ABSTRACT
CaMn1-x Nb x O3 (x = 0, 0.5, 0.6, 0.7 and 0.10) thin films have been grown by a two-step sputtering/annealing method. First, rock-salt-structured (Ca,Mn1-x ,Nb x )O thin films were deposited on 11Ì00 sapphire using reactive RF magnetron co-sputtering from elemental targets of Ca, Mn and Nb. The CaMn1-x Nb x O3 films were then obtained by thermally induced phase transformation from rock-salt-structured (Ca,Mn1-x Nb x )O to orthorhombic during post-deposition annealing at 700 °C for 3 h in oxygen flow. The X-ray diffraction patterns of pure CaMnO3 showed mixed orientation, while Nb-containing films were epitaxially grown in [101] out of-plane-direction. Scanning transmission electron microscopy showed a Ruddlesden-Popper (R-P) secondary phase in the films, which results in reduction of the electrical and thermal conductivity of CaMn1-x Nb x O3. The electrical resistivity and Seebeck coefficient of the pure CaMnO3 film were measured to 2.7 Ω cm and -270 µV K-1 at room temperature, respectively. The electrical resistivity and Seebeck coefficient were reduced by alloying with Nb and was measured to 0.09 Ω cm and -145 µV K-1 for x = 0.05. Yielding a power factor of 21.5 µW K-2 m-1 near room temperature, nearly eight times higher than for pure CaMnO3 (2.8 µW K-2 m-1). The power factors for alloyed samples are low compared to other studies on phase-pure material. This is due to high electrical resistivity originating from the secondary R-P phase. The thermal conductivity of the CaMn1-x Nb x O3 films is low for all samples and is the lowest for x = 0.07 and 0.10, determined to 1.6 W m-1 K-1. The low thermal conductivity is attributed to grain boundary scattering and the secondary R-P phase.
ABSTRACT
Cr2N is commonly found as a minority phase or inclusion in stainless steel, CrN-based hard coatings, etc. However, studies on phase-pure material for characterization of fundamental properties are limited. Here, Cr2N thin films were deposited by reactive magnetron sputtering onto (0001) sapphire substrates. X-ray diffraction and pole figure texture analysis show Cr2N (0001) epitaxial growth. Scanning electron microscopy imaging shows a smooth surface, while transmission electron microscopy and X-ray reflectivity show a uniform and dense film with a density of 6.6 g cm-3, which is comparable to theoretical bulk values. Annealing the films in air at 400 °C for 96 h shows little signs of oxidation. Nano-indentation shows an elastic-plastic behavior with H = 18.9 GPa and E r = 265 GPa. The moderate thermal conductivity is 12 W m-1 K-1, and the electrical resistivity is 70 µΩ cm. This combination of properties means that Cr2N may be of interest in applications such as protective coatings, diffusion barriers, capping layers and contact materials.
ABSTRACT
Bi(1.5-x)Zn(0.92-y)Nb(1.5)O(6.92-δ) thin films have the potential to be implemented in microwave devices. This work aims to establish the effect of the substrate and of the grain size on the optical and dielectric properties. Bi(1.5-x)Zn(0.92-y)Nb(1.5)O(6.92-δ) thin films were grown at 700 °C via pulsed-laser deposition on R-plane sapphire and (100)(pc) LaAlO(3) substrates at various oxygen pressures (30, 50, and 70 Pa). The structure, morphology, dielectric and optical properties were investigated. Despite bismuth and zinc deficiencies, with respect to the Bi(1.5)Zn(0.92)Nb(1.5)O(6.92) stoichiometry, the films show the expected cubic pyrochlore structure with a (100) epitaxial-like growth. Different morphologies and related optical and dielectric properties were achieved, depending on the substrate and the oxygen pressure. In contrast to thin films grown on (100)(pc) LaAlO(3), the films deposited on R-plane sapphire are characterized by a graded refractive index along the layer thickness. The refractive index (n) at 630 nm and the relative permittivity (ε(r)) measured at 10 GHz increase with the grain size: on sapphire, n varies from 2.29 to 2.39 and ε(r) varies from 85 to 135, when the grain size increases from 37 nm to 77 nm. On the basis of this trend, visible ellipsometry can be used to probe the characteristics in the microwave range quickly, nondestructively, and at a low cost.
