Tarek El-Brolossy | Ain Shams University (original) (raw)
Papers by Tarek El-Brolossy
Surface plasmon sensor for NO2 gas
Surface and Interface Analysis, 2008
ABSTRACT Surface plasmon resonance (SPR) based sensors using silver (Ag) thin films have been suc... more ABSTRACT Surface plasmon resonance (SPR) based sensors using silver (Ag) thin films have been successfully applied for the detection of nitrogen dioxide (NO2) gas. The SPR sensors have cobalt–phthalocyanine (CoPc) as an active add-layer. A surface plasmon was generated via a prism coupler in Kretschmann configuration. We found that the detection limit of SPR sensor is 0.07 ppm in an ambient environment at normal temperature and pressure (NTP). The simple structure of the SPR sensor makes it superior to liquid chemical sensors for the detection of NO2. Copyright © 2008 John Wiley & Sons, Ltd.
The European Physical Journal Special Topics, 2008
We report on the optical absorption properties of as prepared gold naoparticles of different shap... more We report on the optical absorption properties of as prepared gold naoparticles of different shapes and sizes measured by photoacoustic (PA) method. The gold nanoparticles of two different shapes (dots, rods) have been prepared using the seed mediated growth method. The shape and the size of these different nanoparticles were determined by STM measurements. PA spectra show the splitting of the surface plasmon resonance (SPR) into two modes (transverse and longitudinal) in case of gold nanorods. The increase in the aspect ratio of the nanorods leads to clear redshifts of the longitudinal SPR. These shifts were used to determine the dielectric constant of the surrounding medium and its variation with the aspect ratios.
Journal de Physique IV (Proceedings), 2005
Photoacoustic (PA) spectroscopy and scanning electron microscopy (SEM) have been employed to inve... more Photoacoustic (PA) spectroscopy and scanning electron microscopy (SEM) have been employed to investigate remineralized artificially carious enamel as well as dentin. The remeniralization process was carried out by applying bioactive glass particles and mineralizing solutions either directly or after the specimen was first treated with Zeolite powder. The PA was carried out to evaluate the change in the thermal parameters (diffusivity, effusivity and conductivity) quantitatively. The remineralization process was evaluated by comparing the thermal parameters to those of the healthy tissue. PA measurements show that; the values of thermal conductivity of the normal tissues (enamel: 0.9 W m-1 K-1 and dentin: 0.58 W m-1 K-1) were altered by caries to be (enamel: ≈ 0.72 W m-1 K-1 and dentin: ≈ 0.44 W m-1 K-1) and they approach their normal values after the application of the different mineralizing agents. Also the results indicate that; Bioactive glass enhances the thermal parameters of artificially carious enamel and dentin (considering the healthy values as a reference), slightly more than the mineralizing solution. Furthermore, PA measurements show that the application of Zeolite powder enhances the effect of the mineralizing agent. In order to augment the PA results, SEM was used to depict surface topography, for each treated tissue.
Chinese Physics B, 2013
Determining the thermophysical properties of Al-doped ZnO nanoparticles by the photoacoustic tech... more Determining the thermophysical properties of Al-doped ZnO nanoparticles by the photoacoustic technique * T. A. El-Brolossy a)b) † , O. Saber a)c) , and S. S. Ibrahim a)d) a
Photoacoustic spectroscopy characterization of CdSe quantum rods
The European Physical Journal Special Topics, 2008
Abstract. The optical absorption properties of as prepared CdSe quantum rods (QRs) are measured b... more Abstract. The optical absorption properties of as prepared CdSe quantum rods (QRs) are measured by the photoacoustic (PA) method. CdSe QRs were fabricated by the chemical solution deposition (CD) technique. Decreasing the rod size (width and length) that is ...
Interfacial electronic traps at ZnSe/GaAs heterostructures studied by photomodulation Raman scattering
Journal of Physics: Condensed Matter, 2006
Photomodulation Raman scattering spectroscopy has been employed to study free charge trapping mec... more Photomodulation Raman scattering spectroscopy has been employed to study free charge trapping mechanisms at ZnSe-GaAs(001) heterostructure interfaces. This technique reveals that the interfacial region contains predominantly hole traps. Time dependent measurements of the photomodulated Raman scattering intensity show that interfacial charge-trap lifetime is ≈30 s for both electrons and holes.
Photoacoustic measurement of thermal properties of a thin polyester film
Applied Physics Letters, 1984
... Photoacoustic measurement of thermal properties of a thin polyester film. ... Abstract. The p... more ... Photoacoustic measurement of thermal properties of a thin polyester film. ... Abstract. The phase and the amplitude of the photoacoustic signal are measured as a function of chopping frequency for a thin polyester film, using two different backing materials (water and ethanol). ...
