to a side wall 3 which is also e g hydrophilic in fig1 c the type a domains have been removed by selective chemical etching leaving the type b domains to form a relief pattern in the trench where they may serve as a template for subsequent patterning of the bottom surface 4 for instance by further chemical etching selective removal may be achieved for instance by selective photo degradation or photo cleavage of a linking agent between blocks of the copolymer and subsequent solubilization of one of the blocks the pitch or wavelength of the self assembled polymer structure 5 and the width of the trench 4 are arranged so that a number of alternating stripes of domains can fit into the trench with a type a domain against each side wall fig2 a shows a substrate 10 with a chemical pattern in the form of pinning stripes 11 which have been chemically formed on the surface 13 to provide regions with a higher affinity for the type a blocks of the polymer in fig2 b a self assemblable a b block copolymer with e g hydrophilic a blocks and e g hydrophobic b blocks has been deposited onto the surface 13 of substrate 10 to form a lamellar phase layer 12 with alternating stripes of a and b domains which have phase separated into discrete micro separated periodic domains during deposition of the block copolymer this is referred to as chemical pre patterning or chemical epitaxy the type a domains have nucleated atop the pinning or nucleation stripes 11 which are also e g hydrophilic in.