Physics Colloquium - Paul Scheier (16.3.2020)
Monday 16.3.2020 at 15:00, Lecture room C
prof. Paul Scheier (University of Innsbruck):
Highly charged helium droplets: a cool tool to grow size selected clusters and nanoparticles
Abstract:
Almost every existing method of cluster and nanoparticle formation leads to a wide distribution of sizes. Thus, the limiting factor in all cluster studies is creating a sufficiently high concentration of the desired species and separating them from the overall distribution [1]. Recently, we discovered that large helium droplets can become highly-charged [2]. The charge centers self-organize as twodimensional Wigner crystals at the surface of the droplets and act as seeds for the growth of dopant clusters [3]. Cluster ions of a specific size and composition can be formed by this technique with unprecedented efficiency. Soft-landing of metal nanoparticles formed in highly-charged helium droplets can be achieved by deposition onto a target surface. The figure below shows two transmission electron microscope images of amorphous carbon surfaces decorated with metal nanoparticles formed upon pickup into helium droplets. In the case of neutral droplets (left image, taken from [4]), a single nanoparticle is formed in every droplet and its size depends strongly on the size of the helium droplet. As a result, a wide size distribution of nanoparticles is observed and the deposition time was several hours. In contrast, pickup of gold vapor into highly-charged helium droplets (right image) results in a narrow size distribution of nanoparticles. Due to the fact that several hundred nanoparticles are formed simultaneously in one helium droplet, the deposition time was reduced to a few seconds. Several applications for cluster physics, ion spectroscopy and nanotechnology will be presented.
[1] E.C. Tyo and S. Vajda, Nat. Nanotechnol. 10 (2015) 577
[2] F. Laimer et al., Phys. Rev. Lett. 123 (2019) 165301
[3] L. Tiefenthaler et al. Rev. Sci. Instrum. (2020) in print
[4] A. Boatwright, et al. Faraday Discuss. 162 (2013) 113