Visualizing the structural evolution of thermally-decaying platinum nanowires

Visualizing the structural evolution of thermally-decaying platinum nanowires

Using our Wildfire system, scientists gain an exceptional in-depth understanding of the morphological changes of platinum nanowires at certain temperatures

Original article by Torsten Walbert, Falk Muench, Yangyiwei Yang, Ulrike Kunz, Bai-Xiang Xu, Wolfgang Ensinger, and Leopoldo Molina-Luna

Torsten feature image

The morphological transformation of a platinum nanowire as temperature increases and the two domain types observed

Metal nanowires represent a main class of one-dimensional nanomaterials and have been proven essential for a wide range of applications. Previous works on electrodeposited nanowires focused on ex situ SEM characterization, which is limited in terms of resolution and unable to monitor internal nanostructure changes. Using the DENSsolutions Wildfire system, Torsten Walbert and his colleagues from the Materials Analysis group and Prof. Leopoldo Molina-Luna from the Advanced Electron Microscopy (AEM) Division at the Institute for Materials Science, TU Darmstadt were able to investigate via in situ TEM the influence of temperature on polycrystalline platinum nanowires. Observing this process under remarkably high resolution enabled them to capture for the first time the internal transformations during both early and intermediate stages of the platinum nanowire decay. 

The structural evolution of nanowire decay 

Although nanowires are crucial for a wide range of applications, they are frequently prone to degradation. It is important that we understand these underlying failure mechanisms to better ensure reliable performance under operating conditions. Previous studies observing the thermal decay of nanowires have typically focused on ex situ investigations inside an SEM. Only a handful of studies look at the in situ characterization of nanowire decay using TEM, but even those focus specifically on gold nanowires. In this study, Torsten and his team observe the temperature influence on the degradation of platinum nanowires. Platinum is used due to its high mechanical, chemical and thermal stability as well as catalytic activity.

Below you can see an overview of the morphological transformation of a platinum nanowire after a thermal treatment between 250°C and 1100°C. It is observed that the main external transformation starts after 800°C, illustrated by the corresponding diameter evolution.

Structural evolution of pt nanowires

The morphological transformation of a platinum nanowire after thermal treatment and corresponding diameter evolution

Changes in internal nanostructure

Although external shape transformations occur after 800°C, changes in the internal nanostructure happen a lot earlier at markedly lower temperatures. As shown in the figure below, after heating to 250°C, no pronounced changes in the internal structure are observed compared to the initial state. After increasing the temperature to 450°C, the nanowire outline is still unaltered, but voids of low contrast (indicated by red circles) already start appearing. At 800°C, these voids begin to propagate and the shape slightly changes.

Further increasing the temperature to 850°C causes a grain boundary to extend, which is indicated by the dashed green line in the figure below. Finally, at 875°C, the grain boundary straightens while the voids increase and accumulate. Ultimately, these results confirm that internal nanowire restructuring considerably precedes the permanent changes of the outer nanowire shape. In fact, the observed faceted voids and grain boundaries are crucial factors guiding their transformation and final splitting, which is discussed in the next section.

TEM image showing the formation of voids (red circles) and straightening of grain boundary (green dashed line) at low and high temperatures

TEM video showing a void disappearing from a single-crystalline wire segment

Two surprising domain types

Some surprising results are observed after when the temperature goes beyond 875°C. Interestingly, the nanowires segregated into two domain types, one being single-crystalline and essentially void-free, while the other preserves void-pinned grain boundaries. This is the first time in academia that researchers observe this type of segregation, as it was neither described in previous experimental studies nor predicted by simulations.

You can see in the simulation and TEM video below that the wire separates into two domains, a single-crystalline domain and void-containing domain. Whereas the single-crystalline areas exhibit fast platinum transport, the void-containing areas show an unexpected morphological stability, retaining their nanostructure even at temperatures above 1000°C. In fact, the subsequent splitting of the nanowires is only observed in single-crystalline areas and thus leads to the formation of fragments with varying lengths and diameters. 

A simulation of the platinum nanowire disintegration, showing the curvature-driven mass transfer dominating the nanowire transformation

TEM video showing the disintegration of a platinum nanowire into two fragments

Novelty in findings

Performing in situ TEM in a controlled temperature environment represents a powerful approach for investigating the structural transformations of metal nanowires. Obtaining detailed insights into the internal nanostructure of nanowires and their evolution over time would otherwise be impossible without in situ TEM. Torsten and his team were able to relate the onset of shape changes to distinct nanostructural features acting as starting points in the disintegration process. This study is not only of great interest for basic research, but also helps in predicting the thermal robustness and reliability of nanowires in devices and can serve as a synthetic tool, enabling the control over the disintegration sequence via defect engineering. If we can understand the mechanism behind the process of decomposition, we can better predict and control the thermal stability of nanowires, adapting their shape and properties according to specific applications and conditions. 

Walbert, Torsten portrait -400 px

“The DENSsolutions Wildfire chip enabled an exact and fast temperature regulation with a homogeneous heat distribution, allowing us to investigate the decomposition process of Pt nanowires in situ. Without it, it would not have been possible to follow the transformations of the nanowires directly and to link them to the internal changes in the nanostructure.”


