of the elongated slits while only two metal layers 26 30 are shown additional alternating layers of metal and dielectric materials can be formed in the same manner as disclosed above preferably the nprs are formed together on a single wafer 40 as an array of nprs 20 of uniform or varying density as shown in fig5 fig6 8 illustrate the photolithographic process used to form the npr structure 44 according to a second embodiment the process begins by performing a pre oxidation clean on the substrate 24 followed by forming a first dielectric layer 46 e g silicon dioxide u2014 sio 2 over substrate 24 e g si for example by thermal oxidation e g 1 u03bcm thick this is followed by forming a sacrificial layer 48 over the structure e g polymer that is 0 2 u03bcm to 0 3 u03bcm thick a barc layer 50 bottom anti reflective coating e g carbon or inorganic material is formed over the polymer layer 48 photo resist 52 is formed over the barc layer 50 and patterned with holes 54 of approximately 50 nm 250 nm in size patterning includes photolithograph exposure and photo resist etch barc and polymer etches are.