Browsing by Author "Chang, Li"

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A novel dilute antimony channel In0.2Ga0.8AsSb/GaAs HEMT
(2007-02-01)
Su, Ke-Hua
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Hsu, Wei-Chou
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Lee, Ching-Sung
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Wu, Tsung-Yeh
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Wu, Yue-Han
This letter reports, for the first time, a high-electron mobility. transistor (HEMT) using A dilute antimony In0.2Ga0.8AsSb channel, which is grown by a molecular-beam epitaxy system. The interfacial quality within the InGaAsSb/GaAs quantum well of the HEMT device was effectively improved by introducing the surfactantlike Sb atoms during the growth of the InGaAs layer. The improved heterostructural quality and electron transport properties have also been verified by various surface characterization techniques. In comparison, the proposed HEMT with (without) the incorporation of Sb atoms has demonstrated the maximum extrinsic transconductance g(m,max) of 227 (180) mS/mm, a drain saturation current density I-DSS of 218 (170) mA/mm, a gate-voltage swing of 1.215 (1.15) V, a cutoff frequency f(T) of 25 (20.6) GHz, and the maximum oscillation frequency f(max) of 28.3 (25.6) GHz at 300 K with gate dimensions of 1.2 x 200 mu m(2).
Atomic Imaging of Molybdenum Oxide Nanowires with Unique and Complex Periodicity by Advanced Electron Microscopy
(2020-03-11)
Ting, Yi-Hsin
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Huang, Chun-Wei
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Yasuhara, Akira
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Chen, Sheng-Yuan
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Chen, Jui-Yuan
Crystalline Mo5O14 exhibits distinctive structural features such as tunnel structure and pseudolamellar arrangement according to the ideal model. However, the spatial resolution of the conventional technique of transmission electron microscopy (TEM) is insufficient to distinguish the actual positions of atoms. In this work, we aimed to systematically analyze and identify the Mo5O14 nanowires fabricated by the chemical vapor deposition (CVD) process. Utilizing high-angle annular dark-field (HAADF), annular bright-field (ABF), and enhanced annular bright-field (E-ABF) within the scanning transmission electron microscope (STEM) mode reveals the structural features at the atomic scale. In addition, the ultrahigh resolution images have confirmed the crystallographic insights in [001] growth direction for the Mo5O14 nanowires with a tunnel structure throughout the nanowire. The cross-sectional images show the unique close-packed plane and atomic arrangement with a network of MoO6 octahedra and MoO7 pentagonal bipyramids. These results are consistent with the theoretical atomic arrangement, supporting the realization of Mo5O14-type catalysts used in the selective oxidation process and battery applications.
Atomic layer deposition of epitaxial ZnO on GaN and YSZ
(2007-01-01)
Lin, Chih-Wei
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Ke, Dong-Jie
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Chao, Yen-Cheng
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Chang, Li
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Liang, Mei-Hui
ZnO thin films were epitaxially grown by atomic layer deposition on both of GaN/c-sapphire and yttria-stabilized zirconia (YSZ) substrates for comparison. X-ray diffraction, cross-sectional transmission electron microscopy (TEM) and photoluminescence (PL) measurements show that epitaxial ZnO films have better structural qualities and optical properties on GaN than on YSZ, whereas atomic force microscopy (AFM) shows that the surface of ZnO films on YSZ is smoother than on GaN. From the ZnO thickness measured by TEM, the growth rate of ZnO on GaN is about one (0 0 0 2) monolayer per cycle, which is roughly four times of that on YSZ. (c) 2006 Elsevier B.V. All rights reserved.
Atomically resolved interface structure between epitaxial TiN film and MgO substrate
(2016-11-01)
Wei, Lin-Lung
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Yen, Tzu-Chun
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Do, Hien
;
Chang, Li
;
材料科學與工程學系
In this study, we used a high quality epitaxial TiN thin film grown on MgO (001) substrate for the investigation of the TiN/MgO interface structure which was characterized with scanning transmission electron microscopy (STEM) at atomic resolution. Analyses of high angle annular dark-field and annular bright-field STEM image contrast with X-ray energy dispersive spectroscopy maps show that a 2-4 nm diffuse interlayer of mixed compositions exists coherently between TiN and MgO with the same structure and across the interface the ionic bonding sequences are maintained without any interruption. (C) 2016 Elsevier B.V. All rights reserved.
