Formation of bimetallic clusters in superfluid helium nanodroplets analysed by atomic resolution electron tomography

Abstract

Structure, shape and composition are the basic parameters responsible for properties of nanoscale materials, distinguishing them from their bulk counterparts. To reveal these in three dimensions at the nanoscale, electron tomography is a powerful tool. Advancing electron tomography to atomic resolution in an aberration-corrected transmission electron microscope remains challenging and has been demonstrated only a few times using strong constraints or extensive filtering. Here we demonstrate atomic resolution electron tomography on silver/gold core/shell nanoclusters grown in superfluid helium nanodroplets. We reveal morphology and composition of a cluster identifying gold-and silver-rich regions in three dimensions and we estimate atomic positions without using any prior information and with minimal filtering. The ability to get full three-dimensional information down to the atomic scale allows understanding the growth and deposition process of the nanoclusters and demonstrates an approach that may be generally applicable to all types of nanoscale materials.

Development of a New Generation of Stable, Tunable, and Catalytically Active Nanoparticles Produced by the Helium Nanodroplet Deposition Method

“…Unexpectedly, the Au NPs remained stable up to 473 K, which was remarkably different from the published studies describing Au NP sintering during the CO oxidation reaction 14 conducted in 300-410 K temperature range. This 15 whereas other deposition studies have demonstrated soft landing 8b, 12 . Calculations by deLara-Castells 16 indicated that an Au atom in a small He droplet landing on TiO2 is indeed a soft landing process.…”

Observation of laser-assisted electron scattering in superfluid helium

“…The contribution of the droplets' superfluid character to the observed energy modulation cannot be deduced from the present results and remains to be investigated, for example with non-superfluid 3 He droplets or mixed 3 He/ 4 He droplets 43 . It will also be important to investigate the ratio of light-induced energy gain and energy dissipation in other materials, like molecular, metal or semiconductor clusters, the creation of which is facilitated by the very flexible opportunities provided by the He droplet approach for the creation of tailor-made bi-material core-shell nanostructures within the droplet 44,45 . Photoionization of the core will allow to observe LAESacceleration and energy dissipation within the shell material.…”

Total generalized variation regularization for multi-modal electron tomography

“…The calculated parameters are used to correct all SI data. 57 Alignment of the tilt series is done using the HAADF STEM data. For alignment in the direction of the tilt axis, common-line alignment is applied, 58 in the direction perpendicular to the tilt axis the center of mass of each projection is used for alignment and for tilt axis alignment, rotational centers are calculated based on the center of mass.…”