Dr. Tobias Vossmeyer
Institut für Physikalische Chemie
tobias.vossmeyer (at) chemie.uni-hamburg.de
Tobias Vossmeyer studied chemistry at the
Philipps-Universität Marburg, Germany, and received his Diploma in
1992. Thereafter, he worked as a Ph.D. student at the Hahn-Meitner
Institute, Berlin, where he investigated the formation of superlattice
assemblies from semiconductor nanoparticles. He received his Ph.D. in
1995 from the Technical University Berlin. After working on the
lithographically controlled deposition of nanoparticle patterns at the
University of California at Los Angeles (UCLA) he started a research
position at Sony’s Stuttgart Technology Center in 1998. Until 2007 he
worked as group leader at Sony’s Materials Science Laboratories where
his work focused on the development of novel nanostructured materials
for applications as chemical sensors. In 2007 he started a faculty
scientist position at the Institut für Physikalische Chemie
(IPhCh) of the University of Hamburg. His current research interests
are functional nanostructured materials and devices, self-assembly,
molecular recognition and design of interfaces, and chemical sensors.
Natalia Olichwer, Elisabeth W. Leib, Annelie H. Halfar, Alexey Petrov and Tobias Vossmeyer:
Cross-Linked Gold Nanoparticles on Polyethylene: Resistive Responses to Tensile Strain and Vapors
In this study coatings of cross-linked gold nanoparticles (AuNPs) on flexible polyethylene (PE) substrates were prepared via layer-by-layer deposition and their application as strain gauges and chemiresistors was investigated. Special emphasis was placed on characterizing the influence of strain on the chemiresistive responses. The coatings were deposited using amine stabilized AuNPs (4 and 9 nm diameter) and 1,9-nonanedithiol (NDT) or pentaerythritol tetrakis(3-mercaptopropionate) (PTM) as cross-linkers. In order to prepare films with homogeneous optical appearance, it was necessary to treat the substrates with oxygen plasma directly before film assembly. SEM images revealed film thicknesses between ~60 and ~90 nm and porous nanoscale morphology. All films showed ohmic IV-characteristics with conductivities ranging from 10-4 to 10‑2 Ohm-1cm-1, depending on the structure of the linker and the nanoparticle size. When up to 3% strain was induced their resistance increased linearly and reversibly (gauge factors: ~20). A comparative SEM investigation indicated that the stress induced formation and extension of nanocracks are important components of the signal transduction mechanism. Further, all films responded with a reversible increase in resistance when dosed with toluene, 4-methyl-2-pentanone, 1-propanol or water vapor (concentrations: 50 - 10 000 ppm). Films deposited onto high density PE substrates showed much faster response-recovery dynamics than films deposited onto low density PE. The chemical selectivity of the coatings was controlled by the chemical nature of the cross-linkers, with the highest sensitivities (~10-5 ppm-1) measured with analytes of matching solubility. The response isotherms of all film/vapor pairs could be fitted using a Langmuir-Henry model suggesting selective and bulk sorption. Under tensile stress (1% strain) all chemiresistors showed a reversible increase in their response amplitudes (~30%), regardless of the analytes’ permittivity. Taking into consideration the thermally activated tunneling model for charge transport, this behavior was assigned to stress induced formation of nanocracks, which enhance the films’ ability to swell in lateral directions during analyte sorption.
ACS App. Mater. Interfaces 2012, 4, 6151 (DOI: 10.1021/am301780b)
Hendrik Schlicke, Jan H. Schröder, Martin Trebbin, Alexey Petrov, Michael Ijeh, Horst Weller, and Tobias Vossmeyer:
Freestanding films of crosslinked gold nanoparticles prepared via layer-by-layer spin-coating
A new, extremely efficient method for the fabrication of films comprised of gold-nanoparticles (GNPs) crosslinked by organic dithiols is presented. The method is based on layer-by-layer spin-coating of both components, GNPs and crosslinker, and enables the deposition of films with several tens of nanometers in thickness within a few minutes. X-ray diffraction and conductance measurements reveal the concentration of the crosslinker solution being critical to adjust properly in order to prevent destabilization and coalescence of particles. UV/vis spectroscopy, atomic force microscopy, and conductivity measurements indicate that films prepared via layer-by-layer spin-coating are of comparable quality as coatings prepared via laborious layer-by-layer self-assembly using immersion baths. Because spin-coated films are not bound chemically to the substrate they can be lifted-off by alkaline underetching and transferred onto 3d-electrodes to produce electrically addressable, freely suspended films. Comparative measurements of sheet resistances indicate that the transfer process does not compromise the film quality.
Tobias Vossmeyer, Carsten Stolte, Michael Ijeh, Andreas Kornowski, Horst Weller:
Flexible polyethylene substrates are coated with networked gold nanoparticles via layer-by-layer deposition. The strain sensitive charge transport combined with the mechanical robustness of the coatings establishes a base for their potential application as resistive strain sensors.