# Berlin 2015 – wissenschaftliches Programm

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# DS: Fachverband Dünne Schichten

## DS 8: Application of Thin Films

### DS 8.5: Vortrag

### Montag, 16. März 2015, 19:45–20:00, H 0111

**Tip radius dependence of Young's modulus of 2D materials extracted via nanoindentation** — •Gerard Verbiest, Jan-Felix Moneke, and Christoph Stampfer — JARA-FIT and 2nd Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany

Tow-dimensional (2D) materials are known for their remarkable electronic, optical, and mechanical properties. For example, graphene is only one atomic layer thick, but it is far stronger than steel and has an extremely high Young's Modulus of 1.02 TPa.

The standard way of determining the Young's Modulus of 2D materials is via nanoindentation experiments. In these experiments, a cantilever is used to indent a suspended part of the 2D material. From these measurements, one obtains the force on the 2D material as a function of the indentation depth into the 2D material. These curves strongly depend on the Young's modulus of the material. However, to extract the Young's modulus, one has to resort to an analytical model. Usually, one assumes a point load indenter in the center of the suspended 2D material.

Here we show that this model of a point load indenter in the center is not valid. Using the full nonlinear elasticity theory, we calculated the force vs. indentation depth for various tip radii of the cantilever and various indentation positions. Analyzing these curves with the point load model shows an overestimation of the Young's modulus by more than a factor 4 for a tip radius of 10 nm.