u um ▁se al ▁of ▁sufficient ▁quality , ▁when ▁inserted ▁into ▁the ▁stage . ▁The ▁stage ▁is ▁thus ▁designed ▁to ▁accommod ate ▁the ▁rod , ▁placing ▁the ▁sample ▁either ▁in ▁between ▁or ▁near ▁the ▁objective ▁l ens , ▁dependent ▁upon ▁the ▁objective ▁design . ▁When ▁inserted ▁into ▁the ▁stage , ▁the ▁side ▁entry ▁holder ▁has ▁its ▁tip ▁contained ▁within ▁the ▁T EM ▁vac u um , ▁and ▁the ▁base ▁is ▁presented ▁to ▁atmosphere , ▁the ▁air lock ▁formed ▁by ▁the ▁vac u um ▁rings . ▁ ▁Insert ion ▁procedures ▁for ▁side - entry ▁T EM ▁hold ers ▁typically ▁involve ▁the ▁rotation ▁of ▁the ▁sample ▁to ▁trigger ▁micro ▁switch es ▁that ▁initi ate ▁ev acu ation ▁of ▁the ▁air lock ▁before ▁the ▁sample ▁is ▁inserted ▁into ▁the ▁T EM ▁column . ▁ ▁The ▁second ▁design ▁is ▁the ▁top - entry ▁holder ▁consists ▁of ▁a ▁cart ridge ▁that ▁is ▁several ▁cm ▁long ▁with ▁a ▁bore ▁d ril led ▁down ▁the ▁cart ridge ▁axis . ▁The ▁spec imen ▁is ▁loaded ▁into ▁the ▁bore , ▁possibly ▁using ▁a ▁small ▁sc rew ▁ring ▁to ▁hold ▁the ▁sample ▁in ▁place . ▁This ▁cart ridge ▁is ▁inserted ▁into ▁an ▁air lock ▁with ▁the ▁bore ▁per pend icular ▁to ▁the ▁T EM ▁opt ic ▁axis . ▁When ▁se aled , ▁the ▁air lock ▁is ▁manip ulated ▁to ▁push ▁the ▁cart ridge ▁such ▁that ▁the ▁cart ridge ▁falls ▁into ▁place , ▁where ▁the ▁bore ▁hole ▁becomes ▁aligned ▁with ▁the ▁beam ▁axis , ▁such ▁that ▁the ▁beam ▁travel s ▁down ▁the ▁cart ridge