Beam brightness

Equations 4a and 5a both show that exposure time can be shortened by increasing the beam brightness, or decreasing the spherical aberration Cs. By plotting these equations in normalized form in Figure 1, absolute pixel... 

Do you realize what s in your drinking water he asked Tom. Before Tom could answer, he continued Let me demonstrate. First he fdled a glass of water from the kitchen faucet, then he produced an electrical device that had a pair of probes and a light bulb. It resembled a standard conductivity tester. He inserted the probes into the water and the bulb immediately beamed brightly. Next the salesman poured some water from a jar labeled distilled water into another glass. This time when he inserted the probes into the water, the bulb did not hght. 

The cathode emits electrons that are accelerated towards the anode with a defined voltage, typically 50-30,000 V. There are basically two types of electrodes thermionic cathodes (tungsten or LaBs (lanthanum hexaboride)) and field emission cathodes. The Wehnelt cylinder controls the current density and brightness of the electron beam. Brightness is defined as current per unit area normal to the given direction, per unit solid angle, and a criterion for beam quality. 

Several different types of diffraction condition are used to characterise radiation damage. These are achieved by tilting the specimen with reference to the Kikuchi pattern. These include dynamical two-beam , bright-field kinematical and weak-beam conditions - see Jenkins and Kirk for a full description. Under dynamical two-beam conditions, small dislocation loops located close to foil surfaces exhibit black-white contrast (Fig. 9.3), and their symmetry can be used to determine the Burgers vectors and habit-planes. 

Fig. 19. Metadislocations in a -Al-Pd-Mn at a low magnification, (a) Under bright-fleld Lane conditions along the (010) zone axis, (b) Under two-beam bright-field conditions using the (006) reflection imaged...

Figure 6.7 Cross-sectional g = 1100 two-beam bright-field TEM micrograph near the [1120] zone axis of a GaN film grown on an LAO substrate.

In classical TEM, the electron beam is stationary and the image is formed using the transmitted beam (bright-field TEM or TEM-BF) or one of the diffracted beams (dark field or TEM-DF). 

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