Spectroscopic analysis on the carbon nanostructured thin films deposited by Thermionic Vacuum Arc (TVA) method

Spectroscopic analysis on the carbon nanostructured thin films deposited by Thermionic Vacuum Arc (TVA) method

R. Vladoiu¹, V. Ciupina¹, A. Mandes¹, C. Surdu-Bob² , S. Saied³, J. Sullivan³,

G. Musa¹

Dept. of Physics, Ovidius University, Constanta 900527 Romania,

National Institute for Laser, Plasma and Radiation Physics, PO Box MG-36, 077125, Bucharest Romania

Dept. of Electr. & Electron. Eng. & Appl. Phys., Aston Univ., Birmingham, UK

This paper reports the X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy (XAES) studies of the carbon nanostructured thin film deposited by Thermionic Vacuum Arc (TVA) method.

The film deposition process by Thermionic Vacuum Arc, an original discharge type in pure metal vapor plasma, might become one of the most suitable technologies to significantly improve the quality of the surfaces coated with different materials using present technologies. The thermionic vacuum arc can be ignited in vacuum (or ultrahigh vacuum) between a heated cathode surrounded by an electron focusing Wehnelt cylinder and an anode (tungsten crucible) containing the material to be deposited. At further increase of the applied high voltage, a bright discharge is established inside of the deposition chamber in the vapors of the anode material.

X-ray photoelectron spectroscopy (XPS) and X-ray generated Auger electron spectroscopy (XAES) were used to determine composition and sp² to sp³ ratios in the outer layers of the film surfaces.

The analyses were conducted in a Thermoelectron ESCALAB 250 electron spectrometer equipped with a hemispherical sector energy analyzer. Monochromated Al Ka X-radiation was employed for the XPS examination, at source excitation energy of 15 KeV and emission current of 20 mA.

XPS Survey scans were first recorded for all samples at analyzer take-off angles of 0^o (normal to the surface) and then narrow region energy scans were collected for all the elements identified on the surface.

The base pressure within the spectrometer during examinations was always better than 5 x 10^-10 mBar and this ensured that all signals recorded were from the sample surface. The area of analysis was chosen to be 500 mm diameter for each analysis during the coating sample analysis.

The best electron spectroscopic method for determining the sp²:sp³ ratio in amorphous carbon films is to monitor the energy separation, in eV, between the major negative-going and positive-going excursion in the first derivative of the XAES C KLL spectra. The resulting separation or the D value, gives a measure of the sp²:sp³ ratio. We have determined D values for pure graphite (wholly sp²) and pure diamond (wholly sp³) to be 22.1 eV and 14.0 eV respectively.