H. G. Duan

Co-doped anatase TiO2 nanofibers fabricated by electrospinning

Co-doped TiO2 nanofibers with an average diameter of ∼70nm were fabricated with electrospinning method. X-ray diffraction measurements show that the nanofibers possess pure anatase structure. The obtained nanofibers exhibit evident room temperature ferromagnetism through magnetic measurement. The photoluminescence of the Co-doped TiO2 nanofibers is composed of two emission bands attributed to self-trapped excitons and oxygen vacancies, different from that of pure TiO2 nanofibers which only includes emission due to self-trapped excitons. Photoluminescence intensity due to oxygen vacancies vary with annealing atmosphere and Co concentration, and the ferromagnetic moment increases with the increment of oxygen vacancies.

Turning electrospun poly(methyl methacrylate) nanofibers into graphitic nanostructures by in situ electron beam irradiation

Using ultrathin electrospun poly(methyl methacrylate) (PMMA) nanofibers as precursor, graphitic nanofibers, nanobridges, nanocones, and fullerenelike onions could be prepared by electron beam irradiation in a controlled manner. With the help of the high resolution transmission electron microscopy, the real time processing of the carbonization and graphitization of the PMMA nanofibers could be investigated. This way to obtain graphitic nanostructures has promising applications in graphitic carbon nanostructure electronics and devices. Because PMMA is a widely used standard high resolution electron resist, this graphitization could be combined with electron beam lithography to obtain high resolution patterned graphitic circuits.

Study on Field Emission from Hafnium Oxynitride Prepared by DC Sputtering

Hafnium oxynitride films were prepared by direct current sputtering with subsequently annealed in atmosphere air. Their field emission characteristics were investigated. Low turn-on field, high field emission current density, and very good field emission stability were showed, which can be attributed to their electrically nanostructured heterogeneous frame in the hafnium oxynitride. High voltage activation played a critical role in improving the field emission of HfOxNy which was thought that the chemical structure and the surface character of the samples were changed when at high voltage. The field emission mechanism for HfOxNy accords very well with the classical Fowler-Nordheim tunneling theory.

Field emission from gadolinium silicide prepared by ion implantation with electron beam annealing

A silicon-based field emission cathode, the rare earth silicide GdSi2 was prepared by implanting Gd ions into silicon using a metal vapor vacuum arc ion source and subsequently annealed by electron beam. For as-implanted samples, turn-on field was about 21V∕μm at a current density of 1μA∕cm2 and a field emission current density of 1mA∕cm2 was reached at an applied field of 34V∕μm. After annealing, the turn-on field could be as low as 9V∕μm and the current density of 1mA∕cm2 can be reached at an applied field of 14V∕μm. X-ray diffraction with x-ray photoelectron spectroscopy analyses and atomic force microscopy were used to characterize microstructure changes of the samples. The results showed that these excellent field emission characteristics were attributed to the GdSi2 compounds formed in the samples. The field emission mechanism was discussed in terms of Fowler-Nordheim (FN) theory. It was found that FN plots could be divided into two segments obviously, and this was perhaps because of the thermal eff...