Fractal Nanostructures Research Articles

Combinatorial targeting and nanotechnology applications

The development of improved methods for targeted cell detection is of general interest in many fields of research and drug development. There are a number of well-established techniques for the study and detection of biomarkers expressed in living cells and tissues. Many of them rely on multi-step procedures that might not meet ideal assay requirements for speed, cost, sensitivity, and specificity. Here we report and further validate an approach that enables spontaneous molecular assembly to generate biologically active networks of bacteriophage (phage) assembled with gold (Au) nanoparticles (termed Au-phage nanoshuttles). Here, the nanoshuttles preserve the cell binding and internalization attributes mediated by a displayed peptide targeted to a cell surface receptor. The organization of such targeted assemblies can be further manipulated to be used as a multimodal detection assembly, and they can be characterized as fractal nanostructures by angle-dependent light scattering fractal dimension analysis. Targeted Au-phage nanoshuttles offer multiple functionalities for nanotechnology-based sensing and reporting, including enhanced fluorescence and improved contrast for darkfield microscopy.

STM Investigation of Large π-Conjugated Oligomers and Tetrahydrofuran Codeposited on Cu(111) by Pulse Injection

The π-conjugated oligomer consisting of ethynyl interlinked thiophene and benzene subunits C114H158O8S2Si2 has been deposited on clean Cu(111) substrates at room temperature using the pulse-injection method with tetrahydrofuran (THF) as solvent. Scanning tunneling microscopy measurements in ultrahigh vacuum at room temperature demonstrate that the CHOSSi and THF molecules coadsorb on the copper surface. The solvent molecules form ordered structures with distinct orientations and domain boundaries, suggesting a strong interaction of THF with the substrate. Individual and small clusters of CHOSSi molecules appear randomly distributed on the surface with no apparent correlation with the solvent molecules. Subsequent thermal treatment removing the solvent causes a degradation of the CHOSSi oligomers which aggregate forming fractal nanostructures.

Some questions in fractal nanotechnology

Some issues are studied, which are related to the state-of-the-art in nanotechnology in general and, in particular, to the development of methods for obtaining fractal nanostructures and to their possible applications. The results of experimental and theoretical investigations of the weak interactions of various physical fields with material objects are analyzed for the conditions, where the interaction magnitude can be considered as small or ultrasmall perturbation. Various types of resonance interactions related to such processes and prospects of their use in nanotechnology are considered. Results of experimental investigations in the field of fractal nanotechnology are summarized.

Fractal nanostructures arising under the ablation of graphite and silicon by millisecond-laser radiation

A mechanism for the formation of fractal nanostructures with micro- and macroscopic sizes under 10-ms laser-pulse irradiation of carbon, silicon, and their mixtures is investigated. The appearance of linear fragments containing nanoclusters is considered based on the diffusion-limited aggregation model with the dipole-dipole interaction. It is shown that the competition between the thermophoretic and gradient forces acting upon particles and their aggregates in a plume determines the area of congestion and the formation of the macroscopical fractal nanostructures.

Formation of silicon nanostructures when a target is ablated by a quasi-continuous laser pulse

When a target is ablated in an atmosphere of an inert buffer gas by low-intensity laser radiation (no greater than 105W∕cm2), nanoparticles self-assemble into low-dimensional fractal structures. The dependences of the efficiency of the self-assembly process on the composition of the silicon–silica target and the pressure of the buffer gas manifest a distinct correlation with percolation in the plasma of the laser flare. A structure with a fractal dimension of df>2 is formed most efficiently close to the three-dimensional percolation threshold pc≈0.3, where pc is the ratio of the number density of silicon atoms to the number of all the atoms in the laser flare. Close to the two-dimensional percolation threshold (pc≈0.5), fractal structures are observed with df<2, assembled on a plane. The main structural elements of the observed objects are one-dimensional structures—chains of tens of nanoparticles, with a characteristic size of about 80nm. Results of a study of fractal nanostructures by scanning electron microscope are presented, an x-ray structural analysis is carried out, and the photoluminescence is studied.

