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Chemical Engineering

Memory in glass

Innovative material will store digital data in 3-dimensions

The storage of large quantities of digital data in a small piece of glass is the new possibility that has opened up with the research from the Photonic Materials Group at the Chemistry Institute of the São Paulo State University (Unesp), in Araraquara. The researchers have managed to develop a type of glassy material, produced with a high concentration of tungsten oxide, which may receive recordings in three dimensions, covering height, length and width. This represents an advance in relation to the principal electronic methods that store optical memory in two dimensions, such as CDs and DVDs, capable of accumulating data only on the material’s surface. With the capacity of three-dimensional storage in the glassy tungsten, the applications could advance in various fields of informatics and in the electro-electronic industry, in the manufacture of chips and memory for computers and in the production of devices for audiovisual recording. All of this clearly depends upon whether the research, still ongoing, can prove the efficiency of the new material and its possibilities of interaction with electronic equipment. “During the last three years lots of research has been done throughout the world in relation to materials with the capacity for three-dimensional recording, but, as far as we know, not a single other national or international group has reached the stage at which we find ourselves”, says the chemist Younès Messaddeq, the coordinator of the Unesp Photonic Materials Group.

The major advantage of the new material, which has a yellowish coloration due to the presence of tungsten in its composition, is that it can largely overtake the current storage capacity of the methods used with digital optical memory. For example, a common CD can store 700 megabytes of information, a quantity sufficient for an hour and fifteen minutes of high quality music or more than 300,000 pages of a text written with double spacing. The most advanced DVDs, on their part, can count upon 20 gigabytes of memory and are capable of storing a full-length film. “The glass could be used as a device for a recording or for transforming into a fine film, with some nanometers of thickness, similar to the films existing today in CDs and DVDs”, says the chemist Gaël Poirier, a post-doctorate student and one of the inventors of the new material. These compact discs possess a polymer film, which is also of nanometric thickness, deposited upon polished glass, where the information is recorded. There is a fine layer of photosensitive resin (for example, polycarbonate or polyester) produced from the evaporation of glass or special polymers. “We’re going to test direct recording on the glassy tungsten and on the fine film with the same material to see which of the two is the more efficient”, the researcher says.

The Unesp researchers guarantee that the storage capacity of the glassy material, based on tungsten oxide, will be infinitely greater than the current diskettes, although, for now, they cannot say precisely what will be the size of this memory. “As yet we haven’t made the necessary measurements, but the theoretical storage limit is 1.6 terabytes (1,600 gigabytes) per cubic centimeter (cm3)”, says Poirier. This capacity, according to Messaddeq, will be fundamental for the projection of the commercial success of the new glassy material, which now needs to be higher than 200 gigabytes because this is the highest volume of electronic memory information on the market, scheduled to be launched this year by the American company InPhase Technologies, a spin-off originating from the gigantic telecommunications company Lucent Technologies, which specializes in holographic storage, a technique that also allows for storing data in three dimensions. “The fundamental difference between our glass and the holographic materials that record in three dimensions is that the latter are polymers or porous glass containing polymers. They record in three dimensions, but the process is not reversible”, says Messaddeq.

With the Unesp glassy material things are different. It could be a counterbalance to the materials used today, experimentally, since when recording in three dimensions a major limitation is the fact that they cannot be reversed. “Not being able to re-record is a serious limitation in the field of data storage application because these materials can only be used as ‘definite’ memories”, argues Messaddeq. The recordings done on the glass synthesized in the Unesp laboratory can be wiped out by a thermal treatment or when exposed to appropriate lasers. This results in the fact that the material can be used as a re-recordable support or high capacity memory. As well as this, the new tungsten glass has a preparation cost that is a lot lower than the other special vitreous materials used as optical memory, such as the so-called chalcogenide glasses, which, although they allow for the expansion of memory recorded in two dimensions, are not three dimensional. Chemist Messaddeq is also involved in projects with chalcogenide glass (see Pesquisa FAPESP No. 86).

In 2002, the Japanese company Panasonic presented a DVD with a chalcogenide based film of high recording capacity (9.4 gigabytes) with the re-recording source. This material is produced with selenium, sulfur and tellurium, elements in the Periodic Table that are called the chalcogens. “The new tungsten glass is one hundred times cheaper in relation to the other materials that are being researched and used, in the future, for the storage of data.”

