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Graphene Research and the Evolution of 2D Nano Materials: A Revolutionary Advancement in Science

byZEISS Microscopy 20 November 2024 5 min read

Introduction

Graphene – an isolated one-atom-thick layered form of graphite – is a hot topic in materials science. Due to its strength, flexibility, and conductivity, graphene is a fascinating material that has captured the attention of scientists around the world. This two-dimensional material is composed of a single layer of carbon atoms arranged in a honeycomb lattice. Its unique electronic, mechanical, and thermal properties make it a promising material for a wide range of applications, from flexible electronics and transparent conductive films to advanced composite materials and energy storage solutions.

Over the years, researchers have used a variety of techniques to study graphene. Microscopes have played a crucial role in the understanding and advancement of graphene research, allowing scientists to visualize and manipulate individual atoms and molecules. The use of microscopes has also led to the discovery of new properties and behaviors of graphene that were previously unknown. With continued research and development, graphene has the potential to revolutionize various fields, including electronics, energy, nanotechnology, and medicine.

Back to the Roots – Graphene Research in Manchester

This year, we commemorate the 20th anniversary of the first-ever image of graphene, a pivotal moment in materials science. Captured using a ZEISS field emission scanning electron microscope (FE-SEM) with Gemini electron optics, this groundbreaking image was published by the researchers Andre Geim and Konstantin Novoselov. They discovered graphene at the University of Manchester in 2004. In 2010, they were awarded the Nobel Prize in Physics for their pioneering work on graphene.

Science Paper: Electric Field Effect in Atomically Thin Carbon Films

Exfoliation of single-layer graphene by Andre Geim — Creative Commons
A lump of graphite, a graphene transistor, and a tape dispenser, a tool that was used for the exfolitation of single-layer graphene from graphite in 2004. Donated to the Nobel Museum in Stockholm by Andre Geim and Konstantin Novoselov in 2010.

This seminal achievement not only unveiled the remarkable properties of graphene but also catalyzed the emergence of a new field dedicated to 2D materials. The impact of this discovery has been profound, giving rise to a multi-billion-dollar industry that continues to push the boundaries of technology and innovation.

Today, Professor Sarah Haigh is a leading electron microscopist in the Faculty of Engineering and Physical Sciences at the University of Manchester, UK. She and her team explore various new types of nanomaterials for electronic and chemical applications. They are using electron microscopy to interrogate the atomic structure and elemental distribution of materials at the nanoscale.

My research directly allows us to see and visualize what’s happening inside the materials. And in that way, we can learn what influences performance and make the materials better.

Sarah Haigh The University of Manchester

Haigh’s work in advanced electron microscopy techniques, including new imaging methods for investigating the atomic structure of two-dimensional materials, has significantly impacted the discovery of new nanomaterials. Her research has a broad range of applications, including next-generation electronic hardware, adopted by scientists worldwide.

The properties of materials depend critically on their atomic structures and their chemistry. And to improve these properties, we need to understand the structure-property relationships.

Sarah Haigh The University of Manchester

The role of Scanning Electron Microscopy in Graphene Research

Scanning Electron Microscopy (SEM) plays a pivotal role in the microscopic analysis of graphene. The SEM allows scientists to visualize surfaces that are only one atom thick by detecting electrons emitted from the material's surface. This is possible because graphene, being an excellent conductor, alters the behavior of electrons at its surface, enhancing the contrast in SEM images.

By visualizing graphene, high-powered microscopes like the SEM have helped improve the quality of graphene electronics. For instance, during the early stages of graphene research, SEM revealed undesirable "blobby features", which correlated with poorer performance of electronic circuits. By slicing these features and examining them in cross-section, it was discovered that they were trapped bubbles of contaminants, such as polymer residues used in transferring graphene onto silicon oxide wafers. Identifying and removing such contaminants is essential for enhancing the performance of graphene in electronic devices.

Nature Materials Paper: Cross-sectional imaging of individual layers and buried interfaces of graphene-based heterostructures and superlattices

We are investigating with lots of different characterization methods, but together with optical microscopy, SEM really is an absolutely essential tool as part of the new materials discovery process.

Sarah Haigh The University of Manchester

Insights into Graphene

Images acquired with ZEISS scanning electron microscopy

Graphite in pencils

Mechanically exfoliated graphite flakes and electrical devices

The University of Manchester | Graphene on TEM grid — Image credit: Nick Clark

Graphene on transmission electron microscopy (TEM) grid

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Prof. Haigh speaks about how her research can benefit the public.

The Future of Graphene

The application of graphene in various industries is already underway. Its physical properties, such as strength, lightness, and stiffness, make it ideal for sports equipment and automotive applications. In Formula One, for example, graphene is used to improve the properties of rubber in tires, enhancing durability and grip.

