Experimental Set-ups for Highly Charged Ion Experiments
The Two-Source-Facility in the Helmholtz-Zentrum Dresden-Rossendorf is a unique combination of two different highly charged ion sources. An electron cyclotron resonance (ECR) ion source and a room-temperature electron beam ion trap (EBIT) can be used for irradiation experiments. Both ion source are connected to the same target chamber, thus the advantages of both ion source types, i.e. high output currents with the ECR and very high charge states with the EBIT, are combined. An electrostatic potential can be applied to the ion sources and the beam-line such that the ions are decelerated upon entry in the target chamber. This design feature offers the use of very slow ions with energies even below 50eV*q (q: ion’s charge state).
Fig. 1: Schematic view of the Two-Source-Facility with the ion sources on the right hand side and the target chamber on in the upper left corner.
The in-situ irradiation facility SNIPER
The influence of atmospheric conditions on the size and shape of created nano-structures is always an important question. To clearly link the size and shape of ion-induced nano-structures to the amount of deposited potential and kinetic energy it is important to maintain very clean and controlled conditions during irradiation and analysis. For this purpose the in-situ irradiation facility SNIPER (Surface Nanostructures by Ion’s Potential Energy Release) has been designed and built as part of the Ion Beam Center of the Helmholtz-Zentrum Dresden-Rossendorf. This facility (Fig. 1) allows the use of slow highly charged ions from an electron beam ion trap (EBIT) for irradiation experiments. The ion’s kinetic energy can be adjusted in a very similar way as in the Two-Source Facility between 10eV*q and 4.5keV*q. The sample is already mounted during irradiation in a scanning probe microscope under ultra-high vacuum conditions.
The fact, that the scanning probe tip is mounted right in front of the surface during ion irradiation is a design feature, which may be used for single ion implantation experiments. By using a pierced atomic force microscopy tip the special geometry of SNIPER allows the positioning of ions in lateral direction very precisely. By additionally tuning the ion’s kinetic energy also the vertical implantation depth can be adjusted. Thus, SNIPER may enable experiments of single ion implantation with a nano-meter precision in three dimensions. This set-up could than be used to produce quantum dots and quantum dot arrays on surfaces to investigate new and unexpected phenomena. A sketch of this kind of experiments is shown in Fig. 2.
|Fig. 1: The compact highly charged ion irradiation facility SNIPER.||Fig. 2: SNIPER facility for single ion implantation. Ions are produced in an EBIT on the right side (green) and transmitted through a pierced AFM tip on the left side (see inset).