| Density of States imaging |
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| STM | |
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As long as measured in STM current is determined by
the tunneling processes through tip-sample surface gap its value
depends not only on the barrier height but on the electron density of
states also. Accordingly obtained in STM images are not simply images
of sample surface relief (topography), these images can be hardly
affected by the density of electronic states distribution over the
sample surface. Good example of Local Density of States (LDOS)
influence on the STM image is well-known image of highly oriented
pyrolitic graphite (HOPG) atomic lattice. Only half atoms are visible
in STM. Similar case is image of GaAs atomic lattice.
LDOS determining can also help to distinguish chemical nature of the surface atoms. LDOS acquisition is provided simultaneously with the STM images obtaining. During scanning the Bias Voltage is modulated on the value dU, the modulation period is chosen to be much shorter than the time constant of the feedback loop in the STM. Suitable modulation of tunnel current dI is measured, divided by dU and presented as LDOS image. On Example the topography and LDOS image of HOPG sample are presented. References
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