Archive for September 25th, 2008

Ultrasmooth mirrors for a new microscope

September 25, 2008

Nature News reports that a new ultrasmooth mirror could herald the birth of a new microscope:

Electron microscopes can produce highly magnified images, but they have serious drawbacks. The samples must conduct electricity; electrons penetrate into the sample, leading to an image that doesn’t accurately represent the surface; and, worst of all, the very-high-energy electron beams can obliterate the precious samples.

An atomic microscope with a low-energy beam of helium atoms could get around these problems. Neutral helium can bounce off any surface, conducting or insulating, and the beam would be deflected by the electrons at the very edge of the sample, giving a true image of the surface. But an atomic microscope demands a focused beam of helium atoms — and that requires a mirror that reflects the beam with very little scattering of the atoms.

A metal coating would reflect and focus helium much more tightly, but metals grown on silicon tend to clump into islands that scatter incoming atoms in all directions. “The point is to try to reproduce the perfection of the underlying surface,” says Miranda.

Miranda managed this by exploiting a quantum stabilization effect previously seen in ultrathin lead films. For certain thicknesses of lead, the metal’s electrons can sit in very stable energy levels so that, under the right conditions, the surface simply smooths itself out to a continuous thickness.

The resulting 2-centimetre-wide flat mirror is atomically smooth, even after it has warmed up to room temperature, and it can reflect 15% of incoming helium atoms.

A very interesting piece; take a look!