Optical constants of tetrahedral amorphous carbon films in the infrared region and at a wavelength of 633 nm

The optical constants of tetrahedral amorphous carbon (ta-C) films in the i nfrared region and at a wavelength of 633 nm were investigated. The ta-C fi lms were prepared by the filtered arc deposition technique under different carbon ion energies of 22-320 eV. The ta-C films contained high sp(3) bondi ng of 82%-93% and had very smooth surfaces. The optical band gap was found to be controlled essentially by the presence and arrangement of the sp(2) s ites in the ta-C films. The real and imaginary parts, epsilon(1) and epsilo n(2), of the dielectric constant, refractive index, n, and extinction coeff icient, k, of ta-C films were determined from measurements of infrared refl ection and spectroscopic ellipsometry. The results indicated that in our re gion of investigation ta-C films exhibited a fine transparency at a wavelen gth of 633 nm, especially in the infrared region. Both n and k, and consequ ently, epsilon(1) and epsilon(2), showed considerable variation in ion ener gy, and had minimum values approaching those of diamond for film prepared a t an ion energy around 220 eV. The dependence of the optical constants on t he sp(3) content of ta-C films indicated that with increased sp(3) content, ta-C film possessed a dielectric constant, refractive index and extinction coefficient much closer to that of diamond. (C) 2000 American Institute of Physics. [S0021- 8979(00)09009-5].