Research advances and typical applications of atomic deposition grating based on quantum technology

Significance  The implementation of the new definitions of international basic units based on fundamental physical constants in 2019 marked the official and comprehensive entry of precision measurement into the quantum era. In 2022, China clearly stated its intention to establish a national modern advanced measurement system centered on quantum metrology, with a focus on researching and establishing quantum measurement standards, exploring quantum metrology technologies based on quantum effects and physical constants, and promoting the upgrading and renewal of the measurement standard system. The atomic lithography grating, a nano-length scale based on quantum effects, has a grating pitch that is traced back to atomic transition frequencies. It can be directly used for instrument calibration without relying on the fixed value of metrological instruments, effectively shortening the traceability chain of nano-length measurement. The "Quantization of Measurement Units" has overturned the traditional hierarchical metrological traceability system. By adopting quantum measurement standards, it significantly improves the accuracy and stability of value reproduction, enabling the reproduction of values at any time, in any place, and by any entity, thereby achieving a flat traceability. Atomic lithography gratings achieve sub-nanometer accuracy with good consistency and can be mass-produced, making them promising for applications in the establishment of nano-scale length measurement systems, quantum precision measurement, instrument calibration, and other fields.

Progress  First, the preparation principle and technology of atomic lithography quantum gratings are analyzed. A laser wavelength of 425.55 nm is selected, corresponding to the transition energy level of chromium atoms from ₇S³ to ₇P⁴, with a silicon substrate. In a vacuum environment, the atomic furnace containing chromium powder is heated to a certain temperature, causing the atoms to erupt and form a chromium metal atomic beam. A pair of laser beams with the same wavelength but opposite propagation directions create a one-dimensional laser standing wave field with an optical intensity period of λ/2. After laser cooling and collimation, the atomic beam is vertically incident into the laser standing wave field. Within this field, the atoms are subjected to a dipole force, causing them to move towards the peaks or troughs of the standing wave. Eventually, they deposit onto the silicon substrate, forming a nanoscale quantum grating with a period equal to half the laser wavelength. The grating pitch can be traced directly to specific natural constants, allowing the grating to serve as a ruler without the need for metrological instrument calibration. Theoretically, the accuracy of atomic lithography gratings can reach the picometer level, similar to the precision of metrological testing instruments equipped with laser interferometers.

Subsequently, the research progress in the preparation of atomic lithography gratings, both domestically and internationally, is elaborated upon. As early as 1992, G. Timp and his team successfully utilized atomic lithography technology to produce a sodium grating, albeit an unstable one. Consequently, MCCLELLAND J J and colleagues opted for chromium atoms, successfully fabricating a chromium grating. Since then, numerous researchers have embarked on preparing quantum gratings using various metal atoms. Domestic research into the preparation technology of quantum gratings commenced in 1999, and in 2002, LI Tongbao and his team achieved a milestone by utilizing atomic lithography technology to produce China's first quantum grating. Currently, the preparation technology of atomic lithography gratings is continually optimized and upgraded, with researchers actively exploring specific applications for these gratings. Finally, the applications of atomic lithography gratings in instrument calibration, ultra-precise displacement measurement, grating pitch calibration, and nano-positioning stage calibration are introduced.

Conclusions and Prospects  Currently, both domestic and international research on the application of atomic lithography gratings is in a vigorous stage of development. The inherent metrological advantage of atomic lithography gratings stems from their ability to be directly traced back to atomic transition frequencies. This paper analyzes the research progress and typical applications of atomic lithography gratings, aiming to provide guidance for future research directions in this field and new insights for the development of key instruments such as photolithography machines in integrated circuits, as well as for the study of metrological traceability systems in China.