New measuring technique proves exceptional temperature accuracy of our Wildfire Nanochip

New measuring technique proves exceptional temperature accuracy of our Wildfire Nanochip

In collaboration with Utrecht University, we develop a novel technique to measure temperature at the nanoscale, showing the remarkable temperature accuracy and homogeneity of our Wildfire Nanochip

Original article by Thomas P. van Swieten, Tijn van Omme, Dave J. van den Heuvel, Sander J.W. Vonk, Ronald G. Spruit, Florian Meirer, Hugo Pérez Garza , Bert M. Weckhuysen, Andries Meijerink, Freddy T. Rabouw and Robin G. Geitenbeek
Thomas article feature image

The temperature-sensitive luminescence of nanoparticles enables their application as remote thermometers. In fact, the size of these nanothermometers makes them ideal to map temperatures with a high spatial resolution. Yet, conducting high spatial resolution mapping of temperatures that exceed 100°C poses some challenges.

In collaboration with Thomas van Swieten and his fellow colleagues at Utrecht University, we were able to jointly develop a new technique to measure temperature at the nanoscale. In fact, we tested this novel technique on our Wildfire Nanochip and were able to further confirm the Nanochip’s unparalleled temperature accuracy and homogeneity. These experiments also proved how well our models work to predict the temperature distribution across the microheater. Importantly, this particular technique will improve the accuracy of nanothermometry as a whole, not only in micro- and nano-electronics but also in other fields with photonically inhomogeneous substrates.  

The technique: Luminescence nanothermometry

Thermometry on the microscopic scale is an essential characterization tool for the development of nano- and microelectronic devices. However, conventional thermometers like thermocouples are often unable to reliably measure the temperature on this length scale due to their size. This is precisely where remote temperature sensing via optical thermometry techniques comes into play. Thermometry based on luminescence is particularly interesting since it is easily implemented, requiring only the deposition of a luminescent material in or on a sample of interest and the detection of its luminescence. For this reason, luminescence nanothermometry is currently developing into the method of choice for temperature measurements in microscopy.

Homogeneous heat distribution

Our Wildfire Nanochip was specifically designed to enable users a homogeneous heat distribution across the microheater where a sample is positioned. It is particularly due to the unique geometry of the metal spiral, where the windows are placed right at the center, that users are able to enjoy such a remarkable temperature homogeneity. In fact, our Wildfire Nanochip has a temperature uniformity of 98% across the window area and 99.5% across the two central windows. The figure on the right below is a perfect illustration of the chip’s exceptional temperature homogeneity, showing the temperature profile across the membrane and the microheater for a center temperature of 523 K simulated with a finite element model.

The high temperature homogeneity of our Wildfire Nanochips is also owed to the fact that the metal heating spiral is embedded in a silicon nitride membrane. Silicon nitride has many advantages including being chemically inert, mechanically robust and can withstand harsh chemical and temperature environments. 

Tijn article - figure 2 wildfire nanochip homogeneous distribution

On the left: The Wildfire Nanochip, where the metal spiral is represented in orange and the silicon nitride membrane in blue. On the right: Finite element model simulation showing the remarkable temperature homogeneity of the Wildfire Nanochip

Reliable temperature mapping

In this work, the luminescent particles that were used are NaYF₄ nanoparticles doped with Er³⁺ and Yb³⁺. These particles exhibit a strong upconversion when excited with an infrared laser. In other words, they emit photons with a shorter wavelength than the excitation photons. As shown in the figure below, we found that the spectrum of the emitted (green) photons is quite sensitive to temperature.

Tijn article - Figure 1 Intensity vs Wavelength

Green upconversion luminescence of the nanoparticles upon excitation at various temperatures ranging from 303 K (dark red) to 573 K (yellow)

By scanning the laser across a layer of deposited nanoparticles in the confocal microscope, we were able to capture an array of emission spectra. We then converted this emission spectra into a temperature map using the luminescence intensity ratio of the 2 peaks at each pixel. After a number of correction steps, the technique showed a remarkable precision of 1-4 K with a spatial resolution of ∼1 micrometer. It is noteworthy to mention that most other techniques are unable to achieve such a high accuracy like this.

Tijn article - Figure 3 DESKTOP reliable temperature mapping

In a) we scanned the laser across the microheater with the deposited luminescent nanoparticles to generate a map of intensity ratios. b) shows the spectrum at each pixel converted into a temperature to provide a temperature map of the microheater.

