Nano-Electronics
| Tunable generation of correlated vortices in open superconductor tubesWe theoretically apply transport currents and magnetic fields to open superconducting tubes. In such tubes, which can be created by rolled-up nanotech, vortices nucleate periodically at one edge of the tube, subsequently move along the tube axis under the action of the Lorentz force and denucleate at the opposite edge of the tube. The characteristic times of the vortex motions are efficiently controlled by the tube radius and are significantly different to the situation in a planar film under the same magnetic field. Our results open perspectives towards tailoring non-equilibrium properties of vortices and their application as tunable superconducting flux generators for fluxon-based information technologies. V. M. Fomin et al., Nano Lett. 12, 1282 (2012) URL PDF *click on pictures to see animation | |
 | Spin selective tunneling through SiGe quantum dotsWhen contacting a quantum dot (QD) with normal metallic leads no spin selective tunnel rates are expected. However, low-temperature magneto-transport measurements through individual SiGe self-assembled QDs have now revealed that this assumption is not always true. Indeed, we have observed that spin-selective tunnel rates through individual QDs can be achieved with normal metallic contacts. The surprising spin selectivity arises from the interplay of the orbital effect of the magnetic field with the strong spin-orbit interaction present in the valence band of the semiconductor. This work was carried out in collaboration with CEA-Grenoble and Yale University. G. Katsaros et al., Phys. Rev. Lett. 107, 246601 (2011) URL PDF | |
Hybrid organic/inorganic molecular heterojunctionsWe combine self-assembly and top-down methods to create hybrid junctions consisting of single organic molecular monolayers sandwiched between metal and/or single-crystalline semiconductor nanomembrane based electrodes. The fabrication process is fully integrative and produces a yield loss of less than 5% on-chip. The nanomembrane-based electrodes guarantee a soft yet robust contact to the molecules where the presence of pinholes and other defects becomes almost irrelevant. We also pioneer the fabrication and characterization of semiconductor/molecule/semiconductor tunneling heterojunctions which exhibit a double transition from direct tunneling to field emission and back to direct tunneling, a phenomenon which has not been reported previously.C. C. Bof Bufon et al., Nano Letters 11, 3727 (2011) URL PDF This work was highlighted in: Nature Materials, 10, 724 (2011) (Sep 23, 2011) URL | ||
The DotFET becomes realityOn May 18, 2001 a patent to speed up Si transistors was filed by Schmidt and Eberl (US 6,498,359), which relies on a SiGe dot positioned below the channel of a Si transistor (see left image). The 3D geometry of the dot provides huge amounts of tensile strain to the Si, which decisively affects the band structure and enhances the mobility of electrons in the channel, and thus the performance of the heart of electronics: The Metal Oxide Semiconductor Field Effect Transistor (MOSFET). In a mutual effort funded by the European Union this concept was eventually brought into reality by a consortium of research groups in Delft, Linz, Jülich, Milano, and Dresden.V. Jovanovic et al., IEEE Electron Device Lett. 31, 1083 (2010) URL PDF | ||
Rolled-up mesoscopic Josephson junctionsJosephson junctions are crucial to many areas of high precision science and technology. However, the fabrication of nanoscale Josephson junctions is still tedious and often requires complex preocessing steps such as electron beam lithography with highest resolution. Here, mesoscopic SNS Josephson junctions are developed simply relying on natural metallic film roughnesses, self-assembly and standard optical lithography. We achieve high critical currents, and an IcRn product placing the characteristic frequency in the THz regime. These properties make them interesting candidates for many applications ranging from quantum metrology over THz radiation sensors to flux-qubits.D. J. Thurmer et al., Nano Letters 10, 3704 (2010) URL PDF | ||
Photovoltaic effect in ultrathin Si nanomembranesUnder local illumination, ultrathin silicon nanomembranes (SiNMs) on insulator reveal a gate-controlled photovoltaic effect and negative transconductance in Schottky transistors applying both homo- and hetero-contacts. Tiny variations of Schottky barriers between source and drain contacts are responsible for the photovoltaic effect (see the image) and can be enhanced by gate voltage and/or contact design. Our results provide a useful method to disclose contact properties of nanomaterials and open alternative ways for novel nano-optoelectronic devices based on the photovoltaic effect.P. Feng et al., Advanced Materials 22, 3667 (2010) URL PDF | ||
 | Quantum transport through SiGe quantum dotsWe have realized single-hole transistors based on self-assembled SiGe quantum dots. Charge transport measurements reveal discrete energy spectra, with the confined hole states displaying anisotropic gyromagnetic factors and strong spin-orbit coupling strength with pronounced gate-voltage and magnetic-field dependence. For strongly coupled devices single-hole supercurrent transistors were realized. Our observations render SiGe quantum dots exciting candidates for the development of spin-based devices and the study of new transport regimes. This work was carried out in collaboration with CEA-Grenoble and CNRS-Grenoble.G. Katsaros et al., Nature Nanotechnology 5, 458 (2010) URL PDF | |
 | Giant persistent photoconductivity in Si nanomembranesThis paper reports the observation of giant persistent photoconductivity from rough Si nanomembranes. When exposed to light, the current in Si nanomembranes is enhanced by roughly 3 orders of magnitude and can persist for days at a high conductive state after the light is switched off. An applied gate voltage can tune the persistent photocurrent and accelerate the response to light. By analyzing the band structure of the devices and the surfaces through various coatings, we attribute the observed effect to the rough surfaces of the nanomembranes, where light activates localised charge carriers.P. Feng et al., Nano Letters 9, 3453 (2009) URL PDF | |
Integrated microtube resistorsIntegrated ohmic devices are fabricated from Si-based microtubes, and linear I-V curves are measured for rolled-up tubes suspended between two electrodes. The combination of tubular geometry, biocompatibility, and good electrical and thermal conductivity render the fabricated devices good candidates for thermoelectric gas sensors or electrically activated micropumps and microfluidic delivery systems.F. Cavallo et al., Applied Physics Letters 93, 143113 (2008) URL PDF | ||
