ABSTRACT
In this Letter we highlight direct experimental evidence of Fe(2+)-Fe3+ charge ordering at room temperature in hematite-ilmenite Fe(1.35)Ti(0.65)O(3-δ) epitaxial thin films grown by pulsed laser deposition, using aberration-corrected scanning transmission electron microscopy coupled to high-resolution energy electron-loss spectroscopy. These advanced spectromicroscopy techniques demonstrate a strong modulation of the Fe2+ valence state along the c axis. Density functional theory calculations provide crucial information on the key role of oxygen vacancies in the observed charge distributions. Their presence at significant levels leads to the localization of extra electrons onto reduced Fe2+ sites, while Ti remains solely +4. The magnetic and transport properties of these films are reviewed in the light of the present results regarding their ferrimagnetic character correlated with the Fe2+ modulation and their semiconducting behavior interpreted by an Efros-Shklovskii variable-range hopping conduction regime via Fe2+ and Fe3+ centers. The experimental evidence of only one type of mixed valence state, i.e., Fe2+ and Fe3+, in the Fe(2-x)Ti(x)O(3-δ) system will thus help to interpret further the origin of its geomagnetic properties and to illuminate fundamental issues regarding its spintronic potential.
ABSTRACT
This paper presents a review of the properties induced by the presence of hydrogen in monocrystalline boron-doped diamond (BDD) and proposes a comparison with results obtained on polycrystalline materials. Hydrogen diffusion, luminescence and electrical properties show the passivation of boron acceptors in diamond by the formation of (B,H) complexes, in both monocrystalline and polycrystalline forms, but at a different level. This behaviour raises open questions concerning the role of structural defects in the passivation of boron impurities by hydrogenation. Based on the assessment of the high thermal stability of (B,H) complexes, this approach leads to a route to provide patterned diamond conductive structures for micro as well as for nanotechnology applications.
ABSTRACT
In-vivo optical spectroscopy and the determination of tissue absorption and scattering properties have a central role in the development of novel optical diagnostic and therapeutic modalities in medicine. A number of techniques are available for the optical characterization of tissue in the visible near-IR region of the spectrum. An important consideration for many of these techniques is the reliability of the absorption spectrum of the various constituents of tissue. The availability of accurate absorption spectra in the range 600 to 1100 nm may allow for the determination of the concentration of key tissue constituents such as oxy- and deoxy-hemoglobin, water, and lipids. The objective of the current study is the determination of a reliable absorption spectrum of lipid(s) that can be used for component analysis of in-vivo spectra. We report the absorption spectrum of a clear purified oil obtained from pig lard. In the liquid phase above 36 degrees C, the oil is transparent and thus suitable for collimated transmission measurements. At room temperature, the oil is a solid grease that is highly scattering. The absorption and scattering properties in this solid phase are measured using time- and spatially resolved diffuse reflectance spectroscopy. Using these three independent measurement techniques, we have determined an accurate estimate for the absorption spectrum of mammalian fat.
