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Graphene: What is it? What are some of its applications?

Posted by MSE Supplies Admin on

What is Graphene?

Graphene is a form of carbon material that is made up of carbon atoms which form a single layer of aromatic rings (see Figure 1).[i]  Other types of carbon include graphite, coal, carbon nanotubes, fullerenes, and diamond.

 

Figure 1. Graphene (atomic scale), hexagonal lattice of carbon atoms.

Graphene is not a metal but it conducts electricity very well. This is because carbon has four electrons that are easily available for bonding and only three are being used in the two dimensional sheet of graphene to bond to other carbon atoms leaving one “free” electron.  This “free” electron sits above the plane of the graphene sheet in the carbons’ p-orbital. These p-orbitals create a conductive layer for the graphene sheet. 

What are some electrical properties of Graphene?

The electrical conductivity of graphene is one of its most important properties. At room temperature, the charge carrier concentration is 1013 cm-2 with an electron mobility of 1x104 cm2V-1s-1. The material does not have an electrical band gap because the valence and conduction bands overlap. Since graphene acts like Dirac Fermion quasi-particles, it also exhibits a half integer Quantum Hall Effect (QHE). The relationship of the density, charge, and velocity of the charge carriers defines the QHE. This happens when a magnetic field is applied perpendicular to the plane of the conducting material. Under these conditions, the carrier path becomes curved leading to the partial polarization of the material.  

Why is the thermal conductivity of Graphene so varied?

Graphene has an extremely high thermal conductivity for a single layer of the material of 3000-5000 W m-1K-1 due to the holes in the structure that allow the phonons to pass through unobstructed.  The thermal conductivity drops significantly because of phonon scatter when on another substrate and can be as low as 600 W m-1K-1. But this is still twice that of coppers thermal conductivity.  The thermal conductivity for in plane single layer is high however, because of weak van der Waals forces the inter-plane thermal conductivity between sheets can be as low as 6 W m-1K-1

Is Graphene a strong material?

Graphene is one of the strongest materials ever made.  In relation to its thickness, it is about 100 times stronger than the strongest steel. Its density is dramatically lower than any steel, with a surface mass of 0.763 mg per square meter.  In their Noble prize announcement for physics in 2010, Geim and Novoselov illustrated this by saying that a 1 square meter graphene hammock would support a 4 kg cat but would weigh only as much as one of the cat's whiskers. A single layer of graphene has an intrinsic tensile strength of 130 GPa with a Youngs modulus near 1 TPa but the material is brittle in nature. 

Is Graphene Hydrophilic or Hydrophobic?

It has been a widely held belief that graphene is hydrophobic because graphite is hydrophobic. This belief was challenged when researchers at the National Physics Laboratory in UK found that the hydrophobic nature of the material is highly thickness dependent, with monolayer graphene being hydrophilic.[ii]  Materials scientist in the Netherlands furthered this study by measuring the contact angle of water on the graphene and several other materials. They found that with water the graphene surface was smooth and clean meaning the graphene material was indeed hydrophilic.[iii]  This finding will have major impacts on the use of graphene in water-based applications. It is worth mentioning that graphene oxide is more commonly used in water dispersions. 

Forms of Graphene.

There are many forms of graphene and MSE Supplies offers some of them.  Graphene is truly only one atomic layer thick, otherwise known as monolayer graphene. If you oxidize the graphene monolayer, you will form graphene oxide (GO).  The GO monolayer is characterized by having oxygen or hydroxyl groups on the surface of the sheet. One can further chemically process the GO to produce reduced GO or functionalize the surface chemistry to suite your specific needs.

What Monolayer Graphene does MSE Supplies offer?

MSE Supplies offers chemical vapor deposition monolayer graphene on a wide variety of substrates. The substrate materials range from quartz, copper foil, Silicon, and PET films.  Additionally, MSE Supplies has some Bilayer Graphene and Trilayer Graphene.  MSE Supplies also offers the service of putting monolayer graphene on your custom substrates, please email us at sales@msesupplies.com for more information on this process.  

What Graphene Oxide products does MSE Supplies offer?

MSE Supplies offers Graphene Oxide in two different forms. The graphene oxide powders we have are monolayer graphene oxide, an amine functionalized graphene oxide, and a reduced graphene oxide. MSE Supplies offers several different concentrations of monolayer graphene oxide water dispersions. We have concentrations of 0.5 to 25 mg/ml in volumes of 250 ml to 10L. 

 

 

 What Multilayer Graphene does MSE Supplies offer?

MSE Supplies has multilayer graphene for several different uses. We have a hydroxyl and carboxyl functionalized multilayer graphene powder for the reinforcement of polymers and fibers. This powder will enhance the mechanical strength of polymers and fiber glass. MSE Supplies has an anti-corrosion multilayer graphene powder.  This powder when mixed with zinc oxide and used in the powder coating process can improve the powder coating by helping adhesion and the wear resistance of the coating layer.  In addition, MSE Supplies offers multilayer graphene powder for electrical and thermal conduction.  It is highly reduced (C ≥98 wt%) which delivers a super conductivity of ≥8000 S/m. It has a lower percolation threshold value than that of conductive carbon black. 

 

What Graphene Field-Effect Transistors (GFET) does MSE Supplies offer?

MSE Supplies offers Graphene Field-Effect Transistors (GFET).  The GFETs offered are state of the art and composed of a graphene channel between two electrodes with a gate contact to modulate the electronic response of the channel. The graphene is exposed to enable functionalization of the channel surface and binding of receptor molecules to the channel surface. The surface of the GFET channel is functionalized by binding receptor molecules for the specific target of interest.  GFET sensors utilizing a 2D channel material have several advantages over bulk semiconductor devices (including silicon). With a GFET, the graphene channel is only one atom thick, meaning the entire channel is effectively on the surface and directly exposed to the environment. Any molecule attached to the surface of the channel impacts electronic transfer through the entire depth of the device. Near atomically thin silicon or other bulk semiconductors are not effective because at such a thickness, surface defects dominate the material characteristics. Two-dimensional materials, such as graphene, do not have surface dangling bonds to form defects.  MSE Supplies offers two different GFET devices on that is unencapsulated and ready for your functionalization.  It has 36 individual GFETs per chip. The other, has the contacts fully encapsulated and ready to use in a liquid environment. It has 12 individual GFETs per chip.

MSE Supplies, LLC (https://www.msesupplies.com/) is a major supplier of graphene materials. We offer monolayer graphene film on a wide variety of substrates, monolayer graphene oxide in water dispersions, and we also offer monolayer graphene film on your custom substrates.  Please visit our online store to purchase our graphene products through this linkGraphene and Graphene Oxide

 

[] Picture taken from Wikipedia https://en.wikipedia.org/wiki/Graphene

[ii] Martin Munz, Cristina E. Giusca, Rachael L. Myers-Ward, D. Kurt Gaskill, and Olga Kazakova ACS Nano 2015 9 (8), 8401-8411 DOI: 10.1021/acsnano.5b03220

[iii] Belyaeva, L. A., van Deursen, P. M. G., Barbetsea, K. I., Schneider, G. F., Adv. Mater. 2018, 30, 1703274. https://doi.org/10.1002/adma.201703274


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