DENSsolutions’ Lightning system helps uncover the interaction mechanism in reactive metal-ceramic system, Al-SiC

DENSsolutions’ Lightning system helps uncover the interaction mechanism in reactive metal-ceramic system, Al-SiC

Using the DENSsolutions Lightning system, researchers were able to provide an electrical, chemical and structural analysis of the Al–amorphous SiO₂–SiC interface at high temperatures.

Original article by Adabifiroozjaei et al.

The use of hybrid materials containing both metals and ceramics has become increasingly popular within manufacturing and microelectronic industries due to their optimized and well-balanced properties. Aluminum-silicon carbide (Al-SiC) is a widely known metal-ceramic composite material, commonly used in microelectronic packaging for automotive and aerospace applications. In Al-SiC an amorphous oxide layer (AOL) of SiO₂ is known to exist between the Al and SiC. Notably, the mechanism of interaction between the reactive metal (Al) and ceramic (SiC) and the AOL (SiO₂) under the heat-treatment process is still not well-understood. In fact, numerous theories about the interaction mechanism have been proposed over the past few decades. The major problem is that the studies conducted so far, regardless of the mechanism proposed in them, were ex situ and therefore not capable of resolving the atomic-scale nanostructural and chemical changes occurring at the interfaces during the heat-treatment process. In a recent paper published in the Journal of Materials Science, involving our valued users at TU Darmstadt, Dr. Esmaeil Adabifiroozjaei and Dr. Leopoldo Molina-Luna, the DENSsolutions Lightning system was utilized to reveal the evolution mechanism of the Al–AOL–SiC system under heating and biasing conditions. This study involved a team of researchers from institutes all over the world, including the University of Tabriz in Iran, NIMS and Shibaura Institute of Technology in Japan, and UNSW Sydney in Australia. 

Sample preparation

The first step for Dr. Adabifiroozjaei and his fellow collaborators was to carefully prepare the Al-SiC sample. After ultrasonically cleaning the SiC wafer, removing the oxide layer and allowing its regrowth by inserting the wafer into a desiccator, an Al layer with a thickness of ~1 µm was sputtered on the wafer using Shibaura’s CFS-4EP-LL sputtering machine. Next, in order to prepare the lamella, the researchers applied focused ion beam milling using JEOL’s JIB-4000 FIB. The prepared lamella was then loaded onto the DENSsolutions Lightning Nano-Chip (see Figure 1a). The low- and high-magnification scanning electron microscopy (SEM) images of the chip and the loaded lamella are shown below in Figure 1b) and 1c), respectively. Next, an Au lamella was prepared by FIB and connected to Al–AOL–SiC lamella and chip in order to ensure electrical current passes through Al–AOL–SiC lamella.

Figure 1: a) DENSsolutions Lightning Nano-Chip used for the in situ heating and biasing experiment, b) low- c) and high-magnification SEM images of the loaded lamella on the Nano-Chip, respectively.

Experimental results

The researchers performed EDX and EELS elemental mapping to determine the chemical composition of the phases across the Al–AOL–SiC interface. The EDS mapping of the interface is shown in Figure 2a), while the high-resolution EELS elemental mapping of the interface is shown in Figure 3b) – both of which reveal the consistent presence of a narrow oxide layer with a thickness in the range of 3–5 nm. 

Figure 2: a) EDS elemental mapping of Al–AOL–SiC interface, showing the presence of the AOL, b) STEM-HAADF image of Al–AOL–SiC interface and its EELS map profile.

Next, the researchers began with the in situ heating and biasing experiment to study the electrical characteristics of the lamella. First, a compliance current was set to 3 nA, then the voltage required to reach such a current was recorded at each temperature. The acquired I–V curves for room temperature, 500 ° and 600 °C after 30 minutes of application of the field are presented in Figure 3a–c), respectively. The I–V curves and high resolution TEM images (shown in Figure 3d–f) indicate that the resistivity of the Al–AOL–SiC device decreased three orders of magnitudes at 500 °C with no apparent change in the nanostructure. 

