Home > Press > Shedding light on the absorption of light by titanium dioxide
Lattice structure of anatase TiO2 with a graphical representation of the 2-D exciton that is generated by the absorption of light (purple wavy arrow). This 2-D exciton is the lowest energy excitation of the material. CREDIT Majed Chergui/EPFL |
Abstract:
Titanium dioxide (TiO2) is one of the most promising materials for photovoltaics and photocatalysis nowadays. This material appears in different crystalline forms, but the most attractive one for applications is called "anatase". Despite decades of studies on the conversion of the absorbed light into electrical charges in anatase TiO2, the very nature of its fundamental electronic and optical properties was still unknown. EPFL scientists, with national and international partners, have now shed light onto the problem by a combination of cutting-edge steady-state and ultrafast spectroscopic techniques, as well as theoretical calculations. The work is published in Nature Communications.
Anatase TiO2 is involved in a wide range of applications, ranging from photovoltaics and photocatalysis to self-cleaning glasses, and water and air purification. All of these are based on the absorption of light and its subsequent conversion into electrical charges. Given its widespread use in various applications, TiO2 has been one of the most studied materials in the twentieth century, both experimentally and theoretically.
When light shines on a semiconducting material such as TiO2, it generates either free negative (electrons) and positive (holes) charges or a bound neutral electron-hole pair, called an exciton. Excitons are of great interest because they can transport both energy and charges on a nanoscale level, and form the basis of an entire field of next-generation electronics, called "excitonics". The problem with TiO2 so far is that we have not been able to clearly identify the nature and properties of the physical object that absorbs light and characterize its properties.
The group of Majed Chergui at EPFL, along with national and international colleagues, have shed light on this long-standing question by using a combination of cutting-edge experimental methods: steady-state angle-resolved photoemission spectroscopy (ARPES), which maps the energetics of the electrons along the different axis in the solid; spectroscopic ellipsometry, which determines the optical properties of the solid with high accuracy; and ultrafast two-dimensional deep-ultraviolet spectroscopy, used for the first time in the study of materials, along with state-of-the-art first-principles theoretical tools.
They discovered that the threshold of the optical absorption spectrum is due to a strongly bound exciton, which exhibits two remarkable novel properties: First, it is confined on a two-dimensional (2D) plane of the three-dimensional lattice of the material. This is the first such case ever reported in condensed matter. And secondly, this 2D exciton is stable at room temperature and robust against defects, as it is present in any type of TiO2 -- single crystals, thin films, and even nanoparticles used in devices.
This "immunity" of the exciton to long-range structural disorder and defects implies that it can store the incoming energy in the form of light and guide it at the nanoscale in a selective way. This promises a huge improvement compared to current technology, in which the absorbed light energy is dissipated as heat to the crystal lattice, making the conventional excitation schemes extremely inefficient.
Furthermore, the newly discovered exciton is very sensitive to a variety of external and internal stimuli in the material (temperature, pressure, excess electron density), paving the way to a powerful, accurate and cheap detection scheme for sensors with an optical read-out.
"Given that it is cheap and easy to fabricate anatase TiO2 materials, these findings are crucial for many applications and beyond", says Majed Chergui. "To know how electrical charges are generated after light is absorbed is a key ingredient for efficient photocatalysts."
###
This work was carried out in a collaboration of the EPFL's Laboratoire de Spectroscopie Ultrarapide (LSU) and the Institute of Physics (IPHYS) within the Lausanne Centre for Ultrafast Science (LACUS), with the Max Planck Institute for the Structure and Dynamics of Matter, the University of Fribourg, the Università Campus Bio-Medico di Roma, the Università Roma "Tor Vergata", and the Universidad del Pais Vasco. It was funded by the Swiss National Science foundation (SNSF; NCCR:MUST), the European Research Council Advanced Grants "DYNAMOX" and "Qspec-Newmat", the Grupos Consolidados del Gobierno Vasco and COST Actions, EUSpec.
Reference
E. Baldini, L. Chiodo, A. Dominguez, M. Palummo, S. Moser, M. Yazdi-Rizi, G. Auböck, B.P.P. Mallett, H. Berger, A. Magrez, C. Bernhard, M. Grioni, A. Rubio, M. Chergui. Strongly bound excitons in anatase TiO2 single crystals and nanoparticles. Nature Communications 13 April 2017. DOI: s41467-017-00016-6.
####
For more information, please click here
Contacts:
Nik Papageorgiou
41-216-932-105
Copyright © Ecole Polytechnique Fédérale de Lausanne
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.
Related News Press |
Chemistry
What heat can tell us about battery chemistry: using the Peltier effect to study lithium-ion cells March 8th, 2024
News and information
Researchers develop artificial building blocks of life March 8th, 2024
Govt.-Legislation/Regulation/Funding/Policy
What heat can tell us about battery chemistry: using the Peltier effect to study lithium-ion cells March 8th, 2024
Researchers’ approach may protect quantum computers from attacks March 8th, 2024
Optically trapped quantum droplets of light can bind together to form macroscopic complexes March 8th, 2024
Possible Futures
Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024
Discoveries
What heat can tell us about battery chemistry: using the Peltier effect to study lithium-ion cells March 8th, 2024
Researchers’ approach may protect quantum computers from attacks March 8th, 2024
High-tech 'paint' could spare patients repeated surgeries March 8th, 2024
Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024
Announcements
What heat can tell us about battery chemistry: using the Peltier effect to study lithium-ion cells March 8th, 2024
Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024
Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers/Posters
Researchers develop artificial building blocks of life March 8th, 2024
Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024
Environment
Billions of nanoplastics released when microwaving baby food containers: Exposure to plastic particles kills up to 75% of cultured kidney cells July 21st, 2023
Energy
Development of zinc oxide nanopagoda array photoelectrode: photoelectrochemical water-splitting hydrogen production January 12th, 2024
Shedding light on unique conduction mechanisms in a new type of perovskite oxide November 17th, 2023
Inverted perovskite solar cell breaks 25% efficiency record: Researchers improve cell efficiency using a combination of molecules to address different November 17th, 2023
The efficient perovskite cells with a structured anti-reflective layer – another step towards commercialization on a wider scale October 6th, 2023
Water
Taking salt out of the water equation October 7th, 2022
Grants/Sponsored Research/Awards/Scholarships/Gifts/Contests/Honors/Records
'Sudden death' of quantum fluctuations defies current theories of superconductivity: Study challenges the conventional wisdom of superconducting quantum transitions January 12th, 2024
Research partnerships
Researchers’ approach may protect quantum computers from attacks March 8th, 2024
'Sudden death' of quantum fluctuations defies current theories of superconductivity: Study challenges the conventional wisdom of superconducting quantum transitions January 12th, 2024
Development of zinc oxide nanopagoda array photoelectrode: photoelectrochemical water-splitting hydrogen production January 12th, 2024
Solar/Photovoltaic
Development of zinc oxide nanopagoda array photoelectrode: photoelectrochemical water-splitting hydrogen production January 12th, 2024
Shedding light on unique conduction mechanisms in a new type of perovskite oxide November 17th, 2023
Inverted perovskite solar cell breaks 25% efficiency record: Researchers improve cell efficiency using a combination of molecules to address different November 17th, 2023
Charged “molecular beasts” the basis for new compounds: Researchers at Leipzig University use “aggressive” fragments of molecular ions for chemical synthesis November 3rd, 2023
The latest news from around the world, FREE | ||
Premium Products | ||
Only the news you want to read!
Learn More |
||
Full-service, expert consulting
Learn More |
||