A research team led by chemists from the University of California, Irvine, discovered a previously unknown way in which light interacts with matter; This discovery is one that could lead to improvements in solar power systems, light-emitting diodes, semiconductor lasers, and other technological advances.
In a paper recently published in the journal ACS Nano, scientists, along with colleagues from Russia’s Kazan Federal University, describe how they learned that when confined to the nanometer, photons can gain significant momentum, similar to that of electrons in solid materials. sized gaps in silicon.
“Silicon is the second most abundant element on Earth and the basis of modern electronics. However, because it is an indirect semiconductor, its use in optoelectronics is limited by poor optical properties,” said senior author Dmytro Fishman, a professor of chemistry at the University of California, Irvine.
According to him, although silicon in bulk does not emit light, porous and nanostructured silicon can produce visible light after exposure to visible radiation. Scientists have known about this phenomenon for decades, but the exact origin of the light has been a matter of debate.
“In 1923, Arthur Compton discovered that gamma photons had sufficient momentum to interact strongly with free or bound electrons. This helped prove that light has both wave and particle properties; this discovery earned Compton the Nobel Prize in Physics in 1927 “It earned . said Fishman.
“In our experiments, we showed that a pulse of visible light confined to nanoscale silicon crystals creates a similar optical interaction in semiconductors.”
Understanding the origins of interaction requires another journey to the early 20th century. In 1928, Indian physicist KV Raman, who won the Nobel Prize in Physics in 1930, tried to repeat Compton’s experiment with visible light. However, he encountered a major obstacle in the form of a significant difference between the momentum of electrons and the momentum of visible photons.
Despite this setback, Raman’s investigation of inelastic scattering in liquids and gases led to the discovery of what is now known as the vibrational Raman effect, and the most important spectroscopic study of matter, spectroscopy, became known as Raman scattering.
“Our discovery of a photon pulse in disordered silicon relates to a type of electron Raman scattering,” said study co-author Eric Potma, a professor of chemistry at the University of California, Irvine. “But unlike conventional vibrational Raman scattering, electron Raman scattering involves different initial and final states for the electron, a phenomenon previously observed only in metals.”
For their experiments, the researchers produced silicon glass samples in the laboratory, ranging in transparency from amorphous to crystalline. They exposed a 300-nanometer-thick silicon film to a tightly focused, continuous laser beam that scanned to record a series of straight lines.
In regions where the temperature did not exceed 500 degrees Celsius, the procedure resulted in the formation of a homogeneous cross-linked glass. Heterogeneous semiconductor glass was formed in regions where the temperature exceeded 500 C. This “lightweight foam film” allowed the researchers to observe how electronic, optical and thermal properties change at the nanometer scale.
“This work challenges our understanding of the interaction between light and matter by highlighting the critical role of photon momentum,” Fishman said.
“In disordered systems, coupling of electron and photon momentum enhances interaction, a property previously associated only with high-energy gamma photons in classical Compton scattering. Ultimately, our research shows that conventional optical spectroscopies are closely related to the momentum of the photon, beyond their typical applications in chemical analysis, such as conventional vibrational Raman spectroscopy.” “It paves the way for expansion into the field of structural studies, which is the knowledge that needs to be.”
Potma added: “This newly discovered property of light will undoubtedly open a new field of applications in optoelectronics. This phenomenon will increase the efficiency of solar energy conversion devices and light-emitting materials, including materials that were previously considered unsuitable for emitting light.”
Source: Port Altele
