Optical Properties and Optimization of LaB₆ Thin Films for Photothermal Applications

Abstract

The growth of highly crystalline LaB6 films with an excellent optical response and low loss is reported, which will be useful for high‐performance photothermal device applications when combined with their inherent refractory properties. Optimum growth parameters for realizing uniaxial and coherent LaB6 thin films, exhibiting an excellent plasmonic response for near‐ to mid‐infrared device applications, are established. Numerical electromagnetic simulations of the epitaxial LaB6 nanostructures revealed that the electromagnetic field at the LaB6 surface can be as high as that of the Au nanostructures. Furthermore, the LaB6 nanostructures show resonance in the visible (red) to mid‐infrared region comparable to those of Au with the added advantage of improved temperature stability that can withstand harsh photothermal device operations.

A Simultaneous Material‐Device Optimization for Plasmonic Devices: A Combined Ab Initio and Electromagnetic Simulation for Photothermal Transducers

“…The crossover frequency (ω c ), which is defined as the energy when the material becomes metal, reveals that LaB 6 exhibits metallic properties in the IR-vis transition region. The experimental carrier density values [46,53,55] are within the range of 1.39 − 1.45 × 10 22 cm −3 . Theoretically, these values correspond to the number of La 3+ ions per unit volume of the LaB 6 bulk crystal.…”

“…Since these field enhancements are very high, the CeB 6 MIM stripe could be also used for surface enhanced infrared absorption spectroscopy (SEIRA) applications. [10,62,63] The experimental realization of high-quality LaB 6 film and the proposed devices are reported elsewhere [46,64] and the experimental results for newly proposed CeB 6 are of much interest and are currently under way.…”

“…The carrier density (n) was referenced from our high-quality film published in Ref. [46]. These films were grown in the same conditions to exhibit good reproducibility and high optical figure of merit.…”

“…For the theoretical simulation, LaB 6 crystal has an ideal perfect structure. Therefore in the experiment, as we will explain below, we took a special care to use the highly crystalline epitaxially grown films, [46] or mirror-polished single crystal surfaces. This is to minimize the discrepancy between the experimental and theoretical results that may come from the surface roughness or defects in the real films that are not considered in the ab initio simulation.…”

“…We plotted experimental results (dashed red lines) using the highly crystalline LaB 6 film published in Ref. [46] for comparison with the theoretical optical permittivities predicted by various DFT approaches. The dashed vertical lines separated the three main wavelength regions: infrared (IR), visible (vis), and ultraviolet (UV).…”