Browsing by Author "Hsin, Cheng-Lun"

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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
;
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.
Cobalt silicide nanocables grown on Co films: synthesis and physical properties
(2010-12-03)
Hsin, Cheng-Lun
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Yu, Shih-Ying
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Wu, Wen-Wei
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材料科學與工程學系
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Department of Materials Science and Engineering
Single-crystalline cobalt silicide/SiO(x) nanocables have been grown on Co thin films on an SiO(2) layer by a self-catalysis process via vapor-liquid-solid mechanism. The nanocables consist of a core of CoSi nanowires and a silicon oxide shell with a length of several tens of micrometers. In the confined space in the oxide shell, the CoSi phase is stable and free from agglomeration in samples annealed in air ambient at 900 degrees C for 1 h. The nanocable structure came to a clear conclusion that the thermal stability of the silicide nanowires can be resolved by the shell encapsulation. Cobalt silicide nanowires were obtained from the nanocable structure. The electrical properties of the CoSi nanowires have been found to be compatible with their thin film counterpart and a high maximum current density of the nanowires has been measured. One way to obtain silicate nanowires has been demonstrated. The silicate compound, which is composed of cobalt, silicon and oxygen, was achieved. The Co silicide/oxide nanocables are potentially useful as a key component of silicate nanowires, interconnects and magnetic units in nanoelectronics.
Controlled growth of the silicide nanostructures on Si bicrystal nanotemplate at a precision of a few nanometres
(2011)
Hsin, Cheng-Lun
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Wu, Wen-Wei
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Chu, Li-Wei
;
Hsu, Hung-Chang
;
Chen, Lih-Juann
A nanotemplate of Si bicrystal was fabricated by wafer bonding. The surface electronic energy arrangement on the surface of the Si bicrystal has been measured by scanning tunneling microscopy. The stress effect on the stepped growth of titanium silicide nanorods on Si bicrystal was observed in an ultrahigh vacuum transmission electron microscope in real time. The growth behavior of the nanorods was found to be affected by the underlying dislocation arrays significantly. For a dislocation interspacing of 3.1 nm, the dislocation arrays confined the shape of the nanoclusters and nanorods. Compared to the time of the nanorod remaining at the same length, the elongating time is more than two orders of magnitude shorter. The stepped growth behavior is attributed to the stress contour of the surface strain induced by the underlying dislocation network. This study is constructive to the basic understanding of the stress effect on the initial stage of the reaction of metals on Si and the observation may be applied to nanostructure growth for future applications and design.
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
;
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 melting behaviors at the nanoscale under electron beam and heat to form hollow nanostructures
(2012)
Huang, Chun-Wei
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Hsin, Cheng-Lun
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Wang, Chun-Wen
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Chu, Fu-Hsuan
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Kao, Chen-Yen
"We report the melting behaviours of ZnO nanowire by heating ZnO-Al2O3 core-shell heterostructures to form Al2O3 nanotubes in an in situ ultrahigh vacuum transmission electron microscope (UHV-TEM). When the ZnO-Al2O3 core-shell nanowire heterostructures were annealed at 600 degrees C under electron irradiation, the amorphous Al2O3 shell became single crystalline and then the ZnO core melted. The average vanishing rate of the ZnO core was measured to be 4.2 nm s(-1). The thickness of the Al2O3 nanotubes can be precisely controlled by the deposition process. Additionally, the inner geometry of nanotubes can be defined by the initial ZnO core. The result shows a promising method to obtain the biocompatible Al2O3 nanotubes, which may be applied in drug delivery, biochemistry and resistive switching random access memory (ReRAM)."
Direct Observation of Sublimation Behaviors in One-Dimensional In2Se3/In2O3 Nanoheterostructures
(2015-06-02)
Hsin, Cheng-Lun
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Huang, Chun-Wei
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Chen, Jui-Yuan
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Liao, Kuo-Cheng
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Liu, Po-Liang
Recently, in situ transmission electron microscopy (TEM) has provided a route to analyze structural characterization and chemical evolution with its powerful and unique applications. In this paper, we disclose the detailed phenomenon of sublimation on the atomic scale. In2Se3/In2O3 nanowires were synthesized via the vapor-liquid-solid mechanism and studied in an ultra-high-vacuum (UHV) TEM at high temperature in real time. During in situ observation of the sublimation process of the nanowires, the evolution and reconstruction of the exposed In2Se3 surface progressed in different manners with time. The surface structure was decomposed by mass-desorption and stepwise-migration processes, which are also energetically favored processes in the ab initio calculation. This study developed a new concept and will be essential in the development of atomic kinetics.
