Tag Archives: Panagiotis Grammatikopoulos

Achieving precise control by decorating iron nanocubes with gold

A June 17,2019 news item on phys.org describes a new technique for producing nanoparticles,

One of the major challenges in nanotechnology is the precise control of shape, size and elemental composition of every single nanoparticle. Physical methods are able to produce homogeneous nanoparticles free of surface contamination. However, they offer limited opportunity to control the shape and specific composition of the nanoobjects when they are being built up.

A recent collaboration between the University of Helsinki and the Okinawa Institute of Science and Technology (OIST) Graduate University revealed that hybrid Au/Fe nanoparticles can grow in an unprecedentedly complex structure with a single-step fabrication method. Using a computational modeling framework, the groups of Professor Flyura Djurabekova at the University of Helsinki and Prof. Sowwan at OIST succeeded in deciphering the growth mechanism by a detailed multistage model.

A June 14, 2019 University of Helsinki press release (also on EurekAlert but published June 17, 2019), which originated the news item, expands on the theme,

Elegantly combined considerations of kinetic and thermodynamic effects explained the formation of embedded gold layers and the site-specific surface gold decoration. These results open up a possibility for engineering a multitude of hybrid nanoparticles for a wide range of emerging applications. Their research was recently published in the highly ranked open access journal Advanced Science.

“When nature surprises us with an unexpectedly beautiful pattern, we must recognize it and explain. This is the way to cooperate with nature that is always ready to teach and expecting us to learn,” says Dr. Junlei Zhao, a postdoctoral researcher in the group of Prof. Djurabekova.

Nowadays, scientists are able to study nano-scale phenomena with great accuracy by using high-performance computational software and modern supercomputing infrastructures. These are of great support, not only for advancing fundamental science but also for finding promising solutions for many challenges of humanity.

Here’s a link to and a citation for the paper,

Site‐Specific Wetting of Iron Nanocubes by Gold Atoms in Gas‐Phase Synthesis by Jerome Vernieres, Stephan Steinhauer, Junlei Zhao, Panagiotis Grammatikopoulos, Riccardo Ferrando, Kai Nordlund, Flyura Djurabekova, Mukhles Sowwan. Advanced Science Volume 6, Issue 13
1900447 uly 3, 2019 DOI: https://doi.org/10.1002/advs.201900447 First published online: 02 May 2019

This paper is open access.

Ukidama-structured nanoparticles discovered

The researchers discovered a new nanoparticle structure that resemble the ukidama, glass fishing floats, used regularly by Japanese fishermen. The nanoparticle has a core of one element (copper) and is surrounded by a “cage” of another element (silver). The silver does not cover certain areas of the copper core, which is very similar to the rope that surrounds the glass float. Courtesy: Okinawa Institute of Science and Technology (OIST)

The researchers discovered a new nanoparticle structure that resemble the ukidama, glass fishing floats, used regularly by Japanese fishermen. The nanoparticle has a core of one element (copper) and is surrounded by a “cage” of another element (silver). The silver does not cover certain areas of the copper core, which is very similar to the rope that surrounds the glass float. Courtesy: Okinawa Institute of Science and Technology (OIST)

What a beautiful image to illustrate the new ukidama nanoparticle structure! Here’s the announcement in a June 13, 2016 news item on ScienceDaily,

Sometimes it is the tiny things in the world that can make an incredible difference. One of these things is the nanoparticle. Nanoparticles may be small, but they have a variety of important applications in areas such as, medicine, manufacturing, and energy. A team of researchers from Okinawa Institute of Science and Technology Graduate University (OIST) recently discovered a unique copper-silver nanoparticle structure that has a core of one element surrounded by a “cage” of the other element. However, the cage does not cover certain areas of the core, which very much resembles the Japanese glass fishing floats traditionally covered with rope called ukidama.

This previously undiscovered ukidama structure may have properties that can help the team on their mission for optimal nanotechnology. …

A June 13, 2016 OIST press release by Rebecca Holland (also on EurekAlert; the June 12, 2016 publication date discrepancy is likely due to timezone issues), which originated the news item, provides more insight into the research team’s workings,

“The ukidama is a unique structure, which means that it can likely give us unique properties,” said Panagiotis Grammatikopoulos, first author and group leader of the OIST Nanoparticles by Design Unit. “The idea is that now that we know about this structure we may be able to fine tune it to our applications.”

The OIST researchers are continually working to create and design nanoparticles that can be used in biomedical technology. Specifically, the team works to design the optimal nanoparticles for technologies like smart gas sensors that can send information about what is going on inside your body to your smart phone for better diagnoses. Another application is the label free biosensor, a device that can detect chemical substances without the hindrance of fluorescent or radioactive labels. The identification of the ukidama structure is important in this endeavour because having a new structure increases the possibilities for technological advancements.

“The more parameters that we can control the more flexibility we have in our applications and devices,” Prof. Mukhles Sowwan, author and head of OIST’s Nanoparticles by Design Unit said. “Therefore, we need to optimize many properties of these nanoparticles: the size, chemical composition, crystallinity, shape, and structure.”

The discovery of the ukidama structure was found through sputtering copper and silver atoms simultaneously, but independently, through a magnetron-sputtering system at high temperatures. When the atoms began to cool they combined into bi-metallic nanoparticles. During the sputtering process, researchers could control the ratio of silver to copper, with the rate of power with which the atoms were sputtered. They found that the ukidama structure was possible, especially when the copper was the dominant element, since silver atoms have a higher tendency to diffuse on the nanoparticle surface. From their experimental findings, the team was able to create simulations that can clearly show how the ukidama nanoparticles form.

The team is now looking to see if this structure can be recreated in other types of nanoparticles, which could be an even bigger step in the optimization of nanoparticles for biomedical application and nanotechnology.

