How to Use RHEED Converter X

Table of Contents

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Brief Introduction

RHEED Converter X is an application software which converts a RHEED (Reflection High-Energy Electron Diffraction) pattern into a 2-dimensional reciprocal lattice image. It is useful for surface reconstruction study with RHEED. This software can read any kind of image which is supported by MacOS X (TIFF(8/16 bits), JPEG, PICT, BMP, PDF etc.). The converted image can be exported as a TIFF, JPEG or PNG image file.

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Reading a RHEED Pattern

When you launch the application, the following blank window will appear.

There are several ways to read a RHEED pattern image into the document.

The last two methods create a new document and read the image file into the document. Not all image file types are supported by the last two methods, while the first 5 methods support all available image file types. After reading a RHEED pattern, document window may be as follows.

You can change the image scale by dragging the scale slider or enter magnification value into the text field beside the slider. The slider only moves from 0.2 to 2 (exactly, 1.995), however, you can enter the value between 0.1 and 4 into the text field. There are green lines and circles in the pattern, which are called guide lines. Usage of the guides are explained later. If the color is not suitable for the pattern, you can change it by clicking on the guide color box.

Before adjusting the guides, you should specify a screen tilt angle (in degrees). The tilt angle is defined as shown in the figure below. The tilt effect is very small, so that you don't need to consider much about it If the angle is less than few degrees.

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Adjusting Guides and the Pattern

As shown in the above figure, RHEED pattern always has an incline. At first, you should correct the inclination of the image using the rotation slider or the text field beside the slider. The slider only moves from -5 to 5 degree, however, you can enter the value between -180 and 180 into the text field. You can use the vertical guide line for the adjustment as shown below.

As written in the above figure, there are 5 guide lines and markers:

Shadow Edige Line
It corresponds to a shadow edge position of the RHEED pattern. The shadow edge is usually vague, so that it is difficult to decide exact position from the pattern. You can move this guide line vertically.
Vertical Line
It corresponds to the vertical (surface normal) direction. This line should pass through the specular (00) spot. You can move this guide line horizontally.
Origin Marker
It is a cross point of the above two guide lines. You can move this marker anywhere.
Specular Spot Marker
It corresponds to the specular spot position. You should place it on the specular spot exactly as possible. This marker moves only vertically.
0-th Laue Zone
It corresponds to the 0-th Laue zone if the pattern was taken under symmetric incident condition. This guide can not be dragged directly, however, you can use it as a guide when you determine the shadow edge position.

After all adjustment, it should be as follows.

Next, you should enter glancing angle of incident electron and/or camera length of the pattern. Respective units for those values are degrees and pixels. If the camera length is not known, you should prepare a reference pattern which glancing angle is known (you can simulate RHEED patterns and Kikuchi lines using KikuchiLines X application which is provided by the same author). Using the reference pattern, the camera length is automatically calculated from the glancing angle and the radius of the 0-th Laue zone. Once you obtain the camera length, you don't need to bother with those values. You can store the value as a default as explained later in the preferences section.

If you lost guides (moved away from the pattern), ctrl-click (or right mouse button) on the pattern and choose [Reset Guide Lines] menu.

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Conversion Conditions

Before conversion, you should choose conversion conditions. One is a vertical expansion factor and the other is a magnification factor. Under a normal RHEED condition, converted RHEED pattern is shrank vertically. The vertical expansion factor is used to compensate the shrinkage. If you set 2 to the vertical expansion, x:y axis length ratio of a converted pattern is 1:2. It is also possible to use fractions such as 2.5.

The magnification factor is related to an image resolution. If you set it as 1, a converted image width is almost the same as an original pattern. If you are intended to print out the converted image, it is recommended to increase magnification factor such as x4.

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Conversion

Press [Convert] button at the bottom right to start conversion. During the conversion, [Convert] button changes to [Stop] button which is used to abort calculation. After the conversion, resulting image is obtained as follows.

The converted image can also be scaled with the scale slider and the text field as same as the original pattern. As shown in the above figure, reciprocal axes are drawn on the image. You can turn on/off axes by the [Show Axes] checkbox.

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Point Markers

RHEED Converter X can show you corresponding points in the original pattern and converted pattern. If you cmd-click (hold down the command key and click) on somewhere on the original or converted pattern, clicked point and corresponding point in the other image is marked by red colored circles. Shift-cmd-click can append another marker. The marker color and its size (radius in pixels) can be changed by the marker color box and the text field beside it. [Clear All] button is used to clear markers. The figure below shows point markers on the pattern.

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Exporting Images

You can export original patterns and converted images using the following 3 ways.

You can choose whether guide/axes and/or markers to be included in an exported image. For copy&paste and drag&drop, those choices can be changed in the preferences settings explained in the next section. For save, those choices are in the save dialog.

There are two ways to access [Save Original/Converted Pattern As] menu, one is under the [File] menu and the other is in the context menu (the menu displayed when you ctrl-click or click right mouse button on the image). You can choose a file format (TIFF/JPEG/PNG) and their options in the save dialog. Please note that TIFF and PNG format does not lose any information (loss-less), while JPEG loses some. On the other hand, generated file size is very large in TIFF/PNG format, while it is several tenth of them in JPEG format (depending on its quality).

This application does not have a functionality to print out documents.

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Preferences

You can change default settings (camera length etc.) in the preferences panel. Choose [RHEED Converter X]-[Preferences] menu to open the panel as shown below.

Meanings of settings in conversion and display sections are the same as a document settings explained above.

In addition to conversion and display settings, there is ‘On Copy or Drag an Image’ section. In this section you can choose whether guides/axes (for original/converted pattern) and markers should be included in a copied image.

If you click [Read Settings from Current Document] button, current (frontmost) document settings are imported. If you click [Revert to Factory Settings] button, all setting are revert to initial settings.

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