Progress in the development of ultrafast laser ultra-high vacuum scanning probe microscope system

[ China Instrument Network Instrument Development ] The acquisition of high-precision scientific instruments is one of the most important factors in the exploration and discovery of basic frontier science. In the past few years, China has a huge gap with developed countries in the development of ultra-high vacuum-molecular beam epitaxy and related equipment, and has become an important bottleneck in the scientific research, application development level and major original scientific research results in related fields in China. Elbow.

As an important tool for the study of low-dimensional materials and surface science, the invention of scanning tunneling microscopy (STM) and its related scanning microscopy (SPM) has greatly promoted the development of nanotechnology. However, as a complex comprehensive system, this type of equipment involves many fields such as ultra-high vacuum, low temperature, extremely low vibration, precision machining, precision electronic detection and control, etc. China's SPM equipment has long relied mainly on imports from developed countries.

The Gao Hongyu Research Group (N04 Group) of the Institute of Physics of the Chinese Academy of Sciences has been working on scanning probe microscopy and its application in low-dimensional quantum structures for many years, and has achieved a series of important results. At the same time, it has also accumulated in the independent development of related high-precision instruments, laying a solid foundation. Working closely with Zhaoqing, a researcher at the Institute of Physics, they independently developed a number of core key components and successfully completed a comprehensive upgrade of a commercial four-probe system [Review of Scientific Instruments, 88(6):063704, 2017].

In view of the problems of large noise, significant temperature drift and low resolution of the original system, they have completely modified the system in many aspects, including vibration and damping, scanning structure, thermal link and thermal screen, and needle tip positioning scanning electron microscope. The replacement, etc., fundamentally solves the problems of system signal-to-noise ratio, mechanical and temperature stability, imaging resolution and cooling. At the same time, they developed a "time-sharing re-control circuit unit" to provide a low-cost time-sharing control solution for multi-probe SPM systems, further exploiting the features and advantages of the system. The research team's doctoral student Ma Ruisong and associate researcher Bao Lihong and others used a completely modified and upgraded four-probe system to systematically study the transport properties such as graphene grain boundary resistivity and mobility, and expanded the graphene crystal. The understanding of the intrinsic electron transport properties at the boundary/pleat shows the unique advantages of the modified four-probe scanning tunneling microscope system in studying the effects of microstructural properties such as defects on the transport properties of materials [Nano Letters, 17 (9 ): 5291, 2017].

Recently, under the direct guidance and guidance of the researcher from Zhaoqing, Wu Zebin and Gao Zhaoyan, Ph.D. students of the N04 group, successfully developed and built a number of new low-temperature optical SPM combined molecular beam epitaxy (MBE) systems with stable performance and scalability. Strong, good sample preparation ability and good optical compatibility, the main technical indicators have reached the international level of similar commercial systems.

Since many of the core components used are self-developed, the system has many advantages that are not available in commercial systems: 1) The modular design of the scanning probe can be compatible with both STM probes and qPlus AFM sensors, with high rigidity and structure. Compact features, while achieving extremely low vibration levels, the probe can be adjusted in-situ in ultra-high vacuum and low temperature environment, which significantly improves the debugging efficiency and ease of use of the device; 2) Patented scanning probe lock The structure can realize the probe locking at the low temperature end to further reduce the leakage heat from the room temperature; 3) The mechanical and piezoelectric driving lens adjustment mode can be flexibly selected according to the specific experimental requirements to ensure accurate introduction and efficient collection of optical signals; 4) The integrated MBE subsystem features a low temperature adsorption cold screen for up to six different materials and RHEED, LEED, QCM and other in-situ growth monitoring capabilities.

The R&D team performed repeated debugging and design improvements on the system and completed a comprehensive performance test. They can obtain high-resolution atomic resolution images on clean HOPG surface and Au(111) surface, and further verify the performance of the system by scanning tunneling spectrum, tunneling junction noise spectrum and two-dimensional periodic atomic structure preparation.

In addition, the R&D team has optimized and customized the system according to the specific needs of the research application unit, and conducted long-term reliability tests on multiple core key components and the system as a whole. At present, many sets of systems have been delivered to the Institute of Physics, Tsinghua University, National Nanoscience Center, Zhongshan University and other cooperative units to carry out research and application in different directions, and verified the system through remote transportation and remote installation testing. Design rationality and reliability. Further, according to the special requirements of major scientific instruments of the Ministry of Science and Technology, the R&D team has promoted and applied the research results on a larger scale.

At present, components and complete systems including various evaporation sources and controllers, scanning probes, optical adjustment tables, and molecular beam epitaxy systems have been promoted and applied in dozens of universities and research institutions at home and abroad.

The detailed work of this optically compatible low temperature scanning probe microscope system is published in the recent issue of Scientific Instruments Review [Review of Scientific Instruments 89, 113705 (2018); doi: 10.1063/1.5046466]. The work was supported by the major scientific instruments of the Ministry of Science and Technology and the key technology research and development team project of the Chinese Academy of Sciences.

(Original title: Progress in the development of ultrafast laser ultra-high vacuum scanning probe microscope system)