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The thinnest CD-RW
(Nanowerk Spotlight) Using a focused laser beam, scientists can manipulate the properties of nanomaterials, thereby 'writing' information onto monolayer materials. The result is a demonstration of the thinnest light disk with data storage and encryption functionalities at the atomic level.
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, led 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.
Direct-Writing, Erasable Data Storage and Encryption on WS2 Monolayers.
Design of The Thinnest Light Disk: Direct-Writing, Erasable Data Storage and Encryption on WS2 Monolayers. The writing-in and reading-out of information are enabled by the directly controlling of fluorescence contrast of WS2 monolayers. (Image: Prof. Zhenhua Ni's Lab)
"In our childhood, most of us were likely to have experimented with focusing sunlight onto a piece of paper by a magnifying glass and trying to ignite the paper," says Prof. Lu. "The scorched spot on the paper is a sort of data recording at that moment. Instead of focusing sunlight, we focus a laser beam on modified atomic level materials and study the effects of the focused laser beam on photoluminescence (PL) emissions of the materials."

Data storage and encryption: Information 'drawn' on ozone treated WS2 films
Information security has become a growing global issue in economic and military fields as well as in daily lives. Owing to its advantage of direct visibility, PL is usually considered an ideal technology in terms of encryption and decryption of stored data.
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, the researchers demonstrated 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 directly controlling the fluorescence contrast of WS2 monolayers. Ozone and focused laser beam scanning are employed to manipulate PL emission on demand 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 store encrypted data. In addition, the written data is erasable, making the monolayer light disk reusable.
Interestingly, the evolution of PL emission with different writing laser powers could be used to assign different grey levels. By assigning 16 gray levels, a typical triangle WS2 monolayer with the side length of 60 µm can store ∼1 KB data. The gray level assignment is archived by manipulating the laser power. Owing to high spatial resolution and power sensitivity, the storage capacity within 1 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 exchanging data.
This innovation was first published online in the journal Advanced Functional Materials ("The Thinnest Light Disk: Rewritable Data Storage and Encryption on WS2 Monolayers").

Future research
The fast-growing information field demands higher security and larger storage capability. To develop light disks that cater to industry standards, 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 storage capability of light disks via normal direction stacking.
Source: Provided by Nanjing Normal University as a Nanowerk exclusive

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