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The surface modification of dielectrics by a CW electron beam
Vacuum 62 (2001) 237}240
The surface modi"cation of dielectrics by a CW electron beam Sergey Korenev*, Jerry Kriebel STERIS Corporation, STERIS Isomedix Services, 2500 Commerce Drive, Libertyville, IL 60048, USA
Abstract The e!ect of surface modi"cation of dielectric materials on a sample of Te#on and dielectric with low dielectric constant by scanning a parallel electron beam is considered in this report. The irradiation of samples has been performed on the CW (Continuous Wave) electron accelerator `Rhodotrona, with the following main parameters: kinetic energy 5 MeV and a current of 1}16 mA in air conditions. The nature of physical processes in dielectric materials during irradiation is di!erent in comparison with conducting materials. The distribution of absorbed doses and electrons in the dielectric material is discussed. The e!ect of surface modi"cation of dielectrics consists in the treatment of its surface by surface electrical discharge from charging the dielectric by the electron beam. The e!ect of the in#uence of magnitude of internal electric charge on the surface discharge is discussed. 2001 Elsevier Science Ltd. All rights reserved. Keywords: Electron beam; Irradiation; Surface treatment; Surface discharge; Dielectrics
1. Introduction
parameters of the electron beams are:
The question of surface modi"cation of dielectrics with low dielectric constant by high energy electron beams is very important for understanding the physics and chemistry of these materials. Te#on is a simple material for investigation [1], is stable to corrosion e!ects from ozone in the area of irradiation and is considered in this report.
E kinetic energy, 5.0 MeV; E beam current, 1}16 mA; E frequency of operating RF accelerating structure, 107.5 MHz; E full diameter of electron beam, 8 cm; E repetition of scanning for beam, 100 Hz; E The trajectories of scanning electron beams are parallel.
2. Experimental 2.1. Electron accelerators The experiments were conducted on the electron accelerator `Rhodotrona [2,3]. The main
The accumulated absorbed doses in the irradiation of samples were of the order of 10}200 kGy. Absorbed dose D is de"ned as the mean energy imparted, d, to an incremental quantity of matter, divided by the mass of that matter, dm [4]: D"d/dm"Gy.
(1)
2.2. Samples * Corresponding author. Tel.: #1-847-573-3223; fax: #1847-247-0882. E-mail address: sergey}[email protected] (S. Korenev).
The irradiation was made in air static conditions.
0042-207X/01/$ - see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 4 2 - 2 0 7 X ( 0 0 ) 0 0 4 2 2 - X
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S. Korenev, J. Kriebel / Vacuum 62 (2001) 237}240
The dielectric samples from Te#on (dielectric constant &2), glass (&6), polyethylene (&2) and BaTiO (&1000}3000) are presented as plates with thickness 1.5 mm and are "xed in the unit with a total thickness of 15 mm. The methods of investigations of samples included SEM methods and the electrical measurements of surface resistance and plasma resistance on the surface of dielectrics.
3. Computer simulation The computer simulations include the simulation of the propagation of electrons in the dielectrics and the e!ect of back scattering. The results of computer modelling for dielectrics with low dielectric constant have more homogeneous distribution of absorbed doses in comparison with the same distribution for metals (see Fig. 1). The electron trajectories in Te#on and polyethylene have the same form. As an example, electron trajectories for Te#on are shown in Fig. 2.
4. Experimental results The SEM photographs of surface for Te#on before irradiation and after electron beam irradiation are shown in Fig. 3a and b. The analysis of surfaces of other dielectrics shows the same type of picture. The measurements of surface resistance of these dielectric samples indicated a weak dependence of surface resistance on absorbed doses in the range 10}200 kGy. However, the resistance of surface plasma on Te#on varied. The resistance was 14 k for an electron beam current 1 mA and 100 k for 16 mA. The irradiation of a dielectric with a low dielectric constant allows the formation of stable surface plasma. The irradiation of BaTiO with a high dielectric constant leads to an electrical discharge inside the dielectric. The surface has a multipoint character of surface discharge [5].
5. Discussion The question of surface modi"cation of dielectrics having di!erent dielectric constants is not
Fig. 1. The distribution of absorbed doses in Te#on for electron with kinetic energy 5 MeV.
S. Korenev, J. Kriebel / Vacuum 62 (2001) 237}240
239
Fig. 2. The distribution of 5 MeV electron trajectories in Te#on.
