Investigation of nanostructured thin films on surface acoustic wave and conductometric transducers for gas sensing applications

In this thesis, the author proposed and developed nanostructured materials based Surface Acoustic Wave (SAW) and conductometric transducers for gas sensing applications. The device fabrication, nanostructured materials synthesis and characterization, as well as their gas sensing performance have been undertaken. The investigated structures are based on two structures: lithium niobate (LiNbO3) and lithium tantalate (LiTaO3). These two substrates were chosen for their high electromechanical coupling coefficient. The conductometric structure is based on langasite (LGS) substrate. LGS was selected because it does not exhibit any phase transition up to its melting point (1470°C). Four types of nanostructured materials were investigated as gas sensing layers, they are: polyaniline, polyvinylpyrrolidone (PVP), graphene and antimony oxide (Sb2O3). The developed nanostructured materials based sensors have high surface to volume ratio, resulting in high sensitivity towards di¤erent gas species. Several synthesis methods were conducted to deposit nanostructured materials on the whole area of SAW based and conductometric transducers. Electropolymerization method was used to synthesize and deposit polyaniline nanofibers on 36° YX LiTaO3 and 64° YX LiNbO3 SAW substrates. By varying several parameters during electropolymerization, the effect on gas sensing properties were investigated. The author also extended her research to successfully develop polyaniline/inorganic nanocomposites based SAW structures for room temperature gas sensing applications. Via electrospinning method, PVP fibres and its composites were successfully deposited on 36° YX LiTaO3 SAW transducers. Again in this method, the author varied several parameters of electrospinning such as distance and concentration, and investigated the effect on gas sensing performance. Graphene-like nano-sheets were synthesized on 36° YX LiTaO3 SAW devices. This material was synthesized by spin-coating graphite oxide (GO) on the substrate and then exposin g the GO to hydrazine to reduce it to graphene. X-ray photoelectron spectroscopy (XPS) and Raman characterizations showed that the reduced GO was not an ideal graphene. This information was required to understand the properties of the deposited graphene and link its properties to the gas sensing properties. Thermal evaporation method was used to grow Sb2O3 nanostructures on LGS conductometric transducers. Using this method, different nanoscale structures such as nanorods and lobe-like shapes were found on the gold interdigitated transducers (IDTs) and LGS substrate. The gas sensing performance of the deposited nanostructured Sb2O3 based LGS conductometric sensors was investigated at elevated temperatures. The gas sensing performance of the investigated nanostructured materials/SAW and conductometric structures provide a way for further investigation to future commerciallization of these types of sensors

Comparison of deposition methods of ZnO thin film on flexible substrate

This paper reports the effect of the different deposition methods towards the ZnO nanostructure crystal quality and film thickness on the polyimide substrate. The ZnO film has been deposited by using the spray pyrolysis technique, sol-gel and RF Sputtering. Different methods give a different nanostructure of the ZnO thin film. Sol gel methods, results of nanoflowers ZnO thin film with the thickness of thin film is 600nm. It also produces the best of the piezoelectric effect in term of electrical performance, which is 5.0 V and 12 MHz of frequency which is higher than other frequency obtained by spray pyrolysis and RF sputtering

Graphene-like nano-sheets/36° LiTaO3 surface acoustic wave hydrogen gas sensor

Presented is the material and gas sensing properties of graphene-like nano-sheets deposited on 36deg YX lithium tantalate (LiTaO3) surface acoustic wave (SAW) transducers. The graphene-like nano-sheets were characterized via scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The graphenelike nano-sheet/SAW sensors were exposed to different concentrations of hydrogen (H2) gas in a synthetic air at room temperature. The developed sensors exhibit good sensitivity towards low concentrations of H2 in ambient conditions, as well as excellent dynamic performance towards H2 at room temperature

Comparison of deposition methods of ZnO thin film on flexible substrate

This paper reports the effect of the different deposition methods towards the ZnO nanostructure crystal quality and film thickness on the polyimide substrate. The ZnO film has been deposited by using the spray pyrolysis technique, sol-gel and RF Sputtering. Different methods give a different nanostructure of the ZnO thin film. Sol gel methods, results of nanoflowers ZnO thin film with the thickness of thin film is 600nm. It also produces the best of the piezoelectric effect in term of electrical performance, which is 5.0 V and 12 MHz of frequency which is higher than other frequency obtained by spray pyrolysis and RF sputtering

Arthropods-mediated green synthesis of zinc oxide nanoparticles using cellar spider extract: a biocompatible remediation for environmental approach

