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."