Zouheir Sekkat

Estimation of optical constants of a bio-thin layer (onion epidermis), using SPR spectroscopy

We estimate the optical constants of a biological thin layer (Allium cepa) by surface plasmon resonance (SPR) spectroscopy. For this study, the fresh inner thin epidermis of an onion bulb was used and stacked directly on gold (Au) and silver (Ag) film surfaces in order to identify the shift in SPR mode of each metal film at an operating wavelength of 632.8 nm. The thickness and dielectric constants of the biological thin layer were determined by matching the experimental SPR curves to theoretical ones. The thickness and roughness of bare Au and Ag thin films were also measured by atomic force microscopy (AFM); the results of which are in good agreement with those obtained through experiment. Due to the high surface roughness of the natural onion epidermis layer, AFM could not measure the exact thickness of an onion epidermis. It is estimated that the value of the real part of the dielectric constant of an onion epidermis is between the dielectric constants of water and air.

Lasers and Plasmonics: SPR Measurements of Metal Thin Films, Clusters and Bio-Layers

An extensive research has been carried out in synthesizing and characterizing single and double layer metal thin films of different thicknesses including ultrathin films. We discuss the experimental data of surface plasmon resonance (SPR) occurring at the interface between air, single and bimetallic thin layers of gold (Au) and silver (Ag) prepared on glass substrates. The bilayer configuration allowed for the measurements of the optical constants of metallic films that are ultra thin; e.g., below 10 nm of thickness since SPR modes on such thin films in a single layer configuration are shallow. In addition, using SPR technique, the optical constants of a natural biological thin layer (Allium cepa) is also estimated. Thickness and refractive index of metallic films were determined by matching experimental SPR curves to the theoretical ones. Thickness and roughness of the films were also measured by atomic force microscopy. The results obtained by experimental measurements are in good agreement with AFM analysis. It is estimated that the value of the real part of the dielectric constant of an onion epidermis is existing between the dielectric constants of water and air.

Kesterite / wurtzite Cu 2 ZnSnS 4 nanocrystals: Synthesis and characterization for PV applications

Wet chemical synthesis and characterizations of quaternary chalcogenide Cu2ZnSnS4 (CZTS) nanocrystals, as an alternative solar absorber material to conventional quaternary CuInxGa(1−x)S2 (CIGS), is given in detailed. Dodecanethiol and oleylamine are used as hot organic solvents and capping ligands, as for oleic acid is used with dodecanethiol to control the nanocrystals morphology. Two kinds of metal precursors ae used: metal chlorides and metal acetate as precursors of Cu, Zn and Sn, respectively, while elemental sulfur is used as sulfur source. The effect of dodecanethiol and oleylamine on the final phase of the CZTS nanocrystals is studied. The as-synthesized (CZTS) nanocrystals are characterized by X-ray diffraction (XRD), Raman spectroscopy, and Transmission electron microscopy (TEM). Our results showed that CZTS nanocrystals can be obtained with different crystallographic phases, kesterite and wurtzite structures. Furthermore, we found that the CZTS nanocrystals structure can be controlled as kesterite phase or wurtzite phase using dodecanethiol-sulfur solution and oleic acid instead of oleylamine during the synthetic procedure.

Optical, structural and Photoconductivity properties of organic photovoltaic thin films based on polymer/fullerene

Morphological properties of two p-type semiconductors, used separately with fullerene: MEH-PPV and the commonly used P3HT, are investigated in order to study their influence on optical and Photoconductivity properties of organic thin films based on MEH-PPV/P3HT, separately, with and without PCBM. The aim is to better understand the charge carriers mechanisms inside the polymers and the effect of PCBM when added in blend. To measure morphologic and optical properties of the prepared thin films, different characterizations are performed. A comparative study of both polymers is discussed using X ray diffraction, absorption, photolumenescence and Raman spectra.

Nanoscale probing of optical and structural properties of polymeric photovoltaic thin films

Herein, we performed a comparative study of bulk heterojunction, bilayer architectures of thin films based MEH-PPV and PCBM dissolved in chlorobenzene. This study aims to investigate the impact of deposition of successive layers on optical characteristics of the active layer. The films were examined using UV-absorption, Photoluminescence X-ray diffraction and Scanning electron microscopy SEM.

Thickness effect on Cu 2 ZnSnS 4 properties using non-toxic and low-cost process

CZTS thin films were prepared by simple Sol-gel method. CZTS sol-gel mixture contains tin chloride, copper acetate, zinc acetate and thiourea as a source of sulfur. CZTS solution was then deposited on molybdenum coated glass substrates. The prepared thin films were annealed at 540 °C in sulfur atmosphere for one hour. CZTS films showed good crystalline quality and optical properties that depend on the film thickness. The measured films band gap was close to 1.43 eV with a good kesterite phase. The CZTS layer was used as an absorber in solar cell with the structure glass/Mo/CZTS/CdS/ZnO/AZO/Al and demonstrated an open circuit voltage of 66 mV and a short circuit current of 6.8 µA/cm2.

Study of sprayed CZTS thin films containing various copper content

By ultrasonic spray, we have deposited CZTS films on Mo coated substrates. A sulfurization treatment was systematically performed under Argon atmosphere at 500 °C for one hour. Copper content effect of CZTS thin films of about 1 µm was studied by X-ray diffraction, Raman spectroscopy and optical transmittance measurements. The films exhibited the kesterite structure despite the appearance of some secondary phases for a high and poor copper content. The gap energy value was sensitive to the copper content and ranged between 1.42 eV and 1.68 eV.

Properties of Cu 2 ZnSnS 4 films elaborated by modified spray process

By spray assisted chemical vapor deposition process, we have elaborated Cu2ZnSnS4 thin films at various deposition temperatures without any sulfurization treatment. The (112) preferential orientation was showed by X-ray diffraction. Raman spectroscopy confirmed the CZTS kesterite structure. Band gap values ranging from 1.35 eV to 1.5 eV were obtained by optical measurements.