Plasmonic Nanolenses: Electrostatic Self-Assembly of Hierarchical Nanoparticle Trimers and Their Response to Optical and Electron Beam Stimuli

Significance Statement

Plasmonic nanostructures can now be used in several fields such as energy harvesting, sensing, light guiding, imaging gadgets, and biomedical applications. One aspect of these nanostructures stands out; their capacity to focus electromagnetic energy. It’s an effect that is further amplified in nanostructures with nanometer scale gaps owing to the excitation of the plasmonic hotspots. It has been found that the size between the gaps of the plasmonic nanoparticles is central for localization as well as the intensity of the electric field in the hotspots.

Lithographic methods proposed for surface pattering and fabrication necessary for characterizing the properties of hierarchical trimers (structures with three nanoparticles) limited the inter-particle spacing to approximately more than 10 nm and, accordingly, the intensity of field confinement. These spacings were found to be much larger than those achieved through self-assembly methods. Smaller gaps are desirable for strong inter-particle plasmon modes coupling, which leads to strong field localization.

However, only selected self-assembly methods are applicable for reproducible production of large scale trimers necessary for a number of applications. Therefore, Australian researchers led by professor Udo Bach investigated the plasmonic attributes as well as the lensing effect of the hierarchical gold trimer nanolenses. They adopted an electrostatic self-assembly method owing to its simplicity and required control. They also ascertained the ability of the trimers to confine light through cathodoluminescence. Their research work is now published in ACS Nano.

The authors obtained 30 nm particles from citrate stabilized gold particles. The particles were then modified with single-stranded DNA in a bid to convey a negative charge on their surface. The approach of hierarchical assembly of trimers was based on protocol used for assembly of dimers. The method was a three step assembly process that relied on electrostatic interactions between charged substrates and particles with alternating positive and negative charges. Glass substrates and silicon dioxide coated silicon substrates were functionalized to confer a positive charge.

In the first step, a (3-aminopropyl)-triethyoxysilane modified substrate with positive surface charges was immersed into a colloidal solution of gold nanoparticles with negative charges. In the second step, the produced substrates were immersed in a solution of positively charged 20 nm satellites. Finally, in the last step the authors completed trimer formation by immersing the gold nanoparticle dimer substrates in a solution of positively charged 50 nm satellites.

The wet chemical electrostatically driven gold nanoparticles assembly process allowed the authors to realize nanolenses with below 2 nm inter-particles spacing at high density on a macroscopic scale. They achieved a trimer yield of over 60%. With the characterization of the plasmonic behavior through UV-vis, cathodoluminescence and electron energy loss spectroscopy, they were able to pinpoint lower energy resonance that was pivotal for the strong lensing effect towards the smallest particle gap. In the paper, the authors demonstrated that the resonance could be excited effectively when focusing an electron beam on the smallest particle.

Plasmonic Nanolenses Electrostatic Self-Assembly of Hierarchical Nanoparticle Trimers and Their Response to Optical and Electron Beam Stimuli - advances in engineering

About the author

Udo Bach is a full professor at Monash University, the Deputy Director of the ARC Centre of Excellence in Exciton Science and an ANFF-VIC Technology Fellow at the Melbourne Centre of Nanofabrication (MCN). He received his PhD from the Swiss Federal Institute of Technology (EPFL, Switzerland) working in the research group of Prof Michael Grätzel and worked for 3 years in a technology start-up company in Dublin (Ireland). Subsequently he spent 15 months as a postdoc in the group of Prof. Paul Alivisatos at UC Berkeley (USA) before moving to Monash University in November 2005 to establishing his own research group.

Prof Bach has a strong background in the area of photovoltaics and nanofabrication. He is involved in fundamental and applied research in the area of perovskite and dye-sensitized solar cells. He has additional research activities in the area of nanofabrication, DNA-directed self-assembly, nanoprinting, plasmonics for sensing, photovoltaic applications and combinatorial photovoltaic materials discovery.

About the author

Dr. Ye Zhu is currently an assistant professor in the Department of Applied Physics, The Hong Kong Polytechnic University. He received his undergraduate degree from Tsinghua University in China, and his PhD in Materials Science from the University of Wisconsin-Madison in 2008. After graduation, he did postdoc first at 3M Corporate Research Materials Lab and then at the Department of Applied Physics, Cornell University. In 2012 he started working as a research fellow at Monash University in Australia, until joining The Hong Kong Polytechnic University in 2016. Dr. Zhu has over a decade of research experience in advanced electron microscopy, focusing on the development of cutting-edge microscopy and spectroscopy techniques, and their applications on novel materials. In 2014, he received the Young Scientist award from the International Federation of Societies for Microscopy. He has published over 40 journal articles with over 2000 citations, 1 invited book chapter, and ~30 conference proceedings.

