Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button


DHgate

Home > Press > Explained: Phonons

A computer simulation shows phonons, depicted as color variations, traveling through a crystal lattice. The lattice in this case is broken up by round rods whose spacing has been chosen to block the passage of phonons of certain wavelengths.
A computer simulation shows phonons, depicted as color variations, traveling through a crystal lattice. The lattice in this case is broken up by round rods whose spacing has been chosen to block the passage of phonons of certain wavelengths.

Abstract:
When trying to control the way heat moves through solids, it is often useful to think of it as a flow of particles.

By David L. Chandler, MIT News Office

Explained: Phonons

Cambridge, MA | Posted on July 10th, 2010

For the engineers who design cell phones, solar panels and computer chips, it's increasingly important to be able to control the way heat moves through the crystalline materials — such as silicon — that these devices are based on. In computer and cell-phone chips, for example, one of the key limitations to increasing speed and memory is the need to dissipate the heat generated by the chips.

To understand how heat spreads through a material, consider that heat — as well as sound — is actually the motion or vibration of atoms and molecules: Low-frequency vibrations correspond to sound, while higher frequencies correspond to heat. At each frequency, quantum mechanics principles dictate that the vibrational energy must be a multiple of a basic amount of energy, called a quantum, that is proportional to the frequency. Physicists call these basic levels of energy phonons.

In a sense, then, "phonon" is just a fancy word for a particle of heat.

Phonons are especially relevant in the behavior of heat and sound in crystals, explains Gang Chen, the Rohsenow Professor of Mechanical Engineering at MIT. In a crystal, the atoms are neatly arranged in a uniform, repeating structure; when heated, the atoms can oscillate at specific frequencies. The bonds between the individual atoms in a crystal behave essentially like springs, Chen says. When one of the atoms gets pushed or pulled, it sets off a wave (or phonon) travelling through the crystal, just as sitting down on one edge of a trampoline can set off vibrations through the entire surface.

In practice, most materials are filled with a chaotic mix of phonons that have different frequencies and are traveling in different directions, all superimposed on each other, in the same way that the seemingly chaotic movements of a choppy sea can (theoretically) be untangled to reveal a variety of superimposed waveforms of different frequencies and directions.

But unlike photons (the particles that carry light or other electromagnetic radiation), which generally don't interact at all if they have different wavelengths, phonons of different wavelengths can interact and mix when they bump into each other, producing a different wavelength. This makes their behavior much more chaotic and thus difficult to predict and control.

Just as photons of a given frequency can only exist at certain specific energy levels — exact multiples of the basic quanta —so, too, can phonons, Chen says. And when working on applied physics relating to the transfer of heat within solids, which is a specific focus of Chen's research, thinking in terms of phonons has proved to be especially useful.

For example, in the quest for better ways to dissipate heat from computer chips — a key requirement as chips get faster and pack in more components — finding ways to manipulate the behavior of the phonons in those chips, so the heat can be removed easily, is the key. Conversely, in designing thermoelectric devices to generate electricity from temperature differences, it's important to develop materials that can conduct electricity (the motion of electrons) easily, but block the motion of phonons (that is, heat).

"In some cases, you want strong conduction of phonons, and in some cases you want to reduce their propagation," Chen says. "Sometimes they're good guys, and sometimes they're bad guys."

####

For more information, please click here

Copyright © Massachusetts Institute of Technology

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

Study reveals how herpes virus tricks the immune system February 5th, 2016

Hepatitis virus-like particles as potential cancer treatment February 5th, 2016

Organic crystals allow creating flexible electronic devices: The researchers from the Faculty of Physics of the Moscow State University have grown organic crystals that allow creating flexible electronic devices February 5th, 2016

Researchers discover new phase of boron nitride and a new way to create pure c-BN February 5th, 2016

Physics

Polar vortices observed in ferroelectric: New state of matter holds promise for ultracompact data storage and processing February 4th, 2016

The quantum fridge: It all comes down to quantum physics: scientists at TU Wien have analyzed why some gases can be cooled down to extremely low temperatures February 2nd, 2016

Unconventional superconductivity near absolute zero temperature: Quantum critical point could be the reason for high temperature superconductivity February 2nd, 2016

Electrons and liquid helium advance understanding of zero-resistance: Study of electrons on liquid helium systems sheds light on zero-resistance phenomenon in semiconductors February 2nd, 2016

Academic/Education

COD Grad Begins Postdoctoral Fellow at Harvard University: Marsela Jorgolli's Passion for Physics Has Led to a Decade of Academic Research That Continues at Harvard University as a Postdoctoral Fellow February 2nd, 2016

Heriot-Watt's Institute of Photonics & Quantum Sciences uses the Deben Microtest 2 kN tensile stage to characterise ceramics and engineering plastics January 21st, 2016

Multiple uses for the JPK NanoWizard AFM system in the Smart Interfaces in Environmental Nanotechnology Group at the University of Illinois at Urbana-Champaign January 20th, 2016

BioSolar Extends Research Agreement With UCSB for Next Phase of Its Super Battery Technology: Development Effort to Continue Under the Supervision of Nobel Laureate, Dr. Alan Heeger January 13th, 2016

Announcements

Study reveals how herpes virus tricks the immune system February 5th, 2016

Hepatitis virus-like particles as potential cancer treatment February 5th, 2016

Organic crystals allow creating flexible electronic devices: The researchers from the Faculty of Physics of the Moscow State University have grown organic crystals that allow creating flexible electronic devices February 5th, 2016

Researchers discover new phase of boron nitride and a new way to create pure c-BN February 5th, 2016

Quantum nanoscience

Spin dynamics in an atomically thin semi-conductor February 1st, 2016

New record in nanoelectronics at ultralow temperatures January 28th, 2016

Leti to Host Workshop on New Photonics Applications During SPIE Photonics West: Researchers also Will Present Four Invited Papers At Feb. 13-18 Conference, 14 Papers, Overall January 25th, 2016

Mechanical quanta see the light January 20th, 2016

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project







Car Brands
Buy website traffic