A new property of light discovered

Photon momentum discovery unlocks novel, silicon-based optoelectronic capabilities.

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Chemists at the University of California, Irvine, have discovered a new property of light and a previously unknown way in which light interacts with matter.

Scientists discovered that when photons are confined to nanoscale gaps in silicon, they can gain significant momentum, akin to electrons in solid materials.

Silicon is the backbone of modern electronics. However, being an indirect semiconductor, its utilization in optoelectronics has been hindered by poor optical properties.

Although bulk silicon does not naturally emit light, porous and nanostructured silicon can produce observable light when exposed to visible light. Although the exact cause of the light has been disputed, scientists have been aware of this phenomenon for decades.

Senior author Dmitry Fishman, a UC Irvine adjunct professor of chemistry, said, “In 1923, Arthur Compton discovered that gamma photons possessed sufficient momentum to interact strongly with free or bound electrons. This helped prove that light had both wave and particle properties, a finding that led to Compton receiving the Nobel Prize in physics in 1927.”

In experiments, scientists showed that the momentum of visible light confined to nanoscale silicon crystals produces a similar optical interaction in semiconductors.

This discovery of photon momentum in disordered silicon is due to electronic Raman scattering.

However, electronic Raman differs from traditional vibrational Raman in that it uses distinct electron starting and final states—a phenomenon previously seen only in metals.

The scientists created silicon glass samples for their trials in their lab, varying in clarity from amorphous to crystal. They wrote an array of straight lines on a 300-nanometer-thick silicon film by scanning it with a closely focused continuous-wave laser beam.

The process created a uniform cross-linked glass in regions where the temperature did not rise above 500 degrees Celsius. When the temperature rose over 500 C, a heterogeneous semiconductor glass emerged. The researchers could see how thermal, optical, and electrical characteristics changed on a nanoscale scale thanks to this “light-foamed film.”

Fishman said, “This work challenges our understanding of light and matter interaction, underscoring the critical role of photon momenta.”

“In disordered systems, electron-photon momentum matching amplifies interaction—an aspect previously associated only with high-energy—gamma—photons in classical Compton scattering. Ultimately, our research paves the way to broaden conventional optical spectroscopies beyond their typical applications in chemical analysis. One is traditional vibrational Raman spectroscopy in structural studies—the information that should be intimately linked with photon momentum.”

Co-author Eric Potma, UC Irvine professor of chemistry, said“This newly realized property of light no doubt will open a new realm of applications in optoelectronics. The phenomenon will boost the efficiency of solar energy conversion devices and light-emitting materials, including previously considered unsuitable for light emission.”

Journal Reference:

  1. Sergey S. Kharintsev et al., Photon-Momentum-Enabled Electronic Raman Scattering in Silicon Glass, ACS Nano (2024). DOI: 10.1021/acsnano.3c12666

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