The ease of production of the photosensitive tungsten oxide glass is another major advantage of this material. It is prepared from a classical glass manufacturing process, based on a mixture of starting components, the constituent chemical reagents of glass – tungsten oxide (WO3), sodium polyphosphate (Na3PO3) and barium fluoride (BaF2). They are homogenized and placed in a crucible, a ceramic receptacle that supports high temperatures, which is put in an oven for melting. Next, the founded liquid is poured, with the help of a stainless steel pincer, tipped with platinum, into the appropriate metallic mold that has the desired geometry. The crucible used (made from aluminum oxide or platinum), as well as the melting temperature, depending on the material’s initial composition, varies from 1,000 to 1,600°C. After the synthesizing of the glass, the sample is submitted to re-heating during four hours, and thereafter is gradually cooled until it reaches room temperature. The final stage in the process is the surface polishing, an important point for improving the material’s optical quality. In order to confirm the vitreous state of the sample, the material is submitted to description techniques, such as X-ray diffraction, thermal analysis and visual observation. “The secret in our glass is not so much in the materials used, but in its chemical composition”, says Messaddeq.

By chance
Like some of the most important discoveries in human history, this new material came about almost by chance when Poirier was carrying out experiments during his doctorate degree work. ‘some two years ago I had been studying certain optical properties of glass containing tungsten oxide and by chance I tested its photosensitivity using a visible blue laser beam. This allowed me to verify that the glass was photosensitive in volume and could receive recordings in three dimensions”, says Poirier. In order to demonstrate this new property of the material (three dimensional recording or engraving), the researchers entered into a partnership with the Advanced Studies Institute of the Aerospace Technical Center (IEAv/ CTA), in Sao José dos Campos, which engraved by laser, in three dimensions, the famous face of the physicist Albert Einstein onto a sample of the glass that measured 1 centimeter in width by 3 centimeters in height.

In order to store data in the tungsten glass, ultraviolet lasers can be used (in the case of superficial engravings in two dimensions) or visible lasers, with a wavelength of 488 nanometers (nm) or 514 nm. This last mentioned laser was used to engrave the face of Albert Einstein in a three dimensional form. Infrared pulse lasers are also used for engraving data in three dimensions. In this case, the lasers have a very high power peak, of some megawatts or gigawatts, during a very short irradiation time (in the order of nanoseconds, one billionth part of a second, or nanosecond or femtosecond which correspond respectively to 10-9 and 10-12 seconds) in order to induce optical processes and the photosensitive effect.

The unprecedented discovery made the researchers decide to register a patent for the tungsten glass at the National Industrial Property Institute (INPI) with the assistance of FAPESP’s Patenting and Technology Licensing Center (Nuplitec). “This patent, entitled Three Dimensional Photosensitive Material for the Storage of Three Dimensional Data and Holography, is only valid for Brazil but within a year, as international agreements allow, we’ll carry out the protection of our discovery in other countries: United States, Japan, United Kingdom, France Germany, Sweden, Italy, Australia and China”, says Messaddeq. With the registration of the patent, the new synthesized material from the Unesp Photonic Materials Group at Araraquara will begin to be shown at congresses and events in this sector. Up until now, the only demonstration given abroad occurred during a workshop on advanced materials that took place in June last year at the University of Münster, in Germany. “I showed only a slide of the glass sample with the face of Albert Einstein and everyone present was impressed”, says Messaddeq.

National partnership
The next step for the researchers is to carry out a description of the material in order to determine its memory capacity. “These studies are going to point out if we need to upgrade the tungsten glass, improving its composition, or if it’s already reached the point for being produced on a pilot scale”, adds the group’s coordinator. In order to carry out this work, the scientists are looking for a national partner. “We don’t know if some research group in Brazil has the available technology to carry out these measurements. If we perceive that it doesn’t exist, then we’ll attempt to find a partner abroad”, says Messaddeq, who hopes to conclude this stage of the work by the end of this year.

Parallel to the description work, the group is researching forms of producing fine films starting from the glass. The development of adequate technology and the control of the parameters for preserving the phenomenon’s properties observed in the vitreous material are being carried out by the master’s student Bianca Montanari. “As tungsten shows different oxidation states, the preparation conditions were the key to the success of Bianca’s research”, says Messaddeq. “During the first year of her studies, she managed to explore the conditions for obtaining homogenous films of good optical quality, but she still needs to confirm various other properties existing in the glass material.”

The Photonic Material Laboratory at Unesp’s Chemistry Institute at Araraquara, coordinated by professors Messaddeq and Sidney José Lima Ribeiro, is made up of around forty professionals and students; there being eight researchers doing post doctorate work, ten doctorate degree students, seven studying for their master’s degree, along with two visiting researchers. Up until now the team has published about twenty articles in indexed international scientific magazines, such as the Journal of Chemical Physics, Journal of Physics and Chemistry of Solids and Applied Physics Letters.

The Projects
1. Development of glass containing tungsten oxide for application in optics.
2. Reversible photosensitivity in the ultraviolet and visible spectrums of glass
based on WO3
1. Regular Line of Research Assistance
2. Intellectual Property Support Program (PAPI)
Younès Messaddeq – Unesp
1. R$ 53,750.00 (FAPESP)
2. R$ 6,000.00 (FAPESP)