MEIS Accelerator

The UK Medium Energy Ion Scattering facility, (MEIS) uses an ion beam probe which enables the investigation of the surface structure and properties of crystalline materials as well as the high resolution depth profiling of non-crystalline nano metre thin layers. An ion source generates a beam of positively charged light ions, typically hydrogen or helium, which is accelerated to energy between 50 keV and 200 keV and scattered off the sample under investigation. Although a very powerful technique, the comparatively high equipment cost means that there are fewer than ten MEIS machines world-wide. 

The experimental station facilities comprise four interconnected UHV systems between which samples can be transferred under UHV conditions:

1. The scattering chamber, in which the MEIS experiments are performed houses the ion energy analyser, sample goniometer and a 2-dimensional (energy and angle) position sensitive detector.
   
   
2. The preparation chamber, whose facilities include LEED, Auger, sputter cleaning, evaporation sources and gas dosing  is used for sample preparation and characterisation prior to ion scattering experiments.
   
   
3. The storage chamber, where six samples can be stored and which forms the junction of the sample transfer system.
   
   
4. The loading chamber which is a fast pump down chamber used for introducing samples into the vacuum systems. The chambers are fitted with sample heating facilities. 

We hope that the MEIS system will support a thriving user community. Potential users, for research and commercial applications are invited to contact either Professor Jaap Van Den Berg (J.VanDenBerg@hud.ac.uk) or Dr. Andrew Rossall (A.Rossall@hud.ac.uk) to discuss possibilities.    

Technical specification

Ion beam

• Energy range; 50-200 keV 
• Species: elemental gases - typically H+ and He+ 
• Divergence < 0.1° 
• Spot size at sample:1 mm horizontal by 0.5 mm vertical 
• Current at sample: 0.1 - 1.0 μA dependent on beam energy and species

Ion Energy Analyser

• Type: toroidal electrostatic 
• Analysing energy: (pass energy) 0-400 keV 
• Analyser angular movement: 140° in horizontal plane  

Two-dimensional (energy and angle) ion detector

• Chevron array anode with micro channel plates
• Energy window: 2% of analyser pass energy
• Resolving power: ΔE/E = 2.4x10-3 
• Angle window: 27° 
• Angular resolution:  φ = 0.3°

Sample 

• Size:minimum 5x5 mm, maximum 15x15 mm diameter 
• Temperature range: 300-1300 K 
• Environment: UHV 
• Alignment: goniometer with 3 rotational and 3 translational degrees of freedom 
• Loading time from air: typically 30 minutes

Preparation facilities

• Sputter cleaning 
• Annealing to 1300 K
• Low Energy Electron Diffraction (LEED)
• Electron Auger 
• Gas dosing 
• Spare ports for evaporators and k-cells 
• Sample transfer under UHV