Hydrogen removal from hydrogenated diamond-like carbon films by exposure to photon and energetic atomic oxygen beams

Yokota, Kumiko*; Tagawa, Masahito*; Matsumoto, Koji*; Furuyama, Yuichi*; Kitamura, Akira*; Kanda, Kazuhiro*; Tode, Mayumi; Yoshigoe, Akitaka; Teraoka, Yuden

Protection of Materials and Structures from the Space Environment; Astrophysics and Space Science Proceedings, Vol.32, p.531 - 539, 2012/08

https://doi.org/10.1007/978-3-642-30229-9_49

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.

Passive oxidation of Si(001) by hyperthermal atomic oxygen beam; A Synchrotron radiation photoemission spectroscopic study

Tagawa, Masahito*; Sogo, Chie*; Miyagai, Suguru*; Yokota, Kumiko*; Yoshigoe, Akitaka; Teraoka, Yuden

no journal, , 

Ultra-thin oxide-layers on Si(001) surfaces, formed by an atomic oxygen beam with hyperthermal incident energy, were analysed by photoemission spectroscopy with synchrotron radiation. The formation of ultra-thin oxide-layers was performed in Kobe University. The photoemission spectroscopy was performed at the surface chemistry experimental station installed in the JAEA soft X-ray beamline in the SPring-8. Comparing the photoemission spectra with those of thermal oxidation with oxygen gas, it was found that a few suboxides were observed in the ultra-thin oxide-layers formed by atomic oxygem beams.

Formation of silicon oxynitride film using 5eV O atom and hyperthermal N beam exposures

Tagawa, Masahito*; Yokota, Kumiko*; Nishizaki, Noriaki*; Miyagai, Suguru*; Yoshigoe, Akitaka; Teraoka, Yuden

no journal, , 

Fast nitrogen molecular beams with 2 keV kinetic energy were irradiated at an Si(001) surface with an ultra-thin oxide overlayer. Photoemission peaks of bulk Si atoms became to be not clear. This fact indicates that nitrogen molecules transmitted from the oxide film react with bulk Si atoms. On the other hand, slow nitrogen molecular beams with 1.6 eV to 6.9 eV incident energy were irradiated at the oxide film. The surfaces were observed by photoemission spectroscopy with synchrotron radiation. With increasing the incident energy, SiN-related part in the Si2p photoemission peak increased in the bulk-sensitive measurements rather than surface-sensitive measurements. This fact reveals that nitrogen molecules are impinged into the oxide film even in such low energy and chemical bonds with Si atoms are formed near the interface.

A Novel room temperature oxidation technique using hyperthermal broad atomic/molecular beams

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

no journal, , 

Synchrotron radiation photoelectron spectroscopy (SR-PES) and crystal truncation rod (CTR) scattering profiles were used to investigate an ultra-thin 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 oxidized film formed by the O atom beams were concentrated on the SiO surface rather than at the Si/SiO interface. The CTR scattering data of the O-atom-beam oxidation film suggested 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.