Browsing by Author "Chou, Yi-Chia"

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A Fast Route Towards Freestanding Single-Crystalline Oxide Thin Films by Using YBa(2)Cu(3)O(7-x)as a Sacrificial Layer
(2020-08-28)
Chang, Yao-Wen
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Wu, Ping-Chun
;
Yi, Jhih-Bang
;
Liu, Yu-Chen
;
Chou, Yi
Researchers have long been seeking multifunctional materials that can be adopted for next-generation nanoelectronics, and which, hopefully, are compatible with current semiconductor processing for further integration. Along this vein, complex oxides have gained numerous attention due to their versatile functionalities. Despite the fact that unbounded potential of complex oxides has been examined over the past years, one of the major challenges lies in the direct integration of these functional oxides onto existing devices or targeted substrates that are inherently incompatible in terms of oxide growth. To fulfill this goal, freestanding processes have been proposed, in which wet etching of inserted sacrificial layers is regarded as one of the most efficient ways to obtain epitaxial high-quality thin films. In this study, we propose using an alternative oxide, YBa2Cu3O7(YCBO), as a sacrificial layer, which can be easily dissolved in light hydrochloric acid in a more efficient way, while protecting selected complex oxides intact. The high epitaxial quality of the selected complex oxide before and after freestanding process using YBCO as a sacrificial layer is comprehensively studied via a combination of atomic force microscopy, X-ray diffraction, transmission electron microscopy, and electrical transports. This approach enables direct integration of complex oxides with arbitrary substrates and devices and is expected to offer a faster route towards the development of low-dimensional quantum materials.
A precise pH microsensor using RF-sputtering IrO2 and Ta2O5 films on Pt-electrode
(2014-03-01)
Kuo, Li-Min
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Chou, Yi-Chia
;
Chen, Kuan-Neng
;
Lu, Chien-Chia
;
Chao, Shuchi
In this study, an easily implemented surface modification scheme is reported employing Ta2O5 membrane which covers IrO2 electrode in response to H+ and eliminating redox species interference. Evidence shows that H+ can pass through Ta2O5 films and react with IrO2/Pt electrodes due to proton-electron double injection. A Ta2O5 membrane, an ionic conductor with an insulating property, blocks the transport of electrons generated from oxygen perturbation in the solution. The conduction of both electrons and protons preserve the current continuity across the interface. Owing to proton-electron double injection, IrO2 will be reduced to Ir(OH)(3) during pH detection. The [IrO2]/[Ir(OH)(3)] will remain constant and therefore the Nernstian electrode potential performs stably as a function of pH (-59.447 to -59.504 mV/pH, 2< pH <13). In addition, the proposed pH microsensor displayed high ion selectivity with respect to K+, Na+, and Li+, with log K-H,K-M values (similar to-12.4) and has a working lifetime over one week. (C) 2013 Elsevier B.V. All rights reserved.
Controlling bottom-up rapid growth of single crystalline gallium nitride nanowires on silicon
(2017-12-20)
Wu, Ko-Li
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Chou, Yi
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Su, Chang-Chou
;
Yang, Chih-Chaing
;
Lee, Wei-I.
We report single crystalline gallium nitride nanowire growth from Ni and Ni-Au catalysts on silicon using hydride vapor phase epitaxy. The growth takes place rapidly; efficiency in time is higher than the conventional nanowire growth in metal-organic chemical vapor deposition and thin film growth in molecular beam epitaxy. The effects of V/III ratio and carrier gas flow on growth are discussed regarding surface polarity and sticking coefficient of molecules. The nanowires of gallium nitride exhibit excellent crystallinity with smooth and straight morphology and uniform orientation. The growth mechanism follows self-assembly from both catalysts, where Au acts as a protection from etching during growth enabling the growth of ultra-long nanowires. The photoluminescence of such nanowires are adjustable by tuning the growth parameters to achieve blue emission. The practical range of parameters for mass production of such high crystal quality and uniformity of nanowires is suggested.
