An exhaust gas turbocharger for an internal combustion engine may include a rotor with a turbine wheel of a turbine, a compressor wheel of a compressor and a shaft. The second index of refraction, and the third index of refraction are both greater than the first index of refraction. The ground contacting element contains a plurality of projections, with the projections divided into at least two sets. The metal or semiconductor layer may be subjected to an oxidation process.