SFB 616

 

Pictures SFB616
  
  

 Project A6:
Interaction Between Highly Charged Ions and Surfaces


 The central idea of this project is to obtain a quantitative characterisation of energy dissipation processes during and after the impact of highly charged ions (HCI) on surfaces. The use of HCI offers the unique possibility to study both, the effects of kinetic and potential energy on energy dissipation during the ion-solid interaction.

 
Slow ions: Slow highly charged Ions on Metal Surfaces

While the HCI is approaching the metal surface multiple processes take place within a few femtoseconds. A so called hollow atom is created with empty inner shells inside a quasi neutral atom. Subsequent Auger-processes lead to electron emission from the ion as well as from the surface.

The neutralization of the ion is completed above the surface but the deexcitation continues inside the solid. During the impact most of the electrons are still in highly excited states. They are screened by the metal electrons and transferred to the conduction band. This scenario results in a highly charged ion below the surface with most of its original potential energy left which will then be dissipated completely to the electronic system. These excited electrons will be measured by metal-insulator-metal contacts (MIM). From this data the electron temperature can be determined.

Methods and Instrumentation

beamline 3d The HCI are produced by an Electron Beam Ion Trap (Dresden-EBIT). The attached beamline (see right picture) offers the opportunity to seperate the charge states and to decelerate the ions (approx. q x 50 eV).

The MIM detectors (Preparation and characterization see project A2), have already been used for the detection of kinetically produced hot electrons in project A4.

 

Experiments in this project have shown that the energy dissipation of the ions potential and kinetic energy can be detected by the application of MIM (see figure below). The tunneling yield as a significant parameter for electron excitation is the net number of electrons overcoming the insulator barrier (approx. 3 eV) per impinging ion.

plotFurther on in this project the sputtering caused by nuclear stopping of the slow ions will be subject of investigation by SNMS. Experimental data including neutral particles are more or less missing. The quantitative detection of neutral particles is experimentally challenging and estimates of neutral particle emission seem to be rather unreliable. The sputtered particles will be measured by a ToF-technique combined with resonant and non-resonant laser postionisation.


Sroubek et al. provide an ionisation model which employs assumption of a transient local electron excitation with the electron temperature as the fundamental parameter. Theoretical estimations and simulations indicate that electron temperatures of about a few 1000 K are generated dynamically in the collision cascade and could be fitted to measured ionisation probabilities. To confirm this model experimentally the electronic excitation has to be varied without changing the particle dynamics in the collision cascade. This is only possible with HCIs. By varying the charge state a wide range of potential energy compard to the kinetic energy is available.

 
Fast ions: Swift Heavy Ions on Insulator Surfaces

Fig 2 The bombardement of layered insulator materials (SrTiO3, CaF2...) with swift heavy ions under grazing incident leads to a well organized structure. Multiple hillock like surface defects in a row are caused by an impact of one single ion. Geometric dependencies like length of the hillock chain can be found. In order to understand the mechanism of how the hillocks are generated a theoretical model has been invented and will be further improved.

The geometry of the surface defetcs can be understood as a kind of imaging of the electron density below the surface. Since the ion impinges the surface with kinetic energies of about 100 MeV electronic stopping is farly dominant. For this reason electronic stopping can only take place when the electron density inside the layered structure excesses a certain threshold.

 

 

 

Obviously is the lattice structure changed after the ion impact. In which way is the energy dissipated from the ion via the electronic system to the lattice? This answer can be given by calculations of electronic stopping power along glancing swift heavy ion tracks using ab-initio electron density data.

lattice


 The project has close collaborations with other projects: A2, A3, A4, C1, C6

 
  Poster:

Internationaler Workshop 2008


SFB616 Workshop
Remagen 2011

A6 Akcöltekin et al.
PDF (10.0 MB)

Internationaler Workshop 2008


Internationaler
Workshop 2008

A6 Haake et al.
PDF (0.4 MB)

Internationaler Workshop 2008


Internationaler
Workshop 2008

A6 Osmani et al.
 PDF (1.7 MB)

Begehung 2005


SFB616 Workshop
Remagen 2007/II

A6 Peters et al.
 PDF (1.0 MB)

 

 
  Publications: