▁include ▁systems ▁to ▁detect ▁when ▁the ▁sample ▁has ▁been ▁th inned ▁to ▁a ▁sufficient ▁level ▁of ▁optical ▁trans par ency . ▁ ▁I on ▁et ch ing ▁ ▁I on ▁et ch ing ▁is ▁a ▁s put ter ing ▁process ▁that ▁can ▁remove ▁very ▁fine ▁quantities ▁of ▁material . ▁This ▁is ▁used ▁to ▁perform ▁a ▁finishing ▁pol ish ▁of ▁spec im ens ▁pol ished ▁by ▁other ▁means . ▁I on ▁et ch ing ▁uses ▁an ▁in ert ▁gas ▁passed ▁through ▁an ▁electric ▁field ▁to ▁generate ▁a ▁pl asma ▁stream ▁that ▁is ▁directed ▁to ▁the ▁sample ▁surface . ▁Acc eler ation ▁energ ies ▁for ▁g ases ▁such ▁as ▁arg on ▁are ▁typically ▁a ▁few ▁kil ov ol ts . ▁The ▁sample ▁may ▁be ▁rot ated ▁to ▁promote ▁even ▁pol ishing ▁of ▁the ▁sample ▁surface . ▁The ▁s put ter ing ▁rate ▁of ▁such ▁methods ▁is ▁on ▁the ▁order ▁of ▁tens ▁of ▁mic rom eters ▁per ▁hour , ▁limit ing ▁the ▁method ▁to ▁only ▁extremely ▁fine ▁pol ishing . ▁ ▁I on ▁et ch ing ▁by ▁arg on ▁gas ▁has ▁been ▁recently ▁shown ▁to ▁be ▁able ▁to ▁file ▁down ▁M T J ▁stack ▁structures ▁to ▁a ▁specific ▁layer ▁which ▁has ▁then ▁been ▁atom ically ▁resolved . ▁The ▁T EM ▁images ▁taken ▁in ▁plan ▁view ▁rather ▁than ▁cross - section ▁reve al ▁that ▁the ▁M g O ▁layer ▁within ▁M T Js ▁contains ▁a ▁large ▁number ▁of ▁gra in ▁boundaries ▁that ▁may ▁be ▁dimin ishing ▁the ▁properties ▁of ▁devices . ▁ ▁I on ▁mill ing ▁