Verlag des Forschungszentrums Jülich
JUEL-4033
The clean Ni3A1(100) surface
The LEED pattern of clean Ni3A1(100) Shows a (1 x 1) structure .
STM images of the
Ni3A1(100) surface display flat and large terraces (500 - 1000 A) separated by steps with
a step height of 3 .5 A which corresponds to the lattice constant of Ni3A1 and represents
a double atomic step. This suggests that different terraces have always the Same termination.
Co/Ni3Al(100)
At low coverage (0 .1 ML) and 300 K, the cobalt deposited an the Ni3Al(100) surface
Shows a two-dimensional growth mode. For deposition of 0.3 ML the nucleation takes
also place in the second layer . After deposition of 3 .5 ML Co, the surface consists of Co
islands with a mean diameter of ti 901 Annealing at 700 K leads to the growth of large
terraces of fcc-Co which are arranged with the (100) plane parallel to the (100) surface of
the Substrate. Co is stable an Ni3A1(100) up to 750 K when it Starts to diffuse into the
substrate. At 1100 K, Co is disappeared completely from the surface via diffusion into
the substrate .
A1203/Ni3Al(100)
At room temperature oxygen adsorption an Ni3A1(100) leads to the formation of a thin
amorphous Al-oxide (a-A1203 ) layer (- 5Ä) . Oxidation at 1100 K leads to formation of a
well ordered δ-A1203 film with a thickness of - 101 The STM images of the completely
oxide-covered surface exhibit hexagonal superstructures with lattice constants of 18, 24
and 54 Ä. The band gap of A1203 formed an Ni3A1(100) amounts for the amorphous
film to ti 3.2 and to - 4 .3 eV for the well ordered A1203 film, respectively and both are
strongly diminished with respect to the bulk values.
Co/A1203/Ni3A1(100)
Co deposited at room temperature an a A1203 film, which was grown an Ni3A1(100)
at 1100 K, Shows a three dimensional (Volmer-Weber) growth mode. After a nominal
deposition of 30 A the 3D cobalt clusters have a mean diameter of 70 A and a roughness
of ti 10 Ä . Annealing at 700 and 900 K leads to a coalescence of the Co clusters, and to
a gradually diffusion of Co through the oxide into the Substrate . After annealing at 1000
K the entire surface of alumina is Co free.
A1203/CoAl(100)
Oxygen adsorption at 300 K leads to the formation of an amorphous A1203 film an
CoAl(100) . Annealing at temperatures between 800 - 1000 K induces a phase transformation
from a-A1203 into the θ-A1203 phase, which exhibits a (2x1) structure with
respect to the Substrate . After annealing at temperatures > 1200 K a transition to αA1203
occurs, while above 1300 K the decomposition and removal of the oxide film from
the surface is observed.
Costina, Ioan
The oxidation of the (100) surface of the intermetallic alloys Ni3Al and CoAl and the growth of Co on the clean and oxidized N3Al(199) surface
X, 152 S., 2003
The aim of this work was the preparation and characterization of thin Al-oxide films an
the (100) surface of the intermetallic compounds Ni3A1 and COAT, as well as the study of
Co growth an the clean and oxidized Ni3A1(100) surface. The films were characterized by
Auger electron spectroscopy (AES), Low Energy Electron Diffraction (LEED), Electron
Energy Loss Spectroscopy (EELS) and Scanning Tunneling Microscopy (STM) .
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