Browsing by Author "Chen, Jul-Yuan"

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Atomic Visualization of the Phase Transition in Highly Strained BiFeO3 Thin Films with Excellent Pyroelectric Response
(2015-10-01)
Chiu, Chung-Hua
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Liang, Wen-I
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Huang, Chun-Wei
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Chen, Jul-Yuan
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Liu, Yun-Ya
Great attention is paid to that stimulus response of materials, which is a prerequisite for energy harvesting applications. Driven by advances in nanotechnology, the atomic motions, involved in phase transitions and associated with stimulus responses, require detailed investigation on the nanoscale. Recently, strain engineering of BiFeO3 (BFO) has become the subject of broad research interest due to its promising potential in energy conversion applications, such as piezoelectric, pyroelectric and shape memory effect (SME) devices. In this study, an excellent pyroelectric response is associated with reversible phase transitions in mixed-phase BFO films using thermal stimuli. Using an in situ high-resolution transmission electron microscope (HRTEM), we observed that phase transition between rhombohedral-like (R-like) and tetragonal-like (1-like) BFO involved the migration of the phase boundary, which is a prerequisite for the growth of the T-like phase and requires an intermediate phase. Moreover, the origin of the phase transition is attributed to competition between thermodynamic stability and substrate-induced strain, as suggested by phase-field simulations. The results provide a fundamental understanding of the atomic processes that underlie the stimulus response of the strained BFO films and demonstrate the potential of this extraordinary material for novel energy harvesting applications. (C) 2015 Elsevier Ltd. All rights reserved.
Excellent piezoelectric and electrical properties of lithium-doped ZnO nanowires for nanogenerator applications
(2014-09-01)
Chang, Yu-Tsui
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Chen, Jul-Yuan
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Yang, Tzu-Ping
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Huang, Chun-Wei
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Chiu, Chung-Hua
The well-aligned Li-doped zinc oxide nanowires (ZnO NWs) were successfully grown on Si substrates with seed layer by the hydrothermal method. The presence of Li in ZnO NWs is confirmed through EELS spectrum analysis. The acceptor energy level of the Li dopant is estimated to be 93.6 meV from the temperature-dependent PL spectra. From the SQUID measurements, the coercivity and saturation magnetization of the Li-doped ZnO NWs at room temperature are found to be 166 Oe and 9.64 memu/g, respectively. Additionally, the Li-doped ZnO NWFET confirms that the NWs were p-type with a high carrier mobility of 14.59 cm(2/)V s and an effective hole carrier concentration of 1.13 x 10(17) CM-3. The piezoelectric response of the Li-doped ZnO NWs produces much higher piezoelectric output current, voltage, and power than pure ZnO NWs. These results indicated that p-type ZnO NWs are a promising candidate for nanogenerator devices. (C) 2014 Elsevier Ltd. All rights reserved.
Phosphorus-Doped p-n Homojunction ZnO Nanowires: Growth Kinetics in Liquid and Their Optoelectronic Properties
(2015-06-23)
Lee, Wei-Che
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Chen, Jul-Yuan
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Huang, Chun-Wei
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Chiu, Chung-Hua
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Lin, Ting-Yi
For wide-ranging applications in nanoscale electronic devices, durable and reproducible p-type nanostructures are essential. In this work, simple ZnO nano-wire (NW) p-n homojunctions were grown using a two-step hydrothermal synthesis method. P2O5 served as a doping source to obtain p-type ZnO NW\'s. The morphology of the ZnO NW arrays was examined using field emission scanning electron microscopy. The high-resolution transmission electron microscopy (HRTEM) image indicated that the ZnO NW p-n homojunction is single-crystalline with a < 0001 > growth direction. The distribution of P element was analyzed using energy-dispersive spectroscopy. The dynamic growth observation was conducted using liquid in situ TEM to investigate the ZnO nucleation and growth mechanism. We divided the ZnO nanocrystal precipitation into three processes. Whether two adjacent particles grow stably or not was found to be related to the distance. Moreover, the temperature-dependent photoluminescence spectra revealed that two extra emission peaks located at 416 and 435 nm were emitted from the ZnO NW p-n homojunction, which resulted from donor-acceptor recombination. In addition, the electron transport properties confirmed the rectification behavior of the multi ZnO NW p-n homojunctions. The turn-on voltage and the current were approximately 2.8 V and 10(-4) to 10(-5) A, respectively, under forward bias. The results indicate the potential application of ZnO NW p-n homojunctions as nanoscale light-emitting diodes.