Emerging laser technologies for precise manufacturing of multifunctional nanomaterials and nanostructures

The use of photons to directly or indirectly drive chemical reactions has fundamentally changed the field of nanomaterial synthesis, leading to the emergence of new sustainable laser chemistry methods for manufacturing micro - and nanostructures. The incident laser radiation triggers complex interactions between chemical and physical processes at the interface between solid surfaces and liquid or gas environments.

In such a multi parameter system, it is impossible to precisely control the resulting nanostructures without a deep understanding of the chemical and physical processes influenced by the environment.

This review aims to provide a detailed and systematic exposition of these processes, examining mature and emerging laser technologies used for producing advanced nanostructures and nanomaterials. Both gases and liquids are considered potential reaction environments that affect the manufacturing process, and subtractive and additive manufacturing methods are also analyzed. Finally, the prospects and emerging applications of such technologies were also discussed.

Through an overview of the history and latest achievements in the field of laser chemistry, researchers have concluded that the development of laser technology, green chemistry methods, and nanophotonics has led to a paradigm shift in modern nanomanufacturing. By changing parameters such as laser beam intensity, environmental composition, and absorption spectra, people can switch between additive manufacturing and subtractive manufacturing or between chemical modification and morphological surface modification under almost the same processing arrangement.

Laser radiation triggers these processes in two different ways:
1) Photochemical action: Photons excite molecular oscillations or electrons in the environment, or generate electron hole pairs on the surface. In this case, the laser wavelength corresponds to certain absorption bands of the material. Therefore, at a time scale greater than that required for chemical reactions, the material will be displaced from thermal equilibrium. Chemical reactions are activated by free charge carriers, or the threshold is lowered due to this excitation.

2) Thermal induction effect: The absorbed laser radiation raises the interface temperature and becomes a local heat source. In this case, thermal equilibrium can be assumed, and chemical reactions are activated by the increased temperature at the interface.

Both of these physical pathways can save a significant amount of energy during the production process. The photochemical method can avoid the Maxwell Boltzmann energy distribution of reactants, in which case only the high-energy "tail" can overcome the reaction barrier, and the rest only dissipate energy. The efficiency of laser-induced thermochemical patterning is higher than that of traditional chemical reactors because light is only localized in the area that needs to be processed. The ultimate goal of this direction is to achieve high control over reaction product parameters, high spatial accuracy, low toxicity, and cost-effectiveness, making laser chemistry methods suitable for industrial scale applications in fields such as flexible electronics, planar optics, sensing, catalysis, supercapacitors, and solar energy.

Source: Yangtze River Delta Laser Alliance