Figure 3: a), b), and c) show the I–V curves of Al–AOL–SiC interface measured at room temperature, 500° and 600 °C, respectively. d), e), and f) show the high-magnification images of Al–AOL–SiC interface from a small area of low-magnification images.

The chemical changes occurring at the interface during the heating process were investigated on another lamella using the same DENSsolutions Lightning holder, but on a Wildfire (heating-only) Nano-Chip. HAADF-STEM images and EELS chemical profiles were acquired and the results are shown in Figure 4 below. 

Figure 4: a), b), c ) and d) show changes in chemistry (line profiles of Al (Aqua), Si (Violet), C (Lime), and O (Yellow)) of Al–AOL–SiC interface at room temperature (25°), 550°, 500° and 600 °C, respectively.

During this analysis, the researchers observed that at 550 °C, the AOL width was reduced, which was specifically due to AOL dissolution into the Al. Moreover, the analysis of the structural changes at the interface nanostructure at 600 °C showed that the dissolution of the SiO₂ amorphous layer resulted in the formation of α-AlO and Si within the Al. In contrast, the elemental interdiffusion (Al³⁺ ⇄ Si⁴⁺) between Al and SiC was observed to occur, resulting in formation of AlC. From the results, we can infer that the reaction mechanism between Al and crystalline SiC is different with that between Al and SiO₂ amorphous phase.

Conclusion

Dr. Adabifiroozjaei and his fellow collaborators performed a comprehensive in situ STEM heating and biasing study using the DENSsolutions Lightning system, investigating the electrical, chemical and microstructural features of the interface of a Al–AOL–SiC system. Performing this study under an ultrahigh resolution of 4 Å allowed the researchers to confirm, for the first time in literature, that the reaction mechanism between reactive Al and crystalline SiC is different than between Al and amorphous SiO₂. Specifically, they found that whereas the reaction between SiO₂ and Al follows the dissolution mechanism, the reaction between SiC and Al proceeds through elemental interdiffusion. Importantly, these findings might be applicable to other reactive metal-ceramic systems that are currently used in manufacturing and electronic industries.

“With the stability and accuracy provided by DENSsolutions Lightning system, we could reveal features of an interfacial interaction in a common metal-ceramic system (Al-SiC) that were not previously observed. Such studies at very high resolution are absolutely necessary for the understanding and future development of composite materials at elevated temperatures.” 

Prof. Dr. Leopoldo Molina-Luna   Professor  |  TU Darmstadt

Original article:

 

Discover our Lightning solution:

Discover more publications made possible by Lightning:

Thomas article feature image

Liquid flow control: Unlock untapped research capabilities within in situ LPEM

Using the DENSsolutions Stream system, researchers were able to create a highly controlled chemical environment for visualizing the nanoscale metallic electrodeposition of copper crystals.

Subscribe to our newsletter to stay up-to-date with the latest in situ microscopy news.

Liquid flow control: Unlock untapped research capabilities within in situ LPEM

Liquid flow control: Unlock untapped research capabilities within in situ LPEM

Via the unique on-chip microfluidic channel of the DENSsolutions Stream system, researchers were able to create a highly controlled chemical environment for visualizing the nanoscale metallic electrodeposition of copper crystals.

Original article by Cheng et al.

Liquid phase transmission electron microscopy (LPTEM) enables the observation of time-resolved dynamics in liquid state at high spatial resolution. The technique has gained exponential popularity over the last decade, and has contributed greatly to a wide range of fields, including materials science, chemistry and life science. With LPEM, researchers can explore the dynamical evolution of key materials and uncover fundamental insights into nucleation and growth. Only in recent years have researchers been able to control the chemical environment within an in situ LPEM experiment, owing to the award-winning innovation that is the DENSsolutions Stream system. In a recent publication, researchers including Dr. Ningyan Cheng from Anhui University utilized the Stream system to visualize the metallic electrodeposition of copper crystals in a highly controlled chemical environment. This was made possible due to the unique on-chip flow channel of Stream, which enables numerous advantages such as the ability to flush away beam-induced species, explore flow-dependent liquid dynamics and easily change electrolyte composition.

