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Dive into the research topics where Chengfang Li is active.

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Featured researches published by Chengfang Li.


Journal of Chemical Physics | 2008

Temperature effect of the local structure in liquid Sb studied with x-ray absorption spectroscopy

Q. Wang; Chengfang Li; Zhonghua Wu; Lianwen Wang; Xiaojuan Niu; Wensheng Yan; Yiyang Xie; Shenghui Wei; K. Lu

The temperature dependence of the local structure of liquid Sb has been studied by x-ray absorption spectroscopy. It is shown that about 10% of the atoms with coordination of 3 and weak Peierls distortion exist in liquid Sb just above its melting point. The Peierls distortion weakens gradually with increasing temperature and vanishes at about 750 degrees C. This structural variation in liquid Sb is different from the normal liquid-liquid phase transition. This work reveals the relationship between the variation in the local structure and the change in the physical properties, such as the electrical resisitvity of liquid Sb, with temperature. The complete agreement between the measured electrical resistivity values during heating and cooling processes suggests that the structural units with the features of a rhombohedron appear above the melting point of Sb during solidification.


Applied Physics Letters | 1997

Subband separation energy dependence of intersubband relaxation time in wide quantum wells

Kejian Luo; Houzhi Zheng; Zhendong Lü; Jizong Xu; Ting Zhang; Chengfang Li; Xiaoping Yang; Jinfa Tian

Subband separation energy dependence of intersubband relaxation time in a wide quantum well (250 A) was studied by steady-state and time-resolved photoluminescence. By applying a perpendicular electrical field, the subband separation energy in the quantum well is continuously tuned from 21 to 40 meV. As a result, it is found that the intersubband relaxation time undergoes a drastic change from several hundred picoseconds to subpicoseconds. It is also found that the intersubband relaxation has already become very fast before the energy separation really reaches one optical phonon energy.


Applied Physics Letters | 1998

Suppression of sequential tunneling current by a perpendicular magnetic field in a three-barrier, two-well heterostructure

Yang Ji; Yuanzhen Chen; Kejian Luo; Houzhi Zheng; Yuexia Li; Chengfang Li; W.-D. Cheng; Fuhua Yang

When an intersubband relaxation is involved in vertical transport in a tunneling heterostructure, the magnetic suppression of the intersubband LO or LA phonon scattering may also give rise to a noticeable depression of the resonant tunneling current, unrelated to the Coulomb correlation effect. The slowdown of the intersubband scattering rate makes fewer electrons able to tunnel resonantly between two adjacent quantum wells (QWs) in a three-barrier, two-well heterostructure. The influence of the magnetic field on the intersubband relaxation can be studied in an explicit way by a physical model based on the dynamics of carrier populations in the ground and excited subbands of the incident QW.


Photonics Technology into the 21st Century: Semiconductors, Microstructures, and Nanostructures | 1999

Photoluminescence characteristics of GaAs/AlGaAs quantum dot arrays fabricated by dry and dry-wet etching

Xinghua Wang; Aiming Song; Jian Liu; Winchao Cheng; Guohua Li; Chengfang Li; Yuexia Li; Jinzhong Yu

GaAs/AlGaAs quantum dot arrays with different dot sizes made by different fabrication processes were studied in this work. In comparison with the reference quantum well, photoluminescence (PL) spectra from the samples at low temperature have demonstrated that PL peak positions shift to higher energy side due to quantization confinement effects and the blue-shift increases with decreasing dot size, PL linewidths are broadened and intensities are much reduced. It is also found that wet chemical etching after reactive ion etching can improve optical properties of the quantum dot arrays.


Chinese Physics Letters | 1996

Photoluminescence Investigation of Charge Build-Up Process in the Emitter of a Double-Barrier Resonant Tunneling Structure

Kejian Luo; Houzhi Zheng; Ting Zhang; Chengfang Li; Xiaoping Yang; Penghua Zhang; Wei Zhang; Jinfa Tian

Charge build-up process in the emitter of a double-barrier resonant tunneling structure is studied by using photoluminescence spectroscopy. Clear evidence is obtained that the charge accumulation in the emitter keeps almost constant with bias voltages in the resonant regime, while it increases remarkably with bias voltages beyond resonant regime. The optical results are in good agreement with the electrical measurement. It is demonstrated that the band gap renormalization plays a certain role in the experiment.


Materials Science and Engineering B-advanced Functional Solid-state Materials | 1995

Quantum interference effect in GaAs/AlGaAs double quantum wells

Xinghua Wang; Qi Yu; R. Laiho; Chengfang Li; Jian Liu; Xiaoping Yang; Houzhi Zheng

Abstract Quantum interference properties of GaAs AlGaAs symmetric double quantum wells were investigated in a magnetic field parallel to heterointerfaces at 1.9 K. For two types of samples used in our experiments, two GaAs quantum wells with the same width of 60 A are separated by an AlGaAs barrier layer of 120 A and 20 A thick, respectively. The channels with the length of 2 μm are defined by alloyed ohmic contacts. The conductance oscillation as a function of the magnetic flux Φ(= B s) was observed and oscillation period is approximately equal to h e . The results are in agreement with the theoretical expectation of the Aharonov-Bohm effect. Conductance oscillations are apparent slightly in the samples with a thinner AlGaAs barrier.


Physical Review B | 2007

Layering in water adsorption and desorption on porous Vycor observed by dielectric measurements

Lianwen Wang; Qian Wang; Chengfang Li; Xiaojuan Niu; Guo-Xin Sun; K. Lu


Journal of Crystal Growth | 2006

Densities of Li2O–B2O3 melts

X.M. Shi; Q. Wang; Chengfang Li; Xiaojuan Niu; F.P. Wang; K. Lu


Physical Review B | 2001

Electrical manifestation of the quantum-confined Stark effect by quantum capacitance response in an optically excited quantum well

Yan Tang; Houzhi Zheng; Fuhua Yang; Ping-Heng Tan; Chengfang Li; Yuexia Li


Physical Review B | 1996

PERPENDICULAR-ELECTRIC-FIELD DEPENDENCE OF EXCITON BINDING ENERGY STUDIED BY CONTINUOUS-WAVE PHOTOLUMINESCENCE

Kejian Luo; Houzhi Zheng; S. J. Xu; Xiaoping Yang; Penghua Zhang; Wei Zhang; Chengfang Li

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Houzhi Zheng

Chinese Academy of Sciences

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Kejian Luo

Chinese Academy of Sciences

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Xiaoping Yang

Chinese Academy of Sciences

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Jian Liu

Chinese Academy of Sciences

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K. Lu

Chinese Academy of Sciences

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Penghua Zhang

Chinese Academy of Sciences

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Wei Zhang

Chinese Academy of Sciences

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Xiaojuan Niu

Chinese Academy of Sciences

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S. J. Xu

University of Hong Kong

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Fuhua Yang

Chinese Academy of Sciences

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