An Investigation about the Reminerlization Potential of Bio-active glass on Artificially Carious Enamel and Dentin using Raman Spectroscopy
ABSTRACT
Thermal diffusivity measurements of transparent liquid and powder materials using PAS
Proceedings of the 10th international conference on photoacoustic and photothermal phenomena, 1999
Thermal diffusivity of organic dye CV in powder form has been measured using PA effect. It is sho... more Thermal diffusivity of organic dye CV in powder form has been measured using PA effect. It is shown that this method permits to estimate the thermal diffusivity for transparent solvents using the dye at low concentration as a precursor.
Thermal conductivity and heat capacity of poly(3-octylthiophene-2,5 diyl) and its multi-wall carbon nanotube composites
Physica Scripta, 2014
ABSTRACT Poly (3-octylthiophene-2,5-diyl) (P3OT) is one of the most important semiconducting poly... more ABSTRACT Poly (3-octylthiophene-2,5-diyl) (P3OT) is one of the most important semiconducting polymer materials used for organic solar cells. Thermal properties data, especially the thermal conductivity of the active material of solar cells, is of fundamental importance. Such data for P3OT are barely available in the literature. The photoacoustic technique is employed to measure thermophysical properties of P3OT including thermal diffusivity, thermal effusivity, specific heat capacity and thermal conductivity. The obtained results are confirmed by many measurements as well as by using more than one method. A remarkable method for thermal effusivity measurements of surface coating as well as bulk samples is introduced. The development of P3OT thermophysical properties with multi-wall carbon nanotube (MWCNT) loading as high as 6% volume fraction is investigated. Continuous enhancement of thermal diffusivity as well as thermal effusivity of P3OT is obtained with increasing MWCNT content. By using the mixed model for the thermal conductivity of a two phase system, we are able to estimate the thermal diffusivity and the thermal effusivity of MWCNTs. A considerable enhancement in thermal conductivity of larger than twice that of neat P3OT at nanotube loading ≈6% volume fraction is obtained. Theoretical analysis of the experimental results generating an interfacial thermal resistance of MWCNTs as Rk = 5.8 × 10−8 m2K W−1.
Indian Journal of Physics, 2012
Photoacoustic (PA) technique was applied to study the optical absorption and measure the optical ... more Photoacoustic (PA) technique was applied to study the optical absorption and measure the optical energy gap of porous silicon (PSi) as a suitable example of the two layer samples (porous layer and Si substrate). The PSi layers were prepared by the electrochemical anodization etching process with different current density of p-type silicon wafers. The formation of the porous layer has been identified by photoluminescence (PL) and AFM measurements. Thermal diffusivity of the prepared samples was also measured to confirm thermal isolation properties of the formed PSi. The optical absorption, energy gap, and thermal diffusivity of PSi were investigated by analyzing the experimental data from PA measurements. The values of energy gap have been found to be porosity-dependent. In contrast to the conventional techniques, PA measures the energy band gap of both layers simultaneously with high accuracy. In the range of porosity (27-52%) of the studies, our results show that the optical band-gap energy of p-type PSi (1.7-1.92 eV) was higher than that obtained for silicon substrate (1.11 eV). These energies were used to obtain the diameter of the Si quantum dots in the porous layer. These results introduce PA technique as a suitable candidate for optical depth profile analysis of multilayer solids. Moreover, PA technique can be used for particles size estimation of low dimensional materials.
Thermal properties stability of UV irradiated PVA nanohybrid composites
Polymers for Advanced Technologies, 2012
ABSTRACT Zn‐Al‐salicylic nanohybrid layers have been prepared and used as fillers for polyvinyl a... more ABSTRACT Zn‐Al‐salicylic nanohybrid layers have been prepared and used as fillers for polyvinyl alcohol (PVA). Nanohybrid layers of a broad absorption area in UV region were completely and uniformly dispersed in a continuous polymer matrix. PVA and PVA nanohybrid composite (NHC) films were exposed to UV irradiation. Thermal properties (diffusivity, effusivity, and conductivity) of both have been measured through photoacoustic technique before and after UV irradiation. Thermal parameters of PVA suffered from a quick deterioration with UV exposure due to reduction of the phonon mean free path as a result of molecular chain scissions. However, significant stability in such parameters of NHC has been obtained under the influence of UV irradiation. This thermal properties stability may be an important step on the way of obtaining photostable polymer NHC. Copyright © 2012 John Wiley & Sons, Ltd.
