22. Marsden, A. J. et al. Electrical percolation in graphene–polymer composites. 2D Mater. 5, 032003 (2018).
21. He, D., …, Marsden, A. J., Bissett, M. A. Reduced graphene oxide/Fe-phthalocyanine nanosphere cathodes for lithium-ion batteries. J. Mater. Sci. (2018).
Our growing dependence on transportable energy drives battery technology. Batteries must be cheap, light, kind to the environment, and powerful. Materials science is racing to satisfy these requirements. Organic materials—carbon-based compounds—are promising candidates but their performance is inadequate. In this paper we build porous nanoparticles from organic molecules called phthalocyanines. We then attach these particles to sheets of graphene to form an electrode in a battery. When testing these materials, we found improvements in their stability over other organic-based electrodes.
20. Wood, G. E., Laker, Z. P. L., Marsden, A. J., Bell, G. R. & Wilson, N. R. In situ gas analysis during the growth of hexagonal boron nitride from ammonia borane. Mater. Res. Express 4, 115905 (2017).
Growing 2D materials using chemical vapour deposition (CVD) is a promising routes for their large-scale production. Hexagonal boron nitride (hBN) can be grown using precursors that contain boron and nitrogen. The most popular of these precursors is ammonia borane. This is a solid powder which we heat during the growth, releasing chemical species into the chamber. It is these species that combine to grow into hBN. The chemical species released from ammonia borane have a crucial impact on the result of the growth. In this paper we analyse the gas inside the CVD chamber using mass spectrometry, while hBN is growing. This helps us understand what is the most optimal temperature to heat the ammonia borane. We found that lower temperatures release smaller molecules, and these are better at growing larger, higher quality hBN.
19. Laker, Z.P.L., Marsden, A.J. et al. Monolayer-to-thin-film transition in supramolecular assemblies: The role of topological protection Nanoscale 33, 11959-11968 (2017).
Bottom-up synthesis involves forming larger structures from small components, and is extensively used in many forms of nanotechnology. The larger structures can be flat – or two dimensional – when the components lie next to each other in a certain arrangement on a substrate, and they can also be three dimensional. For some of these structures, the assembly will start as a 2D flat structure that will then build into a larger 3D version. Studying this transition from 2D to 3D presents a challenge, as the experimental techniques that allow us to look at the 2D structure are not as easily applied to the 3D structures. In this paper, we use transmission electron microscopy (TEM) to look at how molecules assemble on graphene. The graphene acts like a “transparent” substrate in TEM, so that we can study the structure as they grow in thickness. We found that molecules that were chemically similar formed distinctive 3D structures. This could provide some insight into how molecules can be chosen specifically to form a required 3D structure.
18. Bissett, M. A., Hattle, A. G., Marsden, A. J., Kinloch, I. A. & Dryfe, R. A. W. Enhanced Photoluminescence of Solution-Exfoliated Transition Metal Dichalcogenides by Laser Etching. ACS Omega 2, 738–745 (2017).
Producing high-quality 2D materials in large quantities remains a significant challenge. In one method, called solution exfoliation, ultrasound is used to separate larger chunks of material into thin sheets. But the thin sheets are not thin enough for many applications. In this paper, we demonstrate a way to thin the flakes that are produced through solution exfoliation. The large flakes are deposited onto a surface, and then a laser is passed over them. The upper layers are removed by the heat of the laser, but the bottom layers that are in contact with the surface can dissipate the heat, and remain intact. This method can have a high throughput and so could be a promising route to reducing the thickness of flakes of 2D materials.
17. Wilson, N. R., …Marsden, A. J. et al. Determination of band offsets, hybridization, and exciton binding in 2D semiconductor heterostructures. Sci. Adv. 3, e1601832 (2017).
Understanding the electronic properties of 2D materials is essential if they are to be used in the next generation of electronic devices. In this paper, we show how the technique of angle-resolved photoemission can be used to study the electronic properties of small sheets of 2D materials. In particular, it is possible to see how two different 2D materials interact when stacked on top of each other. This gives crucial insight into how the materials could be combined in future devices. A full write of these results is available in this post.
16. Bosch-Navarro, C., Laker, Z. P. L., Marsden, A. J., Wilson, N. R. & Rourke, J. P. Non-covalent functionalization of graphene with a hydrophilic self-limiting monolayer for macro-molecule immobilization. FlatChem Chem. Flat Mater. 1, 52–56 (2016).
