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

Lead Research Organisation: University of Southampton
Department Name: Faculty of Engineering & the Environment

Abstract

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.

Planned Impact

LIFT is a direct-write microfabrication and microprinting technique that can offer significant advantages in terms of precision, resolution, speed, simplicity and flexibility over other competing printing methodologies. It uses a laser pulse to transfer a portion of the donor material over a short distance into a receiver substrate, resulting in controlled and high precision deposition. By varying the laser fluence and/or pulse duration, the deposition can be larger, equal or smaller than the laser spot size. Our recent experimental work has demonstrated the capability to deposit nanoscale features using femtosecond laser pulses. Other studies have shown that, in addition to metals, the donor materials can be superconductors, oxides, inorganic materials, biomolecules, DNA, living cells and microorganisms. Therefore, LIFT not only constitutes an attractive alternative to more conventional printing techniques, but also has a potentially wide range of applications in nanotechnology in general, microfabrication, micropatterning, microelectronics, lab-on-a-chip devices, biosensors, tissue engineering and scaffolding, and so on. The proposed research addresses the EPSRC's priority research areas of Nanoscience through Engineering and Digital Economy directly and Next Generation Healthcare and Energy indirectly. For the first time to our knowledge, a laser-based printing technique will benefit from rigorous modelling guidance. Given the high cost of doing experiments on LIFT and the empirical nature of tuning test conditions, the modelling tool based on sound physical principles would cut cost and shorten the time for designing and optimising LIFT technologies. Both investigators have extensive contacts with industries, and spin-outs from the University. Under a recently awarded EU programme titled e-LIFT, we are working with four SMEs and one larger company which manufacture RFID tags for security, product labelling and tracking. The final phase is to specify and demonstrate a laser LIFT printer, which involves a laser machining company in the UK. All these companies have as a fundamental interest the ability to print materials using LIFT to extreme precision, and the importance of the modelling, validation and further refinements that we are offering via this proposed programme is hard to overstate. We have had recent discussions and secured direct funding from TNO, Holland, for injection of micron-scale metal interconnects between stackable Si integrated circuit chips. If we can perfect this, with the help of the detailed modelling in this proposal, then the benefit to microelectronics will be extreme. The world is waiting for, and the manufacturing roadmap dictates that further decrease in feature size, and higher packing density is paramount for the continued growth in semiconductor chip manufacture. Success here will certainly lead to both technological and financial benefits to the UK and the EU. Indeed, if our results turn out to be as expected, we would consider the route of spin-out. Within the ORC in particular, there is a long history of spin-outs with more than 10 companies emerging as a direct consequence of ORC research activities. Laser printing via LIFT might well be a suitable candidate for the next successful spin-out. The SES has a dedicated technology transfer unit, Research Institute for Industry (RIfI), who routinely works with a network of over 80 companies. Within the University of Southampton, the Research and Innovation Services (RIS) provide dedicated support on a broad range of research and enterprise activities, from contractual negotiation through to commercialisation of IP. Once we are at the stage of technology transfer and/or spin-out, we will use these established services. And finally, there will be ample opportunities for dissemination of results to wider audiences via local colloquia, open days, outreach activities and a dedicated website.

Publications

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Li Q (2012) Forcing scheme in pseudopotential lattice Boltzmann model for multiphase flows. in Physical review. E, Statistical, nonlinear, and soft matter physics

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Li Q (2012) Coupling lattice Boltzmann model for simulation of thermal flows on standard lattices. in Physical review. E, Statistical, nonlinear, and soft matter physics

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Li Q (2012) Additional interfacial force in lattice Boltzmann models for incompressible multiphase flows. in Physical review. E, Statistical, nonlinear, and soft matter physics

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Li Q (2014) Contact angles in the pseudopotential lattice Boltzmann modeling of wetting. in Physical review. E, Statistical, nonlinear, and soft matter physics

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Li Q (2013) Achieving tunable surface tension in the pseudopotential lattice Boltzmann modeling of multiphase flows. in Physical review. E, Statistical, nonlinear, and soft matter physics

