Low‐temperature atomic layer deposition of MoO_x for silicon heterojunction solar cells

Abstract

ContentsFull text on our homepage at www.pss-rapid.com FRONT COVERDespite its simple formula, AgO is a complex transition metal oxide, which contains both mono-and trivalent silver cations, i.e. Ag(I)Ag(III)O 2 . Ag(I) (represented by silver balls in the cover image) and Ag(III) (blue balls in the image) form separate layers in the crystal structure of this compound. Disproportionation (i.e. charge density wave) opens up a band gap at the Fermi level and AgO is a narrow band gap semiconductor (ca. 1.0-1.1 eV). The question arises whether this mixed-valence system might be turned into metal at large external pressures. As shown by , theoretical density functional theory calculations with use of an expensive hybrid functional reproduce very well the band gap of AgO. The calculations also indicate that AgO could be turned into a metal at pressures exceeding 45 GPa. Metallization is concomitant with the phase transition to the more stable polymorphic form, which is nevertheless disproportionated, just like its predecessor. The new metallic polymorph preserves a pseudo-gap and it shows rather small density of states at the Fermi level. Comproportionation, i.e. reversal of the charge density wave and the concomitant formation of genuine Ag(II) oxide, must require pressures larger than 70 GPa, which was the highest pressure studied here. Chemistry of silver(II) again proves to be very different from that of copper(II), as seen from the AgO-CuO comparison. BACK COVERPerforated systems constitute one of the rising and most promising fields in the study of mechanical metamaterials capable of exhibiting auxetic behavior. This is mainly due to the fact that these systems have the potential to exhibit a large range of Poisson's ratios whilst being relatively easy to produce. In this work (Mizzi et al.,, novel slit perforation patterns which can be used to produce systems capable of exhibiting giant negative Poisson's ratios have been proposed for the first time. These systems, which are produced either through straight line or 'I'-shaped slits, mimic the deformation mechanisms of a variety of auxetic systems, such as rotating rectangles and parallelograms, re-entrant honeycombs and anti-tetrachiral systems (see back cover). Besides exhibiting giant negative Poisson's ratios, these systems also have the added advantages of being easy to manufacture, and involve minimal material waste, since the perforations are introduced as cuts or slits rather than, for example, area perforations.This work has been funded through the Malta Council for Science and Technology through the R&I-2012-061 (SMESH) Project. The authors would also like to thank Jean Claude Vancell for designing the back cover. Towards a metallic quasi-d 9 system without copper: AgO at high pressure AgO is a prototypical mixed-valence compound, and a narrow-bandgap semiconductor. The authors show, using hybrid DFT calculations, that AgO should undergo the imaginary phonon-driven structural phase transition at a pressure of ca. 45 GPa with a concomitant metallization. T...

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