Fig. 3a and b. SEM photographs of surface before and after electron beam irradiation.
understood at present. The use of a dielectric with high dielectric constant causes internal electrical discharges [5,6]. For low dielectric constant materials these e!ects must be reduced to make correct measurements of the surface discharge. The forming plasma allows observation of e!ects of ion etching of the surface of dielectrics. The SEM pho-
tographs con"rm this. Te#on has high resistance to corrosion. The ozone in the area of irradiation is very active and other dielectrics have fast oxidation. The processes of dissipation of energy in the irradiated product have di!erent characters for dielectrics when compared to metals. Fig. 1 con"rms
240
S. Korenev, J. Kriebel / Vacuum 62 (2001) 237}240
this. For metals, we have the e!ect of thermal processes and we have a classical distribution of absorbed doses on the level of 20% for average absorbed doses. The e!ect of accumulation of charge inside a dielectric leads to an in#uence on electrical "eld from space charge, accumulated during irradiation.
6. Conclusion The following conclusions can be made from this study: E the irradiation of a dielectric with low dielectric constant leads to more homogeneous distribution of absorbed doses in these dielectrics in comparison with metals; E etching of the surface of a dielectric by the surface plasma was observed;
E dielectrics with low dielectric constant allow the formation of a homogeneous surface discharge.
References [1] Korenev S, Mase"eld J, Kriebel J, Johnson S. Proceedings of the Tenth International Seminar of Laboratory of Surface Science, Rutgers University, 1999. p. 23. [2] Pottier J. Nucl Instr and Meth 1989; B40/41:p. 943. [3] Jongen Y. Manufacturing of electron accelerators. Proceedings of the European Particle Accelerator Conference (EPAC '96), Barcelona, Spain, 1996. p. 260. [4] McLaughlin WL, Boyd AW, Chadwick KH, McDonald JC, Miller A. Dosimetry for radiation processing. London: TaylorFrancis, 1989. [5] Gromov VV. Electrical discharge in the irradiated materials. Moscow: Energoizdat, 1982. [6] Korenev SA. Determination of admittance irradiation loads by electron beam on The BaTiO . Proceedings of the all Soviet Union Conference on Physics of Dielectrics, Tomsk, vol. IV. 1988. p. 103.
The surface modi"cation of dielectrics by a CW electron beam Sergey Korenev*, Jerry Kriebel STERIS Corporation, STERIS Isomedix Services, 2500 Commerce Drive, Libertyville, IL 60048, USA
Abstract The e!ect of surface modi"cation of dielectric materials on a sample of Te#on and dielectric with low dielectric constant by scanning a parallel electron beam is considered in this report. The irradiation of samples has been performed on the CW (Continuous Wave) electron accelerator `Rhodotrona, with the following main parameters: kinetic energy 5 MeV and a current of 1}16 mA in air conditions. The nature of physical processes in dielectric materials during irradiation is di!erent in comparison with conducting materials. The distribution of absorbed doses and electrons in the dielectric material is discussed. The e!ect of surface modi"cation of dielectrics consists in the treatment of its surface by surface electrical discharge from charging the dielectric by the electron beam. The e!ect of the in#uence of magnitude of internal electric charge on the surface discharge is discussed. 2001 Elsevier Science Ltd. All rights reserved. Keywords: Electron beam; Irradiation; Surface treatment; Surface discharge; Dielectrics
1. Introduction
parameters of the electron beams are:
The question of surface modi"cation of dielectrics with low dielectric constant by high energy electron beams is very important for understanding the physics and chemistry of these materials. Te#on is a simple material for investigation [1], is stable to corrosion e!ects from ozone in the area of irradiation and is considered in this report.
E kinetic energy, 5.0 MeV; E beam current, 1}16 mA; E frequency of operating RF accelerating structure, 107.5 MHz; E full diameter of electron beam, 8 cm; E repetition of scanning for beam, 100 Hz; E The trajectories of scanning electron beams are parallel.
2. Experimental 2.1. Electron accelerators The experiments were conducted on the electron accelerator `Rhodotrona [2,3]. The main
The accumulated absorbed doses in the irradiation of samples were of the order of 10}200 kGy. Absorbed dose D is de"ned as the mean energy imparted, d, to an incremental quantity of matter, divided by the mass of that matter, dm [4]: D"d/dm"Gy.