Dependence of the structure and orientation of VSS grown Si nanowires on an epitaxy process
(2019-08-07)
Chiang, Yi-Ting
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Chou, Yi
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Huang, Chang-Hsun
;
Lin, Wei-Ting
;
Chou, Yi-Chia
We investigated the vapor-solid-solid growth of Si nanowires from Ni silicides on Si(111), Si(110), and GaN substrates. The morphology and structures of Si on these substrates are distinct, and are dependent on substrate lattices and an epitaxy process during growth. The sidewall facets and epitaxy of silicides and Si were discussed. In addition, Si grown on GaN nanowires was investigated which led to the formation of branched nanowire structures. The Si nanowires/nanodots lie on the surface of GaN nanowires to maintain lower system energy. We manipulated the whole process in a UHV and studied the crystal growth of Si on different lattice substrates. Meanwhile, the process which occurred in a non-UHV led to less regularity on the NiSi2 crystal facets and interface epitaxy between NiSi2 and Si nanowires.
Effect of Elastic Strain Fluctuation on Atomic Layer Growth of Epitaxial Silicide in Si Nanowires by Point Contact Reactions
(2015-06-01)
Chou, Yi-Chia
;
Tang, Wei
;
Chiou, Chien-Jyun
;
Chen, Kai
;
Minor, Andrew M.
Effects of strain impact a range of applications involving mobility change in field-effect-transistors. We report the effect of strain fluctuation on epitaxial growth of NiSi2 in a nanowire via point contact and atomic layer reactions, and we discuss the thermodynamic, kinetic, and mechanical implications. The generation and relaxation of strain shown by in situ TEM is periodic and in synchronization with the atomic layer reaction. The Si lattice at the epitaxial interface is under tensile strain, which enables a high solubility of supersaturated interstitial Ni atoms for homogeneous nucleation of an epitaxial atomic layer of the disilicide phase. The tensile strain is reduced locally during the incubation period of nucleation by the dissolution of supersaturated Ni atoms in the Si lattice but the strained-Si state returns once the atomic layer epitaxial growth of NiSi2 occurs by consuming the supersaturated Ni.
Effects of atomic scale imperfection at the interfaces of CoSi2 and Si (100) on Schottky barrier contacts
(2015-01-01)
Chiou, Chien-Jyun
;
Chiu, Shao-Pin
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Lin, Juhn-Jong
;
Chou, Yi-Chia
;
電子物理學系
We report here the correlation of electrical properties on Schottky barrier contacts and atomic scale imperfections based on the degree of lattice distortion and moire fringes at the interfaces of CoSi2 and Si. The I-V measurements showed that the higher levels of perfection of the interfaces gave better Schottky barrier characteristics and we discuss the implications of the transport property at Schottky barrier contacts.
Electrohydrodynamic-assisted Assembly of Hierarchically Structured, 3D Crumpled Nanostructures for Efficient Solar Conversions
(2016-12-07)
Ishihara, Hidetaka
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Chen, Yen-Chang
;
De Marco, Nicholas
;
Lin, Oliver
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Huang, Chih-Meng
The tantalizing prospect of harnessing the unique properties of graphene crumpled nanostructures continues to fuel tremendous interest in energy storage and harvesting applications. However, the paper ball-like, hard texture, and closed-sphere morphology of current 3D graphitic nanostructure production not only constricts the conductive pathways but also limits the accessible surface area. Here, we report new insights into electrohydrodynamically-generated droplets as colloidal nanoreactors in that the stimuli-responsive nature of reduced graphene oxide can lead to the formation of crumpled nanostructures with a combination of open structures and doubly curved, saddle-shaped edges. In particular, the crumpled nanostructures dynamically adapt to non-spherical, polyhedral shapes under continuous deposition, ultimately assembling into foam-like microstructures with a highly accessible surface area and spatially interconnected transport pathways. The implementation of such crumpled nanostructures as three-dimensional rear contacts for solar conversion applications realize benefits of a high aspect ratio, electrically addressable and energetically favorable interfaces, and substantial enhancement of both short-circuit currents and fill-factors compared to those made of planar graphene counterparts. Further, the 3D crumpled nanostructures may shed lights onto the development of effective electrocatalytic electrodes due to their open structure that simultaneously allows for efficient water flow and hydrogen escape.
