How Does Tungsten Needle to Obtain a Precise Tip Radius?

Tungsten needle is a kind of tungsten rod with sharp ends. Usually, it is made of high-density tungsten metal so that it can be widely used in many fields. For its production, it adopts powder metallurgy, but this method is not enough when very sharp tips are required. 

As one of the core components of the field emission electron microscope, the performance of the field emission electron source determines the main electron optical performance parameters in the field emission electron microscope, which includes the emission angular current density of the electron gun, the total emission current of the electron beam and the stability of the electron beam, etc.

In order to meet the requirements of high brightness, large beam current, good beam stability, and small electron energy dispersion of the field emission electron source, it is necessary to sharpen the tip of the single crystal tungsten wire of the field emission electron source. Generally, the tip radius is required between 0.5-1.0μm.

The researchers with the patent number CN102339704B proposed a preparation method for obtaining a field emission electron source needle with a radius between 0.5-1.0 μm. Its specific operation is as follows:

1) Pour a certain amount of sodium hydroxide powder into a beaker with a balance, and then add a certain amount of pure water to prepare a corrosion solution with a concentration of 3-5mol/L; 2) Put the prepared corrosion solution from the U-shaped One end of the tube is poured into the U-shaped tube, and an electrode is inserted; 3) Fix the ceramic seat welded with the single crystal tungsten wire to the fixed frame with the micrometer head, and adjust the micrometer head so that the single crystal tungsten wire is immersed in the container. Put a certain distance below the liquid surface of one end of the U-shaped tube containing the corrosive liquid, and put an electrode under the liquid surface of the other end of the U-shaped tube containing the corrosive liquid; 4) Connect the connecting wire with the electrode clip and the switch to the The signal source is connected, connect one electrode clamp to the electrode on the ceramic seat for welding single crystal tungsten wire, and connect the other electrode clamp to the electrode at the other end of the U-shaped tube; 5) Turn on the signal source and adjust the signal source required for corrosion Parameters; 6) Start the switch on the connecting wire to start corrosion; 7) After the corrosion is over, turn off the switch; 8) Adjust the micrometer head so that the tungsten wire on the filament ceramic seat completely exits the corrosion solution.

Compared with other manufacturing methods, the AC electrochemical corrosion method is easier to be adopted by everyone, mainly because it has many controllable parameters, high corrosion precision, and good product stability.

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