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Surface erosion of pyrolytic graphite and glassy carbons by ion bombardment
Journal of Nuclear Materials 71 (1977) 178.-180 0 North-Holland Publishing Company
Plakings have been observed on pyre-graphites bombarded by various ions, and explained qualitatively on the basis of the anisotropic nature of the crystals [ 11. Expel-imental evidence is needed of the relation between the anisotropy of the crystal and surface erosion. The simplest experiment for this purpose will be to compare surface erosion of crystalline and amurphous materials. Accordingly. differences in surface topography between pyre-graphites and glassy carbons bombarded with Ne+ ions are reported in this letter. The monochromator grade pyro-graphite crystal used in the experiment was obtained from the Union Carbide Corporation, and glassy carbon, type GC-30, from the Tokai Carbon Corporation. In the cxperi‘nent, samples set in a scanning microscope (JEOLSOA), wet-e connected to a 2 MV Van de Graaff accelerator. Surface erosion was examined in stages at irradiation doses from 1 X IO’” to 3 X 1Ol8 Ne+/cm’. 850 and 350 keV NC’ ions wet-e used at a bean’ density of about 0. I5 pA/mm2. The projected I-anges of 350 and X50 keV Nc’ 1on5:it’ carbon material were 0.50 and 0.05 ytn. respectively 12 1. With 350 keV ions. grooves 4.5 PI” wide appeared on the surface of pyre-graphite at a dose of I X IO” Net/cm*, and widened to IO ym at 3.5 X IO’” Neti cm’. With 850 keV ions. the width was 0.5 pm at dose I X IO” Ne+/cm* and became 30 pm at 0 X lOI Net/cm’. Gr-ooves were exfoliated at their edges at a dose of’ 2 X I 016 Net/cm’. which corresponds to the ct-itical Jose of flaking for 850 keV Ne+ ions. Many flakings were obsc’-ved on the surface at 2 X IO” Net/ cm*. The flakings caused by Ne+ ion bombardment are sintilar to those caused by Iv+ ion bombardment [ 11. The thicknesses of tlakrs produced by 350 and
8.50 keV Ne+ ions are the same as the lengths of‘ the projected ranges. The surface of the glassy carbon is not as smooth as that of the pyro-graphite; some spots have small cracks (before bombardment) as shown in fig. 1. Fig. I (right) shows an enlargement of 3 spot which is seen as oval with a black middle surrounded by a halo. Sur[‘ace damage with X50 keV Ne’.ion bombardment started at the periphery, which then took the form of Y groove at dose 2 X lOI Ne’/cm’. Many of the spots became hollow at dose 1 X lo’* Ne+/cm’, the removed material being deposited nearby. Diameters of the hollows were about 5 - 10 PITI, and heights of the deposits were about 4 pm. which is several times the projected range of 850 keV Ne’ ions. The nu’nber density of the hollows was about 100/cm2, which is the same as density of the spots before bombardment. Flat portions of the surface without spots was little damaged by bombardment up to dose 4 X IO1HNe’i LYl12.
Fig. 2 shows the surfaces of the pyre-graphite and glassy Cal-bon, respectively, after bombardment with 850 keV Net ions to close 6 X IO” Ne+/cm2. Flakings are present on pyra-graphite, and hollows on the glassy carbon. Fig. 3 depicts complete and incomplete hollows. With 850 keV Ne’ ions, about half the hollows were complete at dose 6 X lOI Ne+t/cm’, and with 350 keV ions, most of the hollows remain incomplete at dose 4 X IO” Ne’/cm’. Hollows and deposits are seen in fig. 4. .4s can be seen, the surface erosion of glassy carbon with ion bombardment is totally different from that ot‘pyro-graphite. It is possible that in glassy carbon. 178
Y. Knzurmfa
/ Erosion
P’ig. 1. (Left) Surface of glassy carbon before bombardment. spot which is seen as oval with a black middle. surrounded
Fig. 2. Comparison of the surfaces between Ne+/cm’: (Left) Flakings on pyro-graphite,
of’graphirr
arld
gless~~
179
carhons
Many spots are seen on the surface. by a halo.
pyro-graphite and glassy carbon, bombarded and (right) hollows on glassy carbon.
(Rightj
An enlargement
of the
with 8.50 keV Nef ions at dose 6 X 1Ol7
without the initia1 spots, no hollows would be produced by bonlbardment and erosion would only be by generalized sputtering. The difference in surface erosion between the two materials is caused mainly by the difference in crystal structure. Reportedly, no sig nificant surface damage is observed in crystalline graphites bol~lbarded with low-energy light ions such as Hi, D’., and He+ ions, but damage is caused in fibrous graphites 131. In a preliminary experiment with 1.9 MeV 3Het ions, grooves were produced in pyro-graphite but little change of the surface was caused in glassy carbon. Therefore, surface erosion of‘ carbon materials by ion bombardnlent largely depends on their crystal structure. Further details of the present results will be reported in the near future.
Fteferences
I ig. 4. IloIlo\l;s and deposits observed on glassq carbon b~)Illb~lrdcd with 850 keV ions :tt J.5 X 10” * Ne’jcmz.
1) Y. Kazumata, J. Nucl. Mat. 68 (1977) 2.57. 21 I..C. Northcliffe and R.1:. Schillinp, Nuclear Data Tables A7 ClY70) 233. 31 S.K. Das and M. Kaminsky. 4NL Report, CONI’-760882-t (1977).
