Everyone　familiar　with　two-dimensional　(2D)　materials　is　aware　of　fluorophlogopite　mica　(FM),　which　has　an　atomic-level　flat　surface　that　provides　an　ideal　platform　for　the　growth　of　2D　materials.　Since　it　has　been　demonstrated　that　the　alkali　metal　ions　(AMI)　can　aid　in　the　growth　of　large-sized　2D　materials　by　chemical　vapor　deposition　(CVD)　in　recent　years,　it　became　a　major　mystery　whether　FM　which　contains　AMI　benefits　from　them　in　the　preparation　of　2D　materials　by　CVD,　too.　In　this　article,　we　dispelled　this　ambiguity　and　discovered　that　temperature　is　the　key　for　FM　as　an　AMI　source　to　boost　the　growth　of　large-sized　2D　materials.　We　carried　out　variable　temperature　experiments　and　found　that　FM　can　indeed　be　incorporated　into　the　growth　of　large-sized　2D　materials　as　an　AMI　source　at　high　temperatures　and　successfully　obtained　the　highly　crystalline　MoO2　with　a　larger　size　compared　to　those　without　FM.　This　finding　is　of　great　importance　to　the　understanding　of　the　growth　mechanism　of　FM　for　2D　materials　by　CVD　and　to　better　exploit　its　role　in　the　growth　of　2D　materials.　©　2022