This paper reports the fabrication of nanocrystalline Strontium Barium Bismuth Titanate Sr1-xBaxBi4Ti4O15 (SBBT) thin films for piezoelectric pressure sensors. The SBBT films and capacitance devices with structure of Al/TiO2/SBBT/TiO2/RuO2/SiO2/Si were fabricated using sol-gel technique. Different nanostructures of the films were prepared with un-annealed condition as well as after annealing at three temperatures; 400, 500 and 600oC, in air for 2 minutes. The nanostructure of SBBT thin films have been systematically studied by XRD, AFM, SEM and dielectric constant. For the sensor device measurement, the SBBT thin film pressure sensors were tested by pneumatic loading method at pressure range between 0 to 450 kPa. It was found that the sensing properties of the films were affected by the nanostructure of the films. It was shown that there was a linear relationship between the crystallization, grains size and dielectric properties with the sensing response of the film towards pressure. The film with higher crystallization, grains size and dielectric properties demonstrates better sensitivity and repeatability compared to others. The correlation between nanostructure of the SBBT films and the piezoelectric pressure sensing properties will be discussed.
BaTiO3 thin films are commonly used as a pyroelecrtic sensor because this material has a good dielectric, ferroelectric and piezoelectric properties. This paper reports the pyroelectric sensor performance of BaTiO3/SiO2 nanocomposite thin films. The BaTiO3 nanoparticles were synthesized and deposited as nanocomposite thin films on Si/SiO2 substrates using spin coating technique. The deposited films were dried at 200 °C for 2 hours and annealed at 700 °C for 1 hour in air. Pyroelectric performance of the fabricated sensors was carried out at temperature in the range of 30 to 58 °C using short-circuit current method. The heating rate was set up to 0.4 °C/s. It was found the devices showed the pyroelectric response when heated and the pyroelectric coefficients of the devices are in the range of 43-1300 μC cm-2 K-1.
Nanocrystalline Bi4Ti3O12 (BTO) thin film pressure sensor was fabricated by sol gel method. The multiple Bi-Ti-O layers were spin coated over the TiO2 buffered Si/SiO2/RuO2 substrate, followed by heating of each layer at 300 °C for 15 mins. The nanocrystalline Bi4Ti3O12 film was formed after the sample was rapid thermal annealed at 450 °C in air for 60 s. The scanning electron microscope result showed that the film exhibited crack free, fine and uniform grain structure, where the grain size obtained was around 10 to 15 nm. For the sensor response measurement, Al film was deposited as top electrode and the sensor tested by pneumatic loading method. The nanocrystalline Bi4Ti3O12 (BTO) thin film demonstrated good repeatability for the pressure sensing. The sensor achieved a linear characteristic response between 17.5 psi and 65 psi with sensitivity of 0.3 mV / psi.
This paper reports the fabrication of an optical receptor for cyclohexane vapour using self-assembly monolayer (SAM) of 1-amino, 9-fluorenone compound. The SAM was built up on quartz substrate and quartz substrate-coated monolayer Langmuir-Blodgett (LB) film of arachidic acid. The UV-VIS spectroscopy technique was used to characterize the self-assembled film. It was found that the SAM on the quartz-coated LB film indicated a clearer optical absorption profile than the SAM on the quartz surface. The optical sensing characteristic of the SAM to the presence of the saturated vapour of cyclohexane indicated that the thin film features a good sensing sensitivity.
