Optical Phonons in Single Atom Crystals: Unraveling the Mystery

In summary, while it is commonly believed that optical phonons only exist in crystals with two or more types of atoms in a unit cell, there have been references to optical phonons in single atom crystals, such as silicon. This is due to the fact that even in single atom crystals, the crystal symmetry does not eliminate the possibility of optical transitions. However, the deformation potentials and dipole moments in silicon are very small, resulting in small transition intensities. Additionally, the <111> direction in silicon has two different spacings between atoms, leading to two spring constants and a similar eigenvalue equation as if there were two different masses. This is because the total number of phonon modes is equal to the number of atoms, and the number
  • #1
BeauGeste
49
0
I thought optical phonons only existed in crystals with two or more types of atoms in a unit cell. But I keep reading references of optical phonons in single atom crystals, like silicon.
What's the deal here?
 
Physics news on Phys.org
  • #2
The crystal symmetry, [itex] O_h [/itex] doesn't eliminate the possibility of optical transitions in Si, but the deformation potentials and dipole mements in silicon are very small yeilding quite small transition intensities.
 
  • #3
<111> direction in silicon has two different spacings between atoms and thus two spring constants. The eigenvalue equation sets up the same as if there were two different masses.
 
  • #4
Remember that the total number of phonon modes is equal to the number of atoms. The number of distinct wave-vectors possible is equal to the number of lattice sites. There are therefore a number of different modes at each wavevector equal to the number of atoms per lattice site.

Even in mono-atomic structures, you can have a non-trivial lattice (not a simple cubic) and so have more than one atom per lattice point.
 
  • #5
To put it differently, silicium cristallizes in the diamond lattice. A primitive cell of the diamond lattice contains two atoms. Compare this to some simpler monoatomic lattice, e.g. I_2 (Iodine).
 

1. What are optical phonons?

Optical phonons are vibrations or oscillations in the crystal lattice of a material that are caused by the interaction of light with the atoms. They are also known as lattice vibrations or lattice modes.

2. What are single atom crystals?

Single atom crystals are materials that are composed of a single layer of atoms, commonly referred to as monolayers. They are considered to be two-dimensional materials and have unique properties due to their thinness.

3. How do optical phonons play a role in single atom crystals?

In single atom crystals, the vibrations of the atoms in the crystal lattice are greatly influenced by external factors such as light. These vibrations, known as optical phonons, can affect the electronic and thermal properties of the material, making them important for understanding the behavior of these materials.

4. What techniques are used to study optical phonons in single atom crystals?

Various techniques can be used to study optical phonons in single atom crystals, such as Raman spectroscopy, infrared spectroscopy, and ultrafast laser spectroscopy. These techniques involve shining light onto the material and measuring the changes in the light that are caused by the vibrations of the atoms.

5. Why is understanding optical phonons in single atom crystals important?

Understanding optical phonons in single atom crystals is important because it can provide insight into the unique properties of these materials and their potential applications. It can also help in the design and development of new technologies based on these materials, such as ultra-sensitive sensors, energy-efficient electronics, and advanced optoelectronic devices.

Similar threads

  • Atomic and Condensed Matter
Replies
7
Views
2K
  • Atomic and Condensed Matter
Replies
2
Views
1K
  • Atomic and Condensed Matter
Replies
2
Views
4K
  • Atomic and Condensed Matter
Replies
4
Views
2K
  • Atomic and Condensed Matter
Replies
9
Views
10K
  • Atomic and Condensed Matter
Replies
1
Views
2K
  • Atomic and Condensed Matter
Replies
9
Views
1K
  • Atomic and Condensed Matter
Replies
1
Views
4K
Replies
3
Views
2K
  • Atomic and Condensed Matter
Replies
18
Views
2K
Back
Top