Layer deposition Langmuir-Blodgett

Atoms or molecules adsorbed on a metal surface do not fluoresce because of highly effective quenching via creation of electron-hole pairs in the substrate. However, their fluorescence can be observed if they are separated from a metal by a dielectric spacer layer. The Langmuir-Blodgett technique allows one to deposit a fatty acid layer of a well-controlled thickness and thus provides an opportunity to study fluorescence of an adsorbate versus its distance from the surface (see Fig. 5.9). 

From what you know about wetting, contact angles, and spread monolayers, explain why a Langmuir-Blodgett layer will deposit as a F type if there are nonpolar fatty acids, yet will switch to a Z-type deposition if bipolar alcohols or amines are added (see Refs. 175, 176). What defines the critical contact angle for the deposition change ... 

Langmuir-Blodgett films (LB) and self assembled monolayers (SAM) deposited on metal surfaces have been studied by SERS spectroscopy in several investigations. For example, mono- and bilayers of phospholipids and cholesterol deposited on a rutile prism with a silver coating have been analyzed in contact with water. The study showed that in these models of biological membranes the second layer modified the fluidity of the first monolayer, and revealed the conformation of the polar head close to the silver [4.300]. 

The Langmuir-Blodgett (LB) technique was successfully applied for the deposition of thin protein layers (Langmuir and Schaefer 1938, Tiede 1985, Lvov et al. 1991). LB organization of protein molecules in film not only preserved the structure and functionality of the molecules, but also resulted in the appearance of new, useful properties, such as enhanced thermal stability (Nicolini et al. 1993 Erokhin et al. 1995). 

Supported lipid bilayers on planar silicon substrates have been formed using S-layer protein from B. coagulans E38/vl and from B. sphaericus CCM 2177 as support onto which l,2-dimyristoyl-OT-glycero-3-phosphocholine (DMPC) (pure or mixtures with 30% cholesterol) or DPPC bilayers were deposited by the Langmuir-Blodgett-technique (Pig. 

DE Gennes, P. G., Deposition of Langmuir-Blodgett layers, ). Colloid Polym. Sd. 264, 463-465. 

In contrast to the flow-directed and Langmuir-Blodgett approaches described above, the printing approach used to deposit the NWs is a dry stamping approach analogous to that described in Chapter 13. Up to 10 addressable vertically stacked layers have been demonstrated. Each layer... 

Multilayer Langmuir-Blodgett films doped with a cyanine dye have been deposited on the surface of a quartz multimode optical fiber and the fluorescence properties investigated. 49 The fluorescence intensity of the films was found to be a periodic function of the number of layers due to the waveguide properties of the films. 

In both cases the top layer of these layered polyelectrolyte films contains many ion sites that can bind redox ions by ion exchange vdth the electrolyte solution. Homo polypeptides such as poly(L-lysine) and poly(L-glutamic add) have been employed to form layered polyelectrolyte films with Fe(CN)6 " electrostatically adsorbed onto ammonium sites in poly(lysine) [45]. Modified electrodes with polyelectrolytes mono-layers have also been deposited using the Langmuir-Blodgett technique [46-48]. 

Some decades ago (Langmuir, 1920), it was reported that, when a clean glass plate was dipped into water covered by a monolayer of oleic acid, an area of the monolayer equal to the area of the plate dipped was deposited on withdrawing the plate. Later, it was found that any number of layers could be deposited successively by repeated drippings, later called the Langmuir-Blodgett (LB) method (Petty, 1996 Roberts, 1990 Birdi, 1989). 

In the case of adsorption from solution, the surfactant layers are in equilibrium with the solution and will de-sorb on dilution. However, it would be very useful to produce adsorbed layers in both air and water, which will remain adsorbed. This can be achieved using the Langmuir-Blodgett deposition technique. The technique is based on the observation that if a surfactant, which is insoluble in water, is dissolved in a volatile, non-aqueous solvent and then spread on water, an insoluble monolayer of orientated surfactant molecules will remain at the air/solution interface. The effect of the spreading surfactant and its surface film pressure can be dramatically demonstrated by spreading hydrophobic talc powder on a clean water surface and then placing a... 

Figure 4.1. Schematic diagram of the formation of a Langmuir-Blodgett film. Each amphiphilic molecule is represented by a circle with a tail, where the circle denotes the hydrophilic end of the molecule. The left hand diagram represents the deposition of a monolayer on a hydrophilic substrate moving upwards. The right hand diagram represents the deposition of a second layer during the downward movement of the substrate.

We have studied the photoelectrochemical behavior of Chi a and Chi b on an n-type Sn02 (60) optically transparent electrode (OTE thickness of the Sn02 layer on the glass substrate, ca. 2000 A donor density, 1020-21cm-3). Chi monolayer assemblies, deposited by means of the Langmuir-Blodgett technique (20,21), were employed. The use of such monolayer assemblies as interfacial dye layers... 

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