Browsing by Author "Phuoc Huu Le"

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Enhanced Photocatalytic Performance of Nitrogen-Doped TiO2 Nanotube Arrays Using a Simple Annealing Process
(2018-12-01)
Phuoc Huu Le
;
Le Trung Hieu
;
Tu-Ngoc Lam
;
Nguyen Thi Nhat Hang
;
Nguyen Van Truong
Nitrogen-doped TiO2 nanotube arrays (N-TNAs) were successfully fabricated by a simple thermal annealing process in ambient N-2 gas at 450 degrees C for 3 h. TNAs with modified morphologies were prepared by a two-step anodization using an aqueous NH4F/ethylene glycol solution. The N-doping concentration (0-9.47 at %) can be varied by controlling N-2 gas flow rates between 0 and 500 cc/min during the annealing process. Photocatalytic performance of as-prepared TNAs and N-TNAs was studied by monitoring the methylene blue degradation under visible light ( 400 nm) illumination at 120 mWcm(-2). N-TNAs exhibited appreciably enhanced photocatalytic activity as compared to TNAs. The reaction rate constant for N-TNAs (9.47 at % N) reached 0.26 h(-1), which was a 125% improvement over that of TNAs (0.115 h(-1)). The significant enhanced photocatalytic activity of N-TNAs over TNAs is attributed to the synergistic effects of (1) a reduced band gap associated with the introduction of N-doping states to serve as carrier reservoir, and (2) a reduced electronhole recombination rate.
Growth and characterization of topological insulator Bi2Se3 thin films on SrTiO3 using pulsed laser deposition
(2013-05-01)
Phuoc Huu Le
;
Wu, Kaung Hsiung
;
Luo, Chih Wei
;
Leu, Jihperng
;
材料科學與工程學系
Bismuth selenide (Bi2Se3) thin films were grown on SrTiO3(111) (STO) substrates using pulsed laser deposition (PLD). The structural, morphological, electrical, and transport properties were studied at various substrate temperatures (T-S) from 120 to 350 degrees C. Amorphous films grown at T-S < 180 degrees C exhibited semiconducting behavior, and highly c-axis-oriented textured films deposited at T-S >= 180 degrees C exhibited metallic behavior. Bi2Se3 thin-films were epitaxially grown on STO substrates at 300 and 350 degrees C. Thickness-dependent characteristics were also investigated for optimized Bi2Se3 films deposited at T-S = 230 degrees C. The semiconducting or metallic characteristics of Bi2Se3 films prepared using PLD were observed through electrical and transport results. (C) 2013 Elsevier B. V. All rights reserved.
Localized Deformation and Fracture Behaviors in InP Single Crystals by Indentation
(2018-12-01)
Chiu, Yi-Jui
;
Jian, Sheng-Rui
;
Liu, Ti-Ju
;
Phuoc Huu Le
;
Juang, Jenh-Yih
The indentation-induced deformation mechanisms in InP(100) single crystals were investigated by using nanoindentation and cross-sectional transmission electron microscopy (XTEM) techniques. The results indicated that there were multiple pop-in events randomly distributed in the loading curves, which were conceived to arise primarily from the dislocation nucleation and propagation activities. An energetic estimation on the number of nanoindentation-induced dislocations associated with pop-in effects is discussed. Furthermore, the fracture patterns were performed by Vickers indentation. The fracture toughness and the fracture energy of InP(100) single crystals were calculated to be around 1.2 MPam(1/2) and 14.1 J/m(2), respectively.
Nanoindentation of Bi2Se3 Thin Films
(2018-10-01)
Lai, Hong-Da
;
Jian, Sheng-Rui
;
Tuyen, Le Thi Cam
;
Phuoc Huu Le
;
Luo, Chih-Wei
The nanomechanical properties and nanoindentation responses of bismuth selenide (Bi2Se3) thin films are investigated in this study. The Bi2Se3 thin films are deposited on c-plane sapphire substrates using pulsed laser deposition. The microstructural properties of Bi2Se3 thin films are analyzed by means of X-ray diffraction (XRD). The XRD results indicated that Bi2Se3 thin films are exhibited the hexagonal crystal structure with a c-axis preferred growth orientation. Nanoindentation results showed the multiple pop-ins displayed in the loading segments of the load-displacement curves, suggesting that the deformation mechanisms in the hexagonal-structured Bi2Se3 films might have been governed by the nucleation and propagation of dislocations. Further, an energetic estimation of nanoindentation-induced dislocation associated with the observed pop-in effects was made using the classical dislocation theory.
