Surface Crystal Structure, Reconstruction, and Relaxation

The concept of a shadow cone was introduced in Section 3.3.2.3 for the case of LEIS. The differences that arise in MEIS are 

This description neglects the thermal vibration amplitude of the atoms, which means that rather than representing the nucleus as a stationary point mass (diameter m), it is better represented as a three-dimensional Gaussian 

The scattered ion is free to leave the solid unless it encounters an overlaying atom, in which case there will be particular directions blocked to the projectile. The angles of these blocking directions will relate the surface structure to the second atomic layer. 

In many real crystal surfaces, the surface atomic layer experiences a net inward attraction, which means that the spacing between the first and second atomic layers is less than that of the bulk (see Chapter 3.2.1). In that case, there will be a greater flux of projectiles onto second layer atoms, and the blocking directions for projectiles scattered off the second layer will be different from that for the bulk. From the shift in the blocking dips in the angular distribution, it is possible to 

To extract more detailed information about the characteristics of the relaxation and thermal vibration amplitudes of the surface atomic layers, it is necessary to perform model calculations using a computer simulation (e.g., VEGAS [45-47]) of 

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