Friday Lecture | 24 November

How to visualize and characterize soft-hard materials?

By: Nathalie Claes - EMAT

Location: U.408
Time: 11:30am

Abstract:
Metallic nanoparticles show interesting properties which makes them widely applicable. After combination with soft materials, such as polymers or proteins, the properties of the system can be drastically improved. A decrease of aggregation, encouragement of self-assembly and counteraction of oxidation are only a few examples of the functionalities that can be tuned. However, the size, thickness, uniformity and morphology of the components in the soft-hard material will affect the properties of the system. This makes a thorough structural characterization of great importance.
Simultaneously visualizing the soft and hard material is far from straightforward due to the sensitivity of the soft material towards the electron beam. Furthermore, the contrast of the soft materials is weak, which makes the visualization and characterization more challenging. We used different 2D and 3D electron microscopy techniques to overcome these difficulties. In this talk we will discuss the different challenges and solutions we encountered in three different soft-hard systems.

Friday Lecture | 1 December

Adventures in pixelated STEM: practicalities and applications

By: Magnus Nord - University of Glasgow, UK

Location: U.408
Time: 11:30am

Abstract:
Scanning transmission electron microscopy (STEM) is a well established experimental technique for characterizing materials down to sub-Ångstrøm resolutions. It is based on scanning a convergent beam across a thin sample, giving a convergent beam electron diffraction pattern in the back focal plane. Historically, one has used detectors which integrate up large fractions of these scattered electrons into a single intensity value for each scan point. However, this discards much of the rich information contained in the back focal plane. Recently, advances in fast electron detectors has enabled the imaging of these diffraction patterns at 1000+ frames per second.
This lecture will focus on the practical aspects and applications of using such a fast pixelated detector: the Medipix3. It will cover aspects such as live processing and visualization, file formats and data processing. In addition, it will cover applications such as magnetic differential phase contrast imaging, 3D-structure mapping using higher order laue zones, and fluctuation electron microscopy of amorphous thin films.

Friday Lecture | 8 December

The use of radiation chemical methods in liquid cell electron microscopy: main concepts and limitations

By: Patricia Abellan - SuperSTEM Laboratory, SciTech Daresbury campus, United Kingdom

Location: U.408
Time: 11:30am

Abstract:
Radiolytic synthesis routes and wastewater remediation methodologies exploit the chemical effects produced by the interaction of high-energy γ-rays and electrons with liquids to produce nanomaterials and to break-down water pollutants, respectively. In the (scanning) transmission electron microscope, (S)TEM, the formation and degradation dynamics of nanomaterials can be investigated in-situ using the effect of the 60-300kV incident electrons in combination with liquid cells. Many theoretical and experimental efforts have been devoted to understanding how irradiation in the (S)TEM affects DI water and different aqueous solutions, since water is the most common solvent used in the electron microscope. Furthermore, radiation chemists have used water for decades for general kinetics studies, thus producing a large amount of information that is now available for potential EM applications. These kinetics studies provide a base to understand drastic experimental differences observed when small changes to the initial composition of the solution are made. For instance, competing kinetics can explain why the pH decreases during irradiation of DI water while it can increase when including certain solutes in the solution. More generally, radiation-chemical methods can be applied to liquid cell experiments to tune the environment for specific applications in the fields of chemistry and materials sciences.

In this seminar I will introduce experimental conditions for which the solvent in a solution dictates the radiation chemistry during in-situ liquid cell EM, which main factors change the production of radicals and the basics of competing kinetics in radiation chemistry. I will discuss the case of water more in detail but also introduce some general concepts on the radiation chemistry of organic solvents and specific properties that can benefit liquid cells experiments; such as the possibility of minimal production of reactive species or of net production of molecular species of lower reducing/oxidizing power. Finally, I will discuss general methods for finding more suitable synthesis/corrosive environments for controlled nanoparticles formation or dissolution using the electron beam by either reproducing a selective reducing or oxidizing environment and show examples in the (S)TEM when available.

Upcoming Friday Lectures

November 24  Nathalie Claes

December 01  Magnus Nord
December 08  Patricia Abellan

Location: U.408
Time: 11:30am