On the origins of transport inefficiencies in mesoscopic networks.

A counter-intuitive behavior analogous to the Braess paradox is encountered in a two-terminal mesoscopic network patterned in a two-dimensional electron system (2DES). Decreasing locally the electron density of one channel of the network paradoxically leads to an increased network electrical conductance. Our low temperature scanning gate microscopy experiments reveal different occurrences of such puzzling conductance variations, thanks to tip-induced localized modifications of electron flow throughout the network's channels in the ballistic and coherent regime of transport. The robustness of the puzzling behavior is inspected by varying the global 2DES density, magnetic field and the tip-surface distance. Depending on the overall 2DES density, we show that either Coulomb Blockade resonances due to disorder-induced localized states or Fabry-Perot interferences tuned by the tip-induced electrostatic perturbation are at the origin of transport inefficiencies in the network, which are lifted when gradually closing one channel of the network with the tip.

A new transport phenomenon in nanostructures: a mesoscopic analog of the Braess paradox encountered in road networks.

The Braess paradox, known for traffic and other classical networks, lies in the fact that adding a new route to a congested network in an attempt to relieve congestion can degrade counterintuitively the overall network performance. Recently, we have extended the concept of the Braess paradox to semiconductor mesoscopic networks, whose transport properties are governed by quantum physics. In this paper, we demonstrate theoretically that, alike in classical systems, congestion plays a key role in the occurrence of a Braess paradox in mesoscopic networks.

Direct protein detection with a nano-interdigitated array gate MOSFET.

A new protein sensor is demonstrated by replacing the gate of a metal oxide semiconductor field effect transistor (MOSFET) with a nano-interdigitated array (nIDA). The sensor is able to detect the binding reaction of a typical antibody Ixodes ricinus immunosuppressor (anti-Iris) protein at a concentration lower than 1 ng/ml. The sensor exhibits a high selectivity and reproducible specific detection. We provide a simple model that describes the behavior of the sensor and explains the origin of its high sensitivity. The simulated and experimental results indicate that the drain current of nIDA-gate MOSFET sensor is significantly increased with the successive binding of the thiol layer, Iris and anti-Iris protein layers. It is found that the sensor detection limit can be improved by well optimizing the geometrical parameters of nIDA-gate MOSFET. This nanobiosensor, with real-time and label-free capabilities, can easily be used for the detection of other proteins, DNA, virus and cancer markers. Moreover, an on-chip associated electronics nearby the sensor can be integrated since its fabrication is compatible with complementary metal oxide semiconductor (CMOS) technology.

Characterization of ultrathin SOI film and application to short channel MOSFETs.

In this study, a very dilute solution (NH(4)OH:H(2)O(2):H(2)O 1:8:64 mixture) was employed to reduce the thickness of commercially available SOI wafers down to 3 nm. The etch rate is precisely controlled at 0.11 Å s(-1) based on the self-limited etching speed of the solution. The thickness uniformity of the thin film, evaluated by spectroscopic ellipsometry and by high-resolution x-ray reflectivity, remains constant through the thinning process. Moreover, the film roughness, analyzed by atomic force microscopy, slightly improves during the thinning process. The residual stress in the thin film is much smaller than that obtained by sacrificial oxidation. Mobility, measured by means of a bridge-type Hall bar on 15 nm film, is not significantly reduced compared to the value of bulk silicon. Finally, the thinned SOI wafers were used to fabricate Schottky-barrier metal-oxide-semiconductor field-effect transistors with a gate length down to 30 nm, featuring state-of-the-art current drive performance.

Nanoscale control of polymer crystallization by nanoimprint lithography.

Polymer crystallization is notoriously difficult to control. Here, we demonstrate that the orientation of polymer crystals can be fully controlled at the nanoscale by using nanoimprint lithography (NIL) with molds bearing nanotrenches to shape thin films of poly(vinylidene fluoride). This unprecedented control is due to the thermomechanical history experienced by the polymer during embossing, to the shift of the nucleation mechanism from heterogeneous to homogeneous in confined regions of the mold, and to the constraining of the fast growth axis along the direction of the trenches. NIL thus appears as an ideal tool to realize smart polymer surfaces where crystal ordering can be tuned locally.