Plasmonic strain sensors based on Au-TiO2 thin films on flexible substrates

This study aimed at introducing thin films exhibiting the localized surface plasmon resonance (LSPR) phenomenon with a reversible optical response to repeated uniaxial strain. The sensing platform was prepared by growing gold (Au) nanoparticles throughout a titanium dioxide dielectric matrix. The thin films were deposited on transparent polymeric substrates, using reactive magnetron sputtering, followed by a low temperature thermal treatment to grow the nanoparticles. The microstructural characterization of the thin films’ surface revealed Au nanoparticle with an average size of 15.9 nm, an aspect ratio of 1.29 and an average nearest neighbor nanoparticle at 16.3 nm distance. The plasmonic response of the flexible nanoplasmonic transducers was characterized with custom-made mechanical testing equipment using simultaneous optical transmittance measurements. The higher sensitivity that was obtained at a maximum strain of 6.7%, reached the values of 420 nm/ε and 110 pp/ε when measured at the wavelength or transmittance coordinates of the transmittance-LSPR band minimum, respectively. The higher transmittance gauge factor of 4.5 was obtained for a strain of 10.1%. Optical modelling, using discrete dipole approximation, seems to correlate the optical response of the strained thin film sensor to a reduction in the refractive index of the matrix surrounding the gold nanoparticles when uniaxial strain is applied.This research was funded by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/04650/2020 and by the projects NANO4BIO: POCI01-0145-FEDER-032299, with FCT reference PTDC/FIS-MAC/32299/2017, and CO2Plasmon with FCT reference EXPL/CTM-REF/0750/2021

Enhancing the sensitivity of nanoplasmonic thin films for ethanol vapor detection

Nanoplasmonic thin films, composed of noble metal nanoparticles (gold) embedded in an oxide matrix, have been a subject of considerable interest for Localized Surface Plasmon Resonance (LSPR) sensing. Ethanol is one of the promising materials for fuel cells, and there is an urgent need of a new generation of safe optical sensors for its detection. In this work, we propose the development of sensitive plasmonic platforms to detect molecular analytes (ethanol) through changes of the LSPR band. The thin films were deposited by sputtering followed by a heat treatment to promote the growth of the gold nanoparticles. To enhance the sensitivity of the thin films and the signal-to-noise ratio (SNR) of the transmittance–LSPR sensing system, physical plasma etching was used, resulting in a six-fold increase of the exposed gold nanoparticle area. The transmittance signal at the LSPR peak position increased nine-fold after plasma treatment, and the quality of the signal increased six times (SNR up to 16.5). The optimized thin films seem to be promising candidates to be used for ethanol vapor detection. This conclusion is based not only on the current sensitivity response but also on its enhancement resulting from the optimization routines of thin films’ architectures, which are still under investigation.This research was funded by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2019 and by the projects NANOSENSING: POCI-01-0145-FEDER-016902, with FCT reference PTDC/FIS-NAN/1154/2014, and NANO4BIO: POCI-01-0145-FEDER-032299, with FCT reference PTDC/FIS-MAC/32299/201

