Mária Mátéfi-Tempfli

Nanowire-decorated microscale metallic electrodes.

One of the challenging aspects of science and technology on a nanometer-scale is the precise three-dimensional control of nano-objects. Scanning probe microscopy manipulation, magneticor electric-field alignment and lithography-based techniques are only a few of the techniques that have been reported so far. Nevertheless, most of these techniques are still being developed and their integration for device fabrication represents a real challenge for the scientific community. Within this context, nanowires and nanotubes are of great interest because they lie between the macroscopic and atomic scales. The ability to fabricate andmanipulate such objects in a reliablemanner on a large scale will foster their use in electronic, photonic, and sensing applications. Templatebased methods have been successfully used for nanowire fabrication as they allow the realization of complex organic/ inorganic nanostructures. To date, nanoporous anodic alumina oxide (AAO) made by the electrochemical oxidation of aluminum has been extensively used because it provides a good platform for the development of various nanostructures. This interest originates from the fact that AAO membranes, having a high density of nanopores (up to 10 cm ), are easily produced over large areas with variable thicknesses. Moreover, a good chemical and mechanical stability combined with interesting electrical properties make AAO membranes good candidates for nanowire fabrication. However, the use of such nanostructures as passive or active components in emerging electronic devices requires smartly engineered arrays of nanowires with well defined position and pitch.

Controlled growth of single nanowires within a supported alumina template.

A simple technique for fabricating single nanowires with well-defined position is presented. The process implies the use of a silicon nitride mask for selective electrochemical growth of the nanowires in a porous alumina template. We show that this method allows the realization of complex nanowire patterns as well as arrays of single nanowires with a precise position and spacing.

Nanowire-templated microelectrodes for high-sensitivity pH detection

A highly sensitive pH capacitive sensor has been designed by confined growth of vertically aligned nanowire arrays on interdigited microelectrodes. The active surface of the device has been functionalized with an electrochemical pH transducer (polyaniline). We easily tune the device features by combining lithographic techniques with electrochemical synthesis. The reported electrical LC resonance measurements show considerable sensitivity enhancement compared to conventional capacitive pH sensors realized with microfabricated interdigited electrodes. The sensitivity can be easily improved by changing only the thickness of the functional layer.

Vertical nanowire architectures: Statistical processing of porous templates towards discrete nanochannel integration.

While the process simplicity, the variety of synthesized systems, and the order control over large areas have led nanoporous materials [ 1–9 ] to the top of nanotechnology fabrication strategies, the major drawback that restricts their integration into devices is the mismatch between their characteristic sizes and present technological ability. General characterization approaches have studied large assemblies of nanostructures fabricated inside templates or single nano-objects. [ 10–16 ] Though they provided breakthrough results, these techniques essentially exploit the reduced dimensionality rather than the high density imposed by the nanoporous templates. In templateless synthesized systems, such as epitaxially grown semiconductor nanowires, [ 17–20 ] carbon nanotubes, [ 21 , 22 ] or various chemically designed functional nanostructures, [ 23 , 24 ] the dense vertical packing and order are often neglected as the subsequent device integration proceeds through the destruction of the initial fabricated morphology followed by planar repositioning of only few nanostructures. The number of integrated nanowires – as compared to the quantity of the synthesized ones – is thus small. It may be more interesting to grow nanowires in ultradense vertical architectures and read well defi ned numbers of nanowires. Interestingly, nanotechnology’s armamentarium includes few methods that are random by nature, in which an item (e.g., a scanning-probe tip or a nanoengineered opening) is arbitrarily positioned relative to a porous template with the prospect of interrogating a single grown nanowire. [ 11 , 25–27 ]

Transmission of electrons through Al2O3 nanocapillaries

We investigate transmission of low-energy electrons (250 eV) through insulating Al2O3 nanocapillaries (270 nm diameter and 15 ?m length). Kinetic energy distribution of electrons transmitted through the nanocapillaries in the straightforward direction, time dependence of the transmission rate both in the straightforward direction and for tilted capillaries and angular distributions of electrons transmitted at the incident energy are presented and discussed.

Statistical processing of nanoporous templates with high-yield single-pore resolution

We address the statistical patterning of nanoscale lattices and discuss the probability to overlap a finite number of lattice features with a given entity. The experimental exemplification is done through selective nanowire growth using nanoporous alumina templates. This random patterning approach is found to provide rigorous selection rules for locating definite sets of objects into nanoporous templates. Remarkably, no alignment with respect to the templates features is required to achieve single-nanopore resolution with probabilities as high as 92% upon properly choosing the size of the processing mask. The approach is found to be scale-invariant with a minimal influence of the masking item symmetry and with good reliability of the mask-to-nanopore overlapping threshold. Routed in surface optimization, this study dives into the discrete geometry of quasi-periodic lattices through simple technological processing and analytical approaches.

Electrodeposited L10 CoPt nanowires

Arrays of face-centred cubic (fcc) CoxPt1-x (0.45 < x < 0.55) nanowires were electrodeposited into thin film nanoporous alumina supported on a Si substrate. The heat treatment under specific conditions was then carried out in order to transform the fcc phase into the face-centred tetragonal or L1(0) ordered phase. The influence of both the phase transition and the temperature on the magnetic properties of CoxPt1-x nanowires has been studied. Coercive fields higher than 1 T (10 kOe) have been obtained at room temperature with ordered nanowires, 80 nm in diameter.