Band gap of cubic and hexagonal CdS quantum dots - experimental and theoretical studies

CdS quantum dots of face centered cubic (fcc) and hexagonal close packed (hcp) structures were synthesized from sulphur source of sodium sulphide and thioacetamide respectively via microwave-hydrothermal method. The synthesized quantum dots were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-visible spectrophotometry. The average particle size in the range 8.5 - 12.5 nm increases with the increase of microwave exposure time from 10 to 40 min. Particles with hcp structure are larger than those with the fcc structure. The band gap in the range 2.54 - 2.65 eV decreases with the increase of microwave exposure time and the particles with the hcp structure have larger band gap than those with the fcc structure. The band gap of the CdS quantum dots were also derived from time independent Schrodinger equations for CdS system and calculated using the density functional theory (DFT). There is good agreement between the measured and calculated band gap values. The results also reveal that the band gap decreases with the increase of particle size due to the quantum size effects

Application of INAA to determine major elements concentrations in head hair of street children of Isfahan city, Iran

The street children phenomena and the number of street children is an increasing social problem in Isfahan and other big and growing towns. Because of the number of street children and the way that they affect society in childhood and when they become old, it is important to study their health and have baseline data on theire health problems. Hair element analysis is an important tool in the nutritional and environmental pollutions and measuring pollutions and measuring elemental concentrations in recently-grown hair provides a good way of studing their health. This study aimed to assess major element concentrations in the hair of street children in Isfahan using instrumental neutron activation analysis method. Six major elements (Ca, Cl, K, Mg, Na and S) of 17 Iranian street children (Isfahan) were determined. Data analysis found different profiles of the concentrations of Ca, K, Mg and S in samples. These results were discussed with reference to show of nutritional and environmental effects

Optical properties of CdS/PVA nanocomposite films synthesized using the gamma-irradiation-induced method

Monodispersed spherical CdS nanoparticles embedded into polyvinyl alcohol (PVA) films are synthesized by using an in-situ gamma-irradiation-induced method. The formation mechanism of CdS nanoparticles capped by two united cells of PVA is purposed by means of surrounding the CdS nanoparticles with OH bonds of the PVA chain. CdS nanoparticles are found to possess an unusual orthorhombic structure in monoclinic crystalline PVA. The polymer matrix affords protection from agglomeration and controls the particle size. It is found that the distribution of the prepared nanoparticles increases and a narrower size distribution is observed when the gamma radiation is varied from 10 to 50 kGy. While the average size of the nanoparticles is found to be less affected by the variation of the gamma radiation doses. The size range of the synthesized nanoparticles is 14±1 nm. The optical absorption spectra of synthesized CdS nanoparticles in a polymer matrix reveal the blue shift in the band gap energy with respect to CdS bulk materials owing to quantum confinement effect. The photoluminescence study of nanocomposite films shows the green emission arising from the crystalline defects

Thermoluminescence properties of nanostructured calcium borate as a sensitive radiation dosimeter for high radiation doses

The crystalline calcium tetraborate (CaB4O7) nanoparticles were synthesized using a combination of facile co-precipitation and thermal treatment. The synthesized phosphor nanoparticles were found to possess a monoclinic nanostructure of particle size of about 8 nm. The thermoluminescence (TL) glow curve of the nanoparticles shows a single peak centred at about 150°C. The TL nanophosphor revealed an excellent dosimetric response with a respectable linearity in the dose range of 0.05 to 1000 Gy, which is wider than its counterparts prepared by non nanosynthesis methods. They exhibited good luminescence efficiency and wide range linearity, suggesting the present phosphor nanoparticles may be considered as a suitable candidate for the dosimetric applications

The Experiences of Healthcare Professional Students about the Educational Impacts of Mobile Learning

The role of mobile devices in learning processes is growing rapidly and it is imperative to assess the effect of this technology. This paper explores the experience of healthcare professional students with regard to the educational impacts of mobile learning. We conducted a qualitative study using a conventional qualitative content analysis based on Graneheim and Lundman (2004) method to collect and analyze the experiences of 23 healthcare professional students. Two themes, each with subthemes, emerged from the findings: (1) perceived benefit in learning process, and (2) reflective self-assessment. The results revealed that mobile learning has a positive impact on both the process and the outcome of learning in healthcare professional students. Therefore, creating a supportive condition to promote mobile learning is recommended

Synthesis and characterization of silicon nanorod on n-type porous silicon

This work reports a new method for growing semiconductor nanorods on a porous silicon substrate. After preparation of n-type porous silicon samples, a thin layer of gold was deposited on them. Gold deposited samples were annealed at different temperatures. The structural, thermal, and optical properties of the samples were studied using a field emission scanning electron microscope (FESEM), photoacoustic spectroscopy, and photoluminescence spectroscopy, respectively. FESEM analysis revealed that silicon nanorods of different sizes grew on the annealed samples. Thermal behavior of the samples was studied using photoacoustic spectroscopy. Photoluminescence spectroscopy showed that the emission peaks were degraded by gold deposition and attenuated for all samples by annealing

