Tailoring Mechanical Properties of Suspended Graphene by Energetic Ion Beams

In this article, we report a systematic study of the mechanical strength of mono-, bi- and five- layer graphene subjected to controlled defect formation. Suspended graphene nanomechanical devices were fabricated and exposed to 500 keV helium ions and modifications in the mechanical properties have been investigated using AFM nanoindentation. We observed an initial increase in the Young's modulus of irradiated bilayer and five layer graphene compared to their pristine counterpart at an ion fluence of $\mathbf{8}\times \mathbf{10}^{15}\ \mathbf{ions}/\mathbf{cm}^{2}$ and subsequent decrease with further irradiations up to $\mathbf{1.1}\times \mathbf{10}^{17}$ ions/cm 2 , Even after consecutive irradiation of the samples with an increase in ion fluence did not cause any detrimental effects to the mechanical properties. The extraordinary strength of graphene (Young's modulus remains in TPa range) is retained even when exposed at an ion fluence of $\mathbf{1.1}\times \mathbf{10}^{17}\mathbf{ions}/\mathbf{cm}^{2}$, and bubbles were found to form on all the ion exposed samples and remain undamaged for sufficiently long period of time which indicates that the impermeability of graphene is preserved. The stability of suspended graphene along with its superior stiffness under harsh radiation environment opens up possibilities for its use in high frequency resonator and sensor applications.