Bashir Ahmmad - Academia.edu (original) (raw)

Papers by Bashir Ahmmad

Journal of Advanced Simulation in Science and Engineering

To improve the performance of organic photovoltaics, we investigate an integrated device design i... more To improve the performance of organic photovoltaics, we investigate an integrated device design in which the hybrid antireflection structure, composed of a surface moth-eye nanotexture and a multilayer interference film, is applied with a high-refractive-index glass substrate. The moth eye texture with a relatively long period, which is near the bandgap wavelength of organic semiconductors, is used to enhance light absorption. We perform the optical finite-difference time-domain simulation for the integrated device and find the optimal layer configuration of the multilayer interference film to maximize the photocurrent generation. In addition, we compare the absorption spectrum of the integrated device and that of the device with only moth eye coating, and show that the integrated structure is beneficial to realize a high level of absorption relatively uniformly as function of wavelength.

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

The authors developed a room temperature atomic layer deposition (ALD) system that can deposit Ti... more The authors developed a room temperature atomic layer deposition (ALD) system that can deposit TiO 2 on gold nanoparticles by using tetrakis(dimethylamino)titanium and plasma-excited humidified argon. The growth per cycle of TiO 2 was measured to be 0.25 nm/cycle on a monitored Si sample. For applying the nanoparticle coating, the source material, i.e., gold particles, is electrostatically attached to the susceptor in the ALD system to avoid their gas transport. These particles are then mixed by a rotating scraper during the ALD process. This system allows a conformal deposition of TiO 2 without the aggregation of nanoparticles. The thickness of TiO 2 for shell coating is controlled by counting the number of ALD cycles. The deposition of TiO 2 coating with a nanometer scale thickness on the gold nanoparticle is demonstrated in this paper.

Materials Research Express

A simple route to prepare Gd 0.7 Sr 0.3 MnO 3 nanoparticles by ultrasonication of their bulk powd... more A simple route to prepare Gd 0.7 Sr 0.3 MnO 3 nanoparticles by ultrasonication of their bulk powder materials is presented in this article. For comparison, Gd 0.7 Sr 0.3 MnO 3 nanoparticles are also prepared by ball milling. The prepared samples are characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive X-ray (EDX), X-ray photoelectron spectroscope (XPS), and Superconducting Quantum Interference Device (SQUID) magnetometer. XRD Rietveld analysis is carried out extensively for the determination of crystallographic parameters and the amount of crystalline and amorphous phases. FESEM images demonstrate the formation of nanoparticles with average particle size in the range of 50-100 nm for both ultrasonication and 4 hours (h) of ball milling. The bulk materials and nanoparticles synthesized by both ultrasonication and 4 h ball milling exhibit a paramagnetic to spin-glass transition. However, nanoparticles synthesized by 8 h and 12 h ball milling do not reveal any phase transition, rather show an upturn of magnetization at low temperature. The degradation of the magnetic properties in ball milled nanoparticles may be associated with amorphization of the nanoparticles due to ball milling particularly for milling time exceeding 8 h. This investigation demonstrates the potential of ultrasonication as a simple route to prepare high crystalline rare-earth based manganite nanoparticles with improved control compared to the traditional ball milling technique.

2016 9th International Conference on Electrical and Computer Engineering (ICECE), 2016

Journal of Advanced Oxidation Technologies, 2007

The photocatalytic hydrogen production from aqueous solutions of two diacids, i.e., oxalic acid a... more The photocatalytic hydrogen production from aqueous solutions of two diacids, i.e., oxalic acid and fumaric acid, was performed using the mixtures of TiO

Journal of Alloys and Compounds, 2017

In this investigation, undoped BiFeO3, Gd doped Bi0.9Gd0.1FeO3, and Gd-Ti co-doped Bi0.9Gd0.1Fe1−... more In this investigation, undoped BiFeO3, Gd doped Bi0.9Gd0.1FeO3, and Gd-Ti co-doped Bi0.9Gd0.1Fe1−xTixO3 (x = 0.10, 0.20) materials were synthesized to report their multiferroic properties. The structural analysis and phase identification of these multiferroic ceramics were performed using Rietveld refinement. The Rietveld analysis has confirmed the high phase purity of the 10% Gd-Ti co-doped Bi0.9Gd0.1Fe0.9Ti0.1O3 sample compared to that of other compositions under investigation. The major phase of this particular composition is of rhombohedral R3c type structure (wt% > 99%) with negligible amount of impurity phases. In terms of characterization, we address magnetic properties of this co-doped ceramic system by applying substantially higher magnetic fields than that applied in previously reported investigations. The dependence of temperature and maximum applied magnetic fields on their magnetization behavior have also been investigated. Additionally, the leakage current density has been measured to explore its effect on the ferroelectric properties of this multiferroic system. The outcome of this investigation suggests that the substitution of 10% Gd and Ti in place of Bi and Fe, respectively, in BiFeO3 significantly enhances its multiferroic properties. The improved properties of this specific composition is associated with homogeneous reduced grain size, significant suppression of impurity phases and reduction in leakage current density which is further asserted by polarization vs. electric field hysteresis loop measurements.

