Laser-Induced Forward Transfer Nano-Printing Process - Multiscale Modelling, Experimental Validation and Optimization

LIFT是一种直写微加工和微纳米打印技术，近年来受到了研究界和工业界的广泛关注。与其他竞争的印刷方法相比，它具有显著的优势，并在许多高科技高价值行业中具有潜在的应用前景。然而，关于如何选择一小组实验可控参数来产生最精细、最均匀、最理想的单打印特征和打印阵列的问题仍然存在。尽管申请人和世界各地的其他团体进行了广泛而昂贵的实验，但对LIFT所涉及的现象仍缺乏基本的理解。这是由于实验中有限的空间和时间分辨率，以及许多数量/性质不能直接测量的事实，特别是在纳米尺度上。至关重要的是，如果没有详尽的大量昂贵的实验，很难建立各种参数之间的因果关系。因此，非常需要开发理论和/或数值模型来捕捉LIFT的基本物理，以便更容易地预测趋势，并使LIFT设计更基于基本物理。这里的成功将彻底改变以光子学、等离子体学和微电子学为基础的关键行业。由于LIFT的多尺度和多物理场特性，传统的宏观建模方法不能直接解决LIFT问题。对于LIFT来说，最有前途的方法是LBM，它可以被视为一种粗粒度的分子动力学方法，尽管使用了非常不同的数值算法和可负担的计算费用来解决实际问题。LBM保留了微观动力学原理，同时在宏观尺度上恢复了完整的Navier-Stokes方程。因此，LBM在微观尺度和宏观尺度之间架起了桥梁，这使得它成为解决像LIFT这样的多尺度问题的一种有价值的方法。在这里，我们提出了LIFT的第一个多尺度建模研究，并得到了在南安普敦最先进的FASTlab设施进行的现有和进一步实验测量的支持。这是建立在我们和其他研究人员最近使用LBM模拟与LIFT相关的一些孤立子过程的成功基础上的。所提出的多尺度LBM方法的新颖和重要之处在于它能够模拟完整的LIFT过程，包括供体材料熔化、熔融液滴形成、液滴生长、转移和沉积过程。模型的开发将以系统的方式进行，以增加复杂性的顺序。首先，采用等温多相LBM模型将多相流动力学效应与热效应分离开来。然后，将对热多相LBM进行LIFT工艺测试，以确定当前（纯）LBM方法的能力和局限性。然而，重点是发展一种新的多尺度LBM方法来研究激光加热、供体材料熔化、热传导、热膨胀和再凝固。这种多尺度方法将LBM与宏观Navier-Stokes解算器无缝耦合，利用了每种方法在不同雷诺数和Knudsen数范围内的尺度分辨能力和数值效率。最后，马兰戈尼效应将通过将温度依赖的表面张力纳入LBM模型来研究。马兰戈尼效应被认为会影响打印特征的最终形态，但之前还没有详细研究过。在整个项目中，建模和实验团队以及我们的学术和工业合作伙伴将密切合作，以确保及时交流想法、数据和信息。最后阶段是根据第一原则和建模指导，创建单个打印点和打印阵列的最佳优化特征。

LIFT is a direct-write microfabrication and micro/nano printing technique that has received much attention in the research communities and industries in recent years. It offers significant advantages over other competing printing methodologies and has potential applications in many high-tech high-value industries. However, questions remain regarding how to select a small set of experimentally controllable parameters to produce the finest, the most uniform, the most desirable single printed feature and print arrays. Despite the extensive and expensive experiments carried out by the applicants and other groups around the world, fundamental understanding of the phenomena involved in LIFT is lacking. This is attributed to the limited spatial and temporal resolutions in experiments and to the fact that many quantities/properties are not directly measurable especially at nanoscales. Crucially, the causal relationships among the various parameters are difficult to establish without an exhaustive number of expensive experiments. Therefore, it is highly desirable to develop theoretical and/or numerical models to capture the essential physics in LIFT so that trends can be predicted more easily and LIFT design more grounded on fundamental physics. Success here will revolutionise key industries that have photonics, plasmonics and microelectronics as their cornerstone.Conventional macroscopic modelling methods do not directly lend the solution to the LIFT problem, due to the truly multiscale and multiphysics features of LIFT. The most promising approach for LIFT is the LBM, which can be viewed as a coarse-grained molecular dynamics approach, albeit with very different numerical algorithms and affordable computational expenses for real-world problems. LBM preserves the microscopic kinetic principles while recovering the full Navier-Stokes equations at the macroscales. Therefore, LBM bridges the microscales and macroscales, which makes it a valuable method for multiscale problems like LIFT. Here, we propose the very first multiscale modelling study of LIFT, supported by existing and further experimental measurements conducted at the state-of-the-art FASTlab facilities in Southampton. This is built upon the recent successes of ours and other researchers in simulating some isolated sub-processes relevant to LIFT using LBM. The novelty and significance of the proposed multiscale LBM approach is its ability to simulate the complete LIFT process including donor material melting, molten droplet formation, droplet growth, transfer, and deposition processes. The model development will proceed in a systematic manner in order of increasing sophistication. First, an isothermal multiphase LBM model will be employed to isolate the multiphase flow dynamics effects from the thermal effects. Then a thermal multiphase LBM will be tested for LIFT processes to determine the capabilities and limitations of the current (pure) LBM methodologies. The focus, however, is to develop a new multiscale LBM approach to study laser heating, donor material melting, heat conduction, thermal expansion and re-solidification. Such a multiscale approach couples LBM seamlessly with a macroscopic Navier-Stokes solver, taking advantage of each method's scale-resolving capability and numerical efficiency in different ranges of the Reynolds and Knudsen numbers. Finally, Marangoni effects will be investigated by incorporating temperature-dependent surface tension into the LBM modelling. The Marangoni effects are believed to affect the final morphology of the printed features but have not been studied in detail before. Throughout the project, the modelling and experimental teams as well as our academic and industrial partners will work closely with each other to ensure timely exchange of ideas, data and information. The final phase is to create the finest optimized features of a single printed dot and print arrays following first principles and modelling guidance.