Zainal Abidin Ali

C-Band Q-Switched Fiber Laser Using Titanium Dioxide (TiO 2 ) As Saturable Absorber

We demonstrate a passively Q-switched erbium fiber laser using titanium dioxide (TiO2) as a saturable absorber. The TiO2 saturable absorber was fabricated as a polymer composite film and sandwiched between fiber ferrules. Q-switched pulsing starts with the assistance of physical disturbance of the laser cavity (by lightly tapping the cavity to induce instability) at 140 mW and lasts until 240 mW. The repetition rate increases with the pump power from 80.28 to 120.48 kHz. On the other hand, the pulsewidth decreases from 2.054 μs until it reaches a plateau at 1.84 μs. The Q-switched fiber laser exhibits two competing modes: at 1558.1 and 1558.9 nm as the pump power increases. A high signal-tonoise ratio of 49.65 dB is obtained.

Green Synthesis of Silver Nanoparticles Using Apple Extract and Its Antibacterial Properties

Silver nanoparticles (AgNPs) were synthesized using apple extract as a reducing agent and aqueous silver nitrate as the precursor. The AgNPs formation was observed as a color change of the mixture from colorless to dark-brownish. The X-ray diffraction pattern confirmed the presence of only Ag crystallites, and the dynamic light scattering estimates the average sizes of the AgNPs to be 30.25 ± 5.26 nm. Furthermore, Fourier Transform Infrared as well as UV-vis spectroscopy identifies ethylene groups as the reducing agent and capping agent for the formation of the AgNPs. This green synthesis provides an economic, eco-friendly, and clean synthesis route to AgNPs. AgNPs in suspension showed activity against Gram-negative and Gram-positive bacteria with minimum bactericidal concentrations (MBCs) to be in the range from 125 μg/mL to 1000 μg/mL.

Transparent nanocrystallite silver for antibacterial coating

Transparent sol-gel film with antibacterial coating property incorporating silver nanoparticles has been successfully developed. Silver nanoparticles were synthesized by precipitation method at room temperature. XRD structural studies show that crystallite sizes in the range of 18nm to 40nm were produced. The coating system used methyltrimethoxy silane as binder and N-propanol as diluent to obtain the highest transperancy. 2.5% wt of nanosilver crystallites was added as antibacterial agent. The coating mixture was applied onto glass plates using sponges and tested against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. Values of antimicrobial activity of 4.6, 7.2, and 4.2 were, respectively, obtained for Staphylococcus aureus, Escherichia coli and Pseudomonas Aeruginosa. Coating with antimicrobial activity greater than 2 classified as antibacterial.

Tunable Q-switched fiber laser using zinc oxide nanoparticles as a saturable absorber.

Nanomaterials have ignited new interest due to their distinctive electronic, mechanical, and optical properties. Zinc oxide nanostructures are fabricated into thin film and then inserted between two fiber ferrules to act as a saturable absorber (SA). The modulation depth and insertion loss of the SA are 5% and 3.5 dB, respectively. When the ZnO-SA is incorporated into the laser cavity, a stable Q-switched pulse tunable from 1536 to 1586 nm (50 nm range) with pulse energy up to 46 nJ was observed. Our result suggests that ZnO is a promising broadband SA to generate passively Q-switched fiber lasers.

Silver nanoparticle-film based saturable absorber for passivelyQ-switched erbium-doped fiber laser (EDFL) in ring cavity configuration

We report a passive Q-switched erbium-doped fiber laser based on silver (Ag) nanoparticle thin-film saturable absorber (SA). The thin film was sandwiched between two fiber ferrules, which offer flexibility and easy integration into the ring cavity. Self-started and stable Q-switching is achieved at a central wavelength of 1558.7 nm; within the C-band region. The repetition rate and pulse duration shows a typical Q-switched laser profile as we increase the pump power; the repetition rate increases from 19.471–74.074 kHz while pulse duration decreases from 8.88–3.2 µs. A signal-to-noise ratio value of 35 dB was obtained at 100 mW pump power. By using a balanced twin-detector method, the modulation depth and saturation intensity of the Ag nanoparticle thin film were measured to be 31.6% and 0.54 MW cm−2 respectively. This result offers another alternative to the existing SA materials.

Optical and Physical Properties of Methyltrimethoxysilane Transparent Film Incorporated with Nanoparticles

Methyltrimethoxysilane has been used as a base in the formation of transparent sol-gel coatings on glass substrates. Several types of alcohol were used as solvents in order to obtain the highest transparency and scratch hardness of the film. The coating cures at room temperature (26∘C). The clarity of the coated film on the glass substrate was measured using haze meter. The best formulation based on the lowest haze values and light diffusion is the ratio of 1 : 1 trimethoxy silane to N-propanol. The haze value obtained for this system is 0.86, and the light diffusion was measured at 0.77%. Tack-free time and hardness were within acceptable value. Nanoparticles of silver, zinc oxide, and titanium dioxide were incorporated into the coating system from 0.5% to 2.5% by weight, and the haze values of the dried film were measured. The highest transparency was obtained from the samples that were mixed with 0.5% silver. The haze value for this sample is of 0.5.

Eco-friendly synthesis of silver nanoparticles and its larvicidal property against fourth instar larvae of Aedes aegypti

In this study, larvicidal activity of silver nanoparticles (AgNPs) synthesised using apple extract against fourth instar larvae of Aedes aegypti was determined. As a result, the AgNPs showed moderate larvicidal effects against Ae. aegypti larvae (LC50 = 15.76 ppm and LC90 = 27.7 ppm). In addition, comparison of larvicidal activity performance of AgNPs at high concentration prepared using two different methods showed that Ae. aegypti larvae was fully eliminated within the duration of 2.5 h. From X-ray diffraction, the AgNP crystallites were found to exhibit face centred cubic structure. The average size of these AgNPs as estimated by particle size distribution was in the range of 50-120 nm. The absorption maxima of the synthesised Ag showed characteristic Ag surface plasmon resonance peak. This green synthesis provides an economic, eco-friendly and clean synthesis route to Ag.

Antibacterial coating for elimination of pseudomonas aeruginosa and escherichia coli

A polymer antibacterial surface has been successfully developed. The coating system used silane as binder and Ag particles as antibacterial agent. The silver was synthesized using precipitation method. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Brunauer-Emmett-Teller (BET) tests, energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) were carried out to evaluate the silver particles. Antibacterial properties of the coating system were tested against gram-negative bacteria, namely, Pseudomonas aeruginosa and Escherichia coli. Different amounts of Ag were used in the coating to optimize its usage. The Japanese International Standard, JISZ2801, was used for bacteria test and the surface developed complies with the standard being antibacterial.

Synthesis of ZnO Nanowires for Hydrogen Sensor Application Using Simple Heating Technique

In this work, ZnO nanowires have been successfully grown and developed into a hydrogen gas sensor. The growth technique uses a modified carbothermal reduction at 900 °C to produce ZnO nanowires. This technique has been achieved without using carrier gas and omitted several others parameters. Silicon wafer was used as substrate and gold as catalyst. Elemental analysis and crystal structure were evaluated using Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray (EDX) and X-ray Diffraction (XRD) analysis. Nanowires with the smallest diameter of approximately 25 nm were observed. The hydrogen sensor developed showed response to 500 ppm hydrogen at temperature of 250 °C, 175 °C and 100 °C. The highest and lowest sensitivities were achieved at 250 C (~ 80%- 90%) and 100 °C (~ 15%), respectively. The response times were 10 to 15 s whereas the lowest recovery time was 240 s.