Synchrotron-radiation topographic observations have shown that the Cu-doped (Ba 0.25 Sr 0.75 ) 0.9 (K 0.5 Na 0.5 ) 0.2 Nb 2 O 6 crystal has a strong ferroelectric x-ray anomalous-scattering effect at the wavelength near the absorption edge of Ba atoms. The reversal of anomalous contrast of antiparallel domains in the crystal was directly revealed in the topographs of hkl and hkl̄ reflections. It was found that the domain walls are all polar and are formed to compensate the charges resulting from the inhomogeneous distributions of the metal atoms in the bulk crystal.© 1995 American Institute of Physics.

Huang X. R.;Jiang S. S.;Zeng W.;Hu X. B.;Liu W. J.;Feng D.;Chen H. C.;Jiang Q. Z.;Jiang J. H.;Wang Z. G.

Applied Physics Letters

1995

Visible photoluminescence has been observed in crystallized a-Si:H/a-SiNx:H multiquantum-well structures at room temperature. The MQW heterostructures consisting of 72 layers were formed by computer controlled plasma-enhanced chemical-vapor deposition method and then crystallized by Ar⁺ laser annealing technique. The crystallinity and average grain size of the silicon microcrystals were determined by means of Raman and x-ray diffraction spectroscopy. The crystallized samples with well-layer thickness Ls=40 Å showed an intense photoluminescence which is peaked at 2.1 eV with a full width at half-maximum of 0.25 eV. This is consistent with calculations based on the quantum confinement model.

Chen Kunji;Huang Xinfan;Xu Jun;Feng Duan

Applied Physics Letters

1992

Chen Kunji;Huang Xinfan;Jun J.;Feng Duan

Applied Physics Letters

1995

Raman spectra of the porous structure with intense blue emission formed on C⁺-implanted silicon were examined using a 488 nm line of Ar ⁺ laser. A Raman peak with full width at half-maximum of 37 cm ^-1 was obtained at about 492 cm^-1. No Raman signals related to the β-SiC were detected. The experimental result indicates that the porous structure mainly consists of Si nanometer crystallites. The existence of β-SiC precipitates with nanometer sizes may be beneficial to the reduction of crystallite sizes and strengthen the Si skeleton, which will lead to an increase in the energy band gap of Si to the blue light emission. Using a model of phonon confinement, the obtained Raman spectra could be fitted on the basis of Si quantum crystallites and the average crystallite size was estimated to be 1.4 nm. © 1996 American Institute of Physics.

Wu Xing-Long;Yan Feng;Bao Xi-Mao;Li Ning-Sheng;Liao Liang-Sheng;Zhang Ming-Sheng;Jiang Shu-Sheng;Feng Duan

Applied Physics Letters

1995

A new type of hydrogenated nanocrystalline Si film with high electronic conductivity is investigated by means of transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). Nearly parallel columnar structures with growth orientation along the [110] zone axis of Si are found from cross-sectional TEM images of the film. HRTEM observation reveals that these columns are composed of nanocrystallites (3-6 nm size) and dendritelike growth morphology, while in the region between columns the texture consists of smaller sized (<3 nm) grains embedded in a hydrogenated amorphous Si. The volume fraction of the crystalline component is about 58% measured by Raman spectroscopy. The conductivity of the film is very high, about 10^-1 (Ω cm)^-1. It is considered that this is directly related to the characteristic structure of the film.© 1995 American Institute of Physics.

Wang L. C.;Feng D.;Xia H.;He Y. L.;Li Q.;Chu Y. M.;Ming N. B.;Epicier T.;Esnouf C.

