J. G. Tao

Density functional study on ferromagnetism in nitrogen-doped anatase TiO2

We report first principles calculations on the magnetism and electronic structures for nitrogen-doped anatase TiO2 (N:TiO2). Our calculations indicate that magnetic state is the ground state for N:TiO2 systems. An isolated N atom produces a total magnetic moment of 1.00μB and introduces spin-polarized 2p states in the band gap. The origin of the magnetic moments is the holes in N 2p π band of the N dopant. Several doping configurations studied suggest the existence of ferromagnetic coupling between N dopants. The ferromagnetism in N:TiO2 can be attributed to the hole-mediated double exchange through the strong p-p interaction between N and O.

First-principles study on ferromagnetism in nitrogen-doped In2O3

We report stable room temperature ferromagnetism in nitrogen doped In2O3 (N–In2O3) based on density functional theory. Our investigation on the electronic and magnetic properties of N–In2O3 suggests that N dopant introduces spin-polarized hole states in the band gap generating a total magnetic moment of 1.0μB per N, which is mainly localized on the doped N atoms. The ferromagnetic interaction in N–In2O3 system is mainly driven by the occurrence of coupling chains between a first N (N1)-2p to a second N (N2)-2p via a bridging In 5p and 4d orbitals.

Morphology-controlled synthesis and a comparative study of the physical properties of SnO2 nanostructures: from ultrathin nanowires to ultrawide nanobelts.

Controlled synthesis of one-dimensional materials, such as nanowires and nanobelts, is of vital importance for achieving the desired properties and fabricating functional devices. We report a systematic investigation of the vapor transport growth of one-dimensional SnO(2) nanostructures, aiming to achieve precise morphology control. SnO(2) nanowires are obtained when SnO(2) mixed with graphite is used as the source material; adding TiO(2) into the source reliably leads to the formation of nanobelts. Ti-induced modification of crystal surface energy is proposed to be the origin of the morphology change. In addition, control of the lateral dimensions of both SnO(2) nanowires (from approximately 15 to approximately 115 nm in diameter) and nanobelts (from approximately 30 nm to approximately 2 microm in width) is achieved by adjusting the growth conditions. The physical properties of SnO(2) nanowires and nanobelts are further characterized and compared using room temperature photoluminescence, resonant Raman scattering, and field emission measurements.

Nonconventional magnetism in pristine and alkali doped In2O3: density functional study

Using In2O3 as a host matrix, extensive calculations based on density functional theory have been carried out to understand the electronic and magnetic properties of native defects, alkali and alkaline-earth metal substitutions as disputed in recent theoretical and experimental studies. Our calculations show that the magnetism in undoped In2O3 is originated from In vacancies (VIn) instead of O vacancies. The ferromagnetic (FM) coupling between the moments introduced by VIn is found strong enough to achieve room temperature ferromagnetism. Moreover, FM coupling is also strongly favored in alkali metal doping cases with negative formation energy. For all XIn (XIn=VIn, LiIn, NaIn, and KIn) doped In2O3, the induced magnetic moments are mainly localized on the first shell of O atoms around XIn sites. The FM coupling between the moments induced by XIn defects is activated by intra- and intercorrelation of the XIn–6ONN complexes. A XIn–ONN–InNN–ONN–XIn chain is required to mediate the long-range FM coupling. How...

Evolution of the 2p satellite of Ni nano-clusters on TiO2(001) surfaces

Correlation enhancement of electrons in Ni nano-clusters due to confinement in reduced dimensions has been observed. Both the size and shape of the nano-clusters have a strong influence on the Ni 2p satellite structures. For small Ni clusters, apart from the 6 eV satellite, a 3 eV satellite structure emerges in Ni 2p3/2 photoemission spectra due to the existence of the 3F atomic state. However, the intensity of the 3 eV satellite decreases with increasing cluster size because the Ni 3d level becomes increasingly occupied in large clusters. The increased electron population in the 3d level is achieved through electron transfer from the free-electron-like 4sp states to the unhybridized pure 3d spin down states; the latter is lower in energy than the 3d–4sp hybridized states. The correlation-induced 6 eV satellite energy is enhanced by Ar+ bombardment. These observations make it feasible to gauge the Ni 3d electron population by probing the 2p photoemission spectra and to modify the supported Ni nano-clusters through thermal treatment and/or ion bombardment.

Doping Cu into ZnO nanostructures

Controlled doping appropriate elements into semiconductor nanostructures is of vital importance to develop novel materials and functional devices. Herein, we present three methods to synthesize Cu-doped ZnO nanostructures using a simple vapor phase transport process and adopting CuCl2, CuO or Cu as doping precursors. The corresponding morphology, structure, and chemical composition were investigated using field emission scanning electron microscope, transmission electron microscope, X-ray diffraction and X-ray photoelectron spectroscopy. We show that these three methods produce nanostructures with different morphologies and doping levels. This work paves the way for investigating the physical properties of Cu-doped ZnO nanostructures and furthermore facilitates the synthesis of other transition-metal-doped nanomaterials.