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Related Concept Videos

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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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...
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The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene...
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Biasing of Metal-Semiconductor Junctions01:27

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Biasing metal-semiconductor junctions involves applying a voltage across the junction. Specifically, the metal is connected to a voltage source, while the semiconductor is grounded. This technique is essential for controlling the direction and magnitude of current flow in electronic devices, including diodes, transistors, and photovoltaic cells.
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Spin–Spin Coupling: One-Bond Coupling01:17

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Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
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Metal-Semiconductor Junctions01:24

Metal-Semiconductor Junctions

1.2K
The contact of metal and semiconductor can lead to the formation of a junction with either Schottky or Ohmic behavior.
Schottky Barriers
Schottky barriers arise when a metal with a work function (Φm) contacts a semiconductor with a different work function (Φs). Initially, electrons transfer until the Fermi levels of the metal and semiconductor align at equilibrium. For instance, if Φm > Φs, the semiconductor Fermi level is higher than the metal's before contact. The...
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Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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1.6K
Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
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Ultra-weak interlayer coupling in two-dimensional gallium selenide.

R Longuinhos1, J Ribeiro-Soares1

  • 1Departamento de Física, Universidade Federal de Lavras, PO Box 3037, Lavras, MG 37200-000, Brazil. jenaina.soares@dfi.ufla.br.

Physical Chemistry Chemical Physics : PCCP
|October 11, 2016
PubMed
Summary
This summary is machine-generated.

Few-layer gallium selenide (GaSe) exhibits ultra-weak interlayer coupling, suggesting potential as a nanoscale lubricant similar to graphite. This study clarifies polytype stability and vibrational modes for 2D materials.

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Area of Science:

  • Materials Science
  • Condensed Matter Physics
  • Nanotechnology

Background:

  • Two-dimensional (2D) materials beyond graphene are crucial for future optoelectronics.
  • Group IIIA metal monochalcogenides (GIIIAMMs) in 2D form represent an emerging research area.
  • Bulk gallium selenide (GaSe) is known for nonlinear optics and lubrication, but its few-layer properties are unexplored.

Purpose of the Study:

  • Investigate the phase stability and interlayer coupling in few-layer GaSe.
  • Determine the Raman and infrared activity of low-frequency shear and breathing modes.
  • Provide strategies to differentiate between polytypes (β and ε) and layer numbers.

Main Methods:

  • Symmetry arguments and first-principles calculations were employed.
  • A linear chain model was used to analyze force constants.
  • Analysis focused on low-frequency vibrational modes.

Main Results:

  • Phase stability and polytype characteristics of few-layer GaSe were elucidated.
  • Ultra-weak interlayer coupling was quantified using shear and breathing force constants.
  • Strategies for identifying layer number and polytypes were proposed.

Conclusions:

  • Few-layer GaSe, particularly β and ε polytypes, exhibits lubrication properties comparable to few-layer graphite due to weak interlayer coupling.
  • The findings offer insights into interlayer interactions in 2D GIIIAMMs, impacting their mechanical and electrical properties.