Researchers at the University of Hong Kong (HKU) have discovered that ultrathin, highly flexible diamond membranes can produce a measurable piezoelectric response, challenging a scientific assumption that has stood for more than a century. The work was led by Professor Zhiqin Chu, Associate Professor in the Department of Electrical and Computer Engineering, and Professor Yuan Lin, Professor in the Department of Mechanical Engineering, Faculty of Engineering at the University of Hong Kong (HKU). Since the early 1900s, diamond has generally been classified as a non-piezoelectric material, meaning it was not expected to generate an electrical voltage when mechanically deformed.
That limitation has shaped how diamond has been used in engineering. Despite its exceptional hardness, strength, chemical stability, high acoustic velocity, thermal conductivity, dielectric breakdown strength and ultrawide bandgap, diamond has typically served only as a structural support for other piezoelectric materials in microelectromechanical systems (MEMS). For that reason, the idea of "generating electricity from diamonds" was long considered impractical.
To test whether diamond could behave differently under extreme mechanical conditions, the HKU team used a recently developed edge exfoliation method to produce an ultrathin, flexible polycrystalline diamond membrane. Reducing the material to such a thin form allowed the normally rigid diamond to bend much more than bulk diamond can. When the researchers deliberately flexed the membrane, they observed stable voltage signals.
The team then carried out extensive mechanical cycling experiments under carefully controlled conditions to make sure the electrical output was genuine. These tests were designed to rule out environmental interference and triboelectric effects, which can generate electrical signals when surfaces contact or rub against one another. The voltage appeared consistently and repeatedly, providing strong evidence that the diamond membrane itself was producing a piezoelectric response.
Grain Boundaries Create the Electrical Effect To understand why the effect occurs, the researchers performed detailed first-principles calculations. Their analysis points to asymmetry at the grain boundaries inside the polycrystalline diamond membrane. These boundaries separate the many tiny diamond crystals that make up the material.
As the membrane bends more strongly, electrical charge polarization builds up around those grain boundaries. This creates a difference in electrical potential between the upper and lower surfaces of the membrane, producing the observed voltage. Potential for Medical Devices and Tiny Power Systems The discovery could open new possibilities for diamond in areas where durability and safety are especially important.
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