High spatial frequency periodic structures formation on silicon using near UV femtosecond laser irradiation

Observation of a nanoscale island-like periodic surface structure in silicon using 390 nm ultrafast laser irradiation in vacuum is reported. A strong correlation is observed between the island structure and the formation of a high-spatial frequency laser induced periodic surface structure below the single pulse melt threshold. Further hexagonal and quasi-hexagonal arrangements of the islands concurrent with bifurcation suggest the existence of a strain ordering mechanism. Island bifurcation suggests a high stress state induced by point-defect generation during and after femtosecond laser induced band-gap closure. Published by AIP Publishing.