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Li Q (2013) Lattice Boltzmann modeling of multiphase flows at large density ratio with an improved pseudopotential model. in Physical review. E, Statistical, nonlinear, and soft matter physics

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Li Q (2014) Effect of the forcing term in the pseudopotential lattice Boltzmann modeling of thermal flows. in Physical review. E, Statistical, nonlinear, and soft matter physics

 
Description 1. An advanced lattice Boltzmann method (LBM) and a LBM-finite difference hybrid method have been developed for multiphase and/or thermal flows without or with phase change.

2. The LBM approach has been used to investigate physical phenomena that are relevant to nanoscale printing process by laser-induced forward transfer (LIFT).

3. Extensive parametric studies have been performed to study the effects of density ratio, viscosity ratio, surface tension, temperature change, substrate materials, etc.

4. Comparison with experimental data from the FASTLab laser facilities has been conducted as much as possible.
Exploitation Route The research has been extremely successful through the collaboration of engineers and physicists, between computational scientists and experimentalists. Valuable fundamental insight has been obtained regarding the nanoscale printing process by laser-induced forward transfer (LIFT), leading to a large number of high-quality papers in quality journals. Powerful predict tools based LBM and LBM-finite difference hybrid methods have been developed, which will be of great value to fundamental research as well as industrial research and design.

On the other hand, LIFT processes are excessively complex, including donor material melting, molten droplet formation, droplet growth, release, transfer, and deposition with phase change, etc. While the developed methods have captured the main features, some aspects such as donor metarila melting are not captured well. The extreme temperature ratio and the local change in surface tension have not been simulated faithfully. The plan is to conduct further research and exploit the results further in collaboration with industrial partners such as TNO Science and Industry.

One LBM model developed from this research has been implemented in PowerFLOW of Exa corporation, the world's most influential commercial LBM software. In addition, two papers arising from this research are "Highly Cited Papers" in the Web of Science.
Sectors Chemicals,Digital/Communication/Information Technologies (including Software),Electronics,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology

 
Description The findings and methodologies developed (lattice Boltzmann methods) from the project contributed to the formation of the UK Consortium on Mesoscale Engineering Sciences (UKCOMES, http://www.ukcomes.org), funded by the EPSRC grant No. EP/L00030X/1 (06/2013 - 05/2018) and grant No. EP/R029598/1 (01/06/2018 - 31/05/2022). UKCOMES is the world's largest gathering of researchers in the field of mesoscopic modelling and simulation, which has significant impact on the economy, society and policies.
Sector Aerospace, Defence and Marine,Agriculture, Food and Drink,Chemicals,Communities and Social Services/Policy,Education,Energy,Environment,Healthcare,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology,Transport
Impact Types Societal,Economic,Policy & public services

 
Description EPSRC Standard Grant
Amount £580,960 (GBP)
Funding ID EP/J020184/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 01/2014 
End 09/2015
 
Description Enhancement and Control of Turbulent Reactive Flows via Electrical Fields - A Mesoscopic Perspective
Amount £357,032 (GBP)
Funding ID EP/S012559/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 02/2019 
End 01/2022
 
Description High-end Computing Consortia
Amount £397,424 (GBP)
Funding ID EP/L00030X/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 06/2013 
End 05/2018
 
Description Newton International Fellowship
Amount £100,000 (GBP)
Funding ID NF110280 
Organisation The Royal Society 
Sector Academic/University
Country United Kingdom
Start 02/2012 
End 04/2014
 
Description The Royal Society Newton International Fellowship
Amount £100,000 (GBP)
Funding ID NF110280 
Organisation The Royal Society 
Sector Academic/University
Country United Kingdom
Start 02/2012 
End 06/2016
 
Description UK Consortium on Mesoscale Engineering Sciences (UKCOMES)
Amount £331,316 (GBP)
Funding ID EP/R029598/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 06/2018 
End 05/2022