Atomic Layer Deposition Technology Provides Atomic-Level Precision Solutions for Surface Modification of Micro- and Nanopowders
Atomic Layer Deposition (ALD) technology emerged in the late 20th century, initially successfully applied by Finnish scientists to the preparation of fluorescent materials such as ZnS and Mn, and Al₂O₃ insulating thin films, serving the flat panel display industry. Since the 1990s, with the rapid development of the semiconductor industry, ALD has quickly become a hot research topic internationally due to its unique advantages in thin film growth control. After nearly thirty years of development, this technology has expanded from the semiconductor field to several cutting-edge fields such as catalysis, optics, and energy, and has gradually become one of the core methods for the preparation of functional thin films.
I. Technical Principles of Atomic Layer Deposition
Atomic layer deposition is a thin film growth technology based on sequential, self-limiting surface chemical reactions. It can achieve highly controllable material deposition on the substrate surface, layer by layer, in units of single atomic layers. Its core mechanism lies in the self-terminating nature of each chemical reaction, ensuring that only a single layer of atoms or molecules is formed in each cycle, thus achieving nanometer-level or even atomic-level precise control of the film thickness and composition.
A typical ALD deposition cycle includes four steps:
Precursor A exposure: The first precursor vapor is introduced into the reaction chamber, where it undergoes chemical adsorption or reaction with the substrate surface until a saturated monolayer is adsorbed;
Purging: An inert gas is introduced to remove all unreacted precursor A and gaseous byproducts from the chamber;
Precursor B exposure: The second precursor is introduced, reacting with the chemically adsorbed first precursor layer on the surface to form the target solid thin film layer;
Secondary purging: An inert gas is introduced again to remove excess precursor B and reaction byproducts.
By repeating the above cycle and precisely controlling the number of deposition cycles, a uniform thin film with the desired thickness and properties can be obtained.
II. Application Directions for Micro- and Nanopowder Modification
With its excellent conformality, uniformity, and thickness control capabilities, ALD technology demonstrates unique value in the surface engineering of micro- and nanopowder materials. The main application directions include:
Uniform Nanocoatings: It can form complete, pinhole-free coating layers on the surface of nanoparticles with complex shapes and high specific surface areas. This ultra-thin film effectively prevents direct contact between particles and the environment (such as moisture and oxygen), preventing material performance degradation while maximizing the retention of the core material's intrinsic properties.
Porous/Nanostructured Coating Construction: In addition to dense encapsulation, ALD can also be used to construct functional nanocoatings on material surfaces or within pores, exposing active sites and regulating pore structures, demonstrating great potential in catalysis, sensing, and energy storage.
Selective Surface Functionalization: By adjusting reaction parameters or utilizing differences in surface chemistry, precise modification and passivation of specific crystal facets, defects, or active sites of particles can be achieved, providing a powerful tool for atomic-scale design of material properties.
With industrial upgrading, high-performance micro- and nano-powder materials often face stability challenges while maintaining high activity; furthermore, there is a growing demand for advanced structural materials with designable optical, electrical, and catalytic properties. ALD technology provides solutions to these needs: for example, improving powder stability through ultra-thin protective layers, or endowing materials with novel physicochemical properties through core-shell structures and heterojunction designs.
