Adel Najar

• PhD
• Researcher at Nippon Telegraph and Telephone

The purpose of this study is to predict student quiz assignments in the General Physics I course during one semester using the Grey system GM (1,1) model. The prediction model integrates the first-order two-variable grey differential equation model from the Grey system theory. Additionally, a MATLAB program for the GM (1,1) prediction model was dev...

Perovskite single crystals have garnered significant interest in photodetector applications due to their exceptional optoelectronic properties. The outstanding crystalline quality of these materials further enhances their potential for efficient charge transport, making them promising candidates for next-generation photodetector devices. This artic...

Organic-inorganic trihalide, ABX 3 perovskite are excellent candidates for advanced optoelectronic applications beyond photovoltaics. Perovskite single crystals offer several advantageous special features, such as a long diffusion length, low trapped carrier density, and outstanding environmental stability to use in optoelectronics. In this work, Z...

Perovskite solar cells (PSCs) represent a promising and rapidly evolving technology in the field of photovoltaics due to their easy fabrication, low‐cost materials, and remarkable efficiency improvements over a relatively short period. However, the grain boundaries in the polycrystalline films exhibit a high density of defects, resulting in not onl...

Surfaces display discontinuities in the kesterite‐based polycrystalline films can produce large defect densities, including strained and dangling bonds. These physical defects tend to introduce electronic defects and surface states, which can greatly promote nonradiative recombination of electron–hole pairs and damage device performance. Here, an e...

Perovskite solar cells (PSCs) have demonstrated remarkable photovoltaic performance, positioning themselves as promising devices in the field. Theoretical calculations suggest that copper (Cu) can serve as an effective dopant, potentially occupying interstitial sites in the perovskite structure, thereby reducing the energy barrier and enhancing car...

Metal halide perovskite single crystals (MHP‐SCs) are known for their facile fabrication into large sizes using inexpensive solution methods. Owing to their combination of large mobility‐lifetime products and strong X‐ray absorption, they are considered promising materials for efficient X‐ray detection. However, they suffer from large dark currents...

A 3-D porous Au/CuO/Pt hybrid platform is proposed to overcome the drawbacks of non-enzymatic H2O2 sensing. The Au/CuO/Pt hybrid sensor exhibits an extraordinary catalytic performance towardsb H2O2 reduction with an ultra-high sensitivity of 25,836 µA mM-1 cm-2 and a limit of detection of 1.8 nM (S/N = 3). It demonstrates an excellent anti-interfer...

Surface defect-triggered nonradiative charge recombination and poor stability have become the main roadblock to continued improvement in inorganic perovskite solar cells (PSCs). Herein, we identified the main culprits on the inorganic perovskite surface by first-principles calculations, and to purposefully design a brand-new passivator, Boc-S-4-met...

Halide‐related surface defects on inorganic halide perovskite not only induce charge recombination but also severely limit the long‐term stability of perovskite solar cells. Herein, adopting density functional theory calculation, we verify that iodine interstitials (Ii) has a low formation energy similar to that of the iodine vacancy (VI) and is al...

Halide‐related surface defects on inorganic halide perovskite not only induce charge recombination but also severely limit the long‐term stability of perovskite solar cells. Herein, adopting density functional theory calculation, we verify that iodine interstitials (I i ) has a low formation energy similar to that of the iodine vacancy (V I ) and i...

Based on the widely used wet metal-assisted electroless etching, we develop in this work a novel vapor-phase silver-assisted chemical etching (VP-Ag-ACE) suitable for the elaboration of highly doped p-silicon (Si) nanostructures with strong, visible, and multi-peak photoluminescence (PL) emissions. The lateral and vertical etching rates (LER and VE...

Lead‐free A3Bi2I9‐type perovskites have been demonstrated as a class of promising semiconductors for high‐performance X‐ray detection due to their high bulk resistivity and strong X‐ray absorption, as well as reduced ion migration. However, due to their long interlamellar distance along their c‐axis, their limited carrier transport along the vertic...

