Researchers at the University of Hong Kong (HKU) have discovered that ultra-thin, flexible diamond films can produce measurable piezoelectric voltage when bent. The breakthrough challenges more than a century of scientific understanding that diamond is not a piezoelectric material.
The study 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, both from the HKU Faculty of Engineering.
Flexible diamond films challenge a century-old scientific rule
Since the early 20th century, diamond has generally been classified as a non-piezoelectric material. In other words, scientists did not expect diamond to generate an electrical voltage when exposed to mechanical stress or deformation.
This assumption has influenced how diamond is used in engineering. Although diamond offers exceptional hardness, mechanical strength, chemical stability, sound velocity, thermal conductivity, dielectric breakdown strength, and an ultra-wide bandgap, it has primarily functioned as a durable structural support for other piezoelectric materials in microelectromechanical systems (MEMS).
As a result, the concept of “generating electricity from diamonds” was long considered impractical.
Making diamond thin enough to bend
To investigate whether diamond could display piezoelectric behavior under extreme mechanical conditions, the HKU research team used a recently developed edge-exfoliation technique to create ultra-thin, flexible polycrystalline diamond films.
Reducing diamond to a nanoscale thickness enabled the normally rigid material to bend far more easily than bulk diamond. When the researchers deliberately flexed the diamond membrane, they detected a stable electrical voltage signal.
The team carried out extensive mechanical cycling tests under carefully controlled conditions to verify that the electrical output was genuine. The experiments helped rule out environmental interference and triboelectric effects, which can produce electrical signals when materials come into contact or rub against one another.
The voltage was detected consistently and repeatedly, offering strong evidence that the diamond film itself was generating a piezoelectric response.
Diamond grain boundaries generate electrical polarization
To determine the source of this unexpected effect, the researchers conducted detailed first-principles calculations.
Their findings indicate that the electrical response is linked to asymmetries within the internal grain boundaries of the polycrystalline diamond films. These grain boundaries form where the material’s many small diamond crystals meet.
When the flexible film bends, electrical charge polarization increases around these grain boundaries. This creates a potential difference between the upper and lower surfaces of the membrane, resulting in the measurable voltage observed by the researchers.
Potential applications in medical devices and micro-energy systems
The discovery could expand the use of diamond in technologies that require exceptional durability, reliability, and biocompatibility.
Diamond is chemically stable, non-toxic, and highly compatible with biological environments, making piezoelectric diamond films promising for medical and energy-related applications. Future implantable medical devices could use these films as self-powered energy sources or as sensors capable of detecting bending, movement, and deformation.
More broadly, the research demonstrates a new method for giving diamond active electrical functionality instead of using it solely as a passive structural material.
The findings could help advance next-generation micro-energy harvesters, highly reliable MEMS components, and self-powered sensing technologies based on flexible piezoelectric diamond films.
Source: www.sciencedaily.com