Nanoscale Manipulation of Pristine and Functionalized Freestanding Graphene Using Scanning Tunneling Microscopy

Over the past ten years the 2D material graphene has attracted an enourmous amount of attention from researchers from across diciplines and all over the world. Many of its outstanding electronic properties are present only when it is not interacting with a substrate but is instead freestanding. In this work I demonstrate that pristine and functionalized freestanding graphene can be imaged using a scanning tunneling microscope (STM) and that imaging a flexible 2D surface is fundamentally different from imaging a bulk material due to the attraction between the STM tip and the sample. This attraction can be used to manipulate the graphene sample on atomic and even nanometer scales. I first show that the electrostatic attraction between the tip and sample during imaging results in enhanced corrugation in the image. Next, I introduce constant-current spectroscopy measurements and demonstrate the ability to perpendicularly displace the graphene sheet at a single point over a range of tens of nanometers. An electrostatic model is then developed which characterizes the electrostatic force that is used to displace the sheet. Finally, STM images and spectroscopy measurements, along with electron microscope images and molecular dynamics simulations, are used to characterize freestanding graphene sheets functionalized with platinum nanoparticles. It is shown that the platinum particles are self-organized but are not encapsulated by the graphene. Instead the nanoparticles are anchored to the sheet by a small number of covalent bonds. In the future the techniques shown here could be used to characterize other functionalized graphene systems