Teruyuki Kitagawa

Characterization of Hard Diamond-Like Carbon Films Formed by Ar Gas Cluster Ion Beam-Assisted Fullerene Deposition

The coordination of carbon atoms in diamond-like carbon (DLC) thin films formed by Ar gas cluster ion beam (GCIB) assisted deposition using fullerene as the carbon source was investigated by measuring near-edge X-ray absorption fine structure (NEXAFS) spectra of the carbon K-edge over the excitation energy range 275–320 eV, using synchrotron radiation. With attention to the peak corresponding to the transition of the excitation electron from a carbon 1s orbital to a π* orbital, relative sp2 contents of various DLC films were estimated. The sp2 contents of the DLC films formed by the GCIB-assisted deposition were observed to be lower than those of the DLC films formed by other methods. The hardness value measured with a nano-indentation technique was found to be strongly related to the sp2 content of the DLC film.

Hard DLC film formation by gas cluster ion beam assisted deposition

Abstract Diamond-like carbon (DLC) films with high hardness were formed by Ar cluster ion beam assisted deposition at room temperature, using C 60 as a carbon source. The gas cluster ion beam (GCIB) assisted deposition was useful to form hard DLC films, as the bombardments induced high-pressure and high-temperature effects at the impact surface, and ultra low energy effects. When the acceleration energy of Ar cluster ion was 5 keV, the hardness of 50 GPa was obtained. This value was approximately two times higher than that of the films deposited with conventional methods. Wear-resistance properties were also higher than that of conventional films. Rough estimations of sp 2 orbital in the films were carried out with Raman spectra, the films formed with Ar cluster ion bombardment had lower sp 2 contents, which meant films had low fraction of graphite bonding. Thus DLC films exhibiting higher physical characteristics and lower graphite bonding were obtained with GCIB assisted deposition.

Near Edge X-Ray Absorption Fine Structure Study for Optimization of Hard Diamond-Like Carbon Film Formation with Ar Cluster Ion Beam

Diamond-like carbon (DLC) film deposited using C60 vapor with simultaneous irradiation of an Ar cluster ion beam was characterized by a near edge X-ray absorption fine structure (NEXAFS), in order to optimize the hard DLC film deposition conditions. Contents of sp2 orbitals in the films, which were estimated from NEXAFS spectra, are 30% lower than that of a conventional DLC film deposited by a RF plasma method. Those contents were obtained under the flux ratio of the C60 molecules to the Ar cluster ions to range from 1 to 20, at 5 keV of Ar cluster ion acceleration energy. Average hardness of the films was 50 GPa under these flux ratios. This hardness was three times higher than that of a conventional DLC film. Furthermore, the lowest sp2 content and above-mentioned high hardness were obtained at room temperature of the substrate when the depositions were performed in the range of the substrate temperature from room temperature to 250°C.

Optimum incident angle of Ar cluster ion beam for super hard carbon film deposition

In this paper, we study influences of incident angles of Ar cluster ions during depositions on the carbon film properties, by bombardment of Ar cluster ions with various incident angles. Additionally, the angles to obtain the super hard carbon film were also optimized.

NEXAFS study on substrate temperature dependence of DLC films formed by Ar cluster ion beam assisted deposition

Abstract For the optimization of the synthesis condition of the production of diamond-like carbon (DLC) thin films by Ar gas cluster ion beam (GCIB) assisted deposition of fullerene, the local structure of DLC thin films was investigated by measuring near-edge X-ray absorption fine structure spectra of the carbon K-edge over the excitation energy range 275–320 eV, using synchrotron radiation. The DLC thin films were formed by GCIB assisted deposition at substrate temperatures ranging from room temperature to 250 °C. The sp2 content estimated from the analysis of the peak corresponding to the transition of the excitation electron from a carbon 1s orbital to a π* orbital was found to increase with the substrate temperature during GCIB assisted deposition.

