▁Electron . ▁ ▁Com ponents ▁ ▁A ▁T EM ▁is ▁composed ▁of ▁several ▁components , ▁which ▁include ▁a ▁vac u um ▁system ▁in ▁which ▁the ▁electrons ▁travel , ▁an ▁electron ▁emission ▁source ▁for ▁generation ▁of ▁the ▁electron ▁stream , ▁a ▁series ▁of ▁elect romagnet ic ▁l enses , ▁as ▁well ▁as ▁electro static ▁pl ates . ▁The ▁latter ▁two ▁allow ▁the ▁operator ▁to ▁guide ▁and ▁manipulate ▁the ▁beam ▁as ▁required . ▁Also ▁required ▁is ▁a ▁device ▁to ▁allow ▁the ▁insert ion ▁into , ▁motion ▁within , ▁and ▁removal ▁of ▁spec im ens ▁from ▁the ▁beam ▁path . ▁Im aging ▁devices ▁are ▁subsequently ▁used ▁to ▁create ▁an ▁image ▁from ▁the ▁electrons ▁that ▁exit ▁the ▁system . ▁ ▁V acu um ▁system ▁To ▁increase ▁the ▁mean ▁free ▁path ▁of ▁the ▁electron ▁gas ▁interaction , ▁a ▁standard ▁T EM ▁is ▁ev acu ated ▁to ▁low ▁press ures , ▁typically ▁on ▁the ▁order ▁of ▁ 1 0 − 4 ▁Pa . ▁The ▁need ▁for ▁this ▁is ▁two fold : ▁first ▁the ▁allow ance ▁for ▁the ▁voltage ▁difference ▁between ▁the ▁c ath ode ▁and ▁the ▁ground ▁without ▁generating ▁an ▁arc , ▁and ▁second ly ▁to ▁reduce ▁the ▁collision ▁frequency ▁of ▁electrons ▁with ▁gas ▁atoms ▁to ▁neg lig ible ▁levels — this ▁effect ▁is ▁character ized ▁by ▁the ▁mean ▁free ▁path . ▁T EM ▁components ▁such ▁as ▁spec imen ▁hold ers ▁and ▁film ▁cart rid ges ▁must ▁be ▁rout in ely ▁inserted ▁or ▁replaced ▁requiring ▁a ▁system ▁with ▁the ▁ability ▁to ▁re - ev acu ate ▁on ▁a ▁regular