A super-porous Pt/CuO/Pt hybrid electrode is demonstrated with extremely high sensing performance parameters for the hydrogen peroxide (H2O2) detection. A unique physiochemical approach is adapted for the fabrication of 3-D super-porous Pt/CuO/Pt sensing platform. The super-porous Pt/CuO/Pt hybrid platform demonstrates a superior sensitivity of 16,...

Organic-inorganic Pb-based halide perovskite photoelectrical materials, especially perovskite solar cells (PSCs), have attracted attention due to the significant efforts in improving the power conversion efficiency (PCE) to above 25%. However, the stability issue of the PSCs restricts their further development for commercialization. Strategies are...

Just over a decade, perovskite solar cells (PSCs) have been emerged as a next‐generation photovoltaic technology due to their skyrocketing power conversion efficiency (PCE), low cost, and easy manufacturing techniques compared to Si solar cells. Several methods and procedures have been developed to fabricate high‐quality perovskite films to improve...

Under the groundswell of calls for the industrialization of perovskite solar cells (PSCs), wide‐bandgap (>1.7 eV) mixed halide perovskites are equally or more appealing in comparison with typical bandgap perovskites when the former's various potential applications are taken into account. In this review, the progress of wide‐bandgap organic–inorgani...

The distorted lead iodide octahedra of all‐inorganic perovskite based on triple halide‐mixed CsPb(I2.85Br0.149Cl0.001) framework have made a tremendous breakthrough in its black phase stability and photovoltaic efficiency. However, their performance still suffers from severe ion migration, trap‐induced nonradiative recombination, and black phase in...

Perovskite quantum dots (PQDs) have captured a host of researchers’ attention due to their unique properties, which have been introduced to lots of optoelectronics areas, such as light-emitting diodes, lasers, photodetectors, and solar cells. Herein, the authors aim at reviewing the achievements of PQDs applied to solar cells in recent years. The e...

Just over a decade ago, perovskite solar cells (PSCs) established themselves as the next generation of photovoltaic technology due to their comparably higher power conversion efficiency (PCE) (25.6%), cheaper and simpler manufacturing processes to that of Silicon solar cells. Based on the potential, several methods and processes have been developed...

We report the passivation of FA 0.97 MA 0.03 PbI 3 perovskites grains by Zn-porphyrin blended anti-solvent treatment. The efficiency was improved to 16.75% because Zn-porphyrin passivated the grain-boundary defects and improved hole transport across the perovskite film.

Less toxic perovskite is realized with a rapid crystal growth process obtaining Zn-PP incorporated MAPbBr3 single crystals. After Zn-PP passivation, there was more than 4-fold rise in photoluminescence intensity with a 7 nm redshift.

Narrow bandgap semiconductors like InSb are very suitable for high-performance room temperature infrared photodetectors, but the fragile nature of the wafer materials hinders their application as inflexible/wearable devices. Here, we present a method to fabricate a photodetector device of assembled crystalline InSb nanowires (NWs) arrays on a flexi...

This review summarizes the recent research on nitride nanostructures and their applications. We cover recent advances in the synthesis and growth of porous structures and low-dimensional nitride nanostructures via metal-assisted photochemical etching and molecular beam epitaxy. The growth of nitride materials on various substrates, which improves t...

Solution-processed organic–inorganic hybrid perovskites have attracted attention as light-harvesting materials for solar cells and photonic applications. The present study focusses on cubic single crystal; microstructures of CH3NH3PbBr3 perovskite fabricated by a one-step solution based self-assembly method. It is seen that, in addition to the nucl...

High-performance chemiresistor gas sensor made of sulfide porous GaN decorated with Pt nanoparticles, which shows tunable sensor response and enhanced sensitivity. The fabricated gas sensors show detection of H2 down to 30 ppm at 23 °C after sulfide treatment and Pt decorated porous GaN. The response time and recovery time were equal to 47 s and 11...

