Nanoscale printing research supported by multiscale and multiphysics modelling

1st June 2011

Printing of materials is a universal requirement in modern technology, from the laser printer in the office, to much more sophisticated printing of ‘inks’ that may contain useful materials such as metals, nano-scale particles or even biomaterials such as DNA. What is difficult however is to directly print metals, at feature sizes that may well be less than one micron (1 thousandth of a millimetre) in dimension, onto a substrate that might be a plastic, or contain microscopic holes into which the metal must be injected.

During the last 5 years, the Optoelectronics Research Centre (ORC) team led by Prof Rob Eason has developed the LIFT (laser-induced forward transfer) technique of laser direct printing using ultrashort laser pulses, whose duration is only 150 femtoseconds (1 femtosecond = 10-15 s), and have achieved results that represent the smallest features printed to date. The figure here shows a 330nm (one third of a micron) diameter dot of Cr metal, and these tiny dots have also been printed in an array format.

This research project is a cross-disciplinary collaboration between a modelling group in SES and the experimental group in ORC, facilitated by the Computational Modelling Group. The aim is to determine the interrelationships between the large number of physical parameters involved and provide a sound basis for further optimisation of this nano-printing technique. The research will be linked with the EU-funded e-LIFT project, working with research partners from France, Switzerland, Greece, Italy, Spain, Romania as well as the UK. Exploitation of result outcomes will be conducted with project partner TNO in the Netherlands

The LIFT technique involves multi-physics processes such as heat transfer, multiphase dynamics, phase changes and material properties modification over a wide range of timescales (fs to μs) and length scales (nm to mm).

Conventional modelling and numerical simulation are based on either macroscopic, continuum approaches or discrete-particle molecular kinetics, which target a narrow range of scales. In this project, a novel multiscale modelling methodology will be developed to predict the complete LIFT process including the laser pulse donor material melting, molten droplet formation, droplet growth, release, transfer, and deposition processes. The key is to bridge the widely disparate scales between the macro-world and the micro-world using a mesoscale technique called the Lattice Boltzmann Method (LBM). The method had its origin in kinetics-based molecular dynamics, but significant developments in the field in recent years have enabled LBM to simulate nanoscale to macroscale problems on present-day computers. Therefore, it has found a wide range of applications in engineering, physical sciences, biosciences and nanotechnology. However, previous studies using LBM have mainly focused on single-physics problems such as single-phase microfluidics or multiphases. The present project will look at LIFT-related multiphysics processes such as laser heating and the consequent phase changes (melting and re-solidification), building on the expertise developed at the Energy Technology Research Group led by Prof Kai Luo. The multiscale modelling tools being developed are expected to capture the essential physics and guide the design of LIFT, without a large number of expensive, precision experiments.