ORC Seminars 2011

Speaker: Dr Valeria Nicolosi, Department of Materials, University of Oxford

Date:  29 July 2011

Time: 2.30pm

Venue: Building 53, room 4025

Abstract: 

Many nanomaterials generating  interest in recent years are not found as individual nanostructures but as van der Waals bonded aggregates or crystals. For example nanotubes generally exist in cylindrical aggregates known as bundles while graphene sheets are almost always confined to graphitic crystals. While individual nanotubes  and graphene sheets have unprecedented mechanical, electrical and thermal properties, the aggregated forms are almost always less interesting. Thus, exfoliation of nanotubes has been well studied for the last decade [1] while exfoliation of graphene has been gaining momentum in the last two years [2]. In this talk I describe the exfoliation of both nanotubes and graphene using both special solvents  and surfactants [3]. Solvent choice for both nanotubes and graphene can be described using standard solubility parameters. We have used the techniques developed in this work to  explore the exfoliation of other van der Waals bonded materials., leading to the liquid phase exfoliation of a wide range of layered compounds including MoS2, WS2, MoSe2, MoTe2, TaSe2, NbSe2, NiTe2, BN, MnO2 and Bi2Te3 [4, 5]. These are potentially important because they occur in >100 different types with a wide range  of electronic properties, varying from metallic to semiconducting.

Once exfoliated, these materials can be deposited as individual flakes or formed into films or composites. By blending with other dispersed nanomaterials we can form hybrids [4]. We  envisage the combination of high conductivity materials and the intrinsic properties of the layered material will be of interest for a wide range of applications [5].

However, before applying these processing methods for real high-tech purposes it is imperative to see whether the graphene structure endures the exfoliation procedure. In order to  do so, flakes  were characterized by aberration-corrected High Resolution Transmission Electron Microscopy (HRTEM), revealing extremely high quality structures [3, 6]. New advances in aberration-corrected annular dark field Scanning Transmission Electron Microscopy (STEM) allowed us to identify low-atomic number individual adatoms, vacancies  and molecular-scale adsorbated in single-layer atomic crystals in which the nearest neighbours are 1.45 Å apart [7,8].

Biography:

Dr. Nicolosi is an internationally regarded expert in the processing, manipulation and electron microscopy characterization of nanomaterials. Her most notable contribution, developed in the last few years, has been the development of processing methods which are universally applicable to nanomaterials of very diverse nature, such as inorganic nanowires, carbon nanotubes, graphene and in particular inorganic two-dimensional nano-sheets. This has changed the general approach towards producing these materials allowing the focus of research to become more application-oriented.

Following a PhD in Physics in 2006 from Trinity College Dublin (TCD, Ireland) under Prof. W. Blau,  she worked as  a Postdoctoral Researcher in the group of Prof. J Coleman in TCD. During her PhD studies  and postdoctoral work she succeeded in the liquid-phase processing and solubilisation of a novel class of inorganic nanowires and soon after carbon nanotubes: published in Advanced Materials and featured on Science as Editors’ Choice in 2008. In 2008 Dr Nicolosi developed the first liquid-phase exfoliation method for obtaining easily processable graphene with high yield. This method offers low-costs and high-throughput,  opening the door to many real applications. This work was published in Nature Nanotechnology and featured on the Nature Nanotechnology Editorial twice more in the same year. The method is now in the process of being scaled up through the formation of a start-up company leading to larger, industrial scale production.

Dr Nicolosi moved to the University of Oxford in February 2008 with an IEF Marie Curie Fellowship, extending her findings to the hundreds of inorganic materials and leading to the development of a general method for stripping single- or few-layer sheets from a range of stacked materials, such as transition metal chalcogenides and boron nitride. Her work, published on Science in February 2011 has generated widespread media interest. In 2009 she was  awarded a UK Royal Academy of Engineering/EPSRC Fellowship.

Since the beginning of her scientific carrier Dr Nicolosi has published more than 70 papers in major peer-reviewed international journals, including Science, Nature, Nature Nanotechnology, Nano Letters, Advanced Materials and JACS. Nature recently recognized the significance of one of Dr. Nicolosi’s works by giving it the prized cover spot.

1. S. Bergin et al., Advanced Materials, 20, 10 (2008) 1876

2. Y. Hernandez et al., Nature Nanotechnology, 3, 9 (2008) 563

3. M. Lotya et al., J. Am. Chem. Soc, 131, 10 (2009) 3611

4. J. N. Coleman et al., Science, 331, 6017 (2011) 568

5. R.J. Smith et al., Advanced Materials (2011) In Press

6. J. Kim et al., ACS Nano, 24;5, 5 (2011) 3977

7.  O. L. Krivanek, et al., Ultramicroscopy, 110, 8 (2010) 935

8. O. L. Krivanek et al., Nature, 464, 7288 (2010) 571

 

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