Etched Ion Tracks Research Articles

Transport properties of track-etched membranes having variable effective pore-lengths

The transport rate of molecules through polymeric membranes is normally limited because of their micrometer-scale thickness which restricts their suitability for more practical application. To study the effect of effective pore length on the transport behavior, polymer membranes containing cylindrical and asymmetric-shaped nanopores were prepared through a two-step ion track-etching technique. Permeation experiments were performed separately to investigate the transport properties (molecular flux and selectivity) of these track-etched membranes. The permeation data shows that the molecular flux across membranes containing asymmetric nanopores is higher compared to those having cylindrical pores. On the other hand, the cylindrical pore membranes exhibit higher selectivity than asymmetric pores for the permeation of charged molecules across the membrane. Current–voltage (I–V) measurements of single-pore membranes further verify that asymmetric pores exhibit lower resistance for the flow of ions and therefore show higher currents than cylindrical pores. Moreover, unmodified and polyethyleneimine (PEI) modified asymmetric-shaped pore membranes were successfully used for the separation of cationic and anionic analyte molecules from their mixture, respectively. In this study, two distinct effects (pore geometry and pore density, i.e. number of pores cm−2), which mainly influence membrane selectivity and molecular transport rates, were thoroughly investigated in order to optimize the membrane performance. In this context, we believe that membranes with high molecular transport rates could readily find their application in molecular separation and controlled drug delivery processes.

A model of chemical etching of olivine in the vicinity of the trajectory of a swift heavy ion

Searching of superheavy elements, the charge spectra of heavy nuclei in Galactic Cosmic Rays was investigated within the OLYMPIA experiment using the database of etched ion tracks in meteorite olivine. Etching results in the formation of hollow syringe-like channels with diameters of 1–10μm along the trajectories of these swift heavy ions (SHI). According to the activated complex theory, the local chemical activity is determined by an increase of the specific Gibbs energy of the lattice stimulated by structure transformations, long-range elastic fields, and interatomic bonds breaking generated in the vicinity of the ion trajectory. To determine the dependencies of the Gibbs free energy increase in SHI tracks in olivine on the mass, energy and charge of a projectile, we apply a multiscale model of excitation and relaxation of materials in the vicinity of the SHI trajectory (SHI tracks). Effect of spreading of fast electrons from the ion trajectory causing neutralization of metallic atoms resulting in an increase of the chemical activity of olivine at long distances from the ion trajectory (up to 5μm) is estimated and discussed.

Surface Enrichment in Au–Ag Alloy Nanowires and Investigation of the Dealloying Process

The fabrication of nanowires by electrodeposition of Au−Ag alloy into the pores of etched ion track polymer membrane is presented. The crystallinity, morphology, and composition of wires with diameters of 85, 45, and 30 nm are investigated by means of X-ray diffraction, high-resolution scanning transmission electron microscopy, and energy-dispersive X-ray analysis. Energy-dispersive X-ray analysis with very high spatial resolution (below 1 nm) reveals the presence of surface enrichment. A Ag-rich layer in Au40Ag60 wires and a Au-rich layer in Au60Ag40 wires with thicknesses between 1 and 4 nm are observed. After dealloying in nitric acid, Ag-rich wires exhibit porous morphologies whereas Au-rich wires remain solid cylinders. The results clearly indicate that the analyzed AuAg alloy nanowires do not consist of homogeneous solid solution, but surface effects before and during the dealloying play an important role for the final morphology of dealloyed nanowires.

Fabrication of hard-coated optical absorbers with microstructured surfaces using etched ion tracks: Toward broadband ultra-low reflectance

Broadband low reflectance materials have various applications in the field of optical energy management; however, materials with ultra-low reflectance (below 0.1%) have been considered as mechanically delicate. We have developed a novel hard-surface optical absorber with microstructured, diamond-like carbon coated ion tracks on CR-39 plastic substrate. The spectral reflectance of the first prototype was below 2% for wavelengths ranging from 400nm to 1400nm; moreover, the optical absorber had mechanically hard surface and exhibited temporal durability. Choosing the appropriate design of the surface structure and coating layer is likely to reduce the reflectance to the order of 0.1%. This technique yields easy-to-handle broadband ultra-low reflectance absorbers.

