Using first-principles density functional theory calculations within the generalized gradient approximation (GGA) as well as the GGA+U approach, we study Al-doped α-Fe2O3 crystals. Structural, electronic, magnetic and optical properties due to impurity incorporation have been investigated and discussed in detail. Atomic displacements and Bader charges on atoms have been computed, showing that Al dopant converts the chemical bonding in its neighbourhood into a more ionic one. This work enhances our knowledge about how a crystalline lattice reacts in the presence of an Al impurity. It was found that Al incorporation produces some local changes in the band structure of the material without the creation of local energy levels within the band gap. The results provide evidence for changes in the magnetic moments in the vicinity of a defect, which means that α-Fe2O3 doped with aluminum might not act as an antiferromagnetic substance.

In this work, a study of the molecular adsorption and geometry of phenol on the nonpolar (101̅0) ZnO surface has been carried out. In an attempt to reproduce a more realistic system, an oxygen vacancy has been introduced in the surface, which leads to an increase in the band gap, from 1.16 eV for the pristine surface to 1.38 eV in the defective one, and a local level within the band gap, which corresponds to an F-center type. Calculations performed after the introduction of a phenol molecule in different configurations over the surface suggest that dissociative chemisorption is the main phenomena, with two interesting scenarios: first, the charge can be transferred from the molecule toward the surface, and vice versa, depending on the adsorption site.

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In this work, 50-nm thick Al 2 O 3 thin films were deposited at room temperature by magnetron sputtering from an Al 2 O 3 ceramic target at different RF power and argon pressure values. The sputtering technique could be preferred to conventional atomic layer deposition for an industrial application, owing to its simplicity, availability, and higher deposition rate. The resulting thin films were characterized by UV/Vis/NIR spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The deposited Al 2 O 3 material was always highly transparent and amorphous in nature. It was found that the O/Al ratio is higher when the Al 2 O 3 layer is deposited at lower RF power or higher argon pressure. Also, some argon incorporation into the films was observed at low deposition pressure. On the other hand, the performance of the previously characterized Al 2 O 3 thin films in the passivation of 2.25-Ωcm p-type float zone c-Si wafer surfaces was evaluated by the quasi-steady-state photoconductance technique. The best effective carrier lifetime value at one-sun illumination, 0.34 ms (corresponding to a surface recombination velocity of 41 cm/s), was obtained with the 50-nm Al 2 O 3 deposited at the higher argon pressure studied, 0.67 Pa (5.0 mTorr), with the lowest RF power studied, 150 W (corresponding to a power density of 3.3 W/cm 2), and after an annealing process, in this case at 350 ºC for 20 min with forming gas. It was assumed that the reduction of the surface passivation quality at higher RF power or lower argon pressure is a consequence of an increased surface damage, and, probably, to a decrease of the O/Al ratio of the Al 2 O 3 passivation material. These assumptions were confirmed with the obtainment of a lifetime of 0.73 ms (a surface recombination velocity equal to 19 cm/s) with a simple experiment with Al 2 O 3 deposited with progressively varied sputtering conditions started from minimal silicon surface damage conditions: 50 W (corresponding to a power density of 1.1 W/cm 2) and 6.67 Pa (50 mTorr). Finally, comments about further improvement of the effective lifetime (up to 1.25 ms, corresponding to a surface recombination velocity of 11 cm/s) with preliminary experiments about the incorporation of an intrinsic hydrogenated amorphous silicon interlayer are included.

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