Real time monitoring of the in situ growth of silver nanoparticles in a polymer film under ambient conditions

Direct monitoring of the formation and growth of nanoparticles by microscopy in real time is of fundamental interest in understanding the chemical and self assembly processes involved. Such studies are difficult to implement in solution, but have been carried out on solid substrates, mostly under specialized conditions, including ultra high vacuum. The present study illustrates the facility with which in situ growth of metal nanoparticles in thin polymer films under ambient conditions can be monitored by real time atomic force microscopy. Formation of silver nanoparticles inside spin-coated thin films of poly(vinylpyrrolidone) containing silver nitrate, under ambient conditions, is revealed by the emergence and growth of surface plasmon resonance absorption extending over several hours. Atomic force microscopy allows 'direct observation' of structures growing near the surface; individual nanostructures can be monitored in the case of very thin films. A plausible mechanism is proposed for the chemical reactions occurring inside the film with the polymer itself acting as the reducing agent leading to the formation and growth of the nanoparticles. The present study opens up new avenues to carry out investigations into the mechanisms and kinetics of nanoparticle growth.