Data storage applications

Like many simple data storage applications, its operations don t seem veiy interesting they are different ways of entering, searching, and updating the attributes. There is a current... 

World consumption in 1995 was ca. 1800t, of which ca. 75% was used in the manufacture of video tapes ca. 14% for audio and 11 % for data storage applications. Consumption is expected to increase. 

With LM, the magnetic field is kept constant while the laser is switched according to the signal. Because only the laser power is modulated, possible data rates are higher than for MFM. They are limited by the present coding electronics to about 2 Mbyte/s, the same as for magnetic hard disks. Therefore, LM is the preferred mode for data storage applications. The main drawback of this method is that only new domains are written but no old information is erased. Whole sectors have to be erased in a separate mn before new information can be stored (no DOW). A solution to this problem is the use of multilayers. 

Second, in addition to the above, the fact that many expanded porphyrins are highly colored makes their use as dyes an obvious possibihty. Here their planar nature makes them particularly attractive as chromophores for use in liquid crystals and optical data storage applications. Also, these properties could make them of interest as photo-sensors in various clinical or pseudo-clinical situations. For instance, the high affinity by certain sapphyrins for enveloped viruses and cholesterol rich liposomes suggests that expanded porphyrins could be used to detect and/or destroy a variety of unwanted biological targets, including arterial sclerotic plaque. 

The largest producers of metallic iron pigments are Dowa Mining and Toda Kogyo (Japan). World consumption in 2002 was ca. 1800 t, of which ca. 65% were used in the manufacture of broadcasting media, 2% for audiotapes, and 33% for data storage applications this last being expected to increase later. 

This chapter discusses photochromic azobenzene polymers and photochromic molecules capable of undergoing photodimerization as materials for potential use in optical data storage applications. A brief introduction to photochromism, including recent examples of some photochromic systems, other than azobenzenes, based on variety of applications is presented at the outset. Thereafter, we shall focus on azobenzene photoaddressable polymers (PAPs) and [4 + 4]-photocycloaddition as materials for ultrahigh capacity optical data storage. 

We shall now embark on the main focus of this chapter photochromic azobenzene polymers and photochromic materials capable of undergoing photodimerization for potential use in optical data storage applications. Herein, the photochromic polymers described are those in which the photochromic molecule is covalently linked, either as part of the main chain or as a side-chain, to the polymeric system. 

A novel approach to data storage applications involves a glassy carbon electrode with a coating of [Ru(bipy)2(PVP)Cl]Cl, where PVP is poly-4-vinylpyridine. The rotating electrode oxidizes iron(II) at 640 mV [the polymer coating will inhibit iron(II) oxidation until ruthenium(II) centres are oxidized to ruthenium(III)]. If the electrode is irradiated, a photochemically mediated substitution of the chloro hgand by an aquo ligand will occur and, after this radiation, a more positive potential (740 mV) is required to oxidize iron(II). Thus if the electrode potential is held between 640 and 740 mV a yes / no device is possible since irradiation will eliminate the flow of current. ... 

We have prepared multi-component photorefractive polymers for optical data storage applications (8). This photorefractivity is a combination of two functionalities electro-optic effect and photoconductivity. We have achieved holographic diffraction efficiencies up to >30% in our composites. 

Figure 14.24 Copolycarbonates for optical data storage applications.

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