Growth Of Periodic Structures Research Articles

Coordination sequences and layer-by-layer growth of periodic structures

Abstract A new approach to the problem of coordination sequences of periodic structures is proposed. It is based on the concept of layer-by-layer growth and on the study of geodesics in periodic graphs. We represent coordination numbers as sums of so called sector coordination numbers arising from the growth polygon of the graph. In each sector we obtain a canonical form of the geodesic chains and reduce the calculation of the sector coordination numbers to solution of the linear Diophantine equations. The approach is illustrated by the example of the 2-homogeneous kra graph. We obtain three alternative descriptions of the coordination sequences: explicit formulas, generating functions and recurrent relations.

Time-Resolved Structured Illumination Microscopy for Phase Separation Dynamics of Water and 2-Butoxyethanol Mixtures: Interpretation of "Early Stage" Involving Micelle-Like Structures.

Phase separation dynamics of a water/2-butoxyethanol (2BE) mixture was studied with newly developed time-resolved structured illumination microscopy (SIM). Interestingly, an employed hydrophobic fluorescent probe for SIM showed spectral shifts up to 500 ns after a laser-induced temperature jump, which suggests 2BE micellar-like aggregates become more hydrophobic at the initial stage of phase separation. This hydrophobic environment in 2BE aggregates, probably due to the ejection of water molecules, continued up to at least 10 μs. Time-resolved SIM and previously reported light scattering data clearly showed that the size of a periodic structure remained constant (ca. 300 nm) from 3 to 10 μs, and then the growth of periodic structures having the self-similarity started. We think that the former and the latter processes correspond to "early stage" (concentration growth) and "late stage" (size growth), respectively, in phase separation dynamics. Here we suggest that, in the early stage, the entity to bear 2BE phase be water-poor 2BE aggregates, and the number density of these aggregates would simply increase in time.

Morphogenesis of crystal structures in the discrete modeling of packings

Within the framework of the discrete modeling of molecular packings, a metric approach to the investigation of the mechanisms of crystal formation is proposed. This method is based on the construction of a combination of polyhedra in a space in which the space division into polyhedra (or the periodic packing of polyhedra) is specified by the multistage addition to the initial “seeding” polyhedron set of this division (packing) of the adjacent polyhedra. Crystal growth is modeled using the constructions of bounding boxes in the division of the plane into polyominoes and the three-dimensional space, into polycubes. The formation of phenomenological polygons (polyhedra) in the growth of periodic structures is revealed and theoretically grounded.

Influence of photoinduced gyrotropy on the formation of spontaneous periodic structures in light-sensitive AgCl–Ag thin films

The temporal evolution of spontaneous periodic structures was studied under successive action of circularly and linearly polarized laser radiation in light-sensitive waveguide AgCl–Ag films. The essential role of positive feedback in the growth of periodic structures is established by measuring the differential diffraction efficiency. An asymmetry in the azimuthal distribution of diffraction efficiency is found due to gyrotropy induced by circularly polarized radiation. The existence of induced gyrotropy in the AgCl–Ag films was determined directly by measuring circular dichroism and optical rotatory dispersion. It is established that TE 0 mode scattering on anisotropic Ag particles leads to amplification of the gyrotropy influence on spontaneous grating growth at initial stages of irradiation by the linearly polarized laser beam.

Growth of periodic structures on the surface of germanium subjected to pulsed laser radiation

An experimental investigation was made of the dynamics of growth of periodic surface structures due to the interaction with pulsed laser radiation. Samples of Ge were subjected to laser pulses (λ = 1.06 μm, τ = 70 ns) with energy densities in the range 0.5–5.5 J/cm2. An investigation was made of the dynamics of the first-order diffraction of probe (λ = 0.53 μm) laser pulses with a time resolution 4 ns when p- and s-polarized laser radiation was incident at angles close to normal. A strong nonlinearity of the growth of such periodic surface structures was observed. The energy density from which such growth began depended on the quality of the polished Ge surface. The parameters of the dynamics of the growth of these structures were estimated.

Growth of periodic structures in pyrolytic laser-deposited SiC

Nonmelting surface interference ripples have been conclusively observed for the first time in thermally driven deposition of SiC from SiH4 and CH4. One set of ripples with a spatial frequency close to the primary beam wavelength (9.27 μm) is formed normal to the E field of the incident beam. An additional set of small-amplitude ripples of 1 μm or less in spacing and oriented parallel to the E field is also observed. These structural features are more pronounced in samples with higher melting points and completely disappear as the irradiated surface melts.

Growth of Periodic Structures by the Molecular-Beam Method

Molecular-beam epitaxy has been used successfully for the attainment of single-crystal multiple-layer structures with alternating types of conductivities (p/n) or band-gap energies (GaAs/AlxGa1−xAs). Deposition by the molecular-beam method offers the possibility of growing periodic-structure layers with constant chemical composition profiles and controlled uniform thicknesses.