Search

The dynamical behavior of carrier electrons varies from metals to insulators depending upon their intrinsic energy levels. The anomalous behavior of carriers in topological insulators makes it a prior candidate for numerous applications in the field of spintronics, optoelectronics, terahertz generation, and detection. This article reports the excited state dynamics of a thin shining flake of Bi2Se3 single crystal in which the kinetic profile is extensively analyzed. The ultrafast carrier dynamics of this crystal were studied over a wide NIR spectral range with several optical excitations using ultrafast transient reflectance spectroscopy. The thermalization of generated hot carriers due to the implication of pump beam and their relaxation pathways through different energy levels are predicted. The signal comprises optical (1–10 ps) and acoustic (10–50 ps) coherent phonon vibrations in the crystal. The FFD (filtering high-frequency component followed by fitting data) analysis is carried out to investigate the terahertz frequency generation dependence. This article has clearly shown the tunability of terahertz generation with external electromagnetic excitations and probe radiations. [ABSTRACT FROM AUTHOR]

Recently, the demand for an accurate and precise determination of the properties of phase change materials (PCM) has increased considerably owing to the dependence of various applications based on latent heat storage (LHS). As reported earlier, PCM has a higher latent heat of fusion and is the cheapest material to store thermal energy. Still, it has poor thermal conductivity and less heat storage retentivity. For this reason, there is a significant interest in PCM-nanoparticles composites because the incorporation of nanoparticles can enhance the thermal properties of PCM. In the present work, TiO2 NPs were synthesized and incorporated with paraffin and sorbitol (PCM) by varying their mass concentration (0, 5, 10, and 20%) to study and compare the thermal properties of NCs. Different characterizations such as X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and melting temperature testing of nanocomposites by temperature variation method were studied and analyzed. An appreciable decrement in melting point of 19.19, 27.59, 18.57, and 23.89% from 0 to 20% TiO2 concentrations in paraffin and sorbitol was observed from the temperature variation and DSC results, respectively. TGA/DTG results show minimum wt% loss of 57.76% at 316.24 °C and 90.88% at 317.27 °C calculated for 20 and 10% TiO2 concentrations in sorbitol and paraffin, respectively, which corresponds to the thermal stability of NCs. It was verified by both the methods that melting point decreases linearly with an increase in the concentration of NPs in PCM, which further corresponds to the increment in thermal conductivity and thermal storage capacity. Sorbitol exhibits better stability with TiO2 than paraffin as it consists of low strain, less weight loss, and more thermal compatibility. Uncertainty in the determination of the melting point temperature from temperature variation test method and DSC measurements can mainly be ascribed to the difference in the polarity of paraffin/TiO2 and Sorbitol/TiO2 nanocomposites and on the boundary conditions during heating and cooling which markedly affects the dispersion quality of TiO2 nanoparticles within the PCM (paraffin, sorbitol) matrix and these aspects have been modeled pictorially. [ABSTRACT FROM AUTHOR]

Nanostructured zinc oxide sensing film was deposited on the Si/SiO2/Pt substrate by the RF magnetron sputtering process. The film was characterized by FESEM (field-emission scanning electron microscope) and XRD (X-ray diffraction) for their morphology and structural analysis. The FESEM results show that the film morphology is in nanophase with an average nanostructure size of ~ 50 nm. XRD results show that the film is polycrystalline. The AFM (atomic force microscopy) and Raman spectroscopy were done to analyze the surface roughness and the structural properties of the film, respectively. FTIR (Fourier-transform infrared spectroscopy) was used to analyze the presence of ZnO. Further, the ZnO nanostructure film has been explored for pH sensing for pH (4–12). The sensitivity of the film was found to be 31.81 mV/pH. The drift characteristics of the film were also done to find out the stability of the film. [ABSTRACT FROM AUTHOR]

Quantum confined germanium (Ge) nanocrystals were synthesized by a thermal annealing of germanium oxide thin films fabricated by an e-beam evaporation method. The nanocrystal formation, structure, and sizes upon annealing are evaluated by a combination of X-ray diffraction, transmission electron microscopy, and Raman spectroscopy studies. Spherical nanocrystals with sizes of around 3 nm and having both diamond and tetragonal phases are formed for an annealing temperature of 500 °C. The thermally induced transformation and phase separation of amorphous germanium oxide to nanocrystalline Ge is discussed using X-ray photoelectron spectroscopy. The bandgap agrees with the calculated values using effective mass approximation. The visible photoluminescence is investigated as a function of the annealing temperature. This disproportionation mechanism of germanium oxide films showing favorable optical properties suggests its scope for forming quantum confined Ge nanocrystals embedded in its amorphous matrix relevant for both electronic and optoelectronic applications. [ABSTRACT FROM AUTHOR]