Survivability of silicon-doped diamond-like carbon films in energetic atomic/molecular oxygen beam environments

Tagawa, Masahito*; Kishida, Kazuhiro*; Yokota, Kumiko*; Matsumoto, Koji*; Yoshigoe, Akitaka; Teraoka, Yuden; Zhang, J.*; Minton, T. K.*

Protection of Materials and Structures from the Space Environment; Astrophysics and Space Science Proceedings, Vol.32, p.547 - 555, 2012/08

https://doi.org/10.1007/978-3-642-30229-9_51

Effect of the soft X-rays on highly hydrogenated diamond-like carbon films

Kanda, Kazuhiro*; Yokota, Kumiko*; Tagawa, Masahito*; Tode, Mayumi; Teraoka, Yuden; Matsui, Shinji*

Japanese Journal of Applied Physics, 50(5), p.055801_1 - 055801_3, 2011/05

https://doi.org/10.1143/JJAP.50.055801

Recently, the irradiation of soft X-ray synchrotron radiation (SR) to highly-hydrogenated diamond-like-carbon (H-DLC) films in vacuum results in the desorption of hydrogen and the increase of film density, hardness and refractive index. In this study, we investigated SR irradiation effects on the H-DLC with different hydrogen contents. The H-DLC thin films were deposited on an Si wafer with 200 nm thickness by an amplitude-modulated radio frequency plasma chemical vapor deposition method. The SR irradiation was carried out at NewSUBARU BL6. The SR has a continuous spectrum from IR to soft X-ray, which is lower than 1 keV. The hydrogen content dependence on SR dose was estimated using elastic recoil detection analysis (ERDA) and Rutherford backscattering (RBS) techniques. The hydrogen content was kept constant in the low-hydrogenated DLC film, while that in the high-hydrogenated DLC film decreased exponentially with soft X-ray dose.

Synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure study on oxidative etching of diamond-like carbon films by hyperthermal atomic oxygen

Tagawa, Masahito*; Yokota, Kumiko*; Kitamura, Akira*; Matsumoto, Koji*; Yoshigoe, Akitaka; Teraoka, Yuden; Kanda, Kazuhiro*; Niibe, Masahito*

Applied Surface Science, 256(24), p.7678 - 7683, 2010/10

https://doi.org/10.1016/j.apsusc.2010.06.030

Surface structural changes of a hydrogenated diamond-like carbon (DLC) film exposed to a hyperthermal atomic oxygen beam were investigated by Rutherford backscattering spectroscopy (RBS), synchrotron radiation photoelectron spectroscopy (SR-PES), and near-edge X-ray absorption fine structure (NEXAFS). It was confirmed that the DLC surface was oxidized and etched by high-energy collisions of atomic oxygen. RBS and real-time mass-loss data showed a linear relationship between etching and atomic oxygen fluence. SR-PES data suggested that the oxide layer was restricted to the topmost surface of the DLC film. NEXAFS data were interpreted to mean that the sp structure at the DLC surface was selectively etched by collisions with hyperthermal atomic oxygen, and an sp-rich region remained at the topmost DLC surface. The formation of an sp-rich layer at the DLC surface led to surface roughening and a reduced erosion yield relative to the pristine DLC surface.

Atomic layer fluorination of highly oriented pyrolytic graphite using hyperthermal atomic fluorine beam

Tagawa, Masahito*; Yokota, Kumiko*; Maeda, Kenichi*; Yoshigoe, Akitaka; Teraoka, Yuden

Applied Physics Express, 2(6), p.066002_1 - 066002_3, 2009/06

https://doi.org/10.1143/APEX.2.066002

Hyperthermal (kinetic energy of 10 eV) fluorine atom beam interaction with highly oriented pyrolytic graphite (HOPG) was studied. Surface analytical results of atomic fluorine-exposed HOPG using synchrotron radiation photoelectron spectroscopy showed that the fluorine reaction was limited at the topmost HOPG(0001) layer. This is due to the fact that the kinetic energy of 10 eV is not sufficient to penetrate graphite layer but is enough for breaking C-C bonds and forms CF and CF functional groups through the beam-induced fluorination reactions. It was demonstrated that the use of hyperthermal energy in the range of 10 eV is advantageous for damage-free modification of the topmost surface of carbon-based materials.

Hydrogen desorption from a diamond-like carbon film by hyperthermal atomic oxygen exposure

Yokota, Kumiko*; Tagawa, Masahito*; Kitamura, Akira*; Matsumoto, Koji*; Yoshigoe, Akitaka; Teraoka, Yuden

Applied Surface Science, 255(13-14), p.6710 - 6714, 2009/04

https://doi.org/10.1016/j.apsusc.2009.02.064

The densities of hydrogen and carbon atoms in a hydrogenated diamond-like carbon (DLC) film exposed to a hyperthermal atomic oxygen beam were investigated by Rutherford backscattering spectroscopy and elastic recoil detection analysis. The hydrogen density in DLC decreased upon atomic oxygen exposure with collision energy as low as 2 eV, whereas an exposure greater than 3 eV was necessary to remove carbon atoms. A high collision energy also led to hydrogen desorption in the deeper region of DLC. The surface density of hydrogen decreased 6% by atomic oxygen exposure, and was independent of the collision energy. Additionally, the non-bonded hydrogen, which could diffuse in DLC, was desorbed by the energy transfer from the atomic oxygen collisions.

