Ning Xu

Fudan University, Shanghai, Shanghai Shi, China

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Publications (71)158.07 Total impact

  • Peipei Liang · Xu Yang · Hui Li · Hua Cai · Jian Sun · Ning Xu · Jiada Wu ·
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    ABSTRACT: A nitrogen-carbon plasma was generated during the deposition of carbon nitride (CNx) thin films by pulsed laser ablation of a graphite target in a discharge nitrogen plasma, and the optical emission of the generated nitrogen-carbon plasma was measured for the diagnostics of the plasma and the characterization of the process of CNx film deposition. The nitrogen-carbon plasma was recognized to contain various species including nitrogen molecules and molecular ions excited in the ambient N2 gas, carbon atoms and atomic ions ablated from the graphite target and CN radicals. The temporal evolution and spatial distribution of the CN emission and their dependence on the substrate bias voltage show two groups of CN radicals flying in opposite directions. One represents the CN radicals formed as the products of the reactions occurring in the nitrogen-carbon plasma, revealing the reactive deposition of CNx film due to the reactive expansion of the ablation carbon plasma in the discharge nitrogen plasma and the effective formation of gaseous CN radicals as precursors for CNx film growth. The other one represents the CN radicals re-sputtered from the growing CNx film by energetic plasma species, evidencing the re-sputtering of the growing film accompanying film growth. And, the re-sputtering presents ion-induced sputtering features.
    Physics of Plasmas 10/2015; 22(10):103504. DOI:10.1063/1.4932326 · 2.14 Impact Factor
  • Peipei Liang · Yanli Li · Hua Cai · Xu Yang · Hui Li · Jian Sun · Ning Xu · Jiada Wu ·
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    ABSTRACT: Violet and blue luminescent Si nanowires were fabricated by annealing an amorphous Si film on a Ni-coated Si substrate via solid-liquid-solid growth. The fabricated Si nanowires have an average diameter of 50 nm. The wire stem is composed of a crystalline Si core of several nanometers and an amorphous oxide sheath. The Si nanowires are capable of emitting strong violet and blue luminescence in the spectral region ranging from 380 to 500 nm, which has a very short decay time of tens of nanoseconds, and is remarkably different in spectral region and luminescence time from the luminescence emitted by Si nanocrystals.
    Applied Physics Express 08/2015; 8(8):085002. DOI:10.7567/APEX.8.085002 · 2.37 Impact Factor
  • Xu Yang · Qin Yang · Zhigao Hu · Shuang Guo · Yanli Li · Jian Sun · Ning Xu · Jiada Wu ·
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    ABSTRACT: We report the study on the influences of shell thickness and core–shell structure on the optical properties of ZnO/CdS core/shell nanorods (NRs) for an elucidation of the mechanisms responsible for the extended photoresponse of ZnO/CdS core/shell NRs to solar radiation. Well aligned ZnO/CdS core/shell NRs were fabricated on indium tin oxide substrates using hydrothermally grown ZnO NRs as the cores and pulsed laser deposited CdS coatings as the shells. The sample structure was characterized by X-ray diffraction and Raman backscattering spectroscopy, revealing the wurtzite structure of both the ZnO cores and CdS shells, and the improvement in the structure after annealing. The optical properties were studied through optical transmittance, absorbance and photoluminescence measurements, showing the optical properties featured with type-II heterogeneous nanostructures constructed from ZnO and CdS. The results provide a support that the optical properties of the CdS covered ZnO NRs are attributed to the suppressed radiative recombination of photogenerated carriers due to the efficient spatial separation of electrons and holes in the nanosized ZnO–CdS heterostructures.
    Solar Energy Materials and Solar Cells 06/2015; 137. DOI:10.1016/j.solmat.2015.02.015 · 5.34 Impact Factor
  • Peipei Liang · Hua Cai · Yanli Li · Xu Yang · Qinghu You · Jian Sun · Ning Xu · Jiada Wu ·
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    ABSTRACT: A nitrogen–aluminum–gallium–arsenic plasma is formed by pulsed laser co-ablation of an Al target and a GaAs target in electron cyclotron resonance discharge-generated nitrogen plasma for Alx Ga1−x N film deposition. The formed plasma was characterized by time-integrated and time-resolved optical emission spectroscopy measurements and the process of Alx Ga1−x N deposition was discussed. The plasma contains excited species originally present in the working N2 gas and energetic species ablated from the targets, and its emission is abundant in the emission bands of diatomic nitrogen molecules and molecular ions and the emission lines of monoatomic aluminum, gallium, and arsenic atoms and atomic ions. The temporal and spatial features of the plasma emission reveal that the nitrogen species in the electron cyclotron resonance nitrogen plasma experience additional excitations due to the expanding ablation plumes, and the ablated species are excited frequently when traveling with the expanding plumes in the nitrogen plasma, making the formed plasma very reactive, which is very important in the process of Alx Ga1−x N film deposition. The deposited film was evaluated for composition analysis by energy-dispersive x-ray spectroscopy and structure characterization by x-ray diffraction. The Alx Ga1−x N film is slightly nitrogen rich with an aluminum content x of about 0.6 and featured with hexagonal wurtzite crystal structure with preferred c-axis orientation.