Plakings have been observed on pyre-graphites bombarded by various ions, and explained qualitatively on the basis of the anisotropic nature of the crystals [ 11. Expel-imental evidence is needed of the relation between the anisotropy of the crystal and surface erosion. The simplest experiment for this purpose will be to compare surface erosion of crystalline and amurphous materials. Accordingly. differences in surface topography between pyre-graphites and glassy carbons bombarded with Ne+ ions are reported in this letter. The monochromator grade pyro-graphite crystal used in the experiment was obtained from the Union Carbide Corporation, and glassy carbon, type GC-30, from the Tokai Carbon Corporation. In the cxperi‘nent, samples set in a scanning microscope (JEOLSOA), wet-e connected to a 2 MV Van de Graaff accelerator. Surface erosion was examined in stages at irradiation doses from 1 X IO’” to 3 X 1Ol8 Ne+/cm’. 850 and 350 keV NC’ ions wet-e used at a bean’ density of about 0. I5 pA/mm2. The projected I-anges of 350 and X50 keV Nc’ 1on5:it’ carbon material were 0.50 and 0.05 ytn. respectively 12 1. With 350 keV ions. grooves 4.5 PI” wide appeared on the surface of pyre-graphite at a dose of I X IO” Net/cm*, and widened to IO ym at 3.5 X IO’” Neti cm’. With 850 keV ions. the width was 0.5 pm at dose I X IO” Ne+/cm* and became 30 pm at 0 X lOI Net/cm’. Gr-ooves were exfoliated at their edges at a dose of’ 2 X I 016 Net/cm’. which corresponds to the ct-itical Jose of flaking for 850 keV Ne+ ions. Many flakings were obsc’-ved on the surface at 2 X IO” Net/ cm*. The flakings caused by Ne+ ion bombardment are sintilar to those caused by Iv+ ion bombardment [ 11. The thicknesses of tlakrs produced by 350 and
8.50 keV Ne+ ions are the same as the lengths of‘ the projected ranges. The surface of the glassy carbon is not as smooth as that of the pyro-graphite; some spots have small cracks (before bombardment) as shown in fig. 1. Fig. I (right) shows an enlargement of 3 spot which is seen as oval with a black middle surrounded by a halo. Sur[‘ace damage with X50 keV Ne’.ion bombardment started at the periphery, which then took the form of Y groove at dose 2 X lOI Ne’/cm’. Many of the spots became hollow at dose 1 X lo’* Ne+/cm’, the removed material being deposited nearby. Diameters of the hollows were about 5 - 10 PITI, and heights of the deposits were about 4 pm. which is several times the projected range of 850 keV Ne’ ions. The nu’nber density of the hollows was about 100/cm2, which is the same as density of the spots before bombardment. Flat portions of the surface without spots was little damaged by bombardment up to dose 4 X IO1HNe’i LYl12.
Fig. 2 shows the surfaces of the pyre-graphite and glassy Cal-bon, respectively, after bombardment with 850 keV Net ions to close 6 X IO” Ne+/cm2. Flakings are present on pyra-graphite, and hollows on the glassy carbon. Fig. 3 depicts complete and incomplete hollows. With 850 keV Ne’ ions, about half the hollows were complete at dose 6 X lOI Ne+t/cm’, and with 350 keV ions, most of the hollows remain incomplete at dose 4 X IO” Ne’/cm’. Hollows and deposits are seen in fig. 4. .4s can be seen, the surface erosion of glassy carbon with ion bombardment is totally different from that ot‘pyro-graphite. It is possible that in glassy carbon. 178
Y. Knzurmfa
/ Erosion
P’ig. 1. (Left) Surface of glassy carbon before bombardment. spot which is seen as oval with a black middle. surrounded
Fig. 2. Comparison of the surfaces between Ne+/cm’: (Left) Flakings on pyro-graphite,
of’graphirr
arld
gless~~
179
carhons
Many spots are seen on the surface. by a halo.
pyro-graphite and glassy carbon, bombarded and (right) hollows on glassy carbon.
(Rightj
An enlargement
of the
with 8.50 keV Nef ions at dose 6 X 1Ol7
without the initia1 spots, no hollows would be produced by bonlbardment and erosion would only be by generalized sputtering. The difference in surface erosion between the two materials is caused mainly by the difference in crystal structure. Reportedly, no sig nificant surface damage is observed in crystalline graphites bol~lbarded with low-energy light ions such as Hi, D’., and He+ ions, but damage is caused in fibrous graphites 131. In a preliminary experiment with 1.9 MeV 3Het ions, grooves were produced in pyro-graphite but little change of the surface was caused in glassy carbon. Therefore, surface erosion of‘ carbon materials by ion bombardnlent largely depends on their crystal structure. Further details of the present results will be reported in the near future.
Fteferences
I ig. 4. IloIlo\l;s and deposits observed on glassq carbon b~)Illb~lrdcd with 850 keV ions :tt J.5 X 10” * Ne’jcmz.
1) Y. Kazumata, J. Nucl. Mat. 68 (1977) 2.57. 21 I..C. Northcliffe and R.1:. Schillinp, Nuclear Data Tables A7 ClY70) 233. 31 S.K. Das and M. Kaminsky. 4NL Report, CONI’-760882-t (1977).