Diluted manganese on the bond-centered site in germanium

The functional properties of Mn-doped Ge depend to large extent on the lattice location of the Mn impurities. Here, we present a lattice location study of implanted diluted Mn by means of electron emission channeling. Surprisingly, in addition to the expected substitutional lattice position, a large fraction of the Mn impurities occupies the bond-centered site. Corroborated by ab initio calculations, the bond-centered Mn is related to Mn-vacancy complexes. These unexpected results call for a reassessment of the theoretical studies on the electrical and magnetic behavior of Mn-doped Ge, hereby including the possible role of Mn-vacancy complexes

Formation of ultrathin Ni germanides : solid-phase reaction, morphology and texture

The solid-phase reaction of ultrathin (<= 10 nm) Ni films with different Ge substrates (single-crystalline (100), polycrystalline, and amorphous) was studied. As thickness goes down, thin film texture becomes a dominant factor in both the film's phase formation and morphological evolution. As a consequence, certain metastable microstructures are epitaxially stabilized on crystalline substrates, such as the epsilon-Ni5Ge3 phase or a strained NiGe crystal structure on the single-crystalline substrates. Similarly, the destabilizing effect of axiotaxial texture on the film's morphology becomes more pronounced as film thicknesses become smaller. These effects are contrasted by the evolution of germanide films on amorphous substrates, on which neither epitaxy nor axiotaxy can form, i.e. none of the (de) stabilizing effects of texture are observed. The crystallization of such amorphous substrates however, drives the film breakup

Analytical methods applied to diverse types of Brazilian propolis

Propolis is a bee product, composed mainly of plant resins and beeswax, therefore its chemical composition varies due to the geographic and plant origins of these resins, as well as the species of bee. Brazil is an important supplier of propolis on the world market and, although green colored propolis from the southeast is the most known and studied, several other types of propolis from Apis mellifera and native stingless bees (also called cerumen) can be found. Propolis is usually consumed as an extract, so the type of solvent and extractive procedures employed further affect its composition. Methods used for the extraction; analysis the percentage of resins, wax and insoluble material in crude propolis; determination of phenolic, flavonoid, amino acid and heavy metal contents are reviewed herein. Different chromatographic methods applied to the separation, identification and quantification of Brazilian propolis components and their relative strengths are discussed; as well as direct insertion mass spectrometry fingerprinting

Searching Room Temperature Ferromagnetism in Wide Gap Semiconductors: Fe-doped Strontium Titanate and Zinc Oxide

Scientific findings in the very beginning of the millennium are taking us a step further in the new paradigm of technology: spintronics. Upgrading charge-based electronics with the additional degree of freedom of the carriers spin-state, spintronics opens a path to the birth of a new generation of devices with the potential advantages of non-volatility and higher processing speed, integration densities and power efficiency. A decisive step towards this new age lies on the attribution of magnetic properties to semiconductors, the building block of today's electronics, that is, the realization of ferromagnetic semiconductors (FS) with critical temperatures above room temperature. Unfruitful search for intrinsic RT FS lead to the concept of Dilute(d) Magnetic Semiconductors (DMS): ordinary semiconductor materials where 3 d transition metals randomly substitute a few percent of the matrix cations and, by some long-range mechanism, order ferromagnetically. The times are of intense research activity and the last few years were astonishingly prolific. Room temperature ferromagnetism has already been reported for a number of such systems based on wide band gap semiconductors. Whereas low-temperature ferromagnetism, e.g. in GaMnAs, can be well described on the basis of carrier-mediated mean-field models, the nature of the high temperature ferromagnetism in wide band gap semiconductors is poorly understood. Indeed, such exotic new materials represent new unexplored grounds of condensed matter physics as dilute ferromagnetic semiconductors with Curie temperatures well above 300K and large ordered moments per magnetic atom challenge our understanding of magnetism in solids. This work addresses the main topic of search for new above room temperature and giant moment DMSs: Fe ion implanted ZnO and SrTiO$_{3}$. The giant moment FM state was observed in the whole investigated temperature ranges, up to 300K and 100 K, respectively, with strong indications of a much higher T$_{C}$ for both systems, along with evidence of the diluted configuration of the implanted Fe . Additionally, a simplified picture of defect-related magnetic ordering is forwarded. Special effort was devoted to SQUID measurements for magnetic characterization and to electron emission channeling (EC) experiments for lattice location of the implanted impurities. Furthermore, the lattice dynamics of Fe:SrTiO$_{3}$ was studied by means of Raman spectroscopy and some selected samples were analyzed by means of RBS/C and PIXE for complementary structural characterization. The demonstrated potential of ion implantation to produce FM layers in commercially available semiconductor materials takes semiconductor industry a step closer to the realization of above room temperature DMSs for a variety of new multifunctional phenomena in spintronic devices. Together with the forwarded insight over the mechanisms involved, it strongly motivates further thorough research