lock s ▁to ▁allow ▁for ▁insert ion ▁of ▁the ▁spec imen ▁holder ▁into ▁the ▁vac u um ▁with ▁minimal ▁loss ▁of ▁vac u um ▁in ▁other ▁areas ▁of ▁the ▁mic ros cope . ▁The ▁spec imen ▁hold ers ▁hold ▁a ▁standard ▁size ▁of ▁sample ▁grid ▁or ▁self - support ing ▁spec imen . ▁Standard ▁T EM ▁grid ▁sizes ▁are ▁ 3 . 0 5   mm ▁diameter , ▁with ▁a ▁thick ness ▁and ▁mesh ▁size ▁r anging ▁from ▁a ▁few ▁to ▁ 1 0 0   μ m . ▁The ▁sample ▁is ▁placed ▁onto ▁the ▁mes hed ▁area ▁having ▁a ▁diameter ▁of ▁approximately ▁ 2 . 5   mm . ▁Us ual ▁grid ▁materials ▁are ▁co pper , ▁mol y b den um , ▁gold ▁or ▁plat in um . ▁This ▁grid ▁is ▁placed ▁into ▁the ▁sample ▁holder , ▁which ▁is ▁pa ired ▁with ▁the ▁spec imen ▁stage . ▁A ▁wide ▁variety ▁of ▁designs ▁of ▁stages ▁and ▁hold ers ▁exist , ▁depending ▁upon ▁the ▁type ▁of ▁experiment ▁being ▁performed . ▁In ▁addition ▁to ▁ 3 . 0 5   mm ▁gr ids , ▁ 2 . 3   mm ▁gr ids ▁are ▁sometimes , ▁if ▁rarely , ▁used . ▁These ▁gr ids ▁were ▁particularly ▁used ▁in ▁the ▁min eral ▁sciences ▁where ▁a ▁large ▁degree ▁of ▁t ilt ▁can ▁be ▁required ▁and ▁where ▁spec imen ▁material ▁may ▁be ▁extremely ▁rare . ▁Electron ▁transparent ▁spec im ens ▁have ▁a ▁thick ness ▁usually ▁less ▁than ▁ 1 0 0   nm , ▁but ▁this ▁value ▁depends