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J Genser, M. Bartmann, V Ritter, D Nazzari, O. Bethge, E. Bertagnolli, A. Lugstein:
"Ultra-High Strain of Freestanding 2D Materials";
Vortrag: MRS Boston, Boston; 01.12.2019 - 06.12.2019.

Due to the ever-growing need of small-scale and high-performance semiconductor devices, two-dimensional (2D) materials have emerged as promising candidates for future device integration. Due to their exceptional mechanical properties, strain engineering is effectively used to exploit induced mechanical strain in order to tune the carrier mobility and optoelectronic properties of 2D materials. Although strain in 2D materials has been well studied in recent years, most straining methods rely on stretchable substrates to introduce strain and are thus limited to rather low strain values. Here, we present a novel straining approach enabling the application of ultra-high uniaxial strain on freestanding 2D materials and 2D heterostructures, while simultaneously allowing in-situ electrical and optical characterization.

The micromechanical straining devices patterned from SOI wafers enables ultra-high strain levels up to 15%. Mono and few layer 2D materials are transferred onto the straining device using state of the art mechanical exfoliation and dry viscoelastic stamping techniques minimizing unintentional contaminants. To enable reliable electrical contacts and to avoid slipping of the 2D materials they are pinned down by extended Ti/Au contacts. The applied strain was investigated by in-situ Raman measurements in a back-scattering geometry using a confocal μ-Raman setup. The Raman-active modes of graphene, hBN and MoS2 are very sensitive to strain-induced shifts and are clearly observable during the experiments, thus proving the viability of this approach.