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Last spring, students in EP 415 unwrapped a new passion in nanoengineering: holographic chocolate.

Tasked with devising a protocol to give chocolate an iridescent shimmer, nanoengineering and optical engineering students Janine Dias, Samuel Sheeder, and Emma McMillan let their knowledge of lens fabrication and light waves shine.

Though the project initially seemed like they'd bitten off more than they could chew, the students quickly realized that their courses had given them the perfect recipe for the project.

"A hologram is just an image that's formed by the interference of light," Dias shrugged. "When we read the underlying principles of it, we realized this is actually relevant to our major."

The students used diffraction grating to achieve the desired holographic effect.

Diffraction grating requires etching a repeating pattern of hills and valleys onto a surface.

The depth of this textured pattern intercepts and reflect waves light, causing certain wavelengths to appear and create an iridescent shimmer.

"It's just very captivating because when you look at that chocolate and see the rainbow, there are no colors transferred onto the chocolate," Sheeder explained.

"It's just a slit diffraction pattern cut into the chocolate that's manipulating the light in the room."

Over the span of three weeks, the students tackled the project from three key objectives: creating a silicon wafer, processing the wafer to be food safe, and tempering the chocolate to take the mold.

Using equipment in Rose's Micro-Nanoscale Device and Systems (MiNDs) clean room laboratory, Sheeder took the lead on creating the silicon wafer.

He used a plasma etch tool to create the diffraction grating, based on the team's calculated etch rate and material needed.

Sheeder then used a nanoimprint machine - or, as he described it, a "high-tech panini press" - to press the diffraction grating into plastic.

The project brought Sheeder's path deliciously full-circle: in using the plasma etch, he learned to operate the vacuum pump valves, and last summer, Sheeder completed an internship with Leybold, the oldest vacuum pump company in the world.

Once the mold was made, McMillan was charged with making it food safe. Working in the food science laboratory in the New Academic Building, McMillan thoroughly sanitized the mold.

For McMillan, a now-senior from Sheridan, Indiana, chocolate has molded her journey.

She attended Operation Catapult in high school, where one of her favorite projects involved converting an old 3D printer into a 3D chocolate printer.

"It's a fun full-circle thing because the 3D-printing chocolate is what made me want to come to Rose and the hologram chocolate is just the reason why I love Rose so much," she said.

Dias was also surprised at how the project melted different aspects of her life together.

"As a double major (nanoengineering and optical engineering), sometimes it is a little difficult to see how I could use skills from both my majors in a project or job in the future," she said.

"This really showed the overlap between the physics of light that I learned in optical engineering curriculum and the clean room skills I've been learning in my nanoengineering (engineering physics) courses."

Dias's task was to temper the chocolate so that it developed the crystallization structure necessary to make the diffracted hologram visible to human eyes.

The team had to create the holographic chocolate on the spot during their project demo period, and the process had to be repeatable; they had to create five functioning diffraction molds. The team ultimately created a tasty triumph, reframing setbacks they faced along the way into even sweeter success.

They had originally aimed to only refract green light, but when they struggled to hit their target with the diffraction grating, they realized that a slight tweak to their calculations enabled to refract several color wavelengths.

They also broke one of their wafers, which turned out to be one of McMillan's favorite parts of the process.

"I've never seen a broken wafer, and I think that was really cool getting to see how that looks and see those actual wells," she said.

Sheeder, McMillan, and Dias cooked up a unique project, unwrapping hands-on experience and a pretty sweet application of knowledge to mix into their future careers.

Their holographic chocolate project provided them with the perfect ingredients to thrive in optical and nanoengineering - and yes, they did get to eat the chocolate.

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