研究人员发现新纳米级电现象

At the scale of the very small, physics can get peculiar¹（特殊的，罕见的） . A University of Michigan biomedical engineering professor has discovered a new instance of such a nanoscale phenomenon---one that could lead to faster, less expensive portable diagnostic devices and push back frontiers（尖端科学，边疆） in building micro-mechanical and "lab on a chip" devices. In our macroscale world, materials called conductors effectively transmit electricity and materials called insulators²（绝缘体） or dielectrics（电介质） don't, unless they are jolted³ with an extremely high voltage. Under such "dielectric breakdown⁴（介质击穿） " circumstances, as when a bolt of lightening hits a rooftop, the dielectric (the rooftop in this example) suffers irreversible damage.

This isn't the case at the nanoscale, according to a new discovery by Alan Hunt, an associate professor in the Department of Biomedical Engineering. Hunt and his research team were able to get an electric current to pass nondestructively through a sliver⁵ of glass, which isn't usually a conductor.

A paper on the research is newly published online in Nature Nanotechnology.

"This is a new, truly nanoscale physical phenomenon," Hunt said. "At larger scales, it doesn't work. You get extreme heating and damage.

"What matters is how steep the voltage drop is across the distance of the dielectric. When you get down to the nanoscale and you make your dielectric exceedingly（非常，极其） thin, you can achieve the breakdown with modest voltages that batteries can provide. You don't get the damage because you're at such a small scale that heat dissipates（浪费，驱散） extraordinarily⁶ quickly."

These conducting nanoscale dielectric slivers⁷ are what Hunt calls liquid glass electrodes, fabricated（制造，组装） at the U-M Center for Ultrafast Optical Science with a femtosecond（飞秒） laser, which emits light pulses that are only quadrillionths（千万亿分之一） of a second long.

The glass electrodes are ideal for use in lab-on-a-chip devices that integrate multiple laboratory functions onto one chip just millimeters or centimeters in size. The devices could lead to instant home tests for illnesses, food contaminants（污染物） and toxic⁸ gases. But most of them need a power source to operate, and right now they rely on wires to route this power. It's often difficult for engineers to insert these wires into the tiny machines, Hunt said.

"The design of microfluidic（微流体） devices is constrained⁹（强迫，驱使） because of the power problem," Hunt said. "But we can machine electrodes right into the device."

Instead of using wires to route electricity, Hunt's team etches（蚀刻，铭记） channels through which ionic fluid can transmit electricity. These channels, 10 thousand times thinner than the dot of this "i," physically¹⁰ dead-end at their intersections¹¹ with the microfluidic or nanofluidic channels in which analysis is being conducted on the lab-on a-chip (this is important to avoid contamination). But the electricity in the ionic channels can zip through the thin glass dead-end without harming the device in the process.

This discovery is the result of an accident. Two channels in an experimental nanofluidic device didn't line up properly, Hunt said, but the researchers found that electricity did pass through the device.

"We were surprised by this, as it runs counter to accepted thinking about the behavior of nonconductive materials," Hunt said. "Upon further study we were able to understand why this could happen, but only at the nanometer scale."

As for electronics applications, Hunt said that the wiring necessary in integrated circuits（集成电路） fundamentally limits their size.

"If you could utilize¹² reversible（可逆的） dielectric breakdown to work for you instead of against you, that might significantly change things," Hunt said.