N. A. Sapoletova

Double stacking faults in convectively assembled crystals of colloidal spheres.

Using microradian X-ray diffraction, we investigated the crystal structure of convectively assembled colloidal photonic crystals over macroscopic (0.5 mm) distances. Through adaptation of Wilsons theory for X-ray diffraction, we show that certain types of line defects that are often observed in scanning electron microscopy images of the surface of these crystals are actually planar defects at 70.5 degrees angles with the substrate. The defects consist of two parallel hexagonal close-packed planes in otherwise face-centered cubic crystals. Our measurements indicate that these stacking faults cause at least 10% of stacking disorder, which has to be reduced to fabricate high-quality colloidal photonic crystals.

Fabrication of artificial opals by electric-field-assisted vertical deposition.

We present a new technique for large-scale fabrication of colloidal crystals with controllable quality and thickness. The method is based on vertical deposition in the presence of a DC electric field normal to the conducting substrate. The crystal structure and quality are quantitatively characterized by microradian X-ray diffraction, scanning electron microscopy, and optical reflectometry. Attraction between the charged colloidal spheres and the substrate promotes growth of thicker crystalline films, while the best-quality crystals are formed in the presence of repulsion. Highly ordered thick crystalline layers with a small amount of stacking faults and a low mosaic spread can be obtained by optimizing the growth conditions.

Controlled growth of metallic inverse opals by electrodeposition

The kinetics of nickel electrodeposition through a template of ordered polystyrene spheres is addressed experimentally and applied to prepare a series of metallic inverse opals with a non-integer number of layers. The observed layer-by-layer growth is discussed in terms of subsequently increasing disorder of the growth front. Reflection and transmission spectra of the samples demonstrate that the key optical features of these photonic crystals are most pronounced when the thickness does not essentially exceed two layers. The intensities and band positions can be additionally tuned by varying the height of the metal coating continuously, not discretely. These findings are confirmed semi-quantitatively by means of computational modeling of the spectra. Specific deposition current transients for in situ control of geometric parameters are discussed.

Magnetoplasmonic nanostructures based on nickel inverse opal slabs

Nanostructured nickel surfaces representing periodically arranged spherical voids in a nickel film are obtained by electrochemical deposition through a self-assembled opaline template. Excitation of surface plasmon-polaritons (SPPs) on the surface of the sample is experimentally observed as the Wood’s anomaly in the reflectance spectra. Transversal magneto-optical Kerr effect (TMOKE) spectra are measured at the different angles of incidence and azimuthal angles. The two- to-threefold enhancement of TMOKE caused by the excitation of mixed plasmons in two selected azimuthal configurations is observed.

Optical properties of γ-ferric oxide nanoparticles in a mesoporous silica matrix

Magnetic γ-Fe2O3/SiO2 nanocomposites have been synthesized by impregnating a mesoporous silica matrix with a hexane solution of γ-ferric oxide nanoparticles. The subsequent heat treatment of samples in the course of synthesis influences the optical properties of the final nanostructural material. It is established that an increase in the temperature of annealing (crystallization) leads to a decrease in the energies of both direct and indirect allowed electron transitions to the conduction band.

Determination of the real structure of artificial and natural opals on the basis of three-dimensional reconstructions of reciprocal space

The distribution of the scattering intensity in the reciprocal space for natural and artificial opals has been reconstructed from a set of small-angle X-ray diffraction patterns. The resulting three-dimensional intensity maps are used to analyze the defect structure of opals. The structure of artificial opals can be satisfactorily described in the Wilson probability model with the prevalence of layers in the fcc environment. The diffraction patterns observed for a natural opal confirm the presence of sufficiently long unequally occupied fcc domains.

Electric-Field-Assisted Self-Assembly of Colloidal Particles

A method for formation of photonic crystals has been proposed. The method is based on convective deposition of colloidal particles onto vertical substrates in the presence of a direct-current electric field directed perpendicular to the surface of the formed film and an alternating-current electric field applied parallel to the substrate plane. The structure and optical properties of the prepared colloidal crystals have been investigated using scanning electron microscopy, high resolution small-angle X-ray diffraction, and optical spectroscopy.

