E.Q. Xie

Preparation and characterisation of ultrafine and uniform TiO2 nanofibres

Abstract Ultrafine and uniform TiO2 nanofibres were prepared by electrospinning. The morphology of the nanofibres was characterised by field emission scanning electron microscopy, which showed that the nanofibres were composed of ultrasmall nanoparticles. The structure was characterised by X-ray diffraction and resonant Raman spectrum. The optical properties of the nanofibres were characterised by photoluminescence spectrum and ultraviolet visible spectrum. The results showed that anatase phase of TiO2 formed with the nanofibres annealed at 450°C for 3 h and showed good optical characteristics.

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.

The irradiation studies on diamond-like carbon films

Abstract Diamond-like carbon (DLC) films have been deposited on glass substrates using radio-frequency (r.f.) plasma deposition method. γ-ray, ultraviolet (UV) ray and neutron beam were used to irradiate the DLC films. Raman spectroscopy and infrared (IR) spectroscopy were used to characterize the changing characteristics of SP3C–H bond and hydrogen content in the films due to the irradiations. It showed that, the damage degrees of the γ-ray, UV ray and neutron beam on the SP3C–H bonds are different. Among them, the damage of γ-ray on the SP3C–H bond is the weakest. When the irradiation dose of γ-ray reaches 10×104 Gy, the SP3C–H bond reduces about 50% in number. The square resistance of the films is reduced due to the irradiation of UV ray and this is caused by severe oxidation of the films. Compared with that of the as-deposited one, the IR transmittance of the films irradiated by both γ-ray and neutron beam is increased to some extent. By using the results on optical gap of the films and the fully constrained network theory, the hydrogen content in the as-deposited films is estimated to be 10–25 at.%.

Irradiation effect of swift heavy ions on C60 films

In this paper we present experimental results on irradiation effects of C-60 films induced by 2.0 GeV Xe-136 ions, delivered by HIRFL at Lanzhou of China. The irradiated C-60 films were analyzed by means of Fourier transform infrared, Raman scattering and X-ray diffraction spectroscopies. The analysis results indicated that electronic energy transfer dominates the damage process of C-60 films. The partial recovery of the damage in irradiated C-60 films at certain electronic energy loss is attributed to an annealing effect of strong electronic excitation. The ion velocity also plays a role in the process of the damage creation

Preparation and optical properties of GaN nanocrystalline powders

Abstract GaN nanocrystalline powders were synthesised by decomposition of gallium nitrate, followed by nitrogenising with ammonia under different temperature. X-ray diffraction (XRD) and the transmission electron microscopy (TEM) indicated that the crystallinity of the powder is improved and the average size of the GaN nanocrystallites increases from 4·8 to 23·9 nm as the temperature increases from 850 to 1050°C. The Raman spectra displayed four broadened peaks corresponding to A1 (LO), A1 (TO), E1 (TO) and E2 (high) modes of würtzite GaN respectively. Two additional modes at 252 and 421 cm–1 attributed to boundary phonons activated by the finite size effects and octahedral Ga–N6 bonds were observed respectively. A strong blue photoluminescence (∼353 nm) was detected for room temperature measurement, indicating that the GaN nanocrystalline powders have few defects and high quality.

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...