However, graphene’s electronic properties, which are exceptionally unusual and promising, have perhaps even greater potential for transformative applications. Graphene is an ideal conductor of heat and electricity which has the potential to revolutionize electronics by enabling the development of low-power devices, reducing the need for large batteries, and facilitating solar-powered technologies. Graphene-based electronic circuitry could lead to significant breakthroughs in increasing the speed, reducing weight of electronic devices, and could even enable electronics that are fully, flexible, wearable and transparent.

One of the challenges hindering the widespread adoption of graphene in industrial applications is the lack of standardization in its characterization. Haigh and her team are collaborating with institutions like the National Physical Laboratory in the UK to address this issue. Standardization will ensure consistent quality and performance of graphene across different applications, much like how the food industry differentiates between types of fats – saturated and unsaturated – rather than just their quantity.

Although two suppliers may produce graphene materials the quality can be very different. SEM is able to identify difference between batches or sources of graphene which can be used to optimize behaviour in applications or for understanding what features of a material can give certain beneficial properties or effects.

Sarah Haigh The University of Manchester

In conclusion, the microscopic analysis of graphene using techniques like SEM is essential for advancing our understanding and utilization of this remarkable material. As research progresses, we can expect further innovations and applications of graphene, particularly in the realm of electronics, leading to a future where its full potential is realized.

Listen to the latest Science Podcast with Prof. Haigh as she discusses the discovery of graphene and the development of its sister materials.

It has a combination of exceptional properties that are not found in any other material and differ significantly from those of bulk graphite. These include:

Electrical Conductivity: Graphene conducts electricity better than any other known material.
Strength: It is incredibly strong, approximately 200 times stronger than steel.
Flexibility: Despite its strength, graphene is extremely flexible.
Transparency: It is almost entirely transparent, absorbing only about 2.3% of light
Scanning Electron Microscopy (SEM) plays a pivotal role in graphene research by providing several essential capabilities:

Morphology Analysis: SEM allows researchers to examine the morphology of graphene on a surface with high resolution. This is crucial for identifying defects, wrinkles, and grain boundaries that can significantly affect the properties of graphene.
Flake Size Analysis: SEM allows researchers to examine the lateral size of graphene sheets. This is essential as small diameter sheets may work better for some applications like batteries, while larger sheets may be better for other applications such as for strengthening composites for sports equipment.
Layer Thickness Determination: While SEM is not as effective as Transmission Electron Microscopy (TEM) in resolving atomic-level details, it can still provide valuable information about the thickness of graphene layers. By analyzing the contrast produced by secondary electrons, researchers can distinguish surface steps and the difference between single-layer and few-layer graphene.
Stacking sequence differentiation: While it is often assumed that TEM is required for detailed information on atomic stacking, the contrast of an SEM image can also suggest the presence of two different stacking orders due to channeling contrast.
Large Area Imaging: SEM allows rapid scanning of much larger areas of graphene samples than is possible with TEM or atomic force microscopy. This capability is essential for quality control in graphene production, enabling rapid assessment of the uniformity and integrity of the graphene over extended regions.
Elemental Composition: Coupled with Energy Dispersive X-ray Spectroscopy (EDS or EDX), SEM can provide elemental analysis of graphene and its substrates. This is important for identifying contaminants or verifying the presence of specific elements that may have been introduced during the fabrication process.
Ease of Sample Preparation: SEM requires relatively straightforward sample preparation compared to other microscopy techniques like TEM. This makes it a more accessible and faster option for routine inspections and preliminary studies.

In summary, SEM is a valuable tool in graphene research, offering insights into surface morphology, layer thickness, large-area imaging, and elemental composition. These capabilities make SEM indispensable for both fundamental research and industrial applications of graphene.
SEM is crucial for characterizing the structural and electronic properties of graphene, yet it presents several hurdles:

Sample Preparation: Preparing graphene samples for SEM examination is more routine than for TEM, as special substrates are typically not required as long as the graphene is close to the surface. Most challenging is often the need to minimize contamination, as even a nanometer thick layer of hydrocarbon contamination can create a stronger signal than a single atomic layer of graphene.
Contrast Issues: Graphene's extreme thinness also leads to low contrast in electron microscopes, making it difficult to distinguish graphene layers from the substrate or differentiating single-layer graphene from few-layer graphene. The contrast can also vary depending on the substrate and local electronic conductivity, which can make interpretation of SEM images challenging
Damage from Electron Beam: The low accelerating voltage of the SEM generally means it does not introduce holes or large defects in the graphene, as can happen for TEM imaging. Despite this, care must be taken, as for the most challenging electrical components imaging with the SEM electron beam has the potential to change the behavior of the graphene.

These challenges necessitate ongoing advancements in microscopy techniques to allow researchers to investigate and manipulate graphene accurately and efficiently.