Design and Construction of Optimized Electrochemical Cell and Data Analysis System for Etching of Ion Tracks and Electro Deposition of Nano and Micro Wires in Porous Ion Tracks Foils

In this work, an optimized computer controlled electrochemical cell were designed and constructed. This Electrolytic cell was used for etching latent ion tracks and electrochemical deposition of wires in pores of etched-ion tracks foils. The applied voltage and current through the electrochemical cell during the etching and electrodeposition were measured and monitored in real time by a Data Analysis system. Monitoring the current time curve during the filling of pores and growth of micro and nano wires allows one to stop the deposition process after a given time to obtain nano- and micro wire of a predefined length. In this work, Design and manufacture of a sealed electrochemical cell was done in a manner that one can change distance between electrodes and geometry of cathodes. Data analysis system was used to measuring and monitoring of applied voltage and current through the cell consists of three parts: Amplifier, Data acquisition (DAQ) system and Software. A current amplifier that used in data analysis system is a log ratio amplifier. A log ratio amplifier provides an output voltage proportional to the log base 10 of the ratio input current I1 (current during the electrodeposition of wire in cell) and Input current I2(flexible current of precision current source). A DAQ reading output voltage of amplifier and send to Computer. With lab view software analyzed the voltage and converted to the current corresponding to the electrodeposition of wires. Current amplifier designed and built in this work is a noise suppression that can measure small current through the cell with high accuracy. Advantage of proposed log ratio amplifier is one can used this amplifier for measuring and monitoring of current during the filling of pores and growth of wires in the etched ion track foils with various track density.

Xe- and U-tracks in apatite and muscovite near the etching threshold

Ion irradiation of a wedge-shaped Durango apatite backed by a mica detector allows investigating ion track ranges and etching properties at different points along the tracks. Transmission profiles obtained by irradiation with 2×106cm−2 11.1MeV/amu 132Xe and 2×106cm−2 11.1MeV/amu 238U parallel to the apatite c-axis correspond to ranges calculated with SRIM (Xe: 76.3μm; U: 81.1μm). However, the measured profiles show much greater etchable track-length variations than the calculated longitudinal straggles. The probable cause is that the length deficit exhibits significant variation from track to track. The measured length deficit in muscovite is in agreement with most existing data. In contrast, the length deficit in apatite appears to be close to zero, which is in conflict with all earlier estimates. This probably results from the etching properties of the apatite basal face, which permit surface-assisted sub-threshold etching of track sections in the nuclear stopping regime. These sections are not accessible from the opposite direction, i.e. by etching towards the endpoint of the tracks or in the direction of the ion beam. This conclusion is supported by the fact that linear dislocations are revealed in apatite basal faces and by the observation of imperfect etch pits that are separated from the etched ion track channel by a section that appears unetched under the microscope.

Hierarchically porous carbon membranes containing designed nanochannel architectures obtained by pyrolysis of ion-track etched polyimide

