Ahmad A. Joraid - Academia.edu (original) (raw)

Papers by Ahmad A. Joraid

Chalcogenide Letters

The modulated differential scanning calorimetry study of amorphous Se 90-x Te 10 Sn x (x = 0, 2.5... more The modulated differential scanning calorimetry study of amorphous Se 90-x Te 10 Sn x (x = 0, 2.5, 5, 7.5, and 10) is reported. The glass samples were fabricated using a conventional melt-quenching method. The processing of the non-isothermal data was performed using the advanced thermokinetics software package. To determine the variation of the activation energy for crystallisation as a function of reaction progress the main three isoconversional methods, namely the differential method of Friedman and the integral methods of Ozawa-Flynn-Wall and Vyazovkin, were used. Based on an ASTM E698 analysis of the data, the effect of Sn content was determined. The Avrami exponent of Se 90-x Te 10 Sn x was determined and found to be dependent on the Sn content, indicating different dimensions of growth. The prediction of the isothermal reaction progress was employed to calculate the reaction model, g(α). A very large increase in the specific heat values of Se 90-x Te 10 Sn x was observed at t...

The chalcogenide glass system Sb 9.1 Te 20.1 Se 70.8 was studied by differential scanning calorim... more The chalcogenide glass system Sb 9.1 Te 20.1 Se 70.8 was studied by differential scanning calorimetry (DSC) under non-isothermal conditions. The analyses were focused on the endothermic peaks of the DSC curves. The models used for calculation of the crystallization kinetics from the exothermic peaks were applied to obtain the pre-crystallization kinetics. A comparison of different methods of analysis is presented. The effect of heating rate on the activation energy of glass transition E g and the Avrami index n are reported.

Two types of Se films were deposited on glass substrates by the thermal evaporation technique. Th... more Two types of Se films were deposited on glass substrates by the thermal evaporation technique. Thin films of thickness 393 and 652 nm and thick films of thickness 2642 nm were deposited. A range of annealing tempera-tures from 323 up to 373 K was used for the films which had a thickness of 652 nm. X-ray diffraction (XRD) investigations indicate the develop-ment of crystalline phases as the annealing temperature reaches a transi-tion temperature of 347 K. The effects of annealing were revealed by studying the morphology of the samples using scanning electron micros-copy (SEM) and atomic force microscopy (AFM). The refractive index, n, was found to be dependent on the annealing temperature and film thick-ness. The mechanism of the optical absorption follows both the direct and indirect transitions. The indirect, E gi , and direct, E gd , optical band gaps were found to be nearly constant with increasing annealing temperature, fol-lowed by a sharp decrease after the transition temperat...

Thermochimica Acta, 2014

The kinetic parameters of amorphous Se 85 Te 10 Pb 5 glasses were studied for nonisothermal and p... more The kinetic parameters of amorphous Se 85 Te 10 Pb 5 glasses were studied for nonisothermal and predicted isothermal conditions. Differential scanning calorimetry (DSC) was used to study the kinetics of the amorphous-to-crystalline transformation at heating rates in three regimes (3-15, 20-50 and 60-99 K min À1). Analysis of the obtained data shows that the activation energy of crystallization is not constant but varies with the degree of conversion and, hence, with temperature; thus, the variation depends on the heating rate. The Avrami exponents indicate that the mechanism of crystallization varies from one-to two-to three-dimensional growth at low, medium and high heating rates, respectively. The reduced reaction model was observed to follow the Avrami-Erofeev mechanism, but varies from A1.5 to A2 to A3 for the different heating-rate regimes. A good fit was achieved between experimental and predicted sigmoidal curves for the crystallization fraction with increasing temperature. 2014 Elsevier B.V. All rights reserved.

Physica B: Condensed Matter, 2007

In this work, the crystallization kinetics of Se thin films has been studied under nonisothermal ... more In this work, the crystallization kinetics of Se thin films has been studied under nonisothermal conditions using a differential scanning calorimetric (DSC) technique. The analysis focuses on the effect of temperature (385K⩽T⩽418K) on the DSC results. Two methods were used to determine the variation of the activation energy for crystallization Eα with temperature. It was found to change from 69±4kJmol−1 down to 23±3.2kJmol-1 and from 83±3.3kJmol-1 down to 55±2.5kJmol-1 for results obtained using the Friedman and Kissinger–Akahira–Sunose methods, respectively. The effects of annealing were revealed by studying the morphology of the samples using scanning electron microscopy and atomic force microscopy. The Johnson–Mehl–Avrami and Prout–Tompkins models have been used for the description of DSC crystallization data. It seems that two-dimensional growth is the most probable mechanism of the crystallization, particularly at high temperature.

