Source: http://aoot.osa.org/ome/abstract.cfm?uri=ome-9-3-1459
Timestamp: 2019-04-26 12:17:11+00:00

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The optical properties of a TiN/(Al,Sc)N superstructures deposited on MgO substrates are studied by using first principles approaches. The modifications of the plasmonic response of ultrathin TiN layers when faced to MgO and nitride surfaces are interpreted at the microscopic level, in terms of the electronic structure of the TiN/dielectric interfaces. The hyperbolic behavior of the multi-stacked metamaterial, described both via the effective medium theory and first principles simulations of periodic TiN/(Al,Sc)N superlattices, is closely investigated and directly compared to recent experimental results. The latter comparison underlines the crucial role of quantum confinement especially for the ultrathin dielectric layers.
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Fig. 1 Scheme of a TiN/(Al,Sc)N superlattice deposited on MgO substrate. Gray, yellow and blue layers represent MgO, TiN and Al 0.7Sc 0.3N materials, respectively. Atomic structures of the simulated MgO/TiN and TiN/(Al,Sc)N interfaces are shown on the lateral sides.
Fig. 2 Real (a) and imaginary (b) part of the complex dielectric function of TiN(001) film (black), MgO (001) substrate (blue) and TiN/MgO single interface (orange). Black (orange) vertical dashed lines mark the position of TiN (TiN/MgO) crossover energy E p, respectively. (c) Total and projected density of states of the TiN/MgO interface; color assignement follows panels (a) and (b). Zero energy reference in panel is set to the Fermi level of the interface. Vertical blue dashed lines mark the bandgap (E g) of MgO.
Fig. 3 Real (a) and imaginary (b) part of the complex dielectric function of TiN(001) film (black), Al 0.7Sc 0.3N(001) (red) and TiN/(Al,Sc)N single interface (green). Dashed red lines correspond to the AlN layer in the rocksalt phase. Black(green) vertical dashed lines mark the position of TiN (TiN/Al 0.7Sc 0.3N) crossover energy E p ( E ′ p), respectively. (c) Total and projected density of states of TiN/(Al,Sc)N interface; color assignement follows panels (a) and (b). Zero energy reference in panel is set to the Fermi level of the interface. Vertical red dashed lines mark the bandgap (E g) of (Al,Sc)N dielectric.
Fig. 4 Parallel ( / /) and perpendicular ( ⊥) components of the real part of the dielectric function εr, obtained from (a) effective medium theory and (b) slab buried interface.
Fig. 5 2D plot of sign function S ( E , f ) as a function of the incoming radiation energy E and the filling fraction f. Black areas identify regions where S is negative, i.e. where a hyperbolic behavior is expected. Horizontal dashed line corresponds to the selected filling fraction f = 0.5, whose optical properties are shown in Fig. 4a.

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