2D materials investigations for hybrid quantum systems

Hybrid Quantum systems in their structure involve various elements, one of which may be mechanical quantum transducers. Typically they form cantilever or suspended membranes and they are very sensitive to applied forces. In... [ view full abstract ]

Hybrid Quantum systems in their structure involve various elements, one of which may be mechanical quantum transducers. Typically they form cantilever or suspended membranes and they are very sensitive to applied forces. In case of optomechanical interactions it is important for membranes to be semitransparent for light and act both as capacitor and mirror. One of potential candidates which may be used for such application are 2D materials, especially graphene. Using this material it is possible to prepare freestanding layer with dimensions up to tens of micrometers. But development of such ultrathin devices is still demanding. Thus appropriate characterization methods are needed. One of them are scanning probe microscopy. Using atomic force microscopy (and related techniques; AFM) it is possible to estimate membrane mechanical properties like stiffness and bending or electrical properties like work function and conductivity. Additionally, with scanning tunneling microscopy (STM) it is possible to observe electromechanical coupling between scanning tip and membrane.

In this work we present the results of the electromechanical studies of graphene membranes using scanning probe microscopy. Graphene was grown using chemical vapor deposition and poly(methyl methacrylate)-transferred onto predefined cavities. Typical size of obtained membranes was 2 up to 10 µm. Membranes morphology as well as their work function (4.70 eV typically) was estimated by the use of Kelvin probe force microscopy. This work function was changing approximately of 50 meV in dependence of the membrane bulge. Additionally, it was observed potential drop on suspended graphene in comparison with supported one. These data were correlated with conductivity dips recorded using conductive AFM and Raman spectroscopy. In parallel membrane stiffness was estimated. STM tip–graphene membrane coupling was also probed – 4 µm diameter membrane dip up to 120 nm per volt of sample bias. Based on obtained measurement data forces acting between STM/AFM probes and graphene membranes were modelled.