Papers by Author: S. Grammatikopoulos

Abstract: In the Current Study, the Structural Characteristics of Siox Thin Films Grown by Magnetron Sputtering on Si Substrates Are Reported. High Resolution Transmission Electron Microscopy Revealed the Formation of Amorphous Siox Films for the as-Deposited Samples, as Well as the Ones Annealed in Ambient Air for 30 Min at 950oC and of Si Nanocrystals, Embedded in Amorphous Siox, after Ar Annealing for 1-4 Hours at 1000oC. the Nanocrystals, with Sizes up to 6 Nm, Predominately Exhibit {111} Lattice Planes. Energy-Dispersive X-Ray Analysis Showed that the Si/O Ratio Is between 0.5-1, I.e. the Amorphous Films Comprise of a Mixture of Sio2 and Sio. Phase Images and Corresponding Strain Maps Created Using Fourier Filtering Revealed a Uniform Contrast in the Nanocrystals, which Shows that the Si Lattice Constant Does Not Vary Significantly. the Residual Strain Variations, around 4%, May Account for the Possible Existence of a Small Percentage of Highly Disordered Si or Siox Residual Clusters inside the Regular Si Matrix, in Full Agreement with Photoluminescence Measurements Performed on the same Materials.

Abstract: Thin Cu films of thickness 0.4 – 150 nm were deposited via radio frequency magnetron sputtering on Si(100) wafers, corning glass and quartz. Subsequently the Cu films were oxidized in ambient air at 230oC and 425oC in order to produce single-phase Cu2O and CuO, respectively. Selected samples were measured in the transmission geometry with the help of an ultraviolet – visible spectrophotometer. From the absorption spectra of the films, it was found that the gap EB for the dipole allowed transitions showed blue shifts of about 1.2 eV for the Cu2O thinnest film (0.75 nm), whereas the Edirect for the direct gap transitions showed blue shifts of about 0.16 eV for the CuO thinnest film (0.7 nm). The blue shift of the energy gap in the copper-oxide semiconductors is an indication of the presence of strong quantum confinement effects.