Veeco Dimension 3100, Руководство пользователя

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Scanning Tunneling Microscopy (STM)
STM-Specific Information and Operations
182 Dimension 3100 Manual Rev. D
11.3.2 Fine Points of STM Operation
Getting the best images on NanoScope requires a good interface between sample and tip,
reasonable vibration isolation, and proper settings in the Computer Workstation menus. This
section provides greater detail on the operation of the STM.
11.3.3 STM Operating Modes
The two operating modes available on the NanoScope STM are selected with the Data type option
in the Channel panel (see Figure 11.3a ). Height data reflects the change in tip position required to
maintain a constant tunneling current. The DSP senses the tunneling current, calculates the
difference from the desired tunneling current, and determines the voltage that must be applied to
the piezo tube to keep the tunneling current constant. Due to the known characteristics of the
piezoelectric material, the change in voltage applied to the piezo tube translates directly to a change
in distance. This distance data is recorded throughout the scan and displayed on the screen as the
“height” of the sample.
Figure 11.3a Typical STM Channel 1 Control Panel Parameters
Current data is a measure of the tunneling current at each point tested on the sample. The DSP
measures the voltage drop across a resistor in series with the tip and calculates the tunneling current
as the tip scans the surface of the sample. The tunneling current at each data point is recorded and
displayed on the screen.
The two scan modes (height and current) require subtle changes in the menu parameters to operate
effectively. The parameter changes also affect the application of the two modes. To operate
effectively in collecting height data, the tip must closely track the sample surface. The gains must
be maximized to force the piezo to respond quickly to the variations in the sample surface. The
height mode is used for most applications. Conversely, the gains must be very low to keep the piezo
from responding while collecting current data. After engaging, the tip scans the surface of the
sample with very little variation in the piezo height. This constant height provides a reference from
which to measure and record the fluctuations in the tunneling current. The current mode is most
useful for imaging atoms with relatively small scan sizes.
Channel 1
Data type:
Z range:
Line direction:
Scan line:
Highpass filter:
Lowpass filter:
Height
30 nm
Retrace
Main
Off
Off
Realtime Planefit:
Offline Planefit:
Main
Main