F.A. Al-Agel

Synthesis and characterization of highly stoichiometric AgInSe2 thin films via a sol–gel spin-coating technique

Highly stoichiometric AgInSe2 thin films have been prepared on a p-type Si(111) substrate by a sol–gel spin-coating technique. These films were annealed at different temperatures. The as-prepared and annealed films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS). The XRD spectra showed that the crystal structure of the AgInSe2 film was that of cubic fluorite chalcopyrite with lattice constants a = 6.102 A and c = 11.69 A. The SEM images depicted the surface morphology as smooth and the spherical particles as uniformly distributed. The average particle size was increased as the annealing temperature increased. Using HRTEM images and SAED patterns for the as-synthesized and annealed thin films, the AgInSe2 film was indexed to a pure polycrystalline chalcopyrite AgInSe2 structure with a lattice spacing of around 0.3 nm. XPS spectra showed that the as-deposited AgInSe2 film was Ag rich, while the AgInSe2 films annealed at 523 and 623 K were In rich.

Optical and structural properties of amorphous SexTe100-x aligned nanorods

In the present work, we report studies on optical and structural phenomenon in as-deposited thin films composed of aligned nanorods of amorphous SexTe100-x (x = 3, 6, 9, and 12). In structural studies, field emission scanning electron microscopic (FESEM) images suggest that these thin films contain high yield of aligned nanorods. These nanorods show a completely amorphous nature, which is verified by X-ray diffraction patterns of these thin films. Optical studies include the measurement of spectral dependence of absorption, reflection, and transmission of these thin films, respectively. On the basis of optical absorption data, a direct optical band gap is observed. This observation of a direct optical band gap in these nanorods is interesting as chalcogenides normally show an indirect band gap, and due to this reason, these materials could not become very popular for semiconducting devices. Therefore, this is an important report and will open up new directions for the application of these materials in semiconducting devices. The value of this optical band gap is found to decrease with the increase in selenium (Se) concentration. The reflection and absorption data are employed to estimate the values of optical constants (extinction coefficient (k) and refractive index (n)). From the spectral dependence of these optical constants, it is found that the values of refractive index (n) increase, whereas the values of extinction coefficient (k) decrease with the increase in photon energy. The real and imaginary parts of dielectric constants calculated with the values of extinction coefficient (k) and refractive index (n), are found to vary with photon energy and dopant concentration.