▁towns ▁in ▁Bul dh ana ▁district ▁Category : T al uk as ▁in ▁Mah ar as ht ra <0x0A> </s> ▁Th in - film ▁thick ness ▁mon itors , ▁de position ▁rate ▁controllers , ▁and ▁so ▁on , ▁are ▁a ▁family ▁of ▁instruments ▁used ▁in ▁high ▁and ▁ult ra - high ▁vac u um ▁systems . ▁ ▁They ▁can ▁measure ▁the ▁thick ness ▁of ▁a ▁thin ▁film , ▁not ▁only ▁after ▁it ▁has ▁been ▁made , ▁but ▁while ▁it ▁is ▁still ▁being ▁depos ited , ▁and ▁some ▁can ▁control ▁either ▁the ▁final ▁thick ness ▁of ▁the ▁film , ▁the ▁rate ▁at ▁which ▁it ▁is ▁depos ited , ▁or ▁both . ▁ ▁Not ▁surprising ly , ▁the ▁devices ▁which ▁control ▁some ▁aspect ▁of ▁the ▁process ▁tend ▁to ▁be ▁called ▁controllers , ▁and ▁those ▁that ▁simply ▁monitor ▁the ▁process ▁tend ▁to ▁be ▁called ▁mon itors . ▁ ▁Most ▁such ▁instruments ▁use ▁a ▁quart z ▁cry stal ▁micro bal ance ▁as ▁the ▁sensor . ▁ ▁Opt ical ▁measurements ▁are ▁sometimes ▁used ; ▁this ▁may ▁be ▁especially ▁appropriate ▁if ▁the ▁film ▁being ▁depos ited ▁is ▁part ▁of ▁a ▁thin ▁film ▁optical ▁device . ▁ ▁A ▁thick ness ▁monitor ▁measures ▁how ▁much ▁material ▁depos ited ▁on ▁its ▁sensor . ▁ ▁Most ▁de position ▁processes ▁are ▁at ▁least ▁somewhat ▁direction al . ▁ ▁The ▁sensor ▁and ▁the ▁sample ▁generally ▁cannot ▁be ▁in ▁the ▁same ▁direction ▁from ▁the ▁de position ▁source ▁( if ▁they ▁were , ▁the ▁one ▁closer ▁to ▁the ▁source ▁would ▁shadow ▁the ▁other ), ▁and ▁may ▁not