Microwave irradiation effects on hydrothermal and polyol synthesis of ZnS nanoparticles

Cubic structure of spherical ZnS nanoparticles with relatively small size and narrow size distribution were synthesized via microwave-hydrothermal (M-H) and microwave-polyol (M-P) methods from zinc acetate and thioacetamide as starting materials. Distilled water and ethylene glycol were used as solvents for the M-H and M-P method respectively. To monitor the effect of microwave irradiation, the reactions were carried out in different irradiation time from 5 to 40 min. An increase in irradiation time increases the reaction yield and the average particle size, which subsequently decreases the optical band gap. ZnS nanoparticles synthesized by M-H method have narrower size distribution between 3 and 7 nm, while those synthesized by M-P method were between 2 and 9 nm. Moreover, the formation of hierarchical nanoballs ZnS were observed in the M-H method after 25 min irradiation time. Because of lower dielectric constant, higher dielectric loss, and higher boiling point of ethylene glycol compared to water, in the M-P method the heating rate and final temperature are higher than in M-H method, leading to the decomposition of thiocetamide, promoting higher rate of nucleation. ZnS nanocrystals synthesized with the polyol method have a higher degree of crystallinity compare with those synthesized using the hydrothermal method

Magnetic-property enhancement of sized controlled cobalt-gold core-shell nanocrystals

Cobalt nanoparticles and cobalt-gold core-shell nanoparticles were synthesized via reverse-micelle microemulsion method with emphasis on size control. Cobalt nanoparticles become easily oxidized therefore coating a gold shell on cobalt nanoparticles was necessary and can effectively reduce the oxidation of Co while maintaining most of its magnetic properties. Controlling the size of nanoparticles was performed by adjusting the water to surfactant ratio of reverse micelle solution during synthesis. X-ray diffraction data was used to calculate the crystallinity percentage and percentage of phases presented in Co-Au core-shell nanoparticles. The results from transmission electron microscopy, and field emission electron microscopy combined to energy dispersive x-ray spectroscopy provide direct evidence for shell growth. The average coating layer (shell thickness) in all cases observed to be 4-5 nm. Magnetic properties of samples were investigated using a vibrating sample magnetometer before and after annealing. Magnetic properties enhanced after annealing in all cases. An increase in saturation magnetization after annealing was due to increase in cystallinity percentage. A simple method was applied to measure a totally intrinsic blocking temperature in zero field cooled-warmed (ZFC-W) curves without employing an external magnetic field. The B-field dependence temperature data of Co-Au nanoparticles before and after annealing showed an intrinsic blocking temperature of 45 and 40 K respectively

Influence of exposure time on structural, optical and electrical properties of zinc sulphide nanoparticles synthesized by microwave technique

Zinc sulphide (ZnS) nanoparticles were synthesized via simple, rapid and energy efficient microwave technique. The obtained nanoparticles were found to possess a cubic structure with an average particle size of less than 5 nm. By changing the microwave irradiation time from 5 to 30 min, the average size of nanoparticles increased and a broader size distribution was obtained. The degree of crystallinity also increased with increasing irradiation time and reached to maximum at 25 min and then fell by rising further the irradiation time. The absorption spectra of prepared ZnS nanoparticles revealed a blue shift in the band gap energy with respect to the bulk counterpart owing to the quantum confinement effect. The photoluminescence study showed the emission intensity increased with increasing the irradiation time up to 25 min due to the increment in crystallinity of the obtained nanoparticles. Further study indicated that the microwave irradiation time has also influenced the electrical properties of nanoparticles, so that the DC conductivity increased from 1.08×10-6 to 1.67×10-4 S/m for irradiation time of 5-25min and decreased to 1.74×10-6 S/m for further irradiation time at 30 min. The dielectric constant showed a power law dispersion with no observed peak for all samples with different irradiation times

Distribution of heavy metals in surface sediments from the South China Sea ecosystem, Malaysia

The concentrations of arsenic, cadmium, chromium, copper, mercury, nickel, lead and zinc in surface sediments collected from the east coast of peninsular Malaysia, along the South China Sea, were measured by two methods instrumental neutron activation analysis and inductively coupled plasma mass spectroscopy. The obtained results were use to determine the areal distribution of the metals of in the east coast of peninsular Malaysia and potential sources of these metals to this environment. The geochemical data propose that most of the metals found in the east coast of peninsular Malaysia constitute a redistribution of territorial materials within the ecosystem. Then, the metal concentrations can be considered to be present at natural background levels in surface sediments