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The structural modifications of an Si(111)- 7x7 reconstructed surface and the evolution of growth induced by Ga adsorption in the submonolayer regime at various substrate temperatures ranging from room temperature (RT) to 600 °C, with a low Ga flux rate of 0.1 ML/min (1 ML∼6.8×1014 atoms/cm2) have been studied in-situ in Ultra High Vacuum (UHV) using Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED) and Electron Energy Loss Spectroscopy (EELS) as characterization probes. Ga grows in the Stranski–Krastanov (SK) growth mode for temperatures ranging from RT to 350 °C, where 3D-islands form after one and two flat monolayers of Ga adsorption, while for higher temperatures ranging from 450 to 550 °C, Ga grows in the Volmer–Weber (VW) growth mode. A comprehensive 2D-phase diagram for this Ga/Si(111) system for adsorption, which provides pathways to attain the observed superstructural phases, viz., √3x√3-R30°, 6.3x6.3, 6.3√3x6.3√3-R30° and 11x11, has been investigated. The characteristic EELS spectrum for each superstructural phase is also reported in this study.