About the author

Dr. Amelia C. Y. Liu graduated from the University of Melbourne with a PhD in Physics in 2004. She was a post-doctoral research associate at Argonne National Laboratory until 2008 when she returned to Australia and completed fellowships in Materials Science and Engineering and Physics until 2014. In 2014, Amelia joined the Monash Centre of Electron Microscopy and now manages the focused ion beam and cathodoluminescence capabilities in the centre. In 2014 she was awarded the Australian Microscopy and Microanalysis Society FEI Cowley-Moodie Award for Research in the Physical Sciences for the development of new S/TEM-based techniques.

About the author

Wei Chao obtained her Bachelor degree (Honours) in Engineering in 2016 at Monash University. She is currently a PhD candidate with Prof. Joanne Etheridge and Dr. Changlin Zheng in Material Science and Engineering and Monash Centre of Electron Microscopy at Monash University. Her research is focused on the use of novel transmission electron microscopy techniques to characterize nanoparticles.

About the author

Toon Coenen studied at University College Utrecht. After obtaining his BSc degree there he went on to study chemistry and physics at Utrecht University where he obtained an MSc degree in 2010. He continued for a PhD at the FOM Institute AMOLF in Amsterdam, the Netherlands, in 2014 in Professor Albert Polman’s group. There he co-developed the first version of the SPARC cathodoluminescence detection system and used it to investigate the nanoscale optical properties of various metallic and dielectric nanostructures. During his PhD he also was a visiting scientist at Stanford University in the group of Professor Mark Brongersma, performing EELS experiments on plasmonic structures. He now works at Delmic BV as application specialist, developing novel cathodoluminescence applications and improving the cathodoluminescence system as a whole.

About the author

Daniel Gomez is an Associate Professor and ARC Future Fellow at RMIT University and a Technology Fellow at the Melbourne Centre for Nanofabrication. His research group studies the spectroscopy of metal nanostructure both experimentally and theoretically with a strong emphasis on applications in photo-chemistry.

About the author

Joanne Etheridge is the Director of the Monash Centre for Electron Microscopy and Professor in the Department of Materials Science and Engineering at Monash University. She obtained her degree and PhD in physics at the University of Melbourne and RMIT University, respectively. She then held appointments at the University of Cambridge in the Department of Materials Science and Metallurgy and Newnham College, including a Rosalind Franklin Research Fellowship and a Royal Society University Research Fellowship. She returned to Melbourne to join Monash University where she established the Monash Centre for Electron Microscopy. She conducts research in the theory and development of new electron scattering methods for determining the atomic and electronic structure of condensed matter. She also applies these methods to the study of structure-property relationships in functional materials, including perovskite, nanoparticle and semiconductor systems.

About the author

Soon Hock Ng is a SIEF STEM+ business fellow at Swinburne University of Technology. He completed his BSc and BEng at Monash University, where he also completed his PhD in 2016, with a focus on lithography and the self-assembly of nanoparticles. He began working at the Melbourne Centre for Nanofabrication as a Process Engineer in the latter half of 2016 before pursuing postdoctoral research in the Centre for Microphotonics at Swinburne University of Technology in early 2017. His interests include self-assembly of nanoparticles in lithographically defined templates, PVD and RIE of nanostructured thin films and recently, porous silicon.

About the author

Julian A. Lloyd is currently working at Udo Bach’s group at Monash University. He obtained his BSc and MSc studying physics at the Technical University of Munich. After that, he started a PhD at Monash University under the supervision of Udo Bach and Daniel Gómez. After submitting his thesis, he is currently awaiting graduation. His research is focused on molecular and nanoparticle self-assembly and their use in plasmonics.


Julian A. Lloyd1,2, Soon Hock Ng1,2, Amelia C. Y. Liu3,4, Ye Zhu1, Wei Chao1, Toon Coenen5, Joanne Etheridge1,3, Daniel E. Gómez2,6,7, and Udo Bach1,2,6. Plasmonic Nanolenses: Electrostatic Self Assembly of Hierarchical Nanoparticle Trimers and Their Response to Optical and Electron Beam Stimuli. ACS Nano, volume 11 (2017), pages 1604−1612.

Show Affiliations
  1. Department of Materials Science and Engineering, Monash University , Clayton, Victoria 3800, Australia.
  2. Melbourne Centre for Nanofabrication , Wellington Road 151, Clayton, Victoria 3168, Australia.
  3. Monash Centre for Electron Microscopy, Monash University , Clayton, Victoria 3800, Australia.
  4. School of Physics, Monash University , Clayton, Victoria 3800, Australia.
  5. DELMIC BV , Thijsseweg 11, 2629 JA, Delft, The Netherlands.
  6. Commonwealth Scientific and Industrial Research Organisation , Manufacturing, Research Way, Clayton, Victoria 3168, Australia.
  7. School of Applied Science, RMIT University , Melbourne, Victoria 3000, Australia.


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