Growth of Gold Fractal Nanostructures by Electrochemical Deposition in Organic Electrolytes: Morphologies and Their Transitions

We have studied the growth of gold fractal nanostructures by a novel electrochemical deposition (ECD) method. In our ECD process, instead of an aqueous solution of metallic salt, we use an organic solution (such as N,N-dimethylformamide (DMF) or acetonitrile) as the electrolyte and integrate the microscale ECD system into the SiO2/Si chip. Quasi-two-dimensional gold fractal nanostructures can be formed using the organic electrolyte. The morphology of the deposit strongly depends on the kind of organic electrolyte that has been used. A diffusion-limited aggregation (DLA) pattern can be formed in DMF. While in acetonitrile, aside from the DLA pattern, a variety of other typical morphologies can be identified, and they appear in consecutive patterns varying from a DLA fractal, to a dense branching morphology (DBM), to a ramified structure. In some cases the ramified structures can even evolve into nanoscale dendrites or nanowires. To the best of our knowledge, these phenomena have not been reported before. We propose a qualitative explanation for these phenomena based on the mass transfer equation and discuss possible applications of these nanostructures.

Surfactant-promoted formation of fractal and dendritic nanostructures of gold and silver at the organic–aqueous interface

The effect of surfactants such as tetraoctylammoniumbromide (TOAB) and cetyltrimethylammoniumbromide (CTAB) on the type of nanostructures formed when gold ions present in the organic phase are reduced at the interface by hydrazine in the aqueous phase has been investigated. Extended fractal structures are formed at the liquid–liquid interface, the fractal structures themselves comprising cauliflower type units formed by gold nanorods. Accordingly, the nanostructures exhibit transverse and longitudinal plasmon adsorption bands in the 550 and 800 nm regions, respectively. Dendritic structures of silver are formed at the interface when Ag ions are reduced similarly in the presence of surfactants. The nanostructures consist of nanoparticles or nanorods with five-fold symmetry.

Fractal growth of single-crystal α-Fe2O3: From dendritic micro-pines to hexagonal micro-snowflakes

The fractal nanostructures of single-crystal α-Fe2O3 with micro-pine and micro-snowflake like morphologies have been synthesized via a hydrothermal route. The crystallinity, composition, purity, morphology and microstructure of the synthesized hematite were characterized by X-ray diffraction, Mössbauer spectrometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). A possible growth mechanism for these two kinds of fractal structures was proposed based on careful SEM and TEM observations. The role of the surfactant NP-9 in the conversion of the two kinds of fractal structures was discussed.

Notes on hydrated cement fractals investigated by SANS

Hydrated cement pastes with different water-to-cement ratios have been investigated by the small-angle scattering neutron technique. Special attention has been paid to the fractal nanostructure of the calcium silicate hydrate (C–S–H solid gel) and its basic building particles, i.e. nanometric globules. The inner stability of these particles has been tested and shown to be sufficiently persistent to withstand all spatial regroupings of the overall nanostructure caused by variations of w/c ratios.

Seeding Method for Three-dimensional Dendritic Growth of Gold Nanoparticles Stabilized by Hexatrimethylammonium Bromide

Abstract Three-dimensional gold dendrites with fractal nanostructure were prepared with HAuCl4 and l-ascorbic acid via seeding growth method in the presence of hexatrimethylammomium bromide (HTAB) as a protecting agent and architecture soft template. Spherical gold, previously generated, plays as a seed for particle growth. The surfactant HTAB helps to induce various branched nanostructures. The growth of first branches on the seeds leads to the formation of second branches by seed amount.

Formation of nanostructures upon laser ablation of a binary Six(SiO2)1-x mixture

The formation efficiency of fractal nanostructures is studied experimentally depending on the composition of the binary silicon–silica mixture during evaporation by millisecond laser pulse. The influence of percolation on the efficiency of nanostructure formation in a laser plume is discovered. It is found that the efficiency is maximal near the critical densities of atoms in the plasma, which correspond both to the three-dimensional and two-dimensional percolation. The dependences of the effective temperatures of the laser plasma and the intensity of spectral lines on the target composition are presented.

Computer simulation of growing fractal nanodendrites by using of the multi-directed cellular automatic device

Computer simulation of self-assembly growth of fractal nanodendrites is suggested by using a new model of multi-directed cellular automatic device. The novelty is that in a framework of the multiparticle diffusion limited aggregation (DLA) model, atoms stick to the growing cluster according to specific kinematics multi-directional contact bonds. The aggregation is limited by initial concentration of particles confined inside definite nano-sized enclosures. Self-organizing process results in the formation of fractal dendrite nanostructures. From results of computer experiments, some equations for cluster fractal dimension D, depending on the initial concentration C of diffusing particles in 2d and 3d space enclosures, are deduced. Correlations between cluster fractal dimension D and number of aggregated particles N are found also.

