( a – d ) SEM images of lambda DNAs attached by electrophoresis for 15 min at different electric potentials; 1, 3, 15, and 30 V, respectively. The scale bar is 500 nm. ( e ) Gaps inside nanochannel. ( f ) SEM image of nanochannels with interface showing lambda DNAs attached by electrophoresis at 15 V for 15 min (scale bar =500 nm). ( g ) Ultra high-resolution FE-SEM images of linearly aligned DNAs attachment in nanochannels L 1 , L 2 , L 3 , and L 4 at 15 V for 15 min. All scale bar are 50 nm.