Ayaz Bayramov - Academia.edu (original) (raw)

Papers by Ayaz Bayramov

Research paper thumbnail of Radiative and non-radiative processes of Ce related transitions in CaGa 2S 4 and SrGa 2S 4

Journal of Physics and Chemistry of Solids, 2003

The Ce emission appearing in the blue-green region was investigated for CaGa 2 S 4 and SrGa 2 S 4... more The Ce emission appearing in the blue-green region was investigated for CaGa 2 S 4 and SrGa 2 S 4. The room temperature quantum efficiency as high as 73% was observed for a 0.4 wt% Ce-doped CaGa 2 S 4 single crystal grown by the melt method. The quantum efficiency decreased for a 0.8 wt% Ce-doped CaGa 2 S 4 crystal and clear photoacoustic signal was detected in this sample, indicating an increase of non-radiative transition. For each of these compounds, ultraviolet (UV) excitation produced a hitherto unreported new UV emission which is thought to originate from 5d(E g) level of the Ce ion. Temperature dependent intensity changes observed in this UV emission and in the blue-green emission suggest temperature dependent population transfer from the upper level of E g to the lower level of T 2g in the excited state of 5d electrons.

Research paper thumbnail of Structure and optical properties of CdS:O films by cathode sputtering

physica status solidi (c), 2015

ABSTRACT We have studied the structure and optical properties of CdS:O films deposited on SLG (so... more ABSTRACT We have studied the structure and optical properties of CdS:O films deposited on SLG (soda lime glass) substrates by cathode sputtering in the atmosphere of oxygen/argon gases. According to X-ray diffraction (XRD) and confocal Raman scattering data, the films annealed in vacuum at temperatures above 300 °C exhibited crystalline structure of CdS. On the other hand, XRD, confocal Raman scattering, AFM (atomic force microscopy) and TEM (transmission electron microscopy) data indicated amorphous structure nano-crystallization in CdS:O films annealed in vacuum at 400 °C. For the films, the emissions located at 3.35 eV were evident from photoluminescence measurements. The origin of this energy gap is discussed by taking into account redistribution of electronic density of states in the amorphous phase and quantum-size effect. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Research paper thumbnail of Optimization of preparation techno- logy of ZnO and ZnO: Al thin films for solar cell applications

physica status solidi (c), 2015

Research paper thumbnail of Use of the luciferase reporter constructs for investigation of the capacity of Noggin2 protein to inhibit cell signaling pathways in Xenopus laevis embryos

Russian Journal of Bioorganic Chemistry, 2012

ABSTRACT Noggin (Noggin1) protein inhibits Smad1-dependent TGF-β (BMP) signaling cascades by extr... more ABSTRACT Noggin (Noggin1) protein inhibits Smad1-dependent TGF-β (BMP) signaling cascades by extracellular binding of BMP proteins. Recently, we identified two previously unknown members of the Noggin family, Noggin2 and Noggin4 proteins. In this work, using luciferase reporter constructs, it was shown that Noggin2 is able to inhibit in addition to the BMP-signaling cascade, the Activin/Nodal and Wnt signaling pathways in Xenopus laevis early embryos. The inhibition efficiency of Noggin2 is comparable to well-known extracellular inhibitors Cerberus and Follistatin. In addition to revealing novel properties of Noggin2, this work demonstrates that luciferase reporter constructs are a convenient tool for studying the regulation of molecular signaling cascades in the model of Xenopus laevis embryos.

Research paper thumbnail of Optical characterization of non-annealed CdS:O films for window layers in solar cells

physica status solidi (c), 2013

ABSTRACT Optical constants of CdS:O window layers for solar cells were studied as a function of t... more ABSTRACT Optical constants of CdS:O window layers for solar cells were studied as a function of the oxygen content. The CdS:O thin films were deposited on glass substrates in the presence of oxygen at 0, 2, 3 and 5% values of O/Ar ratio by rf magnetron sputtering. Ellipsometric measurements on CdS:O thin films were carried out over 0.75–6.0 eV photon energies at room temperature. Optical constants were determined by using a the best-fit dispersion model. Broadening of spectral features of the obtained optical constants is found to increase with increasing O/Ar ratio. Besides, the CdS:O films grown at 100 °C as compared to those grown at 200 °C exhibit increased spectral broadening. In fact, almost complete smearing of band gap spectral feature is observed for CdS:O films deposited at 5% value of O/Ar ratio, resulting in appreciable transparency of the films in a spectral range above the energy gap of CdS. This, in turn, leads to an increased carrier collection in the UV spectral range and allows to considering CdS:O film as a candidate for improved window-layer material for solar cell application. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Research paper thumbnail of Raman scattering and electric conductivity in Bi 2 (Te 0.9 Se 0.1 ) 3 thin films

