International best Peking University independently develops qPlus-type optical coupled scanning probe microscope
Recently, Professor Jiang Ying's group in the School of Physics and Light Element Advanced Materials Research Center of Peking University and Professor Liu Kaihui's group have independently developed a qPlus type optical coupled scanning probe microscope. The performance of this microscope has reached the best international level, in which the atomic force sensor amplitude noise and quality factor are international leading. The technical details were published in Review of Scientific Instruments, a leading international scientific instrumentation journal. The related patented technology has been successfully transferred and the first commercial prototype has been completed.
Scanning probe microscopy (SPM) is one of the greatest inventions in the field of nanotechnology. It uses a sharp needle tip to scan a sample point by point to obtain surface topography and rich physical properties at the atomic/molecular/nanometer scale. Scanning probe microscopy mainly includes scanning tunneling microscopy (STM, 1986 Nobel Prize in Physics) and atomic force microscopy (AFM, 2016 Kavli Prize). Since its inception, scanning probe microscopy has been widely used in a variety of fields including physics, chemistry, materials science, and biology, changing the paradigm and fundamental perception of human research on matter.
Due to technical limitations and lack of experience, China has been heavily dependent on imports of high-end scanning probe microscopes for many years. In this passive situation, Jiang Ying's group has been dedicated to developing the core components of scanning probe microscopy as well as high-resolution imaging and spectroscopy techniques for more than a decade, continuously challenging the detection limits of scanning probe technology. In particular, the group has successfully developed a set of non-intrusive scanning probe microscopy based on qPlus sensor with independent intellectual property rights, which refreshes the spatial resolution of scanning probe microscopy by detecting extremely weak high-order electrostatic forces and achieves the direct imaging of hydrogen atoms in water molecules for the first time in the world, bringing the microscopic experimental study of water into a brand new era.
On the basis of the breakthrough in key technologies, Dr. Bo-Wei Cheng, PhD student Da Wu and Associate Researcher Ke Bian from Ying Jiang's group further worked closely with Kaihui Liu's group to successfully build a qPlus-type light-coupled scanning probe microscope prototype for commercialization (Patent 1). The device is compatible with ultra-high vacuum and cryogenic (liquid helium) environments, with circuit noise backbone as low as 5 fA/Hz1/2, needle tip height vibration noise peak less than 200 fm/Hz1/2, and thermal drift less than 0.1 pm/min, with all indicators reaching the best international level. Meanwhile, the device's qPlus sensor has extremely low back-bottom amplitude noise (~2 pm) and excellent quality factor (up to 140,000), reaching the international leading level. In addition, the microscope system has a unique design with a 3D nano-positioner (Patent 2) directly integrated into the scanning probe that can drive the optical lens, which greatly improves the optical excitation and light collection efficiency and avoids the micro-jitter problem of the laser focused spot, making the microscope with excellent optical compatibility, which is ideal for studying the structure, chemical composition and kinetic behavior of a variety of molecules and material systems. It is an ideal tool for studying the structure, chemical composition and kinetic behavior of a wide range of molecular and material systems.
Recently, Peking University has signed a contract with a domestic instrumentation company for the transfer of two utility model patents, including "a qPlus-based optical coupling scanning probe microscope", and is actively promoting the localization of high-end scanning probe microscopes with independent intellectual property rights, which is expected to break the long-term international monopoly situation. The research and development of this equipment has received financial support from the National Natural Science Foundation of China, the Ministry of Science and Technology, the Ministry of Education, the Chinese Academy of Sciences and the Beijing Municipal Government.
Related papers：
Bowei Cheng, Da Wu, Ke Bian, Ye Tian, Chaoyu Guo, Kaihui Liu, Ying Jiang, A qPlus-based scanning probe microscope compatible with optical measurements. Review of Scientific Instruments 93, 043701 (2022).
(https://doi.org/10.1063/5.0082369)
Related patents：
[1] Y. Jiang, B. Cheng, K. Bian, D. Wu, A qPlus-based optical coupled scanning probe microscope, China, 202121333378.5, 2021-09-03.
[2] Ying Jiang, Bowei Cheng, Da Wu, Ke Bian, A lens three-dimensional moving device, China, 202120697032.7, 2021-05-07.
Fig. 1 Commercial prototype of self-developed qPlus-type optical coupled scanning probe microscope.
Fig. 2 Core components of a homemade qPlus-type optically coupled scanning probe microscope. a and b, 3D design drawings and physical drawings of the optically coupled scanning probe. c, qPlus atomic force sensor. d, needle tip after focused ion beam etching.
Fig. 3 Results of atomic force microscopy imaging tests with a homemade qPlus-type optically coupled scanning probe microscope. a, qPlus force sensor frequency scan curve. b and d, constant height atomic force microscopy images (frequency shift maps) of two-dimensional ice on Au(111) surface at different tip heights. c, force spectra at different locations on the two-dimensional ice surface. e and f, atomic structure maps of two-dimensional ice.
