Ion track etching revisited: II. Electronic properties of aged tracks in polymers

ABSTRACT

We compile here electronic ion track etching effects, such as capacitive-type currents, current spike emission, phase shift, rectification and background currents that eventually emerge upon application of sinusoidal alternating voltages across thin, aged swift heavy ion-irradiated polymer foils during etching. Both capacitive-type currents and current spike emission occur as long as obstacles still prevent a smooth continuous charge carrier passage across the foils. In the case of sufficiently high applied electric fields, these obstacles are overcome by spike emission. These effects vanish upon etchant breakthrough. Subsequent transmitted currents are usually of Ohmic type, but shortly after breakthrough (during the track’ core etching) often still exhibit deviations such as strong positive phase shifts. They stem from very slow charge carrier mobility across the etched ion tracks due to retarding trapping/detrapping processes. Upon etching the track’s penumbra, one occasionally observes a split-up into two transmitted current components, one with positive and another one with negative phase shifts. Usually, these phase shifts vanish when bulk etching starts. Current rectification upon track etching is a very frequent phenomenon. Rectification uses to inverse when core etching ends and penumbra etching begins. When the latter ends, rectification largely vanishes. Occasionally, some residual rectification remains which we attribute to the aged polymeric bulk itself. Last not least, we still consider background currents which often emerge transiently during track etching. We could assign them clearly to differences in the electrochemical potential of the liquids on both sides of the etched polymer foils. Transient relaxation effects during the track etching cause their eventually chaotic behaviour.

KEYWORDS:

• Polymers
• ion tracks
• etching
• conductometry
• rectification
• phase shift

Acknowledgements

D. F. is grateful to the Universidad Autónoma Metropolitana-Iztapalapa, Mexico City, for the guest professorship in the frame of the Cathedra “Alonso Fernandez”. We are further obliged to Dr P. Apel from JNRI Dubna, Russia for providing us with many of the examined ion-irradiated polymer foils.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1 Rectifying funnel tracks emerge only at a later stage.

2 That foil side where etchant breakthrough occurred first was denoted as ‘side A’, and the opposite as ‘side B’.

3 Only in one case (foil #17, sample 285, side A), a bimodal behaviour was found to occur during ion track core etching, but possibly the assignment was not correct in this case.

4 Rectification of degraded polymeric bulk is thought to stem from different craze densities on both foil surfaces. The larger the craze density, the larger the overall surface charges on the walls of the etchant-filled crazes. Even after SHI impact, bulk rectification is preserved as the bulk compaction of impinging SHIs (19) may compress the craze sizes but not alter the charge distribution ratios between both foil sides.

5 For details, see the caption of Figure 5, or Table 1(b) in (1).

Additional information

Funding

The project was supported by the Grant Agency of the Czech Republic (P108-12G-108).