The effect of germanium wetting layer on the percolation processes in ultrathin copper films and their microwave transmission, reflection and absorption coefficients

The microwave coefficients of copper films with a thickness of 1...16 nm grown on a 1.8 nm germanium sublayer deposited on the surface of quartz glass substrates with a thickness of 4 mm are studied. The measurements have been carried out in a rectangular waveguide with a cross section of 23×10 mm² in the frequency range of 8.5...12.5 GHz. A smooth change in the microwave coefficients of the samples studied is detected in the range of copper film thicknesses of 2...16 nm. It is established that the critical percolation thickness of the copper films grown on germanium sublayer is in the range between 1 and 2 nm. A significant internal size effect is found in the films grown on Ge sublayer due to the scattering of conduction electrons mainly by intercrystalline boundaries. It is determined that the coefficient of reflection of conduction electrons by the intercrystalline boundaries of the copper films with Ge sublayer is more than three times higher than a similar coefficient in Cu films grown directly on the glass substrates.