Water, Air, & Soil Pollution, 2012
The photocatalytic degradation of dyes under sunlight irradiation has received much attention not... more The photocatalytic degradation of dyes under sunlight irradiation has received much attention not only because the attempt is aimed at decomposition of pollutants but also at finding methods of making use of solar energy. Following this line, zinc oxide nano-particles were prepared using solvent thermal method in order to decompose Naphthol Green B in presence of sunlight. Complete mineralization and decolorization of Naphthol Green B were achieved in 14 h. In order to reduce the band gap of zinc oxide and increase its photocatalytic activity in sunlight, it was doped with different concentrations of aluminum (1 %, 3 %, 5 %, and 10 %). The obtained band gap energy of the Al-doped ZnO nanoparticles was investigated as a function of Al content. Reduction of band gap energy for the heavily doped ZnO nanoparticles (10 % Al) was observed from 3.29 to 3.23 eV leading to fast transfer for electron from the excited state of dye to conduction band of ZnO. Therefore, by using the 10 % Al-doped ZnO nanoparticles, the complete mineralization and decolorization of Naphthol Green B were achieved in 6 h under sunlight. These results suggested that the heavily doped ZnO nanoparticles with aluminum has a positive effect towards photocatalytic reactions with dye under solar energy.
Carbon nanotube functionalization effects on thermal properties of multiwall carbon nanotube/polycarbonate composites
Polymer Composites, 2014
ABSTRACT The thermal properties of composites based on polycarbonate (PC) filed with ultraviolet/... more ABSTRACT The thermal properties of composites based on polycarbonate (PC) filed with ultraviolet/ozone (UVO) treated multiwall carbon nanotubes (MWCNTs) in low limit (less than 0.01) volume fractions have been investigated. The composites were prepared in the form of films of relatively small thickness (23–33 μm) with random orientation of treated MWCNTs. Functionalization of MWCNTs has been confirmed through Fourier transform infrared measurements. Thermal conductivity was obtained by measuring both of thermal diffusivity and thermal effusivity using photoacoustic technique. The results reveal that the addition of UVO treated MWCNTs lead to enhance both the thermal diffusivity and thermal effusivity of the composites. Insertion of 0.95% MWCNTs into PC improves the thermal conductivity of the composites by ∼22%. This enhancement is reasonable using such low content of MWCNTs of moderate aspect ratio. The experimental results were analyzed using a simple model concerning some relevant parameters such as volume fractions, interfacial thermal resistance, aspect ratio, and nonstraightness of nanotubes. An interface thermal resistance in the low limit of about 2.1 × 10−8 m2K/W has been estimated. In the light of these results, the role of MWCNTs functionalization on the overall thermal transport properties of MWCNTs-polymer composites has been discussed. POLYM. COMPOS., 2014. © 2014 Society of Plastics Engineers
Journal of Raman Spectroscopy, 2008
ZnSe/semi-insulating GaAs interfaces were studied by observing photogenerated plasmon-LO (PPL) co... more ZnSe/semi-insulating GaAs interfaces were studied by observing photogenerated plasmon-LO (PPL) coupled modes by nonresonant micro-Raman spectroscopy. The effect of the carriers generated by the focused laser beam was investigated for a series of different thicknesses of ZnSe epitaxial layers. The PPL mode in GaAs was observed in the micro-Raman spectra for all samples, but with different magnitude. The plasma is believed to be an electron gas as a result of the negative nature of the interfacial region that contains predominantly hole traps. The free carrier concentration is estimated to be >10 18 cm −3 and their lifetime ∼0.1 ns. This relatively long lifetime suggests that the ZnSe/GaAs interface has to be of high structural quality leading to a low recombination velocity. ZnSe/GaAs heterostructures of less crystalline quality (as determined by resonant Raman measurements) shows the effect of photogenerated carriers only to lesser extent.
Interfacial electronic properties of AuGaAs interfaces studied by photomodulation Raman spectroscopy (pump-probe technique)
Journal of Raman Spectroscopy, 2011
ABSTRACT Photomodulation Raman spectroscopy (PM-RS) was employed to investigate the interfacial p... more ABSTRACT Photomodulation Raman spectroscopy (PM-RS) was employed to investigate the interfacial properties of Au: n-type GaAs interfaces, using the forbidden longitudinal optical (LO) phonon scattering as a probe. In PM-RS, the photomodulating pump beam (PB) is incident on the sample while the Raman measurements are in progress; hence, PM-RS can be viewed as a pump-probe technique. The photogenerated carriers partly neutralize the surface charges, which decreases the interfacial field and consequently the intensity of forbidden LO scattering. Two molecular beam epitaxy (MBE) junctions of 80 angstrom Au on n-type GaAs (001) substrate with two different doping densities were used. The total surface charge density and change in the band bending were obtained as a function of the PB intensity considering a constant depletion electric field for the lower doped sample. Furthermore, the interfacial minority carrier trap lifetime was determined through dynamical measurements of the PM-RS intensity. Copyright (C) 2010 John Wiley & Sons, Ltd.
