Mechanic properties modification of SiO2 thin films by femtosecond laser

Abstract

SiO2 films were deposited on fused silica substrates by ALD technology. The properties of ALD SiO2 films irradiated by femtosecond laser were investigated. Raman spectra confirms the molecular structure of SiO2 films is identical to that of fused silica. The relative content of the three- and four-membered ring of films irradiated is increased. Photoluminescence (PL) spectra shows that the defects of the films irradiated by laser of 10% power ratio are reduced. Indentation tests show that both hardness and elastic modulus are decreased by 1.8%, their standard deviations are decreased by 73.8% and 46.8% respectively. Scratch experiments exhibit that femtosecond irradiation improves the bonding performance of the films, and the critical load is increased by 10.8%. Meanwhile, the standard deviations of the lateral load and penetration depth are decreased on average from 0.0636 to 0.0336, from 8.3478 to 1.6747, individually. The plastic deformation ratio of the films are increased from 19.80% to 28.89%. The morphology and cross section of the scratches observed by optical microscopy and confocal laser microscopy suggest that the damage form of the films irradiated by laser is changed from the brittle fracture removal form to the mixed removal form of brittle fracture and plastic.