Breaking the Planck's law, at the nanoscale

Jul 29, 2009 by David L. Chandler
A diagram of the setup, including a cantilever from an atomic force microscope, used to measure the heat transfer between objects separated by nanoscale distances. Courtesy / Sheng Shen

(PhysOrg.com) -- A well-established physical law describes the transfer of heat between two objects, but some physicists have long predicted that the law should break down when the objects are very close together. Scientists had never been able to confirm, or measure, this breakdown in practice. For the first time, however, MIT researchers have achieved this feat, and determined that the heat transfer can be 1,000 times greater than the law predicts.

The new findings could lead to significant new applications, including better design of the recording heads of the hard disks used for computer data storage, and new kinds of devices for harvesting energy from heat that would otherwise be wasted.

Planck's blackbody radiation law, formulated in 1900 by German physicist , describes how energy is dissipated, in the form of different wavelengths of radiation, from an idealized non-reflective black object, called a blackbody. The law says that the relative of radiation at different wavelengths follows a precise pattern that varies according to the temperature of the object. The emission from a blackbody is usually considered as the maximum that an object can radiate.

The law works reliably in most cases, but Planck himself had suggested that when objects are very close together, the predictions of his law would break down. But actually controlling objects to maintain the tiny separations required to demonstrate this phenomenon has proved incredibly difficult.

"Planck was very careful, saying his theory was only valid for large systems," explains Gang Chen, MIT's Carl Richard Soderberg Professor of Power Engineering and director of the Pappalardo Micro and Nano Engineering Laboratories. "So he kind of anticipated this [breakdown], but most people don't know this."

Professor Gang Chen with the vacuum chamber used in this research. Courtesy / Gang Chen

Part of the problem in measuring the way energy is radiated when objects are very close is the mechanical difficulty of maintaining two objects in very close proximity, without letting them actually touch. Chen and his team, graduate student Sheng Shen and Columbia University Professor Arvind Narayaswamy, solved this problem in two ways, as described in a paper to be published in the August issue of the journal Nano Letters (available now online). First, instead of using two flat surfaces and trying to maintain a tiny gap between them, they used a flat surface next to a small round glass bead, whose position is easier to control. "If we use two parallel surfaces, it is very hard to push to nanometer scale without some parts touching each other," Chen explains, but by using a bead there is just a single point of near-contact, which is much easier to maintain. Then, they used the technology of the bi-metallic cantilever from an atomic-force microscope to measure the temperature changes with great precision.

"We tried for many years doing it with parallel plates," Chen says. But with that method, they were unable to sustain separations of closer than about a micron (one millionth of a meter). By using the glass (silica) beads, they were able to get separations as small as 10 nanometers (10 billionths of a meter, or one-hundredth the distance achieved before), and are now working on getting even closer spacings.

Professor Sir John Pendry of Imperial College London, who has done extensive work in this field, calls the results "very exciting," noting that theorists have long predicted such a breakdown in the formula and the activation of a more powerful mechanism.

"Experimental confirmation has proved elusive because of the extreme difficulty in measuring temperature differences over very small distances," Pendry says. "Gang Chen's experiments provide a beautiful solution to this difficulty and confirm the dominant contribution of near field effects to ."

In today's magnetic data recording systems - such as the hard disks used in computers - the spacing between the recording head and the disk surface is typically in the 5 to 6 nanometer range, Chen says. The head tends to heat up, and researchers have been looking for ways to manage the heat or even exploit the heating to control the gap. "It's a very important issue for magnetic storage," he says. Such applications could be developed quite rapidly, he says, and some companies have already shown a strong interest in this work

The new findings could also help in the development of new photovoltaic energy conversion devices to harness photons emitted by a heat source, called thermophovoltaic, Chen says. "The high photon flux can potentially enable higher efficiency and energy density thermophovoltaic energy converters, and new energy conversion devices," he says.

The new findings could have "a broad impact," says Shen. People working with devices using small separations will now have a clear understanding that Planck's law "is not a fundamental limitation," as many people now think, he says. But further work is needed to explore even closer spacings, Chen says, because "we don't know exactly what the limit is yet" in terms of how much heat can be dissipated in closely spaced systems. "Current theory will not be valid once we push down to 1 nanometer spacing."

And in addition to practical applications, he says, such experiments "might provide a useful tool to understand some basic physics."

More information: Nano Letters paper.

Provided by Massachusetts Institute of Technology (news : web)

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BXCellent
not rated yet Jul 29, 2009
One thing confuses me a little. The article states:
"By using the glass (silica) beads, they were able to get separations as small as 10 nanometers (10 billionths of a meter, or one-hundredth the distance achieved before), and are now working on getting even closer spacings."

However, later on we learn:
"...the spacing between the recording head and the disk surface is typically in the 5 to 6 nanometer range"

So if a hard disk head has a spacing two times closer than they could manage with the glass bead, why didn't they just use a hard drive in their experiments?
PPihkala
5 / 5 (2) Jul 29, 2009
So if a hard disk head has a spacing two times closer than they could manage with the glass bead, why didn't they just use a hard drive in their experiments?

