Chang-Feng Yu

Origin of ferromagnetism in nitrogen embedded ZnO?:?N thin films

Nitrogen embedded ZnO : N films prepared by pulsed laser deposition exhibit significant ferromagnetism. The presence of nitrogen ions contained in ZnO is confirmed by the secondary ion microscopic spectrum and by Raman experiments, and the embedded nitrogen ions can be regarded as defects. According to the experimental results, a mechanism is proposed based on one of the electrons in the completely filled d-orbits of Zn that compensates the dangling bonds of nitrogen ions and leads to a net spin of one-half in the Zn orbits. These one-half spins strongly correlate with localized electrons that are captured by defects to form ferromagnetism. Eventually, the magnetism of nitrogen embedded ZnO : N films could be described by a bound magnetic polaron model.

Influence of the substrate temperature on the electrical and magnetic properties of ZnO : N thin films grown by pulse laser deposition

We investigated the effect of the substrate temperature on the magnetic, electrical and optical properties of nitrogen-doped ZnO thin films. Experiments showed that a high substrate temperature depresses the deposition rate and produces much thinner films displaying more robust ferromagnetism. In addition, the resistivity decreased as the substrate temperature increased and all of the nitrogen-doped films, at different substrate temperatures, had larger gaps than the pure ZnO film.

UV-assisted deposition of ZnO nanorods

An enhanced preferred crystalline orientation in ZnO nanorods is achieved by applying ultraviolet (UV) illumination during sample deposition. The crystal field, generated from internal charge transfer between different energy bands by carrier excitations, drives crystalline growth in a preferred orientation. This work applies a novel crystalline engineering model, such that the preferred crystalline orientation in sample growth can be controlled by exciting carriers between assigned bands, which match the direction of crystal momentum between assigned bands via UV illumination.

Dependence of local structural and electrical properties of nitride doped zinc oxide films on growth temperature

Conducting atomic force microscopy was utilized to study the nanoscale surface electrical properties of N-doped zinc oxide films that had been prepared by pulsed laser deposition at different substrate temperatures. Current-voltage measurements were made while the conducting tip was fixed at different contact current points after scanning for normal imaging. Experimental results indicated that changes in the substrate temperature caused the redistribution of n-type carrier (Ohmic contact) and p-type carrier (Schottky contact) regions on the surface. Such a microscopic measurement method can be adopted to observe precisely the variances in the local carriers on the surface of films, benefiting future studies of nanoscale p-n homojunctions.

Mechanism of ferromagnetism in non-magnetic ion-doped zinc oxides

Zinc oxide (ZnO) that contains non-magnetic ionic dopants, such as nitrogen (N)-doped zinc oxide (ZnO:N), has been observed to exhibit ferromagnetism. Ferromagnetism is proposed to arise from the Coulomb excitation in the localized states that is induced by the oxygen vacancy, V O. A model based on the Coulomb excitation that is associated with the electron–phonon interaction theoretically explains the ferromagnetic mechanism of ZnO:N. This study reveals that the ferromagnetism will be induced by either deep localized states with a small V O concentration or shallow localized states with a high V O concentration. Additionally, electron–phonon coupling either suppresses the ferromagnetism that is induced by the deep donor states of V O or enhances the ferromagnetism that is induced by the shallow donor states of V O.