Etching and Doping of Pores in Polyethylene Terephthalate Analyzed by Ion Transmission Spectroscopy and Nuclear Depth Profiling.

This work is devoted to the study of controlled preparation and filling of pores in polyethylene terephthalate (PET) membranes. A standard wet chemical etching with different protocols (isothermal and isochronous etching for different times and temperatures and etching from one or both sides of the films) was used to prepare the micrometric pores. The pores were filled with either a LiCl solution or boron deposited by magnetron sputtering. Subsequent control of the pore shape and dopant filling was performed using the nuclear methods of ion transmission spectroscopy (ITS) and neutron depth profiling (NDP). It turned out that wet chemical etching, monitored and quantified by ITS, was shown to enable the preparation of the desired simple pore geometry. Furthermore, the effect of dopant filling on the pore shape could be well observed and analyzed by ITS and, for relevant light elements, by NDP, which can determine their depth (and spatial) distribution. In addition, both non-destructive methods were proven to be suitable and effective tools for studying the preparation and filling of pores in thin films. Thus, they can be considered promising for research into nanostructure technologies of thin porous membranes.

Microstructural and plasmonic modifications in Ag-TiO2 and Au-TiO2 nanocomposites through ion beam irradiation.

The development of new fabrication techniques of plasmonic nanocomposites with specific properties is an ongoing issue in the plasmonic and nanophotonics community. In this paper we report detailed investigations on the modifications of the microstructural and plasmonic properties of metal-titania nanocomposite films induced by swift heavy ions. Au-TiO2 and Ag-TiO2 nanocomposite thin films with varying metal volume fractions were deposited by co-sputtering and were subsequently irradiated by 100 MeV Ag(8+) ions at various ion fluences. The morphology of these nanocomposite thin films before and after ion beam irradiation has been investigated in detail by transmission electron microscopy studies, which showed interesting changes in the titania matrix. Additionally, interesting modifications in the plasmonic absorption behavior for both Au-TiO2 and Ag-TiO2 nanocomposites were observed, which have been discussed in terms of ion beam induced growth of nanoparticles and structural modifications in the titania matrix.

Label-free DNA detection using the narrow side of funnel-type etched nanopores.

A sensitive; simple and label-free method for DNA detection is presented. Irradiated polyethylene terephthalate foils were etched to present conical tracks at a density of approximately 5×107 tracks per cm². Probe DNA was immobilized at the narrow opening of the tracks (2-4 nm diameter). The presence of target DNA resulted in changes in both conductance and rectification ratios in a concentration-dependent manner. DNA concentrations as low as 2 nM could be detected using this simple two-step detection scheme.

Study of ferrofluids in confined geometry.

The passage of swift heavy ions through dielectric layers (SiO(2) or SiON) on silicon, creates ion tracks in them. After the etching and filling of these ion tracks with a suitable material, a novel electronic structure acronymed TEMPOS--'Tunable Electronic Materials with Pores in Oxide on Silicon' has been realized. Several electronic devices, both, active and passive, have been fabricated and systematically studied in the last few years. Sensors have also been successfully made and characterized using the TEMPOS structure as it offers a high surface to volume ratio resulting in fast response time and high sensitivity of the sensor. In continuation with these studies, in the present paper, ferrofluids have been inserted in the ion tracks to study their behaviour in confined geometry and for subsequently obtaining magnetic sensors. A comparative study has been done between the aqueous and non-aqueous ferrofluids. Insertion of the ferrofluids in the ion tracks exhibits a change in the I-V behaviour in the presence of a magnetic field which can be exploited for obtaining the above said sensor.

Glucose determination using a re-usable enzyme-modified ion track membrane sensor.

A novel concept for a glucose biosensor based on the enzyme glucose oxidase covalently linked to nanopores of etched nuclear track membranes is presented. This device can be used to detect physiologically relevant glucose concentrations between 10 microM and 1 M. The sensitive catalytic sensor can be made re-usable due to the production of diffusible products from the oxidative biomolecular recognition event. We have demonstrated both the simplicity with which this sensor can be produced and the stability of the enzyme embedded in the nanopores. We strongly believe that the approach could be expanded for different enzymes and variable configurations of sensing and catalysis using membranes with nanopores for biocatalysis and enrichment of substrates and products. This is the first time that such devices are being used for biocatalytic transformations.

Room Temperature Ammonia Gas Sensing Using Mixed Conductor based TEMPOS Structures.

The current/voltage characteristics of mixed (ion+electron) conductor-based 'TEMPOS' (Tunable Electronic Material with Pores in Oxide on Silicon) structures are reported. TEMPOS are novel electronic MOS-like structures having etched swift heavy ion tracks (i.e., nanopores) in the dielectric layer filled with some conducting material. The three contacts (two on top and one on the bottom), which resemble the classical bipolar or field effect transistor arrangements are, in principle, interchangeable when the overall electrical resistance along the tracks and on the surface are similar. Consequently, three configurations are obtained by interchanging the top contacts with the base contact in electronic circuits. The current/voltage characteristics show a diode like behaviour. Impedance measurements have been made for TEMPOS structures with tracks filled with ion conductors and also mixed conductors to study the ammonia sensing behaviour. The impedance has been found to be a function of frequency and magnitude of the applied signal and concentration of the ammonia solution. This is attributed to the large number of charge carriers (here protons) available for conduction on exposure to ammonia and also to the large surface to volume ratio of the polymer composites embedded in the ion tracks. The measurement of both, the real and imaginary parts of impedance allows one to enhance the detection sensitivity greatly.