Approaching zero: using fractured crystals in metrology for replica molding

This report presents a simple and convenient method to generate nanoscale fractures (cracks) in smooth, single-crystalline Si substrates. The cracks propagated as approximately straight lines along the {100} crystal planes with controllable length defined by a stabilizing backlayer. Close to its tip, the crack presented a vertical offset of the two planes as step of smoothly decreasing height, ranging from the microscale to the atomic scale. The edges of a crack were in close contact at the tip of the crack but were separated at the edge where the crack was initiated. These steps served as ideal test features for probing the limits of the replication of soft lithography. Analysis of topography of original and replicated features (in "hard" poly(dimethylsiloxane and polyurethane) by atomic force microscopy demonstrated that steps down to 0.4 nm could be reproduced; these features approach the dimensions of atoms.