Johann Vetter

Pore geometry of etched ion tracks in polyimide

Abstract Tracks of energetic heavy ions in the polyimide Kapton were etched in a NaOCl solution. It was found that the pH value of the etchant plays a crucial role for the selectivity of track etching. The bulk etching rate νb increased exponentially with pH. From the temperature dependence of the bulk etching rate an activation energy of Ea = 0.74 eV was deduced. In contrast to νb, only a slight and linear increase with pH value was observed for the track etching rate νt. As a consequence, the etch ratio ν t ν b can be adjusted over one order of magnitude by controlled varying the pH of the etchant. This is a new way to tailor the pore geometry from nearly cylindrical to funnel-shaped pores.

Electrochemical preparation of metal microstructures on large areas of etched ion track membranes

A microgalvanic method for metal filling of etched ion tracks in organic foils on large areas is described. The method and the used galvanic cell permit the deposition of stable standing individual metal whiskers with high aspect ratio and a density of 105–108 per cm2 on an area of 12.5 cm2. The method was verified with copper and it is suitable also for various other metals. It can be applied for the replication of etched ion tracks and for the fabrication of microstructures containing large numbers of individual metal whiskers.

Reversible on-off switch function of ion-track pores for thermo-responsive films based on copolymers consisting of diethyleneglycol-bis-allylcarbonate and acryloyl-L-proline methyl ester

Abstract Intelligent chemical valves responding to a slight change of temperature were created by the combination of ion beam-chemical etching technique and a novel material consisting of an ion track detector material diethyleneglycol-bis-allylcarbonate (CR-39) and a thermo-responsive gel acryloyl-L-proline methyl ester (A-ProOMe). The changes in size of ion-track pores in etched films were measured microscopically by repetition between 0 and 30°C at 24-h intervals for a 50 μm thick copoly(CR-39/A-ProOMe, 60 40 mol % ) film which was obtained by etching in aqueous 6M NaOH solution at 60°C after an 11.6 MeV/n 208Pb ion irradiation and, as a result, it was found that the pore size in the film obtained by etching for 10 min is reversibly changed from a perfectly closed pore at 0°C to a fully opened pore with a diameter of 0.30 μm at 30°C.

Stimulus-responsive track pores

Abstract Ion track grafting enables the manufacture of chemically responsive track pores analogous to the discrete membrane channels found in biology. For this purpose etched ion tracks generated in CR-39 are surface-grafted by methacryloyl-L-alaninemethylester. In the future, the responsive track pores could be used to model the actively controlled channels in biomembranes and may lead to interesting technological applications.

Thermo-response of ion track pores in copolymer films of methacryloyl-L-alanine methyl ester and diethyleneglycol-bis-allylcarbonate

Abstract Copolymer films (100 μm thick) were prepared by cast polymerization of methacryloyl- l -alanine methyl ester (MA- l -AlaOMe) and diethyleneglycol-bis-allylcarbonate (CR-39). The films swell in water at temperatures below 60°C. The degree of swelling increases with decreasing temperature down to 0°C. The swelling capacity of the films increases with increasing MA- l -AlaOMe content. The thermal response is reversible. Swelling and shrinkage have different time constants of ∼24 h for swelling and ∼10 min for shrinkage. The films were subject to an ion track etching process consisting of a heavy ion irradiation using gold ions of 11.4 MeV per nucleon specific energy followed by subsequent etching of the latent ion tracks in NaOH solution. The resulting porous membranes show a reversible change of the pore diameters of ∼12% between 0°C and 60°C for a copolymer with 70 vol% MA- l -AlaOMe.

Scanning force microscopy of heavy-ion tracks

Abstract Polycarbonate, polyimide, and glass samples were irradiated with heavy ions in the 11.4–14.0 MeV/amu energy range at the UNILAC of GSI. After etching and partly coating the specimens with a thin gold layer, ion tracks were studied with scanning force microscopy, including imaging in the lateral-force mode. Results on pore features such as the radius as a function of etching time are presented.

GROWTH OF POTASSIUM IODIDE SINGLE-CRYSTALS USING ION TRACK MEMBRANES AS TEMPLATES

Abstract A principle possibility is demonstrated to apply the ion track membranes as a template for the crystallization of inorganic salts. As an example, potassium iodide has been grown in a matrix of etched ion tracks produced in polycarbonate foils. Arrays of stable free-standing cylindrical microcolumns are observed after dissolution of the organic matrix. They represent single crystals oriented with their 〈1 0 0〉 or 〈1 1 0〉 crystallographic directions along the cylinder axes. Possible ways to govern their predominant orientations are briefly discussed.

Filters with <100 nm radius pores for gas separation formed by high-energy ion irradiation of polymers

In the industry, often gases have to be separated from each other for cleaning and other purposes. In principle, this can be achieved by passing a gas mixture through a filter system when the filter pore diameter is very small being comparable to the size of the mean free path of the gases. Such well-defined pores can be fabricated by high-energy ion irradiation of polymers, combined with chemical etching of the resulting damage in the polymer. Polyimide foil was irradiated with high-energy lead ions. The pores were evolved from the ion tracks by exposing the polymer to a chemical etching agent. The pore radius was determined by scanning electron microscopy (SEM). The shape of the pores through the foil was determined by filling them electrochemically with metal, cutting them into small pieces and investigating the edges again by SEM. The results showed that uniform cylindrical pores with radii below 100 nm could be formed. Using the gas mixture CO/CO2 as a model system for the gas separation the filters were tested for their efficiency. The gas mixture was pumped through the filter and analysed by gas chromatography. The results show that a separation of the gas mixture is possible. Filters fabricated by ion irradiation may act as efficient gas separators.

Search for superfluid Josephson effect

Abstract The superfluid Josephson effect is based on the weak coupling between two adjacent superfluid reservoirs, relates their pressure difference to a frequency and promises the realization of high-precision sensors for pressure and rotation. Ion tracks provide obstacles sufficiently small to interfere with superfluids. These so-called “weak links” represent potential barriers through which tunneling occurs between the two neighboring superfluid reservoirs. The experimental status is described.

Sensitization of track etching in CR-39 by copolymerization with methacryloyl-L-alanine methyl ester

Abstract Copolymer films of diethyleneglycol-bis-allylcarbonate (monomer of CR-39) and selected volume percentages of methacryloyl- L -alanine methyl ester (MA- L -AlaOMe) between 5 and 60% were irradiated with Au ions of 13 MeV nucl -1 and etched in NaOH solution at 60°C. Sensitization of track etching was observed for NaOH concentrations of 4 and 6 N. The maximum reduced etch-rate ratio, V t / V b -1, was obtained for the copolymer of 90% of CR-39 monomer and 10% of MA- L -AlaOMe at 4 N NaOH, which was 3.6 times higher than that for pure CR-39. The sensitization was accompanied by an increase in V b so that the etching time could be reduced to ca 1/30 in comparison with that for pure CR-39.