i e without substantial discontinuity the globules 5 are deposited between the tracks 3 4 in the manner previously described by means of the stm probe 2 since the conductive tracks 3 4 are recessed into the substrate the tip of the probe 2 can be used to deposit the globules in direct contact with the tracks 3 4 thereby overcoming the problem associated with the configuration shown in fig1 to 3 the substrate 1 may also include further recessed metal deposits 4 39 4 34 for use in the formation of further devices not shown referring now to fig8 another embodiment is shown in which the substrate 1 is provided with an overlying epitaxial layer 8 which is lightly doped so that at normal operating temperatures for example room temperature of say 300 u00b0 k it exhibits a relatively low conductivity formed in the layer 8 is a plurality of spaced heavily doped regions 9 which at the operating temperature are normally conductive and thus perform the function of the buried metal conductive strips 3 4 shown in fig7 the heavily doped regions 9 can be formed by focused ion beam lithography with the contact structures shown in fig7 and 8 it is possible to form devices using a tip 2 of substantially any suitable radius as previously mentioned the substrate needs to be in a conductive condition at the time of deposition of the globules 5 and thereafter needs to be.