1. Borisov V.T., Golikov I.N. and Matveev Y.E., J. Cryst. Growth 6 (1969) 72
2. Barraclough P.B. and Hall P.G., Surf. Sci. 46 (1974) 393
3. Bienfait M., Boistelle R. and Kern R., in Absorption et Crois-sanoe Cristalline, CNRS, Paris, 1965, pp 515–531
4. Neuhaus A., Z. Krist. 68 (1928) 15
5. Kern R., Bull. Soc. Fr. Min. Crist., 78 (1955) 461–474