Properties of MeNxOy thin films prepared by reactive DC magnetron sputtering

Poster apresentado no E-MRS 2012 SPRING MEETING, Simposio U "Carbon- or Nitrogen-Containing Nanostructured Thin Films"The addition of small amount of nitrogen to a growing MeOy (Me = Metal) film originates a new class of materials with a wide range of different properties, where the optical, electrical and mechanical ones may be tailored between those of the pure oxide, MeOy, and oxynitride, MeNxOy, films, according to the particular application envisaged. The main reason for this is related with the change in the nitride content (which can be either metallic or even insulating-type) of the films promoted by the increasing amounts of nitrogen that are introduced in the films. In this work thin films of MeNxOy were produced using reactive DC magnetron sputtering, using a metallic (Me) target and an Ar/(N2,O2) gas mixture. Preliminary results revealed that the incorporation of nitrogen in the MeOy matrix induces the production of films with electrical and optical responses rather different than the pure oxide that are strongly correlated with its structural arrangement, chemical composition an d morphology changes. On one hand the electrical resistivity and temperature coefficient of resistance were found to have a wide variation, which can be explained using a tunnel barrier conduction mechanism for the electric charge transport through the film, with possible applications in microelectronic devices. The particular morphology of the films induced a broadband optical response with high optical absorption from 290 to 2500 nm, with potential applications in solar cells and thermal photovoltaics.FEDER - Programa Operacional Factores de Competitividade (COMPETE)Fundação para a Ciência e a Tecnologia (FCT) - PTDC/CTM-NAN/112574/2009, PEst-C-FIS/UI607/2011-2012, SFRH/BD/47118/200

AlNxOy thin films deposited by DC reactive magnetron sputtering

AlNxOy thin films were produced by DC reactive magnetron sputtering, using an atmosphere of argon and a reactive gas mixture of nitrogen and oxygen, for a wide range of partial pressures of reactive gas. During the deposition, the discharge current was kept constant and the discharge parameters were monitored. The deposition rate, chemical composition, morphology, structure and electrical resistivity of the coatings are strongly correlated with discharge parameters. Varying the reactive gas mixture partial pressure, the film properties change gradually from metallic-like films, for low reactive gas partial pressures, to stoichiometric amorphous Al2O3 insulator films, at high pressures. For intermediate reactive gas pressures, sub-stoichiometric AlN x O y films were obtained, with the electrical resistivity of the films increasing with the non metallic/metallic ratio.FEDER - Program COMPETE - Programa Operacional Factores de CompetitividadeFundação para a Ciência e a Tecnologia (FCT) - Project PTDC/CTM/69362/2006; PhD grant Nº SFRH/BD/47118/200

Desenvolvimento de protótipo de sistema especialista para projeto pneumático

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Mecânica

Process monitoring during AlNxOy deposition by reactive magnetron sputtering and correlation with the film’s properties

In this work, AlNxOy thin films were deposited by reactive magnetron sputtering, using an aluminum target and an Ar/(N2+O2) atmosphere. The DC magnetron discharge parameters during the deposition process were investigated by optical emission spectroscopy and a plasma floating probe was used. The discharge voltage, the electron temperature, the ion flux and the optical emission lines were recorded for different reactive gas flows, near the target and close to the substrate. This information was correlated with the structural features of the deposits as a first step in the development of a system to control the structure and properties of the films during reactive magnetron sputtering. As the target becomes poisoned, the discharge voltage suffers an important variation, due to the modification of the secondary electron emission coefficient of the target, which is also supported by the evolution of the electron temperature and ion flux to the target. The sputtering yield of the target was also affected, leading to a reduction of the amount of Al atoms arriving to the substrate, according to optical emission spectroscopy results for Al emission line intensity. This behavior, together with the increase of non-metallic elements in the films, allowed obtaining different microstructures, over a wide range of compositions, which induced different electrical and optical responses of films.This research was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST-C/FIS/UI607/2011. J. Borges also acknowledges FCT financial support under PhD grant Nº SFRH/BD/47118/2008 (financiado por POPH – QREN – Tipologia 4.1 – Formação Avançada, comparticipado pelo Fundo Social Europeu e por fundos nacionais do MCTES)

Otimização do processo de deposição de oxinitretos metálicos por pulverização reativa magnetrão