Directed assembly of nano-scale phase variants in highly strained BiFeO3 thin films
(2012-09-15)
Zhou, Jian
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Trassin, Morgan
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He, Qing
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Tamura, Nobumichi
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Kunz, Martin
The delicate balance between elastic energy and electrostatic energy in highly strained BiFeO3 (BFO) thin films results in complex mixed-phase patterns, which poses significant challenges for theoretical understanding and complicates the realization of its full potential in magnetoelectric, electromechanical, and photovoltaic devices. In this letter, we explore in-plane electric field induced phase transition in strain engineered BFO thin films and elucidate the mechanism behind the assembly behavior of complex nano-scale phase domains. Our approach enables deterministic control of phase variants with well-defined structures and orientation, paving the way for designing novel data storage devices based on mixed phase BFO. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4752395]
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.
Growth and properties of single-crystalline Ge nanowires and germanide/Ge nano-heterostructures
(2012)
Tsai, Cheng-Yu
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Yu, Shih-Ying
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Hsin, Cheng-Lun
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Huang, Chun-Wei
;
Wang, Chun-Wen
Single-crystalline Ge nanowires have been synthesized on Au-coated Si substrates through a thermal evaporation, condensation method and vapor-liquid-solidmechanism. The [111] growth direction of the Ge nanowires was analyzed using HRTEM and fast Fourier transform diffraction patterns. Global back-gated Ge nanowire field-effect transistors (FETs) on the Si3N4 dielectrics were fabricated and studied, showing p-type behavior and a field effect hole mobility of 44.3 cm(2) V-1 s(-1). The Ge channel length could be well controlled through the annealing process. After a rapid thermal annealing (RTA) process, Ni2Ge/Ge/Ni2Ge nano-heterostructures were formed. The electrical transport properties were effectively improved by the heterojunction rather than the metal contact. The epitaxial relationship between Ge and orthorhombic Ni2Ge was Ge [110]//Ni2Ge[110] and Ge(-11-1)//Ni2Ge(1-1-2). From electrical transport properties, the measured resistivity of the Ge nanowires was much lower than intrinsic bulk Ge material. A room temperature photoluminescence spectrum of the Ge nanowires possessed a broad blue emission with a peak at 462 nm in wavelength, which was attributed to the oxide-related defect states. Due to the existence of the defects, a Ge nanowire FET was able to detect visible light and serve as a nanowire photodetector.
Growth of CuInSe(2) and In(2)Se(3)/CuInSe(2) Nano-Heterostructures through Solid State Reactions
(2011-10-01)
Hsin, Cheng-Lun
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Lee, Wei-Fan
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Huang, Chi-Te
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Huang, Chun-Wei
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Wu, Wen-Wei
In(2)Se(3) is an essential phase change material and CuInSe(2) is the fundamental basis of the copper-indium-gallium-diselenide (CIGS) solar energy material. In this paper, we demonstrate the feasibility to transform the phase change material to the solar energy material via the solid state reaction. The In(2)Se(3) nanobelts (NBs) were synthesized via the vapor-liquid-solid mechanism. The chemical composition and the optical properties were investigated by energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and reflectance and photoluminescence spectra. In the in situ observation of the solid state reaction with Cu to form the CuInSe(2) NBs with ultrahigh vacuum transmission electron microscopy, we observed the In(2)Se(3)/CuInSe(2) transformation at atomic scale in real time. The progression of the atomic layer at the interface provided the pertinent information on the kinetic mechanism. In(2)Se(3)/CuInSe(2) nano-heterostructures were also obtained in the present investigation. The approach to the CIGS nanosolar cell was also proposed. This study shall be beneficial in the development of high-performance nanowire solar cells and nanodevices with In(2)Se(3)/CuInSe(2) nano-heterostructures.
