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Many studies have already been performed on the thermal annealing of fresh and aged swift heavy ion-irradiated polymers in a vacuum. In this paper we examine the influence of different environments on annealing behaviour. The basic tool for this study is current/voltage spectroscopy with the alternating voltage applied across the etched tracks. In previous work of this series it was shown for etching of previously annealed aged swift heavy ion-irradiated polyethylene terephthalate foils in dry air that at ∼ 50°C, a dip overlapped the expected Arrhenius correlation in the Arrhenius plot of the etchant breakthrough times. We had attributed that dip tentatively to the etching of the swift heavy ion track core material, as the latter had been subjected to extremely high radiation-damage and thus differs strongly in its composition from pristine bulk material. Repetition of this experiment under different annealing environments enables us to draw conclusions about the competition between the different polymeric disintegration and healing mechanisms in swift heavy ion tracks. These results should be useful for better estimation of the polymeric durability in different environments. First tests with polyimide reveals that a similar dip structure also shows up here, indicating that this finding may be a general effect for annealing of ion-irradiated polymers. [ABSTRACT FROM AUTHOR]

In the previous papers of this series, the result of etching of fresh swift heavy ion (SHI)-irradiated polyethylene terephthalate (PET) foils after thermal annealing in various environments was studied to determine the extent to which thermal annealing is able not only to simulate aging of pristine polymer foils, but also SHI-irradiated foils. The etching results of these foils (obtained using breakthrough times of the etchant across the PET foils that were pre-annealed at different temperatures for constant times) did not always follow the predicted Arrhenius behavior, but showed dip-like deviations that were tentatively attributed to both SHI radiation and ambient effects to the glass transition temperature. To determine whether deviations from the simple Arrhenius behavior also occur for other irradiated polymers, we examined the effect of thermal annealing at different temperatures T of aged SHI-irradiated Kapton foils via the etchant breakthrough times across the SHI tracks. Interestingly, there appeared unexpected wide dip-like deviations from straight Arrhenius plots. Comparison of this curve with corresponding ones of aged non-irradiated Kapton foils, by determining the etchant breakthrough times across the foils, enabled us to assign the obtained high-temperature Arrhenius branch (for T > 80°C) to heal both aged and irradiated polymer foils from aging and/or radiation defects. In contrast, the pristine and irradiated aged samples annealed at lower temperatures follow completely different trends. As in the previous article on PET, we tend to assign the dip-like deviation of the SHI-irradiated Kapton again to the glass transition temperature of this highly radiation-damaged material. [ABSTRACT FROM AUTHOR]

In the recent papers of this series the formation and characterisation of Ag2O and LiF membranes within etched swift heavy ion tracks in thin polymer foils by the 'Coupled Chemical Reaction' (CCR) approach was described. Such membrane-containing etched tracks were shown to be useful to create enzyme-clad biosensors of optimum efficiency. Some planned biosensors of higher complexity would, however, require the re-dissolution of the membranes after the enzyme deposition step, without affecting the enzyme's performance. To accomplish this, we looked for membrane materials that could, on the one hand, be easily produced by the CCR strategy, but on the other hand, be also easily re-dissolved thereafter in a bio-friendly way. As we think that earth alkali carbonates would fulfil these requirements (they dissolve already in very weak organic acids), we studied here the formation of membranes of Calcium carbonate. Interestingly it turned out that their membrane formation mechanism differs somewhat from that of the previously studied systems. Their basic 'fingerprints' are stable capacitive current responses – rather than the 'quiet phases' during else highly agitated spiky Ohmic current responses, as was observed for the earlier studied membrane materials Ag2O and LiF. [ABSTRACT FROM AUTHOR]

In the paper, thin films of polyethylene-terephthalate, pristine or irradiated with 170 MeV Xe+ ions to the fluence of 105 cm−2, were etched in the mild 1 M NaOH medium at 60°C for different times. The main aspects of the etching process (i.e. development of the pores, dependence of the foil thickness and transparency on the time of etching) were studied by the ion transmission technique (ion energy loss spectroscopy) that was previously introduced by the author's team. It has been shown that the transmission method makes it possible to closely monitor the development of the polymeric porosity and to determine the important parameters of the etching process (e.g. etching rate along the latent tracks, bulk etching rate, radial etching rate, breakthrough, foil transparency). The measurement was carried out at the NPI Rez using the alpha particle microprobe on the Tandetron accelerator. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In previous papers it was shown that the coupling of the two chemical reactions: {NaOH etchant – PET polymer} and {NaOH etchant – AgNO3solution} within the dynamic confinement of etched swift heavy ion tracks eventually leads to the formation of tiny Ag2O membranes within these nanopores, thus separating the latter ones into two adjacent segments. It is shown here that the deposition of enzymes in these two segments transforms these structures into biosensors. In our earlier developed sensors with transparent etched ion tracks, we frequently used glucose oxidase as enzyme and glucose as analyte. In these cases, the enzymatic reaction within the tracks leads to a change in the pH value of the confined solution and hence also in the track conductivity, so these structures can be used for biosensing. When applying, for easy comparison, the same enzyme/analyte combination to the segmented sensor arrangement presented here, we find a striking improvement in detection sensitivity which points at a different biosensing mechanism due to intrinsic polarisation effects across the newly inserted membranes. [ABSTRACT FROM PUBLISHER]