Thermochimica Acta, 2007

In this work, the activation energies of crystallization of amorphous Sb 9.1 Te 20.1 Se 70.8 have... more In this work, the activation energies of crystallization of amorphous Sb 9.1 Te 20.1 Se 70.8 have been studied under non-isothermal conditions using a differential scanning calorimetric (DSC) technique. The analysis focuses on the effect of temperature (413 ≤ T ≤ 437 K) on the DSC results. The three isoconversional methods of Friedman, Kissinger-Akahira-Sunose (KAS) and Vyazovkin were used to determine the variation of the activation energy for crystallization with temperature, E α (T). The KAS and Vyazovkin methods gave identical values, and the range of E α (T) was found to vary from 128.7 down to 77.8 kJ mol −1 , while the Friedman method gave lower values with E α (T) from 84.1 to 31.2 kJ mol −1. The effects of annealing were revealed by studying the morphology of the samples using scanning electron microscopy.

Thermochimica Acta, 2005

The crystallization kinetics of Sb 9.1 Te 20.1 Se 70.8 chalcogenide glass have been studied by di... more The crystallization kinetics of Sb 9.1 Te 20.1 Se 70.8 chalcogenide glass have been studied by differential scanning calorimetry (DSC). The effective activation energy of crystallization has been evaluated on the basis of the Kissinger equation and the method of Matusita et al. The Sestak-Berggren model has been used for the description of DSC crystallization data as it provides the best fit to the experimental results. It has been found that the Johnson-Mehl-Avrami model could be applied at very high rates of heating.

Current Applied Physics, 2009

Tungsten oxide (WO 3) thin films were prepared by an electron beam deposition technique. Films we... more Tungsten oxide (WO 3) thin films were prepared by an electron beam deposition technique. Films were deposited onto fluorine-doped tin oxide (FTO)-coated glass substrates maintained at 523 K. The as-deposited films were found to be amorphous and crystallized after annealing at 673 K. The electrochromic and optical properties, structure, and morphology are strongly dependent on the annealing conditions. Cyclic voltammetry (C-V) was carried out in the potential range À1 to +1 V. Before and after colouration, the films were characterized by measuring transmittance and reflectance. The colouration efficiencies at 630 nm are about 39.4 cm 2 C À1 and 122.2 cm 2 C À1 for amorphous and crystalline films, respectively. An investigation of self-bleaching for the coloured film revealed that the film fades gradually over time.

Chalcogenide Letters

Thin films of As46Te46S8 with different thicknesses were prepared via thermal evaporation onto ‎c... more Thin films of As46Te46S8 with different thicknesses were prepared via thermal evaporation onto ‎chemically cleaned glass substrates at different temperatures. X-ray diffraction of the deposited film at ‎room temperature revealed the formation of an amorphous structure. In addition, the selected-area ‎electron diffraction (SAED) patterns confirmed the amorphous phase. The mechanism of the optical ‎absorption was observed to follow the rule of direct transition. An increase in the optical gap (E0) from ‎‎2.35 to 2.73 eV was observed when the substrate temperature TS was varied from room temperature to ‎‎463 K (film thickness = 100 nm). In addition, E0 was observed to be dependent on the film thickness ‎and increased from 1.7 to 2.38 eV when the film thickness was increased from 35 to 135 nm (TS = ‎room temperature). The effect of TS on the electrical properties was also studied. The electrical ‎resistivity (ρ) and the activation energy for conduction ( ) decreased from 7.74 x105 to 6....

