Browsing by Author "Chiu, Yu-Kai"

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Electrochemical Capacitors of Horizontally Aligned Carbon Nanotube Electrodes with Oxygen Plasma Treatment
(2017-01-01)
Wang, Kuang-Yu
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Chiu, Yu-Kai
;
Cheng, Huang-Chung
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A electrochemical capacitor (EC) composed of horizontally aligned carbon nanotube (HACNT) electrodes treated with oxygen plasma has been successfully shown to achieve superior specific capacitance. Cyclic voltammetry (CV) measurement reveals that the HACNT thin films on the Si substrate modified by the oxygen plasma with a bias power of 60 W obtain the highest specific capacitance of 6.81 mF/cm(2), which is 5.6 times that of non-plasma-treated ones. Such improvement can be attributed to the increase of oxygen-containing functional groups, such as C-OH, C=O, and COOH as well as to structural defects which remarkably increase the extra redox reactions to enhance the specific capacitance. The electrochemical stabilities of the oxygen-plasma-treated (OPT) HACNT thin films were also verified. Finally, the OPT HACNT thin films were transferred to the flexible PET thin foil and still achieved characteristics similar to those on the hard Si substrate. Even after a bending test of 200 bends with a bending radius of 1 cm and bending angle of 90 degrees, the variation of specific capacitance is less than 3% for such flexible ECs. The electrochemical stability of the OPT HACNT thin films after mechanical bending is equal to that of the Si substrate. This shows that such OPT HACNT ECs have promise for the future flexible applications in the energy storage field. (C) The Author(s) 2017. Published by ECS. All rights reserved.
High-sensitivity extended-gate field-effect transistors as pH sensors with oxygen-modified reduced graphene oxide films coated on different reverse-pyramid silicon structures as sensing heads
(2016-04)
Li, Yu-Ren
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Chang, Shih-hsueh
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Chang, Chia-Tsung
;
Tsai, Wan-Lin
;
Chiu, Yu-Kai
A high-performance extended-gate field-effect transistor (EGFET) as pH sensor with its microstructured sensing head composed of an oxygen-modified reduced graphene oxide film (RGOF) on a reverse-pyramid (RP) Si structure was developed to achieve a high sensitivity of 57.5mV/pH with an excellent linearity of 0.9929 in a wide pH sensing range of 1-13. These features were ascribed to the large amount of sensing sites and large sensing area. In contrast, the planar Si substrate with the oxygen-plasma-treated RGOF (OPT-RGOF) at the optimal bias power showed a sensitivity of 52.9mV/pH compared with 45.0mV/pH for that without plasma treatment. It reveals that oxygen plasma can produce oxygen-containing groups as sensing sites, enhancing proton sensing characteristics. However, oxygen plasma treatment at high bias powers would cause damage to the RGOFs, resulting in poor conducting and sensing properties. On the other hand, the use of the RP structures could increase the effective sensing area and further promote the sensing performance. (C) 2016 The Japan Society of Applied Physics
High-sensitivity extended-gate field-effect transistors as pH sensors with oxygen-modified reduced graphene oxide films coated on different reverse-pyramid silicon structures as sensing heads
(2016-04-01)
Li, Yu-Ren
;
Chang, Shih-hsueh
;
Chang, Chia-Tsung
;
Tsai, Wan-Lin
;
Chiu, Yu-Kai
A high-performance extended-gate field-effect transistor (EGFET) as pH sensor with its microstructured sensing head composed of an oxygen-modified reduced graphene oxide film (RGOF) on a reverse-pyramid (RP) Si structure was developed to achieve a high sensitivity of 57.5mV/pH with an excellent linearity of 0.9929 in a wide pH sensing range of 1-13. These features were ascribed to the large amount of sensing sites and large sensing area. In contrast, the planar Si substrate with the oxygen-plasma-treated RGOF (OPT-RGOF) at the optimal bias power showed a sensitivity of 52.9mV/pH compared with 45.0mV/pH for that without plasma treatment. It reveals that oxygen plasma can produce oxygen-containing groups as sensing sites, enhancing proton sensing characteristics. However, oxygen plasma treatment at high bias powers would cause damage to the RGOFs, resulting in poor conducting and sensing properties. On the other hand, the use of the RP structures could increase the effective sensing area and further promote the sensing performance. (C) 2016 The Japan Society of Applied Physics