Applied Physics Letters

1995

A tunneling-type magnetoresistance (MR) as large as 158% is observed at T = 300 K in a polycrystalline Zn 0.41 Fe 2.59 O 4 sample, in which the Zn 0.41 Fe 2.59 O 4 grains are separated by insulating α-Fe 2 O 3 boundaries. The huge room-temperature MR is attributed to the high spin polarization of Zn 0.41 Fe 2.59 O 4 grains and antiferromagnetic correlations between magnetic domains on both sides of the insulating α-Fe 2 O 3 boundary. The MR exhibits strong temperature dependence below 100 K and its magnitude is enhanced to reach 1280% at 4.2 K, which may arise from the Coulomb blockade effect. © 2001 The American Physical Society.

Chen P.;Xing D. Y.;Du Y. W.;Zhu J. M.;Feng D.

Physical Review Letters

2001

Polymerization of C60 is realized under high temperature and high pressure. X-ray diffraction reveals a rhombohedral lattice structure in the product, and solid-state ¹³C nuclear magnetic resonance spectroscopy confirms the formation of sp³ bonds between C60 molecules. Specific heat is then measured over the temperature range of 300-2 K. It is found that its specific heat values are significantly less than those in fullerite within the region of 80-2K, and this huge reduction is attributed to the suppression of intermolecular librational modes in polymerized C 60. An excellent fit to the experimental data over the entire temperature range is provided by a model, which needs to include only three-dimensional and two-dimensional translational modes in various contributions at different temperatures. © 2008 Chinese Physical Society and IOP Publishing Ltd.

Cui Guang-Lei;Gu Min;Yu Yao;Xu Xi-Bin;Wang Li-Hang;Chen Xiao;Feng Duan;Tang Tong Bor

Chinese Physics Letters

2008

Intensive blue photoluminescence (PL) was observed at room temperature from the nanocrystalline-Si/SiO2 (nc-Si/SiO2) multilayers (MLs) obtained by thermal annealing of SiO/SiO2 MLs for the first time. By controlling the size of nc-Si formed in SiO sublayer from 3.5 to 1.5 nm, the PL peak blueshifts from 457 to 411 nm. Combining the analysis of TEM, Raman and absorption measurement, this paper attributes the blue PL to multiple luminescent centres at the interface of nc-Si and SiO2. © 2008 Chin. Phys. Soc. and IOP Publishing Ltd.

Ma Zhong-Yuan;Guo Si-Hua;Chen De-Yuan;Wei De-Yuan;Yao Yao;Zhou Jiang;Huang Rui;Li Wei;Xu Jun;Xu Ling;Huang Xin-Fan;Chen Kun-Ji;Feng Duan

Chinese Physics B

2008

The synthesis and the characterization of the quantum dot quantum well (QDQW) system are described. The chemical synthesis and substitution method are used to synthesize the three-layered structure compound CdS/CuS/CdS which consists of a core of the CdS nanocrystal and a well of monolayers of CuS capped by monolayers of CdS acting as the outermost shell. The results of Inductive Coupled Plasma Mass Spectroscopy (ICP-MS) measurement and the absorption spectra confirm the formation of the three-layered system CdS/CuS/CdS.

Chen Hongming;Huang Xinfan;Huang Hongbin;Xu Ling;Xu Jun;Chen Kunji;Feng Duan

Proceedings of SPIE the International Society for Optical Engineering

1998

The fact that a magnetic hysteresis loop is observed only in polymerized C60 and is absent in both pristine and depolymerized C60 establishes a close link between the weak ferromagnetism and the underlying structure. Furthermore, the correlation between the weak ferromagnetism and hydrogen presence has been explored by ¹H NMR and ¹H-¹³C cross-polarization NMR, whereby strong bonding between the H adducts and C60 has been verified. The adducted hydrogens most likely form bonds with the carbon atoms of inter-C60 four-membered rings. This conclusion is further supported by the formation energy of adducted H and the exchange energy among adducted H obtained from first-principle calculations on Rh-C60. © 2009 Elsevier B.V. All rights reserved.

Yu Yao;Wu Jianbao;Gu Min;Zhang Weiyi;Cui Guanglei;Xu Xibin;Feng Duan;Tang Tong Bor

Chemical Physics Letters

2009