Graphene’s surface is extremely inert, and this makes it unsuitable for some applications. Here we have attached pyrene molecules to the graphene surface that can charge the layer depending on what group is stuck on the side of the pyrene molecule. Pyrene has a hexagonal lattice like graphene’s, and this means the pyrene would like to stack on the graphene surface, without having to modify the graphene surface. We used this to attach biomolecules to graphene, and this could be used more generally for catalysis and sensors.
15. Marsden, A. J. et al. Growth of Large Crystalline Grains of Vanadyl-Phthalocyanine without Epitaxy on Graphene. Adv. Func. Mater. 26, 1188–1196 (2016).
Graphene provides an interesting substrate for the growth of organic semiconducting crystals because it is technologically relevant and weakly interacting. In this paper we show how graphene promotes the growth of large, single-crystals of vanadyl-phthalocyanine without relying on epitaxy. This shows how graphene could be used to apply further improvements to organic semiconducting technology. A more detailed explanation of the results can be found here.
14. Grigg, A. T., Marsden, A. J. et al. Vitrification of β-tricalcium phosphate in sodium aluminoborophosphate glass and the effect of Ga3+ substitution. J. Solid State Chem. 231, 175-184 (2015).
13. Marsden, A. J. et al. Effect of oxygen and nitrogen functionalization on the physical and electronic structure of graphene. Nano Res. 8, 2620–2635 (2015).
Although pristine graphene has displayed many interesting properties, changing graphene to find new properties is also attracting a lot of attention. One way to do this is to attach atoms of elements other than carbon to the graphene sheet and observe how the properties change. In this paper, we attached oxygen and nitrogen to graphene and measured the physical, chemical, and electronic changes. One highlight of these results is that only a few atoms on the surface (about 5%) are sufficient to severely disrupt the electronic quality of the graphene. This means that attaching elements like this to change the electronic properties of graphene should be approached with caution.
12. Bosch-Navarro, C. … Marsden, A. J. et al. Covalently Binding Atomically Designed Au 9 Clusters to Chemically Modified Graphene. Angew. Chemie Int. Ed. 54, 9560–9563 (2015).
Graphene has an extremely large surface area because it is only one atom thick. This large surface area makes it a promising candidate for applications like catalysis or sensors. But these applications often require other structures attached to the graphene to perform their function. In this paper, we demonstrated how 9-gold-atom clusters could be strongly attached to a sheet of chemically modified graphene. From these results there is a lot of scope to design and attach specific clusters for a variety of applications.
11. Turyanska, L. … Marsden, A. J. et al. Ligand-Induced Control of Photoconductive Gain and Doping in a Hybrid Graphene-Quantum Dot Transistor. Adv. Electron. Mater. 1, (2015).
10. Mudd, G. W. … Marsden, A. J. et al. High Broad-Band Photoresponsivity of Mechanically Formed InSe-Graphene van der Waals Heterostructures. Adv. Mater. 27, 3760–3766 (2015).
9. Wood, G. E., Marsden A.J., et al. van der Waals epitaxy of monolayer hexagonal boron nitride on copper foil: growth, crystallography and electronic band structure. 2D Mater. 2, 025003 (2015).
Being able to grow single crystals of 2D materials will produce large amounts of high quality material. This can be done by allowing single grains to grow alone until they are the required size, but this can take days. Another option is to exploit epitaxy: the structural relationship between the overlayer and the substrate it grows on. In this paper, we examine the growth of hexagonal boron nitride (hBN). hBN is structurally the same as graphene but with alternating boron and nitrogen atoms instead of carbon. We find that there is an epitaxial link between hBN and the copper it grows on. Further, just as we found for graphene on copper, the interaction between the hBN and the copper is weak enough that the two do not interact electronically.
8. Li, Z., Young, R.J., Kinloch, I.A., Wilson, N.R., Marsden, A.J., Raju, A.P.A. Quantitative Determination of the Spatial Orientation of Graphene by Polarized Raman Spectroscopy. Carbon 88, 215–224 (2015).
Graphene could be used to reinforce composites because it is so strong and thin. How much reinforcement a material provides depends on the alignment of the material; for example, rods (like metal bars in concrete) reinforce better when they are all aligned. For graphene it can be challenging to measure how aligned the sheets are. In this paper, we show how Raman spectroscopy can give a measure of how ordered the graphene-sheet-alignment is. This could be used to help characterise how graphene is reinforcing the composites it is mixed into.
