UC Riverside

Laser ablation of solids in liquids (LASL) is a straightforward, clean and versatile method that has been used successfully to synthesize nanostructures (NS) with very different sizes, compositions and structures. However, due to the complexity of the laser-matter processes and the technical difficulty to study the phenomena involved, the physical and chemical mechanisms in which NS are generated and evolved in time respectively are not well understood.

On the other hand, one of the oxides that has attracted the attention of several researchers mainly due to its optical and chemical properties is molybdenum oxide (MoOx). These NS have been synthesized mainly by chemical methods and proposed to be used for several potential applications, from optical and electronic to energy and biological systems since its optical properties can be tuned from the ultraviolet (UV) to near infrared (NIR) range by modifying their size, chemical composition and/or structure.

However, in spite of the recent popularity of MoOx NS, the LASL method and their potential applications, there are very few studies that report the generation of this type of NS by this method and they lack the explanation of the oxidation process which plays an important part on the optical properties as the first part of this work shows. A picosecond pulsed laser is used for inducing ablation of the Mo target and generate nanoparticles (NPs). Besides, a mechanism of the NPs oxidation process is proposed, and the average diameter and size distribution as function of irradiation energy are discussed.

Furthermore, MoOx NS have been successfully synthesized by chemical methods and utilized in pothothermal therapy (PTT) in in vitro experiments, as PTT agents. This can be possible due to these NS show good biocompability and NIR light absorption, and great phothermal conversion efficiency. Nevertheless, these NS had never been synthesized by the LASL method with the idea of using them as PPT agents with a nanosecond pulsed laser before this work as far as we know.

A Nd:YAG pulsed laser was utilized to generate the core-shell type NPs and the spectroscopy studies show these NS exhibit a peak of absorption in the NIR range, which makes them suitable for PTT. Besides, in order to study the NPs fragmentation phenomena, two irradiation times were used, and a correlation with the average diameter and size distribution was found.

In summary, this research studies how different laser parameters influence the composition of the diverse NS generated, focusing on the effect of intensity, duration of the pulse and time of irradiation when synthesizing molybdenum oxide NS by the LASL method.