Coalescence threshold temperature in Ag nanoisland growth by pulsed laser deposition

In this study, Ag nanoislands were deposited on glass and Si(100) at substrate temperature from 25 to 450 °C by Pulsed Laser Depositions (PLD). The growth of Ag nanoislands was evidenced from optical absorption surface plasmon resonance (SPR) bands. SPR peaks was not evidently observed in the spectrum of sample deposited at 25 °C, but sample deposited at 150 °C presented a broad SPR peak around λ=870 nm. SPR peak showed a blue shift to 540-550 nm and became narrower as the substrate temperature increases. Atomic Force Microscope (AFM) showed that by increasing deposition temperature to 350 and 450 °C, Ag islands grow in height and diameter and the number of island decrease among the surface. Two-probe measurement of electrical resistance of films was also recorded during deposition processes to recognize the coalescence of Ag nanoislands. The results show that the deposition at temperatures below 250 °C leads to a sharp decrease in film resistance while at higher temperatures the islands were separated without resistance decline. To determine coalescence threshold temperature, resistance variation was measured for a cooling substrate, from 300 down to 200 °C, substrate. The result revealed that the coalescence of Ag begins near 230 °C.