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Dual photoluminescence peaks observed during the synthesis of colloidal PbS nanosheets reveal their growth mechanism - two-dimensional attachments of the quantum dots. Well-grown nanosheets show the photoluminescence linewidth of 95 meV at room temperature. Aged nanosheets in toluene have enhanced photoluminescence with intensity improved by an order of magnitude.

a strong semi-metallic ferromagnet having robust spin polarization and magnetic transition temperature (T c) well above 300 K, has attracted significant attention as a possible candidate for a wide range of memory, spintronic, and multifunctional devices. Since varying the oxygen partial pressure during growth is likely to change the structural and other physical functionalities of La 0.7 Sr 0.3 MnO 3 (LSMO) films, here we report detailed investigations on structure, along with magnetic behavior of LSMO films with same thickness (~30 nm) but synthesized at various oxygen partial pressures: 10, 30, 50, 100, 150, 200 and 250 mTorr. The observation of only (00 l) reflections without any secondary peaks in the XRD patterns confirms the high-quality synthesis of the above-mentioned films. Surface morphology of the films reveals that these films are very smooth with low roughness, the thin films synthesized at 150 mTorr having the lowest average roughness. The increasing of magnetic T c and sharpness of the magnetic phase transitions with increasing oxygen growth pressure suggests that by decreasing the oxygen growth pressure leads to oxygen deficiencies in grown films which induce oxygen inhomogeneity. Thin films grown at 150 mTorr exhibits the highest magnetization with T C = 340 K as these thin films possess the lowest roughness and might exhibit lowest oxygen vacancies and defects. Interpretation and significance of these results in the 30 nm LSMO thin films prepared at different oxygen growth pressures are also presented, along with the existence and growth pressure dependence of negative remanent magnetization (NRM) of the above-mentioned thin films. The miniaturization of devices to increase speed and reduce the cost of materials is an ongoing need for many current and potential magnetic technologies such as spintronics, highly dense non-volatile memory, spin-caloritronics, and different multifunctional micro and nanoscale devices 1-5. Among important materials for device applications are room temperature ferromagnetic oxides such as the manganites, La 1−x Sr x MnO 3 , since their properties can be tuned using a number of degrees of freedom including charge, spin, orbital, and magnetic ordering phenomena 6,7. They are also excellent candidates for novel engineered nanostructures as they exhibit colossal magnetoresistance (CMR) effect which has been used for different multifunctional applications 8-10. La 1− x Sr x MnO 3 also shows CMR phenomena under smaller external magnetic fields compared to the other manganites and strongly correlated materials 11,12. Among the La 1−x Sr x MnO 3 manganites, the optimized stoichiometry La 0.7 Sr 0.3 MnO 3 (LSMO) is one of the most prominent members with outstanding magnetic and magneto-transport properties. Compared to other typical magnetic oxides, LSMO exhibits semi-metallic behavior, outstanding ferromagnetism, high Fermi-level spin polarization, with a bulk magnetic ordering temperature, T C (= 370 K) well above room temperature 13,14. Also, the spin polarization of LSMO ...

Aspects of the optoelectronic performance of thin-film ferromagnetic materials are evaluated for application in ultrafast devices. Dynamics of photocarriers and their associated spin polarization are measured using transient reflectivity (TR) measurements in cross linear and circular polarization configurations for La0.7Sr0.3MnO3 films with a range of thicknesses. Three spin-related recombination mechanisms have been observed for thicker films (thickness of d ≥ 20 nm) at different time regimes (τ), which are attributed to the electron–phonon recombination (τ < 1 ps), phonon-assisted spin–lattice recombination (τ ∼ 100 ps), and thermal diffusion and radiative recombination (τ > 1 ns). Density functional theory (DFT+U) based first-principles calculations provide information about the nature of the optical transitions and their probabilities for the majority and the minority spin channels. These transitions are partly responsible for the aforementioned recombination mechanisms, identified through the comparison of linear and circular TR measurements. The same sets of measurements for thinner films (4.4 nm ≤ d < 20 nm) revealed an additional relaxation dynamic (τ ∼ 10 ps), which is attributed to the enhanced surface recombination of charge carriers. Our DFT+U calculations further corroborate this observation, indicating an increase in the surface density of states with decreasing film thickness which results in higher amplitude and smaller time constant for surface recombination as the film thickness decreases.

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