Browsing by Author "Yeh, P. H."

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A solid-state cation exchange reaction to form multiple metal oxide heterostructure nanowires
(2016)
Chen, Y. H.
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Huang, C. W.
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Yeh, P. H.
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Chen, J. Y.
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Lin, T. Y.
Metal oxide nanostructures have been investigated extensively due to their wide range of physical properties; zinc oxide is one of the most promising materials. It exhibits fascinating functional properties and various types of morphologies. In particular, ZnO heterostructures have attracted great attention because their performance can be modified and further improved by the addition of other materials. In this study, we successfully transformed ZnO nanowires (NWs) into multiple ZnO/Al2O3 heterostructure NWs via a solid-state cation exchange reaction. The experiment was carried out in situ via an ultrahigh vacuum transmission electron microscope (UHV-TEM), which was equipped with a video recorder. Moreover, we analyzed the structure and composition of the heterostructure NWs by Cs-corrected STEM equipped with EDS. Based on these experimental results, we inferred a cation exchange reaction ion path model. Additionally, we investigated the defects that appeared after the cation reaction, which resulted from the remaining zinc ions. These multiple heterostructure ZnO/Al2O3 NWs exhibited excellent UV sensing sensitivity and efficiency.
Controlled large strain of Ni silicide/Si/Ni silicide nanowire heterostructures and their electron transport properties
(2010-11-15)
Wu, W. W.
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Lu, K. C.
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Chen, K. N.
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Yeh, P. H.
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Wang, C. W.
Unusually large and compressively strained Si in nanoheterostructures of Ni silicide/Si/Ni silicide, in which the strain of the Si region can be achieved up to 10%, has been produced with point contact reactions between Si and Ni nanowires in an ultrahigh vacuum transmission electron microscope. The growth rate and relationships between the strain and the spacing of the Si region have been measured. Based on the rate and relationships, we can control the Si dimension and, in turn, the strain of remaining Si can be tuned with appropriate spacing. Since one-dimensional nanoheterostructures may have potential applications in nanoelectronic devices, the existent strain will further affect carrier mobility and piezoresistance coefficients in the Si region. Electrical measurements on the nanodevices from such nanoheterostructures show that the current output closely correlates with the Si channel length and compressive strain. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3515421]
Effect of geometry on the magnetic properties of CoFe2O4-PbTiO3 multiferroic composites
(2013)
Wang, B. Y.
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Wang, H. T.
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Singh, Shashi B.
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Shao, Y. C.
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Wang, Y. F.
In this study, X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), X-ray magnetic circular dichroism (XMCD) and element-and site-specific magnetic hysteresis (ESMH) are used to elucidate the effect of geometry (0-3- and 2-2-type) on the magnetic properties of CoFe2O4-PbTiO3 (CFO-PTO) multiferroic composites by comparison with those of the reference CFO and PTO powders. Magnetic Co ions in CFO have been confirmed to be located at both the tetrahedral (A)- and octahedral (B)-sites. CFO retains its mixed-spinel structure as verified by the EXAFS, XMCD and ESMH measurements. ESMH measurements further demonstrate that the magnetic moments of Co2+ and Fe3+/Fe2+ cations at both the A-and B-sites in the composites are smaller than those of the CFO powder. The reduction of the magnetic moments in the 2-2-type composite was larger than that in the 0-3-type composite. The reduction of the magnetic moments in the composites was attributable to the formation of anti-phase boundaries owing to the compressive strain in CFO, which is the largest strain in the 2-2-type composite. Based on the Ti L-3,L-2-edge XMCD measurements of the CFO-PTO composites, no induced magnetic moment was observed at the Ti sites in the PTO matrix, excluding the possibility that the Ti ions in the PTO matrix affect the magnetic properties of these CFO-PTO composites.
Memory characteristics of Co nanocrystal memory device with HfO(2) as blocking oxide
(2007-03-26)
Yang, F. M.
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Chang, T. C.
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Liu, P. T.
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Yeh, P. H.
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Yu, Y. C.
In this letter, the Co nanocrystals using SiO(2) and HfO(2) as the tunneling and the control dielectric with memory effect has been fabricated. A significant memory effect was observed through the electrical measurements. Under the low voltage operation of 5 V, the memory window was estimated to similar to 1 V. The retention characteristics were tested to be robust. Also, the endurance of the memory device was not degraded up to 10(6) write/erase cycles. The processing of the structure is compatible with the current manufacturing technology of semiconductor industry. (c) 2007 American Institute of Physics.
Memory characteristics of Co nanocrystal memory device with HfO2 as blocking oxide
(2007-03-26)
Yang, F. M.
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Chang, T. C.
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Liu, P. T.
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Yeh, P. H.
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Yu, Y. C.
In this letter, the Co nanocrystals using SiO2 and HfO2 as the tunneling and the control dielectric with memory effect has been fabricated. A significant memory effect was observed through the electrical measurements. Under the low voltage operation of 5 V, the memory window was estimated to similar to 1 V. The retention characteristics were tested to be robust. Also, the endurance of the memory device was not degraded up to 10(6) write/erase cycles. The processing of the structure is compatible with the current manufacturing technology of semiconductor industry. (c) 2007 American Institute of Physics.
Metal nanocrystals as charge storage nodes for nonvolatile memory devices
(2007-02-10)
Yeh, P. H.
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Chen, L. J.
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Liu, P. T.
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Wang, D. Y.
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Chang, T. C.
The memory effects of the metal nanocrystals were found to be more pronounced than those of the semiconductor nanocrystals. Various metal nanocrystals as charge storage nodes are reviewed. The memory effects have strong relationship with the work function, and the work function can be modulated by changing the metal species. By tunneling dielectrics engineering, the optimum I-GWrite/Erase/I-G Retention ratio can be obtained. (c) 2006 Elsevier Ltd. All rights reserved.
Nickel nanocrystals with HfO2 blocking oxide for nonvolatile memory application
(2007-05-28)
Yang, F. M.
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Chang, T. C.
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Liu, P. T.
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Chen, U. S.
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Yeh, P. H.
A distributed charge storage with Ni nanocrystals embedded in the SiO2 and HfO2 layer has been fabricated in this study. The mean size and aerial density of the Ni nanocrystals are estimated to be about 5 nm and 3.9x10(12)/cm(2), respectively. The nonvolatile memory device with Ni nanocrystals exhibits 1 V threshold voltage shift under 4 V write operation. The device has a long retention time with a small charge lose rate. Besides, the endurance of the memory device is not degraded up to 10(6) write/erase cycles. (C) 2007 American Institute of Physics.
Using double layer CoSi2 nanocrystals to improve the memory effects of nonvolatile memory devices
(2007-05-21)
Yang, F. M.
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Chang, T. C.
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Liu, P. T.
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Yeh, P. H.
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Chen, U. S.
The nonvolatile memory device with multilayer nanocrystals has advantages such as the memory effects can be increased by the increasing density of the nanocrystals and the whole retention characteristic can be improved. There are much more electrons that can be stored in the double layer than single layer nanocrystal memory device. The double layer CoSi2 nanocrystals have better retention characteristic than the single layer. The good retention characteristic of the double layer device is due to the Coulomb-blockage effects on the top layer nanocrystals from the bottom layer nanocrystals. So, the memory effects of the nonvolatile memory device can be improved by using the double layer nanocrystals. (c) 2007 American Institute of Physics.