Study of the formation of 3-D titania nanofibrous structure by MHz femtosecond laser in ambient air

Journal Article · Mon Jan 14 04:00:00 EST 2013 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4771667· OSTI ID:22102200

Tavangar, Amirhossein; Venkatakrishnan, K. ^[1]; Bo, Tan ^[2]

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1. Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, ON M5B 2K3 (Canada)
2. Department of Aerospace Engineering, Ryerson University, Toronto, ON M5B 2K3 (Canada)

In this study, we describe the formation mechanism of web-like three-dimensional (3-D) titania nanofibrous structures during femtosecond laser ablation of titanium (Ti) targets in the presence of background air. First, we demonstrate the mechanism of ablation of Ti targets by multiple femtosecond laser pulses at ambient air in an explicit analytical form. The formulas for evaporation rates and the number of ablated particles, which is analogous to the deposition rate of the synthesized nanofibers, for the ablation by a single pulse and multiple pulses as a function of laser parameters, background gas, and material properties are predicted and compared to experimental results. Afterwards, the formation of nanofibrous structures is demonstrated by applying an existing simplified kinetic model to Ti targets and ambient conditions. The predicted theory provides nanofiber diameter dependency with the combination of laser parameters, target properties, and ambient gas characteristics. Experimental studies are then performed on titania nanofibrous structures synthesized by laser ablation of Ti targets using MHz repletion-rate femtosecond laser at ambient air. The models' predictions are then compared with the experimental results, where nanostructures with different morphologies are manufactured by altering laser parameters. Our results indicate that femtosecond laser ablation of Ti targets at air background yields crystalline titania nanostructures. The formation of crystalline titania nanostructures is preceded by thermal mechanism of nucleation and growth. The results point out that laser pulse repetition and dwell time can control the density, size, and pore size of the engineered nanofibrous structure. As the deposition rate of nanostructures is analogous to the ablation rate of the target, higher density of nanofibrous structure is seen at greater laser fluences. The predicted theory can be applied to predict ablation mechanism and nanofiber formation of different materials.

• OSTI ID: 22102200
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 2 Vol. 113; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
77 NANOSCIENCE AND NANOTECHNOLOGY
ABLATION
DENSITY
ENERGY BEAM DEPOSITION
EVAPORATION
LASER RADIATION
NANOSTRUCTURES
NUCLEATION
POROSITY
PULSED IRRADIATION
PULSES
TITANIUM
TITANIUM OXIDES