Tese de doutoramento em Ciências (área de especialização em Física)O sistema ternário de oxinitreto de alumínio (AlNxOy) oferece a possibilidade de obter um gradiente de respostas, combinando as propriedades do Al, AlN e do Al2O3 no A evolução da taxa de deposição dos filmes foi também correlacionada com o aumento da pressão parcial de gás reativo e com as características da deposição, encontrando-se quatro tendências de variação. O tipo de crescimento dos filmes evoluiu de colunar (zona Ia) para “couve-flor” (zona T), terminando denso e compacto (zona II-C). As razões atómicas de CN+O/CAl aumentaram progressivamente desde 0.0 até 0.85, dentro das zonas Ia e T, assistindo-se à formação de filmes quase estequiométricos de Al2O3 na zona II-C. A caracterização da estrutura e da ligação química revelou uma gradual diminuição do carácter metálico do filmes, devido ao aumento das ligações iónicas e/ou covalentes. Foi observada uma estrutura típica do alumínio na zona Ia e na zona T, com uma gradual perda de cristalinidade nesta última, até que uma completa amorfização foi obtida para os filmes indexados à zona II-C. A microestrutura granular, rugosa e com vazios, de alguns filmes (zona T), foi correlacionada com a inibição da coalescência dos grãos durante o seu crescimento, devido à baixa mobilidade dos átomos de alumínio em camadas de óxido e à diminuição da temperatura do substrato em função da pressão parcial de N2+O2. Os resultados da caracterização dos filmes sugeriram, também, a formação de materiais nanocompósitos (zona T), nos quais nanopartículas de Al estão dispersas numa matriz amorfa de AlNxOy. As nanopartículas podem estar em contacto ou separadas por material semicondutor/isolante, formando uma rede de percolação que confere aos filmes resistividades elétricas até quatro ordens de grandeza acima do alumínio. Por outro lado, as características estruturais e morfológicas dos filmes provocaram uma transição gradual nos coeficientes de temperatura, desde valores positivos até valores negativos, à medida que a razão atómica de CN+O/CAl aumentou. Os filmes revelaram igualmente propriedades ópticas peculiares, com os perfis de reflectância a variar, desde os típicos do alumínio metálico, para espectros aproximadamente constantes e com valores tão baixos quanto 5%. Com o propósito de estabelecer os limites práticos de aplicação destes filmes em futuras aplicações, quer elétricas, quer óticas, foi também estudada a estabilidade térmica das amostras depositadas (em termos estruturais e de propriedades óticas) e ainda a sua resistência à corrosão ao longo do tempo, usando métodos de caracterização eletroquímica (voltametria e espectroscopia de impedância eletroquímica). Os resultados demonstraram um aumento da resistência à corrosão, mesmo quando imersos durante algumas semanas, e boa estabilidade térmica, até temperaturas de recozimento de 600 ºC. mesmo material, abrindo um leque variado de possíveis aplicações. Um dos principais objetivos deste trabalho foi correlacionar as propriedades elétricas e óticas de filmes finos de AlNxOy, com a sua composição, tipo de ligações químicas e características microestruturais, tomando como referência os sistemas binários base de AlNx e AlOy. As condições de processamento dos filmes (estado do alvo, parâmetros de plasma e características de deposição) foram monitorizadas e correlacionadas com o fluxo de gás reativo, visando a otimização do processo de produção e facilitar a sua transposição para outros sistemas de deposição e/ou para a indústria. Os filmes finos de AlNxOy foram produzidos usando a técnica de pulverização catódica reativa por descarga magnetrão de corrente contínua, com recurso a um alvo de alumínio e a uma atmosfera gasosa composta por árgon e uma mistura de gás reativo de N2+O2 (17:3). A pressão parcial de N2+O2 foi gradualmente aumentada, mantendo a corrente de descarga constante (75 A.m-2), obtendo-se um largo gradiente de composições. De acordo com os resultados de espectroscopia ótica de emissão, o gás reativo é essencialmente consumido pelas superfícies da câmara de deposição (alvo, paredes e substratos), uma vez que apenas foram detetadas linhas de emissão do árgon e do alumínio. O aumento da pressão parcial de gás reativo (N2+O2) promoveu um gradual envenenamento do alvo e, consequentemente, o aumento do coeficiente de emissão secundária de eletrões por impacto iónico, sendo este um dos fatores determinantes nas características da descarga, bem como nas variações observadas nos parâmetros de plasma. Com efeito, foi observada uma diminuição quase linear do potencial do alvo (regime I), até atingir valores aproximadamente constantes (regime II). Assistiu-se também a um gradual aumento da temperatura eletrónica e a uma ligeira diminuição do fluxo iónico perto do cátodo, à medida que a pressão parcial de N2+O2 foi aumentada.The ternary aluminium oxynitride (AlNxOy) system offers the possibility to obtain a wide range of responses, by tailoring the properties between Al, AlN and Al 2O3, opening a significant number of possible