Diamond-like carbon (DLC) films are excellent prospects for a wide range of high-technology applications but their precise structure and properties are not well understood, The purpose of the present work was to use several complementary techniques to characterize the nature, structure and microstructure of DLC films. Thin DLC films were deposited on various substrates in the presence of a Si interlayer (500 Angstrom thick) using CH4 ion-beam deposition at an acceleration energy of 750 eV and a current density of about 2.5 mA cm(-2). The Si interlayer was deposited by either e-beam evaporation or Si evaporation enhanced by Ar+ beam bombardment (1 keV). The produced DLC films were featureless, very smooth and of high hardness (2900-3300 kg mm(-2)). Auger electron spectroscopy and electron diffraction showed that the films were mainly amorphous. Their microstructure was characterized by a three-dimensional network structure with a medium-range order of about 25 nm. Fourier transform infrared and Raman spectroscopies showed that the films were mainly composed of sp(3) and sp(2) carbon-bonded hydrogen. The sp(3)/sp(2) ratio varied from 3.2 to 4.1 and was found to depend on the nature of the Si bond layer. The results showed that the nucleation of the diamondlike structure was promoted on the Si interlayer that was deposited under Ar+ beam bombardment. This effect can be explained by the higher surface roughness produced in this interlayer as suggested by the reflectivity measurements. Spectroscopic ellipsometry revealed that the films had an optical band gap between 1.56-1.64 eV. The present results are consistent with previous proposals suggesting that the DLC structure is composed of small graphitelike clusters (involving fused six-fold rings) that are interconnected by sp(3)-bonded carbon.