From nanocrystal synthesis to functional nanostructure fabrication: laser ablation in liquid

Although nanomaterials investigations have been carried over the recent decades, researchers still face a fundamental challenge: how to control the phase, size and shape of nanocrystals in the synthesis of nanomaterials, i.e., how to achieve the transformation from nanocrytsal synthesis to functional nanostructure fabrication. For this issue, we, in this review, introduce recent developments in laser ablation in liquid (LAL) for the synthesis and fabrication of novel nanostructures with metastable phases and shapes. Laser ablation of solid targets in liquid has actually opened a door toward to synthesize nanocrystals and fabricate nanostructures due to these advantages as follows: (i) LAL is a chemically "simple and clean" synthesis due to the process with reduced byproduct formation, simpler starting materials, no need for catalyst, etc. (ii) Under ambient conditions, not extreme temperature and pressure, a variety of metastable phases that may not usually be attainable, can be generated by mild preparation methods. (iii) New phase formation involves in both liquid and solid upon LAL, which allows researchers to choose and combine interesting solid target and liquid to synthesize nanocrystals and fabricate nanostructures of new compounds for purpose of fundamental research and potential applications. (iv) The phase, size and shape of the synthesized nanocrystals can be readily controlled by tuning laser parameters and applying assistances such as inorganic salts or electrical field upon LAL. For example, we have synthesized the micro- and nanocubes of carbon with C(8)-like structures by the inorganic salts assisted LAL, and the micro- and nanocubes and spindles of GeO(2) by the electrical field assisted LAL. Additionally, we have developed a new technique to fabricate functional nanopatterns on the basis of the pulsed-laser deposition in liquid. Accordingly, LAL could greatly extend its application in fabrication of functional nanostructures in the future.