Experimental explanation of the formation mechanism of surface mound-structures by femtosecond laser on polycrystalline Ni₆₀Nb₄₀

Authors

Edwin Peng, University of Nebraska-Lincoln
A. Tsubaki, University of Nebraska-Lincoln
Craig A. Zuhlke, University of Nebraska-LincolnFollow
Meiyu Wang, University of Nebraska-Lincoln
Ryan Bell, University of Nebraska-Lincoln
Michael J. Lucis, University of Nebraska-Lincoln
Troy P. Anderson, University of Nebraska-LincolnFollow
Dennis R. Alexander, University of Nebraska-LincolnFollow
George Gogos, University of Nebraska-LincolnFollow
Jeffrey E. Shield, University of Nebraska-LincolnFollow

Document Type

Article

Date of this Version

2016

Citation

APPLIED PHYSICS LETTERS 108, 031602 (2016)

Comments

Copyright 2016 AIP Publishing LLC

Abstract

Femtosecond laser surface processing (FLSP) is an emerging technique for creating functionalized surfaces with specialized properties, such as broadband optical absorption or superhydrophobicity/ superhydrophilicity. It has been demonstrated in the past that FLSP can be used to form two distinct classes of mound-like, self-organized micro/nanostructures on the surfaces of various metals. Here, the formation mechanisms of below surface growth (BSG) and above surface growth (ASG) mounds on polycrystalline Ni₆₀Nb₄₀ are studied. Cross-sectional imaging of these mounds by focused ion beam milling and subsequent scanning electron microscopy revealed evidence of the unique formation processes for each class of microstructure. BSG-mound formation during FLSP did not alter the microstructure of the base material, indicating preferential valley ablation as the primary formation mechanism. For ASG-mounds, the microstructure at the peaks of the mounds was clearly different from the base material. Transmission electron microscopy revealed that hydrodynamic melting of the surface occurred during FLSP under ASG-mound forming conditions. Thus, there is a clear difference in the formation mechanisms of ASG- and BSG-mounds during FLSP.