By means of thermal decomposition, we prepared single-phase spherical Ni nanoparticles (23 to 114 nm in diameter) that are face-centered cubic in structure. The magnetic properties of the Ni nanoparticles were experimentally as well as theoretically investigated as a function of particle size. By means of thermogravimetric/differential thermal analysis, the Curie temperature TC of the 23-, 45-, 80-, and 114-nm Ni particles was found to be 335°C, 346°C, 351°C, and 354°C, respectively. Based on the size-and-shape dependence model of cohesive energy, a theoretical model is proposed to explain the size dependence of TC. The measurement of magnetic hysteresis loop reveals that the saturation magnetization MS and remanent magnetization increase and the coercivity decreases monotonously with increasing particle size, indicating a distinct size effect. By adopting a simplified theoretical model, we obtained MS values that are in good agreement with the experimental ones. Furthermore, with increase of surface-to-volume ratio of Ni nanoparticles due to decrease of particle size, there is increase of the percentage of magnetically inactive layer.

An optimal power to exfoliate MoS2nanoflakes for high yield and small lateral size with narrow size distribution was obtained.

A simple pyrolysis method has been developed to synthesize microstructure-controlled CoO nanoparticles from cobalt acetylacetonate in oleylamine at or above 200 °C. XRD, SEM, and HRTEM analyses indicate that the cubic and hexagonal CoO nanoparticles with different morphologies, viz. spherical, quasi-cubic, and pyramidal, could be obtained via varying the precursor concentration, and the average size of hexagonal CoO nanoparticles increases with increasing reaction time or reaction temperature. XPS, TG-DTA, and FTIR analyses reveal that the as-synthesized nanoparticles are pure CoO with good thermal stability. Raman and UV–vis absorption spectra show that the optical properties of CoO nanoparticles are of obvious size effect, which revealed their characteristic feature. Whatever the crystal structure and particle shape are, the CoO nanoparticles with sizes of 33, 59, and 85 nm exhibit two band gaps, and the corresponding band gap differences are 1.84, 1.62, and 1.42 eV, respectively. The pure hexagonal CoO nanoparticles display complete room temperature paramagnetism, while the CoO nanoparticles that contain cubic phase show interesting magnetic behavior due to intrinsic antiferromagnetic structure and uncompensated surface spins, which were confirmed by VSM and ESR studies.