Microwave driven synthesis of narrow bandgap alpha-tin nanoparticles on silicon

•A CMOS-compatible MW-driven process resulting into α-Sn over Si was proposed.•A 52 meV direct bandgap was extrapolated from FTIR measurements.•An α-Sn phase stable up to 200 °C was synthesized.•MW-enhanced atomic diffusion and fast cooling may favor formation of α-Sn domains.•α-Sn domains/amorphous oxide core/shell structure was found.