The objective of this work is to obtain the thermodynamic parameters, namely, the changes of enth... more The objective of this work is to obtain the thermodynamic parameters, namely, the changes of enthalpy, Gibbs free energy, and the entropy of two degradation steps observed in three of a new family of organometallic dendrimers. The isoconversional Flynn-Wall-Ozawa (FWO) model was employed to calculate the effective activation energy and pre-exponential factor. The changes of enthalpy and the entropy was consistent with the activation energy, whereas the change of Gibbs free energy remains positive during the entire degradation process, implying that the degradation is non-spontaneous and thus requires external heat supply.

Journal of Taibah University for Science, 2008

Thin films of 1, 4, 8, 11, 15, 18, 22, 25-octahexylphthalocyanine were deposited on glass substra... more Thin films of 1, 4, 8, 11, 15, 18, 22, 25-octahexylphthalocyanine were deposited on glass substrates by the thermal evaporation and spin coating techniques. The structure of the both types of films was found to be in α form. The crystallite size assumed the values of 88.65 and 44.32 nm for thermal and spin coated films, respectively. The surface morphology of the thin films was investigated by atomic force microscopy and showed that the molecules of 1, 4, 8, 11, 15, 18, 22, 25-octahexylphthalocyanine grew in stacks of parallel rows. The optical properties of thermally evaporated and spin coated films are reported here. The spectrophotometric measurements of transmittance and reflectance were carried out at UV-Vis-NIR region for the films that showed two absorption bands, namely the Qand Soret bands. The mechanism of the optical absorption follows the indirect transitions. Almost there was no remarkable difference was observed between the two types of films. Other optical parameters, such as absorption coefficientα , the absorption index, k, and refractive index, n, were also determined.

Journal of Taibah University for Science, 2009

In this research, the activation energy of amorphous S b T e S e 9.1 2 0 .1 7 0 .8 crystallizatio... more In this research, the activation energy of amorphous S b T e S e 9.1 2 0 .1 7 0 .8 crystallization was studied under isothermal conditions using a differential scanning calorimetric (DSC) technique. The activation energy for S b T e S e 9.1 20 .1 70 .8 crystallization was determined to be 1 1 2 4 4 k J m o l − ±. The Avrami exponent was observed to decrease from 2.22 to 1.88 as the annealing temperature was increased from 413 to 421 K, and remained constant at higher temperatures. The local Avrami exponent was investigated and was observed to primarily indicate two-dimensional growth. The effects of annealing were revealed by studying the morphology of the samples with a scanning electron microscope (SEM).

Thin Solid Films, 2009

The crystallization kinetics of Se thin films were determined under nonisothermal conditions usin... more The crystallization kinetics of Se thin films were determined under nonisothermal conditions using a differential scanning calorimetry (DSC) technique. The development of crystal phases by thermal treatment of the film at various temperatures was analyzed by X-ray diffraction. Microstructures were identified by studying the morphology of the films using scanning electron microscopy and atomic force microscopy. This study reveals the simultaneous presence of distinct hexagonal and monoclinic phases; the DSC crystallization curve is formed by overlapping the exothermic crystallization curves of both phases. Two isoconversional methods, the Kissinger–Akahira–Sunose and Vyazovkin methods, were used to determine the variation of the activation energy for crystallization with temperature. The results show that the crystallization activation energy decreases with the extent of crystallization or temperature, which suggests that the examined phases follow multi-step kinetics.

Materials Science Forum, 2011

Smart windows were fabricated with different thicknesses of amorphous V2O5, which acts as an ion ... more Smart windows were fabricated with different thicknesses of amorphous V2O5, which acts as an ion storage layer. In these devices, V2O5 was deposited by thermal evaporation at a substrate temperature of 200 oC, and an electrochromic layer (WO3) was deposited by electron beam evaporation at a substrate temperature of 250 oC. Both layers were amorphous. V2O5 was found to exhibit direct-forbidden electron transitions, whereas the WO3 layer exhibited indirect-allowed electron transitions. An increase in the thickness of V2O5 from 78 nm to 313 nm reduced the colouration efficiency from 64 to 48 cm2/C, and the time of the transmission variation curve from the coloured state to the bleached state was increased from 82.41 s to 558 s.