X-ray Photoelectron Spectroscopy Study of Diamond-Like Carbon Thin Films Formed by Ar Gas Cluster Ion Beam-Assisted Fullerene Deposition

The coordination of C atoms in diamond-like carbon (DLC) thin films formed by Ar gas cluster ion beam (GCIB) assisted deposition using fullerene as a carbon source was investigated using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. From the curve fitting analysis of XPS spectra of the C 1s core level, the absolute sp2 and sp3 contents in the DLC films formed by Ar GCIB-assisted deposition were evaluated for the first time. The absolute sp3 content of DLC films formed by the GCIB-assisted deposition at an acceleration voltage of 5 kV was the highest compared with that formed at 7 and 9 kV. In addition, the absolute sp2 contents evaluated from XPS spectra were compared to the relative sp2 contents evaluated from NEXAFS spectra.

Optimization of flux ratio of C60 molecule to Ar cluster ion for diamond-like carbon film deposition by NEXAFS measurement

Abstract To optimize the flux ratio of C 60 to Ar cluster ion during diamond-like carbon (DLC) film deposition, DLC films deposited under various flux ratios were characterized with Raman spectrometry and near edge X-ray absorption fine structure (NEXAFS). From Raman spectrometry, DLC films were deposited when the flux ratio of C 60 to Ar cluster ion was between 0.7 and 4. When the ratio was over 10, C 60 films were mainly deposited. As it was difficult to do precise characterization of DLC with Raman spectrometry, NEXAFS measurements were performed for the films deposited in the DLC deposition range of flux ratio. From NEXAFS spectra, there was no significant difference in sp 2 contents when the flux ratios were between 1 and 4. Hardness of these DLC films was between 40 and 45 GPa. Therefore very hard DLC film could be deposited with Ar cluster ion beam assist deposition over wide range of flux ratios, and this deposition process was very stable against changes of the flux ratio.

Influence of residual Ar+ in Ar cluster ion beam for DLC film formation

Abstract In order to study the influences of residual Ar monomer ion (Ar + ) on sp 2 content and hardness of diamond like carbon (DLC) films formed by Ar cluster ion beam assisted deposition, Ar cluster ion, Ar + and their mixed ions (Ar cluster ion and Ar + ) bombardments were performed during evaporation of C 60 . From near edge X-ray absorption fine structure (NEXAFS) and Raman spectroscopy measurements, lower sp 2 content in the carbon films was obtained with Ar cluster ion bombardment than that with Ar + and mixed ion. Furthermore higher hardness and smooth surface were shown with Ar cluster ion bombardments. Therefore it was important to reduce Ar + in Ar cluster ion beams to obtain hard DLC films with flat surface.

Difference of Irradiation Effects between Ar Cluster Ion and Ar+ for DLC film formation

In order to study the influences of Ar monomer ion (Ar+) on carbon film properties induced by ion beams assisted deposition, Ar cluster ion, Ar+, and their mixed ions (Ar cluster ion and Ar+) irradiated surface during evaporation and deposition of C60. From Near Edge X‐ray Absorption Fine Structure (NEXAFS) and Raman spectroscopy measurements, lower sp2 content in carbon films was obtained via Ar cluster ion beam bombardment in comparison with bombardment by Ar+ and mixed ion beams. Furthermore higher hardness and smoothness of surface were demonstrated via Ar cluster ion bombardments. Thus, it was important to irradiate using higher fraction Ar cluster ions in the beam, in order to obtain hard DLC films with flat surface.

Photoelectron Spectroscopy Study of the Valence Band Region in Diamond-Like Carbon Thin Films

Photoelectron spectra of the valence band region in diamond, diamond-like carbon (DLC), glassy carbon, and graphite were measured in order to investigate the influence of the carbon atom coordination on photoelectron spectra. Differences in the photoelectron spectra were observed, depending on the coordination of the carbon atoms. The photoelectron spectra for DLC and glassy carbon were compared to those simulated using the photoelectron spectra for diamond and graphite. From this comparison, it was found that the photoelectron spectra in DLC could not be simply reproduced using those for diamond and graphite. In addition, the photoelectron spectra of the valence band region in DLC were compared to the density of states previously calculated using the molecular dynamics method.