UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2003 Meeting


Section: Optics, Spectroscopy, Plasma and Lasers


Title:
Thermionic Vacuum Arc – a new technique for high purity carbon thin film deposition


Authors:
G. Musa1, I. Mustata1, M. Blideran1, V. Ciupina2, R. Vladoiu2, G. Prodan2, E. Vasile2, H. Ehrich3


Affiliation:
1 National Institute for Physics of Laser, Plasma and Radiation, Bucharest-Magurele, Romania

2 Department of Physics, “ Ovidius” University, Constanta,, Romania

3 Department of Physics, University of Essen, Essen, Germany


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Keywords:


Abstract:
Thermionic Vacuum Arc ( TVA ) is an externally heated cathode arc which can be established in high vacuum conditions, in the vapors of the anode material, continuously generated due to the incoming power P given by the relation P=Uanode*Iarc where Uanode is the anode potential fall and Iarc is the arc current. This new type of arc offers the unique opportunity to generate energetic ions, with a controlled value of the directed energy, which are bombarding the condensing thin film on the substrate. The ions nature is just that of the depositing atoms on substrate. The directed energy of ions is related to the cathode fall. Indeed because cathode is at ground potential, the plasma is against the wall of the vacuum vessel at a potential equal with the cathode fall. Consequently, a potential difference equal with cathode fall will accelerate the ions towards the walls of the vacuum vessel up to energy of 500 eV, for characteristics anode currents of 1 A. Simple means are available to control the value of the ions energy like cathode-anode distance, relative position of electrodes, cathode heating current, etc. Even during deposition, the value of the cathode fall can be changed at will in the range some of hundreds volts. The deposited C thin films were studied using TEM electronic microscopy with a magnification of 1.4 M and a resolution of 1.4 Ǻ. The samples of deposited carbon films ( deposited on NaCl or KCl monocristals, solved in water before TEM examination ) show nanostructured films. The size of cylindrical structure has a diameter of 2.40-2.70 nm and a length of only 10-20 Ǻ sustaining the nanostructured thin films. Preliminary Raman spectra have confirmed the existence of sp3 bounds beside sp2 ones. The grain size distribution graphs show an average value of 6.52 nm. The electron diffraction diagrams show the existence of crystalline structure in the deposited thin films using TVA technique. The new system of deposition is peculiarly adequate for hydrogen free, high quality-smooth and compact-DLC film deposition. TVA easily ensures the needed high value of the energy to evaporate pure carbon. In this paper, we present first results on characteristics of DLC film obtained using TVA. The main used working parameters were: cathode filament-thoriated tungsten wire with 1.5 mm diameter, too times wound and heated by a current of 100 A; end vacuum during deposition - 10-6 torr; applied high voltage during arc running in pure carbon - 1100 V; interelectrodic distance ( cathode-anode ) - 4 mm; sizes of the carbon anode ( mounted on a Ö=1.5 mm tungsten wire ) - Ö=10 mm, h=10 mm; deposition time - 300 s; deposition rate - 3 Ǻ/s; final thickness of the deposited pure carbon thin film - 90nm. During the arc running and C thin film deposition, the anode was continuously rotating with 6 rotation/minute and also the cathode-anode distance was adjusted each time when the arc current was decreasing more than 10%. This way, a continuous working of the TVA was ensured. References: 1. G. Musa, V. Ciupina, C.P. Lungu, I. Mustata, H. Ehrich, T. Hegemann Thermionic Vacuum Arc carbon plasma generation for hydrogen free carbon thin film deposition Proceed. XXV-th Int. Conf. on Phenomena in Ionized Gases-ICPIG, Nagoya, 3, 219-0, (2001) 2. I. Mustata, M. Cretu, C. Cudalbu, C.P. Lungu, G. Musa, H. Ehrich, J. Schumann, T. Hegemann The discharge energy dependence of the deposition rate in TVA technology Proceed.XXV-th Int. Conf. on Phenomena in Ionized Gases-ICPIG, Nagoya, 3, 313-4, (2001)