W. Aslam Farooq

Damage Profile of HDPE Polymer using Laser-Induced Plasma

In this paper we studied the laser-induced crater depth, mass, and emission spectra of laser-ablated high-density polyethylene (HDPE) polymer using the laser-induced plasma spectroscopy (LIPS) technique. This study was performed using a Nd:YAG laser with 100 mJ energy and 7 ns pulse width, focused normal to the surface of the sample. The nanoscale change in ablated depth versus number of laser pulses was studied. By using scanning electron microscope (SEM) images, the crater depth and ablated mass were estimated. The LIPS spectral intensities were observed for major and minor elements with depth. The comparison between the LIPS results and SEM images showed that LIPS could be used to estimate the crater depth, which is of interest for some applications such as thin-film lithography measurements and online measurements of thickness in film deposition techniques.

Qualitative Analysis and Plasma Characteristics of Soil from a Desert Area using LIBS Technique

In this work, laser induced breakdown spectroscopy (LIBS) is used to investigate soil samples collected from different desert areas of Riyadh city in Saudi Arabia. Both qualitative analysis and plasma parameters are studied via the observed LIBS spectra. These experiments have been done using a Spectrolaser-7000 system with 50 mJ fundamental wavelength of Nd:YAG laser and detection delay time of 1 microsecond. Many spectral lines are highly resolved for many elements like Al, Fe, Mg, Si, Mn, Na, Ca and K. The electron temperatures Te and electron densities Ne, for the constituent of generated LIBS plasma, are determined for all the collected samples. It is found that both Te and Ne vary from one desert area to other. This variation is due to the change of the elemental concentration in different desert areas that affects the sample’s matrices. Time dependent measurements have also been performed on the soil samples. While the signal-to-base ratio (SBR) reached its optimal value at 1 microsecond, the plasma parameters Ne and Te reach values of 4×10 17 cm -3 and 9235 K, respectively, at 2.5 microsecond. The later indicate that the plasma cooling processes are slow in comparison to the previously observed results for metallic samples. The observed results show also that in the future it is possible to enhance the exploitation of LIBS in the remote on-line environmental monitoring application, by following up only the values of Ne and Te for one element of the soil desert sample using an optical fiber probe.

Effects of 1064 nm laser on the structural and optical properties of nanostructured TiO2 thin film

TiO2 thin film has been widely used as photoelectrode in dye-sensitized solar cells. It can also be used in quantum dot synthesized solar cells. Study of its effects in different spectrum of light is important for its use in solar cells. We have reported effects of 1064 nm laser on the surface morphology, structural and optical properties of nanostructured TiO2 thin film deposited on glass substrates using sol-gel spin coating technique. Q-Switched Nd:YAG pulsed laser at various power densities is used in this study. Surface morphology of the film is investigated using X-ray diffraction (XRD) and atomic force microscopy technique. The XRD pattern of as deposited TiO2 thin film is amorphous and after laser exposure it became TiO2 anatase structure. Atomic force microscopy of the crystalline TiO2 thin film shows that the grain size increases by increasing laser power density. The calculations of the band gap are carried out from UV/Visible spectroscopy measurements with JASCO spectrometer. For laser power density of 25 MW/cm2 there is an increase in the transmission and it decreases at the value of 38 MW/cm2 and band gap decreases with increasing laser power density. Photoluminescence spectra of the crystalline TiO2 thin film indicate two broad peaks in the range of 415 and 463 nm, one for band gap peak (415 nm) and other for oxygen defect during film deposition process.

Characterization and analysis of nanostructured CdO thin film using LIBS technique

Nanostructured thin films of cadmium oxide (CdO) have been synthesized using sol-gel technique on slide glass substrates. Thickness of the film is about 250 nm with average grain sizes of CdO in the range of 93-250 nm. Laser induced breakdown spectroscopy (LIBS) is used to investigate the synthesized CdO thin film. We have investigated LIBS spectrum of CdO thin film in air atmosphere using Spectrolaser-7000 system with 100 mJ fundamental laser beam from Nd:YaG laser and varied delay times from 200 ns to 2 microseconds. Many atomic and ionic lines of Cd were resolved and the variation with the delay time was studied. The plasma parameters have also been studied for Cd 508.58 nm. It is found that plasma cooled very fast after 500 ns as compared to the bulk material. The later showed that the recombination processes are growing very fast with time for nanostructured CdO thin film.

Hydrogen Peroxide Assisted Selective Oxidation of 5‐Hydroxymethylfurfural in Water under Mild Conditions

An effective and selective method for the oxidation of 5‐hydroxymethylfurfural (HMF) by using hydrogen peroxide (H2O2) as the liquid oxygen source and activated‐carbon‐supported ruthenium (Ru/AC) as the catalyst was developed. This reaction system allowed HMF to be oxidized in water under mild reaction conditions efficiently, as it was shown to have lower mass‐transfer resistance than gaseous oxygen‐assisted oxidation systems. In addition, we could selectively control the components of the oxidation products by adjusting the reaction conditions. We optimized several reaction parameters such as the reaction temperature (75 °C), time (t=1 or 6 h), base additive (sodium carbonate), and the HMF/catalyst ratio (50 or 10) to attain the desired products in maximum yields. Thus, 5‐formyl‐2‐furoic acid was obtained in a high yield up to 92 % with a HMF/catalyst ratio of 50 and a reaction time of 1 h, whereas 2,5‐furandicarboxylic acid was obtained in a maximum yield of 91.3 % with a HMF/catalyst ratio of 10 and a reaction time of 6 h. A possible mechanism for the selective oxidation of HMF was also discussed. We envision that the H2O2‐mediated oxidation systems proposed in this study would be of great benefit to other organic oxidation systems.

Study of the structural analysis of dye-silica core-shell nanoparticles (DSCSNPs)

The core-shell structure of dye-silica nanoparticles have been successfully prepared by incorporation of fluorescent coumarin 445 dye inside the silica network by subsequent sol-gel reaction of dye-silane and tetraethylorthosilicate (TEOS). The characteristic of DSCSNPs have been studied by TEM, SEM, AFM, XRD, DLS, analysis. Structural studies revealed the formation of three groups of samples, (1) dense (coumarin dye core / silica shell) nanoparticles, (2) dense coumarin dye core / porous silica shell nanoparticles were spherical in shape and the size was about 100 nm that agreed with DLS results, (3) hollow silica particles is spherical and have sizes 10nm in diameter. The x-ray diffraction pattern of DSCSNPs thin film shows hexagonal structure with crystallite size 30 nm.

Spectroscopic analysis of dye-silica core-shell nanoparticles (DSCSNPs)

Absorption and Fluorescence spectra of DSCSNPs are investigated at different concentrations, it was found that the shapes of the absorption and fluorescence spectra remained the same irrespective of an increase in the concentration, the absorption and fluorescence wavelengths peaks are located around 365nm and 440nm respectively. The intensities of DSCSNPs were observed to be greater than that of free C445 dye. Aging effects on fluorescence spectra of free C445 dye, dye-silane and DSCSNPs are studied after upon one month of preparation the samples. The results showed that the aging degradation slope of free C445 dye is more than seven times greater than that of DSCSNPs and the aging degradation slope of dye-silane is more than three times greater than that of DSCSNPs, so DSCSNPs seems to be more stable than free C445 dye and dye-silane. DSCSNPs showed severe photobleaching, presumably due to the penetration of amount of aerial oxygen molecules through the porous silica shell that caused photodegradation of majority of dye molecules, however, DSCSNPs showed better photostability than free dye.