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Related Concept Videos

π Electron Effects on Chemical Shift: Overview01:27

π Electron Effects on Chemical Shift: Overview

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An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0,...
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Diamagnetic Shielding of Nuclei: Local Diamagnetic Current01:14

Diamagnetic Shielding of Nuclei: Local Diamagnetic Current

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An applied magnetic field causes the electrons present in the molecule to circulate, setting up a local diamagnetic current within the molecule. The local diamagnetic current arising from circulating sigma-bonding electrons induces a magnetic field, Blocal that opposes the applied magnetic field, B0. The effective magnetic field experienced by these nuclei is given by the difference between the applied and local magnetic fields in a phenomenon called local diamagnetic shielding. Essentially,...
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¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

1.2K
The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
1.2K
π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds01:14

π Electron Effects on Chemical Shift: Aromatic and Antiaromatic Compounds

1.3K
In aromatic compounds, such as benzene, the circulation of (4n + 2) π-electrons sets up a diamagnetic or diatropic ring current around the perimeter of the molecule. This current induces a magnetic field that opposes the external field inside the ring and reinforces it on the outside. The protons in benzene are deshielded and exhibit high chemical shifts in the range 6.5–8.5 ppm. The shielding effect at the center of the ring is evident in complex aromatic molecules, such as...
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Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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

1.1K
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...
1.1K
¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

1.1K
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
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Characterization of Nanocrystal Size Distribution using Raman Spectroscopy with a Multi-particle Phonon Confinement Model
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Matrix-Embedding Effects on Nanodiamond Phonons.

Caleb Stamper1, David L Cortie1,2, Abdulhakim Bake1

  • 1School of Physics and Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2500, Australia.

Nano Letters
|August 20, 2025
PubMed
Summary

Embedding diamond nanocrystals in a tin telluride matrix alters their phonon spectra, quenching surface phonons and softening core phonons. These findings impact understanding of nanocrystal composite properties.

Keywords:
compositenanocrystalnanodiamondneutronphononthermal

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Area of Science:

  • Materials Science
  • Condensed Matter Physics
  • Nanotechnology

Background:

  • Lattice dynamics of nanocrystals are unique but less understood when embedded in matrices.
  • Investigating changes in phonon spectra upon matrix embedding is crucial for composite materials.

Purpose of the Study:

  • To systematically compare phonon spectra of diamond nanocrystals before and after embedding in a tin telluride matrix.
  • To explore the effects of matrix embedding on nanocrystal surface and core phonon dynamics.

Main Methods:

  • Time-of-flight neutron spectroscopy to measure phonon spectra (0.5-250 meV) in light nanocrystals within a heavy matrix.
  • Classical molecular dynamics simulations for interpreting spectral changes.

Main Results:

  • Embedding diamond nanocrystals in tin telluride matrix leads to quenched surface phonons and softened core phonons.
  • Phonon line widths narrow due to matrix-induced boundary conditions and tensile strain.
  • Anharmonic surface dynamics are suppressed, with variations observed between agglomerated and isolated nanodiamonds.

Conclusions:

  • Matrix embedding significantly modifies nanocrystal lattice dynamics.
  • The observed changes are critical for optimizing vibrational and thermodynamic properties of nanocomposite materials, particularly thermoelectrics.