scanning tunneling microscopy (stm)
DESCRIPTION
Scanning Tunneling Microscopy (STM). Primeira Geração. Segunda Geração. Corrente de Tunelamento. d: distância amostra-ponta : constante que depende da altura da barreira de pontecial. Para funções trabalho entre 4eV e 5eV ~1 Å -1. - PowerPoint PPT PresentationTRANSCRIPT
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Scanning Tunneling Microscopy (STM)
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Primeira Geração
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Segunda Geração
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d: distância amostra-ponta: constante que depende da altura da barreira de pontecial
Corrente de Tunelamento
dt eI 2
Para funções trabalho entre 4eV e 5eV ~1Å-1
Aumento de 1Å na distância => em um aumento de aproximadamente uma ordem de magnitude na corrente de tunelamento!
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Modos de Medida
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Clusters de In sobre Si(111)(7x7) Resuloção atômica: NaCl
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Figure 9.5. LEED structure for the same Rh(111)+(3x3)+C6H6-2CO surface.
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STM images of Si(111)-(7x7). Top left: atomic model with adatoms in yellow and rest atoms in blue; the yellow lines delimit a (7x7) unit cell. Center left: constant-current topograph at +2 V bias showing the 12 adatoms per cell.
Top right: adatom surface states between EF and -0.4 eV,
showing an asymmetry between the two halves of the (7x7) unit cell. Center right: rest atom surface states between -0.6 and -1.0 eV.
Bottom: cross-section of atomic model along the long diagonal of the (7x7) unit cell.
(R.M. Tromp, E.J. van Loenen, R.J. Hamers, J.E. Demuth, in "The Structure of Surfaces II", eds. J.F. van der Veen and M.A. Van Hove, Springer-Verlag, Berlin, 1988, p. 282.)
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Também se faz simulação usando espalhamento
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XPS: KE = h – BE
Verificando a composição química
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Mapeamento químico
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Bandas de valência
E(k) de Ag e Au
Na direção L-gamma,
ou seja na direção
(111) do cristal
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Band structure of Cu in some selected high-symmetry directions. Lines: calculation, markers: data from
ARUPS.
An angle-resolved electron analyzer mounted on a two-axis goniometer
Levantamento da
estrutura de bandas
experimental por UPS
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ARUPS: Fotoemissão com resolução angular
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ARUPS: Fotoemissão com resolução angular
Dispersão de um
Estado de superfície
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Estados eletrônicos em superfícies vicinais
Vicinais de Cu(111) e Au(111)
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Preparação das amostras:
v-Cu(111):
• cortadas a partir de um monocristal na forma de barra• orietadas por Laue• polimento mecânico até 0.1 m com pasta de alumínio + eletropolimento• ciclos de sputtering (Ar+@500eV) e annealing (800K)• erro no miscut: melhor que 0.5º
v-Au(111):
• comercial (MaTeck)• ciclos de sputtering (Ar+@500eV) e annealing (800K)• erro no miscut: melhor do que 0.2º
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Superfícies estudadas
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v-Cu(111)
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