Molecular dynamics simulations of nanoimprinting lithography.

We have performed coarse-grained molecular dynamics simulations of molding and replication of nanometer-size objects. Nanoimprinting of hemispherical particles was modeled as a three-step process: (1) a mold was created by pressing a hard hemispherical particle (master template) into a polymeric film; (2) a polymeric film was cross-linked fixing a negative image of a master mold into a polymeric film; (3) a polymeric mold was pressed into a monomeric liquid replicating an original master. The quality of the replication process was analyzed by comparing the shape of the replica with the shape of the master. It is shown that deformation of a polymeric stamp during the replication process (Step 3) is a result of optimization of the surface energy of the mold-liquid interface and the elastic energy of the polymeric mold. The relative deformation, epsilon, of the replica is a function of the universal parameter gamma/(GR(0)), where gamma is the surface energy of the polymer-liquid interface, G is the shear modulus of the polymer network, and R(0) is the radius of the master. In the case of small deformations, this function reduces to epsilon proportional to gamma/(GR(0)).