Diamonds are known for being exceptionally hard. Scientists have now found that when the material is made extremely thin and flexible, it can also generate electricity.
Researchers at the University of Hong Kong discovered that ultrathin diamond membranes produced a repeatable electrical response when they were mechanically deformed. The finding challenges a scientific assumption dating back more than a century that diamond could not generate electricity through mechanical deformation.
The discovery could eventually be useful for tiny sensors and self-powered devices, including possible medical implants. But before engineers can put the finding to work, they first need to understand why a material that normally resists bending suddenly behaves so differently when reduced to a thin membrane.
Why Diamond Was Thought to Be Electrically Inactive
The phenomenon the researchers observed is known as piezoelectricity. It occurs when certain materials develop an electrical voltage after being squeezed, stretched, or otherwise mechanically deformed.
Diamond has traditionally been classified as non-piezoelectric. Its extreme hardness and rigidity made it difficult to imagine the material producing an electrical response simply by being bent.
That changed when the researchers worked with polycrystalline diamond, a material made up of many tiny diamond crystals rather than one continuous crystal.
The team used an edge-exfoliation technique to create membranes thin enough to bend substantially. Once the normally rigid material could flex, the researchers began seeing something unexpected: stable voltage signals.
Bending the Diamond Revealed an Electrical Response
Seeing a voltage was only the beginning. The researchers had to determine whether the signal genuinely came from the diamond or from another effect created during the experiment.
One possibility was triboelectricity, an electrical effect that can occur when surfaces come into contact or rub against each other.
To rule out that explanation and other sources of interference, the team repeatedly subjected the diamond membranes to controlled mechanical cycles.
The electrical signal continued to appear.
Its consistency and repeatability provided evidence that the flexible diamond itself was exhibiting a piezoelectric response rather than producing an accidental electrical signal.
That left another question: what was happening inside the membrane to make the effect possible?
Tiny Boundaries May Hold the Answer
The researchers turned to detailed calculations to investigate the mechanism.
Their analysis pointed to grain boundaries, the microscopic interfaces where the individual crystals within polycrystalline diamonds meet.
These boundaries have an asymmetric structure. When the thin membrane bends, electrical charge can become polarised around those regions.
That creates a difference in electrical potential between the two surfaces of the membrane, producing the voltage that the researchers detected.
The result suggests that making diamond extremely thin did more than make it flexible. The microscopic structure of the material also became important to how it responded to mechanical movement.
Why the Discovery Could Matter for Medicine
The finding becomes particularly interesting when the properties of diamond are considered alongside the demands of tiny medical devices.
Future implants may need sensors that monitor movement or physical changes while operating in extremely small spaces. Some devices also need reliable sources of very small amounts of power.
A flexible diamond membrane could potentially perform both roles.
Because the material can generate an electrical response when it bends, future devices might use mechanical movement to produce small amounts of electricity or to detect deformation. Researchers suggest this could eventually have applications in implantable medical devices and self-powered sensors.
Diamond's chemical stability and biocompatibility also make it attractive for technologies designed to operate around the human body.
But those applications remain theoretical at this stage.
The researchers have demonstrated the electrical effect in laboratory-made diamond membranes. They have not shown that the technology can power a medical implant in a human patient.
A New Role for an Old Material
The significance of the discovery, therefore, goes beyond the possibility of making electricity from diamonds.
For decades, diamond's unusual properties have made it valuable as a durable material in advanced technologies. It has generally served as a structural or protective component rather than as a material that actively generates an electrical signal.
The new findings suggest that role could change.
By engineering diamond at an ultrathin scale, researchers have revealed an electrical behavior that was not expected from the material in its conventional form. The same hardness that makes ordinary diamond difficult to deform may become an advantage when combined with a flexible membrane design.
Whether that will eventually lead to self-powered medical implants or other miniature technologies remains to be seen.
For now, the discovery has accomplished something more fundamental: it has shown that one of the world's most familiar materials still has an electrical trick that scientists did not expect it to have.
