Researchers build a heat shield of only 10 atoms thick to protect electronic devices

The excess heat generated by smartphones, laptops and other electronic devices can be troublesome, but beyond that, it contributes to malfunctions and, in extreme cases, can even blow up lithium batteries.

Engineers often insert glass, plastic, or even layers of air as insulation to protect themselves from such malfunctions to prevent heat-generating components, such as microprocessors, from damaging or annoying users.

Stanford researchers have now shown that a few layers of atomically thin material, stacked like sheets of paper at the top of hot spots, could provide the same insulation as a 100 times thicker glass sheet. In the short term, thinner thermal displays will enable engineers to make electronic devices even more compact than today's, said Eric Pop, professor of electrical engineering and lead author of an article published Aug. 16 in Progress of science.

"We are looking at the heat in electronic devices in a totally new way," Pop said.

Detect sound in the form of heat

The warmth we feel from smartphones or laptops is actually an inaudible form of its high frequency. If this sounds crazy, consider the underlying physics. Electricity flows through the wires in the form of electron streams. When these electrons move, they collide with the atoms of the materials through which they pass. At each collision, an electron vibrates an atom, and the more the current circulates, the more collisions, until the electrons beat on the atoms like so many hammers on as many bells – except that this cacophony Vibration moves through the solid material at frequencies well above the threshold of hearing, generating energy that we feel as heat.

Thinking of heat as a form of sound has pushed Stanford researchers to borrow certain principles from the physical world. From his time as a radio DJ at Stanford's KZSU 90.1 FM, Pop knew that the music recording studios were quiet thanks to large glass windows that block out the sound. A similar principle applies to thermal screens in electronics today. If better insulation was their only concern, researchers could simply borrow the principle of the music studio and thicken their thermal barriers. But this would hinder efforts to make electronics thinner. Their solution was to borrow a trick from the owners, who install multi-paned windows – usually layers of air between sheets of glass of different thicknesses – to make the interiors warmer and quieter.

"We adapted this idea by creating an insulator using multiple layers of atomically thin material instead of a thick mass of glass," said postdoctoral researcher Sam Vaziri, the newspaper's lead author.

Atomic thin materials are a relatively recent discovery. Only 15 years ago, scientists were able to isolate certain materials in such thin layers. The first example discovered is graphene, which is a unique layer of carbon atoms and, since its discovery, scientists have researched and experimented with other sheet-shaped materials. The Stanford team used a layer of graphene and three other sheet-like materials, each three atoms thick, to create a four-layer insulator with a depth of only 10 atoms. Despite its fineness, the insulator is effective because the vibrations of atomic heat are damped and lose much of their energy as they pass through each layer.

To make nanoscale heat shields more practical, researchers will need to find a mass production technique to spray or otherwise deposit thin layers of atomic material onto electronic components during fabrication. But the immediate goal of developing thinner insulators suggests a greater ambition: scientists hope to one day control the vibrational energy in materials, as they now control electricity and light. By the time they understand the warmth of solid objects as a form of sound, a new field of phononics is being born, a name borrowing from the Greek root that hides behind telephone, phonograph and phonetic.

"As engineers, we know a lot about how to control electricity.Light improves, but we are just beginning to understand how to handle the high frequency sound that manifests itself under form of heat at the atomic scale, "Pop said.