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Spring is a wonderful time to stop and smell the roses, but when those roses are smaller than a speck of dust, the best place to get a whiff is through a scanning electron microscope.
Engineers working with lead researcher Wim Noorduin, a postdoctoral fellow in Harvard’s School of Engineering and Applied Sciences, have designed a way to create nano-scaled sculptures of roses, violets and tulips that are just as pretty as those in your backyard. They’re so small that the researchers were able to carpet the steps of the Lincoln Memorial -- the one embossed on the back of a penny -- with thousands of flowers.
Click through the following images as Noorduin explains his methods for creating such decorative flower arrangements on a nano level.
The technique used to create the flowers is not complicated. “You can do it a kitchen,” Noorduin told Discovery News.
Noorduin explained that he dips a glass slide into a beaker full of silicon, water and minerals such as barium chloride, and the microcrystals begin to form naturally.
“I just wait approximately two hours for the carbon dioxide from the air to diffuse into the water and this triggers an interesting reaction,” he said. “The CO2 reacts with the barium ions to form barium carbonate crystals.”
This reaction is extremely sensitive to the set conditions that exist around the slide. The amount of chemicals used, how much CO2 is allowed into the solution and the set acidity all factor into the final shape of the crystal flowers.
By altering the environment of the crystals, the shape of the flowers can be refined. Growth fronds or petals can be made thicker by lowering the temperature, while a pulse of carbon dioxide can give a rippled contour to the petals and leaves.
“We found that there are two growth regimes and you can deliberately switch between these regimes,” Noorduin said. “In one regime, the growth structures really like the surrounding liquid, so they grow towards it. They literally blossom open and that’s how you grow stem structures, vase structures and coral-like structures.”
He added: “If you lower the pH of the solution, you enter a different growth regime in which the structures don’t like the solution and they curl up towards themselves and bend away from the solution, giving you all kinds of spiral shapes.”
While the structures are growing, Noorduin says that chemical conditions can be modulated. For example, small amounts of carbon dioxide can be allowed to enter, simply by lifting the plate that’s on top of the beaker. “That instantly gives you a reaction on the growth forms. For instance, you can make very controlled ripples,” he said.
Noorduin says that if a stronger burst of carbon dioxide is added, it’s possible to completely split the structures.
“We showed that you can grow a stem-like structure,” he said. “If you add a larger CO2 burst, instead of just forming a ripple, you can completely split them open so that you get a face structure on top of the stem. So you can really make different shapes.”
Noorduin also wanted to see if he could “hierarchically assemble” the structures together, or stack the crystals on top of each other. Active growth sites on the crystal structures can also be used to control the formation of a new structure.
“First, you grow a spiral shape, then you stop the growth of the spiral, take out the sample and place it in a new solution. You’ve now changed the growth condition in such a way that you can grow a coral structure,” he said. “They don’t form randomly on the sample, they form exactly on top of the active growth sites of the previous formed structure."
Therefore, these active growth sites can be used to control the formation of new structures.
Changing the solution means new dyes can be mixed into the solution, bringing color to the flowers. “In the case of the rose structure, I added different dyes to make a green spiral, then added a red rose on top of it,” Noorduin said.
However, electron microscopes only capture images in black and white, so engineers use Photoshop to reestablish color. Although the images you see have been digitally enhanced, Noorduin says he tries to match the colors in Photoshop with the original pigments of the real micro flowers.
Most impressively, Noorduin and his colleagues were able to sprout flowers that appear to be growing out of vases.
“What we do is first grow a vase. Then we coat the active growth sites around the rim of the vase with silicon. Now those growth sites don’t work anymore,” he said. “But it turns out there are still active growth sites inside the vase.”
When the slide is placed into a new solution, Noorduin was able to grow a stem in the middle of this vase. While the stem was growing, he added a CO2 burst by taking off the lid of the beaker. That resulted in the opening of the stems to give a flower-like structure.
“You can grow these flowers on a lot of materials,” he said. “You’re absolutely not restricted to glass slides.”
After publishing their study in the current issue of Science, Noorduin and his colleagues want to improve their models and gather more details. They believe their technology could one day be used in medical sensors, mircoelectronics and new optical materials.
“At this length scale you can have interesting properties with light because light starts to interact with structures on the micrometer scale,” he said. “This might be interesting for catalytic purposes. People are looking into these things.”
In the meantime, Noorduin speaks as if he’s awestruck at the world around him, much like someone who makes a habit of stopping to smell the roses.
“There seems to be so many different and complex shapes in nature, so we were wondering if it was possible to use a very simple method to not only generate these shapes, but to get a very big spectrum of shapes and learn how to control them. That was the motivation of this research.”
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