by Glow Discharge. M.A. Botero, A. Devia, E. Restrepo, L. Alvarez .... W. F. Smith, Fundamentos de la ciencia e ingenieria de materiales, Me Graw Hill, 1993. 4.
Characterization of Polymeric Films Produced by Glow Discharge M.A. Botero, A. Devia, E. Restrepo, L. Alvarez Labor-atorio de Fisica del Plasma Universidad National de Colombia A.A. 127, Manizales Colombia Labplaun(a),manizales. cetcol net, co
Abstract. Polymeric coatings have been grown on steel 1016 substrates; the process has been performed by glow discharge in a chamber with acetylene at 1 mbar of pressure. Emission spectra have been taken during the discharge in order to identify the species of the plasma and to study plasma reactions. High-resolution atomic force microscopic (AFM) images of the coatings have been carried out. Moreover, infrared spectra were taken on the coating.
INTRODUCTION The PECVD (Plasma Enhanced Chemical Vapor Deposition) coatings have several advantages compared to traditional CVD coatings (Chemical Vapor Deposition). Among these are: synthesis and deposition conditions are easily adjustable, several elements and compounds can be deposited at low temperatures, multi-layer coatings to achieve layers with better properties are easily obtainable, useful life of the material. The polymeric coatings produced by PECVD are applied for protection of electronic circuits and dielectric materials for conversion devices and capacitors of thin films, optic windows and eyeglasses, barriers for certain gases, liquids or solutions; nonreflecting coatings; membranes of inverse osmosis, protective coatings, etc. In this work the details of the production of polymers on steel 1016 substrates are presented, as well as the results of some characterizations carried out on the samples.
DESCRIPTION OF THE SYSTEM The reaction camera has a cylindrical geometry and it is built in stainless steel 304 with a length of 322mm, inner diameter of 102mm and external diameter of 114mm. The reaction camera has a window of lateral observation which allows to place an spectrograph to identify the atomic and molecular species involved in the process. The vacuum system is compound for a mechanical pump of 1725rpm and 1A hp (pressure: 1x10"2 mbar); and a diffusion pump with a maximum speed of 75 liter/s and pressure of 1x10"6 mbar.
CP563, Plasma Physics: IX Latin American Workshop, edited by H. Chuaqui and M. Favre ©2001 American Institute of Physics l-56396-999-8/01/$18.00 78
The electric system is formed by a variable voltage source (0 -3000 V), at 900 W of power; the system of mixture of gases are compound for a regulated valve, fed by two gas line coming from the cylinders that contains gases (acetylene and nitrogen). The characteristic process parameters are: the electric current and the work pressure. For that reason it is necessary to quantify these parameters by means of measurement systems. For pressure is used a TPG 300 and a pirani sensor TPR 010 which measure range is from 1000 mbar up to 2x10~3 mbar and the current is measured with a miliamperimeter. Piram.Sensor
AT C2H2 N2 FIGURE 1. Experimental Setup
DESCRIPTION OF THE EXPERIMENT One would like to obtain a polymeric film on steel 1016 through a plasma generated in a glow discharge, using acetylene (monomer) in an environment of nitrogen. The preparation of the sample was made taking a cylindrical bar of steel 1016 which was cut in disks of 3mm of thickness. These disks are refined with sandpapers with grain sizes from 60 to 1500 beginning with the sandpaper of 60. Finally, alumina is used until achieving a shine mirror. The sample is degreased with ethyl ether. Then the sample is placed inside of the reaction chamber, in which a glow discharge is generated with Argon to eliminate sludge that have not been eliminated in the previous stage because it produces a non reagents ion current generating an effect of cleaning. This discharge is mantained during several minutes. After this time the sample is ready to be recovered. Nitrogen is introduced into the camera up to a pressure of 5-10"1 mbar. Next, acetylene is introduced up to Imbar of pressure and the discharge begins under these conditions during different periods of time.
