“…Both methods lead to nanochannels that have their smallest dimension perpendicular to the substrate (i.e., running parallel to the substrate surface); however, by combining them with deep-UV photolithography, laser interference lithography, or nanoimprint lithography (NIL) [69,70], it also becomes possible to control the lateral dimension (i.e., the dimension parallel to the substrate surface) down to several tens of nanometers. Alternative methods of achieving nano dimensions in the lateral direction without sophisticated lithography make use of shadowing effects at step edges [71,72], the special structures that arise after stiction of a surface-machined cantilever [72], or of nonuniform film step coverage in deep trenches, followed by an annealing step that leads to reflow of the film material and shrinkage of the channel [73]. In these methods, the limitations on dimensional control derive from either the lithographic definition, the control over the thin film thickness (and its uniformity), the control over the etching depth (and its uniformity), or the surface roughness (which is usually below 0.5 nm on average when polished silicon or glass substrates are used).…”