Fluorinated diamond-like carbon (F-DLC) films were prepared by radio frequency plasma-enhanced chemical vapor deposition technique with CF4 and CH4 as source gases under different deposition conditions. The chemical bonding structure and composition of the films were detected by Raman, Fourier transform infrared absorption spectrometry (FTIR), and X-ray photoelectron spectroscopy (XPS) characterization. The micromorphology and surface roughness of the film were observed and analyzed by atomic force microscopy (AFM). The results indicated that all the prepared films presented a diamond-like carbon structure. The relative content of fluorine in the films increased, containing more CF2 groups. The ratio of hybrid structure sp3/sp2 decreased. The surface roughness of the films increased when the gas flow ratio
In recent years, fluorinated amorphous carbon film (a-C:F) has attracted the attention of researchers for its application as a film with a low dielectric constant [
This paper investigated the relationship among the chemical bonding structure, composition, surface morphology, and hydrophobic properties of F-DLC films prepared under different gas flow ratios
The radio frequency plasma-enhanced chemical vapor deposition (PECVD) equipment used in the experiment was designed and developed by Shenyang Scientific Instruments Co., Ltd. at the Chinese Academy of Sciences. CF4 and CH4 were used as source gases, whereas Ar was used as a working gas. The total gas flow was 45 sccm, whereas that of Ar was kept at 5 sccm. The deposition temperature was 100°C, whereas the deposition power and gas flow ratio
Raman is a common technique that uses a Raman spectrum to characterize and detect the sp hybrids of carbon-based material. In this paper, the scattering spectra of the films prepared under different flow ratios were tested by Dilor LabRam Infinity (the wavelength of the laser is 632.8 nm), and the relative content of sp hybridizations in the films was detected. The chemical bonding structure of the films was analyzed with a Fourier transform infrared absorption spectrometry (FTIR; NEXUS470). The surface structures of the films were performed to characterize by an X-ray photoelectron spectroscopy (XPS, Microlab 310-F). Variations in micromorphology and surface roughness of the films under different flow ratios were observed by an atomic force microscopy (AFM; SOLVER P47).
The contact angle between a liquid and a solid surface is a manifestation of hydrophobic property. The size of the contact angle is determined by the surface free energy. The interfacial total energy remains constant when the interface between liquid and solid is stable, that is, satisfying Young’s equation [
Figure
Variation of peak position, width, and
Gas flow ratio |
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Position |
Width | Position |
Width | ||
0.25 | 1389.6 | 251.7 | 1572.5 | 102.8 | 1.70 |
0.50 | 1401.8 | 318.4 | 1574.5 | 101.5 | 4.19 |
0.75 | 1407.1 | 356.3 | 1574.6 | 107.7 | 5.17 |
Raman spectra of the F-DLC films prepared with various values of
The FTIR absorption peaks of the diamond-like structure had a wavenumber of 900 cm−1 to 1400 cm−1. For the main absorption peaks, 1030, 1070, 1160, and 1260 cm−1 corresponded to the C-C, CF, CF2(SS), and CF2(AS) absorption peaks, respectively [
FTIR spectra of the F-DLC films prepared with various values of
Figure
Typical XPS spectrum of the films. Illustration: deconvolution of the XPS C1s peaks of the films.
The contact angles of water with the DLC film surface before and after fluorine doping are presented in Figure
Liquid droplet on the surface of DLC films before and after F doped: (a) DLC films; (b) F-DLC films.
Figure
Surface roughness of the films as a function of gas flow ratio
Variation of contact of the F-DLC films at various (a) gas flow ratios
The mechanism behind the lotus effect is the cells on lotus leaf surface having a micro-/nanodual-scale structure of papillae and the surface microstructure containing hydrophobic wax resinite [
AFM 3D image of F-DLC films prepared at (a) 100 w and (b) 250 w.
Curve (a): surface roughness as a function of deposition power. Curve (b): contact angle as a function of deposition power.
The hydrophobic properties of F-DLC films mainly depend on the chemical bonding structure of the film surface, the fluorine content in the film, polarization, and the surface roughness of the film. The content of weakly polarized radical CF2 increased with the increase of
This work was supported by the National Science Foundation of China (Grant nos. 11064003 and 11364011), the Guangxi Natural Science Foundation (Grant no. 2010GXNSFA013122), and the Research Funds of the Guangxi Key Laboratory of Information Materials (Grant no. 0710908-06-K). The authors also genuinely thank Ph.D. Yanwei Li for his help in the technical and language checking.