Nanoelectronics and MEMS Laboratory

Pathum Thani, Thailand

Nanoelectronics and MEMS Laboratory

Pathum Thani, Thailand
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Pongpaiboonkul S.,Chulalongkorn University | Kasa Y.,Chulalongkorn University | Phokharatkul D.,Nanoelectronics and MEMS Laboratory | Putasaeng B.,National Metal and Materials Technology Center | And 4 more authors.
Applied Surface Science | Year: 2016

Researchers have paid considerable attention to CaCu3Ti4O12 (CCTO) due to the colossal dielectric constant over a wide range of frequency and temperature. Despite of the growing number of works dealing with CCTO, there have been few studies of the role played by the substrate in inducing structural and dielectric effects of this material. In this work, highly-oriented CCTO thin films have been deposited on LaAlO3(100), NdGaO3(100) and NdGaO3(110) substrates using a sol-gel method. These single crystal substrates were chosen in terms of small lattice mismatch between CCTO and the substrate. The X-ray diffraction patterns showed that the CCTO film layers grow with different orientations depending upon the substrate used. We show that the preferred orientation of CCTO thin films can be manipulated to a high degree by growing it on specific crystal planes of the substrates without the use of buffer layers. Colossal dielectric constants are observed in our films which appear to correlate with the film crystallinity and preferred orientation. © 2016 Elsevier B.V.

Pongpaiboonkul S.,Chulalongkorn University | Phokharatkul D.,Nanoelectronics and MEMS Laboratory | Hodak J.H.,University of Buenos Aires | Hodak J.H.,Chulalongkorn University | And 2 more authors.
Sensors and Actuators, B: Chemical | Year: 2016

In this work, the effects of Fe-doping on structural and gas-sensing properties of CaCu3Ti4O12 (CCTO) thin film prepared by a sol-gel method were systematically studied. Sol-gel-derived CCTO thin films with different Fe-doping concentrations were deposited on alumina substrates by spin-coating and Au/Cr interdigitated electrodes were patterned onto the films by photolithography, sputtering and lift-off processes. Characterizations by X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy, X-ray photoemission spectroscopy and X-ray absorption near edge structure confirmed the perovskite CCTO phase with TiO2 and CuO secondary phases and suggested the substitution of Fe3+ ions at Ti4+ sites of CCTO structure. From gas-sensing measurements, Fe dopants greatly enhance H2S response, response time and H2S selectivity against NH3, CO, C2H2, CH4, ethanol and NO2. In particular, 9 wt% (∼3 at%) Fe-doped CCTO sensor exhibited the highest response of ∼126 to 10 ppm H2S, which was more than one order of magnitude higher than that of the undoped CCTO sensor at a low optimum operating temperature of 250 °C. The roles of Fe-dopant on gas-sensing mechanisms of CCTO sensor were proposed. © 2015 Elsevier B.V. All rights reserved.

Kit-Anan W.,Chulalongkorn University | Olarnwanich A.,Chulalongkorn University | Sriprachuabwong C.,Nanoelectronics and MEMS Laboratory | Karuwan C.,Nanoelectronics and MEMS Laboratory | And 4 more authors.
Journal of Electroanalytical Chemistry | Year: 2012

In this work, a new paper-based electrochemical sensor is developed as a low-cost and disposable point-of-care device for pre-screening purpose. Electrodes of this new sensor are fabricated using two printing techniques, i.e. screen-printing for base material and inkjet-printing for modifying functional material, and the performance of fabricated sensors for Ascorbic acid detection is demonstrated. The paper-based device consists of three electrodes including Polyaniline (PANI) modified Screen-Printed Carbon Electrode (SPCE) as working electrode and two bare SPCEs as reference and counter electrodes. Three SPCEs are initially screen-printed on a filter paper, and PANI is consecutively inkjet-printed on the designated working SPCE. Its electrochemical performances are systematically investigated towards Ascorbic acid using Cyclic Voltammetry (CV) with different Acetate buffer pHs and numbers of printed-PANI layers. The CV results show that the optimal buffer pH and number of PANI layers are 4.0-5.0 and 5, respectively. Consequently, real-time detection of Ascorbic acid concentration is performed using Chronoamperometry technique under the optimal conditions from previous CV studies. From the results, the sensor exhibits a good sensitivity of 17.7 μA/mM and a moderately low limit-of-detection of 30 ± 3 μM in a concentration range of 30-270 μM. According to cost versus performance, the utilization of paper-based sensor with inkjet-printed PANI modified SCPE is an alternative choice for low-cost and disposable point-of-care applications. © 2012 Elsevier B.V. All rights reserved.

Yaacob M.H.,RMIT University | Yaacob M.H.,University Putra Malaysia | Campbell J.L.,RMIT University | Wisitsoraat A.,Nanoelectronics and MEMS Laboratory | Wlodarski W.,RMIT University
Sensor Letters | Year: 2011

The gasochromic performance of nanostructured nickel oxide (NiO) films coated with 25 Å catalytic palladium (Pd) layer were investigated for low concentration hydrogen (H2) sensing. NiO nanostructures of 20-30 nm sizes were produced via RF sputtering deposition of NiOx on quartz substrates and subsequently annealed at 500 °C. It was found that the Pd/NiO films show significant gasochromic response when exposed to H2 at elevated temperatures. Integrating the absorbance change over a range of visible wavelengths (500-800 nm), has enabled very low concentrations of H2 (0.06%) to be sensed in real time. T90% response of 25 Å Pd/100 nm NiO film towards 0.06% H2 in a balance of synthetic air was approximately 120 s at 170 °C. Similar H2 concentration can be recovered in as little as 240 s at 170 °C. Copyright © 2011 American Scientific Publishers All rights reserved.

Kruefu V.,Maejo University | Wisitsoraat A.,Nanoelectronics and MEMS Laboratory | Phanichphant S.,Chiang Mai University
Journal of Nanoscience and Nanotechnology | Year: 2014

Sensing characteristics of the spin-coated Au/ZnO nanoparticles thick films with different Au concentrations have been studied for various gases, namely, CO, SO2, ethanol and acetone. The influence on a dynamic range of Au concentration on ethanol response (0.005-0.1 vol.%) of thick film sensor elements was studied at the operating temperatures ranging from 300 to 400 °C in the presence of dry air. The optimum Au concentration was found to be 0.5 mol%. 0.5 mol% Au exhibited an optimum ethanol response of 5.0 × 102and a short response time (10 s) for ethanol concentration of 0.1 vol.% at 400 °C. Plausible mechanisms explaining the enhanced ethanol selectivity by thick films of Au/ZnO are discussed. Copyright © 2014 American Scientific Publishers All rights reserved.

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