Publicação
Development of nanostructured thin films for humidity and temperature sensors
| Resumo: | This work aims to present the entire production and response process of a set of multifunctional films capable of sensing temperature or relative humidity produced using the Physical Vapor Deposition, (PVD) with the assistance of the Glancing Angle Deposition technique - GLAD. In this work, two sets of thin films were prepared (chromium nitride (CrN) and chromium oxinitride (CrNxOy) grown with a zigzag like nanostructure, varying the amount of nitrogen and oxygen in order to obtain a variation in the electrical response when subjected to a variation in temperature or relative humidity. The films produced were analyzed by different characterization techniques in order to evaluate their structural, morphological and electrical properties. In order to obtain thin films with the capability to sense variations in temperature, a systematic study of the thermo-resistive effect of chromium nitride (CrNx) thin films with negative temperature coefficient of resistance (TCR) has been carried out. A systematic study of the thermoresistive effect of chromium nitride (CrNx) thin films with negative temperature coefficient of resistance (TCR) has been carried out. CrNx nanostructures were grown by reactive magnetron sputtering, with oblique angle deposition, under distinct Ar+N2 conditions. This experimental setup enables to confer a zigzag columnar morphology to the CrNx thin films and thus modify the structural, morphological and physical properties of the samples. X-ray diffraction and Scanning Electron Microscopy allowed to evaluate the evolution of the structural and morphological properties of the samples as a function of the N2 flux during the deposition. The thermoresistive response was evaluated by measuring the electrical resistivity as a function of temperature by the two-point method. The thin films with N2 flux between 4 and 8 sccm presented a negative TCR with values ranging from 9.18×10-4 ± 2.47×10-6 ºC-1 to 1.48×10-2 ± 1.74×10-5 ºC-1, respectively, and a very stable time response at a given temperature. The grain-boundary model was used to describe the experimental results and, in particular, the negative TCR values of the samples. In order to obtain thin films with relative humidity sensing capability, thin films based on chromium oxynitride (CrNxOy) were prepared with zigzag nanostructures and varying the amount of nitrogen and oxygen in order to enhance the humidity response. The obtained CrNxOy thin films show an increasing amount of oxygen as the N2+O2 mixture flux increased, leading to a transition from chromium nitride to chromium oxide. Further, a change from a BCC-Cr to a pure FCC-CrN phase is obtained as the oxygen in the sample increases. The amount of oxygen present in the composition of the coating leads to high electrical resistivity, raging from 1.27×10-6 ± 5.02×10-8 Ω.m for the sample with 16 at.% of O2 to 4.50×109 ± 4.20×107 Ω.m for the sample with 60 at.% of O2. The highest sensibility to the relative humidity (RH) variation from 40 % to 80 % was 1.87×10-2 ± 7.00×10-5 (RH%)-1. The obtained results demonstrate the potential of CrNx and of CrNxOy for sensor applications. |
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| Autores principais: | Silva, João Paulo Carmo da |
| Assunto: | Multifunctional hard coatings DC sputtering Temperature coefficient of resistance Thermal properties Temperature sensing Chromium nitride Chromium oxynitride Relative humidity Humidity sensing Revestimentos duros multifuncionais Pulverização catódica em corrente continua Coeficiente de resistência de temperatura Propriedades térmicas Sensorização de temperatura Nitreto de crómio Oxinitreto de crómio Humidade relativa Sensorização de humidade |
| Ano: | 2021 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | This work aims to present the entire production and response process of a set of multifunctional films capable of sensing temperature or relative humidity produced using the Physical Vapor Deposition, (PVD) with the assistance of the Glancing Angle Deposition technique - GLAD. In this work, two sets of thin films were prepared (chromium nitride (CrN) and chromium oxinitride (CrNxOy) grown with a zigzag like nanostructure, varying the amount of nitrogen and oxygen in order to obtain a variation in the electrical response when subjected to a variation in temperature or relative humidity. The films produced were analyzed by different characterization techniques in order to evaluate their structural, morphological and electrical properties. In order to obtain thin films with the capability to sense variations in temperature, a systematic study of the thermo-resistive effect of chromium nitride (CrNx) thin films with negative temperature coefficient of resistance (TCR) has been carried out. A systematic study of the thermoresistive effect of chromium nitride (CrNx) thin films with negative temperature coefficient of resistance (TCR) has been carried out. CrNx nanostructures were grown by reactive magnetron sputtering, with oblique angle deposition, under distinct Ar+N2 conditions. This experimental setup enables to confer a zigzag columnar morphology to the CrNx thin films and thus modify the structural, morphological and physical properties of the samples. X-ray diffraction and Scanning Electron Microscopy allowed to evaluate the evolution of the structural and morphological properties of the samples as a function of the N2 flux during the deposition. The thermoresistive response was evaluated by measuring the electrical resistivity as a function of temperature by the two-point method. The thin films with N2 flux between 4 and 8 sccm presented a negative TCR with values ranging from 9.18×10-4 ± 2.47×10-6 ºC-1 to 1.48×10-2 ± 1.74×10-5 ºC-1, respectively, and a very stable time response at a given temperature. The grain-boundary model was used to describe the experimental results and, in particular, the negative TCR values of the samples. In order to obtain thin films with relative humidity sensing capability, thin films based on chromium oxynitride (CrNxOy) were prepared with zigzag nanostructures and varying the amount of nitrogen and oxygen in order to enhance the humidity response. The obtained CrNxOy thin films show an increasing amount of oxygen as the N2+O2 mixture flux increased, leading to a transition from chromium nitride to chromium oxide. Further, a change from a BCC-Cr to a pure FCC-CrN phase is obtained as the oxygen in the sample increases. The amount of oxygen present in the composition of the coating leads to high electrical resistivity, raging from 1.27×10-6 ± 5.02×10-8 Ω.m for the sample with 16 at.% of O2 to 4.50×109 ± 4.20×107 Ω.m for the sample with 60 at.% of O2. The highest sensibility to the relative humidity (RH) variation from 40 % to 80 % was 1.87×10-2 ± 7.00×10-5 (RH%)-1. The obtained results demonstrate the potential of CrNx and of CrNxOy for sensor applications. |
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