Simulation and model accuracy

Using the fully corrected temperature maps, we were able to analyze in depth the temperature homogeneity of the microheater. The figure below shows the horizontal traces through the center of these maps. The simulated temperature profiles (lines) show an excellent match with the experimental traces (dots).This confirms both the reliability of the finite element model as a design tool and the strength of our temperature mapping technique as a characterization tool, achieving a high accuracy and a spatial resolution of ∼1 μm.

Tijn article - temperature mapping in graph

A graph showing the mapping of elevated temperatures. The lines represent the simulated temperature profiles and the experimental traces represent the dots.

We determine the standard deviation of the temperature in the center to quantify the accuracy of this thermometry method and find values of 1 K at 323 K increasing to only 4 K at 513 K. Conclusively, this makes nanothermometry using confocal luminescence spectroscopy a promising method to map temperature profiles not only for microheaters but also in other fields such as biology and catalysis where temperature variations are important but hard to monitor with conventional methods.
Tijn portrait image
“Thanks to the exceptionally good spatial and temperature resolution of this method, we were able to obtain an accurate temperature map of our microheater spiral. This confirmed the excellent temperature homogeneity which was predicted by our finite element models.”
Tijn van Omme
Microsystems Engineer |  DENSsolutions

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The first in situ observation of layered metastable heterostructure formation

Using our Wildfire system, scientists are able to thoroughly investigate the formation of heterostructures from starting materials with vastly different properties

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The first in situ observation of layered metastable heterostructure formation

The first in situ observation of layered metastable heterostructure formation

Using our Wildfire system, scientists are able to thoroughly investigate the formation of heterostructures from starting materials with vastly different properties

Original article by Markus Terker, Lars Nicolai, Samuel Gaucher, Jens Herfort and Achim Trampert

Markus Terker top image in article graph

A plot showing the STEM images taken of the heterostructure demonstrating a tendency for disordered layers to order over time with annealing

Heterostructures, semiconductor structures composed of solid-state materials with different chemical properties, have found use in a variety of specialized applications where their unique characteristics are critical. The engineering of heterostructures is an important means in creating novel device concepts. In fact, it has already revolutionized the development of solar cells, transistors and even lasers. However, layering materials with vastly differing properties poses complex challenges.

Using the DENSsolutions Wildfire system, Markus Terker and his colleagues from the Paul-Drude-Institut in Berlin, Germany observe for the first time the atomic formation of a layered, metastable iron germanium crystal via two-step phase transformation. This research opens doors towards the design and formation of novel hybrid materials that combine vastly different properties, such as ferromagnets and semiconductors, and has appealing implications for optical-electronic industries.

Heterostructural interfaces and stability

Heterostructural interfaces are fundamental and versatile tools when designing electronics with varying properties, such as magnetic, optical, and transport capabilities. Since these interfaces can be used to stabilize otherwise metastable structures, understanding their structures and formation is essential to harnessing the full potential of these materials. Shedding new light on the growth of these interfaces from disordered to ordered states opens up the potential for new applications of this technology.

In this research, Terker and his colleagues observed the in situ annealing of two materials and the resulting FeGe₂ alloy interface between them. This gradual process, catalogued in the figure below, shows the crystallized FeGe₂ at the interface slowly ordering itself into layers of material.

Markus Terker figure 1 showing snap shots of annealing

In situ snapshots of the alloy interface ordering itself into periodic layers over the span of 60 minutes

From disorder to order

The starting sample consisted of a layer of Fe₃Si interfaced with amorphous germanium, a semiconductor. Heating the sample to 300 °C initiated the crystallization process and a thin layer of FeGe₂ crystal formed at the interface. This layer then grew as the sample was sustained at this temperature for the duration of an hour.

Whilst the sample was heated, in situ images were taken of the progression of the FeGe₂ crystal as it grew along the surface of the Fe₃Si base. After 15 minutes of annealing, the majority of the amorphous germanium film completely crystalized and reduced in size and disorder. However, this stage was still not completely ordered. By the 30-minute mark, the amorphous film completely crystalized and gradually ordered itself layer by layer until the entire film was in an ordered phase. 

STEM images of the (b) disordered and (c) vacancy-ordered structure of FeGe₂ observed. Atomic models of the (a) disordered and (d) ordered phase of FeGe₂ observed. The colored dots indicate the atomic stacking order.

Metastable structure

Although it was expected that pure germanium would form during this solid-phase epitaxy, the researchers observed something else entirely. A strong diffusion of iron into the germanium film was detected at relatively low crystallization temperatures. Moreover, instead of pure germanium with a diamond structure, an epitaxial film with iron content was obtained. High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) confirmed that the resulting crystal had a different metastable crystal structure to what was expected. The figure below shows the heterostructure produced after the annealing process. 

