Microscience Microscopy Congress 2021 (mmc2021) will be held as a virtual conference from July 5 to July 9, 2021.

Dr. Vladimir Korolkov, the senior applications scientist at Park Systems UK presents:

• ⏩ WORKSHOP, Tuesday, July 6 at 14:00 pm (BST): “Graphene Under the Tip: Ultra-High Resolution Atomic Force Microscopy Of Chemically Decorated 2D-materials” 
• ⏩POSTER PRESENTATION: “Chemical decoration of graphene and 2D-materials: An AFM Outlook.”

Please see the abstracts below.  

Link: https://www.mmc-series.org.uk/

ABSTRACTS

Graphene Under the Tip: Ultra-High Resolution Atomic Force Microscopy Of Chemically Decorated 2D-materials

This past decade has amassed an ignition of expansive interest into the research and application of graphene and other 2D-materials. With a thickness of just one atom, these materials present a myriad of challenges in: fabrication, handling and characterization. The continued emergence of more complex vertical assemblies of 2D-materials, known as Van-der-Waals heterostructures, also opens new avenues of research as well as creates new challenges for the scientific community. One of these challenges is embedding molecular structures into such 2D-materials; effectively, creating a new class of functionals molecules i.e. hybrid organic-inorganic 2D-materials with self-assembled molecular layers. Given the vast libraries of synthetic organic molecules with various tunable functional properties, this creates endless opportunities for the design of new hybrid materials.

Common 2D materials, as well as their new variations, require robust characterization techniques which can analyze both the structure and properties at the highest level. The investigation technique such as Atomic Force Microscopy (AFM) becomes not just a curiosity, but a need to acquire reliable and accurate data. AFM is a technique that can easily image molecular and atomic structures within different environments, at the highest levels of resolution.

During this workshop, Park Systems will present some examples of imaging graphene/hBN heterostructures in the ambient on Park Systems NX20 large sample AFM. We will begin by focusing on resolving and understanding Moiré patterns on graphene (Fig. 1) and show how one can manipulate them with use of an AFM probe. We will then discuss the challenges and breakthroughs in chemical decoration of graphene. In particular, we will demonstrate the imaging of various molecular structures on graphene down to single molecular levels.

Figure caption: A contact mode AFM image of a Moiré pattern on graphene on a single crystal of hBN, using Park Systems NX20 large sample AFM.

ABSTRACT

Chemical decoration of graphene and 2D-materials: An AFM Outlook

The formation of two-dimensional (2D) supramolecular arrays has been proven as a highly versatile route to the control of the spatial organization, down to the molecular scale, of the chemical functionality of a surface. These molecular networks, which can be formed through self-assembly processes on a variety of different substrates, including semiconductors, metals, insulators and layered materials, are, in almost all cases, limited to surfaces of bulk crystals. Progress towards chemical decoration of graphene and other 2D-materials, that have a thickness of an atom, has been quite limited so far. Likewise, the growth of higher layers on such materials has not even been reported. Although, similar inorganic structures – Van-der-Waals heterostructures – are a very popular research subject. Specifically, the additional functional control, which may be achieved through the formation of heterostructures realized by placing one supramolecular layer on another to result in growth into the third dimension perpendicular to the substrate, has not been widely explored for these materials. Here we describe the successful formation of heterostructures formed by the sequential growth of distinct 1D and 2D arrays on graphene. It is possible, using high-resolution atomic force microscopy (AFM), to determine an epitaxial alignment between successive layers. We chose to investigate a combination of a bicomponent hexagonal network (CAM) formed by cyanuric acid (CA) and melamine (M), and monocomponent honeycomb and linear arrays formed by, respectively, trimesic acid (TMA) and 2,6-Naphthalenedicarboxylic acid (NDA). The heterostructures are formed by first depositing a CAM monolayer that is then used as the substrate for a further deposition cycle whereby monolayers of TMA or NDA are adsorbed to form a heterostructure. The layers are deposited via sequential immersion in solutions, and we have investigated heterostructure formation on the surface of graphene. We use ambient AFM to acquire images of the molecular arrangements in adsorbed networks. This work represents a significant advance in chemical decoration of graphene and the application of AFM to imaging such networks through the acquisition of images, under ambient conditions, with sufficiently high resolution to identify the relative placement of molecules in different layers of the resulting heterostructures.

In the future, we envisage that this approach to chemical decoration of graphene and building supramolecular heterostructures will provide the foundation for the growth of much more complex materials in which multiple layers can be deposited sequentially with the possibilities to tune the chemical, optical and electronic properties of the resulting organic/inorganic heterostructure. The exploitation of hydrogen bonding stabilizes the growth of 2D sheets that have highly parallel interfaces. The use of graphene as a substrate suggests that this approach can be combined with 2D materials to introduce molecular functionality into stacked device architectures, and may also provide a complete molecular analogue approach to the stacking of layered materials.