For a material located at least in {HEAD ~ an upper layer} of a plurality of materials forming the object, {TAIL ~ the secondary electron yield ratio} can be made nearly unity and appropriate contrast of an obtained image can be provided with minimized influence of charge up 
For a material located at least in { HEAD ~ an upper layer } of a plurality of materials forming the object , { TAIL ~ the secondary electron yield ratio } can be made nearly unity and appropriate contrast of an obtained image can be provided with minimized influence of charge up
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