The features of the Raman spectra of Co 3 O 4 30-nm nanoparticles depend strongly on their agglomeration state. When measured at low incident laser power, the spectrum of isolated nanoparticles corresponds to that found in bulk materials, whereas the agglomerated nanoparticles present a clear red-shift and broadening of the Raman bands. On the other hand, when measured at even lower power, both agglomerated and isolated nanoparticles show the same spectrum of microscopic particles. These effects have been studied by variations of the 532-nm laser power and the environmental temperature. The thermal dependence of Raman spectra of agglomerated nanoparticles is different to that of isolated nanoparticles but is comparable to the one of bulk material. The different behaviour of the nanoparticles at different agglomeration state is associated to the transmission of phonons among the particles. On the other hand, an increase of the laser power causes a larger number of acoustic phonons, producing a variation of the vibration anharmonicity of the nanoparticles. This increase is more pronounced in the agglomerated nanoparticles, due to the transmission of phonons, causing a much intense modification of the Raman spectrum produced by the laser power. These results clearly indicate that the agglomeration state of the nanoparticles affects their Raman properties. Figure 2. MicroRaman spectroscopy of Co 3 O 4 microparticles, Co 3 O 4 nanoparticles, Co 3 O 4 dispersed nanoparticles, AlCo1 at a power laser excitation of a) 0.3 mW and b) minimun power laser to acquire the Raman spectra. Al 2 O 3 used as substrate is marked by squares.

We report the existence of magnetic order at room temperature in Li-doped ZnO microwires after low energy H+ implantation. The microwires with diameters between 0.3 and 10 μm were prepared by a carbothermal process. We combine spectroscopy techniques to elucidate the influence of the electronic structure and local environment of Zn, O, and Li and their vacancies on the magnetic response. Ferromagnetism at room temperature is obtained only after implanting H+ in Li-doped ZnO. The overall results indicate that low-energy proton implantation is an effective method to produce the necessary amount of stable Zn vacancies near the Li ions to trigger the magnetic order.

The origin of room temperature ferromagnetic like behavior (RT-FM) in ZnO-based diluted magnetic semiconductors (DMS) is still an unclear question. The present work concentrates on the appearance of Room temperature magnetic moments in just mixed ZnO/Co 3 O 4 mixtures without thermal treatment. In this study is shown that the magnetism seems to be related to surface reduction of the Co 3 O 4 nanoparticles. In which, an antiferromagnetic Co 3 O 4 nanoparticle (core) is surrounded by CoO-like shell. This singular superficial magnetism has also been found in others mixtures with semiconductors like TiO 2 and insulators like Al 2 O 3 .

A careful and wide comparison between Al and Ga as substitutional dopants in the ZnO wurtzite structure is presented. Both cations behave as n-type dopants and their inclusion improves the optical and electrical properties of the ZnO matrix, making it more transparent in the visible range and rising up its electrical conductivity. However, the same dopant/Zn ratio leads to a very different doping efficiency when comparing Al and Ga, being the Ga cation a more effective dopant of the ZnO film. The measured differences between Al-and Ga-doped films are explained with the hypothesis that different quantities of these dopant cations are able to enter substitutionally in the ZnO matrix. Ga cations seem to behave as perfect substitutional dopants, while Al cation might occupy either substitutional or interstitial sites. Moreover, the subsequent charge balance after doping appear to be related with the formation of different intrinsic defects that depends on the dopant cation. The knowledge of the doped-ZnO films microstructure is a crucial step to optimize the deposition of transparent conducting electrodes for solar cells, displays, and other photoelectronic devices. V