AsianScientist (Nov. 10, 2017) – Scientists in Japan have directly measured the force required to separate the layers of a crystal. They also demonstrated the improved strength of a composite crystal using their measurement system. Their findings are published in the Journal of Applied Physics.
The amount of force required to overcome the van der Waals bonding between layers in a crystal was predicted eighty years ago. However, efforts to directly measure this force have eluded scientists until now.
In this study, engineering researchers at Tohoku University devised a method to directly measure the force required to pull apart the layers of crystals. They used special double-sided tape on either side of a crystal to hold it between an anchored stage and a moveable one that could be pulled away slowly, at a rate of 50 millionths of a meter per second. This system allowed them to measure with exquisite detail the tensile strength, the force required to pull a crystal until it breaks.
“Our system enabled us to very precisely measure the interlayer force at which the crystal broke,” said Associate Professor Tadao Tanabe.
The researchers also created more durable gallium selenide crystals by adding tellurium to the crystals. Gallium selenide crystals are considered promising for many technologies, but are notoriously fragile, hampering their practical application. The researchers surmised that tellurium’s larger electron cloud would produce greater van der Waals forces between the crystal layers, strengthening the overall structure.
They grew and compared three different types of crystals: one of pure gallium selenide, one with 0.6 percent tellurium and one with 10.6 percent tellurium. They then used their tensile testing system to measure the force required to pull apart layers of the three crystal variants.
The researchers found that the interlayer van der Waals bonding in the tellurium-doped crystals was seven times stronger than in pure gallium selenide ones. With the addition of tellurium, the soft and cleavable gallium selenide crystal became rigid by enhancement of the van der Waals bonding force, the authors report, paving the way for using this system to improve crystal-based technologies.
These findings could advance the development of terahertz and spintronics technologies, used in a range of applications from medical imaging to quantum computers.
The article can be found at: Tanabe et al. (2017) Effect of Adding Te to Layered GaSe Crystals to Increase the Van der Waals Bonding Force.
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Source: American Institute of Physics; Photo: Shutterstock.
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