Erasable media

In this chapter the properties of organic molecules which are potentially useful as archival digital optical memory media, mainly erasable media, will be described. The memory media which require wet development/fixing processes will not be mentioned. Photopolymers and photoresists are also beyond the scope of this chapter. 

Read Only media are already on the scene in the form of laser discs (videoK compact discs (audio) and CD-ROM s, while developments are still occurring in the area of WORM and erasable media. It is the latter two categories to which the remainder of this paper is devoted. 

Yet another report on an erasable media utilizes the broadening and shifting of an absorption band which occurs upon annealing amorphous solid dyes.25 In the examples reported, writing was done with anthraquinone dyes using microsecond write pulses at 22.5 mW (Kr laser) and millisecond erase pulses at 4 mW. About 100 cycles were possible before failure occurred due to irreversible hole opening. 

Figure 12. Polymeric liquid crystals studied as erasable media.

Recent work on plasma polymerization [31] shows promise for providing good barrier layers (especially for magneto-optic erasable media) and abrasion-resistant coatings. But plasma-polymerized materials (such as diamond-like carbon, produced by polymerization of ethene or ethyne) are so disordered, crosslinked and ill understood that they hardly qualify for the term polymer, and will not be discussed further in this chapter. 

Takenaga, M. et al. 1983. New optical erasable medium using tellerium suboxide thin film. SPIE Proc. 420 173. 

In a related phenomenon, the spectral shifts which accompany aggregation-deaggregation have been reported as a basis of yet another erasable medium.24 The active layer consists of discrete particles of a cocrystalline complex of a pyrylium dye with a polymer such as polycarbonate. Pulsed irradiation of this aggregated film resulted in an instantaneous deaggregation process which was accompanied by a hypsochromic shift of about 100 nm. The recording mechanism is believed to be thermal and a thermal erasure (reaggregation of the dye-polymer complex) was also demonstrated. 

Switching-Field Distribution. Both and have a strong relation with the recording process. determines the maximum output signal of a recording medium and hence the signal-to-noise ratio. ascertains how easily data can be recorded and erased or changed, but it also determines the maximum head field. On the other hand it also controls the ease with which data can be destroyed, eg, by stray fields. The lower the the more sensitive the medium is to all kinds of fields. In this way, influences the noise level as well. The squareness ratio S (= /Af ) can also be derived from the... 

CD-R was something of a surprise invention as, in the late 1980s, most of the major manufacturers in the optical memory area were commercializing the non-standard and relatively expensive WORM media, while focusing their research and development efforts on erasable optical storage. It was also believed that a writeable CD-Audio/CD-ROM-compatible medium was not feasible, due to the high reflectivity needed to meet the CD standard as defined by the Red and Orange Books.196... 

The mechanism of WORM recording and indeed of all currently available optical disc media, whether erasible or write-once, depends upon the heat generated by a focused laser beam impinging on an absorbing medium. The energy, normally near-IR radiation, is transmitted to the absorbing material in a time much shorter than the time it takes for the heat generated to dissipate by thermal conduction. 

For liquid as the flowing medium, the maximum bed diameter allowed is in the millimetre range, and this implies that one cannot rely on liquid diffusion to erase velocity profiles in microflow and bench-scale reactors of the usual size. 

Prepare your illustration in any medium, but try to keep it simple (non-electronic) and openly visual to the team. Thus, a flipchart or dry erase board is probably most effective. Artist skills are not required ... 

The cycloreversion quantum yield of 17b (0 = 0.00013) was much lower than that of 15b (O = 0.075). The very low cycloreversion quantum yield was found to increase steeply as much as 34-fold when the temperature was raised from 25 to 150°C. The large temperature dependence provides 17 with thermal-gated reactivity. The recorded memory in this system can be read many times with a weak laser, which does not raise the temperature of the medium. The memory can be erased with a high-intensity laser, which can raise the temperature of the medium to as high as 100-150 °C. 

Fukaminato, T., Kobatake, S., Kawai, T, and Irie, M. Three-dimensional erasable optical memory using a photochromic diarylethene single cry stal as the recording medium. Proc. Jpn. Acad. 77, B, 30, 2001. 

---