Increasing the structural and compositional diversity of ion-track templated 1D nanostructures through multistep etching, plastic deformation, and deposition.

Ion-track etching represents a highly versatile way of introducing artificial pores with diameters down into the nm-regime into polymers, which offers considerable synthetic flexibility in template-assisted nanofabrication schemes. While the mechanistic foundations of ion-track technology are well understood, its potential for creating structurally and compositionally complex nano-architectures is far from being fully tapped. In this study, we showcase different strategies to expand the synthetic repertoire of ion-track membrane templating by creating several new 1D nanostructures, namely metal nanotubes of elliptical cross-section, funnel-shaped nanotubes optionally overcoated with titania or nickel nanospike layers, and concentrical as well as stacked metal nanotube-nanowire heterostructures. These nano-architectures are obtained solely by applying different wet-chemical deposition methods (electroless plating, electrodeposition, and chemical bath deposition) to ion-track etched polycarbonate templates, whose pore geometry is modified through plastic deformation, consecutive etching steps under differing conditions, and etching steps intermitted by spatially confined deposition, providing new motifs for nanoscale replication.

Designing voltage multipliers with nanofluidic diodes immersed in aqueous salt solutions.

Membranes with nanofluidic diodes allow the selective control of molecules in physiological salt solutions at ambient temperature. The electrical coupling of the membranes with conventional electronic elements such as capacitors suggests opportunities for the external monitoring of sensors and actuators. We demonstrate experimentally and theoretically the voltage multiplier functionality of simple electrical networks composed of membranes with conical nanopores coupled to load capacitors. The robust operation of half and full wave voltage multipliers is achieved in a broad range of experimental conditions (single pore and multipore membranes, electrolyte concentrations, voltage amplitudes, and solid-state capacitances). The designed voltage multipliers operate in the liquid state and can be used in sensing devices because different electrical, optical, and chemical inputs are known to modulate the individual nanofluidic diode resistances in the electrical network.

Thermal stability of electrodeposited platinum nanowires and morphological transformations at elevated temperatures.

Pt nanowires were prepared by template electrodeposition using ion track etched polymer membranes and analysed with respect to their thermal stability. Driven by Rayleigh instability, the polycrystalline Pt nanostructures experienced structural transformations and finally fragmented into linear chains of nanospheres at temperatures much below the melting point of bulk Pt. Morphological changes were systematically studied by electron microscopy and compared with previously reported results on other metal nanowires and theoretical predictions. In addition, nanowires could readily be interconnected to two-dimensional assemblies by taking advantage of the rapid diffusion processes. This study will help to predict the durability of integrated nanowires and contributes to the understanding of thermal-induced transformations for polycrystalline nanowires.

Chemical interactions in the layered system BCxNy/Ni(Cu)/Si, produced by CVD at high temperature.

Layered samples Si(100)/C/Ni/BC(x)N(y) and Si(100)/C/Cu/BC(x)N(y) were produced by physical vapor deposition of a metal (Ni, Cu, resp.) and low-pressure chemical vapor deposition of the boron carbonitride on a Si(100) substrate. Between the Si and the Ni (Cu) and on the surface of the Ni (Cu) layer, thin carbon layers were deposited, as a diffusion barrier or as a protection against oxidation, respectively. Afterwards, the surface carbon layer was removed. As precursor, trimethylamine borane and, as an auxiliary gas, H(2) and NH(3) were used, respectively. The chemical compositions of the layers and of the interfaces in between were characterized by total-reflection X-ray fluorescence spectrometry combined with near-edge X-ray absorption fine-structure spectroscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectrometry. The application of H(2) yielded the BC(x)N(y) compound whereas the use of NH(3) led to a mixture of h-BN and graphitic carbon. At the BC(x)N(y)/metal interface, metal borides could be identified. At the relatively high synthesis temperature of 700 °C, broad regions of Cu or Ni and Si were observed between the metal layer and the substrate Si.

Cerium (IV) oxide nanotubes prepared by low temperature deposition at normal pressure.

This paper reports the synthesis of cerium dioxide nanotubes (CeNTs) by electroless deposition using ion-track-etched polycarbonate templates. To achieve nanotubes with thin walls and small surface roughness the tubes were generated by a several-step-containing procedure under aqueous conditions. The approach reported below will process open end nanotubes with well-defined outer diameter and wall thickness.

Tuning the characteristics of electrochemically fabricated gold nanowires.

We have developed different electrochemical procedures for the production of gold nanowires with variable and controllable crystallographic and morphological properties using etched ion track templates. The texture of the nanowires is tuned by the variation of the electrodeposition parameters. Potentiostatic plating at low overvoltage provides strongly (110) textured wires for diameters below 100 nm. With the increase in diameter above 100 nm, this texture decreases and the signal from ({111} planes becomes more pronounced. Under reverse pulse deposition conditions, (100) textured wires are generated. The growth mechanism is discussed in detail in terms of the surface energy minimum principle. In addition, wires are shaped in a reliable way from cylindrical to conical geometry by engineering the pore structure in the template.