    Journal of Physics D Applied Physics 06/2015; 48(24). DOI:10.1088/0022-3727/48/24/245203 · 2.72 Impact Factor
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    ABSTRACT: The spatial confinement effects of shock waves on the laser-induced plasma (LIP) from a graphite target in air were studied by probe beam deflection (PBD) measurements and optical emission spectroscopy (OES). A clear relationship between the confinement of the LIP by the shock wave and the effects on the LIP emission was observed, and the underlying mechanisms are discussed. PBD monitoring revealed that the laser-ablation induced shock wave could be well analogized to the shock wave generated by a point explosion and would be reflected by a block. OES measurements indicated that the optical emission of the LIP exhibited significant variations with the block placement. A first enhancement and then a fast decay of CN molecular emission as well as a suppression of carbon atomic emission were observed in the presence of the block. The results revealed that the reflected shock wave spatially confined the expansion of the LIP and compressed the LIP after encountering it, pushing back the species of the LIP and changing the density of the LIP species including luminous carbon atoms and CN molecules. It is suggested that the change of the LIP emission is attributed to the density variation of the LIP species due to the compression of the LIP and the reactions occurring in the plasma.
    Physics of Plasmas 06/2015; 22(6):063509. DOI:10.1063/1.4922850 · 2.14 Impact Factor
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    ABSTRACT: Al doped ZnO (ZnO:Al) and Al-N co-doped ZnO (ZnO:Al-N) films were synthesized based on plasma assisted reactive deposition of ZnO matrix and in-situ doping of Al or co-doping of Al and N. Similar with undoped ZnO, the synthesized ZnO:Al and ZnO:Al-N films are hexagonal wurtzite in structure and exhibit high optical transparency in a wide spectral region. Al doping and Al-N co-doping in ZnO result in a significant variation of the optical properties in the ultraviolet (UV) region and an UV extension of the transparent range. Compared with undoped ZnO, the doped films show blue-shifted absorption edge of 320 nm and widened band gap of 3.69 eV after annealing in H2/N2 mixed gas because of the incorporation of dopants and the improvement in the crystal structure. The ZnO:Al film exhibits declined transparency in the near infrared (IR) region, while the ZnO film co-doped with Al and N preserves high transparency from near UV to medium IR in addition to the UV extension of the transparent range. The annealed ZnO:Al and ZnO:Al-N films show good electrical properties with higher electrical conductivity and carrier concentration than those of the undoped ZnO film.
    Journal of Alloys and Compounds 05/2015; 644. DOI:10.1016/j.jallcom.2015.05.060 · 3.00 Impact Factor
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    ABSTRACT: Ternary AlxGa1-xN films with different Al compositions were synthesized on sapphire and Si substrates by pulsed laser co-ablation of a polycrystalline GaAs target and a metallic Al target in nitrogen plasma generated by electron cyclotron resonance discharge of N2 gas. Spectroscopy was used to characterize the synthesis process for the mechanisms responsible forAlxGa1-xN synthesis and film deposition. The synthesized AlxGa1-xN films were evaluated using field emission scanning electron microscopy, atomic force microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, Raman scattering spectroscopy, transmission electron microscopy and optical transmission measurements. The AlxGa1-xN films are featured with hexagonal wurtzite structure which is degenerated as the Al composition increases and show high optical transparency with the absorption edge blue shifted and the bandgap widened with the Al composition increasing. A comparison of the synthesized AlxGa1-xN films with the binary GaN and AlN films synthesized with similar method reveals their similarity in the structure and the optical properties.