Thermochimica Acta, 2012

ABSTRACT The Vyazovkin model-free method were applied to study non-isothermal degradation of an a... more ABSTRACT The Vyazovkin model-free method were applied to study non-isothermal degradation of an aryl and hetaryl azo dye-containing polynorbornene using a differential scanning calorimetric (DSC) technique. The samples were heated in nitrogen, with heating rates in the range 5–50 K min−1. The isoconversional method of Vyazovkin was used to determine the variation of the activation energy for degradation with temperature, Eα(T). The values of Eα(T) were found to be almost independent of temperature. The results of isoconversional methods used suggest that the transition follows a single-step kinetics reaction mechanism.

Advanced Materials Research, 2012

This study investigates the preparation of the three main layers of a CdS/CdTe thin film solar ce... more This study investigates the preparation of the three main layers of a CdS/CdTe thin film solar cell using a single vacuum system. A Close Space Sublimation System was constructed to deposit CdS, CdTe and CdCl2 solar cell layers. Two hot plates were used to heat the source and the substrate. Three fused silica melting dishes were used as containers for the sources. The properties of the deposited CdS and CdTe films were determined via Atomic force microscopy, scanning electron microscopy, X-ray diffraction and optical transmission spectroscopy. An J-V characterization of the fabricated CdS/CdTe solar cells was performed under solar radiation. The short-circuit current density, Jsc, the open-circuit voltage, Voc, fill factor, FF and conversion efficiency, η, were measured and yielded values of 27 mA/cm2, 0.619 V, 58% and 9.8%, respectively.

Polyhedron, 2008

Novel symmetrical 1,4,8,11,15,18,22,25-octahexyloxy-2,3,9,10,16,17,23,24-octa-(3,5- dichloropheno... more Novel symmetrical 1,4,8,11,15,18,22,25-octahexyloxy-2,3,9,10,16,17,23,24-octa-(3,5- dichlorophenoxy)phthalocyaninato zinc(II) was synthesized and characterized by 1H NMR, 13C NMR, MS, UV–Vis, XRD, and IR spectrometry. The synthesized ZnPc complex is soluble in various organic solvents such as CH2Cl2, THF, acetone, and ethyl acetate. This property helped to obtain thin films of the new ZnPc complex by spin coating method. The surface morphology of the thin

Thermochimica Acta, 2013

The dynamics of the glass transition in Se 76 Te 21 Sb 3 chalcogenide glass was studied under non... more The dynamics of the glass transition in Se 76 Te 21 Sb 3 chalcogenide glass was studied under non-isothermal measurements using differential scanning calorimetry (DSC). The experimental result of the kinetic glass transition phenomenon, at different heating rates (5-40 K/min), was analyzed on the basis of the relaxation process occurring in the transition temperature range. The activation energy of the glass transition was determined using an advanced isoconversion kinetic methods as well as from the heating rate dependence of the glass transition temperature. The fragility index m of the glass was estimated from the measurements of the activation energy of the relaxation process, which characterizes the glass transition. Moreover, the isoconversional kinetic analysis of the experimental data show that the activation energy of glass transition process is varying with the degree of transformation (and hence with temperature) from the glassy to the super cooled phase.

Thermochimica Acta, 2008

The structure and kinetics of the crystallization reaction of amorphous Te 51.3 As 45.7 Cu 3 were... more The structure and kinetics of the crystallization reaction of amorphous Te 51.3 As 45.7 Cu 3 were studied under nonisothermal conditions using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Two exothermic changes were reported. Five isoconversional methods, of Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), Tang, Starink, and Vyazovkin, were used to determine the variation of the activation energy for crystallization with temperature, E ␣ (T). The results show that the activation energy for crystallization associated with the first peak first decreases with increasing temperature and then increases. Different behaviour was observed for the second peak, where an increase of E ␣ with temperature followed by a decrease. The effect of heating rate on the reaction model, g(α), was also different for the two crystallization peaks.

Thermochimica Acta, 2011

The kinetics involved in the thermal degradation of an aryl azo dye-containing polynorbornene was... more The kinetics involved in the thermal degradation of an aryl azo dye-containing polynorbornene was investigated by using isothermal DSC data. The activation energy of the degradation was found to be temperature dependent with two different values of 140 ± 5 and 21 ± 2 kJ mol −1 , and the Avrami exponent was observed to increase from 2 to 4 in the temperature range 573-608 K. The degradation mechanism follows the Avrami-Erofeev mechanism for solid state reaction models and it changes from A2 toward A4 for the same temperature range.

