Abstract
Optical-absorption spectroscopy of inorganic fullerenelike and ( and ) is reported in the range 400–800 nm, at temperatures between 4–300 K, and compared to the corresponding bulk (2H) material. A systematic study of the effect of IF size and number of atomic layers on the optical properties shows that the semiconductivity of the layered material is preserved in the IF structures. Nevertheless, all IF with number of layers exhibit a decrease in the and exciton energies. This redshift becomes larger as additional inner layers are formed, until a saturation value is reached We assign this redshift to the deformations, curvature, and discommensuration between adjacent atomic layers the structure must accommodate in order to form an IF structure. An increase in the exciton energies is observed in IF consisting of a few sulfide layers This blueshift is attributed to a quantum confinement in the direction. Band-structure calculations show that an expansion of along the axis leads to a convergence of the levels and which is displayed in the absorption spectra of IF with 1 or 2 layers.
- Received 8 May 1997
DOI:https://doi.org/10.1103/PhysRevB.57.6666
©1998 American Physical Society