Within this integration theme, modeling support for the fabrication activities will be developed and applied. Activities include computational materials science and mesoscale simulation to understand the formation of the fabricated structures, and MEMs scale modelling for optimisation of the fabrication tools.

Polymer Rheology for NIL integrates many crucial aspects of the life cycle of NIL fabricated nano-structures, it has been formulated to be an essential building stone for WPs 3-7 and 13-15. The models and experiments will be developed with direct input from these WPs in order to serve the largest number of users. Considering that constitutive behavior at the nano-scale are anticipated to be more universal than at the macro-scale, similar models will be used to characterise the resulting structure and properties of the materials for various processing conditions. For instance, it is expected that, although the structures and properties of NIL and soft lithography nano-patterns should be essentially different, their constitutive behavior will only differ through a finite number of materials parameters that can be evaluated experimentally. These results will serve as a starting point to define proper processing windows for nano-patterning.

Modelling for MEMs Structures to develop numerical models that will be of use in the analysis of data from work-packages 9 through 12, concentrating on MEMS based nano-patterning. The thermo-mechanical modelling of cantilevers, which will determine the residual stress due to fabrication will be used in WP9 where prototype cantilever arrays are developed. Also, the effect of introducing an aperture into the tip of the cantilever on its mechanical characteristics is to be examined. The modelling of high aspect ratio structures undertaken in T19.2 is linked to WP12 (T12.1), which deal with the characterisation of structures fabricated by NADIS and NanoStencil. The interaction of the cantilever apertures with nano-droplets is examined in tasks T19.4 and T19.5. These tasks are essential to WP10 where the flow through confined geometries is studied experimentally.

Surface Molecule Interactions for Self-Assembly will provide theoretical support the soft lithograph activities. In common with WP Monolayer Assisted Assembly, the focus is on assembly of molecules on surfaces and their use for selective assembly, for interaction force studies, and for anchoring of assembly towards the third dimension. Atomic scale models for well-characterised SAM layers will be produced and used in simulations for studies of the interaction with adsorbed molecular ligands. The anchoring of the adsorbed molecules to the SAM layer will be investigated, with particular emphasis on controlling conformational degrees of freedom for design and control of self-assembly onto patterned monolayers

The modelling and simulation group is working on development of a process library for nanoimprint through a combination of characterisation and modelling. Modelling for MEMS based nanopatterning is also carried out. Modelling with the use of molecular dynamics (MD) is  important part of the activity for soft lithography applications.

The constitutive behaviour of polymers are extended to nanoscale and applied to the prediction of the patterning of structures. This is achieved beginning with complete  (mechanical, tribological, adhesive/stiction) characterization of the materials ( within the close collaboration with NIL and materials groups of the project) , followed by model parameters extracted based upon the characterization data. Resulting model predictions are validated against nanoimprint structures, with final model refinement on the feature scale. The work on wafer scale modelling was also undertaken using coarse grained averaging over the feature scale (Fig.1).

Fig.1. Left: Imprint (violet color relates to thicker residual layer) ,right: Results of modelling of pressure distribution in resist film and calculated distribution of elastic deformation of stamp during imprinting (in nm).

One of the modelling tasks within the NaPa project is to reduce the undesirable effects during the deposition through stencils  such as the clogging of apertures and the membrane deformation due to the deposition induced stresses.  It was proposed to stabilise the stencils mechanically by introducing corrugation structures/rims. Modelling group is working on predicting the deposition stress induced deformation of stencils and subsequently establishing optimal corrugation geometries. Work on modelling the clogging effect on stencilled patterns and subsequent prediction of stencil lifetime is currently underway.

For the assembly of nanoparticles we are studying ligand protected gold clusters in order to make predictions about materials consisting of assembled nanoparticles. For the studies of structure, dynamics and binding specificity the atomistic molecular dynamics simulations are applied  to probe the structure, stability and binding specificity of the molecular printboards (b-CD terminated SAMs) used for nanopatterning. We also use MD simulations to calculate the guest binding specificity at these printboards. The knowledge generated from these fundamental studies facilitates the construction of more complex, more finely-tuned nanopatterning systems (Fig.2).


Fig.2. The figures on show plan and side-on views of the molecular printboard, a hexagonally-packed array of b-cyclodextrin molecules anchored to gold using alkane-thioether chains. MD simulations provide atomic scale information on the stability and flexibility of such architectures

Nanoscale fluid flows in the vicinity of patterned surfaces is studied by MD   simulations  of dense and rarefied fluids comprising small chain molecules in chemically patterned nano-channels to  predict a novel switching from Poiseuille to plug flow along the channel. We also demonstrate behaviour akin to the lotus effect for a nanodrop on a chemically patterned substrate and on a substrate consisting of needle-like pillars.

Modelling  and simulations of interaction between nanoparticles, solvent and surface to elucidate the mechanism for deposition of nanoparticles in different conditions are also performed. MD simulations of flows in channels with walls of homogeneous and mixed wetting properties are used  in the context of particles separation. Other areas of modelling for soft lithography applications  are: stretching of proteins through fluid flows and comparison to stretching in force-   clamps ; stretching of DNA and other biomolecules through fluid flows- molecular combining; studies  of the role of hydrodynamic effects on conformational changes in  proteins and homopolymers.