This study presents an eco-friendly approach to synthesizing zinc oxide nanoparticles (ZnO NPs) using extracts from cellar spiders, addressing environmental and health concerns associated with conventional methods. The spider extract efficiently reduced zinc acetate dihydrate, and the synthesized ZnO NPs underwent comprehensive quantitative characterization, including size, shape, morphology, surface chemistry, thermal stability, and optical properties using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), zeta potential measurements, thermogravimetric analysis (TGA), and UV-vis spectroscopy. The nanoparticles exhibited intended characteristics, and their adsorption capability for methylene blue (MB) was quantitatively assessed using the Freundlich isotherm model and pseudo-second-order kinetic model, providing numerical insights into MB removal efficiency. The study demonstrates the potential of these green-synthesized ZnO NPs for applications in environmental remediation, wastewater treatment, and antibacterial therapies, contributing to both sustainable nanomaterial development and quantitative understanding of their functional properties

Polyaniline/palladium nanohybrids for moisture and hydrogen detection.

Palladium nanoparticles display fascinating electronic, optical and catalytic properties, thus they can be used for various applications such as sensor fabrication. Conducting polymers such as polyaniline have also been widely used in sensor technology due to its cost effectiveness, versatility, and ease of synthesis. In this research, attention was given to unify the exceptional properties of these two materials and construct palladium nanoparticle coated polyaniline films to detect hydrogen and moisture. Electrochemical polymerization of aniline was carried out on gold sputtered epoxy resin boards. Polyaniline film was generated across a gap of 0.2 mm created by a scratch made on the gold coating prior to electrochemical polymerization. A palladium nanoparticle dispersion was prepared using sonochemical reduction method and coated on to polyaniline film using drop-drying technique. Polyaniline only films were also fabricated for comparative analysis. Sensitivity of films towards humidity and hydrogen was evaluated using impedance spectroscopy in the presence of the respective species. According to the results, polyaniline films exhibited an impedance drop in the presence of humidity and the response was significantly improved once palladium nanoparticles were incorporated. Interestingly, polyaniline only films did not respond to hydrogen. Nevertheless, palladium nanoparticle coated polyaniline films exhibited remarkable response towards hydrogen

Hydrogen gas sensor based on highly ordered polyaniline/multiwall carbon nanotubes composite

In this work, the structural and gas sensing properties of an electropolymerized, polyaniline (PANI)/multiwall carbon nanotube (MWNT) composite based surface acoustic wave (SAW) sensor are reported. Thin films made of PANI nanofibers were deposited onto 36 lithium tantalate (LiTaO3) SAW transducers using electropolymerization and were subsequently dedoped. Scanning electron microscopy (SEM) revealed the compact growth of the composites which is much denser than that of PANI nanofibers. The PANI/MWNT composite based SAW sensor was then exposed to different concentrations of hydrogen (H2) gas at room temperature with a demonstrated electrical response

Integrating sustainability in a student-centered learning environment for engineering education

The integration of Sustainability in engineering education is increasingly implemented in engineering programs worldwide. Initially, the integration is implemented to meet the accreditation requirements for local and international accreditation bodies. In this study however, it was rather impractical to introduce a stand-alone Sustainability course considering the university-wide approach of traditional teaching and the complexity of the engineering program. This study therefore applies student-centered learning as a medium to integrate Sustainability in the engineering curriculum. Six engineering courses were examined and empirical evidence from faculty interviews and program documents were presented. The findings were analyzed in a systems approach and presented in three factors: input, throughput and output factors. The final part of the paper concludes by presenting the reflections of the study. There are three key findings of this study: (i) the integration of Sustainability is not fully implemented in all engineering courses, (ii) student-centered learning environment offers a learning medium to integrate Sustainability without compensating the technical and engineering contents, and (iii) when implemented, the integration of Sustainability is mainly focus on one pillar i.e., environment pillar (a singular approach)

Performance enhancement by implementation of nanostructure sensing element for bendable SAW gas sensor: Simulation

Flexible technology is current promising area in electronics devices and sensors. There are several advantages such as lightweight, low cost and mechanically flexible which attract the market growth. A rigid Surface Acoustic Wave (SAW) gas sensor that conventionally fabricated on crystals or thin film on substrates is less suitable for uneven surfaces. In addition the interest of applying nanostructure as sensing element has emerged to amplify the performance of the sensors. This study presents comparisons simulation on basic Surface Acoustic Wave (SAW) gas sensor and also the enhanced version by employing nanostructure as a sensitive layer on flexible substrate using COMSOL multiphysics. For the first part, simulation on the sensing element was in thin film form. Next, nanowires were designed and stacked on top of the Inter Digitated Transducer (IDTs), so that it will improve the sensitivity of the gas sensor. In both parts, simulation were done in three different model design condition namely flat, bend in and bend out. The main objective is to investigate the effect of implementing nanostructure as sensing element. The results show increase in sensitivity of the sensor up to 9179.8 kHz/kgm–3 and maximum frequency shift of 91.9 Hz after implementing nanostructured