Evidence of indirect gap in monolayer WSe2
(2017-10-13)
Hsu, Wei-Ting
;
Lu, Li-Syuan
;
Wang, Dean
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Huang, Jing-Kai
;
Li, Ming-Yang
Monolayer transition metal dichalcogenides, such as MoS2 and WSe2, have been known as direct gap semiconductors and emerged as new optically active materials for novel device applications. Here we reexamine their direct gap properties by investigating the strain effects on the photoluminescence of monolayer MoS2 and WSe2. Instead of applying stress, we investigate the strain effects by imaging the direct exciton populations in monolayer WSe2-MoS2 and MoSe2-WSe2 lateral heterojunctions with inherent strain inhomogeneity. We find that unstrained monolayer WSe2 is actually an indirect gap material, as manifested in the observed photoluminescence intensity-energy correlation, from which the difference between the direct and indirect optical gaps can be extracted by analyzing the exciton thermal populations. Our findings combined with the estimated exciton binding energy further indicate that monolayer WSe2 exhibits an indirect quasiparticle gap, which has to be reconsidered in further studies for its fundamental properties and device applications.
Heterogeneous and Homogeneous Nucleation of Epitaxial NiSi(2) in [110] Si Nanowires
(2011-01-20)
Chou, Yi-Chia
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Wu, Wen-Wei
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Lee, Chung-Yang
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Liu, Chun-Yi
;
Chen, Lih-Juann
We report here both heterogeneous and homogeneous nucleation of epitaxial suicide of NiSi(2) in Si nanowires grown in [110] direction by in situ observation in high-resolution transmission electron microscopy (TEM). Owing to the excellent lattice match between Si and NiSi(2), a giant epitaxial step of 2-8 nm wide forms at the interface between Si and NiSi(2) during the growth of the latter. The step formation results in two suicide/Si interfaces parallel to each other in TEM observations. Heterogeneous nucleation of NiSi(2) occurs at the intersection where the step meets the interfaces. However, we have also observed the epitaxial growth of NiSi(2) having a single interface with the Si, i.e., without a giant step. Homogeneous nucleation of NiSi(2) occurs on the single interface. Incubation time of heterogeneous nucleation of NiSi(2) has been measured by high-resolution video to be much shorter than that of homogeneous nucleation. The overall growth rate of NiSi(2) for the case of heterogeneous nucleation is faster than that for the case of homogeneous nucleation. Kinetic analysis of both types of nucleation is presented for a direct comparison in order to have a better understanding of the nucleation events.
Heterogeneous and Homogeneous Nucleation of Epitaxial NiSi2 in [110] Si Nanowires
(2011-01-20)
Chou, Yi-Chia
;
Wu, Wen-Wei
;
Lee, Chung-Yang
;
Liu, Chun-Yi
;
Chen, Lih-Juann
We report here both heterogeneous and homogeneous nucleation of epitaxial suicide of NiSi2 in Si nanowires grown in [110] direction by in situ observation in high-resolution transmission electron microscopy (TEM). Owing to the excellent lattice match between Si and NiSi2, a giant epitaxial step of 2-8 nm wide forms at the interface between Si and NiSi2 during the growth of the latter. The step formation results in two suicide/Si interfaces parallel to each other in TEM observations. Heterogeneous nucleation of NiSi2 occurs at the intersection where the step meets the interfaces. However, we have also observed the epitaxial growth of NiSi2 having a single interface with the Si, i.e., without a giant step. Homogeneous nucleation of NiSi2 occurs on the single interface. Incubation time of heterogeneous nucleation of NiSi2 has been measured by high-resolution video to be much shorter than that of homogeneous nucleation. The overall growth rate of NiSi2 for the case of heterogeneous nucleation is faster than that for the case of homogeneous nucleation. Kinetic analysis of both types of nucleation is presented for a direct comparison in order to have a better understanding of the nucleation events.
