Revealing local variations in nanoparticle size distributions in supported catalysts: a generic TEM specimen preparation method

Focused ion beam-scanning electron microscopy provides novel insights of drug delivery phenomena

Scanning electron microscopy (SEM) has long been a standard tool for morphological analyses, providing sub micrometer resolution of pharmaceutical formulations. However, analysis of internal morphologies of such formulations can often be biased due to the introduction of artifacts that originate from sample preparation. A recent advancement in SEM, is the focused ion beam scanning electron microscopy (FIB-SEM). This technique uses a focused ion beam (FIB) to remove material with nanometer precision, to provide virtually sample-independent access to sub-surface structures. The FIB can be combined with SEM imaging capabilities within the same instrumentation. As a powerful analytical tool, electron microscopy and FIB-milling are performed sequentially to produce high-resolution 3D models of structural peculiarities of diverse drug delivery systems or their behavior in a biological environment, i.e. intracellular or -tissue distribution. This review paper briefly describes the technical background of the method, outlines a wide array of potential uses within the drug delivery field, and focuses on intracellular transport where high-resolution images are an essential tool for mechanistical insights.

Transmission electron microscopy sample preparation method for micrometer-sized powder particles using focused ion beam

A TEM sample preparation technique for micrometer-sized powder particles in the 1-10 μm size range is proposed, using a focused ion beam (FIB) system. It is useful for characterizing elemental distributions across an entire cross-section of a particle. It is a simple and universal method without using any embedding agent, enabling the powder particles with different size, shape or orientation to be easily selected based on the SEM observations. The suitable particle is covered with Pt coating layers through an ion-beam-assisted deposition. The Pt coating layers provide sufficient support for the TEM lamella. A small piece of tungsten needle is used as a support under the particle by taking a series of operations using a micromanipulator. The particle can be precisely thinned by the ion beam to be suitable for both TEM observation and EDX elemental mapping. This novel technique reduces the TEM sample preparation time to a few hours, allowing much higher efficiency compared to complicated and time-consuming embedding methods.

Well-Defined Materials for Heterogeneous Catalysis: From Nanoparticles to Isolated Single-Atom Sites

The use of well-defined materials in heterogeneous catalysis will open up numerous new opportunities for the development of advanced catalysts to address the global challenges in energy and the environment. This review surveys the roles of nanoparticles and isolated single atom sites in catalytic reactions. In the second section, the effects of size, shape, and metal-support interactions are discussed for nanostructured catalysts. Case studies are summarized to illustrate the dynamics of structure evolution of well-defined nanoparticles under certain reaction conditions. In the third section, we review the syntheses and catalytic applications of isolated single atomic sites anchored on different types of supports. In the final part, we conclude by highlighting the challenges and opportunities of well-defined materials for catalyst development and gaining a fundamental understanding of their active sites.