Etched Ion Tracks Research Articles

Etched ion tracks in amorphous SiO2 characterized by small angle x-ray scattering: influence of ion energy and etching conditions

Small angle x-ray scattering was used to study the morphology of conical structures formed in thin films of amorphous SiO2. Samples were irradiated with 1.1 GeV Au ions at the GSI UNILAC in Darmstadt, Germany, and with 185, 89 and 54 MeV Au ions at the Heavy Ion Accelerator Facility at ANU in Canberra, Australia. The irradiated material was subsequently etched in HF using two different etchant concentrations over a series of etch times to reveal conically shaped etched channels of various sizes. Synchrotron based SAXS measurements were used to characterize both the radial and axial ion track etch rates with unprecedented precision. The results show that the ion energy has a significant effect on the morphology of the etched channels, and that at short etch times resulting in very small cones, the increased etching rate of the damaged region in the radial direction with respect to the ion trajectory is significant.

Ion track etching in polyethylene-terephthalate studied by charge particle transmission technique

ABSTRACTIn 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.

Ferromagnetic Nanowires for Nonreciprocal Millimeter-Wave Applications: Investigations of Artificial Ferrites for Realizing High-Frequency Communication Components

As far back as the 1850s, workers applying decorative and anticorrosive coatings of metallic surfaces used a technique [1] that would later be referred to as anodic aluminum oxide (AAO) synthesis. About 100 years later, the morphologies of such coatings were investigated and found to consist of highly ordered/quasiregular arrays of high aspect ratio nanopores [2]. During the same decade, nuclear scientists detected the tracks of energetic heavy ions in polymer membranes, and, by the 1960s, chemical etching of ion tracks was used as a standard nuclear diagnostic [3], [4]. Although track-etched polymer membranes offer arrays of nanopores with uniform diameters, the nanopore spacing is random. In the mid-1970s, ferromagnetic nanowires (FMNW

Surface Enhanced DNP Assisted Solid-State NMR of Functionalized SiO2 Coated Polycarbonate Membranes

Abstract Surface enhanced solid-state NMR by dynamic nuclear polarization (DNP SENS) enables the characterization of the inner-pore surface functionalization of porous etched ion-track membranes exhibiting low specific surface areas compared to typical SBA- or MCM-type mesoporous silica materials. The membranes were conformally coated with a 5 nm thin SiO2 layer by atomic layer deposition. This layer was subsequently modified by aminopropyl silane linkers that allow further functionalization via the terminal amine group. The results evidence that in principle DNP SENS is a capable tool to analyze more complex porous systems, e.g. bioinspired functional etched ion-track membranes down to the molecular level. These results are relevant also for single nanopore systems, for which a direct analysis of the channel surface functionalization is not feasible by classical characterization methods. The applicability of DNP SENS to complex porous systems requires the optimization of the sample preparation and measurement parameters.

Ion track etching revisited: I. Correlations between track parameters in aged polymers

Abstract Some yet poorly understood problems of etching of pristine and swift heavy ion track-irradiated aged polymers were treated, by applying conductometry across the irradiated foils during etching. The onset times of etchant penetration across pristine foils, and the onset times of the different etched track regimes in irradiated foils were determined for polymers of various proveniences, fluences and ages, as well as their corresponding etching speeds. From the results, correlations of the parameters with each other were deduced. The normalization of these parameters enables one to compare irradiated polymer foils of different origin and treatment with one another. In a number of cases, also polymeric gel formation and swelling occur which influence the track etching behaviour. The polymer degradation during aging influences the track etching parameters, which differ from each other on both sides of the foils. With increasing sample age, these differences increase.

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

ABSTRACTWe 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.

Conical etched ion tracks in SiO2 characterised by small angle X-ray scattering

Abstract We present a systematic study of the evolution of chemically etched ion tracks formed in thermally grown a-SiO2 after irradiation with 1.1 GeV and 185 MeV Au ions. The irradiated material was subsequently etched with 2.5% hydrofluoric acid (HF) for different times yielding hollow conical shaped structures of various sizes. The characterisation of these structures was carried out by synchrotron-based small-angle X-ray scattering (SAXS) measurements, enabling the determination of the geometry and dimensions of the etched conical structures with sub-nanometre precision. The results indicate that the track etching behavior is influenced by the ion energy, and that at short etching times the latent track damage in the radial direction becomes significant.