Homogeneous Nucleation of Epitaxial CoSi(2) and NiSi in Si Nanowires
(2009-06-01)
Chou, Yi-Chia
;
Wu, Wen-Wei
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Chen, Lih-Juann
;
Tu, King-Ning
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材料科學與工程學系
Homogeneous nucleation is rare except in theory. We observed repeating events of homogeneous nucleation in epitaxial growth of CoSi(2) and NiSi silicides in nanowires of silicon by using high resolution TEM. The growth of every single atomic layer requires nucleation. Heterogeneous nucleation is prevented because of non-microreversibility between the oxide/Si and oxide/silicide interfaces. We determined the incubation time of homogeneous nucleation. The calculated and the measured nucleation rates are in good agreement. We used Zeldovich factor to estimate the number of molecules in the critical nucleus; it is about 10 and reasonable. A very high supersaturation is found for the homogeneous nucleation.
Homogeneous Nucleation of Epitaxial CoSi2 and NiSi in Si Nanowires
(2009-06-01)
Chou, Yi-Chia
;
Wu, Wen-Wei
;
Chen, Lih-Juann
;
Tu, King-Ning
;
材料科學與工程學系
Homogeneous nucleation is rare except in theory. We observed repeating events of homogeneous nucleation in epitaxial growth of CoSi2 and NiSi silicides in nanowires of silicon by using high resolution TEM. The growth of every single atomic layer requires nucleation. Heterogeneous nucleation is prevented because of non-microreversibility between the oxide/Si and oxide/silicide interfaces. We determined the incubation time of homogeneous nucleation. The calculated and the measured nucleation rates are in good agreement. We used Zeldovich factor to estimate the number of molecules in the critical nucleus; it is about 10 and reasonable. A very high supersaturation is found for the homogeneous nucleation.
Interdiffusion of Cu-Sn System with Ni Ultra-thin Buffer Layer and Material Analysis of IMC Growth Mechanism
(2014)
Fan, Cheng-Han
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Chang, Yao-Jen
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Chou, Yi-Chia
;
Chen, Kuan-Neng
;
電子物理學系
In this paper, Ni ultra-thin diffusion buffer layer between Cu/Sn is inserted to suppress the IMC (n-phase) inter-diffusion reaction. We analogy the bonding condition by using single side Cu/Ni buffer layer/Sn structure. The inter-diffusion behaviors and IMC growth are investigated under the same thermal budget of bonding temperature during the heating step. Cu/Sn IMC formation behavior with Ni buffer layer is summarized by the SEM inspection. In the results of different Ni buffer layers (t(Ni) = 0, 50, 100, 150 angstrom) and thermal durations (0 to 60 sec), Ni buffer layer insertion can effectively reduce Cu/Sn IMC thickness. In addition, rapid growth of similar to 1.5 mu m Cu/Sn IMC thickness at 250 degrees C for only 10 sec is discovered. As results, 100 angstrom Ni buffer layer is necessary to apply as the Cu/Sn system enters the submicron pad bonding interconnects.
Nanowire growth kinetics in aberration corrected environmental transmission electron microscopy
(2016)
Chou, Yi-Chia
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Panciera, Federico
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Reuter, Mark C.
;
Stach, Eric A.
;
Ross, Frances M.
We visualize atomic level dynamics during Si nanowire growth using aberration corrected environmental transmission electron microscopy, and compare with lower pressure results from ultra-high vacuum microscopy. We discuss the importance of higher pressure observations for understanding growth mechanisms and describe protocols tominimize effects of the higher pressure background gas.