Journal of Raman Spectroscopy, 2012
Surface enhanced Raman scattering (SERS) of adsorbed molecule on colloidal gold nanoparticles of ... more Surface enhanced Raman scattering (SERS) of adsorbed molecule on colloidal gold nanoparticles of different shapes, namely nanospheres (NSs), nanorods (NRs), and nanoprisms (NPs) as well as the three NPs arrays of different interstice prepared by NS lithography, are studied with incident wavenumbers in the near-dipole and near-quadrpole regions of the nanoparticles. In the colloidal gold nanoparticles, the SERS enhancement is the largest for the sharp tip followed by the truncated tip NPs, then the NRs and least enhancement for the NSs. This decreasing order of enhancement occurs although the incident wavenumber was near the dipole resonance of NSs and the quadrupole resonance for the NPs. These varied enhancements are explained in part as due to the binding energies of the nanocrystal facets, but the larger contribution results from the plasmon electromagnetic fields. A parallel finite difference time domain (FDTD) calculations were carried out, which corporate the experimental results and show agreement with ratios of the SERS enhancement for the different shapes. The normalized SERS intensity for NPs of different interstice distances show a sharp rise with the decrease of the interstice distances because of interparticle dipolar and quadrupolar coupling as evidenced also by FDTD calculations. Furthermore, these calculations show that the enhancement is polarization independent for an incident wavelength near quadrupole resonance but polarization dependent for an incident wavelength near the plasmon dipole transition. In the last case, the enhancement is larger by an order of magnitude for a polarization parallel to the NPs bisector than for polarization normal to the bisector with no hot spots for the relatively large interstice dimensions used.
Journal of Physics: Condensed Matter, 2003
Photomodulation of the coupled plasmon-LO phonon modes has been employed to determine the change ... more Photomodulation of the coupled plasmon-LO phonon modes has been employed to determine the change in both the surface charge density and the depletion electric field as a function of photomodulation beam (PMB) intensity. The samples are two pieces of highly doped (001) n-type GaAs. The total surface charge density has been obtained as a function of the photomodulating intensity using the dependence of the unscreened LO phonon on the depletion width. We are able to separate the impact of the PMB on the surface electric field from the impact on the depletion width. This allows a separate determination of the change in depletion electric field, which reaches ∼73% of its original value at the highest intensity used for PMB.
Journal of Physics and Chemistry of Solids, 2012
The effect of sintering temperature on ZnO varistor properties is investigated in the range of 70... more The effect of sintering temperature on ZnO varistor properties is investigated in the range of 700-1400 1C. The increase of sintering temperature does not influence the well-known peaks related to hexagonal wurtzite structure of ZnO ceramics, whereas the average grain size is increased from (1.08 to 2.1 mm). With increasing sintering temperature up to 1200 1C, the nonlinear region is clearly observed in the I-V characteristics, whereas this region is completely absent only for the sample sintered at 1400 1C. As the sintering temperature increased, the breakdown field decreased over a wide range from 2838.7 to 6.41 V/cm, while the nonlinear coefficient is increased in the range of (23.86-47.76). Furthermore, the barrier height decreased from 1.76 to 0.974 eV, whereas electrical conductivity is improved. On the other hand, the optical band gap is gradually decreased in the range of 3.08-2.70 eV with increasing sintering temperature. These results showed a strong correlation between sintering temperature and the properties of ZnO ceramic varistor.
Journal of Physics: Conference Series, 2010
Photomodulation Raman spectroscopy (PM-RS) has been employed to study the surface depletion elect... more Photomodulation Raman spectroscopy (PM-RS) has been employed to study the surface depletion electric field Es and to monitor the change in surface charge density in n-type GaAs, using the forbidden LO phonon scattering for low doping samples and coupled plasmon-LO phonon modes for high doping samples. In PM-RS, the photomodulating pumping beam (PB) is incident on the sample while the Raman measurements are in progress hence PM-RS can be viewed as a pump-probe technique. The photogenerated carriers partly neutralize the surface charges. Two different GaAs surfaces (011) with low and moderate doping density and (001) with high doping density were used. The total surface charge density has been obtained as a function of the PB intensity considering a constant depletion electric field for the lower doping sample of (011) surface and using the dependence of the unscreened LO phonon on the depletion width for the higher doping samples of (001) surface. The minority carrier's lifetime was also determined through dynamical measurements for the PM-RS of the low doping sample as ≈ 21 s, in a good agreement with other techniques
Surface plasmon sensor for NO2 gas
Surface and Interface Analysis, 2008
ABSTRACT Surface plasmon resonance (SPR) based sensors using silver (Ag) thin films have been suc... more ABSTRACT Surface plasmon resonance (SPR) based sensors using silver (Ag) thin films have been successfully applied for the detection of nitrogen dioxide (NO2) gas. The SPR sensors have cobalt–phthalocyanine (CoPc) as an active add-layer. A surface plasmon was generated via a prism coupler in Kretschmann configuration. We found that the detection limit of SPR sensor is 0.07 ppm in an ambient environment at normal temperature and pressure (NTP). The simple structure of the SPR sensor makes it superior to liquid chemical sensors for the detection of NO2. Copyright © 2008 John Wiley & Sons, Ltd.
