Nanosecond pulsed laser annealing is a controlled and selective heat treatment process to achieve desired material properties. Here, we take a look at nanosecond pulsed laser annealing, its advantages over other annealing techniques, and recent research findings.
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Nanosecond Pulsed Laser Annealing: An Overview
Annealing is a heat treatment process that improves a material's ductility and workability by reducing its hardness. Traditionally, annealing involves heating the entire material to a specific temperature and then cooling it. However, high-intensity lasers are used for more precise and selective material heating.
Nanosecond pulsed laser annealing is a type of laser annealing that uses high-energy, short-duration laser pulses in the nanosecond range to rapidly heat the material. The rapid and intense heating induces localized melting and recrystallization, modifying the material's physical and chemical properties.
How Nanosecond Pulsed Laser Annealing Modifies Material Properties
A laser pulse is focused on the sample's surface, generating a high-energy density at the point of impact. The material absorbs this energy, causing rapid heating of the surface layer.
The material is held above its recrystallization temperature for a specific duration before cooling. During this heating process, atom migration in the crystal lattice occurs, reducing the number of dislocations, which impacts hardness and ductility. Finally, the material recrystallizes through rapid water quenching or slow air cooling.
The heating and cooling rates impact the crystal phase composition and grain size, ultimately dictating material properties.
What Sets Nanosecond Pulsed Laser Annealing Apart from Other Laser Annealing Methods?
The primary benefit of nanosecond pulsed laser annealing is its high degree of adjustability, which enables precise control over the material's properties and structures. In addition, various material properties can be achieved by adjusting the pulse's duration and intensity.
Due to its localized and brief heating, nanosecond pulsed laser annealing is ideal for materials susceptible to sublimation, such as carbon.
Nanosecond pulses prevent thermal spreading and excessive heat transmission to the surrounding material due to their small size. This enables precise control over the energy provided to the material and the thickness of the annealed layer.
Nanosecond pulsed laser annealing offers the advantage of providing rapid, surface-localized high-temperature processing. This feature can be beneficial in reducing metal line resistance in thin films while sustaining the strength and functionality of surrounding materials.
Research and Development
Nanosecond Pulsed Laser Annealing Induced Defects Improve Li-Ion Battery Performance
A recent study from North Carolina State University, performed in collaboration with the US Department of Energy's Oak Ridge National Laboratory, demonstrated that short pulses from a high-intensity laser cause tiny defects in materials of lithium-ion batteries, resulting in improved battery performance.
This improvement was accomplished through controlled engineering of graphite's (anode) microstructure and defect fillings using nanosecond pulsed laser annealing. The pulsed lasers created surface grooves and steps, improving Li+ ion intercalation and charging rates.
The process also removed inactive binder material and generated carbon vacancies, serving as additional Li+ charging sites. As a result, the improved Li+ ion absorption during charge and discharge cycles enhanced the batteries' current carrying capacity and cyclability by 20%.
However, an excessive concentration of defects may lead to Li plating and the reduction of current capacity.
"Material defects can be a nuisance, but if you engineer them correctly you can make them an advantage. This technique opens the door, so to speak, for lithium ions, so it enhances the current capacity." - Jagdish Narayan, corresponding author of the study
UV Nanosecond Pulsed Laser Annealing Boosts Performance of Copper Interconnects
In a study published in IEEE, researchers used ultraviolet (UV) nanosecond pulsed laser annealing to investigate its effect on a thin copper (Cu) film to control grain growth and reduce metal line resistance.
Under sub-melt conditions, the grain size increased about eightfold compared to the as-deposited film with a regulated grain orientation distribution. However, in the melting state, the grain growth continued without consistent control of grain orientation, leading to a constant reduction in the film's resistivity.
This study demonstrates the potential of UV nanosecond pulsed laser annealing to enlarge metal grains and reduce metal line resistance without affecting the performance and integrity of surrounding materials in advanced metal interconnects.
Converting Carbon Nanotubes into Diamond Fibers
A study published in Nanoscale reported a nanosecond pulsed laser annealing method to convert carbon nanotubes and nanofibers into diamond fibers at ambient pressure and temperature in the air.
High-intensity nanosecond pulsed laser melts the carbon nanotubes and nanofibers in a super undercooled state, followed by rapid quenching to convert them into diamond rods free from impurities. This cost-effective method yields higher than previous methods requiring extreme heat and pressure.
This opens up new opportunities for the processing and synthesis of diamond nanostructures for various applications such as quantum computing, tool coatings for deep-sea drilling or fuel extraction, and diamond jewelry.
Future Outlook
As technology progresses and the demand for more precise and efficient laser processing techniques increases, nanosecond pulsed laser annealing is expected to play a significant role in material modification and synthesis applications.
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References and Further Reading
Khosla, N., Narayan, J., Narayan, R., Sun, X. G., & Paranthaman, M. P. (2023). Microstructure and defect engineering of graphite anodes by pulsed laser annealing for enhanced performance of lithium-ion batteries. Carbon. https://doi.org/10.1016/j.carbon.2023.01.009
Tabata, T., Raynal, P. E., Rozé, F., Halty, S., Thuries, L., Cristiano, F., ... & Mazzamuto, F. (2021, July). Copper Large-scale Grain Growth by UV Nanosecond Pulsed Laser Annealing. In 2021 IEEE International Interconnect Technology Conference (IITC) (pp. 1-3). IEEE. https://doi.org/10.1109/IITC51362.2021.9537312
Narayan, J., Bhaumik, A., Sachan, R., Haque, A., Gupta, S., & Pant, P. (2019). Direct conversion of carbon nanofibers and nanotubes into diamond nanofibers and the subsequent growth of large-sized diamonds. Nanoscale, 11(5), 2238-2248. https://doi.org/10.1039/C8NR08823C
Skorupa, W., & Schmidt, H. (Eds.). (2013). Subsecond annealing of advanced materials: annealing by lasers, flash lamps and swift heavy ions (Vol. 192). Springer Science & Business Media.
Lawrence, J. R. (Ed.). (2017). Advances in laser materials processing: technology, research and applications. Woodhead Publishing.
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