On-chip microfluidic channel

The core of the DENSsolutions Stream system is our patented Nano-Cell, which consists of a top and bottom chip, together forming a sealed compartment that enables users to safely perform liquid experiments inside the TEM. The bottom chip contains spacers, an integrated liquid inlet, flow channel and an outlet. Via pressure-based pumps, a liquid sample can be driven from the inlet through the field of view and then through the outlet. This process is demonstrated in the video below. Importantly, users can independently control the pressure at the inlet and outlet of the Nano-Cell, and therefore the absolute pressure in the microfluidic channel. This then enables full control over the liquid flow rate within the cell.

Movie 1: Animation depicting the microfluidic channel of the Stream Nano-Cell

Efficient liquid flow

Before observing any liquid phenomena in the TEM, Dr. Cheng and her fellow collaborators first had to ensure that the flow was efficient and well-controlled. To do this, the researchers first assembled a dry Nano-Cell. The flow was then initiated by turning on the pressure-based pump, while keeping all imaging parameters constant. After 30 seconds, the imaging contrast changed abruptly, implying that the liquid had definitely flowed into the Nano-Cell. This process is shown in the video below. The time taken to completely fill the Nano-Cell ranges anywhere from tens of seconds to just 3 minutes when a flow rate of 8 μl/min is applied.

Movie 2: In situ TEM movie showing the liquid flow into the Nano-Cell in just 30 seconds

Removal of beam-induced species

A key benefit of controlling the liquid flow within an LPEM experiment is the ability to remove beam-induced particles. The researchers first generated particles by increasing the electron flux on purpose through changing the spot size from 5 to 1. The process of removing the beam-induced species in this experiment is detailed in the video below, with the direction of the flow going from top to bottom. As soon as the flow was cut off at 6.4s, the particles started to form and grow on the membrane. The flow was then switched on again at 11.7 seconds, which is when the particles that were stuck to the membrane started to peel off and move from the top to the bottom area in the field of view. It took just 2 minutes to fully flush away the particles, which is a reproducible process. The direction of the particles’ movement is the same as the direction of the flow (top to bottom), confirming the effectiveness and power of the liquid flow control. 

Movie 3: Removal of beam-induced species via liquid flow control

Capturing flow-dependent liquid dynamics

The next step for the researchers was to explore the effect of the flow rate on the electrochemical copper crystallization and dissolution processes in real time. They first observed the effect of using a higher flow rate of 1.4 μl/min on the Cu deposition and dissolution processes, which showed to be reversible. The protocol included the initial electrode cleaning, deposition (−0.9 V, 10 s), dissolution (+0.4 V, 15 s) and repeating the process for 4 cycles. As demonstrated in the video below, the researchers found that uniform copper deposition can be obtained at a higher liquid flow rate (~1.4 μl/min), whereas at a lower liquid flow rate (0.1 μl/min), the growth of copper dendrites was observed. 

Movie 4: Copper electrodeposition at a flow rate of 1.4 μl/min (left) and 0.1 μl/min (right)

Changing electrolyte composition

Besides exploring the effects of altering the flow rate, a major point of interest in this study was observing the effect of adding foreign ions, such as phosphates, on the electrodeposition. Such additives can affect the electrochemically deposited crystals by, for example, changing the nuclei structures. The researchers first studied the electrodeposition of copper from a pure CuSO₄ aqueous solution. In this case, no obvious dendritic morphology was observed and instead only granules were formed (see below Figure 1, Left).

After the experiment, the electrolyte in the sample source was replaced by a mixture of CuSO and KHPO solution. The liquid was kept flowing with a flow rate of 3 μl/min for 15 min, which enabled the researchers to directly study the electrolyte effect on the depositions in the same liquid cell by excluding all the uncertainties during different cell assembly. Contrastingly in this case, copper dendrites were observed to grow and the addition of HPO− ions in the electrolyte led to the formation of Cu-phosphate complexes (see Figure 1, Right). These results further confirm the importance of being able to modulate the electrolyte composition, and demonstrate the effectiveness of the environment control that Stream enables.

