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R&D From Nanjing Normal University: Thinnest CD-RW, Atomic-Scale Storage Possible

Demonstrated that photoluminescence emission of WS2 monolayers can be controlled and modified, and consequently, it works as thinnest light disk with rewritable data storage and encryption capability.

By Nanjing Normal University

Using a focused laser beam, scientists can manipulate properties of nanomaterials, thus ‘writing’ information onto monolayer materials. By this means, the thinnest light disk at atomic level was demonstrated.

The bottleneck in atomic-scale data storage area may be broken by a simple technique, thanks to recent innovative studies conducted by scientists from Nanjing Normal University (NJNU) and Southeast University (SEU).

Through a simple, efficient and low-cost technique involving the focused laser beam and ozone treatment, the NJNU and SEU research teams, leading by Prof. Hongwei Liu, Prof. Junpeng Lu and Prof. Zhenhua Ni demonstrated that the photoluminescence (PL) emission of WS2 monolayers can be controlled and modified, and consequently, it works as the thinnest light disk with rewritable data storage and encryption capability.

In our childhood, most of us are likely to have experience of focusing sunlight onto a piece of paper by magnifying glass and trying to ignite the paper. The scorched spot on paper is a sort of data recording at the moment. Instead of focusing sunlight, we focus laser beam on modified atomic level materials and study effects of the focused laser beam on PL emissions of the materials,” said Prof. Lu.

Data storage and encryption: information ‘drawn’ on ozone treated WS2 films
Owing to its advantage of direct visibility, PL is usually considered as an ideal technology in terms of encryption and decryption data storage. For a straightforward and effective encryption data storage method, the following aspects are desired: (i) direct writing (fast writing-in speed); (ii) high security level; (iii) large data storage capacity; (iv) visual decryption reading; (v) erasing capability.

To address these technological challenges, researchers demonstrate the thinnest light disk with encryption functionality.

The write-through and erasable encryption are realized on WS2 monolayers. The writing-in and reading-out of information are enabled by the directly controlling of fluorescence contrast of WS2 monolayers. Ozone and focused laser beam scanning are employed to on-demand manipulate PL emission and realize encryption.

With this simple and low cost approach, the scientists were able to use the focused laser beam to selectively ‘write’ information onto any region of the film to storage encrypted data. In addition, the written data are erasable, making the monolayer light disk reusable.

Interestingly, the evolution of PL emission with different writing laser powers could be used to assign different gray levels. The 16 gray levels assignment indicates a typical triangle WS2 monolayer with the side length of 60μm can storage ~1 KB data. Owing the high spatial resolution and power sensitivity, the storage capacity within one nm thickness could be up to ~62.5 MB/cm2 and the writing speed can reach ~6.25 MB/s. This technology will be beneficial to extend the optical encryption into low dimensional regime, offering an unexpected information-secure solution to exchange data.

This innovation was published online in the journal Advanced Functional Materials on 24 June 2021.

The fast-growing information field demands higher security and larger storage capability. To develop light disk that cater to the industry standard, The research teams from NJNU and SEU will extend the versatile focused laser beam technique to wafer-scale monolayer material. In addition, they will look into further improving the storge capability of light disk via normal direction stacking.

Article: The Thinnest Light Disk: Rewritable Data Storage and Encryption on WS2 Monolayers

Advanced Functional Materials has published an article written by Weiwei Zhao, School of Physics and Key Laboratory of MEMS of Ministry of Education, Southeast University, Nanjing, 211189 China, Shuang Cai, Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, School of Mechanical Engineering, Southeast University, Nanjing, 211189 China, Xin Wei, Ting Zheng, School of Physics and Key Laboratory of MEMS of Ministry of Education, Southeast University, Nanjing, 211189 China, Xin Xu, Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371 Singapore, Amina Zafar, School of Physics and Key Laboratory of MEMS of Ministry of Education, Southeast University, Nanjing, 211189 China, Hongwei Liu, iangsu Key Laboratory on Opto-Electronic Technology, School of Physics and Technology, Nanjing Normal University, 1 Wenyuan Road, Nanjing, 210023 China, Ting Yu, Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371 Singapore, Junpeng Lu, School of Physics and Key Laboratory of MEMS of Ministry of Education, Southeast University, Nanjing, 211189 China, Yunfei Chen, Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, School of Mechanical Engineering, Southeast University, Nanjing, 211189 China, and Zhenhua Ni, School of Physics and Key Laboratory of MEMS of Ministry of Education, Southeast University, Nanjing, 211189 China.

Abstract: The thinnest light disk is demonstrated at the atomic level by developing an erasable method to directly write encrypted information onto WS2 monolayers. The write-in is realized by precise control of photoluminescence emission by means of ozone functionalization and scanning focused laser beam. The visual decryption and reading-out of information are enabled by fluorescence contrast. The high encryption level is ensured by the threshold power upon which the data deletion will be triggered. Owing to the high spatial resolution and power sensitivity, the storage capacity within <1nm thickness can be up to ≈62.5MB cm−2, and the writing speed can reach ≈6.25MB s−1. Density functional theory calculations suggest that the disk formatting is realized by ozone molecule adsorption induced localized unoccupied states, while the read-in relies on the passivation of defects via substitution of the sulfur vacancies with oxygen atoms. The results of this study promote data storage and encryption on the atomic scale.

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