Applied Surface Science 261 (2012) 101–109 Contents lists available at SciVerse ScienceDirect Applied Surface Science j our nal ho me p age: www.elsevier.com/loc ate/apsusc Effect of ambient environment on excimer laser induced micro and nano-structuring of stainless steel Umm-i-Kalsoom, Shazia Bashir ∗ , Nisar Ali, Mahreen Akram, Khaliq Mahmood, Riaz Ahmad Center for Advanced Studies in Physics, Govt. College University, Lahore 54000, Pakistan a r t i c l e i n f o Article history: Received 14 February 2012 Received in revised form 11 June 2012 Accepted 21 July 2012 Available online 9 August 2012 Keywords: Stainless steel Laser ablation Microstructure formation a b s t r a c t The effect of laser fluence and an ambient environment on the formation and development of the micro and nano-structures on the laser irradiated stainless steel (AISI-304) targets have been investigated. For this purpose KrF excimer laser ( = 248 nm, t = 20 ns, repetition rate 20 Hz) has been used. The targets are exposed for various laser fluences ranging from 0.72 J cm -2 to 1.27 J cm -2 under the vacuum condi- tion and in the oxygen environment at a pressure of 133 mbar. Various features of treated targets, such as surface morphology, chemical composition and crystalline structure are analyzed by scanning elec- tron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction techniques, respectively. Scanning electron microscope analysis reveals the formation of laser-induced periodic surface structures (LIPSS), cavities, hillocks in both ambient environments (vacuum, oxygen). Cone-formation on the top of wave like ridges is observed under vacuum condition. In case of oxygen only redeposition is observed. Energy dispersive X-ray spectroscopy analysis exhibits that there is variation in chemical composition in both environments. When the target is treated in oxygen environment enhancement of the surface oxygen content is observed. X-ray diffraction exhibits that no new phases are formed under vacuum condition but a phase change in oxygen ambient is observed. For various fluences the variation in the peak intensity, crystallinity and d-spacing is observed under both ambient conditions. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Laser ablation of materials is a topic of current research due to its vast range of applications in the field of industry, materials processing, micromachining, nano-structuring, laser welding, and pulsed laser deposition of thin films [1–6]. A substantial work is reported on the micro/nanostructuring of stainless steel using excimer laser irradiation. Micro and nanostruc- tures have been used for fluidic, electronic, optic, and mechanical devices in various fields [3,7]. Excimer lasers are useful tool for the growth and fabrication of these structures [7]. UV nanosec- ond pulsed lasers-induced micro/nanostructuring of stainless steel is reported to be useful for enhancing the surface mechanical properties [8]. A lot of work is also reported on the formation of femtosecond pulsed laser-induced periodic surface structures on stainless steel. These structures are useful as an anti-reflective, for enhancing the optical absorptance and coloring the surface [9–11]. During laser ablation of materials, it is reported [12,13] that the nature and pressure of ambient environment are some of the controlling factors of plasma characteristics, as well as the fac- tors related to the laser energy absorption for surface modification. ∗ Corresponding author. Tel.: +92 322 8455405. E-mail address: shaziabashir@gcu.edu.pk (S. Bashir). Therefore the role of ambient environment is crucial for micro and nanostructuring of material. The influence of the ambient atmo- sphere of vacuum and air on the performance of laser ablation of various metals, such as nickel, copper, molybdenum, indium, tungsten and gold has been investigated by Preuss et al. [14]. It is suggested in this work that metal ablation in air is signif- icantly less efficient than in vacuum due to shielding effect and re-deposition of ablated material. Pedraza et al. [15] investigated the effect of various environments of air, oxygen and nitrogen on nano/microstructuring and growth of microcolumns on the surface of Si. In case of oxygen environment small droplets on the tip of columns are also observed. In another work reported by Lavisse et al. [16] reported the Nd:YAG laser irradiation effects on tita- nium in the ambient environment of oxygen and nitrogen. In this work the influence of laser power and repetition rate on oxygen and nitrogen insertion into titanium for the formation of oxide and nitride layers has been investigated. Dolgaev et al. [17] reported multipulse irradiation effects of Nd:YAG laser on the growth of conical microstructure arrays on a stainless steel substrate under various pressures of air. The present work investigates the effect of laser fluence and ambient environmental conditions (vacuum, oxygen) on the micro and nanostructuring of stainless steel (AISI-304) after excimer laser irradiation. For the surface morphological investigation of these structures, scanning electron microscope (SEM) analysis is 0169-4332/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2012.07.107