Photons can achieve substantial momentum, similar to that of electrons in solid materials, when confined to nanometer-scale silicon spaces.

This new property of light was identified in a study conducted by a team of researchers from Kazan Federal University in Russia and the University of California, Irvine (UCI) in the United States.

"Silicon is the second most abundant element on Earth and forms the backbone of modern electronics. However, as an indirect semiconductor, its use in optoelectronics has been hampered by its poor optical properties," explains Dmitry Fishman, a chemist at UCI and co-author of the study, whose results were presented in an article published in ACS Nano.

"Although silicon does not naturally emit light in its raw form, porous and nanostructured silicon can produce detectable light after being exposed to visible radiation," adds Fishman.

Scientists have been aware of this phenomenon for decades, but the exact origins of lighting have been the subject of debate.

"In 1923, Arthur Compton discovered that gamma photons possessed sufficient momentum to interact strongly with free or bound electrons," explains Fishman. "This helped prove that light had both wave and particle properties, a discovery that led to Compton receiving the Nobel Prize for Physics in 1927″.

"In our study, we showed that the momentum of visible light when it is confined to nanoscale silicon crystals produces a similar optical interaction in semiconductors," says the researcher, in a statement published on the UCI website.

To understand the origin of the interaction, it is necessary to travel back to the beginning of the 20th century. In 1928, the Indian physicist C.V. Raman, who won the Nobel Prize for Physics in 1930, tried to repeat Compton's experiment with visible light.

However, he came up against a formidable obstacle: the great disparity between the momentum of electrons and that of visible photons.

Despite this obstacle, Raman's research into inelastic scattering in liquids and gases provided the first evidence of what would come to be known as the vibrational Raman effect, or Raman scattering.

Since then, this discovery has become fundamental in spectroscopy, a critical technique in the spectroscopic study of matter.

"Our discovery of the photon momentum in silicon originates from a form of electronic Raman scattering," explains Eric Potma, also a researcher at UCI and co-author of the study.

"But unlike the conventional vibrational Raman effect, electronic Raman involves different initial and final states for the electron, a phenomenon previously only observed in metals," the researcher explains.

For their experiments, the researchers produced samples of silicon glass in their laboratory that varied in their degree of crystallinity - from amorphous to crystalline.

The researchers subjected a 300 nm thick silicon film to a tightly focused continuous wave laser beam, which swept across the film to write a series of straight lines.

In areas where the temperature did not exceed 500°C, the procedure resulted in the formation of a homogeneous cross-linked glass. Where the temperature exceeded this value, a heterogeneous semiconductor glass was formed.

This film allowed the scientists to observe how the electronic, optical and thermal properties varied at the nanometer scale.

"The results of the study challenge our understanding of the interaction between light and matter, underlining the critical role of photon moments," says Fishman.

"In disordered systems, the correspondence between electron and photon momentum amplifies the interaction - an aspect that was previously associated only with high-energy gamma photons in classical Compton scattering," he adds.

"Ultimately, we have paved the way for conventional optical spectroscopy techniques to be extended from their typical applications in chemical analysis, such as traditional vibrational Raman spectroscopy, into the realm of structural studies - information closely linked to photon momentum."

"This new property of light will undoubtedly open up a new field of applications in optoelectronics," concludes Eric Potma. "It will increase the efficiency of solar energy conversion devices and light-emitting materials, including materials that were previously not considered suitable for emitting light."