Atomically resolved interface structure between epitaxial TiN film and MgO substrate
(2016-11-01)
Wei, Lin-Lung
;
Yen, Tzu-Chun
;
Do, Hien
;
Chang, Li
;
材料科學與工程學系
In this study, we used a high quality epitaxial TiN thin film grown on MgO (001) substrate for the investigation of the TiN/MgO interface structure which was characterized with scanning transmission electron microscopy (STEM) at atomic resolution. Analyses of high angle annular dark-field and annular bright-field STEM image contrast with X-ray energy dispersive spectroscopy maps show that a 2-4 nm diffuse interlayer of mixed compositions exists coherently between TiN and MgO with the same structure and across the interface the ionic bonding sequences are maintained without any interruption. (C) 2016 Elsevier B.V. All rights reserved.
Atomistic nucleation sites of Pt nanoparticles on N-doped carbon nanotubes
(2013)
Sun, Chia-Liang
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Pao, Chih-Wen
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Tsai, Huang-Ming
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Chiou, Jau-Wern
;
Ray, Sekhar C.
The atomistic nucleation sites of Pt nanoparticles (Pt NPs) on N-doped carbon nanotubes (N-CNTs) were investigated using C and N K-edge and Pt L-3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) spectroscopy. Transmission electron microscopy and XANES/EXAFS results revealed that the self-organized Pt NPs on N-CNTs are uniformly distributed because of the relatively high binding energies of the adsorbed Pt atoms at the imperfect sites. During the atomistic nucleation process of Pt NPs on N-CNTs, stable Pt-C and Pt-N bonds are presumably formed, and charge transfer occurs at the surface/interface of the N-CNTs. The findings in this study were consistent with density functional theory calculations performed using cluster models for the undoped, substitutional-N-doped and pyridine-like-N-doped CNTs.
Bias-enhanced nucleation of oriented diamonds on cone-like Si
(2008-04-01)
Chang, Li
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Yan, Jhih-Kun
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材料科學與工程學系
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Department of Materials Science and Engineering
Uniform distribution of bias-enhanced nucleation of diamond has been improved on Si substrate of an area of 1 x 1 cm(2) by using a domeshaped Mo counter electrode in a microwave plasma chemical vapor deposition reactor. A nucleation density of 10(9) cm(2) can be reached within a few minutes when the bias voltage of - 100 V is applied on the substrates. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that a single-crystalline diamond in a few nanometered size can be deposited on a volcano-shaped cubic SiC which is epitaxially formed on a Si cone. Examination reveals a large fraction of diamond nuclei are oriented along with one side of SiC on each Si cone. The Si cone formed on the Si substrate is due to plasma etching. The diamond nuclei have a shape close to rhombus in TEM. With further growth, secondary nucleation of diamond occurs on top of diamond nuclei and SiC which grows with Si cones. As a result, polycrystalline diamonds are deposited on each Si cone. (C) 2008 Elsevier B.V. All fights reserved.
Chemical polishing method of GaAs specimens for transmission electron microscopy
(2010-01-01)
Wu, Yue-Han
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Chang, Li
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材料科學與工程學系
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Department of Materials Science and Engineering
A practical method for transmission electron microscopy specimen preparation of GaAs-based materials with quantum dot structures is presented to show that high-quality image observations in high-resolution transmission electron microscopy (HRTEM) can be effectively obtained. Specimens were prepared in plan-view and cross-section using ion milling, followed by two-steps chemical fine polishing with an ammonia solution (NH(4)OH) and a dilute H(2)SO(4) solution. Measurements of electron energy loss spectroscopy (EELS) and atomic force microscopy (AFM) proved that clean and flat specimens can be obtained without chemical residues. HRTEM images show that the amorphous regions of carbon and GaAs can be significantly reduced to enhance the contrast of lattice images of GaAs-based quantum structure. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.
Chemical Precursor for the Synthesis of Diamond Films at Low Temperature
(2010)
Tiwari, Rajanish N.
