Gold-Coated Spherical Spheres and the Casimir Force

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As gold-plated spheres are a key component of many optical devices, the ability to precisely control their shape has become critical. Now, scientists have taken one step closer to doing just that by using an atomic force microscope to measure the Casimir force between arbitrarily-shaped objects — something previously impossible with today’s atomic force microscopes.

The team’s experiment used a pair of gold-coated spheres that were positioned about 50 nanometers apart, and they found that the Casimir force between them varied based on their distance. The result is similar to what was reported for a flat surface and a sphere, but it could allow scientists to more accurately predict how the Casimir force would work between a wide range of geometric objects.

Another discovery from the work was that a-CD, an inexpensive and environmentally benign carbohydrate, is an effective host for capturing gold ions in solution. The resulting gold complex, [K(OH2)6][AuBr4](a-CD)2n, can be separated from mixtures of gold and other noble metal salts using simple dilute acid solutions. This gold recovery method demonstrates the usefulness of second-sphere coordination to isolate metals in aqueous solution, and provides a potentially useful procedure for separating precious metals from industrial waste streams.

Lastly, the team found that the amount of spherical gold particles produced by PLA depended on the fluid density. At low densities, the a-CD-Gold complex fragmented to give gold nanonetworks, whereas at higher densities, the liquid gold droplets solidified into submicron-sized particles.