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

LIFT是一种直写微加工和微/纳米印刷技术，近年来在研究界和工业界受到了广泛关注。与其他竞争性印刷方法相比，它具有显着的优势，并在许多高科技高价值行业中具有潜在的应用。然而，关于如何选择一小组实验可控参数以产生最精细、最均匀、最期望的单个印刷特征和印刷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和昂贵的实验，但对LIFT所涉及的现象缺乏基本的理解。这归因于实验中有限的空间和时间分辨率，以及许多量/属性无法直接测量的事实，特别是在纳米尺度下。至关重要的是，如果没有大量昂贵的实验，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/或数值模型来捕获LIFT中的基本物理，以便可以更容易地预测趋势，并且LIFT设计更基于基础物理。这方面的成功将彻底改变以光子学、等离子体激元学和微电子学为基石的关键行业。由于LIFT真正的多尺度和多物理特性，传统的宏观建模方法无法直接解决LIFT问题。LIFT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，尽管具有非常不同的数值算法和负担得起的计算费用，用于现实世界的问题。LBM在宏观尺度上恢复完整的Navier-Stokes方程的同时，保留了微观动力学原理。因此，LBM桥接了微观尺度和宏观尺度，这使得它成为解决LIFT等多尺度问题的有价值的方法。在这里，我们提出了LIFT的第一个多尺度建模研究，支持现有的和进一步的实验测量进行的最先进的FASTlab设施在南安普顿。这是建立在我们和其他研究人员最近成功地模拟一些孤立的子过程相关的LIFT使用LBM。所提出的多尺度LBM方法的新奇和意义在于其能够模拟完整的LIFT过程，包括供体材料熔化、熔滴形成、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。首先，将采用等温多相LBM模型来将多相流动力学效应与热效应隔离。然后，将测试热多相LBM的LIFT过程，以确定当前（纯）LBM方法的能力和局限性。然而，重点是开发一种新的多尺度LBM方法来研究激光加热，施主材料熔化，热传导，热膨胀和再凝固。这种多尺度方法将LBM与宏观Navier-Stokes求解器无缝耦合，利用每种方法在不同雷诺数和克努森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到LBM建模进行研究。Marangoni效应被认为会影响印刷特征的最终形态，但之前没有详细研究。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。最后一个阶段是创建最好的优化功能的一个单一的打印点和打印阵列以下的第一原则和建模指导。

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.