title: Chromatic annuli formation and sample oxidation on copper thin films by femtosecond laser.
abstract: We report an experimental investigation on the irradiation of copper thin films with high repetition rate femtosecond laser pulses (1040 nm, 50 MHz), in ambient air and liquid water. We observe a novel, striking phenomenon of chromatic copper oxides (CuO and Cu2O) annuli generation. The characteristic features of the chromatic copper oxide annuli are studied by exploiting micro-Raman spectroscopy, optical and scanning electron microscopies. In the case of irradiation in water, the seldom investigated effects of the immersion time, tw, after irradiation with a fixed number of pulses are analyzed, and an intriguing dependence of the color of the chromatic annuli on tw is observed. This remarkable behavior is explained by proposing an interpretation scenario addressing the various processes involved in the process. Our experimental findings show that Cu2O nanoparticles (size of ≈20 nm) and Cu2O nanocubes (nanocube edges of ≈30, ≈60 nm) can be effectively generated by exploiting high repetition rate laser-assisted oxidation.
authors.affiliation: Ultrafast Laser Laboratory, Key Laboratory of Opto-Electronic Information Technical Science of Ministry of Education, College of Precision Instruments and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China.
authors.forename: Shutong
authors.initials: S
authors.lastname: He
authors.affiliation: Dipartimento di Fisica, Università di Napoli Federico II, Complesso Universitario di Monte S. Angelo, Via Cintia, I-80126 Napoli, Italy.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Amoruso
authors.affiliation: Ultrafast Laser Laboratory, Key Laboratory of Opto-Electronic Information Technical Science of Ministry of Education, College of Precision Instruments and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China.
authors.forename: Dongqing
authors.initials: D
authors.lastname: Pang
authors.affiliation: Ultrafast Laser Laboratory, Key Laboratory of Opto-Electronic Information Technical Science of Ministry of Education, College of Precision Instruments and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China.
authors.forename: Chingyue
authors.initials: C
authors.lastname: Wang
authors.affiliation: Ultrafast Laser Laboratory, Key Laboratory of Opto-Electronic Information Technical Science of Ministry of Education, College of Precision Instruments and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, China.
authors.forename: Minglie
authors.initials: M
authors.lastname: Hu