Browsing by Author "Martins, Bruno"
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- Can ZrAlN thin films be used as thermistor sensors for temperature assessment?Publication . Martins, Bruno; Patacas, Carlos; Cavaleiro, Albano; Faia, Pedro; Bondarchuk, Oleksandr; Fernandes, FilipeThe electrical characteristics and conduction mechanisms of ZrAlN thin films for their potential use as thermistor sensors were assessed. Various compositions of Zr1-xAlxN were synthesized by sputtering and studied up to 200 °C to understand their sensitivity and applicability. Among the compositions studied, the ones with x = 0.34 and x = 0.46 showed the highest sensitivities, reaching values close to 3000 K. However, the thermo-resistive properties exhibited by these compositions limited their utilization above 100 °C. Zr1-xAlxN film compositions with x higher than 0.46 showed amorphous structures and were found to be insulative. Composition with x = 0.26, within the cubic phase, showed the most promising electrical properties regarding temperature sensing in the studied range. XPS analysis of this composition confirmed the presence of Zr-N and Al-N bonds, with a Zr3+ oxidation state, which suggests the availability of a free electron contributing to the electrical conduction. Impedance measurements performed at different temperatures for this composition revealed the dominant role of the grain boundaries in the conduction mechanism, based upon electron hopping between grains, overcoming the energy barrier imposed by the grain boundaries. ZrAlN thin films demonstrate negative temperature coefficient (NTC) thermistor behavior, expanding their applications beyond protective coatings to temperature monitoring.
- Electrical properties and thermistor behavior of TiAlN thin films deposited by combinatorial sputteringPublication . Martins, Bruno; Patacas, Carlos; Cavaleiro, Albano; Faia, Pedro; Bondarchuk, Oleksandr; Fernandes, FilipeA combinatorial deposition was performed by direct current magnetron sputtering (DCMS) to develop Ti1-xAlxN thin films with different Ti/Al ratios and investigate the electrical response to temperature. The crystal structure as a function of the x was studied by X-ray diffraction, and sheet resistance response was measured up to 200 ◦C. From x = 0.16 to x = 0.56, the film shows an fcc phase with Al in solid solution in the TiN matrix, whilst, from x ≥ 0.69, a mixture of hcp (AlN) and fcc phases is observed. A negative temperature coefficient (NTC) thermistor behavior was found from x = 0.21 onwards, and a maximum sensitivity β of 1600 K was observed for x = 0.56 and 0.69. One fcc sample (x = 0.46) was selected to analyze the chemical states by X-ray photoelectron spectroscopy and the impedance behavior with the temperature by electrical impedance spectroscopy. The crystal structure, bond states and impedance analysis were compared with an AlN thin film. It is concluded that the conduction mechanism for x = 0.46 is based upon electron hopping, and the effect of the grain boundary is more relevant than the grain at low temperatures. We demonstrate that it is possible to use TiAlN as an NTC-thermistor with different crystal structures and chemical compositions.
- Expanding the applications of the wear-resistant titanium aluminum nitride thin-film to include temperature sensingPublication . Martins, Bruno; Patacas, Carlos; Cavaleiro, Albano; Faia, Pedro; Zorro, Fátima; Carbo-Argibay, Enrique; FGerreira, Paulo J.; Fernandes, Filipe; Fernandes, FilipeThis study investigates an approach to temperature sensing by integrating Titanium Aluminum Nitride (TiAlN), originally engineered for wear and corrosion applications, as a temperature sensor within a multilayered thin film system. A nitride multilayer system was developed by physical vapor deposition (PVD) using a single four-target magnetron sputtering chamber; intermediate vacuum interruption steps were employed for masking procedures. The multilayer architecture design aimed to provide the sensor layer with mechanical protection and electrical shielding. Structural and electrical characterization of the TiAlN single layer revealed semiconductor behavior and stable electrical resistance up to 750 °C, with minimal signal stabilization requirements. Despite the higher Al content, the TiAlN temperature sensor exhibited a cubic crystal structure characterized by diffuse nanolayers, resulting from a two-fold rotational deposition and target configuration. A detailed examination of the multilayer system cross-section containing the TiAlN sensor was conducted using scanning transmission electron microscopy (STEM). The analysis revealed its columnar morphology with the presence of typical PVD growth defects, including voids and droplets. While the presence of these defects may impact the electrical characteristics of the sensor, the selected experimental conditions effectively maintained the structural integrity of the multilayer system despite the vacuum interruptions caused by masking procedures. Validation experiments confirmed the functionality of the multilayer system for temperature measurements up to 400 °C. The signal acquisition system addressed room temperature resistance variations and low sensitivity (thermistor coefficient ∼100 K), resulting in a measured error of approximately 6%. This study demonstrates promising results of TiAlN as a temperature sensor within a multilayered system, expanding its range of potential applications.
