Until now, such nanostructures have been mainly generated from materials such as ZnO, AlN, single and polycrystalline silicon, gold, and carbon whose growth is dependent on the crystallographic

orientation. These nanostructures have been synthesized by techniques such as thermal evaporation, various types of chemical vapor deposition, resonance plasma etching, and chemical etching [2–8]. The aforementioned techniques require a long processing time, multiple steps, catalyst-assisted growth, Z-VAD-FMK concentration high processing temperatures, very sophisticated equipment, vacuum, and clean room operations. In the past few years, various types of lasers have also been utilized to produce micronanostructures with sharp ends (nanobumps, nanojets, nanoprotrusions) from the irradiation of thin metal films and bulk materials using tightly focused laser beams. Such sharp nanojet structures have been MCC950 order S3I-201 in vitro produced on gold thin films by irradiation of single nano- or femtosecond laser pulse in ambient or under

low-vacuum conditions using circular laser spots [9]. In most of these cases, the gold films with certain thicknesses were deposited onto borosilicate glass or single-crystal silicon substrates by RF sputtering with the help of in situ coating of adhesion layers [9, 10]. In these techniques, for each laser pulse interaction with the film, only one nanostructure is produced at a time, and the distance between two laser incident spots on the film has to be maintained at a certain value to avoid potential rupture of the film

and the damage of aminophylline the previously formed nanostructure via intersection of laser irradiation spots [11]. This eventually limits the number of nanostructures that can be produced on a surface area of the target. The study of these nanostructures for various parameters has been conducted by various researchers on various metal films [9–12]. The number of laser pulses that can be applied onto a particular spot on the target film is limited due to the fact that multiple laser pulses could ablate all the film material from the irradiation spot and could eventually start ablating the substrate surface. However, the multiple laser pulses have been used to produce sharp spikes on bulk silicon surfaces in vacuum chamber filled with 500 Torr of Cl2, SF6, N2, or He gas [13]. They have reported that the silicon surface irradiated in SF6 and Cl2 gas background exhibits the growth of sharp spikes roughly aligned in rows whereas in the case of vacuum, N2, or He gas background, very blunt spikes with irregular sides and rounded tops with much larger tip diameter are formed.