PORTFOLIO

Electronic devices become every day smaller and more efficient. In this process of circuit miniaturization, engineers are more and more approaching the limits of a «top-down» approach. Fabrication costs increase drastically and problems such as the heat evacuation become more critical to handle in densely-packed circuits.

In the past years, scientists have been following a «bottom-up» approach as an alternative: making use of the self-assembling properties of organic compounds to produce complex hybrid structures (mixing soft organic compounds with hard silicon structures) with interesting electrical properties. If organic materials have nowadays made their way into daily electronic appliances such as electronic displays for instance, the fabrication of building blocks on the basis of a single molecule approach still faces enormous challenges. The major difficulty lies in the proper contacting of individual molecules a few nm long (a few millionth of a mm): conventional micro- and nano-fabrication techniques reach there their limits.

This project proposes to bridge the size mismatch between the top-down and bottom-up routes via metallic and/or semiconducting nanoparticles. Self-assembled arrays of nanoparticles can act as platform for the subsequent insertion of molecular compounds, designed for a specific function [1]. The project aims at exploring the possibilities of such nanoparticle platforms for molecular electronics with possible applications in sensing technologies.

With its support Gebert Rüf Stiftung makes it possible to explore application-oriented developments of a strong interdisciplinary project initiated within the National Center of Competence for Nanoscience. The project brings together two research groups of the University of Basel in nanoelectronics and synthetic organic chemistry with complementary expertise and strong national and international collaborations. The know-how of the research groups combined with the competence network in Nanosciences head by the University of Basel form an ideal context for investigating the impact of this new nanoparticle platform for environmental sensing and possibly biosensing.

We have demonstrated that Au nanoparticles arrays represent, in a simplified description, an electronic breadboard for molecular compounds. The backbone structure is formed by self-assembled nanoparticles transferred to Si/SiO2 surfaces by a «stamping» technique using a patterned polymer mold [1]. In parallel, the synthesis of dedicated molecularlinkers as well as building blocks made from two or a few gold clusters has been pursued [2-5]. Simple linkers in the form of conjugated oligo(phenylene ethynilene) compounds have been tested in two different experimental platforms. We characterized the compounds in a system suited for basic studies of individual molecular junctions [6] and also succeeded in integrating these linkers in a nanoparticle platform [7]. Interesting physics emerges from the response of such nanoparticle arrays to optical excitations and we have investigated these effects as well [8,9]. Recently, we have been able to demonstrate that photoactive as well as redox-active molecular compounds can keep their switching ability after being inserted within our nanoparticle platform [10,11]. This is a major step towards the realization of functional molecular devices. A brief overview of this research is provided in Reference 12.

1. Reversible formation of molecular junctions in 2d nanoparticles arrays, J. Liao et al., Adv. Mat., 18, 2444 (2006)
2. Multidentate thioether ligands coating gold nanoparticles, T. Peterle et al., Chem. Commun., 3438 – 3440 (2008)
3. Gold Nanoparticles Stabilized by Acetylene-Functionalized Multidentate Thioether Ligands: Building Blocks for Nanoparticle Superstructures, T. Peterle et al., Adv. Func. Mat. 19, 3497-3506 (2009)
4. Loops versus Stems: Benzylic Sulfide Oligomers Forming Carpet Type Monolayers, F. Sander et al., J. Phys. Chem. C, 114, 4118–4125 (2010)
5. Oligoaryl Cruciform Structures as Model Compounds for Coordination-Induced Single-Molecule Switches, S. Grunder et al., Mayor, Eur. J. Org. Chem., 833–845 (2010)
6. Molecular Junctions based on aromatic coupling, S. Wu et al., Nature Nanotechnology, 3, 569-574 (2008)
7. Interlinking Au nanoparticles in 2D arrays via conjugated dithiolated molecules, J. Liao et al., New J. Phys., 10, 065019 (2008)
8. Spectroscopy of Molecular Junction Networks Obtained by Place Exchange in 2D Nanoparticle Arrays, L. Bernard et al., J. Phys. Chem. C, 111, 18445-18450 (2007)
9. Surface Plasmon Enhanced Photoconductance of Gold Nanoparticle Arrays with Incorporated Alkane Linkers, M. Mangold et al., Appl. Phys. Lett., 94, 161104 (2009)
10. Light-controlled conductance switching of ordered metal-molecule-metal devices, S. van der Molen et al., Nano Letters, 9, 76-80 (2009)
11. Cyclic conductance switching in networks of redox-active molecular junctions J. Liao et al., Nano Letters, 10 (3), 759–764 (2010)
12. Molecular junctions: from tunneling to function, M. Calame, CHIMIA Int. J. Chem, 64 (6), 391-397 (2010)

Basler Physiker schürfen Nanogold, Chemische Rundschau, 21 Nov. 2006;
Elektrische leitende molekular Netzwerke, Chemie Plus, 12 Oct. 2006;
Ein Baukasten für die molekulare Elektronik, Neu Zürcher Zeitung, 20 Sept. 2006;
Testplatform für Moleküle, Basler Zeitung, 15 Sept. 2006;
Forscher entwickeln Miniaturschalter aus Molekülen, Basler Zeitung online, 30 Sept. 2008;
Ziehbrücke für Elektronen, Chemie.de, 1. Oct. 2008.