INTERNATIONAL NANO LETTERS (INL)
Year:2013 | Volume:3 | Issue:3|Papers Count:4

TiO2 nanoparticles acquire complete crystalline anatase phase on thermal treatment of as-prepared anatase TiO2 at 450oC. Anatase-rutile mixed phase and rutile phase are achieved by annealing anatase TiO2 at 700oC and 950oC respectively. The anatase-rutile mixed phase TiO2 has 87.8% rutile phase. This signifies that the percentage of rutile fraction in mixed phase can be tailored by changing the annealing temperature. As-prepared anatase TiO2 with a crystallite size of 5 nm has a positive strain (h) of 0.0345, which is due to the presence of oxygen defects on the surface and on the grain boundary. Removal of defects releases the strain and relaxes the lattice to its normal state, and thus, a negative strain h of (-) 0.0006 is observed in complete rutile phase. The interface between nearest anatase crystallites and between anatase and rutile crystallites contains oxygen vacancies that act as nucleation site for the growth of rutile nuclei. These oxygen defects are responsible for the broadening of the Raman Eg peak of anatase and for the shortening of the phonon lifetime in a 5-nm-sized anatase nanocrystallite. Removal of defects decreases the Raman peak width and increases the phonon lifetime in a larger rutile crystallite. The long lifetime of phonon in a larger rutile crystallite is due to temperature-dependent anharmonic phonon coupling.

Water-soluble cadmium telluride (CdTe) quantum dots (QDs) were synthesized using thioglycolic acid as capping agent; this reaction was carried out at pH=10.2 and refluxed at 100oC for 18 h. The CdTe QDs prepared at various reflux times from 1 to 18 h were coated on the glass substrates to obtain thin films of the CdTe QDs with the same thickness. The CdTe thin films were characterized by X-ray diffraction, ultraviolet-vis spectroscopy, and photoluminescence spectroscopy. The absorption thresholds of the CdTe thin films are blueshifted by about 0.65 eV with respect to the bulk value (1.5 eV), due to the quantum size effect as expected from the nanocrystalline nature of the CdTe QDs. X-ray diffraction showed that the films consisted of small CdTe nanocrystallites, 2.91 to 3.57 nm in size, showing quantum size effects. The effects of temperature on the electrical properties of the films were studied in detail. Electrical resistivity measurements were carried out for different films in the temperature range from 343 to 463 K. It is shown that activation energy increases by increasing the reflux time.

Cadmium-doped zinc oxide (CZO) has been the potential candidate for the fabrication of low-cost transparent conductors having applications in energy conversion devices such as thin-film solar cells and light-emitting diodes.In this work, the effect of different precursor solvents on the structural, morphological, and optical properties of sol-gel spin-coated CZO films was investigated. The X-ray diffraction study has revealed the hexagonal wurtzite crystal structure with crystallite size ranging from 45 to 49 nm for these films. The surface morphology of these films was analyzed by the atomic force microscopy. The precursor solvent effect was also analyzed using the UV-vis spectroscopy and fluorescence spectroscopic techniques. All the prepared films show the larger values of optical transparency (>80%) along with the shift in the fundamental absorption edge and the direct optical gap was found to be between 3.14 and 3.19 eV. The highly intense band edge emission for the sample was synthesized using the 2-ethoxyethanol while the presence of other defect-related bands in the other samples has been observed. The change in the precursor solvent volatility influences the crystal structure to favor the change in the density/type of defect states in the bandgap is used to discuss the present results. The formation of highly porous films will be suitable for gas sensor applications while the larger value of optical transparency and lower surface roughness have their probable application as the transparent electrodes in optoelectronics.

This paper presents molecular dynamics (MD) modeling for calculating the specific heat of nanofluids containing copper nanoparticles. The Cu nanoparticles with 2-nm diameter were considered to be dispersed in water as base liquid. The MD modeling procedure presented and implemented to calculate the specific heat of nanofluids with volume fractions of 2 to 10%. Obtained results show that the specific heat capacity of Cu-water nanofluids decreases gradually with increasing volume concentration of nanoparticles. The simulation results are compared with two existing applied models for prediction of the specific heat of the nanofluid. The obtained specific heat results from the MD simulation and the prediction from the thermal equilibrium model for calculating specific heat of nanofluids exhibit good agreement and the other simple mixing model fails to predict the specific heat capacity of Cu-water nanofluids particularly at high volume fractions.