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Temperature-dependent electrical transport, Hall effect, and Seebeck properties of bulk chemically reduced graphene oxide with bipolar charge carrier materials
(2023-03-01)
Maneesai, Keerati
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Silakaew, Kanyapak
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Khammahong, Sunisar
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Phrompet, Chaiwat
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Sriwong, Chaval
The temperature-dependent electrical transport, Hall effect, and Seebeck properties of bulk-reduced graphene oxide (rGO) prepared by a chemical reduction process were investigated in a temperature range of 310-475 K. The bulk rGO contained bipolar charge carriers with p-type to n-type switching at a temperature of 420 K. The materials illustrated a p-type characteristic in the temperature range of 310-420 K and n-type characteristic in the temperature range of 420-475 K. The charge transport mechanism was that of the graphene-derived 2D material in the p-type regime and governed by polaronic charge carriers.
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PMMA/High-k Self-assembled TiO2 /PMMA Multi-layer Gate Dielectric for P3HT Organic Field Effect Transistors
(2022-01-01)
Inpor, Kroekchai
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Houngkamhang, Nongluck
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Thanachayanont, Chanchana
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Prichanont, Seeroong
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Kayunkid, Navaphun
In this work, a multi-layer structure of poly (methyl methacrylate)/ titanium dioxide/poly (methyl methacrylate) (PMMA/TiO₂ /PMMA; PTP) was proposed as a top-gate insulator for P3HT-based organic field-effect transistors (OFETs). Adding a TiO₂ interlayer as a high dielectric constant (high-k) material into PMMA film enables the modification of the dielectric constant of the multi-layers PTP film. The content of TiO₂ in the PTP film, which can be varied by changing the number of soaking cycles in TiO₂ solution, plays a crucial rule in modifying the dielectric constant of the PTP film. The higher the TiO₂ content used in the PTP film, the higher the dielectric constant of PTP film can be obtained. However, using high TiO₂ content led to a reduction in the dielectric constant of the PTP film due to leakage current induced by the agglomeration of TiO₂. The utilization of the top-gate insulator containing TiO₂ significantly enhanced several P3HT-OFETs characteristics, e.g., an increase in the I<inf>on</inf>/I<inf>off</inf> ratio, and a decrease in the threshold voltage. However, the use of the PTP top-gate insulator with a high content of TiO₂ resulted in regressions in the OFETs characteristics, such as a decrease in carrier mobility and reduction in the I<inf>on</inf>/I<inf>off</inf> ratio. OFETs operating at the optimum conditions of the PTP gate-insulator, with PTP thickness of 225 nm and RMS roughness of 20.0 nm, provided a dielectric constant of 7.13, a threshold voltage of-8.49 V, a saturation mobility of 2.2× 10-4 cm²V-1s-1, I<inf>on</inf>/I<inf>off</inf> ratio of 37.9, and a subthreshold slope of 0.39 V/decade.
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Molecularly Imprinted Polymers Near Field Communication sensors for pesticide detection
(2022-01-01)
Leepheng, Piyawan
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Phromyothin, Darinee
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Thanachayanont, Chanchana
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Inpor, Kroekchai
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Olarnwanich, Aricha
For a healthy and convenient daily lifestyle, co-development of pesticide residue detectors to integrate molecularly imprinted polymers (MIPs) modified electrodes and industrial innovative Near Field Communication (NFC) sensor for smartphones interface devices has been established. It targets cypermethrin and carbaryl which are usually detected in fruits and vegetables. Pesticide-MIPs were fabricated on commercial screen-printed electrodes (SPEs) by bulk polymeri-zation of methyl methacrylate (MMA) monomer, ethylene glycol dimethacrylate (EGDMA) cross-linker, azobis(2-methyl-propionitrile (AIBN) initiator with cypermethrin and carbaryl templates in cypermethrin-MIPs/SPE and carbaryl-MIPs/SPE, respectively. The surface morphology of modified electrodes was characterized by field-emission scanning electron microscope (FE-SEM) and atomic force microscope (AFM), which present cavities of a template on the surface of MIPs/SPE. The experiments of NFC pesticide residue detectors were conducted in real vegetable samples, where a selectivity of 32.18 μA/ppb and a detection limit of 5.4 ppb for cypermethrin-MIPs/SPE and a selectivity of 22.15 μA/ppb and a limit of detection of 9.3 ppb for carbaryl-MIPs/SPE have been obtained. The electrodes can be used four times and have more than six months storage duration.
