Morphological evolution of Ag nanoclusters grown on hydrogen-terminated si(111)-(1 × 1) surface: Appearance of quantum size effect at room-temperature

•Growth of Ag on H-terminated Si(111)-(1 × 1) is investigated by STM at room temperature.•Morphology and growth mode of Ag nanoclusters change dramatically after coalescence.•Ag atoms initially grow as dome-like 3D clusters and transform into flat-top 2D islands.•Flat-top 2D islands show uniform height owing to quantum size effect emerging at RT. We have observed the early stages of Ag nanocluster evolution on a hydrogen-terminated Si(111)-(1 × 1) surface at room temperature (RT) by using scanning tunneling microscopy and low energy electron diffraction, and examined changes in number density, height, base diameter, volume and shapes of the nanocluster with a deposition amount from 0.2 to 8 ML. It is found that Ag nanoclusters evolve by repeating the stages of nucleation/growth and coalescence, and change the growth morphology and the growth mode after the coalescence. Transition from initially formed dome-like three dimensional clusters to flat-top two dimensional (2D) islands evidently shows that quantum size effect emerges during the growth process of Ag nanoclusters even at RT. The characteristic stability of 8 atomic layer height in the 2D islands is well interpreted based on a free-electron gas model for free-standing nanofilms. [Display omitted]