Dependence of Backscattered Electrons on Atomic Number
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The material contrast, also called atomic number (Z-) contrast, originate from the difference of secondary electrons (SE) or backscattering electrons (BSEs) yields of the chemical elements in the specimen. The spatial resolution of SE mode normally is higher than that of BSE. However, unlike the generation of SEs, the fraction of BSEs produced is highly dependent of the atomic number (Z) as shown in Figure 4801. Table 4801 lists some examples of BSE coefficient of elements in periodic table, generated with incident electron irradiation at voltages from 2 keV to 100 keV.

Emission Coefficients of Backscattering Electrons (η) and Secondary Electrons (δ)

Figure 4801. Schematic shows emission coefficients of backscattering electrons (η) and secondary electrons (δ), depending on atomic number (Z).


Table 4801. Backscattered electron coefficients of elements in periodic table (at 2 keV to 100 keV of incident electron irradiation).
Name Symbol 2 keV 5 keV 10 keV 20 keV 50 keV 100 keV Electron
energy (eV)
11.0079HydrogenH            1s113.5984
24.0026HeliumHe        1s224.5874
36.941LithiumLi          [He] 2s15.3917
49.0122BerylliumBe          [He] 2s29.3227
510.811BoronB          [He] 2s2 2p18.298
612.0107CarbonC            [He] 2s2 2p211.2603
714.0067NitrogenN     [He] 2s2 2p314.5341
815.9994OxygenO      [He] 2s2 2p413.6181
918.9984FluorineF      [He] 2s2 2p517.4228
1020.1797NeonNe    [He] 2s2 2p621.5645
1122.9897SodiumNa      [Ne] 3s15.1391
1224.305MagnesiumMg      [Ne] 3s27.6462
1326.9815AluminumAl      [Ne] 3s2 3p15.9858
1428.0855SiliconSi      [Ne] 3s2 3p28.1517
1530.9738PhosphorusP      [Ne] 3s2 3p310.4867
1632.065SulfurS      [Ne] 3s2 3p410.36
1735.453ChlorineCl      [Ne] 3s2 3p512.9676
1839.948ArgonAr    [Ne] 3s2 3p615.7596
1939.0983PotassiumK      [Ar] 4s14.3407
2040.078CalciumCa      [Ar] 4s26.1132
2144.9559ScandiumSc     [Ar] 3d1 4s26.5615
2247.867TitaniumTi      [Ar] 3d2 4s26.8281
2350.9415VanadiumV     [Ar] 3d3 4s26.7462
2451.9961ChromiumCr      [Ar] 3d5 4s16.7665
2554.938ManganeseMn      [Ar] 3d5 4s27.434
2655.845IronFe      [Ar] 3d6 4s27.9024
2758.9332CobaltCo     [Ar] 3d7 4s27.881
2858.6934NickelNi      [Ar] 3d8 4s27.6398
2963.546CopperCu     [Ar] 3d10 4s17.7264
3065.39ZincZn     [Ar] 3d10 4s29.3942
3169.723GalliumGa     [Ar] 3d10 4s2 4p15.9993
3272.64GermaniumGe     [Ar] 3d10 4s2 4p27.8994
3374.9216ArsenicAs     [Ar] 3d10 4s2 4p39.7886
3478.96SeleniumSe     [Ar] 3d10 4s2 4p49.7524
3579.904BromineBr     [Ar] 3d10 4s2 4p511.8138
3683.8KryptonKr    [Ar] 3d10 4s2 4p613.9996
3785.4678RubidiumRb     [Kr] 5s14.1771
3887.62StrontiumSr     [Kr] 5s25.6949
3988.9059YttriumY     [Kr] 4d1 5s26.2173
4091.224ZirconiumZr      [Kr] 4d2 5s26.6339
