EpitaxialGrowthofMetalCyanideNanostructuresfortheMeasurementofCrystalStructurein2DMaterials

Abstract

Thecrystallographicorientationof2Dmaterialsplaysacriticalroleindeterminingtheirpropertiesandperformanceinvariousapplications.However,identifyingthecrystallographicorientationoflarge-area2Dmaterialsremainsasignificantchallengeduetotheirultrathinnature.Here,thisthesisintroducesanovelapproachusingepitaxialmetalcyanidestodeterminethecrystallographicorientationofdiverse2Dmaterials.Twotypesofmetalcyanides,Au1/2Ag1/2CNandAgCN,areusedasvisualmarkerstovisualizethelatticedirectionof2Dmaterials.Diagonal-shapednanocrystalsofAu1/2Ag1/2CNaresynthesizedonpolycrystallinegraphene,providingcrystallographicinformation.Thesynthesisofthesenanocrystalsisachievedthroughadropcastingmethod,offeringasimpleandefficientapproach.EpitaxialAgCNmicrowiresareuniformlydepositedontographene,hBN,MoS2,WS2,andWSe2throughaspincoatingprocesswithin-situheating.Sincespin-coatedmicrowiresarealsoalignedaccordingtothelatticedirectionof2Dmaterialsandcanbeidentifiedbytheconventionalopticalmicroscopy,theycanprovidealargeareavisualizationoflatticestructuresin2Dmaterials.Themainachievementofthisstudyisthatthismethodenableslarge-areacrystallographicmappingofgrainsinpolycrystallinegrapheneandprecisecontroloftwistanglesinvanderWaalsheterostructure.Thisaccomplishmentisattributedtothegrowthcharacteristicsofthespin-coatedmicrowires,characterizedbytheirexceptionalarealdensityanduniformity.Also,theunconventionalliquidphaseepitaxyofmetalcyanideson2Dmaterialsfacilitatesthefacileidentificationofcrystalstructures,offeringvaluableinsightsfortheirreliableproductionandtailoredproperties.|2차원물질은원자수준의얇은두께에도불구하고우수한기계적,화학적,전기적특성을가지고있어,최근반도체와전자기기분야에서신소재로서주목받고있다.그러나,물질특성에큰영향을미치는2차원물질의결정구조를파악하기위해선원자수준의이미징이가능한주사터널링현미경,투과전자현미경과같은이미징도구를필요로하며,이는복잡한시료준비와대면적식별이어렵다는한계점을가지고있다.또한,최근2차원물질을특정비틀림각도에따라수직으로쌓아올린2차원반데르발스헤테로구조체에서지금까지관찰되지않았던다양한양자현상들이발견되고있으며,이는2차원물질의결정방향측정에대한중요성을한층더가중시키고있다.본학위논문에서는,2차원물질의결정방향을더욱쉽고간편하게측정하는방법을보고하고자하며,더나아가이를활용하여대면적다결정그래핀의결정방향및결정립경계면식별과이종접합헤테로구조체를제작에응용하였다.본연구에서사용한두가지의금속사이안화무기물(Au1/2Ag1/2CN,AgCN)은2차원물질의지그재그결정방향에따라자가정렬하는성질을가지고있어,주사전사현미경및광학현미경을통해이를관찰함으로써2차원물질의결정방향을간접적으로측정할수있다.Au1/2Ag1/2CN은간단한드롭캐스팅방법을통해다이아몬드형태의나노물질로그래핀위에합성되며,구조체의축방향이그래핀의결정방향과동일하게합성됨을투과전자현미경을통해식별및관찰하였다.AgCN은마이크로와이어의형태로다양한2차원물질위에합성되며,본연구에서는유기용매를혼합한스핀코팅기술을활용하여균일하고고밀도의마이크로와이어를합성하였다.이렇게합성된균일한고밀도의마이크로와이어는광학현미경으로식별할수있으며,이를이용하여밀리미터영역의대면적에서화학기상증착법으로합성된다결정그래핀의결정방향과결정립경계(grainboundary)를분석하였다. 본학위논문에서는위기술들의원리와결과분석에대해자세히다루었으며,향후잠재력을검증하고자이종반데르발스헤테로구조체제작과같은응용사례를시연및검증하였다.