Graphene and related 2D materials are anticipated to become the compounds of the century. It is not surprising - graphene is extremely thin and strong, as well as possesses outstanding electrical and thermal characteristics. However, the stumbling block is that many unique properties and capabilities are related to only perfect graphene with controlled number of defects. A convenient procedure to visualize defects on graphene layers by mapping the surface of carbon materials with an appropriate contrast agent was introduced by a team of researchers from Zelinsky Institute of Organic Chemistry of Russian Academy of Sciences (Moscow) involved in international collaborative project. Developed imaging (tomography) procedure has revealed organized patterns of defects on large areas of carbon surfaces. Several types of defects on the carbon surface can be caught and captured on the microscopic image within a few minutes. The article describing the research was published in Chemical Science journal of Royal Society of Chemistry.
The impact of material with such unique properties may be really impressive. Scientists foresight the imminent appearance of novel biomedical applications, new generation of smart materials, highly efficient light conversion and photocatalysis reinforced by graphene.
The main problem in finding defects on graphene surface is that defects may vary in sizes and shapes. The process of scanning of large areas of graphene sheets in order to find out defect locations and to estimate the quality of the material is a time-consuming task. Let alone a lack of simple direct methods to capture and visualize defects on the carbon surface.
Scientists from IOC RAS suggested using specific contrast agent soluble palladium complex that selectively attaches to defect areas on the surface of carbon materials. Pd attachment leads to formation of nanopartilces, which can be easily detected using a routine electron microscope.
"The compound marker is the key to successful creation of a contrast agent", - Valentine Ananikov said. The ideal contrast agent must possess two key properties. Firstly, it has to attach to the investigated surface without altering the image of existing defects. In other words, the reagent itself should not affect the structure of the material. Secondly, the marker must selectively choose only those areas of the surface of the carbon material that contain defects.
"Soluble palladium complex (Pd2dba3) meets these parameters and shows good results in the visualization of defects. In addition, the complex is a well-known and widely available", - the scientist said.
The stronger the defect - the stronger the binding of carbon with particles of reagent and the faster is the imaging. The developed method allows to create a 3D map of the graphene layers, pointing out all the damages. It is important that defect are characterized not only in terms of disorders of geometrical parameters, but also in terms reactivity variation. Thus, this approach helps to visualize the chemical reactivity of the material.
The majority of industries require perfectly smooth surface. Due to electrical conductivity and transparency to light, graphene is viewed as the base for a new type of electrodes for solar cells, LCD screens and other electronic devices. But in some cases defects may be an advantage.
"Chemical applications, catalysis and creation of graphene sensor systems require some types of defects.
Defective areas are the ones where the most interesting chemical reactions occur. In some cases, defects are specifically created in the area", - Ananikov said.
As revealed in the study, more than 2000 reactive centers can be located per 1 μm2 of the surface area of regular carbon material. Mapping of surface defect density showed substantial gradients and variations across the surface area, which can possess a kind of organized structures of defects.
The researchers learned to recognize damages on graphene surfaces,
"Now when we can get information about the types and locations of defects, the next step is the study of their behavior -
Valentine Ananikov said. It is expected that some defects are dynamic, meaning they are not localized in one place, and can migrate over the surface of the graphene. If we will be able to manage the migration, we will get an opportunity to form an ideal surface. This is the main goals of our research in the nearest future".