Browsing by Author "Liao, Chien-Neng"

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Fabrication of large-scale single-crystal bismuth telluride (Bi2Te3) nanosheet arrays by a single-step electrolysis process
(2014)
Tsai, Hung-Wei
;
Wang, Tsang-Hsiu
;
Chan, Tsung-Cheng
;
Chen, Pei-Ju
;
Chung, Chih-Chun
Nanolizing of thermoelectric materials is one approach to reduce the thermal conductivity and hence enhance the figure of merit. Bismuth telluride (Bi2Te3)-based materials have excellent figure of merit at room temperature. For device applications, precise control and rapid fabrication for the nanostructure of thermoelectric materials are essential issues. In the present study, we demonstrate a one-step electrolysis process to directly form Bi2Te3 nanosheet arrays (NSAs) on the surface of bulk Bi2Te3 with controllable spacing distance and depth by tuning the applied bias and duration. The single sheet of NSAs reveals that the average thickness and electrical resistivity of single crystalline Bi2Te3 in composition are 399.8 nm and 137.34 mu Omega m, respectively. The formation mechanism of NSAs has been proposed. A 1.12% efficiency of quantum dot-sensitized solar cells with Bi2Te3 NSAs for counter electrode has been demonstrated, indicating that Bi2Te3 NSAs from top-down processing with a high ratio of surface area to volume are a promising candidate for possible applications such as thermoelectrics, dye-sensitized solar cells (DSSCs), and lithium-ion batteries.
In-situ Transmission Electron Microscopy Study of Nanotwinned Copper under Electromigration
(2010)
Liao, Chien-Neng
;
Chen, Kuan-Chia
;
Wu, Wen-Wei
;
Chen, Lih-Juann
;
Tu, K. N.
Nanotwinned copper has drawn growing attention recently due to its substantially enhanced mechanical strength and negligible increase in electrical resistivity. The stability of nanotwins under mechanical and electrical stressing becomes a critical consideration. Using a high resolution transmission electron microscopy, we observed that the {112} incoherent twin boundary (TB) and {111} coherent TB migrate at a rate of 0.06 similar to 0.09 nm/s in copper under an electric current density of 2x10(6) A/cm(2). The TB migration is possibly associated with an atomic step moving along either (111) or {112} plane and the TB migration rate is mainly controlled by the incubation time of forming new atomic steps. To form such atomic steps, EM-induced diffusion at junctions where TBs meet a grain boundary or free surface may play an important role.
Mass transport phenomena in copper nanowires at high current density
(2016-04)
Huang, Yu-Ting
;
Huang, Chun-Wei
;
Chen, Jui-Yuan
;
Ting, Yi-Hsin
;
Cheng, Shao-Liang
Electromigration in Cu has been extensively investigated as the root cause of typical breakdown failure in Cu interconnects. In this study, Cu nanowires connected to Au electrodes are fabricated and observed using in situ transmission electron microscopy to investigate the electro- and thermo-migration processes that are induced by direct current sweeps. We observe the dynamic evolution of different mass transport mechanisms. A current density on the order of 10(6) A/cm(2) and a temperature of approximately 400 A degrees C are sufficient to induce electro- and thermo-migration, respectively. Observations of the migration processes activated by increasing temperatures indicate that the migration direction of Cu atoms is dependent on the net force from the electric field and electron wind. This work is expected to support future design efforts to improve the robustness of Cu interconnects.
Observation of atomic diffusion at twin-modified grain boundaries in copper
(2008-08-22)
Chen, Kuan-Chia
;
Wu, Wen-Wei
;
Liao, Chien-Neng
;
Chen, Lih-Juann
;
Tu, K. N.
