Using scanning tunnelling microscopy (STM), extremely high resolution imaging of the molecule-covered surface structures of silver nanoparticles is possible, even down to the recognition of individual parts of the molecules protecting the surface. This was the finding of joint research between China and Finland, led in Finland by Academy Professor Hannu Häkkinen of the University of Jyväskylä. The research was recently published in the prestigious Nature Communications series and the publication was selected by the journal editors to the journal's monthly collection of highlighted papers.
Studying the surface structures of nanoparticles at atomic resolution is vital to understanding the chemical properties of their structures, molecular interactions and the functioning of particles in their environments. Experimental research on surface structures has long involved imaging techniques suitable for nanometer-level resolution, the most common of which are based on electron tunnelling, the abovementioned scanning tunnelling microscopy (STM), and atomic force microscopy (AFM) based on the measurement of small, atomic-scale forces.
However, achieving molecular resolution in imaging has proven highly challenging, for example because the curvature of the object to be imaged i.e. the nanoparticle's surface, is of the same order as the curvature of the scanning tip. Measurements are also sensitive to environmental disturbances, which may affect the thermal movement of molecules, for example.
The researchers used previously characterised silver nanoparticles, with a known atomic structure. The metal core of the particles has 374 silver atoms and the surface is protected by a set of 113 TBTT molecules. TBBT (tert-butyl-benzene thiol) is a molecule with three separate carbon groups on its end. The particle's outer surface has a total of 339 such groups.
When this type of nano-particle sample was imaged at low temperatures in the STM experiment, clear sequential modulations were observed in the tunnelling current formed by the image (see left part of the image). Similar modulations were noted when individual TBBT molecules were imaged on a flat surface.
Based on density functional theory (DFT), the simulations performed by Häkkinen's research team showed that each of the three carbon groups of the TBBT molecule provides its own current maximum in the STM image (see the right part of the image) and that the distances between the maxima corresponded to the STM measurement results.
This confirmed that measurement was successful at sub-molecular level. The simulations also predicted that accurate STM measurement can no longer be successful at room temperature, as the thermal movement of the molecules is so high that the current maxima of individual carbon groups blend into the background.
"This is the first time that STM imaging of nanoparticle surface structures has been able to 'see' the individual parts of molecules. Our computational work was important to verifying the experimental results. However, we wanted to go one step further. As the atomic structure of particles is well known, we had grounds for asking whether the precise orientation of the imaged particle could be identified using simulations," says Häkkinen, describing the research.
To this end, Häkkinen's group computed a simulated STM image of the silver particle from 1,665 different orientations and developed a pattern recognition algorithm to determine which simulated images best matched the experimental data.
"We believe that our work demonstrates a new useful strategy for the imaging of nanostructures. In the future, pattern recognition algorithms and artificial intelligence based on machine learning will become indispensable to the interpretation of images of nanostructures. Our work represents the first step in that direction. That's why we have also decided to openly distribute the pattern recognition software we had developed to other researchers," says Häkkinen.
The nanoparticle synthesis was performed in Xiamen University by Professor Nanfeng Zheng's research group and the STM measurements were carried out at Dalian Institute of Chemical Physics under the direction of Professor Zhibo Man. PhD student Sami Kaappa and senior researcher Sami Malola from Professor Häkkinen's group performed the calculations for the project. The research of Professor Häkkinen's group is in receipt of funding from the AIPSE programme of the Academy of Finland. The CSC - IT Center for Science in Finland and the Barcelona Supercomputing Center provided the resources for all simulations requiring high-power computing. The Barcelona simulations were part of the NANOMETALS project supported by the PRACE organisation.
- Published article: Qin Zhou, Sami Kaappa, Sami Malola, Hui Lu, Dawei Guan, Yajuan Li, Haochen Wang, Zhaoxiong Xie, Zhibo Ma, Hannu Häkkinen, Nanfeng Zheng Xueming Yang & Lansun Zheng, "Real-space imaging with pattern recognition of a ligand-protected Ag374 nanocluster at sub-molecular resolution", Nature Communications 9, 2948 (2018), DOI 10.1038/s41467-018-05372-5, https:/
- Academy Professor Hannu Häkkinen, University of Jyvaskyla, Hannu.email@example.com,
tel. +358 29 247 973
Academy of Finland, Communications
Leena Vähäkylä, Communications Specialist
tel. +358 29 5335 139
The Academy of Finland's mission is to fund high-quality scientific research, provide expertise in science and science policy, and strengthen the position of science and research. In 2018, our funding for research amounts to 444 million euros. Part of our funds come from proceeds of Finland's national gaming company Veikkaus. In 2018, these proceeds account for 70.7 million euros of our total funding for scientific research.
In focus: Peptides, the “little brothers and sisters” of proteins
12.11.2018 | Technische Universität Berlin
How to produce fluorescent nanoparticles for medical applications in a nuclear reactor
09.11.2018 | Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences (IOCB Prague)
Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.
In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...
On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.
When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure
Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...
Physicists at ETH Zurich demonstrate how errors that occur during the manipulation of quantum system can be monitored and corrected on the fly
The field of quantum computation has seen tremendous progress in recent years. Bit by bit, quantum devices start to challenge conventional computers, at least...
Scientists developed specially coated nanometer-sized vehicles that can be actively moved through dense tissue like the vitreous of the eye. So far, the transport of nano-vehicles has only been demonstrated in model systems or biological fluids, but not in real tissue. The work was published in the journal Science Advances and constitutes one step further towards nanorobots becoming minimally-invasive tools for precisely delivering medicine to where it is needed.
Researchers of the “Micro, Nano and Molecular Systems” Lab at the Max Planck Institute for Intelligent Systems in Stuttgart, together with an international...
09.11.2018 | Event News
06.11.2018 | Event News
23.10.2018 | Event News
12.11.2018 | Life Sciences
12.11.2018 | Materials Sciences
12.11.2018 | Physics and Astronomy