Browsing by Author "Tuyen, Le Thi Cam"

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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.
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.