Characterization studies of diamond-like carbon films grown using a saddle-field fast-atom-beam source

Abstract

In this article, we report results of an extensive characterization study involving scanning electron microscopy, spectroscopic ellipsometry (SE), photothermal deflection spectroscopy (PDS), x-ray photoelectron spectroscopy, x-ray Auger electron spectroscopy (XAES), current–voltage (I–V) measurements, hydrogen content evaluated from Fourier transform infrared spectroscopy and elastic recoil detection analysis, and also measurement of stress and hardness of diamond-like carbon (DLC) films. These films were grown using methane (CH4), acetylene (C2H2) gases, and benzene (C6H6) vapors into a saddle-field fast-atom-beam (FAB) source. DLC films formed by the saddle-field FAB source technique exhibit extremely low residual stress (0.12–0.26 GPa) and high Knoop hardness (9–22 GPa) measured at 50 g load. The values of optical constants (n, k, ε1, ε2) evaluated from SE, characteristic energy of band tail (Urbach energy, E0) evaluated from PDS studies, sp2 percentage evaluated from XAES data, the density of states [N(EF)] derived from space-charge-limited conduction, and the hydrogen content are found to decrease, and the sp3/sp2 ratio evaluated are found to increase with the increase of carbon-to-hydrogen ratio in the hydrocarbon gases/vapors used for growing DLC films by this technique. The values of E0, N(EF), hydrogen content, and sp3/sp2 ratio of these DLC films are found to be in the range of 180–280 meV, 1–6×1017 eV−1 cm−3, 3–8 at. % and 5.2–12.3, respectively, which are lower than the values of E0 (300–500 meV), N(EF) (∼1018 eV−1 cm−3), and hydrogen content (15–40 at. %) and higher than sp3/sp2 ratio (1.3–2.5) of DLC films grown by the more conventional rf self-bias technique reported in the literature.