Sensitive label-free immunoglobulin G detection using a MEMS quartz crystal microbalance biosensor with a 125 MHz wireless quartz resonator

We present a wireless quartz crystal microbalance (QCM) biosensor fabricated using MEMS technology. The MEMS QCM biosensor contains a 125 MHz AT-cut quartz resonator embedded in the microchannel. Because of the compact design, the MEMS QCM biosensor is suitable for mass production and device miniaturization. We performed immunoglobulin G (IgG) detection measurements with different concentrations of IgG. The detection limit was 1 ng ml-1 or less, which is superior to that of the gold-standard surface plasma resonance method. Furthermore, we studied the binding affinity between protein A and IgG by studying the frequency response of the QCM biosensor. We found good agreement with reported values. Therefore, the presented MEMS QCM biosensor has the advantages of compactness, low cost, low power consumption, high sensitivity, and reliability.This is the Accepted Manuscript version of an article accepted for publication in Japanese Journal of Applied Physics. IOP Publishing Ltd are not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.35848/1347-4065/abea50

Elastic constant of dielectric nano-thin films using three-layer resonance studied by picosecond ultrasonics

Elastic constants and sound velocities of nm order thin films are essential for designing acoustic filters. However, it is difficult to measure them for dielectric thin films. In this study, we use a three-layer structure where a dielectric nano-thin film is sandwiched between thicker metallic films to measure the longitudinal elastic constant of the dielectric film. We propose an efficiency function to estimate the optimal thicknesses of the components. We use Pt/NiO/Pt three-layer films for confirming our proposed method. The determined elastic constant of NiO deposited at room temperature is smaller than the bulk value by ∼40%. However, it approaches the bulk value as the deposition temperature increases. We also reveal that the uncertainty of the elastic constant of the Pt film insignificantly affects the accuracy of the determined elastic constant of NiO in this structure.This is the Accepted Manuscript version of an article accepted for publication in Japanese Journal of Applied Physics. IOP Publishing Ltd are not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.35848/1347-4065/abec5a

Enhancement of sensitivity of Pd-based hydrogen-gas sensor by plasma exposure studied by wireless quartz resonator

This is the Accepted Manuscript version of an article accepted for publication in Japanese Journal of Applied Physics. IOP Publishing Ltd are not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.35848/1347-4065/ab78e2

Restructuring in bimetallic core-shell nanoparticles: Real-time observation

The formation process of core-shell bimetallic nanoparticles synthesized by sputtering onto a substrate is observed in real time using an originally developed acoustic technique. The technique enables us to evaluate the structural change of nanoparticles at room temperature without contacting the nanoparticles or substrate. In the experiments, the sputtering of metal A followed by metal B tended to form B-shell/A-core nanoparticles. However, in Pd-Au alloy system, notable restructuring occurred during synthesis, resulting in the formation of A-shell/B-core nanoparticles. The formation process is analyzed using the molecular dynamics simulation, revealing that this restructuring occurs on a short timescale, and high diffusivity of Au plays an important role.Nakamura Nobutomo, Matsuura Koji, Ishii Akio and Ogi Hirotsugu. Restructuring in bimetallic core-shell nanoparticles: Real-time observation. Physical Review B, 105, 125401, 2022. https://doi.org/10.1103/PhysRevB.105.125401

Point-Focusing Electromagnetic-Acoustic Transducer for Crack Inspection

Stress corrosion cracking in stainless-steel pipes is a critical failure in atomic power plants and chemical plants. In ultrasonic testing, piezoelectric transducers are generally used, in which reproducibility of amplitude measurements is not necessarily high because of effects of coupling materials and contacting conditions between the transducers and specimens. Comparing to the transducers, an electromagnetic acoustic transducer (EMAT) requires no coupling materials and is less sensitive to the contacting conditions, making the reproducibility higher. However, lower signal to noise (S/N) ratio has been a disadvantage. For increasing the S/N ratio, we developed a point-focusing EMAT (PF-EMAT) [1]. It generated shear-vertical (SV) waves from concentric line sources on a top surface of a specimen. Coil configuration of the EMAT was designed so that the SV waves were accumulated in phase at a focal point on the bottom surface, which increased the S/N ratio and improved the spatial resolution. We have designed PF-EMATs operated at different frequencies, and applied to artificially fabricated defects on stainless steel specimens. In this presentation, we show the results, and discuss availability of the PF-EMAT to crack inspection

Deep-Learning-Assisted Resonant Ultrasound Spectroscopy for Cubic Solids

This paper solves a long-standing problem in resonant ultrasound spectroscopy (RUS) for cubic solids through the use of two-dimensional deep learning (DL). By means of inverse methods, conventional RUS can determine all independent elastic constants of a crystalline solid specimen by comparing measured and calculated free-vibration resonance frequencies. However, to avoid invalid local minima in the inverse process, good initial guesses of the elastic constants must be available. Here, we propose a DL scheme to remedy this problem, which utilizes an input elasticity image composed of three layers obtained from resonance frequency data. After network training, this scheme is executed in two steps: DL processing by a neural network to output elastic constants in a Blackman diagram classification, followed by the use of a regression network around the classified point in this diagram for more accurate determination. By means of simulations, we demonstrate that this DL scheme yields the principal elastic constants within an error of approximately 5% without any inverse processing even in the unfavorable case of five missing modes for 111 existing cubic crystals.Fukuda Hiroki, Nagakubo Akira, Wright Oliver B., et al. Deep-Learning-Assisted Resonant Ultrasound Spectroscopy for Cubic Solids. Physical Review Applied 20, 228 (2023); https://doi.org/10.1103/physrevapplied.20.034048

Interplanar stiffness in defect-free monocrystalline graphite

The interplanar bond strength in graphite has been identified to be very low owing to the contribution of the van der Waals interaction. However, in this study, we use microscopic picosecond ultrasound to demonstrate that the elastic constant, $C_{33}$, along the $c$ axis of defect-free monocrystalline graphite exceeds 45 GPa, which is higher than reported values by 20\%. Existing theories fail to reproduce this strongly correlated interplanar system, and our results, thus, indicate the necessity for improvement. Since the LDA+U+RPA method, including both random phase approximation correlation and short-range correlation in $p$ Wannier orbitals, shows better agreement with the observation than LDA or even than ACFDT-RPA, the experimental results indicate non-negligible electron correlation effects with respect to both the short-range and long-range interactions.Comment: (Main text) 5 pages, 3 figures, (Supplementary material A) 2 pages, 2 figures, (Supplementary material B) 12 pages, 1 figur

Field dependence of coupling efficiency between electromagnetic field and ultrasonic bulk waves

Ogi H. "Field dependence of coupling efficiency between electromagnetic field and ultrasonic bulk waves", Journal of Applied Physics, 82(8), 3940-3949 (1997) https://doi.org/10.1063/1.365701