. The morphology of the obtained BFO nano structures indicates that MWCNTs act as template to grow 1D structure of BFO. Magnetic measurements on these BFO nanostructures revealed a week ferromagnetic hysteresis loop with a coercive field of 956 Oe at 5 K. We also exploited the possible use of vertically-aligned multiwall carbon nanotubes (VA-MWCNTs) as bottom electrodes for microelectronics, for example for memory applications. As a proof of concept BiFeO3 (BFO) films were in-situ deposited on the surface of VA-MWCNTs by RF (Radio Frequency) magnetron sputtering. For in situ deposition temperature of 400 ºC and deposition time up to 2 h, BFO films cover the VA-MWCNTs and no damage occurs either in the film or MWCNTs. In spite of the macroscopic lossy polarization behaviour, the ferroelectric nature, domain structure and switching of these conformal BFO films was verified by PFM. A week ferromagnetic ordering loop was proved for BFO films on VA-MWCNTs having a coercive field of 700 Oe. Our systematic work is a significant step forward in the development of 3D memory cells; it clearly demonstrates that CNTs can be combined with FE oxides and can be used, for example, as the next 3D generation of FERAMs, not excluding however other different applications in microelectronics.
Este trabalho é sobre a combinação de óxidos ferroelétricos funcionais com nanotubos de carbono (CNTs) para aplicações na microeletrónica, como por exemplo em potenciais memórias ferroelétricas não voláteis (Non Volatile Ferroelectric Random Access Memories (NV-FeRAM)) de estrutura tridimensional (3D). A eletrónica miniaturizada é nos dias de hoje omnipresente. A necessidade de reduzir o tamanho dos componentes eletrónicos tem sido estimulada por necessidades de maior desempenho em dispositivos de menores dimensões e a custos cada vez mais baixos. Mas esta tendência de miniaturização da eletrónica desafia consideravelmente os processos de fabrico, os materiais a serem utilizados nas montagens das placas e a fiabilidade, entre outros aspetos. Dispositivos semicondutores e tecnologia de circuitos integrados, juntamente com a embalagem eletrónica associada, constituem a espinha dorsal dos sistemas eletrónicos miniaturizados de alto desempenho. No entanto, à medida que o tamanho diminui e a funcionalização aumenta, a redução das dimensões destes dipositivos é cada vez mais difícil; é bem conhecido que abaixo de um tamanho limite o desempenho do dispositivo deteriora-se. Assim, a miniaturização da eletrónica à base de silício tem limitações. É precisamente neste contexto que desde 2011 o Road Map for Semiconductor Industry (ITRS) sugere tecnologias alternativas às atualmente em uso, designadas por Mais de Moore (More than Moore); sendo uma delas com base em carbono (CNTs e grafeno) [1]. Os CNTs com o seu desempenho único e tridimensionalidade à escala nanométrica, foram considerados como elementos muito promissores para a eletrónica miniaturizada [2]. Nanotubos de carbono possuem uma geometria tubular e um conjunto único de propriedades, incluindo o transporte balístico de eletrões e uma capacidade enorme de transportar a corrente elétrica, o que os tornou de grande interesse para o futuro da microeletrónica [2]. Na verdade, os CNTs podem ter um papel fundamental na miniaturização das memórias ferroelétricas não voláteis (NV-FeRAM). A mudança de uma construção tradicional bidimensional (2D) (ou seja, a duas dimensões, como são os filmes finos) para uma construção tridimensional 3D, com base num arranjo tridimensional de estruturas unidimensionais (1D), como são as estruturas nanotubulares, resultará num desempenho melhorado com deteção de sinal elétrico optimizada, devido à grande contribuição do elétrodo inferior. Uma maneira de conseguir esta configuração 3D é usando nanotubos de carbono. Os materiais ferroelétricos (FE) são polarizados espontaneamente e possuem constantes dielétricas altas e as suas propriedades piroelétricas, piezoelétricas e eletroópticas tornam-nos materiais funcionais importantes na eletrónica, sendo