Chalcogenide Letters

The modulated differential scanning calorimetry study of amorphous Se 90-x Te 10 Sn x (x = 0, 2.5... more The modulated differential scanning calorimetry study of amorphous Se 90-x Te 10 Sn x (x = 0, 2.5, 5, 7.5, and 10) is reported. The glass samples were fabricated using a conventional melt-quenching method. The processing of the non-isothermal data was performed using the advanced thermokinetics software package. To determine the variation of the activation energy for crystallisation as a function of reaction progress the main three isoconversional methods, namely the differential method of Friedman and the integral methods of Ozawa-Flynn-Wall and Vyazovkin, were used. Based on an ASTM E698 analysis of the data, the effect of Sn content was determined. The Avrami exponent of Se 90-x Te 10 Sn x was determined and found to be dependent on the Sn content, indicating different dimensions of growth. The prediction of the isothermal reaction progress was employed to calculate the reaction model, g(α). A very large increase in the specific heat values of Se 90-x Te 10 Sn x was observed at t...

The chalcogenide glass system Sb 9.1 Te 20.1 Se 70.8 was studied by differential scanning calorim... more The chalcogenide glass system Sb 9.1 Te 20.1 Se 70.8 was studied by differential scanning calorimetry (DSC) under non-isothermal conditions. The analyses were focused on the endothermic peaks of the DSC curves. The models used for calculation of the crystallization kinetics from the exothermic peaks were applied to obtain the pre-crystallization kinetics. A comparison of different methods of analysis is presented. The effect of heating rate on the activation energy of glass transition E g and the Avrami index n are reported.

Two types of Se films were deposited on glass substrates by the thermal evaporation technique. Th... more Two types of Se films were deposited on glass substrates by the thermal evaporation technique. Thin films of thickness 393 and 652 nm and thick films of thickness 2642 nm were deposited. A range of annealing tempera-tures from 323 up to 373 K was used for the films which had a thickness of 652 nm. X-ray diffraction (XRD) investigations indicate the develop-ment of crystalline phases as the annealing temperature reaches a transi-tion temperature of 347 K. The effects of annealing were revealed by studying the morphology of the samples using scanning electron micros-copy (SEM) and atomic force microscopy (AFM). The refractive index, n, was found to be dependent on the annealing temperature and film thick-ness. The mechanism of the optical absorption follows both the direct and indirect transitions. The indirect, E gi , and direct, E gd , optical band gaps were found to be nearly constant with increasing annealing temperature, fol-lowed by a sharp decrease after the transition temperat...

Thermochimica Acta, 2014

The kinetic parameters of amorphous Se 85 Te 10 Pb 5 glasses were studied for nonisothermal and p... more The kinetic parameters of amorphous Se 85 Te 10 Pb 5 glasses were studied for nonisothermal and predicted isothermal conditions. Differential scanning calorimetry (DSC) was used to study the kinetics of the amorphous-to-crystalline transformation at heating rates in three regimes (3-15, 20-50 and 60-99 K min À1). Analysis of the obtained data shows that the activation energy of crystallization is not constant but varies with the degree of conversion and, hence, with temperature; thus, the variation depends on the heating rate. The Avrami exponents indicate that the mechanism of crystallization varies from one-to two-to three-dimensional growth at low, medium and high heating rates, respectively. The reduced reaction model was observed to follow the Avrami-Erofeev mechanism, but varies from A1.5 to A2 to A3 for the different heating-rate regimes. A good fit was achieved between experimental and predicted sigmoidal curves for the crystallization fraction with increasing temperature. 2014 Elsevier B.V. All rights reserved.

Physica B: Condensed Matter, 2007

In this work, the crystallization kinetics of Se thin films has been studied under nonisothermal ... more In this work, the crystallization kinetics of Se thin films has been studied under nonisothermal conditions using a differential scanning calorimetric (DSC) technique. The analysis focuses on the effect of temperature (385K⩽T⩽418K) on the DSC results. Two methods were used to determine the variation of the activation energy for crystallization Eα with temperature. It was found to change from 69±4kJmol−1 down to 23±3.2kJmol-1 and from 83±3.3kJmol-1 down to 55±2.5kJmol-1 for results obtained using the Friedman and Kissinger–Akahira–Sunose methods, respectively. The effects of annealing were revealed by studying the morphology of the samples using scanning electron microscopy and atomic force microscopy. The Johnson–Mehl–Avrami and Prout–Tompkins models have been used for the description of DSC crystallization data. It seems that two-dimensional growth is the most probable mechanism of the crystallization, particularly at high temperature.

