Preparation of self-assembled cobalt nanocrystal arrays

Abstract

Abstract-Processing of self-assembled magnetic nanocrystals has vitally scientific and technological interests. In this paper, three different kinds of self-assemblies of cobalt nanocrystals were processed using particles processed by thermal decomposition of cobalt carbonyl in toluene. In case 1, two-dimensional self-assembly of cobalt nanocrystals with an average particle size of 9.2 nm and polydispersity of 9% has been formed. In case 2, macroscopic whisker structures composed of self assembled cobalt nanocrystals (with an average size of 8 nm) were formed during the thermal decomposition under an externally applied magnetic field. The whiskers can be aligned in the longitudinal axis direction during drying using an external magnetic field. In case 3, one-dimensionally ordered, densely packed self-assemblies have also been prepared using cobalt nanocrystals with irregular shape and larger particle sizes (10 -20 nm). The formation of these different structures is attributed to the magnetic properties of cobalt particles with different sizes.

Nonprecious metal catalysts for the molecular oxygen‐reduction reaction

“…This method is based on the thermal decomposition of metal carbonyls to produce metal particles, and then the reaction between the metal particles and selenium powder. It is a clean chemical route without any impurity that has been recently widely applied to synthesize monodispersive metal nanoparticles [64][65][66][67][68][69][70][71][72][73][74][75]. Three points, however, should be noted: first, selenium cannot dissolve completely in the general solvents such as p-xylene and 1,2-dichlorobenzene, leading to partially nonreacted selenium in the product; second, the toxicity of metal carbonyl compounds should be paid attention during the synthesis process [76]; third, this low-temperature route cannot obtain some metal chalcogenides, e.g., CoS 2 , possibly due to a kinetic barrier [59].…”

Magnetic Nanoparticles: Synthesis, Protection, Functionalization, and Application

“…[49,208,209] Self-assembly of cobalt nanoparticles with a size of approximately 9.2 nm and polydispersity of only 9 % into 2D ordered structures has been performed by a vertical drying technique. [210] Cobalt nanocrystals (5-8 nm) can self-assemble into whisker shapes, if the carbonyl precursor is decomposed in an applied magnetic field. [210] More recently, Wang and co-workers reported a large-scale, hierarchical self-assembly of dendritic nanostructures of magnetic a-Fe 2 O 3 (so-called micro-pine structure, as shown in Figure 12) through the hydrothermal reaction of K 3 [Fe(CN) 6 ] in aqueous solution at suitable temperatures.…”

“…[210] Cobalt nanocrystals (5-8 nm) can self-assemble into whisker shapes, if the carbonyl precursor is decomposed in an applied magnetic field. [210] More recently, Wang and co-workers reported a large-scale, hierarchical self-assembly of dendritic nanostructures of magnetic a-Fe 2 O 3 (so-called micro-pine structure, as shown in Figure 12) through the hydrothermal reaction of K 3 [Fe(CN) 6 ] in aqueous solution at suitable temperatures. [211] The structure was formed as a result of fast growth along six crystallographically equivalent directions, and shows a lower Morin transition temperature of À57 8C.…”

Self-assembly of shape-controlled nanocrystals and their in-situ thermodynamic properties

“…For ultra-high density data storage, the most useful size range is 10-20 nm because the transition from ferromagnetism for large size particles to superparamagnetism for small size particles occurs at 10 nm, and the monolayer self-assembling is the most desirable structure [15]. Monolayer self-assembling of ferromagnetic nanocrystals is difficult experimentally because of the strong agglomeration of magnetic nanocrystals due to their magnetic interaction.…”