The NIST team took a completely different approach to generating a focused ion beam that opens up the possibility for use of non-contaminating elements. Instead of starting with a sharp metal point, they generate a small "cloud" of atoms and then combine magnetic fields with laser light to trap and cool these atoms to extremely low temperatures. Another laser is used to ionize the atoms, and the charged particles are accelerated through a small hole to create a small but energetic beam of ions. Researchers have named the groundbreaking device "MOTIS," for "Magneto-Optical Trap Ion Source." (For more on MOTs, see "Bon MOT: Innovative Atom Trap Catches Highly Magnetic Atoms," NIST Tech Beat Apr. 1, 2008.)
"Because the lasers cool the atoms to a very low temperature, they're not moving around in random directions very much. As a result, when we accelerate them the ions travel in a highly parallel beam, which is necessary for focusing them down to a very small spot," explains Jabez McClelland of the NIST Center for Nanoscale Science and Technology. The team was able to measure the tiny spread of the beam and show that it was indeed small enough to allow the beam to be focused to a spot size less than 1 nanometer. The initial demonstration used chromium atoms, establishing that other elements besides gallium can achieve the brightness and intensity to work as a focused ion beam "nano-scalpel." The same technique, says McClelland, can be used with a wide variety of other atoms, which could be selected for special tasks such as milling nanoscale features without introducing contaminants, or to enhance contrast for ion beam microscopy. ###
* J. L. Hanssen, S. B. Hill, J. Orloff and J. J. McClelland. Magneto-optical trap-based, high brightness ion source for use as a nanoscale probe. Nano Letters 8, 2844 (2008).
Contact: Mark Bello firstname.lastname@example.org 301-975-3776 National Institute of Standards and Technology (NIST)