Related Experiment Video
Updated: Jun 18, 2026
08:39
Liquid-cell Transmission Electron Microscopy for Tracking Self-assembly of Nanoparticles
Published on: October 16, 2017
Size-dependent multiple twinning in nanocrystal superlattices.
Sara M Rupich1, Elena V Shevchenko, Maryna I Bodnarchuk
1Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, USA.
Journal of the American Chemical Society
|December 9, 2009
Summary
The size of lead sulfide (PbS) nanocrystal superlattices influences their structure. Larger PbS nanocrystals form multiply twinned superlattices with unique symmetries, while smaller ones do not.
Area of Science:
- Materials Science
- Nanotechnology
- Crystallography
Background:
- Colloidal nanocrystals self-assemble into ordered superlattices.
- The morphology and symmetry of these superlattices are crucial for their properties.
- Understanding factors controlling superlattice formation is key for materials design.
Purpose of the Study:
- To investigate the influence of nanocrystal size on the morphology of lead sulfide (PbS) superlattices.
- To elucidate the mechanisms behind the observed size-dependent structural changes.
- To explore the implications for designing novel materials with tunable properties.
Main Methods:
- Synthesis of monodisperse PbS nanocrystals of varying sizes (<4 nm and >7 nm).
- Self-assembly of PbS nanocrystals into superlattices.
- Characterization of superlattice morphology and symmetry using electron microscopy and diffraction techniques.
Main Results:
- Superlattices formed from large PbS nanocrystals (>7 nm) exhibited multiply twinned face-centered cubic structures with decahedral and icosahedral symmetry.
- These large nanocrystal superlattices displayed crystallographically forbidden five-fold symmetry elements due to multiple twinning.
- Superlattices composed of small PbS nanocrystals (<4 nm) did not show any twinning.
- Twinning energy was found to be strongly size-dependent, decreasing with increasing nanocrystal size.
- Softer interparticle potentials for larger nanocrystals favored the formation of multiply twinned superlattices.
Conclusions:
- Nanocrystal size is a critical determinant of superlattice morphology and twinning behavior.
- The size-dependent twinning energy and interparticle potentials govern the self-assembly outcome.
- This study introduces a new class of multiply twinned materials with potential for tailored interparticle interactions.
Related Concept Videos
02:33Lattice Centering and Coordination Number
The structure of a crystalline solid, whether a metal or not, is best described by considering its simplest repeating unit, which is referred to as its unit cell. The unit cell consists of lattice points that represent the locations of atoms or ions. The entire structure then consists of this unit cell repeating in three dimensions. The three different types of unit cells present in the cubic lattice are illustrated in Figure 1.
Types of Unit Cells
Imagine taking a large number of identical...
Types of Unit Cells
Imagine taking a large number of identical...
01:18Unit Cells
A crystal's internal structure is an orderly array of atoms, ions, or molecules, and the details of this array significantly influence the solid's properties. In a crystal, periodically repeating 'structural motifs' - which could be atoms, molecules, or groups thereof - create a 'space lattice.' This is essentially a three-dimensional, infinite array of points, each surrounded by its neighbors in an identical way, forming the basic structure of the crystal.A 'unit cell' is a theoretical...
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
01:10Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule
In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1 triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.
01:20Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)
Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
01:27Symmetry Elements in a Crystal
Crystal symmetry operations are isometric transformations that map objects onto indistinguishable copies while preserving distances, angles, and volumes. The simplest symmetry operation is translation, which shifts the entire infinite crystal lattice parallelly by a translation vector.Crystallographic rotations involve rotations by an angle of 2π/n around an axis without changing the positions of points on the axis. It is called the rotational axis of the symmetry, denoted by n. The combination...