Advancing Nanoscale Chemical Reactions: New Insights from Thin Gold Films

2024-04-29 10:10:23

New research on thin gold films has revealed new photoluminescence behaviors, advancing our understanding of nanoscale chemical reactions and temperature measurements. This breakthrough improves the use of metals in energy research and offers new methods for probing surface processes essential to solar fuel development. Credit: twoday.co.il.com

Researchers at EPFL have created the first detailed model explaining the quantum-mechanical effects that cause photoluminescence in thin gold films, a breakthrough that could advance the development of solar fuels and batteries.

Luminescence, the process by which materials emit photons when exposed to light, has long been observed in semiconductor materials such as silicon. This phenomenon involves electrons in

nanoscale

The nanoscale refers to a length scale that is extremely small, typically on the order of nanometers (nm), which is one billionth of a meter. At this scale, materials and systems exhibit unique properties and behaviors that are different from those observed at larger length scales. The prefix "nano-" is derived from the Greek word "application," which means "dwarf" or "very small." Nanoscale phenomena are relevant to many fields, including materials science, chemistry, biology, and physics.

” data-gt-translate-attributes=”({” attribute=”” tabindex=”0″ role=”link”>ננומטרי Absorbs light and then re-emits it. Such behavior provides researchers with important insights into the characteristics of

semiconductors

Semiconductors are a type of material that has electrical conductivity between that of a conductor (such as copper) and an insulator (such as rubber). Semiconductors are used in a wide range of electronic devices, including transistors, diodes, solar cells, and integrated circuits. The electrical conductivity of a semiconductor can be controlled by adding impurities to the material through a process called doping. Silicon is the most widely used material for semiconductor devices, but other materials such as gallium arsenide and indium phosphide are also used in certain applications.

” data-gt-translate-attributes=”({” attribute=”” tabindex=”0″ role=”link”>SemiconductorsWhich makes them useful tools for probing electronic processes, such as those in solar cells.

In 1969, scientists discovered that all metals glow to some extent, but the years that have passed have failed to yield a clear understanding of how this occurs. A renewed interest in this light emission, driven by nanoscale temperature mapping and photochemistry applications, has reignited the debate surrounding its origins. But the answer was still not clear – until now.

“We developed very high-quality metallic gold films, which put us in a unique position to elucidate this process without the confounding factors of previous experiments,” says Julia Tagliabo, head of the Laboratory of Nanoscience for Energy Technologies (LNET) in the School of Engineering.

In a recently published study by Light: Science and Applications, Tagliabue and the LNET team focused the laser beams on the thinnest gold films – between 13 and 113 nanometers – and then analyzed the resulting faint glow. The data generated from their precise experiments was so detailed – and so unpredictable – that they collaborated with theorists at the Barcelona Institute of Science and Technology, the University of Southern Denmark and Rensselaer Polytechnic Institute (USA) to rework and implement quantum mechanical modeling methods.

The researchers’ comprehensive approach allowed them to settle the debate surrounding the type of glow emanating from the films – photoluminescence – which is defined by the specific way electrons and their oppositely charged counterparts (holes) behave in response to light. It also allowed them to produce the first complete and fully quantitative model of this phenomenon in gold, which can be applied to any metal.

Unexpected quantum effects

Tagliabue explains that, using a thin film of single-crystal gold produced by a new synthesis technique, the team studied the photoluminescence process as they made the metal thinner and thinner. “We observed certain quantum mechanical effects appearing in films down to about 40 nm, which was unexpected because normally for a metal, you don’t see such effects until you go well below 10 nm,” she says.

These observations provided key spatial information about exactly where the photoluminescence process occurred in gold, which is a prerequisite for using the metal as a probe. Another unexpected result of the research was the discovery that the photoluminescent signal of the gold (Stokes) could be used to probe the surface temperature of the material itself – a boon for scientists working at the nanoscale.

“For many chemical reactions on the surface of metals, there is great debate about why and under what conditions these reactions occur. Temperature is a key parameter, but measuring temperature at the nanoscale is extremely difficult, because a thermometer can affect your measurement. So it’s a huge advantage to be able to To study a material using the material itself as the probe,” says Tagliabo.

Gold standard for solar fuel development

The researchers believe their findings will make it possible to use metals to gain unprecedented detailed insights into chemical reactions, especially those involved in energy research. Metals such as gold and copper – the next research target of the LNET – can trigger certain key reactions, such as reducing carbon dioxide (CO2) back into carbon-based products such as solar fuel, which store solar energy in chemical bonds.

“To combat climate change, we will need technologies to convert CO2 into other useful chemicals in one way or another,” says LNET postdoctoral fellow Alan Bowman, first author of the study.

“Using metals is one way to do this, but if we don’t have a good understanding of how these reactions happen on their surface, then we can’t optimize them. Zohar offers a new way to understand what happens in these metals.”