    04/2015; 3(20). DOI:10.1039/C5TC00475F
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    ABSTRACT: Highly optically transparent and electrically conductive Al-doped ZnO (AZO) thin films were deposited by pulsed laser co-ablation of a Zn target and an Al target in an oxygen plasma. Zn ablation resulted in the reactive deposition of ZnO films assisted by the plasma, while Al ablation provided the growing ZnO films with Al dopants. The morphology, composition and structure as well as the optical and electrical properties were characterized and the effects of Al doping and annealing treatment were investigated. The deposited AZO films have a hexagonal wurtzite structure with deteriorated crystal quality which can be improved by annealing. The AZO films are highly transparent from ultraviolet up to 1450 nm and present an obvious blue shift in absorption edge and a widening of band gap compared with undoped ZnO. The electrical properties were also improved after annealing with the resistivity decreasing by over two orders of magnitude because of the increase of free carrier concentration. The variation in the carrier concentration also affects the absorption edge and the band gap of the films as well as the transparency in the infrared region. Meanwhile, this method offers an approach for in-situ doping preparation of other doped compound films with different dopant concentrations.
    Journal of Alloys and Compounds 03/2015; 626:415-420. DOI:10.1016/j.jallcom.2014.11.153 · 3.00 Impact Factor
  • Hui Li · Leilei Guan · Yu Zhao · Zhuoqi Xu · Jian Sun · Jiada Wu · Ning Xu ·
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    ABSTRACT: By the method of pulsed laser deposition accompanied by annealing in N2 environment, single-crystalline NiCx nanorods (NCNRs) were first synthesized on C/Ni-coated quartz substrates. Field emission scanning electron microscopy images show that the densely and uniformly distributed NCNRs were synthesized on quartz substrates at the temperature of 1000-1250 °C and the optimum annealing temperature for their growth is 1200 °C. The results of transmission electron microscopy and selected area electron diffraction show that the grown NCNRs are single-crystalline hexagonal NiCx. The analyses of energy dispersive X-ray spectroscopy reveal that the NCNRs are grown by the Ni-leading vapor-liquid-solid mode. Transmission spectra demonstrate that the as-grown NCNR thin films can have about 98% visible-light transmittance and are candidates for transparent electrodes in thin film solar cells or photoelectric sensors.
    Materials Letters 02/2015; 145. DOI:10.1016/j.matlet.2015.01.120 · 2.49 Impact Factor
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    ABSTRACT: An in-situ doping method for the preparation of Al-doped ZnO (AZO) thin films based on pulsed laser co-ablation of Zn and Al targets with the assistance of an oxygen plasma is reported. The deposited films were characterized for morphological, structural, optical and electrical properties and the effects of post-deposition annealing. The films have a smooth surface, dense structure and well-distributed composition, and show high optical transparency and electrical conductivity. Annealing in 5%H2+95%N2 mixed gas results in the improvement in structural, crystal, optical and electrical properties. Compared with undoped ZnO, the AZO films exhibit a blue shift in absorption edge and an increase of band gap. This method also has potential for preparing AZO and other doped films with different dopant concentrations.
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    ABSTRACT: Single-crystalline Cu7In3/CuIn0.8Ga0.2Se2 (CI/CIGS) core/shell nanowires are fabricated by pulsed laser deposition with Ni nanoparticles as catalyst. The CI/CIGS core/shell nanowires are made up of single-crystalline CI cores surrounded by single-crystalline CIGS shells. The CI/CIGS nanowires are grown at a considerably low temperature (350°C ~ 450°C) by vapor-liquid-solid mode combined with vapor-solid mode. The distribution density of the nanowires increases with the increasing of the deposition duration, and the substrate temperature determines the lengths of the nanowires. The U-V absorption spectra of the CIGS thin films with and without the CI/CIGS core/shell nanowires demonstrate that the CI/CIGS nanowires can remarkably enhance the absorption of CIGS thin films in the spectrum range of 300 to 900 nm. 61.46. + w; 61.41.e; 81.15.Fg; 81.07.b.
    Nanoscale Research Letters 12/2014; 9(1):650. DOI:10.1186/1556-276X-9-650 · 2.78 Impact Factor
  • Hua Cai · Qinghu You · Zhigao Hu · Shuang Guo · Xu Yang · Jian Sun · Ning Xu · Jiada Wu ·
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    ABSTRACT: We present the synthesis of AlxGa1−xN ternary films by pulsed laser co-ablation of a polycrystalline GaAs target and a metallic Al target in the environment of nitrogen plasma which provides nitrogen for the films and assists the formation of nitride films. Field emission scanning electron microscopy exposes the smooth surface appearance and dense film structure. X-ray diffraction, Fourier-transform infrared spectroscopy and Raman scattering spectroscopy reveal the hexagonal wurtzite structure. Optical characterization shows high optical transmittance with an absorption edge of about 260 nm and a band gap of 4.7 eV. Compositional analysis gives the Al content of about 0.6. The structure and optical properties of the AlxGa1−xN films are compared with those of binary GaN and AlN films synthesized by ablating GaAs or Al target with the same nitrogen plasma assistance.
