Various methods of lithography are used in the top–down approach,
including serial and parallel techniques for patterning two-dimensional
nanoscale features [2,6]. In conventional lithography, required material
is usually protected by a mask and the exposed material is etched away.
Chemical etching using acids or mechanical etching using ultraviolet
light, X-rays, or electron beams is performed that determines the feature
resolutions of the final product. Other top–down approaches include
methods such as scanning probe lithography, nanoimprint
lithography and block co-polymer lithography, etc.