omega filter
omega filter
One of the in-column type energy filters, which is installed between the intermediate and projector lenses in a TEM. The filter (spectrometer) is composed of four electromagnets and has a shape of the letter “omega.” Thus, this is called “omega filter.” Its energy dispersion is approximately 1 μm/eV for a 200 kV electron beam. The omega filter is used to date to acquire filtered (zero-loss) images, energy-loss images and zero-loss CBED patterns.
Schematic of the action of the omega filter and an acquired spectrum.
A blue curve shows the trajectory of electrons passing through the optical axis with an energy E. A red curve shows the trajectory of electrons suffered by energy dispersion with an energy loss of ⊿E. When the optical plane at which energy dispersion (S) is created is projected onto the screen, the intensity distribution against energy losses, or an energy spectrum is observed.
When the achromatic plane (A), at which energy dispersion disappears, is projected onto the screen, an image without energy dispersion is observed. In this case, if the energy slit placed on plane S is inserted to pass no energy-loss electrons, a zero-loss image (so called “filtered image”) is acquired. If the energy slit selects energy-loss electrons, an energy-loss image is obtained.
(a) Energy spectrum of Si acquired at an accelerating voltage of 200 kV. (b) Line profile of the energy spectrum. ZLP is the zero-loss peak. P1 is a peak of a plasmon loss electrons (Ep = 16.7 eV). P2, P3… are peaks produced by multiple scattering of the plasmon. Weak and broad peaks L2,3 are the spectra due to excitation of inner-shell electrons.
![cubic-BN [110]のCBED図形(加速電圧100kV)](./glossary_file/file/omega_filter_cbed.png)
CBED patterns of cubic-BN [110] acquired at an accelerating voltage of 100 kV. The two patterns were taken by projecting the CBED patterns formed at the achromatic plane onto the screen. (a) CBED pattern without using the energy slit (unfiltered pattern). (b) Filtered CBED pattern by selecting zero-loss energy with the energy slit. The graphs below the patterns are line profiles of each line A-B.
In the unfiltered pattern at the left, the patterns inside the CBED disks are unclear. To the contrary in the filtered pattern at the right, where the lost energies approximately more than 10 eV are cut, the patterns in the disks are clearly seen. The energy filter is indispensable for quantitative analysis of CBED patterns.
TEM images of ice-embedded liposome acquired at an accelerating voltage of 200 kV, taken by projecting the images formed at the achromatic plane onto the screen. (a) Conventional image without using the energy filter (unfiltered image). (b) Zero-loss image using the energy filter (filtered image).
It is seen that the image contrast of liposome is enhanced in the filtered image (b).
Schematic of the action of the omega filter and an acquired spectrum.
A blue curve shows the trajectory of electrons passing through the optical axis with an energy E. A red curve shows the trajectory of electrons suffered by energy dispersion with an energy loss of ⊿E. When the optical plane at which energy dispersion (S) is created is projected onto the screen, the intensity distribution against energy losses, or an energy spectrum is observed.
When the achromatic plane (A), at which energy dispersion disappears, is projected onto the screen, an image without energy dispersion is observed. In this case, if the energy slit placed on plane S is inserted to pass no energy-loss electrons, a zero-loss image (so called “filtered image”) is acquired. If the energy slit selects energy-loss electrons, an energy-loss image is obtained.
(a) Energy spectrum of Si acquired at an accelerating voltage of 200 kV. (b) Line profile of the energy spectrum. ZLP is the zero-loss peak. P1 is a peak of a plasmon loss electrons (Ep = 16.7 eV). P2, P3… are peaks produced by multiple scattering of the plasmon. Weak and broad peaks L2,3 are the spectra due to excitation of inner-shell electrons.
CBED patterns of cubic-BN [110] acquired at an accelerating voltage of 100 kV. The two patterns were taken by projecting the CBED patterns formed at the achromatic plane onto the screen. (a) CBED pattern without using the energy slit (unfiltered pattern). (b) Filtered CBED pattern by selecting zero-loss energy with the energy slit. The graphs below the patterns are line profiles of each line A-B.
In the unfiltered pattern at the left, the patterns inside the CBED disks are unclear. To the contrary in the filtered pattern at the right, where the lost energies approximately more than 10 eV are cut, the patterns in the disks are clearly seen. The energy filter is indispensable for quantitative analysis of CBED patterns.
TEM images of ice-embedded liposome acquired at an accelerating voltage of 200 kV, taken by projecting the images formed at the achromatic plane onto the screen. (a) Conventional image without using the energy filter (unfiltered image). (b) Zero-loss image using the energy filter (filtered image).
It is seen that the image contrast of liposome is enhanced in the filtered image (b).
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