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Scanning Tunneling Microscopy (STM)

STM-Speciﬁc Information and Operations

180 Dimension 3100 Manual Rev. D

8. After a clean image has been obtained, it can be saved onto disk with the Capture command

in the Capture menu (or click on the Capture icon). The Capture command saves the

current scan image (or the next image if any changes have been made in the STM control

panel) into the Capture directory. The Capture Filename command can be used to define a

custom filename or the captured file will be named with the concatenation of a date/time

stamp. In either case, a three-digit suffix which incrementally increases after each capture

operation is appended to the filename. If the date/time stamp is used, a file captured at 3:32

p.m. on July 31 would be assigned the file name 07311532.001. A second file captured the

same minute would be named 07311532.002.

9. Some simple filtering operations can improve the look of the captured image. Enter the

Offline mode and select the image to work on by clicking on it in the file list. There are a

number of image processing options available in the Modify menu. Click on Modify in the

menu bar to display the menu. The simplest way to remove high frequency noise is with the

lowpass filter.

Pull-down the Modify menu and click on the Lowpass command to apply the lowpass ﬁlter to the

image and redraw it on the display monitor. Successive Re-execute clicks will continue to ﬁlter and

redraw the image. The entire ﬁltering operation can be undone with the Undo command, the

ﬁltered image can be saved, or the Quit command will return the system to the Modify menu.

There is also the option of changing the display with the Color table, Color contrast, or Color

offset parameters.

Note: The Z range parameter will have no effect if the Plot type parameter in the

Top View menu is set to Equal area.

11.3 STM-Speciﬁc Information and Operations

The NanoScope STM is a digitally-controlled instrument capable of producing high resolution,

three-dimensional images. The sample is held in position while a piezoelectric crystal in the form

of a cylindrical tube scans the sharp metallic probe over the surface in a raster pattern. The digital

signal processor (DSP) calculates the desired separation of the tip from the sample by sensing the

tunneling current ﬂowing between the sample and the tip. The bias voltage applied to the sample

encourages the tunneling current to ﬂow. The DSP completes the digital feedback loop by

outputting the desired voltage to the piezoelectric tube. The NanoScope STM can be operated in

two modes. In one case the feedback gains are set high, the tunneling tip closely tracks the sample

surface, and the variation in the tip height required to maintain constant tunneling current is

measured by the change in the voltage applied to the piezo tube. In the other case, the feedback

gains are set low, the tip remains at a nearly constant height as it sweeps over the sample surface,

and the tunneling current is imaged. This section provides greater insight into the operation of the

STM.

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