Figure 1: The effect of phosphate addition on Cu electrodeposition

Exploiting electrode design to alter the chemical environment

When studying Cu electrodeposition in the previous experiment, the researchers saw that dendrite formation can be further promoted by the in situ addition of foreign ions, such as phosphates. In order to confirm the generality of this technique, they also took a look at Zn electrodeposition in an aqueous solution of ZnSO. The figure below shows the total growth of the zinc layer at b) a lower potential of −0.9 V (versus Pt) in the first 10 seconds, and c) a higher potential of −1.1 V (versus Pt) in the next 10 seconds. In d) the total growth of the Zn depositions in the first 20 seconds is shown. The researchers observed in the first 10 seconds (−0.9 V) that the deposition on the inner edge is rougher compared to the outer edge. In the following growth at −1.1 V, dendritic depositions are nucleated and grown on the previous outer edge, while no further growth can be observed in the inner edge. This experiment demonstrates that the special electrode design of Stream enables the exploration of rich liquid dynamics within different chemical environments. 

Figure 2: Zinc electrodeposition in b) the first 10 seconds with a potential of −0.9 V and c) in the next 10 seconds with a potential of −1.1 V. d) shows the total Zn growth in the 20 seconds.

Conclusion

Through this study, it is shown that Stream’s distinctive ability to enable liquid flow control opens the doors for researchers to truly alter the chemical environment within the liquid cell. By controlling the liquid flow, a user can flush away beam-induced species, explore flow-dependent liquid dynamics and easily change electrolyte composition. Moreover, the unique design of the electrodes in the Stream system allows researchers to explore complex liquid dynamics within different chemical environments within the same liquid cell. Importantly, the direct observations made by Cheng et al. not only provide new insights into understanding the nucleation and growth, but also give guidelines for the design and synthesis of desired nanostructures for specific applications, such as high performance electrocatalysis for energy conversion and electrodes for secondary batteries. 

Hanglong Wu portrait

Image of Dr. Ningyan Cheng from Max-Planck-Institut für Eisenforschung GmbH

“The DENSsolutions Stream System not only provides a useful means to study a wide range of dynamics in solution, but also enables systematic studies of the effect of the chemical environment on the corresponding reactions through precise control of the flow rate, liquid composition and other significant parameters.” 

Prof. Dr. Ningyan Cheng   Associate Professor  |  Anhui University

Original article:

Discover our Stream solution:

Discover more publications made possible by Stream:

Thomas article feature image

Climate helps uncover phase coexistence and structural dynamics of redox metal catalysts

Using our Climate system, scientists are able to interrelate the atomic-scale structural dynamics of redox metal catalysts to their activity.

Subscribe to our newsletter to stay up-to-date with the latest in situ microscopy news.

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

Original article:

Discover our Wildfire solution:

Discover more publications made possible by Wildfire:

Markus article feature image

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

Do you want to receive great articles like this in your mailbox? Subscribe to our newsletter.

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 

Original article:

 

Discover our Wildfire solution:

Discover more publications made possible by Wildfire:

Torsten feature image

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

Do you want to receive great articles like this in your mailbox? Subscribe to our newsletter.

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

Original article:

 

Discover our Wildfire solution:

Discover more publications made possible by Wildfire:

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

Do you want to receive great articles like this in your mailbox? Subscribe to our newsletter.

The first direct observation of pharmaceutical non-classical crystallization

The first direct observation of pharmaceutical non-classical crystallization

Using the Ocean system, scientists achieve supersaturation in LPEM experiments, revolutionizing pharmaceutical crystallization

 

Original article by Jennifer Cookman, Victoria Hamilton, Simon Hall and Ursel Bangert

LPEM video showing the pre-crystallization process of flufenamic acid

Whereas classical crystallization deals with layer-by-layer growth of crystals, non-classical crystallization (NCC) involves multiple different crystallization pathways towards the formation of final stable crystals. Although NCC has been widely documented in research, there is still much to be explored regarding the intermediate stages of crystallization and their direct observation. This is especially true for small organic molecules like flufenamic acid (FFA), an anti-inflammatory drug used for the treatment of rheumatic disorders.

