Information transfer monolayer

Monolayer FOms Transferred to Solid Substrates. Historically, the spectroscopic investigation of monolayer physical structure has been performed on films transferred to solid substrates, usually through conventional L-B techniques. A wide variety of methods may then be employed in the study of these films. For example, ultraviolet, circular dichroism, and IR spectroscopy, as well as electron microscopy have been performed on monolayers transferred to quartz (for UV and CD), Ge (for IR), and mica (for EM). While much useful information has been obtained in the study of transferred monolayers, there is always a concern about whether the actual physical process of transfer from a gas-liquid to a gas-solid interface induces a change in the structure of the molecule. 

Transfer of Photons, Electrons, and Information in Monolayer Organizates... 

Figure 6. Information transfer in monolayer organizates. Absorption spectra before separation of the dye B copy monolayer from the original dye A monolayer (top), and of the two plates after separation of the monolayers (bottom). Composition of the mixed monolayers (molar ratios) is dye A methylarachidate arachidic acid — 1 9 1 and dye B behenic acid = 1 10. (Reproduced, with permission, from Ref. 25. Copyright 1981, Pergamon Press, Ltd.)...

Obviously, the original monolayer (dye A) is unchanged after the separation procedure. The anisotropy is the same as in Figure 6, top, no loss of dye or of preferential orientation is observed. From the absorption spectra of the copy monolayer (dye B) it must be concluded, that information transfer from the original monolayer has been obtained and preserved through the entire procedure, although some loss of dye and of anisotropy has occured. Through the described sequence of manipulations information can be transferred in molecular dimensions. 

It is known that even condensed films must have surface diffusional mobility Rideal and Tadayon [64] found that stearic acid films transferred from one surface to another by a process that seemed to involve surface diffusion to the occasional points of contact between the solids. Such transfer, of course, is observed in actual friction experiments in that an uncoated rider quickly acquires a layer of boundary lubricant from the surface over which it is passed [46]. However, there is little quantitative information available about actual surface diffusion coefficients. One value that may be relevant is that of Ross and Good [65] for butane on Spheron 6, which, for a monolayer, was about 5 x 10 cm /sec. If the average junction is about 10 cm in size, this would also be about the average distance that a film molecule would have to migrate, and the time required would be about 10 sec. This rate of Junctions passing each other corresponds to a sliding speed of 100 cm/sec so that the usual speeds of 0.01 cm/sec should not be too fast for pressurized film formation. See Ref. 62 for a study of another mechanism for surface mobility, that of evaporative hopping. 

The results presented here seem to indicate that 1) the local order about ruthenium centers in the polymers is essentially unchanged from that in the monomer complex and 2) that the interaction with the electrode surface occurs without appreciable electronic and structural change. This spectroscopic information corroborates previous electrochemical results which showed that redox properties (e.g. as measured by formal potentials) of dissolved species could be transferred from solution to the electrode surface by electrodepositions as polymer films on the electrode. Furthermore, it is apparent that the initiation of polymerization at these surfaces (i.e. growth of up to one monolayer of polymer) involves no gross structural change. 

I1M isotherms of amphiphile monolayers on aqueous subphase have been used to determine occupied molecular areas (Am[,i) and other (implied) structural properties. The area of the monolayer can be monitored during film transfer to obtain information on film structure. An example is seen in Figure 3.5.12 (10) for a DDAB mono-layer, sustained at a surface pressure of 20 mN m on a K2PtCl4 subphase. A uniform transfer is demonstrated over 10 dip cycles (average transfer of 1.03), and a Y-type film is evident from the same transfer for both up and down portions of... 

We are currently exploiting the unique ability to control the architecture in these monolayers to further investigate their photoelectrochemical properties with respect to such factors as light intensity, solution and film redox components, assembly structure, dye orientation, etc. We are particularly interested in using the monolayer structural information we now have to correlate film electronic properties with charge transfer effects at both the dye-solid and dye-liquid interfaces. 

Underpotential deposition (UPD) is the electrochemical adsorption and (partial) reduction of a submonolayer or monolayer of cations on a foreign metal substrate at potentials more positive than the reversible potential of the deposited metal [141]. The UPD phenomenon is used in many fundamental and applied studies because it offers a means of controlling coverages during electrodeposition in a very concise manner. Until recently, most of the information obtained about the structure of the overlayers deposited on single crystal surfaces has come from indirect means such as current-voltage analysis or by analysis of the deposited films after transfer to a UHV chamber [141]. 

Photoisomerization of the monolayer to the c/s-azobenzene configuration removes the threaded Fc- i-CD to a spatially separated position which retards the electron transfer rate. Therefore, the assembly functions as a molecular optoelectronic system which records optical information and transduces it into an electronic signal. 

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