In recent papers, it was shown that coupled chemical-topological reactions (CCRs) with both NaOH etchant and silver salts, performed in thin swift-heavy ion-irradiated polymers under the application of a test voltage across the polymer foils, eventually gave rise to characteristic current/voltage features and Bode plots that were tentatively attributed to the formation of Ag2O membranes within the etched tracks. The same was also found when replacing the silver ions by lithium ions, and adding fluoride ions to the NaOH etchant, to promote LiF membrane formation. Ion Transmission Spectrometry (ITS) enabled us to reconfirm the existence of these membranes beyond doubt. The membrane thickness was determined to be ∼0.2–0.4 µm in the best cases. ITS also revealed that hitherto membrane formation occurs only in ∼1% of all tracks, or even less. The reason for this poor abundance seems to be that the decisive factor for membrane formation, which is the firm anchoring of the emerging solid Ag2O or LiF reaction products on the etched track walls, was hitherto rarely fulfilled. We attribute this tentatively to the too high test voltage applied for controlling the CCR process that might hinder the product anchoring on the walls by promoting nanofluidic electromigration. Indeed, voltage reduction seems to improve the situation. [ABSTRACT FROM PUBLISHER]

Etching of continuous nuclear tracks in thin polymer foils from both sides is known to lead to the formation of double-conical nanopores. In this work and related ones we try to find out how this etching kinetics is modified when materials are added which react with each other upon their contact towards some new product that influences the etching. For that purpose we have chosen here Li+and F−ions as the additions, which react with each other to form LiF precipitations. The coupled etching and precipitation kinetics is recorded by measuring the electrical current that is transmitted through the foils upon application of a low-frequency alternating sinusoidal voltage. Depending on the etchant concentrations, the etching temperature and the time of Li+and F−addition, different effects are found that range from (a) no alteration of the transmitted current at all, via (b) the emergence of an alternating current with a temperature-dependent amplitude, and (c) the complete vanishing of any transmitted current at all, towards (d) chaotic transmitted current histories with phases with strong current spike emission and (e) rather quiet phases, alternating with each other in a rather unsystematic way. The observed effects are ascribed to (a) the enhanced penetration efficiency of both the Li+and F−ions through the polymeric bulk and/or latent ion tracks after the removal of the polymer's protective surface layer by the etchant, (b) the high mobility of preferentially the F−ions within the polymer, (c) the LiF precipitation within the polymer or on its surface upon encounter of Li+and F−ions, (d) the nanofluidic properties of narrow etched tracks covered with Li+ions on the wall surfaces and F−ions beyond, and/or (e) the formation of LiF membranes within the etched tracks. [ABSTRACT FROM PUBLISHER]

It is shown that conical track etching is a much more complicated process than generally assumed. The choice of the corresponding parameters (i.e. the ratios of concentrations and diffusion coefficients of both etchant (e.g. NaOH) and stopping solutions (e.g. HCl) and the etching temperature) determines the ratio of polymer dissolution to etchant penetration. The latter value controls the counterplay of diffusion, etching, ionic conductivity, field emission and capacitive effects, which is decisive for both the final track shapes and their electronic properties. The stages of track evolution during etching under different conditions are outlined in detail. Both transparent conical nanopores and “funnel-type” tracks can be obtained, the latter consisting of a shorter cone and a residual latent track. Depending on the internal structure of that latent track segment, such funnel-type tracks either allow smooth transmission of the rectified currents or they emit unipolar current spikes. Not only the study of electronic properties of single ion tracks, but also of a multitude of tracks makes sense. Depending on the applied parameters, the individual track properties may either just add up, or new effects may be found that emerge from the interaction of the tracks among each other. This is preferentially the case for spike-emitting tracks, where effects such as phase-locked spike synchronization can be found as described by neural network theory. [ABSTRACT FROM AUTHOR]

In swift heavy ion track-based polymeric biosensor foils with incorporated enzymes one exploits the correlation between the analyte concentration and the sensor current, via the enrichment of charged enzymatic reaction products in the track’s confinement. Here we study the influence of the etched track radius on the biosensor’s efficiency. These sensors are analyte-specific only if both the track radii and the analyte concentration exceed certain threshold values of ∼15 nm and ∼10 −6  M (for glucose sensing), respectively. Below these limits the sensor signal stems un-specifically from any charge carrier. In its proper working regime, the inner track walls are smoothly covered by enzymes and the efficiency is practically radius independent. Theory shows that the measured current should be slightly sub-proportional to the analyte concentration; the measurements roughly reconfirm this. Narrower tracks (∼5–15 nm radius) with reduced enzyme coverage lead to decreasing efficiency. Tiny signals visible when the tracks are etched to effective radii between 0 and ∼5 nm are tentatively ascribed to enzymes bonded to surface-near nano-cracks in the polymer foil, resulting from its degradation due to aging, rather than to the tracks. Precondition for this study was the accurate determination of the etched track radii, which is possible only by a nanofluidic approach. This holds to some extent even for enzyme-covered tracks, though in this case most of the wall charges are compensated by enzyme bonding. [ABSTRACT FROM AUTHOR]