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Preface
(2021-09-20)
Thammavintorn, Preecha
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Limkaisang, Viroj
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Charoenprakdee, Anek
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Seetawan, Tosawat
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Kimura, Kaoru
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Effect of Ag mixing in thermoelectric Ge2Sb2Te5 thin films
(2019-01-01)
Vora-ud, Athorn
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Horprathum, Mati
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Kumar, Manish
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Muthitamongkol, Pennapa
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Chananonnawathorn, Chanunthorn
Ag-added Ge<inf>2</inf>Sb<inf>2</inf>Te<inf>5</inf> thin films were prepared by a pulsed-DC co-magnetron sputtering process using Ge<inf>2</inf>Sb<inf>2</inf>Te<inf>5</inf> and Ag targets. The effect of variation in Ag content through variable power on Ag target was studied on the microstructural and thermoelectric properties of as-deposited and fast annealed thin films at 400 °C in a vacuum. It is found that Ag addition induces enhancement in conductivity. When the power on Ag target is exceeded to a critical power, Ag<inf>8</inf>GeTe<inf>6</inf> phase formation occurs mixed with Ge<inf>2</inf>Sb<inf>2</inf>Te<inf>5</inf> cubic structure which limits the thermoelectric performance. Best conditions provide the films having a lowest electrical resistivity as 0.98 × 10−4 Ω cm and the maximum power factor as 5.83 × 10−3 W m−1 K−2.
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Radio-frequency characterization of multi-walled carbon nanotube/poly-lactic acid composites
(2017-01-01)
Sukgorn, Nuttaya
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Siraleartmukul, Krisana
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Yordsri, Visittapong
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Chudpooti, Nonchanutt
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Chaimool, Sarawuth
Nowadays radio and microwave frequencies are widely used in wireless broadcastings and communications. But these waves can cause electromagnetic interferences in some electronic devices, including the equipment used in hospitals. The problems of the electromagnetic interference can be solved by using the materials that can reflect and/or absorb radio-frequency (RF) and microwaves. The shielding effectiveness (SE) of a material depends on its conductivity and the electrical permittivity. Recently, carbon nanotubes (CNTs) have been proposed as promising materials for shielding applications owing to its flexibility, durability, lightweight and exceptional electrical conductivity compared to conventional metal. In this work, the RF properties of multi-walled carbon nanotube (MWCNT) composites were investigated. Poly-lactic acid (PLA), a natural bio-degradable material, is used as the polymer matrix. The composites with different MWCNT concentrations (0 to 0.4 wt%) were prepared and molded into thin rectangular samples (5.6 cm x 6.3cm). The surfaces of the composites were morphologically characterized by a scanning electron microscope. The electrical permittivity of the samples was measured by using a vector network analyzer and a microstrip resonator within a range of 1-11 GHz. The effects of MWCNT concentration on electrical permittivity will be discussed.
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Extended-gate field effect transistor (EGFET) for carbaryl pesticide detection based on enzyme inhibition assay
(2017-01-01)
Sasipongpana, Supanat
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Rayanasukha, Yossawat
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Prichanont, Seeroong
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Thanachayanont, Chanchana
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Porntheeraphat, Supanit
An extended - gate filed effect transistor (EGFET) is a device which can be applied to chemical sensing devices. In this study, EGFET was constructed by using an indium tin oxide (ITO) glass substrate. The small piece ITO with sensing area around 3x3 mm2 was used as carbaryl pesticide sensor based on enzyme inhibition assay. The prepared ITO-EGFET sensors were test with pH solutions to obtain sensitivity compared with commercial ion sensitive field effect transistor (ISFET). Preparation of ITO substrate for enzyme inhibition assay by dropped acetylcolinesterase enzyme at 0.5 Unit which were trapped in an agarose gel matrix onto substrates. This prepared ITO acts as extended gate sensing membrane for EGFET. The amounts of drop volume of enzyme were varied to obtain the highest signal for reaction with acetylcholine substrate. Cabaryl can inhibit enzyme function resulting in the decreasing signal of interaction between enzyme and acetylcholine substrate. This ITO-EGFET can be used to detect carbaryl in concentration rage 0.001 - 1 mM by using the ITO-EGFET without enzyme as control condition. This work shows possibility of ITO-EGFET for application in pesticide detection with an easy substrate preparation, low cost and can be applied in field used with others pesticides.
