A team of scientists led by the Department of Applied Physics at Osaka University, the Department of Physics and Electronics at Osaka Prefecture University and the Department of Materials Chemistry at Nagoya University used photoinduced force microscopy to map the forces acting on quantum dots in three dimensions. By eliminating sources of noise, the team was able to achieve subnanometric precision for the first time, which could lead to further advancements in photocatalysts and optical tweezers.
Force fields are not the invisible barriers of science fiction but are a collection of vectors indicating the magnitude and direction of forces acting in a region of space. Nanotechnology, which involves making and manipulating tiny devices such as quantum dots, sometimes uses lasers to optically trap and move these objects. However, the ability to analyze and manage such small systems requires a better way to visualize the 3D forces acting on them.
Today, a team of researchers from Osaka University, Osaka Prefecture University and Nagoya University demonstrated for the first time how photoinduced force microscopy can be used to obtain 3D force field diagrams with subnanometric resolution. “We were able to image the optical near field of nanoparticles using a photo-induced force microscope. This measures the optical force between the sample and the probe caused by the light irradiation,” says first author Junsuke Yamanishi .
The laser light was directed at a quantum dot placed under an atomic force microscopy tip. The displacement of the point relative to the tip allowed the microscope to map the photo-induced force field in 3D. The team was able to achieve such a level of precision using some experimental improvements. They used ultra-high vacuum conditions to increase force sensitivity and used heterodyne frequency modulation, which involves mixing two other frequencies, to significantly reduce the impact of thermal heating. “We have reduced the photothermal effect with this unique technology and achieved a resolution of less than one nanometer for the very first time,” said lead author Yasuhiro Sugawara.
This research may represent fundamentally new technology for the design and evaluation of functional nanomaterials. It can also help complete the toolbox of methods available to scientists working with photocatalysts and functional optical devices to move them using lasers.