Thin silicon membranes on silicon on insulator substrates are used to fabricate point contacts with a well-defined interface in the nanoconstriction between the two metal electrodes. Transmission electron microscope images of heterointerfaces in conjunction with energy dispersive x-ray analysis of the interfacial region show the capabilities of the process and its limitations. The latter involve material-specific phenomena on a nanoscale, such as an interfacial reaction between a metal film and SiO2 and metal diffusion across the heterointerface. These adverse effects can be avoided by a proper choice of the metals and the deposition temperature, as demonstrated with results of electrical measurements on a Au/Cu heterocontact.