Considering that the hard disk head is flying at enormous speed over the surface of the disk platter, I quess it would be next to impossible to measure heat energy transfer between the head and the platter. Also I think that the 'wind' created by the flying is not helping any with that said measuring.
Neurons_At_Work
not rated yet Jul 29, 2009
Considering that the hard disk head is flying at enormous speed over the surface of the disk platter, I quess it would be next to impossible to measure heat energy transfer between the head and the platter. Also I think that the 'wind' created by the flying is not helping any with that said measuring.


I'm sure this is correct. When a hard drive is not spinning, the heads are resting against the platters using springs. It's only when the hard drive spins up that a film of air, created by the Bernoulli effect (which also helps generate lift for aircraft), lifts and actually 'flies' the heads just above the spinning platters. I would think it would be impossible to make the required heat transfer measurements when one surface is rotating at something like 100 feet per second...
douglas2
not rated yet Jul 29, 2009
What about tunneling of phonons as an additional mode of heat transfer?
kasen
not rated yet Jul 30, 2009
I guess the next logical step would be bead-bead, for even smaller separations. It's kinda hard to believe they spent years before someone came up with the idea of using a sphere. What about all those jokes with physicists approximating stuff to spheres to solve a problem?
KBK
1 / 5 (1) Jul 30, 2009
"Planck's blackbody radiation law"

Utter bullshit.

Planck called it his backbody THEORY. What fool called it a LAW? What complete dogmatic imbecile working at an academic engineering 'corporation' first called it a law? Find that asshole and you find a man who colors theories into laws. Hold that man down and slap him about until near death. Maybe he might get the hint that anchoring things that are theories into law is a severe detriment to the advancement of science, as it makes people think that theories are inescapable, when in fact, many will fail under scrutiny.

Some of the so called 'laws of science' or physics even have 100's and up to thousands of anomalies that they don't deal with. If you feel that is false-start looking------- you will find them.


The idea of allowing dogmatic religious standards into science really needs to be eradicated. The act of calling a theory a law, which is very common in science..this is religion. Dogmatism. Never forget that, and banish the ideas of 'Theories as Laws' out of your thinking. Forever. Otherwise, science will never advance.

In essence, the idea of calling any scientific theory a law needs to be abolished.

Completely.
david_42
not rated yet Jul 30, 2009
"the 'wind' created by the flying "

Is a form of conductive heat exchange.

Planck's Theory addresses radiative heat transfer. This can only be accurately measured in a vacuum. The same applies even more so to Chen's work.
kasen
not rated yet Jul 30, 2009
"In essence, the idea of calling any scientific theory a law needs to be abolished."
I don't think any proper "pure" scientist, i.e. someone motivated by thirst of knowledge alone, actually gives a damn whether his observations are called laws, rules, theories, magic formulas or whatnot. I say maintain the confusion. Anybody unwilling to relinquish false certainty should be left to their ignorance.
NeilFarbstein
1 / 5 (2) Jul 30, 2009
If the silica beadstouching the disk why do they say there is a 20nm gap where they are not touching?
KBK
1 / 5 (1) Aug 10, 2009
"In essence, the idea of calling any scientific theory a law needs to be abolished."

I don't think any proper "pure" scientist, i.e. someone motivated by thirst of knowledge alone, actually gives a damn whether his observations are called laws, rules, theories, magic formulas or whatnot. I say maintain the confusion. Anybody unwilling to relinquish false certainty should be left to their ignorance.


It is a critical point. It creates the initial mindset and then follows through into 'groupthink', or the '100th monkey syndrome'. Which is part and parcel of how and why it has been ushered into science. Science, by most, be they in or outside science, do not put as much discerning powers that they should into their musings on such subjects.

Thus, the whole idea of open ended science is curtailed at the subliminal level. At the initial and base training level and throughout the system like a cancer that never ends. It castrates the thinking before it even begins in the budding thinkers that may and do attempt to get involved.

This is crucial,and of utmost and fundamental importance.

Think about it. Ie, muse and discern.

Even this article itself perfectly outlines and states the danger CLEARLY. It states that due to people not being aware that Planck stated it covered the concept of large bodies ONLY... well they did not dig deeper. After all, it's a LAW, isn't it?

Loose the law connotation and be absolutely sure to introduce and talk only 'theories'. Every time you hear a friend in science or physics us the term 'law'....CORRECT THEM.
kasen
not rated yet Aug 10, 2009
Again, anyone easily affected by such subliminal cues deserves what they get and wouldn't be of much use in the science world. I can't imagine a situation where the misunderstanding a theory for an immuable law of nature by an untrained person could lead to disastrous consequences for the human race. Except maybe with social/human sciences, but hopefully we learned our lesson with Hitler.


Huh...Bit early in the thread for Godwin's Law.

LE: Caught your edit after I posted.

"Every time you hear a friend in science or physics us the term 'law'....CORRECT THEM."

That sounds like a law to me.