Afaf El-Sayed - Academia.edu (original) (raw)

Papers by Afaf El-Sayed

Research paper thumbnail of EFFECT OF AGING PERIOD ON THE STRUCTURAL CHARACTERIZATION OF FRESH AND THERMALLY-ANNEALED CdS NANOPARTICLES

Research paper thumbnail of Synthesis of Graphene Nanoribbons on a Kinked Au Surface: Revealing the Frontier Valence Band at the Brillouin Zone Center

The Journal of Physical Chemistry C, 2020

Graphene nanoribbons (GNRs) can be synthesized with atomic precision through on-surface chemistry... more Graphene nanoribbons (GNRs) can be synthesized with atomic precision through on-surface chemistry of self-assembled organic precursors on metal surfaces. Here we examine the growth of 7-armchair GNRs (7-AGNRs) on the Au(16 14 15) vicinal surface, namely, a surface vicinal to Au(111) that features kinked steps. During the thermal activation of the polymerization and cyclodehydrogenation processes that produce the GNRs, the kinked substrate undergoes a strong step-edge reshaping, accompanied by a massive missing-row reconstruction within (111) terraces that aligns GNRs preferentially along two equivalent [110] directions. Using angle-resolved photoemission we are able to detect the occupied frontier band of the 7-AGNR at the center of the first Brillouin zone, as predicted by theoretical calculations. This allows to unambiguously determine the relevant 7-AGNRs band properties, namely energy and effective mass.

Research paper thumbnail of Diode performance of silica nanoparticles extracted from Pleurosira laevis diatom frustules

Optical and Quantum Electronics

In this work, we measured the I-V characteristics of silica nanoparticles (SNPs) extracted from t... more In this work, we measured the I-V characteristics of silica nanoparticles (SNPs) extracted from the Pleurosira laevis diatom and deposited on top of a p-type Si(111) wafer. The electric response of the SNPs-based diode is found to be more sensitive to thermal and optical power than the fresh frustules-based diode by about 3 and 5 times, respectively. Moreover, the chemically processed SNPs exhibit better diode parameters, i.e. for them the ideality factor is closer to 1, the series resistance is 3 times lower, and the shunt resistance is 4 times higher than those of the fresh frustules silica. It is stimulating to use the extracted SNPs in innovative electronic and optoelectronic applications as an abundant, cheap, and easy-to-process material.

Research paper thumbnail of Interesting Photodiode Characteristics of Silica Nanoparticles Extracted from Pleurosira laevis Diatom Frustules

In this work, we measured the I-V characteristics for silica nanoparticles (SNPs) extracted from ... more In this work, we measured the I-V characteristics for silica nanoparticles (SNPs) extracted from the Pleurosira laevis diatom and deposited on top of p-type Si(111) wafer. The electric response of SNPs-based photodiode is found to be more sensitive to thermal and optical powers than the fresh frustules-based photodiode by about 3 and 4 times, respectively. Moreover, they exhibit better photodiode parameters, e.g. ideality factor, series resistance, and shunt resistance. This is stimulating to use the extracted SNPs in innovative electronic and optoelectronic applications as an abundant, cheap, and easy-to-process material.

Research paper thumbnail of Optimizing the dielectric constant and dissipation factor of PVA/n-Si Schottky diode

Materials Chemistry and Physics, 2021

Abstract In this article, we map the dielectric properties of manufactured metal-polymer-semicond... more Abstract In this article, we map the dielectric properties of manufactured metal-polymer-semiconductor (MPS) Schottky barrier diode consisting of aluminum (Al), polyvinyl alcohol (PVA), and n-type silicon (n-Si), under different conditions of applied frequency (1 Hz–20 MHz), voltage (-2–2 volts), and temperature (-50–90 °C). By tuning all these parameters, we could activate all possible polarization modes at the PVA/Si interface and reach tremendous values for the dielectric constant of our sample (e′ >3000) with a conveniently low dissipation factor (tan δ ≥ 30 °C. These promising values are motivating for using Al/PVA/n-Si Scottky diode structure in innovative energy storage applications.

Research paper thumbnail of Stimulating photodiode characteristics of hybrid ZnPc-MWCNTs

Journal of Alloys and Compounds, 2021

Research paper thumbnail of Supramolecular Environment-Dependent Electronic Properties of Metal−Organic Interfaces

Model donor−acceptor assemblies at metal−organic interfaces, namely, fluorinated copper-phthalocy... more Model donor−acceptor assemblies at metal−organic interfaces, namely, fluorinated copper-phthalocyanines (F 16 CuPC) and pentacene (PEN) assemblies on the Au(111) surface, have been the focus of the present study. A full picture of the crystallographic and electronic structure of PEN and F 16 CuPC monolayers as well as of their 1:1 binary mixture on the Au(111) surface has been explored by means of a variety of surface-sensitive techniques, providing important information on the intermolecular and molecule−substrate interactions governing the self-assembly process. A longrange ordered donor−acceptor network is observed for the mixture as a result of the greatly enhanced intermolecular interaction via C−F···H−C hydrogen bonds. Interestingly, the new supramolecular structure involves changes in the electronic structure of the molecular components. In particular, the strongest changes are observed at the C and F atoms of the F 16 CuPc, as opposed to the F 16 CuPc N, Cu, or PEN C atoms. With the aid of theoretical calculations, such effects are found to be at least partially related to an upward shift in energy of the F 16 CuPc molecular orbitals, concomitant with a molecule-to-metal charge donation, not from the HOMO, but deeper lying orbitals.

