Discovered by Jacques and Pierre Curie in 1880, the piezoelectric effect was first observed when they applied pressure to a quartz crystal, which generated electric charges. This effect was called a direct piezoelectric effect. Later on, the converse piezoelectric effect was verified when they applied an electric field to quartz, producing deformations in the crystal.
Improving Piezoelectricity of Materials
One known technique for enhancing the piezoelectricity of a substance by reducing its dimensionality. For instance, researchers have been venturing into piezoelectricity in a single layer of molecules. Further reducing this two-dimensional array of molecules result in individual molecules manifesting electromechanical responses.
This demonstration marks the beginning of a revolution in comprehending the electromechanical behavior of individual molecules, and subsequently provide a different approach in developing low-power logic switches, molecular motors, ultrasensitive biological sensors, and energy harvesting at the nanoscale.
“In a close collaboration with physicists, it was proved for the first time that a strong converse piezoelectric effect can be observed at individual molecules of the heptahelicene derivative, which is a screw-like carbon molecule resembling a spring,” said Ivo Starý, co-author and leader of the study and chemist at IOCB Prague.
Co-leader and physicist Pavel Jelínek describes the unprecedented results of the study: “The magnitude of the piezoelectric constant calculated from the experimental data is significantly higher than that one of known piezoelectric polymers and is comparable to the magnitudes measured at some inorganic materials such as zinc oxide. Moreover, we explained the origin of the single molecule piezoelectric effect by employing quantum mechanics calculations.”
How Was the Converse Piezoelectricity Demonstrated?
The effect was experimentally demonstrated in individual polar molecules grafted on a silver surface using an atomic force microscope (AFM).
Polar molecules have an intrinsically uneven distribution of charges due to its unsymmetrical molecular structure such that one end is positively charged while the other end is negatively charged. This effect is called dipole. An example of molecules exhibiting dipole is hydrochloric acid or HCl. Its hydrogen atom is the positive end, while its chlorine atom is the negative pole.
[Via EurekAlert]