Percolation threshold in ultrathin titanium films determined by in situ spectroscopic ellipsometry

We report on the use of in situ spectroscopic ellipsometry to determine the film thickness, optical constants, and growth rate for titanium films grown on silicon oxide by pulsed filtered cathodic vacuum arc. The growth rate and film thickness are shown to be highly controllable. We also report the results of simultaneous in situ spectroscopic ellipsometry and in situ conductivity measurements to independently verify the ability of both techniques to determine the percolation threshold. Percolation is shown to occur at a film thickness in the range 2.7 to 3.1(+∕−0.1)nm. The ability of spectroscopic ellipsometry to accurately determine the void fraction in a thin film enables us to apply the percolation formalism based on a critical exponent to this system.