uma das suas aplicações chave em memórias eletrónicas. No entanto, combinar os nanotubos de carbono com óxidos FE funcionais é um desafio. Começa logo com a compatibilidade entre os materiais e o seu processamento, já que as temperaturas de cristalização do FE e as temperaturas de oxidação dos CNTs se sobrepõem. Neste caso, o processamento a baixa temperatura dos óxidos FE é absolutamente fundamental. Dentro deste contexto, neste trabalho foi realizado um estudo sistemático sobre a fabricação e caracterização estruturas combinadas de CNTs – FE, usando métodos de baixa temperatura e de baixo custo. Os FE em estudo foram compostos de titanato zirconato de chumbo (Pb1-xZrxTiO3, PZT), titanato de bário (BaTiO3, BT) e ferrite de bismuto (BiFeO3, BFO). Os diversos aspetos relacionados com a síntese e fabricação, como efeito sobre a estabilidade térmica dos nanotubos de carbono multiparede (multiwall CNTs, MWCNTs), formação da fase FE na presença de MWCNTs e interfaces entre CNTs / FE foram abordados neste trabalho. A resposta ferroelétrica medida localmente através de microscopia de ponta de prova piezoelétrica (Piezoresponse Force Microscopy (PFM)), evidenciou claramente que, mesmo para baixas temperaturas de processamento óxidos FE sobre CNTs mantém a sua natureza ferroelétrica. O trabalho começou pela identificação do comportamento de decomposição térmica em diferentes condições dos nanotubos utilizados neste trabalho. Verificou-se que os MWCNTs purificados são estáveis até 420 ºC no ar, já que não ocorre perda de peso sob condições não isotérmicas, mas foram observadas, por espectroscopia Raman e microscopia eletrónica de transmissão (TEM), alterações na morfologia dos tubos para condições isotérmicas a 400 ºC. Em atmosfera rica em oxigénio os MWCNTs começam a oxidar-se a 200 ºC. No entanto, em atmosfera rica em árgon e sob uma taxa de aquecimento elevada os MWCNTs permanecem estáveis até 1300 ºC com uma sublimação mínima. A energia de ativação para a decomposição destes MWCNTs em ar foi calculada situar-se entre 80 e 108 kJ / mol. Estes resultados são relevantes para a fabricação de estruturas MWCNTs - FE. De facto, demonstramos que o PZT pode ser depositado por sol-gel a baixas temperaturas sobre MWCNTs. E, particularmente interessante foi provar que a presença de MWCNTs diminui a temperatura e tempo para a formação de PZT, em cerca de ~ 100 ºC comensuráveis com uma diminuição na energia de ativação de 68 ± 15 kJ / mol a 27 ± 2 kJ / mol. Como consequência, foi obtido PZT monofásico a 575 ºC para as estruturas MWCNTs – PZT, enquanto que para PZT (na ausência de MWCNTs) a presença da fase de pirocloro era ainda notória a 650 ºC e onde a fase de PZT foi formada por nucleação homogénea. A natureza piezoelétrica das estruturas de MWCNTs - PZT sintetizadas a 500 ºC por 1 h foi provada por PFM. Na continuação deste trabalho foi desenvolvida uma metodologia de baixo custo para revestimento de MWCNTs usando uma combinação entre o processamento sol – gel e o processamento hidrotermal. Neste caso o FE usado como prova de conceito foi o BT. BT é uma perovesquita sem chumbo bem conhecida e utilizada em muitas aplicações microeletrónicas. No entanto, a síntese por reação no estado sólido é normalmente realizada entre 1100 - 1300 ºC o que coloca seriamente em risco a combinação com MWCNTs. Neste âmbito, também se ilustrou claramente a ineficácia da síntese hidrotérmica convencional, devido à formação de carbonatos, nomeadamente BaCO3. As estruturas MWCNTs - BT aqui preparadas são ferroelétricas e exibem resposta electromecânica (15 pm / V). Considera-se que estes resultados têm impacto elevado, uma vez que esta estratégia também pode ser estendida a outros compostos de materiais com elevadas temperaturas de cristalização. Além disso, foi também verificado no decurso deste trabalho que a cobertura de MWCNTs com FE pode ser optimizada, neste caso com funcionalização não covalente dos tubos, ou seja, por exemplo com sodium dodecyl sulfate (SDS).

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.

