Laser Generation and Applications of Micron and Submicron Scale Features on Metals

UoM administered thesis: Phd

  • Authors:
  • Robert Lloyd

Abstract

This thesis describes the formation of and applications of self-assembled structures onmetals. Primarily the focus of this PhD project is on the formation of surfaces structureson stainless steel (AISI 304) but other metals have been studied. Laser generated surfacestructures have been applied to the modification of wettability and reflectivity with aview towards developing these processes for industrial applications. Compared toconventional techniques for the modification of wettabililty, lasers offer the advantageof being a relatively simple technique for the modification of surface structure, reducingthe need for complex processes. It is hoped that investigations into the reduction ofsurface reflectivity will have applications in the conversion of solar energy into useablepower in the form of solar thermal energy.The production of self assembled structures is demonstrated using diode pumped solidstate (DPSS) Nd:YVO4 lasers operating at wavelengths of 532 and 1064 nm. It isshown that the production of surface microstructures is highly dependant on the correctlaser fluence and requires multiple pulses and processing passes. At 1064 nmwavelengths, it has been found highly reproducible surface structures can be formed bycarefully controlling laser fluence and scanning speed while keeping the opticalarrangement relatively simple. In addition to microstructure formation, the use ofultrafast femtosecond lasers, operating at 400 and 800 nm wavelengths has verified theproduction of laser induced periodic surface structures. Additionally, the stationarymethod used to produce these surfaces has been adapted to cover large surface areaswith sub wavelength ripple structures with periods of ~295nm and 600nm.Applications of laser surface microstructures on metals have been studied in an effort toproduce hydrophobic and superhydrophobic surfaces on metals. It has been found thatthe roughness change produced by laser processing induces composite wetting whenwater droplets are introduced to the surface. Contact angle measurements and smallangle XRD analysis of laser processed stainless steel (AISI 304) have shown thatsurface wettability decreased over a period of approximately one month, leading tosteady contact angles of over 140°. This is attributed to the formation of a magnetite(Fe3O4) oxide layer in the period after laser processing.The effect of surface microstructure on surface reflectivity has also been studied. It wasfound that laser induced surface microstructures on copper can decrease surfacereflectivity by almost 90%. A comparative study of the effects of surface roughness andchemistry on the optical absorption of copper is given, finding that these surfaces arecompetitive with contemporary coatings.

Details

Original languageEnglish
Awarding Institution
Supervisors/Advisors
Award date1 Aug 2011