Spontaneous magnetization of aluminum nanowires deposited on the NaCl(100) surface

We investigate electronic structures of Al quantum wires, both unsupported and supported on the (100) NaCl surface, using the density-functional theory. We confirm that unsupported nanowires, constrained to be linear, show magnetization when elongated beyond the equilibrium length. Allowing ions to relax, the wires deform to zig-zag structures with lower magnetization but no dimerization occurs. When an Al wire is deposited on the NaCl surface, a zig-zag geometry emerges again. The magnetization changes moderately from that for the corresponding unsupported wire. We analyse the findings using electron band structures and simple model wires.Comment: submitted to PHys. Rev.

Effects of anharmonic strain on phase stability of epitaxial films and superlattices: applications to noble metals

Epitaxial strain energies of epitaxial films and bulk superlattices are studied via first-principles total energy calculations using the local-density approximation. Anharmonic effects due to large lattice mismatch, beyond the reach of the harmonic elasticity theory, are found to be very important in Cu/Au (lattice mismatch 12%), Cu/Ag (12%) and Ni/Au (15%). We find that is the elastically soft direction for biaxial expansion of Cu and Ni, but it is for large biaxial compression of Cu, Ag, and Au. The stability of superlattices is discussed in terms of the coherency strain and interfacial energies. We find that in phase-separating systems such as Cu-Ag the superlattice formation energies decrease with superlattice period, and the interfacial energy is positive. Superlattices are formed easiest on (001) and hardest on (111) substrates. For ordering systems, such as Cu-Au and Ag-Au, the formation energy of superlattices increases with period, and interfacial energies are negative. These superlattices are formed easiest on (001) or (110) and hardest on (111) substrates. For Ni-Au we find a hybrid behavior: superlattices along and like in phase-separating systems, while for they behave like in ordering systems. Finally, recent experimental results on epitaxial stabilization of disordered Ni-Au and Cu-Ag alloys, immiscible in the bulk form, are explained in terms of destabilization of the phase separated state due to lattice mismatch between the substrate and constituents.Comment: RevTeX galley format, 16 pages, includes 9 EPS figures, to appear in Physical Review

Screening of diamond-like carbon coatings in search of a prospective solid lubricant suitable for both atmosphere and high vacuum applications

The tribological performance of three types of amorphous carbon coatings was screened in search of potential candidates for solid lubricants suitable for working under both atmospheric and vacuum conditions. A coating obtained through ion assisted condensation of silicon oil vapours behaved well under atmosphere but failed in vacuum. Two types of hydrogenated amorphous carbon coatings, with and without Si doping, obtained by physical vapour deposition showed good performance in vacuum reaching superlow friction. The Si-doped amorphous carbon coatings were likewise good under atmospheric conditions with the coefficient of friction ranged between 0.1 and 0.15. The degradation of the coatings under vacuum was further studied using Mechanically Stimulated Gas Emission Mass-Spectrometry and Fourier-Transformed Infra-Red Spectrometry.The partners acknowledge funding received from the Basque Country (program EMAITEK >GENESUP>), the EUREKA Program Eurostars project E! 4653 financed by the Spanish National Agency CDTI, the Spanish Ministry of Economy and Competitiveness (project BIA2016-79582) and the project ADEC for the benefit of SME's (ref. 3152239)