7. Svatek, S. A. … Marsden, A. J. et al. Adsorbate-Induced Curvature and Stiffening of Graphene. Nano Lett. (2014).
Modifying graphene’s properties are important for its inclusion in future technology. In this paper we modify graphene’s mechanical properties by placing molecules onto its surface. First, graphene is suspended over a thin layer of water. Then, TTC molecules are placed on top. The spacing of carbon atoms in TTC is similar to graphene, but slightly different, and the graphene tries to curve so that its carbon atoms match up with the carbon atoms in TTC. This curvature also makes the graphene stiffer.
6. Skilbeck, M. S., Marsden, A. J. et al. Multimodal microscopy using “half and half” contact mode and ultrasonic force microscopy. Nanotechnology 25, 335708 (2014).
Atomic force microscopy (AFM) is a powerful technique for mapping a surface with information from force interactions. Some of these forces require the AFM tip to be touching the surface, in what is called contact mode. But when the tip is in contact mode, the surface can be damaged by the tip as it maps. In this paper, we demonstrate one way to alleviate this problem. By sending ultrasound though the sample and using contact mode, all the usual information is available but the tip does not damage the sample. As an example, we showed how you can look at the conductivity of a network of carbon nanotubes without moving the delicate nanotubes around the surface.
5. Thomas, H. R., Marsden, A. J., Walker, M., Wilson, N. R. and Rourke, J. P. Sulfur-Functionalized Graphene Oxide by Epoxide Ring-Opening. Angew. Chem. Int. Ed. Engl. 7613–7618 (2014).
One of graphene’s attractive properties is its large surface area. Materials with large surface areas make good sensors and catalysts because the chemical processes underlying these functions happen almost exclusively at the surface. The chemical processes often occur at certain sites, and attaching these sites to graphene is a crucial step in exploiting its large surface area. In this paper, we attached sulphur to graphene oxide sheets, which then attracted gold. Atomic resolution transmission electron microscopy can then see the structure of these gold nanoparticles directly.
4. Lai, C.-Y., Tang, T.-C., Amadei, C. A., Marsden, A. J. et al. A nanoscopic approach to studying evolution in graphene wettability. Carbon 80, 784–792 (2014).
To incorporate graphene into applications like filters and barrier coatings understanding how it interacts with water is crucial. Just as crucial is how this interaction changes over time and what causes these changes. In this paper we investigate the interaction between an AFM tip and a graphene surface, and try to understand how water affects this interaction. We found that the graphene surface goes from being hydrophilic (water-loving) to hydrophobic (water-hating) as the surface is exposed to air. This was caused by contaminants and water absorbing onto the surface of graphene, and it is the combination of these two absorbents that change the surface interaction.
3. Marsden, A. J. et al. Is graphene on copper doped? Phys. status solidi – Rapid Res. Lett. 7, 643–646 (2013).
Graphene’s interesting electronic structure is one of the reasons that it has attracted so much attention. For graphene grown on copper, how does the copper underneath the graphene affect its electronic structure? Normally, metals have a sea of free electrons (which makes them good conductors) and some of these electrons can transfer over to the graphene above. This results in something called electron-doping of the graphene and changes its electronic structure. In this paper, we found that this transfer takes place when graphene on copper is heated in vacuum to above 500°C. However, below this temperature, the doping is not present. This provides interesting questions about how, and when, charge transfer occurs in graphene on copper.
2. Marsden, A. J., Phillips, M. and Wilson, N. R. Friction force microscopy: a simple technique for identifying graphene on rough substrates and mapping the orientation of graphene grains on copper. Nanotechnology 24, 255704 (2013).
Identifying graphene on a copper surface poses challenges to conventional microscopy techniques. In this paper, we show how you can use graphene’s low coefficient of friction to identify it against a background of higher friction copper. This is done by sliding an AFM across the surface and measuring how much it twists (a more detailed write up is here). Further, a similar technique can measure the orientation of the graphene flakes. These techniques allow quick identification of graphene on copper, and to measure its orientation, without time-consuming sample preparation.
1. Wilson, N. R., Marsden, A. J. et al. Weak mismatch epitaxy and structural feedback in graphene growth on copper foil. Nano Res. 6, 99–112 (2013).
Producing graphene remains a problem. One solution is growing graphene on cheap copper foils. This gives large areas of graphene for low cost. But the quality remains below that of single-crystals. This is because grown-graphene is composed of smaller crystals of graphene stitched together. This papers shows a link between the orientation of the graphene and the copper beneath. This epitaxy is weak in that it doesn’t occur everywhere. There is also no electronic interaction between the copper and the graphene. However, the evidence of epitaxy suggests a route to controlling graphene’s orientation by changing the growth substrate.