Negative circular polarization emissions from WSe2/MoSe2 commensurate heterobilayers
(2018-04-10)
Hsu, Wei-Ting
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Lu, Li-Syuan
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Wu, Po-Hsun
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Lee, Ming-Hao
;
Chen, Peng-Jen
Van der Waals heterobilayers of transition metal dichalcogenides with spin-valley coupling of carriers in different layers have emerged as a new platform for exploring spin/valleytronic applications. The interlayer coupling was predicted to exhibit subtle changes with the interlayer atomic registry. Manually stacked heterobilayers, however, are incommensurate with the inevitable interlayer twist and/or lattice mismatch, where the properties associated with atomic registry are difficult to access by optical means. Here, we unveil the distinct polarization properties of valley-specific interlayer excitons using epitaxially grown, commensurate WSe2/MoSe2 heterobilayers with well-defined (AA and AB) atomic registry. We observe circularly polarized photoluminescence from interlayer excitons, but with a helicity opposite to the optical excitation. The negative circular polarization arises from the quantum interference imposed by interlayer atomic registry, giving rise to distinct polarization selection rules for interlayer excitons. Using selective excitation schemes, we demonstrate the optical addressability for interlayer excitons with different valley configurations and polarization helicities.
Oxidation-boosted charge trapping in ultra-sensitive van der Waals materials for artificial synaptic features
(2020-06-12)
Yang, Feng-Shou
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Li, Mengjiao
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Lee, Mu-Pai
;
Ho, I-Ying
;
Chen, Jiann-Yeu
Exploitation of the oxidation behaviour in an environmentally sensitive semiconductor is significant to modulate its electronic properties and develop unique applications. Here, we demonstrate a native oxidation-inspired InSe field-effect transistor as an artificial synapse in device level that benefits from the boosted charge trapping under ambient conditions. A thin InOx layer is confirmed under the InSe channel, which can serve as an effective charge trapping layer for information storage. The dynamic characteristic measurement is further performed to reveal the corresponding uniform charge trapping and releasing process, which coincides with its surface-effect-governed carrier fluctuations. As a result, the oxide-decorated InSe device exhibits nonvolatile memory characteristics with flexible programming/erasing operations. Furthermore, an InSe-based artificial synapse is implemented to emulate the essential synaptic functions. The pattern recognition capability of the designed artificial neural network is believed to provide an excellent paradigm for ultra-sensitive van der Waals materials to develop electric-modulated neuromorphic computation architectures. Developing efficient memory and artificial synaptic systems based on environmentally sensitive van der Waals materials remains a challenge. Here, the authors present a native oxidation-inspired InSe field-effect transistor that benefits from a boosted charge trapping behavior under ambient conditions.
Second Harmonic Generation from Artificially Stacked Transition Metal Dichalcogenide Twisted Bilayers
(2014-03-01)
Hsu, Wei-Ting
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Zhao, Zi-Ang
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Li, Lain-Jong
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Chen, Chang-Hsiao
;
Chiu, Ming-Hui
Optical second harmonic generation (SHG) is known as a sensitive probe to the crystalline symmetry of few-layer transition metal dichalcogenides (TMDs). Layer-number dependent and polarization resolved SHG have been observed for the special case of Bernal stacked few-layer TMDs, but it remains largely unexplored for structures deviated from this ideal stacking order. Here we report on the SHG from homo- and heterostructural TMD bilayers formed by artificial stacking with an arbitrary stacking angle. The SHG from the twisted bilayers is a coherent superposition of the SH fields from the individual layers, with a phase difference depending on the stacking angle. Such an interference effect is insensitive to the constituent layered materials and thus applicable to hetero-stacked bilayers. A proof-of-concept demonstration of using the SHG to probe the domain boundary and crystal polarity of mirror twins formed in chemically grown TMDs is also presented. We show here that the SHG is an efficient, sensitive, and nondestructive characterization for the stacking orientation, crystal polarity, and domain boundary of van der Waals heterostructures made of noncentrosymmetric layered materials.
