Browsing by Author "Chiu, Chung-Hua"

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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.
Copper silicide/silicon nanowire heterostructures: in situ TEM observation of growth behaviors and electron transport properties
(2013)
Chiu, Chung-Hua
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Huang, Chun-Wei
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Chen, Jui-Yuan
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Huang, Yu-Ting
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Hu, Jung-Chih
Copper silicide has been studied in the applications of electronic devices and catalysts. In this study, Cu3Si/Si nanowire heterostructures were fabricated through solid state reaction in an in situ transmission electron microscope (TEM). The dynamic diffusion of the copper atoms in the growth process and the formation mechanism are characterized. We found that two dimensional stacking faults (SF) may retard the growth of Cu3Si. Due to the evidence of the block of edge-nucleation (heterogeneous) by the surface oxide, center-nucleation (homogeneous) is suggested to dominate the silicidation. Furthermore, the electrical transport properties of various silicon channel length with Cu3Si/Si heterostructure interfaces and metallic Cu3Si NWs have been investigated. The observations not only provided an alternative pathway to explore the formation mechanisms and interface properties of Cu3Si/Si, but also suggested the potential application of Cu3Si at nanoscale for future processing in nanotechnology.
Direct Observation of Dual-Filament Switching Behaviors in Ta2O5-Based Memristors
(2017-04-18)
Chang, Chia-Fu
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Chen, Jui-Yuan
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Huang, Chun-Wei
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Chiu, Chung-Hua
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Lin, Ting-Yi
Dynamic Evolution of Conducting Nanofilament in Resistive Switching Memories
(2013-08-01)
Chen, Jui-Yuan
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Hsin, Cheng-Lun
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Huang, Chun-Wei
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Chiu, Chung-Hua
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Huang, Yu-Ting
Resistive random access memory (ReRAM) has been considered the most promising next-generation nonvolatile memory. In recent years, the switching behavior has been widely reported, and understanding the switching mechanism can improve the stability and scalability of devices. We designed an innovative sample structure for in situ transmission electron microscopy (TEM) to observe the formation of conductive filaments in the Pt/ZnO/Pt structure in real time. The corresponding current-voltage measurements help us to understand the switching mechanism of ZnO film. In addition, high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) have been used to identify the atomic structure and components of the filament/disrupted region, determining that the conducting paths are caused by the conglomeration of zinc atoms. The behavior of resistive switching is due to the migration of oxygen ions, leading to transformation between Zn-dominated ZnO1-x and ZnO.
Dynamic observation on the growth behaviors in manganese silicide/silicon nanowire heterostructures
(2015-01-01)
Hsieh, Yu-Hsun
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Chiu, Chung-Hua
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Huang, Chun-Wei
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Chen, Jui-Yuan
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Lin, Wan-Jhen
Metal silicide nanowires (NWs) are very interesting materials with diverse physical properties. Among the silicides, manganese silicide nanostructures have attracted wide attention due to their several potential applications, including in microelectronics, optoelectronics, spintronics and thermoelectric devices. In this work, we exhibited the formation of pure manganese silicide and manganese silicide/silicon nanowire heterostructures through solid state reaction with line contacts between manganese pads and silicon NWs. Dynamical process and phase characterization were investigated by in situ transmission electron microscopy (in situ TEM) and spherical aberration corrected scanning transmission electron microscopy (Cs-corrected STEM), respectively. The growth dynamics of the manganese silicide phase under thermal effects were systematically studied. Additionally, Al2O3, serving as the surface oxide, altered the growth behavior of the MnSi nanowire, enhancing the silicide/Si epitaxial growth and effecting the diffusion process in the silicon nanowire as well. In addition to fundamental science, this significant study has great potential in advancing future processing techniques in nanotechnology and related applications.
Dynamics of Nanoscale Dendrite Formation in Solution Growth Revealed Through in Situ Liquid Cell Electron Microscopy
(2018-10-01)
Hauwiller, Matthew R.
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Zhang, Xiaowei
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Liang, Wen-I
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Chiu, Chung-Hua
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Zhang, Qian
Formation mechanisms of dendrite structures have been extensively explored theoretically, and many theoretical predictions have been validated for micro- or macroscale dendrites. However, it is challenging to determine whether classical dendrite growth theories are applicable at the nanoscale due to the lack of detailed information on the nanodendrite growth dynamics. Here, we study iron oxide nanodendrite formation using liquid cell transmission electron microscopy (TEM). We observe "seaweed"-like iron oxide nanodendrites growing predominantly in two dimensions on the membrane of a liquid cell. By tracking the trajectories of their morphology development with high spatial and temporal resolution, it is possible to explore the relationship between the tip curvature and growth rate, tip splitting mechanisms, and the effects of precursor diffusion and depletion on the morphology evolution. We show that the growth of iron oxide nanodendrites is remarkably consistent with the existing theoretical predictions on dendritic morphology evolution during growth, despite occurring at the nanoscale.
