Amanda Barnard tells Journal of Materials Chemistry about her hot paper.

1. Could you explain the significance of your article to the non-specialist? 
Gold nanostructures are proving very promising for a variety of applications, all of which require considerable selectivity and reproducibility in terms of size, shape and structure, to ensure reliability during their use. Although it is possible to surmise a relationship between the structural features of gold nanostructures (such as size, shape, aspect ratio and growth direction), it impossible to definitely isolate the underlying link, using experimental methods. Using theoretical modelling this study systematically tests the relationship between these parameters, and demonstrates how changing one feature (such as aspect ratio) can consequently alter another (such as growth direction), at a given size or temperature.

2. What has motivated you to conduct this work? 
The motivation for the present work is two-fold. Gold nanostructures are an excellent test system for the development of general theories of nanomorphology, since they have been the subject of many detailed experimental investigations which are necessary to compare with the theory.  Therefore, as part of our on-going work examining the structure, shape and phase of nanomaterials, gold nanorods were a natural choice for studying dimensional anisotropy.  In addition to this, as mentioned above, gold nanostructures are attracting much technological interest, and we were keen to contribute to the development of a more fundamental understanding of gold nanorod formation, so as to complement and guide experimentation in the field.

3. Where do you see this work developing in the future? 
Although there are a number of possible avenues, there are two main directions that the research could take, in response to the most immediate questions arising from this work.  Firstly, there is the question of the effect of surface chemistry, and in particular how the length and concentration of surfactants are likely to change the equilibrium shape, aspect ratio and morphological stability. The results in the present study assume 'clean' surfaces, whereas gold nanorods are usually grown in solution and are usually passivated by molecules such as alkanethiols. Secondly, there is the question of how defects will affect the same properties, since (like gold nanoparticles) gold nanorods often exhibit a number of structural modifications such as twinning. Gold nanorods have been reported with a variety of twinning configurations, including the unusual 5-fold cyclic twinning, that seem to depend empirically on the size, axial orientation and aspect ratio.  Both these issues are currently under consideration.

4. Are there any particular challenges facing future research in this area? 
The next big challenge in this type of modelling of nanostructures, and in the study of metallic nanorods of this type, is an integrated method of treating bimetallics. As the cost of precious metals increases, the need for nanoalloys and controlled production of core-shell metallic nanostructures will also increase, and it is currently unclear how alloying or surface-segregation phenomena will affect the morphology of these materials. Extending the present study to include variations on composition, while still capturing the myriad of different atomic distributions, without the need for large numbers of explicit computer simulations is certainly necessary, but is not trivial.

Amanda Barnard is the Violette & Samuel Glasstone Fellow in the Department of Materials at the University of Oxford. She received her B.Sc with Honours in 2001 and Ph.D. (Physics) in 2003 from the Royal Melbourne Institute of Technology (RMIT) University, one of Australia's leading academic institutions.  Her thesis investigated the relationship between shape and phase stability in carbon nanoparticles and the structure of and stability of diamond nanowires. After two years as a Distinguished Postdoctoral Fellow in the Center for Nanoscale Materials at Argonne National Laboratory (USA) working on a variety of nanomaterials, she moved to the United Kingdom to begin her research developing new methods for the theory and simulation of nanomorphology. Using primarily thermodynamic modeling and ab initio methods, her research focuses more on the fundamentals of nanomorphology, and the role of structure, shape and surface chemistry in the moderation of nanoscale properties, including size dependent phase transitions.  A fervent advocate of partnering theory and experimentation, her interests lie in the development of multi-scale models dependent upon experimentally relevant factors such as size, composition, temperature and defects.