Relative humidity and alcohol sensors based on mesoporous silica thin films synthesised from block copolymers (original) (raw)
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Humidity sensors based on mesoporous silica thin films synthesised by block copolymers
Journal of the European …, 2004
The application of mesostructured thin films to fabricate electrochemical sensors requires the control of dimension, shape and distribution of pores in the material. Silica mesoporous thin films were deposited via dip coating on silicon and alumina substrates with interdigitated electrodes. Mesostructured films were obtained by sol-gel self-assembled process using di-block, tri-block or starblock copolymers: 2-D hexagonal mesoporous phases in silica were formed. After deposition the films were calcined in air to remove the surfactant and were characterised by Fourier transform infrared spectroscopy and low angle X-ray diffraction. Current variations with relative humidity were measured using different applied d.c. voltage; I/V characteristics were performed at various relative humidity values. Moreover the dependence of response from temperature and behaviour during cyclic test in dry-wet conditions was studied. The electrical response was found to be dependent on dimension of pores and their surface. Electrical characterisation upon exposure to humidity shows that the mesoporous structure is easily accessible by external environment, and the films prepared by non-ionic surfactants exhibit good performances in comparison with commercial humidity sensors. #
Mesoporous silica thin films for alcohol sensors
Journal of the European …, 2001
Silica mesoporous films using cetyltrimethylammonium bromide surfactant as a template have been prepared. The films have been deposited on silicon and alumina substrates by dip-coating and calcined at 250 and 450 C. The films were characterized by Xray diffraction analysis, Fourier transform infrared spectroscopy and Rutherford backscattering spectrometry. The films have been shown to maintain the mesophase after calcination, at 250 C the presence of residual surfactant has been observed. A density of 1.46 and 1.65 g cm À3 has been measured by Rutherford backscattering spectrometry in the 250 and 450 C calcined samples, respectively. These densities are much lower than the value (2.07 g cm À3 ) measured in a reference silica film obtained via sol-gel and with the same thermal history. The electrical response of the silica mesoporous films has been investigated with different concentrations of alcohols. The sensitivity of the material to changes in the atmospheres of ethanol, methanol, 2-propanol, butanol-1 and exane has been tested. The results have shown a large sensitivity to the alcohols at room temperature and the possibility to discriminate between the different alcoholic species. #
Electrical and structural characterisation of mesoporous silica thin films as humidity sensors
Sensors and Actuators B …, 2001
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On the rational design of mesoporous silica humidity sensors
Mesoporous silica is commonly used as matrix for humidity sensors, which operate on the principle of relative humidity-dependent water uptake and read-out by resistive or capacitive means. Although numerous studies have been dedicated to improving the sensing performance, in particular with conductive additives, the effect of pore structure on sensing behaviour has not been systematically investigated so far. Herein, we showcase the effects of pore size and porosity on resistive sensing behaviour in the 0.5-85% relative humidity (RH) range. We employed evaporation-induced self-assembly (EISA) in combination with sol-gel chemistry to fabricate well-defined mesoporous silica thin films with high degree of structural control. Material architectures with pore sizes of 3 to 15 nm and porosities of 40 to 70% were rationally designed by using structure directing agents (SDAs) with increasing molecular weight and tuning the silica to SDA ratio. We found that a combination of pore size of 15...
Analytical Chemistry, 2012
Distributed sensing of gas-phase chemicals is a promising application for mesoporous materials when combined with highly sensitive miniaturized gas sensors. We present a direct application of a mesoporous silica thin film on a highly sensitive miniaturized resonant chemical sensor with a mass sensitivity at the zeptogram scale for relative humidity and CO 2 detection. Using mesoporous silica thin-film, we report one of the lowest volume resolutions and a sensitive detection of 5.1 × 10 −4 % RH/Hz to water vapor in N 2 , which is 70 times higher than a device with a nontemplated silica layer. In addition, a mesoporous thin-film that is functionalized with an amino-group is directly applied on the resonant sensor, which exhibits a volume sensitivity of 1.6 × 10 −4 %/Hz and a volume resolution of 1.82 × 10 −4 % to CO 2 in N 2 .
Ordered Mesostructured Silica Films: Effect of Pore Surface on its Sensing Properties
Journal of Sol-gel Science and Technology, 2004
An electrochemical resistive-type sensor device, with a mesoporous silica thin film as sensitive membrane, has been developed and characterised. The silica film has been obtained via evaporation-induced self-assembly (EISA) using a tri-block copolymer (Pluronic F-127) as templating agent. It has been deposited by dip-coating on a silicon substrate with metallic interdigitated electrodes. Fast, reversible and reproducible electrical responses to relative humidity changes have been observed for the sensor device. The conduction mechanism has been related to chemical properties, structural order and surface morphology of the porosity in the silica film, confirming the dependence on the film preparation method and overall the importance of calcination temperature.
2012
Humidity sensing elements were elaborated by deposition of Ce-doped SiO2 films on alumina ceramic substrates with silver-palladium electrodes, via sol-gel method. The obtained specimens were sintered either at 400°C, or at 800°C, in order to create durable and reliable sensors and to evaluate the impact of the thermal treatment on the features of the obtained sensing elements. The superficial morphology, and composition of the films, and the electrical characteristics of the respective sensors were investigated. The impedance spectra of the sensing elements were fitted to appropriate equivalent electric circuit. The results obtained show that both of the addition Се(NO3)3 and the sintering at 400°С lead to remarkable improvement of the sensitivity of the SiO2-based sensing elements.
Talanta, 2005
A composite material of dispersed organic silicon sol and poly(2-acrylamido-2-methylpropane sulfonate) (poly-AMPS) was used to make humidity sensor without protective film or complicated chemical procedures. The organic silicon sol was dispersed well in the poly-AMPS without using dispersion agent. Parameters that may affect the water-resistive but humidity-sensitive characteristic of composite material, the adding amount of organic silicon sol solution and the film of thermal treatment time, were investigated. The microstructure of the material was analyzed, and the humidity sensing and electrical properties of the sensor were measured. The sensor well responded to humidity with a relatively good linearity, though it depended on the applied frequency. The temperature influence between 15 and 35 • C was within −0.17 % relative humidity (RH)/ • C in the range of 30-90% RH. The activation energy was maximum around 40% RH. The sensor showed the hysteresis within 5.9%, fast response time, long-term stability (75 days at least) and satisfactory resistance to high humidity atmosphere (97% RH) and chemical environment (20% C 2 H 5 OH vapor). Analyzing the structure and complex impedance plots of organic silicon sol/poly-AMPS was used to explain improvement in humidity sensing properties in comparison with nano-sized SiO 2 powder/poly-AMPS films.