Torsten Walbert
PhD Student | Technische Universität Darmstadt

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Meet our Chief Technology Officer, Dr. Hugo Pérez

Meet our Chief Technology Officer, Dr. Hugo Pérez

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At DENSsolutions, we persistently challenge ourselves to develop the most innovative and outstanding solutions that you need to advance your research. This continuous yet passionate pursuit has been led for years by our Chief Technology Officer, Dr. Hugo Pérez, a longstanding pillar within this company. He has played a critical role in positioning DENSsolutions as a global leader in the field of in-situ TEM, and bringing home the Microscopy Today 2020 award. In this latest addition to DENSsolutions Meet the Team series, we interview Chief Technology Officer, Dr. Hugo Pérez, so you can learn all about his diverse educational experiences and wild backstory.

Where it all started

“My name is Hugo Pérez and I’m 35-year-old proud Mexican born in the beautiful city of Chihuahua. Although I was raised in Mexico and it holds a special place in my heart, I have lived in 7 countries around the world including the USA, Canada, France, Italy, Germany, Sweden and the Netherlands.

“I’ve always said that my passion is MEMS and nanotechnology, my obsession is biology, but my heart lies within business management.” – Dr. Hugo Pérez 

When deciding what to study early on in my life, I was doubting whether to go for medicine or engineering. After much deliberation, I decided to go for the latter as I realized that I could later on in my career apply the developed technical skills for medical devices and healthcare purposes. I obtained my BSc in Mechatronics Engineering at the Tecnológico de Monterrey in Mexico. It was during my bachelor’s studies, and especially during my time in Canada and Germany, that I was introduced to the world of nanotechnology and realized that there was nothing more I wanted to do. I was amazed by the wide scope of possibilities in which this disruptive technology could be used. So, I started discussing with my supervisors, expressing my intention of specializing in micro/nano-mechatronics, with the aim of one day having the knowledge to develop electromechanical systems at the molecular scale for biomedical purposes. Funnily enough, I was partly inspired by the movie Fantastic Voyage, where a submarine and its crew were shrunken to microscopic size and injected into the bloodstream of a scientist in order to save his life.


Stream LPEM system wins the Microscopy Today 2020 Innovation award


A conversation with our CTO Dr. Hugo Pérez who has been leading the development of the award-winning system.

The first of many MSc degrees

“Coincidentally, both my supervisors in Canada and Germany, who didn’t know each other, gave me the exact same advice: to pursue a MSc in Molecular Bioengineering at TU-Dresden, in Germany. But before doing so, I had my first professional experience working within the industry, where I spent a bit over 1.5 years working as an Automation Engineer at GCC, a large cement company in Mexico. This job gave me a lot of exposure to chemistry and material science, and allowed me to discover much more about the power of using nanomaterials like carbon nanotubes. As you can imagine, this experience only grew my desire further to specialize in nanotechnology.

“From that point onwards, and for the next many years, I would be spending most of my time inside the cleanroom, learning all kinds of processes and tips & tricks to manufacture nanodevices.”

So, after this rewarding experience, I took my supervisors’ advice to heart, and jumped back to Germany to start my first (of three) Master’s degree. Studying molecular bioengineering gave me the opportunity to learn about molecular biology and all kinds of exciting applications in genetics and proteomics. However, as interesting as it was, I was still missing the engineering side that would allow me to design and manufacture nanodevices. This is precisely why I moved to Sweden to pursue a second MSc degree in Nanotechnology at the Chalmers University of Technology. It was thanks to this second MSc degree that I properly got immersed in the world of NEMS/MEMS and micro/nano-fabrication. From that point onwards, and for the next many years, I would be spending most of my time inside the cleanroom, learning all kinds of processes and tips & tricks to manufacture nanodevices.”

Mission impossible

“After finishing my second MSc, and given the fact that this was all very intense, I was prepared to go back to the industry with the aim of slowly starting to move towards a highly ranked management position in a high-tech company. However, destiny had something else prepared for me. I ended up getting a PhD position at TU-Delft in the Netherlands. Although pursuing a PhD was not part of the plan, I couldn’t deny this opportunity given the fact that the project was exactly what I was looking for. Not only that, but my promotor would be Dr. Urs Staufer, a remarkable scientist who led NASA’s Phoenix Mars Mission and developed the first nanosensor for planetary science able to measure the presence of water molecules on Mars. I took this opportunity as a great chance to learn from one of the best.

“At a certain point I was working in parallel on two different PhD projects while simultaneously pursuing an MBA.”

To make the story more complicated, another opportunity came up to pursue a third Master’s degree in Business Administration at the University of Cumbria. Of course, I didn’t hesitate to jump on this considering my goal has always been to become a successful businessman. However, destiny still had another surprise for me: the appearance of another PhD project on graphene manipulation. Therefore, at a certain point I was working in parallel on two different PhD projects while simultaneously pursuing an MBA. This complete academic experience, which was extremely demanding, forced me to become a very structured and time-efficient person. This is partly the reason why I’ve won the best scientific paper on a number of occasions at prestigious international conferences.

Now, at DENSsolutions, I’m trying to exploit all these experiences to the most, not just to lead the company on the right technological path, but also to bring the business to a higher level. I enjoy acting as a coach to my colleagues and ensuring there’s always something they can learn from me. From a commercial perspective, what I enjoy the most is pitching our technology to convince people of our solutions, as well as trying to close new deals. It excites me that researchers all over the world in a wide variety of applications rely on our advanced technologies to conduct their research. Keeping the right balance between business and science is what has allowed me to strengthen my international network, and what has given me the possibility to be in contact with global industrial leaders and some of the greatest scientific minds in the community.”

Thank you for reading this article! If you would like to ask Hugo any questions, whether it’s about his education, experience or knowledge, please don’t hesitate to contact him via the form below

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