Grain boundaries affect the migration of atoms and electrons in polycrystalline solids, thus influencing many of the mechanical and electrical properties. By introducing nanometer- scale twin defects into copper grains, we show that we can change the grain- boundary structure and atomic- diffusion behavior along the boundary. Using in situ ultrahigh- vacuum and high- resolution transmission electron microscopy, we observed electromigration- induced atomic diffusion in the twin- modified grain boundaries. The triple point where a twin boundary meets a grain boundary was found to slow down grain- boundary and surface electromigration by one order of magnitude. We propose that this occurs because of the incubation time of nucleation of a new step at the triple points. The long incubation time slows down the overall rate of atomic transport.
Optimization of the nanotwin-induced zigzag surface of copper by electromigration
(2016)
Chen, Hsin-Ping
;
Huang, Chun-Wei
;
Wang, Chun-Wen
;
Wu, Wen-Wei
;
Liao, Chien-Neng
By adding nanotwins to Cu, the surface electromigration (EM) slows down. The atomic mobility of the surface step-edges is retarded by the triple points where a twin meets a free surface to form a zigzag-type surface. We observed that EM can alter the zigzag surface structure to optimize the reduction of EM, according to Le Chatelier\'s principle. Statistically, the optimal alternation is to change an arbitrary (111)/(hkl) zigzag pair to a pair having a very low index (hkl) plane, especially the (200) plane. Using in situ ultrahigh vacuum and high-resolution transmission electron microscopy, we examined the effects of different zigzag surfaces on the rate of EM. The calculated rate of surface EM can be decreased by a factor of ten.
Stability of nanoscale twins in copper under electric current stressing
(2010-09-15)
Chen, Kuan-Chia
;
Wu, Wen-Wei
;
Liao, Chien-Neng
;
Chen, Lih-Juann
;
Tu, K. N.
Migration of {112} incoherent twin boundary (ITB) in nanotwinned Cu under electric current stressing has been observed using in situ high-resolution transmission electron microscopy. The current-driven ITB migration is found to be four orders of magnitude faster than that driven thermally. We propose that electric current plays a role of shuffling Cu atoms at ITB/coherent twin boundary junctions, which enhances nucleation of {112} steps and facilitates twin boundary migration in Cu. By understanding how twin boundaries respond to electric current force we shall be able to trace the property change in nanotwinned Cu under electric current stressing, which would be an essential assessment of interconnect reliability. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3483949]
Stability of nanoscale twins in copper under electric current stressing
(2010-09-15)
Chen, Kuan-Chia
;
Wu, Wen-Wei
;
Liao, Chien-Neng
;
Chen, Lih-Juann
;
Tu, K. N.
Migration of {112} incoherent twin boundary (ITB) in nanotwinned Cu under electric current stressing has been observed using in situ high-resolution transmission electron microscopy. The current-driven ITB migration is found to be four orders of magnitude faster than that driven thermally. We propose that electric current plays a role of shuffling Cu atoms at ITB/coherent twin boundary junctions, which enhances nucleation of {112} steps and facilitates twin boundary migration in Cu. By understanding how twin boundaries respond to electric current force we shall be able to trace the property change in nanotwinned Cu under electric current stressing, which would be an essential assessment of interconnect reliability. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3483949]
Thermodynamic Routes to Ultralow Thermal Conductivity and High Thermoelectric Performance
(1970-01-01)
Wei, Pai-Chun
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Liao, Chien-Neng
;
Wu, Hsin-Jay
;
Yang, Dongwang
;
He, Jian
Thermoelectric (TE) research is not only a course of materials by discovery but also a seedbed of novel concepts and methodologies. Herein, the focus is on recent advances in three emerging paradigms: entropy engineering, phase-boundary mapping, and liquid-like TE materials in the context of thermodynamic routes. Specifically, entropy engineering is underpinned by the core effects of high-entropy alloys; the extended solubility limit, the tendency to form a high-symmetry crystal structure, severe lattice distortions, and sluggish diffusion processes afford large phase space for performance optimization, high electronic-band degeneracy, rich multiscale microstructures, and low lattice thermal conductivity toward higher-performance TE materials. Entropy engineering is successfully implemented in half-Huesler and IV-VI compounds. In Zintl phases and skutterudites, the efficacy of phase-boundary mapping is demonstrated through unraveling the profound relations among chemical compositions, mutual solubilities of constituent elements, phase instability, microstructures, and resulting TE properties at the operation temperatures. Attention is also given to liquid-like TE materials that exhibit lattice thermal conductivity at lower than the amorphous limit due to intensive mobile ion disorder and reduced vibrational entropy. To conclude, an outlook on the development of next-generation TE materials in line with these thermodynamic routes is given.
