Multilayer deposition

Optical Coatings. Thin surface coatings are appHed to optical components to improve performance. Wideband antireflection coatings for the visible and ir regions need materials with a refractive iadex of for the best efficieacy. Cerium fluoride, a stable material resistant to humidity damage, has a suitable iadex, 1.63 ia the visible, 1.59 ia the iafrared, and is transparent over the range 0.5 p.m to 5 p.m. It is one of the compounds used to build up the multilayers deposited on lenses, sensors, and the like. 

Mishina, E. D., Nagai, K. and Nakabayashi, S. (2001) Self-assembled CU/CU2O multilayers Deposition, structure and optical properties. Nano Lett., 1, 401 104. 

Formation of subsequent layers can occur either in the way of formation of a single nucleus which then spreads undisturbed over the whole face or by formation of other nuclei before the face is completely covered (multinuclear multilayer deposition). Now let us discuss the first case in more detail. 

Multilayer deposition of halloysite is possible not only on large solid surfaces but also on soft biological surfaces such as wood or cotton cellulose microfibers (Figure 14.18). This coating allows a drastic increase in the porosity of the fibers and materials made from them (paper and textile). 

The use of UPD layers can in principle generate deposits with composition modulated on the atomic scale, and Pauling et al. have produced what they call hetero-structured ultra-thin films containing Ag, Pd and T1 by this method [158], Stickney and coworkers have assembled multilayered deposits of CdTe and GaAs by addition of one atomic layer of the individual components at a time, a process they call electrochemical atomic-layer epitaxy [159 162], The essential controlling feature in the UPD mechanism is that the deposited layers are allowed to reach equilibrium. Hence, the process represents an extreme of local, reversible control. 

The final film thicknesses were increased either by increasing the deposition time or by multilayer deposition. Although the film thickness increases with longer deposition time, the film morphology tends to be poor, as shown in Fig. 7.9. A two-layer technique that used two layers of TBSBCCO films, with an intermediate layer of Ag, improved the film uniformity and morphology, as shown in Fig. 7.10. The deposition process for the multiple layer is as follows (1) Single-crystal substrates are coated with 300 A of Ag (2) TBSBCCO films (0.4-1.3 pm) are prepared by electrodeposition (ED) on Ag/LAO (3) 300 A of Ag are deposited on ED-TBSBCCO/Ag/LAO (4) the second layer of TBSBCCO is electrodeposited (0.4-1.3 pm) on Ag/ED-TBSBCCO/Ag/LAO and (5) the complete two-layer system is reacted. 

No significant decrease was recorded from the area-time isotherm of the PS 1 monolayers at 10 mN/m, which indicates that the PS I monolayers formed are rather stable. This stability makes it possible for a multilayer deposition by the LB method. 

The films are epitaxial in the sense that the lattice constant is intermediate between those of copper and nickel. As indicated above, that modulated strain is probably responsible for the increased hardness. Other authors (5) have tried to explain similar effects by stating that the layers were specifically oriented. Our example (6) demonstrates that these considerations must be reexamined since it was possible to achieve the effect in a crystalline multilayer deposited on an amorphous nickel-phosphorus underlayer. It appears that layer thickness is the important parameter here. 

Ryde, N. Kihira, H. Matijevic, E. (1992) Particle adhesion in model systems. 15. Effect of colloid stability in multilayer deposition. J. 

Moller etal. [462] have performed in situ STM observations of Ni electrodeposition on reconstructed Au(lll) electrodes. Ni nucleation proceeded in three distinct potential-dependent steps. The same group of researchers [463] has studied electrodeposition and electrodissolution of Ni on Au(lOO) electrodes. Pronounced differences were observed for the nucleation and submonolayer growth on the reconstructed and unreconstructed surfaces. On perfectly reconstructed Au(lOO), the formation of Ni islands started at overpotentials significantly higher (rj > 100 mV) than on unreconstructed surface (rj > 40 mV), where Ni monolayer islands were formed. Dissolution of the Ni film exhibited better monolayer stability in comparison to the multilayer deposit. 

Ordered multilayer deposits were grown on both the Cu(l 11) and Cu(lOO) substrates. Electron beam damage to the phthalocyanine molecules was not observed. Space-charge effects due to electron bombardment were not apparent below an incident electron energy of 25 eV. 

The surface structures observed for the multilayer deposits of the phthalocyanines on both substrate faces, Cu(l 11) and Cu(lOO), were not those of any plane in the bulk crystal structure of the phthalocyanines. 

Ordered multilayer deposits of phthalocyanine molecules could be observed by low-energy electron diffraciton with no apparent electron beam induced chemical effects. This appears consistent with the general trend for molecules with highly conjugated electron systems to be more stable under electron bombardment than other organic molecules. 

Traditionally, monolayer and multilayer adsorption have been used in detergency, mineral processing, flotation, stability of food and pharmaceutical emulsions, and the like, and, as a consequence, the topics of this chapter have been a central part of colloid science. In recent years, however, research on monolayer and multilayer deposition has mushroomed rapidly because of significant new opportunities. 

FIG. 7.1 Deposition of multilayers using the Langmuir-Blodgett technique (a and b) monolayer deposition and (c and d) multilayer deposition. 

Fig. 42. Magnetoelastic coefficient versus magnetic field applied parallel and perpendicular to the long axis of the cantilever (parallel measurement direction) of an as-sputtered TbFe/Fe multilayer deposited (a) without a dc field (H

Multilayer depositions may be performed using, say, an EG G Princeton Applied Research (PAR) Model 173 potentiostat/galvanostat with a PAR Model 276 interface providing computer control capability. A PC furnished with a GPIB-... 

While preparation of multilayers by the self-assembly method is less straightforward than that by the LB method, it still can be accomplished [11-13], The amphiphilic molecule should have a functionalized terminal group. In order to avoid either uncontrolled multilayer deposition or the simultaneous attachment of both head and terminal groups to the substrate, the terminal group should be protected. After the first monolayer is deposited, the sample should be removed from the solution, the terminal groups should be deprotected and the sample should be returned to the solution for deposition of the second layer. Subsequent deprotections and reimmersions allow one to coat the desired number of layers onto the substrate. 

---