Nanomechanical and wettability properties of Bi2Te3 thin films: Effects of post-annealing
(2017-05-07)
Jian, Sheng-Rui
;
Phuoc Huu Le
;
Luo, Chih-Wei
;
Juang, Jenh-Yih
;
電子物理學系
In this study, Bi2Te3 thin films were deposited on SiO2/Si(100) substrates by pulsed laser deposition (PLD) at 250 degrees C. The films were then annealed in-situ in the deposition chamber at various annealing temperatures (T-a) ranging from 200 to 300 degrees C. The microstructural, morphological, and nanomechanical properties of the Bi2Te3 thin films were investigated by X-ray diffraction (XRD), scanning electron microscopy, and nanoindentation techniques, respectively. The XRD results indicated that all the Bi2Te3 thin films have high crystalline quality with predominant (0015) texture. Nano-indentation measurements performed with a Berkovich nanoindenter operating under the continuous contact stiffness measurement mode revealed that both the hardness and Young's modulus of the Bi2Te3 films decreased with increasing Ta. In addition, the water contact angle measurements were carried out to delineate the effects of annealing on the changes in the surface energy and wettability of the films. Published by AIP Publishing.
Nanomechanical Properties and Fracture Behaviors of Bi3Se2Te Thin Films by Nanoindentation
(2017-11-01)
Jian, Sheng-Rui
;
Phuoc Huu Le
;
Luo, Chih-Wei
;
Jenh-YihJuang
;
Wu, Kaung-Hsiung
Polycrystalline Bi3Se2Te thin films were grown on c-plane sapphire substrates by pulsed laser deposition (PLD) in helium atmosphere. Two different helium gas pressures of P-He = 2.7x10(-3) and 8.7x10(1) Pa were used during deposition. The microstructure, surface morphology, and nanomechanical properties of the obtained Bi3Se2Te films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and nanoindentation, respectively. Results indicated that the films deposited under different P-He's all exhibited highly c-axis-oriented characteristics with granular morphology. Nevertheless, the surface roughness showed strong dependence on PHe, increased from 1.3 nm to 11.8 nm for films grown at lower and higher P-He, respectively, suggesting a prominent role played by the helium gas in the nucleation and growth behavior during deposition. The Weibull statistical analysis was adopted to calculate the characteristic values of hardness and Young's modulus of the Bi3Se2Te films. In addition, the values of the fracture toughness and the nanoindentation-induced fracture behaviors of Bi3Se2Te thin films were also investigated and the results indicated that films with smaller grain size and larger surface roughness give rise to larger fracture toughness.
Nanomechanical properties and fracture toughness of Bi3Se2Te thin films grown using pulsed laser deposition
(2016-10-01)
Phuoc Huu Le
;
Luo, Chih-Wei
;
Jian, Sheng-Rui
;
Lin, Ting-Chun
;
Yang, Ping-Feng
Mechanical properties of thermoelectric (TE) materials are crucial for fabricating efficient and endurable TE devices. In this study, polycrystalline Bi3Se2Te thin films are grown on c-plane sapphire substrates at 250 degrees C and helium gas pressure of 6.5 x 10(-1) Torr using pulsed laser deposition (PLD). The structural, compositional, morphological and mechanical properties of Bi3Se2Te thin films are studied. The Bi3Se2Te thin films are highly c-axis oriented structure and exhibit the stoichiometric compositions of Bi3Se2Te phase. The hardness and Young\'s modulus of the Bi3Se2Te thin films are 5.6 +/- 0.2 GPa and 197.2 +/- 5.4 GPa, respectively, which determined by nanoindentation tests with the continuous stiffness measurement (CSM) mode. The true hardness of the Bi3Se2Te thin films is also calculated using the energy principle of nanoindentation contact. The micro-Vicker indentation-induced fracture behavior of the Bi3Se2Te thin films is observed and discussed. (C) 2016 Elsevier B.V. All rights reserved.