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RESULTS AND ANALYSIS Plasma Analysis
The plasma used to produce these coatings was characterized by means of optical emission spectroscopy, by using a spectrograph for identifying the substances that intervene in this process during the discharge. The species detected by optical emission spectroscopy in our CiHi/Ni/Ar discharges are summarized in table 1. These are essentially the same as those reported by others [7] TABLE 1. Species Detected in polymer forming discharges
Species
Wavelength (nm)
Band system
449.5 457.8 466. 1 483. 3 472.3 466.3 357. 6 470.9
B2z-x2n
CH CN CO CHO H2 C2 N2 N
52E-X2Z
cli,-Aln Vaidya's hydrocarbon flame band Q-B1S\ d *Pg-a *PU
Cnu-B*ng (3F)sp y3D - (2D)5d h3D
1200 1100 CT1000 "^ =5 900 o • eg 800 7
O X
o
o
7 J
~ 700
: I 600
5 tJ J z
1 1 500
400 300
J
°
- 1J / w W/
-V I
440
.
I
450
.
O
o N 1 1 Ij ^
'- /11
uy%r »w/ 1
460
8
JWA
1
1
1
470
480
490
.
500
Wavelenght (nm) FIGURE 2. Optical Emission Spectra of the plasma uSsed to produce Polymeric Coatings.
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Introducing appropriate gases or vapors into nitrogen active, the excitation often being accompanied by chemical reactions can excite many band systems. Thus organic compounds such as CC14 and C2H2 yield CN, CH, C2 and sometimes NH. The bands produced in active nitrogen have much shorter branches than the arc but many more bands of the system are observed; fewer states of rotation are excited than of vibration. The following are the possible reactions into the chamber [8]
C2H2+hv ->2CH+ hv O2+ CH->CHO+ O CH*+N-»CN+ H* Analysis of the Coating
Figure 3 shows an infrared spectrum of the obtained samples on substrates of steel 1016 whit a polymeric coating. In this spectrum it is possible to observe polymers such as stylbene, polystyrene and polyethylene.
s ot r b a( n c e
Wavenumbers FIGURE 3. Infrared Spectrum on Polymeric Coating
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In the figure 4 are shown atomic force microscopy (AFM) images of the polymeric film. In these images is possible to observe a homogeneous morphology, pinhole-free, with an average roughness of 0.215jam. The surface coating is made of grains which have more or less the same diameter(=0.0160um) and the same height(=600um), and in the figure 5 is shown an image of lOOxlOOum of area, in which is possible to observe a pinhole on the coating, with a diameter of 16um approximately, this film was made on the glow discharge of 20 minutes and in the figure 4 was during 1 hour, the another conditions was the same.
•jam. 2'
FIGURE 5. AFM Image from a 100x£06fim area
CONCLUSIONS First of all, the infrared spectroscopy analysis showed it is possible to grow polymeric coatings by using glow discharge. Besides, the detected species during the discharge are according to the composition of the final coating. Using optical emission spectroscopy we can identify the substances in the plasma, and knowing the gases which filled the chamber, it is possible to study the plasma reactions.
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ACKNOWLEDGEMENT This work was partially supported by the Institute Colombiano para el Desarrollo de la Ciencia y la Tecnologia (COLCIENCIAS), contract #104 code 1119-05-400-93 and the Universidad Nacional de Colombia Sede Manizales
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6. 7. 8.
A. G. Negrete, J. A. Tagle, J. C. Mugica, J. I. Onate, Tecnologias Asistidas por plasma, Iberdrola, EVE, Me Graw Hill, 1997 F. J. Alvarez, Tecnicas de Recubrimientos por Plasma CVD, Comision Nacional de Energia Atomica, Agencia de Cooperation International del Japon, 1999 W. F. Smith, Fundamentos de la ciencia e ingenieria de materiales, Me Graw Hill, 1993 V. Milantiev, S. Temko, Fisica del Plasma Editorial, Mir Moscu, 1987 Rojas, A. F., Ortiz, J. A. Recubrimiento de metales con peliculas delgadas de polimeros por el metodo de deposition en plasma. Tesis de grado. Universidad Nacional de Colombia Sede Manizales. Colombia. Boening, Herman, Plasma science and technology, Cornell University Press Pearse R.W.B, Gaydon A.G, The identification of molecular spectra, Chapman and Hall, London, 1976 J.A. Mucha, Flamm D.L., and Ibbotson D.E., J. Appl. Phys. Letters 65 (9), 3448-3452, (1989)
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