The dispersion of phonons on the (111) surface was measured and reproduced on the basis of lattice dynamics calculations. The surface force constants were found to be different to the bulk force constants (tables 3 and 4). In particular, the force constant of an inter-octahedral boron-boron bond at the surface increased by 50% from the corresponding bulk force constant. From the relationship between the force constant and bond length in various hexaborides, the contraction of the inter-octahedral bond length was estimated to be 0.007nm. The deformation of the boron network on the (111) surface, the behavior of which was similar to that on the (100) surface, was explained by the inherent nature of the boron network.
Deformation of Boron Networks at the LaB6(111) Surface. Rokuta, E., Yamamoto, N., Hasegawa, Y., Trenary, M., Nagao, T., Oshima, C., Otani, S.: Surface Science, 1998, 416[3], 363-70
Table 4
Surface Force Constants
Bond | Plane | Constant | Value (erg/cm2) |
B-B | (111) | α1s | 26.01 x 104 |
B-B | (111) | β1s | 6.11 x 104 |
B-B | (111) | α2o | 7.51 x 104 |
B-B | (111) | β2o | 2.98 x 104 |
B-B | (111) | α2m | 10.98 x 104 |
B-B | (111) | β2m | 4.35 x 104 |
B-B | (111) | α2i | 11.56 x 104 |
B-B | (111) | β2i | 4.58 x 104 |
B-B | (100) | α1s | 21.68 x 104 |
B-B | (100) | β1s | 5.09 x 104 |
B-B | (100) | α2o | 5.78 x 104 |
B-B | (100) | β2o | 2.29 x 104 |
B-B | (100) | α2i | 8.67 x 104 |
B-B | (100) | β2m | 3.44 x 104 |