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Effect of Strong Correlation of Mg2+-doped into Cr3+ Sites of CuCrO2 on Thermoelectric Properties
(2015-09-02)
Ruttanapun, Chesta
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Charoenphakdee, Anek
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Nisoa, Mudtorlep
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Muthitamongkol, Pennapa
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Thanachayanont, Chanchana
This study aims to investigate the strong correlation effect of spin and charge carriers for the Mg2+-substituted into Cr3+ sites of CuCrO2 delafossite on thermoelectric properties. The CuCr0.98Mg0.02O2 sample was synthesized by a solid state reaction. The starting powder CuO, Cr2O3 and MgO were ball milled with poly vinyl alcohol solution for 24 h. The ball milled powder was pressed and sintered in air atmosphere at temperature 1050 C for 6 h. The crystal structure was characterized by XRD, TGA, XPS and the thermoelectric properties were measured at high temperature. The XRD displayed peaks of the pure phase CuCrO2 structure as hexagonal delafossite-type structure space group: Rm. The Seebeck coefficient of the samples displayed positive sign as p-type (hole) conductor. The XPS results displayed Mg2+, Cu1+, Cr3+ and Cr4+ ion states. The Mg2+ induced mixed-valance Cr3+/Cr4+ states resulting in enhanced Seebeck coefficient due to a strong correlation of the spin-entropy. The experimental results of Seebeck value were close to calculated results by the extended Heikes formula confirming of the strong correlation effect. In addition, the Mg-doped CuCrO2 resulted in increased electrical conductivity and reduced thermal conductivity with increasing temperature. These indicate that the Mg2+-substituted for Cr3+ of CuCrO2 delafossite enhance the thermoelectric properties. © 2015
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Facile growth of carbon nanaotube electrode from electroplated Ni catalyst for supercapacitor
(2015-01-01)
Yordsri, Visittapong
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Wongwiriyapan, Winadda
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Thanachayanont, Chanchana
A facile growth of carbon nanotubes (CNTs) was facilitated by the use of direct-current plating technique for catalyst preparation. Ni nanoparticles (NPs) were deposited on Cu foil at different applied voltages of 1.0, 1.5 and 2.0 V. The Ni-deposited foil was subsequently used as catalyst for CNTs synthesis by chemical vapour deposition (CVD) method. CVD was carried out at 800 °C using ethanol as carbon source. A voltage of 1.5 V was the optimum condition to deposit uniform Ni NPs that had a narrow size distribution of 55±3 nm, which in turn, yielded synthesized CNTs with a uniform diameter of approximately 60±5 nm with graphitic layers parallel to the CNTs axis. On the other hand, electroplated Ni at 1.0 V produced CNTs with graphitic layers at an angle to the CNTs axis, while electroplated Ni at 2.0 V produced curly CNTs with a wide distribution of diameters. These results show that Ni NPs size distribution could be controlled by electroplated voltage. Our observation was that Ni NPs with a narrow distribution of sizes and a uniform diameter is a key to uniform CNT synthesis. Furthermore, the synthesized CNTs electrode shows a faradic pseudo capacitance property, which can be attributed to the existence of oxidized Ni NPs. These results propose that the synthesized CNTs are promising materials for future super capacitor application. The optimization of ratio of Ni NPs and CNTs may improve the supercapacitors performance.
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Preparation, characterization and finite element computation of Cu(Al 1/2Fe1/2)O2 Delafossite-oxide themoelectric generator module
(2014-09-02)
Ruttanapun, Chesta
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Jindajitawat, Phumin
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Buranasiri, Prathan
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Naenkieng, Daengdesh
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Boonyopakorn, Narongchai
The CuAl<inf>1/2</inf>Fe<inf>1/2</inf>O<inf>2</inf> delafossite oxide has been synthesized by solid state reaction method for studying thermoelectric properties and measuring thermoelectric generator output electric power. The Finite Element technique was used to compute the output voltage of thermoelectric generator in applying temperature difference on a single bar and a module model with compared to the measurement results. The measurement results of positive sign Seebeck coefficient confirm the p-type conductor of the sample. The properties of Seebeck coefficient, electrical conductivity, and thermal conductivity are range from 260 to 310V/K, from 7 to16 S/cm and from 2.5 to 3.5 W/cm-K,respectively, in the temperature range of 300 to 960 K. The output voltage of the single bar in dimension 4.2 × 2.5 × 20 mm 3 obtained 0.5 to 3 mV on applying temperature difference from 1 to 10 K closely to the Finite Element result. The computing results of the thermoelectric single bar and module in high temperature reveal the output electric voltage of CuAl<inf>1/2</inf>Fe<inf>1/2</inf>O<inf>2</inf> oxide raises with the temperature and the number of thermoelectric leg increase. In important results, the high value of electric voltage is obtained 0.2 and 0.4 V for the single bar and the module at 950 K. © 2014 Taylor & Francis Group, LLC.

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