Evaluation of Optical and Acoustical Properties of Ba1-xSrxTiO3 Thin Film Material Library via Conjugation of Picosecond Laser Ultrasonics with X-ray Diffraction, Energy Dispersive Spectroscopy, Electron Probe Micro Analysis, Scanning Electron and Atomic Force Microscopies.

Sathyan Sandeep,Samuel Raetz,Jerome Wolfman,Jean-Louis Longuet,Beatrice Negulescu,Vitalyi E Gusev,Guozhen Liu,Théo Thréard

doi:10.3390/nano11113131

Abstract

Wide-range continuous spatial variation of the film composition in lateral compositionally graded epitaxial films requires the development of high throughput measurement techniques for their local and non-destructive characterization with the highest possible spatial resolution. Here we report on the first application of the picosecond laser ultrasonics (PLU) technique for the evaluation of acoustical and optical parameters of lateral compositionally graded film, the Ba1−xSrxTiO3 (0 ≤ x ≤ 1) material library. The film was not dedicatedly prepared for its opto-acousto-optic evaluation by PLU, exhibiting significant lateral variations in thickness and surface roughness. Therefore, the achieved measurements of the sound velocity and of the optical refractive index, and characterization of the surface roughness confirm the robustness of the PLU technique for thin film evaluation. We hope that the first measurements of the acoustical and optical properties of epitaxial grown Ba1−xSrxTiO3 (0 ≤ x ≤ 1) by PLU technique accomplished here provide the parameters required for more extended predictive design of the phononic, photonic and phoxonic mirrors and cavities with superior properties/functionalities for novel multifunctional nanodevices.

Highlights

Several different strategies could be potentially used to determine the parameters of the transparent films of known thickness from the picosecond laser ultrasonics (PLU) signals, we found the acoustic velocities by measuring the times of coherent acoustic pulses (CAPs) propagation across the film and the refractive index from the measured Brillouin frequencies
We demonstrated an application of PLU in combination with X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), electron probe microanalysis (EPMA), SEM
A continuous composition spread thin film of BSTx was deposited over an opaque optoacoustic thin film transducer, required for the application of PLU in transparent films/coatings, by combinatorial pulsed laser deposition (CPLD) on a single substrate

Summary

Introduction

Among the most known functionally graded materials are, perhaps, the laterally graded aperiodic crystals (on the basis of mixed Si1−x Gex crystals) in optical elements for synchrotron radiation [1] and out-of-plane graded band gap semiconductors in solar cells [2]. The applications of the former include radiation path control (diffraction, focusing) in high-resolution X-ray monochromators [1].

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Results

Conclusion