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.
In Situ Study of Spinel Ferrite Nanocrystal Growth Using Liquid Cell Transmission Electron Microscopy
(2015-12-08)
Liang, Wen-I
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Zhang, Xiaowei
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Bustillo, Karen
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Chiu, Chung-Hua
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Wu, Wen-Wei
We report transition metal oxide nanocrystal formation in a liquid cell using. transmission electron microscopy (TEM). The growth of M-Fe-oxide (M = Ni, Mn, Co, or Zn) nanoparticles from a growth solution of metal acetylacetonates dissolved in oleylamine, oleic acid, and benzyl ether was studied. Nickel iron oxide nanocrystals with spinel structure were obtained under electron beam irradiation of the Ni-Fe growth solution, whereas iron oxide nanocrystals were achieved with Mn remaining in the Mn-Fe growth solution. Similarly, we achieved cobalt iron oxide nanocrystals in the Co-Fe precursor solution, while iron oxide nanoparticles were obtained in the Zn-Fe solution. By tracking nanoparticle size evolution as a function of time along the Ni-Fe oxide nanoparticle growth trajectories, we found the growth kinetics follow a Lifshitz-Slyozov-Wagner (LSW) model suggesting surface reaction-limited growth. Ex situ characterization shows elemental distribution and structural and valence state of the different nanoparticles. The trend of nanoparticle growth in a liquid cell shares many similarities with those in "one-pot" flask synthesis by thermal heating. We compare reduction potentials (E-r) of the metal ions and thermal decomposition temperatures (T-d) of the precursors and correlate them with nanoparticle growth in a liquid cell under TEM. We found a tendency to form mixed metal ion oxide nanoparticles instead of single metal ion (iron) oxides when the two precursors have similar values of T-d and metal ion reduction potential. The higher T-d and smaller E-r values of Mn and Zn precursors than those of Fe precursor, as well as Ni and Co precursors, may have resulted in the single metal ion (iron) oxide formation in M-Fe (M = Mn and Zn) precursor systems. This study sheds light on nanoparticle growth mechanisms by liquid cell TEM. In situ study of oxide nanocrystal growth using liquid cell TEM provides the opportunity to explore solution chemistry during nanocrystal growth beyond the nanoparticle growth that occurs in a TEM cell.
In-situ TEM observation of Multilevel Storage Behavior in low power FeRAM device
(2017-04-01)
Chiu, Chung-Hua
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Huang, Chun-Wei
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Hsieh, Ying-Hui
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Chen, Jui-Yuan
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Chang, Chia-Fu
The quest for non-volatile memories has attracted tremendous attention, especially in mature ferroelectric random access memory (FeRAM) with properties of high read/write speed and low power consumption. Strain engineering of multiferroic BiFeO3 (BFO) has recently become the subject of broad research interest because of its intriguing properties. In this study, we demonstrate the switchable diode characteristics in highly strained BFO thin films. Using a unique in situ electrical transmission electron microscopy (TEM), we verify the correlation between ferroelectric resistive switching with multilevel states and polarization reversal. Structural investigation confirms that the phase transition from mixed phase to pure T-like phase, accompanying with the polarization reversal by external bias, is the origin of the multilevel states. The switchable diode with multilevel resistive switching can be explained in terms of the variation of the barrier height, governed by ferroelectric polarization and polarity of the external bias. This research model, i.e., engineering of the room inside, can offer an approach toward high-density memories.
Interface Engineering for High-Performance Top-Gated MoS2 Field-Effect Transistors
(2014-09-24)
Zou, Xuming
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Wang, Jingli
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Chiu, Chung-Hua
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Wu, Yun
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Xiao, Xiangheng
Experimental evidence of the optimized interface engineering effects in MoS2 transistors is demonstrated. The MoS2/Y2O3/HfO2 stack offers excellent interface control. Results show that HfO2 layer can be scaled down to 9 nm, yet achieving a near-ideal sub-threshold slope (65 mv/dec) and the highest saturation current (526 mu A/mu m) of any MoS2 transistor reported to date.