The European Physical Journal Special Topics, 2008
We report on the optical absorption properties of as prepared gold naoparticles of different shap... more We report on the optical absorption properties of as prepared gold naoparticles of different shapes and sizes measured by photoacoustic (PA) method. The gold nanoparticles of two different shapes (dots, rods) have been prepared using the seed mediated growth method. The shape and the size of these different nanoparticles were determined by STM measurements. PA spectra show the splitting of the surface plasmon resonance (SPR) into two modes (transverse and longitudinal) in case of gold nanorods. The increase in the aspect ratio of the nanorods leads to clear redshifts of the longitudinal SPR. These shifts were used to determine the dielectric constant of the surrounding medium and its variation with the aspect ratios.
Journal de Physique IV (Proceedings), 2005
Photoacoustic (PA) spectroscopy and scanning electron microscopy (SEM) have been employed to inve... more Photoacoustic (PA) spectroscopy and scanning electron microscopy (SEM) have been employed to investigate remineralized artificially carious enamel as well as dentin. The remeniralization process was carried out by applying bioactive glass particles and mineralizing solutions either directly or after the specimen was first treated with Zeolite powder. The PA was carried out to evaluate the change in the thermal parameters (diffusivity, effusivity and conductivity) quantitatively. The remineralization process was evaluated by comparing the thermal parameters to those of the healthy tissue. PA measurements show that; the values of thermal conductivity of the normal tissues (enamel: 0.9 W m-1 K-1 and dentin: 0.58 W m-1 K-1) were altered by caries to be (enamel: ≈ 0.72 W m-1 K-1 and dentin: ≈ 0.44 W m-1 K-1) and they approach their normal values after the application of the different mineralizing agents. Also the results indicate that; Bioactive glass enhances the thermal parameters of artificially carious enamel and dentin (considering the healthy values as a reference), slightly more than the mineralizing solution. Furthermore, PA measurements show that the application of Zeolite powder enhances the effect of the mineralizing agent. In order to augment the PA results, SEM was used to depict surface topography, for each treated tissue.
Chinese Physics B, 2013
Determining the thermophysical properties of Al-doped ZnO nanoparticles by the photoacoustic tech... more Determining the thermophysical properties of Al-doped ZnO nanoparticles by the photoacoustic technique * T. A. El-Brolossy a)b) † , O. Saber a)c) , and S. S. Ibrahim a)d) a
Photoacoustic spectroscopy characterization of CdSe quantum rods
The European Physical Journal Special Topics, 2008
Abstract. The optical absorption properties of as prepared CdSe quantum rods (QRs) are measured b... more Abstract. The optical absorption properties of as prepared CdSe quantum rods (QRs) are measured by the photoacoustic (PA) method. CdSe QRs were fabricated by the chemical solution deposition (CD) technique. Decreasing the rod size (width and length) that is ...
Interfacial electronic traps at ZnSe/GaAs heterostructures studied by photomodulation Raman scattering
Journal of Physics: Condensed Matter, 2006
Photomodulation Raman scattering spectroscopy has been employed to study free charge trapping mec... more Photomodulation Raman scattering spectroscopy has been employed to study free charge trapping mechanisms at ZnSe-GaAs(001) heterostructure interfaces. This technique reveals that the interfacial region contains predominantly hole traps. Time dependent measurements of the photomodulated Raman scattering intensity show that interfacial charge-trap lifetime is ≈30 s for both electrons and holes.
Photoacoustic measurement of thermal properties of a thin polyester film
Applied Physics Letters, 1984
... Photoacoustic measurement of thermal properties of a thin polyester film. ... Abstract. The p... more ... Photoacoustic measurement of thermal properties of a thin polyester film. ... Abstract. The phase and the amplitude of the photoacoustic signal are measured as a function of chopping frequency for a thin polyester film, using two different backing materials (water and ethanol). ...
