Browsing by Author "Cheng, Chun"

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Directed assembly of nano-scale phase variants in highly strained BiFeO3 thin films
(2012-09-15)
Zhou, Jian
;
Trassin, Morgan
;
He, Qing
;
Tamura, Nobumichi
;
Kunz, Martin
The delicate balance between elastic energy and electrostatic energy in highly strained BiFeO3 (BFO) thin films results in complex mixed-phase patterns, which poses significant challenges for theoretical understanding and complicates the realization of its full potential in magnetoelectric, electromechanical, and photovoltaic devices. In this letter, we explore in-plane electric field induced phase transition in strain engineered BFO thin films and elucidate the mechanism behind the assembly behavior of complex nano-scale phase domains. Our approach enables deterministic control of phase variants with well-defined structures and orientation, paving the way for designing novel data storage devices based on mixed phase BFO. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4752395]
Imbalanced initial populations between dark and bright states in semiconductor quantum dots
(2012-08-27)
Lin, Sheng-Di
;
Fu, Ying-Jhe
;
Cheng, Chun
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We present the observation and analysis of long-lived exciton in individual InAs quantum dots (QDs). The general model considering the interplay between dark and bright states reveals the two key factors responsible for the long decay time: the shortened spin-flip time at elevated temperature and the imbalanced initial populations between the dark and bright states. The later one plays a key role in the unusual phenomena and leads to the possibility of spin-dependent relaxation process in QDs. (C) 2012 Optical Society of America
Observation of long-lived excitons in InAs quantum dots under thermal redistribution temperature
(2012-03-26)
Cheng, Chun
;
Lin, Sheng-Di
;
Pan, Chien-Hung
;
Lin, Chien-Hung
;
Fu, Ying-Jhe
We study the temperature-dependent time-resolved photoluminescence (TRPL) of self-assembled InAs quantum dots (QDs). Under low excitation power, a surprisingly long PL decay time is observed at about 60 K, under the thermal redistribution temperature. The long decay time decreases with increasing excitation power but is nearly independent of the detection energy of TRPL measurements. A model considering the spin relaxation through the excited excitonic state is proposed to quantitatively explain the unusual phenomena. The rate equation analysis indicates that the observation of long-lived excitons is caused by the shortened spin-flip time. (c) 2012 Elsevier B.V. All rights reserved.