Nickel/Platinum Dual Silicide Axial Nanowire Heterostructures with Excellent Photosensor Applications
(2016-02)
Wu, Yen-Ting
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Huang, Chun-Wei
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Chiu, Chung-Hua
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Chang, Chia-Fu
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Chen, Jui-Yuan
Transition metal silicide nanowires (NWs) have attracted increasing attention as they possess advantages of both silicon NWs and transition metals. Over the past years, there have been reported with efforts on one silicide in a single silicon NW. However, the research on multicomponent silicides in a single silicon NW is still rare, leading to limited functionalities. In this work, we successfully fabricated beta-Pt2Si/Si/theta-Ni2Si, beta-Pt2Si/theta-Ni2Si, and Pt, Ni, and Si ternary phase axial NW heterostructures through solid state reactions at 650 degrees C. Using in situ transmission electron microscope (in situ TEM), the growth mechanism of silicide NW heterostructures and the diffusion behaviors of transition metals were systematically studied. Spherical aberration corrected scanning transmission electron microscope (Cs-corrected STEM) equipped with energy dispersive spectroscopy (EDS) was used to analyze the phase structure and composition of silicide NW heterostructures. Moreover, electrical and photon properties for the silicide nanowire heterostructures demonstrated promising applications in nano-optoeletronic devices. We found that Ni, Pt, and Si ternary phase nanowire heterostructures have an excellent infrared light sensing property which is absent in bulk Ni2Si or Pt2Si. The above results would benefit the further understanding of heterostructured nano materials. sensing
Observing the evolution of graphene layers at high current density
(2016-12)
Huang, Chun-Wei
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Chen, Jui-Yuan
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Chiu, Chung-Hua
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Hsin, Cheng-Lun
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Tseng, Tseung-Yuen
Graphene has demonstrated its potential in several practical applications owing to its remarkable electronic and physical properties. In this study, we successfully fabricated a suspended graphene device with a width down to 20 nm. The morphological evolution of graphene under various electric field effects was systematically examined using an in-situ transmission electron microscope (TEM). The hourglass-shaped graphene sample instantly broke apart at 7.5 mA, indicating an impressive breakdown current density. The current-carrying capacity was calculated to be similar to 1.6 x 10(9) A center dot cm(-2), which is several orders higher than that of copper. The current-carrying capacity depended on the resistivity of graphene. In addition, atomic volume changes occurred in the multilayer graphene samples due to surface diffusion and Ostwald ripening (OR), indicating that the breakdown mechanism is well approximated by the electric field. This study not only provides a theory to explain the breakdown behavior but also presents the effects on materials contacted with a graphene layer used as the transmission path.
Opto-electrical properties of Sb-doped p-type ZnO nanowires
(2014-03-17)
Kao, Tzu-Hsuan
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Chen, Jui-Yuan
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Chiu, Chung-Hua
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Huang, Chun-Wei
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Wu, Wen-Wei
P-type ZnO nanowires (NWs) have attracted much attention in the past years due to the potential applications for optoelectronics and piezotronics. In this study, we have synthesized Sb-doped p-type ZnO NWs on Si (100) substrates by chemical vapor deposition with Aucatalyst. The Sb-doped ZnO NWs are single crystalline with high density, grown along [1-1-2] direction. The doping percentage of Sb is about 2.49%, which has been confirmed by X-ray photoelectron spectroscopy. The ZnO NW field effect transistor demonstrated its p-type characteristics. A high responsivity to ultraviolet photodetection was also observed. In addition, compared to intrinsic ZnO NWs, the conductivity of the Sb-doped ZnO NWs exhibited similar to 2 orders of magnitude higher. These properties make the p-type ZnO NWs a promising candidate for electronic and optoelectronic devices. (C) 2014 AIP Publishing LLC.
Optoelectronic Properties of Single-Crystalline Zn2GeO4 Nanowires
(2014-04-17)
Liao, Chi-Hung
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Huang, Chun-Wei
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Chen, Jui-Yuan
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Chiu, Chung-Hua
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Tsai, TzungChuen
In this work, Zn2GeO4 nanowires (NWs) were successfully synthesized on Si(100) substrates through carbon thermal reduction and a vapor liquid solid method. The NWs were of around 100 nm diameter and high aspect ratio (AR > 150). High-resolution transmission electron microscopy studies indicate that the NWs are single-crystalline with [110] growth direction. Moreover, the atomic resolution high-angle annular dark-field and bright-field images of scanning transmission electron microscopy have distinguished the different elements. They also further identified the structure of Zn2GeO4 and located the positions of the elements. Additionally, we have fabricated devices and measured the electrical properties of a single NW. It is remarkable that individual Zn2GeO4 NW devices exhibited excellent optoelectronic properties with fast switching speed under 254 nm UV illuminations. Furthermore, with short wavelength UV illumination, as we soaked Zn2GeO4 NWs in methyl orange solution, the methyl orange was degraded. Therefore, Zn2GeO4 NWs have potential applications in UV photodetectors and degradation of organic pollutants.
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.
