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Featured researches published by Dapeng Zhu.


Nanoscale Research Letters | 2013

ZnO nanoneedle/H2O solid-liquid heterojunction-based self-powered ultraviolet detector

Qinghao Li; Lin Wei; Yanru Xie; Kai Zhang; Lei Liu; Dapeng Zhu; Jun Jiao; Yanxue Chen; Shishen Yan; Guolei Liu; Liangmo Mei

ZnO nanoneedle arrays were grown vertically on a fluorine-doped tin oxide-coated glass by hydrothermal method at a relatively low temperature. A self-powered photoelectrochemical cell-type UV detector was fabricated using the ZnO nanoneedles as the active photoanode and H2O as the electrolyte. This solid-liquid heterojunction offers an enlarged ZnO/water contact area and a direct pathway for electron transport simultaneously. By connecting this UV photodetector to an ammeter, the intensity of UV light can be quantified using the output short-circuit photocurrent without a power source. High photosensitivity, excellent spectral selectivity, and fast photoresponse at zero bias are observed in this UV detector. The self-powered behavior can be well explained by the formation of a space charge layer near the interface of the solid-liquid heterojunction, which results in a built-in potential and makes the solid-liquid heterojunction work in photovoltaic mode.


Applied Physics Letters | 2014

Decoupled scenario between the conductive carriers and the ferromagnetism in epitaxial Zn0.85−xMgxCo0.15O thin films

Dapeng Zhu; Guolei Liu; Yufeng Tian; Shishen Yan; Qiang Cao; Li Cai; Maoxiang Fu; Jie Zhang; Kun Zhang; Shengtao Ye; Huan-huan Li; Shu-jun Hu; Yanxue Chen; Shishou Kang; Youyong Dai; Liangmo Mei

A series of Zn0.85−xMgxCo0.15O (0 ≤ x ≤ 0.3) thin films were fabricated by plasma-assisted molecular-beam epitaxy to investigate the correlation between the electrical transport properties and the ferromagnetism. It is observed that the saturation magnetization remains almost unchanged even though the resistivity of the Zn0.85−xMgxCo0.15O films dramatically increases more than 6 orders with increasing Mg concentration. Moreover, the absence of detectable anomalous Hall effects and very small magnetoresistance in the films reveal the absence of spin polarization of conductive carriers and very weak spin-dependent scattering or tunneling processes. All these results suggest that the conductive carriers are decoupled with the ferromagnetism in the Zn0.85−xMgxCo0.15O films.


Applied Physics Letters | 2016

Robust ferromagnetism of single crystalline CoxZn1−xO (0.3 ≤ x ≤ 0.45) epitaxial films with high Co concentration

Qiang Cao; Dapeng Zhu; Maoxiang Fu; Li Cai; Ping Yang; Shuang Li; Yin-Lian Zhu; X. L. Ma; Guolei Liu; Yanxue Chen; Shishen Yan; Liangmo Mei; Xiaolin Wang

In contrast to conventional dilute magnetic semiconductors with concentrations of magnetic ions of just a few percent, here, we report the fabrication of epitaxial CoxZn1−xO single crystalline films with Co concentrations from x = 0.3 up to 0.45 by radio-frequency oxygen-plasma-assisted molecular beam epitaxy. The films retain their single crystalline wurtzite structure without any other crystallographic phase from precipitates, based on reflection high energy electron diffraction, X-ray diffraction, transmission electron microscopy, and Raman scattering. The results of X-ray diffraction, optical transmission spectroscopy, and in-situ X-ray photoelectron spectroscopy confirm the incorporation of Co2+ cations into the wurtzite lattice. The films exhibit robust ferromagnetism and the magneto-optical Kerr effect at room temperature. The saturation magnetization reaches 265 emu/cm3 at x = 0.45, which corresponds to the average magnetic moment of 1.5 μB per Co atom.


Applied Physics Letters | 2017

Enhancing s, p–d exchange interactions at room temperature by carrier doping in single crystalline Co0.4Zn0.6O epitaxial films

Qiang Cao; Maoxiang Fu; Dapeng Zhu; Li Cai; Kun Zhang; Guolei Liu; Yanxue Chen; Shishou Kang; Shishen Yan; Liangmo Mei; Xiaolin Wang

Magnetic doping of semiconductors has been actively pursued because of their potential applications in the spintronic devices. Central to these efforts is a drive to control the mutual interactions between their magnetic properties (supported by d electrons of the magnetic ions) and their semiconductor properties (supported by s and/or p electrons) at room temperature (RT). Despite the long, intensive efforts, the experimental evidence of thermally robust s, p–d coupling in a semiconductor remains scarce and controversial. Here, we report the enhancement of RT ferromagnetic s, p–d exchange interaction by means of carrier doping in single crystalline Co0.4Zn0.6O epitaxial films with a high Co concentration. Magneto-transport measurements reveal that spin-polarized conducting carriers are produced at RT and are increased with the carrier density through Ga3+ doping, owing to the s, p–d coupling between Ga (4s), O (2p), and Co (3d) orbitals. With the ability to individually control carrier density and magnet...