(1)
2.2. Samples * Corresponding author. Tel.: #1-847-573-3223; fax: #1847-247-0882. E-mail address: sergey}[email protected] (S. Korenev).
The irradiation was made in air static conditions.
0042-207X/01/$ - see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 4 2 - 2 0 7 X ( 0 0 ) 0 0 4 2 2 - X
238
S. Korenev, J. Kriebel / Vacuum 62 (2001) 237}240
The dielectric samples from Te#on (dielectric constant &2), glass (&6), polyethylene (&2) and BaTiO (&1000}3000) are presented as plates with thickness 1.5 mm and are "xed in the unit with a total thickness of 15 mm. The methods of investigations of samples included SEM methods and the electrical measurements of surface resistance and plasma resistance on the surface of dielectrics.
3. Computer simulation The computer simulations include the simulation of the propagation of electrons in the dielectrics and the e!ect of back scattering. The results of computer modelling for dielectrics with low dielectric constant have more homogeneous distribution of absorbed doses in comparison with the same distribution for metals (see Fig. 1). The electron trajectories in Te#on and polyethylene have the same form. As an example, electron trajectories for Te#on are shown in Fig. 2.
4. Experimental results The SEM photographs of surface for Te#on before irradiation and after electron beam irradiation are shown in Fig. 3a and b. The analysis of surfaces of other dielectrics shows the same type of picture. The measurements of surface resistance of these dielectric samples indicated a weak dependence of surface resistance on absorbed doses in the range 10}200 kGy. However, the resistance of surface plasma on Te#on varied. The resistance was 14 k for an electron beam current 1 mA and 100 k for 16 mA. The irradiation of a dielectric with a low dielectric constant allows the formation of stable surface plasma. The irradiation of BaTiO with a high dielectric constant leads to an electrical discharge inside the dielectric. The surface has a multipoint character of surface discharge [5].
5. Discussion The question of surface modi"cation of dielectrics having di!erent dielectric constants is not
Fig. 1. The distribution of absorbed doses in Te#on for electron with kinetic energy 5 MeV.
S. Korenev, J. Kriebel / Vacuum 62 (2001) 237}240
239
Fig. 2. The distribution of 5 MeV electron trajectories in Te#on.
Fig. 3a and b. SEM photographs of surface before and after electron beam irradiation.
understood at present. The use of a dielectric with high dielectric constant causes internal electrical discharges [5,6]. For low dielectric constant materials these e!ects must be reduced to make correct measurements of the surface discharge. The forming plasma allows observation of e!ects of ion etching of the surface of dielectrics. The SEM pho-
tographs con"rm this. Te#on has high resistance to corrosion. The ozone in the area of irradiation is very active and other dielectrics have fast oxidation. The processes of dissipation of energy in the irradiated product have di!erent characters for dielectrics when compared to metals. Fig. 1 con"rms
240
S. Korenev, J. Kriebel / Vacuum 62 (2001) 237}240
this. For metals, we have the e!ect of thermal processes and we have a classical distribution of absorbed doses on the level of 20% for average absorbed doses. The e!ect of accumulation of charge inside a dielectric leads to an in#uence on electrical "eld from space charge, accumulated during irradiation.
6. Conclusion The following conclusions can be made from this study: E the irradiation of a dielectric with low dielectric constant leads to more homogeneous distribution of absorbed doses in these dielectrics in comparison with metals; E etching of the surface of a dielectric by the surface plasma was observed;
E dielectrics with low dielectric constant allow the formation of a homogeneous surface discharge.
References [1] Korenev S, Mase"eld J, Kriebel J, Johnson S. Proceedings of the Tenth International Seminar of Laboratory of Surface Science, Rutgers University, 1999. p. 23. [2] Pottier J. Nucl Instr and Meth 1989; B40/41:p. 943. [3] Jongen Y. Manufacturing of electron accelerators. Proceedings of the European Particle Accelerator Conference (EPAC '96), Barcelona, Spain, 1996. p. 260. [4] McLaughlin WL, Boyd AW, Chadwick KH, McDonald JC, Miller A. Dosimetry for radiation processing. London: TaylorFrancis, 1989. [5] Gromov VV. Electrical discharge in the irradiated materials. Moscow: Energoizdat, 1982. [6] Korenev SA. Determination of admittance irradiation loads by electron beam on The BaTiO . Proceedings of the all Soviet Union Conference on Physics of Dielectrics, Tomsk, vol. IV. 1988. p. 103.