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Atomic Force Microscopy

Graphene and 2D Materials

Bruker AFMs enable advanced property measurements and other 2D materials

With its ability to probe individual graphene flakes, providing nanoscale detail to the atomic level, atomic force microscopy has been part of graphene research since Geim and Novoselov’s Nobel prize winning discovery started the field. The early TappingMode images, acquired with a Bruker MultiMode® AFM at locations pinpointed by an optical survey, unambiguously identified the single graphene layers that had previously been thought to be inaccessible.

The years following this discovery have seen an explosion of graphene research activity, with well over 100 publications using Bruker AFMs. These studies include investigations into the fabrication of graphene and graphene oxide, where consistent product purity and known, low defect density are a key challenge, especially for scalable graphene production. They also address the wide ranging applications envisioned for graphene, from flexible displays and fast electronics to actuators, biosensors, and composites. Researchers at nearly every leading graphene research center are also using our Dimension XRDimension FastScan® and Dimension Icon® systems to drive their research in graphene and other 2D materials.

TappingMode images of NbSe2 (a) and Graphene (b) by the Graphene Nobel Prize recipient, using a Bruker MultiMode. Revealing the existence, layering, and adsorbate-substrate distance of these 2D materials. From K. S. Novoselov, D. Jiang, F. Schedin, T. J. Booth, V. V. Khotkevich, S. V. Morozov, and A. K. Geim, Proceedings of the National Academy of Sciences of the United States of America 102, 10451 (2005). Copyright (2005) National Academy of Sciences, U.S.A.

Advanced Property Measurements

Advanced property measurements have played a key role in the exciting AFM discoveries in graphene research. This research includes quantitative mechanical property mapping with Bruker’s exclusive PeakForce QNM® as utilized by Chu et al (J. Procedia Eng 36, 571 (2012) for unraveling graphene layering and by Lazar et al (J. ACS Nano ASAP 2013) for quantifying the graphene metal interactions controlling the electrode bonding in electrical device applications. Other examples are the nanoscale conductivity investigations on composites (Bhaskar et al., J. Power Sources 216, 169, 2012) and functionalized graphene (Felten et al., Small 9 (4), 631, 2013), as well as KPFM investigations clarifying the charge percolation pathway in optimized graphene oxide – organic hybrid FET devices (Liscio et al., J. Materials Chem 21, 2924, 2011).

PeakForce QNM modulus images of graphene on hexagonal boron nitride, revealing a transition to a commensurate lattice upon alignment with highly localized strain relief.

Capabilities to Advance Future Research

The latest Bruker technology promises more exciting advances yet to come. PeakForce KPFM™ may permit extending the hybrid device investigations to higher spatial resolution, more quantitative measurements, and correlation with local material variations that could be revealed in simultaneous mechanical property mapping. Future conductivity studies may benefit from the proven ability of PeakForce TUNA™ to provide the highest spatial resolution on the most mechanically fragile samples. The investigation of defects in the 2D material graphene might be enriched by further PeakForce QNM studies, as this mode has been shown on 3D crystals to open the door to property mapping with atomic defect resolution.

This current map produced in TUNA mode on HOPG demonstrates “lattice resolution” with spacing of 0.25nm.