    Journal of Alloys and Compounds 12/2014; 616:137–141. DOI:10.1016/j.jallcom.2014.07.090 · 3.00 Impact Factor
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    ABSTRACT: Single-crystalline g-C3N4 nanocones (g-CNNCs) were successfully synthesized on nickel-covered silicon (100) substrates supported on a graphite frame by a novel plasma sputtering reaction deposition method. The g-CNNCs have the characteristic photoluminescence-peak of g-C3N4 and the longitudinal resistivity belonging to semiconductor, which make them have many potential applications.
    CrystEngComm 11/2014; 17(3). DOI:10.1039/C4CE02091J · 4.03 Impact Factor
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    ABSTRACT: A reactive nitrogen-aluminum plasma generated by electron cyclotron resonance (ECR) microwave discharge of N2 gas and pulsed laser ablation of an Al target is characterized spectroscopically by time-integrated and time-resolved optical emission spectroscopy (OES). The vibrational and rotational temperatures of N2 species are determined by spectral simulation. The generated plasma strongly emits radiation from a variety of excited species including ambient nitrogen and ablated aluminum and exhibits unique features in optical emission and temperature evolution compared with the plasmas generated by a pure ECR discharge or by the expansion of the ablation plume. The working N2 gas is first excited by ECR discharge and the excitation of nitrogen is further enhanced due to the fast expansion of the aluminum plume induced by target ablation, while the excitation of the ablated aluminum is prolonged during the plume expansion in the ECR nitrogen plasma, resulting in the formation of strongly reactive nitrogen-aluminum plasma which contains highly excited species with high vibrational and rotational temperatures. The enhanced intensities and the prolonged duration of the optical emissions of the combined plasma would provide an improved analytical capability for spectrochemical analysis.
    Spectrochimica Acta Part B Atomic Spectroscopy 11/2014; 101. DOI:10.1016/j.sab.2014.09.007 · 3.18 Impact Factor
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    ABSTRACT: Vertically and neatly arranged crystalline graphitic C3N4 (g-C3N4) nanocone arrays were firstly synthesized on nickel-covered silicon (1 0 0) substrates supported on a graphite frame. Synthesis was accomplished using an abnormal glow discharge plasma sputtering reaction deposition method with a feed gas mixture of CH4, N2 and H2. The experimental results show that the morphologies, structures, composition and photoluminescence of the grown nanostructures strongly depend on the CH4/(N2 + H2) ratios (0-1/10). The hexagonal g-C3N4 nanocone arrays were well grown at a CH4/(N2 + H2) ratio of around 1/150 as a result of the hydrogen ion sputtering of the graphite frame to generate a lot of carbon atoms, the hydrogen ion etching on the growing graphite structures, and the reaction between the active nitrogen atoms and the sputtered carbon atoms. The g-C3N4 nanocone arrays have the characteristic photoluminescence-peak of g-C3N4 and very nice wettability to the polymer absorber layers. At the higher or lower CH4/(N2 + H2) ratios, the silicon or diamond nanocone arrays were grown respectively due to the ion-sputtering of the silicon substrate and the inhibition of CHn-radicals on the H+-sputtering of the graphite frame or the mismatch between the sputtered carbon atoms and the dissociated nitrogen atoms.
    Carbon 11/2014; 79(1):578-589. DOI:10.1016/j.carbon.2014.08.019 · 6.20 Impact Factor
  • Yanli Li · Peipei Liang · Xu Yang · Hua Cai · Qinghu You · Jian Sun · Ning Xu · Jiada Wu ·
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    ABSTRACT: Via quasi-solid–liquid–solid growth, large quantities of blue-luminescent Si nanowires were fabricated by annealing a pulsed laser deposited Si film on a Ni layer at 1100 °C in N2. While diffusing to the sample surface at high temperature, the underlying Ni reacts with Si to form Ni-rich silicide which catalyzes the growth of nanowires. Composition analysis and microstructure characterization reveal that the fabricated nanowires have an average diameter of 50 nm and are composed of crystalline Si core of several nanometers and amorphous oxide sheath. Intense and stable luminescence in the spectral region from ultraviolet to blue is observed at room temperature under light excitation.