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Chang, Li
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材料科學與工程學系
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Department of Materials Science and Engineering
In this study, diamond films have been synthesized on adamantane-coated (100) Si substrates at 530 degrees C by microwave plasma chemical vapor deposition from a gaseous mixture of methane and hydrogen. Scanning electron microscopy, Raman spectroscopy, and X-ray diffraction were employed to characterize the carbon chemical species on the Si substrate from adamantane into diamond. These measurements provide definitive evidence for formation of high-crystalline diamond film on Si substrate without any other pretreatments. Moreover, the possible mechanisms for the diamond formation are presented. (C) 2010 The Japan Society of Applied Physics
Chemical vapor deposition of diamond on an adamantane-coated sapphire substrate
(2014)
Chen, Yi-Chun
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Chang, Li
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材料科學與工程學系
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Department of Materials Science and Engineering
Continuous diamond thin films can be grown on sapphire substrates by microwave plasma chemical vapor deposition utilizing a pretreatment of adamantane dip coating on the substrate for enhanced nucleation. Scanning electron microscopy, X-ray diffraction and Raman spectroscopy show that < 111 > oriented diamond films of good crystallinity can be deposited on adamantane-coated sapphire substrates. Cross-sectional transmission electron microscopy at the diamond/sapphire interface shows that diamond can be directly synthesized on sapphire without any interlayer.
Chemical vapor deposition of diamond on silicon substrates coated with adamantane in glycol chemical solutions
(2013)
Chen, Yi-Chun
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Chang, Li
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材料科學與工程學系
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Department of Materials Science and Engineering
Diamonds were synthesized on adamantane-coated mirror-polished Si (100) substrates by microwave plasma chemical vapor deposition (MPCVD) using a gas mixture of H-2 and CH4. Before MPCVD deposition, Si substrates were dip-coated in chemical solutions of ethylene glycol and diethylene glycol with adamantane. With the coating of adamantane, the diamond nucleation can be enhanced with a density over 1 x 10(8) cm(-2) and the deposited diamond films are shown to be of good crystallinity by scanning electron microscopy and Raman spectrometry. The study demonstrates a simple and efficient way of diamond deposition on a smooth Si substrate.
Chemical vapour deposition of oriented diamond nanocrystallites by a bias-enhanced nucleation method
(2006-11-28)
Yan, Jhih-Kun
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Chang, Li
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材料科學與工程學系
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Department of Materials Science and Engineering
A microwave plasma chemical vapour deposition (MPCVD) system has been used to deposit nanometre-sized single-crystalline diamonds on 1 x 1 cm(2) Si(100) substrates. The distribution of deposited diamonds has good uniformity over the whole Si substrate surface by using a dome-shaped Mo anode which allows the application of bias-enhanced nucleation. The morphology and crystallinity of the deposits on Si were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with electron diffraction and lattice images. SEM and TEM observations show that oriented diamond nuclei as single crystals with facets can form on self-formed Si cones through epitaxial SiC within a short bias period. After a longer bias time, it has been observed that polycrystalline diamonds formed as a result of secondary nucleation.
Crystal Quality of 3C-SiC Influenced by the Diffusion Step in the Modified Four-Step Method
(2010)
Chen, Wei-Yu
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Wang, Wei-Lin
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Liu, Jui-Min
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Chen, Chien-Cheng
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Hwang, Jenn-Chang
The atomic arrangement and bonding characteristics of void-free 3C-SiC/Si(100) grown by the modified four-step method are presented. Without the diffusion step, Si-C bonds are partially formed in the as-carburized layer on Si(100). The ratio of C-C bonds to Si-C bonds is about 7:3, which can be lowered to about 1:9 after the diffusion step at 1350 degrees C for 5 min or at 1300 degrees C for 7 min according to C 1s core level spectra. The residual C-C bonds cannot be removed, which is associated with an irregular atomic arrangement (amorphous) located either at the 3C-SiC/Si(100) interface or at the intersection of twin boundaries in the 3C-SiC buffer layer based on the lattice image taken by transmission electron microscope. The diffusion step helps the formation of Si-C bonds more completely and results in a SiC buffer layer of high quality formed on Si(100) before the growth step. However, twins and stacking faults still appear in the 3C-SiC buffer layer after the diffusion step. The formation mechanism of the 3C-SiC buffer layer is proposed and discussed.
