In　this　paper,　the　crystallization　along　the　film　thickness　of　amorphous　Ge2Sb2Te5　(a-GST)　films　induced　by　a　single-pulse　ultraviolet　laser　was　investigated　by　using　transmission　electron　microscopy　(TEM)　integrated　with　SAED.　TEM　observations　showed　that　the　crystalline　GST　(c-GST)　was　composed　of　columnar　grains　at　the　top　surface　and　equaixed　grains　inside　the　film.　Moreover,　the　columnar　grains　became　larger　with　the　increase　of　laser　fluence.　A　three-dimensional　finite　element　method　simulation　was　further　used　to　elucidate　the　temperature　field　by　a　nanosecond　excimer　laser　in　the　cross　section　of　the　a-GST　film.　A　big　temperature　gradient　obtained　at　the　top　surface　in　the　cooling　process　caused　the　formation　of　columnar　grains,　while　columnar　grains　were　gradually　substituted　by　small　equaixed　grains　with　the　decrease　of　temperature　gradient　downwards　the　film　interior.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.