Martin J. Süess

Stretchable heterogeneous composites with extreme mechanical gradients

Heterogeneous composite materials with variable local stiffness are widespread in nature, but are far less explored in engineering structural applications. The development of heterogeneous synthetic composites with locally tuned elastic properties would allow us to extend the lifetime of functional devices with mechanically incompatible interfaces, and to create new enabling materials for applications ranging from flexible electronics to regenerative medicine. Here we show that heterogeneous composites with local elastic moduli tunable over five orders of magnitude can be prepared through the site-specific reinforcement of an entangled elastomeric matrix at progressively larger length scales. Using such a hierarchical reinforcement approach, we designed and produced composites exhibiting regions with extreme soft-to-hard transitions, while still being reversibly stretchable up to 350%. The implementation of the proposed methodology in a mechanically challenging application is illustrated here with the development of locally stiff and globally stretchable substrates for flexible electronics.

Top-down fabricated silicon nanowires under tensile elastic strain up to 4.5%

Strained Si nanowires are among the most promising transistor structures for implementation in very large-scale integration due to of their superior electrostatic control and enhanced transport properties. Realizing even higher strain levels within such nanowires are thus one of the current challenges in microelectronics. Here we achieve 4.5% of elastic strain (7.6 GPa uniaxial tensile stress) in 30 nm wide Si nanowires, which considerably exceeds the limit that can be obtained using SiGe-based virtual substrates. Our approach is based on strain accumulation mechanisms in suspended dumbbell-shaped bridges patterned on strained Si-on-insulator, and is compatible with complementary metal oxide semiconductor fabrication. Potentially, this method can be applied to any tensile prestrained layer, provided the layer can be released from the substrate, enabling the fabrication of a variety of strained semiconductors with unique properties for applications in nanoelectronics, photonics and photovoltaics. This method also opens up opportunities for research on strained materials.

Template-free co-assembly of preformed Au and TiO2 nanoparticles into multicomponent 3D aerogels

The self-assembly properties of titania nanoparticles, which are strong enough to bridge several lengths scales, make it possible to use them as building blocks for aerogels. Controlled by their surface functionalization, the nanoparticles undergo an oriented attachment process during gelation, building up a 3-dimensional macroporous network. The presence of other nanoparticles in the initial reaction mixture results in the formation of multicomponent aerogels, offering a flexible tool to vary the composition of the gels and thus the chemical properties. Exemplarily this is shown by the co-assembly of titania with gold nanoparticles, leading to a Au–TiO2 composite aerogel with enhanced photocatalytic activity under visible light.

Excess carrier lifetimes in Ge layers on Si

Electron/hole lifetimes in thermally strained Ge layers on Si are deduced from time-resolved infrared pump-probe transmission spectroscopy. A doping scheme with n-doped Ge on intrinsic Ge yields maximum lifetimes of approximately 3 ns.

Assembly of BaTiO3 nanocrystals into macroscopic aerogel monoliths with high surface area.

Aerogels with their low density and high surface area are fascinating materials. However, their advantageous morphology is still far from being fully exploited owing to their limited compositional variety and low crystallinity. Replacing the sol-gel process by a particle-based assembly route is a powerful alternative to expand the accessible functionalities of aerogels. A strategy is presented for the controlled destabilization of concentrated dispersions of BaTiO3 nanoparticles, resulting in the assembly of the fully crystalline building blocks into cylindrically shaped monolithic gels, thereby combining the inherent properties of ternary oxides with the highly porous microstructure of aerogels. The obtained aerogels showed an unprecedentedly high surface area of over 300 m(2)  g(-1).

Dispersion engineering of Quantum Cascade Lasers frequency combs

Quantum cascade lasers are compact sources capable of generating frequency combs. Yet key characteristics - such as optical bandwidth and power-per-mode distribution - have to be improved for better addressing spectroscopy applications. Group delay dispersion plays an important role in the comb formation. In this work, we demonstrate that a dispersion compensation scheme based on a Gires-Tournois Interferometer integrated into the QCL-comb dramatically improves the comb operation regime, preventing the formation of high-phase noise regimes previously observed. The continuous-wave output power of these combs is typically

Anatase–silica composite aerogels: a nanoparticle-based approach

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Microwave-assisted nonaqueous synthesis of WO3 nanoparticles for crystallographically oriented photoanodes for water splitting

100 mW with optical spectra centered at 1330 cm

Power-dependent Raman analysis of highly strained Si nanobridges.

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On-chip dual-comb based on quantum cascade laser frequency combs

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