Research Applications

Eleven research applications on which our research group focuses most of its energy and time!

Nanomaterials

The field of applications of nanomaterials has been increasing exponentially in the last decades, part of this being related to the development of high spatial resolution TEMs and SEMs to characterize them. From the beginning of the nano-research, TEM has been the technique of choice for their study. However, since two decades, new types of field-emission SEMs (FE-SEMs) have been developed with a sub-nanometer probe size. Especially, cold-field emission SEMs (CFE-SEMs) provide the highest brightness and the smallest energy spread available in the FE-SEMs family. This allows imaging nanoparticles of just a few nanometers at very low voltage (E0 < 1 kV) when using the deceleration mode, and details of the order of 0.5 nm have been measured at high voltage in bright-field STEM mode. Moreover, when combined with an annular silicon drift detector, a spatial resolution of a few nanometers was achieved in x-ray spectral imaging of carbon nanotubes covered with platinum nanoparticles.

 

Development of new methods for quantitative X-Ray microanalysis

 

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Biological Applications

 

The development of low voltage electron microscopy for surface of fracture imaging (E0 < 5 kV) as well as for imaging of electron transparent thin slices in STEM mode (E0 < 30 kV) is now well established in the biological community. By reducing the beam voltage, higher surface sensitive imaging is possible and images closer to the reality are obtained. On the transmission side, low voltage is revisited by the TEM community and is a new field of interest for the SEM community. The increase of electron scattering when the beam voltage is decreased enhances greatly the contrast of the image, especially in bright-field mode. This advantage, in addition to preventing from knock-on damage which is catastrophic for bio-studies, combined with a sub-nanometer probe size, makes new generation SEMs a highly complementary tool in regards to TEM.

 
 

Mining and Geological Applications

The knowledge of the chemical composition of rocks and mining ores is mandatory to optimize extraction procedures and understand phase transformations and interactions all along the rock timescale. X-ray microanalysis and electron backscatter diffraction (EBSD) are the most indicated techniques to obtain chemical and crystallographic information from the macroscopic scale to the nanoscale. Moreover, fast screening is necessary to refine the extraction process applied to mineral ores. From Nechalocho ores (Northern West Territories, Canada), fast x-ray mapping with an annular EDS detector providing 1.2 sr collection angle with a very fast acquisition time and high resolution EBSD maps were recorded and permitted to identify nanometers sized Y-fergusonite, a REEs rich phase, crystallites intimately mixed with zircon particles.

 

Diffusion in materials


The diffusion of constituent elements in a material during its manufacturing determines its mechanical and physical properties via the specific microstructure resulting from their concentration. Hence, the knowledge of the diffusion coefficients is of primary importance when studying a particular alloying system. Based on the newly developed f-ratio method, low voltage x-ray microanalysis quantitative line profiles were recorded on aluminum-magnesium systems and the diffusion coefficients calculated for specific conditions. The spatial resolution due to the low beam energy is highly necessary to represent precisely the diffusion steps of the profile. Combined with electron backscatter diffraction (EBSD), the Mg diffusion coefficient at grain boundaries in Al was shown to be highly dependent on the misorientation angle and the calculated diffusion coefficient values fitted perfectly those obtained from the model.

Imaging of Advanced Metallic Alloys

 

Because of the large range of accelerating voltages and the large field of view it provides combined with specific detection devices, the SEM is the most adapted tool for assessing the microstructure of advanced metallic alloys. By a combination of BSE imaging, EBSD, EDS and STEM analysis, a full characterization of the chemistry, crystallography, and magnetic properties is now possible with a single instrument. By varying the accelerating voltage, a volume distribution characterization of precipitates and inclusions is achieved with a spatial resolution of less than 10 nm in bulk specimens coupled with high throughput SDD detectors for their chemical analysis. Plastic deformation micro-structure and texture as well as dislocation structures are revealed through the use of EBSD combined with electron channelling contrast imaging in a wide range of processes. STEM, combined with transmission electron forwardscatter diffraction (t-EFSD), allows going into the characterization of chemistry and crystallography in depth when thin specimens are used and orientation mapping has been performed with spatial resolution better than 5 nm.

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Specific techniques in the SEM

 

At the McGill Electron Microscopy Research Group (MEMRG), the development and improvement of innovative techniques in the SEM is at the core of our research. From sample preparation to data post-processing, new approaches to characterize advanced materials have been developed in the recent years. A new technique, based on the immersion of geological materials in a diluted solution of ionic liquid (BMI-BF4) prior to the SEM analysis, was applied and permitted to obtain high resolution Kikuchi patterns with reduced charging issues and EBSD maps were acquired without drift or signal distortion. An EBSD camera fitted with a forescatter detector (FSD) was used to take advantage of its full capabilities for imaging and analysis. By placing the camera below a thin sample, the acquisition of Kikuchi patterns and orientation maps close to the nanoscale were possible. With the same configuration, the two bottom diodes of the FSD were used to collect high angle scattered electrons to generate dark-field images with nanometer resolution. Finally, magnetic domain imaging is now possible with the normal EBSD configuration when the FSD is used to collect the forwarded electrons deviated by the magnetic force inside each domains, permitting to related texture obtained by EBSD with the magnetic domain structure of the same area.

 
 

Development of Monte Carlo methods

 

 

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Polymer-based nano-composites

 

Polymer nano-composites manufacturing is an important field of research at McGill University. To understand the mechanical and electrical properties of these materials, a FE-SEM can provide invaluable information about the nano-particles (NPs) distribution inside the polymeric matrix due to the high contrasts available at low voltage in bulk (< 5 kV)  and thin (< 30 kV) specimens with STEM and energy filtered in-lens detectors. When conductive NPs are added to the polymer, charge imaging permits to image the NPs with very high contrast and roughly evaluate the electrical conductivity of the material.

 

Energy storage

 

To support the development of clean vehicles, an increasing research in electrode materials for ion-lithium batteries is ongoing. In addition to electrochemical tests, morphological, chemical and crystallographic characterizations are necessary to understand its properties at the nanoscale and finally provide the highest efficiency and lifetime to the final product. The FE-SEM provides high spatial resolution at a wide range of beam energy combined with chemical analysis at the nanoscale (annular SDD) and high contrast detectors. This allows an controlled refinement of the fabrication process with high speed and precise characterization of by-products that may reduce the efficiency of the final electrode.

 

Related references:

 

 

 

 
 

Other research applications:

  • Biomaterials

 

 

© 2014 by the McGill Electron Microscopy Research Group | Raynald Gauvin.

V. 1.2.7 (June 14, 2019)

Diffusion in materials

By the McGill Electron Microscopy Research Group