How can we keep our smart phones, hard drives from overheating?

Andrea Pickel’s CAREER award will help her pinpoint ‘hot spots’ in a nanoscale landscape

The electronic devices that surround us in everyday life—our computer hard drives and smartphones, for example—operate at increasingly high levels of power that flow through increasingly smaller components.

The devices can easily overheat, decreasing their performance, reliability, and longevity. Pinpointing the “hot spots” that cause the overheating has proved elusive in this landscape where key features are measured in mere nanometers.

“What we really need in a lot of these devices is a temperature map with nanoscale spatial resolution, but you also need to measure the temperature in a noninvasive way,” says Andrea Pickel, assistant professor of mechanical engineering at the University of Rochester. “So, the challenge is, how do we get the best of both worlds?”

Pickel believes she has the answer to that question. With the support of a National Science Foundation CAREER award, her lab is adapting, for the first time, a Nobel Prize-winning optical imaging technique to generate accurate, high spatial resolution temperature maps from photons emitted by luminescent nanoparticle coatings placed on the surfaces of nanoscale devices.

The technique could provide an invaluable tool for researchers to determine and address the primary causes of thermal failure associated with different device types and operating modes. This “can ultimately benefit industrial device design and fabrication,” Pickel says.

A non-invasive way to gather accurate temperatures at the nanoscale

Existing nanoscale thermometry techniques place a probe in direct contact with the material. This can alter the temperature of the sample, resulting in less accurate measurements, Pickel says. Meanwhile, the spatial resolution of conventional laser-based thermometry techniques is fundamentally limited by optical diffraction.

To address the problem, Pickel drew inspiration from STED (stimulated emission depletion) microscopy, a technique that revolutionized bioimaging and earned Stefan Hell a share of the Nobel Prize for chemistry in 2014.

STED is a type of “super-resolution” microscopy that bypasses the diffraction limit of light, increasing the resolution of images illuminated by lasers or other light sources.

“I thought it would be really cool if we could do the same thing for thermometry,” Pickel says. STED allows Pickel to place the laser source far enough from the sample material to avoid perturbing the sample, while simultaneously achieving nanoscale spatial resolution.

“You also need some kind of luminescent material that you can apply to the surface of the sample in a continuous layer to map the temperatures,” also without affecting the temperature of the sample material, she says.

In this case, her lab uses upconverting nanoparticles, consisting of a fluoride or an oxide host doped with lanthanide ions. The “upconversion” occurs when two or more photons from the laser are absorbed and converted into one emitted photon with higher energy.

Open-source repository, outreach to students, broadens the impact

The Faculty Early Career Development (CAREER) award is NSF’s most prestigious recognition for early-career faculty members. It provides recipients with five years of funding to help lay the foundation for their future research. It also requires recipients to demonstrate how their research can have a broader impact to benefit society.

Pickel will further the impact of her project by: 

• Creating an open-source hardware repository that provides access to the designs and building instructions for Pickel’s new thermal imaging technique, so other researchers can build the same system for their labs. “There’s a growing community for this,” Pickel says. “There’s really no one so far who has done any open-source project focused on applying optical microscopy to thermal measurements.” Undergraduate researchers in Pickel’s lab will help design, fabricate, and document the custom hardware components.
• Engaging students at a new, all-girls STEM elementary charter school in the Rochester City School District with a demonstration of how light can interact with materials. Members of Pickel’s lab will shine white light consisting of multiple colors on phosphorescent paper. Different filters will then limit the light hitting the paper to one color of the spectrum at time. This will “show that some colors have more energy than others, and if you have enough energy, you can make the paper glow,” Pickel explains. “My students and I will build the educational kits, take them to the school to give presentations, and ultimately donate them to the school.” 

Andrea Pickel will broaden the impact of her CAREER award
with an educational demonstration showing how different colors
of light have different amounts of energy.