physica status solidi (c), 2013

Research paper thumbnail of Structure and optical properties of CdS:O thin films

physica status solidi (c), 2013

ABSTRACT We have studied structure and optical properties of CdS:O thin films deposited on soda l... more ABSTRACT We have studied structure and optical properties of CdS:O thin films deposited on soda lime glass substrates by rf magnetron sputtering in the atmosphere of oxygen/argon gases. According to X-ray diffraction and confocal Raman scattering data, the films deposited under oxygen partial pressure below 3% show crystalline structure of CdS. On the other hand, X-ray diffraction, confocal Raman scattering, TEM (transmission electron microscopy) and XPS (X-ray photoelectron spectroscopy) data are indicative of amorphization, nano-crystallization, and inclusion of CdO2 in CdS:O thin films obtained under oxygen partial pressure of 5%. The last films have shown significantly increased transmittance in a spectral range above the energy gap of CdS. The origin of this transmittance is discussed by taking into account redistribution of electronic density-of-states in amorphous phase, quantum size effect and contribution of CdO2. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Research paper thumbnail of Effect of Ce Co-Doping on CaGa 2 S 4 :Eu Phosphor: I. Energy Transfer from Ce to Eu Ions

Japanese Journal of Applied Physics, 2002

Research paper thumbnail of Effect of Ce Co-Doping on CaGa 2 S 4 :Eu Phosphor: II. Thermoluminescence

Japanese Journal of Applied Physics, 2002

Research paper thumbnail of Effects of Ce Doping on Phosphor Characteristics of CaGa 2 S 4 :Eu

Japanese Journal of Applied Physics, 2000

ABSTRACT

Research paper thumbnail of Effect of “CdCl 2 Treatment” on Properties of CdTe-Based Solar Cells Prepared by Physical Vapor Deposition and Close-Spaced Sublimation Methods

Japanese Journal of Applied Physics, 2011

ABSTRACT

Research paper thumbnail of Spectroscopic Ellipsometry Studies of CdS:O Layers for Solar Cells

Japanese Journal of Applied Physics, 2011

This work reports the results of spectroscopic ellipsometry study of CdS thin films, deposited on... more This work reports the results of spectroscopic ellipsometry study of CdS thin films, deposited on glass substrates in the presence of oxygen at room temperature by rf sputtering. The data acquisition, together with the subsequent linear regression analysis to restore dielectric function has been performed over the photon energy range 1.5--5.0 eV. The obtained oxygen-free CdS films and reference bulk

Research paper thumbnail of Semiconducting asphaltene thin films: preparation and characterization

physica status solidi (c), 2015

Research paper thumbnail of Radiative and non-radiative processes of Ce related transitions in CaGa 2S 4 and SrGa 2S 4

Journal of Physics and Chemistry of Solids, 2003

The Ce emission appearing in the blue-green region was investigated for CaGa 2 S 4 and SrGa 2 S 4... more The Ce emission appearing in the blue-green region was investigated for CaGa 2 S 4 and SrGa 2 S 4. The room temperature quantum efficiency as high as 73% was observed for a 0.4 wt% Ce-doped CaGa 2 S 4 single crystal grown by the melt method. The quantum efficiency decreased for a 0.8 wt% Ce-doped CaGa 2 S 4 crystal and clear photoacoustic signal was detected in this sample, indicating an increase of non-radiative transition. For each of these compounds, ultraviolet (UV) excitation produced a hitherto unreported new UV emission which is thought to originate from 5d(E g) level of the Ce ion. Temperature dependent intensity changes observed in this UV emission and in the blue-green emission suggest temperature dependent population transfer from the upper level of E g to the lower level of T 2g in the excited state of 5d electrons.

Research paper thumbnail of Structure and optical properties of CdS:O films by cathode sputtering

physica status solidi (c), 2015

ABSTRACT We have studied the structure and optical properties of CdS:O films deposited on SLG (so... more ABSTRACT We have studied the structure and optical properties of CdS:O films deposited on SLG (soda lime glass) substrates by cathode sputtering in the atmosphere of oxygen/argon gases. According to X-ray diffraction (XRD) and confocal Raman scattering data, the films annealed in vacuum at temperatures above 300 °C exhibited crystalline structure of CdS. On the other hand, XRD, confocal Raman scattering, AFM (atomic force microscopy) and TEM (transmission electron microscopy) data indicated amorphous structure nano-crystallization in CdS:O films annealed in vacuum at 400 °C. For the films, the emissions located at 3.35 eV were evident from photoluminescence measurements. The origin of this energy gap is discussed by taking into account redistribution of electronic density of states in the amorphous phase and quantum-size effect. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Research paper thumbnail of Optimization of preparation techno- logy of ZnO and ZnO: Al thin films for solar cell applications

physica status solidi (c), 2015

Research paper thumbnail of Use of the luciferase reporter constructs for investigation of the capacity of Noggin2 protein to inhibit cell signaling pathways in Xenopus laevis embryos

