Browsing by Author "Wang, Zhong Lin"

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Electricity generation based on vertically aligned PbZr0.2Ti0.8O3 nanowire arrays
(2012-05-01)
Chen, Cheng-Ying
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Liu, Te-Hsiang
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Zhou, Yusheng
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Zhang, Yan
;
Chueh, Yu-Lun
We statistically demonstrated the electricity generation from individual vertically-aligned/epitaxial PbZr0.2Ti0.8O3 (PZT) nanowires (NWs) using a conductive atomic force microscope (AFM). The measured outputs were analyzed in reference to the theoretically calculated piezopotential distribution in a bent NW. Our results show that the performance of the PZT NWs for electricity generation is at the same level as that of ZnO NWs although the piezocoefficient of PZT is high, due to high relative dielectric constant of PZT. Systematic investigating piezoelectricity from single PZT NWs will be useful for optimizing the performance for PZT nanogenerator applications. (C) 2012 Elsevier Ltd. All rights reserved.
In Situ Observation of Dehydration-Induced Phase Transformation from Na2Nb2O6-H2O to NaNbO3
(2012-10-25)
Jung, Jong Hoon
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Chen, Chih-Yen
;
Wu, Wen-Wei
;
Hong, Jung-Il
;
Yun, Byung Kil
We have monitored the phase transformation from a Sandia octahedral molecular sieve Na2Nb2O6-H2O to a piezoelectric NaNbO3 nanowire through in situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) measurements at high temperatures. After dehydration at 288 degrees C, the Na2Nb2O6-H2O becomes significantly destabilized and transforms into NaNbO3 with the increase of time. The phase transformation time is exponentially proportional to the inverse of temperature, for example, similar to 10(5) is at 300 degrees C and similar to 10(1) at 500 degrees C, and follows an Arrhenius equation with the activation energy of 2.0 eV. Real time TEM investigation directly reveals that the phase transformation occurs through a thermally excited atomic rearrangement due to the small difference of Gibbs free energy between two phases. This work may provide a clue of kinetic control for the development of high piezoelectric lead-free alkaline niobates and a deep insight for the crystallization of oxide nanostructures during a hydrothermal process.
Intercrossed Sheet-Like Ga-Doped ZnS Nanostructures with Superb Photocatalytic Actvitiy and Photoresponse
(2009-07-23)
Lu, Ming-Yen
;
Lu, Ming-Pei
;
Chung, Yao-An
;
Chen, Ming-Jer
;
Wang, Zhong Lin
Intercrossed ZnS nanostructures doped with Ga (ZnS:Ga nanowalls) have been synthesized in high yield from mixed powders in a vacuum furnace. ZnS:Ga nanowalls were grown vertically on the substrate with the size in the range of several micrometers and the thickness down to similar to 15 nm and have very rough edges. Due to the high surface area and distinctive morphology of ZnS:Ga nanowalls, the photocatalytic activity and the photoresponse show superior properties compared to ZnS:Ga films. The increased conductivity of metal-semiconductor-metal (Ag-ZnS:Ga nanowalls-Ag) Schottky photodetectors under light illumination is attributed to the photogenerated electron-hole pairs, the desorption of oxygen molecules on the ZnS:Ga surface, and the lowering of the Schottky barrier height. The results indicate that ZnS:Ga nanowalls are promising candidate materials for photocatalysts and applicable as photodetectors, optical switches, and sensors in the visible light region.
Multidirection Piezoelectricity in Mono- and Multilayered Hexagonal alpha-In2Se3
(2018-05-01)
Xue, Fei
;
Zhang, Junwei
;
Hu, Weijin
;
Hsu, Wei-Ting
;
Han, Ali
Piezoelectric materials have been widely used for sensors, actuators, electronics, and energy conversion. Two-dimensional (2D) ultrathin semiconductors, such as monolayer h-BN and MoS2 with their atom-level geometry, are currently emerging as new and attractive members of the piezoelectric family. However, their piezoelectric polarization is commonly limited to the in-plane direction of odd-number ultrathin layers, largely restricting their application in integrated nanoelectromechanical systems. Recently, theoretical calculations have predicted the existence of out-of-plane and in-plane piezoelectricity in monolayer alpha-In2Se3. Here, we experimentally report the coexistence of out-of-plane and in-plane piezoelectricity in monolayer to bulk alpha-In2Se3, attributed to their noncentrosymmetry originating from the hexagonal stacking. Specifically, the corresponding d(33) piezoelectric coefficient of alpha-In2Se3 increases from 0.34 pm/V (monolayer) to 5.6 pm/V (bulk) without any odd even effect. In addition, we also demonstrate a type of alpha-In2Se3-based flexible piezoelectric nanogenerator as an energy-harvesting cell and electronic skin. The out-of-plane and in-plane piezoelectricity in alpha-In2Se3 flakes offers an opportunity to enable both directional and nondirectional piezoelectric devices to be applicable for self-powered systems and adaptive and strain tunable electronics/optoelectronics.
Taper PbZr0.2Ti0.8O3 Nanowire Arrays: From Controlled Growth by Pulsed Laser Deposition to Piezopotential Measurements
(2012-03-01)
Chen, Yu-Ze
;
Liu, Te-Hsiang
;
Chen, Cheng-Ying
;
Liu, Chin-Hung
;
Chen, Szu-Ying
Single crystalline PbZr0.2Ti0.8 (PIT) nanowires arrays (NWAs) with taper morphology were epitaxially grown on SrTiO3 (STO) substrate using pulse laser deposition. The taper morphology was attributed to the overcoating of PIT layer via a lateral growth of Pit clusters/adatoms during PIT NW growth.. The growth window for PZT film or nanowire was systematically studied at varied temperatures and pressures. The proposed growth mechanism of the taper PIT NWAs was investigated from a layer by layer growth via Frank-Van Der Merwe growth, followed by a formation of three-dimensional islands via Stranski-Krastanow growth, and then axial growth on the lowest energy (001) plane with growth direction of [001] via vapor-solid growth mechanism. However, under certain conditions such as at higher or lower pressure (>400 or <200 mTorr) or substrate temperatures (>850 degrees C and <725 degrees C), formation of the PIT NWs is suppressed while the epltaxial Pit thin film via the layer-by-layer growth remains. The controllable growth directions of the PZT NWAs on (001), (110), and (111) STO substrates were demonstrated. The piezopotential of the taper PIT NWAs using a conducting atomic force microscope with the average voltage output of similar to 18 mV was measured. The theoretical piezopotential of a PIT NW was calculated to compare with the measured outputs, providing a comprehensively experimental and theoretical understanding of the piezoelectricity for the PZT NW.