An Investigation about the Reminerlization Potential of Bio-active glass on Artificially Carious Enamel and Dentin using Raman Spectroscopy
ABSTRACT
Thermal diffusivity measurements of transparent liquid and powder materials using PAS
Proceedings of the 10th international conference on photoacoustic and photothermal phenomena, 1999
Thermal diffusivity of organic dye CV in powder form has been measured using PA effect. It is sho... more Thermal diffusivity of organic dye CV in powder form has been measured using PA effect. It is shown that this method permits to estimate the thermal diffusivity for transparent solvents using the dye at low concentration as a precursor.
Thermal conductivity and heat capacity of poly(3-octylthiophene-2,5 diyl) and its multi-wall carbon nanotube composites
Physica Scripta, 2014
ABSTRACT Poly (3-octylthiophene-2,5-diyl) (P3OT) is one of the most important semiconducting poly... more ABSTRACT Poly (3-octylthiophene-2,5-diyl) (P3OT) is one of the most important semiconducting polymer materials used for organic solar cells. Thermal properties data, especially the thermal conductivity of the active material of solar cells, is of fundamental importance. Such data for P3OT are barely available in the literature. The photoacoustic technique is employed to measure thermophysical properties of P3OT including thermal diffusivity, thermal effusivity, specific heat capacity and thermal conductivity. The obtained results are confirmed by many measurements as well as by using more than one method. A remarkable method for thermal effusivity measurements of surface coating as well as bulk samples is introduced. The development of P3OT thermophysical properties with multi-wall carbon nanotube (MWCNT) loading as high as 6% volume fraction is investigated. Continuous enhancement of thermal diffusivity as well as thermal effusivity of P3OT is obtained with increasing MWCNT content. By using the mixed model for the thermal conductivity of a two phase system, we are able to estimate the thermal diffusivity and the thermal effusivity of MWCNTs. A considerable enhancement in thermal conductivity of larger than twice that of neat P3OT at nanotube loading ≈6% volume fraction is obtained. Theoretical analysis of the experimental results generating an interfacial thermal resistance of MWCNTs as Rk = 5.8 × 10−8 m2K W−1.
Indian Journal of Physics, 2012
Photoacoustic (PA) technique was applied to study the optical absorption and measure the optical ... more Photoacoustic (PA) technique was applied to study the optical absorption and measure the optical energy gap of porous silicon (PSi) as a suitable example of the two layer samples (porous layer and Si substrate). The PSi layers were prepared by the electrochemical anodization etching process with different current density of p-type silicon wafers. The formation of the porous layer has been identified by photoluminescence (PL) and AFM measurements. Thermal diffusivity of the prepared samples was also measured to confirm thermal isolation properties of the formed PSi. The optical absorption, energy gap, and thermal diffusivity of PSi were investigated by analyzing the experimental data from PA measurements. The values of energy gap have been found to be porosity-dependent. In contrast to the conventional techniques, PA measures the energy band gap of both layers simultaneously with high accuracy. In the range of porosity (27-52%) of the studies, our results show that the optical band-gap energy of p-type PSi (1.7-1.92 eV) was higher than that obtained for silicon substrate (1.11 eV). These energies were used to obtain the diameter of the Si quantum dots in the porous layer. These results introduce PA technique as a suitable candidate for optical depth profile analysis of multilayer solids. Moreover, PA technique can be used for particles size estimation of low dimensional materials.
Thermal properties stability of UV irradiated PVA nanohybrid composites
Polymers for Advanced Technologies, 2012
ABSTRACT Zn‐Al‐salicylic nanohybrid layers have been prepared and used as fillers for polyvinyl a... more ABSTRACT Zn‐Al‐salicylic nanohybrid layers have been prepared and used as fillers for polyvinyl alcohol (PVA). Nanohybrid layers of a broad absorption area in UV region were completely and uniformly dispersed in a continuous polymer matrix. PVA and PVA nanohybrid composite (NHC) films were exposed to UV irradiation. Thermal properties (diffusivity, effusivity, and conductivity) of both have been measured through photoacoustic technique before and after UV irradiation. Thermal parameters of PVA suffered from a quick deterioration with UV exposure due to reduction of the phonon mean free path as a result of molecular chain scissions. However, significant stability in such parameters of NHC has been obtained under the influence of UV irradiation. This thermal properties stability may be an important step on the way of obtaining photostable polymer NHC. Copyright © 2012 John Wiley & Sons, Ltd.
