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関連する概念動画

Ionic Crystal Structures02:42

Ionic Crystal Structures

18.0K
Ionic crystals consist of two or more different kinds of ions that usually have different sizes. The packing of these ions into a crystal structure is more complex than the packing of metal atoms that are the same size.
Most monatomic ions behave as charged spheres, and their attraction for ions of opposite charge is the same in every direction. Consequently, stable structures for ionic compounds result (1) when ions of one charge are surrounded by as many ions as possible of the opposite...
18.0K
Metallic Solids02:37

Metallic Solids

16.4K
Metallic solids such as crystals of copper, aluminum, and iron are formed by metal atoms. The structure of metallic crystals is often described as a uniform distribution of atomic nuclei within a “sea” of delocalized electrons. The atoms within such a metallic solid are held together by a unique force known as metallic bonding that gives rise to many useful and varied bulk properties.
All metallic solids exhibit high thermal and electrical conductivity, metallic luster, and...
16.4K
Valence Bond Theory02:42

Valence Bond Theory

8.9K
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
8.9K
Radicals: Electronic Structure and Geometry01:07

Radicals: Electronic Structure and Geometry

4.1K
This lesson delves into the geometry of a radical, which is influenced by the electronic structure of the molecule. The principle is similar to that of a lone pair, where the unpaired electron influences the geometry at the radical center.
Accordingly, the structure of a trivalent radical lies between the geometries of carbocations and carbanions. An sp2-hybridized carbocation is trigonal planar, while an sp3-hybridized carbanion is trigonal pyramidal. Here, the difference in geometry is...
4.1K
Polymers: Molecular Weight Distribution01:10

Polymers: Molecular Weight Distribution

4.0K
For any given polymer, the weight average molecular weight (Mw) is higher than, if not equal to, the number average molecular weight (Mn). The only situation in which the weight average molecular weight and the number average molecular weight are equal is when a polymer consists only of chains with equal molecular weight. However, this never happens in a synthetic polymer, since it is difficult to control the polymerization process up to a molecular level with accuracy to a hundred percent.
4.0K
Types of Semiconductors01:20

Types of Semiconductors

1.8K
Intrinsic semiconductors are highly pure materials with no impurities. At absolute zero, these semiconductors behave as perfect insulators because all the valence electrons are bound, and the conduction band is empty, disallowing electrical conduction. The Fermi level is a concept used to describe the probability of occupancy of energy levels by electrons at thermal equilibrium. In intrinsic semiconductors, the Fermi level is positioned at the midpoint of the energy gap at absolute zero. When...
1.8K

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関連する実験動画

Updated: May 3, 2026

Characterization of Nanocrystal Size Distribution using Raman Spectroscopy with a Multi-particle Phonon Confinement Model
06:54

Characterization of Nanocrystal Size Distribution using Raman Spectroscopy with a Multi-particle Phonon Confinement Model

Published on: August 22, 2015

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環恒星性カルビドシリコンのポリタイプ分布

T L Daulton1, T J Bernatowicz, R S Lewis

  • 1Materials Science Division, Argonne National Laboratory, Argonne IL, 60439-4838, USA. tdaulton@nrlssc.navy.mil

Science (New York, N.Y.)
|June 8, 2002
PubMed
まとめ

炭化シリコン (SiC) の天文学的赤外線スペクトルは論争の的です. 隕石からのプレソラーSiCの直接的な分析は,2つの一般的なポリタイプのみを明らかにし,以前のモデルを簡素化しています.

科学分野:

  • * 天体化学と材料科学.
  • * プレソラー粒子の特徴.
  • * 恒星の進化と核合成.

背景:

  • * 環恒星性炭化シリコン (SiC) の結晶構造は議論されており,天文学的赤外線スペクトルは複合型の複雑な混合物を示唆しています.
  • * 過去の研究は間接的なスペクトル分析に依存しており,恒星の流出で形成された実際のSiC構造に関する不確実性をもたらしました.

研究 の 目的:

  • * 円周カービッド (SiC) のポリタイプ分布を直接決定する.
  • * 天文データから推論されたSiCの結晶学クラスに関する論争を解決する.
  • * 星の環境におけるSiCの形成条件を理解する.

主な方法:

  • * 伝送電子顕微鏡 (TEM) を用いた直接構造分析.
  • *マーチソン炭酸隕石から抽出したプレソラー炭酸シリコン (SiC) の粒子の試験.
  • * サンプルに含まれるSiCポリタイプの識別と定量化.

主要な成果:

  • *SiCのポリタイプは3Cの立方体と2Hの六角形と2種類しか特定されなかった.
  • *この2つのポリタイプの交差も観察されました.
  • * 観察された構造的簡素性は,スペクトル分析によって示唆された多種多様なポリタイプと対照的です.

さらに関連する動画

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics
13:58

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

Published on: September 28, 2016

10.5K
Fabrication and Optimization of Type II Silicon Clathrate Films
06:53

Fabrication and Optimization of Type II Silicon Clathrate Films

Published on: October 14, 2025

1.3K

関連する実験動画

Last Updated: May 3, 2026

Characterization of Nanocrystal Size Distribution using Raman Spectroscopy with a Multi-particle Phonon Confinement Model
06:54

Characterization of Nanocrystal Size Distribution using Raman Spectroscopy with a Multi-particle Phonon Confinement Model

Published on: August 22, 2015

13.2K
Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics
13:58

Probing C84-embedded Si Substrate Using Scanning Probe Microscopy and Molecular Dynamics

Published on: September 28, 2016

10.5K
Fabrication and Optimization of Type II Silicon Clathrate Films
06:53

Fabrication and Optimization of Type II Silicon Clathrate Films

Published on: October 14, 2025

1.3K

結論:

  • * 限られたポリタイプ分布は,星周流出における低圧に起因する.
  • *これらの環境におけるカルビドシリコンの低濃縮温度は,3Cと2Hのポリタイプのみの形成を好む.
  • *この発見は,進化した恒星におけるSiC形成の理解を簡素化しています.