Diamond Can Generate Electricity When Bent, Hong Kong Study Finds

Researchers at the University of Hong Kong (HKU) have found that ultrathin, flexible diamond membranes can generate electricity when bent, challenging a scientific assumption that has stood for more than a century. The team was led by Professor Zhiqin Chu of HKU's Department of Electrical and Computer Engineering and Professor Yuan Lin of its Department of Mechanical Engineering.

Since the early 1900s, diamond has generally been classified as a non-piezoelectric material, meaning it was not expected to produce a voltage when mechanically deformed. That assumption limited how diamond could be used in engineering: despite its hardness, chemical stability, high thermal conductivity and ultrawide electronic bandgap, it has typically served only as a passive structural support for other piezoelectric materials inside microelectromechanical systems (MEMS) — tiny mechanical devices built using chip-making techniques.

To test whether diamond could behave differently under extreme bending, the HKU team used a method called edge exfoliation to produce an ultrathin, flexible polycrystalline diamond membrane — a sheet made of many tiny diamond crystals fused together, thin enough to bend far more than ordinary bulk diamond. When the researchers flexed the membrane, they measured stable voltage signals. Repeated mechanical cycling tests, designed to rule out interference from the environment and from triboelectric effects — voltage produced simply by surfaces rubbing or touching — confirmed that the diamond itself was producing the voltage.

First-principles calculations pointed to the cause: asymmetry at the grain boundaries, the internal surfaces where the diamond's many tiny crystals meet. As the membrane bends further, electrical charge builds up unevenly around these boundaries, creating a difference in electrical potential between the membrane's two surfaces.

Because diamond is biocompatible, chemically stable and non-toxic, the researchers say piezoelectric diamond membranes could eventually be used in implantable medical devices as self-powered sensors or power sources, and in other high-reliability micro energy systems that need durable, self-generating electrical components.