Journal of Photochemistry and Photobiology a Chemistry, Dec 1, 2006

The photocatalytic production of hydrogen gas from water–methanol mixtures was performed in conta... more The photocatalytic production of hydrogen gas from water–methanol mixtures was performed in contact with a suspended mixture of powdered titanium dioxide (TiO2) and graphite silica (GS), a naturally available mineral. A drastic synergy effect for hydrogen production was found for GS in collaboration with TiO2. The amount of hydrogen gas evolved from water–methanol mixtures was increased by a factor of

Journal of nanoscience and nanotechnology, 2015

This article discusses the hydrothermal synthesis of well-dispersed faceted α-GaOOH in the presen... more This article discusses the hydrothermal synthesis of well-dispersed faceted α-GaOOH in the presence of sodium acetate by the self-assembly method. The synthesized α-GaOOH possesses a mixture of hexagonal and rectangular plates, cubic and diamond-like morphologies. The presence of ethanol as a co-solvent with water (1:1) facilitates scroll-like cylindrical morphology. The influences of sodium acetate concentration, hydrothermal temperatures, time and solvent on the formation of the above-mentioned morphologies were investigated. The synthesized α-GaOOH was characterized using X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM) and High-Resolution Transmission Electron Microscopy (HR-TEM), thermal analysis and nitrogen adsorption analysis. The XRD pattern confirmed the formation of orthorhombic α-GaOOH. The increase of the sodium acetate concentration from 0.031 mol/L to 0.250 mol/L facilitates the formation of more cubic and diamond-shaped particles than pla...

Photochem Photobiol Sci, 2007

Hydrogen production was accomplished under visible-light irradiation by using a system consisting... more Hydrogen production was accomplished under visible-light irradiation by using a system consisting of a biomolecule (chlorophyll a), methylviologen, ethylenediaminetetraacetic acid disodium salt and Pt-loaded poly(l-glutamate) (Poly(Glu)), in aqueous decylammonium chloride (DeAC) solution. Spectroscopic studies revealed that chlorophyll a is solubilized in the hydrophobic clusters of Pt-loaded Poly(Glu)-decylammonium chloride. In the Poly(Glu)-DeAC complex, the electron transfer occurred between chlorophyll a and methylviologen leading to hydrogen production. The most noticeable result is that the rate of hydrogen evolution depends on the change from the random coil to the alpha-helix in conformation of Poly(Glu) induced by the cooperative binding with DeAC.

Journal of Energy Engineering, Apr 1, 2013

A three-phase solid-state solar cell (SSSC) has been developed successfully using TaON nanopartic... more A three-phase solid-state solar cell (SSSC) has been developed successfully using TaON nanoparticles or BiOI microspheres as a sensitizer material over a TiO 2 film and CuI as a hole collector. Stable current (I sc)-voltage (V oc) curves are found under ultraviolet (UV)visible light irradiation with an efficiency of 0.15% and 0.10% for TaON-and BiOI-based solar cells, respectively. The observed photocurrents in SSSCs are approximately 10 and 48 times higher than those in wet-type solar cells (WSCs) based on TaON and BiOI, respectively. A plausible mechanism of charge transfer and hole filling is discussed in terms of the band gap energy and band position of the semiconductor materials.

Advanced Powder Technology the International Journal of the Society of Powder Technology Japan, May 1, 2010

Without using an external precursor a simple and one-step method for the synthesis of C-doped TiO... more Without using an external precursor a simple and one-step method for the synthesis of C-doped TiO 2 submicrospheres has been developed via hydrolysis of titanium tetraisopropoxide in pure methanol followed by calcination under air at 500°C. Also, with the addition of D-glucose and NH 4 OH solution during the hydrolysis process, C-or N-doped and C, N co-doped TiO 2 submicrospheres can be prepared by the same method. The size of the submicrosphere was homogeneous ranging from 300 to 400 nm. The resulting submicrospheres were characterized by FE-SEM, TEM, XRD, XPS and UV-vis diffuse reflectance spectroscopy. The C-or N-doped and C, N co-doped submicrospheres showed obvious absorption in the wavelength up to around 650, 500 and 650 nm, respectively. The activity of the photocatalysts was evaluated by the hydroxyl radical formation under visible light irradiation. Finally, the mechanism of sphere formation is discussed.