- Fatores e processos em ravinas permanentes em ambiente mediterrâneo (Centro de Portugal)Publication . Martins, Bruno; Nunes, Adélia; Meira Castro, Ana C.; Lourenço, LucianoNa bacia do rio Alva, à semelhança de outras áreas serranas do nosso território, algumas ravinas atingem uma dimensão espetacular. Neste trabalho procuramos analisar alguns fatores responsáveis pela evolução da ravina do Corgo, localizada no vale do rio Alva, no Centro de Portugal, nos últimos 4 anos (2015-2019), considerando o declive, a percentagem de coberto vegetal, a resistência do solo à penetração e torção, e a forma da vertente. Para o efeito, aplicou-se modelo de regressão múltipla (stepwise), ferramenta usada na construção de modelos para identificar um subconjunto útil de preditores. No período em análise, a ravina, com um comprimento de 130 metros, localizada sobre um manto de alteração granítico, teve um alargamento médio de 27.8 cm (DP: 72.0 cm) e um aprofundamento médio de 66 cm (DP: 85.5cm). Na evolução da ravina, o modelo de regressão explica entre 26% e 45 % do seu alargamento. Os resultados indicam 26% da variabilidade pela resistência do solo à penetração; 35,4% quando à variável anterior se associa o declive; e 44,5% quando se considera também a forma da vertente. Por sua vez, o aprofundamento assinalado pela ravina é explicado, entre 26% e 44,5%, a partir do mesmo modelo de regressão. A forma da vertente explica 32% da variância observada. Quando, além desta variável, se considera a percentagem de coberto vegetal, o resultado aumenta cerca de 10%. O modelo com o melhor resultado, 44,5%, considera as variáveis: forma da vertente, percentagem do coberto vegetal e resistência do solo à penetração. Confirmando os fatores envolvidos na evolução da ravina e optimizando a ligação estatística entre os fatores e a evolução, os resultados podem fornecer informações importantes para prever taxas de erosão em ambientes semelhantes.
- Gullies mitigation and control measures: A case study of the Seirós gullies (North of Portugal)Publication . Martins, Bruno; Meira Castro, Ana C.; Ferreira, Carmen; Lourenço, Luciano; Nunes, AdéliaIt is known that the erosion process triggered by gullies contributes to significant soil loss and land degradation, and this can limit the options for the occupation and development of a territory in terms of the suitability and quality of the farmland area. The variety of physical factors associated with gully formation hinders straightforward interpretations and requires well-grounded analysis based on local observation. This work presents an example of gullies formed in a colluvial hill-slope agricultural area in Seirós, North of Portugal. The gullies were formed by intense rainfall events in 2015 that led to a channel overflowing. The channel in question was 49 m long, 0.50 m wide and 0.50 m deep and had been built by the landowner to protect his farmland from hillslope drainage. The adequacy of the strategy implemented to prevent gully formation with a view to the rehabilitation of the area is validated.
- Local Factors Controlling Gully Development in a Mediterranean EnvironmentPublication . Martins, Bruno; Nunes, Adélia; Meira-Castro, Ana C.; Lourenço, Luciano; Hermenegildo, CarlosGullies contribute very efficiently to soil loss and degradation, particularly in Mediterranean environments. While natural factors are involved in gully formation and further development, anthropic action is almost always an element. Knowledge of formation and development factors are important if soil protection strategies and measures are to be effective. In this paper, we identify the most important factors in the development of gullies in a Mediterranean setting based on a study of the Alva gully (central Portugal). Its development in the last four years is examined, based on a study of the modification of its morphological characteristics. The analysis was based on principal component analysis (PCA) to estimate the correlation between the quantitative characteristics, geomorphological processes, and biophysical variables. The results show that the main factors that seem to control the spatial variation of soil erosion are the soil penetration resistance, slope, slope shape, and vegetation cover.
- Ravinas de Seirós (Norte de portugal). Simulação com vista a prevenir o seu reaparecimentoPublication . Martins, Bruno; Meira Castro, Ana C.; Ferreira, Carmen; Lourenço, Luciano; Nunes, AdéliaNeste trabalho são analisadas as ravinas de Seirós, localizadas próximo de Ribeira de Pena, no Norte de Portugal, e que, numa área agrícola, se instalaram sobre um coluvião. As ravinas formaram-se após um episódio de chuva intensa e concentrada, entre os dias 14 e 15 de dezembro de 2015. Este episódio chuvoso permitiu o galgamento de um canal, de geometria retangular, com cerca de 49 metros de comprimento, 0,70 metros de largura e 0,75 metros de profundidade, construído pelo proprietário do terreno agrícola como forma de proteção da escorrência proveniente de montante. Para além da caracterização e a análise dos factores que estiveram na génese das ravinas, este estudo também pretende discutir a adequação desta estratégia como forma de prevenção e mitigação do risco de ravinamento. Com base nos resultados obtidos pela simulação apresentada, torna-se claro que, para episódios de precipitação semelhantes o canal não é eficaz. Como medida mitigadora, sugere-se o aumento da profundidade da secção transversal do canal, cuja altura mínima recomendada deverá ser de 120 cm.
