Facility Description

The MEIS facility

The MEIS beamline
MEIS enables the investigation of the surface structure and properties of crystalline materials using an ion beam probe. An ion source generates a positively charged beam of light mass ions, typically hydrogen or helium, which can be accelerated in the energy range 50 keV to a maximum of 400 keV. Although a very powerful technique, the high equipment cost means that there are less than ten machines world-wide.

The experimental station

The experimental station facilities include four interconnected UHV systems between which samples can be transferred under UHV; the scattering chamber, which houses the ion analyser, sample goniometer and 2 dimensional (energy and angle) position sensitive detector and is where the ion scattering experiments are performed the preparation chamber, whose facilities include LEED, Auger, sputter cleaning, evaporation sources and gas dosing and is used for sample preparation and characterization prior to ion scattering experiments the storage chamber, where six samples can be stored and which forms the junction of the sample transfer system the loading chamber which is a fast pumpdown chamber used for introducing samples into the vacuum systems.

All four chambers include sample heating facilities.
Data acquisition is computer controlled via the MIDAS graphical user interface originally developed for the nuclear physics EUROGAM programme

For further information contact Paul Bailey, senior scientist.

MEIS facility technical specification

Ion beam

energy range; 50-400 keV
species; elemental gases - typically H+ and He+
divergence < 0.1º
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 analyser

type; toroidal electrostatic
analysing energy; (pass energy) 0-400 keV
analyser angular movement; 140º in horizontal plane  

Two-dimensional (energy and angle) ion detector

type chevron array anode with micro channel plates
energy window; 2% of analyser pass energy
resolving power; DE/E = 2.4x10-3
angle window; 27º
angular resolution;  ø = 0.3º

Sample

size; minimum 5x5 mm, maximum 15 mm diameter
temperature range; 300-1300 K
environment; UHV
alignment; 3 rotational and 3 translational degrees of freedom
loading time from air; typically 30 minutes

 Preparation facilities

sputter cleaning
annealing to 1300 K
LEED
electron Auger
gas dosing
spare ports for evaporators and k-cells
UHV sample transfer