الفهرس 
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Abstract
First, we prepared thin films (at bath temperature 336 K) using modified chemical bath deposition (MCBD) method with cobalt chloride (CoCl ) and sodium sulfide (Na S) aqueous solutions as starting materials. Grazing Incidence X-ray diffraction studies proved that these films are single-phase polycrystalline material corresponding to the cubic structure of cobalt oxide (CoCo O ).We are obliged to prepare cobalt sulfide in powder form, avoiding the cause of formation of cobalt oxide, by performing the same experiment at room temperature and drying the precipitate at 373 K under vacuum.The crystal structural investigations were carried out on the as-dried and annealed powder samples obtained from MCBD technique using X-ray diffractometer. XRD studies revealed that the as-dried (373 K) powder samples are amorphous in nature, while the samples annealed under vacuum at 423, 473, 523, 573, 623, 673, and 723 K revealed the following:1- The powder samples annealed at 423, 473, and 523 K are single-phase polycrystalline materials with the same crystal structure corresponding to the hexagonal type structure of CoS. - The samples annealed at 573 and 623 K have the same crystal structures and each of them has two crystal structural phases, predominant phase of CoS and minor secondary phase of Co S . 3- The samples annealed at 673 and 723 K have the same crystal structures and each of them has three crystal structural phases, predominant phase of Co S , secondary phase of CoS, and minor secondary phase of Co S . The unit-cell lattice parameters were determined for all the crystal structural phases of the investigated samples. The determined unit-cell lattice parameters for phases that have the same chemical formula in different annealed powder samples were found to be in good agreement.Nearly stoichiometric thin films of Co S were deposited on precleaned glass and KBr disks as substrates at 573 K by using the pulsed laser deposition technique using the pre-synthesized powder of cobalt sulfide in compressed disk form as source material.The crystal structural investigations were carried out on the produced pulsed laser deposition films and their source material using X-ray diffractometer. In addition, the elemental composition of the source material for PLD films as well as the as-deposited PLD films was determined using an energy-dispersive X-ray spectrometer (EDXS). Besides, the surface morphology of the PLD films of cobalt sulfide (Co S ) was investigated using the atomic force microscopy (AFM).The analysis of XRD data revealed that the source material annealed at 573 K is polycrystalline and has three crystal structural phases, predominant, secondary, and minor secondary phases, corresponding to the hexagonal type structure for CoS, the cubic type structure for Co S , and the cubic type structure for Co S ; respectively. The analysis of XRD data revealed also that the pulsed laser deposition films are single-phase polycrystalline materials corresponding to the cubic type structure, the same as that of cobalt sulfide with chemical formula of Co S . The unit-cell lattice parameters were determined for both the source material and pulsed laser deposition films.In addition, the composition analysis of pulsed laser deposition films and their source material revealed that they are nearly stoichiometric, and the chemical compositions were found to be in good agreement with the obtained results from X-ray analysis.The quantitative analyses on AFM images of the pulsed laser deposition Co S films (PLDF1 & PLDF2) with deposition time (DT) 15 and 10 min; respectively, revealed that:- Both the two samples appear more homogeneous and consisting of smaller grains with average radius of grain size of 83 and 93 nm, respectively; indicating that they have nano-crystalline structures.- The thickness values obtained are 502 and 207 nm with small surface roughness of 1.35 and 1.40 nm; respectively.The I.R optical absorptions of the pulsed laser deposited Co S films on KBr substrates at 573 K, were determined from spectrophotometric measurements of the transmittance at normal incidence of light in the wavelength range 2.9 - m, after correcting for the absorptance and reflectance of the substrate. The analysis of the spectral behaviour of the optical absorption coefficient of the samples, in the investigated range, indicated the existence of an optical transition from valence band to the conduction band. This transition is a direct allowed transition with an energy gap, Eg= 0.23 eV. The dark electrical conductivity, σdc, the Hall voltage, VH, and the thermoelectric power S, of the PLD Co S films were measured simultaneously on the same sample over the temperature range from ~300 to 573 K using van der Pauw method.** The conductivity, σ, of the investigated films showed weak negative temperature dependence in the investigated temperature range, indicating that the conductivity behaviour of Co S sample is consistent with semimetal or narrow-gap semiconductor.** The temperature dependence of the Hall voltage, VH, for the investigated films showed that: 1- The Hall constant, RH, is constant through the investigated temperature range indicating degeneracy of the Co S compound, which is in agreement with the results of the conductivity. Also, the value of RH is negative indicating n-type conduction.- The number of free carriers, n, is temperature independent with a nearly constant value, n (= 3.7 × 10 cm- ), for the composition Co S nano-crystals, which proves the degeneracy of the indicated compound.- The analysis of the temperature dependence of the Hall mobility, μH, revealed that the scattering mechanism is due to neutral impurities. ** The temperature dependence of the thermoelectric power, S, for the investigated films showed that:1- The thermoelectric power has a negative sign over the whole investigated temperature range, indicating that the majority carriers are electrons and all the PLD films have n-type conduction (in agreement with Hall effect measurements).- The thermoelectric power coefficient linearly decreases with increasing temperature, as most narrow gap semiconductor or semimetal behaviour.- The analysis of the temperature dependence of the thermoelectric power, S, revealed that the effective mass, m*, is temperature independent with a nearly constant value of m me) for the Co S composition.4- Finally, the number of free carrier concentration, n, was found to be more than the conduction band states at room temperature (n » NC) indicating that the degeneracy in Co S starts at room temperature.