Le développement des dispositifs microélectroniques a dopé la recherche dans le domaine des microbatteries tout solide rechargeables. Mais actuellement, les performances de ces microbatteries élaborées par des technologies couche mince (2D) sont limitées et le passage à une géométrie 3D adoptant le concept “Li-ion” ou“rocking chair” est incontournable. Cette dernière condition implique de combiner des matériaux de cathode comme LiCoO2, LiMn2O4 or LiFePO4 avec des anodes pouvant réagir de manière réversible avec les ions lithium. Parmi tous les matériaux pouvant servir potentiellement d'anode, les nanotubes de TiO2 révèlent des propriétés intéressantes pour concevoir des microbatteries Li-ion 3D. Facilement réalisable, la nano-architecture auto-organisée a montré des résultats très prometteurs en termes de capacités à des cinétiques relativement modérées. L'utilisation des nanotubes de TiO2 en tant qu'anode conduit à des cellules présentant de faible autodéchargeet élimine le risque de surcharge grâce au haut potentiel de fonctionnement (1.72 V vs. Li+/Li). Dans ce travail de thèse, nous avons étudié la substitution des ions Ti4+ par Sn4+ et Fe2+ dans les nanotubes de TiO2. Bien que la présence d'ions Fe2+ n'ait pas amélioré les performances électrochimiques des nanotubes, nous avons pu mettre en évidence l'effet bénéfique des ions Sn4+. Nous avons aussi pu montré que la fabrication de matériaux composites à base de nanotubes de TiO2 et d'oxyde de métaux de transition électrodéposés se présentant sous forme de particules (NiO et Co3O4 ) augmentait les capacités d'un facteur 4
The advent of modern microelectronic devices has necessitated the search for high-performance all-solid-state (rechargeable) microbatteries. So far, only lithium-based systems fulfill the voltage and energy density requirements of microbatteries. Presently, there is a need to move from 2D to 3D configurations, and also a necessity to adopt the “Li-ion” or the “rocking-chair” concept in designing these lithium-based (thin-film) microbatteries. This implies the combination of cathode materials such as LiCoO2, LiMn2O4 or LiFePO4 with the wide range of possible anode materials that can react reversibly with lithium. Among all the potential anode materials, TiO2 nanotubes possess a spectacular characteristic for designing 3D Li-ion microbatteries. Besides the self-organized nano-architecture, TiO2 is non-toxic and inexpensive, and the nanotubes have been demonstrated to exhibit very good capacity retention particularly at moderate kinetic rates. The use of TiO2 as anode provides cells with low self-discharge and eliminates the risk of overcharging due to its higher operating voltage (ca. 1.72 V vs. Li+/Li). Moreover, their overall performance can be improved. Hence, TiO2 nanotubes and their derivatives were synthesized and characterized, and their electrochemical behaviour versus lithium was evaluated in lithium test cells. As a first step towards the fabrication of a 3D microbattery based on TiO2 nanotubes, electrodeposition of polymer electrolytes into the synthesized TiO2 nanotubes was also studied; the inter-phase morphology and the electrochemical behaviour of the resulting material were studied

This thesis presents work relating to the fabrication of novel thin film electrodes for energy storage applications, with a focus on low cost, nanostructured transition metal oxides, and electrode manufacture by atomised spray deposition. Iron oxide (FeO_x) nanowires were synthesised hydrothermally and combined with multi-walled carbon nanotubes (MWNT) in sprayed electrodes, which provided the necessary conductivity enhancement for effective energy storage. The spray processing technique allowed for facile control over the relative fraction of MWNTs in the sprayed electrodes. Optimised electrodes were investigated in a range of aqueous electrolytes, and the best energy storage behaviour occurred in Na₂SO₃ with a maximum capacitance from cyclic voltammetry of 312 Fg^-1 at a scan rate of 2 mVs^-1. The FeO_x/MWNT electrodes were investigated for their suitability as lithium-ion battery anodes and showed reasonable energy storage behaviour. Nickel oxide (NiO) electrodes were manufactured by hydrothermal synthesis and annealing followed atomised spray deposition. The performance of the NiO electrodes was enhanced though combination with aqueous graphene suspensions, produced in-house by ultrasonic exfoliation of graphite. The processing route used to combine the nanomaterials was considered and a co-synthesis route resulted in the best performing electrodes. Different substrates were investigated, as the most commonly used Ni-foam substrate reacted with the basic electrolytes necessary for electrochemical activity of NiO. NiO/graphene electrodes showed charge/discharge capacitances of up to 571 Fg^-1 at a current density of 10 Ag^-1, which was maintained at over 300 F/g at a very high current density of 100 Ag^-1. Asymmetric supercapacitor devices were constructed using various combinations of FeO_x, NiO, and commercial carbon black electrodes to extend the operating potential window beyond the ~1.23 V limit of symmetric aqueous-electrolyte devices. Power densities of over 20 kWkg^-1 were achieved for an FeO_x/MWNT-carbon device, which was comparable with current commercial carbon-only supercapacitors.