4192.9064NiobiumNb     [Kr] 4d4 5s16.7589
4295.94MolybdenumMo     [Kr] 4d5 5s17.0924
43*98TechnetiumTc     [Kr] 4d5 5s27.28
44101.07RutheniumRu     [Kr] 4d7 5s17.3605
45102.9055RhodiumRh     [Kr] 4d8 5s17.4589
46106.42PalladiumPd     [Kr] 4d108.3369
47107.8682SilverAg     [Kr] 4d10 5s17.5762
48112.411CadmiumCd     [Kr] 4d10 5s28.9938
49114.818IndiumIn     [Kr] 4d10 5s2 5p15.7864
50118.71TinSn     [Kr] 4d10 5s2 5p27.3439
51121.76AntimonySb     [Kr] 4d10 5s2 5p38.6084
52127.6TelluriumTe          [Kr] 4d10 5s2 5p49.0096
53126.9045IodineI          [Kr] 4d10 5s2 5p510.4513
54131.293XenonXe        [Kr] 4d10 5s2 5p612.1298
55132.9055CesiumCs          [Xe] 6s13.8939
56137.327BariumBa            [Xe] 6s25.2117
57138.9055LanthanumLa          [Xe] 5d1 6s25.5769
58140.116CeriumCe          [Xe] 4f1 5d1 6s25.5387
59140.9077PraseodymiumPr          [Xe] 4f3 6s25.473
60144.24NeodymiumNd          [Xe] 4f4 6s25.525
61*145PromethiumPm     [Xe] 4f5 6s25.582
62150.36SamariumSm     [Xe] 4f6 6s25.6437
63151.964EuropiumEu     [Xe] 4f7 6s25.6704
64157.25GadoliniumGd     [Xe] 4f7 5d1 6s26.1501
65158.9253TerbiumTb     [Xe] 4f9 6s25.8638
66162.5DysprosiumDy     [Xe] 4f10 6s25.9389
67164.9303HolmiumHo     [Xe] 4f11 6s26.0215
68167.259ErbiumEr     [Xe] 4f12 6s26.1077
69168.9342ThuliumTm     [Xe] 4f13 6s26.1843
70173.04YtterbiumYb     [Xe] 4f14 6s26.2542
71174.967LutetiumLu     [Xe] 4f14 5d1 6s25.4259
72178.49HafniumHf     [Xe] 4f14 5d2 6s26.8251
73180.9479TantalumTa     [Xe] 4f14 5d3 6s27.5496
74183.84TungstenW     [Xe] 4f14 5d4 6s27.864
75186.207RheniumRe     [Xe] 4f14 5d5 6s27.8335
76190.23OsmiumOs     [Xe] 4f14 5d6 6s28.4382
77192.217IridiumIr     [Xe] 4f14 5d7 6s28.967
78195.078PlatinumPt     [Xe] 4f14 5d9 6s18.9587
79196.9665GoldAu     [Xe] 4f14 5d10 6s19.2255
80200.59MercuryHg     [Xe] 4f14 5d10 6s210.4375
81204.3833ThalliumTl     [Xe] 4f14 5d10 6s2 6p16.1082
82207.2LeadPb     [Xe] 4f14 5d10 6s2 6p27.4167
83208.9804BismuthBi     [Xe] 4f14 5d10 6s2 6p37.2856
84*209PoloniumPo     [Xe] 4f14 5d10 6s2 6p48.417
85*210AstatineAt    [Xe] 4f14 5d10 6s2 6p59.3
86*222RadonRn    [Xe] 4f14 5d10 6s2 6p610.7485
87*223FranciumFr    [Rn] 7s14.0727
88*226RadiumRa     [Rn] 7s25.2784
89*227ActiniumAc     [Rn] 6d1 7s25.17
90232.0381ThoriumTh     [Rn] 6d2 7s26.3067
91231.0359ProtactiniumPa    [Rn] 5f2 6d1 7s25.89
92238.0289UraniumU     [Rn] 5f3 6d1 7s26.1941
93*237NeptuniumNp     [Rn] 5f4 6d1 7s26.2657
94*244PlutoniumPu     [Rn] 5f6 7s26.0262
95*243AmericiumAm     [Rn] 5f7 7s25.9738
96*247CuriumCm    5.9915
97*247BerkeliumBk    6.1979
98*251CaliforniumCf    6.2817
99*252EinsteiniumEs   6.42
100*257FermiumFm   6.5
101*258MendeleviumMd  6.58
102*259NobeliumNo   6.65
103*262LawrenciumLr   4.9
Name Symbol 2 keV 5 keV 10 keV 20 keV 50 keV 100 keV Electron
energy (eV)



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