Research paper thumbnail of EFFECT OF AGING PERIOD ON THE STRUCTURAL CHARACTERIZATION OF FRESH AND THERMALLY-ANNEALED CdS NANOPARTICLES

Research paper thumbnail of Synthesis of Graphene Nanoribbons on a Kinked Au Surface: Revealing the Frontier Valence Band at the Brillouin Zone Center

The Journal of Physical Chemistry C, 2020

Graphene nanoribbons (GNRs) can be synthesized with atomic precision through on-surface chemistry... more Graphene nanoribbons (GNRs) can be synthesized with atomic precision through on-surface chemistry of self-assembled organic precursors on metal surfaces. Here we examine the growth of 7-armchair GNRs (7-AGNRs) on the Au(16 14 15) vicinal surface, namely, a surface vicinal to Au(111) that features kinked steps. During the thermal activation of the polymerization and cyclodehydrogenation processes that produce the GNRs, the kinked substrate undergoes a strong step-edge reshaping, accompanied by a massive missing-row reconstruction within (111) terraces that aligns GNRs preferentially along two equivalent [110] directions. Using angle-resolved photoemission we are able to detect the occupied frontier band of the 7-AGNR at the center of the first Brillouin zone, as predicted by theoretical calculations. This allows to unambiguously determine the relevant 7-AGNRs band properties, namely energy and effective mass.

Research paper thumbnail of Diode performance of silica nanoparticles extracted from Pleurosira laevis diatom frustules

Optical and Quantum Electronics

In this work, we measured the I-V characteristics of silica nanoparticles (SNPs) extracted from t... more In this work, we measured the I-V characteristics of silica nanoparticles (SNPs) extracted from the Pleurosira laevis diatom and deposited on top of a p-type Si(111) wafer. The electric response of the SNPs-based diode is found to be more sensitive to thermal and optical power than the fresh frustules-based diode by about 3 and 5 times, respectively. Moreover, the chemically processed SNPs exhibit better diode parameters, i.e. for them the ideality factor is closer to 1, the series resistance is 3 times lower, and the shunt resistance is 4 times higher than those of the fresh frustules silica. It is stimulating to use the extracted SNPs in innovative electronic and optoelectronic applications as an abundant, cheap, and easy-to-process material.

Research paper thumbnail of Interesting Photodiode Characteristics of Silica Nanoparticles Extracted from Pleurosira laevis Diatom Frustules

In this work, we measured the I-V characteristics for silica nanoparticles (SNPs) extracted from ... more In this work, we measured the I-V characteristics for silica nanoparticles (SNPs) extracted from the Pleurosira laevis diatom and deposited on top of p-type Si(111) wafer. The electric response of SNPs-based photodiode is found to be more sensitive to thermal and optical powers than the fresh frustules-based photodiode by about 3 and 4 times, respectively. Moreover, they exhibit better photodiode parameters, e.g. ideality factor, series resistance, and shunt resistance. This is stimulating to use the extracted SNPs in innovative electronic and optoelectronic applications as an abundant, cheap, and easy-to-process material.

Research paper thumbnail of Optimizing the dielectric constant and dissipation factor of PVA/n-Si Schottky diode

Materials Chemistry and Physics, 2021

Abstract In this article, we map the dielectric properties of manufactured metal-polymer-semicond... more Abstract In this article, we map the dielectric properties of manufactured metal-polymer-semiconductor (MPS) Schottky barrier diode consisting of aluminum (Al), polyvinyl alcohol (PVA), and n-type silicon (n-Si), under different conditions of applied frequency (1 Hz–20 MHz), voltage (-2–2 volts), and temperature (-50–90 °C). By tuning all these parameters, we could activate all possible polarization modes at the PVA/Si interface and reach tremendous values for the dielectric constant of our sample (e′ >3000) with a conveniently low dissipation factor (tan δ ≥ 30 °C. These promising values are motivating for using Al/PVA/n-Si Scottky diode structure in innovative energy storage applications.

Research paper thumbnail of Stimulating photodiode characteristics of hybrid ZnPc-MWCNTs

Journal of Alloys and Compounds, 2021

Research paper thumbnail of Supramolecular Environment-Dependent Electronic Properties of Metal−Organic Interfaces

Model donor−acceptor assemblies at metal−organic interfaces, namely, fluorinated copper-phthalocy... more Model donor−acceptor assemblies at metal−organic interfaces, namely, fluorinated copper-phthalocyanines (F 16 CuPC) and pentacene (PEN) assemblies on the Au(111) surface, have been the focus of the present study. A full picture of the crystallographic and electronic structure of PEN and F 16 CuPC monolayers as well as of their 1:1 binary mixture on the Au(111) surface has been explored by means of a variety of surface-sensitive techniques, providing important information on the intermolecular and molecule−substrate interactions governing the self-assembly process. A longrange ordered donor−acceptor network is observed for the mixture as a result of the greatly enhanced intermolecular interaction via C−F···H−C hydrogen bonds. Interestingly, the new supramolecular structure involves changes in the electronic structure of the molecular components. In particular, the strongest changes are observed at the C and F atoms of the F 16 CuPc, as opposed to the F 16 CuPc N, Cu, or PEN C atoms. With the aid of theoretical calculations, such effects are found to be at least partially related to an upward shift in energy of the F 16 CuPc molecular orbitals, concomitant with a molecule-to-metal charge donation, not from the HOMO, but deeper lying orbitals.