Well-defined, porous carbon monoliths are highly promising materials for electrochemical applications, separation, purification and catalysis. In this work, we present an approach allowing to transfer the remarkable degree of synthetic control given by the ion-track etching technology to the fabrication of carbon membranes with porosity structured on multiple length scales. The carbonization and pore formation processes were examined with Raman, Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements, while model experiments demonstrated the viability of the carbon membranes as catalyst support and pollutant adsorbent. Using ion-track etching, specifically designed, continuous channel-shaped pores were introduced into polyimide foils with precise control over channel diameter, orientation, density and interconnection. At a pyrolysis temperature of 950 °C, the artificially created channels shrunk in size, but their shape was preserved, while the polymer was transformed to microporous, amorphous carbon. Channel diameters ranging from ∼10 to several 100 nm could be achieved. The channels also gave access to previously closed micropore volume. Substantial surface increase was realized, as it was shown by introducing a network consisting of 1.4 × 1010 channels per cm2 of 30 nm diameter, which more than tripled the mass-normalized surface of the pyrolytic carbon from 205 m2 g−1 to 732 m2 g−1. At a pyrolysis temperature of 3000 °C, membranes consisting of highly ordered graphite were obtained. In this case, the channel shape was severely altered, resulting in a pronounced conical geometry in which the channel diameter quickly decreased with increasing distance to the membrane surface.

Fabrication of single cylindrical Au-coated nanopores with non-homogeneous fixed charge distribution exhibiting high current rectifications.

We designed and characterized a cylindrical nanopore that exhibits high electrochemical current rectification ratios at low and intermediate electrolyte concentrations. For this purpose, the track-etched single cylindrical nanopore in polymer membrane was coated with a gold (Au) layer via electroless plating technique. Then, a non-homogeneous fixed charge distribution inside the Au-coated nanopore was obtained by incorporating thiol-terminated uncharged poly(N-isopropylacrylamide) chains in series to poly(4-vinylpyridine) chains, which were positively charged at acidic pH values. The functionalization reaction was checked by measuring the current-voltage curves prior to and after the chemisorption of polymer chains. The experimental nanopore characterization included the effects of temperature, adsorption of chloride ions, electrolyte concentration, and pH of the external solutions. The results obtained are further explained in terms of a theoretical continuous model. The combination of well-established chemical procedures (thiol and self-assembled monolayer formation chemistry, electroless plating, ion track etching) and physical models (two-region pore and Nernst-Planck equations) permits the obtainment of a new nanopore with high current rectification ratios. The single pore could be scaled up to multipore membranes of potential interest for pH sensing and chemical actuators.

Lotus bioinspired superhydrophobic, self‐cleaning surfaces from hierarchically assembled templates

ABSTRACTThe super hydrophobic, self‐cleaning properties of natural species derive from the fine hierarchical topography evolved on their surfaces. Hierarchical architectures which are function‐mimetic of the lotus leaf are here described and created from multi‐scale hierarchical assembled templates. The first level of hierarchy was a micromachined dome structure template and the second level of hierarchy was added by layering a thin nanoporous membrane such as porous anodized alumina or an ion track etch membrane. The assembled templates were nanoimprinted by a single step process on thermoplastic films. The wetting angle of the surfaces reached a value of 160° and the self‐cleaning behavior was observed. The superhydrophobic behavior remained over 1 year after fabrication, which demonstrates the stability of these polymeric self‐cleaning topographies. © 2014 Wiley Periodicals, Inc. J. Polym. Sci. Part B. Polym. Phys. 2014, 52, 603–609

Facile preparation and magnetic properties of Ni nanotubes in polycarbonate ion-track templates

Ni nanotubes, with an inner diameter of about 100nm and different wall thicknesses (approximately 20, 50, 80 and 110nm), were successfully fabricated in porous polycarbonate (PC) ion-track templates by a novel method including two-step ion-track etching, two-step electrochemical deposition and one-step electrolysis. In our experiment, wall thickness of Ni nanotubes can be effectively controlled through the etching time of templates. The morphologies and crystal structures of the nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The magnetic hysteresis loops measured via vibrating sample magnetometry (VSM) indicate that Ni nanotubes with thinner wall thickness possess larger squareness and coercivity value when magnetic field applied parallel to the nanotube׳s axis, which can be attributed to the shape anisotropy and the formation of multi-domain structure.

