Faculty of Engineering

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Research Highlights

Nanoengineering will change the future and how we think

What happens when a substance is made as small as possible? For example, what new characteristics could iron take on if it were used it was used at the nanometer scale in the production of frying pans, or how strong can a single carbon fiber be made in the body of an F1 race car? To answer these questions, we need devices that can measure the properties of micro/nano-sized materials. Devices that can measure the characteristics of materials include tensile test and bending test devices, but these are useless at the micro or nanometer scale. Thus, we must develop devices that can directly measure the characteristics of micro/nano-sized materials.

Micro Electro-Mechanical Systems (MEMS) technology has produced products like accelerometers, pressure sensors, gyro sensors, and actuators, all of which have made our lives safer and more convenient. These technologies are also of great use in material evaluation testers for nanomaterials. Thus far, researchers have designed and developed their own MEMS devices in order to measure the mechanical properties of nanomaterials. The Nanomechatronics Laboratory at KUAS has developed a silicon MEMS device for uniaxial tensile testing at the nanometer scale, which is capable of operation inside a scanning electron microscope. Using this novel device, we could discover the precise mechanical reaction of a nanoscale specimen during uniaxial tension loading at a resolution of approximately 1nN and 1nm for applied tensile force and elongation respectively while also observing deformation in real-time. Using this system, we will attempt to experimentally determine the smallest scale at which the concept of continuum can be adopted through the investigation of size effects on the Young’s modulus of single-crystal silicon. In this project, we are studying the size where the Young’s modulus of single-crystal silicon starts deviating from the bulk value, or 168.9GPa for Si(110), as the threshold size where the concept of continuum can be adopted. So far, we have succeeded in the quantitative mechanical characterization of a 20nm-width beam specimen, in which no change in the modulus value was observed. Needless-to-say, it is a big challenge to fabricate and evaluate specimens smaller than 10nm in diameter. We are currently endeavoring to discover the size threshold through nanoscale experimental technologies, and once this is achieved these findings will be published in a textbook.

Recently, we adapted our novel testing system for the purpose of identifying the characteristics of carbon nanotubes (CNTs). CNTs are a candidate material for future space elevator construction because they possess tremendous strength while remaining chemically intert. Basically, CNTs can be classified into single-walled CNTs (SWCNT), double-walled CNTs, and multi-walled CNTs, as well as various “bundles” thereof. Among them, SWCNTs are the smallest possible CNT material unit, the diameter of which is somewhere around a few nanometers. With our testing system at KUAS, we have succeeded in directly measuring the strength of SWCNTs with a diameter of 1.6nm. The strength value of this SWCNT was 66GPa, or approximately 340 times stronger than that of pure iron. SWCNTs are commonly classified into three types of structures: zigzag, chiral, and armchair. These structural difference can be defined by their chiral angle, and the mechanical or electrical characteristics of SWCNTs depend on this angle. At KUAS, for the first time, we have successfully identified the characteristics structure-defined SWCNTs and revealed the correlation between chiral angle and strength. Most remarkably, we have discovered that higher chiral angle

SWCNTs possess greater fracture strength, indicating that the armchair type of SWCNT is strongest. In the future, if armchair-type SWCNTs can be deliberately produced, and their sizes can be enlarged creating bundles and yarns without defects, it could be possible to take a space elevator to the moon.

The two topics mentioned above are categorized as nanomechanics research. But to introduce another example of size effect research, we are also researching how shrinking material sizes can enable us to find new functions not seen in macro materials. About 15 years ago, researchers found a very interesting functional material called self-propagating exothermic reactive film, which is produced by repeatedly depositing a transition metal (for example, Ni, Ti, Zr) and light metal (for example, Al, Si) at nanometer thickness onto a film. By applying a small amount of energy, such as a spark or a mechanical impact, compound formation occurs locally and simultaneously generates heat. The energy from the heat is then used to ignite the surrounding unreacted portion, so the exothermic reaction automatically propagates along the surface of the film. These heating characteristics, such as total heat energy, maximum temperature, and reaction propagation speed, can be tuned, making this exothermic reactive film a novel and useful heat source. In our lab, we are using an Al/Ni multilayer film as a local heat source for soldering. Using this film, two Si wafers can be bonded with solder in a very short period of time. During the reaction, no gases are emitted, thus this reactive bonding technique can be regarded as an eco-friendly future bonding technology. Using this discovery, we will endeavor to establish a method of crack-free reactive bonding that can be used for SiC power devices used in electric vehicles. Thus, it may be possible to realize zero-emission manufacturing for future cars.

Without superior experimental technologies, new scientific and engineering outcomes will not emerge. Exploring nanomaterials using superior experimental technologies gives us a chance to discover interesting phenomena that we have never seen before in macro materials. By taking on big technological challenges at KUAS, we can continue to pursue new discoveries in nano-to-atomic-scale materials and make strong contributions to invigorating Japanese industries while solving environmental problems.

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