LB-monolayers

The lubricant properties of alkanethiols and fluorinated alkanes have been studied extensively by scanning probe techniques [163]. In agreement with experiments on LB monolayers it was found that the fluorocarbon monolayers show considerably higher friction than the corresponding hydrocarbon monolayers [164, 165 and 166] even though the fluorocarbons are known to have the lowest surface free energy of all organic materials. 

The observation that Langmuir monolayers often exist as phase-separated domains has begun to be exploited as a means to produce LB monolayers with two-dimensional patterns. This approach aims to form, transfer, and stabilize these domains on appropriate substrates by combining the Langmuir-Blodgett method with the covalent bonding aspect of self-assembly. There are a small number of studies, and the possible further functionalization of the domains and use of different combinations of materials make this area promising for the construction of patterned films. 

Fulda and Tieke [77] studied the effect of a bidisperse-size distribution of latex particles on the structure of the resulting LB monolayer. For this purpose, a mixed colloidal solution of particles la and lb was spread at the air-water interface. Particles la had a diameter of 434 nm, particles lb of 214 nm. The monolayer was compressed, transferred onto a solid substrate, and viewed in a scanning electron microscope (SEM). In Figure 10, SEM pictures of LB layers obtained from various bidisperse mixtures are shown. 

FIG. 9 Typical SEM pictures of LB monolayers of particles la on a glass support at different magnifications. (From Ref. 156.)... 

In Figure 12, LB monolayers of particles 2 on a glass substrate are shown after immersion in a nickel-plating bath for 15 and 40 sec. The metal coating of the particles is clearly recognizable. 

FIG. 12 SEM pictures of LB monolayers of particles 2 on a glass support, deposited from an aqueous solution containing disodium tetrachloropalladate (cone. 10 mol L and subsequently immersed in a plating bath for electrodeless nickel deposition for (a) 15 and (b) 40 sec. Typical SEM pictures of particle monolayers not subjected to nickel coating are shown in Figure 9. (From Ref. 156.)... 

Fig. 18 The rectification of MOM (Metal I Organic I Metal) sandwiches consisting of three elements (1) a macroscopic bottom Au or A1 electrode, (2) an 0.3 mm2 top A1 or cold Au electrode pad, and, between them (3) (a) an LB monolayer of 36a [38] (b) an LB monolayer...

Fig. 25 STS curves (normalized I/V plots of LB monolayers of isomers 55 (crosses) and 56 (dots), deposited on an Au film over HOPG (highly oriented pyrolytic graphite), and scanned with a Pt/Ir nanotip. The films exhibit rectification in opposite quadrants of the plot, where the polarity is defined by the sign of the substrate electrode. Electron flow at forward bias in each case is from the acceptor to the donor [127]...

Fig. 8 (a) The I-V curve measured for a junction consisting of an LB monolayer of margaric acid formed on an Al bottom electrode and a top Au electrode fabricated via the PALO technique, (b) Semilogarithmic plot of current density vs the chain-length of fatty-acid monolayers. The fit to a straight line gives a slope of fl = 0.86 A-1. (Reprinted with permission from [78])... 

Figure 7.2. Dependence of the film conductivity on the number of LB monolayers deposited onto an AI microelectrode array with a 0.1-mm distance between fingers.

The feasibility of the fabrication of comb like fluorocarbonpolymer LB films has been shown. These films can be deposited onto different kinds of substrates as y-type layers by the usual LB technique. In this case the deposition procedure is much simpler than the one for polyimide LB films, but the temperature, chemical and mechanical stability, and dielectricproperties of the fluorocarbonpolymers are not inferior to those of polyimides. The fluorocarbons are more hydrophobic than ordinary hydrocarbons, hence shorter hydrophobic chains can be used and thinner monolayers can be prepared (the PFHA-AA LB monolayer thickness investigated was 16.5 x l(L8cm). 

It is obvious that such processes involving monomolecular film transfers will easily be disturbed by defects arising from various sources. As will be shown in the following text, these defects are in most cases easily detected. The structural analysis of the molecular ordering within a single LB monolayer is important both to understand how the environment in the immediate vicinity of the surface (i.e., solid) affects the structure of the molecular monolayer and to ascertain how the structure of one layer forms a template for subsequent layers in a multilayer formation. 

The LB monolayers of dimethyldioctyadecylammonium ions on molecularly smooth muscovite mica surfaces were investigated. Direct measurements of the interaction between such surfaces were carried out using the surface force apparatus. A long-range attractive force considerably stronger than the expected van der Waals force was measured. Studies on the electrolyte dependence of this force indicate that it does not have an electrostatic origin but that the water molecules were involved in this. 

The focus in this chapter is on the scientific issues and challenges in the application of vapor deposited top metal contacts to devices fabricated from self-assembled monolayers (SAMs) and related films such as Langmuir Blodgett (LB) monolayers. Specifically the chapter will review the types of possible interactions... 

Use of an organic monolayer can be either as prepared on the surface of a liquid or after being transferred to a solid substrate to make an LB monolayer. Use of such a molecular assembly as a stencil or a template has many advantages. Besides its relatively simple procedure for template preparation, the periodicity of the functional groups or particular ions can be regulated by appropriate additives and the surface area of the monolayer by using a known surface area-surface pressure relationship. 

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