Applied Mechanics and Materials, Apr 2, 2014

Room-temperature SiO2 atomic layer deposition (ALD) on soft, flexible materials of acrylic resin ... more Room-temperature SiO2 atomic layer deposition (ALD) on soft, flexible materials of acrylic resin and polystyrene is developed using tris (dimethylamino) silane and plasma-excited water vapor. The growth rate is measured to be 0.13 nm/cycle at room temperature on the acrylic resin surface. The SiO2 coating on the soft materials was examined by X-ray photoelectron spectroscopy and an organic solvent resistant test. This process is applicable as a surface treatment for improving chemical resistivity of the soft materials.

A green synthesis method of α-Fe 2 O 3 microparticles has been developed using the extract of gre... more A green synthesis method of α-Fe 2 O 3 microparticles has been developed using the extract of green tea (camellia sinensis) leaves. The as-prepared microparticles were characterized by SEM, TEM, XRD, XPS, UV-visible spectroscopy, and N 2 adsorption analysis. The crystallized microparticles were elliptical in shape with a diameter and length of 1µm and 2 µm, respectively. The photocatalytic activity of the microparticles was evaluated by the amount of hydroxyl radical formation under visible light irradiation detected by fluorescence spectroscopy. The as-prepared α-Fe 2 O 3 showed similar photocatalytic activity as the commercial α-Fe 2 O 3 in terms of hydroxyl radical formation. The microparticles were easy to separate from the aqueous suspension by gravity settling after water treatment. A plausible mechanism for the formation of α-Fe 2 O 3 microparticles was suggested.

The study was conducted to reinforce starch-based biocomposite films using cellulose nanocrystals... more The study was conducted to reinforce starch-based biocomposite films using cellulose nanocrystals (CNCs) from garlic stalks. An average yield of 4.6% by mass based from air-dried garlic stalks was obtained through alkali delignification, acid hydrolysis and sonication. The isolated CNCs are spherical and have an average diameter of 35 nm and crystallinity of 62%. Fourier transform infrared spectra correspond to the structure of cellulose, but some absorption bands corresponding to hemicelluloses were also noticed. Starch-based biocomposite films with varying amount of the isolated CNCs as reinforcing filler were prepared by solution casting and evaporation method. Scanning electron micrographs of the films showed homogeneous dispersion of CNC in the starch matrix. Improvement in tensile strength and modulus was at maximum when the starch to CNC ratio is 100:5. The thermal stability of the films, on the other hand, decreased with the addition of CNC. Finally, CNC-reinforced films had lower moisture uptake than nonreinforced films.

Journal of Applied Physics, 2015

The exchange bias (EB) effect has been observed in magnetic Bi0.9Gd0.1Fe0.9Ti0.1O3 nanoparticles.... more The exchange bias (EB) effect has been observed in magnetic Bi0.9Gd0.1Fe0.9Ti0.1O3 nanoparticles. The influence of magnetic field cooling on the exchange bias effect has also been investigated. The magnitude of the exchange bias field (HEB) increases with the cooling magnetic field, showing that the strength of the exchange bias effect is tunable by the field cooling. The HEB values are also found to be dependent on the temperature. This magnetically tunable exchange bias obtained at temperatures up to 250 K in Bi0.9Gd0.1Fe0.9Ti0.1O3 nanoparticles may be worthwhile for potential applications.

2015 International Conference on Electronic Packaging and iMAPS All Asia Conference (ICEP-IAAC), 2015

IEICE Transactions on Electronics, 2015

ABSTRACT Nitrogen adsorption on thermally cleaned Si (100) surfaces by pure and plasma excited NH... more ABSTRACT Nitrogen adsorption on thermally cleaned Si (100) surfaces by pure and plasma excited NH3 is investigated by in situ IR absorption spectroscopy and ex-situ X-ray photoelectron spectroscopy with various temperatures from RT (25°C) to 800°C and with a treatment time of 5 min. The nitrogen coverage after the treatment varies according to the treatment temperature for both pure and plasma excited NH3. In case of the pure NH3, the nitrogen coverage is saturated as low as 0.13-0.25 mono layer (ML) while the growth of the nitride film commenced at 550°C. For the plasma excited NH3, the saturation coverage was measured at 0.54 ML at RT and it remained unincreased from RT to 550°C. This indicates that the plasma excited NH3 enhances the nitrogen adsorption near at RT. It is found that main species of N is Si2=NH in case of the plasma excited NH3 at RT while the pure NH3 treatment gives rise to the Si−NH2 passivation with Si−H at RT. We discuss the mechanism of the nitrogen adsorption on Si(100) surfaces with the plasma excited NH3 in comparison with the study on the pure NH3 treatment. key words: Plasma, plasma excited NH3, IR absorption spectroscopy, XPS.