Tohoku University · Engineering
Professor Hironori Tohmyoh's research lab specializes in nanoscale materials characterization and interfacial phenomena, with a focus on the mechanical, thermal, and acoustic behaviors of nanostructures. Key research directions include the development of in-situ electron microscopy techniques for nanowire welding and cutting via Joule heating, molecular dynamics simulations of carbon nanotube–metal nanowire heterostructures, and advanced ultrasonic spectroscopy for thin-film property evaluation. The lab also investigates dry-contact ultrasonic imaging and acoustic impedance measurement in low-density polymer films, emphasizing high-precision, non-destructive characterization methods at the micro- and nanoscale.
Figures are computed from collected data and may differ slightly.
Two Pt wires with diameters of about 800 nm were successfully welded by Joule heating in a scanning electron microscope. Melting and solidification at the point contact of the thin wires occurred continuously under a constant current supply and the welding process was completed within several seconds. This rapid and self-completed welding is due to the geometrical features of the nanocontact and the heat transport properties of the thin wires. The current required for joining wires in a scanning
For cutting and joining extremely thin metallic wires, the issue of Joule heating in the wires is considered. The middle of a section of a thin Pt wire with a diameter of about 800 nm was melted locally by a direct current supply, and the wire was cut at a predetermined point by applying a force to shear the molten part of the wire. Furthermore, a constant current was applied to a system in which the free ends of two Pt wires were contacted, and the wires were joined together. A parameter, which
We investigated the interfacial contact behavior of the side-to-side biaxial heterostructure between carbon nanotubes and silver nanowires on an atomic scale. The nanotubes can move along the nanowire periphery and keep pace with the silver nanowires, and in some cases, a collapse occurs and quickly creates a domino effect that readily forms the bilayer graphene-like structures with a face-to-face π–π stacking effect that adhere firmly to the nanowire surface. When the diameter of an armchair na
The behavior at an interface between carbon nanotubes (CNTs) and silver nanowire (AgNW) could hardly be observed experimentally on an atomic scale, and the interaction is difficult to accurately calculate due to nanometer size effects. In this work, the contact behavior is studied with the molecular dynamics (MD) simulation, which indicates that the CNTs and AgNW can move towards each other to form aligned structures with their interfaces in full contact. In these different composite systems, na
An acoustic resonant spectroscopy technique for measuring the acoustic impedance, ultrasonic velocity, and density of micron-scale polymer films is developed. The method, which is based on spectral analysis, observes the acoustic resonance between water, the film, and a tungsten plate with high acoustic impedance in the frequency range of 20–70MHz. The interface between the film being examined and the plate is vacuum sealed, enabling us to characterize the low-density polyethylene film with acou
To accomplish a high-resolution ultrasonic imaging without wetting a sample, the efficiency of the dry-contact ultrasonic transmission is discussed. In this study, a dry-contact interface is formed on a sample by inserting a thin film between water and a sample, and the pressure is working on the interface by evacuating the air between the film and the sample. A model of dry-contact ultrasonic transmission is presented to assess the signal loss accompanied with the transmission. From the determi
A polymer acoustic matching layer has been designed that can act as a frequency filter between water and a test sample, and a method for controlling the high-frequency components of broadband ultrasound by using the designed layer is described. Acoustic imaging of a silicon-bonding sample using a very-low-scale matching layer fabricated from poly(vinylidene chloride) is demonstrated, in which the air gaps between the layer and the sample are evacuated. The experimental results show that the laye
This paper deals with typical mechanical problems that are encountered in a solderless press-fit assembly process. First, the elastic-plastic properties of two types of press-fit pins and the friction coefficients of the pins in thin plated through holes are determined both experimentally and by three-dimensional finite element analysis. The elastic-plastic properties of the press-fit pins are determined by small-scale testing under three-point bending. The coefficients of friction of the pins i
Acoustic resonance phenomena at the front and back surfaces of a plate coated with thin layers were successfully observed in the amplitude spectrum of the back surface echo. The amplitude ratio of spectra with and without layers takes its maximum and minimum values at the resonant frequencies of the front and back coatings and both frequencies can clearly be distinguished from each other. As an application, the thicknesses of the front and back coatings on a steel plate were measured simultaneou
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