What determines the spatial resolution of an SEM? o Even though the electron beam can be focus to a small size,the reaction volume is the real factor that counts. Understanding the dependence of reaction volume is a key. 16
What determines the spatial resolution of an SEM? • Even though the electron beam can be focus to a small size, the reaction volume is the real factor that counts. • Understanding the dependence of reaction volume is a key. 16
p.142 in the textbook Fr(Df)= do do tand C Incident beam Incident beam Depth of field: The range of position for an object in which image sharpness does not change. do:resolution do do Relationship between depth of field and convergence angle a 17
Incident beam 𝜶 𝒅𝟎 𝑭𝒇 Incident beam 𝜶 𝒅𝟎 𝑭𝒇 Relationship between depth of field and convergence angle 17 𝐹𝑓(𝐷𝑓) = 𝑑0 𝑡𝑎𝑛α ≈ 𝑑0 α p.142 in the textbook d0 : resolution Depth of field: The range of position for an object in which image sharpness does not change
D,:depth of field Surface of solar cell (0.15~0.30)n OM Df= (N.A.)M (uum) Depth of Field Ranges Low NA High NA Object Plane SEM Depth of Field Figure 1 000×T0.0dm
18 Df：depth of field OM SEM Surface of solar cell
Depth of field of SEM and optical microscope Depth of field (um) Magnification SEM Optical 20 5000 5 100 1000 2 1000 100 0.7 5000 20 10000 10 Images taken at low magnification obtain the maximum depth of field. 19
Magnification Depth of field (μm) SEM Optical 20 5000 5 100 1000 2 1000 100 0.7 5000 20 - 10000 10 - Images taken at low magnification obtain the maximum depth of field. Depth of field of SEM and optical microscope 19
Applications of large depth of field Region of slow crack propasation Mechanical 2 cm shaire Chapter 9 Region of rapid failure 38 Fractured surface,Failure analysis. 20
Applications of large depth of field Fractured surface, Failure analysis. 20