The improvement in conductivity in going from earlier aluminium to copper based conductors was modest, and not as good as to be expected by a simple comparison of bulk conductivities of aluminium and copper. The addition of barrier metals on all four sides of the copper conductor significantly reduces the cross-sectional area of the conductor that is composed of pure, low resistance, copper. Aluminium, while requiring a thin barrier metal to promote low ohmic resistance when making a contact directly to silicon or aluminium layers, did not require barrier metals on the sides of the metal lines to isolate aluminium from the surrounding silicon oxide insulators. Therefore scientists are looking for new ways to reduce the diffusion of copper into silicon substrates without using the buffer layer. One method is to use copper-germanium alloy as the interconnect material so that buffer layer (e.g. titanium nitride) is no longer needed. Epitaxial Cu3Ge layer has been fabricated with an average resistivity of 6 ± 1 μΩ cm and work function of ~4.47 ± 0.02 eV respectively, qualifying it as a good alternative to copper.