Optical Switching in Thin Film NdNiO 3
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ABSTRACT Crystalline thin films of NdNiO 3 are known to exhibit characteristic metal-insulator electrical transitions. Infrared transmission measurements of these films have demonstrated the corresponding reversible optical switching response, transforming between IR-transparent and IR-opaque states. Their low-temperature transmission spectra exhibit a sharp increase in transmittance at an onset wavelength of approximately 3 mm (-0.4eV), with an appearance suggesting formation of a distinct band gap structure. The transmission and reflection characteristics of these films differ significantly from those reported for bulk polycrystalline material. INTRODUCTION A number of crystalline oxide materials exhibit sharply nonlinear electrical and optical properties with temperature. Examples of these include the phase transition oxides such as V0 2 and V 2 0 3 , as well as the copper oxide-based high-Tc superconductors and the perovskitestructured manganates exhibiting colossal magnetoresistance (CMR). Interest in these materials stems not only from their relevance to electrical and optical device applications, but also from their contribution to a fundamental understanding of the band structure and conduction mechanisms of crystalline ceramic oxides. In recent years, electrical switching has been demonstrated in a class of perovskite-structured rare-earth nickel oxides of the composition ReNiO 3 (Re=Nd, Pr, Sm, Eu) [1-4]. Bulk polycrystalline ceramics of the NdNiO 3 compound, for example, have shown excursions in
electrical resistivity in excess of 3 orders of magnitude upon switching. One notable feature of the ReNiO 3 ceramics is the correlation between the lattice distortion and the electrical transition temperature, providing the ability to tune the transition temperature with rare-earth species [1]. The mechanism of the metal-to-insulator transition in the ReNiO 3 materials is attributed to the collapse of a charge transfer gap, and while there is a slight volume change upon switching, there is no alteration in structural symmetry [1,2,3,5-10]. In a previous paper, we have demonstrated that crystalline thin films of NdNiO 3 which exhibit the electrical switching characteristics of the bulk ceramics can be fabricated [11]. In the current work, we describe the infrared optical properties of these films and demonstrate their optical switching response.
EXPERIMENTAL Thin films of NdNiO 3 were deposited using RF magnetron sputtering and post-deposition annealing as described in ref. [11]. Films were grown to a thickness of approximately 200 mn as measured by stylus profilometry. The substrates for these depositions included single crystal LaAIO 3 and Si. The samples were subsequently annealed under 2800 psi 02 at 950 °C for 30
min. 145 Mat. Res. Soc. Symp. Proc. Vol. 479 ©1997 Materials Research Society
Electrical switching measurements were performed in a temperature-controlled cryostat using a van der Pauw four-point probe technique with inverting current polarity. X-ray diffraction characterization of the films in
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