We investigate the optical and structural properties of GaN and InGaN nanowires (NWs) fabricated by metal-assisted electroless etching in a hydrofluoric acid (HF) solution. The emission spectra of GaN and InGaN NWs exhibit a red shift compared to the as-grown samples resulting from an increase in the surface-to-volume ratio and stress relaxation in...

Organic‐inorganic halide perovskite solar cells (PSCs) have drawn tremendous attention as their power conversion efficiency (PCE) has soared to 25.2%. Yet the most efficient halide perovskite materials all contain the toxic element lead (Pb). The search for an alternative element is a crucial research direction. Among all candidates, tin (Sn) appea...

Solution-processed organic–inorganic hybrid perovskites have attracted attention as light-harvesting materials for solar cells and photonic applications. The present study focuses on cubic single crystals and microstructures of CH3NH3PbBr3 perovskite fabricated by a one-step solution-based self-assembly method. It is seen that, in addition to the n...

Thin films of polycrystalline gallium antimonide (GaSb) were grown on widely available mica substrates using the physical vapor deposition method. The as-grown films contain grains of nano-scale with regular symmetries, as identified by x-ray diffraction and scanning electron microscope analysis. Two-terminal devices with coplanar electrodes were f...

The incorporation of Cu+, and Ag+ in CH3NH3PbI3 perovskite strongly affects the morphology of the perovskite layer. In addition, doping with Ag ions increase the absorption and photoluminescence of perovskite layer.

Attempts have been made to explore the electronic properties and photovoltaic functionality of Zn-doped orthorhombic CH3NH3PbI3 using the generalized gradient approximation method with van der Waals correction (GGA+vdW). Results show that Zn doping effectively decreases the band gap of orthorhombic CH3NH3PbI3, extending the optical absorption into...

The achievement of H2 detection, up to 25 ppm, at room temperature using sulfur-treated, platinum (Pt)-decorated porous GaN is reported in this study. This achievement is attributed to the large lateral pore size, Pt catalyst, and surface treatment using organic sulfide. The performance of H2-gas sensors is studied as a function of the operating te...

Rapid and accurate label-free-based discrimination techniques between normal and cancer cells play an important role in non-invasive screening systems. Significant differences in cell composition for normal and cancer cells have been reported. Their interaction with light will cause a change in the optical absorption and transmission response. Henc...

We report a simple precipitation method for the synthesis of organic–inorganic hybrid composite Alq3–WO3 materials. The incorporation of WO3 into Alq3 samples was demonstrated using different techniques. The surface morphology signifies the aggregation in the particles. Conversely, the decrease in the photoluminescence, band gap, prolonged excited-...

The synthesis of a perovskite based on lead halide CH3NH3PbI3 is reported. Simple precursors such as PbI and CH3NH3I are used to synthesize this material under ambient conditions. The variation in the number of solution droplets on the substrate leads to different perovskites film thicknesses. The morphology, structure, optical gap of these perovsk...

Herein, we report on the studies of GaN nanowires (GaN NWs) prepared via a metal-assisted photochemical electroless etching method with Pt as the catalyst. It has been found that etching time greatly influences the growth of GaN NWs. The density and the length of nanowires increased with longer etching time, and excellent substrate coverage was obs...

Visible up-conversion luminescence induced by 1535-nm excitation in (ErSc)2O3 epitaxial layers are observed. We investigate fast up-conversion rate and propose its suppression structure by photonic band-gap for realizing higher optical gain devices on Si wafers.

High density vertically aligned Porous Silicon NanoWires (PSiNWs) were fabricated on silicon substrate using metal assisted chemical etching process. A linear dependency of nanowire length to the etching time was obtained and the change in the growth rate of PSiNWs by increasing etching durations was shown. A typical 3D TEM image for volume reconst...

Polycrystalline Er-Sc silicates (ErxSc2-xSiO5 and ErxSc2-xSi2O7) were fabricated using multilayer nanostructured films of Er2O3/SiO2/Sc2O3 deposited on SiO2/Si substrates by RF- sputtering and thermal annealing at high temperature. RBS, TEM, GIXD, and PL results show the presence of ErxSc2-xSiO5 with an emission peak at 1528 nm for annealing from 9...

