PbS–Organic Mesocrystals: The Relationship between Nanocrystal Orientation and Superlattice Array

Abstract

The ability to prepare nanostructured and/or nanocomposite materials on a large scale by simple and controllable routes still remains a challenge in chemistry and material science. By employing well-established synthetic strategies, nanoparticles with different sizes, shapes and compositions can be readily produced. The high tendency for self-aggregation and selforganization of these nanosized building blocks, which are surface-stabilized by organic molecules, into superstructures has been used to create 2D and 3D assemblies. [1][2][3][4][5][6][7][8][9] In the last decade, a series of 3D colloidal superlattices composed of different nanoparticles (Ag, Au, PbS, PbSe, CeO 2 , FePt, CoPt 3 , Fe 3 O 4 , PbSe/Au, Fe 2 O 3 /PbSe, PbSe/Pd, CdSe/PbSe, etc.) has been reported. [10][11][12][13][14][15][16][17][18][19][20] Particularly, PbS-organic nanoparticles of different shapes (including cubes, octahedra, truncated octahedra, rhombicuboctahedra, etc.) can be easily synthesized on a large scale, and attracted much attention [15,16,21,22] because of a variety of possible applications. [23][24][25][26][27] Therefore, this kind of system provides a chance to study diverse packing arrangements (e.g., fcc, bcc, etc.) and specific orientational ordering of nanoparticles. [11,13,15,16,28,29] Experimental observations [16,[29][30][31][32][33][34] suggest that nanoparticles within a colloidal crystal tend to arrange in such a way that the optimal packing efficiency is achieved (principle of maximum space filling [35] ). In a relatively common case of truncated octahedrally shaped nanoparticles, the available experimental data [4,5,16,[29][30][31][32][33]36] allow to rationalize the formation of a particular type of the superlattice array (depending on the degree of coverage of nanocrystals by organic molecules) by considering four phenomenological models: A) Rigid, anisotropically shaped space-filling nanoparticles (inorganic part) without or with a tiny shell of organic molecules; B) Hard spheres with a comparatively large anisotropic core (inorganic part) covered by a relatively thin shell of organic molecules; C) Hard spheres with a comparatively small anisotropic core (inorganic part) and a thick shell of organic molecules; D) Soft and easily deformable spheres with a small anisotropic core (inorganic part) and an even thicker shell of organic molecules.For each case (A-D) the type of superlattice packing (translational order [37] ) and orientational ordering of nanoparticles within the superlattice array is significantly different. In the simplest case (A), the more or less pure, inorganic, truncated octahedrally shaped nanoparticles assemble into a bcc superlattice [33] with 100 % packing efficiency and strong orientational relationship (crystallographic directions of nanocrystals are coaxial with those of the superlattice). [35,37] In case of models B and C, by increasing the degree of coverage of anisotropic (inorganic) nanoparticles by organic molecules, their faces are continuously smoothed, thereby introducing a certa...

Interconnection of Nanoparticles within 2D Superlattices of PbS/Oleic Acid Thin Films

“…[ 26 ] To model the structure of an individual nanoparticle, a cluster with the shape of a truncated octahedron was cut out of the crystal structure of PbS (galena). For computational effi ciency, the size of this cluster was chosen to be ∼5.6 nm that is ∼1.5 times smaller than the actual size of the nanocrystals observed in experiment.…”

“…Synthesis : Samples were prepared as described in our previous publication concerning the 3D structure, [ 26 ] which is a modifi ed synthesis route taken from Nagel et al [ 37 ] Lead acetate trihydrate (1.14 g, 3 mmol), oleic acid (3.5 mL, 11 mmol), tri-n-octylphosphine (5 mL, 11.2 mmol), and diphenylether (10 mL, 63 mmol) were heated to 80 °C and maintained under vacuum for 1 h. Subsequently the temperature was raised to 135 °C under argon atmosphere and allowed to stabilize after which the fi rst solution, containing thioacetamide (0.08 g, 1.1 mmol), N,N-dimethylformamide (0.4 mL, 5.1 mmol), and tri-n-octylphosphine (6 mL, 13.5 mmol), was injected. After allowing a reaction time of 10 min a second solution, consisting of thioacetamide (0.02 g, 0.3 mmol), N,N-dimethylformamide (0.1 mL, 1.3 mmol), and tri-n-octylphosphine (0.9 mL, 2 mmol), was rapidly added.…”

“…The structure of the 2D single layer fi lm assembly bears a close relationship to the recently determined 3D structure of the PbS -oleic acid nanoparticle self-assemblies. [ 26 ] The 2D monolayer fi lm, however, shows less orientational ordering than the 3D mesocrystal, and thus, a greater number of deviations from the main [110] and [111]. This is due to the lack of the stabilizing effect of the capping layers in the case of the 2D structure.…”

“…[ 26 ] In that system, the truncated octahedrally shaped PbS nanocrystals are stabilized by organic molecules and assembled into an fcc superlattice with long-range "translational" order, while still maintaining their preferable crystallographic orientation limited to shorter ranges. Such a situation is reminiscent of a special type of colloidal crystal classifi ed as a "mesocrystal" which represents superstructures of nanoparticles with certain mutual orientation relations.…”

Anisotropic3DColloidal Quantum Nanostructures

“…The authors believe that this structure represents a missing link to understand the general principles governing the formation of PbS-organic colloidal superlattices of nanoparticles with nonspherical (namely truncated octahedrally shaped) inorganic cores. 150 Over the past few years, Cao and coworkers developed a very interesting CIS interactions technique, 139,151-154 which uses water-soluble NC micelles as precursors for the synthesis of supercrystalline colloidal superparticles. This method was employed for the self-assembly of CdSe/CdS core-shell quantum rods, into mesoscopic colloidal superparticles having multiple well-defined supercrystalline domains ( Figure 12).…”