Water, Air, & Soil Pollution, 2012
The photocatalytic degradation of dyes under sunlight irradiation has received much attention not... more The photocatalytic degradation of dyes under sunlight irradiation has received much attention not only because the attempt is aimed at decomposition of pollutants but also at finding methods of making use of solar energy. Following this line, zinc oxide nano-particles were prepared using solvent thermal method in order to decompose Naphthol Green B in presence of sunlight. Complete mineralization and decolorization of Naphthol Green B were achieved in 14 h. In order to reduce the band gap of zinc oxide and increase its photocatalytic activity in sunlight, it was doped with different concentrations of aluminum (1 %, 3 %, 5 %, and 10 %). The obtained band gap energy of the Al-doped ZnO nanoparticles was investigated as a function of Al content. Reduction of band gap energy for the heavily doped ZnO nanoparticles (10 % Al) was observed from 3.29 to 3.23 eV leading to fast transfer for electron from the excited state of dye to conduction band of ZnO. Therefore, by using the 10 % Al-doped ZnO nanoparticles, the complete mineralization and decolorization of Naphthol Green B were achieved in 6 h under sunlight. These results suggested that the heavily doped ZnO nanoparticles with aluminum has a positive effect towards photocatalytic reactions with dye under solar energy.
Carbon nanotube functionalization effects on thermal properties of multiwall carbon nanotube/polycarbonate composites
Polymer Composites, 2014
ABSTRACT The thermal properties of composites based on polycarbonate (PC) filed with ultraviolet/... more ABSTRACT The thermal properties of composites based on polycarbonate (PC) filed with ultraviolet/ozone (UVO) treated multiwall carbon nanotubes (MWCNTs) in low limit (less than 0.01) volume fractions have been investigated. The composites were prepared in the form of films of relatively small thickness (23–33 μm) with random orientation of treated MWCNTs. Functionalization of MWCNTs has been confirmed through Fourier transform infrared measurements. Thermal conductivity was obtained by measuring both of thermal diffusivity and thermal effusivity using photoacoustic technique. The results reveal that the addition of UVO treated MWCNTs lead to enhance both the thermal diffusivity and thermal effusivity of the composites. Insertion of 0.95% MWCNTs into PC improves the thermal conductivity of the composites by ∼22%. This enhancement is reasonable using such low content of MWCNTs of moderate aspect ratio. The experimental results were analyzed using a simple model concerning some relevant parameters such as volume fractions, interfacial thermal resistance, aspect ratio, and nonstraightness of nanotubes. An interface thermal resistance in the low limit of about 2.1 × 10−8 m2K/W has been estimated. In the light of these results, the role of MWCNTs functionalization on the overall thermal transport properties of MWCNTs-polymer composites has been discussed. POLYM. COMPOS., 2014. © 2014 Society of Plastics Engineers
Journal of Raman Spectroscopy, 2008
ZnSe/semi-insulating GaAs interfaces were studied by observing photogenerated plasmon-LO (PPL) co... more ZnSe/semi-insulating GaAs interfaces were studied by observing photogenerated plasmon-LO (PPL) coupled modes by nonresonant micro-Raman spectroscopy. The effect of the carriers generated by the focused laser beam was investigated for a series of different thicknesses of ZnSe epitaxial layers. The PPL mode in GaAs was observed in the micro-Raman spectra for all samples, but with different magnitude. The plasma is believed to be an electron gas as a result of the negative nature of the interfacial region that contains predominantly hole traps. The free carrier concentration is estimated to be >10 18 cm −3 and their lifetime ∼0.1 ns. This relatively long lifetime suggests that the ZnSe/GaAs interface has to be of high structural quality leading to a low recombination velocity. ZnSe/GaAs heterostructures of less crystalline quality (as determined by resonant Raman measurements) shows the effect of photogenerated carriers only to lesser extent.
Interfacial electronic properties of AuGaAs interfaces studied by photomodulation Raman spectroscopy (pump-probe technique)
Journal of Raman Spectroscopy, 2011
ABSTRACT Photomodulation Raman spectroscopy (PM-RS) was employed to investigate the interfacial p... more ABSTRACT Photomodulation Raman spectroscopy (PM-RS) was employed to investigate the interfacial properties of Au: n-type GaAs interfaces, using the forbidden longitudinal optical (LO) phonon scattering as a probe. In PM-RS, the photomodulating pump beam (PB) is incident on the sample while the Raman measurements are in progress; hence, PM-RS can be viewed as a pump-probe technique. The photogenerated carriers partly neutralize the surface charges, which decreases the interfacial field and consequently the intensity of forbidden LO scattering. Two molecular beam epitaxy (MBE) junctions of 80 angstrom Au on n-type GaAs (001) substrate with two different doping densities were used. The total surface charge density and change in the band bending were obtained as a function of the PB intensity considering a constant depletion electric field for the lower doped sample. Furthermore, the interfacial minority carrier trap lifetime was determined through dynamical measurements of the PM-RS intensity. Copyright (C) 2010 John Wiley & Sons, Ltd.