Using the DENSsolutions Ocean LPEM system, Dr. Jennifer Cookman from the Bernal Institute in the University of Limerick and her colleagues were able to capture the intermediate pre-crystalline stages of this small organic molecule. This research marks the first ever direct observation of a pharmaceutical material undergoing NCC, highlighting the rising value and importance of in-situ TEM techniques in the pharmaceutical industry. 

The observed processes of NCC

Crystallization is a fundamental process that occurs in nature to produce some of the most common materials in daily life, such as the popular active pharmaceutical ingredient (API) ibuprofen or FFA. Properties such as solubility and bioavailability are linked to the crystal structure of the active compound. Considering APIs are commonly polymorphic, it is important to understand the intermediate stages of their crystallization. Specifically, if we can identify polymorphs with more desirable properties in the intermediate stages of crystallization, then this opens the door to harnessing and potentially directing their formation.

In this study, Dr. Cookman and her colleagues observed in situ the processes involved in the nanoscale crystallization of FFA. As illustrated in the figure below, this process involves four stages: aggregation, coalescence into a metastable entity, nucleus formation, and finally, crystallization.

A summary of the observed processes involved in the nanoscale crystallization of FFA

The researchers observed that FFA begins as a collection of small independent pre-nucleation clusters (PNCs). These PNCs are essentially stable particle clusters that form prior to the nucleation of a solid phase. They were able to follow three notable aggregates of PNCs that each followed the same transformational events. Particularly, after aggregation, these PNCs each independently coalesced, or merged, and formed a metastable phase. After this, the densification and development of a nucleus occurs, leading to the formation of FFA crystals. The processes of coalescence and densification will be further discussed and depicted below.

Coalescence

The aggregation of the PNCs were shown to have occurred prior to the researchers’ initial observations. Therefore the primary transformation observed for the three aggregates was actually that of coalescence. In the image below, you can see clearly that for each of the three selected aggregates, the individual clusters merge to form one cohesive entity after approximately 3 minutes.

A time-lapse of each of the three aggregates of PNCs undergoing coalescence

Densification towards crystallization

Following coalescence is the densification and development of a nucleus. This nucleus is formed by the successive sacrifice of surrounding material, leading to the formation of a new crystalline-like object, significantly more electron dense than before. Whereas coalescence took around 3 minutes, this densification occurred rapidly in under 10 seconds. The image and three videos below depict this rapid pre-crystallization process of FFA. 

A frame-by-frame summary of the three aggregates illustrating the pre-crystallization process of FFA

Aggregate 1

Aggregate 2

Aggregate 3

Novelty in findings

This research contributes academically in that the direct observations reported for the crystallization of FFA reveal insightful new information about the potential pathways towards crystallization. Moreover, it highlights the need to further investigate the nucleation and resulting crystallization of other small organic molecules via in situ techniques such as LPEM. LPEM presents itself as a required and complementary tool to not only comprehend but also probe chemistry at the nanoscale. This is true especially in regards to the crystallization of pharmaceutical ingredients, in which the development of the end product highly depends on controlling at the molecular building block level. 

The novelty of this research also lies in that it sheds light on the crystallization and nucleation of pharmaceutical products, providing the necessary information to further refine industrial-scale processes. If we can observe and understand the crystallization pathways that small organic molecular crystals like FFA take, we can better streamline production activities and develop effective manufacturing processes for generic drugs. It is precisely our goal at DENSsolutions to enable researchers like Dr. Jennifer Cookman to continue to bridge gaps in research using our solutions and uncover results that can impact this world, in the pharmaceutical industry and beyond.  

DENSsolutions Jennifer Cookman

“The DENSsolutions Ocean holder is a simple solution to native environment metrology that has the potential to revolutionize how we view pharmaceutical crystallization.”

 

“The DENSsolutions Ocean holder is a simple solution to native environment metrology that has the potential to revolutionize how we view pharmaceutical crystallization.”

Dr. Jennifer Cookman
Post Doctoral Researcher | University of Limerick

Original article:

 

Discover our latest LPEM solution, Stream:

Discover more publications made possible by Ocean:

Do you want to receive great articles like this in your mailbox? Subscribe to our newsletter.