Production of
nanoparticles with high repetition rate picosecond laser

Application note № AN1106IL01

Marijus BRIKAS ¹, Stephan BARCIKOWSKI ², Boris CHICHKOV ², Gediminas RAČIUKAITIS ¹ , ³

¹ Institute of Physics, Savanoriu Ave. 231, LT-02300 Vilnius, Lithuania
² Laser Zentrum Hannover, Hollerithallee 8, D-30419 Hannover, Germany
³ Ekspla Ltd, Savanoriu Ave. 231, LT-02300 Vilnius, Lithuania

Keywords: Laser ablation, nanoparticle, picosecond laser, colloidal solution.

Abstract
The fabrication of silver and gold nanoparticle colloids using the picosecond (10 ps) laser ablation in liquids was studied. The maximum productivity of 8.6 μg/s nanoparticles was achieved with the 10 ps-laser pulses at high pulse energy (110 μJ) and the repetition rate of 50 kHz. A special stirred flow chamber was constructed in order to improve reproducibility and generation speed of nanoparticles in flowing liquid during the ps-laser ablation.

Introduction
Laser ablation in liquids is attracting much attention as a new technique to prepare nanoparticles. An advantage of this technique is simplicity of the procedure. In principle, nanoparticles of various species of materials can be prepared by using one procedure [1]. Nanoparticles are used in biomedical applications such as antibacterial implants or catheters, modification of textiles, and refinement of polymers. Very often the desired range of applications is restricted due to a limited availability of nanoparticle materials, their purity and their redispersability from agglomerates [2-6]. Over the last decade, the major effort has been directed to the production of stable solutions of small nanoparticles with narrow size distributions and controlled surface chemistry. Although 5–100 nm nanoparticles can be produced by a relatively simple chemical reduction method, the surface of these nanoparticles is likely to be contaminated with reaction by-products such as anions and reducing agents, which can interfere with subsequent stabilization and functionalization steps [7]. Compared to chemical synthesis, the advantages of the laser ablation method are the simplicity of the procedure and absence of chemical reagents in solution. Pulsed laser ablation has also appeared to be the most flexible and promising technique because of its ability to ablate almost all kinds of materials due the ultra-high energy density and control over the growth process by manipulating the process parameters such as irradiation time, duration, energy density, wavelength, etc. [8] Furthermore, the stoichiometry (e.g. of nanoparticle alloys) is less altered during the conversion of the bulk material (alloy) into nanoparticles when ultrashort pulsed lasers are applied instead of nanosecond laser pulses [9]. It has been shown that high repetition rate picosecond (ps) lasers are advantageous compared to femtosecond (fs) lasers if the total thermal load produced by laser irradiation can be redistributed across a larger area [10]. In case of laser ablation in a liquid flow, the thermal energy is dissipated into the liquid and drained by the flow. It has been shown that laser ablation in liquid produces surface-charged nanoparticles with a shell of dipole molecules (e.g., water) formed around them, preventing agglomeration [2]. In this work, the high power and high repetition rate picosecond laser was applied for the production of silver nanoparticles in water and gold nanoparticles in n-hexane.

EKSPLA note: due to the continuous product improvements, laser models were replaced respectively: NL640 and NL15100 were replaced by Baltic and BalticHP series, PL10100 was replaced by Atlantic series.