These false-color SEM images reveal microscopic flower structures created by manipulating a chemical gradient to control crystalline self-assembly.
Credit: Wim L. Noorduin, Harvard University
Imagine peering into a microscope and finding yourself in a garden.
That's the case at Harvard School of Engineering and Applied Sciences, where researchers have found a way to shape microscopic crystals into complex and often beautiful structures.
Inspired by coral reefs, seashells and other naturally occurring complex mineral structures, postdoctoral fellow Wim L. Noorduin and Harvard colleagues have been researching ways to manually recreate similar designs.
These "flowers" were created by mixing barium chloride and sodium silicate, also known as waterglass, in a beaker of water. The resulting reaction also combines with carbon dioxide in the air to create crystals made of barium carbonate in the water.
Noorduin found that as the crystals self-assembled, he could control their shape, size and direction of growth by altering the temperature, the amount of carbon dioxide allowed into the reaction and the acidity of the water.
Increasing the carbon dioxide levels creates the broad, flat leaves, for example. Fluctuating the acidity level creates the ruffled wave in the petals.
The curved petals, slender stems and jagged thorns formed by the carbonate-silica crystals as they grew demonstrate the effectiveness of Noorduin's technique. The team was able to create the structures on glass slides and metal plates as well, and even grew a "garden" of flowers in front of the Lincoln Memorial imprinted on the back of a penny.
The images were taken with a scanning electron microscope, which uses electrons to create images of microscopic images. The color was added digitally.
"When you look through the electron microscope, it really feels a bit like you’re diving in the ocean, seeing huge fields of coral and sponges … Sometimes I forget to take images because it's so nice to explore," Noorduin said in Harvard's press release.
Crystal manipulation has more applications than just the aesthetic. Aside from the valuable insight into the way silicon-based structures are formed in nature, this technique can be used in nanotechnology fields such as optics and electronics.
Noorduin's findings follow a similar discovery from Harvard biologist Howard Berg, who found that certain bacterial colonies take intricate geometric shapes in response to concentrations of chemicals around them.
Noorduin's paper, "Rationally Designed Complex, Hierarchical Microarchitectures," was published in the journal Science on May 17.