Thermochimica Acta, 2007

In this work, the activation energies of crystallization of amorphous Sb 9.1 Te 20.1 Se 70.8 have... more In this work, the activation energies of crystallization of amorphous Sb 9.1 Te 20.1 Se 70.8 have been studied under non-isothermal conditions using a differential scanning calorimetric (DSC) technique. The analysis focuses on the effect of temperature (413 ≤ T ≤ 437 K) on the DSC results. The three isoconversional methods of Friedman, Kissinger-Akahira-Sunose (KAS) and Vyazovkin were used to determine the variation of the activation energy for crystallization with temperature, E α (T). The KAS and Vyazovkin methods gave identical values, and the range of E α (T) was found to vary from 128.7 down to 77.8 kJ mol −1 , while the Friedman method gave lower values with E α (T) from 84.1 to 31.2 kJ mol −1. The effects of annealing were revealed by studying the morphology of the samples using scanning electron microscopy.

Thermochimica Acta, 2005

The crystallization kinetics of Sb 9.1 Te 20.1 Se 70.8 chalcogenide glass have been studied by di... more The crystallization kinetics of Sb 9.1 Te 20.1 Se 70.8 chalcogenide glass have been studied by differential scanning calorimetry (DSC). The effective activation energy of crystallization has been evaluated on the basis of the Kissinger equation and the method of Matusita et al. The Sestak-Berggren model has been used for the description of DSC crystallization data as it provides the best fit to the experimental results. It has been found that the Johnson-Mehl-Avrami model could be applied at very high rates of heating.

Current Applied Physics, 2009

Tungsten oxide (WO 3) thin films were prepared by an electron beam deposition technique. Films we... more Tungsten oxide (WO 3) thin films were prepared by an electron beam deposition technique. Films were deposited onto fluorine-doped tin oxide (FTO)-coated glass substrates maintained at 523 K. The as-deposited films were found to be amorphous and crystallized after annealing at 673 K. The electrochromic and optical properties, structure, and morphology are strongly dependent on the annealing conditions. Cyclic voltammetry (C-V) was carried out in the potential range À1 to +1 V. Before and after colouration, the films were characterized by measuring transmittance and reflectance. The colouration efficiencies at 630 nm are about 39.4 cm 2 C À1 and 122.2 cm 2 C À1 for amorphous and crystalline films, respectively. An investigation of self-bleaching for the coloured film revealed that the film fades gradually over time.

Chalcogenide Letters

Thin films of As46Te46S8 with different thicknesses were prepared via thermal evaporation onto ‎c... more Thin films of As46Te46S8 with different thicknesses were prepared via thermal evaporation onto ‎chemically cleaned glass substrates at different temperatures. X-ray diffraction of the deposited film at ‎room temperature revealed the formation of an amorphous structure. In addition, the selected-area ‎electron diffraction (SAED) patterns confirmed the amorphous phase. The mechanism of the optical ‎absorption was observed to follow the rule of direct transition. An increase in the optical gap (E0) from ‎‎2.35 to 2.73 eV was observed when the substrate temperature TS was varied from room temperature to ‎‎463 K (film thickness = 100 nm). In addition, E0 was observed to be dependent on the film thickness ‎and increased from 1.7 to 2.38 eV when the film thickness was increased from 35 to 135 nm (TS = ‎room temperature). The effect of TS on the electrical properties was also studied. The electrical ‎resistivity (ρ) and the activation energy for conduction ( ) decreased from 7.74 x105 to 6....

The objective of this work is to obtain the thermodynamic parameters, namely, the changes of enth... more The objective of this work is to obtain the thermodynamic parameters, namely, the changes of enthalpy, Gibbs free energy, and the entropy of two degradation steps observed in three of a new family of organometallic dendrimers. The isoconversional Flynn-Wall-Ozawa (FWO) model was employed to calculate the effective activation energy and pre-exponential factor. The changes of enthalpy and the entropy was consistent with the activation energy, whereas the change of Gibbs free energy remains positive during the entire degradation process, implying that the degradation is non-spontaneous and thus requires external heat supply.

