Ultrashort-Pulse Optically-Assisted Domain Engineering in Lithium Niobate
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Abstract:
Ultrashort laser pulses (∼120–150 fs) of near-ultraviolet (305 nm) to near-infrared (800 nm) wavelengths have been used to optically-assist domain nucleation and growth in lithium niobate. Within illuminated areas, the electric field required for domain nucleation is reduced by up to 41% in undoped and up to 98% in 5-mol% Mg-doped congruently melting materials, allowing direct-writing of inverted domains with electric fields as small as 100 V mm− 1. A first step towards the formation of optically-defined periodically poled lithium niobate was achieved by illumination via a phase mask, demonstrated over small areas with a period of 5.25 microns.Keywords:
Ultraviolet
Nucleation of barite (BaSO4) has broad implications in geological, environmental, and materials sciences. While impurity metals are common, our understanding of how they impact nucleation remains dim. Here, we used classical optical microscopy compared to fast X-ray nanotomography (XnT) to investigate heterogeneous nucleation of barite on silica in situ with Sr2+ as an impurity ion. The observed barite nucleation rates were consistent with classical nucleation theory (CNT), where barite crystals displayed a nonuniform size distribution, exhibiting distinct morphologies and incubation periods in Sr-free solutions. While undetectable with optical microscopy, nanotomography revealed that addition of Sr2+ enhances nucleation rates driven by the pre-factor in CNT, likely because both adsorbed Ba2+ and Sr2+ act as precursor sites on which nucleation occurs. Sr2+ simultaneously inhibits growth, however, leading to a homogeneous distribution of smaller crystals. This finding will enable an improved predictive understanding of nucleation in natural and synthetic environments.
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We have studied the possibilities of decreasing the photoinduced lithium niobate acoustic characteristics. We have shown that doping of lithium niobate crystals with Mg impurity and special ultrasonic treatment significantly decreases the sound speed and electromechanical parameter changes in lithium niobate, which were caused by visible light.
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The induction times for electrodeposition of individual Ag nanoparticles on Pt nanodisk electrodes in acetonitrile were used to determine the critical nucleus size and activation energy barrier associated with the formation of Ag nuclei. Induction times for the nucleation and growth of a single Ag nanoparticle were determined following the application of a potential step to reduce Ag+ at overpotentials, η, ranging from −130 to −70 mV. Sufficiently small Pt electrodes (5.1 × 10–10–2.6 × 10–11 cm2) were used to ensure that the detection of a single Ag nucleation event occurred during the experimental observation time (150 ms–1000 s). Multiple measurements of Ag nucleation induction times were recorded to determine nucleation rates as a function of η using cumulative probability theory. Both classical nucleation theory (CNT) and the atomistic theory of electrochemical nucleation were employed to analyze experimental nucleation rates, without a requisite knowledge of the nucleus geometry or surface free energy. Using the CNT, the number of atoms comprising the critical size nucleus, Nc, was estimated to be 1–9 atoms for η ranging from −130 to −70 mV, in good agreement with 1–5 atoms obtained using atomistic theory. The experimental nucleation rates were also used to determine the activation energy barriers for nucleation from the CNT, which varied from 3.31 ± 0.05 to 13 ± 1 kT over the same range of η.
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