Influence of ultraviolet radiation on surface electric potential of P(VDF-TrFE) films

Ultraviolet (UV) radiation is able to cause biological changes at the cellular and molecular level. To study biological effects of UV radiation, UV detector is required. 10 monolayer thick ferroelectric P(VDF-TrFE) films consisting of 70% vinylidene fluoride (VDF) and 30% trifluoroethylene (TrFE), or P(VDF-TrFE 70:30), were investigated as a possible material of UV detector. The films were deposited on a glass substrate using Langmuir-Blodgett technique. Changes in surface electric potential of P(VDF-TrFE 70:30) films under influence of UV radiation were investigated by Kelvin force microscopy. A hypothesis was proposed that UV radiation was well absorbed by the glass substrate changing its surface charge. This charge in turn changed polarization of P(VDF-TrFE 70:30) film leading to changes in its surface electric potential. It was found that after 6 minutes of UV irradiation surface electric potential of P(VDF-TrFE 70:30) films decreased and no changes were observed further increasing irradiation time. However, surface electric potential of the bare glass substrate continued to decrease increasing irradiation time. It was also found that surface electric potential of P(VDF-TrFE 70:30) films relaxed to its initial value within half an hour after the irradiation was stopped. The relaxation obeyed exponential law. The study suggests that P(VDF-TrFE 70:30) films deposited on the glass substrate are sensitive to UV radiation and might be able to serve as a material for an UV dosimeter, however, further studies are required.