HICS: Highly charged ion collisions with surfaces
Abstract The layout of a new instrument designed to study the interaction of highly charged ions with surfaces, which consists of an ion source, a beamline including charge separation and a target chamber, is presented here. By varying the charge state and impact velocity of the projectiles separately, the dissipation of potential and kinetic energy at or below the surface can be studied independently. The target chamber offers the use of tunable metal–insulator–metal devices as detectors for internal electronic excitation, a time-of-flight system to study the impact induced particle emission and the possibility to transfer samples in situ to an ultra high vacuum (UHV) scanning probe microscope. Samples and detectors can be prepared in situ as well. As a first example data on graphene layers on SrTiO3 which have been irradiated with Xe36+ are presented.
Perforating Freestanding Molybdenum Disulfide Monolayers with Highly Charged Ions.
Porous single-layer molybdenum disulfide (MoS2) is a promising material for applications such as DNA sequencing and water desalination. In this work, we introduce irradiation with highly charged ions (HCIs) as a new technique to fabricate well-defined pores in MoS2. Surprisingly, we find a linear increase of the pore creation efficiency over a broad range of potential energies. Comparison to atomistic simulations reveals the critical role of energy deposition from the ion to the material through electronic excitation in the defect creation process and suggests an enrichment in molybdenum in the vicinity of the pore edges at least for ions with low potential energies. Analysis of the irradiated samples with atomic resolution scanning transmission electron microscopy reveals a clear dependence of the pore size on the potential energy of the projectiles, establishing irradiation with highly charged ions as an effective method to create pores with narrow size distributions and radii between ca. 0.3 and 3 nm.
Electron emission in multiply charged noble gas ion-gold solid target collisions: Total and Auger yields
Abstract Total secondary electron emission coefficients, γ, and absolute values of ArL 23 Auger yields, ϱ A , were determined for collisions between highly charged noble gas ions and polycrystalline gold targets. Results concerning the electron emission coefficient show that, in the explored ion velocity range, γ is due to both potential and kinetic process contributions. From Ar 9+ the Auger yield decreases from 4.6 to 2% for incident kinetic energy from 16 keV to 70 keV respectively. The position of the ArL 23 Auger structure indicates that the decay takes place from an Ar ion with an L 23 vacancy and electronic outer shells already filled. With Ar 8+ ions, the Auger yield remains negligible showing that the major part of the emission observed with higher charge states is due to the initial L 23 vacancy in the incoming projectile. From Ar 11+ , the shift of the Auger structure towards higher energies indicates that it is essentially the 2p 3 initial configurations which are efficient.