Aperfeiçoamento da adesão de filmes finos de carbono amorfo hidrogenado através do entendimento físico-químico de intercamadas de silício

Abstract

The diamond-like carbon (DLC) thin films family, in particular hydrogenated amorphous carbon films (a-C:H) have interesting properties for academic and technological purposes. High wear and ultra-low friction can be found in a-C:H films that contain 40% to 50% hydrogen in its composition. However, these films have low/null adhesion to ferrous alloys. Thus, silicon-based interlayers play an important role on film adhesion lessening thermic and chemical incompatibilities to ferrous alloy (substrate-film) by increasing stronger chemical bonds in the interfaces of a sandwich-like structure. Two boundary conditions have been analyzed in deposition of a-SiCx:H interlayer from hexamethyldisiloxane (HMDSO) employing plasma enhanced chemical vapor deposition (PECVD) process. Considering the first series, the interlayer was deposited in different temperatures from 85°C to 180°C, after submitted to 6 min hydrogen etching and 1h a-C:H film deposition to adhesion evaluation of films. For the second series the interlayer was deposited in different plasma voltages (-500V to -800V), submitted to 1 min H2 etching and 1 min a-C:H driving the study to physical-chemical properties of the outermost interface (a-C:H/a-SiCx:H). Both series have been investigated by scanning electron microscopy (SEM), glow discharge optical emission spectroscopy (GDOES). For the first temperature interlayer deposition series the critical load was measured for evaluate a-C:H films adhesion. The outermost interface of different voltage interlayers depositions (second series) were analyzed by X-ray photoelectron spectroscopy (XPS) in order to investigate chemical environment and composition and by Fourier transform infrared spectroscopy (FTIR) for vibrational structures. The results for the first series are: the effect of hydrogen etching in selective chemical cleaning inducts the reduction of harmful elements and passivating bonds. Meanwhile it creates stronger ones like Si-C, C-C bonds in lower temperatures. This guarantees a critical load (3,4 N) for 85°C as interlayers deposited in 300°C without etching. For the second series in higher deposition voltage of a-SiCx:H interlayers, oxygen content diminishes. Since oxygen atoms desorb in more energetic plasma the formation of silicon carbide (Si-C) is more likely to improve a-C:H thin films adhesion. New process parameters and more accurate control of the variables can create a-C:H thin films more adhered to ferrous alloys, reducing industrial costs and increasing the application spectrum in several areas.