    Materials Letters 11/2014; 134:5–8. DOI:10.1016/j.matlet.2014.07.015 · 2.49 Impact Factor
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    ABSTRACT: The effects on the photoluminescence (PL) from Si nanocrystals embedded in a SiO2 matrix (Si-NCs/SiO2) by annealing in air have been examined, and the correlation between the PL properties and the passivation of luminescence-quenching defects at the Si nanocrystal/SiO2 interface has been studied. Si-NCs/SiO2 were fabricated by annealing amorphous silicon suboxide (a-SiOx) in a N2 atmosphere at 1100 °C and the passivation of Si-NCs/SiO2 was performed by annealing Si-NCs/SiO2 in air at temperatures ranging from 400 to 800 °C for varied times. The heating of Si-NCs/SiO2 in air is very effective for passivating dangling bonds and an enhancement about 5 times in PL intensity was obtained. High-temperature passivation in air is accompanied by oxidation of Si nanocrystals. Additional N2-treatment of the passivated Si-NCs/SiO2 at elevated temperatures depassivates Si-NCs/SiO2, generating new dangling bonds which can also be passivated in the subsequent repassivation process. The effect of passivation on the PL intensity is reversible, while high-temperature passivation results in an irreversible blue shift of PL spectra. PL decay time can be indicative of passivating or generating of dangling bonds.
    Applied Surface Science 11/2014; 320:804-809. DOI:10.1016/j.apsusc.2014.09.123 · 2.71 Impact Factor
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    ABSTRACT: Evenly separated crystalline CuIn0.8Ga0.2Se2 (CIGS) nanoparticles are deposited on ITO-glass substrate by pulsed laser deposition. Such CIGS layers are introduced between conjugated polymer layers and ITO-glass substrates for enhancing light absorbance of polymer solar cells. The P3HT:PCBM absorbance between 300 and 650 nm is enhanced obviously due to the introduction of CIGS nanoparticles. The current density-voltage curves of a P3HT:PCBM/CIGS solar cell demonstrate that the short-circuit current density is improved from 0.77 to 1.20 mA/cm2. The photoluminescence spectra show that the excitons in the polymer are obviously quenched, suggesting that the charge transfer between the P3HT:PCBM and CIGS occurred. The results reveal that the CIGS nanoparticles may exhibit the localized surface plasmon resonance effect just as metallic nanostructures. PACS 61.46. + w; 61.41.e; 81.15.Fg; 81.07.b
    Nanoscale Research Letters 06/2014; 9(1):308. DOI:10.1186/1556-276X-9-308 · 2.78 Impact Factor
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    ABSTRACT: Si nanocrystals embedded in SiO2 (Si-NCs/SiO2) with efficient light emission were prepared by N2-annealing of amorphous SiOx (a-SiOx) and subsequent H2-passivation, and the effects of passivation on the photoluminescence (PL) from Si-NCs/SiO2 were studied. The H2-passivation was performed in a mixed gas of 5% H2 + 95% N2 at temperatures ranging from 400 to 700 °C for varied times, which is effective for passivating dangling bonds and enhancing luminescence. The PL intensity increases with passivation time, shortly followed by a saturation that depends on the passivation temperature. The H2-passivation also results in a red shift of PL spectra. The effects of H2-passivation show nearly complete reversibility as revealed by the emitted luminescence. Subsequent heating of the passivated samples in N2 has an effect of depassivation which regenerates dangling bonds and the regenerated dangling bonds can also be passivated. Si-NCs/SiO2 are found to exhibit stable behaviors in passivation and depassivation processes after three cycles of passivation and depassivation treatments.
    Applied Surface Science 05/2014; 300:178–183. DOI:10.1016/j.apsusc.2014.02.047 · 2.71 Impact Factor
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    ABSTRACT: Heterogenous nanostructures shaped with CdS covered ZnO (ZnO/CdS) core/shell nanorods (NRs) are fabricated on indium-tin-oxide by pulsed laser deposition of CdS on hydrothermally grown ZnO NRs and characterized through morphology examination, structure characterization, photoluminescence and optical absorption measurements. Both the ZnO cores and the CdS shells are hexagonal wurtzite in structure. Compared with bare ZnO NRs, the fabricated ZnO/CdS core/shell NRs present an extended photo-response and have optical properties corresponding to the two excitonic band-gaps of ZnO and CdS as well as the effective band-gap formed between the conduction band minimum of ZnO and the valence band maximum of CdS.
    Optics Express 04/2014; 22(7):8617-23. DOI:10.1364/OE.22.008617 · 3.49 Impact Factor

Publication Stats

307 Citations
158.07 Total Impact Points


  • 1996-2015
    • Fudan University
      • • Department of Optical Science and Engineering
      • • Department of Physics
      Shanghai, Shanghai Shi, China
  • 2003
    • Chungnam National University
      • Department of Chemistry
      Sŏngnam, Gyeonggi Province, South Korea