applications. One of the main objectives of this work was to correlate the electrical and optical properties of AlNxOy thin films with their composition, bonding characteristics and microstructural features, taking as reference the binary systems AlNx and AlOy. Furthermore, the processing conditions, such as the target condition, plasma parameters and deposition characteristics were also monitored and correlated with the flow of reactive gas, aiming to optimize the deposition process and facilitate the transfer of technology to other deposition systems and/or to the industry. The AlNxOy thin films were produced by reactive DC magnetron sputtering, in a wide composition range, using an aluminium target, and an atmosphere composed of argon and a reactive gas mixture of N2+O2 (17:3 ratio). The partial pressure of the reactive gas mixture was increased, maintaining the discharge current constant (75 A.m-2). According to optical emission spectroscopy results, the reactive gas should be mainly consumed by the chamber surfaces (target, walls and the substrates), since it was only detected the presence of argon and aluminium lines. The increase of the partial pressure of the reactive gas (N2+O2) promoted a gradual poisoning of the target, and a consequent increase of its ion induced secondary electron emission coefficient. This was one of the main factors controlling the discharge characteristics and, as well, the changes observed in the plasma parameters. In fact, it was measured an almost linear decrease of the target potential (regime I), until it reached constant values (regime II) for higher partial pressures of the reactive gas, as well as a gradual increase of the electron temperature (Te) and a slight decrease of the ion flux (Γ+) near the cathode, as the partial pressure of N2+O2 increased. Within the two identified regimes of the target, four different tendencies for the deposition rate were found and a morphological evolution of the films from columnar (zone Ia) towards cauliflower-type (zone T), ending up as dense and featureless (zone II-C). The atomic ratio of CN+O/CAl progressively increased from 0.0 to 0.85, within zone Ia and T, and it increased up to ~1.5 in zone II-C, where close stoichiometric Al2O3 films were formed. Both bonding characteristics results and structural characterization revealed a gradual decrease of the metallic character of the films, due to the rise of ionic/covalent bonds. Furthermore, it was observed an Al-type structure in zone Ia and zone T, with a gradual loss in crystallinity in the latter, until a complete amorphization was achieved by the films lying in zone II-C. The voided and rough microstructure found in some films (zone T) was correlated to the inhibition of the grain coalescence during film growth, due to the low mobility of aluminium adatoms on oxide layers and also to the decrease of the substrate temperature, as a function of the partial pressure of N2+O2. These films developed also a nanocomposite structure, where Al nanoparticles are dispersed in an amorphous matrix of AlNxOy compounds (zone T), with a wide range of electrical and optical responses, tailored between metallic-like to semiconducting and insulating ones. The nanoparticles can be in contact or separated by semiconducting/insulating layers, forming a percolation network, which induced an increase of the electrical resistivity up to four orders of magnitude higher than Al. The particular combination of morphological and structural features also provoked a gradual transition from positive to negative TCR values, as the atomic ratio of CN+O/CAl increased. Furthermore, the films revealed unusual optical properties, with the reflectance profiles evolving from those typical of metallic aluminium to flat and low reflectance ones, with values as low as 5 %. In order to establish the limits of practical applicability of these films in future applications, either electrical or optical, the thermal stability (in terms of structure and properties) of the deposited samples was studied, as well as the corrosion behaviour, using electrochemical methods (voltammetry and electrochemical impedance spectroscopy). The results showed an increase of the corrosion resistance, even when immersed for several weeks, and good stability for annealing temperatures up to 600 ºC.Agradeço à Fundação para a Ciência e Tecnologia o financiamento obtido através da bolsa de Investigação (Doutoramento), com a referência SFRH/BD/47118/2008 (financiada pelo POPH – QREN – Tipologia 4.1 – Formação Avançada, comparticipado pelo Fundo Social Europeu e por fundos nacionais do MCTES). Este trabalho foi também financiado por outros projetos: Fundos FEDER através do Programa Operacional Factores de Competitividade – COMPETE e por Fundos Nacionais através da FCT – Fundação para a Ciência e a Tecnologia, no âmbito do projecto estratégico PEST-C/FIS/UI607/2011; Projeto PTDC/CTM/69362/2006; Projeto PTDC/CTM-NAN/112574/2009 e Programa Pessoa 2010/2011, Cooperação Portugal/França, Proc.º441.00, Project“COLOURCLUSTER”

