The interfacial structure plays a crucial role in controlling the
growth of epitaxial film. However, it is still a formidable task to
observe the interface structure at the atomic scale, because the detected
signals from the interface become very weak due to the strong attenuation
and decoherence when the incident wave passes through the films. With
the advent of scanning tunneling microscopy (STM), significant progress
has been made in observing the interface structure of thin films.
Many studies have demonstrated the typical Si(111)-7×7 superstructure
below the metal films in the past. Although the 7×7 superstructures
are visible, the 12 Si adatoms in the unit cells can not be resolved.
Hence, imaging the 7×7 superstructures below thin films at the atomic
scale has not been achieved. In this work, we have grown the Cd epitaxial
films with high quality on Si(111)-7×7 substrate, and realized the
imaging of interface structure of Cd(0001) at atomic scale by using
low temperature scanning tunneling microscopy. Under
国家自然科学基金资助项目(10974156)
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Figure 1
(Color online) Morphology of the epitaxial Cd films. (a) Cd films at 3.5 monolayers, 500 nm×500 nm, 4.0 V; (b) Cd films at 10.0 monolayers, 500 nm×500 nm, 4.0 V, the red dashed line marks the position of Si step; (c) the cross-sectional line profile along the black line in (b).
Figure 2
(Color online) The transparences of Cd film under different bias voltages. (a) STM image of the Cd film under 1.5 V, 20 nm×20 nm; (b) STM image of the Cd films under 0.1 V, 30 nm×30 nm; (c) STM image of a pristine Si (111)-7×7 surface, 30 nm×30 nm, 1.9 V; (d) a close-up view of (b), 10 nm×10 nm, 0.1 V; (e) and (f) are the Fourier transform of (b) and(c), respectively.
Figure 3
(Color online) Difference of the lateral resolutions for the even and odd monolayers of Cd films. The vertical boundary is a Si step. (a) STM image under 1.0 V. 24 nm×24 nm; (b) STM image under 0.1 V. 24 nm×24 nm; (c) the d
Figure 4
Difference in the surface roughness of the even and odd monolayers of Cd. (a) STM image of a Cd island crossing a Si step at high bias,
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