Transition metal oxides in etched ion tracks: Surface morphological studies

Transition metal oxide (TMO) nanoparticles comprising of different magnetic properties, have been inserted in ion tracks which have been created by swift heavy ion bombardment of the SiO2/Si substrate and further etched by hydrofluoric acid. To study the surface morphology of the system, pore structure (diameter, shape, size and depth), pore volume and surface area before and after filling of TMOs, atomic force microscopy (AFM) and Brunauer–Emmett–Teller (BET) techniques have been used. These TMO filled structures have been subjected to perpendicular magnetic field to study the alignment of the metal oxide particles. In this paper, the surface morphology of TMO based nanostructures is being reported corroborating the findings with vibrating sample magnetometer (VSM) and transmission electron microscopy (TEM) studies.

Threshold and criterion for ion track etching in SiO2 layers grown on Si

SiO2 layers thermally grown on Si wafers were irradiated with swift heavy ions in the energy range of (20–710) MeV. Subsequent chemical etching in 4% HF for 6 min produced conical pores with diameters from ∼20 to ∼80 nm in the SiO2 layers. We have calculated radii and lifetime of the molten regions in the SiO2 layers and compared them with the pore diameters and diameter dispersions estimated from scanning electron microscopy and atomic force microscopy. It is shown that the existence of a molten region and its radius can serve as a valid criterion for track “etchability”. In the same etching conditions the etched track diameter and the etching velocity in the track region are proportional to the radius and the lifetime of the molten region.

Polypropylene track membranes as a promising material for targets with polarized protons

Polypropylene track membranes made by irradiation of polypropylene films with a beam of high-energy heavy ions followed by chemical etching of latent ion tracks are proposed for being used as a polarized target material. To give membranes paramagnetic properties needed for allowing dynamic polarization of nuclei, the nitroxyl radical 2,2,6,6-tetramethylpiperidine-1-oxyl was introduced in the samples by the thermal diffusion technique. Using the electron paramagnetic resonance method, we obtained information on paramagnetic centers in the polymer matrix of the membranes and determined the nitroxyl radical concentration and rotational mobility of the spin probe in them.

Synthesis of SiC Nanoporous Membrane Using Ion Track Etching Technique

Synthesis of SiC Nanoporous Membrane Using Ion Track Etching Technique

Coupled chemical reactions in dynamic nanometric confinement: Ag2O membrane formation during ion track etching

In this study, continuous swift heavy ion tracks in thin polymer foils were etched from both sides to create two conical nanopores opposing each other. Shortly before both cones merged, one of the nanopores was filled with a silver salt solution, whereas etching of the other cone continued. At the moment of track breakthrough, the etchant reacted with the silver salt solution by forming an impermeable and insulating membrane. Continued etching around the thus-created obstacle led to repetitive {etchant – silver salt solution} interactions. The coupling of the two chemical reactions, {etchant – polymer} and {etchant – silver salt solution}, within the confinement of etched tracks, with continuously changing shapes, showed a highly dynamic nature as recorded by measuring both the electrical current and the optical transmission across the foils. At low etching speeds, a central membrane that grew in radius and thickness with time until, at a critical thickness, the membrane became rather impermeable was formed. However, at high etching speeds, the emerging reaction products exhibited a sponge-like consistency, which allowed for their infinite growth. This precipitation was accompanied by a pronounced current spike formation. A simple theoretical model explains, at a minimum, the basic features.

Polycarbonate electron beam resist using solvent developer

Polycarbonate is a popular membrane material fabricated by ion track etching method and used for filtration, thus it is a sort of ion beam resist. Here we show that it can also be used as a positive electron beam resist using solvent development. Compared to the popular resist PMMA, polycarbonate is more chemically and thermally stable, and is more resistant to plasma dry etching. Various solvents, including cyclopentanone, xylene, pentyl acetate and methyl isobutyl ketone, were found to be suitable developers for polycarbonate when diluted properly with 2-propanol. The resist showed a low contrast between 0.5 and 1.0 when using those solvent developers, and thus it is not a good resist for defining high resolution dense patterns, yet is ideal for grayscale lithography to generate quasi-three dimensional structures like Fresnel zone-plate lens. Nevertheless, we achieved sub-50nm resolution for sparse line array pattern.

