By direct observation of coherent acoustic phonons, we demonstrate a novel extrinsic piezoelectric response in colloidal CdSe semiconductor quantum dots. This response is driven by the migration of charges to the surface of the quantum dot on a vibrationally impulsive time scale. Surface- and fluence-dependent studies reveal that the observed carrier capture based piezo response is controllable and is at least an order of magnitude larger than the intrinsic piezo response of wurtzite CdSe.
The generation of an electric field by the compression and expansion of solid materials is known as the piezoelectric effect, and it has a wide range of applications ranging from everyday items such as watches, motion sensors and precise positioning systems. Researchers at McGill University’s Department of Chemistry have now discovered how to control this effect in nanoscale semiconductors called “quantum dots,” enabling the development of incredibly tiny new products.
The piezoelectric effect has never been manipulated at this scale before, so the range of possible applications is very exciting,” explained Pooja Tyagi, a PhD researcher in Professor Patanjali Kambhampati’s laboratory. “For example, the vibrations of a material can be analyzed to calculate the pressure of the solvent they are in. With further development and research, maybe we could measure blood pressure non-invasively by injecting the dots, shining a laser on them, and analyzing their vibration to determine the pressure.” Tyagi notes that Cadium Selenide is a toxic metal, and so one of the hurdles to overcome with regard to this particular example would be finding a replacement material.