Electrochemical X-ray Photolithography†

Recent progress in information technologies has made microand nanolithography key processes in modern industry. Today these methods are among the most rapidly developing areas in both science and engineering. In the last two decades, wellknown and widespread methods of photoand electron-beam lithography have been complemented by a number of novel approaches that include direct writing processes, such as scanning probe lithography and dip-pen nanolithography, mask-based techniques including soft-lithography, nanoimprint, nanostencil and nanosphere lithography, and unconventional wet lithographies. Progress in the development of these methods has allowed high throughput to be attained at an ultimate resolution of less than 10 nm and enabled massproduction of microelectronic components. Further improvements in this method were introduced by the addition of chemical transformations, which can be applied through the integration of lithography with chemical or electrochemical processes. Electrochemical processing possesses a number of important advantages, including room-temperature synthesis (thereby avoiding thermal expansion problems), ability to control deposition rates, increased deposition density, and enhanced versatility. Moreover, electrochemical processes are easy to control through manipulation of charge values and current transient shapes. Several electrochemical lithography methods have been reported that achieve resolution down to 10 nm. However, all of these methods require contact lithography processing, as electrochemical photolithographic pattern-transfer techniques have yet to be developed. Nevertheless, numerous papers have been published on light-induced electrochemical effects, which have the potential to be further utilized for the development of non-contact electrochemical lithography techniques. One drawback to this approach however, is that the wavelengths of visible and UV light restrict the resolution level. A possible solution to this problem is the use of X-rays, which have long been known to trigger surface charging and radiolysis in matter. It could be expected that these effects would provide the conditions necessary for the electrochemical equilibrium shift required for electrochemical etching or deposition. Despite this, there have been only a few reports on X-rayassisted electrochemical processing. While some chemical X-ray lithography methods use X-rays for induced chemical transformations, they are restricted to reactions where radiolysis products are formed within the solution volume. Some work discusses reactions driven by photoelectrons ejected from the substrate surface, but do not complete the electrochemical circuit to control Helmholtz layer. Lastly, we also failed to find any studies concerning direct electrochemical lithography under X-ray irradiation. Thus in the present study we have focused our attention on the development of an electrochemical X-ray photolithography approach for direct pattern transfer to a liquid– solid interface by coherent X-ray irradiation. The concept is based upon variation in electrochemical deposition/etching rates provided by local photoionization effects. Local reduction of electrolyte components by photoelectrons generated on the working electrode surface under X-rays was chosen to test the concept. The electrochemical X-ray photolithography method was investigated by pattern transfer onto electrochemically deposited nickel, which plays a pivotal role in industry, particularly in microelectronics. The experiment is shown in Figure 1. A parallel X-ray beam collimated by slits was passed through a 4 mm pitch silicon grating and guided to the

Formation of ordered cobalt nanowire arrays in the mesoporous silica channels

Here we report the synthesis and investigation of cobalt nanowire arrays using mesoporous silica as a host material. In the present work, a novel variant of synthesis of ordered magnetic nanowires in the mesoporous silica matrix was suggested. The method is based on incorporation of a hydrophobic metal compound Co2(CO)8 into the hydrophobic part of the silica-surfactant composite. The amount of cobalt intercalated into the mesoporous matrix was measured by chemical analysis (~5 wt %). Additional thermal modification was performed in order to provide a crystallization process of the cobalt nanowires. The prepared nanocomposites were characterized by X-ray diffraction (XRD), small-angle X-ray spectroscopy (SAXS), transmission electron microscopy (TEM), nitrogen capillary adsorption method (BET and BJH), and magnetic measurements. The anisotropy parameters of nanowires were determined using temperature dependence of magnetic susceptibility. For cobalt-containing sample annealed at 300 °C (form factor of nanowire higher than 16), the coercive force at room temperature was found to be 42.2 kA/m at saturation magnetization of 0.5 A.m2/kg, which is nearly sufficient for modern information recording media. According to TEM studies, cobalt particles are uniform and well ordered in the silica matrix. Thus, the suggested method leads to one-dimensional anisotropic nanostructures, which could find an application in high-density data storage devices.

Magnetic properties of γ-iron oxide nanoparticles in a mesoporous silica matrix

Magnetic γ-Fe2O3/SiO2 nanocomposites are synthesized by impregnating mesoporous silica with a hexane solution of γ-iron oxide nanoparticles. Materials with various structural and magnetic properties can be obtained using a subsequent thermal treatment of the synthesized samples (annealing for three hours in an air flow).