ナノ結晶のスーパーラットスのサイズ依存多重結合
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
まとめ
鉛硫化物 (PbS) ナノ結晶のスーパーラットスのサイズは,その構造に影響します. より大きなPbSナノ結晶は,ユニークな対称性を持つ複数の双子超網を形成し,小さいものはそうではありません.
科学分野:
- マテリアルサイエンス 材料科学
- ナノテクノロジー ナノテクノロジー
- クリスタログラフィーです.
背景:
- コロイドナノ結晶は,自己組織化して,オーダーされた超格子状になります.
- これらの超格子の形態学と対称性は,それらの性質にとって極めて重要です.
- 超格子形成を制御する要因を理解することは,材料設計の鍵です.
研究 の 目的:
- 鉛硫化物 (PbS) スーパーラットシスの形態学に対するナノ結晶の大きさの影響を調査する.
- 観測されたサイズ依存構造変化の背後にあるメカニズムを解明する.
- 調節可能な特性を有する新しい材料の設計への影響を調査する.
主な方法:
- 単分散のPbSナノ結晶の合成,サイズが異なる (<4 nmと>7 nm).
- PbSナノ結晶の自己組み立てにより,超格子状になる.
- 電子顕微鏡と光技術を使用して,超格子形態と対称性の特徴付け.
主要な成果:
- 大型のPbSナノ結晶 (>7 nm) から形成された超網状は,デカエドールとイコアエドール対称性の多重双子面を中心とした立方体の構造を示した.
- これらの大きなナノ結晶の超格子には,多重結合による,結晶学的に禁じられた5倍対称性の要素が描かれていた.
- 小型のPbSナノ結晶 (<4 nm) で構成されたスーパーグリッドは,いかなる双子化も示さなかった.
- 双子のエネルギーは大きさに強く依存し,ナノ結晶の大きさの増加に伴い減少することが判明しました.
- より大きなナノ結晶のためのより柔らかい粒子間電位は,複数の双子の超線形の形成を好みました.
結論:
- ナノ結晶のサイズは,超格子形態学と双子形成の行動を決定する重要な要因です.
- 大きさに依存する双子のエネルギーと粒子間のポテンシャルが,自己組み立ての結果を支配する.
- この研究は,パーティクル間の相互作用を調整する可能性を秘めた,複数の双子の材料の新種を導入しています.
関連する概念動画
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...