The microstructure, mechanical properties and thermal stability of Al x Ti 1− x N and Al 1 Ti 1-x BN coatings grown by reactive high-power impulse magnetron sputtering (HiPIMS) have been analyzed as a function of Al/(Al + Ti) ratio (x) between 0.5 and 0.8. The coatings were predominantly formed by a face-centered cubic Ti(Al)N crystalline phase, both with and without B, even for x ratios as high as 0.6, which is higher than the ratio typically encountered for Al x Ti 1− x N coatings deposited by reactive magnetron sputtering. B doping, in combination with the highly energetic deposition conditions offered by HiPIMS, results in the suppression of the columnar grain morphology typically encountered in Al x Ti 1− x N coatings. On the contrary, the Al x Ti 1− x BN coatings grown by HiPIMS present a dense nanocomposite type microstructure, formed by nanocrystalline Ti(Al) N domains and amorphous regions composed of Ti(Al)B 2 and BN. As a result, high-Al content (x ≈ 0.6) Al x-Ti 1− x BN coatings grown by HiPIMS offer higher hardness, elasticity and fracture toughness than Al x Ti 1− x N coatings. Moreover, the thermal stability and the hot hardness are substantially enhanced, delaying the onset of formation of the detrimental hexagonal AlN phase from 850 • C in the case of Al 0.6 Ti 0.4 N, to 1000 • C in the case of Al 0.6 Ti 0.4 BN.
A fundamental
problem for thermal energy harvesting is the development
of atomistic design strategies for smart nanodevices and nanomaterials
that can be used to selectively transmit heat. We carry out here an
extensive computational study demonstrating that heterogeneous molecular
junctions, consisting of molecular wires bridging two different nanocontacts,
can act as a selective phonon filter. The most important finding is
the appearance of gaps on the phonon transmittance spectrum, which
are strongly correlated to the properties of the vibrational spectrum
of the specific molecular species in the junction. The filtering effect
results from a delicate interplay between the intrinsic vibrational
structure of the molecular chains and the different Debye cutoffs
of the nanoscopic electrodes used as thermal baths.
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