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RIKEN Accel. Próg. Rep. 24 (1990)

111-2-28. Development of Nuclear Track Microfilters

N. Nakanishi, S. Nakajima, and S. Wakasa¹

Fig. 2. Scanning electron micrograph of etched pores in a 10 /im Makrofol irradiated by 1 MeV/u ⁸⁴Kr⁸⁺ ions. Magnification x 10,000. Diameter is 0.2 /zm.

Energetic charged particles leave their latent tracks in a polymer, polycarbonate Makrofol, irradiated with them. Pierced pores can be observed in it after Chemical etching. The phenomenon is applicable to the production of microfilters for industrial uses.

The etch phenomenon is considered geometri-cally as shown in Fig. 1. In this simplified case, the surface A before etch is corroded to go to the surface B at a balk etching ratę V_b after an etching time T. On the other hand, as etching goes on, an etch pit is formed along the latent track at a track etching ratę V_t. Until docking, etch pits in both sides of the films proceed a the cone angle for which we can get a relation of 6=sin^-1

It is desirable to get pores with 6 as smali as pos-sible.

Fig. 1. Schematic cross section of etch pits.

We have examined irradiating and etching condi-tions for thin polycarbonate Makrofol films.¹¹ The present goals are to realize pores of less than 0.05 /i.m and to find the best conditions for polyimid films. Figurę 2 shows an example of etched pores in a 10 /rm film irradiated with 1 MeV/u ^Kr⁸"¹". We have also tried to observe cross sections of etch pits.

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References

1) N. Nakanishi et al.: RIKEN Accel. Próg. Rep., 23, 88 (1989).

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Japan Steel Work Ltd.