Polyimide as a versatile enabling material for microsystems fabrication: surface micromachining and electrodeposited nanowires integration

The interest of using polyimide as a sacrificial and anchoring layer is demonstrated for post-processing surface micromachining and for the incorporation of metallic nanowires into microsystems. In addition to properties like a high planarization factor, a good resistance to most non-oxidizing acids and bases, and CMOS compatibility, polyimide can also be used as a mold for nanostructures after ion track-etching. Moreover, specific polyimide grades, such as PI-2611 from HD Microsystems™, involve a thermal expansion coefficient similar to silicon and low internal stress. The process developed in this study permits higher gaps compared to the state-of-the-art, limits stiction problems with the substrate and is adapted to various top-layer materials. Most metals, semiconductors or ceramics will not be affected by the oxygen plasma required for polyimide etching. Released structures with vertical gaps from one to several tens of μm have been obtained, possibly using multiple layers of polyimide. Furthermore, patterned freestanding nanowires have been synthesized with diameters from 20 to 60 nm and up to 3 μm in length. These results have been applied to the fabrication of two specific devices: a generic nanomechanical testing lab-on-chip platform and a miniaturized ionization sensor.

Symphony and cacophony in ion track etching: how to control etching results

In general, etching of two identical ion-irradiated polymer foils in the same vessel with the same etchant for the same times does not lead to identical track shapes in both foils. In contrast, the track shapes, the etching speeds, and consequently also the etchant consumption of the two foils diverge increasingly with increasing etching times, unless this is prevented by forceful external equilibration of the system. This tendency toward divergence of a system of multiple ion tracks originates from its lack of self-synchronization during etching. A theory has been developed for this case that also shows general applicability to other diverging effects in human life.

A novel method for observation by unaided eyes of nitrogen ion tracks and angular distribution in a plasma focus device using 50 Hz–HV electrochemically-etched polycarbonate detectors

Abstract A novel ion detection method has been developed and studied in this paper for the first time to detect and observe tracks of nitrogen ions and their angular distribution by unaided eyes in the Amirkabir 4 kJ plasma focus device (PFD). The method is based on electrochemical etching (ECE) of nitrogen ion tracks in 1 mm thick large area polycarbonate (PC) detectors. The ECE method employed a specially designed and constructed large area ECE chamber by applying a 50 Hz–high voltage (HV) generator under optimized ECE conditions. The nitrogen ion tracks and angular distribution were efficiently (constructed for this study) amplified to a point observable by the unaided eyes. The beam profile and angular distribution of nitrogen ion tracks in the central axes of the beam and two- and three-dimensional iso-ion track density distributions showing micro-beam spots were determined. The distribution of ion track density along the central axes versus angular position shows double humps around a dip at the 0° angular positions. The method introduced in this paper proved to be quite efficient for ion beam profile and characteristic studies in PFDs with potential for ion detection studies and other relevant dosimetry applications.

Magnetic behavior of arrays of nickel nanowires: Effect of microstructure and aspect ratio

Arrays of nickel nanowires with aspect ratio of ∼1200 and diameters ranging between 25 and 100 nm have been fabricated by electrodeposition in etched ion track templates. Samples with different areal densities ranging from 1 × 10 6 cm −2 to 1 × 10 8 cm −2 have been prepared for this study. Magnetic measurements were performed at room temperature for different aspect ratios and diameters of the wires. Coercivity of the wires showed a strong dependence on aspect ratio ( l/ d), diameter and microstructure. In the case of parallel applied field coercivity of the wires has maximum value at ∼40 nm diameter. The wires with high areal densities showed relatively lower coercivities as compared to the low density samples. The results have been discussed by taking into account various magnetic anisotropies originating from the shape and crystalline nature of the wires, and the magnetostatic interactions among the wires.