Form and Function in Multilayer Assembly: New Applications at the Nanoscale

Abstract

New frontiers in materials and polymer science include the development of assembly processes that are flexible, allow the access and implementation of nanoscale structure and order, can provide access to a broad range of materials systems, and yet can be implemented at relatively low cost. The ability to fine tune the composition of nanostructured thin films on the nanometer length scale, when combined with inexpensive patterning and templating routes, provides a powerful tool for nano‐ and microscale assembly of devices and novel new material systems. The layer‐by‐layer electrostatic assembly technique is a rich, versatile, and significantly inexpensive approach to the formation of thin films via alternating adsorption of positively and negatively charged species from aqueous solutions; this method has also been extended to include the alternation of polymers with hydrogen‐bond donor and acceptor groups. Polymer organic and organic/inorganic thin films formed using this technique may contain a number of different functional groups, including electro‐optic, electroluminescent, conducting, and dielectric layers, and functional organic and inorganic nanoparticles. Newly developed materials systems based on alternating layer methods will be addressed, as well as a number of frontier areas and future areas for the use of these systems, ranging from nanomechanical composites to electrochemical devices and templated deposition of functional microspheres. Both new functionalities incorporated within these materials and new means of patterning and templating these structures in two and three dimensions will be addressed in this review.

Multilayered Films Fabricated from Combinations of Degradable Polyamines: Tunable Erosion and Release of Anionic Polyelectrolytes

“…For the (1/SPS) 4 (2/SPS) 4 film, thickness increased linearly for the deposition of the first four 1/SPS bilayers and continued to increase with the same slope (6.4 nm/layer) during the deposition of the final four 2/SPS layers to give a final film thickness of 70 nm. In contrast, the slope of the growth profile for the (2/SPS) 4 (1/SPS) 4 film changed during the deposition of the final four 1/SPS layers (from 6.4 nm/layer to 4.0 nm/layer), resulting in a final film thickness that was lower (10 nm less) than the (1/SPS) 4 (2/SPS) 4 film. In addition, visual inspection of (2/SPS) 4 (1/SPS) 4 films indicated the presence of non-uniform optical patterns and irregular film coverage over large areas of the silicon substrate.…”

“…In contrast, the slope of the growth profile for the (2/SPS) 4 (1/SPS) 4 film changed during the deposition of the final four 1/SPS layers (from 6.4 nm/layer to 4.0 nm/layer), resulting in a final film thickness that was lower (10 nm less) than the (1/SPS) 4 (2/SPS) 4 film. In addition, visual inspection of (2/SPS) 4 (1/SPS) 4 films indicated the presence of non-uniform optical patterns and irregular film coverage over large areas of the silicon substrate. By contrast, (1/SPS) 4 (2/SPS) 4 films were smooth and uniform (RMS roughness was 3.3 nm as determined by atomic force microscopy).…”

“…33,38 We demonstrate here, however, that the incorporation of multiple different layers of polyamines 1-3 into multilayered films can also provide a straightforward and highly tunable approach to exerting control over film erosion and the release of SPS. Figure 4 shows a plot of ellipsometric thickness versus the number of bilayers deposited during the fabrication of a (1/SPS) 4 (2/SPS) 4 film and a (2/SPS) 4 (1/SPS) 4 film (fabricated using the general approach described above). For the (1/SPS) 4 (2/SPS) 4 film, thickness increased linearly for the deposition of the first four 1/SPS bilayers and continued to increase with the same slope (6.4 nm/layer) during the deposition of the final four 2/SPS layers to give a final film thickness of 70 nm.…”

“…Figure 4 shows a plot of ellipsometric thickness versus the number of bilayers deposited during the fabrication of a (1/SPS) 4 (2/SPS) 4 film and a (2/SPS) 4 (1/SPS) 4 film (fabricated using the general approach described above). For the (1/SPS) 4 (2/SPS) 4 film, thickness increased linearly for the deposition of the first four 1/SPS bilayers and continued to increase with the same slope (6.4 nm/layer) during the deposition of the final four 2/SPS layers to give a final film thickness of 70 nm. In contrast, the slope of the growth profile for the (2/SPS) 4 (1/SPS) 4 film changed during the deposition of the final four 1/SPS layers (from 6.4 nm/layer to 4.0 nm/layer), resulting in a final film thickness that was lower (10 nm less) than the (1/SPS) 4 (2/SPS) 4 film.…”

Layer-by-Layer Assembled Films Composed of “Charge Matched” and “Length Matched” Polysaccharides: Self-Patterning and Unexpected Effects of the Degree of Polymerization

“…This is especially true for the field of materials with biological or pharmaceutical applications in which processes such as cell adhesion and tissue growth, gene transfection or drug delivery require control of complex dynamics and transport kinetics [1][2][3][4].…”