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Thin films of Bi2Se3 were deposited on Si (100) substrates using RF magnetron sputtering at a deposition temperature of 633 K. The surface morphology of Bi2Se3 films revealed the variation of grain sizes with thickness, while elemental analysis showed the stoichiometric Bi2Se3 films. The high-intensity x-ray diffraction peaks along (0003), (0006) and (00015) planes showed the dominant orientation of Bi2Se3 along the c-axis on Si (100). Three prominent Raman characteristic peaks, E2g, A11g, and A21g modes, were observed which revealed a pure hexagonal phase. X-ray photoelectron spectroscopy analysis showed the growth of high-purity Bi2Se3 films. The temperature-dependent electrical conductivity measurements showed the increase in conductivity with temperature due to the semiconducting nature. Seebeck coefficient of these films falls in the range of −153 to −236 µV/K near room temperature. These findings pave the way for economically preparing large-area and high-performance Bi2Se3 thin films for future thermoelectric devices. [ABSTRACT FROM AUTHOR]

Lead halide perovskite (CsPbBr3) quantum dots (QDs) and two-dimensional (2D) layered transition metal dichalcogenides have a significant application in solution-processed optoelectronic devices. Here, we report the oleylamine-assisted exfoliation of TiSe2 nanosheets (NSs) in dichlorobenzene with high concentration and stable dispersion. The functionalized TiSe2 NSs were used to synthesize the solution-processed perovskite CsPbBr3 QD/TiSe2 NS-based nanocomposite. The perovskite QDs and TiSe2 NSs were characterized by different techniques. The strong photoluminescence (PL) quenching and decreased lifetime decay of the nanocomposite indicates efficient charge transfer from photo-excited CsPbBr3 to TiSe2 NSs. The calculated charge-transfer rate constant (KET) from photo-excited CsPbBr3 to TiSe2 NSs increased from 1.50 × 108 to 2.79 × 108 s−1 in different concentrations of TiSe2 NSs (5 to 20 μg mL−1), respectively. Furthermore, the photo-currents of CsPbBr3 QD/TiSe2 NS nanocomposite devices were dramatically enhanced ∼2 times compared to pristine CsPbBr3 QD based devices, which supports the charge transfer and charge separation in nanocomposite devices. [ABSTRACT FROM AUTHOR]

Tin doped CuInO2 thin films deposited by rf magnetron sputtering technique show columnar structure with (006) preferred orientation. Conducting atomic force microscopy measurements show the presence of nanoconductivity regions when the current flow direction is along the in-plane InO6 layer and absence of conducting regions when the current direction is along O–Cu–O layers perpendicular to the film surface. The strong anisotropy observed in the electrical properties of tin doped samples is due to the preferred crystallite orientation and highly anisotropic delafossite structure. A large change in the electrical conductivity value and activation energy value in undoped films and tin doped samples has also been explained in terms of change in crystallite orientation on doping. Spectroscopic ellipsometry measurements have been used to determine the optical constant and dielectric function of CuInO2 and CuInO2:Sn films and show a band gap value of 4.5 eV in tin doped samples due to removal of structural defects. [ABSTRACT FROM AUTHOR]

Nanocomposites of polyaniline with barium ferrite and titanium dioxide (TiO2) are synthesized via in situ emulsion polymerization. The transmission electron microscopy (TEM) and high resolution TEM result shows the formation of array of nanoparticles encapsulated within the polymer chains during the synthesis process. The high value of microwave absorption, 58 dB (>99.999% attenuation) results from the combined effect of the nanoparticles and the polymer matrix. The amount of barium ferrite has the profound effect on permittivity ([variant_greek_epsilon]), permeability (μ), and microwave absorption of the nanocomposite. The contribution to the absorption value comes mainly due the magnetic losses (μ″) in barium ferrite and dielectric losses ([variant_greek_epsilon]″) in TiO2 and polyaniline. [ABSTRACT FROM AUTHOR]

Eu3+ doped yttrium aluminum garnet (YAG) nanoparticles were synthesized by sol-gel method. The samples were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy including vacuum ultraviolet (VUV) PL spectroscopy. XRD confirmed that each and every phases of YAG were present, indicating very good quality of sample. The crystallite size, estimated by XRD, increased from 10 to 30 nm with annealing temperatures and significant changes in morphology with annealing temperature was also found in TEM study. The particles were in spherical shape initially but agglomeration of particles started at higher temperatures resulting in hierarchical nanostructures having dimension more than 50 nm. The annealed YAG:Eu3+ hierarchical nanostructures showed strong red luminescence under VUV excitation, corresponding to 5D0→7F2 transition. PL spectra also showed significant increase in luminescence intensity with the increase in annealing temperature. Time evolution studies were also performed continuously for 150 days to check the stability of prepared hierarchical nanostructures and were found to be extremely stable, making them one of the most feasible candidate for red phosphor and seize great potential in flat panel display application that underlies the importance of the current work. [ABSTRACT FROM AUTHOR]

The effect of substrate pretreatments such as ultrasonication or scratching by diamond powder on the microstructure and field emission characteristics of diamond grown over silicon and macroporous (anodized) silicon substrates was investigated. These films were grown in a hot filament chemical vapor deposition (CVD) system. Scanning electron microscope (SEM) studies revealed that ultrasonic pretreatment of the substrates increases nucleation density of CVD diamond by two orders of magnitude. Atomic force microscopy and energy dispersive x-ray analysis of the substrates showed that seeding is responsible for the enhanced nucleation density of diamond. SEM study showed that diamond powder scratching of porous silicon leads to uniform coverage of the substrate by the CVD diamond. Cross-sectional SEM showed growth of diamond inside the pores only after pretreating porous silicon with diamond powder. Raman spectroscopy of all the samples showed a scattering peak corresponding to diamond. Discontinuous diamond films also exhibited Raman bands corresponding to nanocrystalline diamond, diamondlike carbon, graphite, and silicon carbide. The presence of these phases of carbon was further confirmed by high resolution transmission electron microscopy studies. Field emission studies revealed that discontinuous diamond films grown on porous silicon (after diamond powder ultrasonic pretreatment) had the lowest threshold field (5.4 V/μm). [ABSTRACT FROM AUTHOR]