Optical properties of AlNxOy thin films deposited by DC magnetron sputtering

The aluminium oxynitride system offers the possibility to obtain a wide range of optical responses, by combining metallic aluminium, aluminium oxide and aluminium nitride properties, and thus opening a significant number of possible applications. The main purpose of the present work is to study the variation of the optical properties of AlN x O y thin films as a function of their composition (by varying both x and y coefficients), and the correspondent changes in their morphology and structure. The films were deposited by DC reactive magnetron sputtering, with the discharge parameters monitored during the deposition in order to control the chemical composition. The measurements reveal a smooth change of films Reflectance/Transmittance as a function of the concentration ratio of non metallic elements (O+N) to metallic Al, thus revealing the possibility to tailor the films optical properties according to the application envisaged.Fundação para a Ciência e a Tecnologia (FCT) e ao Fundo Europeu de Desenvolvimento Regional (FEDER) – Programa Operacional “Ciência , Tecnologia, Inovação” – PTDC/CTM/69362/2006 e SFRH/BD/47118/200

Plant genetic resources for agriculture, plant breeding, and biotechnology: Experiences from Cameroon, Kenya, the Philippines, and Venezuela

"Local farming communities throughout the world face binding productivity constraints, diverse nutritional needs, environmental concerns, and significant economic and financial pressures. Developing countries address these challenges in different ways, including public and private sector investments in plant breeding and other modern tools for genetic crop improvement. In order to measure the impact of any technology and prioritize investments, we must assess the relevant resources, human capacity, clusters, networks and linkages, as well as the institutions performing technological research and development, and the rate of farmer adoption. However, such measures have not been recently assessed, in part due to the lack of complete standardized information on public plant breeding and biotechnology research in developing countries. To tackle this void, the Food and Agricultural Organization of the United Nations (FAO), in consultation with the International Food Policy Institute (IFPRI) and other organizations, designed a plant breeding and biotechnology capacity survey for implementation by FAO consultants in 100 developing countries. IFPRI, in collaboration with FAO and national experts contracted by FAO to complete in-country surveys, identified and analyzed plant breeding and biotechnology programs in four developing countries: Cameroon, Kenya, the Philippines, and Venezuela. Here, we use an innovation systems framework to examine the investments in human and financial resources and the distribution of resources among the different programs, as well as the capacity and policy development for agricultural research in the four selected countries. Based on our findings, we present recommendations to help sustain and increase the efficiency of publicly- and privately-funded plant breeding programs, while maximizing the use of genetic resources and developing opportunities for GM crop production. Policy makers, private sector breeders, and other stakeholders can use this information to prioritize investments, consider product advancement, and assess the relative magnitude of the potential risks and benefits of their investments." from Author's Abstractplant breeding, biotechnology, public research, Funding, Innovation systems, Capacity building, Biosafety,