Journal of Taibah University for Science, 2008

Thin films of 1, 4, 8, 11, 15, 18, 22, 25-octahexylphthalocyanine were deposited on glass substra... more Thin films of 1, 4, 8, 11, 15, 18, 22, 25-octahexylphthalocyanine were deposited on glass substrates by the thermal evaporation and spin coating techniques. The structure of the both types of films was found to be in α form. The crystallite size assumed the values of 88.65 and 44.32 nm for thermal and spin coated films, respectively. The surface morphology of the thin films was investigated by atomic force microscopy and showed that the molecules of 1, 4, 8, 11, 15, 18, 22, 25-octahexylphthalocyanine grew in stacks of parallel rows. The optical properties of thermally evaporated and spin coated films are reported here. The spectrophotometric measurements of transmittance and reflectance were carried out at UV-Vis-NIR region for the films that showed two absorption bands, namely the Qand Soret bands. The mechanism of the optical absorption follows the indirect transitions. Almost there was no remarkable difference was observed between the two types of films. Other optical parameters, such as absorption coefficientα , the absorption index, k, and refractive index, n, were also determined.

Journal of Taibah University for Science, 2009

In this research, the activation energy of amorphous S b T e S e 9.1 2 0 .1 7 0 .8 crystallizatio... more In this research, the activation energy of amorphous S b T e S e 9.1 2 0 .1 7 0 .8 crystallization was studied under isothermal conditions using a differential scanning calorimetric (DSC) technique. The activation energy for S b T e S e 9.1 20 .1 70 .8 crystallization was determined to be 1 1 2 4 4 k J m o l − ±. The Avrami exponent was observed to decrease from 2.22 to 1.88 as the annealing temperature was increased from 413 to 421 K, and remained constant at higher temperatures. The local Avrami exponent was investigated and was observed to primarily indicate two-dimensional growth. The effects of annealing were revealed by studying the morphology of the samples with a scanning electron microscope (SEM).

Thin Solid Films, 2009

The crystallization kinetics of Se thin films were determined under nonisothermal conditions usin... more The crystallization kinetics of Se thin films were determined under nonisothermal conditions using a differential scanning calorimetry (DSC) technique. The development of crystal phases by thermal treatment of the film at various temperatures was analyzed by X-ray diffraction. Microstructures were identified by studying the morphology of the films using scanning electron microscopy and atomic force microscopy. This study reveals the simultaneous presence of distinct hexagonal and monoclinic phases; the DSC crystallization curve is formed by overlapping the exothermic crystallization curves of both phases. Two isoconversional methods, the Kissinger–Akahira–Sunose and Vyazovkin methods, were used to determine the variation of the activation energy for crystallization with temperature. The results show that the crystallization activation energy decreases with the extent of crystallization or temperature, which suggests that the examined phases follow multi-step kinetics.

Materials Science Forum, 2011

Smart windows were fabricated with different thicknesses of amorphous V2O5, which acts as an ion ... more Smart windows were fabricated with different thicknesses of amorphous V2O5, which acts as an ion storage layer. In these devices, V2O5 was deposited by thermal evaporation at a substrate temperature of 200 oC, and an electrochromic layer (WO3) was deposited by electron beam evaporation at a substrate temperature of 250 oC. Both layers were amorphous. V2O5 was found to exhibit direct-forbidden electron transitions, whereas the WO3 layer exhibited indirect-allowed electron transitions. An increase in the thickness of V2O5 from 78 nm to 313 nm reduced the colouration efficiency from 64 to 48 cm2/C, and the time of the transmission variation curve from the coloured state to the bleached state was increased from 82.41 s to 558 s.