The heterostructure produced after the annealing process

STEM images taken of (a) the heterostructure produced after the annealing process, and (b) a magnified image of the dotted black box showing the vacant layers

Novelty in findings

Phase transformations are one of the most fascinating phenomena in nature. Observing such transformations in real time and with the resolution of individual atoms could revolutionize our understanding of their chemical and physical processes. This research demonstrates that a novel crystal phase of FeGe₂ can be interfaced from two materials with vastly different physical properties: Fe₃Si, a ferromagnet, interfaced with amorphous germanium, a semiconductor. Terker and his colleagues were able to demonstrate that a hybrid sample preparation approach can yield thin samples suitable for high resolution HAADF STEM while at the same time retaining the sample composition and structure. This approach could be applied to many different heterostructures and lead to a much broader applicability of the in situ TEM method in the study of phase transformations.

Markus personal image improved

“For the atomic scale investigation of small nanostructures at high temperatures, the reduction of sample drift is of paramount importance. The new generation of DENSsolutions Wildfire Nanochips offer the ideal solution for this due to their small and reproducible bulging. Their robustness also enables an easy and safe transfer of the specimen lamella of any form or sample geometry.”

Markus Terker
PhD Student |  Paul-Drude-Institut in Berlin, Germany 

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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

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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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Dental crown created by selective laser melting (SLM)

Improving the mechanical properties of 3D printed metal parts

 

Using our Wildfire system, researchers explore the microstructural changes occurring in AlSi10Mg during 3D printing and post processing

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Improving the mechanical properties of 3D printed metal parts

Improving the mechanical properties of 3D printed metal parts

In situ TEM helps to understand the microstructural changes in AlSi10Mg during 3D printing and post processing

 
Original article by Mihaela Albu, Robert Krisper, Judith Lammer, Gerald Kothleitner, Jacopo Fiocchi and
Paola Bassani
Dental crown created by selective laser melting (SLM)

Dental crown created by selective laser melting (SLM)

Selective laser melting (SLM) is an additive manufacturing technique used to create unique products for the medical technique, automotive-, aeronautic- and space industry. AlSi10Mg alloy is widely used for this technique because of its low weight, corrosion resistance, good thermal properties, specific strength, and flexible post processing capabilities. The mechanical properties of 3D printed parts show better values compared to parts that are made using traditional casting of metal. But these values decrease after conventional heat treatment. In this research, scientists from Graz Centre for Electron Microscopy, Austria, tried to understand the fundamental mechanisms responsible for the drop in mechanical properties after heat treatment.
This work provides the first correlative in-situ heating multiscale analysis of the powder and the additive produced AlSi10Mg alloy, allowing a unique insight into material transitions at the micro-and nanoscale. The researchers showed that microstructural changes like crystallization of eventually present amorphous phases and the evolution of Si nanoparticles evenly dispersed in the Al-matrix are the most important factors that contribute to the enhancement or decrease of the mechanical properties.

Towards affordable 3D metal printing

Nowadays, selective laser melting (SLM) refers to the most common system used to create metal parts from powders as feedstock. Despite its popularity, powder based additive manufacturing is still an expensive process, and consequently, getting proof components at the first attempt is of great economic interest. Manufacturers of such parts strive for optimizing their processes, not only to improve material properties, but also to enhance the interchangeability of building platforms and thus, their economic flexibility. Controlling these production aspects and finding an adequate post-processing strategy helps to fine-tune the microstructural features, and therefore the mechanical properties, according to different application fields.

Low magnification HAADF STEM video 80°C to 360°C in 20°C steps for the as-built sample, maintaining the isothermal stages for 4 min each
Atomic resolution video of a Si nanoparticle in the Al-matrix during in-situ heating

Benefits of in situ STEM

In-situ heating experiments in scanning transmission electron microscopes (STEM) enable immediate information about the structural, morphological and chemical changes and are thus helpful for the selection of various post-processing strategies.

DENSsolutions Wildfire System TF FEI

The DENSsolutions Wildfire H +DT system enabled the fast heating and cooling that allowed us to perform nanoscale crystallographic and chemical analyses at certain temperatures that corresponded to the exothermic peaks in DSC measurements and to the in-situ XRD measurements.

Dr. Mihaela Albu
“In-situ heating experiments performed on 3D printed materials enable breakthrough advances in printing and post-process optimization. DENSsolutions Wildfire system proved to have superior thermal and spatial stability, ensuring high-resolution investigations at higher temperatures.”