Surface Modification and Damage of MeV-Energy Heavy Ion Irradiation on Gold Nanowires.

Gold nanowires with diameters ranging from 20 to 90 nm were fabricated by the electrochemical deposition technique in etched ion track polycarbonate templates and were then irradiated by Xe and Kr ions with the energy in MeV range. The surface modification of nanowires was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations. Different craters with and without protrusion on the gold nanowires were analyzed, and the two corresponding formation mechanisms, i.e., plastic flow and micro-explosion, were investigated. In addition, the sputtered gold nanoparticles caused by ion irradiation were studied and it was confirmed that the surface damage produced in gold nanowires was increased as the diameter of the nanowires decreased. It was also found that heavy ion irradiation can also create stacking fault tetrahedrons (SFTs) in gold nanowires and three different SFTs were confirmed in irradiated nanowires. A statistical analysis of the size distribution of SFTs in gold nanowires proved that the average size distribution of SFT was positively related to the nuclear stopping power of incident ions, i.e., the higher nuclear stopping power of incident ions could generate SFT with a larger average size in gold nanowires.

Fabrication of high-transmission microporous membranes by proton beam writing-based molding technique

Porous membranes are widely used as filters in a broad range of micro and nanofluidic applications, e.g. organelle sorters, permeable cell growth substrates, and plasma filtration. Conventional silicon fabrication approaches are not suitable for microporous membranes due to the low mechanical stability of thin film substrates. Other techniques like ion track etching are limited to the production of randomly distributed and randomly orientated pores with non-uniform pore sizes.In this project, we developed a procedure for fabricating high-transmission microporous membranes by proton beam writing (PBW) with a combination of spin-casting and soft lithography. In this approach, focused 2MeV protons were used to lithographically write patterns consisting of hexagonal arrays of high-density pillars of few µm size in a SU-8 layer coated on a silicon wafer. After development, the pillars were conformably coated with a thin film of poly-para-xylylene (Parylene)-C release agent and spin-coated with polydimethylsiloxane (PDMS). To facilitate demolding, a special technique based on the use of a laser-cut sealing tape ring was developed. This method facilitated the successful delamination of 20-μm thick PDMS membrane with high-density micropores from the mold without rupture or damage.

SAXS investigation of un-etched and etched ion tracks in polycarbonate

Investigation of the ion track morphologies and track etching behaviour in polycarbonate (PC) films was carried out using synchrotron based small-angle X-ray scattering (SAXS) measurements. The tracks were induced by Au ions with kinetic energies of 1.7 and 2.2GeV with applied fluences between 1×1010 and 1×1012ions/cm2. The average radii of the un-etched tracks were studied as a function of the irradiation fluence, indicating a general ion induced degradation of the polymer, with a simultaneous increase in ion track radius from 2.6±0.002nm to 3.4±0.03nm. Chemical etching of the ion tracks in PC leads to the formation of cylindrical pores. The pore radius increases linearly with etching time. In 3M NaOH at 55°C, a radial etching rate of 9.2nm/min is observed.

Diffusion kinetics of the glucose/glucose oxidase system in swift heavy ion track-based biosensors

For understanding of the diffusion kinetics and their optimization in swift heavy ion track-based biosensors, recently a diffusion simulation was performed. This simulation aimed at yielding the degree of enrichment of the enzymatic reaction products in the highly confined space of the etched ion tracks. A bunch of curves was obtained for the description of such sensors that depend only on the ratio of the diffusion coefficient of the products to that of the analyte within the tracks. As hitherto none of these two diffusion coefficients is accurately known, the present work was undertaken. The results of this paper allow one to quantify the previous simulation and hence yield realistic predictions of glucose-based biosensors.At this occasion, also the influence of the etched track radius on the diffusion coefficients was measured and compared with earlier prediction.