Structure and Strain Relaxation of GaN Nanorods Grown on Homoepitaxial Surface via Controlling Irregular Mask
(2019-02-07)
Huang, Chang-Hsun
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Pakzad, Anahita
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Lee, Wei-I
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Chou, Yi-Chia
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電子物理學系
We propose a simple and low-cost approach using irregular mask for growing GaN nanorods (NRs) bottom up on a freestanding GaN substrate through hydride vapor-phase epitaxy. The irregular mask consists of uncoalesced SiO2 islands deposited by plasma-enhanced chemical vapor deposition to isolate growth. The selection of the SiO2 amount is investigated to achieve reasonable NR density (high coverage), desired morphology (flat side walls and uniform diameters), and lattice quality (single crystalline; better quality than that of an as-grown layer under the same growth ambient). Using this growth approach with appropriate parameters, we successfully synthesize high coverage of uncoalesced NRs on a homoepitaxial surface in a short growth duration. The morphology, density, and growth rate are controlled by adjusting V/III ratios. The cathodoluminescence and photoluminescence measurements of GaN show that luminescence was obtained near 3.4 eV while the structure was grown with mask but contained defect signals when grown without mask. The residual strain relaxation within the GaN NRs has been confirmed using Raman spectrum and scanning transmission electron microscopy strain mapping. Moreover, we demonstrate the strain distribution between different crystalline qualities and lattice orientations in GaN NR The method provides a quick and inexpensive method for future nanofabrication consideration.
Study of Self-Assembly Technology for 3D Integration Applications
(2015)
Chang, Hsiao-Chun
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Fan, Cheng-Han
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Chou, Yi-Chia
;
Chen, Kuan-Neng
;
電子物理學系
In this paper, the self-assembly technology is investigated in order to apply on the alignment method to achieve rapid and accurate multichip-to-wafer stacking. By virtue of distinct liquid surface tensions between hydrophilic and hydrophobic materials, the hydrophilic chips can be self-aligned to the hydrophilic substrate which is defined by the surrounding hydrophobic substrate. The surface quality of hydrophobic film with self-assembled monolayers (SAMs) based on self-assembled mechanism strongly affects the performance of alignment. The surface quality of SAMs film which depends on experimental parameters such as dip-coating time and heating time is critical to determine the accuracy of alignment. Moreover, the chip shape and size also have an impact on the alignment accuracy. By improving the misalignment, a good design by the self-assembled mechanism for the self-alignment method can be applied in the bonding technology.
Ultralow 1/f Noise in a Heterostructure of Superconducting Epitaxial Cobalt Disilicide Thin Film on Silicon
(2017-01)
Chiu, Shao-Pin
;
Yeh, Sheng-Shiuan
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Chiou, Chien-Jyun
;
Chou, Yi-Chia
;
Lin, Juhn-Jong
High-precision resistance noise measurements indicate that the epitaxial CoSi2/Si heterostructures at 150 and 2 K (slightly above its superconducting transition temperature T-c of 1.54 K) exhibit an unusually low 1/f noise level in the frequency range of 0.008-0.2 Hz. This corresponds to an upper limit of Hooge constant gamma <= 3 X 10(-6), about 100 times lower than that of single-crystalline aluminum films on SiO2 capped Si substrates. Supported by high -resolution cross-sectional transmission electron microscopy studies, our analysis reveals that the 1/f noise is dominated by excess interfacial Si atoms and their dimer reconstruction induced fluctuators. Unbonded orbitals (i.e., dangling bonds) on excess Si atoms are intrinsically rare at the epitaxial CoSi2/Si(100) interface, giving limited trapping-detrapping centers for localized charges. With its excellent normal-state properties, CoSi2 has been used in silicon-based integrated circuits for decades. The intrinsically low noise properties discovered in this work could be utilized for developing quiet qubits and scalable superconducting circuits for future quantum computing.