Electron lenses are the magnetic equivalent of the glass lenses in an optical microscope and to a large extent, we can draw comparisons between the two. A strong magnetic field is generated by passing a current through a set of windings. This field acts as a …

Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through a specimen to form an image. The specimen is most often an ultrathin section less than 100 nm thick or a suspension on a grid.

The condenser lenses in the TEM serve much the same function as that of the condenser in the light microscope. They gather the electrons of the first crossover image and focus them onto the specimen to illuminate only the area being examined.

TEM involves changing magnification or focus; we use electron lenses to magnify and focus the electron beam, the images, and the DPs. These factors are critical in the principal functions of a TEM: imaging, diffraction, and analysis which, respectively, comprise the next three parts of this book. An aperture is used to select different electron ...

In the traditional TEM mode, the first two condenser lenses (C1, C2) are adjusted to illuminate the specimen with a parallel beam of electrons, typically several micrometers across at reasonable magnifications (20,000 –100,000 ). As shown in Figure 9.1, the C1 lens first forms an image of the gun crossover. In

The objective lens/stage system is the heart of the TEM. The critical region usually extended over less than 1 cm along the length of the column. Here is where all the beam-specimen interactions take place and here we create the bright-field, dark-field images, and selected-area diffraction patterns (SAD) that are the fundamental TEM operations.

Principles of TEM Operation: 1. When you want to look at the diffraction pattern (i.e., the back focal plane of the objective lens), you put an SAD aperture into the image plane of the objective lens. 2. When you want to view an image (i.e., the image plane of the objective lens), you insert an aperture into the

TEMs are generally constructed with the radiation source at the top of the instrument: the source is generally situated at the bottom of LMs. This, of course, is a trivial difference. TEMs are operated at high vacuum (since the mean free path of electrons in air is very small) so most specimens (biological) must be dehydrated (and dead!).

Techniques that demand conical illumination in TEM : What should be done if the beam on the TEM screen could not be found? Caustic in TEM : Lenses Equipped with Stigmators : HT Centering of TEM Operation : Techniques needing parallel illumination in TEM : Aberrations in the Electromagnetic Round lenses : contrast mechanisms of the TEM images

All the magnetic lenses in a TEM have wide ranges of focal length and magnification. The final lens (or lenses), the projector, focuses the magnified image onto a phosphorescent screen at the bottom of the lens column. This screen is coated with a layer of crystals that respond to electron bombardment by emitting visible light, thus converting ...