Diamond-like carbon (DLC) films were prepared by plasma enhanced CVD from the mixture of methane and argon on silicon substrates. Films were characterized by multi-sample modification of variable angle spectroscopic ellipsometry. The ellipsometry showed that there is a transition interlayer between the DLC film and the silicon substrate that cannot be attributed to a thin silicon dioxide layer but rather to amorphous silicon and/or modified oxide layer. TRIM calculations revealed that argon or carbon ions could not produce a significant layer of amorphous silicon because the depth of target atom displacements is bellow the thickness of a native oxide layer. The chemical composition of a DLC film profile including a DLC/silicon interface was studied by X-ray photoelectron spectroscopy (XPS) coupled with an argon sputtering of the 34 nm thick DLC film. The DLC/silicon interface composed from less than 6 % of oxygen and gradually decreasing and increasing carbon and silicon percentage, respectively.