Pulsed-Laser Generation of Nanostructures
We discussed two main approaches for generation of nanometer-scale structures using pulsed lasers. In the first, a bulk material is ablated in vacuum, gas or liquid and consequent re-solidification of the evaporated material in clusters generate the desir
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Pulsed-Laser Generation of Nanostructures Selcuk Akturk
Abstract We discussed two main approaches for generation of nanometer-scale structures using pulsed lasers. In the first, a bulk material is ablated in vacuum, gas or liquid and consequent re-solidification of the evaporated material in clusters generate the desired nanoparticles. While one can play with various experimental parameters (laser powers, type of liquids, background gas etc.) to control particle sizes, there is always a relatively broad distribution of particle sizes. Nevertheless, particles with sizes down to few nanometers are achievable. In the second approach, fs lasers are used to pattern material surfaces. This process is more controlled in the sense that the desired geometries are generated by scanning of the sample. On the other hand, best achievable resolutions are worse as compared to the former approach. Resolutions better than 100 nm over large surfaces is very difficult. Finally, special beam shaping methods forms an interesting frontier in pushing forward the fs laser nanomachining methods towards broader practical uses.
7.1
Introduction
Ablation of materials by pulsed lasers constitute a versatile approach to generation of nanometer-scale structures. In this chapter, we will discuss two distinct approaches for pulsed-laser generation of nanostructures. In the first case, laser pulses are sent to the surface of the target material in bulk form. The evaporated material then solidifies in the form of clusters of various sizes, usually in sub-micron range. The cluster formation can take place in liquid or gas environment. In the second approach that we will discuss, the process is more “controlled”. Here, ultrashort laser pulses (with femtosecond pulse durations) are focused to small spots and by working near the ablation-threshold, volumes with sub-micron dimensions are removed. Nanostructures of desired forms and geometries are S. Akturk (&) Department of Physics, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey e-mail: [email protected] © Springer International Publishing Switzerland 2016 H. Ünlü et al. (eds.), Low-Dimensional and Nanostructured Materials and Devices, NanoScience and Technology, DOI 10.1007/978-3-319-25340-4_7
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generated by scanning the sample under laser illumination. We will describe the first approach (which is a relatively more mature field, and many good reviews already exist) in a brief overview manner, while we will elaborate more on the second, more recently emerging case.
7.2
Self-formation of Nanostructures Through Pulsed-Laser Ablation
Laser-assisted formation of nanostructures has a history of nearly three decades. In one of the earlier works, continuous-wave laser are used to manipulate the size distribution of metal clusters [1]. The physical mechanism of size change is basically absorption of laser energy by the particles, consequent heating and division. The method is thus suitable for processing of nanoparticles, already prepared by other means. In 1997, Morales and
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