Dongping Liu

An Atmospheric-Pressure Large-Area Diffuse Surface Dielectric Barrier Discharge Used for Disinfection Application

A large-area diffuse surface dielectric barrier discharge (SDBD) produced using ambient air at atmospheric pressure is investigated with respect to its electrical and optical characteristics. Current-voltage measurements and intensified charge coupled device images show that the multiple-groove SDBD device is able to generate a kind of visible large-area diffuse discharge at the applied voltage more than 22 kV with the repetition frequency of 9 kHz, which is associated with the accumulation of electric charges. Moreover, the multiple-groove SDBD is also found to be very efficient in the inactivation of Escherichia coli and Candida albicans on the surface of chopsticks. It is found that the electrostatic tensile generated by accumulated charges may play a key role on the cell inactivation.

AC driven magnetic domain quantification with 5 nm resolution.

As the magnetic storage density increases in commercial products, e.g. the hard disc drives, a full understanding of dynamic magnetism in nanometer resolution underpins the development of next-generation products. Magnetic force microscopy (MFM) is well suited to exploring ferromagnetic domain structures. However, atomic resolution cannot be achieved because data acquisition involves the sensing of long-range magnetostatic forces between tip and sample. Moreover, the dynamic magnetism cannot be characterized because MFM is only sensitive to the static magnetic fields. Here, we develop a side-band magnetic force microscopy (MFM) to locally observe the alternating magnetic fields in nanometer length scales at an operating distance of 1u2005nm. Variations in alternating magnetic fields and their relating time-variable magnetic domain reversals have been demonstrated by the side-band MFM. The magnetic domain wall motions, relating to the periodical rotation of sample magnetization, are quantified via micromagnetics. Based on the side-band MFM, the magnetic moment can be determined locally in a volume as small as 5 nanometers. The present technique can be applied to investigate the microscopic magnetic domain structures in a variety of magnetic materials, and allows a wide range of future applications, for example, in data storage and biomedicine.

Direct observation of magnetic vortex behavior in an ordered La0.7Sr0.3MnO3 dot arrays

Directly observing the magnetic domain behavior in patterned nanostructures is crucial to the investigation into advanced spin-based devices. Herein, we show that the magnetic vortex behavior can be deterministically observed and controlled in highly spin polarized La0.7Sr0.3MnO3 (LSMO) triangular dots by successive in-field magnetic force microscopy (MFM). Imaging the magnetic domains with MFM shows that most of the LSMO dots exhibit magnetic vortex states with a clockwise or anticlockwise pinwheel structure for decreasing the demagnetization energy. Probing the vortex chirality using in-field MFM indicates that the selective spin circulation of the triangular dots depends on the magnetic orientation of the bias nanomagnet with specially designed geometries. Comparison between measurement and simulation reveals that the vortex behavior should be governed by an interface involved pinning strength at the boundaries, as well as a geometrically induced shape anisotropy of the triangular dot, both of which result in shape-dominated magnetic domain reversals.

Postsynthetic modification of single Pd sites into uncoordinated polypyridine groups of a MOF as the highly efficient catalyst for Heck and Suzuki reactions

A novel holmium(III) metal–organic framework (Ho-MOF), namely, [Ho(2-TriPP-COO)3] (2) has been hydrothermally obtained using 4′-(4-carboxyphenyl)-2,2′:6′,2′′-terpyridine (2-TriPP-COOH) and Ho(NO3)3·5H2O, and it is structurally characterized by single-crystal XRD, powder XRD as well as elemental analysis. The postsynthetic modification of Ho-MOF is based on the utilization of a strong coordination effect between Pd2+ ions and free polypyridine groups in the skeleton of Ho-MOF, which play a critical role to access the highly efficient Pd-HoMOF catalyst. Also, Pd-HoMOF exhibits very high activity in Heck and Suzuki–Miyaura cross-coupling reactions. Moreover, the MOF catalyst displays good thermal stability (up to 400 °C), and it can be recovered and reused for five reaction cycles. The bridging between the MOF structure and homogeneous molecular Pd catalyst represents a good example in designing highly efficient catalysts for various fine chemical transformations.

