We now know how gold crystals begin to form at atomic scale.
For the first time, scientists have noticed – and filmed! – the first milliseconds of gold crystal formation and found that it is much more complex than previous study suggested. Instead of a single, unchanging motion, the atoms come together and fall apart several times before standing into a crystal.
This discovery affects both materials science and manufacturing, as it strengthens our understanding of how materials come together out of a false mass of atoms.
“As scientists try to control matter at smaller blades to produce new materials and tools, this study helps us to understand just how some of crystals forming, “explained physicist Peter Ercius from the Lawrence Berkeley National Laboratory.
According to the classical understanding of nucleation – the first part of crystal formation, in which atoms begin to self-assemble – the process is very linear. You put together a handful of atoms under the right conditions, and they gradually build up into crystals.
However, this process is not easy to observe. It is a dynamic process that takes place on very small blades, both spatially and temporarily, and often involves a random element. But our technology has grown to the point that we can now see processes at an atomic scale.
Just earlier this year, a team of Japanese scientists revealed that they were able to observe the circulation of salt crystals. Now a team from Korea and America led by engineer Sungho Jeon of Hanyang University in the Republic of Korea has done the same with gold.
On graphene-backed films, the team grew tiny nanoribbons of golden cyanide, using one of the most powerful electronic microscopes in the world to watch it, TEAM I. Berkeley Lab. At speeds of up to 625 frames per second (fps) – extremely fast for an electronic microscope. – TEAM I captured the first milliseconds of nucleation in astonishing detail.
The results were amazing. Gold atoms would coalesce in a crystal arrangement, collapse, and reunite in a different arrangement, repeating the process several times, alternating between non-solid states. smooth and crystalline before stabilizing.
It is not unlike what Japanese scientists saw with the salt crystals, in fact; these atoms, too, alternated between elemental and semi-orderly states before coming together in a crystal. But that process was filmed at 25 fps; the gold atoms were changing much, much faster.
Only a 625 fps detector speed was expected to be captured, according to Ercius.
“Slower views would miss this fast, adaptable process and just see a blur instead of the transitions,” he said.
So what causes it? Heat. Circulation and growth of crystals are exothermic processes, which release energy in the form of heat into their environment. Think of a small teenage bomb. This again melts the crystal arrangements, which try to reformulate.
But the reforming process is not helped by the recurring collisions of incoming atoms that dynamically disturb the atomic accumulation. Eventually, however, the atoms come together in a way that withstands the heat they emit doing so.
And voila! We have a stable gold crystal on which more atoms can build up without falling back into the chaotic state.
“We found that the crystal normalization of gold plates on graphene undergoes reversible structural changes between disorder and crystalline states,” the researchers wrote in their paper.
“Our findings highlight basic mechanisms underlying the nucleation rate of material growth including thin film deposition, interface-induced precipitation, and nanoparticle formation.”
The next step is to develop an even faster detector with the hope of finding even more hidden processes.
The team ‘s research was published in Science.