Russian Journal of Bioorganic Chemistry, 2012

ABSTRACT Noggin (Noggin1) protein inhibits Smad1-dependent TGF-β (BMP) signaling cascades by extr... more ABSTRACT Noggin (Noggin1) protein inhibits Smad1-dependent TGF-β (BMP) signaling cascades by extracellular binding of BMP proteins. Recently, we identified two previously unknown members of the Noggin family, Noggin2 and Noggin4 proteins. In this work, using luciferase reporter constructs, it was shown that Noggin2 is able to inhibit in addition to the BMP-signaling cascade, the Activin/Nodal and Wnt signaling pathways in Xenopus laevis early embryos. The inhibition efficiency of Noggin2 is comparable to well-known extracellular inhibitors Cerberus and Follistatin. In addition to revealing novel properties of Noggin2, this work demonstrates that luciferase reporter constructs are a convenient tool for studying the regulation of molecular signaling cascades in the model of Xenopus laevis embryos.

Research paper thumbnail of Optical characterization of non-annealed CdS:O films for window layers in solar cells

physica status solidi (c), 2013

ABSTRACT Optical constants of CdS:O window layers for solar cells were studied as a function of t... more ABSTRACT Optical constants of CdS:O window layers for solar cells were studied as a function of the oxygen content. The CdS:O thin films were deposited on glass substrates in the presence of oxygen at 0, 2, 3 and 5% values of O/Ar ratio by rf magnetron sputtering. Ellipsometric measurements on CdS:O thin films were carried out over 0.75–6.0 eV photon energies at room temperature. Optical constants were determined by using a the best-fit dispersion model. Broadening of spectral features of the obtained optical constants is found to increase with increasing O/Ar ratio. Besides, the CdS:O films grown at 100 °C as compared to those grown at 200 °C exhibit increased spectral broadening. In fact, almost complete smearing of band gap spectral feature is observed for CdS:O films deposited at 5% value of O/Ar ratio, resulting in appreciable transparency of the films in a spectral range above the energy gap of CdS. This, in turn, leads to an increased carrier collection in the UV spectral range and allows to considering CdS:O film as a candidate for improved window-layer material for solar cell application. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Research paper thumbnail of Raman scattering and electric conductivity in Bi 2 (Te 0.9 Se 0.1 ) 3 thin films

physica status solidi (c), 2013

Research paper thumbnail of Structure and optical properties of CdS:O thin films

physica status solidi (c), 2013

ABSTRACT We have studied structure and optical properties of CdS:O thin films deposited on soda l... more ABSTRACT We have studied structure and optical properties of CdS:O thin films deposited on soda lime glass substrates by rf magnetron sputtering in the atmosphere of oxygen/argon gases. According to X-ray diffraction and confocal Raman scattering data, the films deposited under oxygen partial pressure below 3% show crystalline structure of CdS. On the other hand, X-ray diffraction, confocal Raman scattering, TEM (transmission electron microscopy) and XPS (X-ray photoelectron spectroscopy) data are indicative of amorphization, nano-crystallization, and inclusion of CdO2 in CdS:O thin films obtained under oxygen partial pressure of 5%. The last films have shown significantly increased transmittance in a spectral range above the energy gap of CdS. The origin of this transmittance is discussed by taking into account redistribution of electronic density-of-states in amorphous phase, quantum size effect and contribution of CdO2. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Research paper thumbnail of Effect of Ce Co-Doping on CaGa 2 S 4 :Eu Phosphor: I. Energy Transfer from Ce to Eu Ions

Japanese Journal of Applied Physics, 2002

Research paper thumbnail of Effect of Ce Co-Doping on CaGa 2 S 4 :Eu Phosphor: II. Thermoluminescence

Japanese Journal of Applied Physics, 2002

Research paper thumbnail of Effects of Ce Doping on Phosphor Characteristics of CaGa 2 S 4 :Eu

Japanese Journal of Applied Physics, 2000

ABSTRACT

Research paper thumbnail of Effect of “CdCl 2 Treatment” on Properties of CdTe-Based Solar Cells Prepared by Physical Vapor Deposition and Close-Spaced Sublimation Methods

Japanese Journal of Applied Physics, 2011

ABSTRACT

Research paper thumbnail of Spectroscopic Ellipsometry Studies of CdS:O Layers for Solar Cells

Japanese Journal of Applied Physics, 2011

This work reports the results of spectroscopic ellipsometry study of CdS thin films, deposited on... more This work reports the results of spectroscopic ellipsometry study of CdS thin films, deposited on glass substrates in the presence of oxygen at room temperature by rf sputtering. The data acquisition, together with the subsequent linear regression analysis to restore dielectric function has been performed over the photon energy range 1.5--5.0 eV. The obtained oxygen-free CdS films and reference bulk

Research paper thumbnail of Semiconducting asphaltene thin films: preparation and characterization

physica status solidi (c), 2015