Transmission profiles of ions through nano-capillaries of rectangular cross-section in mica

We investigated transmission characteristics of Ne7+ ions through nanocapillaries of rectangular cross-section. The capillaries were produced by chemical etching of ion tracks in phlogopite mica. The two dimensional transmission profiles are rhombic when the capillaries are tilted at angles smaller than the geometrical opening angle given by the aspect ratio of the capillaries. For the angles larger than the geometrical opening angle with respect to the beam direction, the rhombic profile is degrading. Possible reasons for the degrading of the shapes by the deposited charge inside the capillaries are investigated and discussed.

Coupled chemical reactions in dynamic nanometric confinement: VII. Biosensors based on swift heavy ion tracks with membranes

ABSTRACTIn previous papers it was shown that the coupling of the two chemical reactions: {NaOH etchant – PET polymer} and {NaOH etchant – AgNO3 solution} 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.

The rectification of mono- and bivalent ions in single conical nanopores

The polyethylene terephthalate (PET) films were irradiated with single 6.9MeV/u 58Ni19+ ions at the Lanzhou Interdisciplinary Heavy Ion Microbeam (LIHIM), and single conical nanopores were produced by asymmetric chemical etching of the latent ion tracks. Then, the current-voltage (I–V) characteristic was measured in LiCl, NaCl, KCl, MgCl2, and CaCl2 solution at different concentrations to study the transport properties of different cations in the single conical nanopores respectively. The measured I–V data showed that the conical nanopores have rectified transportation of these cations at the applied voltage of between +2V and −2V. The rectification coefficient γ of the mono- and bivalent ions was determined in their solution of 0.0001–1M measured at 1V, the result showed that the rectification coefficient is dependent on the valence of the ions and the electrolyte solution.

Label-free histamine detection with nanofluidic diodes through metal ion displacement mechanism

We design and characterize a nanofluidic device for the label-free specific detection of histamine neurotransmitter based on a metal ion displacement mechanism. The sensor consists of an asymmetric polymer nanopore fabricated via ion track-etching technique. The nanopore sensor surface having metal–nitrilotriacetic (NTA–Ni2+) chelates is obtained by covalent coupling of native carboxylic acid groups with Nα,Nα-bis(carboxymethyl)-l-lysine (BCML), followed by exposure to Ni2+ ion solution. The BCML immobilization and subsequent Ni2+ ion complexation with NTA moieties change the surface charge concentration, which has a significant impact on the current–voltage (I–V) curve after chemical modification of the nanopore. The sensing mechanism is based on the displacement of the metal ion from the NTA–Ni2+ chelates. When the modified pore is exposed to histamine solution, the Ni2+ ion in NTA–Ni2+ chelate recognizes histamine through a metal ion coordination displacement process and formation of stable Ni-histamine complexes, leading to the regeneration of metal-free NTA groups on the pore surface, as shown in the current-voltage characteristics. Nanomolar concentrations of the histamine in the working electrolyte can be detected. On the contrary, other neurotransmitters such as glycine, serotonin, gamma-aminobutyric acid, and dopamine do not provoke significant changes in the nanopore electronic signal due to their inability to displace the metal ion and form a stable complex with Ni2+ ion. The nanofluidic sensor exhibits high sensitivity, specificity and reusability towards histamine detection and can then be used to monitor the concentration of biological important neurotransmitters.

Structure and properties of poly(4-methylpentene-1) track-etched membranes

The influence of irradiation and the subsequent etching of latent tracks in poly(4-methylpentene-1) (PMP) films on the transport parameters of the resulting membranes has been studied. The films have been irradiated with accelerated Kr and Xe ions of 4.5 and 1.2 MeV/nucleon in energy at a fluence of 106–109 cm−2. It has been found that the irradiation followed by etching makes it possible to obtain an anisotropic membrane with a nonporous selective layer between two porous layers with tapered pores. The CH4, CO2, and He transport characteristics of the membranes have been examined. It has been shown that these modification methods can significantly increase the gas flux through the membrane. It is believed that the ion track etching procedure as applied to PMP can form the basis for fabricating membranes with a highly permeable, nonporous, gas-selective layer.

