Communications film, resulting in terraces of bilayer steps. The regions of arachidic acid in the mixed LB film can be removed by washing in ethanol to leave behind islands of cadmium arachidate molecules. ExperimentalLangmuir-Blodgett films of arachidic acidicadmium arachidate were prepared using a constant-perimeter barrier trough (purpose-built) located in a Class 10000 microelectronics clean room. The subphase was ultrapure water obtained from a commercial reverse osmosisideionizationiUV sterilization system. The arachidic acid (eicosanoic acid) was obtained from Sigma (99 % purity). For salt formation, CdCIp (BDH, Analar Grade) was added to the suhphase to give an overall concentration of 2.5 x lo4 M. The pH was adjusted to 5.7i0.1 by the addition of HCI (BDH, Aristar Grade) or ammonia solution (BDH, Aristar Grade). Transfer of the floating monolayers onto hydrophilic silicon wafers ((100) orientation) was undertaken at a suhphase temperature of 19i1 "C and a deposition pressure of 30 mN m-'. The dipping speed was 2 mm m i d . Transfer ratios for all the monolayers deposited were 1.0oi0.05.A Digital Instruments Nanoscope Ill atomic force microscope was used to examine the topographical nature of the arachidic acidicadmium arachidate LB film surface following dipping and after washing in ethanol (to remove the free acid). All of the high resolution AFM images were acquired in air at room temperature using the contact mode and a 1 pm x 1 pm piezoelectric scan head. A 200 pm narrow-legged silicon nitride cantilever with a small spring-constant ( k = 0.06 Nm-') was used to minimize film damage due to high contact forces. The lower resolution images were acquired in air using the tapping mode in conjunction with a 10 ym x 10 Fm piezoelectric scan head. This technique employs a stiff silicon cantilever oscillating at a large amplitude near its resonance frequency (several hundred kilohertz) which is detected by an optical beam system. AFM images are presented as unfiltered data in gray-scale and were found to be stable and unchanged over long periods of observation.

Positively charged polydiallyldimethylammonium chloride, P, was found to bind strongly to the surface of anionic montmorrillonite, M, platelets in aqueous dispersions up to a saturation (estimated to correspond to the binding of five P to one 1.0 nm × 200 nm M platelet) beyond which reversible physisorption occurred. Immersion of a substrate (glass, quartz, silica-wafer, gold, silver, and even Teflon) into an aqueous 1% solution of P and rinsing with ultrapure water for 10 min resulted in the strong adsorption of a 1.6 nm thick P on the substrate. Immersion of the P coated substrate into an aqueous dispersion of M and rinsing with ultrapure water for 10 min led to the adsorption of 2.5 nm thick M. Repeating the self-assembly steps of P and M for n number of times produced (P/M) n self-assembled films. Thickness of the M layer was found to depend on the external voltage applied during its self-assembly:  applying a positive potential during the self-assembly of M increased the thickness of the M layer; application of a small negative potential decreased it slightly; however, larger negative voltages augmented it. The structure of self-assembled (P/M) n films have been characterized by a variety of techniques:  X-ray diffraction, X-ray reflectivity, atomic force microscopy, transmission electron microscopic, and surface plasmon spectroscopic measurements. It was shown that clay platelets form stacks upon adsorption to the polymer layer consisting on the average two aluminosilicate sheets. The evolution of the surface roughness upon sequential deposition of P/M layers was observed by in situ AFM. Large etched pits, up to 700 nm diameter and 30 nm depth, were smoothed during P/M deposition. Small pits (188 nm diameter and 14 nm deep) were capped after one P/M deposition cycle. Surface roughness of (P/M) n films was estimated by a number of methods including surface plasmon spectroscopy. The overall roughness did not appear to correlate with the type of substrate used. On the other hand, application of an external electric field during the self-assembly of P strongly influenced the surface morphology. Application of a negative potential during the self-assembly of P improved the uniformity and regularity of the deposited layers.

A de novo, genetically engineered 687 residue polypeptide expressed in E. coli has been found to form highly rectilinear, beta-sheet containing fibrillar structures. Tapping-mode atomic force microscopy, deep-UV Raman spectroscopy, and transmission electron microscopy definitively established the tendency of the fibrils to predominantly display an apparently planar bilayer or ribbon assemblage. The ordered self-assembly of designed, extremely repetitive, high molecular weight peptides is a harbinger of the utility of similar materials in nanoscience and engineering applications.