Defects in m-plane ZnO epitaxial films grown on (112) LaAlO(3) substrate
(2011-05-01)
Wang, Wei-Lin
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Peng, Chun-Yen
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Ho, Yen-Teng
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Chuang, Shu-Chang
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Chang, Li
The crystallographic orientations of m-plane ZnO on (112) LaAlO(3) (LAO) substrate are [(1) over bar2 (1) over bar0](ZnO)parallel to[11 (1) over bar](LAO) and [0001](ZnO)parallel to[(1) over bar 10](LAO). The defects in m-plane ZnO have been systematically investigated using cross section and plan-view transmission electron microscopy (TEM). High-resolution TEM observations in cross section show misfit dislocations and basal stacking faults (BSFs) at the ZnO/LAO interface. In the films, threading dislocations (TDs) with 1/3 < 11 (2) over bar0 > Burgers vectors are distributed on the basal plane, and BSFs have 1/6 < 20 (2) over bar3 > displacement vector. The densities of dislocations and BSFs are estimated to be 5.1 x 10(10) cm(-2) and 4.3 x 10(5) cm(-1), respectively. In addition to TDs and BSFs, plan-view TEM examination also reveals that stacking mismatch boundaries mainly lie along the m-planes and they connect with planar defect segments along the r-planes. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3539046]
Defects in m-plane ZnO epitaxial films grown on (112) LaAlO3 substrate
(2011-05-01)
Wang, Wei-Lin
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Peng, Chun-Yen
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Ho, Yen-Teng
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Chuang, Shu-Chang
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Chang, Li
The crystallographic orientations of m-plane ZnO on (112) LaAlO3 (LAO) substrate are [(1) over bar2 (1) over bar0](ZnO)parallel to[11 (1) over bar](LAO) and [0001](ZnO)parallel to[(1) over bar 10](LAO). The defects in m-plane ZnO have been systematically investigated using cross section and plan-view transmission electron microscopy (TEM). High-resolution TEM observations in cross section show misfit dislocations and basal stacking faults (BSFs) at the ZnO/LAO interface. In the films, threading dislocations (TDs) with 1/3 < 11 (2) over bar0 > Burgers vectors are distributed on the basal plane, and BSFs have 1/6 < 20 (2) over bar3 > displacement vector. The densities of dislocations and BSFs are estimated to be 5.1 x 10(10) cm(-2) and 4.3 x 10(5) cm(-1), respectively. In addition to TDs and BSFs, plan-view TEM examination also reveals that stacking mismatch boundaries mainly lie along the m-planes and they connect with planar defect segments along the r-planes. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3539046]
Defects in nonpolar (13(4)over-bar0) ZnO epitaxial film grown on (114) LaAlO3 substrate
(2014-03-01)
Yen, Tzu-Chun
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Wang, Wei-Lin
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Peng, Chun-Yen
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Tian, Jr-Sheng
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Ho, Yen-Teng
The defects in (13 (4) over bar0)ZnO epitaxial film grown on (114)LaAlO3 (LAO) have been systematically investigated by using transmission electron microscopy. At the ZnO/LAO interface, the Burgers vectors of misfit dislocations are identified to be 1/3[(1) over bar2 (1) over bar0] and 1/2[0001]. Threading dislocations with the Burgers vectors of 1/3 < 11 (2) over bar0 > and < 0001 > are distributed on the basal plane. In (13 (4) over bar0)ZnO film, the predominant planar defects are basal stacking faults (BSFs) with 1/6 < 20 (2) over bar3 > displacement vectors. The densities of dislocations and BSFs are about 3.8 x 10(10) cm(-2) and 3.1 x 10(5) cm(-1), respectively. (C) 2014 American Vacuum Society.