Note: Sample holder with open area for increased deposition rate in plasma immersion ion implantation and deposition.

A sample holder with a large open area offers several benefits when used in the process of plasma immersion ion implantation and deposition in which the plasma is generated by a high voltage applied to the sample holder: The ignition voltage of the plasma is lower, and the deposition rate can be several times higher than in the case of a normal plate-like holder. There is a more pronounced edge effect regarding the film thickness. Other film properties are also affected; for diamond-like carbon films, the film structure exhibits more disorder. The hardness of the samples is similar, with the surfaces of the samples being very smooth.

Influence of surface texture and charge on the biocompatibility of endovascular stents.

BACKGROUND: The mechanical behaviour and the surface characteristics of endovascular stents are key factors determining stent patency. In-vitro studies have suggested that surface texture and charge alter the biocompatibility of metallic stents. In this study, the influence of surface texture and charge of metallic stents on thrombosis and neointima formation was evaluated in a rabbit model. METHODS: Twenty-four stainless steel Palmaz-Schatz stents were coated either by an electrochemical deposition of metal on the stent surface or were coated with a metallic film which was implanted into the stent surface by argon ion bombardment. The coatings consisted of platinum, gold, or copper. Coated and uncoated control stents were implanted in rabbit iliac arteries. As antithrombotic therapy, 500 IU heparin and 60 mg aspirin was given intravenously before stent implantation, followed by 60 mg aspirin intravenously every third day for 4 weeks. Thrombus and neointima formation in arterial cross-sections of 24 coated stents were compared with 19 uncoated stents using quantitative, computer-assisted histomorphometry and transmission electron microscopy. RESULTS: A higher stent surface porosity and more surface cracks after stent expansion were found after galvanization than after ion implantation. The in-vitro surface potentials of uncoated steel, copper-, and gold-coated or platinized stents were +150, +120, +180, and +180 mV, respectively. Four weeks after implantation, six of 14 galvanized stents, but none of the uncoated or ion bombarded stents, were occluded by a thrombus. Neointimal hyperplasia was increased in stents coated by galvanization compared with stents coated by ion implantation. In both study groups, the most electropositive coating (platinum or gold) induced markedly less neointima formation than the least electropositive (copper). CONCLUSION: Stent surface texture was the most important factor determining biocompatibility of coated Palmaz-Schatz stents in this study. In contrast to suggestions derived from in-vitro studies, the charge of stents does not seem to play a major role with respect to stent thrombogenicity. Low stent charge correlates with an increased neointima formation.

Gross alpha determination in drinking water using a highly specific resin and LSC.

Some results of experiments concerning a new highly specific resin for the extraction of alpha-emitting nuclides from drinking water samples are presented. The product used during these experiments is a new extraction chromatographic resin which consists of a combination of several reagents and extractants supported on inert polymeric substrates, called "Resin" hereafter. It shows strong affinity for Actinides in the tri-, tetra- and hexavalent oxidation state, as well as for radium, even in presence of large amounts of calcium. Gross-alpha activities were determined using alpha-/beta-discrimination liquid scintillation counting (alpha-/beta-LSC) by direct measurement of the dried resin after extraction. Counting conditions were optimised accordingly. A method for the determination of alpha-emitting nuclides in drinking water was developed and tested using intercomparison and spiked drinking water samples.

Modifying the surface charge of single track-etched conical nanopores in polyimide.

Chemical modification of nanopore surfaces is of great interest as it means that the surface composition is no longer fixed by the choice of substrate material, even to the point where large biomolecules can be attached to the pore walls. Controlling nanopore transport characteristics is one important application of surface modification which is very relevant given the significant interest in sensors based on the transport of ions and molecules through nanopores. Reported here is a method to change the surface charge polarity of single track-etched conical nanopores in polyimide, which also has the potential to attach more complex molecules to the carboxyl groups on the nanopore walls. These carboxyl groups were converted into terminal amino groups, first by activation with N-(3-dimethylaminopropyl)-N-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) followed by the covalent coupling of ethylenediamine. This results in a changed surface charge polarity. Regeneration of a carboxyl-terminated surface was also possible, by reaction of the amino groups with succinic anhydride. The success of these reactions was confirmed by measurements of the pore's pH sensitive current-voltage (I-V) characteristics before and after the chemical modification, which depend on surface charge. The permselectivity of the pores also changed accordingly with the modification.

Crystallization in low-energy deposition of titanium ions.

To investigate crystallization in the ion beam deposition process, titanium ions were deposited on silicon wafers at 105 and 55 eV. As titanium is an active metal, titanium compounds are formed by absorbing backfilled or residual gas. At energy levels of 105 or 55 eV, titanium crystallizes in a NaCl-type titanium compound with the backfilling of air. In all samples, (110)-oriented crystals grew with a rectangular lattice arrangement of titanium atoms. The open channel <110> of preferentially oriented crystal growth was parallel to the direction of incident ions normal to the substrate surface.