Thermoelectric properties of bismuth-selenide films with controlled morphology and texture grown using pulsed laser deposition
(2013-11-15)
Phuoc Huu Le
;
Liao, Chien-Neng
;
Luo, Chih Wei
;
Lin, Jiunn-Yuan
;
Leu, Jihperng
Polycrystalline, thermoelectric thin films of bismuth selenide (Bi2Se3) were grown on SiO2/Si (1 1 1) substrates, using pulsed laser deposition (PLD). Bi2Se3 films with highly c-axis-oriented and controlled textures were fabricated by maintaining the helium gas pressure (P) between 0.7 and 173 Pa and the substrate temperature (T-s) between 200 and 350 degrees C. The carrier concentration (n) of films decreased with increasing P, which was attributed to the increase of Se concentration from Se deficiency (P <= 6.7 Pa) to stoichiometry to slight Se enrichment (P >= 40 Pa). The Seebeck coefficient (S) was enhanced considerably because of the reduction in n, following the S similar to n(-2/3) relation approximately. The average grain size increased from approximately 100 to 500 nm when T-s was raised from 200 to 350 degrees C, resulting in enhanced carrier mobility (mu) and electrical conductivity (sigma) and a reduced full width at half maximum of (0 0 6) peaks. The shape of grains transformed from rice-like at T-s of 200-250 degrees C to layered-hexagonal platelets (L-HPs) or super-layered flakes (S-LFs) at T-s of 300-350 degrees C. Films that were grown at 300 degrees C and 40 Pa and contained highly c-axis oriented L-HPs possessed the highest power factor (PF =S-2 sigma), which reached 5.54 mu W cm(-1) K-2, where S=75.8 mu V/K and sigma = 963.8 S cm(-1). (C) 2013 Elsevier B.V. All rights reserved.
Thermoelectric properties of nanostructured bismuth-telluride thin films grown using pulsed laser deposition
(2014-12-05)
Phuoc Huu Le
;
Liao, Chien-Neng
;
Luo, Chih Wei
;
Leu, Jihperng
;
交大名義發表
Nanostructured n-type bismuth telluride (Bi2Te3) thin films were grown on SiO2/Si (100) substrates at argon ambient pressure (P-Ar) of 80 Pa by pulsed laser deposition (PLD). The effects of film morphologies, structures, and compositions on the thermoelectric properties were investigated. At a substrate temperature (T-s) of 220-340 degrees C, stoichiometric films with highly (001)-oriented and layered structures showed the best properties, with a carrier mobility mu of 83.9-122.3 cm(2)/Vs, an absolute Seebeck coefficient vertical bar alpha vertical bar of 172.8-189.7 mu V/K, and a remarkably high power factor (PF) of 18.2-24.3 mu W cm(-1) K-2. By contrast, the Te-rich films deposited at T-s <= 120 degrees C with (015)-preferred orientations and columnar-small grain structures or the Te-deficient film deposited at 380 degrees C with Bi4Te5 polyhedron structure possessed poor properties, with mu < 10.0 cm(2)/Vs, vertical bar alpha vertical bar < 54 mu V/K, and PFs <= 0.44 mu W cm(-1) K-2. The morphology of highly (001) oriented-layered structures and the stoichiometry predominantly contribute to the substantial enhancement of mu and alpha vertical bar, respectively, resulting in remarkable enhancement in PF. (C) 2014 Elsevier B.V. All rights reserved.