Dr. Mihaela Albu
Senior Scientist | TEM at the Austrian Centre for Electron Microscopy and Nanoanalysis

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EUSMI Nanostars Project

EUSMI Nanostars Project

Nothing could better illustrate the excellence of EUSMI Joint Research Activity (JRA), than the Nanostars project, which has combined the expertise of three EUSMI partners from three distinctive areas: CIC biomaGUNE, EMAT and DENSsolutions.

Nanoparticles are a versatile functional material and have much potential in medical applications. The chemists at CIC biomaGUNE have successfully synthesized a novel type of nanoparticles, targeting at cancer diagnosis and therapy. For this, it is crucial to obtain a precise understanding of the particle morphology, especially at high temperature. The electron microscopy experts at EMAT in Belgium have come to help and taken up the challenge to visualize the nanoparticles.

This challenge is formidable but also pushing the frontier of the electron micrsoscope technique. A new component must be developed and implemented into the existing machine. To achieve this, EMAT has jointed force with engineers and experts from DENSsolutions. In the video, you will see how the trio has produced a masterpiece of solution and extended the scientific and technical know-how.

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Wildfire In Situ heating system enables capturing the Structural evolution of co-catalysts

Wildfire In Situ heating system enables capturing the Structural evolution of co-catalysts

Original article by Siyuan Zhang, Leo Diehl, Sina Wrede, Bettina V. Lotsch and Christina Scheu. Published in Catalysts 2020, 10, 13.

There is a pressing need to develop renewable solutions for energy conversion and storage. Photocatalysis feeds both birds by one scone, utilizing a semiconductor to harvest solar energy, and co-catalysts to convert the energy into fuels. Such photocatalytic composites are often synthesized in nanometre-size to benefit from large surface areas. Seeing the structure of these “nano-composites” is a fundamental step for rational designs toward higher catalytic activity.

Controlled Heating

In this study, scientists from the Max Planck Institute (MPIE) designed a photocatalytic nanocomposite system with an ultimately thin semiconductor – a single crystal layer of 1 nm thickness. The co-catalysts are similarly tiny, synthesized with controlled heating by a DENSsolutions Wildfire system inside a transmission electron microscope (TEM). Structural evolution of the co-catalysts is captured by in situ TEM observations, based on which a design of co-catalysts with improved photocatalytic activity was demonstrated.

Figure 1. Growth of Ni nanoparticles from the nanocomposite with 10 wt% Ni loading during in situ heating under vacuum. Scale bars in both image sets (a), (b) are 50 nm. (figure from Siyuan Zhang, Max-Planck-Institut für Eisenforschung GmbH, published in https://doi.org/10.3390/catal10010013)

The NiOx co-catalyst was generated from the Ni(OH)2 precursor using a dehydration process. The reaction is irreversible, and the nucleation of the NiOx nanoparticles occurs in a split second.
“The low bulging of the Wildfire chips allows me to keep the atomic resolution imaging with ease and observe the onset of the fast nucleation kinetics.
The latter process of nanoparticle growth is much slower and requires substantial areas for statistics. The fast and reliable temperature ramp up and quench down of the Wildfire chips enables me to monitor the structural evolution over multitudes of areas from global views to atomic resolution imaging.
Moreover, I have run these heating experiments using two generations of Wildfire chips. The sample preparation has become much easier with the new generation, as the droplet of my nanocomposite suspension can be reproducibly dried on the heating area.”
Dr. Spark (Siyuan) Zhang
Max-Planck-Institut für Eisenforschung

The mystery of x

The research is motivated by the fundamental question in materials science, the relationship between structure and properties. The reaction rate is a number to be optimised in photocatalysis. On the other hand, the structure of the studied nanocomposite is multifarious. In addition to capturing the nucleation and growth of NiOx nanoparticles, we reveal the mystery of x in the chemical composition. By repeated heat treatment protocols, nanoparticles during various stages of growth can be “frozen” for microanalysis. By electron energy loss spectroscopy and multi-variate statistical analysis (https://doi.org/10.1093/jmicro/dfx091), a metallic Ni core and an oxidized shell of NiOx is resolved.

Challenging common wisdom

With the resolution power of a modern TEM plus the accurate and stable heating provided by DENSsolutions, we can study the ultimate miniaturized nanocomposite for photocatalysis. The common wisdom to maximize surface areas of catalysts is challenged by our findings, as we exemplify improved activity from core/shell co-catalysts with sufficient spacing between them.

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