Scientists were able to image the photocatalytic activity of nanoparticles at unprecedented resolution. This may be a new tool in nanotechnology and optical manipulation of small devices.Osaka, Japan – A team of scientists led at Osaka University by the Department of Applied Physics, the Department of Physics and Electronics of Osaka Prefecture University and the Department of Materials Chemistry of Nagoya University used photoinduced forces microscopy to map the forces that act on quantum dots in three dimensions. The team was able, for the first-ever time, to attain subnanometer precision by eliminating noise sources. This could lead to new developments in optical tweezers and photocatalysts.Force fields are not invisible barriers like science fiction. They are a collection of vectors that indicate the direction and magnitude of forces acting in a particular region of space. Sometimes lasers are used to optically trap and move nanotechnology devices, such as quantum dots. To be able to analyse and manipulate such small systems, you need to have a better understanding of the 3D forces that are acting on them.Researchers from Osaka University, Osaka Prefecture University and Nagoya University have demonstrated for the first-time how photoinduced force microscopes can be used to create 3D force field diagrams at sub-nanometer resolution. "We were able to image the optical near-field nanoparticles with a photoinduced force microscope. Junsuke Yamanishi, the first author of this article, says that it measures the optical force created by light irradiation between the probe and the sample.A quantum dot was placed under an atomic force microscope tip. Laser light was directed at it. The microscope was able to map the 3D photoinduced force fields by moving the dot relative the tip. The team achieved such high precision with a few experimental modifications. To increase the force sensitivity, they used ultra-vacuum conditions. They also employed heterodyne frequency modification, which mixes two frequencies to reduce the thermal heating effect. Yasuhiro Sagara, senior author, says that they reduced the photothermal effect and achieved a resolution of less then one nanometer.This research could be a revolutionary technology in the design and evaluation functional nanomaterials. This research can be used to complement the existing toolbox of methods for scientists who work with photocatalysts or optical functional devices to move them by lasers.###Nature Communications published the article "Optical force mapping at a single-nanometer scale", at DOI: https:/// doi. 1038/ s41467-021-24136-2 1038/ s41467 -021-24136-2Contact:Yasuhiro SugwaraProfessorDepartment of Applied Physics at Osaka UniversityTEL: +81-6-86879-7853Email: sugawara@ap.eng.osaka.u.ac.jpHajime IshiharaProfessorDepartment of Physics and Electronics at Osaka Prefecture UniversityTEL: +81-72-254-9216E-mail to ishi@pe.osakafu.u.ac.jpTsukasa ToimotoProfessorNagoya University, Department of Materials ChemistryTEL: +81 52 789 4614Email: torimoto@chembio.nagoya.ac.jpAbout Osaka UniversityOsaka University was established in 1931 as one the seven imperial universities Japan. It is today one of Japan's most prestigious comprehensive universities. This unique strength is complemented by a drive for innovation that spans the entire scientific process, from basic research to the creation and application of technology with positive economic effects. Japan has recognized Osaka University's dedication to innovation. In 2015, it was named Japan's most innovative university (Reuters 2015 Top 100), and in 2017, it was named one of the top 100 most innovative universities in the world (Innovative Universities 2017 and Nature Index Innovation 2017). Osaka University now uses its status as a Designated National University Corporation, selected by the Ministry of Education, Culture, Sports and Technology, to promote innovation for human welfare, sustainable growth of society, and social change.
