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Related Concept Videos

Isotopes01:12

Isotopes

64.2K
Elements have a set number of protons that determines their atomic number (Z). For example, all atoms with eight protons are oxygen; however, the number of neutrons can vary for atoms of the same element. The sum of the number of protons and the number of neutrons is the mass number (A). Atoms with the same atomic number but different mass numbers are called isotopes. Elements can have multiple isotopes, for example, carbon-12, carbon-13, and carbon-14.
An element's atomic mass, or weight,...
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Elements: Chemical Symbols and Isotopes02:31

Elements: Chemical Symbols and Isotopes

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A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is used to indicate one atom of mercury (microscopic domain) or to label a container of many atoms of the element mercury (macroscopic domain).
Some symbols are derived from the common English name of the element; others are abbreviations of the name in another language — Latin, Greek or German. For example, the symbol for aluminum (common name)...
125.8K
Isotopes and Radioisotopes01:28

Isotopes and Radioisotopes

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In the early 1900s, English chemist Frederick Soddy realized that an element could have atoms with different masses that were chemically indistinguishable. These different types are called isotopes — atoms of the same element that differ in mass. Isotopes differ in mass because they have different numbers of neutrons but are chemically identical because they have the same number of protons. Soddy was awarded the Nobel Prize in Chemistry in 1921 for this discovery.
An isotope containing...
11.8K
Mass Spectrometry: Isotope Effect01:13

Mass Spectrometry: Isotope Effect

4.3K
Most elements exist in nature as a mixture of isotopes. The isotopes differ in weight due to their respective number of neutrons. The molecular weight of a molecule is different depending on the specific isotope of its elements involved. As a result, the mass spectrum of the molecule exhibits peaks from the same fragment at multiple positions. The positions of these mass signals depend on the mass differences between isotopes. Furthermore, the intensity of these signals is dependent on the...
4.3K
Assembly of the Lipid Bilayer in the ER01:28

Assembly of the Lipid Bilayer in the ER

4.2K
Biological membranes are more than just a barrier separating cell cytoplasm from the outside environment. They are highly dynamic and help maintain the integrity and physiological stability of the cells as well as membrane-bound organelles. Membranes also play vital roles in cell-to-cell and intracellular communication.
A large chunk of any biological membrane is composed of phospholipids. These lipids have a heterogeneous distribution across different subcellular organelles and even between...
4.2K
Asymmetric Lipid Bilayer01:35

Asymmetric Lipid Bilayer

9.8K
Biological membranes show uneven distribution of different types of lipids in the inner and outer layers, resulting in transverse asymmetric membranes. The treatment of the erythrocyte membrane with the enzyme phospholipase confirmed the asymmetric nature of the lipid bilayer. The enzyme hydrolyzes lipids into fatty acids and hydrophilic groups. The phospholipase acts only on the outer layer of the membrane, while the inner layer remains intact. The phospholipase treatment resulted in 80%...
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Lipid Bilayer Experiments with Contact Bubble Bilayers for Patch-Clampers
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Isotope Effect in Bilayer WSe2.

Wei Wu1,2, Mayra Daniela Morales-Acosta2, Yongqiang Wang3,4

  • 1Department of Mechanical Engineering , University of Connecticut , Storrs , Connecticut 06269 , United States.

Nano Letters
|February 13, 2019
PubMed
Summary
This summary is machine-generated.

The study observed an isotope effect in tungsten diselenide (WSe2) monolayers, showing a larger band gap and altered vibrational properties in isotopically pure samples. This highlights the impact of atomic mass on electronic and optical characteristics.

Keywords:
Isotope engineeringRamanband gap engineeringphotoluminescencetransition metal dichalcogenidetungsten diselenide

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Area of Science:

  • Condensed Matter Physics
  • Materials Science
  • Quantum Chemistry

Background:

  • Isotopes, atoms of the same element with different neutron numbers, influence material properties.
  • Transition metal dichalcogenides (TMDs) like MX2 exhibit thickness-dependent characteristics.
  • The isotopic effect in atomically thin TMDs, particularly for phonon-assisted indirect excitonic transitions, remains poorly understood.

Purpose of the Study:

  • To investigate the isotope effect on the electronic and vibrational properties of transition metal dichalcogenides (TMDs).
  • To explore the influence of isotopic composition on phonon-assisted indirect excitonic transitions in bilayer tungsten diselenide (WSe2).

Main Methods:

  • Utilized naturally abundant WSe2 and isotopically pure 186W80Se2 bilayer single crystals.
  • Conducted experiments over a temperature range of 4.4–300 K.
  • Analyzed electronic and vibrational properties, including optical band gap energy and phonon lifetimes.

Main Results:

  • Demonstrated a higher optical band gap energy in isotopically pure 186W80Se2 compared to naturally abundant WSe2 (3.9 ± 0.7 meV).
  • Observed decreased phonon energies in the isotopically pure crystal due to atomic mass dependence.
  • Reported longer E2g and A21g phonon lifetimes in the isotopically pure sample.

Conclusions:

  • The isotopic composition significantly impacts the electronic and vibrational properties of WSe2.
  • The observed changes in band gap energy are attributed to electronic band gap renormalization.
  • This study provides the first observation of the isotope effect in TMDs, offering insights into their fundamental properties.