No abstract

This work investigates the role of the co-reactant for the atomic layer deposition of cobalt (Co) films using cobaltocene (CoCp2) as the precursor. Three different processes were compared: an AB process using NH3 plasma, an AB process using H2/N2 plasma, and an ABC process using subsequent N2 and H2 plasmas. A connection was made between the plasma composition and film properties, thereby gaining an understanding of the role of the various plasma species. For NH3 plasma, H2 and N2 were identified as the main species apart from the expected NH3, whereas for the H2/N2 plasma, NH3 was detected. Moreover, HCp was observed as a reaction product in the precursor and co-reactant subcycles. Both AB processes showed self-limiting half-reactions and yielded similar material properties, that is, high purity and low resistivity. For the AB process with H2/N2, the resistivity and impurity content depended on the H2/N2 mixing ratio, which was linked to the production of NH3 molecules and related radicals. The ABC process resulted in high-resistivity and low-purity films, attributed to the lack of NHx,x≤3 species during the co-reactant exposures. The obtained insights are summarized in a reaction scheme where CoCp2 chemisorbs in the precursor subcycle and NHx species eliminate the remaining Cp in the consecutive subcycle.

Molybdenum oxide (MoOx) films have been deposited by atomic layer deposition using bis(tert-butylimido)-bis(dimethylamido)molybdenum and oxygen plasma, within a temperature range of 50–350 °C. Amorphous film growth was observed between 50 and 200 °C at a growth per cycle (GPC) around 0.80 Å. For deposition temperatures of 250 °C and higher, a transition to polycrystalline growth was observed, accompanied by an increase in GPC up to 1.88 Å. For all deposition temperatures the O/Mo ratio was found to be just below three, indicating the films were slightly substoichiometric with respect to MoO3 and contained oxygen vacancies. The high purity of the films was demonstrated in the absence of detectable C and N contamination in Rutherford backscattering measurements, and a H content varying between 3 and 11 at. % measured with elastic recoil detection. In addition to the chemical composition, the optical properties are reported as well.

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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