Developed "ultrasound" technology for nanostructures
Ultra-high-frequency acoustic waves visualize structures as small as a few nanometers.Researchers at the Japanese Institute of Physical and Chemical Research (RIKEN) have developed a high-resolution ultrasound imaging technology. Ultra-high-frequency acoustic waves can be used to find hidden nanoscopic defects in materials.
Physicists used an ultrafast transmission electron microscope (UTEM) to detect sound waves generated by a 200-nanometer hole in the center of an ultra-thin silicon wafer. UTEM uses two laser beams with a short delay between them. One beam illuminates the sample, while the other generates an ultrashort pulse of electrons in the microscope.
In a series of experiments, the scientists demonstrated that the created setup provides high image quality and accuracy. At the same time, the established setup allows for the collection of data at the picosecond speed required to observe nanostructures.
Medical ultrasound devices use sound waves with a wavelength of a few millimeters. This is sufficient for observing internal organs or fetal development. But to examine nanostructures, the wavelength must be much shorter, physicists explain.
Technologies for creating such high-frequency sound waves have long been known: ultrashort laser pulses have been used for decades to generate them in metals and semiconductors. But detecting them is much more difficult, as it requires the development of detectors capable of achieving nanometer spatial resolution and capturing picosecond-frequency data.
"If we can learn to use sound waves with a wavelength of about 100 nm or so, we can use them to inspect materials, for example, to detect defects," Asuka Nakamura, co-author of the study from the RIKEN Institute.