Spectral and polarization effects in deterministically non-periodic multilayers containing optically anisotropic and gyrotropic materials

Influence of material anisotropy and gyrotropy on optical properties of fractal multilayer nanostructures is theoretically investigated. Gyrotropy is found to uniformly rotate the output polarization for bi-isotropic multilayers of arbitrary geometrical structure without any changes in transmission spectra. When introduced in a polarization splitter based on a birefringent fractal multilayer, isotropic gyrotropy is found to resonantly alter output polarizations without shifting of transmission peak frequencies. The design of frequency-selective absorptionless polarizers for polarization-sensitive integrated optics is outlined.

Electrospray Ion Beam Deposition of Clusters and Biomolecules

An ion beam source using electrospray ionization is presented for nondestructive vacuum deposition of mass-selected large organic molecules and inorganic clusters. Electrospray ionization is used to create an ion beam from a solution containing the nanoparticles or molecules to be deposited. To form and guide the ion beam, radio frequency and electrostatic ion optics are utilized. The kinetic energy distribution of the particles is measured to control the beam formation and the landing process. The particle mass-to-charge ratio is analyzed by in situ time-of-flight mass spectrometry. To demonstrate the performance of the setup, deposition experiments with gold nanoclusters and bovine serum albumin proteins on graphite surfaces were performed and analyzed by ex situ atomic force microscopy. The small gold clusters are found to form three-dimensional agglomerations at the surface, preferentially decorating the step edges. In contrast, bovine serum albumin creates two-dimensional fractal nanostructures on the substrate terraces due to strong intermolecular interactions.

Formation Mechanism of Mg2SiO4 Fishbone-like Fractal Nanostructures

Mg2SiO4 fishbone-like fractal nanostructures have been investigated using high-resolution transmission electron microscopy. The branches of Mg2SiO4 fibers and detailed structures of cobalt nanopart...

Fractal gold nanostructures produced by the spontaneous reduction ofchloroaurate ions in thermally evaporated hexadecylaniline thin films

The formation of gold nanoparticles by the reduction of chloroaurate ionsentrapped in thermally evaporated hexadecylaniline films is described. Simpleimmersion of the hexadecylaniline films in aqueous chloroauric acid solution leadsto the electrostatic entrapment of the gold ions in the film and is accompanied bytheir spontaneous in situ reduction by the matrix hexadecylaniline molecules. Thegold particles thus formed show a fractal structure of nanoscale dimensionscharacteristic of diffusion-limited aggregation of gold nanoparticles. Possiblereasons for the formation of fractal nanostructures in the host matrix arediscussed.

Selective Co-catalysed growth of novel MgO fishbone fractal nanostructures

Novel MgO fishbone- or fern-like nanostructures, and Al 2O 3 fibre networks, have been generated for the first time from an Al 2O 3 matrix containing MgO and SiO 2. The significance of the selective Co-catalysed growth of the elegant three-dimensional fractal fishbones is discussed. We have adopted the vapour–liquid–solid (V–L–S) and nucleation–aggregation (N–A) mechanisms, which take effect equally during the heating process, to account for the formation of these uniquely stacked fractal structures.

Nonlinear Optical Phenomena in Nanostructured Fractal Materials

The results of theoretical and experimental studies of nonlinear optical phenomena in fractal nanostructures are reviewed. Localization of optical excitations in fractal metal nanocomposites, such as colloidal aggregates, self-affine and semicontinuous films, results in strong enhancements of optical nonlinearities. The localized modes of fractals cover a broad spectral range, from the visible to the far-infrared. A number of optical processes are studied such as the Kerr-type nonlinearities, four-wave mixing, second and third harmonic generation and frequency- and polarization-selective photomodification.

Surface-Enhanced Optical Nonlinearities of Nanostructured Fractal Materials

Localization of optical excitations in fractal metal nanocomposites, such as colloidal aggregates, self-affine and semicontinuous films, results in strong enhancements of optical nonlinearities. The localized modes of fractals cover a broad spectral range, from the visible to the far-infrared. Results of both theoretical and experimental studies of enhanced nonlinear optical responses of fractal nanostructures are considered.

Observation of the two-photon photoelectric effect in low-intensity optical fields during photostimulated fractal aggregation of colloidal silver

The two-photon photoelectric effect enhanced by the characteristic local fields of fractal nanostructures is observed in optical fields with intensity of the order of 10−3 W/cm2.