operation of tip assembly 100 in fig1 a an indentation 135 is formed in cured crosslinking agent layer 130 b by heating indenter tip 120 to a writing temperature tw by passing a current through cantilever 105 and pressing indenter tip 120 cured crosslinking agent layer 130 b heating indenter tip 120 allows the tip to penetrate the cured crosslinking agent layer 130 b forming indentation 135 which remains after the tip is removed in a first example the cured crosslinking agent layer 130 b is heated by heated indenter tip 120 the temperature of the indenter tip being not greater than about 500 u00b0 c to form indentation 135 in a second example the cured crosslinking agent layer 130 b is heated by heated indenter tip 120 the temperature of the indenter tip being not greater than about 400 u00b0 c to form indentation 135 in a third example the cured crosslinking agent layer 130 b is heated by heated indenter tip 120 the temperature of the indenter tip being between about 200 u00b0 c and about 500 u00b0 c to form indentation 135 in a fourth example the cured crosslinking agent layer 130 b is heated by heated indenter tip.