Due to the limitations of the instrument itself, the microscope occasionally "deceives people." For example, electron microscopy does not allow good observation of materials that are not electrically conductive, and its high energy can damage some samples. In an effort to gain more truth from the world of nanomaterials and nanostructures, researchers at the National Institute of Standards and Technology (NIST) have established a low-energy focused ion beam using a lithium-ion source. microscope.
Although the resolution of the new microscope is not as good as that of a scanning electron microscope or a helium ion microscope (HIM), it can more clearly observe the non-conductive material and more clearly observe the chemical composition of the sample surface. By observing the energy of the scattered ions, the researchers can not only distinguish the chemical composition of adjacent materials, but also confirm the element types of different materials.
As early as 2011, Jabez McClelland and his colleagues developed the first low-energy focused ion beam microscope using laser cooling technology. Later, they worked hard to improve the technique to increase the brightness and collimation of the ion beam, ensuring that all ions move in the same direction for better imaging results.
The new instrument captures atoms through a laser beam and a magneto-optical trap, cooling the neutral lithium atomic gas to 600 micro-Kelvin. The laser is then used to ionize the atoms and enter the electric field to accelerate, adjust the direction of flight, and focus the ions into ion beams for the target.
NIST FIB can generate a lithium ion beam with an energy of 500 eV to 5000 eV (the energy of the helium ion beam is about 3000 eV). Researchers say the energy of the ion beam can be reduced to a lower level. However, when the acceleration electric field strength is relatively low, the interaction of the ion source limits the size of the focused ion beam.
In their paper, the researchers showed how this microscope solves some of the common problems in nanoimprint lithography. McClelland said: "In the past, manufacturers had to perform silicon etching, and they must ensure that there is no chemical residue in the space. Usually they use plasma etching to remove residues. But they have to be careful to prevent excessive removal of damaged substrates or chips. Our focus The ion beam microscope can well observe the working condition of the plasma and ensure that the chip is not damaged. Scanning electron microscopy can't do this because it is difficult to observe very little residue, and the high-energy electron beam is likely to cause charging or melting the template. Wait, make the situation worse."
One of the team's plans for the future is to unlock how lithium batteries work by injecting lithium ions into the material to see how they affect battery performance. Some members of the research team also set up their own company to develop low-energy 铯 focused ion beams to achieve single-nanometer milling and engraving functions, and if successful, will be a huge leap in nanomaterial preparation.
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