Polycrystalline Er-Sc silicates (Er x Sc2-x Si2O7 and Er x Sc2-x SiO5) were fabricated using multilayer nanostructured films of Er2O3/SiO2/Sc2O3 deposited on SiO2/Si substrates by RF sputtering and thermal annealing at high temperature. The films were characterized by synchrotron radiation grazing incidence X-ray diffraction, cross-sectional transm...

Toward quantum information applications, we control the interactions between Er ions by alloying epitaxial Er2O3 with scandium and suppress energy transfer and inhomogeneous broadening of Stark levels in the intra-4f band of Er ions.

Polycrystalline ErxSc2-xSi2O7 compounds were fabricated using RF-sputtering by alternating Er2O3, Sc2O3 layers separated by SiO2 layer. This new compounds presents excitation cross section at 980nm around 1.39x10-21cm2 with lifetime of 38 µs.

We report on the large photoluminescence redshift observed in nanostructures fabricated using n-type GaN by ultraviolet (UV) metal-assisted electroless chemical-etching method. The scanning electron microscopy (SEM) characterization showed nanostructures with size dispersion ranging from 10 to 100 nm. We observed the crystalline structure using hig...

Porous silicon nanowires (PSiNWs) layers fabrication was reported. Reflectance spectra were measured as a function of the nanowire length and were inferior to 0.1% and a strong photoluminescence (PL) signal was measured from samples. Models based on cone shape of nanowires located in circular and rectangular bases were used to calculate the reflect...

We report on the observation of broad photoluminescence wavelength tunability from n-type gallium nitride nanoparticles (GaN NPs) fabricated using the ultraviolet metal-assisted electroless etching method. Transmission and scanning electron microscopy measurements performed on the nanoparticles revealed large size dispersion ranging from 10 to 100...

Porous silicon nanowires (PSiNWs) have been prepared by metal-assisted chemical etching method on the n-Si substrate. The presence of nano-pores with pore size ranging between 10-50nm in SiNWs was confirmed by electron tomography (ET) in the transmission electron microscope (TEM). The PSiNWs give strong photoluminescence peak at red wavelength. Ult...

We report the experimental realization of a compact, efficient coupler between silicon waveguides and vertical metal-insulator-silicon-metal (MISM) plasmonic waveguides. Devices were fabricated using complementary metal-oxide-silicon technology processes, with copper layers that support low-loss plasmonic modes in the MISM structures at a wavelengt...

The effect of annealing on strain relaxation in porous GaN fabricated using electroless chemical etching is presented. The Raman shift of 1 cm-1 in phonon frequency of annealed porous GaN with respect to as-grown GaN corresponds to a relaxation of compressive strain by 0.41 ± 0.04 GPa. The strain relief promises a marked reduction in threading disl...

We report on the structural and optical properties of porous silicon nanowires (PSiNWs) fabricated using silver (Ag) ions assisted electroless etching method. Silicon nanocrystallites with sizes <5 nm embedded in amorphous silica have been observed from PSiNW samples etched using the optimum hydrofluoric acid (HF) concentration. The strongest photo...

High density vertically aligned Porous Silicon NanoWires (PSiNWs) were fabricated on silicon substrate using metal assisted chemical etching process. A linear dependency of nanowire length to the etching time was obtained and the change in the growth rate of PSiNWs by increasing etching durations was shown. A typical 2D bright-field TEM image used...

We study the electro optical properties of a Metal-Nitride-Oxide-Silicon (MNOS) stack for a use in CMOS compatible plasmonic active devices. We show that the insertion of an ultrathin stoichiometric Si3N4 layer in a MOS stack lead to an increase in the electrical reliability of a copper gate MNOS capacitance from 50 to 95% thanks to a diffusion bar...

Ultra-long Gallium Nitride Nanowires is synthesized via metal-electroless etching method. The morphologies and optical properties of GaN NWs show a single crystal GaN with hexagonal Wurtzite structure and high luminescence properties.

