Anisotropic growth of water-puckered pentamers on a mica terrace.

Ice nucleation at mica terrace edges in air forms mounds of water molecules that grow larger as the step-edge height increases from a few Angstroms to hundreds of nanometers. The structures of the ice deposits at mica terrace edges were characterized by atomic force microscopy (AFM), and the edges were shown to act as nucleators for water pentamers, thereby forming a zigzag structure with lattice parameters of 0.72 ± 0.07 and 0.60 ± 0.06 nm. A three-dimensional arrangement of three pentamers of water molecules, which formed a parasol-like structure, was assembled to match the AFM images. Seven three-fused pentamers were clustered to form large hexamers that cover the entire surface. The nucleation at the edges reveals a substantially larger growth rate than that on the mica terraces; consequently, highly terraced mica slabs could be used as new and more efficient structures for seeding clouds and causing rain. On the basis of this finding, a new ice-condensation structure was designed with pyramidal features and steps of 100 nm in height and width.

Drainage kinetics of nanochannels fabricated in water films a few molecules thick on mica at room temperature.

Nanochannels of the order of 20 nm in diameter and forming arrangements that were a few micrometres wide were fabricated on nanometre-thick ice-like deposits on planar mica surfaces at room temperature. Because an atomic force microscopy tip can write lines on ice-like layers covering mica substrates in air that are stable under invariant conditions of humidity and temperature, the water films were modulated with nanochannels. By analysing the shape and morphology of the material removed after channel fabrication for various time intervals, the channel profile was shown to vary with a scale of a tenth of a second. In this configuration (hydrophobic tip and hydrophilic substrate, 65% RH), at the channel top region there were only aggregates of loose flakes formed after the film inscription but no liquid. Apparently, the Kelvin effect is responsible for the nanochannel profile variation with time, but the calculated and measured values of the drainage time constant are at variance by six orders of magnitude. This reduction of the mass transfer is associated with the small dimensions of the ∼ 10 nm-wide channels.

Long nanofibers arrays through surfactant self-assembly.

Self assembly of molecules can be a simple and versatile approach that may lead to nanostructures. Here we report the formation of arrangements of exceptionally long nanofibers of cationic surfactant hexadecyltrimethylammonium bromide molecules with highly defined spatial and parallel ordering. Arrangements of approximately 1 microm long nanofibers were observed by non-contact atomic force microscopy. The long nanofiber patterns form structures in approximately 5 x 5 microm2 regions and consist of approximately 6 nm wide lines. The formation mechanism of the fibers is shown to be the coalescence of isolated surfactant micelles (approximately 3.2 nm diameter in solution) in the convection stream of the surfactant solution drop close to the pinned contact-line region during drying. The size of micelles formed in solution determines the diameter of the deposited fibers. New deposition schemes of micelles forming nanorods on bare silicon previous to the formation of surfactant bilayers are now being investigated based on the data obtained in this work.

Quorum sensing detected by atomic force microscopy imaging of corrals surrounding multicellular arrangement of bacteria.

Connectivity of the glycocalyx covering of small communities of Acidithiobacillus ferrooxidans bacteria deposited on hydrophilic mica plates was imaged by atomic force microscopy. When part of the coverage was removed by water rinsing, an insoluble structure formed by corrals surrounding each individual bacterium was observed. A collective ring structure with clustered bacteria (>or=3) was observed, which indicates that the bacteria perceived the neighborhood in order to grow a protective structure that results in smaller production of exopolysaccharides material. The most surprising aspect of these collective corral structures was that they occur at a low bacterial cell density. The deposited layers were also analyzed by confocal Raman microscopy and shown to contain polysaccharides, protein, and glucoronic acid.