(a, b) Computational simulation of electric field stream line (YZ projection) with 7.5 kV applied to the nozzle under different potential differences between mask and substrate: 0 V (a) and 2 kV (b). (c, d) Optical phase contrast and (e, f) fluorescence microcopy images of FITC-polystyrene nanoparticle patterns fabricated under different potential differences between mask and substrate: 0 V (c, e) and 2 kV (d, f) (reprinted from Xie et al., 2010. Copyright 2010 John Wiley & Sons, Inc.).