Scientific Reports | 2016

Oxygen vacancies controlled multiple magnetic phases in epitaxial single crystal Co0.5(Mg0.55Zn0.45)0.5O1-v thin films

Dapeng Zhu; Qiang Cao; Ruimin Qiao; Shimeng Zhu; Wanli Yang; Weixing Xia; Yufeng Tian; Guolei Liu; Shishen Yan

High quality single-crystal fcc-Cox(MgyZn1-y)1-xO1-v epitaxial thin films with high Co concentration up to x = 0.5 have been fabricated by molecular beam epitaxy. Systematic magnetic property characterization and soft X-ray absorption spectroscopy analysis indicate that the coexistence of ferromagnetic regions, superparamagnetic clusters, and non-magnetic boundaries in the as-prepared Cox(MgyZn1-y)1-xO1-v films is a consequence of the intrinsic inhomogeneous distribution of oxygen vacancies. Furthermore, the relative strength of multiple phases could be modulated by controlling the oxygen partial pressure during sample preparation. Armed with both controllable magnetic properties and tunable band-gap, Cox(MgyZn1-y)1-xO1-v films may have promising applications in future spintronics.


Journal of Applied Physics | 2013

Structure, band gap, and Mn-related mid-gap states in epitaxial single crystal (Zn1−xMgx)1−yMnyO thin films

Dapeng Zhu; Guolei Liu; Shu-qin Xiao; Shishen Yan; Shumin He; Li Cai; Qinghao Li; Qiang Cao; Shu-jun Hu; Yanxue Chen; Shishou Kang; Liangmo Mei

Epitaxial (Zn1−xMgx)1−yMnyO thin films were grown on c-Al2O3 substrates by radio frequency oxygen plasma assisted molecular beam epitaxy. Single crystal structure of the (Zn1−xMgx)1−yMnyO films was revealed by reflection high energy electron diffraction and X-ray diffraction. The band gap of the films can be tuned dramatically with increasing the Mg concentration, while the onset energy of Mn-related mid-gap absorption band only shows a small blue shift. Photoconductivity measurements indicate the Mn-related mid-gap states in (Zn1−xMgx)1−yMnyO films can create free carriers and contribute to charge transfer transitions. The conduction band offset ΔEC = 0.13 eV and valence band offset ΔEV = 0.1 eV were obtained for ZnO/Zn0.8Mg0.2O heterostructures, which increase to ΔEC = 0.21 eV and ΔEV = 0.14 eV for ZnO/Zn0.7Mg0.3O heterostructures.


Journal of Alloys and Compounds | 2013

Soft magnetic and high-frequency properties of FeCoB–SiO2 granular films deposited on flexible substrates

Fan Yang; Shishen Yan; M.X. Yu; Shishou Kang; Youyong Dai; Yanxue Chen; S.B. Pan; Jie Zhang; Hongliang Bai; Dapeng Zhu; S.Z. Qiao; W.W. Pan; Guolei Liu; L. M. Mei


Journal of Applied Physics | 2012

High-frequency electromagnetic properties of compositionally graded FeCoB-SiO2 granular films deposited on flexible substrates

F. F. Yang; Shishen Yan; M. X. Yu; Youyong Dai; Shishou Kang; Yanxue Chen; S. B. Pan; Jie Zhang; H. L. Bai; T. S. Xu; Dapeng Zhu; S. Z. Qiao; Guolei Liu; L. M. Mei


Current Applied Physics | 2014

Raman scattering investigations on Co-doped ZnO epitaxial films: Local vibration modes and defect associated ferromagnetism

Qiang Cao; Shumin He; Yuanyuan Deng; Dapeng Zhu; Xiaodong Cui; Guolei Liu; Huaijin Zhang; Shishen Yan; Yanxue Chen; Liangmo Mei


Physica B-condensed Matter | 2012

Photoluminenscence property of ferromagnetic ZnMnO thin films

Hongliang Bai; Shumin He; Guolei Liu; Qiang Cao; Dapeng Zhu; Yanxue Chen; Shishen Yan; Liangmo Mei

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Li Cai

Shandong University

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Jie Zhang

Shanghai Jiao Tong University

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