- Ravinas de Seirós (norte de Portugal). Simulação com vista a prevenir o seu reaparecimentoPublication . Martins, Bruno; Meira Castro, Ana C.; Ferreira, Carmen; Lourenço, Luciano; Nunes, AdéliaNeste trabalho são analisadas as ravinas de Seirós, localizadas próximo de Ribeira de Pena, no Norte de Portugal, e que, numa área agrícola, se instalaram sobre um coluvião. As ravinas formaram-se após um episódio de chuva intensa e concentrada, entre os dias 14 e 15 de dezembro de 2015. Este episódio chuvoso permitiu o galgamento de um canal, de geometria retangular, com cerca de 49 metros de comprimento, 0,70 metros de largura e 0,75 metros de profundidade, construído pelo proprietário do terreno agrícola como forma de proteção da escorrência proveniente de montante. Para além da caracterização e a análise dos factores que estiveram na génese das ravinas, este estudo também pretende discutir a adequação desta estratégia como forma de prevenção e mitigação do risco de ravinamento. Com base nos resultados obtidos pela simulação apresentada, torna-se claro que, para episódios de precipitação semelhantes o canal não é eficaz. Como medida mitigadora, sugere-se o aumento da profundidade da secção transversal do canal, cuja altura mínima recomendada deverá ser de 120 cm.
- O risco de ravinamento: o exemplo das ravinas de Seirós (norte de Portugal)Publication . Martins, Bruno; Meira Castro, Ana C.; Nunes, AdéliaNeste trabalho, é apresentado o exemplo de um conjunto de ravinas formadas numa área agrícola, sobre um coluvião, em Seirós, próximo de Ribeira de Pena, no Norte de Portugal. As ravinas formaram-se durante um episódio de chuva intensa e concentrada, em dezembro de 2015. A existência de um canal retangular de 49 metros de comprimento, 0,70 metros de largura e 0,75 metros de altura, construído pelo proprietário do terreno, como forma de proteção da escorrência a montante do terreno de cultivo, contribuiu para uma concentração excecional da escorrência que, sendo insuficiente para a conter, permitiu o transbordo e a consequente formação de 8 ravinas. A presença dessas ravinas impossibilitou a prática agrícola durante cerca de um ano, após o qual o proprietário, com recurso a maquinaria, não só neutralizou as ravinas, mas também procedeu à reconstrução do canal de proteção, parcialmente destruído durante o episódio chuvoso, tendo voltado a funcionar novamente como único meio de controlo de erosão. O estudo apresentado tem como objetivo a caracterização das ravinas, bem como, analisar os fatores determinantes na sua formação. Além disso, pretende-se ainda discutir a adequação da estratégia existente como forma de prevenção e mitigação do risco de ravinamento
- Wildfires in Portugal: where and why?Publication . Nunes, Adélia; Meira Castro, Ana C.; Lourenço, Luciano; Martins, BrunoFire has been a key tool used by humans for several thousands of years and a vital component in ecosystem dynamics. Uncontrolled fires cause, however, large environmental and economic damages, especially in the Mediterranean region. Nowadays, wildfires rank top of all European forest problems, affecting landscape, wildlife, vegetation, soils, water and air quality, as well as the human wellbeing Portugal has the highest relative burnt area of all southern European countries, between 1980 and 2017. Therefore, several studies have been addressed to the drivers behind wildfires in Portuguese territory, linking them mainly with climate/weather conditions and changes in the landscape mosaic, as a consequence of agricultural abandonment and a marked increase in land covered by shrubs, grass and other light vegetation that is very prone to fire. The association between social and economic vulnerability and wildfire incidence, particularly in terms of burnt area, has received less attention. Based on the assumption that the association between burnt area incidence and socio-economic vulnerability varied geographically, the main goals of this study are: to analyse the spatial patterns of burnt area on a municipal level; to identify the most critical social and economic variables associated with spatial incidence and recurrence of wildfires, by comparing the performance of classical linear regression and geographically weighted regression (GWR) modelling; to map spatial variation in the relationships between social and economic vulnerability and wildfire incidence in order to identify spatial clusters. The results obtained clearly show a strong spatial association between the incidence of burnt areas and some socio-economic variables that contribute to wildfire vulnerability in mainland Portugal. In general, the results demonstrated that the municipalities with high burnt areas displayed high social and economic vulnerability as a result of the higher ageing index and unemployment rates. Conversely, higher income populations and the prevalence of higher livestock densities, namely sheep and goats, influence negatively on the burnt extension. The overlap between socio-economic vulnerability, in terms of low socio-economic status of residents, and wildfire incidence in Portuguese territory suggests a need to evaluate wildfire management policies with regard to social and economic conditions.