Scientists have developed the first low-energy focused ion beam (FIB) microscope that can extract a little more truth from the world of nanomaterials and nanostructures.
"Microscopes don't exactly lie, but their limitations affect the truths they can tell. For example, scanning electron microscopes (SEMs) simply can't see materials that don't conduct electricity very well, and their high energies can actually damage some types of samples," researchers said.
Researchers at the National Institute of Standards and Technology (NIST) have now built the first FIB microscope that uses a lithium ion source.
The team's new approach opens up the possibility of creating a whole category of FIBs using any one of up to 20 different elements, greatly increasing the options for imaging, sculpting, or characterising materials.
Although the new microscope's resolution isn't yet as good as a SEM or a helium ion microscope (HIM), it can image nonconductive materials and can more clearly visualise the chemical composition on the surface of a sample than the higher-energy SEMs and FIBs.
And, by analysing the energy with which the ions scatter, the researchers have shown that the microscope should be able to not only see that adjacent materials are chemically different, but also identify the elements that make them up.
Jabez McClelland and his colleagues at NIST applied Nobel Prize-winning laser cooling techniques to make the first low-energy FIB using lithium ions in 2011.
The new instrument first cools a gas of neutral lithium atoms to a temperature of about 600 microkelvins, just a few millionths of a degree above absolute zero, using lasers and a magneto-optical trap (MOT) to hold the atoms.
Another laser ionises the atoms and then electric fields accelerate them, straightening out their flight and focusing the beam on a target.
The NIST FIB can produce lithium ion beams with energies in the range of 500 electron volts to 5,000 electron volts (compared to about 30,000 electron volts for HIMs.)
The team can reduce the beam's energy even further, but repulsive interaction effects at the source limit how small they can focus the beam when the accelerating field is weaker.
The team demonstrated that their microscope could help to solve a common problem in nanoimprint lithography, a process for stenciling patterns on silicon chips.
