Electrostatic simulation of a complete cluster deposition apparatus

Impact of the gas dynamics on the cluster flux in a magnetron cluster-source: Influence of the chamber shape and gas-inlet position

Although producing clusters by physical methods offers many benefits, low deposition rates have prevented cluster-beam deposition techniques from being adopted more widely. The influence of the gas aerodynamics inside the condensation chamber of a magnetron cluster-source on the cluster throughput is reported, leading to an improved understanding of the influence of gas aerodynamics on cluster transport. In the first part of this paper, the influence of the carrier gas's inlet position on the cluster flux is studied. In particular, two inlet configurations were investigated, i.e., from the rear of the chamber and from within the magnetron sputtering source. It was found experimentally that the latter configuration can lead to an increased cluster flux, under the same conditions of gas pressure and power applied to the magnetron. This behavior is explained with the help of simulations. In the second part of this paper, the gas dynamics behavior inside four chamber shapes, namely, two cylindrical shapes with different cross-sectional diameters and two conical shapes with different apex angles, was simulated. The modeling showed that the fraction of clusters successfully leaving the aggregation zone can be increased by up to eight times from the worst to the best performing chamber geometries studied. Finally, the cluster throughput was determined experimentally using a quartz microbalance in two of the four chamber designs. It was found that the cluster flux increased up to one order of magnitude, reaching ∼20 mg/h for a condensation chamber with a smaller cross section and a conical exit.

From Bulk to Atoms: The Influence of Particle and Cluster Size on the Hydrogen Evolution Reaction

To investigate the influence of particle size in terms of electrocatalysis for the hydrogen evolution reaction (HER), small Pt n species with n = 1 , 10 , 13 $n=1,10,13$ atoms and nanoparticles are deposited onto native titanium dioxide. These species are compared to the bare support as well as to bulk platinum with respect to the catalytic activity. Photoelectron spectroscopy showed Pt4f core-level shifts to higher binding energies with decreasing cluster size. In addition, the various species contribute significant density of states into the valence band gap of TiO2, thereby with larger particle size, the resulting band gap narrows. For nanoparticles, metal-like behaviour was already observed. Electrochemical measurements in 0.1 M H2SO4 showed the highest overall catalytic activity for bulk platinum and large Pt nanoparticles. A different assertion is obtained when the activities are related to the mass of the catalyst used, indicating that clusters with a size of about ten atoms seem to be most active. In comparison with the results from photoelectron spectroscopy regarding the electronic structure, no clear correlation to the catalytic activity was found. In terms of degradation induced due to the electrochemical treatment, the cluster samples showed no sintering effects, but instead, some detachment took place.