Scanning electron microscope image system transformation method

Scanning electron microscopy (SEM) is the main tool for observing the microscopic surface morphology of materials. It is mainly composed of a vacuum system, an electron optical system, an image system, and a control system.

Modern scanning electron microscope image display systems and control systems have achieved digitization under PC control, and at the same time, they have added image processing functions, can be easily combined with general-purpose software, and are convenient for editing reports, papers, and information transmission. Scanning electron microscopes for early analog image systems and special computer-controlled digital image systems can be used to digitize analog images or digitize image systems using an external computer image acquisition system.

What is analog image digitization?

It is to get the image analog signal through the analog-to-digital converter (ADC) into data input to the computer for storage, display and processing. The image system made according to this principle is the passive image system we often say. Its advantages: the acquisition card circuit is simple and inexpensive. Disadvantages: It is difficult to install and debug, because it needs to be synchronized with the scanning electron microscope scanning system. Therefore, if you change the internal circuit of the original scanning electron microscope, accidentally it will cause accidents, which will cause flaws in the scanning electron microscope.

In addition, since it cannot be truly synchronized with the scanning electron microscope, the acquired image is deformed, and the most obvious is that the circle becomes an ellipse. At the same time, it cannot be processed in real time. Only when the collected image is stored and processed, can it be output.

What is the digitization of the image system?

The digital scanning system replaces the analog scanning system. The image signal data thus obtained completely corresponds to the sample information on the electron beam scanning point. The image display resolution corresponds to the number of rows and columns scanned by the electron beam on the sample, and the image scanning and The image display is fully digital.

It should be noted that the custom resolution value of a modern digital scanning electron microscope is: 1024×1024, which is an optimal value (taking into account both the acquisition speed and the resolution). This is not the same as the so-called image resolution of a passive image system. concept. We call this kind of system an active image system. This is also the method used for upgrading the scanning electron microscope abroad. Its advantages: high image quality, high speed, no image distortion, etc. The installation is simple because all scanning electron microscopes have an external image control interface reserved. When the external control signal arrives, the internal scanning part is automatically bypassed. The display section is blanked and there is no need to change any internal circuit structure. Disadvantages: The acquisition card circuit is complicated and costly.

In summary, the above describes two methods of scanning electron microscope to reform the image system. The main difference lies in the “passive image system” or “active image system”. The active image system is commonly used in the world in recent years. Because the passive image system is an early image digital transition product, the so-called image resolution is essentially analog signal sampling points, not digital image resolution, poor image quality, and the nominal resolution of the active image system is really Digital image resolution can effectively improve image quality.