Search

Surface structures with nanoscale size and periodicity are important in controlling the flow of light as well as light-matter interaction. Fabrication of these periodic nanostructure requires sophisticated and expensive nanofabrication methods that limits large scale production of such structures. Laser induced periodic surface structures (LIPSS) is a scalable and cheap method to create periodic structures. However, they suffer from lacking a long-range order. Here, we present a maskless fabrication technique of creating highly uniform subwavelength structures on nickel surface, using two collinear femtosecond laser beams at various temporal delays. Our femtosecond laser induced periodic surface structures (FLIPSSs) show a high spatial uniformity with a grating period ranging between 320–350 nm. The high spatial uniformity is a consequence of using two pulsed beams with short inter-beam delay time due to reduction in the propagation length of excited surface plasmon polaritons (SPPs). The subwavelength period is due to grating splitting mechanism where the two beams sequentially interact with existing structures to create a superimposed grating. The demonstrated fabrication method enables large scale fabrication of regular sub-wavelength structures.

Ultrafast and high intensity laser pulses can drive materials into highly non-equilibrium conditions. At a sufficiently high intensity, femtosecond laser pulses can turn a solid material into a superheated solid or a superheated liquid state. For metals with low electron–phonon coupling strength, e.g., gold (Au), a superheated liquid state can lead to the formation of a family of unique surface structures, the so-called Voronoi partitions (VPs). Although chaotic in nature, we demonstrate here a control of VP formation through varying the laser fluence and pulse number, resulting in a rich variety of VPs. To understand the formation of complex surface geometries under laser irradiation, we utilizes a numerical approach that integrates the finite difference time domain of electromagnetic field method with the two-temperature model. By studying the spatio-temporal distribution of electromagnetic and temperature fields and by analyzing the geometric properties of the VPs, we provide a framework for understanding the emerging surface patterns. With VPs, novel structures are generated with promising potential applications, namely, Gecko-skin-like nano-spikes and nano-cauliflower-like surface structures.

Highlights • We present a detailed study on the formation of various surface structures formed using femtosecond laser treatment. • We show that femtosecond laser processing turns originally hydrophilic Au to super-hydrophobic surface. • We demonstrate the ability of the treated surface to reduce the adhesion of E. coli bacteria., Femtosecond laser-induced surface structuring is a promising technique for the large-scale formation of nano- and microscale structures that can effectively modify materials’ optical, electrical, mechanical, and tribological properties. Here we perform a systematic study on femtosecond laser-induced surface structuring on gold (Au) surface and their effect on both hydrophobicity and bacterial-adhesion properties. We created various structures including subwavelength femtosecond laser-induced periodic surface structures (fs-LIPSSs), fs-LIPSSs covered with nano/microstructures, conic and 1D-rod-like structures (≤ 6 μm), and spherical nanostructures with a diameter ≥10 nm, by raster scanning the laser beam, at different laser fluences. We show that femtosecond laser processing turns originally hydrophilic Au to a superhydrophobic surface. We determine the optimal conditions for the creation of the different surface structures and explain the mechanism behind the formed structures and show that the laser fluence is the main controlling parameter. We demonstrate the ability of all the formed surface structures to reduce the adhesion of Escherichia coli (E. coli) bacteria and show that fs-LIPSSs enjoys superior antibacterial adhesion properties due to its large-scale surface coverage. Approximately 99.03% of the fs-LIPSSs surface is free from bacterial adhesion. The demonstrated physical inhibition of bacterial colonies and biofilm formation without antibiotics is a crucial step towards reducing antimicrobial-resistant infections.