Abstract
The use of atomically thin graphene for molecular sensing has attracted tremendous attention over the years and, in some instances, could displace the use of classical thin films. For nanopore sensing, graphene must be suspended over an aperture so that a single pore can be formed in the free-standing region. Nanopores are typically drilled using an electron beam (e-beam) which is tightly focused until a desired pore size is obtained. E-beam sculpting of graphene however is not just dependent on the ability to displace atoms but also the ability to hinder the migration of ad-atoms on the surface of graphene. Using relatively lower e-beam fluxes from a thermionic electron source, the C-atom knockout rate seems to be comparable to the rate of carbon ad-atom attraction and accumulation at the e-beam/graphene interface (i.e., Rknockout ≈ Raccumulation). Working at this unique regime has allowed the study of carbon ad-atom migration as well as the influence of various substrate materials on e-beam sculpting of graphene. We also show that this information was pivotal to fabricating functional graphene nanopores for studying DNA with increased spatial resolution which is attributed to atomically thin membranes.
Highlights
The guided migration of biological molecules through a pore and their real-time electrical detection is the fundamental premise of most nanopore-based sensors [1,2,3,4,5]
The basic principle of nanopore sensing is that a molecular species will block a certain amount of ions while inside a pore based on physiochemical properties including but not limited to the molecule’s hydrodynamic volume, charge, shape, stability, and orientation [9,10,11,12,13]
We further showed that the amorphous carbon deposited through the electron beam induced deposition (EBID) process could be transformed into graphitic structures at the edge of the pore [27]
Summary
The guided migration of biological molecules through a pore and their real-time electrical detection is the fundamental premise of most nanopore-based sensors [1,2,3,4,5]. An alternative to thinning a local region of a silicon-based membrane is to use graphene which is a 2D material with advantageous mechanical, electrical, and thermal properties [35]. Was drilling possible in graphene using a thermionic source, but nanopores could be shrunk using electron beam induced deposition (EBID) of carbon. Graphene nanopore drilling kinetics are investigated using various support structures to determine if electron beam induced heating plays a role in nanopore formation. Despite focusing the electron beam to a small nanometer-scale point on the graphene membrane, the structure and composition of the support material hundreds of nanometers away are found to still influence the success rate of nanopore fabrication. Owing to the renewed interest in graphene/electron-beam interactions in recent years due to graphene-based DNA sequencing, substrate-dependent drilling in graphene will guide further work in the field of nanopore-based biosensing
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