Electrodeposition and electroless plating of hierarchical metal superstructures composed of 1D nano- and microscale building blocks

The fabrication of ordered superstructures composed of nano- and microscale building blocks is of tremendous interest. In this work, we present a versatile approach for the synthesis of hierarchical and free-standing metal architectures of high structural complexity. Using the ion-track etching technique, hierarchically porous polycarbonate membranes are obtained, which are employed as nanocasting templates. Pore filling is accomplished by the two complementary wet-chemical techniques electrodeposition and electroless plating. Depending on the pore filling mechanism and the template structure, a wide range of novel metal nano-/micro-architectures can be realized. The products can be characterized as hierarchical assemblies of 1D structures (nanotubes, nanowires, microwires, nanorods). With electrodeposition, complete pore filling is achieved, which results in the formation of wire-based morphologies. Special attention is dedicated to the controlled partial filling of the pores with electroless plating, which allows the simultaneous deposition of tubes and – depending on the conformity of the plating reaction and the deposition time – narrower arrays of tubes, wires or rods. To demonstrate the favorable functional properties of the obtainable products, a silver-based wire-tube assembly is employed in the enzyme-free and selective electrochemical detection of hydrogen peroxide. An excellent sensitivity of 1340μAmM−1cm−2 and a fast response time of <2s is achieved, which is explained by the absence of binders, the well-accessible, open-pored structure, the presence of continuous conduction pathways and the high surface area of the material.

Nuclear track-based biosensing: an overview

ABSTRACTAn overview on the development of biosensors based on nuclear tracks in solids is presented. A few decades ago it was found that nuclear tracks in solids can be usefully applied for the creation of biosensors. Meanwhile quite a number of different strategies have emerged to fulfill this task which are summarized here. We ourselves have especially concentrated on the ‘Product Enrichment Strategy’, where the enrichment of products of a given analyte by a suitable biochemical reaction within the narrow confinement of etched ion tracks is used to amplify the product’s signal for high-sensitivity biosensing. We also report on the application of nuclear analysis techniques for obtaining a deeper insight into these sensor structures, for the sake of their further optimization. Last not least we also discuss competing nanopore-based biosensing approaches.

On the structure of etched ion tracks in polymers

Abstract A simple model describing the radial structure of latent tracks produced by energetic ions in polymers is presented and used for examination of the process of preferential track etching and determination of the shape of the etched pores. The model is based on the assumption that the local composition of the latent track results from chemical reactions of transient degradation products created by ion passage, but it does not take into account details of the whole process. In accordance with the established idea the model calculations lead to the latent track structure with an easily etchable core surrounded by a relatively thin layer of cross-linked structures and a far reaching halo with a progressively decreasing concentration of the degradation products. The etching of the latent track with such a structure leads to funnel-type pores which have been observed in recent conductometric experiments.

Shedding light on the mechanism of asymmetric track etching: an interplay between latent track structure, etchant diffusion and osmotic flow.

The method of producing single track-etched conical nanopores has received considerable attention and found many applications in diverse fields such as biosensing, nanofluidics, information processing and others. The performance of an asymmetric nanopore is largely determined by its geometry, especially by the size and shape of its tip. In this paper we reconstruct the profiles of so-called conical pores fabricated by asymmetric chemical etching of ion tracks in polymer foil. Conductometric measurements during etching and field emission scanning electron microscopy examinations of the resulting pores were employed in order to determine the pore geometry. We demonstrate that the pore constriction geometry evolves through a variety of configurations with advancing time after breakthrough. While immediately after breakthrough the pore tips are trumpet-shaped, further etching is strongly affected by osmotic effects which eventually lead to bullet-shaped pore tips. We evidence that the osmotic flow appearing during asymmetric track etching has a determinative effect on pore formation. A convection-diffusion model is presented that semi-quantitatively explains the effect of osmotic processes under asymmetric track etching conditions. In addition, a phenomenon of reagent contaminant precipitation in nanopores is reported and discussed.