In eight years, Mo Yijian Peking University developed a faster domestic scanning tunnel microscope

[ Instrument R&D of Instrument Network ] A microscope is an optical instrument composed of a lens or a combination of several lenses, and it is a sign of human beings entering the atomic age. It can be said that the microscope is one of the greatest inventions of mankind, because before it was invented, the concept of human beings about the surrounding world was limited to what was observed with the naked eye, or to help the naked eye to see things by holding the lens. But since the invention of the microscope, the microscope has shown a whole new world in the field of human vision. People have seen the microscopic world for the first time, which is of great significance for scientific research.

With the development of microscopes, people have divided many types of microscopes. According to the types, microscopes can be divided into biological microscopes, metallographic microscopes, stereo microscopes (anatomical mirrors), polarized light microscopes, and phase contrast microscopes. , Fluorescence microscope, tool measuring microscope, etc.

Recently, Professor Jiang Ying's team at the Quantum Materials Science Center, School of Physics, Peking University and their collaborators have developed a faster scanning tunnel microscope in China, which achieves femtosecond-level time resolution and atomic-level spatial resolution, and captures the single polarization of the metal oxide surface. Non-equilibrium dynamic behavior of the son.

Prior to this, Jiang Ying's team and collaborators also achieved a series of results: Through the double breakthrough of experimental technology and theoretical methods, they were the first in the world to achieve an accurate description of the nuclear quantum state, revealing the nuclear quantum effect of water. In the "Science" journal; through the development of a new scanning probe technology, the atomic level resolution image of a single sodium ion hydrate was obtained internationally. The result was published in the "Nature" journal; the experiment confirmed the ice's two-dimensional limit for the first time in experiments It can exist steadily, photographing and revealing the unique formation process and growth mechanism of two-dimensional ice. The result was published in the journal Nature.

Today, let us understand the quantum science world of Peking University scientists! Committed to improving the temporal resolution of STM, it takes eight years to grind a sword. Scanning tunneling microscope is a microscopic detection tool with spatial resolution up to atomic level.

However, due to the limitation of the bandwidth of the current amplifier, the time resolution can generally only reach the order of microseconds (10-6s), and many microscopic dynamic processes often occur in picoseconds (10-12 s) and femtoseconds (10-15) s) magnitude. In order to improve the time resolution of STM, one of the more feasible methods is to combine the pump-probe technology of ultrafast laser and STM, and realize the coupling between ultrafast light and electron tunneling process. Femtosecond-Angstrom scale extreme detection.

Although the concept of ultra-fast laser technology and STM coupling was proposed in the 1990s, related research is limited by a series of technical difficulties, and progress is very slow. In recent years, the original concept and core technology of ultra-fast STM have begun to undergo innovation. Jiang Ying's research group at the School of Physics of Peking University also joined the fierce international competition in 2012.

The team independently developed and mastered several key technologies. After drawing design, machining, assembly and docking, performance testing and other links, the scanning probe, vacuum system, control circuit, optical coupling system and other key components were all made by themselves. After relay and trial and error, a new generation of ultra-fast STM system was finally developed, which made it possible to detect ultra-fast dynamics on the atomic scale.

The system can work in the ultra-high vacuum liquid helium temperature environment, the higher time resolution can reach 100 femtoseconds, the longest delay can reach the order of microseconds, and the relevant performance parameters have reached internationally good levels. This is also the first STM system in China that can achieve femtosecond time resolution.

Using this device, combined with first-principles calculations, the researchers conducted an in-depth study of the non-equilibrium dynamics of a single polaron.

Polaron is a kind of quasi-particle formed by the interaction of a single electron in the material with the surrounding lattice. Many peculiar physical properties exhibited in metal oxide materials, such as photocatalysis, high temperature superconductivity, thermoelectricity, and giant magnetoresistance, are closely related to polarons.

By measuring the time-resolved single polaron dynamics, the researchers found that when the polaron is bound by two oxygen defects, the trapping time is significantly shorter than when there is only one oxygen defect. However, the free electron lifetime is not sensitive to the atomic scale accumulation of oxygen defects, but it strongly depends on the average defect density at the nanometer scale. This work reveals for the first time the important influence of the atomic scale environment on the non-equilibrium kinetic process of polarons, provides a new microscopic image for the highly active sites in the photocatalytic reaction, and also provides defect engineering for nanophotocatalytic materials. New ideas.

Challenge the controversial puzzles again and again, revealing the unresolved mysteries. From measuring the quantum composition of hydrogen bonds, revealing the nuclear quantum effect of water for the first time at the atomic scale, to developing a new scanning probe technology based on high-order electrostatic forces, enabling direct imaging and localization of hydrogen atoms, and obtaining single sodium ion hydrate atoms Class-resolved images, to the use of non-intrusive atomic force microscope technology to capture the formation of two-dimensional ice with atomic-level resolution, and then to the development of the first ultra-fast scanning tunneling microscope in China, which achieved femtosecond-level time resolution and atomic level Spatial resolution...