Secondary electrons: The extranuclear electrons of the sample atoms that are bombarded out and leave the sample surface under the action of the incident electron beam are called secondary electrons.The secondary electrons are generally within the depth range of 5~10nm of the surface layerlaunchIt is very sensitive to the surface morphology of the sample, so it can display the surface morphology of the sample very effectively.The energy of the secondary electron is low, generally not more than 50eV.Most secondary electrons have only a fewElectron voltEnergy.
Secondary electron(Secondary electrons), also known as secondary electrons, is used to describe the mainradiationLow energy products emitted after irradiationElectronics。The main radiation can beenergyOfIons、Electronicsorphoton。Secondary electron belongs toSecondary emission（en:Secondary emission）One of.
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This is a vacuumfree electron。becauseNucleusAnd outer layervalence electronThe binding energy of is very small, so the electrons in the outer layer are easier to separate from the atom and ionize the atom.When an incident electron with high energy is injected into the sample, many free electrons can be generated. 90% of these free electrons are valence electrons from the outer layer of the sample atom.
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The energy of the secondary electron is low, generally not more than 50eV.Most secondary electrons have only a fewElectron voltEnergy.
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Electron in solidInelastic mean free diameter(inelastic mean free path) is generally universal, that is to say, it is not related to any material.For metal, the distance is usuallynanometer；For insulators, at tens of nanometers, the smaller the distance, the higher the measurement accuracy.For low energy electrons (<5 eV), there is a longer mean free path.
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The secondary electrons are generally emitted from the surface layer within the depth range of 5~10nmsurface topography It is very sensitive, so it can display the surface morphology of the sample very effectively.
But the yield of secondary electrons andAtomic numberThere is no obvious dependency between them, so it cannot be usedcomponent analysis。[1]
Secondary electron avalanche: whenInitial avalancheWhen the anode is developed, the initial electronAvalancheThe electrons in the anode run quickly to neutralize the electricity.The left positive ions as positive space charges distort and strengthen the electric field behind, and emit a lot of photons to the surrounding.These photons cause light dissociation in the nearby gas and generate secondary electrons in space.They form a new electron avalanche, called secondary electron avalanche, under the effect of the distorted and strengthened electric field of the positive space charge[2]。
The secondary electron image mainly reflects the morphological characteristics of the sample surface at about 10nmContrastIt is the shape contrast, which is formed mainly by the inclination of the sample surface relative to the incident electron beam.[2]
If the sample surface is smooth and flat (invisible features), no contrast will be formed;For the sample with a certain surface morphology, its morphology can be seen as a convex tip, step, pit and other details composed of many surfaces with different degrees of inclination. Different parts of these details emit different numbers of secondary electrons, resulting in contrast.
The secondary electron image has high resolution, no obvious shadow effect, large field depth and strong stereoscopic effectscanning electron microscopeThe main imaging methods of (especially suitable for the observation of the morphology of rough sample surface)life sciencesAnd other fields have extensive applications
