Dapeng Dong

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 1 nm. 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.

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.

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.

Synthesis of hexagonal ZnO microdisk on InN substrate by aqueous method and its optical properties

Hexagonal ZnO microdisks were obtained by using InN/sapphire as substrate via the aqueous method. The growth mechanism of the ZnO microdisks was proposed and demonstrated. Moreover, the optical properties of the ZnO microdisks were investigated by micro-photoluminescence, whispering gallery mode (WGM) lasing from the microdisk was observed at moderate excitation density. It will provide a new way to design microlasers by using low temperature method.

Investigate on Structure and Optical Properties of ZnO Nanostructures Grown on a-GaN/r-Sapphire

ZnO nanostructures were directly grown on a-GaN/r-sapphire with different growth time via aqueous method. Structural and optical properties of the nanostructures were investigated by using a variety of techniques including X-ray diffraction (XRD), scan electron microscope (SEM), room-temperature photoluminescence (PL), and Raman scattering. The results showed the growth mechanism of ZnO nanostructures grown on a-GaN is Volmer-Weber (VW) mode, which is due to the high interfacial free-energy between a-plane ZnO and GaN. Meanwhile, compressive strains were revealed to exist by the optical characterizations. And the strengths were found to reduce with increasing growth time.