Here for simplicity, we approximate t as t=t0+0.8 Å, where t0 is the distance between the top and bottom chalcogen atom layers and the 0.8 Å is the total effective decay length (0.4 Å in each layer side) of electron density into the vacuum.
The strong interaction between Ni and Bi leads to co-segregation of Bi to several of the outermost atom layers, which, in turn, drives further segregation of Ni to the surface layer.
The origin of inclined growth is discussed taking into account the role of crystallographic defects in particular twin faults that develop in the lattice of growing crystal and change the stacking sequences of atom layers.
Since these states are restricted to a region only a few atom layers thick at a crystal surface, any signal from them might be swamped by conduction through the underlying bulk semiconductor crystal, as well as greatly perturbed by steps and other defects at the surface.
The Bi atom layers are sandwiched between WO6 octahedral layers [11].
The deformation of the middle two atom layers of the nanotube (in the square of Fig. 2) was further investigated.
