Characterization of n-type and p-type semiconductor gas sensors based on NiOx doped TiO2 thin films

Using the full-potential linearized augmented plane wave method, we have investigated the oxygen vacancy defect induced ferromagnetism in both rutile and anatase TiO2. It has been found that the oxygen vacancy induces lattice distortion in rutile TiO2, whereas there is no such meaningful change in the anatase structure. Interestingly, the lattice distorted rutile TiO2 shows an oxygen vacancy induced ferromagnetic state with a magnetic moment of 0.22 µB in the Ti atom neighboring the vacancy site, while only 0.06 µB is observed in the Ti atom in anatase TiO2. We attribute the sizable magnetic moment due to the oxygen vacancy in rutile TiO2 to the charge redistribution owing to lattice distortion. Experimentally measured magnetic hysteresis curves for undoped rutile and anatase TiO2 films clearly display ferromagnetic behavior at room temperature. The observed magnetic strength of the rutile sample turns out to be larger than that of the anatase sample, in accordance with the theoretical calculations.

http://iopscience.iop.org/article/10.1088/0953-8984/21/19/195405/pdf

The origin of oxygen vacancy induced ferromagnetism in undoped TiO(2).

Raman spectra, photoluminescence and ferromagnetism of pure, Co and Fe doped SnO2 nanoparticles

Cobalt doped zinc oxide nanoparticles (NPs) and nanorods (NRs) were synthesized by a simple chemical method. An increase in the formation of nanorods with an increase in cobalt doping is found to occur from scanning electron microscopy and transmission electron microscopy studies. Powder X-ray diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction confirm the formation of a wurtzite crystal structure of ZnO. Shifting and broadening of the bands at 437 cm−1 and 579 cm−1 in the micro-Raman study of Co-doped ZnO nanostructures indicates the incorporation of Co in ZnO. Shifting of the absorption edge to lower wavelength and blue shift of the band gap is observed in UV-visible spectra of Co-doped ZnO samples. Field-dependent magnetization measurements exhibit diamagnetic behavior down to 2 K in the case of ZnO whereas Co-doped ZnO samples show coexistence of superparamagnetic and ferromagnetic behavior at room temperature and at 2 K. The observed ferromagnetism may have originated due to the exchange interaction between the localized d electrons in Co2+ atoms and free carriers generated due to Co-doping as well as due to cobalt clustering in the Co-doped samples.

/pdf/study-of-structural-optical-and-magnetic-properties-of-1fxptqrmee.pdf

Study of structural, optical and magnetic properties of cobalt doped ZnO nanorods

A route for the synthesis of Cu-doped TiO2 nanoparticles with a very low band gap

Room-temperature ferromagnetism in Cu-doped TiO2 thin films

Oxygen vacancy enhanced the room temperature ferromagnetism in Ni-doped TiO2 thin films

We report here the observation of significant room-temperature ferromagnetism in a semiconductor doped with nonmagnetic impurities, Cu-doped rutile TiO2 thin films grown by reactive magnetron sputtering. Films annealed in air were nonmagnetic while those annealed in vacuum were ferromagnetic with a Curie temperature about 350 K. The magnetic moment per copper atom decreased as the copper concentration increased. These results show that both the oxygen vacancies and the distance between nearest-neighbor copper atoms play a crucial role for the appearance of magnetism.

http://iopscience.iop.org/article/10.1209/0295-5075/78/67001/pdf

Impurity concentration study on ferromagnetism in Cu-doped TiO2 thin films

A series of nitrogen-doped Zn0.93Co0.07O thin films grown on glass substrates were prepared by magnetron sputtering, which have shown ferromagnetic property at room temperature. The largest moment of about 4.92 μB/Co and Curie temperature (Tc) of about 300 K were observed for Zn0.93Co0.07O thin film. P-type Co-doped ZnO thin films with room temperature ferromagnetism were obtained. We demonstrated a clear correlation between nitrogen and transition temperature and an inverse correlation between nitrogen and magnetization per Co ion.

Room Temperature Ferromagnetism in (n, Co)-CODOPED ZnO Thin Films

Twisted graphene multi-layers have been recently demonstrated to share several correlation-driven behaviours with twisted bilayer graphene. In general, the van Hove singularities (VHSs) can be used as a proxy of the tendency for correlated behaviours. In this paper, we adopt an atomistic method by combining tight-binding method with the semi-classical molecular dynamics to investigate the electronic structures of twisted trilayer graphene (TTG) with two independent twist angles. The two independent twist angles can lead to the interference of the moir´e patterns forming a variety of commensurate/incommensurate complex supermoir´e patterns. In particular, the lattice relaxation, twist angle and angle disorder eﬀects on the VHS are discussed. We ﬁnd that the lattice relaxation signiﬁcantly inﬂuence the position and magnitude of the VHSs. In the supermoir´e TTG, the moir´e interference provides constructive or destructive eﬀects depending on the relative twist angle. By modulating the two independent twist angles, novel superstructures, for instance, the Kagome-like lattice, could constructed via the moir´e pattern. Moreover, we demonstrate that a slight change in twist angles (angle disorder) provides a signiﬁcant suppression of the peak of the VHSs. Apart from the moir´e length, the evolution of the VHSs and the LDOS mapping in real space could be used to identify the twist angles in the complicated TTG. In practice, our work could provide a guide for exploring the ﬂat band behaviours in the supermoir´e TTG experimentally.

Hai Juan Meng

Papers

Room-temperature ferromagnetism in Cu-doped TiO2 thin films

Oxygen vacancy enhanced the room temperature ferromagnetism in Ni-doped TiO2 thin films

Impurity concentration study on ferromagnetism in Cu-doped TiO2 thin films

Room Temperature Ferromagnetism in (n, Co)-CODOPED ZnO Thin Films

Commensurate and incommensurate double moiré interference in twisted trilayer graphene