Defects in semipolar (11(2)over-bar(2)over-bar) ZnO grown on (112) LaAlO3/(La, Sr) (Al, Ta)O-3 substrate by pulsed laser deposition
(2013-03-27)
Tian, Jr-Sheng
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Wu, Yue-Han
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Peng, Chun-Yen
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Chiu, Kun-An
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Shih, Yi-Sen
The microstructure of semipolar (11 (2) over bar(2) over bar) ZnO deposited on (112) LaAlO3/(La, Sr) (Al, Ta)O-3 was investigated by transmission electron microscopy. The ZnO shows an in-plane epitaxial relationship of [11 (2) over bar3](ZnO) parallel to [11 (1) over bar](LAO/LSAT) with oxygen-face sense polarity. The misfit strain along [11 (2) over bar3](ZnO) and [1 (1) over bar 00](ZnO) is relieved through the formation of misfit dislocations with the Burgers vectors b = 1/6[11 (2) over bar3](ZnO) and b = 1/3 < 1 (2) over bar 10 >(ZnO), respectively. The line defects in the semipolar ZnO are predominantly perfect dislocations, and the dislocation density decreases with increasing ZnO thickness as a result of dislocation reactions. Planar defects were observed to lie in the M-plane and extend along < 0001 >, whereas basal stacking faults were rarely found.
Diamond plates on dome-like particles: preparation, characterization and field emission properties
(2010-08-01)
Tiwari, Rajanish N.
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Chen, Wei-Chun
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Tiwari, Jitendra N.
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Wang, Wei-Lin
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Chang, Li
Thin diamond microplates have been grown on dome-like/hemispherical carbon particles on titanium carbide by a microwave plasma chemical vapour deposition (MPCVD) method using a gas mixture of methane and hydrogen. The diamond microplates have a thickness of about 200 nm. A thin (300 nm) film of titanium carbide was formed during carburization of sputtered titanium on an Si(100) substrate in MPCVD. The hemispherical carbon particles were covered with diamond microplates. The diamond microplates are isolated electron-emitting spherules and exhibit a low threshold (50 V mu m (1)) and high current density (0.92 mA cm(-2)) in their field emission properties. A possible mechanism for the formation of the diamond microplates and hemispherical carbon particles is presented.
Dislocation reduction in GaN grown on stripe patterned r-plane sapphire substrates
(2007-07-09)
Chen, Hou-Guang
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Ko, Tsung-Shine
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Ling, Shih-Chun
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Lu, Tien-Chang
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Kuo, Hao-Chung
Extended defect reduction in GaN can be achieved via direct growth on stripe patterned (1(-)1 02) r-plane sapphire substrates by metal organic chemical vapor deposition. The striped mesa is along [11 (-)2 0] with two etched sides in {0001} and {1 (-)1 01} faces. GaN grown on both etched facets in epitaxy exhibit different crystallographic relationships with sapphire substrate which are (1 (-)1 02)(sapphire)parallel to(11 (-)2 0)(GaN) and [11 (-)2 0](sapphire)parallel to[ (-)1 100](GaN), and (0001)(sapphire)parallel to(0001)(GaN) and [11 (-)2 0](sapphire)parallel to[ (-)1 100](GaN), respectively. The dislocation densities can be significantly reduced through epitaxial growth on the inclined lateral faces of mesas. Dislocation density in the order of similar to 10(7) cm(-2) can be achieved in the tilted GaN. (C) 2007 American Institute of Physics.
Effect of growth temperature on a-plane ZnO formation on r-plane sapphire
(2011-05-01)
Peng, Chun-Yen
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Tian, Jr-Sheng
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Wang, Wei-Lin
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Ho, Yen-Teng
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Chuang, Shu-Chang
The effect of growth temperature on a-plane ZnO formation on r-plane sapphire has been systematically investigated by employing in situ high pressure reflection high-energy electron diffraction, atomic force microscopy, and high-resolution x-ray diffraction. For film growth above and below 600 degrees C, it is shown that there is a significant difference in growth rate and surface morphology due to the differences in the growth mode. Stripelike morphologies were observed on the surface of a-plane ZnO grown at low temperature (LT) because of differences in the growth rate along the c-axis and the growth rate normal to the c-axis. Furthermore, annealing of films grown at low temperature results in more pronounced stripe morphology and in improvement of crystallinity. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3549141]