In this work, the influence of alloying the porous surface with uniform distributed gold nanoparticles on the characteristic porous silicon gas sensors for petroleum gas detection has been fabricated and studied extensively. Well-controlled gold nanoparticles were prepared by employing the simple dipping process of the macro porous silicon surface in diluted concentrations of HAuCl 4 salt aqueous solution. The sensing properties of the prepared porous silicon-based sensors, sensitivity response and recovery times at room temperature operating in CO gas were studied. The sensitivity of alloyed porous silicon increased from 38% to about 82% incorporation of gold nanoparticles. The lowest gas pressure detection process of CO molecules was improved from 1 mbar to 0.5 mbar. The surface alloying with rounded gold nanoparticles improved the integrated specific surface area of the alloyed porous silicon/gold nanoparticles structure, so efficient gas developed with the low-cost process.
The amount of radioactive isotopes in submerged Ceratophyllum demersum plants samples were estimated using passive track detector CR-39. The samples were collected from four selected sites along the Tigris River in Baghdad city, on a monthly basis for one complete year of 2019. Certain factors like radon concentration (Bq.m-3), radium content (Bq.kg-1) and uranium concentration (ppm) were evaluated. The average values of 222Rn level, 226Ra content and 238U concentration in Ceratophyllum demersum samples for site (1) were (593.1 Bq.m-3, 5.8 Bq.kg-1, 0.113 ppm), site (2) were (413.4 Bq.m-3, 3.8 Bq.kg-1, 0.074 ppm), Site (3) were (465.5 Bq.m-3, 4.3 Bq.kg-1, 0.083 ppm) and site (4) were (431.3 Bq.m-3, 3.9 Bq.kg-1, 0.077 ppm), respectively. The results obtained in this work indicated that the radium content and uranium concentration present in the Ceratophyllum demrsum is acceptable which does not pose any risk to the aquatic ecosystem.
In this work, the morphological and plasmonic features of the AgNPs which formed by ion-reduction process was carried out extensively. The application of the laser beam during the ion- reduction process has significant effect in the reconstruction of the formed AgNPs with small dimensions and non-frequent morphologies, according to the laser illumination intensity. For non-illumination process the deposited form of the AgNPs appear aggregated into cluster of layer AgNPs size due to the chemical reaction at Si interface, the AgNPs sizes varied from 0.85 to1.2 µm; while at lower laser intensity of about 250 mW/cm2 the AgNPs sizes varied from 0.1 to 1.0 µm, while at high intensity upto 400 mW/cm2 the AgNPs sizes varied from 0.05 to 0.4 µm. The hot spot dimension for non-illumination process varied from 1 to 11 nm while at low intensity of 250 mW/cm2 the hot spot dimension varied from 1to 8 nm. At high intensity upto 400 mW/cm2 , the hot spot varied from 0.1 to 14 nm. The XRD for the generated Ag nanoparticles / Si nanocrystallites, for non- illumination the grain size about 6.171 nm and SSD about 92.687 m2 /g while at low intensity of 250 mW/cm2 the grain size about 4.759nm and SSD about 120.191 m2 /g. At high intensity of 350 mW/cm2 , the grain size about 2.037nm and SSD about 280.847m2 /g uniform distributed AgNPs with minimum hot spot regions can be realized with 350mW/cm2 laser illumination intensity. This process is considerable as a novel work which can be adopted modification at the plasmonic features of metallic nanoparticles for SERs application.
A uniform and high-density Si nanopillars-based SERS layer was synthesized; as an efficient means, for detecting ultra-low concentration of chlorpyrifos. A low (20 %) laser pulse duty cycle of 405 nm wavelength and 600mW/cm2 intensity from a laser diode was used to achieve laser–induced etching. A simple, low-cost, and stable current wave driver circuit was utilized to drive the laser diode. Structural and spectroscopic features of the based SERS layer and AuNPs/Si nano-pillars sensor were studied by scanning probe microscopy, (FESEM) images, x-ray diffraction patterns and Raman spectroscopy. The results revealed that the Si nano-pillars layer provided superior features for creating high density hot spot gaps. A uniform, high population and unique size distributions of (AuNPs) layers on the AuNPs/Si nano-pillars layer were achieved by ion reduction process. The sensor performance displays an excellent detection of chlorpyrifos with an exponential relationship with Raman signal. The highest chlorpyrifos enhancement factor (EF= 1.1*106) with minimum limit of detection (LOD= 22*10−8 M); equivalent to 0.07 mg/Kg, was obtained with Si nano pillars of high value altitude populated with partially three dimensions AuNPs layer. This limit of detection is much lower than the recognized (0.1 mg/kg) value by the European Union.
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