Growth of CuInSe2 and In2Se3/CuInSe2 Nano-Heterostructures through Solid State Reactions
(2011-10-01)
Hsin, Cheng-Lun
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Lee, Wei-Fan
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Huang, Chi-Te
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Huang, Chun-Wei
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Wu, Wen-Wei
In2Se3 is an essential phase change material and CuInSe2 is the fundamental basis of the copper-indium-gallium-diselenide (CIGS) solar energy material. In this paper, we demonstrate the feasibility to transform the phase change material to the solar energy material via the solid state reaction. The In2Se3 nanobelts (NBs) were synthesized via the vapor-liquid-solid mechanism. The chemical composition and the optical properties were investigated by energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and reflectance and photoluminescence spectra. In the in situ observation of the solid state reaction with Cu to form the CuInSe2 NBs with ultrahigh vacuum transmission electron microscopy, we observed the In2Se3/CuInSe2 transformation at atomic scale in real time. The progression of the atomic layer at the interface provided the pertinent information on the kinetic mechanism. In2Se3/CuInSe2 nano-heterostructures were also obtained in the present investigation. The approach to the CIGS nanosolar cell was also proposed. This study shall be beneficial in the development of high-performance nanowire solar cells and nanodevices with In2Se3/CuInSe2 nano-heterostructures.
Growth of single-crystalline cobalt silicide nanowires with excellent physical properties
(2011-10-01)
Liang, Yu-Hsin
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Yu, Shih-Ying
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Hsin, Cheng-Lun
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Huang, Chun-Wei
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Wu, Wen-Wei
With the miniaturization of electron devices, the minuscule structures are important to state-of-the-art science and technology. Therefore, the growth methods and properties of nanomaterials have been extensively studied recently. Here, we use chemical vapor transport (CVT) methods to synthesize single-crystalline cobalt silicide nanowires (NWs) by using (CoCl(2)center dot 6H(2)O) as a single-source precursor. By changing reaction temperature and ambient pressure, we can obtain different morphology of cobalt silicide NWs under the appropriate concentration of silicon and cobalt. The field emission measurement of CoSi NWs shows low turn-on field (5.02 V/mu m) and it is outstanding for magnetic properties that differ from the bulk CoSi. The CoSi nanowires with different diameters have diversemagnetic saturation (Ms) and coercive force (Hc). (C) 2011 American Institute of Physics. [doi:10.1063/1.3643007]
High-yield synthesis of ZnO nanowire arrays and their opto-electrical properties
(2012)
Kao, Chen-Yen
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Hsin, Cheng-Lun
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Huang, Chun-Wei
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Yu, Shih-Ying
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Wang, Chun-Wen
In this article, ZnO nanostructures were synthesized via the hydrothermal method which used ZnCl2 and HMTA mixed solution as the precursor. A multistep growth was adopted to improve the growth restriction of a closed system, not only the length but also the aspect ratio were increased with steps of growth, and the shape of nanorods maintained integrity. Furthermore, photoluminescence spectra which have the near-band-edge-emission (similar to 3.37 eV) and defect-related emission show the optical properties of ZnO nanostructures. The defect-related emission intensity was greatly enhanced with the increasing surface area of ZnO nanowires. The level of the OH group was attributed to the yellow-light emission (similar to 580 nm) and the red-shift phenomenon. In addition, we fabricated two types of ultraviolet photodetectors: a single nanowire device and a nanowire-array device, operating at a low bias (less than 5 mV). With the lower energy consumption and the weaker persistent photoconductive effect, our ultraviolet photodetectors have better performance, exhibiting a short response time and higher sensitivity.
In Situ TEM and Energy Dispersion Spectrometer Analysis of Chemical Composition Change in ZnO Nanowire Resistive Memories
(2013-04-16)
Huang, Yu-Ting
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Yu, Shih-Ying
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Hsin, Cheng-Lun
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Huang, Chun-Wei
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Kang, Chen-Fang
Resistive random-access memory (ReRAM) has been of wide interest for its potential to replace flash memory in the next-generation nonvolatile memory roadmap. In this study, we have fabricated the Au/ZnO-nanowire/Au nanomemory device by electron beam lithography and, subsequently, utilized in situ transmission electron microscopy (TEM) to observe the atomic structure evolution from the initial state to the low-resistance state (LRS) in the ZnO nanowire. The element mapping of LRS showing that the nanowire was zinc dominant indicating that the oxygen vacancies were introduced after resistance switching. The results provided direct evidence, suggesting that the resistance change resulted from oxygen migration.