We report the fabrication of porous GaN nanostructures using UV-assisted electroless etching of bulk GaN layer grown on c-plane sapphire substrate in a solution consisting of HF:CH3OH:H2O2. The morphology of the porous GaN nanostructures was characterized for different etching intervals using high resolution scanning electron microscopy. The geomet...

Reaction of Cu(II) salts with a combination of two different types of ligand affords an unusual ‘molecular wheel’, based on a cyclic array of four pyrazolate-bridged dinuclear Cu(II) units which are interconnected by bis-bidentate bridging ligands, in a hierarchical self-assembly process.

Ultra-long Gallium Nitride Nanowires is synthesized via metal-electroless etching method. The morphologies and optical properties of GaN NWs show a single crystal GaN with hexagonal Wurtzite structure and high luminescence properties.

EDX and infrared photoluminescence (IR PL) analyses performed on erbium-doped porous silicon waveguides (PSWG) were studied using different doping conditions. Both parameters of the cathodisation electrochemical method used for Er incorporation and parameters of thermal treatments required for Er optical activation were taken into consideration. Fi...

Erbium–ytterbium (Er–Yb)-co-doped porous silicon planar waveguides were prepared from P+-type (100) oriented silicon wafer. Erbium and ytterbium ions were electrochemically introduced into the porous structure of the waveguide core. The doping profiles of erbium and ytterbium ions were determined by EDX analysis performed on sample cross-section. T...

The on-off optical gain measurements as a function of the pump power were performed on porous silicon planar waveguides codoped by erbium and ytterbium ions. These measurements were obtained for different ratios of Yb concentration to Er concentration. The highest value of the gain was reached when the Yb concentration is three times higher than th...

This paper reports physical properties of porous silicon and oxidized porous silicon, manufactured by anodisation from heavily p-type doped silicon wafers as a function of experimental parameters. The growth rate and refractive index of the layers were studied at different applied current densities and glycerol concentrations in electrolyte. When t...

This manuscript is divided in five chapters dealing with the different aspects of this work. In the first chapter we describe the porous silicon characteristics, its realisation and the various parameters which have to be controlled. Then, the state of art of Erbium Doped Optical Amplifiers based on porous silicon as well as on other materials will...

Planar waveguides were formed from porous silicon layers obtained on P+ substrates. These waveguides were then doped by erbium using an electrochemical method. Erbium concentration in the range 2.2–2.5 at% was determined by energy dispersive X-ray (EDX) analysis performed on SEM cross sections. The refractive index of layers was studied before and...

symposium C " Rare Earth ion doping for photonics: materials, mechanisms and devices ", poster session II " Semiconductors and related materials " [C/PII-22]

Planar and buried channel porous silicon waveguides (WG) were prepared from p+-type silicon substrate by a two-step anodization process. Erbium ions were incorporated into pores of the porous silicon layers by an electrochemical method using ErCl3-saturated solution. Erbium concentration of around 1020 at/cm3 was determined by energy-dispersive X-r...

session Affiches, thème 5 « Composants optiques intégrés actifs et passifs » [A-Th5-3]

Porous silicon (PS) is doped with erbium by electrochemical anodisation. The penetration of erbium into the PS layer is confirmed by Rutherford backscattering spectroscopy (RBS) and energy dispersive X-ray (EDX) measurements. Efficient green and infrared emissions were observed at room temperature. The investigations are focused on the evolutions v...

We demonstrate strong room-temperature photoluminescence (PL) in the visible region of the spectrum from europium (Eu3+)-doped porous GaP (por-GaP) layers. Eu3+ ions were infiltrated into the host matrix by simple impregnation from chloride solution of europium, followed by high temperature annealing in air. From RBS analysis, a rather uniform inco...

Ce manuscrit, divisé en cinq chapitres, présente les différents aspects de ce travail. Le premier chapitre décrit le silicium poreux et sa réalisation, les différents paramètres de formation, ses propriétés structurales. Les propriétés de luminescence des ces ions (Erbium et Ytterbium) sont exposées par la suite. Enfin, un état de l'art est détaill...