The ultra-high-vacuum growth of thin chromium and aluminum films on single diamond crystals at various temperatures was monitored by means of infrared spectroscopy, which provides instant information on electronic and morphological properties of the produced metal films. In accordance with atomic force microscopy results, spectra for Al indicate a clear island-like growth in the beginning followed by a transition to a continuous layer. Cr growth results in much smoother films because of a special growth mechanism. Analysis of infrared spectra of both kinds of ultrathin metal layers yields a high DC conductivity well above 10(6) S/m starting from only a few nanometers thickness for sufficiently high substrate temperatures.