Nanoparticles for Holographic Data Storage

Shencheng Fu and colleagues created a nanofilm that can store data holographically and is environmentally stable. (Source: Northeast Normal University)

As we generate more and more data, the need for high-density data storage that remains stable over time is becoming critical. New nano­particle-based films may help to fill this need by providing materials that can holo­graphically archive more than 1000 times more data than a DVD in a 10-by-10-centi­meter piece of film. The new tech­nology could one day enable tiny wearable devices that capture and store 3-D images of objects or people.

“In the future, these new films could be incor­porated into a tiny storage chip that records 3-D color infor­mation that could later be viewed as a 3-D hologram with realistic detail,” said Shencheng Fu, who led researchers from Northeast Normal Uni­versity in China who developed the new films. “Because the storage medium is environ­mentally stable, the device could be used outside or even brought into the harsh radiation conditions of outer space.” The researchers demon­strated the tech­nology’s ability to be used for an environ­mentally-stable holo­graphic storage system. The films not only hold large amounts of data, but that data can also be retrieved at speeds up to 1 GB per second, which is about twenty times the reading speed of today’s flash memory.

The new films are designed for holo­graphic data storage, a technique that uses lasers to create and read a 3-D holo­graphic recrea­tion of data in a material. Because it can record and read millions of bits at once, holo­graphic data storage is much faster than optical and magnetic approaches typically used for data storage today, which record and read individual bits one at a time. Holo­graphic approaches are also inhe­rently high-density because they record infor­mation throughout the 3-D volume of the material, not just on the surface, and can record multiple images in the same area using light at different angles or consis­ting of different colors.

Recently, researchers have been experi­menting with using metal-semi­conductor nano­composites as a medium for storing nanoscale holo­grams with high spatial reso­lution. Porous films made of the semi­conductor titania and silver nano­particles are promising for this appli­cation because they change color when exposed to various wave­lengths of laser light and because a set of 3-D images can be recorded at the focus area of laser beam using a single step. Although the films could be used for multi­wavelength holo­graphic data storage, exposure to UV light has been shown to erase the data, making the films unstable for long-term infor­mation storage.

Recording a holo­graphic image into titania-silver films involves using a laser to convert the silver particles into silver cations, which have a positive charge due to extra electrons. “We noticed that UV light could erase the data because it caused electrons to transfer from the semi­conductor film to the metal nano­particles, inducing the same photo trans­formation as the laser,” said Fu. “Intro­ducing electron-accepting molecules into the system causes some of the electrons to flow from the semi­conductor to these molecules, weakening the ability of UV light to erase the data and creating an environ­mentally stable high-density data storage medium.”

For the new films, the researchers used electron-accepting molecules that measured only 1 to 2 nano­meters to disrupt the electron flow from the semi­conductor to the metal nano­particles. They fabricated semi­conductor films with a honeycomb nanopore structure that allowed the nano­particles, electron-accepting molecules and the semi­conductor to all interface with each other. The ultrasmall size of the electron-accepting molecules allowed them to attach inside the pores without affec­ting the pore structure. The final films were just 620 nano­meters thick.

The researchers tested their new films and found that holo­grams can be written into them effi­ciently and with high stabi­lity even in the presence of UV light. The researchers also demon­strated that using the electron-acceptors to change the electron flow formed multiple electron trans­ferring paths, making the material respond faster to the laser light and greatly acce­lerating the speed of data writing. “Particles made from noble metals such as silver are typi­cally viewed as a slow-response media for optical storage,” said Fu. “We show that using a new electron transport flow improves the optical response speed of the particles while still main­taining the particle’s other advan­tages for infor­mation storage.”

The researchers plan to test the environ­mental stability of the new films by performing outdoor tests. They also point out that real-life appli­cation of the films would require the develop­ment of high efficiency 3-D image recon­struction techniques and methods for color presen­tation for dis­playing or reading the stored data. (Source: OSA)

Reference: S. Liu et al.: UV-resistant holographic data storage in noble-metal/semiconductor nano­composite films with electron-acceptors, Opt. Mat. Exp. 8, 1143 (2018); DOI: 10.1364/OME.8.001143

Link: Center for Advanced Optoelectronic Functional Material Research, Northeast Normal University, Changchun, China

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