Single-walled zeolitic nanotubes discovered
Structure determination of novel compounds are important in order understand their properties. A new class of nanotube material has been discovered by researchers at Stockholm University together with a research group at GeorgiaTech, USA. The discovery was published in the scientific journal Science.
EMC, SU, is internationally leading in method and software developments of electron crystallography for structure analysis, such as crystallographic image processing and 3D electron diffraction (3D ED). Our competences have attracted collaboration with many internationally leading groups in both academia and industry. We have helped them to determine many structures of interesting zeolites and metal-organic frameworks.
One example of a new materials is the zeolitic nanotube, which was discovered in collaboration with two research groups at GeorigaTech. Through a combination of targeted synthesis and high definition structure elucidation, the zeolitic nanotube was realized. Analogous to the carbon nanotube this material exhibits an extended one-dimensional structure with an ordered wall structure at the atomic-scale. The zeolitic nanotube is composed of a microporous wall, which encapsulates a hollow mesoporous core. The tubular morphology and aluminosilicate composition provide a system with intrinsic multi-length scale ordering, creating unique properties.
Aberration-corrected scanning transmission electron microscopy (STEM) in combination with 3-D electron diffraction provided essential tools to reveal the atomic structure. Information from STEM images acquired from different projections were used in order to reveal its complete atomic structure.
From structure to improved properties with passion
On the journey from nanostructures to improvement in properties of materials, hours in the dark, in front of TEM screens, are probably the most tiresome but hopeful and exciting times for most.
As a doctoral student in material science, using the transmission electron microscope (TEM) to look at what the students cook in the laboratory can be both rewarding and frustrating! After a few years, the joy wears out for most of the people and TEM becomes a dreary routine. But yet, imaging of materials is essential to determine the quality of the nanostructures and provide insight into the applications they are put to work in.
The situation is even starker in the fields of biomedicine and energy research. The specific application drives material scientists into the role of finding the fine-line between art and science in being able to interpret the results with adequate knowledge of contemporary chemistry, physics, biology, and engineering. It is truly an interdisciplinary subject to troll with. Electron microscopy is a tedious task as careful patient interpretation of the obtained results is needed, but there are some people who get excitement out of it. New morphology, size distribution and microstructures are regularly investigated with electron microscopes which often determines the success of their proposed applications.
Two examples of such projects at the Functional Materials Laboratory in KTH focused on development of core-shell type nanocomposite materials for multifunctional biomedical applications. The first, aimed to trigger controlled drug delivery upon heating or by applying an external magnetic field, for killing cancerous cells. FE-TEM provides high resolution imaging down to angstrom level to clearly visualize the magnetic nanoparticles with sizes ranged in single domain limit. A layer of mesoporous silica as drug reservoir was finely coated on single magnetic cores with a few nanometre porous channels that could only be visualized under HRTEM for optimizing the most adequate structures. To endow external-stimuli triggered property, a layer of thermo-sensitive polymer was grafted onto the surface of nanoparticles. Various staining techniques for TEM imaging on polymer coatings allow its proper imaging of dried nanoparticles and cryogenic TEM was used for direct observation of polymer and small-molecule materials and structures in solution preserving the system as synthesised. The other project was to design an all-in-one contrast agent for multiple bio-imaging techniques, which was applied to enhance the imaging contrast to facilitate better diagnosis. Similarly, after obtaining a uniform silica coating on a single gold nanorod, a layer of amorphous gadolinium oxide carbonate was grown on the outermost layer. With the proper combination of gold and gadolinium, photoacoustic imaging, computed-tomography and magnetic resonance imaging could be realized with just one type of particle. Compared to normal imaging under bright field, high angle annular dark field (HAADF) STEM is an ideal tool to characterize 3D morphology especially for the materials containing elements with a large difference in Z number.
The continued enthusiasm of researchers, at the Functional Materials group in KTH and the other nodes in CEM4MAT, for their work is advantageous for other users. CEM4MAT cares about their colleagues’ and external customers' projects and put their vast experiences to obtain superior data and appropriate interpretation in each case. Where others might see it as tedious, researchers at CEM4MAT are used to continuously operate the machine and get excited by the structure and forms they observe. Research groups and SMEs gain by obtaining better and quicker data useful for their requirements. Thus CEM4MAT allows access to research groups and industries alike to obtain the possibility to use the microscopes for individual needs without requiring to make the large infrastructure investments.
Development of a replica method for analysis of carbo-nitrides in steel
Small precipitates and non-metallic inclusions play important role for metallic construction materials. The effects ranges from positive, as for precipitation hardened materials, to negative, as when precipitates acts as nucleation site for ferrite in the heat affected zone in welds. Thus, it is of importance to have methods that correctly detect and quantify precipitates. Investigations on solid bulk samples can accurately be made on samples that are carefully grinded and polished using optical or scanning electron microscopy. However, when precipitates are small problems arises. Very small particles can be seen in modern SEMs, 10 nm particles can be observed and the diameter can be measured. However, particles smaller than about 100 -200 nm is very difficult to identify correctly in a SEM, both chemistry and phase ID becomes difficult. Particles are then hidden in the bulk and due to limitations on resolution for these methods it is sometimes difficult even to find the precipitates. For TEM 10 nm is not a problem resolution wise, but the matrix is still problematic; usually a TEM foil is 50-100 nm thick and if the particle is 10 nm then analysis is difficult also in the TEM.
One method to solve the above mentioned obstacles is to extract particles using the so called “extraction replica method”. Here a film of non-metallic material is deposited on a grinded, polished and lightly etched surface. Thereafter the film is removed from the bulk applying a suitable metal etchant, see Figure 1 for a schematic explanation of the preparation process. The particles are extracted on the film and can now be analyzed without any disturbing signal coming from the bulk material (matrix). Traditionally, carbon is often used as a material for the deposited film material. This however gives the obvious drawback that the carbon content in a precipitate particle cannot be quantified. In the investigation of steel precipitates this is a major drawback since here often mixed carbo-nitrides are to be analyzed. For example, the nitrogen-carbon ratio in titanium carbo-nitrides is often of interest. We have therefore developed routes for using alumina as deposition material. By using alumina the carbon/nitrogen ratio can be determined using EDS or EELS spectroscopy.
Fredrik Lindberg is the researcher behind the development and implementation of the technique at SwereaKIMAB.