Intermetallic Cu 11 In 9 nanoparticles with diameters of 10−30 nm were prepared via a facile, easy-to-scale-up polyol-mediated synthesis. Citrate is used as surface-capping and guarantees for efficient stabilization of the Cu 11 In 9 nanoparticles against oxidation in suspension and of powder samples in contact to air. Moreover, the citrate-capping suppresses particle-to-particle agglomeration and allows to prepare high-quality suspensions and even to redisperse Cu 11 In 9 powder samples. The latter is essential to obtain stable inks with precise element composition that can be directly used for thin-film deposition via doctor blading. Based on as-deposited thin-films, high-quality CuInSe 2 (CIS) solar cells with power-conversion efficiencies up to 7% were produced by a simple and low-cost, vacuum-free selenization process without the need of additional reducing or sintering processes. Cu 11 In 9 nanoparticles and CIS thin-films as well as the completed solar cells were characterized by various independent analytical tools, including electron microscopy (SEM/STEM), DLS, FT-IR spectroscopy, EDX, XFA, XRD, and SIMS/SNMS.
In0 nanoparticles with tunable size are obtained
via
NaBH4-induced reduction of InCl3·4H2O in diethylene glycol. Citrate-capping allows nucleating
almost monodisperse and non-agglomerated In0 nanoparticles.
Effective size tuning is possible in a wide range (10–100 nm)
just by varying the concentration of NaBH4, resulting in
mean diameters of 8, 55, and 105 nm. The citrate-capped In0 nanoparticles, moreover, turn out as surprisingly stable against
air oxidation. According to XRD and SEM analysis, the 8 nm-sized In0 particles are molten at room temperature. Size-dependent
evolution of the plasmon resonance is observed and results in a brownish-red
color and a distinct absorption in the case of the smallest In0 particles.
A wide variety of nanoscale hollow spheres can be obtained via a microemulsion approach. This includes oxides (e.g., ZnO, TiO2, SnO2, AlO(OH), La(OH)3), sulfides (e.g., Cu2S, CuS) as well as elemental metals (e.g., Ag, Au). All hollow spheres are realized with outer diameters of 10−60 nm, an inner cavity size of 2−30 nm and a wall thickness of 2−15 nm. The microemulsion approach allows modification of the composition of the hollow spheres, fine-tuning their diameter and encapsulation of various ingredients inside the resulting “nanocontainers”. This review summarizes the experimental conditions of synthesis and compares them to other methods of preparing hollow spheres. Moreover, the structural characterization and selected properties of the as-prepared hollow spheres are discussed. The latter is especially focused on container-functionalities with the encapsulation of inorganic salts (e.g., KSCN, K2S2O8, KF), biomolecules/bioactive molecules (e.g., phenylalanine, quercetin, nicotinic acid) and fluorescent dyes (e.g., rhodamine, riboflavin) as representative examples.
Nanoscale silver hollow spheres are first prepared via a microemulsion approach with 15-20 nm as the outer diameter, 3-5 nm as the wall thickness, and 10-15 nm as the diameter of the inner cavity. The presence of hollow spheres is confirmed by electron microscopy (SEM, BF-/HAADF-STEM, HRTEM) as well as by X-ray diffraction with a line-shape analysis to characterize the microcrystalline properties. In addition to the hollow spheres, massive silver nanoparticles of similar size (outer diameter of 15-20 nm) are gained via microemulsions. Based on the similarity of experimental conditions and the resulting particle size, as-prepared silver hollow spheres and massive nanoparticles are used to compare their optical properties and surface-plasmon resonance. In contrast to reducing the diameter of massive particles, "hollowing" of silver nanoparticles leads to a red-shift of the plasmon resonance. With a red shift of about 33 nm in the case of the hollow spheres, a quantum-size effect is indeed observed and in accordance with the thin sphere wall.
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