Considering agitation in ultrasonic electroplating through observation of cavitation.

Ultrasonic electroplating produces various effects, including refinement of the plating film structure, by generating localized agitation through cavitation bubbles. However, details of the agitation mechanism have not been clarified because ultrasonic cavitation is very small in scale and occurs rapidly, and its reproducibility is low. Therefore, using laser-induced cavitation, which can generate cavitation similar to ultrasonic waves with high reproducibility, the author attempted to elucidate the conditions and frequency of cavitation generation that affect the agitation phenomenon in ultrasonic electroplating. By controlling the laser irradiation position, three different cavitation conditions were established, and the microstructures of the plated films produced were compared. Microstructural refinement was the most advanced under the condition of microjet generation. The frequency of cavitation generation at any position in the ultrasonic electroplating was estimated to be < 1 Hz.

Understanding diffusion layer agitation by cavitation in electroplating based on high-speed monitoring.

Ultrasonic electroplating has gained attention owing to various advantages such as the promotion of mass transport to the substrate surface, improvement of the surface properties of the film, and improvement of limiting current density. However, no studies have clarified the mechanism in diffusion layer agitation caused by cavitation during ultrasonic electroplating. Here, we investigate the main factor of agitation by using a high-speed imaging technique to capture the agitation effect of shock waves and microjets generated from laser-induced cavitation on the diffusion layer of electroplating. The physical parameters of the agitation were characterized using image analysis and a micro-pressure gauge. The results revealed that only microjets affected the agitation phenomenon. The flow velocity was 21 m/s, and the water hammer pressure was low, at least below 0.05 MPa. Our results suggest that the flow velocity, and not the water hammer pressure, plays an important role in the agitation phenomenon on the substrate surface by cavitation.

High-throughput label-free image cytometry and image-based classification of live Euglena gracilis.

We demonstrate high-throughput label-free single-cell image cytometry and image-based classification of Euglena gracilis (a microalgal species) under different culture conditions. We perform it with our high-throughput optofluidic image cytometer composed of a time-stretch microscope with 780-nm resolution and 75-Hz line rate, and an inertial-focusing microfluidic device. By analyzing a large number of single-cell images from the image cytometer, we identify differences in morphological and intracellular phenotypes between E. gracilis cell groups and statistically classify them under various culture conditions including nitrogen deficiency for lipid induction. Our method holds promise for real-time evaluation of culture techniques for E. gracilis and possibly other microalgae in a non-invasive manner.

High-throughput optofluidic particle profiling with morphological and chemical specificity.

We present a method for high-throughput optofluidic particle analysis that provides both the morphological and chemical profiles of individual particles in a large heterogeneous population. This method is based on an integration of a time-stretch optical microscope with a submicrometer spatial resolution of 780 nm and a three-color fluorescence analyzer on top of an inertial-focusing microfluidic device. The integrated system can perform image- and fluorescence-based screening of particles with a high throughput of 10,000 particles/s, exceeding previously demonstrated imaging particle analyzers in terms of specificity without sacrificing throughput.