Measurement of Interlayer Screening Length of Layered Graphene by Plasmonic Nanostructure Resonances
(2013-10-31)
Chen, Hsiang-An
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Hsin, Cheng-Lun
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Huang, Yu-Ting
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Tang, Ming Lee
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Dhuey, Scott
The variation in localized surface plasmon resonances of single Au nanodisks (diameter 100 nm and height 25 nm) on 0-13 graphene layers is investigated using dark-field scattering spectroscopy to obtain the graphene electric field screening length. For nanodisks (NDs) with and without underlying graphene layers on a SiO2 (300 nm)/Si substrate, the plasmon resonance red shifts from 604 to 620 nm with increasing graphene layers. The spectra of the plasmonic nanostructures obey an exponential saturation function versus increasing number of layers of graphene from 0 to 13. As a conducting film, the graphene layers screen the electric field generated by the plasmonic resonance of the Au NDs in the vicinity of the interface, and the red shifts of the resonance wavelength are explained in the framework of the electromagnetic field coupling between in-plane antiparallel image dipoles in the graphene layers and the ND dipole. A screening length of 1.2 +/- 0.2 nm, equivalent to 3-4 graphene layers, is experimentally obtained, in good agreement with the measurement by field-effect transistors and theoretical calculation in doped graphene. The resonance shift of plasmonic nanostructures on a layered graphene system provides an alternative and convenient method for screening length measurement of graphene films.
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.
Phase transformation and thermoelectric properties of bismuth-telluride nanowires
(2013)
Hsin, Cheng-Lun
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Wingert, Matthew
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Huang, Chun-Wei
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Guo, Hua
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Shih, Ten-Jen
Thermoelectric materials have attracted much attention due to the current interest in energy conversion and recent advancements in nano-engineering. A simple approach to synthesize BiTe and Bi2Te3 micro/nanowires was developed by combining solution chemistry reactions and catalyst-free vapor-solid growth. A pathway to transform the as-grown BiTe nanostructures into Bi2Te3 can be identified through the Bi-Te phase diagram. Structural characterization of these products was identified using standard microscopy practices. Meanwhile, thermoelectric properties of individual Bi-Te compound micro/nanowires were determined by the suspended microdevice technique. This approach provides an applicable route to synthesize advanced high performance thermoelectric materials in quantities and can be used for a wide range of low-dimensional structures.
Shape control of nickel silicide nanocrystals on stress-modified surface
(2014)
Hsin, Cheng-Lun
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Huang, Chun-Wei
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Cheng, Chi-Hsuan
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Teng, Hsu-Shen
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Wu, Wen-Wei
Regularly distributed dislocation networks with a controllable spacing have been formed by wafer bonding. Different kinds of Si bicrystals were fabricated by (001), (111) and (110) Si wafers bonded with (001) silicon-on-insulator (SOI). NiSi2 formed on the bicrystal was found to be affected by the underlying dislocation arrays, confined by the dislocation grids while the surface stress and dislocation density is high enough. It has been demonstrated that through controlling the surface stress arrangement, the shape of the silicide nanostructures can be controlled and various nanostructures can be obtained. This study supports the fundamental understanding of the stress effect on the formation of silicide nanostructures on Si bicrystals and the shape-controlled nanosilicide could be useful for the growth of catalyst-assisted one-dimensional nanostructures.
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.
Single-crystalline Ge nanowires and Cu3Ge/Ge nano-heterostructures
(2012)
Hsu, Shan-Chun
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Hsin, Cheng-Lun
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Huang, Chun-Wei
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Yu, Shih-Ying
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Wang, Chun-Wen
Single-crystalline germanium nanowires were synthesized via vapor-liquid-solid mechanism. The characteristics of the Ge nanowires were investigated by a transmission electron microscope to identify the [111] growth direction. The Ge nanowire-based field-effect-transistors on Si3N4 dielectrics were fabricated, showing a p-type semiconducting behavior with hole mobility of 47.03 cm(2) V-1 s(-1). The formation of Cu3Ge/Ge/Cu3Ge nanoheterostructures was demonstrated with the reaction between copper contacts and Ge nanowires by rapid thermal annealing. The diameter-dependent electrical transport property of Ge nanowires indicates that with diameters of more than 80 nm, the resistivity of Ge nanowires decreased with diameter decrease, while with diameters of less than 80 nm, it increased. With multiple annealing processes, the channel length of the Ge nanowire transistors can be successfully controlled. From electrical measurements of each annealing step, the electrical transport property was significantly improved by sequential formation of Cu3Ge contacts. The gradual formation of the germanide structure reduces Fermi level pinning effect and increases the Ohmic behavior of electrical transportation.