Sub-ppm NO2 sensors based on nanosized thin films of Titanium-Tungsten oxides

We describe the preparation of thin films of Ti---WO3 obtained by means of r.f. sputtering deposition followed by a thermal oxidation. The sensing characteristics of these thin films were obtained by measuring the response towards NO2 in the interval 0.5–20 ppm and to other interfering gases like ethyl alcohol, CH4 and CO; the influence of water vapour to the response towards NO2 was also investigated. The material seems to be a promising detector of NO2for environmental monitoring

Local Electronic Properties and Magnetism of (Cd,Mn)Te Quantum Wells

The electronic properties of heterostructures containing (Cd,Mn)Te quantum wells are probed by soft x-ray spectroscopies. We provide experimental evidence that Mn ions are in the Mn2+ (3d5) electronic configuration, and rule out the possibility that charge transfer and crystal field effects can reduce the magnetic moment of each Mn ion to the value (0.61) extracted from the fitting of the magnetization curve with a Brillouin function. These results confirm that the observed magnetic behavior can be correctly explained by assuming an antiferromagnetic coupling between nearest-neighbor S = 5/2 Mn2+ ions, rather than a paramagnetic response from an ensemble of low-spin Mn ions

Magnetic order in TM-doped TiO2 single crystals.

Needle shaped single crystals of TM-doped rutile TiO2 (TM = Cr, Mn, Fe, Co, Ni, Cu), grown in a sodium tetraborate melt with the flux method, are analysed in their structural and optical properties with a multi-technique approach. The ferromagnetic behaviour, observed up to room temperature, overlapping the prevailing expected paramagnetism, is investigated by means of static magnetization measurements performed at different temperatures and magnetic field

Magnetic polaron percolation on a rutile lattice: A geometrical exploration in the limit of low density of magnetic impurities

The evolution of magnetic polaron clusters on a rutile lattice has been explored, and the results are used to discuss the origin of ferromagnetism in transition-metal (TM)-doped rutile TiO2 oxides. It is shown that percolation on a rutile lattice is characterized by a threshold different from that found for the percolation of randomly distributed spheres, which has been so far assumed as a model to treat the percolation of magnetic polarons in diluted magnetic semiconductors. Furthermore, unlike previous investigations, we explicitly considered the condition of small density n(i) of TM impurities, i.e., a regime that is quite far from that usually regarded for polaron formation, dominated by a high density n(i) of TM ions. Assuming that ferromagnetic coupling arises between polarons that share common TM impurities, we show the effect of this constraint on the magnetic properties of the sample compared to those reported for the ni n(i)>> n(h) regime