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Related Concept Videos

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

Spin–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...
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

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,...
Metal-Semiconductor Junctions01:24

Metal-Semiconductor Junctions

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 semiconductor's...
Biasing of P-N Junction01:16

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The operation of a p-n junction diode involves various biasing conditions, including forward bias, reverse bias, and equilibrium.
In equilibrium, no external voltage is applied across the p-n junction. The depletion region is formed at the junction interface due to the diffusion of carriers, which leaves behind charged dopants, acceptors on the p-side, and donors on the n-side. These immobile charges create an electric field that prevents further diffusion of carriers. The related energy band...
¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

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 π orbitals.
P-N junction01:11

P-N junction

A p-n junction is formed when p-type and n-type semiconductor materials are joined together. At the interface of the p-n junction, holes from the p-side and electrons from the n-side begin to diffuse into the opposite sides due to the concentration gradient. This diffusion of carriers leads to a region around the junction where there are no free charge carriers, known as the depletion region. The charge density within the depletion region for the n-side and p-side can be described by the...

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Single-Molecule F&ouml;rster Resonance Energy Transfer Methods for Real-Time Investigation of the Holliday Junction Resolution by GEN1
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Relating energy level alignment and amine-linked single molecule junction conductance.

M Dell'Angela1, G Kladnik, A Cossaro

  • 1CNR-IOM Laboratorio Nazionale TASC, Trieste, Italy.

Nano Letters
|June 29, 2010
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Summary

This study links electronic energy levels at metal-molecule interfaces to single-molecule conductance. Higher occupied molecular orbital (HOMO) alignment on gold surfaces predicts molecular junction transport properties.

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Area of Science:

  • Surface Science
  • Molecular Electronics
  • Spectroscopy

Background:

  • Understanding metal-molecule interfaces is crucial for molecular electronics.
  • Electronic energy level alignment dictates charge transport properties.
  • Directly comparing spectroscopic measurements with transport data is challenging.

Purpose of the Study:

  • To establish the relationship between electronic energy level alignment and single-molecule junction transport.
  • To investigate how different gold surface facets (Au(111) vs. Au(110)) affect this relationship.
  • To validate theoretical calculations against experimental data.

Main Methods:

  • Photoemission spectroscopy (ultraviolet and resonant X-ray) to measure highest occupied molecular orbital (HOMO) positions relative to the Fermi level.
  • Scanning tunneling microscope (STM)-based break-junction measurements for single-molecule conductance.
  • First-principles calculations incorporating self-energy corrections.

Main Results:

  • A strong correlation was found between the HOMO-Fermi level difference and conductance for molecules on Au(111).
  • Experimental results agree well with computed quasiparticle energies.
  • Lower-coordinated gold atoms on Au(110) caused a shift in the HOMO level away from the Fermi level, impacting conductance.

Conclusions:

  • This work provides the first direct experimental comparison of spectroscopic energy level alignment and single-molecule transport data.
  • Surface atomic arrangement significantly influences electronic structure and transport at metal-molecule interfaces.
  • The findings support the use of theoretical calculations for predicting molecular junction behavior.