Space environmental effects on MoS and diamond-like carbon lubricating films; Atomic oxygen-induced erosion and its effect on tribological properties

Tagawa, Masahito*; Yokota, Kumiko*; Matsumoto, Koji*; Suzuki, Mineo*; Teraoka, Yuden; Kitamura, Akira*; Belin, M.*; Fontaine, J.*; Martin, J. M.*

Surface & Coatings Technology, 202(4-7), p.1003 - 1010, 2007/12

https://doi.org/10.1016/j.surfcoat.2007.07.069

Effects of 5 eV atomic oxygen beam on MoS and diamond-like carbon (DLC) lubrication films are evaluated relevance to space environmental effects in the low Earth orbit. X-ray photoelectron spectra indicate that the loss of S atoms and Mo oxidation at the atomic oxygen irradiated MoS is significant. Depth profiles of S and Mo indicate that the oxidation is restricted within 3 nm from the surface. This is due to the fact that Mo oxide plays as a protective layer against further oxidation. The surface oxidation affects the friction coefficient. However, due to the delamination of oxide layer, wear-life of the film is reduced in some conditions. In contrast, no sever oxidation states of C atoms are detected at DLC surface. However, the loss of DLC itself is measured by Rutherford backscattering spectroscopy. It is concluded that the protection of DLC film is mandatory for the use of DLC in the LEO space applications.

Oxidation of Si(001) with a hyperthermal O-atom beam at room temperature; Suboxide distribution and residual order structure

Tagawa, Masahito*; Sogo, Chie*; Yokota, Kumiko*; Yoshigoe, Akitaka; Teraoka, Yuden; Shimura, Takayoshi*

Applied Physics Letters, 88(13), p.133512_1 - 133512_3, 2006/03

https://doi.org/10.1063/1.2190467

Synchrotron radiation photoelectron spectroscopy (SR-PES) and crystal truncation rod (CTR) scattering profiles were used to investigate an ultrathin SiO overlayer on an Si(001) surface formed by a 5 eV O-atom beam at room temperature. The SR-PES spectra indicated that the suboxides in the O-atom-beam oxidized film were concentrated on the SiO surface rather than at the Si/SiO interface. The CTR scattering data of the O-atom-beam oxidation film had a lower intensity near (1 1 L) (0.3-L-0.8), suggesting a lower content of the SiO ordered structure in the oxide film. An inverse diffusion of the interstitial Si atoms in the oxidation kinetics can explain the data.

Hydrogen desorption processes from DLC films by soft X-ray irradiation

Kanda, Kazuhiro*; Tagawa, Masahito*; Yokota, Kumiko*; Tode, Mayumi; Teraoka, Yuden; Matsui, Shinji*

no journal, , 

In this study, hydrogen desorption processes from highly-hydrogenated DLC films have been investigated by thermal desorption mass stectrometry (TDS) and elastic recoil detection analysis (ERDA). The soft X-ray irradiation was performed at BL-6 in NewSUBARU. The white light is containing infra red to 1000 eV X-ray. The TDS measurements were performed using the thermal desorption measurement system at BL23SU in SPring-8. Although a large peak was observed at around 470 K in the non-X-ray-irradiated DLC film, the peak almost disappeared after irradiation of 300 mAhr synchrotron radiation. ERDA measurements resulted in no change of hydrogen content for lowly-hydrogenated DLC film instead of large decrease of hydrogen for highly-hydrogenated DLC film depending on soft X-ray dose. Hydrogen molecules, which are seen in a TDS spectrum as a low temperature peak, desorb by soft X-ray irradiation so that density and reflective index are changed.

Departure process of hydrogen from highly-hydrogenated diamond-like carbon film by exposure to synchrotron radiation

Kanda, Kazuhiro*; Yokota, Kumiko*; Tagawa, Masahito*; Tode, Mayumi; Teraoka, Yuden; Matsui, Shinji*

no journal, , 

In the present study, we investigated the desorption of hydrogen from highly-hydrogenated diamond-like-carbon (DLC) films by irradiation of synchrotron radiation (SR) soft X-rays in vacuum. The irradiation of SR was carried out at BL-6 of NewSUBARU. The SR energy is ranging from infra red to soft X-ray, which was lower than 1 keV. The hydrogen content in the DLC films has been determined by Rutherford backscattering (RBS) and elastic recoil detection analysis (ERDA) techniques. Although the hydrogen content in the low-hydrogenated DLC film was independent on the soft X-ray dose, that for the high-hydrogenated DLC film decreased exponentially with the soft X-ray dose. This implies that the desorption of hydrogen takes place from the high-hydrogenated DLC films by the soft X-ray irradiation.

Effect of hyperthermal atomic oxygen exposures on hydrogenated diamond-like carbon films

Yokota, Kumiko*; Asada, Hidetoshi*; Tagawa, Masahito*; Ohara, Hisanori*; Nakahigashi, Takahiro*; Yoshigoe, Akitaka; Teraoka, Yuden; Martin, J. M.*; Belin, M.*

no journal, , 

Hydrogenated diamond-like carbon (DLC) is expected as a lubricant for space uses because of its ultra low friction charactor in vacuum. Thus, DLC films were exposed to atomic oxygens which were generated by a laser detonation method simulating a low orbit space environment. The DLC surfaces were analysed and the results are reported in this talk. The hydrogenated amorphous DLC was fabricated by a RF-CVD method on Si substrates. Relative collision energy of space planes against atomic oxygens can be simulated with the space environment experimental apparatus. The DLC films exposed to atomic oxygens were analysed by an SR-PES method etc. The SR-PES was performed at the surface chemical reaction analysis station installed in the BL23SU of SPring-8. It was suggested that some volatile oxides were formed and desorbed from the DLC surface when DLC surface was irradiated by atomic oxygens with an incident energy of 4.2 eV and fluence of 510atoms/cm.