Real Time Observation of the Formation of Hollow Nanostructures through Solid State Reactions
(2014-05-06)
Lai, Huang-Yen
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Huang, Chun-Wei
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Chiu, Chung-Hua
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Wang, Chun-Wen
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Chen, Jui-Yuan
We demonstrate the formation of hollow nickel germanide nanostructures of Ni-Ge core-shell nanoparticles by solid state reactions. The structural evolutions of nickel germanide hollow nanostructures have been investigated in real-time ultrahigh vacuum transmission electron microscopy (UHV-TEM). Annealed above 450 degrees C, the nonequilibrium interdiffusion of core and shell species occurred at the interface; thus, Ni germanide hollow nanostructures were formed by solid state reactions involving the Kirkendall effect. In addition, the different hollow nanostructures formed from different core diameters of Ni-Ge core-shell nanoparticles have been studied. Also, we propose the mechanism with effects of the size and annealing duration on the solid state reactions based on the Kirkendall effect.
Revealing Controllable Nanowire Transformation through Cationic Exchange for RRAM Application
(2014-05-01)
Huang, Chun-Wei
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Chen, Jui-Yuan
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Chiu, Chung-Hua
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Wu, Wen-Wei
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材料科學與工程學系
One dimensional metal oxide nanostructures have attracted much attention owing to their fascinating functional properties. Among them, piezoelectricity and photocatalysts along with their related materials have stirred significant interests and widespread studies in recent years. In this work, we successfully transformed piezoelectric ZnO into photocatalytic TiO2 and formed TiO2/ZnO axial heterostructure nanowires with flat interfaces by solid to solid cationic exchange reactions in high vacuum (approximately 10(-8) Torr) transmission electron microscope (TEM). Kinetic behavior of the single crystalline TiO2 was systematically analyzed. The nanoscale growth rate of TiO2 has been measured using in situ TEM videos. On the basis of the rate, we can control the dimensions of the axial-nanoheterostructure. In addition, the unique Pt/ ZnO / TiO2/ ZnO /Pt heterostructures with complementary resistive switching (CRS) characteristics were designed to solve the important issue of sneak-peak current. The resistive switching behavior was attributed to the migration of oxygen and TiO2 layer served as reservoir, which was confirmed by energy dispersive spectrometry (EDS) analysis. This study not only supplied a distinct method to explore the transformation mechanisms but also exhibited the potential application of ZnO/TiO2 heterostructure in nanoscale crossbar array resistive random-access memory (RRAM).
Single-crystalline CuO nanowires for resistive random access memory applications
(2015-04-27)
Hong, Yi-Siang
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Chen, Jui-Yuan
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Huang, Chun-Wei
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Chiu, Chung-Hua
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Huang, Yu-Ting
Recently, the mechanism of resistive random access memory (RRAM) has been partly clarified and determined to be controlled by the forming and erasing of conducting filaments (CF). However, the size of the CF may restrict the application and development as devices are scaled down. In this work, we synthesized CuO nanowires (NW) (similar to 150 nm in diameter) to fabricate a CuO NW RRAM nanodevice that was much smaller than the filament (similar to 2 mu m) observed in a bulk CuO RRAM device in a previous study. HRTEM indicated that the Cu2O phase was generated after operation, which demonstrated that the filament could be minimize to as small as 3.8 nm when the device is scaled down. In addition, energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS) show the resistive switching of the dielectric layer resulted from the aggregated oxygen vacancies, which also match with the I-V fitting results. Those results not only verify the switching mechanism of CuO RRAM but also show RRAM has the potential to shrink in size, which will be beneficial to the practical application of RRAM devices. (C) 2015 AIP Publishing LLC.
Single-crystalline delta-Ni2Si nanowires with excellent physical properties
(2013-06-19)
Chiu, Wen-Li
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Chiu, Chung-Hua
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Chen, Jui-Yuan
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Huang, Chun-Wei
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Huang, Yu-Ting
In this article, we report the synthesis of single-crystalline nickel silicide nanowires (NWs) via chemical vapor deposition method using NiCl2 center dot 6H(2)O as a single-source precursor. Various morphologies of delta-Ni2Si NWs were successfully acquired by controlling the growth conditions. The growth mechanism of the delta-Ni2Si NWs was thoroughly discussed and identified with microscopy studies. Field emission measurements show a low turn-on field (4.12 V/mu m), and magnetic property measurements show a classic ferromagnetic characteristic, which demonstrates promising potential applications for field emitters, magnetic storage, and biological cell separation.
Switching Kinetic of VCM-Based Memristor: Evolution and Positioning of Nanofilament
(2015-09-09)
Chen, Jui-Yuan
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Huang, Chun-Wei
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Chiu, Chung-Hua
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Huang, Yu-Ting
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Wu, Wen-Wei
The filament in a Au/Ta2O5/Au system is analyzed and determined to be a nanoscaled TaO2-x filament. A shrunken anode localizes the filament formation and the defect boundary leads to faster accumulation of oxygen vacancies. The defect changes the switching domination between electron transport and oxygen-vacancy migration. The migration of oxygen vacancies limits the filament dynamics, indicating the crucial role played by oxygen defects.