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Windows based STM Control and Image Analysis Programs

largely based on the thesis of Michael J. Krueger

Viewer

FIG. 1. Screen shot of the Viewer application. On the left are two STM images acquired with Viewer, int the center is a menue bar of filtering options, beside it is the control pannel for an evaporator, and on the right are the image acquisition controls.

Viewer is the 16-bit Windows application that controls the STM electronics and allows the user to acquire, view, process, store, and retrieve STM images. Viewer began its life as a MS-DOS program for STM control developed at Harvard by Eric Ganz from 1988–1991. At the University of Minnesota, Viewer was ported to 16-bit Windows by Eric Ganz and Peter Gaard in 1992. In 1993 it was modified to fit within the framework of the Microsoft Foundation Classes (MFC) for the 16-bit version of Microsoft Visual C++, and was further improved by Peter Gaard and Xin Shi. A screen shot of Viewer’s user interface is shown in Fig. 1.

With the departure of Peter Gaard and Xin Shi, Michael Krueger assumed responsibility for the maintenance and improvement of Viewer. He made a number of modifications and improvements to the application. Two of the most significant additions to Viewer were support for the atom tracker and a real-time video display mode for the fast STM instrument.

Analysis

FIG. 2. Screen shot of the Analysis application’s user interface. Three single-image documents and one series document are open. The single-image documents are displayed in custom windows that can be dragged by clicking and holding the mouse on any point in the window. One of the single-image document windows is also displaying a tracking file: the large disk marks the position of the tracked dimer, the small dots mark the most recently visited points, and the scroll bar at the bottom represents the location of the currently displayed dimer position within the tracking file. Toolbars at the top of the main window and within the series document window allow the user to perform common functions with a single mouse click. The status bar at the bottom of the main window automatically displays the size, bias voltage, and position of the mouse pointer for the currently selected image.

With the arrival of 32-bit opporating systems (Windows 95 and NT), and the expanding role of Viewer in image analysis, it became desirable to create a 32-bit annalysis program. It duplicates much of the analysis capabilities of Viewer, adds image rotation and skewing, point FFT filter and the ability to compile, view, and filter series of STM images. Analysis may, someday, take over the acquisition role and completely replace Viewer.

A useful feature of Analysis not found in Viewer is the point fast Fourier transform (FFT) filter. An STM image can be displayed simultaneously in real and reciprocal space. Because the x and y scan speeds are constant during the acquisition of an image, electrical noise and mechanical resonances appear as sharp maxima in the 2-D FFT of the STM height data. In point FFT filter mode, the user is able to remove a noise peak from the reciprocal point by clicking on it with the mouse, causing the filter term [1 + (k/K)²]^-n, where , and K and n are specified by the user, to be subtracted from each point in the reciprocal-space image. Because only the periodic noise components are removed, this filtering technique produces dramatic results that cannot be obtained with simpler low-pass filtering methods.

Fig. 3 STM Movie. The series of images tiled on the left are compiled into a movie on the right. In this format, details of the dynamics are more easily observed.

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