Thermochimica Acta, 2012

ABSTRACT The Vyazovkin model-free method were applied to study non-isothermal degradation of an a... more ABSTRACT The Vyazovkin model-free method were applied to study non-isothermal degradation of an aryl and hetaryl azo dye-containing polynorbornene using a differential scanning calorimetric (DSC) technique. The samples were heated in nitrogen, with heating rates in the range 5–50 K min−1. The isoconversional method of Vyazovkin was used to determine the variation of the activation energy for degradation with temperature, Eα(T). The values of Eα(T) were found to be almost independent of temperature. The results of isoconversional methods used suggest that the transition follows a single-step kinetics reaction mechanism.

Advanced Materials Research, 2012

This study investigates the preparation of the three main layers of a CdS/CdTe thin film solar ce... more This study investigates the preparation of the three main layers of a CdS/CdTe thin film solar cell using a single vacuum system. A Close Space Sublimation System was constructed to deposit CdS, CdTe and CdCl2 solar cell layers. Two hot plates were used to heat the source and the substrate. Three fused silica melting dishes were used as containers for the sources. The properties of the deposited CdS and CdTe films were determined via Atomic force microscopy, scanning electron microscopy, X-ray diffraction and optical transmission spectroscopy. An J-V characterization of the fabricated CdS/CdTe solar cells was performed under solar radiation. The short-circuit current density, Jsc, the open-circuit voltage, Voc, fill factor, FF and conversion efficiency, η, were measured and yielded values of 27 mA/cm2, 0.619 V, 58% and 9.8%, respectively.

Polyhedron, 2008

Novel symmetrical 1,4,8,11,15,18,22,25-octahexyloxy-2,3,9,10,16,17,23,24-octa-(3,5- dichloropheno... more Novel symmetrical 1,4,8,11,15,18,22,25-octahexyloxy-2,3,9,10,16,17,23,24-octa-(3,5- dichlorophenoxy)phthalocyaninato zinc(II) was synthesized and characterized by 1H NMR, 13C NMR, MS, UV–Vis, XRD, and IR spectrometry. The synthesized ZnPc complex is soluble in various organic solvents such as CH2Cl2, THF, acetone, and ethyl acetate. This property helped to obtain thin films of the new ZnPc complex by spin coating method. The surface morphology of the thin

Thermochimica Acta, 2013

The dynamics of the glass transition in Se 76 Te 21 Sb 3 chalcogenide glass was studied under non... more The dynamics of the glass transition in Se 76 Te 21 Sb 3 chalcogenide glass was studied under non-isothermal measurements using differential scanning calorimetry (DSC). The experimental result of the kinetic glass transition phenomenon, at different heating rates (5-40 K/min), was analyzed on the basis of the relaxation process occurring in the transition temperature range. The activation energy of the glass transition was determined using an advanced isoconversion kinetic methods as well as from the heating rate dependence of the glass transition temperature. The fragility index m of the glass was estimated from the measurements of the activation energy of the relaxation process, which characterizes the glass transition. Moreover, the isoconversional kinetic analysis of the experimental data show that the activation energy of glass transition process is varying with the degree of transformation (and hence with temperature) from the glassy to the super cooled phase.

Thermochimica Acta, 2008

The structure and kinetics of the crystallization reaction of amorphous Te 51.3 As 45.7 Cu 3 were... more The structure and kinetics of the crystallization reaction of amorphous Te 51.3 As 45.7 Cu 3 were studied under nonisothermal conditions using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Two exothermic changes were reported. Five isoconversional methods, of Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), Tang, Starink, and Vyazovkin, were used to determine the variation of the activation energy for crystallization with temperature, E ␣ (T). The results show that the activation energy for crystallization associated with the first peak first decreases with increasing temperature and then increases. Different behaviour was observed for the second peak, where an increase of E ␣ with temperature followed by a decrease. The effect of heating rate on the reaction model, g(α), was also different for the two crystallization peaks.

Thermochimica Acta, 2011

The kinetics involved in the thermal degradation of an aryl azo dye-containing polynorbornene was... more The kinetics involved in the thermal degradation of an aryl azo dye-containing polynorbornene was investigated by using isothermal DSC data. The activation energy of the degradation was found to be temperature dependent with two different values of 140 ± 5 and 21 ± 2 kJ mol −1 , and the Avrami exponent was observed to increase from 2 to 4 in the temperature range 573-608 K. The degradation mechanism follows the Avrami-Erofeev mechanism for solid state reaction models and it changes from A2 toward A4 for the same temperature range.