Diamonds could one day be used to generate small amounts of electricity. A team of researchers at the University of Hong Kong has successfully produced an electrical voltage by bending extremely thin membranes made from diamond.
This property, known as piezoelectricity, allows certain materials to generate an electrical charge when subjected to mechanical stress. Until now, such behavior was considered incompatible with the conventional structure of diamond.
However, research conducted by a team of twelve physicists and engineers and published in the scientific journal Science Advances shows that diamond membranes can produce a measurable and reproducible electrical response when deformed.
Diamond membranes thin enough to bend
Diamond has several highly sought-after physical properties. It is exceptionally strong and rigid, chemically stable and capable of withstanding high temperatures. These characteristics have already made it useful in certain microelectromechanical systems, also known as MEMS.
Its extreme rigidity, however, made it difficult to study how the material responds to deformation. The researchers therefore worked with extremely thin diamond membranes. At this scale, the material becomes flexible enough to bend.
When the scientists deliberately curved the membranes, they detected an electrical voltage. The team then carried out a series of additional experiments to determine exactly where the signal was coming from.
In particular, the researchers sought to rule out triboelectric effects, in which electrical charges can be generated when two materials come into contact or rub against each other. Despite these controls, the electrical signal continued to appear consistently whenever the diamond membrane was deformed.
Tiny crystals play a key role
The explanation appears to lie in the internal structure of the membranes. They are made up of numerous microscopic diamond crystals separated by what scientists call grain boundaries.
The researchers identified an electrical asymmetry at these boundaries. When the membrane bends, electrical charges accumulate around these areas. This polarization creates a difference in electrical potential between the upper and lower surfaces of the membrane, generating the observed voltage.
The discovery therefore does not necessarily overturn what scientists know about a perfectly uniform diamond crystal. Instead, it is the polycrystalline structure of the membrane and the interfaces between its tiny crystals that appear to make the effect possible.
Potential applications in sensors and medical implants
The discovery could lead to new ways of designing electronic devices capable of harvesting energy from tiny movements or mechanical deformations.
Diamond membranes could potentially be incorporated into miniature sensors or microsystems capable of generating at least part of the electricity required for their operation.
Medical technology could also benefit. Diamond offers several advantages for devices designed to operate in demanding environments, including biocompatibility, chemical stability and exceptional durability.
However, there is still a long way to go before diamond can be considered a practical energy source. The amount of electricity generated by these membranes is better suited to powering extremely small devices than producing electricity on a large scale.
Nevertheless, the findings reveal an unexpected property in a material that has been extensively studied for decades. In the future, diamond could evolve from being primarily a structural material into an active component of miniature electronic and energy-harvesting systems.