Journal of Raman Spectroscopy, 2012
Surface enhanced Raman scattering (SERS) of adsorbed molecule on colloidal gold nanoparticles of ... more Surface enhanced Raman scattering (SERS) of adsorbed molecule on colloidal gold nanoparticles of different shapes, namely nanospheres (NSs), nanorods (NRs), and nanoprisms (NPs) as well as the three NPs arrays of different interstice prepared by NS lithography, are studied with incident wavenumbers in the near-dipole and near-quadrpole regions of the nanoparticles. In the colloidal gold nanoparticles, the SERS enhancement is the largest for the sharp tip followed by the truncated tip NPs, then the NRs and least enhancement for the NSs. This decreasing order of enhancement occurs although the incident wavenumber was near the dipole resonance of NSs and the quadrupole resonance for the NPs. These varied enhancements are explained in part as due to the binding energies of the nanocrystal facets, but the larger contribution results from the plasmon electromagnetic fields. A parallel finite difference time domain (FDTD) calculations were carried out, which corporate the experimental results and show agreement with ratios of the SERS enhancement for the different shapes. The normalized SERS intensity for NPs of different interstice distances show a sharp rise with the decrease of the interstice distances because of interparticle dipolar and quadrupolar coupling as evidenced also by FDTD calculations. Furthermore, these calculations show that the enhancement is polarization independent for an incident wavelength near quadrupole resonance but polarization dependent for an incident wavelength near the plasmon dipole transition. In the last case, the enhancement is larger by an order of magnitude for a polarization parallel to the NPs bisector than for polarization normal to the bisector with no hot spots for the relatively large interstice dimensions used.
Journal of Physics: Condensed Matter, 2003
Photomodulation of the coupled plasmon-LO phonon modes has been employed to determine the change ... more Photomodulation of the coupled plasmon-LO phonon modes has been employed to determine the change in both the surface charge density and the depletion electric field as a function of photomodulation beam (PMB) intensity. The samples are two pieces of highly doped (001) n-type GaAs. The total surface charge density has been obtained as a function of the photomodulating intensity using the dependence of the unscreened LO phonon on the depletion width. We are able to separate the impact of the PMB on the surface electric field from the impact on the depletion width. This allows a separate determination of the change in depletion electric field, which reaches ∼73% of its original value at the highest intensity used for PMB.
Journal of Physics and Chemistry of Solids, 2012
The effect of sintering temperature on ZnO varistor properties is investigated in the range of 70... more The effect of sintering temperature on ZnO varistor properties is investigated in the range of 700-1400 1C. The increase of sintering temperature does not influence the well-known peaks related to hexagonal wurtzite structure of ZnO ceramics, whereas the average grain size is increased from (1.08 to 2.1 mm). With increasing sintering temperature up to 1200 1C, the nonlinear region is clearly observed in the I-V characteristics, whereas this region is completely absent only for the sample sintered at 1400 1C. As the sintering temperature increased, the breakdown field decreased over a wide range from 2838.7 to 6.41 V/cm, while the nonlinear coefficient is increased in the range of (23.86-47.76). Furthermore, the barrier height decreased from 1.76 to 0.974 eV, whereas electrical conductivity is improved. On the other hand, the optical band gap is gradually decreased in the range of 3.08-2.70 eV with increasing sintering temperature. These results showed a strong correlation between sintering temperature and the properties of ZnO ceramic varistor.
Journal of Physics: Conference Series, 2010
Photomodulation Raman spectroscopy (PM-RS) has been employed to study the surface depletion elect... more Photomodulation Raman spectroscopy (PM-RS) has been employed to study the surface depletion electric field Es and to monitor the change in surface charge density in n-type GaAs, using the forbidden LO phonon scattering for low doping samples and coupled plasmon-LO phonon modes for high doping samples. In PM-RS, the photomodulating pumping beam (PB) is incident on the sample while the Raman measurements are in progress hence PM-RS can be viewed as a pump-probe technique. The photogenerated carriers partly neutralize the surface charges. Two different GaAs surfaces (011) with low and moderate doping density and (001) with high doping density were used. The total surface charge density has been obtained as a function of the PB intensity considering a constant depletion electric field for the lower doping sample of (011) surface and using the dependence of the unscreened LO phonon on the depletion width for the higher doping samples of (001) surface. The minority carrier's lifetime was also determined through dynamical measurements for the PM-RS of the low doping sample as ≈ 21 s, in a good agreement with other techniques