4918
Shimaa Ahmed Aly Ahmed Hassan
SOLAR SPECTRUM MODULATION BY CHROMOGENIC THIN FILM MATERIAL TO SAVE CONSUMED ENERGY
chromogenic / Spray pyrolysis / MoO3
This thesis is devoted to the study on chromogenic materials as a promising coating on glass windows of building and vehicles to control the flow of solar radiation in and out of the interior. This coating is transformed from transparent to dim state when exposed either to light or heat or electric potential. Therefore, the flow of solar radiation entering the rooms is reduced resulting in considerable reduction of the consumed electric energy. Molybdenum oxide (MoO3) thin film is selected to be studied as a promising layer; it has reasonable response to solar radiation. The transmission of this film is significantly reduced when exposed to intense light. Spray pyrolysis technique is selected between the other sophisticated preparation techniques, such as: sputtering, pulsed laser deposition, chemical vapor deposition (CVD), electron beam, thermal evaporation and sol-gel, etc…. The used technique has many privileges such as simplicity, low cost, versatile and allows large area deposition. Home made spray system installed and tested to be ready for the deposition of MoO3 film on glass substrates. All relevant spray parameters are kept constant at their optimum values except one, the spray time which is varied from 1 to 5 min. and then the substrate temperature is varied from 200oC to 400oC during all deposition process. The prepared samples are classified into two groups; one for samples preparedat fixed substrate temperature in the range (200oC up to 400oC) and varying spray time (1-5 min.) while the later for samples deposited at constant spray time on the range (1- 5 min.) andvariable substrate temperature (200oC up to 400oC). Each preparation run is repeated three times to ensure the reproducibility of film quality. All prepared samples are checked by optical microscope with reasonable magnification to remove the poor adhering, pin-hole and non homogenous samples before their examination by XRD, AFM, SAM and spectrophotometer. The structural property of the samples is revealed by Grazing angle x-ray diffraction (GAXRD) technique. The surface topography is examined by SEM & AFM. The transmission of the samples is measured by double beam spectrophotometer using bare glass substrate as a reference. The analysis GAXRD patterns elucidate the crystalline nature of samples deposited at substrate temperature 400o C and spray time from one minutes up to 5 minutes added to them thesamples prepared at substrate temperatures 350oC & 325o C and spray time 3, 4 and 5 minutes. Also, the amorphous samples are those prepared at substrate temperatures 200oC, 250oC & 300oC and spray time from 1 to 5 min. added to them the samples prepared at substrate temperatures 325oC, 350oC and spray time one and two minutes. All crystalline samples show only the characteristic peaks of thermodynamically stable α- MoO3 phase with lamellar structure indicated by prevailing of (0 2k0) plane. WinFit program is used to fit the XRD pattern and calculate the crystallite size and internal residual strain. The obtained values for crystallite size ranged from 10, 28 nm while the strain values varied from 0.289 % to 0.054%. SEM and AFM 2D & 3D images combined with the crystallite distribution illustrated by the histogram declare the homogeneity of crystallite size and smoothness of the film surfaceThe prepared MoO3 films were tested for their performance as an optical chromogenic material when exposed to an UV source for varying times, 45 min. and 145 min.. The color of the film varied from colorless to dark blue.
2015
Ph.d
Ain Shams
Faculty of Girls for Art Science