Nanomechanical, structural, and transport properties of Bi3Se2Te thin films
(2016-09-15)
Phuoc Huu Le
;
Chiu, Shao-Pin
;
Jian, Sheng-Rui
;
Luo, Chih Wei
;
Lin, Jiunn-Yuan
New ternary phase of Bi3Se2Te thin films were successfully grown through pulsed laser deposition with a single Bi2Se2Te crystal as the target. Bi-rich and Se-and Te-deficient compositions deposited at a substrate temperature (T-s) of 250 degrees C and helium gas pressures (P-He) ranging from 2.0 x 10(-5) to 6.5 x 10(-1) Torr aided the formation of the dominant Bi-rich phase: Bi3Se2Te. The films were grown epitaxially on Al2O3 (001) substrates with Bi3Se2Te [001]//Al2O3 [001] and Bi3Se2Te [110]//Al2O3 [210]. An increase in P-He remarkably enhanced the hardness and Young\'s modulus of the films, primarily because of the decrease in nanograin size, following the HallePetch relationship. Moreover, the Bi3Se2Te films present linear magnetoresistance under a high perpendicular magnetic field (B >= 4 T) and twodimensional weak antilocalization effect under a low B (+/- 1 T) which may be attributed to topological insulator surface state (TSS). Clearly, further theoretical calculations and experiments are needed to confirm the suggested interpretation. (C) 2016 Elsevier B.V. All rights reserved.
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 nanocrystalline Bi3Se2Te thin films grown using pulsed laser deposition
(2016-07-15)
Tuyen, Le Thi Cam
;
Phuoc Huu Le
;
Luo, Chih Wei
;
Leu, Jihperng
;
材料科學與工程學系
This study reports the material and thermoelectric properties of n-type nanocrystalline Bi-Se-Te thin films grown using pulse laser deposition (PLD) with a Bi2Se2Te single crystal as the target. In order to optimize the transport and thermoelectric properties, Bi-Se-Te thin films are fabricated by maintaining the substrate temperature (T-S) between 200 and 350 degrees C and a helium gas pressure (P-He) from 0.027 to 86.7 Pa. Unlike the target, all deposited films unexpectedly exhibit Bi2Se2Te phase with highly c-axis orientation, because of the high re-evaporation rates of Se and Te at the elevated T-S >= 200 degrees C. The estimated grain (crystalline) size ranges between 18.4 and 39.4 nm, and this monotonically increases as TS increases. The Bi3Se2Te films demonstrate excellent electrical conductivities owning to the high carrier concentration in the order of 10(20) cm(-3). A window of deposition conditions for high thermoelectric power factors (PF) is T-S of 250-350 degrees C and P-He of 40 Pa. The optimal PF is 8.3 mu W/cmK(2) for the Bi3Se2Te film prepared at 250 degrees C and 40 Pa. (C) 2016 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.
Thickness-dependent magnetotransport properties and terahertz response of topological insulator Bi2Te3 thin films
(2017-01-25)
Phuoc Huu Le
;
Liu, Po-Tsun
;
Luo, Chih Wei
;
Lin, Jiunn-Yuan
;
Wu, Kaung Hsiung
We report the thickness (d) dependence of structural, morphological, magneto-transport properties as well as terahertz (THz) response in the 0.25-2.25 THz range of topological insulator Bi2Te3 thin films grown by pulsed laser deposition (PLD). The Bi2Te3 films exhibit a highly c-axis orientation (textured films) and two Raman-active modes of E-g(2) at 102.5 cm(-1) and A(1g)(2) at 134.8 cm(-1). The films obtain relatively low carrier concentration between 2.0 x 10(19) and 4.4 x 10(19) cm(-3). The films present two-dimensional weak (2D WAL) antilocalization magnetoresistance in a low magnetic field (B) and the 2D WAL shows thickness dependence, suggesting the presence of topological surface states (TSS). The THz transmittance increases owing to increased resistivity (associated with a decreased carrier concentration) when film thickness decreases from 152 to 16 QL. The complex conductance is well described by the Drude-Lorentz model with three components of the Drude surface, Drude bulk, and phonon. The Drude spectral weight (SW) of the surface is dominant and independent of the thickness. Besides, the Drude SW of the bulk and phonon SW linearly increase with increasing thickness. (C) 2016 Elsevier B.V. All rights reserved.