Using the solid-liquid-solid method, silicon nanowires were grown by annealing the gold-coated silicon substrates under the nitrogen flow. In this method, gold diffused into the silicon substrate upon heating and AuSi alloy formed at their interface. This alloy was melted when temperature increases above their eutectic point and percentage of Si presence in the mixture increased as heating continues. Rapid cooling occurred at the surface of these alloy melted when nitrogen gas was flowed into the chamber. This had caused the phase separation of the silicon from the surface of the alloy droplets and eventually self-arranged to form nanowires. Controlled growth of the nanowires was achieved by manipulating the annealing parameters. Relatively straight nanowires were produced by annealed the sample at 1000°C with nitrogen flow set to 1.5 liters per minute. The as-growth nanowires had diameters varied between 30 and 70nm. Heating duration was used to control the amount and lengths of the nanowires. Heating for 15 minutes produced less amount and shorter nanowires, while a 4-hour heating produced nanowires more than hundreds of microns long and with much larger amount.
Polycrystalline Bi-Ti-O thin films were prepared by multilayer deposition method using electron beam evaporation. The thin films were obtained by sequentially evaporating Bi2O3 / TiO2 layers on Si / SiO2 substrate followed by a heat treatment for 2 hours in air at 900 °C. The piezoelectric response of the sample was measured by pneumatic loading method. A pressure sensor was fabricated by annealed the deposited multilayer thin films on Si / SiO2 /Au substrate and Al was then deposited as top electrode. When an air pressure was applied and imparted on the sensor, electrical voltage was generated and measured using an electrometer. The sensor’s response was measured at three response cycles. It was found that the sensor has good voltage sensitivity and repeatability. The study shows the possibility to obtain Bi-Ti-O
thin film pressure sensor by electron beam multilayer deposition.
A gas sensor system using the assembled molecular layer of poly amino acid derivative, poly-L-proline has been developed. The thin layer was prepared using self assembly technique which was deposited onto a quartz crystal microbalance (QCM) substrate. The QCM coated self-assembly monolayer (SAM) was used to detect the presence of two vapor samples; saturated vapor of acetone and 2-propanol. The sensing sensitivity was based on the change in the fundamental frequency of the QCM upon exposure towards gas sample. It was found that the SAM-coated QCM sensor system was sensitive towards the vapor samples by reducing its fundamental frequency. It was also found that the SAM exhibited a good stability and reproducibility behaviors.
The electrochromic materials change their optical properties under the action of an electric field and can be change back to the initial state by a field reversal. This paper reports the use of two metalloporphyrins derivatives of; 5, 10, 15, 20-tetraphenyl 21H, 23H-porphine cobalt (II)(CoTPP) and 5, 10, 15, 20-tetraphenyl 21H, 23H-porphine manganese (III) chloride (MnTPPCl), Langmuir-Blodgett thin films as an electrochromic materials to detect the presence of chloride in water. It was found that the both thin films were sensitive towards the presence of chloride by presenting the change in their optical absorption spectrum under a bias potential of 3.0 V. However, the CoTPP thin film was not fully reproducibility under the electrochromic process. Meanwhile, the electrochromic property of the MnTPPCl thin film was stable and reproducible. This thin film is potentially be used as an electrochromic material to detect the presence of chloride ion in water.
Thin films of MoO3 were prepared by electron beam evaporation technique. The films were deposited onto glass substrates maintained at temperatures in the range 100 - 250 degrees Celsius. The films were characterized by studying their structure, electrical and optical properties. The films formed at 100 degrees Celsius are amorphous with conductivity of about 2.5 X 10-5 (Omega) -1 cm-1. The effect of deposition temperature on the properties of the films were studied and discussed.
This paper reports the use of hematin Langmuir-Blodgett (LB) films to detect carbon monoxide gas at the room temperature, based on changes in the optical absorption of the films. Hematin LB films were deposited on quartz and glass substrates. For the film deposited on quartz substrate, an increase in the absorption spectra of the film was achieved by exposing the film to carbon monoxide gas. The absorption spectra of the film recover back when the exposing gas was cut off. While for the film deposited on glass substrate, there is no significant change in the spectra due to this gas. Atomic force microscope images were taken for the hematin LB films both on glass and quartz substrates. Both images show different features indicating that the optical respond of the films to the gas depends on the arrangement of molecules on the substrate.
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