“We design and optimize nanoparticles for biomedical devices and nanotechnology,” Sowwan said. “Because the ukidama is a new structure, it may have properties that could be utilized in our applications.”

Co-author, Antony Galea, formerly of the Nanoparticles by Design Unit, was responsible for the experimental portion of this study and has since moved to OIST’s Technology and Licensing Section to help research – like this work being done with nanoparticles that can be utilized in applications – move into the market.

“Our aim is to take research created by OIST from the lab to the real world,” Galea said. “This is a way that work done at OIST, such as by the Nanoparticles by Design Unit, can benefit society.”

Here’s a link to and a citation for the paper,

Kinetic trapping through coalescence and the formation of patterned Ag–Cu nanoparticles by Panagiotis Grammatikopoulos, Joseph Kioseoglou, Antony Galea, Jerome Vernieres, Maria Benelmekki, Rosa E. Diaz, Mukhles Sowwan. Nanoscale, 2016; 8 (18): 9780 DOI: 10.1039/C5NR08256K

I believe this paper is behind a paywall.

Animating nanoparticles

It’s always good to find new tools for explaining/describing the nanoscale and this July 28, 2014 news item on Nanowerk, which highlights animation that simulates interactions between nanoparticles, helps to fill the bill,

Panagiotis Grammatikopoulos in the OIST [Okinawa Institute of Science and Technology] Nanoparticles by Design Unit simulates the interactions of particles that are too small to see, and too complicated to visualize. In order to study the particles’ behavior, he uses a technique called molecular dynamics. This means that every trillionth of a second, he calculates the location of each individual atom in the particle based on where it is and which forces apply. He uses a computer program to make the calculations, and then animates the motion of the atoms using visualization software. The resulting animation illuminates what happens, atom-by-atom, when two nanoparticles collide.

A July 25, 2014 OIST news release by Poncie Rutsch, which originated the news item, details the process Grammatikopoulos follows, (Note: A link has been removed)

Grammatikopoulos calls this a virtual experiment. He knows what the atoms in his starting nanoparticles look like. He knows their motion follows the laws of Newtonian physics. His colleagues have seen what the resulting particles look like after collision experiments.  Once his simulation is complete, Grammatikopoulos compares his end products with his colleagues to check his accuracy.

Grammatikopoulos most recently simulated how palladium nanoparticles interact, published in Scientific Reports on July 22, 2014. Palladium is an expensive but highly efficient catalyst that lowers the energy required to start many chemical reactions. Researchers can make palladium even more efficient by designing palladium nanoparticles, which use the same mass of palladium in tinier pieces, increasing surface area. The more surface area a catalyst has, the more effective it is, because there are more active sites where elements can meet and reactions can occur.

However, shrinking a material to only a few nanometers can change some of the properties of that material. For example, all nanoparticles melt at cooler temperatures than they would normally, which changes what happens when two particles collide. Ordinarily, two particles will collide and release a small amount of heat, but the particles remain more or less the same. But when two nanoparticles collide, sometimes the heat released melts the surface of the two particles, and they fuse together.

Grammatikopoulos simulated palladium nanoparticles colliding and fusing at different temperatures. He determined that each time the particles fused, their atoms would start to crystallize into orderly rows and planes. At higher temperatures, the particles fuse into one homogeneous structure. At lower temperatures, the products look like classic snowmen, with a few parts that had crystallized with different orientations.

“The simulation gives you an understanding of physical processes,” said Grammatikopoulos. Before his research, Grammatikopoulos could not explain why all the palladium nanoparticles his lab created had a crystalline structure. Furthermore, he noticed that many palladium nanoparticles grew protrusions, giving the particles a lumpy shape. “Since the protrusions stick out, they bond more easily with other molecules,” Grammatikopoulos explained. “I’m not sure yet if it’s beneficial, but it’s definitely affecting the catalytic properties.”

Here’s an image illustrating the process,

Grammatikopoulos simulated two palladium nanoparticles colliding at different temperatures. The hotter the temperature, the more homogenous the resulting product, and the further the atoms in the particle crystallize. Courtesy: OIST

The news release goes on to explain the impact this information could have,

This study establishes some ground rules and explains certain properties of palladium nanoparticles. Understanding these properties could help design other nanoparticles out of other materials that would rival palladium’s abilities as a catalyst.  Palladium plays a role in thousands of important reactions, from making drugs to creating new biofuels. For example, Prof. Mukhles Sowwan’s Nanoparticles by Design Unit and Prof. Igor Goryanin’s Biological Systems Unit at OIST are working with palladium-catalyzed reactions to improve the efficiency of microbial fuel cells. Better palladium nanoparticles will propel this research forward.

“We need to understand the basic science,” explained Sowwan, who is Grammatikopoulos’ advisor. Sowwan says that the field of nanoscience is only starting to move towards applying the research, because there is still so much to learn about the properties of nanoparticles. “If you build something without understanding the basics,” Sowwan said, “you will not be able to explain the results.”

The researchers have made videos available, here’s a video of palladium crystallization at 300K,

As per the information provided by OIST,

Published on Jul 24, 2014

Grammatikopoulos created this simulation of palladium nanoparticles colliding at 300 Kelvin, or about 27 degrees Celsius. The nanoparticles meet, then fuse, then crystallize in orderly planes.

Here’s a link to and a citation for the paper,

Coalescence-induced crystallisation wave in Pd nanoparticles by Panagiotis Grammatikopoulos, Cathal Cassidy, Vidyadhar Singh, & Mukhles Sowwan. Scientific Reports 4, Article number: 5779 doi:10.1038/srep05779 Published 22 July 2014

This is an  open access paper.