表面重构课 薛其坤课件.ppt

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1、表面重构清华大学物理系薛其坤OutlineBriefintroductionBondingatasurface2.PrincipleofSurfaceReconstruction3.ReconstructionElements3.1Chains3.2Dimers(trimers)3.3Adatoms4.Typicalreconstructionsurfaces4.1MetalSurface4.2InsulatorSurface4.3SemiconductorSurface5.Summary1.Briefint

2、roductionTwotypesofatomicrearrangementsRelaxationReconstructionWood：A(hkl)-nm--BExamples1.Si(111)-p2x22.Si(111)-3x3-30º-Ga3.Si(100)-c(2x2)-O常用的研究手段：LEED,RHEED,STM,琼角XRD等BondingatasurfaceWhy原子间的键合（1）Surface:heterogeneousatmicroscopicscale（2）Surfaceproces

3、ses:adsorption/desorption,diffusion,reaction……外来原子与表面原子的相互作用/键合金属键共价键（Si，Ge，GaAs/InAs/AlAs,GaN,ZnO…）离子键（MgO,Al2O3,NaCl…)孤立分子中原子间的成键固体中原子间的成键psahb化学键局域化学键的角度去理解晶体中原子的键合OrbitalsandBondingOne-ElectronPicture1023-bodyproblemTight-BindingApproacha,i(x)=

4、aia(x–Ri)(LCAO)电子的原子能级固体中能带b,jHab(Ri,Rj)–Sab(Ri–Rj)bj=0LöwdinTheorem：Sab(Ri–Rj)=abijH(x)=(x)晶体中单电子的薛定谔方程两个轨道间的成键双原子分子（H2或者LiH）H11–H12–S12H*11–S*12H22–()()12=0a,i(x)=aia(x–Ri)LiHs(H)s(Li)AtomicOrbitalsandTheirInteractionANB8-N三个假

5、定：（1）s,Px,PyandPz（2）Sab(Ri–Rj)=abij（3）最近邻和次近邻相互作用，且Hab(Ri,Rj)=Hab(Ri–Rj)d=Ri–RjpdnnnLöwdinTheorem：Sab(Ri–Rj)=abijInteratomicMatrixElementsVssVspVppVppVabk=abkh2md2ss=1.32sp=1.42pp=2.22pp=0.63SlaterandKoster,Phys.Rev.94.1498(1954)Bo

6、ndingHybridsElectronsarelocalizedbetweenatomsalongthebondingdirectionAtomicorbitalsalongthebondingdirectionsp3杂化sp2杂化sp杂化AB(1)同原子内轨道相互作用1A(1B)2A(2B)(2)原子之间轨道相互作用34465^ahbsp3Hirabayashi,J.Phys.Soc.Jpn.27.1475(1969)DanglingBondsABSi(111)DBB问题：切

7、断一个公价键时，两个电子如何分配？cost=3KJ2DwavevectorJ’对电子态的影响对电子态的影响br=sp3–2DB=sp3+2(110)KJ2DwavevectorJ’2.PrincipleofReconstructionThesurfacestructureobservedwillbethelowestfree-energystructurekineticallyaccessibleunderthepreparationconditions.Si(111)-2x1→7x7

8、byannealingGe(111)-2x1→c(2x8)byannealingBothoftheabovearestableuponsubsequentcoolingindicatethatthefirst2x1structureobtainedbylow-temperaturecleavageisonlyalocalstablestructure,butnotthelowestfree-ener