When measuring optical phonon energy by experiment, optical phonon frequencies are sometimes given in spectroscopic wavenumber notation, where the symbol " ? " represents ordinary frequency ( not angular frequency ), and is expressed in units of units of energy for more details and uses.
22.
When measuring optical phonon energy by experiment, optical phonon frequencies are sometimes given in spectroscopic wavenumber notation, where the symbol " ? " represents ordinary frequency ( not angular frequency ), and is expressed in units of units of energy for more details and uses.
23.
Many models of phonon thermal transport ignores the effects of transverse acoustic phonons ( TA ) at high frequency due to their small group velocity . ( Optical phonon contributions are also ignored for the same reason . ) However, upper branch of TA phonons have non-zero group velocity at the Brillouin zone boundary along the ?-? direction and, in fact, behave similarly to the longitudinal acoustic phonons ( LA ) and can contribute to the heat transport.
24.
The band gap of various semiconductors and semimetals . As outlined above, an efficient pV cell requires a material with an optical phonon mode more energetic than the bandgap, which in turn is much more energetic than the thermal energy at the intended operating temperature ( E _ { p, \ mathrm { O } } \ simeq \ Delta E _ { e, g } \ gg k _ \ mathrm { B } T _ \ mathrm { pV } ).
25.
Early on, while working on optical phonon lifetimes, the basis for his doctoral thesis, he accidentally discovered the white-light supercontinuum laser . " I thought there was something wrong with the experiment, " he said . " For three months I worked to find the source of my error, because what I was seeing just didn't seem possible . " He jokes that he used up a lot of black masking tape trying to seal the spectrograph that he assumed was leaking light.
26.
In general, a material with a first-row element is required to have a highly energetic optical phonon, e . g ., greater than 100 meV . For example, the carbon allotropes ( diamond, graphene, and graphite ) or boron nitride allotropes produce optical phonon modes exceeding 150 meV . However, the high electronegativity of a first-row elements tends to create a very large band gap, as in diamond and the boron nitride allotropes ( band gaps greater than 3 eV ), unless they are sufficiently symmetric, like graphene ( no band gap)
27.
In general, a material with a first-row element is required to have a highly energetic optical phonon, e . g ., greater than 100 meV . For example, the carbon allotropes ( diamond, graphene, and graphite ) or boron nitride allotropes produce optical phonon modes exceeding 150 meV . However, the high electronegativity of a first-row elements tends to create a very large band gap, as in diamond and the boron nitride allotropes ( band gaps greater than 3 eV ), unless they are sufficiently symmetric, like graphene ( no band gap)
