Electron microscopes are great for magnification but they tend to destroy or damage what they are looking at. Similar magnification should be possible using a much lower-energy, gentler beam of helium atoms and recording how they are scattered by a sample. Up to this point only 1% of helium atoms can be reflected and focused from thin film silicon.
Vázquez de Parga and his team found they could avoid surface bumps by depositing the lead onto the silicon surface at low temperatures between -173 and -133°C. The end result is a perfectly smooth lead film that can act as an almost flawless mirror. The surface is atomically flat, more than 90% of the film is exactly the same thickness, down to the level of individual lead atoms. It can focus more than 15% of incoming helium atoms into a tight beam, and Vázquez de Parga hopes to increase this proportion to 40%.
Bill Allison at Cambridge University, UK, leads a team experimenting with thin silicon mirrors to focus beams of helium. “[This work] represents a key step forward in producing a device to focus helium atoms,” he says.
“The remaining step is to combine the high reflectivity with a carefully deformed surface in order to create a focused atomic spot. That is still quite a challenge.”