Photoluminescence changes of C70 nano/submicro-crystals induced by high pressure and high temperature

Hollow C70 nano/submicro-crystals with a fcc lattice structure were treated under various high pressure and high temperature conditions. The energy band structure was visibly changed by the high pressure and high temperature treatment, and the luminescence of the treated C70 nano/submicro-crystals were tuned from the visible to the near infrared range. In-situ high pressure experiments at room temperature indicate that pressure plays a key role in the tuning of the band gap and PL properties in C70 nanocrystals, and temperature plays an important role in the formation of stable intermolecular bonds and thus to define the final red-shift of the PL peaks. The polymeric phases of C70 nanocrystals treated at high pressure and high temperature were identified from their Raman spectra, which showed a change from monomers to a dimer-rich phase and finally to a phase containing larger, disordered C70 oligomers.

Generation of large-area and glow-like surface discharge in atmospheric pressure air

A large-area (6u2009cmu2009×u20096u2009cm) air surface dielectric barrier discharge has been generated at atmospheric pressure by using well-aligned and micron-sized dielectric tubes with tungsten wire electrodes. Intensified CCD images with an exposure time of 5u2009ns show that the uniform surface air discharge can be generated during the rising and falling time of pulsed DC voltage. Current and voltage and optical measurements confirm the formation of glow-like air discharges on the surface of micron-sized dielectric tubes. Simulation results indicate that the microelectrode configuration contributes to the formation of strong surface electric field and plays an important role in the generation of uniform surface air discharge.

Syntheses, structures, and magnetic properties of three new cyano-bridged heterobimetallic chains based on [Fe(Tp*)(CN)3]−

With the use of the tailored cyanometalate precursor, Bu4N[Fe(Tp*)(CN)3] (Tp* = hydridotris(3,5-dimethylpyrazol-1yl)borate), as the building block to react with fully solvated MII cations, three new one-dimensional (1D) heterobimetallic cyano-bridged chain complexes of squares, {[Fe(Tp*)(CN)3]2M (CH3CH2OH)2}·4H2O (M = Mn(1), Fe(2), Co(3)), have been prepared. In these compounds, the MII ions have slightly distorted octahedral coordination geometries, and they were bridged by [Fe(Tp*)(CN)3]− to form similar 1D chains of squares. The magnetic studies demonstrated that compound 1 exhibited weak ferromagnetism due to spin canting, compound 2 showed ferrimagnetic behavior in a low temperature region, whereas compound 3 indicated the presence of typical antiferromagnetic coupling.

The effect of target materials on the propagation of atmospheric-pressure plasma jets

The current study is focused on the effect of target materials (quartz plate, copper sheet, and quartz plate with a grounded copper sheet on the back) on the propagation of atmospheric-pressure helium plasma jets. The dynamics of ionization waves (IWs) and the relative amount of reactive oxygen species (OH and O) in the IW front were compared by using spatial and temporal images and relative optical emission spectroscopy. Our measurements show that the targets can significantly affect the propagation and intensity of the IWs. In addition, strong OH emission lines were detected when the IWs impinged upon the damp surface. Numerical simulations have been carried out to explain the experimental observation. The propagation velocity of IWs predicted by the simulation was in good agreement with the experimental results. Simulation results suggest that the density and velocity of IWs mainly depend on the electric field between the high voltage electrode tip and the target. Analysis indicates that the targets co...

Propagation of Brush-Shaped He/O 2 Plasma Plumes in Ambient Air

In this paper, we report on the propagation behavior of the atmospheric-pressure and brush-shaped He/O2 plasma plumes generated by a specially designed plasma device. The measurements show that the frequency of applied voltage (f) and the O2 fraction and flow rate of the feed gas significantly affect the discharge propagation of the atmospheric-pressure plasma plume in ambient air. The uniformity of the brush-shaped plasma plume is greatly improved at a relatively high f or He/O2 flow rate. Addition of a trace amount of O2 into the He gas can also contribute to the formation of uniform and brush-shaped plasma plumes in ambient air. This paper confirms that the plasma device composed of well-aligned and micrometer-thick fibers can be utilized to generate large-scale plasma plumes for potential applications. The propagation of the He/O2 plasma plume in ambient air results from the applied electric field across the small gas spacing of a barrier discharge electrode configuration, where the He atoms are easily ionized or excited for generating the brush-shaped plasma.