Search

Understanding light-matter interactions in nanomaterials is crucial for optoelectronic, photonic, and plasmonic applications. Specifically, metal nanoparticles (NPs) strongly interact with light and can undergo shape transformations, fragmentation and ablation upon (pulsed) laser excitation. Despite being vital for technological applications, experimental insight into the underlying atomistic processes is still lacking due to the complexity of such measurements. Herein, atomic resolution electron tomography is performed on the same mesoporous-silica-coated gold nanorod, before and after femtosecond laser irradiation, to assess the missing information. Combined with molecular dynamics (MD) simulations based on the experimentally determined 3D atomic-scale morphology, the complex atomistic rearrangements, causing shape deformations and defect generation, are unraveled. These rearrangements are simultaneously driven by surface diffusion, facet restructuring, and strain formation, and are influenced by subtleties in the atomic distribution at the surface.

Colloidal CsPbX3 (X = Br, Cl, and I) perovskite nanocrystals (NCs) have emerged as promising phosphors and solar cell materials due to their remarkable optoelectronic properties. These properties can be tailored by not only controlling the size and shape of the NCs but also postsynthetic composition tuning through topotactic anion exchange. In contrast, property control by cation exchange is still underdeveloped for colloidal CsPbX3 NCs. Here, we present a method that allows partial cation exchange in colloidal CsPbBr3 NCs, whereby Pb2+ is exchanged for several isovalent cations, resulting in doped CsPb1xMxBr3 NCs (M= Sn2+, Cd2+, and Zn2+; 0 < x ≤ 0.1), with preservation of the original NC shape. The size of the parent NCs is also preserved in the product NCs, apart from a small (few %) contraction of the unit cells upon incorporation of the guest cations. The partial Pb2+ for M2+ exchange leads to a blue-shift of the optical spectra, while maintaining the high photoluminescence quantum yields (>50%), sharp absorption features, and narrow emission of the parent CsPbBr3 NCs. The blue-shift in the optical spectra is attributed to the lattice contraction that accompanies the Pb2+ for M2+ cation exchange and is observed to scale linearly with the lattice contraction. This work opens up new possibilities to engineer the properties of halide perovskite NCs, which to date are demonstrated to be the only known system where cation and anion exchange reactions can be sequentially combined while preserving the original NC shape, resulting in compositionally diverse perovskite NCs.

Nanomaterials have attracted increasing scientific interest, because their exact atomic structure may lead to interesting and unexpected physical and chemical properties. Due to several important developments in aberration correction technology, transmission electron microscopy imaging has become an excellent technique to visualise nanomaterials down to sub-angstrom resolution in order to understand their properties. However, a merely visual interpretation of electron microscopy images is inadequate to obtain precise structure information. Therefore, a quantitative approach is required. Hereby, an important assumption is that the number of atomic columns in the image is known. This number can be determined visually from atomic-resolution images of beam-stable materials for which a high incoming electron dose can be used resulting in a sufficiently high signal-to-noise ratio. However, beam-sensitive and light-element materials should be imaged with a sufficiently low electron dose to avoid beam damage, which causes images of such materials to exhibit low signal-to-noise ratio and low contrast. In these cases, a visual determination of the number of atomic columns is not straightforward and may lead to biased structure information. To overcome this problem, an alternative, quantitative method is proposed which determines the number of atomic columns for which there is most evidence in the image data. This method allows detecting atomic columns and even single atoms from atomic-resolution electron microscopy images in an automatic and objective manner. The validity and usefulness of this method have been demonstrated by analysing images of samples of different shape, size, and atom type. Moreover, besides detecting atomic columns from electron microscopy images, the proposed methodology also offers a way to evaluate the relation between image-quality measures. In addition, a superior performance to detect the correct number of atomic columns is observed as compared to alternative detection techniques. In conclusion, the development of a new quantitative method in this thesis has pushed quantitative electron microscopy towards a more objective interpretation. The method generalises the characterisation of nanomaterials at the atomic scale in electron microscopy in order to obtain accurate and precise structure information about a material.